Spinal instrumentation : challenges and solutions [Second edition.] 9781604068955, 1604068957

Table of contents :
Spinal Instrumentation: Challenges and Solutions
Title Page
Copyright
Dedication
Contents
Foreword
Preface
Preface to the First Edition
Contributors
Part 1 Cranial
1. Complications of Occipital Instrumentation
2. Vascular Complications of Posterior Cervical Procedures
3. Complications of C1 Lateral Mass Screw Fixation
4. Complications of C2 Pedicle and Pars Screw Placement
5. Complications of C1–C2 Transarticular Screws
6. Complications of C1–C2 Wiring
7. Complications of C2 Translaminar Screw Placement
8. Complications of Subaxial Lateral Mass Screw Fixation
9. Pedicle Screw Fixation in the Subaxial Cervical Spine: Indications, Contraindications, and Complications
10. Complications Related to Selected Instrumented Fusion Levels for Subaxial Fusions
11. Complications of Laminoplasty
12. Complications Related to Cervicothoracic Instrumentation
13. Anterior C1–C2 Fusion Instrumentation Complications
14. Complications of Odontoid Fracture Treatment
15. Complications of Static Anterior Cervical Plates
16. Complications of Translational Anterior Cervical Plates
17. Ectopic Ossification following Anterior Cervical Discectomy and Fusion or Disc Replacement
18. Failure of Anterior Cervical, Low-Profile, Stand-Alone Screw–Plate Devices
19. Complications of Buttress Plating Multilevel Anterior Cervical Corpectomies
20. Complications of Cervical Arthroplasty
Part 2 Thoracolumbar
21. Lumbar Pedicle Screw Complications
22. Junctional Breakdown in Pedicle Screw Constructs
23. Hook Complications in the Thoracic and Lumbar Spine
24. Sublaminar Wiring Complications
25. Complications of Percutaneous Vertebral Cement Augmentation
26. Complications of Vertebral Body Implants Introduced through the Posterolateral Approach
27. Complications of Vertebral Body Replacement Cages
28. Complications of Anterior Thoracic Instrumentation Systems.
29. Interspinous Spinous Process Fusion Plate Complications
30. Complications of Cortical Screw Fixation
31. Complications of Posterior Screw Fixation in Spine Surgery
32. Interspinous Spacer Complications
33. Complications of Presacral-Approach–Based Fusion Devices
34. Complications of Posterior and Transforaminal Lumbar Interbody Fusion
35. Complications of Open Transforaminal Lumbar Interbody Fusion
36. Complications of Instrumentation in Minimally Invasive Transforaminal Lumbar Interbody Fusion
37. Complications of Percutaneous Pedicle Screw Fixation
38. Complications of Lateral Lumbar Interbody Fusion Cages
39. Complications of Lateral Lumbar Fusion Plates
40. Complications of Lateral Lumbar Arthroplasty Devices
41. Complications of Lumbar Interbody Fusion with Femoral Ring Allograft
42. Complications of Anterior Lumbar Interbody Fusion with Polyether Ether Ketone Spacers
43. Complications of Stand-Alone Anterior Lumbar Interbody Fusion
44. Complications of Anterior Lumbar Disc Replacement
45. Complications of Iliac Screw Fixation
46. Complications of Sacral Alar Iliac Screw Technique
47. Complications of Sacropelvic Reconstruction for Tumor
48. Complications of Instrumentation in Cervical Spondyloarthropathy
49. Thoracolumbar Osteoporosis
50. Complications of Thoracolumbar Instrumentation in Patients with Spondyloarthropathies
51. Infection
52. Instrumentation Complications following Spinal Tumor Surgery
53. Cervical Kyphosis
54. Instrumentation Complications Occurring from Thoracic Hyperkyphosis
55. Flatback
56. Lumbar High-Grade Spondylolisthesis
57. Complications Related to Spinal Instrumentation and Surgical Approaches
58. Complications of Osteobiologics in Spine Surgery
59. Removal and Revision of Broken Thoracolumbar Screws
60. How to Remove/Revise Thoracolumbar Interbody Devices (TLIF Cages/ALIF Cages)
Index

Citation preview

Spinal Instrumentation Challenges and Solutions Second Edition

Daniel H. Kim, MD, FAANS, FACS Nancy, Clive, and Pierce Runnells Distinguished Chair in Neuroscience Professor Director of Spinal Neurosurgery, Reconstructive Peripheral Nerve Surgery Director of Microsurgical Robotic Laboratory Department of Neurosurgery University of Texas Houston, Texas Alexander R. Vaccaro, MD, PhD, MBA Richard H. Rothman Professor and Chairman Department of Orthopaedic Surgery Thomas Jefferson University President The Rothman Institute Co-Director, Delaware Valley Spinal Cord Injury Center Co-Director, Spine Surgery and Spinal Cord Injury Fellowship Philadelphia, Pennsylvania Richard G. Fessler, MD, PhD Professor Department of Neurosurgery Rush University Medical Center Chicago, Illinois Kris E. Radcliff, MD Associate Professor Department of Orthopedic Surgery Thomas Jefferson University Philadelphia, Pennsylvania The Rothman Institute Egg Harbor, New Jersey 248 illustrations Thieme New York • Stuttgart • Delhi • Rio de Janeiro

Executive Editor: Timothy Y. Hiscock Managing Editor: Elizabeth Palumbo Associate Managing Editor: Kenneth Schubach Director, Editorial Services: Mary Jo Casey Production Editor: Naamah Schwartz International Production Director: Andreas Schabert Editorial Director: Sue Hodgson International Marketing Director: Fiona Henderson International Sales Director: Louisa Turrell Director of Sales, North America: Mike Roseman Senior Vice President and Chief Operating Officer: Sarah Vanderbilt President: Brian D. Scanlan Library of Congress Cataloging-in-Publication Data Names: Kim, Daniel H., editor. | Vaccaro, Alexander R., editor. | Fessler, Richard G., editor. | Radcliff, Kris, editor. Title: Spinal instrumentation: challenges and solutions / [edited by] Daniel H. Kim, Alexander R. Vaccaro, Richard G. Fessler, Kris Radcliff. Other titles: Spinal Instrumentation (Kim) Description: Second edition. | New York : Thieme, [2018] | Includes bibliographical references and index. Identifiers: LCCN 2016035778 (print) | LCCN 2016037358 (ebook) | ISBN 9781604068955 (hardcover) | ISBN 9781626230408 (eISBN) | ISBN 9781626230408 (E-book) Subjects: | MESH: Spine–surgery | Orthopedic Fixation Devices | Prostheses and Implants | Orthopedic Procedures–methods | Orthopedic Procedures–instrumentation Classification: LCC RD533 (print) | LCC RD533 (ebook) | NLM WE 725 | DDC 617.4/71–dc23 LC record available at https://lccn.loc.gov/2016035778

Important note: Medicine is an ever-changing science undergoing continual development. Research and clinical experience are continually expanding our knowledge, in particular our knowledge of proper treatment and drug therapy. Insofar as this book mentions any dosage or application, readers may rest assured that the authors, editors, and publishers have made every effort to ensure that such references are in accordance with the state of knowledge at the time of production of the book. Nevertheless, this does not involve, imply, or express any guarantee or responsibility on the part of the publishers in respect to any dosage instructions and forms of applications stated in the book. Every user is requested to examine carefully the manufacturers’ leaflets accompanying each drug and to check, if necessary in consultation with a physician or specialist, whether the dosage schedules mentioned therein or the contraindications stated by the manufacturers differ from the statements made in the present book. Such examination is particularly important with drugs that are either rarely used or have been newly released on the market. Every dosage schedule or every form of application used is entirely at the user’s own risk and responsibility. The authors and publishers request every user to report to the publishers any discrepancies or inaccuracies noticed. If errors in this work are found after publication, errata will be posted at www.thieme.com on the product description page. Some of the product names, patents, and registered designs referred to in this book are in fact registered trademarks or proprietary names even though specific reference to this fact is not always made in the text. Therefore, the appearance of a name without designation as proprietary is not to be construed as a representation by the publisher that it is in the public domain.

© 2018 Thieme Medical Publishers, Inc. Thieme Publishers New York 333 Seventh Avenue, New York, NY 10001 USA +1 800 782 3488, [email protected] Thieme Publishers Stuttgart Rüdigerstrasse 14, 70469 Stuttgart, Germany +49 [0]711 8931 421, [email protected] Thieme Publishers Delhi A-12, Second Floor, Sector-2, Noida-201301 Uttar Pradesh, India +91 120 45 566 00, [email protected] Thieme Publishers Rio de Janeiro, Thieme Publicações Ltda. Edifício Rodolpho de Paoli, 25º andar Av. Nilo Peçanha, 50 – Sala 2508 Rio de Janeiro 20020-906 Brasil +55 21 3172-2297 / +55 21 3172-1896 Cover design: Thieme Publishing Group Typesetting by DiTech Process Solutions Printed in India by Replika Press Pvt Ltd ISBN 978-1-60406-895-5 Also available as an e-book: eISBN 978-1-62623-040-8

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This book, including all parts thereof, is legally protected by copyright. Any use, exploitation, or commercialization outside the narrow limits set by copyright legislation without the publisher’s consent is illegal and liable to prosecution. This applies in particular to photostat reproduction, copying, mimeographing or duplication of any kind, translating, preparation of microfilms, and electronic data processing and storage.

To my wife Anslie, and to Elise, Rebecca, Sarah, and Isaiah Kim. — Daniel H. Kim To my fellow partners, especially Kris Radcliff, whose teamwork, dedication to detail and work ethic have made this project a pure joy to complete. — Alexander R. Vaccaro To all those who question, and for whom the answer, “That’s the way we’ve always done it,” is just not good enough! — Richard G. Fessler To my wife Katherine, my parents Michelle and Andre, and my children Carmen, Donna, and Kristian. Without your love and support, this work would not have been possible. Also, I would like to thank my mentor and friend Dr. Alexander R. Vaccaro, MD, PhD, MBA. His dedication to scholarship, leadership, and tireless work have been exemplary to me. — Kris E. Radcliff

Contents Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii Preface to the First Edition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiv Cranial 1.

Complications of Occipital Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Seyed Babak Kalantar and Tom Sherman

2.

Vascular Complications of Posterior Cervical Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Raymond Hah and Jeremy Smith

3.

Complications of C1 Lateral Mass Screw Fixation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Alex Neusner

4.

Complications of C2 Pedicle and Pars Screw Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Nicholas S. Golinvaux and Jonathan N. Grauer

5.

Complications of C1–C2 Transarticular Screws. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 George M. Ghobrial, Joshua Heller, Alexander R. Vaccaro, and James S. Harrop

6.

Complications of C1–C2 Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Christopher A. Burks, Michael H. Moghimi, Sean N. Shahrestani, and Charles A. Reitman

7.

Complications of C2 Translaminar Screw Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Colin M. Haines, Michael Y. Wang, and Joseph R. O’Brien

8.

Complications of Subaxial Lateral Mass Screw Fixation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Adewale O. Adeniran and Adam Pearson

9.

Pedicle Screw Fixation in the Subaxial Cervical Spine: Indications, Contraindications, and Complications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Ahmer Ghori, Ali Al-Omari, and Thomas Cha

10.

Complications Related to Selected Instrumented Fusion Levels for Subaxial Fusions . . . . . . . . 61 Kim A. Williams Jr., George M. Ghobrial, Alexander R. Vaccaro, and Srinivas Prasad

11.

Complications of Laminoplasty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Ryan S. Murray and Seyed Babak Kalantar

12.

Complications Related to Cervicothoracic Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 Addisu Mesfin

13.

Anterior C1–C2 Fusion Instrumentation Complications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Jesse E. Bible and Clinton J. Devin

vii

Contents

14.

Complications of Odontoid Fracture Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Steven Presciutti, Brian Tinsley, and Isaac Moss

15.

Complications of Static Anterior Cervical Plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Barrett I. Woods, Kris E. Radcliff, and Alexander R. Vaccaro

16.

Complications of Translational Anterior Cervical Plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Gregory D. Schroeder and Jason W. Savage

17.

Ectopic Ossification following Anterior Cervical Discectomy and Fusion or Disc Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Pouya Alijanipour, Gregory D. Schroeder, and Alexander R. Vaccaro

18.

Failure of Anterior Cervical, Low-Profile, Stand-Alone Screw–Plate Devices . . . . . . . . . . . . . . . . 117 Michael P. Kelly and Wilson Z. Ray

19.

Complications of Buttress Plating Multilevel Anterior Cervical Corpectomies . . . . . . . . . . . . . . 122 Christoph P. Hofstetter and Michael Y. Wang

20.

Complications of Cervical Arthroplasty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 Amir M. Abtahi and Brandon D. Lawrence

Thoracolumbar 21.

Lumbar Pedicle Screw Complications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 Barrett I. Woods, Kris E. Radcliff, and Alexander R. Vaccaro

22.

Junctional Breakdown in Pedicle Screw Constructs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 Ivan Cheng and Michael Stauff

23.

Hook Complications in the Thoracic and Lumbar Spine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 Adam J. Bevevino

24.

Sublaminar Wiring Complications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 Gurpreet S. Gandhoke, David O. Okonkwo, and Adam S. Kanter

25.

Complications of Percutaneous Vertebral Cement Augmentation . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 Dennis S. Meredith and Alexander R. Vaccaro

26.

Complications of Vertebral Body Implants Introduced through the Posterolateral Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 David B. McConda, Jonathan M. Karnes, and Scott D. Daffner

27.

Complications of Vertebral Body Replacement Cages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Adam Wollowick, Allison Fillar, Jason Wong, and Woojin Cho

28.

Complications of Anterior Thoracic Instrumentation Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 Michael Silverstein, Daniel Lubelski, and Thomas E. Mroz

29.

Interspinous Spinous Process Fusion Plate Complications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 Andrew H. Milby, Douglas J. Nestorovski, and Harvey E. Smith

viii

Contents

30.

Complications of Cortical Screw Fixation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Andrew Zhang and Peter G. Whang

31.

Complications of Posterior Screw Fixation in Spine Surgery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 Pouya Alijanipour, Gregory D. Schroeder, Christie E. Stawicki, and Alexander R. Vaccaro

32.

Interspinous Spacer Complications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 William Ryan Spiker and Alan S. Hilibrand

33.

Complications of Presacral-Approach–Based Fusion Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 Michael Vives, Saad Chaudhary, and John Koerner

34.

Complications of Posterior and Transforaminal Lumbar Interbody Fusion . . . . . . . . . . . . . . . . . . 214 Jonathan Duncan and Ahmad Nassr

35.

Complications of Open Transforaminal Lumbar Interbody Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230 Louis F. Amorosa, Jeffrey A. Rihn, and Todd J. Albert

36.

Complications of Instrumentation in Minimally Invasive Transforaminal Lumbar Interbody Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242 Steven J. Fineberg, Matthew Oglesby, and Kern Singh

37.

Complications of Percutaneous Pedicle Screw Fixation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 Brandon P. Hirsch and Seth K. Williams

38.

Complications of Lateral Lumbar Interbody Fusion Cages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255 Mohammed A. Khaleel and Andrew P. White

39.

Complications of Lateral Lumbar Fusion Plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 Justin K. Scheer, Alejandro J. Lopez, Alpesh A. Patel, and Zachary A. Smith

40.

Complications of Lateral Lumbar Arthroplasty Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264 Nicholas Schroeder and Rakesh D. Patel

41.

Complications of Lumbar Interbody Fusion with Femoral Ring Allograft . . . . . . . . . . . . . . . . . . . . 267 Adam J. Bevevino and Tristan Fried

42.

Complications of Anterior Lumbar Interbody Fusion with Polyether Ether Ketone Spacers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 Peter G. Passias, Carrie Poorman, Sun Yang, and Matthew Nalbandian

43.

Complications of Stand-Alone Anterior Lumbar Interbody Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 Branko Skovrlj, John M. Caridi, Vikas Varma, and Samuel K. Cho

44.

Complications of Anterior Lumbar Disc Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 Jason Pittman, Anthony Degiacomo, Dan Plev, Tony Tannoury, and Chadi Tannoury

45.

Complications of Iliac Screw Fixation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 Shawn Bifano and John Koerner

46.

Complications of Sacral Alar Iliac Screw Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 Vidyadhar V. Upasani and Richard T. Allen

ix

Contents

47.

Complications of Sacropelvic Reconstruction for Tumor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 Eitan Kohan, Kushagra Verma, and John A. Abraham

48.

Complications of Instrumentation in Cervical Spondyloarthropathy . . . . . . . . . . . . . . . . . . . . . . . . 321 S. Samuel Bederman, Vu H. Le, and Nitin Bhatia

49.

Thoracolumbar Osteoporosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 Namath Syed Hussain, Mick J. Perez-Cruet, and Rod J. Oskouian Jr.

50.

Complications of Thoracolumbar Instrumentation in Patients with Spondyloarthropathies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335 Heidi Martin Hullinger and Rex A. W. Marco

51.

Infection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343 Armen R. Deukmedjian, Yusef I. Mosley, Amir Ahmadian, and Juan S. Uribe

52.

Instrumentation Complications following Spinal Tumor Surgery . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351 Addisu Mesfin and Jacob M. Buchowski

53.

Cervical Kyphosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358 Christopher A. Burks, Lauren M. Burke, and Adam L. Shimer

54.

Instrumentation Complications Occurring from Thoracic Hyperkyphosis . . . . . . . . . . . . . . . . . . . 364 Paul Millhouse, Loren Mead, Christie E. Stawicki, and Kris E. Radcliff

55.

Flatback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369 Jonathan D. Krystal and Alok D. Sharan

56.

Lumbar High-Grade Spondylolisthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376 Evan O. Baird and Sheeraz A. Qureshi

57.

Complications Related to Spinal Instrumentation and Surgical Approaches . . . . . . . . . . . . . . . . 385 Christopher Klifto and Michael Gerling

58.

Complications of Osteobiologics in Spine Surgery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394 Jozef Murar, Gregory D. Schroeder, and Wellington K. Hsu

59.

Removal and Revision of Broken Thoracolumbar Screws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408 Jay M. Zampini and Andre Jakoi

60.

How to Remove/Revise Thoracolumbar Interbody Devices (TLIF Cages/ALIF Cages). . . . . . . . 412 Michael Flippin

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418

x

Foreword Spinal Instrumentation: Challenges and Solutions is the second edition of an outstanding book that really focuses on things that potentially can go wrong and how to avoid them. As doctors, we generally go into procedures figuring out ways we can “win.” However, as time goes on and one sees the challenges with surgical treatment, especially for complex spine conditions, the concern becomes how to avoid ways of “losing.” This textbook really gets to the heart of this question and identifies how specific implant and instrumentation techniques can be done properly. It also provides great insight into the complications that can occur and then identifies ways to avoid the big challenges and complications. The textbook has four editors, of which three are senior editors who are superstars and leaders in their field with one young and up-and-coming surgeon. These are outstanding clinicians who also engage in a significant amount of research, train residents and fellows and have been prolific writers, not only of scientific articles but also of textbooks. They have considerable experience and success, and this textbook is no exception. They have divided the textbook into several sections based on the anatomy. The first section is on cranial and cranial-cervical procedures and instrumentation. The first half focuses on posterior instrumentation while the second is on anterior instrumentation. The second major section contains 40 chapters on thoracolumbar procedures with the focus on posterior instrumentation. Later chapters deal with special instrumentation considerations with a focus on really challenging situations like thoracolumbar osteoporosis and complications associated with spinal tumor surgery. The final chapters focus on the mechanical causes of instrumentation complications.

In looking through the authorship of this second edition, it is a “Who’s Who” of those key thought leaders in our field. The chapters are very well written, identifying those issues and complications that need to be avoided. This requires significant experience by the authors, and this is certainly true of the writers of this book. The value of this book is that it provides great clinical experience and pearls for surgeons to understand and utilize to avoid significant complications with instrumentation. In 2017, the challenges of spine surgery are great as we embark on more aggressive and more sophisticated surgery with all of the inherent risks that go along with it in order to deliver great care and restore spine health. The biomechanical principles, a critical aspect to understand when applying instrumentation to the spine, are nicely outlined in this book and provide a sound foundation for all levels of readers, including residents, fellows, and attending staff. The specific details regarding each implant and instrumentation approach to the spine are beautifully written about and will certainly assist all readers in taking care of patients. As medicine moves forward and we strive to obtain excellent value for what we do, the outcomes are not only going to be radiographic but clinical, and these outstanding outcomes we all desire are optimized when we understand the basic principles, the instrumentation systems, and how they are applied for certain diagnoses and certain anatomical locations of the spine. Our patients will all be better served from the efforts of the editors and the authors of this book. Dan Sucato Texas Scottish Rite Hospital for Children Dallas, Texas

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Preface Spine surgery has evolved dramatically over the last 20 years and particularly since the last edition. Innovative techniques, from the use of the operating microscope to image-guidance, have changed our approach to problems within the operating room. In addition, novel instrumentation techniques (from odontoid screws and lateral mass screws to sacroiliac fixation) have improved the surgical management of countless patients. Collectively, these changes have led to the advancement of spinal surgery. A greater understanding of spinal biomechanics and disease processes of the spine has led to a rapid advancement in the technology of spinal instrumentation. Improved spinal instrumentation, in some circumstances, has led to better patient care and contributed to improved functional outcomes. As the number of spinal implant constructs has increased, the decision-making process regarding appropriate utilization has become more difficult. The first edition of this book was intended to allow for a comparison of various systems in order to facilitate decision-making. To accommodate the rapid advancement of instrumentation systems since the last edition, the layout of the text has changed significantly. There are so many spinal instrumentation companies and systems that it is no longer possible to categorize each system. Furthermore, spinal instrumentation techniques are now taught in training courses. The purpose of the second edition is to educate the reader on the various complications of spinal instrumentation. Each chapter is written to describe the instrumentation

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complications associated with a particular anatomical or clinical situation. The chapters are intended to educate readers on the cause, diagnosis, and avoidance of instrumentation complications. As in the original edition, the surgical anatomy and approaches described in each chapter will assist the medical student as well as the house staff officer. Anatomy and approaches may be hard to conceptualize without a specific clinical application. In this text, the authors describe the relevant anatomical landmarks that must be visualized in order to safely apply spinal instrumentation. With clear examples of surgical approaches and instrumentation for particular spinal problems, this text facilitates the association of classroom knowledge and clinical application. Because of this, in addition to the summaries provided in each chapter, this text will assist the medical student, nurse, and house officer in preparing for the oral and written boards. While this book was initially intended for neurosurgeons and orthopedic surgeons who operate on the spine, it is also geared towards general neurosurgeons and orthopedic surgeons, radiologists, spine fellows, residents, students and nurse practitioners who are interested in pursuing knowledge and experience in spinal instrumentation. In addition, this text acts as a reference for the operating room, the call-room, and the practicing physician’s office.

Preface to the First Edition Spine surgery has evolved dramatically over the last 20 years. Innovative techniques, from the use of the operating microscope to image-guidance, have changed our approach to problems within the operating room. In addition, improved instrumentation (from odontoid screws and lateral mass screws to sacroiliac fixation) has improved the surgical management of countless patients. Collectively, these changes have led to the advancement of spinal surgery and subsequent improved outcomes. One aspect of spine surgery that has evolved is spinal instrumentation, which has gone through significant changes over the past decade. A greater understanding of spinal biomechanics and in the disease processes of the spine has led to a rapid advancement in the technology of spinal instrumentation. This has led to better patient care and contributed to improved functional outcomes. An increasing number of spinal implants are available in the market, which has made the decision-making process regarding their use more difficult. This book allows for a comparison of various systems in order to facilitate decision-making. In this text, there is a case-by-case description of spinal instrumentation sets with these systems. These are written by the inventors of these sets or by surgeons with expertise with these particular instrumentation sets or the inventors of the systems. Clearly differentiating the various systems will help the surgeon to determine which system should be applied under which circumstances. By listing the currently available equipment, this text provides a side-by-side comparison of the various instrumentation sets. While each system is different in one way or another, with advantages and disadvantages, an in-depth description and summary will

guide the spine surgeon away from potential pitfalls and to the best outcome for each set. In addition to text and illustrations, each chapter has a section dedicated to providing helpful hints to the reader in the use of each set. With so many sets currently on the market, many surgeons become lost in the minute details. We hope to circumvent the massive amounts of information available for each set and to address the main points that differentiate one system from another. Lastly, the surgical anatomy and approaches described in each chapter will assist the medical student as well as the house staff officer. Anatomy and approaches may be hard to conceptualize without a specific clinical application. With clear examples of surgical approaches and instrumentation for particular spinal problems, this text facilitates the association of classroom knowledge and clinical application. Because of this, in addition to the summaries provided in each chapter, this text will assist the medical student, nurse, and house officer in preparing for the oral and written boards. While this book was initially intended for neurosurgeons and orthopedic surgeons who operate on the spine, it is also geared towards general neurosurgeons and orthopedic surgeons, radiologists, spine fellows, residents, students and nurse practitioners who are interested in pursuing knowledge and experience in spinal instrumentation. In addition, this text acts as a reference for the operating room. With the immense amount of available instrumentation, we attempted to sort the multitude of instrumentation systems to assist the reader in determining which of the various systems to use in a particular case.

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Contributors John A. Abraham, MD, FACS Associate Professor of Orthopedic Surgery and Radiation Oncology Thomas Jefferson University Director, Musculoskeletal Oncology Program Sidney Kimmel Cancer Center Thomas Jefferson University Hospital Chief, Division of Orthopedic Oncology Rothman Institute Philadelphia, Pennsylvania Amir M. Abtahi, MD Department of Orthopaedics University of Utah Salt Lake City, Utah Adewale O. Adeniran, MD Orthopedic Spine Surgeon The San Antonio Orthopedic Group San Antonio, Texas Amir Ahmadian, MD NeuSpine Institute Tampa, Florida Ali Al-Omari, MBBS Spine Center Department of Orthopaedic Surgery Boston, Massachusetts Todd J. Albert, MD Surgeon in Chief and Medical Director Korein-Wilson Professor of Orthopaedic Surgery Hospital for Special Surgery Weill Cornell Medical College New York, New York Richard T. Allen, MD Assistant Clinical Professor University of California San Diego Health System La Jolla, California Louis F. Amorosa, MD Assistant Professor of Orthopaedic Surgery Montefiore Medical Center/Albert Einstein College of Medicine Bronx, New York

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Evan O. Baird, MD Spine Surgery Department of Orthopaedic Surgery Mount Sinai Health System New York, New York S. Samuel Bederman, MD, PhD, FRCSC Spine Surgeon, Orthopaedic Surgery School of Medicine Department of Orthopaedic Surgery UC Irvine Medical Center University of California, Irvine Orange, California Adam J. Bevevino, MD Thomas Jefferson University Hospital Rothman Institute Philadelphia, Pennsylvania Nitin Bhatia, MD Chairman, Department of Orthopaedic Surgery Chief, Spine Service Residency Program Director Department of Orthopaedic Surgery University of California, Irvine Orange, California Jesse E. Bible, MD, MHS Assistant Professor Department of Orthopaedics Penn State Milton S. Hershey Medical Center Hershey, Pennsylvania Jacob M. Buchowski, MD, MS Professor of Orthopaedic and Neurological Surgery Director, Washington University Spine Fellowship Director, Center for Spinal Tumors Department of Orthopaedic Surgery Washington University in St. Louis BJC Institute of Health St. Louis, Missouri Lauren M. Burke, MD Orthopedic Associates of Hartford Hartford, Connecticut Christopher A. Burks, MD University of Virginia Charlottesville, Virginia

Contributors

John M. Caridi, MD Department of Neurosurgery Icahn School of Medicine at Mount Sinai New York, New York

Clinton J. Devin, MD Associate Professor Department of Orthopaedics Vanderbilt University Medical Center Nashville, Tennessee

Thomas Cha, MD, MBA Spine Center Department of Orthopaedic Surgery Massachusetts General Hospital Boston, Massachusetts

Jonathan Duncan, MD Orthopaedic Spine Surgeon The San Antonio Orthopaedic Group San Antonio, Texas

Saad Chaudhary, MD Assistant Professor Department of Orthopaedic Surgery Icahn School of Medicine at Mount Sinai New York, New York

Richard G. Fessler, MD, PhD Professor Department of Neurosurgery Rush University Medical Center Chicago, Illinois

Ivan Cheng, MD Associate Professor of Orthopaedic Surgery Associate Professor of Neurosurgery Stanford University Medical Center Redwood City, California

Allison Fillar, MD Orthopaedic Sports Medicine Fellow MedStar Union Memorial Hospital Baltimore, Maryland

Samuel K. Cho, MD Department of Orthopaedic Surgery Icahn School of Medicine at Mount Sinai New York, New York Woojin Cho, MD, PhD Assistant Professor of Orthopaedic Surgery Albert Einstein College of Medicine Chief, Orthopaedic Spine Surgery Research Director, Multidisciplinary Spine Group Montefiore Medical Center The University Hospital for Albert Einstein College of Medicine New York, New York Scott D. Daffner, MD Associate Professor Department of Orthopaedics West Virginia University Morgantown, West Virginia Anthony Degiacomo, MD Orthopedic Surgery Resident Department of Orthopaedic Surgery Boston University School of Medicine Boston, Massachusetts Armen R. Deukmedjian, MD NeuSpine Institute Tampa, Florida

Steven J. Fineberg, MD Research Coordinator Department of Orthopaedic Surgery Rush University Medical Center Chicago, Illinois Michael Flippin, MD Orthopedic Surgeon Kaiser-Permanente Medical Center San Diego, California Tristan Fried, BS Drexel University Philadelphia, Pennsylvania Gurpreet S. Gandhoke, MD Chief Resident Department of Neurological Surgery University of Pittsburgh Medical Center Pittsburgh, Pennsylvania Michael Gerling, MD Chief of Spine Surgery NYU Langone Brooklyn Clinical Assistant Professor NYU Langone New York, New York George M. Ghobrial, MD Neurosurgeon Novant Health Winston Salem, North Carolina

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Contributors

Ahmer Ghori, MD Harvard Combined Orthopedics Residency Program Boston, Massachusetts Nicholas S. Golinvaux, MD Department of Orthopaedic Surgery and Rehabilitation Vanderbilt University Medical Center Nashville, Tennessee Jonathan N. Grauer, MD Department of Orthopaedics and Rehabilitation Yale School of Medicine New Haven, Connecticut Raymond Hah, MD Spine Surgery Assistant Professor of Orthopaedic Surgery The Keck School of Medicine of the University of Southern California Los Angeles, California Colin M. Haines, MD Virginia Spine Institute Reston, Virginia James S. Harrop, MD Professor of Neurosurgery Thomas Jefferson University Philadelphia, Pennsylvania Joshua Heller, MD Assistant Professor of Neurosurgery Thomas Jefferson University Philadelphia, Pennsylvania Alan S. Hilibrand, MD The Joseph and Marie Field Professor of Spinal Surgery Vice Chairman, Academic Affairs and Faculty Development Co-Chief of Spinal Surgery Director of Orthopaedic Medical Education Professor of Neurological Surgery Jefferson Medical College/The Rothman Institute, Philadelphia, Pennsylvania Brandon P. Hirsch, MD Fellow Orthopaedic Spine Surgery Midwest Orthopaedics at Rush Rush Medical Center Chicago, Illinois Christoph P. Hofstetter, MD, PhD Assistant Professor Director of Spine Surgery

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University of Washington Medical Center Department of Neurological Surgery University of Washington Seattle, Washington Wellington K. Hsu, MD Department of Orthopaedic Surgery Northwestern University Feinberg School of Medicine Chicago, Illinois Heidi Martin Hullinger, MD Clinical Assistant Professor of Orthopaedics Rutgers-NJMS New Jersey Spine Specialists Summit, New Jersey Namath Syed Hussain, MD, MBA Department of Neurosurgery Loma Linda University School of Medicine Loma Linda, California Andre Jakoi, MD Department of Orthopaedic Surgery Drexel University College of Medicine Hahnemann University Hospital Philadelphia, Pennsylvania Seyed Babak Kalantar, MD Associate Professor Chief, Division of Spinal Surgery Department of Orthopaedics Medstar Georgetown University Hospital Washington, DC Adam S. Kanter, MD Associate Professor Chief, UPMC Presbyterian Spine Service Director, Minimally Invasive Spine Program Co-Director, Spine Fellowship Program Pittsburgh, Pennsylvania Jonathan M. Karnes, MD Department of Orthopaedics West Virginia University Morgantown, West Virginia Michael P. Kelly, MD Assistant Professor of Orthopedic Surgery Assistant Professor of Neurological Surgery Washington University School of Medicine Saint Louis, Missouri

Contributors

Mohammed A. Khaleel, MD, MS Orthopaedic Spine Surgeon Assistant Professor University of Texas Southwestern Medical Center Chief, Orthopaedic Spine Surgery Parkland Health and Hospital System Consultant Spine Surgeon Texas Scottish Rite Hospital for Children Dallas, Texas Daniel H. Kim, MD, FAANS, FACS Nancy, Clive, and Pierce Runnells Distinguished Chair in Neuroscience Professor Director of Spinal Neurosurgery, Reconstructive Peripheral Nerve Surgery Director of Microsurgical Robotic Laboratory Department of Neurosurgery University of Texas Houston, Texas Christopher Klifto, MD Assistant Professor Department of Orthopaedic Surgery Duke University School of Medicine Durham, North Carolina John Koerner, MD Department of Orthopaedic Surgery Hackensack University Medical Center Hackensack, New Jersey Eitan Kohan, MD Department of Orthopaedics Washington University in St. Louis St. Louis, Missouri Jonathan D. Krystal, MD Spine Fellow Rothman Institute Thomas Jefferson University Philadelphia, Pennsylvania Brandon D. Lawrence, MD Assistant Professor Department of Orthopaedic Surgery University of Utah School of Medicine Salt Lake City, Utah Vu H. Le, MD Orthopedic Surgery Hoag Orthopedic Institute Irvine, California

Alejandro J. Lopez, BS Medical Student Midwestern University Downers Grove, Illinois Daniel Lubelski, MD Resident Department of Neurosurgery Johns Hopkins Hospital Baltimore, Maryland Rex A. W. Marco, MD Vice Chairman Chief of Reconstructive Spine Surgery and Musculoskeletal Oncology Houston Methodist Hospital Houston, Texas David B. McConda, MD Orthopaedic Spine Surgeon KentuckyOne Health Flaget Memorial Hospital Bardstown, Kentucky Loren Mead, BA MD Candidate Perelman School of Medicine University of Pennsylvania Philadelphia, Pennsylvania Dennis S. Meredith, MD Woodland Healthcare Woodland California Addisu Mesfin, MD Associate Professor Department of Orthopedic Surgery University of Rochester School of Medicine Rochester, New York Andrew H. Milby, MD Assistant Professor Department of Orthopaedic Surgery University of Pennsylvania Philadelphia, Pennsylvania Paul Millhouse, MD Spine Research Fellow Department of Orthopedic Surgery Thomas Jefferson University Philadelphia, Pennsylvania Michael H. Moghimi, MD Spinal Surgeon Orthopaedic Specialists of Austin Austin, Texas

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Contributors

Yusef I. Mosley, MD USF Department of Neurosurgery Tampa, Florida Isaac Moss, MD Assistant Professor of Orthopaedic Surgery Comprehensive Spine Center, UConn Musculoskeletal Institute Assistant Resident Education Director University of Connecticut School of Medicine Farmington, Connecticut Thomas E. Mroz, MD Director of the Center for Spine Health Director of the Spine Surgery Fellowship at Cleveland Clinic Director, Clinical Research Department of Orthopaedic Surgery Department of Neurological Surgery Center for Spine Health at Cleveland Clinic Cleveland, Ohio Jozef Murar, MD Department of Orthopaedic Surgery Northwestern University Feinberg School of Medicine Chicago, Illinois Ryan S. Murray, MD Resident Physician Department of Orthopaedic Surgery Medstar Georgetown University Hospital Washington, DC Matthew Nalbandian, MD Division of Spinal Surgery Department of Orthopaedic Surgery Department of Neurosurgery NYU Medical Center NYU School of Medicine New York, New York Ahmad Nassr, MD Consultant Associate Professor of Orthopedic Surgery and Biomedical Engineering Mayo Clinic Rochester Minnesota Douglas J. Nestorovski, MD Resident Department of Orthopaedic Surgery Washington University St. Louis, Missouri

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Alex Neusner, MD Department of Surgery Temple University Hospital Philadelphia, Pennsylvania Joseph R. O'Brien, MD Orthopaedic Surgeon OrthoBethesda Bethesda, Maryland Medical Director of Minimally Invasive Orthopaedic Spine Surgery Virginia Hospital Center Arlington, Virginia Matthew Oglesby, MD Research Coordinator Department of Orthopaedic Surgery Rush University Medical Center Chicago, Illinois David O. Okonkwo, MD Professor Executive Vice Chair Clinical Operations Clinical Director Brain Trauma Research Center Department of Neurological Surgery University of Pittsburgh Medical Center Pittsburgh, Pennsylvania Rod J. Oskouian Jr., MD Chief of Spine Swedish Neuroscience Institute Seattle, Washington Peter G. Passias, MD Associate Professor Division of Spinal Surgery Department of Orthopaedic Surgery Department of Neurosurgery NYU Medical Center NYU School of Medicine New York, New York Alpesh A. Patel, MD Director of Orthopedic Spine Surgery Department of Orthopedic Surgery Northwestern University Feinberg School of Medicine Evanston, Illinois Rakesh D. Patel, MD Department of Orthopaedic Surgery University of Michigan Ann Arbor, Michigan

Contributors

Adam Pearson, MD Section Chief of Orthopaedic Surgery Assistant Professor of Orthopaedic Surgery Geisel School of Medicine at Dartmouth Lebanon, New Hampshire Mick J. Perez-Cruet, MD, MS Vice-Chairman, Professor Director, Minimally Invasive Spine Surgery and Spine Program Department of Neurological Surgery Oakland University William Beaumont School of Medicine Royal Oak, Michigan Jason Pittman, MD, PhD Assistant Professor Department of Surgery Division of Orthopedic Surgery The University of Alabama at Birmingham Birmingham, Alabama Dan Plev, MD Consultant Spine Neurosurgeon London Spinal Clinic London, England, United Kingdom American Institute of Minimally Invasive Spine Surgery, American Medical Centre Nicosia, Cyprus Carrie Poorman, BS Division of Spinal Surgery Department of Orthopaedic Surgery Department of Neurosurgery NYU Medical Center NYU School of Medicine New York, New York Srinivas Prasad, MD Associate Professor of Neurosurgery Thomas Jefferson University Philadelphia, Pennsylvania Steven Presciutti, MD Associate Professor of Orthopaedic Surgery Chief of Spine Surgery Department of Orthopaedics Emory University School of Medicine Atlanta, Georgia Sheeraz A. Qureshi, MD Professor Hospital for Special Surgery Weill Cornell Medicine Cornell University New York, New York

Kris E. Radcliff, MD Associate Professor Department of Orthopedic Surgery Thomas Jefferson University Philadelphia, Pennsylvania The Rothman Institute Egg Harbor, New Jersey Wilson Z. Ray, MD Department of Neurological Surgery Washington University School of Medicine Saint Louis, Missouri Charles A. Reitman, MD Professor and Vice Chair Department of Orthopaedics Medical University of South Carolina Charleston, South Carolina Jeffrey A. Rihn, MD Associate Professor of Orthopaedic Surgery Co-Director of Delaware Valley Spinal Cord Injury Center Rothman Institute/Thomas Jefferson University Hospital Philadelphia, Pennsylvania Jason W. Savage, MD Cleveland Clinic Cleveland, Ohio Justin K. Scheer, MD Neurosurgery Resident University of Illinois at Chicago Chicago, Illinois Gregory D. Schroeder, MD Assistant Professor Department of Orthopedic Surgery Thomas Jefferson University Philadelphia, Pennsylvania †Nicholas Schroeder, MD Department of Orthopaedic Surgery University of Michigan Ann Arbor, Michigan Sean N. Shahrestani, MD Department of Orthopedics University of Texas Southwestern Medical Center Dallas, Texas Alok D. Sharan, MD Assistant Professor Chief, Orthopaedic Spine Service Department of Orthopaedic Surgery Montefiore Medical Group New York, New York

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Contributors

Tom Sherman, MD Orthopedic Associates of Lancaster Lancaster, Pennsylvania Adam L. Shimer, MD University of Virginia Charlottesville, Virginia Michael Silverstein, MD Orthopedic Spine Fellow OrthoCarolina Spine Center Charlotte, North Carolina Kern Singh, MD Professor Co-Director of Minimally Invasive Spine Surgery Co-Director of Spine Surgery Fellowship Department of Orthopaedic Surgery Rush University Medical Center Chicago, Illinois Branko Skovrlj, MD Department of Neurosurgery Icahn School of Medicine at Mount Sinai New York, New York Harvey E. Smith, MD Assistant Professor Department of Orthopaedic Surgery University of Pennsylvania Philadelphia, Pennsylvania Jeremy Smith, MD Orthopaedic Spine Surgeon Orthopaedic Specialty Institute Director, Spine Surgery Fellowship Hoag Orthopaedic Institute Orange, California Zachary A. Smith, MD Assistant Professor of Neurosurgery Northwestern University Feinberg School of Medicine Evanston, Illinois William Ryan Spiker, MD Assistant Professor Department of Orthopaedic Surgery University of Utah Salt Lake City, Utah

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Michael Stauff, MD Spine Surgeon Assistant Professor Department of Orthopedics and Physical Rehab University of Massachusetts Medical School UMass Memorial Medical Center Worcester, Massachusetts Christie E. Stawicki, BA Spine Research Fellow Graduate Student Research Assistant The Rothman Institute Thomas Jefferson University Philadelphia, Pennsylvania Chadi Tannoury, MD Assistant Professor Department of Orthopedic Surgery Boston University School of Medicine Boston, Massachusetts Tony Tannoury, MD Professor Department of Orthopedic Surgery Boston University School of Medicine Boston, Massachusetts Brian Tinsley, MD Orthopaedic Associates of Reading West Reading, Pennsylvania Vidyadhar V. Upasani, MD Co-Director International Center for Pediatric and Adolescent Hip Disorders Rady's Children's Hospital – San Diego San Diego, California Juan S. Uribe, MD Professor of Neurosurgery Chief, Division of Spinal Disorders Volker K. H. Sonntag Chair of Spine Research Barrow Neurological Institute Phoenix, Arizona Alexander R. Vaccaro, MD, PhD, MBA Richard H. Rothman Professor and Chairman Department of Orthopaedic Surgery Thomas Jefferson University President The Rothman Institute Co-Director, Delaware Valley Spinal Cord Injury Center Co-Director, Spine Surgery and Spinal Cord Injury Fellowship Philadelphia, Pennsylvania

Contributors

Vikas Varma, MD Department of Orthopaedic Surgery Icahn School of Medicine at Mount Sinai New York, New York Kushagra Verma, MD Assistant Professor Department of Orthopaedics and Sports Medicine University of Washington Seattle, Washington Michael Vives, MD Associate Professor Chief of the Spine Division Department of Orthopedic Surgery Rutgers New Jersey Medical School Newark, New Jersey Michael Y. Wang, MD, FACS Professor Department of Neurosurgery Department of Physical Medicine and Rehabilitation Chief of Neurosurgery University of Miami Hospital University of Miami Miller School of Medicine Miami, Florida Peter G. Whang, MD Associate Professor, Spine Service Department of Orthopaedics and Rehabilitation Yale University School of Medicine New Haven, Connecticut Andrew P. White, MD Orthopaedic Spine Surgeon Assistant Professor Harvard Medical School Chief, Orthopaedic Spine Surgery Co-director, Spine Center - Beth Israel Deaconess Medical Center Director, Spine Surgery Fellowship Beth Israel Deaconess Medical Center Boston, Massachusetts Kim A. Williams Jr., MD Neurosurgeon Alexian Brothers Health Elk Grove Village, Illinois

Seth K. Williams, MD Associate Professor Department of Orthopedics and Rehabilitation University of Wisconsin School of Medicine and Public Health University of Wisconsin–Madison Madison, Wisconsin Adam Wollowick, MD, MBA Senior Director of Business Development Stryker Spine Allendale, New Jersey Jason Wong, MD Attending Physician Maimonides Medical Center Brooklyn, New York Barrett I. Woods, MD Assistant Professor Department of Orthopedic Surgery Department of Neurological Surgery Thomas Jefferson University The Rothman Institute Philadelphia, Pennsylvania Sun Yang, MD Division of Spinal Surgery Department of Orthopaedic Surgery Department of Neurosurgery NYU Medical Center NYU School of Medicine New York, New York Jay M. Zampini, MD Instructor in Orthopaedic Surgery Harvard Medical School Division of Spine Surgery Brigham and Women’s Hospital Boston, Massachusetts Andrew Zhang, MD Resident Physician Department of Surgery Montefiore Medical Center Albert Einstein College of Medicine Bronx, New York

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Part 1

1 Complications of Occipital Instrumentation

Cranial

2 Vascular Complications of Posterior Cervical Procedures

14

3 Complications of C1 Lateral Mass Screw Fixation

23

4 Complications of C2 Pedicle and Pars Screw Placement

31

5 Complications of C1–C2 Transarticular Screws

37

6 Complications of C1–C2 Wiring

43

7 Complications of C2 Translaminar Screw Placement

47

8 Complications of Subaxial Lateral Mass Screw Fixation

53

9 Pedicle Screw Fixation in the Subaxial Cervical Spine: Indications, Contraindications, and Complications

57

10 Complications Related to Selected Instrumented Fusion Levels for Subaxial Fusions

61

11 Complications of Laminoplasty

67

12 Complications Related to Cervicothoracic Instrumentation

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13 Anterior C1–C2 Fusion Instrumentation Complications

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14 Complications of Odontoid Fracture Treatment

85

3

1

15 Complications of Static Anterior Cervical Plates

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16 Complications of Translational Anterior Cervical Plates

102

17 Ectopic Ossification following Anterior Cervical Discectomy and Fusion or Disc Replacement

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18 Failure of Anterior Cervical, Low-Profile, Stand-Alone Screw–Plate Devices

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19 Complications of Buttress Plating Multilevel Anterior Cervical Corpectomies

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20 Complications of Cervical Arthroplasty

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Complications of Occipital Instrumentation

1 Complications of Occipital Instrumentation Seyed Babak Kalantar and Tom Sherman

1.1 Introduction The etiology of occipitocervical and atlantoaxial pathology is broad and includes degenerative processes, trauma, tumor, rheumatologic disease, infection, and congenital malformations. In a comprehensive systematic review, Winegar et al studied the complications and outcomes associated with the various occipitocervical instrumentation techniques. Screw–rod techniques offered the overall greatest fusion rates; however, the underlying etiology of instability also appears to affect the rate of fusion.1 Regardless of the etiology, however, the end result of these disease processes is often instability, which can lead to translation, longitudinal displacement, and/or basilar invagination. Instability at this level may result in pain, paresis, paralysis, respiratory distress, or death. Occipitocervical arthrodesis is a technically challenging procedure indicated in the setting of instability and in conjunction with decompressive surgery. To attain an osseous fusion, decortication of the involved levels with placement of bone graft and immediate rigid internal fixation with appropriate spinal instrumentation are required. Although the majority of these procedures are effective and safe, complications do occur. It is imperative that the surgeon be familiar with potential occipitocervical fusion complications and failures, which consist of cranial venous sinus injury, vertebral artery (VA) injury, hardware/fusion malposition, infection, nonunion, dural tear, and hardware failure.

1.2 Anatomy In considering these complications and mitigating their occurrence, the surgeon must have a broad understanding of the relevant surgical anatomy of the occipitocervical region, as this has important implications for surgical technique and hardware placement. With regard to the base of skull, there are several bony landmarks to be familiar with that will assist in appropriate and safe hardware placement (▶ Fig. 1.1). The external occipital

protuberance, or inion, is a palpable projection superior to the apex of the nuchal line and in the midline of the squama portion of the skull and the attachment site of the nuchal ligament, which serves as an avascular plane of dissection. Bone in this region is thickest, up to 17.5 ± 3 mm, and becomes thinner in a radial distribution from this point. The inion corresponds to the intracranial torcula, which is the confluence of the transverse sinuses. The transverse sinuses correspond to the superior nuchal line, a palpable projection running at a 43-degree angle from the horizontal skull base line.2 The occipitalis, splenius capitis, trapezius, and sternocleidomastoid also attach here, as the rectus capitis attaches to the inferior nuchal line.3 The occipital condyles are biconvex structures, which articulate with the cervical atlas, supporting the head’s 10-pound weight. Each condyle is on average 23.4, 10.6, and 9.2 mm in length, width, and height, respectively. The intercondylar distance decreases from anterior to posterior, with corresponding average distances of 41.6 and 21.0 mm, respectively.4 The atlas, C1, is a ring structure with two lateral masses articulating with the occipital condyles superiorly and the axis, C2, inferiorly. The posterior aspect of the anterior arch of C1 articulates with the odontoid via a synovial joint. Each mass has a mean width, height, and anteroposterior dimension of 15.47, 14.09, and 17.21 mm, respectively. The dimensions of C1 itself are 78.6, 15.4, and 45.8 mm for width, height, and anteroposterior dimension, respectively, and it accommodates the spinal cord and dens.5,6 The VAs traverse the posterior arch of C1 through a sulcus or groove after emerging from the VA foramina of C2 and before entering the foramen magnum. Some individuals possess an ossified posterior atlanto-occipital membrane also known as an arcuate foramen or ponticulus posticus, which essentially envelopes the artery within the posterolateral aspect of C1. It is seen in approximately 1.14 to 18% of individuals and more commonly in females than males.7 Its presence has implications for safe hardware placement. Biomechanically, the occipital–C1–C2 complex is the most mobile of the cervical spine and functions as a single unit, with

Fig. 1.1 Anatomy of the skull relative to occipital fixation. (Reproduced with permission from Bransford RJ, Lee MJ, Reis A. Posterior fixation of the upper cervical spine: contemporary techniques. J Am Acad Orthop Surg. 2011;19(2):63–71.)

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Cranial

Fig. 1.2 Primary and mean movement. (a) The primary movement at the occiput–C1 is flexion and extension. Mean movement is 23 to 24.5 degrees. (b) The primary movement at C1–C2 is axial rotation, and mean movement is 23.3 to 38.9 degrees. (c) Flexion/extension at C1–C2 ranges from 10.1 to 22.4 degrees. (Benzel EC, ed. Biomechanics of Spine Stabilization. Rolling Meadows, II: AANS Press, 2001, with permission from Thieme Publishers.)

the atlas serving as a “washer” between the occiput and the cervical spine (▶ Fig. 1.2).8 The condylar–atlas articulation allows for 23 to 24.5 degrees of flexion and extension, with flexion limited by impingement of the dens and foramen magnum and extension by the tectorial membrane. A total of 6.8 to 11 degrees of lateral bending occurs at this articulation and is limited by the alar ligament, while axial rotation at this articulation averages 2.4 to 7.2 degrees per side.4,8,9 The C1–C2 articulation accounts for rotation mostly, with an average total of 23.3 to 38.9 degrees per side that is limited by the articulation itself, the ipsilateral transverse ligament, the contralateral alar ligament, and capsular ligaments. Rotation here is negatively coupled to that of the occipital–C1 articulation.8 Flexion and extension at C1–C2 are between 10.1 and 22.4 degrees on average and are limited by the transverse ligament and tectorial membrane, respectively. Lateral bending is a minimal 6.7 degrees at the C1-C2 articulation and is limited by the alar ligaments. Instability at this level causes increased motion in all planes. This has been simulated with surgical odontoidectomies, which increases flexion by 70.8%, extension by 104%, and lateral bending by 95%, as well as increases 12.7 mm anteroposterior, 6.7 mm lateral, and 2.0 mm cephalocaudal translation.10 Similar consequences have also been mirrored with disruption of the transverse ligament and bilateral alar ligaments.11

1.3 Instrumentation History The first attempt at occipitocervical arthrodesis was in 1927 by Foerester using a fibular strut onlay graft, and over the next several decades subtle variations of this technique were utilized.12 The first instrumentation attempts were made in the form of posterior wiring; however, rates of pseudoarthrosis were upward of 30% even when used in conjunction with a halo.13 This led to the development of rod-and-wire techniques that were semirigid in nature and composed of a contoured Ushaped rod secured to the occiput and suboccipital spine with wires (▶ Fig. 1.3).14 Screw and plate–based systems were developed in the mid-1990s and were either bilateral straight plates or Y-shaped plates that extended from the lateral masses to the occiput. These posed a technical challenge due to mismatch of the plate configuration and screw trajectory to patients’ variable anatomy. The most modern implants have evolved and generally feature an independent occipital plate with locking screw technology that attaches to two independently contoured rods

4

fixed to upper cervical screws (▶ Fig. 1.4).15 The four constructs available today consist of a one-piece “inverted U or Y” rod/ plate fixed by occipital and cervical wiring and/or screws, a modular occipital plate and cervical rod construct with screws, occipital buttons connected to cervical rods, and condylar polyaxial screws connected to cervical rods.

1.4 Technique In general, once preoperative planning has been completed, the patient should be positioned and secured with three- or fourpoint fixation to aid in reduction. The shoulders are taped to improve intraoperative radiographic visualization and facilitate dissection through posterior neck folds. Placing the patient in a reverse Trendelenburg position facilitates venous drainage and mitigates facial swelling. A midline dissection, proceeding down to the occiput, allows for subperiosteal dissection using electrocautery to minimize blood loss. When using occipital wiring, two small burr holes are made on either side of the rod or plate and the dura dissected off between the holes. A silk tie can then be passed from one hole to facilitate passage of a cable by tying it to one end and pulling it through. The wire is then twisted or cinched around the plate or rod. Should occipital buttons be used, a burr hole large enough in diameter to accommodate the button is made 1 cm away from the intended button position. A small trough is then made with a smaller burr from the hole to the final intended position, and an epidural plane is defined. The inside button, attached to a central rod is slid into its final position. The plate is then placed over the central rod of the button and a nut connected to the inside portion over the plate. The most commonly employed method of fixation with an occipital plate secured with screws (authors’ preferred technique) can be carried out by first marking intended screw locations. The decision to place bicortical or unicortical screws should be determined and the cortical thickness reviewed prior to surgery on preoperative imaging. A drill guide can be used to avoid drilling too deeply while making pilot holes. Each screw hole should be probed to ensure that the dura is intact. A handheld tap can then be used, and a depth gauge to select the appropriate screw length. If condylar screws are to be placed, the entry point, most typically 5 mm superior to the arch of C1 and 5 mm lateral to the

Complications of Occipital Instrumentation

Fig. 1.3 Modes of occipital fixation to exploit the various anatomical features of the skull bone. (a) Contoured rod with occipital and sublaminar wires. (b) Midline occipital plate with variable screws without C1 fixation. (c) Midline occipital plate with variable screws with C1 fixation. (d) Fixed plate spanning the occiput-C2 region. (e) Paired plates with a cross connector. (Reproduced with permission from Stock GH, Vaccaro AR, Brown AK, Anderson PA. Contemporary posterior occipital fixation. J Bone Joint Surg Am. 2006;88(7):1642–1649.)

Fig. 1.4 Example of a modular occipital plate and screw system. The occipital plate is applied separately from the spinal rods and connectors. It is connected to the spinal rods by locking caps. (Reproduced with permission from Bransford RJ, Lee MJ, Reis A. Posterior fixation of the upper cervical spine: contemporary techniques. J Am Acad Orthop Surg. 2011;19(2):63–71.)

foramen magnum, should first be decorticated. The intended trajectory is usually 12 to 22 degrees medial and 5 degrees superior from the entry point but is anatomically dependent.

The hole is tapped with an undersized tap after drilling often to 30 to 35 mm so that a polyaxial screw may be placed. There are multiple options for fixation to the atlas and axis. For transarticular (TA) screw placement, dissection proceeds to the lateral borders of C2’s lateral masses and proximally along the pedicle and pars cephalad to the C1–C2 joint. Should C1 lateral mass screws be placed, dissection of the posterior ring of C1 must be conducted with hemostatic control of the venous plexus encountered between C1 and C2. TA screws should be placed only after drilling from the C2 pars to the C1 lateral mass in small increments and with a clear understanding of the course of the VA. Determination of the appropriate starting points for the C1 lateral mass screws depends on individual anatomy. The Harms technique guides screw placement and requires inferior retraction of the C2 nerve root, identification of the dura medially, and palpation of the medial border of the lateral mass (▶ Fig. 1.5).16 C2 pedicle screws are typically placed in a trajectory oriented less cephalad and more medial than that of the TA screws. Pars screws for C2 are placed with a trajectory more medial than that required for C2 pedicle screws. Both are placed after palpating along the medial border of the pars with a blunt instrument to confirm the proposed trajectory. Typically, pars screws will be significantly shorter than C2 pedicle screws. C2 translaminar screws are placed after dissecting the lamina and while palpating the anterior and posterior laminar walls via a “goalpost technique” to ensure cortical integrity while drilling. To avoid abutment of the screw heads medially, one screw may be placed slightly inferior to the contralateral side.12 Bone graft should be placed after decortication with a highspeed burr. Should tricortical iliac crest allograft or autograft be used, notches should be made to accommodate the C2 spinous process and C1 lamina so that the graft is flush with the occiput. The graft may be secured with cable or suture. Other grafting techniques include cancellous auto- and allograft, local bone, and demineralized bone graft.17

5

Cranial

Fig. 1.5 Anatomy of the C1 lateral masses pertinent to C1 lateral mass screw fixation. The ideal starting point may require distal retraction of the C2 nerve. Lateral to the C1 lateral masses the vertebral arteries are located. Additionally, the vertebral groove in the C1 arch often corresponds to the location of the C1 lateral masses. (Reproduced with permission from Bransford RJ, Lee MJ, Reis A. Posterior fixation of the upper cervical spine: contemporary techniques. J Am Acad Orthop Surg. 2011;19(2):63 -71.)

1.5 Complications As with all surgical spinal arthrodeses, the potential for complications exist, some of which are unique to the region, given the anatomic features as previously described. These will be discussed in detail and include cranial venous sinus injury, VA injury, hardware malposition, infection, nonunion, dural tear, and hardware failure. By understanding these complications and their etiologies, the surgeon will be better equipped to mitigate their occurrence.

1.6 Venous Sinus Injury The advent of independent occipital plates has resulted in improved fixation and a stronger construct; however, it has not totally circumvented the potential risks of venous sinus injury seen with occipital-axial wiring. Venous sinus injury is largely regarded as an unusual event with incidence of less than 1%, most commonly resulting from intracranial screw penetration. Its occurrence rarely results in serious consequence. In a prospective descriptive diagnostic study, Izeki et al analyzed the variability of venous sinuses in individuals and their relationship to intended screw position. They concluded that additional imaging sequences of the venous sinuses can easily and cheaply be acquired in addition to computed tomography angiography (CTA) that is commonly ordered for VA mapping.18,19 In maximizing pullout strength of the occipital plate construct, the thickest portion of bone is targeted (▶ Fig. 1.6). This corresponds to the inion to which the venous sinuses are in close proximity and pose an inherent risk with screw placement in this region.2 In a cadaveric study, Nadim and colleagues demonstrated that venous sinus injury could safely be avoided by placing screws at least 2 cm inferior to the superior nuchal line.20 This landmark has been called into question, as Izeki and colleagues demonstrated that there is large variability in the course and location of the confluence of sinuses and venous sinuses. Thus, some advocate for routine CT-venography (CT-V) to map the sinuses in conjunction with CT-arteriography to best delineate optimal occipital screw placement, which can be performed without significant increased radiation exposure or

6

Fig. 1.6 The thickness of the skull in various locations relative to occipital fixation. (Reproduced with permission from Ebraheim NA, Lu J, Biyani A, Brown JA, Yeasting RA. An anatomic study of the thickness of the occipital bone. Implications for occipitocervical instrumentation. Spine (Phila Pa 1976). 1996;21(15):1725–1729; discussion 1729–1730.)

technologist workload.18 It bears mentioning that some have advocated for unicortical fixation to avoid intracranial penetration altogether, but this may affect pullout strength of the construct, and will be discussed in detail. The sequela of venous sinus injury is variable. Izeki and colleagues reported intracranial bleeding that was encountered with transoccipital drilling and controlled with insertion of the screw that ultimately resulted in an asymptomatic partial transverse sinus occlusion.18 However, Lee and colleagues reported a case in which an iatrogenic injury to the transverse sinus led to an epidural hematoma that was fatal.19 A potential dreaded complication of venous sinus injury is intracranial venous thrombosis (VT), of which infection, hematological disorders, trauma, and cranial surgery are well-described etiologies.18,21 Although there are no reports of this occurring following placement of occipital screws, it is possible that endothelial damage from drilling or screw placement could be a risk factor for VT.18 Sequelae of VT may include venous hypertension resulting in hemiplegia, gait ataxia and convulsive seizures, and more commonly headache, nausea, and visual obscuration.21,22 Symptom onset often varies from the immediate postoperative period to 8 months postsurgery, complicating accurate diagnoses. Should venous sinus violation be recognized intraoperatively, no consensus exists as to immediate management; however, the authors’ preferred management is screw placement to control the hemorrhage and subsequent completion of the planned procedure barring further complication. The authors do not routinely obtain preoperative CTvenography.

Complications of Occipital Instrumentation

1.7 Vertebral Artery Injury Iatrogenic injury to the VA may result in fistula, pseudoaneurysm, dissection, occlusion, or massive bleeding.23,24 It may be encountered with dissection of C1, placement of C1 lateral mass screws, or TA screw placement. This is the case given that the appropriate C1 start point for lateral mass screws has been described as the junction of the C1 posterior arch and the midpoint of the posterior inferior lateral mass, where several critical neurovascular structures are at risk including the spinal cord, C2 nerve root, and venous plexus surrounding the greater occipital nerve.16,25 The VA is also at risk with the novel technique of condylar screws.26,27 The potential variable course of the VA below the C1 arch also poses a risk.28 An anomalous VA course has been reported in 2 to 5.4% of individuals.24,29 Several patterns have been described: Type I: a persistent first intersegmental artery in which the VA bypasses C1’s transverse foramen, coursing anterior to it after exiting the axis’ transverse foramen; Type II: a fenestrated VA (duplicate segment) at the level of the atlas with one segment coursing normally and another entering below the arch and joining the normal segment above again; Type III: a normal VA course with the posterior inferior cerebellar artery (PICA) originating from the VA between C1 and C2 entering the canal caudal to C1 (▶ Fig. 1.7). The incidence of these irregular patterns is found in ▶ Table 1.1.24 Furthermore, some patients may have a “high riding VA,” in which the VA bends more medially, too posterior, or too high, causing the isthmus of C1 to be narrowed and making TA screw placement challenging or not possible.30 The course of the VA when placing C1 lateral mass screws must also be considered, as some have advocated for an entry point on the superior aspect of the posterior arch, where the VA may be traversing within an arcuate foramen and the overlying ponticulus posticus mistaken for a broad lamina.31 Four types of arcuate foramina have been described by Hong and colleagues. Type I: a bony spicule from the superior facet (14%); Type II: bony spicule projects from the posterior arch of the atlas toward the superior facet (9.6%); Type III: bony spicule originating from the superior facet and posterior arch (34.6%);

Table 1.1 Summary of anomalous VAs at the CVJ Course of V3 segment No. of cases

Incidence rate (%)

Normal

958

94.6

Unilateral PIA

39

3.8

Bilateral PIA

8

0.8

Unilateral FA

5

0.5

Unilateral PIA and contralateral FA

1

0.1

PICA between C1 and C2

2

0.2

Abbreviations: CVJ, craniovertebral junction; FA, fenestrated VA; PIA, persistent first intersegmental artery; VAs, vertebral arteries. Source: Hong et al.24

Type IV: complete ponticulus (41.7%) (▶ Fig. 1.8).24 The surgeon should be aware of this potential anomaly, and it is essential that preoperative lateral radiographs and CT imaging be reviewed prior to surgery. Owing to these aberrant VA courses and the prevalence of ponticulus posticus anomalies, the surgeon could give serious consideration to preoperative CTA for VA mapping and instrumentation planning, though a preoperative MRI will often give valuable and adequate information.32,33 Should VA injury occur, which is most common during softtissue dissection around the C1 arch, hemostasis should immediately be obtained and a vascular surgery consult called. If it is encountered during screw placement, a short screw should be placed to achieve tamponade. No additional screws should be placed contralateral to the known or suspected injury given that this could result in brainstem or cerebellar infarct if a contralateral VA injury occurs. Additionally, bone wax may be used, while tamponade may be effective in open space.30 If these techniques are not effective, endovascular embolization of the vessel, ligation of the vessel, or direct suture repair may also be

Fig. 1.7 Three-dimensional CT angiographic images showing six different cases of a fenestrated VA (white arrows) at the V, segment. One segment of the fenestration courses through the C1 transverse foramen, whereas the other enters the spinal canal below the C1 arch and then rejoins the other segment above the C1 arch. The left VA is fenestrated in four cases (a,b,d,f) and the right VA is fenestrated in two cases (c,e).24

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Cranial considered.30 Regardless of the technique chosen, the patient should have angiographic evaluation by the interventional radiologist postoperatively because neurologic sequelae of unilateral VA injury is reported to be 3.7%.32,34

Fig. 1.8 (a-d) Examples of variations in the bony arch of C1 that may affect the position of the vertebral artery in C1. In particularly, drilling through the posterior bony arch in Types III and IV may result in vertebral artery injury. (Reproduced with permission from Hong JT, Lee SW, Son BC, et al. Analysis of anatomical variations of bone and vascular structures around the posterior atlantal arch using threedimensional computed tomography angiography. J Neurosurg Spine. 2008;8(3):230–236.)

1.8 Hardware/Fusion Malposition The optimal position for arthrodesis is the functional neutral position, and failure to achieve this may result in complications, such as dysphagia, dyspnea, subluxation, and horizontal gaze disruption.35 The position of the occiput has the potential for subaxial subluxation and reduction in the oropharyngeal space that can lead to postoperative respiratory and swallowing complications. In a retrospective study of a cohort of patients who underwent occipitocervical fusion that developed alignment complications, Matsunaga et al demonstrated an association between retroversion of the occiput and swan neck deformity and kyphosis and subaxial subluxation with excessive anteversion.19,36 The ideal position of the occipitoaxial fusion has been described in reference to various radiographic measurements and landmarks, most commonly the occipitocervical angle.37 McGregor’s line demonstrates the most reliable and reproducible radiographic result, which extends from the posterosuperior aspect of the hard palate to the most caudal point of the occipital curve. The angle subtended between this line and that of inferior surface of the axis has been described to determine the occipitocervical angle, which should be between 0 and 30 degrees (▶ Fig. 1.9).36 Excessive anteversion of the occipital bone correlates with a higher rate of subaxial subluxation after surgery, and retroversion, which may be used as a means to increase the O–C2 angle, has been found to correlate with postoperative swan neck deformity and kyphosis.36 A severely malpositioned occiput may inhibit the subaxial spine from compensating to keep the head in a functionally neutral position.35 Ota et al demonstrated a strong linear correlation between the O–C2 angle and the narrowest oropharyngeal airway space (nPAS), in that a 10-degree decrease in this angle causes a 37% reduction in the nPAS.38 Clinically, decreasing the O–C2 angle is associated with increased risk of developing postoperative dyspnea and dysphagia, as the postsurgical change in the O–C2 angle correlates directly to that of the oropharyngeal cross-sectional area. In a retrospective study of a cohort of patients who underwent occipitocervical fusion, Miyata et al compared patients who developed postoperative dysphagia and determined a relationship between the O–C2 angle and this symptom. A reduced O–C2 angle decreases the oropharyngeal space and postoperative symptoms, and it should be measured intraoperatively prior to fusion.39 This is especially important to

Fig. 1.9 Measurement technique of the McGregor line, which extends from the posterosuperior aspect of the hard palate to the most caudal point of the occipital curve. The angle subtended between this line and that of inferior surface of the axis has been described to determine the occipitocervical angle, which should be between 0 and 30 degrees. (Left image reproduced from Matsunaga S, Onishi T, Sakou T. Significance of occipitoaxial angle in subaxial lesion after occipitocervical fusion. Spine. 2001; 26(2):161–165. Right image reproduced from Shoda N, Takeshita K, Seichi A, et al. Measurement of occipitocervical angle. Spine. 2004; 29(10):E204–E208.)

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Complications of Occipital Instrumentation consider in patients with associated cranial nerve palsies. Furthermore, patients may experience difficulty with horizontal gaze if the fusion is achieved in a suboptimal position.33 For instance, a patient may be required to extend at the torso to look straight ahead if they are placed in a flexed position and the cervical spine is unable to compensate. The authors prefer to scrub out of the surgery to view the patient’s head position and make necessary angular corrections before locking the instrumentation in place to avoid hardware/fusion malpositioning.

1.9 Infection The rate of infection following occipitocervical arthrodesis is similar to that of patients undergoing posterior cervical arthrodesis.40,41 Deutsch et al reported a 5% infection rate at the arthrodesis site in a long-term follow-up study.42 Infection occurs via three routes: soiling of the immediate postoperative surgical site, hematogenous seeding, or direct inoculation during surgery, the third being the most common. There is no clear difference in patient or procedural risk factors for infection following occipitocervical arthrodesis from those of other spinal surgery. Advanced age; developmental delay; immunosuppression; spinal trauma; diabetes mellitus; obesity; smoking; malignancy; chemotherapy; immunosuppression; indwelling catheters; extended hospitalization; and malnutrition defined as serum albumin level less than 3.5 g/dL, total lymphocyte less than 2,000 cells/mm3, and a serum transferrin level of 150 μg/dL or below are risk factors for infection in spine surgery in general.43 Specific infection risk factors that have been identified for posterior cervical arthrodesis are active smoking status, rheumatoid arthritis, and a body mass index of more than 30 kg/m2.44 Optimization of all modifiable risk factors should be attempted before proceeding with surgical intervention. Taking measures to prevent infection and their potentially disastrous complications is paramount. The use of perioperative intravenous cephalosporin antibiotics should be initiated within 1 hour of incision and administered for a total of 24 hours; however, this regimen is effective against less than half of the staphylococcal species found in the hospital.45 Though intravenous vancomycin may theoretically cover more infectious organisms, it has not been shown to decrease wound infection rates and is associated with hypotension; renal toxicity; and oropharyngeal, respiratory, and genitourinary infection with resistant organisms.46,47 Intrawound vancomycin powder was first described as a means to prevent postsurgical infection in the thoracolumbar spine.48 Its utility is particularly effective for this application because of its poor systemic absorption and high local wound concentration.48,49 Good results with the use of intrawound vancomycin powder have been found without any observed complications or risks with its use even in cases where there was direct dural contact in posterior cervical arthrodesis. In a retrospective study of a cohort of patients who underwent posterior cervical fusion with a year follow-up, Strom et al demonstrated a significantly lower rate of infection with the use of vancomycin powder. There were also no increased rates of complication or

pseudoarthrosis.44,48,50,51 They have also demonstrated costeffectiveness.52 Other methods to mitigate infection rates specifically in posterior cervical cases are perioperative surgical site preparation with alcohol foam combined with intrawound vancomycin powder and subfascial drain.44 Of postoperative infections, superficial infections are most common following posterior cervical arthrodesis, with the differentiating factor from deep infections being extension below the ligamentum nuchae. Exploration of the wound to define the extent of infection with aggressive debridement of necrotic and infected tissue and bone is the basic principle of management. Removal of instrumentation is debatable, and some recommend removal of all bone graft and spinal implants.53 Others support leaving well-fixed posterior instrumentation (particularly titanium) and bone grafts in place, even in the face of active infection.54,55,56 Instances in which hardware cannot feasibly be retained before a bony fusion has occurred pose a difficult challenge that often involves prolonged bracing or halo fixation.57

1.10 Nonunion Ultimately, successful fusion of the occipitocervical junction depends on osseous integration. After internal fixation is applied, surrounding bone is decorticated for placement of autologous or allograft to promote osseous fusion. In choosing the graft type, the properties of bone grafting which should be considered are as follows: osteoconduction, which provides a scaffold for neovascularization and ingrowth of bone; osteoinduction, which allows for promotion of osteoblastic differentiation from nearby mesenchymal cells most typically by bonemorphogenetic proteins; and osteogenesis, which is direct graft supplementation with osteoblastic cells. These properties vary among graft types. Corticocancellous bone autografting in the form of fibular strut, iliac crest, and rib possess all three of these characteristics, which confers a potential benefit to achieve fusion; however, their use is not without risks, which include chronic pain, infection, and seroma.58 No study to our knowledge has directly compared graft options in occipitocervical arthrodesis, particularly with modern instrumentation options. Extrapolation of graft choice from other spinal fusion procedures would indicate that most typically autograft is superior to allograft; however, a composite graft with autologous bone marrow and demineralized bone matrix is also a viable option.59,60,61,62 Fusion rates in modern occipitocervical fusion procedures are good, ranging from 89 to 100%.1,30 Long-term follow-up in 69 patients, in which two-thirds of patients received local autologous bone supplemented with allograft and one-third received iliac crest autograft, revealed no difference in fusion rates.63 No clear recommendation can be made on the basis of the available data with regard to graft choice in combination with modern instrumentation.1 However, use of the osteoinductive adjunct, recombinant human bone morphogenetic protein-2 (rhBMP-2), is not approved for use in occipitocervical fusion and is associated with soft-tissue complications and seroma formation.64 It should be noted that fusion rates are likely influenced by the underlying etiology. That is, although posterior screw–rod

9

Cranial constructs have less adverse events and instrumentation failure when compared to posterior wiring–rod, screw–plate, and in situ grafting alone regardless of the disease process, those with inflammatory disease have greater fusion rates with screw– rods while those with tumor had higher fusion rates with posterior wiring and rods.1 Interpretation of these results does require one to bear in mind that modern techniques have evolved rapidly and there is a relative dearth of long-term outcome data compared to other techniques.

plate failure (0.6%).1 Failure rates were likely given a selection bias for studies with a primary outcome of occipitocervical complications; however, in this group of studies, wiring and onlay grafting failed in all cases, screw–plates in 26.67% of the cases, wiring–rod in 13.54% of the cases, and screw–rod in 7.89% of the cases. This trend held significance when comparing fixation methods among patients with inflammatory diagnoses only. However, the clinical importance of breakage where an osseous fusion has been obtained is not clear.

1.11 Dural Tear

1.12.1 Occipital Fixation

The reported rate of dural tears during drilling of the occiput and screw placement range from 0 to 4.2%.65,66 This is significantly lower than that associated with wire-based fixation methods because dural laceration was associated with drilling of occipital burr holes and the recoil of the wiring, with a reported incidence of 25 to 28%.30,66 With occipital plating, if a cerebrospinal fluid (CSF) leak is encountered while drilling the screw holes, screw placement usually is sufficient to halt the leak.30 If a persistent CSF leak through a surgical wound occurs, raising the head of the bed to 30 degrees is first recommended, as well as decreased Valsalva and confined bed rest. If there is no subsidence, placement of a lumbar drain may be indicated, followed by possible surgical wound revision.30

Stiffness, the implant’s resistance to deformation, must be considered. With regard to occipitocervical fixation, the amount of metallic material and the distribution defined by the moment area of inertia, or resistance to angular acceleration, has a large effect on the biomechanical performance because of its direct correlation with stiffness.15 Along these lines, because the occipital plates have a moment of inertia that is two to three times that of rods, the development of these devices contributed considerably to improving construct stability.69 Despite improvement in the material properties of the plates themselves, the importance of fixation to the occiput should not be overlooked. Screws are ideally placed in areas with thick bone because pullout strength is dependent on bone thickness and number of cortices engaged. In general, bone is thickest in the midline at the external occipital protuberance and is largely dense, cortical bone ranging from 11 to 17.5 mm with the outer table contributing 45% of the thickness and the inner table contributing 10%.69,70 Although pullout strength is maximized with bicortical fixation in general, consideration of screw placement in the occiput is paramount because of the proximity of the intracranial sinuses in the thickest areas so as to avoid intracranial injury. To mitigate this risk, unicortical fixation is an option, but it also decreases contact area of the screw–bone interface and may adversely affect the strength of the construct.71 Biomechanical studies have shown no difference in the strength between bicortical wires and unicortical screws nor with unicortical screws at the occipital protuberance and bicortical screws elsewhere.68 It has also been demonstrated that pullout strengths of unicortical and bicortical screws are equal in areas with cortical thickness greater than 7 mm.72 This is likely due to the fact that the outer table contributes 45% of the thickness throughout the entire occiput. Furthermore, because bone thickness decreases radially from the protuberance, screw pullout strength is greatest above the superior nuchal line.68 Keeping these principles in mind, using a drill guide typically set to a maximum depth of 10 to 16 mm for midline screws and 6 mm for paramedian screws will often optimize screw length while avoiding inadvertent intracranial penetration.33 Screw position also affects the rigidity of the entire construct. That is, although midline screws may have greater pullout strength because the anatomy accommodates longer screws, lateral screws provide increased stiffness in rotation and bending but not flexion and extension.69,73 Thus, most plates are designed such that fixation is provided by a combination of midline and laterally based screws.69 However, construct stiffness in rotation and lateral bending is more greatly influenced by rod diameter.69 The authors prefer to use three midline screws without lateral screw placement.

1.12 Hardware Failure Paramount to obtaining an osseous fusion is immediate postsurgical rigid fixation provided by hardware implantation. Surgical options have evolved considerably since Foerester’s initial description of solitary fibular strut grafting. Earliest implants consisted mostly of posterior wiring techniques often requiring extension to caudal levels to ensure stability, as well as supplemental external stabilization, often in the form of halo vests, because of insufficient initial stabilization.67 Additionally, the occurrence of wire breakage in these constructs suggested that the occipital bone is stronger than the wires, and may be too brittle for optimal fixation.68 Thus, novel techniques were developed to mitigate hardware breakage and the need for supplementary external fixation. Today, the most popular configuration is composed of various cervical screw configurations along with an occipital plate fixed with occipital screws connected by a contoured rod.65 In general, this all-screw construct has demonstrated biomechanical superiority to sublaminar wiring and hook techniques, as well as facile implantation.15,67 The overarching goal of instrumentation is to maximize rigidity, as it is postulated to improve fusion rates.67 This is true for the construct in its entirety, including the occipital fixation, as well as the cervical construct and linking rods. Thus, the surgeon must be familiar with the various implants so that stability is optimized while osseous fusion is obtained. Winegar et al1 investigated the cause of failure of all reported occipitocervical arthrodeses constructs in the literature from 1969 to 2010. They reported a 21% instrumentation failure rate overall with wiring being the most likely to fail (10.1%), followed by screw failure (6.2%), rod failure (0.6%), and occipital

10

Complications of Occipital Instrumentation With regard to occipital screw choice, no biomechanical advantage has been demonstrated between cancellous and cortical screws.72 However, because of occipital bone anatomy, screws have been designed to maximize strength. That is, most current occipital screws are unique in that they have a larger diameter and smaller pitch, which allows for greater contact area in areas of thin bone.15 Additionally, no structural benefit has been demonstrated with use of locked constructs, particularly with the rod–plate connector. Screw dimensions are typically 4.5 × 6 mm for the lateral calvarial screws and 4.5 × 8 to 12 mm for the midline suboccipital keel screws.33 Occipital buttons are another viable alternative for fixation, which allow for bicortical fixation using an “inside” button, with the flat surface facing intracranial and the threads outward so that a nut can be placed over the plate and onto the threads.33,74 Care must be taken during placement of the button to avoid cerebellar, dural, or venous sinus injury. Its safety and biomechanical effectiveness have both been shown in multiple studies.15 Finally, for patients with occipital deficits, condylar screws have demonstrated biomechanical effectiveness as an alternative to occipital plating, while achieving stability with a lower profile implant, though there is limited reported clinical experience.26,27 One of the challenges presented by occipital plates is prominence due to the superficial nature of the occiput. Occipital plates that include a suboccipital extension for direct connection to the cervical spine, such as Y plates, are particularly problematic in this respect. Furthermore, appropriate screw positioning often poses a real surgical challenge because of its limited positioning options. Most modern constructs composed of an independent occipital plate connected by bars to cervical screws permit anatomic contouring and allow for more facile screw placement and less prominence. Most occipital plates offer sagittal and coronal pre-bend regions for contouring in both planes. In most of the systems, fixation of an independent longitudinal rod connected to the occipital plate is achieved via a slotted connector allowing medial–lateral rod placement, as well as rotation. Other rod types do exist and include rods that transition to an occipital plate cephalad. Regardless of the implant chosen, fastidious attention to instrumentation contouring to avoid prominence should be employed.

1.12.2 Suboccipital Fixation The suboccipital fixation must also be strong to achieve a rigid construct amenable to bony fusion. Screws in the C1 lateral mass or C2 pedicle provide greater rigidity, by way of three-column fixation compared to the semirigid construct of laminar hooks, which engage the posterior lamina. Furthermore, wiring techniques provide inferior rotational and lateral stability and require supplemental halo fixation compared to C1–C2 TA screw techniques. Harms and Melcher’s technique of bicortical screw fixation into the lateral mass of C1 and C2 pedicle demonstrated equivalent stability to TA screws but may risk damage to the hypoglossal nerve and carotid artery.16,75 Unicortical lateral mass screws may avoid this potential complications and have demonstrated biomechanical stability as have posterior arch screws.76,77 Recently, unicortical posterior arch screws have demonstrated greater pullout strength than lateral mass

screws.77 Mummaneni and colleagues have reported that C1 lateral mass screws can effectively be combined with C2 pars screws, C2 translaminar screws, and C3 lateral mass screws.32 They also demonstrated higher rates of complications with fusions extending below C2, such as pseudoarthrosis.32

1.12.3 Longitudinal Components Designs of the rods connecting the occipital fixation to the cervical spine are variable. The design that affords the surgeon the greatest modification is modular implants, or those with an independent rod attached to occipital plates by dedicated anchors. This connection also varies; some offer multidirectional tuning and others are fixed angle in nature. The latter requires that the patient’s anatomy be compatible with the hardware’s manufactured specifications. Independent occipital plates allow the greatest flexibility for hardware placement and individual intraoperative component modification without necessitating entire construct removal. An adjustable rod with a manufactured joint may also be selected, which allows for adjustment in one plane and precludes the need for bending, which may result in less fatigue failure. This is especially important to consider when using titanium rods, as these are notch sensitive in fatigue failure, so that longer curves should be implemented at the craniocervical junction rather than acute bends as is often required.69 This transitional region is a stress riser, and the most common location for breakage.78 Most constructs utilize a 3.5-mm rod; however, it is important that the surgeon remember that its moment of inertia varies to the fourth power so that a 3.5-mm rod is twice as stiff as a 2.5-mm rod. In fact, the greater elasticity of a smaller rod affects construct’s stiffness more than the connectors. Failure in one portion of the construct rarely occurs in isolation, and it is postulated that failure or breakage in one part or section predisposes the patient to hardware failure elsewhere with the resulting redistribution of biomechanical forces.78 With regard to instrumentation systems available, several options exist at the time of this publication. The following systems have been granted 510(k) status for implantation: Aesculap Implant Systems’ S4 Cervical Occipital Plating System; DePuy’s Spinal MOUNTAINEER OCT System that is compatible with the Songer Cable Cervical Thoracic System and the ISOLA, TiMX, MONARCH, MOSS MIAMI, and EXPEDIUM Systems; DePuy’s Spinal Summit SI Occipito-Cervico-Thoracic (OCT) Spinal System; DePuy’s Spinal Synapse System; Exactech Gibralt Occipital Spine System; Medtronic Vertex Select Reconstruction System; Alphatech Solanas Avalon Posterior Fixation System; and NuVasive OCT System which is compatible with NuVasive SpheRx. A 510(k) is a premarketing submission made to the Food and Drug Administration (FDA) to demonstrate that the device to be marketed is as safe and effective, that is, substantially equivalent to a legally marketed device that is not subject to premarket approval. Familiarity with the available implants and their potential advantages and disadvantages will assist the surgeon in selecting the instrumentation that is best suited to provide a stable construct and ultimately an osseous fusion. This is especially true, given the unique anatomic characteristics of the occipitocervical region and the specific considerations which must be made to optimize patient outcomes.

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1.13 Conclusion Although occipitocervical arthrodesis has been shown to be an effective procedure, the surgeon must be familiar with the potential complications associated with this surgery. It is our hope that by familiarization with the reported complications and understanding their etiology and pathophysiology, the surgeon may be best equipped to mitigate their occurrence as well as facilitate preoperative patient discussion and understanding.

1.14 Key Points ●

●

●

●

●

Modular systems composed of independent occipital plates connected to cervical screws by rods provide the most stable and adjustable construct to date. Review of preoperative imaging and a fundamental understanding of the relationship of extracranial landmarks with intracranial structures will assist in occipital screw placement. Preoperative planning with advanced imaging is essential to mitigating vascular injury. Preoperative analysis of the desired O–C2 angle and intraoperative assessment of head position is required to ensure proper fusion positioning. Vancomycin powder effectively and safely decreases infection rates.

References [1] Winegar CD, Lawrence JP, Friel BC, et al. A systematic review of occipital cervical fusion: techniques and outcomes. J Neurosurg Spine. 2010; 13 (1):5–16 [2] Wolfla CE. Anatomical, biomechanical, and practical considerations in posterior occipitocervical instrumentation. Spine J. 2006; 6(6) Suppl:225S–232S [3] Zipnick RI, Merola AA, Gorup J, et al. Occipital morphology. An anatomic guide to internal fixation. Spine (Phila Pa 1976). 1996; 21(15):1719–1724, discussion 1729–1730 [4] Goel VK, Clark CR, Gallaes K, Liu YK. Moment-rotation relationships of the ligamentous occipito-atlanto-axial complex. J Biomech. 1988; 21(8):673–680 [5] Doherty BJ, Heggeness MH. The quantitative anatomy of the atlas. Spine. 1994; 19(22):2497–2500 [6] Dong Y, Hong MX, Jianyi L, Lin MY. Quantitative anatomy of the lateral mass of the atlas. Spine. 2003; 28(9):860–863 [7] Huang RC, Girardi FP, Poynton AR, Cammisa FP, Jr. Treatment of multilevel cervical spondylotic myeloradiculopathy with posterior decompression and fusion with lateral mass plate fixation and local bone graft. J Spinal Disord Tech. 2003; 16(2):123–129 [8] Steinmetz MP, Mroz TE, Benzel EC. Craniovertebral junction: biomechanical considerations. Neurosurgery. 2010; 66(3) Suppl:7–12 [9] Goel A, Laheri V. Plate and screw fixation for atlanto-axial subluxation. Acta Neurochir (Wien). 1994; 129(1–2):47–53 [10] Dickman CA, Crawford NR, Brantley AG, Sonntag VK. Biomechanical effects of transoral odontoidectomy. Neurosurgery. 1995; 36(6):1146–1152, discussion 1152–1153 [11] Panjabi M, Dvorak J, Crisco JJ, III, Oda T, Wang P, Grob D. Effects of alar ligament transection on upper cervical spine rotation. J Orthop Res. 1991; 9 (4):584–593 [12] Bransford RJ, Lee MJ, Reis A. Posterior fixation of the upper cervical spine: contemporary techniques. J Am Acad Orthop Surg. 2011; 19(2):63–71 [13] Hamblen DL. Occipito-cervical fusion. Indications, technique and results. J Bone Joint Surg Br. 1967; 49(1):33–45 [14] Sonntag VK, Dickman CA. Craniocervical stabilization. Clin Neurosurg. 1993; 40:243–272 [15] Stock GH, Vaccaro AR, Brown AK, Anderson PA. Contemporary posterior occipital fixation. J Bone Joint Surg Am. 2006; 88(7):1642–1649

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[16] Harms J, Melcher RP. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine. 2001; 26(22):2467–2471 [17] Elia M, Mazzara JT, Fielding JW. Onlay technique for occipitocervical fusion. Clin Orthop Relat Res. 1992(280):170–174 [18] Izeki M, Neo M, Fujibayashi S, et al. Utility of the analysis of intracranial venous sinuses using preoperative computed tomography venography for safe occipital screw insertion. Spine. 2013; 38(18):E1149–E1155 [19] Lee SC, Chen JF, Lee ST. Complications of fixation to the occiput-anatomical and design implications. Br J Neurosurg. 2004; 18(6):590–597 [20] Nadim Y, Lu J, Sabry FF, Ebraheim N. Occipital screws in occipitocervical fusion and their relation to the venous sinuses: an anatomic and radiographic study. Orthopedics. 2000; 23(7):717–719 [21] Altaf F, Derbyshire N, Marshall RW. Cerebral venous sinus thrombosis following cervical disc arthroplasty. J Bone Joint Surg Br. 2010; 92(4):576–578 [22] Owler BK, Parker G, Halmagyi GM, et al. Pseudotumor cerebri syndrome: venous sinus obstruction and its treatment with stent placement. J Neurosurg. 2003; 98(5):1045–1055 [23] Aota Y, Honda A, Uesugi M, et al. Vertebral artery injury in C-1 lateral mass screw fixation. Case illustration. J Neurosurg Spine. 2006; 5(6):554 [24] Hong JT, Lee SW, Son BC, et al. Analysis of anatomical variations of bone and vascular structures around the posterior atlantal arch using three-dimensional computed tomography angiography. J Neurosurg Spine. 2008; 8 (3):230–236 [25] Rocha R, Safavi-Abbasi S, Reis C, et al. Working area, safety zones, and angles of approach for posterior C-1 lateral mass screw placement: a quantitative anatomical and morphometric evaluation. J Neurosurg Spine. 2007; 6 (3):247–254 [26] La Marca F, Zubay G, Morrison T, Karahalios D. Cadaveric study for placement of occipital condyle screws: technique and effects on surrounding anatomic structures. J Neurosurg Spine. 2008; 9(4):347–353 [27] Helgeson MD, Lehman RA, Jr, Sasso RC, Dmitriev AE, Mack AW, Riew KD. Biomechanical analysis of occipitocervical stability afforded by three fixation techniques. Spine J. 2011; 11(3):245–250 [28] Jian FZ, Santoro A, Wang XW, Passacantili E, Seferi A, Liu SS. A vertebral artery tortuous course below the posterior arch of the atlas (without passing through the transverse foramen). Anatomical report and clinical significance. J Neurosurg Sci. 2003; 47(4):183–187 [29] Tokuda K, Miyasaka K, Abe H, et al. Anomalous atlantoaxial portions of vertebral and posterior inferior cerebellar arteries. Neuroradiology. 1985; 27 (5):410–413 [30] Lall R, Patel NJ, Resnick DK. A review of complications associated with craniocervical fusion surgery. Neurosurgery. 2010; 67(5):1396–1402, discussion 1402–1403 [31] Young JP, Young PH, Ackermann MJ, Anderson PA, Riew KD. The ponticulus posticus: implications for screw insertion into the first cervical lateral mass. J Bone Joint Surg Am. 2005; 87(11):2495–2498 [32] Mummaneni PV, Lu DC, Dhall SS, Mummaneni VP, Chou D. C1 lateral mass fixation: a comparison of constructs. Neurosurgery. 2010; 66(3) Suppl:153–160 [33] Lu DC, Roeser AC, Mummaneni VP, Mummaneni PV. Nuances of occipitocervical fixation. Neurosurgery. 2010; 66(3) Suppl:141–146 [34] Wright NM, Lauryssen C, American Association of Neurological Surgeons/ Congress of Neurological Surgeons. Vertebral artery injury in C1–2 transarticular screw fixation: results of a survey of the AANS/CNS section on disorders of the spine and peripheral nerves. J Neurosurg. 1998; 88(4):634–640 [35] Takami T, Ichinose T, Ishibashi K, Goto T, Tsuyuguchi N, Ohata K. Importance of fixation angle in posterior instrumented occipitocervical fusion. Neurol Med Chir (Tokyo). 2008; 48(6):279–282, discussion 282 [36] Matsunaga S, Onishi T, Sakou T. Significance of occipitoaxial angle in subaxial lesion after occipitocervical fusion. Spine. 2001; 26(2):161–165 [37] Shoda N, Takeshita K, Seichi A, et al. Measurement of occipitocervical angle. Spine. 2004; 29(10):E204–E208 [38] Ota M, Neo M, Aoyama T, et al. Impact of the O-C2 angle on the oropharyngeal space in normal patients. Spine. 2011; 36(11):E720–E726 [39] Miyata M, Neo M, Fujibayashi S, Ito H, Takemoto M, Nakamura T. O-C2 angle as a predictor of dyspnea and/or dysphagia after occipitocervical fusion. Spine (Phila Pa 1976). 2009; 34(2):184–188 [40] Heller JG, Edwards CC, II, Murakami H, Rodts GE. Laminoplasty versus laminectomy and fusion for multilevel cervical myelopathy: an independent matched cohort analysis. Spine. 2001; 26(12):1330–1336 [41] Huang MJ, Glaser JA. Complete arcuate foramen precluding C1 lateral mass screw fixation in a patient with rheumatoid arthritis: case report. Iowa Orthop J. 2003; 23:96–99

Complications of Occipital Instrumentation [42] Deutsch H, Haid RW, Jr, Rodts GE, Jr, Mummaneni PV. Occipitocervical fixation: long-term results. Spine. 2005; 30(5):530–535 [43] Schimmel JJ, Horsting PP, de Kleuver M, Wonders G, van Limbeek J. Risk factors for deep surgical site infections after spinal fusion. Eur Spine J. 2010; 19 (10):1711–1719 [44] Pahys JM, Pahys JR, Cho SK, et al. Methods to decrease postoperative infections following posterior cervical spine surgery. J Bone Joint Surg Am. 2013; 95(6):549–554 [45] Klevens RM, Edwards JR, Richards CL, Jr, et al. Estimating health care-associated infections and deaths in U.S. hospitals, 2002. Public Health Rep. 2007; 122(2):160–166 [46] Klevens RM, Morrison MA, Nadle J, et al. Active Bacterial Core surveillance (ABCs) MRSA Investigators. Invasive methicillin-resistant Staphylococcus aureus infections in the United States. JAMA. 2007; 298(15):1763–1771 [47] Moise PA, Smyth DS, El-Fawal N, et al. Microbiological effects of prior vancomycin use in patients with methicillin-resistant Staphylococcus aureus bacteraemia. J Antimicrob Chemother. 2008; 61(1):85–90 [48] Sweet FA, Roh M, Sliva C. Intrawound application of vancomycin for prophylaxis in instrumented thoracolumbar fusions: efficacy, drug levels, and patient outcomes. Spine. 2011; 36(24):2084–2088 [49] Chilukuri DM, Shah JC. Local delivery of vancomycin for the prophylaxis of prosthetic device-related infections. Pharm Res. 2005; 22(4):563–572 [50] Strom RG, Pacione D, Kalhorn SP, Frempong-Boadu AK. Decreased risk of wound infection after posterior cervical fusion with routine local application of vancomycin powder. Spine (Phila Pa 1976). 2013; 38(12):991–994 [51] Caroom C, Tullar JM, Benton EG, Jr, Jones JR, Chaput CD. Intrawound vancomycin powder reduces surgical site infections in posterior cervical fusion. Spine. 2013; 38(14):1183–1187 [52] Godil SS, Parker SL, O’Neill KR, Devin CJ, McGirt MJ. Comparative effectiveness and cost-benefit analysis of local application of vancomycin powder in posterior spinal fusion for spine trauma: clinical article. J Neurosurg Spine. 2013; 19(3):331–335 [53] Devlin VJ, Boachie-Adjei O, Bradford DS, Ogilvie JW, Transfeldt EE. Treatment of adult spinal deformity with fusion to the sacrum using CD instrumentation. J Spinal Disord. 1991; 4(1):1–14 [54] Levi AD, Dickman CA, Sonntag VK. Management of postoperative infections after spinal instrumentation. J Neurosurg. 1997; 86(6):975–980 [55] Moe JH. Complications of scoliosis treatment. Clin Orthop Relat Res. 1967; 53 (53):21–30 [56] Picada R, Winter RB, Lonstein JE, et al. Postoperative deep wound infection in adults after posterior lumbosacral spine fusion with instrumentation: incidence and management. J Spinal Disord. 2000; 13(1):42–45 [57] Chaudhary SB, Vives MJ, Basra SK, Reiter MF. Postoperative spinal wound infections and postprocedural diskitis. J Spinal Cord Med. 2007; 30 (5):441–451 [58] Miyazaki M, Tsumura H, Wang JC, Alanay A. An update on bone substitutes for spinal fusion. Eur Spine J. 2009; 18(6):783–799 [59] Price CT, Connolly JF, Carantzas AC, Ilyas I. Comparison of bone grafts for posterior spinal fusion in adolescent idiopathic scoliosis. Spine. 2003; 28 (8):793–798

[60] An HS, Simpson JM, Glover JM, Stephany J. Comparison between allograft plus demineralized bone matrix versus autograft in anterior cervical fusion. A prospective multicenter study. Spine. 1995; 20(20):2211–2216 [61] Zhang ZH, Yin H, Yang K, et al. Anterior intervertebral disc excision and bone grafting in cervical spondylotic myelopathy. Spine. 1983; 8(1):16–19 [62] Bishop RC, Moore KA, Hadley MN. Anterior cervical interbody fusion using autogeneic and allogeneic bone graft substrate: a prospective comparative analysis. J Neurosurg. 1996; 85(2):206–210 [63] Nockels RP, Shaffrey CI, Kanter AS, Azeem S, York JE. Occipitocervical fusion with rigid internal fixation: long-term follow-up data in 69 patients. J Neurosurg Spine. 2007; 7(2):117–123 [64] Shahlaie K, Kim KD. Occipitocervical fusion using recombinant human bone morphogenetic protein-2: adverse effects due to tissue swelling and seroma. Spine. 2008; 33(21):2361–2366 [65] Abumi K, Takada T, Shono Y, Kaneda K, Fujiya M. Posterior occipitocervical reconstruction using cervical pedicle screws and plate-rod systems. Spine. 1999; 24(14):1425–1434 [66] Hsu YH, Liang ML, Yen YS, Cheng H, Huang CI, Huang WC. Use of screw-rod system in occipitocervical fixation. J Chin Med Assoc. 2009; 72(1):20–28 [67] Oda I, Abumi K, Sell LC, Haggerty CJ, Cunningham BW, McAfee PC. Biomechanical evaluation of five different occipito-atlanto-axial fixation techniques. Spine. 1999; 24(22):2377–2382 [68] Haher TR, Yeung AW, Caruso SA, et al. Occipital screw pullout strength. A biomechanical investigation of occipital morphology. Spine. 1999; 24(1):5–9 [69] Anderson PA, Oza AL, Puschak TJ, Sasso R. Biomechanics of occipitocervical fixation. Spine. 2006; 31(7):755–761 [70] Ebraheim NA, Lu J, Biyani A, Brown JA, Yeasting RA. An anatomic study of the thickness of the occipital bone. Implications for occipitocervical instrumentation. Spine (Phila Pa 1976). 1996; 21(15):1725–1729, discussion 1729–1730 [71] Ryken TC, Goel VK, Clausen JD, Traynelis VC. Assessment of unicortical and bicortical fixation in a quasistatic cadaveric model. Role of bone mineral density and screw torque. Spine. 1995; 20(17):1861–1867 [72] Roberts DA, Doherty BJ, Heggeness MH. Quantitative anatomy of the occiput and the biomechanics of occipital screw fixation. Spine. 1998; 23(10):1100– 1107, discussion 1107–1108 [73] Papagelopoulos PJ, Currier BL, Stone J, et al. Biomechanical evaluation of occipital fixation. J Spinal Disord. 2000; 13(4):336–344 [74] Pait TG, Al-Mefty O, Boop FA, Arnautovic KI, Rahman S, Ceola W. Inside-outside technique for posterior occipitocervical spine instrumentation and stabilization: preliminary results. J Neurosurg. 1999; 90(1) Suppl:1–7 [75] Melcher RP, Puttlitz CM, Kleinstueck FS, Lotz JC, Harms J, Bradford DS. Biomechanical testing of posterior atlantoaxial fixation techniques. Spine. 2002; 27 (22):2435–2440 [76] Eck JC, Walker MP, Currier BL, Chen Q, Yaszemski MJ, An KN. Biomechanical comparison of unicortical versus bicortical C1 lateral mass screw fixation. J Spinal Disord Tech. 2007; 20(7):505–508 [77] Zarro CM, Ludwig SC, Hsieh AH, Seal CN, Gelb DE. Biomechanical comparison of the pullout strengths of C1 lateral mass screws and C1 posterior arch screws. Spine J. 2013; 13(12):1892–1896 [78] Bhatia R, Desouza RM, Bull J, Casey AT. Rigid occipitocervical fixation: indications, outcomes, and complications in the modern era. J Neurosurg Spine. 2013; 18(4):333–339

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2 Vascular Complications of Posterior Cervical Procedures Raymond Hah and Jeremy Smith

2.1 Introduction Vascular complications from posterior cervical surgery are relatively rare, but can be devastating, resulting in massive bleeding, brain stem or cerebellar infarction, and even death.1,2,3,4,5,6 Detailed understanding of relevant anatomy and careful preoperative planning are critical in prevention. In the upper cervical spine and craniocervical junction, the vertebral artery (VA) and venous plexus lie posterior to the lamina and are at risk for direct injury. Posterior instrumentation continues to exponentially increase, and complications of resultant indirect injury are also increasingly reported. This chapter briefly covers relevant anatomy and anatomic variation as related to both exposure and instrumentation of the cervical spine. Next we review complications of specific instrumentation and techniques. We finish with current concepts in operative measures, diagnosis, and additional treatment of vertebral artery injury (VAI).

2.2 Epidemiology Rates of vascular injury in posterior cervical surgery vary based on location and instrumentation. The atlantoaxial region has the highest rates with 1.3 to 8.2% for C1–C2 transarticular screws; in contrast, there are very few reported injuries for cervical pedicle screws and no reported injury for subaxial lateral mass screws.2,7,8,9,10,11,12,13,14 These rates may rise as the use of cervical instrumentation increases and standardized methods of reporting complications improve.

2.3 Surgical Anatomy The VA is divided into four segments.15,16 V1 arises from the subclavian artery, runs ventral to the C7 transverse process, and enters the C6 foramen transversarium. V2 is within the transverse foramina of C6 to C2. V3 exits the foramen of C2 and passes laterally through the transverse foramen of C1. It then runs posteriorly along the lateral mass of C1 below the inferior border of the posterior atlantooccipital membrane until it pierces dura superomedially. V4 enters the dura and travels medially, coalescing with the contralateral vessel to form the basilar artery. In this region, the left VA is dominant in 36%, hypoplastic in 6%, and absent in 2%; the right VA is dominant in 23% of patients, hypoplastic in 9%, and absent in 3%; they are equivalent in 41% of patients.17 Doppler sonography demonstrated that for the majority the left VA carries more flow.18 A recent computed tomography (CT) angiography study demonstrated left-sided VA dominance in 69.3% of cases.19 At the cephalad edge of C1, the VA runs within < 1 cm (8– 12 mm) of midline, and on the caudal C1 border 1.5 cm (12– 23 mm)16,20 The artery is also vulnerable as it passes between the C1 and C2 foramen; here the dorsal ramus of C2 passes dorsally and medially and should be the limit to the extent of lateral dissection (▶ Fig. 2.1).

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Variations and anomalies are well documented. In 3 to 15% of the population, the ponticulus posticus is a bony covering forming the arcuate foramen, which encases the VA on the groove of C1 and can be readily identified on the lateral radiograph21,22,23 (▶ Fig. 2.2). Women are more commonly affected.22 The incidence of VA anomalies in the atlantoaxial region is estimated at 2.3%.24 The VA may be high riding, have a variable bending point under the superior articular facet of C2, and occupy up to 75% of the transverse extent of superior facet of C211,25,26,27,28,29 (▶ Fig. 2.3). Yamazaki et al demonstrated that patients with congenital skeletal anomalies and atlantoaxial subluxation have increased rates of extraosseous and intraosseous VA anomalies.30,31 Anterior to the C1 vertebra, the internal carotid artery (ICA) is at risk of indirect injury by C1 instrumentation.32 The mean distance from the ICA to C1 is 2.8 mm.33 The ICA is usually located in front or at the lateral third of the lateral mass of C1 and is rarely located over the medial third.34 The hypoglossal nerve is also at risk anterior to C1 and is 2 to 3 mm lateral to the ventral aspect of the C1 lateral mass.35 In the subaxial spine, the distance between the dorsal aspect of the lateral mass and transverse foramen is an average of 9 to 12 mm.36 The average angle between the sagittal plane and the line connecting the midpoint of the lateral mass to the lateral limit of the vertebral foramen at C3–C5 is 5 to 6 degrees medial; however, at C6 because the VA is more lateral, this angle is 5 to 6 degrees lateral to the sagittal plane.36 Lateral masses are rhomboid in the mid-cervical levels and become elongated and thinner at lower levels.37

2.4 Fixation Techniques 2.4.1 Atlantoaxial To prevent VAI in posterior exposure of the upper cervical spine, lateral dissection on the cephalad edge of C1 should be limited to < 1 cm (8–12 mm) and on the caudal C1 border to less than 1.5 cm (12–23 mm).16,20 The artery is also vulnerable as it passes between the C1 and C2 foramen; here the dorsal ramus of C2 should be the limit to the extent of lateral dissection (▶ Fig. 2.1). Transarticular atlantoaxial fixation was first described by Magerl and Seemann in 1987.38 The C1–C2 transarticular screw is inserted 2 to 3 mm superomedial to the C2–C3 facet joint and aimed superomedially toward the anterior tubercle of C1 with fluoroscopic guidance.3,39 The rate of resultant VAI ranges from 4 to 8%, with several larger series showing no injury.2,9,11,40,41,42,43 Wright and Lauryssen reported the risk of VAI as 4.1% per patient and 2.2% per screw; however, neurologic sequelae and mortality was rare (0.1%).2 Madawi et al suggested that complete reduction of the C1–C2 joint is essential for avoidance of the VA, with five VA injuries in 61 patients (8%) largely due to incomplete C1–C2 reduction prior to screw fixation (▶ Fig. 2.4). Low and laterally directed trajectories risk VAI; the safest trajectory is through the most medial and most dorsal portion of the

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Fig. 2.1 (a) Posterior view of the occipitocervical junction. Posterior dissection of C2 should remain within 12 mm lateral to the midline. Also shown is the course of the vertebral artery as it turns posteriorly along the dorsal aspect of the C1 arch. Adequate exposure for C1 instrumentation often requires direct exposure by elevating the vertebral artery in a cephalad direction. (b) The axial view through the superior aspect of the atlas (C1). Dissection of the superior aspect of the posterior C1 arch should remain within 8 mm of the midline. The difference in dissection of the cranial and caudal aspect of the C1 arch is illustrated by a difference of about 4 mm in the average patient.

Fig. 2.2 Lateral radiograph of ponticulus posticus and arcuate foramen.23

isthmus11,26,27,28,43,44,45 (▶ Fig. 2.5). CT is essential for preoperative planning to exclude high-riding VA or thin C2 pars/pedicle, which may preclude transarticular screw fixation in 20% of patients.29 If bilateral fixation is unable to be safely performed, unilateral fixation with supplemental interspinous bone graft wiring has shown excellent outcomes.46 Harms and Melcher described polyaxial screw and rod fixation with C1 lateral mass screws and C2 pedicle screws in 2001 as a safer alternative to C1–C2 transarticular fixation, postulating a decreased risk of injury to the VA47 (▶ Fig. 2.6). Others have agreed and no direct VAI has been reported from this technique.48,49,50 Interestingly, direct compression of the VA by the rod has been presented.51 Yeom et al reported on a modified technique of insertion of the C1 lateral mass screw via the posterior arch with no VAI in 102 C1 lateral mass screws.52 Venous plexus bleeding with exposure of the C1 lateral mass may hamper visualization, thereby increasing VAI risk. For the C2 pedicle screw, the trajectory should be parallel to the medial border and superior aspect of the C2 pedicle to avoid lateral perforation of the pedicle and injury to the VA.53 Some anatomic CT studies have reported that C2 pedicle fixation is equally as risky as the transarticular technique54,55 (▶ Fig. 2.7).

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Fig. 2.3 Two representative VA anomalies at the CVJ. (a) Fenestration. (b) Persistent first intersegmental artery. CVJ, craniovertebral junction; VA, vertebral artery.31

Fig. 2.4 Drawings depicting a lateral view of the C1–C2 joint. (a) Drawing showing normal position with normal screw trajectory. (b) Drawing showing the effect of incompletely reduced displacement and the segment in full flexion: with screw trajectory aiming to the anterior tubercle of C1, the screw will be low enough to transect the VA underneath the C2 lateral mass. A VAI would be inevitable in these circumstances.11

Fig. 2.5 Schematic drawing demonstrating the relationship between the vertebral artery (VA) and the transarticular screw. The screw must be inserted superiorly, dorsally, and medially to the VA. The left VA is the so-called high-riding type in which the bending point can exist more superiorly, more medially, or more dorsally than usual, thereby reducing the space available for the screw.26

Fig. 2.6 Upper cervical spine after C1–C2 fixation by the polyaxial screw and rod fixation technique. (a) Lateral view. (b) Posterior view.47

Recent meta-analyses suggest a low risk of VAI with C2 pedicle and pars screws, with a 0.34% occurrence in 2,979 implanted C2 pedicle screws versus a 0.72% occurrence in 3,627 C1–C2 transarticular screws.56,57

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The ICA is also at risk with bicortical screw fixation with both C1 lateral mass screw fixation and C1–C2 transarticular screws.32,33,34 Medial angulation of 10 degrees can avoid ICA injury while allowing bicortical fixation34 (▶ Fig. 2.8). Case

Vascular Complications of Posterior Cervical Procedures

Fig. 2.7 Axial and sagittal computed tomography angiography images demonstrating low trajectory of left C2 pars screw with violation of the transverse foramen.

reports of hypoglossal nerve palsy from C1 lateral mass screw are also found in the literature.9,40,58

2.4.2 Subaxial Lateral mass fixation in the subaxial spine may risk injury to the VA, nerve root, and face joints. Despite the possibility of VAI with lateral mass screw fixation, there are no occurrences in the literature, inclusive of many large series.10,12,14,49,59,60,61 Quadrant anatomy of the lateral masses has been described to guide screw placement, and several techniques and modifications have been proposed to avoid injury62,63,64,65 (▶ Fig. 2.9). In general, comparisons between these techniques revealed that safe screw placement parallels the facet joint in the sagittal plane and angulates maximally lateral in the coronal plane.10,66,

67,68,69,70

Several studies advocate the use of unicortical over bicortical fixation, with a recommended screw length of 14 to 16 mm to avoid neurovascular injury.60,61,71 Cervical pedicle screw fixation was initially reported by Abumi et al and Jeanneret et al in 1994.72,73 The original technique advocated a starting point just medial to the lateral edge of the lateral mass with the aimed transverse angle of 35 degrees.72 Others have suggested a more lateral starting point with a more medially directed transverse angle.13,74 Several techniques have been described to reduce the risk of pedicle wall perforation, including the funnel technique,75 direct visualization of the pedicle via laminoforaminotomy,76,77 partial laminectomy,78 and the key-slot technique.79 Anatomic and cadaveric studies show a narrow margin of safety, with perforation rates between 17 and 88%, most of which are lateral into the transverse foramen and mostly at the

17

Cranial

Fig. 2.8 Measured anatomic remarks for the atlas and internal carotid artery. A, shortest distance between C1 anterior cortical surface and the internal carotid artery (ICA); B, shortest distance from C1 anterior cortical surface to ICA on virtual screw trajectory line (VS line). VS line was indicated as a dotted line. C, virtual screw length (distance from ideal screw entry point to virtual exit point); D, width of C1 lateral mass; E, distance from C1 midsagittal line to inner edge of ICA; F, distance from C1 midsagittal line to inner edge of transverse foramen; alpha, angle made between sagittal axis and VS line. (Adapted from Murakami et al.34)

C3–C5 levels.8,74,75,76,78,80,81 Clinical reports also report high rates of lateral breach with ranges from 6.9 to 29.8% per screw, but low rates of clinically important VAI8,13,82,83,84,85,86 (▶ Table 2.1). Several series report that computer-assisted screw insertion can reduce the clinical perforation rates, but severe malposition is still possible.76,87,88,89,90 The mismatch between high rates of transverse foramen perforation and low rates of vascular injury highlights the fact that penetration does not always injure the VA. Sanelli et al reported that the VA occupies from 8 to 85% of the foramen.91 Tomasino et al suggested a theoretical 2.5-mm distance the VA could be shifted by the cervical pedicle screw without resultant vascular injury.19

2.5 Complications and Management VAI can result in massive hemorrhage, arteriovenous fistulas, pseudoaneurysm, thrombosis, embolism, cerebellar ischemia and infarction, and even death.1,3,4,5,43,92,93,94,95 Initial hemorrhage can be managed by tamponade, direct repair, or ligation, although endovascular techniques may be also necessary. These various methods carry differing risks of resultant morbidity and mortality, although rates are difficult to predict and depend on adequate flow from the contralateral VA or other collaterals. Intraoperatively, VAI results in massive hemorrhage, which if difficult to control can lead to hypotension, cardiac arrest, and death. This bleeding can be nonpulsatile and is either bright or dark red in color.3,14,92 Intraoperative blood gas analysis may be useful for diagnosing unclear cases of VAI.96 Neo et al identified two distinct types of bleeding instances with “VAI in the screw hole” versus “VAI in the open space.”14 In the first instance, bleeding usually is not massive and can be controlled by tamponade with hemostatic agents, bone wax, or screw insertion. Injury “in the open space” is more difficult to control with tamponade and may require ligation or embolization.

18

There exists no consensus for management of iatrogenic VAI. A recent survey reported that after initial intraoperative control of hemorrhage, surgeons employ a wide range of subsequent treatment, including close observation, immediate postoperative angiography, ligation, and primary repair.2 Some authors argue against tamponade alone as definitive treatment given that there are reports of delayed hemorrhage, fistula formation, distal embolization, and late infarction,3,94,95,97 and others strongly recommend immediate postoperative angiography to confirm injury and adequate collateral flow, as well as to intervene as necessary to prevent delayed complications.44,95,98,99 Primary microvascular repair for VAI in anterior cervical surgery has been successful,1,97,100,101 but has only been described for posterior cervical surgery VAI in one case report.102 The difficulty with adequate exposure and visualization is likely the reason this is not widely employed. Permanent occlusion of the VA by ligation, clipping, or endovascular methods can be performed, but carries the risk of neurologic sequelae. Thomas et al described the incidence of unilateral flow via the left VA at 3.1% and via the right VA at 1.8%, implying predictable brain stem infarction rates resultant with ligation.17 Shintani and Zervas reported 12 deaths in a series of 100 patients with VA ligation, but noted that only 5 cases were likely attributable to brain ischemia.93 In contrast, both Taneichi et al and Neo et al reported rare symptoms related to VA occlusion.14,103 The incidence of brain ischemia or death after iatrogenic VAI ranges between 0 and 33%.1,2,4,100 Therefore, permanent occlusion should only be employed if the patient has sufficient contralateral flow to prevent untoward neurologic sequelae, such as cerebellar infarction, cranial nerve paresis, and hemiplegia.4,93,94,97,104 Both proximal and distal ligation should be performed given that proximal ligation may lead to delayed emboli, hemorrhage, and fistula formation.94,97,100 Endovascular treatment is a useful adjunct, and successful cases have been reported with coil embolization, stent-assist coil embolization, balloon embolization, stent grafts, or covered stents.1,92,94,95,98,105,106 Again, complete occlusion can be done

Vascular Complications of Posterior Cervical Procedures

Fig. 2.9 Different starting points and angulation for various lateral mass screw techniques.

only with sufficient collateral circulation.94,97,100 Some authors highlight the value of intraoperative consultation with an endovascular team to determine if collateral flow is sufficient for ligation or if repair of the vessel would be necessary.44 Even after initial treatment, patients should be followed up with magnetic resonance angiography or CT angiography to ensure there is no persistent or growing pseudoaneurysm.107 Antiplatelet or anticoagulation therapy has also been described for prevention of thromboembolic events in

VAI,1,3,11,108,109,110 but no consensus exists on the utility of routine use. If injury is suspected on one side, the other side should not be instrumented and other fixation constructs should be utilized to prevent bilateral VAI.2 Dickerman et al additionally recommended instrumentation should be placed on the nondominant side first, and in the absence of preoperative information on dominance, the right side instrumentation should be placed first.111 Gluf et al stressed the importance of

19

Cranial Table 2.1 Published rates of vertebral artery injury and cervical pedicle screw misplacement Authors (year)

Number of patients (number of CPS)

Number of pedicle breaches/screws Number of vertebral artery injuries evaluated (%)

Abumi et al (2000)8

180 (712)

45/669 (6.7%)

1

Yoshimoto et al (2005)84

26 (134)

15/134 (11.2%)

0

Kast et al

(2006)82

26 (94)

28/94 (29.8%)

0

Neo et al

(2005)13

18 (86)

25/86 (29.1%)

0

100 (419)

60/419 (14.3%)

1

84 (390)

66/390 (16.9%)

2

214 (1,024)

129/1,024 (12.6%)

Number not reported; no clinically apparent sequelae

Yukawa et al

(2006)86

Nakashima et al Wang et al

(2012)85

(2013)83

instrumenting the safer trajectory screw in C1–C2 transarticular fixation.43

2.6 Summary The risk of vascular injury in posterior cervical surgery is low but resultant complications can be catastrophic. Prevention of injury begins with a clear understanding of the pertinent anatomy and careful attention to preoperative imaging to identify anomalies. If injury occurs, initial hemostasis should be followed by primary repair or endovascular intervention to prevent delayed complications. Permanent occlusion by ligation or endovascular techniques should only be performed with the knowledge of adequate collateral circulation.

2.7 Key Points ●

●

●

●

●

VAI is a rare but potentially devastating complication of posterior cervical instrumentation and the majority of cases occur with transarticular screw fixation. Risk is especially pertinent along the posterior arch of C1, in the arcuate foramen if there is a ponticulus posticus, and at C6 where the VA is in a more lateral position from the midline. Anomalous VA anatomy must be identified using preoperative imaging modalities and be taken into careful consideration when placing instrumentation. No consensus exists on management of iatrogenic VAI, and treatment may range from ligation to primary repair. After initial hemostasis, it is essential to determine the presence of adequate contralateral flow before ligation or endovascular occlusion to minimize the occurrence of neurologic sequelae.

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Complications of C1 Lateral Mass Screw Fixation

3 Complications of C1 Lateral Mass Screw Fixation Alex Neusner

3.1 Introduction Atlantoaxial instability is a potentially devastating consequence of traumatic, malignant, degenerative, congenital, or inflammatory disease. Early methods of fixation were accomplished through various wiring techniques that, while moderately effective, required postoperative halo vest stabilization. Subsequently, a technically demanding C1–C2 transarticular screw fixation was described by Magerl that only required a soft collar postoperatively. However, reduction of C1 on C2 is necessary to perform this techique.1 Goel and Laheri were the first to describe posterior stabilization of the atlantoaxial joint with a screw–rod construct.2 While this was introduced in 1994, the technique was later refined in 2001 by Harms and Melcher.3,4 The technique described by Harms and Melcher in 2001 remains the currently accepted procedure for posterior C1–C2 instrumented fusion. Many of the complications described by the authors in this study have proven to be those most common as the procedure has entered common practice. This has proven to be a reliable and overall effective stabilization technique. Nevertheless, the technical demands of the procedure as well as the complex and vulnerable anatomy of the upper cervical spine provide opportunity for myriad complications associated with this procedure. The poor prognosis for healing of many odontoid fractures combined with the complex soft tissue stabilization of the atlantoaxial junction allows for significant potential of local pain, neuropathy, or even myelopathy after an injury. Surgical fixation of this joint by posterior wiring was first described by Gallie in 1939. For much of the 20th century, variations of this technique remained the standard of care for atlantoaxial fixation.5 Yet, multiple biomechanical analyses suggest a failure rate of up to 15% with posterior wiring techniques.5,6,7 While the Magerl transarticular screw has provided improved success, the procedure is technically demanding and not a viable option for all patients.8,9 The C1 lateral mass–C2 pedicle screw–rod construct has been evaluated in comparison to the transarticular screw in numerous studies. In the initial studies by Goel et al and Harms and Melcher, the authors reported a 100% fusion rate without damage to the vertebral artery in any case. The authors suggested a lower risk of vertebral artery damage exists due to improved visualization of the screw trajectory in the lateral mass instrumentation techinque.3,4 A comparison study by Lee et al demonstrated a mildly significantly improved fusion rate and a nonsignificant decrease in postoperative complications with the Harms technique as compared to the transarticular screw.10 An extensive meta-analysis of approximately 3,100 patients by Elliot et al provided similar conclusions. The authors demonstrated excellent rates of fusion in both transarticular screw and screw– rod fixation (95.7 vs. 99.3%). Rates of postoperative complications show minor differences between the two groups. However, there is a significant decrease in vascular injury but an increase in C2 neuropathic pain or numbness with screw–rod fixation. Additionally, screw malposition was found to be much higher with transarticular screw placement.8 Overall conclusions regarding these techniques suggest that both provide excellent

rates of fusion. While screw–rod fixation may reduce risk of vertebral artery injury, this has not yet been definitively demonstrated. Yet, C1 lateral mass–C2 pedicle instrumentation allows for improved control of displacement reduction and obviates the need for integrity of the posterior elements of these vertebrae.10 Hence, patient-specific anatomic factors should play the largest role in determining the appropriate means of fixation. The cornerstone of the Harms–Melcher technique of screw– rod instrumentation is placement of screws into the C1 lateral masses. The operation is performed via a posterior approach with the patient in the prone position. The C1 lateral mass as well as the C2 nerve root, which is retracted caudally, is directly visualized. The working window of the lateral mass is bordered cephalad by the C1 posterior arch, caudad by the C1–C2 articulation, and medial-lateral by the walls of the lateral mass. The starting point should be centered within this window. Optimal drill entry is approximately 22 degrees cephalad and 10 degrees medial. However, approach angle and screw length should be approximated preoperatively with computed tomography (CT) imaging and intraoperatively with fluoroscopic guidance.11,12,13 Posterior screw–rod fixation of the atlantoaxial junction is currently unclassified by the Food and Drug Administration (FDA). However, this instrumentation has been thoroughly studied by the Orthopedic and Rehabilitation Devices Panel. In 2012, the FDA was petitioned to grant class II status to these devices.14

3.2 Relevant Anatomy Successful execution of this procedure requires an intimate knowledge of the atlantoaxial region anatomy. The first cervical vertebra (atlas) is unique among the vertebrae in that it lacks a vertebral body. Rather, its bony elements are composed of an anterior arch and a posterior arch, which are attached to two lateral masses. The posterior arch represents a modified lamina and contains a central posterior tubercle. The anterior arch is of crucial importance, given that its fovea dentis is where the dens articulates with the atlas. Each lateral mass possesses an inferior articular facet which also articulates with the axis and serves as the point of rotation for the atlas on the axis.13,15 There is marked variability in the size and shape of the lateral masses and anterior tubercle among patients, and they change with age. A study by Wait et al demonstrated that the anterior C1 tubercle ranged from 2.7 to 11.2 mm in depth and tended to increase with age. The authors also noted significant differences in lateral mass geometry as related to patient gender and variation between right and left sides.16 Therefore, careful preoperative imaging of these structures is necessary for successful screw placement. The vertebral artery courses out through the C1 transverse foramen to a groove on the upper lateral portion of the C1 posterior arch. From here, it travels medially and superiorly into the foramen magnum. However, a number of variations in vertebral artery anatomy have been reported, namely posterior

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Cranial ponticulus, high-riding vertebral artery, and V3 segment anomaly. When present, these significantly increase to risk of injury to the artery if not properly identified.15,17,18 This segment of the vertebral artery is also surrounded by a dense venous plexus that may present a source of notable bleeding during dissection of this area and should be disrupted as minimally as possible.13 Furthermore, the internal carotid arteries run along the lateral aspect of the anterior arch of C1. While generally found slightly lateral to the lateral mass, there is certainly variability in the position of these vessels and they not infrequently lie directly ventral to the lateral mass.13,19 In an anatomic study, Hong et al found that 47% of internal carotid arteries are located in front of the C1 lateral mass with prevalence increasing in the elderly population.20 The most prominent nervous structure encountered during this operation is the C2 nerve root. C2 exits within the atlantoaxial interspace. It then proceeds to travel medially, inferior to the posterior arch and lateral mass junction. However, the nerve root often obstructs part or all of the screw entry point into the lateral mass. Therefore, it must be identified and retracted or sacrificed prior to proceeding with the procedure. Additionally, the hypoglossal nerve is found emerging within the anterior atlanto-occipital joint. It then progresses inferiorly between the internal carotid artery (ICA) and jugular vein, approximately 2 to 3 mm lateral to the C1 lateral mass.13,15,21

3.3 Implant Complications 3.3.1 Overview While instrumentation of the C1 lateral mass is a relatively recently described procedure, the principals involved are quite similar to those of long-standing pedicle screw placement fixations. As such, complications of this procedure are only novel in that the anatomy at this level is distinct from that of the rest of the axial spine. In general, they stem from misplacement of the hardware due to anatomic anomaly and/or surgeon error. Unsurprisingly, many of the most common complications associated with C1 lateral mass instrumentation are those inherent to all spine surgery such as cerebrospinal fluid (CSF) leak and infection. Elliott et al conducted the largest meta-analysis of atlantoaxial fusion techniques including the screw–rod construct described in this chapter. Many of the generalizations made about complication rates in this discussion come from this meta-analysis.5,8,22,23,24 Elliott et al24 in 2012 conducted a large meta-analysis of complications related to atlantoaxial fusion with screw–rod constructs. In this analysis of 24 studies consisting of 1,073 patients, the overall successful fusion rate was 99.3%. The most common operative complications were C2 numbness or neuropathic pain, occurring in 6.3 and 1.4% of procedures, respectively. Of note, this analysis included studies in which the C2 nerve root was intentionally sacrificed, which leads to a much higher rate of C2 numbness. Overall rate of clinically significant screw malposition was 2.4% (range: 0.3–6.7%). Yet, as noted by the authors of this study, there is no standardization for determining fusion success. As such, it is likely that the rate of pseudoarthrosis or unsuccessful fusion is somewhat underreported.

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Discussion of the complications of this procedure requires the distinction between radiographic hardware misplacement and clinically significant complications. In a study of screw placement by Bransford et al,22 the authors demonstrated that while approximately 4% of screws were unacceptably placed, none led to clinically significant pain or injury. Similarly, Yeom et al23 showed that despite relatively high rates of cortical perforation, there were no vascular injuries and primarily transient neuralgia in the study patients. In regard to complication rate, screw–rod fixation of atlantoaxial instability appears to be similar to or better than that of transarticular screw fixation. A small 2009 study by Lee et al10 examined 53 patients undergoing surgery for atlantoaxial instability. They found no statistical difference in rates of clinically significant complications. Perioperative vertebral artery injury occurred in each group; however, all were repaired intraoperatively and did not cause any clinical complications. In an expansion of the meta-analysis of Elliott et al described previously in this section,24 the authors compared outcomes of screw–rod fixation with transarticular screw fixation.8 In total 2,073 patients treated with transarticular screw and 1,073 patients treated with a screw–rod construct were included. In this study, the authors noted a significant decrease in clinically malpositioned screws in the screw–rod group as compared to the transarticular screw group (0.4 vs. 3.8%, p < 0.0001). Additionally, there is a noted increase in screw-related vascular injury in the transarticular screw group (0.2 vs. 1.2%, p = 0.002). However, the authors noted that marked variation in graft material and technique is present among the studies and may inhibit direct comparison of all groups. Nevertheless, it appears that screw– rod fixation with C1 lateral mass instrumentation offers a somewhat reduced risk of complications as compared to previously used atlantoaxial fixation procedures.

3.3.2 Device Failure Breakage or pullout of C1 lateral mass screws are quite infrequent and are rarely described in the available literature. Pullout strength of lateral mass screws is similar to that of cervical pedicle screws. An anatomic study by Hong et al25 demonstrated lateral mass screws to have an average pullout strength of 1,718.16 N compared to 1,631.94 N in the axial pedicle screws. Certainly, achieving bicortical purchase with the lateral mass screw markedly increases the pullout strength of the device. Ma et al26 found bicortical lateral mass screws to have an average pullout strength of 1,243.8 N compared to 794.5 N in unicortical screws. However, as previously discussed, the region directly anterior to the C1 lateral mass potentially contains a number of vulnerable structures such as the ICA and/or the hypoglossal nerve. As such, great caution must be used when breaching the anterior cortex of the C1 lateral mass. In the initial series of 37 patients described by Harms and Melcher,3 the authors reported that none of the procedures were complicated by hardware failure or hardware-related complications. Since this study, numerous follow-up studies have demonstrated similar findings. In a series reported by Kim et al,27 a total of 65 patients received screw–rod fixation of the atlantoaxial joint and none experience hardware-related complications. In fact, in the meta-analysis performed by Elliott et

Complications of C1 Lateral Mass Screw Fixation al,24 none of the 1,073 patients were reported to have screw pullout or breakage.

3.3.3 Screw Malposition Instrumentation of the C1 lateral mass remains a technically challenging procedure. As such, improper positioning of the screw within the lateral mass occurs with moderate frequency. However, as previously discussed, a large proportion of improperly positioned screws bear little to no clinical significance. This determination comes by way of many radiographic studies evaluating the accuracy of screw placement into the C1 lateral mass. Ringel et al28 examined the results from 35 patients treated with C1–C2 stabilization by a screw–rod construct. Postoperatively, patients were assessed with thinly cut CT scans for cortical violation by the screw. In total, 6% of C1 lateral mass screws violated one of the cortices. However, none of the defects were deemed to be of clinical significance and no reoperation was necessary. In 2011, Bransford et al22 conducted a retrospective study in which 176 patients were treated with procedures requiring a C1 lateral mass screw. Position was assessed as being ideal with screw threads completely within the bony cortex, acceptable, or unacceptable, with greater than 50% of screw diameter violating the cortex, greater than 1 mm protrusion from the anterior cortex, or clear violation of the transverse foramen or spinal canal. In sum, 86% of lateral mass screws were found to be in ideal position, 8% were acceptable, and 6% were unacceptably positioned. Yet, none of the patients experienced any clinical sequelae of the screw positioning. The majority of unacceptable screws were placed medially into the spinal canal; however, none required revision. Only one patient required revision surgery due to a sagittal split with displacement of the lateral mass. Splits in the lateral mass are relatively common and often occur during drilling of the pilot hole for screw placement. In a study by Yeom et al,23 only 48% of lateral mass screws were placed without any form of cortical perforation or splitting during drilling of screw placement. Ten of 102 screws led to a vertical split during drilling, with another 4 developing during tapping or screw placement. However, none led to impairment of lateral mass purchase as assessed intraoperatively and no postoperative screw loosening or breakage was noted in any of the patients. Hence, cortical breach or screw malposition is an inevitable consequence of this challenging procedure. Certainly, these errors may lead to severe unintended consequences, as will be detailed in the remainder of this section. However, it is clear that the vast majority of minor errors in screw placement and positioning are without great clinical significance.

3.4 Vascular Complications 3.4.1 Internal Carotid Artery Injury The ICA has the potential to lie in a rather vulnerable position during C1 lateral mass instrumentation. In a radiographic study, Hong et al20. reported that the ICA is fully lateral to the C1 lateral mass in 52.3% of cases. In 43.8% of cases, it was found anterior to the lateral half of the lateral mass, 3.6% were in front of the medial half, and 0.3% were found medial to the lateral mass. Additionally, in patients older than 60 years, only 42.5% of ICAs

were lateral to the C1 lateral mass. Hoh et al29 presented similar results in their study. Furthermore, they found the average shortest distance from the ICA to the ventral surface of the lateral mass to be 3.5 mm on the left and 3.9 mm on the right. Furthermore, in 96% of cases, the posterior margin of the ICA is posterior to the anterior tubercle of C1.30,31 Hence, in nearly all patients, the internal carotid arteries are either at risk or close to the at-risk zone, should breach of the anterior cortex occur.32 Injury to the ICA during surgery, while rare, is a devastating complication of all cervical spine surgeries. Indeed, such an injury is adequately uncommon that it is only represented in the literature by a select few case reports.30,33 Each of these describes injuries to the internal carotid following transarticular screw atlantoaxial fixation. In fact, despite extensive study of the risk of ICA injury during lateral mass screw placement, no case reports of such a complication can be found in the current available literature. Nevertheless, because such a risk of injury exists, many authors including Currier et al31 recommended a CTA prior to instrumentation of the C1 lateral mass.

3.4.2 Vertebral Artery Injury Injury to the vertebral artery is perhaps the most welldescribed vascular complication of atlantoaxial stabilization surgery. Fortunately, the advent of C1 lateral mass instrumentation has reduced the incidence of vertebral artery injury, even when compared to transarticular screw placement.8 As such, the risk of vertebral artery injury in anatomically normal patients is quite low. In the analysis of Elliott et al,24 of 2,021 C1 lateral mass screws placed, only 1 (0.05%) caused a vertebral artery injury. Recent literature suggests that most vertebral artery injury occurs during dissection and exposure of the soft tissue surrounding the lateral mass rather than during drilling of screw placement.24,34 In the aforementioned study, an additional four patients experienced a vertebral artery injury due to electrocautery during soft-tissue dissection. Injury to the vertebral artery carries with it a relatively high risk of morbidity and mortality. In one study, of 39 cases of vertebral artery injury sustained during cervical spine surgery, 7 patients (17.9%) experienced symptoms of vertebral artery insufficiency. One of these patients died as a result of the injury. Similarly, in the meta-analysis of Elliott et al, the only deaths directly attributable to surgery were due to vertebral artery injury. Brainstem stroke is also a known consequence of transient or permanent interruption of vertebral artery blood flow.24,34,35,36 In most cases, these injuries are noticeable during the primary operation and thus are amenable to primary repair intraoperatively. Adequate exposure of the vessel and the defect is necessary to appreciate the full size and nature of the injury. Aryan et al34 suggested repair by laying or suturing a muscle flap over the vessel defect. These authors reported prompt hemostasis using this method. Alternatively, direct microvascular repair of the defect is an appealing option; however, it requires a high level of technical competency to perform. Surgical ligation of the vertebral artery will achieve hemostasis but with a high risk of significant morbidity and mortality. As such, it should only be considered as an absolute last resort and after the presence of collateral blood flow has been determined. If delayed repair is required, consultation for endovascular

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Cranial treatment such as pseudoaneurysm coiling is advised. Postoperatively, patients with a known or suspected vertebral artery will require angiography to assess vessel patency and to rule out dissection or pseudoaneurysm. Additionally, consideration should be made regarding anticoagulation therapy in patients following a primary vessel repair.24,34,35,36,37 The study of Maughanet al provided guidance on management of intraoperative management of vertebral artery injury. Given the vulnerable position of the artery during this procedure, the surgeon must be aware of immediate management of this complication. There is a moderate degree of heterogeneity of the positions in which the vertebral artery is found. Incidence of a deviant vertebral artery course is estimated to be between 18 and 23%.37 Certainly, the presence of a vertebral artery anomaly markedly increases the risk of injury to that structure during surgery. The most well-described variations are the posterior ponticulus, V3 segment anomaly, and high-riding vertebral artery (discussed in section “Relevant Anatomy”). The optimal entry points described in the literature for lateral mass screws generally do not take these common variants into account. While the commonly described position for screw placement is the inferior lateral mass, in the case of an artery that courses inferior to the C1 arch, the vessel would be at risk. Similarly, a high-riding vertebral artery or a patient with a posterior ponticulus would be at risk of vessel injury with a more superior approach. Given the proven success using alterations of the screw starting point, surgeons should preoperatively assess vertebral artery position and tailor the approach to the lateral mass instrumentation approriately.17,35,36,37,38

plexus of the upper cervical region. The authors described that during the case, brisk bleeding was noted surrounding the screw entry site. They proposed that an improper, medially placed lateral mass screw likely pierced the dura. This allowed the brisk venous bleeding to communicate with the subarachnoid space leading to the earlier-described complication. While certainly unusual, potential for such an event should be noted. Damage to the venous sinus surrounding the vertebral artery is also considered to create a risk of air embolus. In a case report, Dumont et al42 presented a patient who developed a venous air embolus during atlantoaxial fusion. During cervical spine surgery performed in the prone position, incidence of air embolus is exceedingly low with very few reported cases. Yet, this patient illustrates the significance of the venous plexus surrounding the atlas and the vertebral artery. Control of bleeding from the upper cervical venous system is commonly achieved by direct pressure. This tamponade may arise from application and tightening of the intended cervical stabilization hardware.41 Pan et al40 proposed a technique of C1 instrumentation that protects the venous sinus. Here, the venous sinus is carefully exposed and dissected. A cylinder of bone wax wrapped in Surgicel is used to isolate the vertebral operative area from the vascular structure. In a somewhat limited study, the authors demonstrated good success using this novel technique. Regardless of particular technique, great care should be taken to avoid damage to the upper cervical venous structures.

3.4.3 Venous Plexus Injury

Occipital neuropathy is perhaps the most commonly reported complication of C1 lateral mass instrumentation. In general, during placement of C1 lateral mass screws, the C2 nerve root is dissected, identified, and retracted caudally before drilling the lateral mass.13 Nevertheless, given the required manipulation of this nerve root and its intimate relation to the operative area, nerve palsy or permanent damage occurs with moderate frequency. Published studies estimated the rate of occipital neuralgia due to this procedure to be between 0 and 33% with a large study demonstrating an incidence of 6.3% for C2 numbness and 1.4% for C2 pain.24,43,44 The meta-analysis by Elliott et al provided compelling evidence for implementation of the practice of C2 nerve root sectioning during C1 lateral mass instrumentation. It appears to improve outcomes with only moderate risk of clinical consequences.43 The C2 nerve root exits the spinal cord within the C2 foramen. This space is bordered superiorly by the posterior arch of the atlas and inferiorly by the lamina of the axis. The C2 ganglion occupies approximately 76% of the foramen.45 As such, a relatively mild stenosis of this foramen may lead to injury to the C2 root.46 The C2 nerve root joins with C3 to form the occipital nerve, which provides sensation along the occipital portion of the scalp. C2 contributes to the greater and lesser distributions of the occipital nerve.47 Patients who experience an injury to the C2 nerve root most frequently complain of pain and/or numbness in the distribution of the C2 nerve root. In particular, recurrent unilateral headaches during the postoperative period should be a warning sign for C2 impingement.46,48 Additionally, patients may describe typical neuropathic pain symptoms such as burning,

The suboccipital venous plexus is a potential source of significant blood loss during instrumentation of the C1 lateral mass, as it represents the drainage point of major intracerebral sinuses. This venous plexus consists of both superficial and deep components. While the superficial plexus is found extending from the subcutaneous layer, the deep plexus surrounds the vertebral artery and its tributaries.39 This venous plexus also has anastomoses to the jugular vein and sigmoid sinus creating a dense, relatively high-flow vascular area. Of particular concern is that this venous plexus frequently is covering the entry point for a C1 lateral mass screw.13 As such, it is often very difficult to perform this procedure without some degree of damage to the venous plexus. In the majority of cases, the bleeding is easily controlled and the complication is not reported. Thus, there are very few reported instances of morbidity arising from venous plexus bleeding. Nevertheless, bleeding from this area is a major contributor to overall blood loss during atlantoaxial fusion with a screw–rod construct.13,39,40 In a study by Pan et al,40 the authors showed that any atlantoaxial fusion in which damage to the venous plexus occurs led to blood loss of more than 1,000 mL, whereas normal estimated blood loss is approximately 300 mL.22 While the bleeding was controllable, achieving hemostasis markedly increased operative time and difficulty. In a 2013 case report, Stovell and Pillay41 described an extraordinary case of a subarachnoid hemorrhage and hydrocephalus during atlantoaxial fusion. This morbid complication is thought to be in large part due to bleeding from the venous

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3.4.4 Occipital Neuralgia/Neuropathy

Complications of C1 Lateral Mass Screw Fixation shooting, or lightning-like pains in the occipital region of the scalp.47 Management of postoperative occipital neuralgia should be based on the severity of symptoms as well as imaging findings. Rarely, a misplaced screw may be identified as the cause of the neuropathic symptoms. As discussed previously, the C2 foramen is quite unforgiving to the C2 nerve root, so encroachment of that space my lead to nerve root compression. In such cases, reoperation to remove the offending screw has proven successful in relieving symptoms in a limited number of case reports.43, 48,49 However, other case reports provided examples of hardware removal failing to provide relief of neuralgia.50 Hence, the decision to reoperate is a complex one, requiring a meaningful discussion with the patient regarding the potential for relief of symptoms. Many recent studies have focused on the prevention of C2 neuropathy following C1 instrumentation. Use of a modified high entry point for screw insertion has been suggested as a means to avoid contact with the C2 nerve root. A small study by Lee et al44 described a procedure in which a notch is made at the junction of the C1 lateral mass and the inferior aspect of the C1 arch. This allows the surgeon to place the screw farther from the C2 ganglion with less manipulation of the nerve root. In this study of 12 patients, the authors reported one case of transient occipital neuralgia and four misplaced screws. A study by Elliott et al51 compared posterior arch screw placement with standard central lateral mass placement with regard to C2 nerve status. While the posterior arch starting point decreases the incidence of C2 neuralgia compared to the standard approach, C2 nerve section offers an even lower incidence of postoperative neuralgia. Furthermore, screw placement from the posterior arch also leads to a similar, if not higher, rate of screw malposition as compared to the standard approach (3.18–6.08% vs. 2.41–6.73%). A significant amount of recent research has focused on the potential benefits of sacrificing the C2 nerve root during C1 lateral mass instrumentation. In a standard procedure, the nerve root must be identified and retracted, thus potentially limiting access to the lateral mass and still at risk of injury. The benefits offered by this approach include superior visualization of the lateral mass, reduced need for dissecting the venous plexus, and availability of the C2 foramen for placement of bone graft to enhance fusion.43,52,53 In one of the first descriptions of this technique, Squires and Molinari detailed a procedure in which the C2 nerve root is severed using electrocautery to expose the C1 lateral mass. In a nonrandomized study of 23 patients, with 18 undergoing C2 sacrifice, the authors showed a decrease in blood loss and operative time in patients whose C2 nerve roots are sacrificed. However, there was one complication of a CSF leak caused at the time of nerve sectioning. Patient outcomes in terms of pain and functional status were statistically equivalent. Of course, many patients in whom the C2 nerve root was severed lacked sensation throughout the C2 dermatomal distribution with one patient describing it as bothersome.53 Kang et al also examined a cohort of patients who underwent posterior C1–C2 instrumented fusions with sacrifice of the C2 nerve root. In this study of 20 patients, 20% complained of occipital numbness with 10% experiencing paresthesias. On exam, half of the patients were found to have some degree of occipital anesthesia. No operative complications were noted.52

Elliott et al43 performed a meta-analysis of patients undergoing posterior atlantoaxial fusion with and without C2 nerve preservation. This study demonstrated a significant increase in malpositioned screws and neuropathic pain in patients with preserved C2 nerves. Furthermore, a much higher proportion of patients were able to have C1–C2 joint decortication and packing when the C2 nerve was sacrificed. However, there was no change in successful fusion rate. Also, as expected there was a marked increase in the rate of postoperative C2 numbness in patients whose C2 roots were sacrificed. Avoidance of C2 nerve-related complications should be a significant concern of the surgeon performing this procedure. There is a moderate risk of postoperative neuralgia should damage to or impingement of this nerve occur. Furthermore, the nerve lies in a very vulnerable location and thus must be retracted in order to obtain visualization of the lateral mass. As demonstrated in the presented studies, sacrifice of the C2 nerve is a viable option and should at least be considered in patients whose C2 ganglion is providing significant obstruction to the instrumentation entry point.

3.4.5 Hypoglossal Nerve Injury The hypoglossal nerve exits the cranial base and passes between the ICA and the jugular vein dorsal to the ICA. It generally lays approximately 2 to 3 mm lateral to the center of the anterior lateral mass. Of note, the hypoglossal nerve lies anterior to the rectus capitis anterior muscle and the longus capitis muscle. Therefore, these may serve as landmarks to avoid potential injury to the hypoglossal nerve.19 Injury to the hypoglossal nerve during C1 instrumentation is exceedingly rare.19,22,24 In fact, there is only one published case report of such an injury. Hong et al21 described a case of a 67-year-old man who underwent C1–C2 fusion via the Harms– Melcher technique due to a type II odontoid fracture. Immediately postoperatively, the patient was noted to have dysphagia and dysarthria, requiring a nasogastric tube for 4 weeks. The hypoglossal nerve palsy improved without intervention and was undetectable 2 months after the operation. The authors reemphasized that slightly medial angulation of screw placement is recommended to avoid injury to both the vertebral artery and the hypoglossal nerve. In a person with normal anatomy and a properly placed screw, the risk of injury to the hypoglossal nerve is minimal. Indeed, the authors were unable to explain the precise cause of this patient with transient hypoglossal nerve palsy. Nevertheless, this is a vulnerable structure during C1 lateral mass instrumentation and its anatomic position should be taken into account.

3.4.6 Dural Tear/Cerebrospinal Leak Common among nearly every spinal surgery is the risk of a dural tear leading to a leak of CSF. At the level of the atlantoaxial junction, a number of suboccipital muscles attach to the cervical vertebrae. It should be noted that many of these muscles including the rectus capitis posterior major and minor have also been found to communicate with the spinal dura mater.54,55 This relationship is of clinical importance, as traction is placed on these muscles at times during instrumentation of the upper cervical spine. Still, the reported incidence of dural tear with

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Cranial CSF leak during C1 lateral mass instrumentation is extremely rare. In one review of 1,002 patients undergoing screw–rod atlantoaxial fixation, only 2 (0.2%) were noted to have a CSF leak.24 Indeed, incidental durotomy occurs with the least frequency in cervical spine procedures as compared to other locations in the spine. Furthermore, most intraoperative durotomies are noticed before closing the patient and are thus managed with a primary repair of the dura.56 Nevertheless, damage to the dura is a potentially devastating consequence if unnoticed during the initial operation. This is evidenced in the previously discussed case study of the patient suffering a subarachnoid hemorrhage following C1 lateral mass instrumentation. Again, it appears that a dural tear in combination with brisk venous bleeding contributed to this disastrous outcome.41

3.4.7 Infection Infection is certainly the chief complication of concern for any operative procedure. Certainly, given the vulnerable nature of the upper cervical spine, a perioperative infection has the potential to lead to extremely damaging consequences. In the initial modern description of this procedure by Harms and Melcher,3 the authors described their only surgical complication as a patient who developed a deep wound infection. Overall infection rates with this procedure have been reported to be between 0 and 10% with a large analysis demonstrating an infection rate of 1.2%.24 Another study by Fehlings et al57 demonstrated the infection rate after all posterior cervical spine surgery to be 2.3% for superficial wound infections and 0.7% for deep wound infections. Yet, these rates remain well under the 14.9% reported by Campbell et al in a prospective analysis of infection in all instrumented spinal surgery.58 Treatment of a postoperative infection in this area must be aggressive to prevent progression of the abscess. In some cases of superficial infection, antibiotics alone are adequate to control the infection. When surgical debridement is necessary, the surgeon must attempt to predict whether a single-stage debridement and closure will be adequate or if a two-stage debridement with delayed closure is necessary. The Postoperative Infection Treatment Score for the Spine (PITTS) score was developed to assist in this decision making. The score takes into account surgery location, comorbidities, microbiology, distant site infection, instrumentation, and use of bone graft. A higher PITTS score correlates with a higher likelihood of requiring multiple irrigation and debridements. Of note, surgeries performed on the cervical spine add the least of any location to the PITTS score.59,60,61

3.5 Future Directions Instrumentation of the C1 lateral mass is a relatively new procedure, only coming into routine clinical practice within the past decade.2,3 Furthermore, atlantoaxial injuries requiring surgical stabilization are relatively rare. As such, total procedure volume remains somewhat low for making generalizations about complications and their incidence with this procedure. Given these limitations, the currently available data do point to some specific areas for further investigation in the near future in addition to general data collection on the procedure.

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It is clear and certainly expected that many complications related to C1 lateral mass instrumentation result from anomalies in the patient’s anatomy which do not allow the surgeon to use the standardly practiced operating procedure successfully. Yet, many of these abnormalities in anatomy are detectable using imaging techniques. Therefore, establishment of imaging protocols that are both sensitive and specific for the more common anatomic anomalies has the potential to prevent many of the complications described in this chapter. Study of intraoperative imaging techniques has been performed. Standard C-arm fluoroscopy, Oarm imaging in children, and isocentric C-arm three-dimensional imaging have all been demonstrated to improve screw placement accuracy in C1 lateral mass instrumentation.62,63,64 While individual authors have suggested the use of CTA to avoid vertebral artery injury or CT to assess lateral mass anatomy, there does not appear to be investigation into whether this preoperative imaging would improve outcomes.17,38 Advances in atlantoaxial stabilization techniques are being rapidly developed. One of the most significant limitations of the current fixation techniques is the restriction of motion at the atlantoaxial joint. In recent years, artificial atlanto-odontoid joint systems have been developed and studied as an alternative to the posterior atlantoaxial fusion. While these systems are still in cadaveric testing stages, they offer promise of improved range of motion following an injury to the axial spine.65,66,67,68

3.6 Summary The atlantoaxial spine is one of the most vulnerable and challenging regions of the spine on which to operate. In particular, the odontoid is prone to nonhealing and pseudoarthrosis. Yet, the consequences of instability in this region may be disastrous. As such, performance of stabilization procedures such as the posterior screw–rod instrumentation described in the chapter are essential in cases of injury to this region. Instrumentation of the C1 lateral mass is overall a very safe and effective procedure for providing stabilization to the atlantoaxial joint. Nevertheless, the complex and vulnerable arrangement of neurovascular structures here provides ample opportunity for surgical complications. As such, the surgeon must be acutely aware of the location and course of these structures using preoperative imaging as well as careful intraoperative identification and protection when appropriate. Certainly, given the relatively low volume of these procedures performed, data collection and analysis should and is currently being performed to further understand the sources of risk involved in this operation.

3.7 Key Points ●

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Posterior C1–C2 stabilization using the Harms–Melcher technique provides a fusion rate of 99 to 100%. The most common bleeding source is the suboccipital and vertebral venous plexus. Anomalies of C1 lateral mass and neurovascular anatomy lead to the highest risk for operative complications. Most screw malpositions and cortical breaches do not lead to clinical consequences. Optimal screw entry is 22 degrees cephalad and 10 degrees medial starting from the center of the C1 lateral mass.

Complications of C1 Lateral Mass Screw Fixation

References [1] Jeanneret B, Magerl F. Primary posterior fusion C1/2 in odontoid fractures: indications, technique, and results of transarticular screw fixation. J Spinal Disord. 1992; 5(4):464–475 [2] Goel A, Laheri V. Plate and screw fixation for atlanto-axial subluxation. Acta Neurochir (Wien). 1994; 129(1–2):47–53 [3] Harms J, Melcher RP. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine (Phila Pa 1976). 2001; 26(22):2467–2471 [4] Goel A, Desai KI, Muzumdar DP. Atlantoaxial fixation using plate and screw method: a report of 160 treated patients. Neurosurgery. 2002; 51(6):1351– 1356, discussion 1356–1357 [5] Henriques T, Cunningham BW, Olerud C, et al. Biomechanical comparison of five different atlantoaxial posterior fixation techniques. Spine. 2000; 25 (22):2877–2883 [6] Grob D, Crisco JJ, III, Panjabi MM, Wang P, Dvorak J. Biomechanical evaluation of four different posterior atlantoaxial fixation techniques. Spine. 1992; 17 (5):480–490 [7] Grob D, Panjabi M, Dvorak J, et al. The unstable spine—an “in vitro” and “in vivo study” on better understanding of clinical instability [in German]. Orthopade. 1994; 23(4):291–298 [8] Elliott RE, Tanweer O, Boah A, et al. Outcome comparison of atlanto-axial fusion with transarticular screws and screw-rod constructs: meta-analysis and review of literature. J Spinal Disord Tech. 2014; 27(1):11–28 [9] Elliott RE, Tanweer O, Boah A, et al. Atlanto-axial fusion with transarticular screws: Meta-analysis and review of the literature. World Neurosurg. 2013; 80(5):627–641 [10] Lee SH, Kim ES, Sung JK, Park YM, Eoh W. Clinical and radiological comparison of treatment of atlantoaxial instability by posterior C1-C2 transarticular screw fixation or C1 lateral mass-C2 pedicle screw fixation. J Clin Neurosci. 2010; 17(7):886–892 [11] Harms J, Melcher RP. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine. 2001; 26(22):2467–2471 [12] Seal C, Zarro C, Gelb D, Ludwig S. C1 lateral mass anatomy: proper placement of lateral mass screws. J Spinal Disord Tech. 2009; 22(7):516–523 [13] Joaquim AF, Ghizoni E, Rubino PA, et al. Lateral mass screw fixation of the atlas: surgical technique and anatomy. World Neurosurg. 2010; 74 (2–3):359–362 [14] Rhim C, Devlin V, Hill G. Classification of posterior cervical screws including pedicle and lateral mass screws. Presented at Meeting of Orthopedic and Rehabilitation Devices Panel. FDA September 12, 2012. Gaithersburg, MD [15] France JC, Gocke RT. Injuries of the cervicocranium. In: Browner B, Jupiter J, Levine A, Trafton P, Krettek C, eds. Skeletal Trauma. 4th ed. Philadelphia, PA: Saunders Elsevier; 2009:813 [16] Wait SD, Ponce FA, Colle KO, Parry PV, Sonntag VK. Importance of the C1 anterior tubercle depth and lateral mass geometry when placing C1 lateral mass screws. Neurosurgery. 2009; 65(5):952–956, discussion 956–957 [17] Hong JT, Jang WY, Kim IS, et al. Posterior C1 stabilization using superior lateral mass as an entry point in a case with vertebral artery anomaly: technical case report. Neurosurgery. 2011; 68(1) Suppl Operative:246– 249, discussion 249 [18] Riesenburger RI, Jones GA, Roguski M, Krishnaney AA. Risk to the vertebral artery during C-2 translaminar screw placement: a thin-cut computerized tomography angiogram-based morphometric analysis: clinical article. J Neurosurg Spine. 2013; 19(2):217–221 [19] Simsek S, Yigitkanli K, Turba UC, et al. Safe zone for C1 lateral mass screws: anatomic and radiological study. Neurosurgery. 2009; 65(6):1154–1160, discussion 1160 [20] Hong JT, Kim TH, Kim IS, et al. The effect of patient age on the internal carotid artery location around the atlas. J Neurosurg Spine. 2010; 12(6):613–618 [21] Hong JT, Lee SW, Son BC, Sung JH, Kim IS, Park CK. Hypoglossal nerve palsy after posterior screw placement on the C-1 lateral mass. Case report. J Neurosurg Spine. 2006; 5(1):83–85 [22] Bransford RJ, Freeborn MA, Russo AJ, et al. Accuracy and complications associated with posterior C1 screw fixation techniques: a radiographic and clinical assessment. Spine J. 2012; 12(3):231–238 [23] Yeom JS, Kafle D, Nguyen NQ, et al. Routine insertion of the lateral mass screw via the posterior arch for C1 fixation: feasibility and related complications. Spine J. 2012; 12(6):476–483 [24] Elliott RE, Tanweer O, Boah A, et al. Atlanto-axial fusion with screw-rod constructs: Meta-analysis and review of literature. World Neurosurg. 2014; 81

[25] Hong X, Dong Y, Yunbing C, Qingshui Y, Shizheng Z, Jingfa L. Posterior screw placement on the lateral mass of atlas: an anatomic study. Spine. 2004; 29 (5):500–503 [26] Ma XY, Yin QS, Wu ZH, et al. C1 pedicle screws versus C1 lateral mass screws: comparisons of pullout strengths and biomechanical stabilities. Spine (Phila Pa 1976). 2009; 34(4):371–377 [27] Kim SH, Shin DA, Yi S, Yoon DH, Kim KN, Shin HC. Early results from posterior cervical fusion with a screw-rod system. Yonsei Med J. 2007; 48(3):440–448 [28] Ringel F, Reinke A, Stüer C, Meyer B, Stoffel M. Posterior C1–2 fusion with C1 lateral mass and C2 isthmic screws: accuracy of screw position, alignment and patient outcome. Acta Neurochir (Wien). 2012; 154(2):305–312 [29] Hoh DJ, Maya M, Jung A, Ponrartana S, Lauryssen CL. Anatomical relationship of the internal carotid artery to C-1: clinical implications for screw fixation of the atlas. J Neurosurg Spine. 2008; 8(4):335–340 [30] Currier BL, Todd LT, Maus TP, Fisher DR, Yaszemski MJ. Anatomic relationship of the internal carotid artery to the C1 vertebra: a case report of cervical reconstruction for chordoma and pilot study to assess the risk of screw fixation of the atlas. Spine. 2003; 28(22):E461–E467 [31] Currier BL, Maus TP, Eck JC, Larson DR, Yaszemski MJ. Relationship of the internal carotid artery to the anterior aspect of the C1 vertebra: implications for C1-C2 transarticular and C1 lateral mass fixation. Spine (Phila Pa 1976). 2008; 33(6):635–639 [32] Estillore RP, Buchowski JM, Minh V, et al. Risk of internal carotid artery injury during C1 screw placement: analysis of 160 computed tomography angiograms. Spine J. 2011; 11(4):316–323 [33] Bogaerde MV, Viaene P, Thijs V. Iatrogenic perforation of the internal carotid artery by a transarticular screw: an unusual case of repetitive ischemic stroke. Clin Neurol Neurosurg. 2007; 109(5):466–469 [34] Aryan HE, Newman CB, Nottmeier EW, Acosta FL, Jr, Wang VY, Ames CP. Stabilization of the atlantoaxial complex via C-1 lateral mass and C-2 pedicle screw fixation in a multicenter clinical experience in 102 patients: modification of the Harms and Goel techniques. J Neurosurg Spine. 2008; 8(3):222–229 [35] Park HK, Jho HD. The management of vertebral artery injury in anterior cervical spine operation: a systematic review of published cases. Eur Spine J. 2012; 21(12):2475–2485 [36] Peng CW, Chou BT, Bendo JA, Spivak JM. Vertebral artery injury in cervical spine surgery: anatomical considerations, management, and preventive measures. Spine J. 2009; 9(1):70–76 [37] Maughan PH, Ducruet AF, Elhadi AM, et al. Multimodality management of vertebral artery injury sustained during cervical or craniocervical surgery. Neurosurgery. 2013; 73(2) Suppl Operative:ons271–ons281, discussion ons281–ons282 [38] Park YS, Kang DH, Park KB, Hwang SH. Posterior atlantoaxial screw-rod fixation in a case of aberrant vertebral artery course combined with bilateral high-riding vertebral artery. J Korean Neurosurg Soc. 2010; 48(4):367–370 [39] Reis CV, Deshmukh V, Zabramski JM, et al. Anatomy of the mastoid emissary vein and venous system of the posterior neck region: neurosurgical implications. Neurosurgery. 2007; 61(5) Suppl 2:193–200, discussion 200–201 [40] Pan J, Li L, Qian L, Tan J, Sun G, Li X. C1 lateral mass screw insertion with protection of C1-C2 venous sinus: technical note and review of the literature. Spine (Phila Pa 1976). 2010; 35(21):E1133–E1136 [41] George Stovell MM, Pillay MR. Subarachnoid hemorrhage and acute hydrocephalus as a complication of C1 lateral mass screws. Spine. 2013; 38(18): E1162–5 [42] Dumont TM, Stockwell DW, Horgan MA. Venous air embolism: an unusual complication of atlantoaxial arthrodesis: case report. Spine (Phila Pa 1976). 2010; 35(22):E1238–E1240 [43] Elliott RE, Kang MM, Smith ML, Frempong-Boadu A. C2 nerve root sectioning in posterior atlantoaxial instrumented fusions: a structured review of literature. World Neurosurg. 2012; 78(6):697–708 [44] Lee SH, Kim ES, Eoh W. Modified C1 lateral mass screw insertion using a high entry point to avoid postoperative occipital neuralgia. J Clin Neurosci. 2013; 20(1):162–167 [45] Lu J, Ebraheim NA. Anatomic considerations of C2 nerve root ganglion. Spine. 1998; 23(6):649–652 [46] Rhee WT, You SH, Kim SK, Lee SY. Troublesome occipital neuralgia developed by c1-c2 harms construct. J Korean Neurosurg Soc. 2008; 43(2):111–113 [47] Garza I, Swanson J, Cheshire W, et al. Headache and other craniofacial pain. In: Daroff R, Fenichel G, Jankovic J, Mazziotta J, eds. Bradley's Neurology in Clinical Practice. 6th ed. Philadelphia, PA: Elsevier Saunders; 2012

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Cranial [48] Myers KD, Lindley EM, Burger EL, Patel VV. C1-C2 fusion: postoperative C2 nerve impingement-is it a problem? Evid Based Spine Care J. 2012; 3 (1):53–56 [49] Gunnarsson T, Massicotte EM, Govender PV, Raja Rampersaud Y, Fehlings MG. The use of C1 lateral mass screws in complex cervical spine surgery: indications, techniques, and outcome in a prospective consecutive series of 25 cases. J Spinal Disord Tech. 2007; 20(4):308–316 [50] Conroy E, Laing A, Kenneally R, Poynton AR. C1 lateral mass screw-induced occipital neuralgia: a report of two cases. Eur Spine J. 2010; 19(3):474–476 [51] Elliott RE, Tanweer O, Frempong-Boadu A, Smith ML. Impact of starting point and C2 nerve status on the safety and accuracy of C1 lateral mass screws: Meta-analysis and review of the literature. J Spinal Disord Tech. 2015; 28 (5):171–185 [52] Kang MM, Anderer EG, Elliott RE, Kalhorn SP, Frempong-Boadu A. C2 nerve root sectioning in posterior C1–2 instrumented fusions. World Neurosurg. 2012; 78(1–2):170–177 [53] Squires J, Molinari RW. C1 lateral mass screw placement with intentional sacrifice of the C2 ganglion: functional outcomes and morbidity in elderly patients. Eur Spine J. 2010; 19(8):1318–1324 [54] Rutten HP, Szpak K, van Mameren H, Ten Holter J, de Jong JC. Anatomic relation between the rectus capitis posterior minor muscle and the dura mater. Spine. 1997; 22(8):924–926 [55] Scali F, Marsili ES, Pontell ME. Anatomical connection between the rectus capitis posterior major and the dura mater. Spine (Phila Pa 1976). 2011; 36 (25):E1612–E1614 [56] McMahon P, Dididze M, Levi AD. Incidental durotomy after spinal surgery: a prospective study in an academic institution. J Neurosurg Spine. 2012; 17 (1):30–36 [57] Fehlings MG, Smith JS, Kopjar B, et al. Perioperative and delayed complications associated with the surgical treatment of cervical spondylotic myelopathy based on 302 patients from the AOSpine North America Cervical Spondylotic Myelopathy Study. J Neurosurg Spine. 2012; 16(5):425–432 [58] Campbell PG, Yadla S, Malone J, et al. Complications related to instrumentation in spine surgery: a prospective analysis. Neurosurg Focus. 2011; 31(4):E10

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[59] Lonjon G, Dauzac C, Fourniols E, Guigui P, Bonnomet F, Bonnevialle P, French Orthopaedic Surgery Traumatology Society. Early surgical site infections in adult spinal trauma: a prospective, multicentre study of infection rates and risk factors. Orthop Traumatol Surg Res. 2012; 98(7):788–794 [60] Dipaola CP, Saravanja DD, Boriani L, et al. Postoperative infection treatment score for the spine (PITSS): construction and validation of a predictive model to define need for single versus multiple irrigation and debridement for spinal surgical site infection. Spine J. 2012; 12(3):218–230 [61] Cizik AM, Lee MJ, Martin BI, et al. Using the spine surgical invasiveness index to identify risk of surgical site infection: a multivariate analysis. J Bone Joint Surg Am. 2012; 94(4):335–342 [62] Attia W, Orief T, Almusrea K, Alfawareh M, Soualmi L, Orz Y. Role of the O-arm and computer-assisted navigation of safe screw fixation in children with traumatic rotatory atlanto-axial subluxation. Asian Spine J. 2012; 6(4):266–273 [63] Hecht AC, Koehler SM, Laudone JC, Jenkins A, Qureshi S. Is intraoperative CT of posterior cervical spine instrumentation cost-effective and does it reduce complications? Clin Orthop Relat Res. 2011; 469(4):1035–1041 [64] Yang YL, Zhou DS, He JL. Comparison of isocentric C-arm 3-dimensional navigation and conventional fluoroscopy for C1 lateral mass and C2 pedicle screw placement for atlantoaxial instability. J Spinal Disord Tech. 2013; 26(3):127–134 [65] Cai X, He X, Li H, Wang D. Biomechanical evaluation of the Total Atlantoodontoid Joint Arthroplasty System: an in vitro human cadaveric study. Clin Biomech (Bristol, Avon). 2013; 28(4):357–363 [66] Cai X, He X, Li H, Wang D. Total atlanto-odontoid joint arthroplasty system: a novel motion preservation device for atlantoaxial instability after odontoidectomy. Spine (Phila Pa 1976). 2013; 38(8):E451–E457 [67] Hu Y, Gu YJ, Yuan ZS, He XF, Dong WX, Zhao WD. Biomechanical study of the atlantoaxial joint after artificial atlanto-odontoid joint arthroplasty. Chin J Traumatol. 2012; 15(6):329–333 [68] Lu B, He X, Zhao CG, Li HP, Wang D. Biomechanical study of artificial atlantoodontoid joint. Spine (Phila Pa 1976). 2009; 34(18):1893–1899

Complications of C2 Pedicle and Pars Screw Placement

4 Complications of C2 Pedicle and Pars Screw Placement Nicholas S. Golinvaux and Jonathan N. Grauer

4.1 Introduction The purpose of this chapter is to provide relevant context and understanding of the common complications related to placement of C2 pedicle and pars screws. Such instrumentation is commonly considered either in posterior cervical constructs extending up from the subaxial spine or in addressing atlantoaxial or occipitocervical instability. These techniques may be indicated for the treatment of degenerative pathologies, traumatic injuries, congenital malformations, infectious or neoplastic processes, skeletal dysplasias, or inflammatory arthritides. Atlantoaxial stabilization is complex and challenging due to the unique anatomy of the area. Sublaminar wiring and transarticular screws have their advantages, but can be demanding, risky, and are limited in scope. Fixation with polyaxial head screws and rods appears to be a reliable and safe alternative to prior fixation methods.1 The unique and variable C2 anatomy can pose challenges to C2 instrumentation, including increasing the risk of complications. Bransford et al demonstrated lower than previously reported rates of complications following posterior C2 screw placement and advocate that the multiple available techniques of posterior C2 fixation that are now available will allow for flexibility depending on each patient’s unique anatomy.2 Atlantoaxial instability is a complex process that can originate as a result of many different etiologies, including trauma, malignancy, congenital processes, or inflammatory disease. One of the problems with instrumentation in this area is the risk of vertebral artery injury. C2 pedicle and/or pars fixation appears to be the most versatile and efficient fixation method for atlantoaxial instability.3,4 Atlantoaxial stabilization can be challenging and complex, due to high motion at the C1– C2 motion segment. However, Aryan et al concluded that fusion of C1–C2 with the Harms technique is safe and effective for a variety of etiologies of atlantoaxial instability. Modification of

the technique with distraction and placement of an allograft spacer may increase detection of radiographic fusion.5,6,7 For subaxial degenerative pathologies, instrumentation and fusion often end at the C3 level; however, if the posterior elements of C2 need to be removed, or if C2–C3 kyphosis exists, extension of instrumentation to C2 may be considered. Alternatively, upper cervical instability with neurologic symptoms, concern for potential instability, or neurologic sequelae may dictate an upper cervical instrumented fusion. Atlantoaxial instability commonly requires fusion and can result from a number of different etiologies, including degenerative processes, trauma, inflammation, or malignancy. Screw fixation techniques are more technically demanding than previous wiring techniques, but offer higher rates of fusion and less risk to neural structures.8,9,10,11,12,13 As techniques have continued to evolve, screw constructs that include C2 are being used with increasing frequency. One common type of C2 instrumentation is the C2 pedicle screw (▶ Fig. 4.1).1,14,15,16 This screw is placed with lateral to medial angulation, essentially orthogonal to the anatomic axis of the spine, and passes from the posterior elements to the vertebral body (analogous to pedicle screw trajectories in the thoracolumbar spine). Specific to the cervical spine is the fact that the pedicle screw passes medial to the transverse foramen. Another type of C2 instrumentation is the C2 pars screw (▶ Fig. 4.2).3,5,17 This screw is started more medially than the pedicle screw, is placed with less medial angulation, and is angled from caudad to cephalad. The path utilized for this type of instrumentation is somewhat similar to that used for a Magerl screw,18 but does not extend across the C1–C2 articulation, and thus has more flexibility. It should be noted, however, that the difference between these two methods is really not as discrete as designated earlier. Rather, screw placement can often be a blend of the two

Fig. 4.1 Parasagittal (a) and axial (b) CT images showing C2 pedicle screw trajectories (white lines).

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Cranial

Fig. 4.2 Parasagittal (a) and axial (b) CT image images showing C2 pars screw trajectories (white lines).

techniques. By definition, the greatest differentiating factor is that the pedicle screw generally passes anterior to the C2 transverse foramen, as opposed to the pars screw, which terminates posterior to the C2 transverse foramen (▶ Fig. 4.1 and ▶ Fig. 4.2). Pedicle and pars screw instrumentation has increased in popularity for many cervical posterior instrumentation constructs. However, the greatest increase in usage over the past decade is likely attributable to the popularization of C1–C2 fixation with polyaxial screw and rod constructs, originally described by Goel and Laheri and Harms and Melcher.1,19 Biomechanical stability, safety considerations, and greater ease in the setting of more challenging body habitus have all contributed to the recent increase in popularity of this construct.2,5,20,21,22,23 Prior treatment of upper cervical spine fractures was historically based on the use of halos. However, halos are associated with significant morbidity, particularly in the elderly.24,25,26,27 As an alternative, internal fixation has gradually become more common for the treatment of fractures and other pathologies.3,4 Until relatively recently, upper cervical instrumentation was most commonly performed with wiring techniques or transarticular screw fixation.1,3,4,8,19 However, such methods of stabilization have been associated with anatomic constraints, pseudarthrosis, and the need for considering postoperative immobilization.1,2,3,5,8,11,14,23,28,29,30,31,32,33,34,35,36

and pars screw instrumentation were originally developed, in part, as a result of the potential for vertebral artery injury observed with wires or transarticular screw fixation, this risk is not entirely eliminated with current techniques. These injuries may be related to misdirected instrumentation or aberrant vertebral artery anatomy, a finding that is not uncommon near the atlantoaxial complex. The vertebral artery is at potential risk when drilling, tapping, or placing C2 pars or pedicle screws.4,8,14,29 In fact, it must be kept in mind that the cortex of the cervical pedicles has been shown to be thinnest laterally toward the vertebral artery (▶ Fig. 4.1b and ▶ Fig. 4.2b).37 Anatomically speaking, a violation of the vertebral artery generally will occur at the lateral aspect of the C2 pedicle.14,23,29 Unfortunately, aberrant vertebral artery anatomy is common, with as many as 9 to 20% of patients demonstrating a high-riding transverse foramen at C2 that could compromise pedicle screw placement (▶ Fig. 4.3). In several previous studies, a highriding vertebral artery has been defined based on a sagittal image taken at 3 mm lateral to the cortical margin of the spinal canal wall at C2.14,33,38,39

4.2 Complications The bulk of this chapter will focus on the potential complications associated with C2 pedicle and pars screw placement. Each of these complications will be discussed, followed by a discussion of the current recommendations regarding the avoidance, diagnosis, and treatment options available for each scenario.

4.2.1 Arterial Injury All upper cervical instrumentation involves working in close proximity to the vertebral artery, and thus the potential for injury to this vessel is of significant concern. Although pedicle

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Fig. 4.3 Parasagittal CT image showing high-riding vertebral artery foramen (white arrow).

Complications of C2 Pedicle and Pars Screw Placement The incidence of vertebral artery injury in pedicle screw placement has been reported to range between 0.3 and 8.2%.2,14,40,41,42 In fact, some studies report a similar rate of vertebral artery injury in pedicle screws compared to transarticular screws, in large part due to anatomic variations. This is a contentious point, as others maintain that the risk of vertebral artery injury is lower with pedicle screws compared to transarticular screws.1,5 Most would agree, however, that pars screws maintain a safer profile than both transarticular and pedicle screws because the trajectory of a pars screw does not cross the plane of the vertebral artery. A recent meta-analysis evaluated 11 studies encompassing the instrumentation of 405 C2 pars screws and found not a single vertebral artery injury that was caused by a pars screw.43 As with any complication in medicine, the easiest and most effective treatment is avoidance. Avoiding vertebral artery injury remains of the highest importance, as the downstream consequences can be devastating, including posterior cerebral stroke, vertebrobasilar infarction, and death.14,32,34,44 Diligent preoperative planning with the object of defining patient-specific bony anatomy and the course of the vertebral artery must be obtained via imaging such as computed tomography (CT), magnetic resonance imaging (MRI), angiography, or a combination of these modalities. This is paramount to the prevention of vertebral artery injury. In the case of both pedicle and pars screws, it is essential to thoroughly understand the vertebral artery course of each patient, paying particular attention to side dominance, potential aberrancy, and the possibility of a “high-riding” vertebral artery.4,8,14,23, 39 Either an anomalous or dominant vertebral artery can erode into and alter the bony anatomy of the vertebral artery groove at C2. Indications of an anomalous or significantly dominant vertebral artery on preoperative imaging studies may signal the need to plan for use of an alternate trajectory or placement of a shorter screw than would otherwise be used.3 Of similar importance during preoperative planning is a careful assessment of the C2 bony anatomy, particularly to determine whether either pedicle is narrow. A narrow pedicle was defined by Yeom and colleagues as a pedicle in which the greatest measured width is 4 mm or less.14 Normal C2 pedicle width ranges from 7 to 9 mm, which is larger than that found in the pedicles of C3–C7.4,45 Narrow pedicles have been shown to be at higher risk of vertebral artery injury, and as such, this assessment should be made prior to beginning the procedure.14,41 Once in the operating room, avoidance of vertebral artery injury during the placement of pedicle and pars screws depends largely on proper technique. This includes both the proper angling of screw trajectories and consistent use of an instrument such as a Penfield elevator for identification of the medial C2 isthmus/pedicle (▶ Fig. 4.4). By palpating the medial portion of the screw trajectory and heading just lateral to that, the screw path can be kept as far away from the more laterally located vertebral artery as possible.1,4,8,46 The placement and trajectories of a pedicle and pars screw will naturally be different from one another, though the high-risk areas remain the same for both. The vertebral artery is most at risk when drilling, tapping, or screw placement is too lateral or too caudal in nature.3,41 In addition to understanding bony landmarks and screw trajectories, it is also highly advised to utilize intraoperative imaging to achieve the safest placement of both pedicle and pars screws.4 Fluoroscopy should be used to assist in both the

drilling and instrumentation of the screw, as well as to confirm that the screw is in the desired position once it has been placed.1,3,4,8,19 In addition, some now advocate for the use of computer-assisted navigation in the placement of pedicle and pars screws. While the preceding has been focused chiefly on the avoidance of a vertebral artery injury, it is important to know how to proceed should one occur. In the event that an overt vertebral artery injury is suspected intraoperatively, the offending instrument can be removed, followed by direct palpation of the screw path. However, should a vascular injury exist, brisk bleeding may be encountered. Hemostasis can be attempted with hemostatic agents.3,5,7 However, the most common approach to dealing with this bleeding is to place a short screw in the existing screw hole with the goal of achieving mechanical blockage of the opening. Direct repair of a vertebral artery in this setting is a very limited option. If there is any question of an intraoperative screw issue, or if there is a question of screw placement postoperatively, a CT scan should be obtained to confirm whether the screw has violated the vertebral foramen. Even if there are no clinical symptoms, this is important to investigate because pseudoaneurysm, arteriovenous malformation, and embolism can have devastating, and often delayed, sequelae. Should any of the above be identified, MR angiogram, CT angiogram, or a formal catheter angiogram should be considered. Embolization of the artery may also be appropriately considered.5

4.2.2 Venous Bleeding Another complication relevant to the dissection of the C2 anatomy is hemorrhage from the large venous plexus that surrounds the C2 nerve root. This venous plexus can bleed profusely, increase operating room time, and significantly impair the exposure and ability to place either a pedicle or pars screw.3,47,48,49 Because of these considerations, it is important to employ meticulous dissection of this region, ensure that adequate hemostatic agents are available, and maintain a low threshold for packing the hemorrhaging area and adjusting attention to the contralateral side for a period of time.

4.2.3 Neurologic Injury During the placement of C2 pedicle or pars screws, another complication that the spinal surgeon must be aware of is the potential for neurologic injury, either to the spinal cord itself or to neighboring spinal nerve roots. In terms of the spinal cord itself, a degree of safety is afforded by the significant amount of space surrounding the cord in the upper cervical spine. However, one of the reasons transarticular screws were first developed, followed by pedicle and pars screws, was to eliminate the need to introduce instrumentation into the spinal canal, as was formerly necessary with the widely accepted method of sublaminar wiring.6,7,8,29 Accordingly, since the development of these newer techniques, neurologic injury of the spinal cord has fortunately become quite rare. Due to the severity of a potential spinal cord injury in the placement of pedicle or pars screws, every bit of diligence given to avoiding the vertebral artery applies here as well. Many of the tenets, particularly that of careful preparation in order to

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Cranial avoid this type of injury, also remain true. Vigilant preoperative planning is absolutely paramount, again with attention to the patient’s individual bony and soft tissue anatomy.4,14,23 In assessing the patient’s preoperative imaging studies, the surgeon should make careful study of the C2 anatomy, ensuring adequate bone stock for screw placement, as well as taking note of any surrounding structures or soft tissue abnormalities that could challenge the ability to accurately instrument the pedicle or pars screws into place.8,39 Once in the operating room, the technique of palpating the superomedial isthmus/pedicle with a Penfield elevator serves to guide proper screw placement and protect from progressing too far in the medial direction (▶ Fig. 4.4).1,4,8,46 Intraoperative fluoroscopy can be used to confirm proper screw position, protecting both the vascular and neurologic elements of the C2 anatomy.1,3,4,8,19 With regard to the nearby nerve roots, instrumentation of C2 may necessitate some manipulation, though generally to a much lesser extent than when exposing C1 for lateral mass screws. If it becomes necessary to disturb the C2 nerve root, the most common approach is to retract and protect it.1,3,8 Conversely, both Goel and Laheri and Aryan et al described sacrificing the C2 nerve root bilaterally. This served as a means to provide greater exposure and facilitate more accurate screw placement, while exposing the patient to a relatively low increase in risk of complications. Goel and Laheri reported no cases of numbness or neuropathic pain in postoperative patients, while Aryan et al reported one case of neuropathic pain out of the 102 patients studied.5,19

4.3 Complications Related to the Construct Another important set of complications has to do with issues that arise from the fixation construct as a whole. This construct can extend up to the occiput or down to the subaxial spine.1,5

Many of the same neurovascular considerations that are encountered with C2 pedicle and pars screws apply to fixation of the greater construct as well. In addition, mechanical obstructions or patient-specific anatomical abnormalities can often preclude the successful placement of screws that were initially planned for a given construct. Nonunion following internal fixation is another concern relating to the construct as a whole. Risk factors for nonunion in C2 instrumentation include type II odontoid fractures, a previous failed C1–C2 fusion, poor bone quality, smoking history, and the use of cytotoxic or anti-inflammatory therapies that impair bone healing.3,5,50 Fortunately, reported rates of solid fusion following atlantoaxial fixation are generally high, ranging from 98 to 100%.1,3,5,51 However, should nonunion occur following the initial procedure, treatment options are limited to prolonged external immobilization or a second operation. The risks of complications with external immobilization, such as a halo vest, have been previously outlined; depending on the individual patient, the surgeon may instead elect to proceed with a return to the operating room. While this procedure oftentimes involves a more extensive fusion than the original procedure, it fortunately has a high reported success rate, with 88 to 94% of cases achieving a stable construct, by either bony or fibrous union.3,50,52

4.4 Alternative Fixation Methods In light of this discussion on complications associated with C2 pedicle and pars screws, as well as the constructs into which they are often incorporated, it is appropriate to touch briefly on the available alternatives to C2 pedicle or pars screw instrumentation. Though we have previously outlined many of the reasons why transarticular screws have largely been replaced by the techniques presented, this means of fixation remains a

Fig. 4.4 Placement of C2 screws can be facilitated by using an instrument such as a Penfield elevator to palpate the medial aspect of the C2 pars (a). This can be used as reference while drilling the C2 screw path (b,c).

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Complications of C2 Pedicle and Pars Screw Placement

Fig. 4.5 As an alternative to C2 pedicle/pars screw placement, posterior interlaminar screw placement has been described. Screws are placed from one side (a), followed by the other (b).

possible alternative when C2 pedicle or pars screws are contraindicated or not possible.14,53 Another option to consider is the translaminar screw. In this method, a screw is placed down the lamina of the axis from the contralateral side of the spinous process (▶ Fig. 4.5). Because of their significantly posterior position, these screws are much less likely to damage the vertebral artery and are especially useful in situations involving high-risk vertebral artery anatomy.2 However, the screw heads of translaminar screws overlie the lamina, possibly interfering with surface area for bony fusion; these screws also risk violating the spinal canal, and utilization of these screws generally requires offset connectors to connect the screws with the remainder of the construct when performing a multilevel fixation.2 In addition, some believe these screws may deliver a less stable fixation,2,12,54 with questions regarding a possible increase in rate of pseudoarthrosis.55,56,57 Though these costs and benefits must be weighed in each individual situation, the use of a translaminar screw as an alternative to C2 pedicle and pars screws is a robust and viable option to be readily considered in the appropriate cases. A final consideration in a difficult situation is to exclude the C2 screw from the construct entirely. This can be done either by omitting the C2 level in a multilevel construct and bypassing it or by omitting one side, resulting in unilateral C2 fixation within the larger construct.5,21

4.5 Conclusion The use of C2 pedicle and pars screws has grown rapidly and widely in the recent past, in large part due to their tremendous versatility, as well as the rise of multilevel constructs that incorporate this level. While the complication profile of these screws is a significant improvement from the earlier techniques of sublaminar wiring and transarticular screws, pedicle and pars screws certainly come with their own limitations, the most significant of which is inadvertent vertebral artery injury.

4.6 Key Points ●

●

●

●

●

C2 pedicle and pars screw instrumentation is commonly used for atlantoaxial instability resulting from a variety of etiologies, including degenerative pathologies, trauma, congenital malformations, infectious or neoplastic processes, skeletal dysplasias, or inflammatory arthritides. C2 pedicle and pars screw instrumentation has been developed and popularized as both a safer and more stable alternative to earlier stabilization methods of sublaminar wiring and transarticular screw fixation. While C2 pedicle and pars screws are generally accepted as superior compared to previously developed methods, the greatest risk of this technique is injury to the vertebral artery. Though the vertebral artery is most at risk during placement of C2 pedicle and pars screws, other complications can occur with this instrumentation method, including neural injury, venous bleeding, and complications related to the larger construct. Efficient use of preoperative imaging in planning for the unique atlantoaxial anatomy of each patient is of paramount importance to the prevention of complications during C2 pedicle and pars screw placement.

References [1] Harms J, Melcher RP. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine. 2001; 26(22):2467–2471 [2] Bransford RJ, Russo AJ, Freeborn M, et al. Posterior C2 instrumentation: accuracy and complications associated with four techniques. Spine. 2011; 36(14): E936–E943 [3] Rihn JAAD, Patel R, Albert TJ. C1–2 fixation: lateral mass/pars screw-rod fixation. In: Patel VV, Burger E, Brown CW, eds. Spine Trauma: Surgical Techniques. Heidelberg: Springer-Verlag; 2010:145–155 [4] Ludwig SC, Rumi MN. Posterior cervical fixation. In: Vaccaro AR, ed. Fractures of the Cervical, Thoracic, and Lumbar Spine. New York, NY: Marcel Dekker, Inc.; 2003:347–364 [5] Aryan HE, Newman CB, Nottmeier EW, Acosta FL, Jr, Wang VY, Ames CP. Stabilization of the atlantoaxial complex via C-1 lateral mass and C-2 pedicle screw fixation in a multicenter clinical experience in 102 patients: modification of the Harms and Goel techniques. J Neurosurg Spine. 2008; 8(3):222–229

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Cranial [6] Canale ST, Campbell WC. Campbell’s Operative Orthopaedics. 9th ed. St. Louis, MO: Mosby-Year Book; 1998 [7] Wheeless CR, Nunley JA, Urbaniak JR. Wheeless’ Textbook of Orthopaedics. Available at: http://www.wheelessonline.com. Accessed July 2013 [8] Spiker WR, Patel AA. Posterior atlantoaxial arthrodesis techniques: transarticular screws, C1–2 segmental fixation and wiring constructs. In: Eck JC, Vaccaro AR, eds. Surgical Atlas of Spinal Operations. 1st ed. New Delhi: Jaypee Brothers Medical Publishers; 2013:149–156 [9] Weissman BN, Aliabadi P, Weinfeld MS, Thomas WH, Sosman JL. Prognostic features of atlantoaxial subluxation in rheumatoid arthritis patients. Radiology. 1982; 144(4):745–751 [10] Clark CR, Goetz DD, Menezes AH. Arthrodesis of the cervical spine in rheumatoid arthritis. J Bone Joint Surg Am. 1989; 71(3):381–392 [11] Henriques T, Cunningham BW, Olerud C, et al. Biomechanical comparison of five different atlantoaxial posterior fixation techniques. Spine. 2000; 25 (22):2877–2883 [12] Lapsiwala SB, Anderson PA, Oza A, Resnick DK. Biomechanical comparison of four C1 to C2 rigid fixative techniques: anterior transarticular, posterior transarticular, C1 to C2 pedicle, and C1 to C2 intralaminar screws. Neurosurgery. 2006; 58(3):516–521, discussion 516–521 [13] McGraw RW, Rusch RM. Atlanto-axial arthrodesis. J Bone Joint Surg Br. 1973; 55(3):482–489 [14] Yeom JS, Buchowski JM, Kim H-J, Chang BS, Lee CK, Riew KD. Risk of vertebral artery injury: comparison between C1-C2 transarticular and C2 pedicle screws. Spine J. 2013; 13(7):775–785 [15] Shen FH, Samartzis D, Jenis LG, An HS. Rheumatoid arthritis: evaluation and surgical management of the cervical spine. Spine J. 2004; 4(6):689–700 [16] Chen JF, Wu CT, Lee SC, Lee ST. Posterior atlantoaxial transpedicular screw and plate fixation. Technical note. J Neurosurg Spine. 2005; 2(3):386–392 [17] Bristol R, Henn JS, Dickman CA. Pars screw fixation of a hangman’s fracture: technical case report. Neurosurgery. 2005; 56(1) Suppl:E204–, discussion E204 [18] Magerl F, Seemann PS. Stable posterior fusion of the atlas and axis by transarticular screw fixation. In: Kehr P, Weidner A, eds. Cervical Spine I. Wien: Springer; 1986:322–327 [19] Goel A, Laheri V. Plate and screw fixation for atlanto-axial subluxation. Acta Neurochir (Wien). 1994; 129(1–2):47–53 [20] Hott JS, Lynch JJ, Chamberlain RH, Sonntag VK, Crawford NR. Biomechanical comparison of C1–2 posterior fixation techniques. J Neurosurg Spine. 2005; 2 (2):175–181 [21] Kuroki H, Rengachary SS, Goel VK, Holekamp SA, Pitkänen V, Ebraheim NA. Biomechanical comparison of two stabilization techniques of the atlantoaxial joints: transarticular screw fixation versus screw and rod fixation. Neurosurgery. 2005; 56(1) Suppl:151–159, discussion 151–159 [22] Melcher RP, Puttlitz CM, Kleinstueck FS, Lotz JC, Harms J, Bradford DS. Biomechanical testing of posterior atlantoaxial fixation techniques. Spine. 2002; 27 (22):2435–2440 [23] Paramore CG, Dickman CA, Sonntag VK. The anatomical suitability of the C1–2 complex for transarticular screw fixation. J Neurosurg. 1996; 85(2):221–224 [24] Glaser JA, Whitehill R, Stamp WG, Jane JA. Complications associated with the halo-vest. A review of 245 cases. J Neurosurg. 1986; 65(6):762–769 [25] Horn EM, Theodore N, Feiz-Erfan I, Lekovic GP, Dickman CA, Sonntag VK. Complications of halo fixation in the elderly. J Neurosurg Spine. 2006; 5(1):46–49 [26] Majercik S, Tashjian RZ, Biffl WL, Harrington DT, Cioffi WG. Halo vest immobilization in the elderly: a death sentence? J Trauma. 2005; 59(2):350–356, discussion 356–358 [27] Tashjian RZ, Majercik S, Biffl WL, Palumbo MA, Cioffi WG. Halo-vest immobilization increases early morbidity and mortality in elderly odontoid fractures. J Trauma. 2006; 60(1):199–203 [28] Abou Madawi A, Solanki G, Casey AT, Crockard HA. Variation of the groove in the axis vertebra for the vertebral artery. Implications for instrumentation. J Bone Joint Surg Br. 1997; 79(5):820–823 [29] Mandel IM, Kambach BJ, Petersilge CA, Johnstone B, Yoo JU. Morphologic considerations of C2 isthmus dimensions for the placement of transarticular screws. Spine. 2000; 25(12):1542–1547 [30] Hanson PB, Montesano PX, Sharkey NA, Rauschning W. Anatomic and biomechanical assessment of transarticular screw fixation for atlantoaxial instability. Spine. 1991; 16(10):1141–1145 [31] Jun BY. Anatomic study for ideal and safe posterior C1-C2 transarticular screw fixation. Spine. 1998; 23(15):1703–1707 [32] Madawi AA, Casey AT, Solanki GA, Tuite G, Veres R, Crockard HA. Radiological and anatomical evaluation of the atlantoaxial transarticular screw fixation technique. J Neurosurg. 1997; 86(6):961–968

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[33] Bloch O, Holly LT, Park J, Obasi C, Kim K, Johnson JP. Effect of frameless stereotaxy on the accuracy of C1–2 transarticular screw placement. J Neurosurg. 2001; 95(1) Suppl:74–79 [34] Wright NM, Lauryssen C, American Association of Neurological Surgeons/ Congress of Neurological Surgeons. Vertebral artery injury in C1–2 transarticular screw fixation: results of a survey of the AANS/CNS section on disorders of the spine and peripheral nerves. J Neurosurg. 1998; 88 (4):634–640 [35] Gluf WM, Schmidt MH, Apfelbaum RI. Atlantoaxial transarticular screw fixation: a review of surgical indications, fusion rate, complications, and lessons learned in 191 adult patients. J Neurosurg Spine. 2005; 2(2):155–163 [36] Wang MY, Samudrala S. Cadaveric morphometric analysis for atlantal lateral mass screw placement. Neurosurgery. 2004; 54(6):1436–1439, discussion 1439–1440 [37] Karaikovic EE, Daubs MD, Madsen RW, Gaines RW, Jr. Morphologic characteristics of human cervical pedicles. Spine. 1997; 22(5):493–500 [38] Neo M, Matsushita M, Iwashita Y, Yasuda T, Sakamoto T, Nakamura T. Atlantoaxial transarticular screw fixation for a high-riding vertebral artery. Spine. 2003; 28(7):666–670 [39] Abumi K, Shono Y, Ito M, Taneichi H, Kotani Y, Kaneda K. Complications of pedicle screw fixation in reconstructive surgery of the cervical spine. Spine. 2000; 25(8):962–969 [40] Resnick DK, Lapsiwala S, Trost GR. Anatomic suitability of the C1-C2 complex for pedicle screw fixation. Spine. 2002; 27(14):1494–1498 [41] Yoshida M, Neo M, Fujibayashi S, Nakamura T. Comparison of the anatomical risk for vertebral artery injury associated with the C2-pedicle screw and atlantoaxial transarticular screw. Spine. 2006; 31(15):E513–E517 [42] Igarashi T, Kikuchi S, Sato K, Kayama S, Otani K. Anatomic study of the axis for surgical planning of transarticular screw fixation. Clin Orthop Relat Res. 2003(408):162–166 [43] Elliott RE, Tanweer O, Boah A, Smith ML, Frempong-Boadu A. Comparison of safety and stability of C-2 pars and pedicle screws for atlantoaxial fusion: meta-analysis and review of the literature. J Neurosurg Spine. 2012; 17 (6):577–593 [44] Farey ID, Nadkarni S, Smith N. Modified Gallie technique versus transarticular screw fixation in C1-C2 fusion. Clin Orthop Relat Res. 1999; 359(359):126–135 [45] Panjabi MM, Duranceau J, Goel V, Oxland T, Takata K. Cervical human vertebrae. Quantitative three-dimensional anatomy of the middle and lower regions. Spine. 1991; 16(8):861–869 [46] Ebraheim NA, Klausner T, Xu R, Yeasting RA. Safe lateral-mass screw lengths in the Roy-Camille and Magerl techniques. An anatomic study. Spine. 1998; 23(16):1739–1742 [47] Tessitore E, Momjian A, Payer M. Posterior reduction and fixation of an unstable Jefferson fracture with C1 lateral mass screws, C2 isthmus screws, and crosslink fixation: technical case report. Neurosurgery. 2008; 63(1,) Suppl 1: ONSE100–101, discussion :ONS–E101 [48] Ma X-Y, Yin Q-S, Wu Z-H, et al. C1 pedicle screws versus C1 lateral mass screws: comparisons of pullout strengths and biomechanical stabilities. Spine. 2009; 34(4):371–377 [49] Christensen DM, Eastlack RK, Lynch JJ, Yaszemski MJ, Currier BL. C1 anatomy and dimensions relative to lateral mass screw placement. Spine. 2007; 32 (8):844–848 [50] Dickman CA, Sonntag VK. Surgical management of atlantoaxial nonunions. J Neurosurg. 1995; 83(2):248–253 [51] Stulik J, Vyskocil T, Sebesta P, Kryl J. Atlantoaxial fixation using the polyaxial screw-rod system. Eur Spine J. 2007; 16(4):479–484 [52] Platzer P, Vécsei V, Thalhammer G, Oberleitner G, Schurz M, Gaebler C. Posterior atlanto-axial arthrodesis for fixation of odontoid nonunions. Spine. 2008; 33(6):624–630 [53] Hong JT, Lee SW, Son BC, et al. Analysis of anatomical variations of bone and vascular structures around the posterior atlantal arch using three-dimensional computed tomography angiography. J Neurosurg Spine. 2008; 8 (3):230–236 [54] Lehman RA, Jr, Dmitriev AE, Helgeson MD, Sasso RC, Kuklo TR, Riew KD. Salvage of C2 pedicle and pars screws using the intralaminar technique: a biomechanical analysis. Spine. 2008; 33(9):960–965 [55] Parker SL, McGirt MJ, Garcés-Ambrossi GL, et al. Translaminar versus pedicle screw fixation of C2: comparison of surgical morbidity and accuracy of 313 consecutive screws. Neurosurgery. 2009; 64(5) Suppl 2:343– 348, discussion 348–349 [56] Wang MY. Cervical crossing laminar screws: early clinical results and complications. Neurosurgery. 2007; 61(5) Suppl 2:311–315, discussion 315–316 [57] Sciubba DM, Noggle JC, Vellimana AK, et al. Laminar screw fixation of the axis. J Neurosurg Spine. 2008; 8(4):327–334

Complications of C1–C2 Transarticular Screws

5 Complications of C1–C2 Transarticular Screws George M. Ghobrial, Joshua Heller, Alexander R. Vaccaro, and James S. Harrop

5.1 Introduction Atlantoaxial (C1–C2) transarticular screw (TAS) for immobilization of the C1–C2 joint developed as an alternative to prior mainstream posterior cervical fusion and wiring constructs. TAS demonstrated a superior rate of fusion when compared to prior techniques. The normal course of a TAS is through the C2 pars interarticularis, followed by the atlantoaxial joint, and then finally a bicortical position in the C1 lateral mass. Posterior column fusion techniques such as the Gallie, Brooks, and Jenkins fusion methods, as well as with the Halifax clamping method, historically had a high rate of nonunion.1,2,3,4 Moreover, posterior wiring techniques often involved the sublaminar passage of wires, a technically demanding procedure that exposed the patient to additional risk for spinal cord injury especially in the setting of trauma.5,6,7,8,9,10 The indication for TAS placement is for conditions where atlantoaxial instability (AAI) or dislocation persists: trauma, odontoid fracture (Anderson and D’Alonzo Types II and III), os odontoideum, rheumatoid arthritis,11 or conditions predisposing one to congenital ligamentous instability.12,13,14 This procedure was first introduced in 1979 by Magerl and colleagues,3 and early series were reported in 1991 showing a pseudoarthrosis rate as low as 0.6%.15 Prior graft-wiring constructs, such as the Brooks and Gallie methods, had nonunion rates as high as 30%, and did not provide immediate stability to the same extent as screw–rod constructs.5,16 Goel and Laheri17 introduced the combined C1 lateral mass, C2 pars/pedicle screw, and rigid plate construct in 1994 to address the undesirably high risk of vertebral artery (VA) injury associated with TAS.12 Using a maximum of 16-mm C2 isthmic screws substantially lowers the risk to the VA. One additional advantage offered with any screw–rod construct is the ability to perform an open intraoperative reduction of the atlantoaxial joint. This is not as easily achievable with TAS, where safe placement of the screw requires either reduction with traction prior to surgery or manipulation of the posterior elements interop.

5.2 Purpose of Instrumentation and Indications TAS placement is useful in the setting of AAI, a dangerous complication of traumatic, inflammatory, and other underlying etiologies. In traumatic type 2 odontoid fractures, an unstable atlantoaxial segment is created, and the risk of subluxation is present. Ruan et al17 performed a C1–C2 TAS for AAI in 14 patients, with neurologic improvement and fusion in all patients.

5.2.1 Relevant Anatomy Gluf and colleagues18 recommend that the relevant anatomy be reviewed on computed tomography (CT) to determine that a

safe corridor exists for approximately a 3.5- to 4-mm-diameter screw. In particular, VA course, bone quality, and relevant deformities must be reviewed preoperatively. Adjustment of the screw diameter can then be made based on preoperative measurements.18 The single most important aforementioned anatomical structure that must be carefully evaluated is the VA. Paramore and colleagues19 reviewed CT imaging for 94 patients, finding that a high-riding foramen transversarium prevented placement of a TAS on one side in 18%. The left side was contraindicated nine times, versus five times in the case of the right. This is what one would expect as the left-side VA was found to be dominant approximately 50% of the time, followed by 25% of the time for the right, and codominant in the remaining 25%.20 Even in the case of normal anatomy, the corridor for a normal trajectory is narrow and tolerances are minimal.19,21 This technique is less commonly utilized since the screw–rod construct became more commonplace. Additionally, anatomical understanding has evolved, decreasing the rate of this complication by strict maintenance of the screw trajectory as medial and dorsal along the pars of C2 using fluoroscopy.18 With CT imaging, the location of the foramen transversarium of C1 must be evaluated on axial imaging. Identification of variants such as erosion of the pedicle or enlargement of the foramen is key to identify to avoid injury (▶ Fig. 5.1 and ▶ Fig. 5.2). Noncontrasted CT or magnetic resonance imaging can be used to show the course of the VA emerged dorsally along the inner aspect of the C1 ring prior to entering the canal intradurally. Often, the sulcus of the VA on the C1 ring is congenitally housed in bone, termed the ponticulus posticus. Further avoidance of the VA involves review of the point where the VA bends medially below the atlantoaxial joint, called the vertebral groove. In general, this can be avoided more easily with a more medial and superior starting point on the isthmus of C2.22,23,24,25 In anatomical studies of 64 consecutive patients, Jun26 reviewed points of screw insertion, finding an ideal sagittal plane between 3.5 and 6 mm from the spinal canal. Identification of the course of VA and its relation to the pars, pedicle, or isthmus is best undertaken with sagittal CT imaging, and often with specially obtained oblique CT reconstructions. Given the trajectory of the TAS is approximately 50 degrees from a vertical line, an oblique CT reconstruction offers a visualization of the entire screw trajectory, improving the visualization of the screw relative to key structures, namely to the VA (▶ Fig. 5.3).21 Another technique for obtaining oblique CT views involves acquisition of imaging while the head and torso is extended approximately 30 degrees during imaging. Extreme caution when manipulating the unstable neck must be observed at this time. Dull and Toselli argue this technique can achieve ideal views of the trajectory from the rostral inferior C2 facet to the midposition of the anterior C1 tubercle. This technique has been replaced by use of software that can perform the requested trajectory reconstructions without risking atlantoaxial subluxation.21 In some anatomical variants, the VA is dominant as well as enlarges the foramen transversarium, preventing cannulation of the isthmus or pedicle of C2, which prevents safe

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Cranial

Fig. 5.1 Preoperative cervical spine CT, sagittal reconstruction, demonstrating anomalous vertebral artery course that will impede safe transarticular screw placement.

Fig. 5.2 Preoperative cervical spine CT, axial reconstruction, demonstrating a dominant left vertebral artery and enlargement of the foramen transversarium. Careful preoperative trajectory planning of the TAS is needed to avoid violation of this structure.

instrumentation (see ▶ Fig. 5.1). Madawi et al27 found in anatomical studies of 25 consecutive axis measurements a VA groove large enough in 20% of patients to prevent safe instrumentation (see ▶ Fig. 5.2). When analyzing the VA, they evaluated it at its most superior and medial point of trajectory. In these cases where TAS instrumentation is contraindicated, laminar screws may be considered as alternatives to fixation, as well as consideration for additional points of fixation in the subaxial cervical spine.

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Fig. 5.3 Preoperative cervical spine CT, oblique reconstruction. Often preoperative reconstructions can be tailored to the trajectory of the TAS course, providing an oblique reconstruction, which is useful in demonstrating all of the structures that will be traversed during the course of screw placement.

5.3 Preoperative Imaging Use of preoperative lateral fluoroscopy is essential for the positioning and safe insertion of TASs. Often, patient body habitus limits an appropriate trajectory and contributes to suboptimal

Complications of C1–C2 Transarticular Screws screw placement. For an ideal trajectory, approximately 50-degree caudal tilt, the prone patient must be in the “military tuck” position with the head flexed in a neutral position. Preoperative lateral fluoroscopy must be confirmed prior to draping to ensure this angle can be achieved (▶ Fig. 5.4). Adequate placement of these screws is technically demanding, evidenced by an incidence of screw malpositioning of 44% on an earlier study by Madawi et al (see ▶ Fig. 5.5).27 However, when interpreting studies that

Fig. 5.4 Preoperative lateral fluoroscopic views should be obtained to ensure adequate head and neck positioning, prior to draping. A metal guidewire is used to determine if the patient is adequately positioned to allow for an ideal screw trajectory. Often, in the case of a barrelchested body habitus, the trajectory is unable to be easily achieved and may lead to a more horizontal screw placement, risking violation of the vertebral artery.

evaluate malpositioned screws, some definitions are more stringent than others. In this case, the criteria are strict, where a malpositioned screw is defined as too steep of an angle, too short of a screw (not beyond the isthmus), too long of a screw (> 5 mm beyond the cortex of the anterior arch of C1) (see ▶ Fig. 5.6), or the lateral mass of C1 is missed by a trajectory that is suboptimal (see ▶ Fig. 5.7). Regardless of planning, early incidence of VA injury was 2.6% (5 of 191 patients), not an insignificant complication. Case series documenting VA injury are reportedly as high as 8%.4,22,23,24, 25,27,28 In one case, a bilateral VA injury resulted in the patient’s death.18 One meta-analysis of TAS studies found a rate of 0.72% across 41 studies with 3,627 patients and a rate of clinically relevant screw malpositioning of 1.8%.29 Madawi et al27 noted during drilling of three patients immediate brisk bleeding, due to violation of the VA, with a median blood loss of 1.3 L. In two other patients, they noted increased intraoperative venous bleeding, which led to the postoperative diagnosis of VA occlusion on further imaging.27 One anatomical trend noted in this retrospective review was that lateral screws resulted in a VA occlusion, while inferiorly malpositioned screws resulted in laceration and elevated blood loss. Inadequate reduction of C1 on C2 is a common risk for a malpositioned screw (see ▶ Fig. 5.5).12,29 Furthermore, it is important to recognize subluxation that may be a contraindication to safe TAS placement. Modern screw and rod constructs are able to achieve stabilization as well as reduce a subluxation intraoperatively.

5.4 Angle of Insertion Neo and colleagues22,24,25 advocate for the use of imaging guidance, along with a strict corridor of approach. They advocate for a dorsal, inferomedial starting point, as well as a steeper angle of trajectory, to both avoid a high-riding VA and maximize purchase through the atlantoaxial joint.22 A high-riding VA is

Fig. 5.5 Postoperative CT cervical spine imaging, in the sagittal plane, demonstrating fixation in a partially reduced state. Ensuring ideal preoperative positioning and ideal reduction to allow for a caudal tilt of approximately 50 degrees will prevent screw placement in the horizontal plane, as seen here. In a TAS trajectory that has minimal tolerances in normal anatomy, with the addition of subluxation, this screw also has a lateral starting point, where it courses through the foramen transversarium, missing the lateral mass, with an anterior cortical breach in the C1 ring, beyond an acceptable depth of 5 mm.

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Cranial

Fig. 5.6 Postoperative lateral radiograph demonstrating anterior cortical breach of the TAS. Preventing a screw length that is too long can be achieved by a number of means, including intraoperative fluoroscopy, to ensure an adequate cranially oriented approach is taken. In situ measurement of the cannulated screw course to the point of anterior cortical breach is another technique that is helpful when the patient body habitus prevents visualizing the bone anatomy by X-ray.

Fig. 5.7 Postoperative lateral radiograph demonstrating one TAS has likely missed the lateral mass, resulting in an inferior and laterally placed screw. Confirmation with an anteroposterior projection with fluoroscopy is helpful when lateral imaging raises the concern for suboptimal screw placement.

defined as a lateral mass with an internal diameter less than 2 mm or an isthmus height less than 5 mm.30 Lee et al31 evaluated 17 consecutive patients who underwent TAS placement for AAI. They found the angle of insertion to be elevated in the seven patients with a high-riding VA. Madawi and colleagues27 define ideal TAS placement as that which passes through both the C2 lateral masses as well as through the atlantoaxial joint and protrudes through the anterior arch of C1 with minimal breach. Upon completion of the screw placement, there should be no motion at the C1–C2 joint on flexion-extension films.27 One consistent finding among patients who had VA injury was a low-riding atlantoaxial screw. Caution must be exercised with extreme caudal tilt angles as screws penetrating the basiocciput pose a risk not only for arterial injury and brainstem stroke, but also for hypoglossal

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injury.27 Fortunately, case reports show this injury as reversible. Most hypoglossal injuries can be avoided by strict adherence to a maximal screw length through preoperative planning. Moreover, ventral TAS exit points on the anterior cortex of the C1 tubercle should be medial to the hypoglossal nerve, which is normally medial to the lateral portion of the C1 lateral mass. Usually, when screw lengths are surprisingly too long, damage to structures of the retropharynx and basiocciput may occur, including the internal carotid artery, which takes a retropharyngeal course in a small population of patients (▶ Fig. 5.8).32

5.5 Use of Image-Guidance Bloch et al advocate the use of frameless stereotaxy in TAS insertion.30,33 In cadaveric studies, out of 16 cadaveric

Complications of C1–C2 Transarticular Screws intraoperative fidelity to anatomical landmarks, and use of fluoroscopy are key to avoiding complications with screw placement. Despite these precautionary measures, VA complications are not completely avoidable and should be a consideration when undergoing a risk–benefit analysis.

References

Fig. 5.8 Postoperative CT of the cervical spine, axial views of the C1 arch demonstrating placement of C1 lateral mass screws. On the left, an anterior tubercle cortical wall breach is seen in close proximity of the left internal carotid artery (ICA). Anterior cortical breaches greater than 5 mm have an elevated risk of contact with the ICA.

specimens, they found 4 to have a pars interarticularis with an unsafe proximity to the VA, and were able to exclude the use of TAS on a particular side, which would not have been excluded using normal preoperative imaging criteria.30 Other benefits of the use of stereotactic image guidance is the decrease need for fluoroscopy, as found by Welch et al who reported the use of image guidance for a variety of cervical procedures, including four patients with successful TAS placement.34 One drawback of the frame-guided systems is that the mobile skin confounds the fiducial registration, decreasing the accuracy. It is generally recommended that this system be used in addition to proven techniques as an aid only in confirming anatomical landmarks in cases of difficult anatomy.

5.6 Construct Failure TAS breakage occurs at a rate of 0 to 4%27 and, in retrospective series, is associated with malpositioned screws in all cases. In four of the five cases reported by Madawi et al, rheumatoid arthritis and subsequent pseudoarthrosis were cited as the underlying cause of screw breakage. In general, pseudoarthrosis is very rare in TAS placement because of the high immobilizing force and cortical purchase.

5.7 Conclusion The transarticular atlantoaxial screw is a valid tool in the neurosurgical armamentarium for the treatment of diseases of the atlantoaxial joint that cause instability. Careful preoperative planning, review of the preoperative imaging, meticulous

[1] Grob D, Bremerich FH, Dvorak J, Mannion AF. Transarticular screw fixation for osteoarthritis of the atlanto axial segment. Eur Spine J. 2006; 15(3):283– 291 [2] Stillerman CB, Wilson JA. Atlanto-axial stabilization with posterior transarticular screw fixation: technical description and report of 22 cases. Neurosurgery. 1993; 32(6):948–954, discussion 954–955 [3] Jeanneret B, Magerl F. Primary posterior fusion C1/2 in odontoid fractures: indications, technique, and results of transarticular screw fixation. J Spinal Disord. 1992; 5(4):464–475 [4] Grob D, Jeanneret B, Aebi M, Markwalder TM. Atlanto-axial fusion with transarticular screw fixation. J Bone Joint Surg Br. 1991; 73(6):972–976 [5] Reilly TM, Sasso RC, Hall PV. Atlantoaxial stabilization: clinical comparison of posterior cervical wiring technique with transarticular screw fixation. J Spinal Disord Tech. 2003; 16(3):248–253 [6] Dove J. Neurological deterioration after posterior wiring of the cervical spine. J Bone Joint Surg Br. 1998; 80(3):555 [7] Lundy DW, Murray HH. Neurological deterioration after posterior wiring of the cervical spine. J Bone Joint Surg Br. 1997; 79(6):948–951 [8] Lovely TJ, Carl A. Posterior cervical spine fusion with tension-band wiring. J Neurosurg. 1995; 83(4):631–635 [9] Brandt L, Nielsen CF, Säveland H, Wingstrand H. A simple technique of posterior wiring in traumatic instability of the mid to lower cervical spine. Technical note. J Neurosurg. 1990; 73(5):798–800 [10] Stauffer ES. Wiring techniques of the posterior cervical spine for the treatment of trauma. Orthopedics. 1988; 11(11):1543–1548 [11] Nagaria J, Kelleher MO, McEvoy L, Edwards R, Kamel MH, Bolger C. C1-C2 transarticular screw fixation for atlantoaxial instability due to rheumatoid arthritis: a seven-year analysis of outcome. Spine. 2009; 34(26):2880–2885 [12] Meyer B, Kuhlen D. Atlantoaxial fusion: transarticular screws versus screwrod constructs. World Neurosurgery. 2013; 80(5):516–517 [13] Ni B, Zhou F, Xie N, et al. Transarticular screw and C1 hook fixation for os odontoideum with atlantoaxial dislocation. World Neurosurg. 2011; 75(3– 4):540–546 [14] Kulkarni AG, Shah SM. Atlantoaxial arthrodesis using C1-C2 transarticular screw fixation in a case of Morquio syndrome. Indian J Orthop. 2011; 45 (5):470–472 [15] Hanson PB, Montesano PX, Sharkey NA, Rauschning W. Anatomic and biomechanical assessment of transarticular screw fixation for atlantoaxial instability. Spine. 1991; 16(10):1141–1145 [16] Gluf WM, Brockmeyer DL. Atlantoaxial transarticular screw fixation: a review of surgical indications, fusion rate, complications, and lessons learned in 67 pediatric patients. J Neurosurg Spine. 2005; 2(2):164–169 [17] Goel A, Laheri v.. Plate and screw fixation for atlanto-axial subluxation. Acta Neurochir (Wien).. 1994; 129(1-2):47–53 [18] Ruan JW, Fan SW, Fang XQ, et al. Treatment of atlantoaxial instability with C1-C2 posterior transarticular screw fixation [in Chinese]. Zhongguo Gu Shang. 2008; 21(2):135–137 [19] Gluf WM, Schmidt MH, Apfelbaum RI. Atlantoaxial transarticular screw fixation: a review of surgical indications, fusion rate, complications, and lessons learned in 191 adult patients. J Neurosurg Spine. 2005; 2(2):155–163 [20] Paramore CG, Dickman CA, Sonntag VK. The anatomical suitability of the C1– 2 complex for transarticular screw fixation. J Neurosurg. 1996; 85(2):221– 224 [21] Cloud GC, Markus HS. Diagnosis and management of vertebral artery stenosis. QJM. 2003; 96(1):27–54 [22] Dull ST, Toselli RM. Preoperative oblique axial computed tomographic imaging for C1-C2 transarticular screw fixation: technical note. Neurosurgery. 1995; 37(1):150–151, discussion 151–152 [23] Neo M. An essential principle for safe C1–2 transarticular screw insertion. J Spinal Disord Tech. 2008; 21(1):76–77 [24] Neo M, Matsushita M, Iwashita Y, Yasuda T, Sakamoto T, Nakamura T. Atlantoaxial transarticular screw fixation for a high-riding vertebral artery. Spine. 2003; 28(7):666–670

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Cranial [25] Neo M, Matsushita M, Yasuda T, Sakamoto T, Nakamura T. Use of an aiming device in posterior atlantoaxial transarticular screw fixation. Technical note. J Neurosurg. 2002; 97(1) Suppl:123–127 [26] Neo M, Sakamoto T, Fujibayashi S, Nakamura T. A safe screw trajectory for atlantoaxial transarticular fixation achieved using an aiming device. Spine. 2005; 30(9):E236–E242 [27] Jun BY. Anatomic study for ideal and safe posterior C1-C2 transarticular screw fixation. Spine. 1998; 23(15):1703–1707 [28] Madawi AA, Casey AT, Solanki GA, Tuite G, Veres R, Crockard HA. Radiological and anatomical evaluation of the atlantoaxial transarticular screw fixation technique. J Neurosurg. 1997; 86(6):961–968 [29] Farey ID, Nadkarni S, Smith N. Modified Gallie technique versus transarticular screw fixation in C1-C2 fusion. Clin Orthop Relat Res. 1999(359):126–135 [30] Elliott RE, Tanweer O, Boah A, et al. Comparison of screw malposition and vertebral artery injury of C2 pedicle and transarticular screws: meta-analysis and review of the literature. J Spinal Disord Tech. 2014; 27(6):305–315

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[31] Bloch O, Holly LT, Park J, Obasi C, Kim K, Johnson JP. Effect of frameless stereotaxy on the accuracy of C1–2 transarticular screw placement. J Neurosurg. 2001; 95(1) Suppl:74–79 [32] Lee JH, Jahng TA, Chung CK. C1–2 transarticular screw fixation in high-riding vertebral artery: suggestion of new trajectory. J Spinal Disord Tech. 2007; 20 (7):499–504 [33] Ebraheim NA, Misson JR, Xu R, Yeasting RA. The optimal transarticular c1–2 screw length and the location of the hypoglossal nerve. Surg Neurol. 2000; 53(3):208–210 [34] Holly LT, Bloch O, Obasi C, Johnson JP. Frameless stereotaxy for anterior spinal procedures. J Neurosurg. 2001; 95(2) Suppl:196–201 [35] Welch WC, Subach BR, Pollack IF, Jacobs GB. Frameless stereotactic guidance for surgery of the upper cervical spine. Neurosurgery. 1997; 40(5):958–963, discussion 963–964

Complications of C1–C2 Wiring

6 Complications of C1–C2 Wiring Christopher A. Burks, Michael H. Moghimi, Sean N. Shahrestani, and Charles A. Reitman

6.1 Introduction C1–C2 fusion is a relatively common procedure. Owing to variable anatomy as well as more recent emphasis on outcomes and value, a variety of fusion methods may be appropriate depending on the underlying condition. Posterior wiring is an established technique for C1–C2 fusion. Its advantages are many, including operative time and all the sequelae associated with length of surgery, its technical simplicity relative to some other techniques, and the low cost of the implants. The biggest disadvantage is that it is biomechanically inferior to many other techniques, and therefore possibly subject to implant failure and a higher nonunion rate. It provides stability primarily in the sagittal plane, and much less so in the coronal and axial planes.

6.2 Purpose of C1–C2 Wiring C1–C2 wiring is indicated for arthrodesis in the treatment of unstable odontoid fractures and other causes of atlanto-axial instability. It is often used in conjunction with a halo vest or as supplemental fixation with C1–C2 transarticular screws. It is contraindicated in upper cervical stenosis, osteoporosis, and when deficiencies or fractures of the posterior elements of C1 and/or C2 exist, either congenital or traumatic, or as part of the planned procedure, that is, decompressive laminectomy.

6.3 Food and Drug Administration Status The Food and Drug Administration (FDA) has approved the use of bone fixation wiring systems for both sublaminar and intrafacet wiring under title 21 of the Code of Federal Regulations,1 888.3010. Multiple manufacturers make wiring systems for use in both the axial and appendicular skeleton that are available in multiple materials, including surgical stainless steel, cobalt chromium alloys, and titanium alloys, both braided and monofilament. The stainless steel wires are easy to use and very inexpensive, but are much stiffer. If they break, there is considerably more concern for stainless steel wires causing harm than their more flexible counterparts. In addition, the stainless steel is generally tensioned by feel and is less precise than the typical flexible alloys that are traditionally secured with a mechanical tensioning device. For that reason, most posterior C1–C2 wiring is done with a flexible metal alloy wire at this time.

6.4 Surgical Anatomy The upper cervical spine is approached through a midline incision from the inion to the spinous process of C3. The ligamentum nuchae is identified and split creating an internervous plane between the left and right paracervical musculature. The C2 spinous process is distinctly identifiable as the largest bony element in the upper cervical area in

proximity to the occiput. The midline dissection should be taken until the posterior tubercle of C1 can be identified. A sub-periosteal dissection of the C1 posterior arch and C2 lamina can then be performed with electrocautery. The short occipital muscles (rectus capitis major/minor and obliquus capitis superior/inferior) which provide much of the fine motor control of the upper cervical spine are released by electrocautery or C2 spinous process osteotomy to be repaired later. On the superior aspect of the C1, posterior arch dissection should be limited to no more than 15 mm from the midline due to the proximity of the vertebral artery, as it courses superiorly over the atlas and pierces the lateral aspect of the posterior atlantooccipital membrane. Preoperative computed tomography (CT) must be carefully scrutinized to evaluate for aberrant anatomy such as a ponticulus posticus, which could be confused with C1 lamina leading to vertebral artery injury. As the dissection is carried out lateral onto the C2 pars to expose the C1/C2 facet, care must be taken to avoid damage to the exiting C2 nerve root, which lies immediately posterior to the facet joint. Injury of this structure may cause occipital dysesthesias. This area also contains a dense venous plexus that can cause significant bleeding obscuring bony landmarks. The C2/C3 facet must then be exposed carefully to avoid damage to the facet capsule, which in turn could cause potential C2/C3 instability. Prior to passage of sublaminar cables at C1, the posterior atlanto-occipital membrane and atlantoaxial membrane must be carefully separated from the posterior arch of C1. The ligamentum flavum must be elevated off the inferior aspect and the atlantoaxial membrane off the superior aspect of the C2 lamina. This should be carefully performed with blunt dissection to avoid damage to the dura or the epidural venous plexus. At C1, the canal diameter, or space available for the cord (SAC), is widely variable, having been quantified in multiple studies to be between 16 and 30 mm.2,3,4,5 The spinal cord at this level is approximately 10 to 12 mm, making wire passage relatively free of risk to the cord itself. The canal diameter at the level of the axis is on average 19 mm, affording similar safety from damage to the cord with careful wire passage.6,7 The cables may then be secured over the graft, but care should be taken to avoid over tensioning, which could result in fracture of the posterior elements.

6.5 Types of Wiring Techniques Since its first description by Mixter and Osgood in 1910 where silk thread was used to wire the spinous process of C1 to C2,8 many methods of atlantoaxial fixation have been described. The most widely used contemporary techniques are described by Gallie as well as Brooks and Jenkins, and subsequently modified by others.9,10,11 Gallie’s wiring consists of a single cable being passed sublaminar at C1 and then secured under the C2 spinous process before being tightened over a contoured iliac crest bone graft that is

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Cranial notched to sit on the C2 spinous process. This technique was modified by Sonntag10 to include decortication of the C2 spinous process and the inferior aspect of the posterior C1 arch to improve the surface area for fusion. The technique described by Brooks and Jenkins involves sublaminar passage of wire at both C1 and C2 on both sides of the midline before being tensioned over separate iliac crest bone graft segments. Stand alone, the sublaminar wiring is biomechanically superior to interspinous wiring, and this can be strengthened further by doubling the wire on either side. Its main advantage remains in resisting flexion. Although it has not been studied, the type of bone graft probably matters. Fusion rates in general are better with autograft bone than allograft, and this is traditionally a challenging fusion environment. Classically, a large corticocancellous block is harvested from the posterior crest along with some additional morselized bone, and this probably optimizes the chance for fusion over allograft.

6.5.1 Biomechanical Comparison of Atlantoaxial Cervical Instrumentation Techniques C1–C2 posterior wiring is rarely used alone in this age of segmental instrumentation and transarticular screws; however, it has been shown to be an efficacious adjuvant to improve both fusion rates and stability. Naderi and colleagues demonstrated in a cadaveric biomechanical study that transarticular screw constructs were superior to posterior cable grafting with respect to lateral bending and axial rotation, but posterior cable grafting provided better control of flexion and extension.12 Naderi et al advocated increased points of fixation to provide the highest degree of stability. The strongest construct was posterior cable graft with bilateral transarticular screws.13,14 Gallie or Brooks’ wiring alone may not be sufficient for C1–C2 stabilization. Brooks’ wiring with one transarticular screw was superior to Gallie’s wiring with one screw, but when combined with two transarticular screws the type of posterior wiring did not significantly affect stability. Smith et al demonstrated in a similar cadaveric biomechanical study that in one transarticular screw, cable-graft construct, Brooks’ wiring, is superior to Gallie’s wiring, but no difference was noted between Brooks’ and Gallie’s wiring in a two-screw construct.15 Fusion of the upper cervical spine with posterior wiring techniques is laden with complications. In a study of 47 operations of the upper cervical spine, only 11 patients had no complications. While most complications are minor in nature, drastic problems can also arise with the technique.15

6.6 Complications Related to Wiring For the purpose of this discussion, complications will be divided into those that occur around the time of the operation and those that occur postoperatively.

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6.6.1 Perioperative Complications of C1–C2 Wiring Neurologic Injury/Dural Tear One of the most severe complications of any spinal procedure is the risk of neurologic injury to the patient, and posterior wiring techniques are no different. The risk of injury in the perioperative stage is greatest with passage of sublaminar wires or cables. Though SAC is much greater in the upper than subaxial spine, there have been reports of neurologic deficit with wiring techniques of C1 and C2.14,15 Several authors have stated that the risk of neurologic injury is substantially increased with passage of sublaminar wires in more than one level.14,16,17,18 In the Gallie’s technique, passage of a sublaminar wire occurs only at the C1 level. Therefore, the risk of neurologic injury is relatively low, given the large SAC. On the other hand, the Brooks–Jenkins’s fusion technique has the disadvantage of needing passage of bilateral sublaminar cables beneath both C1 and C2. This entails a higher potential rate of neurological or dural injury than does the single-cable passage under the posterior C1 arch for the Gallie’s and Sonntag’s modification technique.15 While wire passage is the most inherently dangerous intraoperatively, residual bowing even after tensioning can cause pressure on the neural elements and result in neurologic injury postoperatively.16 Geremia et al graded the amount of canal encroachment by posterior wires by arbitrarily dividing the spinal canal in quarters in the sagittal plane (▶ Table 6.1), and then later showed that removal of wires when encroachment is evident can help return to neurologic function.16

Iatrogenic Fracture Iatrogenic fracture of the posterior arch or spinous process during tensioning or crimping is a well-known complication of the various posterior wiring techniques. Though its incidence is not specifically reported in the literature, studies have reported the complication and the necessity to extend fusions secondarily.10,19 As mentioned previously, this is a particular risk in patients with poor bone quality, such as those with rheumatoid arthritis, neoplasms, or osteoporosis. Even using alternatives to wires and cables like suture material or polyethylene tape does not negate the risk. While iatrogenic fracture is a risk even in screw constructs, in highly osteoporotic bone, wiring techniques should be avoided if at all possible. Table 6.1 Classification of canal encroachment by posterior wires as per Geremia et al.16 Grade

% Bowing

I

Anterior bowing into first quarter (25%) of the spinal canal

II

Anterior bowing into second quarter (26–50%) of the spinal canal

III

Anterior bowing into third quarter (51–75%) of the spinal canal

IV

Anterior bowing into the fourth quarter (75–100%) of the spinal canal

Complications of C1–C2 Wiring

Extension Malalignment Owing to selective posterior tensioning, the surgeon must pay particular attention to the sagittal alignment, and avoid overtightening into extension. This is particularly important if the injury is already unstable in extension, such as an odontoid fracture that is extended, comminuted, and/or posteriorly translated. Care must be taken to reduce the deformity, either with positioning on the table or by intraoperative manipulation. Hyperextension is then basically avoided with placement of the appropriate-sized, interspinous, cortical, or corticocancellous graft. Conversely, posterior wiring is particularly effective to assist in the reduction of flexion deformities.

6.6.2 Postoperative Complications of C1-C2 Wiring Nonunion While the different posterior wiring techniques are undoubtedly useful, they are not without a number of postoperative risks and complications. Nonunion is a well-established complication of every arthrodesis procedure, and not surprisingly poses a significant risk in the upper cervical spine, given the large amount of physiologic motion allotted at the C1–C2 articulation. In fact, in the landmark article of Grob et al comparing the biomechanical differences of posterior wiring techniques, they suggested the inability to control rotation adequately as the major etiology of pseudarthrosis.20 This study looked at the biomechanical difference between four posterior fusion techniques including Gallie, Brooks, Magerl, and Halifax clamp. All techniques decreased motion compared to intact spine. The Gallie’s technique allowed more rotation in flexion, extension, axial rotation, and lateral bending than the others, while Magerl’s technique allowed the least rotation.20 Gallie’s fusions in particular offer good stability in both flexion and extension, but very poor stability in rotation. Nonunion rates have been reported to be as high as 25% of patients undergoing Gallie’s posterior wiring techniques.21 Posterior cervical arthrodesis is commonly done by wiring techniques. However, newer screw techniques provide a better construct especially for patients with os odontoideum and those with rheumatoid arthritis in which one would like to avoid halo immobilization with wiring techniques.21 Brooks and Jenkins’ wiring techniques have been shown to provide more rotational stability than the Gallie’s method with equal stability in the sagittal plane.15 This improved stability has led to fusion rate reported as high as 93%, with even better results when reinforced with halo placement.10,22 Similarly, Sonntag reported excellent fusion results approaching 97% using his techniques with simultaneous halo bracing.11 Use of autograft versus allograft probably improves fusion rate as well, as mentioned earlier. It has been well established that nonunion occurs more often with posterior wiring than with screw constructs for C1–C2 instability,21,23,24,25,26 validating the trend of fewer surgeons using posterior wiring techniques in a standalone fashion. This has been even more apparent in patients with rheumatoid arthritis or os odontoideum, where failure rates of posterior wiring techniques are as high as 75%.21,27 Wiring does provide

excellent stability to resist flexion, and also excellent compression on the bone graft, making this an appealing technique in combination with either screw fixation or a halo.

Halo Requirement Though not a direct complication, the additional need for a halo brace can cause its own set of complications. Halo bracing has been repeatedly shown to improve fusion results when combined with posterior wiring techniques.28,29 However, it has also been well established that halo devices are beset with complications such as pin site infection, subdural abscess, skull penetration, and neurologic injury to name a few.30,31,32

Implant Failure All spinal hardware, whether wires, plates, or screws, will eventually fail if there is absence of bony arthrodesis. Breakage of sublaminar wires poses a potential threat to the patient, although there have been many reports of implant failures with no significant sequelae aside from revision.33,34 There are those rare cases where substantial injury and neurologic deterioration can occur. Blacklock reported delayed cable fracture resulting in uncoiling and penetration of the dura with neurological injury.35 Similarly, a case of cable breakage in the face of pseudarthrosis in a patient with atlantoaxial instability was reported with resulting intracranial hemorrhage and quadriparesis.36 Current implant options include monofilament stainless steel wires versus the more commonly used multistranded (titanium or stainless) braided cables. The load to failure is four times higher for titanium braided cables and five times higher for stainless braided cables compared to stainless monofilament wire.37,38 Therefore, braided cables are much less likely to fail. However, if they do break, they tend to spring open from the coil with more risk for dural penetration and possible neurological injury than their monofilament counterparts.36 Although stainless steel exhibits a higher failure threshold, another consideration is the need for postoperative imaging, particularly magnetic resonance imaging, where titanium is much more compatible with significantly less artifact, resulting in a much more interpretable image.

6.7 Summary Wiring is an established, traditional technique for C1–C2 arthrodesis. Because of its biomechanical limitations, it is rarely used as a standalone form of fixation. However, in combination with other forms of internal fixation or even a halo brace, it can be very efficacious. It is particularly effective in reducing and maintaining a flexion deformity, stabilizing the sagittal plane, and helps provide compression on the bone graft and therefore likely helps promote fusion. In most cases, it is technically easy to place and is a very safe and cost-effective form of fixation. For reasons of strength combined with imaging, titanium cables are the preferred material. Complications are fairly rare, especially in properly selected patients.

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Cranial

References [1] Food and Drug Administration. Available at: www.accessdata.fda.gov. Accessed March 24, 2014 [2] Boden SD, Dodge LD, Bohlman HH, Rechtine GR. Rheumatoid arthritis of the cervical spine. A long-term analysis with predictors of paralysis and recovery. J Bone Joint Surg Am. 1993; 75(9):1282–1297 [3] Kawaida H, Sakou T, Morizono Y, Yoshikuni N. Magnetic resonance imaging of upper cervical disorders in rheumatoid arthritis. Spine. 1989; 14 (11):1144–1148 [4] Greenberg AD. Atlanto-axial dislocations. Brain. 1968; 91(4):655–684 [5] Wolf BS, Khilnani M, Malis L. The sagittal diameter of the bony cervical spinal canal and its significance in cervical spondylosis. J Mt Sinai Hosp N Y. 1956; 23(3):283–292 [6] Doherty BJ, Heggeness MH. The quantitative anatomy of the atlas. Spine. 1994; 19(22):2497–2500 [7] Mazzara JT, Fielding JW. Effect of C1-C2 rotation on canal size. Clin Orthop Relat Res. 1988(237):115–119 [8] Mixter SJ, Osgood RB. IV. Traumatic lesions of the atlas and axis. Ann Surg. 1910; 51(2):193–207 [9] Gallie W. Fractures and dislocations of the cervical spine. Am J Surg. 1939; 46 (3):495–499 [10] Dickman CA, Sonntag VK, Papadopoulos SM, Hadley MN. The interspinous method of posterior atlantoaxial arthrodesis. J Neurosurg. 1991; 74(2):190–198 [11] Brooks AL, Jenkins EB. Atlanto-axial arthrodesis by the wedge compression method. J Bone Joint Surg Am. 1978; 60(3):279–284 [12] Naderi S, Crawford NR, Song GS, Sonntag VK, Dickman CA. Biomechanical comparison of C1-C2 posterior fixations. Cable, graft, and screw combinations. Spine. 1998; 23(18):1946–1955, discussion 1955–1956 [13] Papagelopoulos PJ, Currier BL, Hokari Y, et al. Biomechanical comparison of C1-C2 posterior arthrodesis techniques. Spine. 2007; 32(13):E363–E370 [14] Lundy DW, Murray HH. Neurological deterioration after posterior wiring of the cervical spine. J Bone Joint Surg Br. 1997; 79(6):948–951 [15] Smith MD, Phillips WA, Hensinger RN. Complications of fusion to the upper cervical spine. Spine. 1991; 16(7):702–705 [16] Geremia GK, Kim KS, Cerullo L, Calenoff L. Complications of sublaminar wiring. Surg Neurol. 1985; 23(6):629–635 [17] Meyer P. Cervical Spine Fractures: Changing Management Concepts. Vol 2. Philadelphia, PA: J.B. Lippincott Company; 1991 [18] Watts C, Smith H, Knoller N. Risks and cost-effectiveness of sublaminar wiring in posterior fusion of cervical spine trauma. Surg Neurol. 1993; 40 (6):457–460 [19] Benzel EC, Kesterson L. Posterior cervical interspinous compression wiring and fusion for mid to low cervical spinal injuries. J Neurosurg. 1989; 70 (6):893–899 [20] Grob D, Crisco JJ, III, Panjabi MM, Wang P, Dvorak J. Biomechanical evaluation of four different posterior atlantoaxial fixation techniques. Spine. 1992; 17 (5):480–490

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[21] Coyne TJ, Fehlings MG, Wallace MC, Bernstein M, Tator CH. C1-C2 posterior cervical fusion: long-term evaluation of results and efficacy. Neurosurgery. 1995; 37(4):688–692, discussion 692–693 [22] Dickman CA, Sonntag VK. Surgical management of atlantoaxial nonunions. J Neurosurg. 1995; 83(2):248–253 [23] Jacobson ME, Khan SN, An HS. C1-C2 posterior fixation: indications, technique, and results. Orthop Clin North Am. 2012; 43(1):11–18, vii [24] Hurlbert RJ, Crawford NR, Choi WG, Dickman CA. A biomechanical evaluation of occipitocervical instrumentation: screw compared with wire fixation. J Neurosurg. 1999; 90(1) Suppl:84–90 [25] Jeanneret B, Magerl F. Primary posterior fusion C1/2 in odontoid fractures: indications, technique, and results of transarticular screw fixation. J Spinal Disord. 1992; 5(4):464–475 [26] Bransford RJ, Lee MJ, Reis A. Posterior fixation of the upper cervical spine: contemporary techniques. J Am Acad Orthop Surg. 2011; 19(2):63–71 [27] Papadopoulos SM, Dickman CA, Sonntag VK. Atlantoaxial stabilization in rheumatoid arthritis. J Neurosurg. 1991; 74(1):1–7 [28] Sherk HH, Snyder B. Posterior fusions of the upper cervical spine: indications, techniques, and prognosis. Orthop Clin North Am. 1978; 9(4):1091–1099 [29] Hwang SW, Gressot LV, Rangel-Castilla L, et al. Outcomes of instrumented fusion in the pediatric cervical spine. J Neurosurg Spine. 2012; 17(5):397–409 [30] Garfin SR, Botte MJ, Triggs KJ, Nickel VL. Subdural abscess associated with halo-pin traction. J Bone Joint Surg Am. 1988; 70(9):1338–1340 [31] Dormans JP, Criscitiello AA, Drummond DS, Davidson RS. Complications in children managed with immobilization in a halo vest. J Bone Joint Surg Am. 1995; 77(9):1370–1373 [32] Limpaphayom N, Skaggs DL, McComb G, Krieger M, Tolo VT. Complications of halo use in children. Spine. 2009; 34(8):779–784 [33] Garcia R, Jr, Gorin S. Failure of posterior titanium atlantoaxial cable fixation. Spine J. 2003; 3(2):166–170 [34] Fraser AB, Sen C, Casden AM, Catalano PJ, Post KD. Cervical transdural intramedullary migration of a sublaminar wire. A complication of cervical fixation. Spine. 1994; 19(4):456–459 [35] Blacklock JB. Fracture of a sublaminar stainless steel cable in the upper cervical spine with neurological injury. Case report. J Neurosurg. 1994; 81(6):932– 933 [36] Kakarla UK, Valdivia JV, Sonntag VK, Bambakidis NC. Intracranial hemorrhage and spinal cord injury from a fractured C1-C2 sublaminar cable: case report. Neurosurgery. 2010; 66(6):E1203–E1204 [37] Doran SE, Papadopoulos SM, Miller LD. Internal fixation of the spine using a braided titanium cable: clinical results and postoperative magnetic resonance imaging. Neurosurgery. 1996; 38(3):493–496, discussion 496–497 [38] Dickman CA, Papadopoulos SM, Crawford NR, Brantley AG, Gealer RL. Comparative mechanical properties of spinal cable and wire fixation systems. Spine. 1997; 22(6):596–604

Complications of C2 Translaminar Screw Placement

7 Complications of C2 Translaminar Screw Placement Colin M. Haines, Michael Y. Wang, and Joseph R. O’Brien

7.1 Introduction Instrumentation of the upper cervical spine presents an intellectual and technical challenge to spine surgeons. Potential surgical indications for fusion include atlantoaxial instability, craniocervical instability, os odontoideum, myelopathy, basilar invagination and cranial settling, trauma, and certain tumors. In general, instrumented fusion may be used to prevent cervical post–laminectomy kyphosis or to maintain spinal alignment. Children experience the highest rates of post– laminectomy kyphosis, reported from 9 to 95% when suboccipital decompression is performed.1,2 In adults, progression to kyphosis is less defined in patients with normal sagittal alignment. Preoperative kyphotic deformity imparts a higher chance for kyphotic progression after decompression3,4,5,6 as does facet resection greater than 25%.3,7,8,9 In addition to prevention, instrumented fusion also allows the surgeon to restore sagittal balance and indirectly increase neuroforaminal height in cases with radiculopathy.10

7.2 Anatomy The axis is the second cervical vertebra and a thorough understanding of its anatomy is mandatory to understand instrumentation techniques. The odontoid is a superiorly projecting process of bone that articulates with the atlas and occiput through predominately ligamentous attachments. The total odontoid height is on average 39.9 and 11 mm in diameter in both the coronal and sagittal planes.11 The odontoid has a variable sagittal inclination, from 2 degrees anteriorly to 42 degrees posteriorly.11 In addition, the anterior dens has 15 mm of articular cartilage that contacts the anterior C1 arch.11 The C2 pedicle sizes have been well studied. In males, the pedicle averages 8.6 mm width × 7.7 mm height × 25.6 mm length, whereas in females it measures 7.9 mm width × 6.9 mm height × 25.5 mm length.12 Importantly, the vertebral artery influences the functional C2 pedicle size. Normally, the vertebral artery bends laterally under the superior articular process of C2. However, in 20% of the population, the vertebral artery bends too medially, posteriorly, or rostrally,13 a variant that is termed a high riding vertebral artery. The presence of a high riding vertebral artery must alert the clinician to changes in the normal pedicle anatomy. The majority of patients with this arterial variant have a resulting ipsilateral pedicle diameter of less than 3.5 mm, which can prevent successful cannulation of the C2 pedicle.14 The C2 lamina is the largest in the upper cervical spine, measuring 11.5 mm in height.15 Overall, laminar thickness has been reported as 5.77 mm, with males as 5.99 mm and females as 5.53. In a study by Cassinelli et al, 420 adult cadaveric C2 laminae were examined. The average laminar thickness was 5.77 + 1.31 mm and the average possible screw length was 2.46 + 0.23 cm.16 (▶ Fig. 7.1). Importantly, this measurement varies depending on its location. Thickness of 2.71 mm at the superior edge, 5.87 mm in the midportion, and 4.46 mm at the inferior

Fig. 7.1 An example of three-sectioned C2 laminae. Note the wide variation in height and thickness.

edge has been reported. Using a cadaveric model, Ma et al reported the average laminar thickness was 2.71 mm superiorly, 5.87 mm in the middle, and 4.46 mm inferiorly (83% of the laminae had central thickness greater than 4.0 mm).17 Also, 9.1% of the population has unilateral central thickness less than 4 mm and 5% have bilateral central thickness less than 4 mm.1,7 The lamina typically has 41 degrees of inclination in the axial plane. The ligamentous restraints of the upper cervical spine are crucial to normal physiologic motion. The transverse ligament attaches to the medial aspects of the C1 lateral masses and provides restraint against flexion and anterior translation of C1.18 It also provides a ligamentous sling that helps allow for rotation. The alar ligaments run from the lateral sides of the odontoid tip to the medial occipital condyles,19 and predominately serve to restrain rotation and side bending.18 The apical ligament lies in between the alar ligaments and attaches from the odontoid tip to the basion. This ligament is difficult to visualize on magnetic resonance imaging (MRI) and is absent in 20% of the population.20

7.3 Preoperative Imaging Advanced imaging of the upper cervical spine is critical before planning surgical intervention. Routine orthogonal X-rays are recommended, which should consider the open mouth view to include the odontoid and lateral masses of C1. An MRI is also usually routine to evaluate the spinal cord, nerve roots, and other soft-tissue structures. Specifically for the upper cervical spine, a preoperative computed tomographic (CT) scan is recommended to quantify both the laminar thickness and the pedicle width of C2 (▶ Fig. 7.2). From 83.3 to 92.6% of the population has a laminar thickness greater than 4 mm16,21 and these details are delineated on preoperative CT scanning. Of the patients who cannot tolerate a C2 pedicle screw, 90% can tolerate laminar screw fixation.21

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Fig. 7.2 A preoperative axial CT scan demonstrating asymmetrical laminar thickness. The left lamina can accommodate instrumentation, but the right side cannot.

In the setting of anomalous vertebral artery anatomy, one may consider a CT angiogram of the cervical spine. In a study of 50 patients, 24% had vertebral artery anatomy that would preclude safe pedicle screw placement.21 However, it is important to note that most vertebral artery anomalies may be diagnosed from routine noncontrast CT and MRI. Thus, the decision to perform angiography should be based on the discretion and experience of the operative surgeon.

drilled and inserted using the medial pars as the starting point with a medial and superior tilt. Similar to transarticular screws, the pedicle screw drilling and placement risks the vertebral artery when instrumenting C2. As mentioned previously, a high riding vertebral artery affects pedicle diameter, which may preclude instrumentation. Independent of vertebral artery variants, the C2 pedicle diameter is often too narrow to safely instrument. Yoshida et al reported that out of a group of 62 patients, none had had C2 pedicles larger than 4 mm.29 Because of the difficult anatomy, the risk of vertebral artery injury has been cited from 0 to 5% in clinical studies28,30 to 12.5% in anatomical studies.31 Screw fixation of the C2 lamina is an option that decreases the risk of vertebral artery injury and is relatively easy to accomplish. The C2 translaminar screw technique was described by Wright in 2004 (the first report of C2 translaminar screw placement in which 10 patient cases were presented and no neurologic or vascular injuries were encountered).32 A standard posterior approach to the spine is utilized. One may open the cortex of C2 with a bur at the junction of the spinous process and superior lamina and a path drilled down the contralateral side using the laminar slope as a guide.33 It is recommended to aim slightly dorsally to avoid ventral penetration. Once a path is drilled, the screw is inserted (▶ Fig. 7.3). This process is repeated on the opposite side at a more inferior position on the C2 lamina to allow for an un-impeded path for the second screw.

7.5 Biomechanics Many authors have studied the biomechanics of C1–C2 instrumentation with C2 translaminar screws. In 2005, Gorek et al

7.4 C2 Instrumentation Options Many techniques exist for C2 instrumentation. Posterior laminar wiring was commonly practiced earlier, but it is performed less commonly now due to a 10 to 30% pseudoarthrosis rate and a lack of rotational control.22 The nonunion rate declines when an adjuvant halo is applied, but its use has associated morbidity and mortality.23 Furthermore, placement of the wires requires canal intrusion, which may be undesirable in the setting of stenosis or myelopathy. In response to the wiring’s downfalls, screw fixation emerged. Magerl24,25 described C1–C2 transarticular screw placement in 1982. Using a posterior approach, a screw is placed from the inferior facet of C2 through the C1–C2 facet joint, and into the C1 lateral mass. Magerl’s transarticular screw placement at C2 has high union rates and favorable biomechanical properties. Despite its benefits, injury of the vertebral artery is reported at 2.2% per screw.26 Subsequent studies have shown that 40% of patients have vertebral artery locations that may preclude safe transarticular screw placement.27 C2 pedicle screw fixation is another popular technique for instrumentation of the upper cervical spine, especially in conjunction with C1 lateral mass screws.28 The C2 pedicle screw is

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Fig. 7.3 An axial CT showing proper location of C2 translaminar screws. A: The superior aspect of acceptable starting location for translaminar screw. B: The measurement of the laminar length. C: The measurement of the laminar width.

Complications of C2 Translaminar Screw Placement compared lateral mass/translaminar screw constructs with lateral mass/pedicle screws in a cadaveric model.34 They reported that both techniques increased stiffness, but that translaminar screws were stronger in lateral bending and flexion. In contrast, Claybrooks et al found that translaminar screws had less stiffness in lateral bending and axial rotation, a strong trend toward less anterior/posterior stiffness translation that did not reach statistical significance, and no difference in flexion/extension strength.35 Similarly, Lapsiwala et al and Sim et al had published that translaminar screws provide less resistance to lateral bending with equivalent stiffness with other motions.36,37 While the data are mixed, general consensus is that C2 translaminar screw constructs have less strength with lateral bending. The biomechanics of C2 translaminar screws when the instrumentation is extended into the subaxial spine have been studied as well. In concordance with much of the data on the upper cervical spine, translaminar screws were weaker in lateral bending. However, they were found to be more rigid in axial rotation and equivalent in flexion and extension when compared to 20-mm C2 pedicle screws.38 Because of the technical difficulties of C2 screw instrumentation, Lehman et al examined pull-out strength and insertional torque for C2 screw placement after a failed first attempt. It was found that in this salvage setting, translaminar screws provided more strength than pars screws. However, he noted a decreased pull-out strength and torque when compared to the index pedicle screw.39 From a biomechanical and anatomic perspective, translaminar screws are a reasonable option for instrumenting C2. A higher percent of patients are candidates for this compared to pedicle screws, simply due to the vertebral artery proximity to the pedicle.21 While cadaveric data predominately show weakness in lateral bending when compared to other constructs, stiffness has been shown to be greater than spines without instrumentation. As with any surgical technique, however, a thorough understanding of potential complications is vital.

7.6 Complications

Fig. 7.4 (a) An axial CT showing a small, right-sided ventral cortical screw penetration. (b) An example of a larger ventral laminar screw violation. Neither was associated with neurologic deficit.

Fig. 7.5 A postoperative CT scan showing a ventral cortical breech of the pedicle finder. This was noticed prior to instrumentation and was not associated with either a dural tear or neurologic symptoms.

7.6.1 Neurologic The most devastating potential complication from translaminar screw placement is neurologic injury. At the C2 level, the sagittal diameter of the bony canal averages 20.8 mm,40 while the spinal cord measures 6.5 mm.41 Importantly, these values are for the normal spine and the pathologic setting. As patients who require C2 instrumentation are often myelopathic and have less space available for the cord, the neurologic safe zone is determined based on an individual’s preoperative imaging. Thus, any ventral breech has the potential to directly injure the cord (▶ Fig. 7.4 and ▶ Fig. 7.5). To the authors’ knowledge, there are no reports of neurologic injury using this technique. In 2011, Dorward and Wright published a series of 52 patients.42 While there were no neurologic injuries, 2.9% of screws broke through the ventral lamina. None of the penetrating screws caused a dural leak in this series. Wang has also documented his outcomes in 30 patients (there were 11 asymptomatic dorsal breeches, 1 ventral breech, and 2 hardware fractures; no neurologic or vascular injury

occurred)43 and did not have any neurologic injuries. Similar to Dorward and Wright, Wang did note a 1.7% rate of asymptomatic ventral screw penetration without durotomy and 18.6% rate of dorsal violation. Along the same lines, Bransford et al have documented 0% neurologic injury in 63 C2 translaminar screws.44 Interestingly, on postoperative CT, they found a 93.1% ideal screw location with a translaminar technique as opposed to 81.5% for both pedicle and transarticular instrumentation. Parker et al also reported a 1.3% ventral laminar screw penetration rate that was not associated with durotomy or neurologic injury. Parker et al compared between 152 translaminar screws and 167 pedicle screws at C2. Pedicle breech occurred more frequently with pedicle screws but was not symptomatic. Subaxial constructs with C2 translaminar screws were associated with more pullout or pseudoarthrosis.45 Although it is imperative that the surgeon makes absolutely sure to avoid severe ventral screw placement, neurologic injury has yet to be reported.

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7.6.2 Vascular Anatomically, the main benefit of C2 translaminar screws when compared to transarticular or pedicle screws is avoidance of the vertebral artery.32 As such, there have been no reports of vertebral artery injury or violation of the transverse foramen.42,43,44 Theoretically, there is a small risk of injury if the surgeon drills far too distally into the lamina, but this complication has not been reported (▶ Fig. 7.6). More importantly with translaminar screws, the surgeon must be cognizant of the vertebral artery after it exits the transverse foramen as part of the routine posterior approach to the upper cervical spine. On average, the vertebral artery approaches 14.6 mm from midline at the C1 arch.46 Exposure of C1 and C2 for surgery does carry a risk of an uncontained vertebral artery injury. Surgeons have recommended avoiding dissecting more than 12 mm laterally in the center of the C1 arch and 8 mm on the superior edge.47 Vertebral artery injury when instrumenting C2 may be more likely during exposure than placement of C2 translaminar screws.

7.7 Pseudoarthrosis A major concern with C2 translaminar screws is the rate of fusion when compared to other upper cervical spine constructs. As discussed previously, translaminar screw constructs have been shown to allow more movement in lateral bending.36,37,38 While studied only in cadaveric models, many surgeons postulated that the decreased stiffness would allow for too much motion to achieve high fusion rates.

Fig. 7.6 A postoperative axial CT scan of C2 with translaminar screws. Note the distance from the screw tips from the transverse foramen. A normally directed translaminar screw should avoid the vertebral arteries.

50

In 2008, Sciubba et al reported 12.5% pseudoarthrosis rate in a series of 16 patients.48 Parker et al subsequently compared translaminar and pedicle screws in the C2 vertebrae. Out of 152 patients with translaminar screws, he found a 6.1% pseudoarthrosis rate in contrast to 0% in pedicle screw constructs, values which reached statistical significance.45 Upon subgroup analysis, the difference between the two groups was only for subaxial constructs. Wang documented a 6.6% rate as indicated by hardware fractures (▶ Fig. 7.7), half of which were caused by falls.43 Most recently, Dorward and Wright reported 2.4% pseudoarthrosis,42 a value comparable to transarticular and pedicle screws.22,28,30 One may postulate that the use of offset connectors when using C2 laminar screws results in decreased construct stiffness38 and thereby contributes to the increased pseudoarthrosis rate. Additionally, the added space taken by offset connectors may also decrease the space for bone grafting at the C2–C3 joint. Overall, nonunion is a concern with this surgical technique. To increase stability, some authors have suggested using 4.0mm screws, as used in Wright’s original report,32 rather than 3.5 mm.43 Based on prior anatomical descriptions, the lamina is more likely to accommodate a 4.0-mm screw than the pedicle at the C2 level. However, direct comparisons between screw sizes have not been made. Additionally, biomechanical studies show that avoiding offset connectors will enhance stability in long constructs.38

Fig. 7.7 An anteroposterior radiograph of a right C2 translaminar screw fracture in a subaxial construct.

Complications of C2 Translaminar Screw Placement

7.8 Infection

Emphasizing ambulation, physical therapy, and pulmonary toilet will minimize pulmonary complications. Obtaining the support of nutritionists as well as speech pathologists will help avoid postoperative complications.

The prevalence of postoperative infection for posterior cervical surgery has been mixed in the literature. Some authors have reported 0% infection rates in large studies,42 while others have reported rates as high as 18%.48 Parker et al retrospectively compared translaminar screws to transarticular fixation and found infection rates of 9 and 2%, respectively.45 While this value did not reach statistical significance, there was a strong trend toward more infections in the translaminar group. In comparison to the other common C2 fixation strategies, translaminar screws seem to have an unfavorable infection profile. Overall, there are somewhat higher values for aggregate translaminar data versus both transarticular30 and pedicle screws.49 However, there are no direct comparisons that reach statistical significance. Thus, infection rates have not been definitively shown to be higher with this technique. However, further studies need to be performed to clarify the putative increased infection rate trend observed in the literature.

Most of the data on instrumentation of the upper cervical spine, including C2 translaminar fixation, is either cadaveric or retrospective data. More prospective and randomized studies are needed for comparison purposes. In addition, longer-term data are needed from preexisting data sets. Specific to C2 translaminar screws, advances to increase stiffness are needed. Specifically, methods and technology to increase lateral bending stiffness to be equivalent with pedicle and transarticular fixation are needed. In addition, new fusion augments are rapidly entering the marketplace. Literature documenting fusion rates using various bone-forming agents may be studied as well.

7.9 Hardware Prominence

7.12 Summary

C2 translaminar screws are more dorsally prominent than C2 pedicle or C1–C2 transarticular screws. Therefore, there is concern for increased neck pain from the translaminar hardware itself. In Wang’s series, 1 of the 30 patients reported incisional pain overlying a palpable screw.43 He noted that this patient was able to be treated symptomatically without further surgical intervention. While not evident on clinical exam, Sciubba et al reported two cases of translaminar screw pullout that caused local neck pain.48 The etiology of increased neck pain may relate to having instrumentation at the insertion of the semispinalis cervicis and semispinalis capitis. Both muscles have been implicated as generators of neck pain in the postoperative laminoplasty patient.49 One may postulate that metallic hardware at the site where the muscle needs to reinsert may cause chronic myofascial irritation. To the author’s knowledge, no further cases of painful and prominent C2 translaminar screws have been reported. Although more dorsal screw heads are in consideration, the literature is sparse in this area.

C2 translaminar screws are an attractive option for fusions in the upper cervical spine. With proper surgical technique, there is essentially no risk to the vertebral artery. The lamina are typically capacious enough to allow for 4.0 mm screw fixation and are inserted essentially under direct visualization without fluoroscopy.39 Although there is a chance of cortical breech, ventral screw penetration is rare in the literature and has not been reported to cause neurologic symptoms. However, a trend toward increased pseudoarthrosis rates has been shown when compared to C2 pedicle screw constructs and C1–C2 transarticular fusion, likely from biomechanical weakness in lateral bending. In addition, comparisons between the two groups have produced a trend toward more infections with translaminar screws. In addition, postoperative mortality is a consideration, though this is likely from patient comorbidities rather than procedure itself. Despite the risks, a spine surgeon may consider C2 translaminar screw placement if fusion of the upper cervical spine is indicated. Proper preoperative planning using advanced imaging studies is mandatory. In particular, one may consider a CT scan to measure the laminar width. The relative simple surgical technique and favorable risk profile have solidified the C2 translaminar screw technique’s place in modern spinal surgery.

7.10 Mortality Patients requiring upper cervical spine fusion are either typically present in the trauma setting or have multiple preexisting comorbidities. Therefore, perioperative morbidity and mortality is a consideration. Death in the perioperative period has ranged from 0% to as high as 9.6%.42,43,48,50 In comparison, C1–C2 transarticular screws have been quoted at 1.6% mortality, one-third of which were due to bilateral vertebral artery injury.30 One series reported a 3% mortality rate in patients receiving C2 pedicle screws.51 It is unlikely that C2 translaminar fixation specifically increases mortality. Rather, it is more likely that such surgery is an additional insult to the body’s already tenuous homeostasis. It is imperative that the treating surgeon carefully calculate a risk–reward analysis and involve other specialties to maximize presurgical medical management. While obvious, it is also worth highlighting the importance of postoperative therapy.

7.11 Future Directives

7.13 Key Points ●

●

●

●

●

Use a preoperative CT scan to measure laminar thickness; 91% are > 4.0 mm. C2 translaminar screws minimize risk of injury to vertebral artery. Using the lamina as a guide, ventral breech is rare and neurologic deficit has not been reported. Translaminar screws are weaker in lateral bending than pedicle or transarticular screws for C1–C2 constructs and C2– subaxial constructs. Translaminar screws have a trend toward a higher pseudoarthrosis rate.

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[27] Lau SW, Sun LK, Lai R, et al. Study of the anatomical variations of vertebral artery in C2 vertebra with magnetic resonance imaging and its application in the C1-C2 transarticular screw fixation. Spine. 2010; 35(11):1136–1143 [28] Harms J, Melcher RP. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine. 2001; 26(22):2467–2471 [29] Yoshida M, Neo M, Fujibayashi S, Nakamura T. Comparison of the anatomical risk for vertebral artery injury associated with the C2-pedicle screw and atlantoaxial transarticular screw. Spine. 2006; 31(15):E513–E517 [30] Gluf WM, Schmidt MH, Apfelbaum RI. Atlantoaxial transarticular screw fixation: a review of surgical indications, fusion rate, complications, and lessons learned in 191 adult patients. J Neurosurg Spine. 2005; 2(2):155–163 [31] Ebraheim N, Rollins JR, Jr, Xu R, Jackson WT. Anatomic consideration of C2 pedicle screw placement. Spine. 1996; 21(6):691–695 [32] Wright NM. Posterior C2 fixation using bilateral, crossing C2 laminar screws: case series and technical note. J Spinal Disord Tech. 2004; 17(2):158–162 [33] Aurich LA, Limalo JB, Silva EB, et al. C2 translaminar screw fixation (Wright’s technique) applicability in atlantoaxial instability. J Bras Neurocirurg. 2012; 23(2):152–156 [34] Gorek J, Acaroglu E, Berven S, Yousef A, Puttlitz CM. Constructs incorporating intralaminar C2 screws provide rigid stability for atlantoaxial fixation. Spine. 2005; 30(13):1513–1518 [35] Claybrooks R, Kayanja M, Milks R, Benzel E. Atlantoaxial fusion: a biomechanical analysis of two C1-C2 fusion techniques. Spine J. 2007; 7(6):682–688 [36] Lapsiwala SB, Anderson PA, Oza A, Resnick DK. Biomechanical comparison of four C1 to C2 rigid fixative techniques: anterior transarticular, posterior transarticular, C1 to C2 pedicle, and C1 to C2 intralaminar screws. Neurosurgery. 2006; 58(3):516–521, discussion 516–521 [37] Sim HB, Lee JW, Park JT, Mindea SA, Lim J, Park J. Biomechanical evaluations of various c1-c2 posterior fixation techniques. Spine. 2011; 36(6):E401–E407 [38] Benke MT, O’Brien JR, Turner AW, Yu WD. Biomechanical comparison of transpedicular versus intralaminar C2 fixation in C2-C6 subaxial constructs. Spine. 2011; 36(1):E33–E37 [39] Lehman RA, Dmitriev AE, Helgeson MD, et al. Salvage of C2 pedicle and pars screws using intralaminar technique. Spine. 2008; 33(9):960–965 [40] Eismont FJ, Clifford S, Goldberg M, Green B. Cervical sagittal spinal canal size in spine injury. Spine. 1984; 9(7):663–666 [41] Thijssen HO, Keyser A, Horstink MW, Meijer E. Morphology of the cervical spinal cord on computed myelography. Neuroradiology. 1979; 18(2):57–62 [42] Dorward IG, Wright NM. Seven years of experience with C2 translaminar screw fixation: clinical series and review of the literature. Neurosurgery. 2011; 68(6):1491–1499, discussion 1499 [43] Wang MY. Cervical crossing laminar screws: early clinical results and complications. Neurosurgery. 2007; 61(5) Suppl 2:311–315, discussion 315–316 [44] Bransford RJ, Russo AJ, Freeborn M, et al. Posterior C2 instrumentation: accuracy and complications associated with four techniques. Spine. 2011; 36(14): E936–E943 [45] Parker SL, McGirt MJ, Garcés-Ambrossi GL, et al. Translaminar versus pedicle screw fixation of C2: comparison of surgical morbidity and accuracy of 313 consecutive screws. Neurosurgery. 2009; 64(5) Suppl 2:343– 348, discussion 348–349 [46] Cacciola F, Phalke U, Goel A. Vertebral artery in relationship to C1-C2 vertebrae: an anatomical study. Neurol India. 2004; 52(2):178–184 [47] Ebraheim NA, Xu R, Ahmad M, Heck B. The quantitative anatomy of the vertebral artery groove of the atlas and its relation to the posterior atlantoaxial approach. Spine. 1998; 23(3):320–323 [48] Sciubba DM, Noggle JC, Vellimana AK, et al. Laminar screw fixation of the axis. J Neurosurg Spine. 2008; 8(4):327–334 [49] Takeuchi K, Yokoyama T, Aburakawa S, et al. Axial symptoms after cervical laminoplasty with C3 laminectomy compared with conventional C3-C7 laminoplasty: a modified laminoplasty preserving the semispinalis cervicis inserted into axis. Spine. 2005; 30(22):2544–2549 [50] Abumi K, Shono Y, Ito M, Taneichi H, Kotani Y, Kaneda K. Complications of pedicle screw fixation in reconstructive surgery of the cervical spine. Spine. 2000; 25(8):962–969 [51] Aryan HE, Newman CB, Nottmeier EW, Acosta FL, Jr, Wang VY, Ames CP. Stabilization of the atlantoaxial complex via C-1 lateral mass and C-2 pedicle screw fixation in a multicenter clinical experience in 102 patients: modification of the Harms and Goel techniques. J Neurosurg Spine. 2008; 8(3):222–229

Complications of Subaxial Lateral Mass Screw Fixation

8 Complications of Subaxial Lateral Mass Screw Fixation Adewale O. Adeniran and Adam Pearson

8.1 Introduction Lateral mass screw and rod fixation is a popular and effective treatment for conditions resulting in instability in the subaxial cervical spine. It is technically straightforward and can be performed safely. It may be biomechanically advantageous over other methods of treating the unstable subaxial cervical spine. Thorough knowledge of the relevant anatomy is crucial to avoid potentially devastating complications of neural element and vertebral artery injury.

8.2 History Dr. Berthold Ernest Hadra1,2 of Chicago first reported posterior instrumentation of the subaxial cervical spine in 1891 after successfully treating a patient with a fracture by wiring the spinous processes of C6 and C7 together using a silver wire and demonstrating the technique on cadavers. He advocated the use of this technique to treat Pott’s disease, the principal concern of spine surgeons of the day. This seminal report identified some precepts of instrumented fusion that remain relevant today—the author emphasized the potential of instrumentation to correct deformity and prevent the skin complications associated with external immobilization. The article further advocated avoiding a large gap between fusion segments and included misgivings about potential iatrogenic neurologic injury if inappropriate technique is used. The discussion section recounts contemporary concerns that spinous process wiring provided resistance against flexion only, without conferring rotational, lateral bending or extension stability. Interspinous wiring techniques were subsequently adopted widely and many modifications were made to the technique. Despite technical improvements, there remained no solution for fusion of the cervical spine with deficient posterior elements. Attempting to provide a solution for fusion in the presence of deficient or absent posterior elements, Roy-Camille and colleagues introduced lateral mass plating in the late 1980s.2,3,4 The technique was lauded at the outset for providing immediate stabilization, negating the need for halo vest immobilization and promoting fusion.2,3 Anatomic studies prompted modifications of the original Roy-Camille technique with different starting points and screw trajectories being advocated by Magerl, Anderson, and An.2 Screw–rod constructs were developed and popularized during the 1990s with the advent of the polyaxial screw head. These constructs allow accommodation of complex deformity and more precise screw placement.

8.3 Indications and Advantages Multiple case series suggest that lateral mass screw–plate and screw–rod constructs can be used in a wide range of conditions that lend instability to the subaxial cervical spine.5,6,7,8,9,10,11 Pateder and Carbone published a series of patients who underwent fixation for traumatic conditions. Lateral mass screw constructs are an effective means of fusing the traumatically unstable

subaxial cervical spine. Wound problems are the most common complication. Hardware-related complications are rare.10 They found the construct reliably fused the neck, had excellent maintenance of sagittal alignment, and minimal complications. These clinical results are consistent with multiple biomechanical studies that suggest excellent pullout strength, three-dimensional control of motion, and stiffness for lateral mass screws that compares favorably to cervical pedicle screws, anterior fixation, and cervical transfacet screw fixation.2,12,13,14,15,16,17

8.4 Relevant Anatomy Vertebral arteries, nerve roots, and adjacent facet joints are potentially at risk with lateral mass screw placement. A solid grasp of the course of the important neurovascular structures and their relationship to the posterior structures is a prerequisite for safe placement of lateral mass screws. The ideal technique avoids these structures while allowing adequate bone purchase. The spinal cord lies medial to the lateral mass at an average of 9.2 mm from the midpoint of the lateral mass and is relatively safe.18 Roy-Camille et al described the vertebral artery as running directly anterior to the intersection of the lamina and the lateral mass and emphasized adequate exposure to expose this point which he referred to as the valley prior to the hill represented by the lateral mass.3 All described techniques start screws lateral to this point to minimize the risk of vertebral artery penetration. Further cadaveric characterization of the vertebral arteries by Ebraheim et al demonstrated that from C3–C5, the vertebral artery foramen is located medial to the parasagittal plane subtended from the superficial posterior midpoint of the lateral mass.19 At C6, however, the lateral limit of the vertebral foramen was lateral to the midpoint of the lateral mass. In this study, the angle between the parasagittal plane and a line connecting the midpoint of the lateral mass to the projected lateral limit of the vertebral artery was measured. From C3–C5, in both men and women, this angle was medial to the parasagittal plane and ranged from 6 to 6.3 degrees for male specimens and 5.3 to 5.5 degrees for female specimens. At C6, the angle was lateral to the parasagittal plane and measured an average of 6.4 degrees for male specimens and 5.4 degrees for female specimens. The vertebral foramen from C2–C5 is medial to the superficial posterior midpoint of the lateral mass. At C6, it is a little lateral to the midpoint.19 These findings suggest that screws starting at the midpoint and projecting more than 7 degrees laterally should be well away from the vertebral artery foramen. The roof of the neuroforamina is formed at every level by the facet joints and the ventral surface of the lateral mass. The exiting root lies inferiorly on average 5.5 mm inferior from the posterior center of the lateral mass. The superior root lies on average 5.7 mm superior from this point.18 The root courses laterally, anteriorly, and inferiorly and divides into ventral and dorsal rami immediately after exiting the neuroforamen (▶ Fig. 8.1).20 While the ventral ramus continues in this direction, the dorsal ramus projects posteriorly and superiorly, running against the anterolateral corner of the base of the

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Cranial superior articular process above the posterior ridge of the transverse process.

8.5 Surgical Technique Multiple techniques have been described for screw placement, each differing in its starting point and in the projection of the

Fig. 8.1 Nerve root image from the study of Barrey et al.20

screw. The superficial posterior midpoint of the lateral mass lies roughly equidistant to two nerve roots in the parasagittal plane.21 Roy-Camille et al advocated a starting point in the center of the lateral mass with the screw oriented perpendicular to the posterior cortex of the vertebral body and directed 10 degrees laterally in the parasagittal plane (▶ Fig. 8.2).3,21,22,23 Jeanneret and Magerl later advocated starting just cranial and medial to the midpoint and directing the screw parallel to the facet and 25 degrees laterally.24 The techniques of Roy-Camille and Magerl are the two most popular techniques, although other authors have made modifications to these two.20 Heller et al14 evaluated the safety and difficulty of these two techniques using bicortical screws in a cadaveric study and found that Magerl’s technique was more likely to put nerve roots at risk and to be placed incorrectly than were screws placed using Roy-Camille’s technique. Roy-Camille’s technique was more likely to violate the caudal facet joint. When results took into account a learning curve, there was no difference between the two techniques.23 Xu et al in another cadaveric study with a single, experienced surgeon compared bicortical screws placed with Magerl’s technique to the subsequently described Anderson and An techniques. Both these techniques start screws just medial to the midpoint with Anderson’s technique aiming the screw 10 degrees laterally and 30 to 40 degrees cranially and An’s technique aiming 30 degrees laterally and only 15 degrees cranially.21 They found that Magerl’s technique had both a higher frequency and higher grade of nerve penetration than did Anderson’s and An’s techniques. The authors noted that the exit point of Magerl’s screw puts it in close proximity to the dorsal ramus of the exiting nerve root, while An’s technique is closer to the ventral nerve root, which is afforded some protection by the posterior ridge of the transverse process (▶ Fig. 8.3). The lateral projection of Roy-Camille’s, Magerl’s, and Anderson’s techniques were modified by Merola et al in a cadaveric study where they recorded the proximity of the screw to vital

Fig. 8.2 Roy-Camille’s vs. Magerl’s trajectories from the study of Xu et al.21

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Complications of Subaxial Lateral Mass Screw Fixation

Fig. 8.3 Exit point of Roy-Camille’s, Magerl’s, and An’s techniques from the study of Xu et al.21

structures, as the lateral trajectory was incrementally increased from 0 to 30 degrees in 10-degree intervals from C2 to C7.24 While C2 is rarely considered appropriate for lateral mass fixation, it is evaluated in this study, which evaluated bicortical fixation. The authors found that at the standard Magerl trajectory of 25 degrees lateral to the sagittal plane, the vertebral artery was violated at C2 and C7. The nerve root was compromised at C7. At all vertebral levels, both the nerve and artery were contacted at the 0- and 10-degree positions. The standard RoyCamille approach protected the nerve and artery at C2 and C3, while violating the nerve root at C4 and C5 and both structures at C6 and C7. The standard Anderson technique only kept the C2 level completely free from harm. At all other levels, the nerve root, artery, or both was violated. Increasing the lateral direction of the Anderson technique to 20 to 30 degrees lateral prevented contact with the vertebral artery or nerve root from C3 to C7. The authors concluded that safe screw placement is obtained by sagittal angulation parallel to the facet joint and coronal positioning with maximal lateral angulation. In an attempt to better quantify the safety of Roy-Camille’s and Magerl’s techniques, Barrey et al placed lateral mass screws from C3 to C6 in cadavers using both Roy-Camille’s and Magerl’s techniques and then sectioned the spines to define a safety zone for both techniques. CT scans of the instrumented cervical spine were then correlated to the anatomically defined safety zone and a sagittal safety angle was determined. The placement of the lateral mass screw in relation to the safety zone was also evaluated.20 The authors found a larger safety zone for Magerl’s technique at all levels. There was a progressive decrease in the safety zone from C3 to C6 in Roy-Camille’s technique that was not observed with Magerl’s technique. At all levels, screw purchase was greater for Magerl’s technique. Approximately the same proportions of screws were out of the safety zone with each technique. Unicortical screw placement theoretically eliminates the risk of nerve root injury but may contribute to a less stiff construct and inadequate screw purchase. Muffoletto et al tested 11 cadaveric specimens from C3 to C5 using bicortical screws, 10-mm unicortical screws, and 14-mm unicortical screws, both with and without having performed a laminectomy.25 The

specimens were tested for stiffness in flexion, extension, lateral bending, and torsion. No statistical differences were found among the different constructs except that bicortical purchase was stiffer than short, unicortical screws in lateral bending if a laminectomy had been performed.

8.6 Authors’ Preferences We advocate the Magerl technique. The interspinous ligaments lend stability to the cervical spine and should not be unnecessarily taken down at the cranial or caudal end of the construct to reduce the chance of junctional instability. Meticulous exposure of the posterior aspect of the lateral mass is crucial. One may palpate the lateral edge of the lateral mass to ensure adequate lateral exposure. The facet capsule above and below should be preserved if the adjacent joint is not being fused, but the location and orientation of the facets must be clear. We start our screws just medial and superior to the midpoint of the posterior lateral mass and direct the screw parallel to the facet joint in the sagittal plane and approximately 25 degrees laterally in the axial plane. Positioning the drill guide against the spinous process caudal to the level being instrumented tends to approximate this trajectory. We advocate unicortical screw placement with 14-mm screws in the patient without bony deficiency.

8.7 Reported Complications Multiple case series of patients undergoing lateral mass screw– plate and screw–rod fixation constructs have demonstrated that complications from the procedure are relatively rare.10,26,27, 28,29 Wound infections and superficial wound dehiscence are the most commonly reported complication, occurring in up to 10% of cases in series of trauma patients. One early series of 88 patients treated with screw–plate constructs found a 9% incidence of screw-related complications.30 Nerve root injury, facet violation, broken screws, screw pullout, and screw loosening were included in the complication list, though none occurred in more than 1% of patients. More recent series demonstrate low incidences of hardware loosening or pseudoarthrosis. Wellman

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Cranial et al reviewed 43 consecutive patients undergoing the fusion with lateral mass plating and found no hardware-related complications after placement of 248 screws. Reoperations occurred only for infection.27 Deen and Nottmeier prospectively reviewed 100 patients undergoing placement of 888 lateral mass screws using polyaxial screw and rods.28 No patient experienced vertebral artery or spinal cord injury. There were four cases of radiculopathy, one infection, three other wound problems, and one cerebrospinal fluid leak. Eight patients underwent reoperation within 6 months of the index procedure. Two of these patients had a malpositioned screw, while others had wound problems or infection (four), a dislodged anterior graft (one), and pseudoarthrosis (one). Notably, there were no complications reported after 6 months.28 Failure to obtain good purchase with a lateral mass screw can occur intraoperatively for a number of reasons: osteopenia, lateral mass fracture, improper starting point or trajectory, iatrogenic splitting of the lateral mass during screw placement, or stripping of the screw threads that can occur if the far cortex is not drilled and the screw is turned while the screw tip is in contact with the far cortex. In general, it is quite difficult to redirect the trajectory of the pilot hole once it has been drilled due to the small dimensions of the lateral mass. If the lateral mass remains intact, improved purchase can be obtained by placing a bicortical screw or using a larger diameter “rescue screw.” If the lateral mass is no longer competent (i.e., due to trauma, a destructive process, or iatrogenic damage), the bail-out options include placement of a pedicle screw or transfacet screw. Because of the proximity of the vertebral artery to the pedicle, pedicle screw placement is recommended only at C2 or C7. If a long construct is planned, leaving a screw out in the middle of the construct is unlikely to compromise its biomechanical integrity and is preferred to leaving a screw with poor purchase.

8.8 Key Points ●

●

●

●

Lateral mass screw–rod and screw–plate fixation is a safe and effective method of fusing the subaxial cervical spine. Excellent knowledge of posterior cervical anatomy is required to place lateral mass screws safely. Regardless of technique, screws must start lateral to the intersection of the lamina and lateral mass and project laterally. In the patient with normal bone, there is no proven clinical advantage to bicortical fixation.

References [1] Hadra BE. Wiring the spinous process in Pott’s disease. J Bone Joint Surg Am. 1891; 4(1):206–210 [2] Omeis I, DeMattia JA, Hillard VH, Murali R, Das K. History of instrumentation for stabilization of the subaxial cervical spine. Neurosurg Focus. 2004; 16(1):E10 [3] Roy-Camille R, Saillant G, Laville C, Benazet JP. Treatment of lower cervical spinal injuries—C3 to C7. Spine. 1992; 17(10) Suppl:S442–S446 [4] Denaro V, Di Martino A. Cervical spine surgery: an historical perspective. Clin Orthop Relat Res. 2011; 469(3):639–648 [5] Kandziora F, Pflugmacher R, Scholz M, et al. Posterior stabilization of subaxial cervical spine trauma: indications and techniques. Injury. 2005; 36 Suppl 2: B36–B43

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[6] Deen HG, Birch BD, Wharen RE, Reimer R. Lateral mass screw-rod fixation of the cervical spine: a prospective clinical series with 1-year follow-up. Spine J. 2003; 3(6):489–495 [7] Aydogan M, Enercan M, Hamzaoglu A, Alanay A. Reconstruction of the subaxial cervical spine using lateral mass and facet screw instrumentation. Spine. 2012; 37(5):E335–E341 [8] Tator CH, Fehlings MG. Review of the secondary injury theory of acute spinal cord trauma with emphasis on vascular mechanisms. J Neurosurg. 1991; 75 (1):15–26 [9] Fehlings MG, Cooper PR, Errico TJ. Posterior plates in the management of cervical instability: long-term results in 44 patients. J Neurosurg. 1994; 81 (3):341–349 [10] Pateder DB, Carbone JJ. Lateral mass screw fixation for cervical spine trauma: associated complications and efficacy in maintaining alignment. Spine J. 2006; 6(1):40–43 [11] Choueka J, Spivak JM, Kummer FJ, Steger T. Flexion failure of posterior cervical lateral mass screws. Influence of insertion technique and position. Spine. 1996; 21(4):462–468 [12] Montesano PX, Jauch E, Jonsson H, Jr. Anatomic and biomechanical study of posterior cervical spine plate arthrodesis: an evaluation of two different techniques of screw placement. J Spinal Disord. 1992; 5(3):301–305 [13] Papagelopoulos PJ, Currier BL, Neale PG, et al. Biomechanical evaluation of posterior screw fixation in cadaveric cervical spines. Clin Orthop Relat Res. 2003(411):13–24 [14] Heller JG, Estes BT, Zaouali M, Diop A. Biomechanical study of screws in the lateral masses: variables affecting pull-out resistance. J Bone Joint Surg Am. 1996; 78(9):1315–1321 [15] Miyanji F, Mahar A, Oka R, Newton P. Biomechanical differences between transfacet and lateral mass screw-rod constructs for multilevel posterior cervical spine stabilization. Spine. 2008; 33(23):E865–E869 [16] Grubb MR, Currier BL, Stone J, Warden KE, An KN. Biomechanical evaluation of posterior cervical stabilization after a wide laminectomy. Spine. 1997; 22 (17):1948–1954 [17] Neurosurgery [Publish Ahead of Print]. DOI: 10.1227/NEU.0b013e31828e20ff. doi:10.1227/NEU.0b013e31828e20ff [18] Xu R, Ebraheim NA, Nadaud MC, Yeasting RA, Stanescu S. The location of the cervical nerve roots on the posterior aspect of the cervical spine. Spine. 1995; 20(21):2267–2271 [19] Ebraheim NA, Xu R, Yeasting RA. The location of the vertebral artery foramen and its relation to posterior lateral mass screw fixation. Spine. 1996; 21 (11):1291–1295 [20] Barrey C, Mertens P, Jund J, Cotton F, Perrin G. Quantitative anatomic evaluation of cervical lateral mass fixation with a comparison of the Roy-Camille and the Magerl screw techniques. Spine. 2005; 30(6):E140–E147 [21] Xu R, Haman SP, Ebraheim NA, Yeasting RA. The anatomic relation of lateral mass screws to the spinal nerves. A comparison of the Magerl, Anderson, and An techniques. Spine. 1999; 24(19):2057–206 [22] Dickerman RD, Reynolds A, Tackett JL. Quantitative anatomy of subaxial cervical lateral mass: an analysis of safe screw lengths for Roy-Camille and Magerl techniques. Spine. 2008; 33(21):2369–, author reply 2369–2370 [23] Heller JG, Carlson GD, Abitbol JJ, Garfin SR. Anatomic comparison of the RoyCamille and Magerl techniques for screw placement in the lower cervical spine. Spine. 1991; 16(10) Suppl:S552–S557 [24] Merola AA, Castro BA, Alongi PR, et al. Anatomic consideration for standard and modified techniques of cervical lateral mass screw placement. Spine J. 2002; 2(6):430–435 [25] Muffoletto AJ, Yang J, Vadhva M, Hadjipavlou AG. Cervical stability with lateral mass plating: unicortical versus bicortical screw purchase. Spine. 2003; 28(8):778–781 [26] Katonis P, Papadakis SA, Galanakos S. Lateral Mass Screw Complications. 2011; 24(7):415–420 [27] Wellman BJ, Follett KA, Traynelis VC. Complications of posterior articular mass plate fixation of the subaxial cervical spine in 43 consecutive patients. Spine. 1998; 23(2):193–200 [28] Deen H, Nottmeier E. P11. Complications of lateral mass screw-rod fixation of the cervical spine. Spine J. 2006; 6(5):88S [29] Ehteshami JR, An HS. Intraoperative complications during surgery on the posterior cervical spine. Semin Spine Surg. 2009; 21(3):156–160 [30] Heller JG, Silcox DH, III, Sutterlin CE, III. Complications of posterior cervical plating. Spine. 1995; 20(22):2442–2448

Pedicle Screw Fixation in the Subaxial Cervical Spine

9 Pedicle Screw Fixation in the Subaxial Cervical Spine: Indications, Contraindications, and Complications Ahmer Ghori, Ali Al-Omari, and Thomas Cha

9.1 Introduction Options for posterior fixation in the subaxial cervical spine include lateral mass screws, laminar screws/sublaminar wiring, spinous process wiring, and pedicle screws. Historically, lateral mass screws have been predominant over pedicle screws in the United States, due in part to technical difficulty of pedicle screws with placing them in the cervical spine. A morphometric analysis found that pedicle size decreases caudal to C2, and reaches a nadir around C3–C4.1 One study found that 75% of C3–C4 pedicles have on average diameter less than 4 mm2, and cadaveric studies have demonstrated high rates of pedicle perforation with screw placement.2,3,4 Furthermore, the lateral wall is the thinnest structure in the pedicle, making screw perforation into the vertebral foramen a real risk.5 The angulation of pedicles in the axial plane increases in the subaxial cervical spine,6 requiring a far lateral exposure to match the pedicle trajectory. Often times it is difficult to retract the neck musculature this far lateral to have a clear working field. Given these challenges, surgeons have preferred using lateral mass screws, whenever possible. There are several well-described techniques to place lateral mass screws, and their safety profile is well documented in literature. Two studies, with a combined 2,687 lateral mass screws placed, found no cases of vertebral artery, exiting nerve, or spinal cord injury that was attributable to the screw placement.7,8 Despite these advantages, lateral mass screws have their limitations. In cases of severe instability, they may not offer sufficient stabilization.6 Such posterior fixation may have to be supported with anterior stabilization, subjecting the patient to an additional procedure.6 In certain trauma cases, spondyloarthropathies, osteoporosis, metastatic disease, and revision surgery, the posterior elements may be deficient enough to

preclude lateral mass fixation.6,9,10 In these situations, lateral mass screw fixation may be insufficient, and cervical pedicle screw fixation may be useful. Several biomechanical studies have demonstrated that pedicle screws offer superior fixation when compared to lateral mass screws.11,12,13 Their relative pullout strengths compared to lateral mass screws in two studies were 1,214 vs. 332 N,11 and 677 vs. 355N.12 Under cyclic loading pedicle screws have been found to fail due to pedicle fracture rather than screw pullout,11 whereas lateral mass screws tend to loosen and pull out due to poor fixation.11 Pedicle screws lead to consistently high rates of fusion, and this has been demonstrated across a variety of challenging scenarios, including spondyloarthropathy/inflammatory arthropathy/metastatic cancer,14,15 trauma,16 cases with deficient lateral masses,17 and kyposhsis,18 offering a solid construct for occipitocervial19 or cervicothoracic fixation.20

9.2 Technique Abumi et al first described the technique for pedicle screw placement in 1994.16 The starting point is 1 mm lateral to the center of the articular mass, near the cranial end of the superior articular process (▶ Fig. 9.1). A high-speed burr is used to decorticate the starting point to expose the pedicle canal. A small pedicle probe is then inserted into the canal with the help of a lateral image intensifier. The pedicle is tapped under fluoroscopic guidance and finally an appropriately sized screw is inserted (▶ Fig. 9.2). While placing pedicle screws, it is important to consider the location of the pedicle in three dimensions. The medial to lateral pedicle angulation is variable and often determined from preoperative imaging. In general, this angle is lowest at C2 and

Fig. 9.1 Starting point for subaxial cervical spine pedicle screw placement as described by Abumi et al (1994).16 (Adapted from Pelton MA, Schwartz J, Singh K. Subaxial cervical and cervicothoracic fixation techniques–indications, techniques, and outcomes. Orthop Clin North Am. 2012; 43(1):19–28, vii.)

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Cranial

Fig. 9.2 Steps of subaxial cervical spine pedicle screw placement. (a) Advancing of pedicle probe into vertebral body. (b) Tapping of screw tract. (c) Sounding with ball tip feeler to check for cortical breach. (d) Insertion of the pedicle screw. (Adapted from Abumi et al.10)

Fig. 9.3 Medial to lateral angulation of subaxial cervical spine pedicles. (Adapted from Abumi et al10 [2012.])

increases caudally. Abumi et al stated that most of their screws ranged from 25 to 45 degrees from the transverse process in the horizontal plane10 (▶ Fig. 9.3). The cranial–caudal angulation of pedicles is superior to the vertebral endplate at C2–C3, parallel to the end plate at C3–C4, and inferior to the endplate at C5–C6.5 Since the initial description by Abumi et al in 1994, several different techniques have been described. They vary in how the starting point is obtained, and options include using surface landmarks, performing a laminoforaminotomy to probe the

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pedicle borders, and using image navigation. The relative merits of these techniques are discussed later in the chapter.

9.3 Complications ▶ Fig. 9.3 demonstrates the horizontal plane trajectory for pedicle screw fixation in the subaxial cervical spine. Given the small pedicle diameter, high medial to lateral angulation, and thin lateral cortex, this is a technically demanding procedure.

Pedicle Screw Fixation in the Subaxial Cervical Spine Complications can be broadly categorized into injury to the vertebral artery, spinal cord, or exiting nerves. A lateral pedicle perforation would lead to violation of the transverse foramen with potential vertebral artery injury (▶ Fig. 9.4). A medial perforation would violate the spinal canal and risk dural tear or spinal cord injury (▶ Fig. 9.5). A superior or inferior breach would violate the neural foramen and could cause nerve injury. There are five studies in literature that have analyzed complications from pedicle screw fixation. The rates of screw perforation ranged from 6.7 to 30% and most breaches occurred through the lateral wall.6,21,22,23,24 The most common risk factor for screw malposition was level of surgery: in one study, 91% percent of the screws at C6 were correctly placed, compared to only 48% of screws at C4.6 This was explained by the small pedicle size and high horizontal angulation of pedicles at C3–C5.

Despite the relatively high rate of pedicle perforation with screw placement, the incidence of neurovascular injury is relatively low. Out of the 350 patients across the five studies, only 2 patients had vertebral artery injury, 5 patients had nerve root injury, and no patient had spinal cord injury.6,21,22,23,24 None of the cases of vertebral artery injury led to cerebral ischemia or other neurologic deficits. All cases of nerve injury led to temporary neurologic deficits, which resolved over time with conservative management. This mismatch between a high incidence of pedicle perforation and a low incidence of neurovascular injury can be explained on an anatomic basis. On average, the vertebral artery occupies only 35% of its foramen; furthermore, the distance from the vertebral artery to the lateral pedicle wall increases from C2 to C7.25 The critical amount of pedicle breach that would predict vertebral artery injury is yet to be determined. In the cervical spine, nerves occupy the inferior half of the neural foramen, and they exit at 45 degrees to the coronal plane and 10 degrees to the sagittal plane.26,27 Exiting nerves lie almost apposed to the superior part of the caudal pedicle, and lie 1.1 to 1.7 mm from the inferior part of the cranial pedicle.27 Therefore, a superiorly placed pedicle screw is more likely to cause nerve damage compared to an inferiorly placed screw. The medial wall of the pedicle is thickest and the dural sac is 2.4 to 3.1 mm away, which may explain why there have been no reported cases of spinal cord injury from subaxial cervical pedicle screws.25

9.4 Avoiding Complications 9.4.1 Learning Curve

Fig. 9.4 Lateral pedicle breach with transverse foramen penetration.

Subaxial cervical pedicle screw placement is not a commonly used technique and is technically demanding. As such, there is a learning curve and published results demonstrate improved outcomes with surgeon’s experience. In one study, screw misplacement was 13% for the first 20 screws, which decreased to 4% for the subsequent screws.6 In another study, all of the pedicle perforations occurred in the first 10 patients, with no perforations in the subsequent patients.22 Therefore, safe subaxial cervical pedicle screw placement requires instruction and appropriate supervision from experienced surgeons.

9.4.2 Technique

Fig. 9.5 Medial pedicle wall breach with spinal canal violation.

As described earlier, the starting point can be obtained based on a number of methods. As one would expect, literature shows improved accuracy with more involved visualization of pedicle anatomy. One study reported a 65% pedicle breach with using surface landmarks alone, 39.5% with laminoforaminotomy, and 10.5% with computer navigation.4 Another study reported an 8% pedicle perforation with surface landmarks and 3% with navigation. Yet another study showed a perforation rate of 6.7% with conventional technique and 1.2% with a surgical navigation system. Overall, literature suggests most accurate pedicle screw placement with computer-assisted navigation. However, previous studies have shown that pedicle perforation does not necessarily translate into neurovascular injury. Therefore, it is unclear if the added expense of computer-assisted navigation would be cost-effective in the long term.

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Cranial

9.4.3 Imaging The main complications with pedicle screw placement—pedicle breach, vertebral artery injury, and nerve injury—can be minimized with appropriate preoperative imaging. Pedicle diameters are small in the subaxial cervical spine and tend to vary across the population. In general, pedicle screws are unsafe when pedicle diameters are less than 4 mm. Therefore, preoperative computed tomographic (CT) scan should be obtained to ensure pedicles are large enough to be instrumented. Vertebral artery occupancy in the transverse foramen can be obtained with preoperative CTA. There have been described cases where there is a tortious artery with a high occupancy or one that erodes into the pedicle wall. In such cases, pedicle screws ought to be avoided. In general, sound understanding of the pedicle anatomy and its associated neurovascular structures for a given patient will help reduce untoward events.

9.5 Summary and Clinical Recommendation Lateral mass screws are commonly used in the subaxial cervical spine because they are technically less challenging, and have an acceptable complication profile. However, they offer insufficient fixation in certain clinical situations. In these scenarios, the biomechanical superiority of pedicle screws offers a good alternative. In spite of having a favorable biomechanical profile, pedicle screws are associated with high rates of pedicle perforation. Despite this, the rate of neurovascular injury is low, and the rate of permanent deficits from injury is even far lower. In general, most accepted indications for subaxial cervical pedicle screws are as follows: ● Fractures/dislocations with comminuted lateral masses. ● Multilevel cervical instability. ● Circumferential instability. ● Poor bone quality due to osteoporosis/neoplastic process/ inflammatory arthritis/other spondyloarthropathies. ● Correction of cervical kyphosis. ● Absent or deficient lateral masses. Complications with cervical subaxial pedicle screw placement decrease with surgeon’s experience, and it would be prudent to seek instruction when starting to use this technique. According to Abumi et al,16 who described this technique, the contraindications of using pedicle screws in the subaxial cervical spine are as follows: ● Infection at the posterior elements of the cervical spine. ● Pedicle destroyed by tumors or injuries. ● Absent or extremely small pedicle. ● A pedicle of the vertebra with major anomalies of the vertebral artery. ● An extremely oblique angle of the pedicle axis. In carefully selected clinical scenarios, and in the hands of experienced surgeons, pedicle screws have a valuable role in the cervical spine, and may be relatively safe. However, unlike in the lumbar and thoracic spine, they are not predominant in the cervical spine, because lateral mass screws are safer, easier, and sufficient for most clinical scenarios.

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References [1] Sanelli PC, Tong S, Gonzalez RG, Eskey CJ. Normal variation of vertebral artery on CT angiography and its implications for diagnosis of acquired pathology. J Comput Assist Tomogr. 2002; 26(3):462–470 [2] Miller RM, Ebraheim NA, Xu R, Yeasting RA. Anatomic consideration of transpedicular screw placement in the cervical spine. An analysis of two approaches. Spine. 1996; 21(20):2317–2322 [3] Karaikovic EE, Yingsakmongkol W, Gaines RW, Jr. Accuracy of cervical pedicle screw placement using the funnel technique. Spine. 2001; 26(22):2456–2462 [4] Ludwig SC, Kramer DL, Balderston RA, Vaccaro AR, Foley KF, Albert TJ. Placement of pedicle screws in the human cadaveric cervical spine: comparative accuracy of three techniques. Spine. 2000; 25(13):1655–1667 [5] Karaikovic EE, Daubs MD, Madsen RW, Gaines RW, Jr. Morphologic characteristics of human cervical pedicles. Spine. 1997; 22(5):493–500 [6] Kast E, Mohr K, Richter HP, Börm W. Complications of transpedicular screw fixation in the cervical spine. Eur Spine J. 2006; 15(3):327–334 [7] Sekhon LH. Posterior cervical lateral mass screw fixation: analysis of 1026 consecutive screws in 143 patients. J Spinal Disord Tech. 2005; 18(4):297–303 [8] Katonis P, Papadakis SA, Galanakos S, et al. Lateral mass screw complications: analysis of 1662 screws. J Spinal Disord Tech. 2011; 24(7):415–420 [9] Pelton MA, Schwartz J, Singh K. Subaxial cervical and cervicothoracic fixation techniques–indications, techniques, and outcomes. Orthop Clin North Am. 2012; 43(1):19–28, vii [10] Abumi K, Ito M, Sudo H. Reconstruction of the subaxial cervical spine using pedicle screw instrumentation. Spine. 2012; 37(5):E349–E356 [11] Johnston TL, Karaikovic EE, Lautenschlager EP, Marcu D. Cervical pedicle screws vs. lateral mass screws: uniplanar fatigue analysis and residual pullout strengths. Spine J. 2006; 6(6):667–672 [12] Jones EL, Heller JG, Silcox DH, Hutton WC. Cervical pedicle screws versus lateral mass screws. Anatomic feasibility and biomechanical comparison. Spine. 1997; 22(9):977–982 [13] Kothe R, Rüther W, Schneider E, Linke B. Biomechanical analysis of transpedicular screw fixation in the subaxial cervical spine. Spine. 2004; 29 (17):1869–1875 [14] Abumi K, Ito M, Kaneda K. Surgical treatment of cervical destructive spondyloarthropathy (DSA). Spine. 2000; 25(22):2899–2905 [15] Oda I, Abumi K, Ito M, et al. Palliative spinal reconstruction using cervical pedicle screws for metastatic lesions of the spine: a retrospective analysis of 32 cases. Spine. 2006; 31(13):1439–1444 [16] Abumi K, Itoh H, Taneichi H, Kaneda K. Transpedicular screw fixation for traumatic lesions of the middle and lower cervical spine: description of the techniques and preliminary report. J Spinal Disord. 1994; 7(1):19–28 [17] Hong JT, Tomoyuki T, Udayakumar R, Espinoza Orías AA, Inoue N, An HS. Biomechanical comparison of three different types of C7 fixation techniques. Spine. 2011; 36(5):393–398 [18] Abumi K, Shono Y, Taneichi H, Ito M, Kaneda K. Correction of cervical kyphosis using pedicle screw fixation systems. Spine. 1999; 24(22):2389–2396 [19] Abumi K, Takada T, Shono Y, Kaneda K, Fujiya M. Posterior occipitocervical reconstruction using cervical pedicle screws and plate-rod systems. Spine. 1999; 24(14):1425–1434 [20] Abumi K, Kaneda K. Pedicle screw fixation for nontraumatic lesions of the cervical spine. Spine. 1997; 22(16):1853–1863 [21] Abumi K, Shono Y, Ito M, Taneichi H, Kotani Y, Kaneda K. Complications of pedicle screw fixation in reconstructive surgery of the cervical spine. Spine. 2000; 25(8):962–969 [22] Yoshimoto H, Sato S, Hyakumachi T, Yanagibashi Y, Masuda T. Spinal reconstruction using a cervical pedicle screw system. Clin Orthop Relat Res. 2005 (431):111–119 [23] Yukawa Y, Kato F, Ito K, et al. Placement and complications of cervical pedicle screws in 144 cervical trauma patients using pedicle axis view techniques by fluoroscope. Eur Spine J. 2009; 18(9):1293–1299 [24] Neo M, Sakamoto T, Fujibayashi S, Nakamura T. The clinical risk of vertebral artery injury from cervical pedicle screws inserted in degenerative vertebrae. Spine. 2005; 30(24):2800–2805 [25] Tomasino A, Parikh K, Koller H, et al. The vertebral artery and the cervical pedicle: morphometric analysis of a critical neighborhood. J Neurosurg Spine. 2010; 13(1):52–60 [26] Pech P, Daniels DL, Williams AL, Haughton VM. The cervical neural foramina: correlation of microtomy and CT anatomy. Radiology. 1985; 155(1):143–146 [27] Xu R, Kang A, Ebraheim NA, Yeasting RA. Anatomic relation between the cervical pedicle and the adjacent neural structures. Spine. 1999; 24(5):451–454

Complications Related to Selected Instrumented Fusion Levels for Subaxial Fusion

10 Complications Related to Selected Instrumented Fusion Levels for Subaxial Fusions Kim A. Williams Jr., George M. Ghobrial, Alexander R. Vaccaro, and Srinivas Prasad

10.1 Introduction Instrumentation of the subaxial spine has been described for the surgical treatment of cervical spine pathology for many years.1,2,3,4,5 Early cervical instrumentation consisted of the use of sublaminar wiring and was generally considered as the gold standard for decades, although it has now been shown to have lower fusion rates when compared to contemporary screw constructs.6,7,8,9,10,11 Recent advances include the transition to more modular systems and the reduction of constructs to incorporate only the levels that are medically necessary. The most significant innovation has been the incorporation of screw fixation in the cervical spine. Screw fixation is unique in that it can now achieve stabilization of all three columns of the cervical spine. This has led to an improvement in fusion rates to nearly 100% in uncomplicated subjects.12,13,14,15

10.2 Purpose of Instrumentation For a variety of pathologies, posterior subaxial cervical spine instrumentation has become a standard technique for stabilizing the spine and promoting arthrodesis.16 White and Panjabi described cervical instability as the primary indication for posterior instrumentation of the subaxial cervical spine. Instability has been defined as loss of the ability of the spine, under physiologic loading, to maintain its alignment and prevent increased deformity or neurological deficit.17 With this in mind, the main indications of posterior cervical spine instrumentation are to provide immediate stability, promote fusion, prevent neurological compromise, and allow early mobilization of the patient.

10.3 Relevant Anatomy The “subaxial” cervical spine refers to segments C3 through C7 and is grouped as such due to the anatomical similarities within these levels that are not seen in the atlantoaxial segments. Despite these morphological similarities, anatomical variation exists and safe surgical intervention requires a thorough understanding of individual anatomy. For example, vertebral artery anatomy is variable and its exact course should be understood when considering posterior cervical instrumentation. Preoperative computed tomographic (CT) imaging is reviewed to analyze the lateral mass anatomy, size, and the relations with the vertebral arteries.12 Moreover, the facet joints, composed of superior and inferior articular processes, are reviewed to gain an understanding of ideal trajectories for screw placement. The average superoinferior length of the lateral mass ranges between 11 mm at C3 and 15 mm at C7, and the mean mediolateral width ranges from 12 to 13 mm at C3 through C7.18 These measurements aid in the selection of appropriate instrumentation, but should be utilized in tandem with patient-specific measurements to avoid malpositioned instrumentation.

The spinal nerve exits the spinal canal through the interpedicular foramen. The mean distance from the posterior center of the lateral mass and the projections of the spinal nerves is about 5.6 mm. On the axial plane, the spinal nerve is situated anteromedially to the anterior aspect of the superior facet.19,20, 21,22 Magerl proposed a lateral mass screw starting point that is 2 to 3 mm medial and inferior to the midpoint of the lateral mass and angling 30 degrees superiorly and 25 degrees laterally.23,24 The ideal trajectory for Magerl’s technique is for bicortical purchase ending at the anterolateral cortex of the superior articular facet. This trajectory permits placement of a longer lateral mass screw and avoids the adjacent neural foramen and vertebral artery. The screw should be as parallel to the plane of the facet as possible, as a drawback of Magerl’s technique is the relatively higher risk of spinal nerve injury exiting the foramen.25 Roy-Camille26 advocated for a starting point at the midpoint of the lateral mass, with a trajectory that is perpendicular to the vertebral plane and 10 degrees lateral. With this technique, a shorter screw is chosen, and is easier to avoid a breach in the setting of rotational deformity. It is imperative to choose a shorter screw, as the risk of vertebral artery violation is higher with Roy-Camille’s method. However, there have been many proposals to what the exact starting point should be—these are just rough guidelines, where patientspecific anatomical variation should always be the deciding factor.

10.4 Preoperative Imaging Review of imaging both preoperatively and intraoperatively is key in helping with clinical and operative decision making. The use of CT is essential in determining bony anatomy as well as allowing for measurement of the lateral masses and pedicles for proper screw insertion. Magnetic resonance imaging (MRI) is useful for determining spinal cord and nerve root architecture. Magnetic resonance angiography and/or CT angiography can be useful for identifying any aberrant vascular anatomy.

10.5 Complications Complications from subaxial cervical spine fusion can be broadly classified into intraoperative and postoperative categories. Within the intraoperative category, there are several subgroups including neural, vascular, bony, and soft-tissue injury. Likewise, the postoperative category can be subdivided into soft tissue, neural, and bony injury.27 There are several other rare postoperative complications that can also occur, such as ocular blindness from prolonged recumbence in the prone position as well as air embolism.28 The rarest of complications should be a part of the informed consent process at the discretion of the surgeon.

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10.6 Neurologic Injury Nerve root injury is a potential consequence of lateral mass screw insertion. Using the techniques of Roy-Camille and Magerl, one group demonstrated a maximum 3.6% incidence of nerve root injury with insertion of articular screws.29 An et al found that the more medial trajectories in the Roy-Camille’s technique were more likely to cause nerve root injury. The more cephalad oriented Magerl’s trajectories were also more likely to produce a nerve root injury.30 There have also been several studies to show high incidences of nerve root injury with lateral mass screw placement. Graham et al reported a nerve root injury rate per screw of 1.8% using the Magerl’s technique. In a clinical study using the RoyCamille’s technique, results showed a 25% risk of new-onset radiculopathy after lateral mass screw insertion.31,32 Heller et al reported that using a trajectory that proceeds 15 to 20 degrees laterally, and no stated superior trajectory, resulted in a 9% incidence of nerve root injury in their series of patients.29 There have been reports of increased risk of neurologic injury with cervical pedicle screw fixation. Intuitively, the relatively smaller pedicles in the all too often osteoporotic patient with limited mechanical feedback contribute to the elevated risk of a malpositioned screw. Abumi et al described complications of cervical pedicle screw fixation in 180 consecutive patients.33 They found 45 screws (6.7%) that penetrated the pedicle, and 2 of those caused radiculopathy. There were three neurovascular complications directly attributed to pedicle screw insertion. Finally, radiculopathy caused by iatrogenic foraminal stenosis from excessive reduction of the translational deformity was observed in one patient.33 Dural tear is a rare complication of subaxial fusion if lateral mass screws are placed, and is usually related to the placement of cervical pedicle screws if no laminectomy is performed as part of the procedure.34,35,36,37,38,39,40 Mummaneni et al described placing lateral mass screws in 32 patients and having a single dural tear, a rate of 3.1%.39

10.7 Vascular Injury Vertebral arteries are the vascular structures most at risk during posterior cervical spine exposure. While injury is a rare complication of spine surgery, with rates of approximately around 0.3 to 0.5%, it can still be associated with severe morbidity and even mortality.41 As previously mentioned, the use of preoperative imaging, either axial CT slices or MRI, should be evaluated to determine the vascular anatomy for proper placement of lateral mass or pedicle screws (▶ Fig. 10.1). These studies can also demonstrate anomalous vertebral arteries. If a vertebral artery injury occurs, direct pressure with thrombin-soaked Gelfoam and patty to control bleeding is the first step. There have been many secondary repair steps discussed in the literature. These include packing and observation, delayed endovascular balloon/coil occlusion, artery ligation, and direct repair. Most authors agree that direct repair is the best first option to prevent significant stroke. If, however, this is not possible, then endovascular techniques should be employed.41,42,43,44,45,46,47 Epidural hematoma (EDH) is another potential complication of subaxial spine fusion. Complications from EDH can be quite

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Fig. 10.1 Axial CT scan of the cervical spine showing an anomaly in transverse foramen.

severe given that the hematoma can rapidly grow and cause severe spinal cord compression. This can lead to significant, even permanent, neurologic deficits.47,48,49 Persistent venous bleeding and or small arterial vessels can continue to hemorrhage until a significant hematoma forms. Care must be taken to ensure meticulous hemostasis to mitigate this complication.50 Despite the potentially devastating nature of this complication, the incidence of symptomatic postoperative spinal EDH requiring reoperation is reported to be about 0.1 to 3%.51,52 Awad et al looked at more than 14,000 patients who developed postoperative EDH and identified several risk factors to be associated with the development of postoperative EDH.52 The preoperative risk factors included patient older than 60 years, the use of nonsteroidal anti-inflammatory drugs preoperatively, and Rh-positive blood type. Intraoperative risks included operating at five or more levels, hemoglobin dropping below 10 g/dL, and blood loss of more than 1 L. Likewise, an increased international normalized ratio (> 2.0) within the first 48 hours postoperatively is associated with increased risk of developing a postoperative hematoma. However, there was no associated change in the risk of developing EDH with the use of surgical drains or with deep vein thrombosis (DVT) prophylaxis.52

10.8 Infection Subaxial cervical spine exposures have a relatively low incidence of wound infection with rates ranging from 1 to 6% since the standardization of preoperative antibiotic prophylaxis given 1 hour prior to surgery per World Health Organization protocol53,54,55 (▶ Fig. 10.2). Preoperative antibiotics such as cephalosporins should be administered as mentioned earlier, and continued for 24 hours postoperatively. The use of irrigation throughout the procedure is also useful in decreasing infection, particularly antibiotic irrigation.56 Al Barbarawi et al included 110 patients who had 785 lateral mass screws placed. They reported six superficial wound infections, which was a rate of

Complications Related to Selected Instrumented Fusion Levels for Subaxial Fusion

Fig. 10.2 Wound breakdown and dehiscence after a posterior cervical decompression and fusion.

5.5%.57 These infections can usually be treated with a short course of intravenous or oral antibiotics. Deeper infections, however, are treated with surgical irrigation and debridement of devascularized tissue. After debridement, treatment is followed with 6 to 8 weeks of intravenous antibiotics. Instrumentation and graft can be left in place until arthrodesis occurs and healing can be expected to occur. If the infection persists and hardware must be removed, external immobilization should be considered if bony fusion has not been achieved.53,54,55 Olsen et al reported a 73% repeat surgery rate for deep tissue postoperative infections.55 In the setting of severe untreated infection, meningitis is another rare potential complication of cervical spine fusion, even more so with a durotomy. Clinical symptoms of nuchal rigidity, headache, and positive Kernigs’ and or Brudzinski’s signs may suggest the presence of meningitis.58

10.9 Pseudarthrosis Pseudarthrosis or nonunion is the failure of a bony union to take place. This complication can be related to poor surgical technique and poor preoperative planning. In posterior cervical fusion, use of autograft bone yields improved fusion rates due to higher intrinsic bone morphogenetic proteins. The use of appropriate arthrodesis techniques between each fused joint is also critical in ensuring the ability to fuse without pseudarthrosis development (▶ Fig. 10.3). Katonis et al looked at posterior cervical fusion in 225 consecutive patients and found a rate of pseudarthrosis of 2.6% (6 patients).59 Patient factors associated with lower fusion rates include smoking, diabetes, and any other immunocompromised states. Revision surgery for pseudarthrosis is usually indicated if there are signs of neurologic deficit or if there is deformity and mechanical axial pain felt to be attributable to the nonunion.60

10.10 Instrumentation and Construct Failure Instrumentation and construct failures can happen for a variety of reasons. The most common instrumentation failure is thought to arise from a construct that is under repetitive stress that cannot be overcome by the load-sharing properties of the construct. Inadequate purchase often due to poor bone quality can lead to screw pullout. Katonis et al reported lateral mass screw pullout in three of their patients, which was a rate of 1.3%.59 Another method of failure is breaking of the rods and/or screws. Typically, the construct failure is associated with a pseudarthrosis and superimposed cycle fatigue of the instrumentation. Fractured implants can be monitored with serial scanning if there is no sign of pseudarthrosis or implant migration. If there are signs of migration, however, then there is potential for serious neurologic complications and removal or replacement of the implant may be prudent. Likewise, improper screw position can lead to instrumentation and construct failure as well. Improper screw placement can also lead to neurologic deficit from canal violation, cortical breach through the lateral mass or pedicle, or vertebral artery violation and subsequent stroke (▶ Fig. 10.4). Placement of lateral mass screws can lead to breaches of the neural foramen causing radiculopathy, or of the central canal causing myelopathy, dural tear, or EDH with cord compression.44,46,61,62,63 The use of image guidance has had limited benefit in preventing improper screw placement.64

10.11 Conclusion Subaxial posterior cervical spine fusion is a staple of orthopaedic or neurological spine surgery for the treatment of various degenerative, infectious, traumatic, neoplastic, and other destabilizing pathologies in the cervical spine. There are numerous

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Fig. 10.3 Sagittal cervical spine X-ray showing a pseudarthrosis after a prior anterior cervical fusion requiring posterior fixation.

potential complications with subaxial cervical spine instrumentation. Careful evaluation of preoperative imaging is paramount in limiting many complications. Likewise, meticulous surgical technique can help limit complications, and appropriate sterilization and antibiotic prophylaxis can help avoid infection. Once a complication has been encountered, rapid diagnosis and treatment are paramount in avoiding worsening neurologic function, increased morbidity, and even death. Most importantly, transparency is key in complication management. In the future, improved image guidance or three-dimensional imaging modalities may help characterize individual anatomy more accurately. This can aid in both preoperative and intraoperative planning to reduce the incidence of many complications caused by surgical technique.

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10.12 Key Points ●

●

●

●

●

Understanding the complication rate of posterior cervical spine surgery. Understanding neurologic injury associated with posterior cervical spine surgery. Understanding vascular injury associated with posterior cervical spine surgery. Understanding superficial versus deep infections and their management. Understanding pseudarthrosis and instrumentation failure.

Complications Related to Selected Instrumented Fusion Levels for Subaxial Fusion

Fig. 10.4 Axial CT scan of the cervical spine showing a left pedicle screw within the canal.

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Cranial [40] Suchomel P, Stulík J, Klézl Z, et al. [Transarticular fixation of C1-C2: a multicenter retrospective study]. Acta Chir Orthop Traumatol Cech. 2004; 71(1):6–12 [41] Devin CJ, Kang JD. Vertebral artery injury in cervical spine surgery. Instr Course Lect. 2009; 58:717–728 [42] Peng CW, Chou BT, Bendo JA, Spivak JM. Vertebral artery injury in cervical spine surgery: anatomical considerations, management, and preventive measures. Spine J. 2009; 9(1):70–76 [43] Deen HG, Nottmeier EW, Reimer R. Early complications of posterior rodscrew fixation of the cervical and upper thoracic spine. Neurosurgery. 2006; 59(5):1062–1067, discussion 1067–1068 [44] Zhao XL, Zhao HB, Wang B, Zhu XS, Li LZ, Zhang CQ. Lower cervical spine injury treated with lateral mass plates and pedicle screws through posterior approach. Chin J Traumatol. 2005; 8(3):160–164 [45] Tubbs RS, Salter EG, Wellons JC, III, Blount JP, Oakes WJ. The triangle of the vertebral artery. Neurosurgery. 2005; 56(2) Suppl:252–255, discussion 252–255 [46] Deen HG, Birch BD, Wharen RE, Reimer R. Lateral mass screw-rod fixation of the cervical spine: a prospective clinical series with 1-year follow-up. Spine J. 2003; 3(6):489–495 [47] Wellman BJ, Follett KA, Traynelis VC. Complications of posterior articular mass plate fixation of the subaxial cervical spine in 43 consecutive patients. Spine. 1998; 23(2):193–200 [48] Yonenobu K, Hosono N, Iwasaki M, Asano M, Ono K. Neurologic complications of surgery for cervical compression myelopathy. Spine. 1991; 16 (11):1277–1282 [49] Horwitz NH, Rizzoli H. V. Herniated Intervertebral Discs and Spinal Stenosis. Baltimore, MD: Williams & Wilkins; 1987 [50] Mayfield FH. Complications of laminectomy. Clin Neurosurg. 1976; 23:435–439 [51] Choi JH, Kim JS, Lee SH. Cervical spinal epidural hematoma following cervical posterior laminoforaminotomy. J Korean Neurosurg Soc. 2013; 53(2):125–128

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[52] Awad JN, Kebaish KM, Donigan J, Cohen DB, Kostuik JP. Analysis of the risk factors for the development of post-operative spinal epidural haematoma. J Bone Joint Surg Br. 2005; 87(9):1248–1252 [53] Pahys JM, Pahys JR, Cho SK, et al. Methods to decrease postoperative infections following posterior cervical spine surgery. J Bone Joint Surg Am. 2013; 95(6):549–554 [54] Olsen MA, Nepple JJ, Riew KD, et al. Risk factors for surgical site infection following orthopaedic spinal operations. J Bone Joint Surg Am. 2008; 90(1):62–69 [55] Olsen MA, Mayfield J, Lauryssen C, et al. Risk factors for surgical site infection in spinal surgery. J Neurosurg. 2003; 98(2) Suppl:149–155 [56] Watanabe M, Sakai D, Matsuyama D, Yamamoto Y, Sato M, Mochida J. Risk factors for surgical site infection following spine surgery: efficacy of intraoperative saline irrigation. J Neurosurg Spine. 2010; 12(5):540–546 [57] Al Barbarawi MM, Audat ZA, Obeidat MM, et al. Decompressive cervical laminectomy and lateral mass screw-rod arthrodesis. Surgical analysis and outcome. Scoliosis. 2011; 6:10 [58] Bertalanffy H, Eggert HR. Complications of anterior cervical discectomy without fusion in 450 consecutive patients. Acta Neurochir (Wien). 1989; 99(1– 2):41–50 [59] Katonis P, Papadakis SA, Galanakos S, et al. Lateral mass screw complications: analysis of 1662 screws. J Spinal Disord Tech. 2011; 24(7):415–420 [60] Park DK, An HS. Problems related to cervical fusion: malalignment and nonunion. Instr Course Lect. 2009; 58:737–745 [61] Gebauer M, Barvencik F, Briem D, et al. Evaluation of anatomic landmarks and safe zones for screw placement in the atlas via the posterior arch. Eur Spine J. 2010; 19(1):85–90 [62] Wang Y, Tang L, Hu J. [Cervical lateral mass plate with its clinical application]. Zhongguo Xiu Fu Chong Jian Wai Ke Za Zhi. 2007; 21(10):1071–1073 [63] Hwang IC, Kang DH, Han JW, Park IS, Lee CH, Park SY. Clinical experiences and usefulness of cervical posterior stabilization with polyaxial screw-rod system. J Korean Neurosurg Soc. 2007; 42(4):311–316 [64] Ludwig SC, Kowalski JM, Edwards CC, II, Heller JG. Cervical pedicle screws: comparative accuracy of two insertion techniques. Spine. 2000; 25 (20):2675–2681

Complications of Laminoplasty

11 Complications of Laminoplasty Ryan S. Murray and Seyed Babak Kalantar

11.1 Introduction Laminoplasty is a useful and effective approach in the treatment of multilevel cervical spondylosis and myelopathy. Prior to the development and adoption of laminoplasty, multilevel laminectomy had been used extensively in the management of myelopathy caused by multilevel spondylosis, ossification of the posterior longitudinal ligament, and developmental cervical spinal stenosis. This approach was reported to carry a risk of intraoperative spinal cord injuries, postoperative progression of cervical kyphosis, and worsening neurological function related to the formation of a laminectomy membrane over the thecal sac.1 With the advent of the high-speed burr and further understanding of the complications of laminectomy alone, techniques were developed to minimize intraoperative complications, postoperative kyphosis, and membrane formation while still adequately decompressing the spinal cord. The first unilateral open-door laminoplasties in the 1980s showed the benefits of simultaneous multilevel decompression and preserved posterior musculature to prevent postoperative progression of cervical kyphosis and instability. As the procedure has been refined and more broadly employed, it is important to discuss outcomes and complications related to the procedure.

11.2 Indications and Contraindications When approaching a patient with cervical spondylosis and myelopathy, there are several factors to consider in weighing the various treatment options. Important considerations include the number of levels requiring decompression, cervical sagittal alignment, the presence of an ossified posterior longitudinal ligament, and whether or not the anterior elements of the cervical spine are ankylosed. The anterior approach is more commonly used when three or fewer levels are involved with concurrent loss of cervical lordosis in the absence of dynamic instability. A posterior approach is generally indicated when greater than three levels are involved and cervical lordosis is preserved. This lordotic alignment of the cervical spine is crucial because posterior decompression of a kyphotic cervical spine fails to allow posterior migration of the cord, which can result in further cord compression and neurologic decline. Options for a posterior decompression include decompressive laminectomy, laminectomy with fusion, and laminoplasty. Prior to the advent of laminoplasty, the typical posterior management of cervical spondylotic myelopathy included the earlier-mentioned laminectomy with or without fusion. Initially, satisfactory results were found, though in recent years postoperative complications, particularly post-laminectomy cervical kyphosis, have given rise to alternative surgical approaches to posterior cervical decompression. Multilevel cervical laminectomy can also be augmented with posterior instrumented fusion constructs largely consisting of pedicle or lateral mass

screw fixation systems. The use of instrumented fixation and fusion of the cervical spine following laminectomy showed improvement in neurologic outcome with a decreased rate of postoperative cervical kyphosis, though dissatisfaction with the degradation of cervical motion, especially in the Japanese population, helped drive the development and implementation of laminoplasty as another option for posterior cervical decompression. The general benefits of laminoplasty include preserved stability and motion, which theoretically decrease the risk of adjacent segment disease or degeneration. In addition, by preserving the muscular attachments posteriorly for the paraspinal muscles, the posterior tension band is maintained, thus theoretically preventing postoperative cervical kyphosis. The ideal candidate for laminoplasty is a patient with multilevel cervical stenosis causing myelopathy, with a lordotic alignment and only a mild or secondary complaint of axial neck pain. Furthermore, laminoplasty is the treatment of choice for cervical myelopathy in patients with increased risk for nonunion such as smokers or patients with metabolic bone disease.2 Laminoplasty is contraindicated in cases of epidural fibrosis (typically following a previous posterior cervical spine surgery), large “hill-shaped” lesions of an ossified posterior longitudinal ligament occupying more than 50 to 60% of the anterior-posterior canal diameter, and in patients with axial neck pain as their chief complaint.2 In addition, fixed cervical kyphosis is another absolute contraindication to laminoplasty for the reasons outlined earlier. Other reasons to forgo laminoplasty in favor of another procedure include morbid obesity and diabetes mellitus, which can result in a two- to eightfold increase in surgical site infections. Furthermore, the technical challenges of positioning these patients on the operating table and achieving the necessary exposure can make laminoplasty an unattractive choice.2

11.3 Laminoplasty Techniques There are currently two major techniques, with many variations thereof, for cervical laminoplasty: the Hirabayashi’s “open-door” technique and the sagittal spinous process splitting “French-door” technique described by Kurokawa1,2 (▶ Fig. 11.1). Variations in these techniques differ largely on how the lamina is secured into its new position or how the exposure in made. Initially, the hinges were sutured or tethered with wire to surrounding tissue or propped open with bone or synthetic grafts. Recent innovations have adapted plates and screws to securely fix the lamina in place and are favored among many high-volume laminoplasty surgeons.2 The open-door technique is technically demanding in that it requires a bicortical trough laminectomy with a unicortical trough laminectomy on the contralateral side, thus creating a

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Cranial

Fig. 11.1 (a–e) Various techniques demonstrating open-door and French-door laminoplasties with fixation methods.2

hinge through the unicortical trough by opening the bicortical laminectomy. This increases the spinal canal diameter and the hinged lamina is held open with a cortical bone graft spacer or specific laminoplasty plates. The sagittal spinous process splitting approach involves splitting the spinous processes with a high-speed burr to create two hemilaminas. Bilateral unicortical trough laminectomies are then created to allow the hemilamina to be opened like a French door to increase the diameter of the spinal canal. This construct is held open with cortical bone graft secured with wire to the lamina. The theoretical advantages of this approach include symmetric reconstruction of the posterior arch with bone graft being secured farther from the spinal cord. Furthermore, by avoiding a bicortical trough laminectomy laterally, the risk of injury to the lateral epidural venous elements is significantly reduced. The obvious disadvantage of this technique is the danger to the spinal cord associated with the sagittal splitting of the spinous processes with a high-speed burr.1

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11.4 Procedure Laminoplasty is performed in the prone position. The ideal neck position is flexed, which allows for less overlap of the lamina. A Mayfield three-pin head holder is used to immobilize the cervical spine. All pressure points as well as the chest and abdomen are well padded. The shoulders are often taped down to allow for lateral fluoroscopic imaging of the lower cervical spine. Tape may also be used to position redundant soft tissues. A reverse Trendelenburg position is used to decrease venous pressure and thus blood loss. Neuromonitoring of somatosensoryevoked potentials is generally recommended and employed for cervical laminoplasty, while the routine use of motor-evoked potentials is less common. Neuromonitoring allows for immediate detection and early intervention in cases of decreased spinal cord perfusion or severe hypotension. For this reason, anesthesia providers typically use an arterial catheter for continuous blood pressure monitoring.2 Roh et al evaluated 809 patients

Complications of Laminoplasty undergoing cervical spine surgery with somatosensory-evoked potential monitoring and found degradation in evoked potentials in 17 (2.1%) patients, which prompted intervention and subsequent prevention of neurologic sequelae in 15 or those 17 patients. They also noted that monitoring is useful in identifying brachial plexopathies related to patient positioning.3 The posterior cervical approach typically involves a skin incision from the inferior aspect of C2 caudally to about one fingerbreadth superior to the vertebra prominens. Intraoperative fluoroscopy can be used to localize the landmarks for skin incision and operative dissection and is especially useful in patients whose body habitus makes palpation of physical landmarks more challenging. Following confirmation of the operative level, a longitudinal subperiosteal dissection is then performed in the midline raphe with dissection carried laterally to the junction of the lamina and lateral mass to allow exposure for trough placement. It is important to preserve the integrity of the facet joint capsule and wherever possible the muscular attachments to C2 and C7 to preserve the extensor mechanism function.4 In both approaches, the “open-door” and “French-door” types, the troughs are placed at the junction between the lamina and lateral mass (▶ Fig. 11.2). In “open-door” procedures, the open bicortical trough is made first prior to the placement of the unicortical hinge trough. In a “French-door” approach, the spinous processes are split sagittally with a high-speed burr and then bilateral unicortical troughs are made at the same junction of the lamina and lateral mass. In both cases, the laminoplasty is opened sequentially at each level with an understanding that adequate opening and subsequent decompression often require multiple levels to be opened. As the laminas are progressively opened, the ligamentum flavum attaching the lamina to the lateral mass of the “open” side is placed on tension and can be removed. It is important to note that in an “open-door” approach, there are epidural veins laterally that can be difficult to manage and should be dealt with prophylactically with bipolar cautery to avoid excessive venous bleeding.4 The opened lamina are then secured by a variety of techniques, including plate fixation which is emerging as a commonly employed method of fixing open lamina in the “open-door”– type procedure. The fascial closure should be watertight and the skin closed meticulously, especially in patients with redundant soft tissue. Postoperative care involves typical wound care

and most importantly limited use of brace immobilization. The evidence strongly suggests that postoperative immobilization following laminoplasty increases the risk of lost motion and axial neck pain.4

11.5 Outcomes The principle outcome to be concerned with in the surgical treatment of cervical myelopathy, including those treated with laminoplasty, is the presence and extent of neurologic recovery. In general, neurologic recovery is expected in the majority of patients treated with laminoplasty, with studies suggesting that approximately 80% of patients will experience some type of improvement. A mean recovery rate of 55% with a range of 20 to 80% has been reported based on Japanese Orthopaedic Association Scale used to assess for myelopathy. The extent of neurologic recovery does not appear to be specific to any laminoplasty technique and is generally consistent across the surgical approaches used today.1 The greatest advantage of laminoplasty compared to multilevel anterior cervical procedures is a lower complication and reoperation rate. These results are largely attributable to the avoidance of fusion, which eliminates the possibility of pseudarthrosis or graft failure. Yonenobu et al compared laminoplasty with multilevel anterior corpectomy and found the complication rates to be four times higher in the corpectomy group, 29 versus 7%.5 Furthermore, large systematic reviews have supported these findings of significantly higher complication rates in anterior cervical fusion groups with an odds ratio of 2.6 in a meta-analysis. This review also demonstrated a higher reoperation rate of 8.6% of multilevel anterior procedures versus 0.3% in patients who underwent laminoplasty.6 Similar attempts to elucidate the relative outcome differences between laminoplasty and laminectomy with fusion have been less clear cut. An extensive systematic review by Yoon et al demonstrated a diverse collection of relatively low-quality outcome data, which demonstrated a similar efficacy of both procedures in the treatment of cervical spondylotic myelopathy. However, there is a 1 to 38% rate of pseudarthrosis inherent to laminectomy with fusion that is eliminated in the laminoplasty procedure.7

11.6 Complications The most common complications of cervical laminoplasty include nerve root palsy, loss of lordosis, loss of cervical motion, axial neck pain, restenosis, hinge fracture, and postoperative wound infection.

11.6.1 Nerve Root Palsy

Fig. 11.2 Location of hinge and trough models demonstrating locations (dotted lines) in which the hinge and trough are created at the lateral mass–laminar junction.4

Postoperative cervical nerve root palsy is a relatively common complication of both anterior and posterior approaches to the cervical spine. The C5 nerve root is most commonly involved and can be a challenging and worrisome complication of anterior and posterior spine surgery at the C4–C5 level, including laminoplasty. The incidence of this complication is thought to be related to the anatomic configuration at the C4–C5 level, where the C5 nerve root travels along a relatively short course

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Cranial and is susceptible to stretch following posterior migration of a decompressed spinal cord. Roselli et al reported a 12% rate of transient C5 palsy in their series.8 In 19 reports detailing the outcomes following a French-door–type laminoplasty in 550 patients, a 5% incidence of transient C5 nerve root palsy was reported.9 In general, it is likely that the presence of this complication is independent of surgical approach or technique when performing the laminoplasty. When comparing the incidence of transient nerve root palsy across multiple approaches to the cervical spine, it is apparent that this complication is least likely in cases of laminoplasty. In the largest ever series of multilevel cervical decompressions Nassr et al found that the incidence of C5 motor palsy was highest with laminectomy and fusion (9.5%) followed by anterior corpectomy (5.1%) when compared with laminoplasty (4.8%).10 The recovery of transient motor root palsy can be unpredictable and can take months to years. Patients who have a postoperative palsy but still have antigravity strength will often recover to full strength, whereas those with a more pronounced palsy will likely continue to have significant deficits.11 In the aforementioned article, Nassr et al reported a maximum neurologic recovery time frame of 1 week to 2 years with a mean of 21 weeks. There were no residual deficits in the laminoplasty group with the highest rate of residual deficits in the laminectomy and fusion group (~ 27.3%).10

11.6.2 Loss of Lordosis Postoperative alignment and spinal deformity is another important endpoint when discussing the outcomes and complications of laminoplasty because progression of cervical kyphosis is a worrisome complication of laminectomy, potentially resulting in progression of neurologic deficits. Several studies evaluating this outcome reported a high incidence of a change from preoperative lordotic alignment to a postoperative straightened or kyphotic alignment, though the overall incidence of new kyphosis following laminoplasty was generally low, approximately 4 to 15%.12 Machino et al evaluated 500 consecutive laminoplasty patients and demonstrated a 1.8-degree increase in cervical lordosis measured from C2 to C7 with an average 33-month follow-up after laminoplasty.13 It has been purported that laminoplasty prevents the onset and progression of postoperative kyphotic deformity as a result of preserved muscle attachments and reattachment of paraspinal musculature to intact lamina. Despite this, Fujimura and Nishi found an 80% decrease in cross-sectional area of cervical musculature following laminoplasty with this atrophy being worse at the deeper levels 1 year postoperatively in their series of 53 patients. Despite this atrophy, there was no correlation between the degree of atrophy and cervical curvature; therefore, it is likely that other factors such as facet joint insults are more important than atrophy of cervical musculature in producing cervical kyphosis following posterior decompression.14 The overall development of postoperative loss of lordosis and any heterogeneity in the data related to this complication is likely related to differences in technique. To this end, evidence has emerged to suggest that loss of lordosis and subsequent kyphosis is in part attributable to detachment of the

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semispinalis cervicis from its C2 insertion.15 Sakaura et al found that in preserving C2 and C7 muscle attachments, cervical lordosis was maintained in patients regardless of C3–C6 muscle detachment.16

11.6.3 Loss of Motion Postoperative loss of motion is noted in nearly every early study examining outcomes following laminoplasty. A mean loss of 50% of cervical range of motion has been reported in the early literature with an open-door–type laminoplasty.12,17 Though other techniques indicate a wider variation in diminution of cervical range of motion, it was generally accepted that cervical range of motion will decrease to a certain extent following laminoplasty. This decrease in range of motion is thought to be important in improving symptoms of myelopathy, whereas others believe preserving cervical range of motion is important for preventing adjacent segment disease.12 Given that laminoplasty is a motion-sparing nonfusion surgery, research evaluating the etiology of postoperative motion restrictions is relatively abundant. Wada et al found a 71% loss of motion in patients who underwent grafting on their hinge side compared with a 27% loss of motion in patients who did not undergo grafting when both cohorts were immobilized for 3 weeks postoperatively.18 Grafting of the hinge side may have resulted in unintended fusion across the operative levels. The issue of fusion and loss of motion following laminoplasty is thought to be, also in large part, related to postoperative immobilization. Maeda et al illustrated that postoperative kyphotic deformity occurred in stiffer spines, whereas lordosis was maintained in more flexible cervical spines after laminoplasty. They concluded that maintaining cervical range of motion in the early postoperative period prevents loss of motion and stiffness in addition to the subsequent kyphotic deformity.19 Most high-volume laminoplasty surgeons would concur with this approach and generally place patients in a soft collar for about 1 week postoperatively followed by mobilization.2

11.6.4 Axial Neck Pain The often challenging complication of postoperative neck pain is difficult to assess and not often reported in the literature. The incidence ranges markedly from 6 to 60% and it is unclear whether this wide range of results is associated with the laminoplasty technique itself, the time at which neck pain is reported relative to surgery, or the assessment of what constitutes significant postoperative neck pain.12 The sources of axial neck pain have been thought to include facet joint injury, denervation of the extensor muscles, C2 and/or C7 muscle detachment, or prolonged external immobilization. Hosono et al reported a significant improvement in axial neck pain in patients who underwent C3–C6 laminoplasty versus C3–C7 with an incidence of 5.4 versus 29%, respectively.20 In addition, Hosono et al21 reported a 42% rate of shoulder pain in addition to a 60% rate of axial neck pain with the shoulder pain consistently on the hinge side of the decompression.5 In acknowledgement of this difficult complication, most surgeons will avoid laminoplasty in patients with a chief complaint of axial neck pain.

Complications of Laminoplasty

11.6.5 Restenosis The most devastating long-term postoperative complication that may occur after laminoplasty is persistent or recurrent stenosis related to insufficient elevation of the lamina to allow for canal expansion. Mochida et al reported a “spring back” rate of 40% with associated deterioration in clinical examination.22 To avoid this, several techniques of suturing the elevated lamina to overlying muscle or fascia have been described. Furthermore, laminoplasty plates have been developed and employed to rigidly fix the lamina in their open positions. When plates are employed, the need for bone graft and substitutes is eliminated. Rhee et al examined 54 cases of laminoplasty with plate fixation and reported a 93% hinge healing rate at 1 year with no evidence of loss of fixation or premature closure. No revision surgeries were required and canal expansion was preserved in the unhealed group as well23,24 (▶ Fig. 11.3). Kimura et al described a “boomerang” deformity, where the spinal cord is compressed during posterior migration in an inadequately split lamina.25 Originally described as resulting in recurrent upper extremity symptoms, a larger case series by this same group found a 21% incidence of this radiographic sign without clinical significance.26 Ultimately, the overall incidence of inadequate canal expansion is difficult to quantify because postoperative neuroimaging data are reported infrequently. The concept of a post-laminectomy membrane formation resulting in compression of neural elements and subsequent recurrence of myelopathic symptoms has been postulated and discussed for some time. Several studies refute this concept and specifically Herkowitz reported that though the post-laminectomy

membrane exists in many cases, it did not compress the spinal cord or nerve roots in patients undergoing reoperation following cervical laminectomy.27

11.6.6 Hinge Fracture Fracture from the unicortical hinge portion of any laminoplasty can occur as can displacement of a “floppy hinge” related to overly aggressive cortical resection. The ideal hinge results in a plastic “greenstick” deformation of the bone as it is opened. If too little bone is resected, the hinge is susceptible to fracture as it is opened, and if too much bone is removed from the ventral cortex of the hinge trough, it can be “floppy” and susceptible to displacement. Either complication can potentially result in spinal cord or nerve root compromise. In the event of this complication, either fracture or displacement, a “hinge plate” or contoured minifragment plate can be used to stabilize the fracture fragment. If a lamina hinge fracture occurs postoperatively, the failed segment may require surgical decompression depending on the presence of neurologic symptoms clinically.2

11.6.7 Wound Infection Postoperative wound infections are worrisome and challenging complications of any orthopaedic surgery, especially those with implanted instrumentation. Wound infections following laminoplasty have been reported to be approximately 3 to 4%, which is consistent with other posterior cervical procedures.23 The risks of wound infection are impacted by patient factors such as medical comorbidities and body habitus. It is important to achieve a watertight fascial closure to minimize the rate of infection. Furthermore, a separate drain for a thick subcutaneous layer may be beneficial in certain patients as is early cervical range of motion because it is thought to reduce the rates of postoperative wound infections in the cervical spine.2

11.7 Conclusion

Fig. 11.3 Postoperative lateral radiograph demonstrating use of laminoplasty plates to maintain canal expansion.2

Complications of laminoplasty overlap to a certain extent with those found in alternative posterior approaches to the cervical spine such as decompression and fusion, though some are unique to the technique itself. Lack of adequate neural decompression and postoperative recurrence or restenosis are devastating complications of cervical spine surgery. The former shared more commonly among laminectomy and laminoplasty patients, whereas the latter is likely more prevalent and unique in the setting of laminoplasty. Furthermore, postoperative alignment and motion are undoubtedly affected by all posterior approaches to the cervical spine, though there is evidence to suggest that lordotic alignment is preserved in the setting of laminoplasty when compared to laminectomy alone. In addition, laminoplasty performed without postoperative immobilization may provide a truly motion-preserving procedure when compared with alternative fusion options. Less severe, though likely more prevalent, complaints including postoperative neck pain and transient C5 nerve root palsies are likely prevalent in all posterior cervical decompressive surgical approaches though the data, specifically related to postoperative axial neck pain, are lacking, while it is quite in the favor of laminoplasty when

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Cranial considering transient nerve root palsies. As such, it is unclear whether or not laminoplasty offers a clear advantage to other posterior procedures in the cervical spine. Surgeons must be aware of the potential complications and management thereof with the laminoplasty procedure.

References [1] Lawrence BD, Brodke DS. Posterior surgery for cervical myelopathy: indications, techniques, and outcomes. Orthop Clin North Am. 2012; 43(1):29–40, vii–viii [2] Thakur NA. Laminoplasty: indication, techniques, and complications. Semin Spine Surg. 2014; 26(2):91–99 [3] Roh MS, Wilson-Holden TJ, Padberg AM, Park JB, Daniel Riew K. The utility of somatosensory evoked potential monitoring during cervical spine surgery: how often does it prompt intervention and affect outcome? Asian Spine J. 2007; 1(1):43–47 [4] Simpson AK, Rhee JM. Laminoplasty: a review of the evidence and detailed technical guide. Semin Spine Surg. 2014; 26(3):141–147 [5] Yonenobu K, Hosono N, Iwasaki M, Asano M, Ono K. Laminoplasty versus subtotal corpectomy. A comparative study of results in multisegmental cervical spondylotic myelopathy. Spine. 1992; 17(11):1281–1284 [6] Zhu B, Xu Y, Liu X, Liu Z, Dang G. Anterior approach versus posterior approach for the treatment of multilevel cervical spondylotic myelopathy: a systemic review and meta-analysis. Eur Spine J. 2013; 22(7):1583–1593 [7] Yoon ST, Hashimoto RE, Raich A, Shaffrey CI, Rhee JM, Riew KD. Outcomes after laminoplasty compared with laminectomy and fusion in patients with cervical myelopathy: a systematic review. Spine. 2013; 38(22) Suppl 1:S183–S194 [8] Roselli R, Pompucci A, Formica F, et al. Open-door laminoplasty for cervical stenotic myelopathy: surgical technique and neurophysiological monitoring. J Neurosurg. 2000; 92(1) Suppl:38–43 [9] Edwards CC, II, Heller JG, Silcox DH, III. T-Saw laminoplasty for the management of cervical spondylotic myelopathy: clinical and radiographic outcome. Spine. 2000; 25(14):1788–1794 [10] Nassr A, Eck JC, Ponnappan RK, Zanoun RR, Donaldson WF, III, Kang JD. The incidence of C5 palsy after multilevel cervical decompression procedures: a review of 750 consecutive cases. Spine. 2012; 37(3):174–178 [11] Sakaura H, Hosono N, Mukai Y, Ishii T, Yoshikawa H. C5 palsy after decompression surgery for cervical myelopathy: review of the literature. Spine. 2003; 28(21):2447–2451 [12] Ratliff JK, Cooper PR. Cervical laminoplasty: a critical review. J Neurosurg. 2003; 98(3) Suppl:230–238 [13] Machino M, Yukawa Y, Hida T, et al. Cervical alignment and range of motion after laminoplasty: radiographical data from more than 500 cases with

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cervical spondylotic myelopathy and a review of the literature. Spine. 2012; 37(20):E1243–E1250 Fujimura Y, Nishi Y. Atrophy of the nuchal muscle and change in cervical curvature after expansive open-door laminoplasty. Arch Orthop Trauma Surg. 1996; 115(3–4):203–205 Takeuchi K, Yokoyama T, Aburakawa S, et al. Axial symptoms after cervical laminoplasty with C3 laminectomy compared with conventional C3-C7 laminoplasty: a modified laminoplasty preserving the semispinalis cervicis inserted into axis. Spine. 2005; 30(22):2544–2549 Sakaura H, Hosono N, Mukai Y, Fujimori T, Iwasaki M, Yoshikawa H. Preservation of muscles attached to the C2 and C7 spinous processes rather than subaxial deep extensors reduces adverse effects after cervical laminoplasty. Spine. 2010; 35(16):E782–E786 Cheng WC, Chang CN, Lui TN, Lee ST, Wong CW, Lin TK. Surgical treatment for ossification of the posterior longitudinal ligament of the cervical spine. Surg Neurol. 1994; 41(2):90–97 Wada E, Suzuki S, Kanazawa A, Matsuoka T, Miyamoto S, Yonenobu K. Subtotal corpectomy versus laminoplasty for multilevel cervical spondylotic myelopathy: a long-term follow-up study over 10 years. Spine. 2001; 26 (13):1443–1447, discussion 1448 Maeda T, Arizono T, Saito T, Iwamoto Y. Cervical alignment, range of motion, and instability after cervical laminoplasty. Clin Orthop Relat Res. 2002 (401):132–138 Hosono N, Sakaura H, Mukai Y, Fujii R, Yoshikawa H. C3–6 laminoplasty takes over C3–7 laminoplasty with significantly lower incidence of axial neck pain. Eur Spine J. 2006; 15(9):1375–1379 Hosono N, Yonenobu K, Ono K. Neck and shoulder pain after laminoplasty. A noticeable complication. Spine. 1996; 21(17):1969–1973 Mochida J, Nomura T, Chiba M, Nishimura K, Toh E. Modified expansive open-door laminoplasty in cervical myelopathy. J Spinal Disord. 1999; 12 (5):386–391 Rhee JM, Basra S. Posterior surgery for cervical myelopathy: laminectomy, laminectomy with fusion, and laminoplasty. Asian Spine J. 2008; 2 (2):114–126 Rhee JM, Register B, Hamasaki T, Franklin B. Plate-only open door laminoplasty maintains stable spinal canal expansion with high rates of hinge union and no plate failures. Spine. 2011; 36(1):9–14 Kimura S, Gomibuchi F, Shimoda H, et al. Boomerang deformity of cervical spinal cord migrating between split laminae after laminoplasty. Eur Spine J. 2000; 9(2):144–151 Kimura S, Homma T, Uchiyama S, Yamazaki A, Imura K. Posterior migration of cervical spinal cord between split laminae as a complication of laminoplasty. Spine. 1995; 20(11):1284–1288 Herkowitz HN. Cervical laminaplasty: its role in the treatment of cervical radiculopathy. J Spinal Disord. 1988; 1(3):179–188

Complications Related to Cervicothoracic Instrumentation

12 Complications Related to Cervicothoracic Instrumentation Addisu Mesfin

12.1 Introduction The cervicothoracic junction (CTJ) can be involved in trauma, tumors, degenerative processes, and deformity. In degenerative processes of the cervical spine requiring multilevel posterior cervical decompression and fusion, some surgeons choose to cross the CTJ. By anchoring a long cervical construct into the upper thoracic spine, it is thought that a stronger foundation to the construct is obtained and as a result a subsequent decrease in instrumentation failure. Conversely, a long thoracic construct, ending at T1, may result in proximal junction kyphosis (PJK) and may be advisable to cross the CTJ and anchor the construct in the cervical spine. Due to the transfer from the flexible cervical spine to the rigid segment, thoracic spine instrumentation failure can still be encountered. Anterior, posterior, and circumferential approaches can be used to address the CTJ. This chapter addresses the potential complications associated with each approach.

12.2 Cervicothoracic Instrumentation Cervicothoracic instrumentation can be divided into anteriorbased and posterior-based instrumentation. Circumferential constructs (anterior/posterior) are also commonly used in the CTJ for increasing construct rigidity. Indications for an anteriorbased instrumentation would be a disc herniation at C7–T1, unstable fracture, and a primary or metastatic lesion at the C7– T1 levels. Posterior-based instrumentation is indicated when performing a long construct in the cervical spine such as a C7 osteotomy for chin on chest deformity1 and for long thoracic constructs ending at T1. Multilevel posterior cervical spine decompression and fusion can also be extended across the CTJ to provide a stronger foundation to the construct. Unstable cervical spine fractures especially in hyperostotic disorders are frequently encountered at C6–C7 level and require crossing of the CTJ.2,3 There are also biomechanical considerations to consider when ending a long cervical construct in the upper thoracic spine rather than ending it at C7. Specifically, the risk of angular and translation forces can cause anterolisthesis of C7 on T1.4

12.3 Anatomy The CTJ is composed of the C7–T1 vertebrae, C7–T1 disc, associated ligaments, and facets. It is a transition zone from the flexible cervical spine to the rigid thoracic spine (▶ Fig. 12.1). Some authors also include T2 and T3 in the designation of CTJ because constructs crossing the CTJ can frequently end at the T2 or T3 level.5,6 Posteriorly, the trapezius and rhomboid minor attach to the spinous processes of C7 and T1. From an anterior approach, the thoracic duct on the left and the recurrent laryngeal nerve on the right are at risk. If

Fig. 12.1 Osseous anatomy of the cervicothoracic junction. Need anatomic diagram of Cervicothoracic junction, prior copyrighted work is fine

performing a sternal or clavicle splitting approach, the brachiocephalic vein, subclavian vein, and brachiocephalic trunk can be at risk of injury. Cadaveric studies documenting the anatomy of the cervicothoracic and upper thoracic regions have performed.7,8,9,10 Cross-sectional ratio of the spinal cord to spinal canal were measured by An et al,7 demonstrating the following ratios (spinal cord to spinal canal): C6, 1:2.3; C7, 1:3.7; T1, 1:4; and T2, 1:3.7. For diameter of the pedicles from C6 to T2, the following were obtained: 6.78 mm at C6, 7.5 mm at C7, 9.23 mm at T1, and 7.9 mm at T2.7 The T1–T2 vertebrae have a small distance from the pedicle to the inferior nerve root at 1.7 to 1.8 mm. Screw length of 30 to 35 mm and diameter of 5.5 mm can be safely placed at T1 and T2.8,9 Mean transverse angulation is 36 degrees and decreases to 23 degrees at T2.7,10 When performing posterior instrumentation across the CTJ, preoperative magnetic resonance imaging (MRI) and computed tomographic scan (CT scan) should be studied to evaluate the location of where the vertebral artery enters the transverse foramen. In 95% of cases, the vertebral artery enters at the C6 level.11 Malpositioned instrumentation at C7 and the upper thoracic spine can lead to nerve root irritation or spinal cord injury. In addition to radicular symptoms in the respective dermatomal distributions, motor deficits may also be encountered. With C7 irritation triceps, wrist flexion and finger extension weakness can be encountered. With C8 irritation, weakness in finger flexion can be expected and also weakness in finger abduction with T1 irritation.

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Cranial

12.4 Anterior Instrumentation CT and radiographs are necessary during the surgical planning for an anterior approach at the CTJ.12,13,14,15 Through a low Smith– Robinson approach, the C7–T1 level can be reached if the clavicle or manubrium is not in the way.16 This is dependent on the patient’s anatomy (short vs. long neck, high vs. low body mass index). The alternative is to perform a manubrium-splitting approach or clavicle-splitting approach.17,18,19,20 When performing a manubrium- or clavicle-splitting approach, increased operative time, bleeding, and postoperative pain should be anticipated. Anterior instrumentation of the CTJ can include a plate and screw construct if performing discectomy at C7–T1. Following a discectomy, a large diameter allograft or two small allografts can be placed. A standalone threaded cage that screws into the disc space followed by posterior-based stabilization is also an option. Corpectomy of C7 or T1 is another indication for anteriorbased instrumentation. If also planning to perform posteriorbased fusion, plating across the corpectomy site could be avoided. However, there is a risk of the corpectomy graft dislodging when positioning the patient to the prone position. A mesh cage or titanium mesh cage may be placed following a C7 or T1 corpectomy.

12.5 Posterior Instrumentation When instrumenting the cervical spine C3–C6, lateral mass screws are commonly used. In a succinct literature review, Coe et al demonstrated the role of subaxial lateral mass screws in the management of the cervical and cervicothoracic pathology.21,22 In the past, plate screw constructs were used in the cervical spine and CTJ with successful outcomes.23 Owing to the high rates of post–laminectomy kyphosis, instrumentation is usually performed in addition to the laminectomy.4,24,25 The cervical spine is more responsive to the disruption of the tension band and kyphosis usually ensues following an un-instrumented laminectomy.26 At C7, pedicle screws can be used for longer screw purchase, average 24 mm, as compared to a C7 lateral mass screw. Skipping the C7 screw or the T1 screw is a consideration when crossing the CTJ to avoid crowding of the construct. Another option is to stagger the construct by placing a C7 screw on one side and a T1 screw on the contralateral side. In a cadaveric study, a C7 pedicle screw and T1 pedicle screw construct was found to be significantly stiffer than a C7 lateral mass construct in axial compression, torsion, bending, and flexion.27

Transitional rod constructs are offered by several implant companies for the CTJ. This allows for small diameter rod (3.5 mm) to be placed in the cervical spine and a larger diameter rod (5.5 mm) to be placed in the thoracic spine. Some downsides of the transitional rod include the challenge of contouring the rod across the CTJ. Domino constructs that link a 3.5-mm cervical rod to a 5.5-mm thoracic rod are also alternatives. The domino can be a side-to-side connector (▶ Fig. 12.2) or an end-to-end connector. In certain instances, the domino constructs are easier to place than the transitional rods. Cervical rods (3.5 mm) can also be used across the CTJ into the thoracic spine (▶ Fig. 12.3). The potential disadvantage of this technique is that a small diameter rod is being used in the thoracic spine. Smaller sized pedicle screws (4.0 and 4.5 mm) are also used in the upper thoracic spine with a small diameter rod. In a biomechanical study, Tatsumi et al,28 using ultra highmolecular-weight polyethylene, compared four CT constructs: 3.5 mm rods spanning the CTJ along with 3.5 mm thoracic screws, a transitional 3.5- to 5.5-mm rod, 3.5- to 5.5-mm rod connected with a solid domino, and 3.5- to 5.5-mm rod connected via hinged domino. In flexion, the 3.5-mm rod construct was found to be the least stiff compared to the other groups. In flexion load to failure, the 3.5-mm rod construct was also found to have the least yield force. In the axial plane, the 3.5-mm construct had the least torsional stiffness. This study demonstrated the weakness of a 3.5-mm rod and screw construct in the thoracic spine. The limitation of the study is that cadaveric testing was not concurrently performed. Biomechanical cadaveric studies using a C7 laminectomy and facetectomy model have compared the side-to-side domino (3.5–5.5 mm) construct to that of a transitional rod construct instrumented from C5 to T2. No differences in stability between the two constructs were noted.29 Posterior-only stabilization of two- and three-column injuries of the CTJ has been evaluated in cadaveric biomechanical studies. A C5 to T2 construct, consisting of C7 pedicle screws, supplemented with one or two crosslinks was tested. A transitional rod was used along with monoaxial pedicle screws. For two-column injuries, the construct reduced motion across the CTJ by 18% and the addition of crosslinks led to significant decrease in axial rotation compared to no crosslinks. In the three-column injury, the C5 to T2 construct supplemented with two crosslinks was found to be the most stable.30 However, in another cadaveric study using 6 degrees of freedom spine stimulator and seven fresh frozen cadavers, three-column injuries demonstrated increased motion in flexion/extension.31 With the addition of anterior column

Fig. 12.2 A 30-year-old man fell off a roof sustaining bilateral C7 pedicle fractures, C6–C7 facet fracture treated with posterior cervical fusion C5 to T2. Dominoes were used to connect the 3.5-mm rod to the 5.5-mm rod. Instrumentation of the C7 level was skipped because of the existing fracture. (a) Axial CT demonstrating the bilateral fractures. (b) Sagittal CT demonstrates C6–C7 facet fracture (arrow). (c) AP radiograph demonstrating C5–T2 fixation.

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Fig. 12.3 A 81-year-old man with diffuse idiopathic skeletal hyperostosis (DISH) involved in a car accident. (a) Sagittal CT demonstrates C6–C7 three-column hyperextension injury with C7 fracture and C6 spinous process fractures (arrows) managed with (b) C3 to T3 posterior cervical fusion and C6–C7 laminectomy. The anteroposterior view demonstrates the use of a single, 3.5-mm diameter rod across the cervicothoracic junction. C7 instrumentation was skipped to avoid instrumentation crowding.

support, the movement was eliminated. Similar findings in regard to inadequacy of posterior-based instrumentation alone for the management of three-column injuries were noted in another biomechanical study.32 However, for three-column injuries, anterior instrumentation alone is clearly inferior-to-posterior instrumentation alone.33 If the patient is medically unstable or cannot tolerate an anterior approach, then the posterior-based instrumentation should be extended to a minimum of T2.33

12.6 Complications

performed at 6 months and Forteo is maintained postoperatively up to 2 years if need be. If anterior construct failure is noted, the options are to revise it or to supplement it with posterior-based instrumentation. In 14 patients managed with anterior approach to the CTJ, five complications were noted. These included two graft fractures, two pseudarthrosis, and one graft migration.37 Two of the cases were managed with posterior-based instrumentation, two underwent anterior revision with halo placement, and one underwent halo placement only.

12.6.1 Anterior Approach

12.6.2 Posterior Approach

Instrumentation complications associated with anterior approach to the CTJ, if using a plate, include broken plate, broken screws, and screws backing out from the plate. If the plate or screws become symptomatic, it can be revised. If performing an unplated construct, graft dislodgment may occur. If using a threaded cage, mesh cage, or expandable cage, dislodgment of the cage may also occur. Cage subsidence may also occur if the patient is osteoporotic. It is advisable if performing an elective construct crossing the CTJ in elderly patients to be aware of the patient’s status in regard to vitamin D and bone mineral density. If need be, appropriate supplementation can be initiated as well as referral to an endocrinologist if osteoporosis is noted. With vitamin D levels of ≤ 20 (deficiency), we routinely start patients with 50,000 IU of vitamin D weekly for 3 months. Patton et al reported the role of preoperative metabolic evaluation of the patient and subsequent treatment if deficiencies are noted.34 With vitamin D levels of less than 30 but greater than 20 (insufficiency), we routinely supplement with vitamin D of 4,000 IU daily.34 Repeat vitamin D levels are obtained postoperatively and supplementation ceased if levels normalize. In elective settings at our center, if osteoporosis is noted (t score ≤ – 2.5), we refer the patients to our Center for Bone Health for considering the initiation of Forteo (Teriparatide; Eli Lilly, Indianapolis, IN). We prefer Forteo over bisphosphonates because of its anabolic properties which strengthen bone and provide stronger fixation points.35,36 Repeat bone density scan is

Instrumentation failures associated with the posterior approach are more common. When instrumenting lateral masses of the subaxial spine, C7 pedicle, and upper thoracic spine, the CT scan should be carefully studied. If it is an elective procedure being performed in a patient with risk factors for osteoporosis, a bone density scan should be performed preoperatively. If osteopenia is noted, T score of -1 to 2.5, then supplementation of calcium and vitamin D should be started as well as referral to an endocrinologist or a center of bone health. If osteoporosis is noted (T score of -2.5 or less), the surgery, if elective, should be postponed for appropriate osteoporosis treatment. An anabolic medication such as Forteo (Teriparatide, Eli Lily) can be useful, although it is contraindicated in patients with prior or active malignancies. Osteoporosis is an important consideration for proximal junctional kyphosis in patients with thoracic constructs ending at T1 or T2.38 Situations where CT instrumentation is needed are frequently not elective. In these instances, complications associated with poor bone quality such as pedicle screw or lateral mass screw backing out may occur. In the thoracic spine, there may be a role to supplement pedicle screws with polymethylmethacrylate (PMMA) when faced with osteoporotic bone.39 Other options include using hydroxyapatite-coated screws. Outside of case reports, clinical studies are pending on the use of PMMA-supplemented screws in the cervical spine.40 However, vertebroplasty for the management of cervical metastatic lesions has shown some promise.41

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Cranial Failure of the rod including rod breakage can also occur in a transitional rod or a cervical rod being extended in the thoracic spine. If using a domino construct to link the cervical and thoracic rods, failure at the domino rod interface may also occur. The failure may occur when the cervical or thoracic rod slides out of the domino (▶ Fig. 12.4) or the domino may break. An additional factor that can predispose to instrumentation failure is spondylolisthesis at C7–T1. In one series that evaluated 58 patients with degenerative spondylolisthesis, a 9.7% prevalence of spondylolisthesis at C7–T1 was noted.42 The spondylolisthesis must be taken into account during surgical planning. With a C7–T1 spondylolisthesis and a long posterior construct, it may be advisable to end the construct at T2 or T3.43 Ending posterior construct at T1 can lead to high stresses and pull of the T1 screws with progressive kyphosis (▶ Fig. 12.5). During the revision, the instrumentation should be extended a minimum of one level and supplemented with anterior instrumentation and fusion. In constructs ending at T1, it is critical to avoid disruption of the superspinous/interspinous ligament between C7–T1 and disruptions of the C7–T1 facet capsule.44 A cadaveric study demonstrated that sectioning of the superspinous/ interspinous complex in constructs ending at T1 increased flexibility of C7–T1 level by 35%. Laminectomy of T1 also involves some disruption of the ligamentous complex and it is advocated to cross the CTJ in cases of all thoracic constructs ending at T1 and subsequent T1 laminectomy.

12.7 FDA Approval Lateral mass screws are not FDA approved.

12.8 Summary The anatomy and biomechanics of the CTJ can predispose to instrumentation failure. Careful surgical planning is needed

when deciding to cross the CTJ. Consideration should be given to anterior versus posterior versus circumferential approach as well as what type of instrumentation and rod to use. Biomechanical studies indicate a domino side-to-side construct or transitional rod construct to be stable. Radiographic and CT imaging can be used in the planning of an anterior approach. The low Smith–Robinson approach is by far the less risker and less morbid approach.

12.9 Future Directions Translaminar screws are being used frequently at C2.45,46 Biomechanical and anatomic studies have evaluated the use of translaminar screws in the subaxial spine, C7, and the upper thoracic spine.47,48 Using CT scans of 72 patients, anatomic parameters of C7 were calculated. Mean laminar thickness was 5.7 mm (3.2–8.8) and mean laminar length was 25.5 mm (18.5–32.2). Spinolaminar angle was 51.3 degrees. Biomechanical cadaveric testing from this same study noted C7 laminar screw pullout strength to be 610N and 666N for C7 pedicle screws with no statistical significance (p = 0.6).48 In a CT-based simulation of C3–C7 laminar screw placement, C7 laminar screws had the highest success rate at 91.4% unilaterally and 68.8% bilaterally.49 The success rate of unilateral laminar screw placement for C6 was 31.9 and 8.8% bilaterally. A cadaveric study of two- and three-injury model of C7–T1 evaluated the use of translaminar screws at T1 and T2.47 Pedicle screws (4.0 mm × 26 mm) at T1 and T2 were compared against the translaminar screws (3.5 mm × 26 mm) and found to have no difference in flexibility following two-column injury. Following three-column injury, increased flexibility with the translaminar screws was noted. However, after anterior column support with anterior cervical discectomy and fusion (ACDF), the translaminar screws and pedicle screws had no difference in flexibility. The advantage of the translaminar screws over

Fig. 12.4 A 73-year-old man with renal cell metastasis to T1. (a) Sagittal CT demonstrating the lesion (arrow); (b) Sagittal MRI STIR sequence demonstrating lesion at T1 with some epidural extension. (c) The patient was managed with C5– T4 posterior spinal fusion with C7 and T1 laminectomy. Dominoes were used to connect the cervical 3.5-mm rod to the thoracic 5.5-mm rod. (d) At 8 months postoperatively, the patient had cervical rod pull out from the domino (arrow). (e) CT confirmed the failure was at the cervico–domino junction on the right. The patient elected nonoperative management because his renal cell metastasis had progressed and he was seeking hospice care.

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Fig. 12.5 A 73-year-old man with cervical spondylotic myelopathy secondary to multilevel foraminal C4–T1 stenosis and C7–T1 spondylolisthesis. (a) Sagittal CT myelogram demonstrates spondylolisthesis at C7–T1 and severe stenosis at this level. (b) Lateral radiograph demonstrating the patient’s C4–T1 posterior cervical fusion with a 3.5-mm rod. No screws were placed at C7. (c) One month postoperatively, radiograph demonstrated the patient had pullout of the T1 screws. (d) Sagittal CT demonstrated worsening spondylolisthesis as well as (e) 3D CT. (f) The patient underwent anterior spinal fusion C6–T1, removal of T1 screws, and extension of instrumentation and fusion to T3. End-to-end connectors were used to link the cervical rod (3.5 mm) to the thoracic rod (5.5 mm). Seven years postoperatively, the patient is doing well with no changes in his instrumentation.

pedicle screws in the upper thoracic spine is the easier placement. Few clinical studies have evaluated subaxial cervical spine and C7 laminar screw constructs. The start points and placement of these screws would be technically easier than the current pedicle screws of the subaxial spine.50,51,52 In clinical studies, the translaminar screws were useful for salvage situations after standard screw failure. With more clinical data and long-term follow-up, there may be a role for the translaminar screws at C7, T1, and T2 in the spine surgeons’ arsenal.

12.10 Key Points ●

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●

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Meticulous surgical planning, including taking into account the patient’s bone mineral density, is critical to avoid instrumentation failure across the CTJ. Biomechanical studies indicate a 3.5-mm rod used to cross the CTJ provides a weaker construct compared to domino construct or a translational rod. During surgical planning for the anterior approach to the CTJ. the location of the clavicle should be studied in order to potentially avoid a clavicle or manubrium-splitting approach. If there is spondylolisthesis at C7–T1, one should plan for a long construct ending at T2 or T3 so as to avoid pedicle screw back out. Future investigations on the role of the translaminar screws at C7 and upper thoracic spine may provide additional points of fixation for the CTJ.

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[36] Rubery PT, Bukata SV. Teriparatide may accelerate healing in delayed unions of type III odontoid fractures: a report of 3 cases. J Spinal Disord Tech. 2010; 23(2):151–155 [37] Boockvar JA, Philips MF, Telfeian AE, O’Rourke DM, Marcotte PJ. Results and risk factors for anterior cervicothoracic junction surgery. J Neurosurg. 2001; 94(1) Suppl:12–17 [38] Arlet V, Aebi M. Junctional spinal disorders in operated adult spinal deformities: present understanding and future perspectives. Eur Spine J. 2013; 22 Suppl 2:S276–S295 [39] Ponnusamy KE, Iyer S, Gupta G, Khanna AJ. Instrumentation of the osteoporotic spine: biomechanical and clinical considerations. Spine J. 2011; 11 (1):54–63 [40] Jo JY, Kang SH, Park SW. Modified polymethylmethacrylate cervical plate and screw augmentation technique for intraoperative screw loosening. J Spinal Disord Tech. 2012; 25(4):235–239 [41] Masala S, Anselmetti GC, Muto M, Mammucari M, Volpi T, Simonetti G. Percutaneous vertebroplasty relieves pain in metastatic cervical fractures. Clin Orthop Relat Res. 2011; 469(3):715–722 [42] Dean CL, Gabriel JP, Cassinelli EH, Bolesta MJ, Bohlman HH. Degenerative spondylolisthesis of the cervical spine: analysis of 58 patients treated with anterior cervical decompression and fusion. Spine J. 2009; 9(6):439–446 [43] Jiang SD, Jiang LS, Dai LY. Degenerative cervical spondylolisthesis: a systematic review. Int Orthop. 2011; 35(6):869–875 [44] Kretzer RM, Hu N, Umekoji H, et al. The effect of spinal instrumentation on kinematics at the cervicothoracic junction: emphasis on soft-tissue response in an in vitro human cadaveric model. J Neurosurg Spine. 2010; 13(4):435–442 [45] Wright NM. Posterior C2 fixation using bilateral, crossing C2 laminar screws: case series and technical note. J Spinal Disord Tech. 2004; 17(2):158–162 [46] Dorward IG, Wright NM. Seven years of experience with C2 translaminar screw fixation: clinical series and review of the literature. Neurosurgery. 2011; 68(6):1491–1499, discussion 1499 [47] Kretzer RM, Hu N, Kikkawa J, et al. Surgical management of two- versus three-column injuries of the cervicothoracic junction: biomechanical comparison of translaminar screw and pedicle screw fixation using a cadaveric model. Spine. 2010; 35(19):E948–E954 [48] Ilgenfritz RM, Gandhi AA, Fredericks DC, Grosland NM, Smucker JD. Considerations for the use of C7 crossing laminar screws in subaxial and cervicothoracic instrumentation. Spine (Phila Pa 1976). 2013; 38(4):E199–E204 [49] Shin SI, Yeom JS, Kim HJ, Chang BS, Lee CK, Riew KD. The feasibility of laminar screw placement in the subaxial spine: analysis using 215 three-dimensional computed tomography scans and simulation software. Spine J. 2012; 12 (7):577–584 [50] Hong JT, Sung JH, Son BC, Lee SW, Park CK. Significance of laminar screw fixation in the subaxial cervical spine. Spine. 2008; 33(16):1739–1743 [51] Hong JT, Yi JS, Kim JT, Ji C, Ryu KS, Park CK. Clinical and radiologic outcome of laminar screw at C2 and C7 for posterior instrumentation—review of 25 cases and comparison of C2 and C7 intralaminar screw fixation. World Neurosurg. 2010; 73(2):112–118, discussion e15 [52] Chamoun RB, Relyea KM, Johnson KK, et al. Use of axial and subaxial translaminar screw fixation in the management of upper cervical spinal instability in a series of 7 children. Neurosurgery. 2009; 64(4):734–739, discussion 739

Anterior C1–C2 Fusion Instrumentation Complications

13 Anterior C1–C2 Fusion Instrumentation Complications Jesse E. Bible and Clinton J. Devin

13.1 Indications Instability involving the C1–C2 segment is frequently tackled using posterior instrumentation, most notably C1 lateral mass and C2 pedicle screws. However, in certain situations, anterior C1–C2 instrumentation may be indicated. These include fractures with incompetent posterior elements, odontoid nonunions, need for a salvage technique following a failed posterior C1–C2 arthrodesis, or patients who cannot tolerate prone positioning due to pulmonary compromise. In the setting of rheumatoid arthritis, anterior instrumentation allows for a single-stage odontoid decompression and stabilization while avoiding posterior surgery. Although an anterior approach to the C1–C2 segment has the advantage of avoiding the morbidity of the posterior approach, it holds its own risk of potential complications. Either an anterior or lateral retropharyngeal approach may be used. Once the C1–C2 segment is visualized, two options exist for anterior instrumentation—transarticular screws and, less commonly, anterior plating.

13.2 Preoperative Evaluation, Patient Positioning, and Operative Setup Preoperative imaging should include computed tomography (CT) for assessing bony anatomy and measuring screw length. Some form of angiography (CT or magnetic resonance angiography) is also warranted at this level to assess the course and patency of the vertebral arteries. The patient is placed supine on a radiolucent table. Fiberoptic nasotracheal intubation is then performed, and dental occlusion maintained throughout the case so not to limit the area of dissection. Intraoperative neurophysiologic monitoring should then be started and continued throughout the case, including somatosensory-evoked potentials and transcranial motorevoked potentials, as well as cranial nerve/electromyography monitoring during exposure of the upper cervical region. Halo or Gardner-Wells traction can then be placed if needed for preoperative reduction and/or intraoperative traction. If not

prohibited by gross instability, the neck should be extended and rotated to the side opposite the approach. However, unlike the subaxial cervical spine, it is imperative to place the head back in neutral prior to fixation placement. Biplanar fluoroscopy can be set up proximally before draping the patient. Finally, the availability of otolaryngology/general surgery colleagues should be verified in case a prophylactic tracheotomy is needed postoperatively, if significant retropharyngeal dissection occurs.

13.2.1 Surgical Approaches Transoral Transpharyngeal Approach The transoral route provides a direct midline approach for the decompression of midline disease from the low clivus to C2. However, due to the contaminated nature of this surgical corridor, the use of instrumentation placement via this approach is not advised. Furthermore, it cannot be extended inferiorly without splitting the mandible and tongue.

Anterior Retropharyngeal Approach In 1957, Southwick and Robinson originally described the anterior retropharyngeal approach to expose C3–T1,1 and later de Andrade and Macnab described a cranial extension permitting access to C1–C2.2 Further modification has included resection of the submandibular gland and transection of the diagnostic muscle if more proximal superior is needed.3 Although technically more difficult than lateral or posterior approaches, the anterior approach is commonly favored, as it provides midline exposure and thus allows for a familiar orientation for the surgeon, and if needed, strut graft placement. Vaccaro et al presented a case of a nonunited posterior atlantoaxial fusion revised using an anterior C1–C2 transarticular screw. This study provides an excellent step-by-step outline for the anterior retropharyngeal approach and retrograde transarticular fixation.4,5 The approach utilizes an incision placed 2 to 4 cm below the angle of mandible in a curvilinear fashion from 2 cm lateral of midline to the middle of the sternocleidomastoid (SCM) muscle (▶ Fig. 13.1a). An incision placed more than 2 cm caudal to the

Fig. 13.1 (a) Incision placement for the anterior and (b) lateral retropharyngeal approaches.

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Cranial mandible lessens the risk of injury to the marginal mandibular branch of the facial nerve. Next, the greater auricular nerve and external jugular vein are identified overlying the SCM muscle and retracted posterior with the SCM muscle after dissecting through the medial edge of its investing fascia. The facial vein is then identified and ligated. Further cephalad dissection remains deep to this transected vein, thereby preserving the marginal mandibular nerve branch. In the study of Batra et al, 50 facial halves were dissected out to investigate the branches of the facial nerve. The marginal mandibular branch of the facial nerve was found superficial to the facial artery and vein in all specimens.6 The carotid sheath is palpated laterally and any arterial and venous branches (superior thyroid, lingual, facial) identified and, if needed, ligated for adequate exposure. Caution is advised during this step, as the superior laryngeal nerve coming from the vagus nerve runs inferomedially immediately deep to these vascular branches. The nerve should be identified and preserved. Finger dissection is then used to open the retropharyngeal space between the esophagus and prevertebral fascia, exposing the C1 tubercle with longus colli muscle attachments.

compressing a relatively small joint. Lapsiwala et al conducted biomechanical studies comparing several C1 to C2 fixation techniques including intralaminar screws, anterior transarticular screws, posterior transarticular screws, and C1–C2 pedicle screws, and found anterior transarticular screws to be as stable as posterior screws. 8,9 Anterior screws hold a potentially decreased risk of vertebral artery injury, as the starting point is closer to the vertebral artery foramen, allowing the path of the screw to be controlled more easily. Furthermore, in a study by Xu et al, using a 3.5-mm screw, anterior screw trajectories were found to pose less anatomic risks of vertebral artery injury than posterior screw trajectories, based on three-dimensional (3D) imaging measurements of C2. This study compared the anatomic risk of vertebral artery injury between percutaneous anterior and posterior transarticular screws using 3D-CT imaging to measure the C2 isthmus and the distance from the medial-most superior facet to the edge of vertebral artery groove of C2. From a anatomic perspective, anterior screw placement poses less risk of vertebral artery injury than posterior screw placement.10

Lateral Retropharyngeal Approach

Technique

In 1966, Whitesides and Kelly described a lateral retropharyngeal approach, going posterior to the carotid sheath, thereby eliminating the need to dissect the superior laryngeal nerve and external carotid vessels.7 However, besides being unfamiliar to most spine surgeons, this approach can place the ipsilateral vertebral artery at greater risk compared to the anterior approach. Prior to incision, the earlobe is taped or sewn anterior to facilitate exposure of the field. A hockey-stick incision is made from the tip of the mastoid process and base of the earlobe, extending caudally along the anterior border of the SCM muscle (▶ Fig. 13.1b). The platysma is divided in a parallel fashion to the skin incision. The greater auricular nerve is then identified and dissected free from the soft tissues overlying the SCM muscle. The neighboring external jugular vein can be ligated. Approximately 3 cm caudal to the mastoid tip, the spinal accessory nerve is identified penetrating the SCM muscle. Once the nerve has been identified and dissected from the internal jugular vein, the SCM muscle can be detached from the mastoid tip, leaving a fascial cuff for later reattachment. During eversion of the muscle, the SCM branches of the occipital artery are ligated. Further dissection proceeds posterior to the carotid sheath and anterior to the spinal accessory nerve and SCM muscle. Dissection continues following along the anterior border of the transverse processes until the prominent C1 anterior tubercle and C2 lateral masses are palpated. Longus colli muscles are then subperiosteally dissected from medial to lateral, and, if necessary, detached from their origin on C1, leaving the C1–C2 intertransverse membrane intact. For bilateral transarticular screws, the same approach is also performed on the contralateral side.

Once both C1 and C2 articulations are exposed, a curved curette and angled bur are used to remove the articular cartilage before placing the morselized iliac crest bone graft. Transarticular screws are then placed using either a caudal (antegrade) trajectory starting from C1 or a cephalad (retrograde) trajectory from C2. For the antegrade technique, a 2.0-mm guidewire is inserted at the anterior base of the C1 transverse process with a trajectory of 25 degrees superolateral to inferomedial in the coronal plane and 10 degrees in the sagittal plane (▶ Fig. 13.2a). Correct wire placement should be confirmed using biplanar fluoroscopy. Drilling should then be performed with a lag technique using a 3.5-mm cannulated drill through the C1 lateral mass followed by a 2.7-mm cannulated drill through C2 (▶ Fig. 13.2b). After a 3.5-mm tap is used, a 3.5-mm cannulated screw of predetermined length, based on preoperative CT imaging, is inserted. A good reference for an average adult is 26 mm. The retrograde technique involves placing the guidewire at the midbody of C2 in the superior and interior plane and at the base or just lateral to the sulcus at the edge of the C2 body and lateral mass in the medial to lateral plane. Trajectory should be perpendicular to the C2–C1 articulation with an aim of approximate 25 degrees posterior in the sagittal plane and 20 to 30 degrees in the coronal plane, remembering that the vertebral artery is lateral to the distal guidewire (▶ Fig. 13.3). Drilling is also done using a lag technique with 3.5-mm drill through C2 and 2.7-mm drill through C1. Similar to antegrade screws, a 26mm screw is a good reference length, to compare with preoperative imaging.

13.3 Instrumentation 13.3.1 Transarticular Screws Similar to the Magerl’s technique for posterior transarticular screws, anterior screws rely on central screw placement

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13.3.2 Anterior Plating Although transarticular screws are the more frequently discussed anterior C1–C2 method of fixation, anterior plating remains an option. This becomes especially pertinent when a patient’s anatomy, as assessed on preoperative axial imaging with sagittal reconstructions, does not allow for the placement

Anterior C1–C2 Fusion Instrumentation Complications

Fig. 13.2 (a) Guidewire starting point and trajectory for antegrade C1–C2 transarticular screw placement, (b) followed by drilling and screw placement using a lag technique with a 3.5-mm then 2.7 cannulated drill.

of transarticular screws and posterior fixation is not an option. Although some biomechanical studies report inferior mechanical stiffness of plate fixation compared to other C1–C2 fixation methods, nonlocking plates were utilized, thereby affecting the construct’s biomechanical stability.11 In 2002, Kandziora et al found atlantoaxial locking plates significantly improved stability compared to previous fixation devices and methods. This biomechanical study compared four different anterior plate constructs for C1–C2 fusion. It found that C1–C2 locking plates provided significantly superior stability compared to the other three nonlocking constructs, including transpedicular plate fixation.12

Technique If a plating technique is planned, an anterior approach should be utilized, providing midline exposure of the C1–C2 segment. Decortication of the C1–C2 articulations is done using curette and/or bur prior to morselized autograft placement. Specially designed T-shaped plates are used allowing screw placement in the lateral masses of C1 bilaterally and into the body of C2. All screws should be placed in a unicortical fashion with screw lengths determined using preoperative axial imaging. For the C1 screw trajectory in the axial plane, it should be remembered that the vertebral artery lays just lateral to the C1 lateral mass.

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Fig. 13.3 (a) Guidewire and (b) screw placement for retrograde C1–C2 transarticular screw placement.

13.4 Complications 13.4.1 Nerve Injury Great Auricular Nerve It can be injured during either the anterior or lateral retropharyngeal approaches. This results in a small deficit around the ear.

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superficial to the vein.6 Therefore, developing the plane of dissection deep to this vein helps preserve the marginal mandibular branch during cephalad dissection. Excessive superior retraction near the parotid gland can also lead to injury to this branch along with other facial nerve branches. If the marginal mandibular branch is damaged, it results in an asymmetrical smile with elevation of the lower lip on the affected side, as it normally supplies muscles of the lower lip and chin.

Marginal Mandibular Branch of the Facial Nerve

Superior Laryngeal Nerve

It can be encountered in anterior approach, especially if the incision and superficial dissection are performed less than 2 cm from the angle of mandible. The facial vein is a key landmark after its identification and ligation, given that the nerve lies

This important nerve is seen in the anterior approach, as it courses medially from its origin at the inferior ganglion of the vagus nerve (nodose ganglion) in close proximity to the superior thyroid artery and vein. The external branch lies

Anterior C1–C2 Fusion Instrumentation Complications just posterior to these vessels at the level of hyoid, while the internal branch courses obliquely just inferior to the genu of the hyoid, piercing the thyrohyoid membrane at approximately the C3–C4 segment. Damage to the external branch, which innervates the cricothyroid muscle, results in increased voice fatigability and loss of high-pitched tone. Damage to the internal branch, which supplies sensory innervation to the supraglottic region, leads to laryngeal anesthesia and reduced cough reflex, predisposing a patient to aspiration pneumonia.

Spinal Accessory Nerve In the lateral approach, this nerve is found approximately 3 cm distal to the mastoid tip penetrating the SCM muscle. It should be freed from any adhesions to the internal jugular vein and dissected proximally up to jugular foramen, thereby allowing it to be retracted posterior with the SCM muscle, while the carotid sheath is retracted anterior. If damaged, this causes diminished or absent function of the ipsilateral SCM and trapezius muscles.

Hypoglossal Nerve During the anterior approach, this nerve lies at the superior extent of the exposure and in close relation to the digastric tendon, lying in its most superficial location at this point. Aggressive superior retraction of the digastric muscle can also injure the nerve. If injured, it leads to an ipsilateral curvature of the tongue and slurring of speech.

13.4.2 Esophagus/Hypopharynx Injury Esophageal perforation is a rare, but devastating, complication if left unrecognized. To help avoid and identify an injury, preoperative placement of a nasogastric tube can allow intraoperative palpation and identification of the esophagus. If injury is suspected intraoperatively, the tip of the tube should be withdrawn just proximal to the suspected injury. Diluted methylene blue is then placed down the tube (~ 60 m) and the wound checked for egressing blue fluid. If no evidence of perforation is seen but still strongly suspected, intraoperative esophagoscopy by otolaryngologist is warranted, given the high morbidity and mortality if left untreated. Once identified, the defect is closed in two layers and the nasogastric tube left in place for 7 to 10 days, along with parenteral antibiotics against anaerobic bacteria administered.

13.4.3 Vertebral Artery Injury The vertebral artery is most at risk when using the lateral approach and during instrumentation. Using the lateral approach, dissection remains on the anterior portion of the transverse process of C1 and C2. For transarticular screw placement, axial imaging must to meticulously reviewed for any medialization of the artery at C2, which would prevent such a technique. For plate placement, the lateral C1 screws should be placed in a near direct anterior to posterior direction on the axial plane and not directed superiorly in the sagittal plane to minimize the risk of vertebral artery injury.

If injury does occur, the site of injury should be packed with Gelfoam or Surgicel to tamponade the bleeding, anesthesia team made aware so that blood products can be ordered, and an intraoperative neurovascular consultation obtained. Further contralateral fixation should be aborted. If the upper cervical spine is unstable at this point, the patient should be placed in halo fixation while the definitive treatment plan is determined.

13.4.4 Fixation Failure Although biomechanical studies have found anterior transarticular screws to limit C1–C2 stiffness as much as posterior C1 lateral mass–C2 pedicle techniques, some concern remains over potential risk of nonunion and hardware failure, given the less bony surface anterior compared to posterior.9 Furthermore, since few T-shaped plates with locking holes have been designed for the cervical spine, nonlocking screws have to commonly be utilized. This hinders the construct’s stability with increased risk of screw pullout during flexion and extension to the point that postoperative halo fixation should be considered. If anterior C1–C2 fixation was chosen due to incompetent posterior elements at this level and it subsequently fails, the definitive salvage procedure is a posterior occipitocervical arthrodesis, spanning the deficient segments with autograft.

13.5 Summary Anterior fixation of the upper cervical spine, transarticular screws and plate fixation, is a useful option when more familiar posterior methods are not an option due to the local anatomy and/or pathology. Many of the potential complications with these techniques are related to the surgical approach and the infrequency of the surgical anatomy in the anterior cervical spine for many spine surgeons. Both the anterior and lateral retropharyngeal approaches each encounter several neurovascular structures that must the identified and preserved.

13.6 Future Directions Currently, T-shaped plates with locking holes specially designed for the cervical spine are very limited. Similar to current anterior cervical discectomy plates for the subaxial spine, the availability of better plates with a wide superior flange for C1 fixation could make anterior plate fixation of the C1–C2 segment a potentially more appealing and stable option.

13.7 Key Points ●

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The C1–C2 segment can be exposed using either a unilateral anterior retropharyngeal approach or bilateral lateral retropharyngeal approach. Given the high-density nature of the upper cervical spine, both hold potential risks to vital nerves by transection and/or excessive traction. The surgeon should remain aware throughout the approach to include the greater auricular nerve, marginal mandibular branch of the facial nerve, superior laryngeal nerve, spinal accessory nerve, and hypoglossal nerves. No matter if transarticular screws are placed using an antegrade or retrograde technique, particular attention should be

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●

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given to the location of the vertebral artery on axial sequences. If the transarticular screws are not anatomically feasible in a patient due to restricted bony anatomy or body habitus, anterior plate fixation with locking screws is a potential option with close attention given to the intimate relationship of both C1 screws and vertebral arteries. In the setting of a failed anterior construct and no viable posterior elements at C1–C2, the definitive salvage procedure is a posterior occipitocervical arthrodesis, spanning the deficient segments with autograft.

References [1] Southwick WO, Robinson RA. Surgical approaches to the vertebral bodies in the cervical and lumbar regions. J Bone Joint Surg Am. 1957; 39-A(3):631–644 [2] de Andrade JR, Macnab I. Anterior occipito-cervical fusion using an extrapharyngeal exposure. J Bone Joint Surg Am. 1969; 51(8):1621–1626 [3] McAfee PC, Bohlman HH, Riley LH, Jr, Robinson RA, Southwick WO, Nachlas NE. The anterior retropharyngeal approach to the upper part of the cervical spine. J Bone Joint Surg Am. 1987; 69(9):1371–1383

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[4] Laus M, Pignatti G, Malaguti MC, Alfonso C, Zappoli FA, Giunti A. Anterior extraoral surgery to the upper cervical spine. Spine. 1996; 21(14):1687–1693 [5] Vaccaro AR, Lehman AP, Ahlgren BD, Garfin SR. Anterior C1-C2 screw fixation and bony fusion through an anterior retropharyngeal approach. Orthopedics. 1999; 22(12):1165–1170 [6] Batra AP, Mahajan A, Gupta K. Marginal mandibular branch of the facial nerve: An anatomical study. Indian J Plast Surg. 2010; 43(1):60–64 [7] Whitesides TE, Jr, Kelly RP. Lateral approach to the upper cervical spine for anterior fusion. South Med J. 1966; 59(8):879–883 [8] Sen MK, Steffen T, Beckman L, Tsantrizos A, Reindl R, Aebi M. Atlantoaxial fusion using anterior transarticular screw fixation of C1-C2: technical innovation and biomechanical study. Eur Spine J. 2005; 14(5):512–518 [9] Lapsiwala SB, Anderson PA, Oza A, Resnick DK. Biomechanical comparison of four C1 to C2 rigid fixative techniques: anterior transarticular, posterior transarticular, C1 to C2 pedicle, and C1 to C2 intralaminar screws. Neurosurgery. 2006; 58(3):516–521, discussion 516–521 [10] Xu H, Chi YL, Wang XY, et al. Comparison of the anatomic risk for vertebral artery injury associated with percutaneous atlantoaxial anterior and posterior transarticular screws. Spine J. 2012; 12(8):656–662 [11] Kim SM, Lim TJ, Paterno J, et al. Biomechanical comparison of anterior and posterior stabilization methods in atlantoaxial instability. J Neurosurg. 2004; 100(3) Suppl Spine:277–283 [12] Kandziora F, Pflugmacher R, Ludwig K, Duda G, Mittlmeier T, Haas NP. Biomechanical comparison of four anterior atlantoaxial plate systems. J Neurosurg. 2002; 96(3) Suppl:313–320

Complications of Odontoid Fracture Treatment

14 Complications of Odontoid Fracture Treatment Steven Presciutti, Brian Tinsley, and Isaac Moss

14.1 Introduction The overall incidence of odontoid fractures ranges from 7 to 14% of all cervical fractures. As with most upper cervical spine injuries, they occur in a bimodal age distribution and are usually the result of falls or motor vehicle collisions. Fracture of the odontoid process can be highly unstable and may result in significant neurologic injury due to its proximity to the brainstem and spinal cord. Approximately 25 to 40% of fractures are estimated to be immediately fatal.1 Among survivors, failure of the fracture to unite is frequently associated with progressive neurological deficits.2 As a result of their significant potential for neurologic injury and difficulty achieving reliable union, perhaps no other injury of the upper cervical spine has generated as much controversy as fractures of the odontoid process. Although many classification schemes exist for odontoid fractures, the most commonly used system is that of Anderson and D’Alonzo (▶ Fig. 14.1).3 A type I fracture is an oblique fracture of the cranial one-third of the odontoid process, most likely representing an avulsion of the alar and/or apical ligaments. Type II injuries are fractures involving the base of the dens, where it meets the body of C2. A type III fracture extends into the cancellous portion of the body of C2 and usually involves one or both of the superior articular processes. Appreciating the variability in the pattern of type II fractures, Grauer and colleagues4 proposed a modification to address these variables present in type II fractures. Three subtypes of type II fractures were described to further stratify fracture pattern (▶ Fig. 14.2). Type IIA fractures are classified as having a transverse pattern with less than 1 mm of displacement. Type IIB fractures have an oblique pattern, extending from the anterosuperior to the posteroinferior portion of the dens. Type IIIC fractures have the opposite oblique pattern beginning anteroinferiorly and extending posterosuperiorly. These may be associated with significant anterior comminution, which has been postulated to signify involvement of the stabilizing ligaments and thus make for a more difficult reduction.5 The distinction between IIB and IIC fractures in terms of fracture orientation is important, as it has implications in the selection of appropriate fixation techniques. The pattern in IIB fractures is perpendicular to the trajectory of an anterior screw, thus making this pattern amenable to achieving compression across the fracture site upon placement of such a screw. A type IIC is analogous to a reverse obliquity fracture in the intertrochanteric region of the

hip femur and is not amenable to anterior screw placement, given the fracture orientation is parallel to the trajectory of the screw. These are generally not amenable to reduction and fixation with an anterior screw and necessitate posterior fixation. Treatment is guided by the type of odontoid fracture and the specific fracture orientation. Most type I fractures can be treated nonoperatively with a cervical collar. By definition, however, the avulsion fracture that makes up a type I indicates that at least one of the two alar ligaments is incompetent. The alar ligaments are important in maintaining craniocervical stability, and thus these type I injuries may be associated with occipitoatlantal instability.6 These fractures are deemed to be stable when at least one alar ligament and the transverse atlantal ligament are intact. In the case of unstable type I fractures, occiput to C2 fusion may be considered. Regardless of how type I fractures are treated, however, it has been shown that there is a very low rate of nonunion.7 After 3 months of immobilization, flexion and extension radiographs are taken to assess for healing and residual ligamentous instability. In general, type III fractures have a better prognosis because the fracture occurs in a large bony contact area with an adequate vascular supply. Historically, these injuries have been treated with a variety of surgical and nonsurgical approaches. In the modern era, however, much of the recent analysis has demonstrated acceptable healing with nonoperative treatment. Multiple recent publications containing data for type III odontoid fractures treated with either cervical collar or cervicothoracic brace show, on average, an 8% rate of nonunion.8,9,10,11 Type II odontoid fractures are the most problematic type. The overall nonunion rate for type II fractures is reported to be about 32%.12 As is the case with fractures elsewhere in the body, odontoid fracture healing in large part depends on a good reduction and subsequent stabilization. Stability is an important concept in these fractures and there is an increased nonunion rate associated with unstable fractures. This is defined as greater than 5 mm of displacement, angulation greater than 10 degrees, and posterior displacement.13 Hadley et al showed a 78% nonunion rate for type II fractures displaced more than 6 mm in comparison with a 10% nonunion rate when the displacement was less than 6 mm.14 This chapter focuses on the complications of odontoid fixation, and since most type I fractures are uncommonly treated operatively in the modern era, the fixation options discussed in the remainder of the chapter primarily pertain to addressing significantly displaced or angulated type II and III fractures.

Fig. 14.1 Anderson and D'Alonzo’s classification of odontoid fractures, types I, II, and III. (Reproduced with permission from Anderson and D’Alonzo.3)

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Fig. 14.2 The Grauer subclassification of type II odontoid fractures. Type IIA injuries demonstrate a transverse fracture pattern and displacement of < 1 mm. Type IIB injuries have an oblique fracture pattern extending from the anterosuperior to the posteroinferior portion of the dens. Type IIC fractures begin from anteroinferior and extend to posterosuperior. These may be associated with significant anterior comminution. (Redrawn with permission from Grauer et al.4)

Many studies in the literature include type III fractures alongside type II, and thus the following sections will generally consider these together. As mentioned previously, unstable type I fractures are typically treated with occiput–C2 fusion, which is addressed elsewhere in this book. The most common surgical treatment of type II and III odontoid fractures is posterior C1–C2 stabilization. Recently, the use of anterior screw fixation for type II fractures has become more popular. A posterior C1–C2 fusion theoretically decreases cervical rotation by as much as 50%, whereas anterior screw fixation does not immobilize the C1–C2 complex and thus theoretically preserves axial rotation. We will review the complications associated with both anterior and posterior fixation options, but will first briefly discuss the

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complications associated with nonoperative management of these fractures.

14.2 Nonoperative Management 14.2.1 Nonrigid Immobilization Nonoperative management of these injuries is an appealing option, given that it avoids any surgery-related complications and allows for early mobilization. While not common, there are many proponents for the use of nonrigid immobilization (i.e., hard cervical collars) in the treatment of odontoid fractures. Perhaps the biggest trade-off of nonoperative treatment of these injuries, however, is a higher risk of nonunion. Much

Complications of Odontoid Fracture Treatment controversy exists, however, around how clinically relevant this complication actually is. Ryan and Taylor9 reported on 29 patients with type II fractures treated with external immobilization ranging from hard collar to halo vest. They reported a very high nonunion rate of 77%, although no evidence of late neurological deterioration was evident on final follow-up. The authors mentioned that “vigorous attempts to secure both primary union and a sound arthrodesis for nonunion were questionable in the elderly except in unusual circumstances.” They found that myelopathy was a rare consequence of nonunion, and that a good functional outcome in this age group was less dependent on radiographic criteria for union and more dependent on return to pain-free, independent living, regardless of union rate. Likewise, other authors have shown favorable outcomes with the use of cervical collars.15,16,17 They concluded that in the elderly, fibrous union of the odontoid is an adequate goal, and that a hard collar provides sufficient immobilization. Similar results are reported with the use of a hard cervical collar in a younger population as well. In a retrospective analysis, Müller and colleagues11 reviewed 26 patients with acute type II and III fractures treated with a hard collar only. Study inclusion was limited to those fractures that were stable. There were 19 (73.1%) type II and 7 (26.9%) type III fractures. In 10 (38.5%) of these fractures, the odontoid was displaced and/or angulated. The overall complication rate was 11.4% (n = 3). One patient suffered from pulmonary embolism. Two patients (7.7%) with initially minimally displaced fractures had to undergo secondary internal stabilization because of persistent instability. The remaining 20 (77%) fractures healed uneventfully. In four nondisplaced fractures (15%), fibrous union was documented. Three of these patients were older than 65 years. The overall fusion rate was 73.7% for type II and 85.7% for type III fractures. At follow-up, 39% of the patients were free of symptoms; however, the clinical outcome did not correlate with the radiological findings. The authors concluded that stable type II and type III fractures of the odontoid can be successfully treated with nonrigid immobilization, even if they are initially displaced. They recommended a thorough assessment of the stability of the odontoid with lateral flexion/extension views or dynamic fluoroscopy and that nonrigid immobilization may be an option in selected cases with stable injuries. A key distinction for the treating physician to realize is that the odontoid fractures reported in these studies were stable. In unstable fractures, similar acceptable results are not reported and the use of hard cervical collars is not typically recommended. Again, surgeons must exercise caution and carefully evaluate odontoid fractures for stability before choosing hard cervical collars as a treatment choice. The idea of fibrous nonunions being an acceptable outcome is very controversial and is not agreed upon among experts. Other authors have shown that malunion of odontoid fractures can ultimately result in cervical myelopathy and posttraumatic C1–C2 arthrosis.2

14.2.2 Halo Vest Immobilization The halo vest offers an advantage over all other cervical orthosis options due to its ability to limit motion in the upper cervical spine. C1–C2 flexion and extension is limited to 3.4 degrees with the halo vest compared to 8.5 degrees of motion in the

Philadelphia collar (normal 13.4 degrees).18 While this is an important advantage that has demonstrated efficacy in clinical studies, complications of halo vest treatment are not infrequent. Absolute contraindications to halo usage include cranial fracture, infection, and severe soft-tissue injury at the proposed pin sites.19 Awareness of the most commonly seen complications can help minimize their severity and avoid catastrophic sequelae. In a retrospective study by Garfin and colleagues,20 records of 179 patients were reviewed to identify complications related to the use of halo vests. The complications identified included pin loosening in 36% of the patients, pin-site infection in 20%, pressure sores in 11%, nerve injury in 2%, dural penetration in 1%, dysphagia in 2%, cosmetically disfiguring scars in 9%, and severe pin discomfort in 18%. Of the 716 pins used, 180 (25%) pins became loose at least once, and an infection developed at 67 pin sites (9%). Two-thirds of the pins that were loose or associated with infection were required to be changed or removed. The authors concluded that these complication rates, particularly those of pin loosening and infection, are exceedingly high. Similarly, Glaser et al21 performed a retrospective review of 245 patients treated by halo vest. No patient developed or suffered progression of a neurological deficit while immobilized. Complications included pneumonia causing death (one patient); loss of reduction or progression of the spinal deformity (23 patients); spinal instability following immobilization for 3 months (24 patients); pin-site infection (13 patients); and cerebrospinal fluid leakage from a halo pin-site (one patient). Other authors have not found such high complication rates with the use of halo vests. Ekong and colleagues22 reported on 22 patients with odontoid fractures that were treated by immobilization in a halo vest. Complications related directly to the halo vest included scalp infection (four patients), parietal bone osteomyelitis (one patient), pressure sores (one patient), and loosening of the halo pins (three patients). Similarly, in a consecutive series of patients with unstable cervical spine injuries treated with halo vest, Lind et al23 reported that the halo vest was well tolerated in all patients and that it assured a high percentage of healing. While pin-site problems are certainly the most common complication associated with the use of halo vests, they do not appear to have a substantial effect on final outcomes. Daentzer and Flörkemeier24 reported that seven out of nine patients with pin infection were cured with oral antibiotics and none led to failure. In their cases, pin-site problems were not directly related to the unfavorable outcome. They asserted that the increased risk for nonunion are more likely to depend on the extent of the fracture, with dislocated bone fragments or wide fracture lines. Meticulous pin-site care with regular cleaning and dressing changes as well as frequent tightening is recommended to decrease complications. Regular screw checkup and regular ambulatory control examinations are also necessary to detect patients with any discomfort under their halo vests. If drainage and erythema continue at a pin site even with aggressive pin care, bacterial cultures should be obtained and appropriate oral antibiotics started. If cellulitis persists, or an abscess forms, the pin should be removed and new pins placed in another location. In severe cases, the patient may require incision and drainage of the abscess with parenteral antibiotics.25

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Cranial Skull and dural penetration by halo pins are rare complications, often precipitated by patients’ falls, and can be a source of significant morbidity. Clinically, the patient may present with a headache, malaise, or visual disturbances if pin penetration has occurred. Radiographs taken tangential to the skull may demonstrate whether pin perforation of the inner table has occurred. Clear cerebrospinal fluid leakage from the pin site is a definitive sign that dural puncture has occurred. In these circumstances, a new pin should be placed in another region and the old pin removed.19 Elevation of the head decreases intracerebral pressure and assists closure of the dural tear. These tears usually heal in 4 to 5 days. If the tear does not heal or an infection is suspected (subdural abscess), axial imaging and formal surgical intervention may be necessary.26 While minor complications related to patient tolerance and pin-site problems are common, it is likely more important to consider the efficacy of halo vest treatment in promoting successful fracture union and satisfactory long-term patient outcomes. Apuzzo et al27 reported on 45 cases of acute type II odontoid fractures. The group consisted of 35 men and 10 women; 24 were between 19 and 40 years of age, and 21 were older than 40 years. Initial evaluation disclosed displacement of the fracture in 17 cases (38%). Following reduction, the initial treatment was posterior fusion in three cases, and halo immobilization in 42 cases. Excluding two deaths within the first week of treatment, 40 cases were available for follow-up analysis. Bone union failed to occur following periods of immobilization ranging from 4 to 6 months in 13 cases (33%). Fibrous union with no evidence of instability was apparent in two cases. Nonunion in displaced fractures was seen in 60%, with a rate of 88% in those displaced more than 4 mm. The rate of nonunion in nondisplaced fractures was 16%. The incidence of displacement during treatment (53 vs. 26%) and nonunion in those displaced (78 vs. 33%) was higher in individuals older than 40 years than in those younger than 40 years. The incidence of nonunion in individuals younger than 40 years with nondisplaced fractures was 12%; it was 25% for individuals older than 40 years. In a prospective study of 144 odontoid fractures reported by the Cervical Spine Research Society,28 there were 96 type II and 48 type III fractures (average age: 43 years). Of the 38 patients with type II fractures treated primarily in a halo vest, only 66% had a successful result, with 7 patients (18%) having nonunions, 3 having malunions, 2 having fracture displacement, and 1 dying before union. Of the 16 patients with type III odontoid fractures treated primarily in a halo vest, 13 (81%) had a successful outcome, with 1 nonunion, 1 fracture displacement, and 1 death, which occurred 1 day after injury due to cardiac arrest. Vieweg and Schultheiss29 reported on a meta-analysis that included 35 relevant studies involving in total 682 patients with 709 different types of injuries to the upper cervical spine treated with immobilization in a halo vest. Studies were analyzed according to the type of injury pattern and in terms of the treatment outcomes following primary treatment with a halo vest. Odontoid fractures comprised 420 of the 709 total injuries of the upper cervical spine. Healing was noted in all isolated odontoid type I fractures, 85% of the isolated odontoid type II fractures, and 67% of the odontoid type II fractures with combined injuries. The isolated odontoid type III fractures had a 97% healing rate. The nonclassifiable odontoid fractures had a

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healing rate of 85%. The author concluded that a halo vest can be used for patients with isolated odontoid type III and type II fractures, with a low dislocation rate. They recommended exercising caution with treating combined injuries that included odontoid type II fractures with a halo vest. Other studies reported better outcomes with the use of halo vests. In a consecutive series of patients with unstable cervical spine injuries treated with halo-vest, Lind et al23 described the complications encountered. The odontoid fracture was reduced by traction and then stabilized with a halo vest for 12 weeks. There were no other serious complications during the treatment. A total of 10 patients were followed up after 2 years. Only one patient had a fracture that failed to unite (type II). Certainly, the reported success rates using a halo vest to achieve bony union in odontoid fractures is quite variable depending on the series. Recently, some of these risk factors for nonunion have come to light. Koivikko et al30 retrospectively identified factors contributing to nonunion in patients treated with halo vest immobilization. Factors that were identified included (1) fracture gap greater than 1 mm, (2) posterior displacement greater than 5 mm, (3) delayed start of treatment (> 4 days), and (4) posterior redisplacement greater than 2 mm. Other risk factors have been identified as well. In a case–control study, Lennarson et al31 defined cases as those with nonunion after halo immobilization and controls as those with successful bony union attained with halo immobilization. The groups were similar with respect to concomitant medical conditions, gender ratios, amount of fracture displacement, direction of fracture displacement, length of hospital stay, and length of follow-up. The authors found age to be a significant factor in outcomes, with the odds ratio indicating that the risk of failure of halo immobilization is 21 times higher in patients 50 years or older. Odontoid fractures in the elderly deserve special consideration. Type II odontoid fractures are the most common cervical spine fracture in patients 65 years of age or older, and these injuries represent the majority of cervical spine fractures in patients older than 80 years.32 They also occur by much lower energy injuries than in the younger population. Taitsman et al33 examined the rate of complications associated with halo immobilization in patients older than 65 years and found a relatively high complication rate, including pin problems (29%), aspiration pneumonia (23%), and significant respiratory compromise or arrest necessitating intubation or tracheostomy and intensive care management (17%). Tashjian and colleagues34 reviewed 78 patients older than 65 years (mean age: 80.7 years) with odontoid fractures. There were 50 type II fractures in their study. Thirty-eight patients were treated with halo vest, while 27 had hard collar and 13 were operated. There was no difference in injury severity score (ISS) or baseline medical conditions. The mortality and morbidity rates in halo vest patients were 42 and 66%, respectively, while that in the surgical patients were 20 and 36%, respectively. This high mortality rate with the use of halo vests in elderly patients has been found by multiple authors. In fact, Majercik et al35 claimed that the use of halo vest in the elderly was similar to a “death sentence.” They retrospectively reviewed the use of the halo vest in elderly patients (n = 418) with cervical spine injuries. In their study, the fracture types were not described. They divided patients into two age-based groups with similar ISS and comorbidities within the

Complications of Odontoid Fracture Treatment subgroups: those older than 66 years and a young group aged 18 to 65 years. They found that following cervical spine trauma, older patients died at nearly four times the rate of their younger counterparts (21 vs. 5%). In addition, older patients with halo vest had a much higher mortality compared to older patients treated with surgery or hard collar (6 and 12%). There are a limited number of studies that have shown much lower rates of complications and mortality, however. In a prospective cohort study of complications associated with halo vest immobilization for cervical spine injuries, Van Middendorp et al36 claimed lower rates of mortality (8%) and pneumonia (4%) among elderly patients. Weller and colleagues37 reported a small series of six patients with odontoid fractures undergoing immobilization in a halo device for 10 to 12 weeks. Interestingly, they reported only one nonunion. This occurred in a 70-year-old woman with a 4-mm posteriorly displaced type II fracture. They also reported that there were no complications in the halo group. Despite these small series with lower complication rates, age greater than 65 years is considered by most to be a relative contraindication to treatment with a halo vest.

14.3 Operative Management In view of the potentially fatal nature of these fractures, operative treatment aims to reestablish stability of the atlantoaxial complex. Treatment priorities should be individualized based on patient age, fracture pattern, associated neurologic deficits, and overall medical condition. Indications for surgical management include an unstable fracture pattern, high risk of nonunion, neurologic deficits, transverse ligament disruption, and contraindication to halo immobilization. There is still debate surrounding operative versus nonoperative approach to odontoid fractures as well as which surgical procedure is most appropriate. Historically, posterior approaches have been used to stabilize type II and some type III odontoid fractures with C1–C2 arthrodesis. Posterior approaches include transarticular screw fixation, C1 lateral mass with C2 pedicle screw fixation, and posterior wiring. Studies of these techniques report high fusion rates; however, C1–C2 motion is lost. The anterior approach spares some motion, but may be associated with a higher overall complication rate. When planning the surgical approach, careful patient selection is necessary to minimize intraoperative and postoperative complications. The overall mortality rate of operatively treated patients older than 65 years has been reported to be 10.1% in a large systematic analysis.38 As the current literature is limited, there is much debate and still no consensus regarding the optimal surgical approach.

14.3.1 Anterior Osteosynthesis Approaching a dens fracture anteriorly allows direct fracture stabilization while preserving motion at C1–C2, reducing neck stiffness and avoiding complications associated with autograft. Overall complications related broadly to the approach include mortality, nonunion, technical failures, and medical complications. Site-specific complications for anterior odontoid screw fixation include nonunion, loss of reduction, screw pullout, airway complications, and medical sequelae from surgery.

Recent studies have demonstrated a union rate of 80.5 to 91% using an anterior odontoid screw,39,40,41 while previous studies have reported union rates ranging from 27 to 92%.42,43 The anterior odontoid screw is indicated for type II odontoid fractures without significant comminution. Additionally, the transverse ligament must be intact in order for the construct to provide adequate stability and the fracture orientation must be such that the screw trajectory is perpendicular in order to achieve compression as opposed to shear at the fracture site. Both single- and double-screw fixation techniques may be used and both clinical and biomechanical evidences suggest that there is no difference in stability or outcome.42,44 In a retrospective clinical study by Arand and colleagues,45 the incidence of complications in 58 consecutive patients with anterior screw fixation was evaluated. Thirty-two patients were treated with single-screw osteosynthesis and 26 patients with a double-screw technique. Significant complications with clinical relevance were registered in 14 patients (24%), and in 10 cases (17%) a reoperation was required. Intraoperatively, one patient sustained a rupture of the carotid artery after winding around the drill. A complete misplacement of the screw posterior to the odontoid process resulting in significant neurologic injury was also observed in another patient. A clearly eccentric positioning of the implant was reported in five patients with a resulting high rate of implant migration in three. Postoperatively, one patient with a wound infection due to an iatrogenic perforation of the esophagus required reoperation as well as four patients with instability because of implant migration. Three patients older than 65 years were significantly overrepresented in that group. Complications without any relevance to the clinical and functional long-term results were malunion of the odontoid process in 14 patients (24%) and marginal screw perforations laterally in 10 patients (17%). While not reaching significance, increasing number of complications in the geriatric cohort was observed. In a retrospective study of 41 patients by Cho and Sung,39 they found that patient age was not a significant predictor of fusion failure. They had an overall fusion rate of 80.5% and a nonunion rate of 12.2%. Importantly, the authors found that when surgery was delayed for more than 1 week, the incidence of fusion failure significantly increased with an increased odds ratio of 37.5. Likewise, a fracture gap of 2 mm or more was found to be significantly associated with fusion failure and a 21 times great chance of fracture nonunion. These two factors should certainly be considered important when considering anterior dens osteosynthesis for these fractures. In contrast, Platzer et al46 found some significant differences in outcomes with respect to patient age. A total of 110 elderly (> 65 years) and younger patients (< 65 years) who received anterior screw fixation for type II odontoid fractures were retrospectively evaluated. They found that 86% of patients returned to their previous activity level, with the remaining patients complaining of some limitations of function, pain symptoms, and reduced cervical spine motion. Six patients had residual neurologic deficits, of which only two had incomplete resolution after conservative management. Successful union was achieved in 96% of younger patients and 88% of older patients. In the younger group, 8% had intraoperative or postoperative complications, while the older group had a 22% complication rate which represents a significant difference. The rate

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Cranial of mortality was also significantly different between the younger group (1%) and the older group (9%). Causes of mortality included cardiac arrest, respiratory failure from pneumonia, and pulmonary embolism. Other studies have also looked at the complications of treating patients older than 65 years. A systematic review of morbidity and mortality after surgical treatment of odontoid fractures evaluated 14 studies of odontoid fracture fixation in the elderly.37 The technical failures described for anterior screw fixation included loosening of screws, implant cutout, inadequate reduction, postoperative loss of reduction, malposition of implants, and perioperative abandoning of approach. The overall rate of technical failure was reported to be 17%; however, specific failure type was not reported. Other rarer complications have also been reported in small case reports. For instance, delayed pharyngeal extrusion of an anterior odontoid screw has been described nearly 3 years after fracture fixation and successful fracture union.47 There have also been case reports of patients who developed an anterior spinal artery pseudoaneurysm associated with delayed subarachnoid hemorrhage after undergoing odontoid screw placement 14 months earlier.48,49 Aside from these more rare complications, age does seem to play an important role in the outcome of treating these injuries with anterior osteosynthesis. Regardless, there are some general techniques and practices that can reduce complication rates despite of the patient’s age. The surgeon should be aware of patients who have a barrel chest and short neck with poor range of motion, as this can make anterior surgical fixation very difficult. It is the authors’ recommendation to use meticulous softtissue handling during these procedures. The use of drill guide and handheld retractors to protect the surrounding soft-tissue structures will significantly decrease the risk of iatrogenic injury to the carotid sheath, recurrent laryngeal nerve, or the esophagus. Injury to the superior laryngeal nerve is also possible with prolonged and aggressive traction of the soft tissues superiorly during screw placement. To minimize these, gentle retraction is a must and it is recommended that intermittent release of retraction is performed when it is not absolutely necessary. In addition, great care must be taken to avoid advancing guidewires, drills, or taps past the cortex of the tip of the

odontoid, or a devastating neurologic injury could occur. This has the greatest chance of occurring when drilling over a guidewire if the cannulated drill binds the wire and inadvertently advances it. Other complications have also been reported with respect to guidewires.50 It is because of this that the authors prefer to use a solid screw technique with judicious use of intraoperative fluoroscopy. Of course, the fracture should be reduced into a position that is as anatomic as possible before attempting fixation. Determining the correct entry point, at the anterior margin of the inferior endplate, is critical. If entry is started more cephalad on the anterior surface of C2, the angle of inclination for fracture fixation often cannot be achieved, and the bone purchase is weaker in this position, which may allow the screw to cut out of or migrate in C2. Poor odontoid purchase with subsequent screw back-out may also occur if the apical cortex of the dens tip is not fully engaged to ensure adequate purchase (▶ Fig. 14.3). This is crucial in order to achieve a lag effect between the fractured odontoid and the body of C2. Prior to wound closure, it is imperative to perform meticulous hemostasis in order to prevent the development of a hematoma. Finally, the patient should be monitored closely during the first postoperative night so that soft-tissue complications, such as breathing abnormalities or inability to clear secretions, can be recognized and acted upon promptly. Mild dysphagia is common secondary to dissection and retraction. The latter can again be minimized using a self-retaining retractor system rather than handheld retractors. Most often, the dysphagia will be mild and usually resolves quickly, but occasionally it can be severe and has been shown to be high in patients older than 70 years.51

14.3.2 Posterior Fusion Posterior C1–C2 fusion can be achieved by a variety of described techniques, including posterior sublaminar wires, C1–C2 transarticular screws, C1 lateral mass and C2 pars instrumentation, and C1 lateral mass with C2 laminar screws. Historically, posterior fusion with C1–C2 sublaminar wiring was the standard surgical fixation for odontoid fractures. Wiring has fallen out of favor with the development of screw fixation techniques, which have better biomechanical stability and a lower nonunion rate.52

Fig. 14.3 A case of an 18-year-old man with an odontoid fracture: (a) One screw went completely through the apical cortex (short arrow), while the other stopped a few millimeters short (longer arrow). That small difference was enough to prevent a firm grip and allow the second screw to back out within 6 weeks of initial surgery (b). (Printed with permission from Apfelbaum RI, Sasso RC. Anterior odontoid fixation. In: Zdeblick T, Albert T, eds., Master Techniques of Orthopaedic Surgery: The Spine. Philadelphia, PA: Lippincott Williams & Wilkins; 2004:75–89.)

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Complications of Odontoid Fracture Treatment Indications for a posterior fusion are similar to those for an anterior fusion; however, a posterior approach is favorable if the transverse ligament is disrupted, comminution is present, the fracture cannot be reduced, or if the obliquity of the fracture is not amenable to anterior screw compression. Furthermore, an obese patient or a patient with significant kyphosis may make anterior screw fixation technically problematic. Surgical stabilization of the C1–C2 joint may also be considered after failure of conservative management of fractures that present with late instability, pain, or myelopathy and in patients in whom external immobilization with a halo vest is contraindicated. In older patients, evidence suggests a lower complication rate after posterior fixation compared to anterior odontoid screw fixation.38

Posterior Wiring There are many techniques described for posterior sublaminar wiring with bone grafting; however, the literature regarding outcomes is limited and consists of mostly small retrospective studies. Nonunion rates vary widely and have been reported ranging from 0 to 25%,53,54,55 although not all of these studies have evaluated a cohort of patients with odontoid fractures. Variation in technique and postoperative care, including prolonged postoperative halo immobilization, make the body of data difficult to compare. Platzer and colleagues53 reported on 19 patients older than 65 years who underwent posterior cervical arthrodesis. In this series, iliac crest autograft was used with sublaminar wiring. There was 100% union in this cohort; however, one death occurred which was excluded from the analysis. There were six patients who had medical complications, including respiratory failure, pneumonia, thromboembolism, and infection. Reported surgical complications included two patients with secondary loss of reduction and one with malpositioned implants. In this series, they reported fewer reoperations and a better union rate in the posterior approach cohort compared to anterior screw fixation. Aside from the risk of nonunion, surgical complications include the risk of a dural tear with wire passage as well as the possibility of spinal cord compression as the wires pass through the central canal. It is also possible to cause a fracture of the posterior arch with tightening of the cables. Over-tightening of midline wires can also theoretically cause narrowing of the foramen with subsequent radiculopathy or even increase fracture displacement (particularly in posteriorly displaced odontoid fractures). These complications can be avoided with the concomitant placement of transarticular screws as well. In addition, posterior wiring in combination with screw fixation reduces flexion extension motion compared to transarticular screws alone.56 In any of these constructs, disruption of the posterior arch of C1 or C2 is a contraindication to posterior wiring.

Posterior Transarticular Screws Posterior C1–C2 transarticular screw fixation is technically more difficult than posterior wiring and requires adequate reduction of C1–C2 prior to screw placement. Transarticular fixation provides improved rotational stability when compared

to posterior wiring alone and unlike posterior wiring, posterior arch disruption does not affect this construct. With this technique, screw malpositioning can lead to vertebral artery injury. The risk for vertebral artery injury becomes even higher in patients who have an anomalous vertebral artery and preoperative advanced imaging should be carefully scrutinized for such an anomalous course. There is also an increased risk of vertebral artery injury when there is fixed anterior subluxation of C1 relative to C2 with this technique.57 Transarticular screw fixation for C1–C2 fusion has reported nonunion rates ranging from 0 to 15%,58,59,60 although these studies mix patients with atlantoaxial instability due to multiple causes, making these data problematic to generalize. While injury to the vertebral artery can occur, larger studies demonstrated that the incidence is low. In a retrospective study of 56 patients with C1–C2 transarticular screw placement, screw position was evaluated and the series reported 69.4% screw perforation of the anterior cortex of C1.61 The authors reported no cases of vertebral artery injury, spinal cord injury, or nerve root injury.61 In a survey that included 1,318 patients, the incidence of vertebral artery injury was reported to be 2.4%.62 Other retrospective studies have reported vertebral artery injury rates from 2 to 4%.63,64 Technical considerations when using transarticular screws must include evaluation of the anatomy to predict potential risk to the vertebral arteries as well as difficulty with screw placement. Intraoperatively, adequate reduction and image guidance must be obtained to reduce the possibility of screw malposition.

C1–C2 Posterior Screw–Rod Fixation Providing even further construct rigidity and higher fusion rates than wiring or transarticular screws, a C1–C2 fusion can also be achieved by using rods to connect C1 lateral mass screws and C2 screws to stabilize the atlantoaxial joint. This technique allows screw placement prior to fracture reduction, and has a potentially lower risk of vascular injury compared to transarticular fixation. The modern technique, originally described by Harms and Melcher in a series of 37 patients, reported 100% fusion with no vertebral artery injuries, dural tears, or subsequent neurologic complications and no need for halo immobilization.65 They reported one wound infection requiring reoperation as well as one death in an elderly patient 6 months after surgery due to pneumonia. The most common indication for surgery is a displaced odontoid fracture in a patient where direct anterior screw fixation is not feasible or is a poor choice. Other indications include less common injury patterns (i.e., displaced fractures of C1, C2, and/ or ligamentous instability). Contraindications are primarily those related to patient factors and inability to tolerate general anesthesia. Fractures with severe comminution of the lateral masses of C1 or C2 are also contraindications of this technique. In some patients, a severe deformity or erosions caused by inflammatory disorders such as rheumatoid arthritis distort the anatomy. Great care must be taken when anatomic landmarks for screw fixation are lost. Similar to the original study by Harms and Melcher, other authors have reported series using this technique without vascular injury. Ringel and colleagues66 evaluated 35 consecutive

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Cranial patients with posterior screw and rod constructs for C1–C2 instability. Twenty of those patients were being treated for traumatic instability; the remaining 6 were being treated for neoplastic instability. They demonstrated 100% union with no vascular injuries. A prospective case series of 26 patients by Bourdillon et al67 reported 100% union at 6 months with no neurovascular compromise. Vascular injuries certainly do occur, however. A larger multicenter retrospective study by Aryan et al68 reported on results of 102 patients treated with C1 lateral mass and C2 pedicle or pars screw fixation for instability. Of those patients, 35 had a fibular allograft spacer placed in addition to the posterior fixation. At 12 months, they reported that 100 patients demonstrated radiographic fusion on computed tomography (CT) and plain radiographs. The C2 nerve root was sacrificed bilaterally in all patients, with one patient developing neuropathic pain postoperatively. Additionally, they reported four wound infections with one reoperation. In 23 patients, the patients’ anatomy did not allow the use of C2 pedicle screws; therefore, pars screws were placed instead. They also reported two vertebral artery injuries created during soft-tissue dissection due to a vertebral artery loop lying posterior to the C1 ring. These were treated with local hemostasis, and were patent on angiography with no further complication postoperatively. The course of the vertebral artery through the lateral mass of the axis can be asymmetric in approximately 50% of patients, making it vulnerable to injury.69 Rates of injury during C1 lateral mass screw placement alone range from 0 to 5.8%.70,71 Careful preoperative planning with a CT is required to try to avoid vertebral artery injury, especially when a ponticulus posticus is present (▶ Fig. 14.4).72 If the vertebral artery is injured, the bleeding may be controlled by placing the screw on that side. The screw length should not be so long that it reaches the artery’s groove. If a screw has not already been placed on the opposite side, it is the authors’ recommendation to avoid placing instrumentation on the contralateral side risking bilateral injury, with the possibility of stroke and death. Prompt angiographic evaluation should be performed postoperatively. The internal carotid artery (ICA) is also at risk for life-threatening hemorrhage and stroke if a drill bit or bicortical screw exits the anterior aspect of the C1 lateral mass (▶ Fig. 14.5). In addition to mapping out the precise course of the vertebral artery, a preoperative CT scan with contrast medium is

Fig. 14.4 Lateral radiograph of the cervical spine demonstrates an arcuate foramen of C1 and a ponticulus posticus (red arrows).

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Fig. 14.5 Diagram (a) and axial section from a fresh-frozen cadaveric specimen (b) of the C1–C2 anatomy shows the proximity of the VA to C1 lateral mass screws as well as the risk of injury to the internal carotid artery with bicortical C1 screw placement. (Redrawn with permission from Currier et al.73)

recommended to do the same with the ICA before placing a screw in C1. The course of the ICA can be tortuous and its location quite variable. Currier and colleagues73 found in a radiographic study that 58% of patients were at moderate risk of ICA injury due to the proximity of the artery relative to the anterior arch of C1 and that 12% were at high risk, on at least one side. The anterior tubercle of C1 can be used as a fluoroscopic guide during screw placement, but it is critical that the surgeon understand the anteroposterior relationship of the lateral mass of C1 relative to the tubercle. The surgeon can then estimate the approximate dimensions of the screws based on the shape of the anterior arch of C1 in the axial plane and the location of the ICA and vertebral artery from the preoperative CT angiogram.

14.4 Summary Odontoid fractures are common injuries that can certainly seem daunting to manage. Potentially serious complications can be encountered during both the operative and nonoperative treatments of these injuries. However, sound judgment and knowledge of the potential pitfalls can mitigate the risk of these complications. If managed appropriately, these injuries can result in reproducibly good results for the patient. There are few studies that limit themselves to treatment of acute odontoid fractures, thus it is difficult to compare. For many patients, nonoperative treatment results in satisfactory outcomes. When operative treatment is indicated, there are several options. Treatment with transarticular screws is biomechanically superior with higher fusion rates compared to posterior wiring alone; however, transarticular screw placement is technically more demanding. Posterior C1 lateral mass screws with C2 screws and rods also have a high fusion rate compared to posterior wiring alone; however, in contrast to transarticular screws, the neurovascular complication rates appear to be lower. Anterior screw fixation, while preserving some motion, may have more complications particularly in elderly patients. With limited data, there is no consensus on the optimal surgical management. When evaluating the data, the consequences of a fibrous union on patient outcomes are also unclear, further

Complications of Odontoid Fracture Treatment confusing the matter. Patient age, fracture pattern, spine anatomy, and surgeon experience are all important considerations when choosing the optimal approach. Larger, high-quality prospective, randomized studies are needed to truly elucidate the true prevalence of these complications and the optimal management of these injuries.

References [1] Greenberg MS. Handbook of Neurosurgery. 5th ed. Lakeland, FL: Greenberg Graphics; 2001 [2] Crockard HA, Heilman AE, Stevens JM. Progressive myelopathy secondary to odontoid fractures: clinical, radiological, and surgical features. J Neurosurg. 1993; 78(4):579–586 [3] Anderson LD, D’Alonzo RT. Fractures of the odontoid process of the axis. J Bone Joint Surg Am. 1974; 56(8):1663–1674 [4] Grauer JN, Shafi B, Hilibrand AS, et al. Proposal of a modified, treatment-oriented classification of odontoid fractures. Spine J. 2005; 5(2):123–129 [5] Hadley MN, Browner CM, Liu SS, Sonntag VK. New subtype of acute odontoid fractures (type IIA). Neurosurgery. 1988; 22(1, Pt 1):67–71 [6] Bellabarba C, Mirza SK, West GA, et al. Diagnosis and treatment of craniocervical dislocation in a series of 17 consecutive survivors during an 8-year period. J Neurosurg Spine. 2006; 4(6):429–440 [7] Julien TD, Frankel B, Traynelis VC, Ryken TC. Evidence-based analysis of odontoid fracture management. Neurosurg Focus. 2000; 8(6):e1 [8] Chiba K, Fujimura Y, Toyama Y, Fujii E, Nakanishi T, Hirabayashi K. Treatment protocol for fractures of the odontoid process. J Spinal Disord. 1996; 9 (4):267–276 [9] Ryan MD, Taylor TK. Odontoid fractures in the elderly. J Spinal Disord. 1993; 6(5):397–401 [10] Polin RS, Szabo T, Bogaev CA, Replogle RE, Jane JA. Nonoperative management of Types II and III odontoid fractures: the Philadelphia collar versus the halo vest. Neurosurgery. 1996; 38(3):450–456, discussion 456–457 [11] Müller EJ, Schwinnen I, Fischer K, Wick M, Muhr G. Non-rigid immobilisation of odontoid fractures. Eur Spine J. 2003; 12(5):522–525 [12] Clark CR, White AA, III. Fractures of the dens. A multicenter study. J Bone Joint Surg Am. 1985; 67(9):1340–1348 [13] Roberts A, Wickstrom J. Prognosis of odontoid fractures. Acta Orthop Scand. 1973; 44(1):21–30 [14] Hadley MN, Dickman CA, Browner CM, Sonntag VK. Acute axis fractures: a review of 229 cases. J Neurosurg. 1989; 71(5, Pt 1):642–647 [15] Hanigan WC, Powell FC, Elwood PW, Henderson JP. Odontoid fractures in elderly patients. J Neurosurg. 1993; 78(1):32–35 [16] Pepin JW, Bourne RB, Hawkins RJ. Odontoid fractures, with special reference to the elderly patient. Clin Orthop Relat Res. 1985(193):178–183 [17] Molinari RW, Khera OA, Gruhn WL, McAssey RW. Rigid cervical collar treatment for geriatric type II odontoid fractures. Eur Spine J. 2012; 21 (5):855–862 [18] Johnson RM, Hart DL, Simmons EF, Ramsby GR, Southwick WO. Cervical orthoses. A study comparing their effectiveness in restricting cervical motion in normal subjects. J Bone Joint Surg Am. 1977; 59(3):332–339 [19] Bono CM. The halo fixator. J Am Acad Orthop Surg. 2007; 15(12):728–737 [20] Garfin SR, Botte MJ, Waters RL, Nickel VL. Complications in the use of the halo fixation device. J Bone Joint Surg Am. 1986; 68(3):320–325 [21] Glaser JA, Whitehill R, Stamp WG, Jane JA. Complications associated with the halo-vest. A review of 245 cases. J Neurosurg. 1986; 65(6):762–769 [22] Ekong CE, Schwartz ML, Tator CH, Rowed DW, Edmonds VE. Odontoid fracture: management with early mobilization using the halo device. Neurosurgery. 1981; 9(6):631–637 [23] Lind B, Nordwall A, Sihlbom H. Odontoid fractures treated with halo-vest. Spine. 1987; 12(2):173–177 [24] Daentzer D, Flörkemeier T. Conservative treatment of upper cervical spine injuries with the halo vest: an appropriate option for all patients independent of their age? J Neurosurg Spine. 2009; 10(6):543–550 [25] Lind B, Sihlbom H, Nordwall A. Halo-vest treatment of unstable traumatic cervical spine injuries. Spine. 1988; 13(4):425–432 [26] Garfin SR, Botte MJ, Triggs KJ, Nickel VL. Subdural abscess associated with halo-pin traction. J Bone Joint Surg Am. 1988; 70(9):1338–1340

[27] Apuzzo ML, Heiden JS, Weiss MH, Ackerson TT, Harvey JP, Kurze T. Acute fractures of the odontoid process. An analysis of 45 cases. J Neurosurg. 1978; 48 (1):85–91 [28] Clark CR, White AA, III. Fractures of the dens. A multicenter study. J Bone Joint Surg Am. 1985; 67(9):1340–1348 [29] Vieweg U, Schultheiss R. A review of halo vest treatment of upper cervical spine injuries. Arch Orthop Trauma Surg. 2001; 121(1–2):50–55 [30] Koivikko MP, Kiuru MJ, Koskinen SK, Myllynen P, Santavirta S, Kivisaari L. Factors associated with nonunion in conservatively-treated type-II fractures of the odontoid process. J Bone Joint Surg Br. 2004; 86(8):1146–1151 [31] Lennarson PJ, Mostafavi H, Traynelis VC, Walters BC. Management of type II dens fractures: a case-control study. Spine. 2000; 25(10):1234–1237 [32] Ryan MD, Henderson JJ. The epidemiology of fractures and fracture-dislocations of the cervical spine. Injury. 1992; 23(1):38–40 [33] Taitsman L, Altman DT, Hecht AC, Pedlow FX. Complications of halo treatment in elderly patients with cervical spine fractures. Orthopedics. 2008; 31(5):446 [34] Tashjian RZ, Majercik S, Biffl WL, Palumbo MA, Cioffi WG. Halo-vest immobilization increases early morbidity and mortality in elderly odontoid fractures. J Trauma. 2006; 60(1):199–203 [35] Majercik S, Tashjian RZ, Biffl WL, Harrington DT, Cioffi WG. Halo vest immobilization in the elderly: a death sentence? J Trauma. 2005; 59(2):350–356, discussion 356–358 [36] van Middendorp JJ, Slooff WB, Nellestein WR, Oner FC. Incidence of and risk factors for complications associated with halo-vest immobilization: a prospective, descriptive cohort study of 239 patients. J Bone Joint Surg Am. 2009; 91(1):71–79 [37] Weller SJ, Malek AM, Rossitch E, Jr. Cervical spine fractures in the elderly. Surg Neurol. 1997; 47(3):274–280, discussion 280–281 [38] White AP, Hashimoto R, Norvell DC, Vaccaro AR. Morbidity and mortality related to odontoid fracture surgery in the elderly population. Spine. 2010; 35(9) Suppl:S146–S157 [39] Cho DC, Sung JK. Analysis of risk factors associated with fusion failure after anterior odontoid screw fixation. Spine. 2012; 37(1):30–34 [40] Rizvi SA, Fredø HL, Lied B, Nakstad PH, Rønning P, Helseth E. Surgical management of acute odontoid fractures: surgery-related complications and longterm outcomes in a consecutive series of 97 patients. J Trauma Acute Care Surg. 2012; 72(3):682–690 [41] Konieczny MR, Gstrein A, Müller EJ. Treatment algorithm for dens fractures: non-halo immobilization, anterior screw fixation, or posterior transarticular C1-C2 fixation. J Bone Joint Surg Am. 2012; 94(19):e144– (1–6) [42] Apfelbaum RI, Lonser RR, Veres R, Casey A. Direct anterior screw fixation for recent and remote odontoid fractures. J Neurosurg. 2000; 93(2) Suppl:227–236 [43] Andersson S, Rodrigues M, Olerud C. Odontoid fractures: high complication rate associated with anterior screw fixation in the elderly. Eur Spine J. 2000; 9(1):56–59 [44] Jenkins JD, Coric D, Branch CL, Jr. A clinical comparison of one- and two-screw odontoid fixation. J Neurosurg. 1998; 89(3):366–370 [45] Arand M, Lemke M, Kinzl L, Hartwig E. Incidence of complications of the screw osteosynthesis of odontoid process fractures [in German]. Zentralbl Chir. 2001; 126(8):610–615 [46] Platzer P, Thalhammer G, Ostermann R, Wieland T, Vécsei V, Gaebler C. Anterior screw fixation of odontoid fractures comparing younger and elderly patients. Spine. 2007; 32(16):1714–1720 [47] Lee EJ, Jang JW, Choi SH, Rhim SC. Delayed pharyngeal extrusion of an anterior odontoid screw. Korean J Spine. 2012; 9(3):289–292 [48] Wilson DA, Fusco DJ, Theodore N. Delayed subarachnoid hemorrhage following failed odontoid screw fixation. J Neurosurg Spine. 2011; 14(6):715–718 [49] Le Corre M, Suleiman N, Lonjon N. Odontoid fracture: long-term subarachnoid hemorrhage after anterior screw fixation. Case report and literature review [in French]. Neurochirurgie. 2012; 58(6):364–368 [50] Orief T, Bin-Nafisah S, Almusrea K, Alfawareh M. Guidewire breakage: an unusual complication of anterior odontoid cannulated screw fixation. Asian Spine J. 2011; 5(4):258–261 [51] Dailey AT, Hart D, Finn MA, Schmidt MH, Apfelbaum RI. Anterior fixation of odontoid fractures in an elderly population. J Neurosurg Spine. 2010; 12(1):1–8 [52] Grob D, Crisco JJ, III, Panjabi MM, Wang P, Dvorak J. Biomechanical evaluation of four different posterior atlantoaxial fixation techniques. Spine. 1992; 17 (5):480–490

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Cranial [53] Platzer P, Thalhammer G, Oberleitner G, Schuster R, Vécsei V, Gaebler C. Surgical treatment of dens fractures in elderly patients. J Bone Joint Surg Am. 2007; 89(8):1716–1722 [54] Brooks AL, Jenkins EB. Atlanto-axial arthrodesis by the wedge compression method. J Bone Joint Surg Am. 1978; 60(3):279–284 [55] Coyne TJ, Fehlings MG, Wallace MC, Bernstein M, Tator CH. C1-C2 posterior cervical fusion: long-term evaluation of results and efficacy. Neurosurgery. 1995; 37(4):688–692, discussion 692–693 [56] Lapsiwala SB, Anderson PA, Oza A, Resnick DK. Biomechanical comparison of four C1 to C2 rigid fixative techniques: anterior transarticular, posterior transarticular, C1 to C2 pedicle, and C1 to C2 intralaminar screws. Neurosurgery. 2006; 58(3):516–521, discussion 516–521 [57] Paramore CG, Dickman CA, Sonntag VK. The anatomical suitability of the C1–2 complex for transarticular screw fixation. J Neurosurg. 1996; 85(2):221–224 [58] Haid RW, Jr, Subach BR, McLaughlin MR, Rodts GE, Jr, Wahlig JB, Jr. C1-C2 transarticular screw fixation for atlantoaxial instability: a 6-year experience. Neurosurgery. 2001; 49(1):65–68, discussion 69–70 [59] Reilly TM, Sasso RC, Hall PV. Atlantoaxial stabilization: clinical comparison of posterior cervical wiring technique with transarticular screw fixation. J Spinal Disord Tech. 2003; 16(3):248–253 [60] Jeanneret B, Magerl F. Primary posterior fusion C1/2 in odontoid fractures: indications, technique, and results of transarticular screw fixation. J Spinal Disord. 1992; 5(4):464–475 [61] Fuji T, Oda T, Kato Y, Fujita S, Tanaka M. Accuracy of atlantoaxial transarticular screw insertion. Spine. 2000; 25(14):1760–1764 [62] Wright NM, Lauryssen C, American Association of Neurological Surgeons/ Congress of Neurological Surgeons. Vertebral artery injury in C1–2 transarticular screw fixation: results of a survey of the AANS/CNS section on disorders of the spine and peripheral nerves. J Neurosurg. 1998; 88(4):634–640 [63] Dickman CA, Sonntag VK. Posterior C1-C2 transarticular screw fixation for atlantoaxial arthrodesis. Neurosurgery. 1998; 43(2):275–280, discussion 280–281

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[64] Farey ID, Nadkarni S, Smith N. Modified Gallie technique versus transarticular screw fixation in C1-C2 fusion. Clin Orthop Relat Res. 1999(359):126–135 [65] Harms J, Melcher RP. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine. 2001; 26(22):2467–2471 [66] Ringel F, Reinke A, Stüer C, Meyer B, Stoffel M. Posterior C1–2 fusion with C1 lateral mass and C2 isthmic screws: accuracy of screw position, alignment and patient outcome. Acta Neurochir (Wien). 2012; 154(2):305–312 [67] Bourdillon, et al. C1–C2 stabilization by harms arthrodesis: indications, techniques, complications and outcomes in a prospective 26-case series. Orthop Traumatol Surg Res. 2014; 100(2):225–231 [68] Aryan HE, Newman CB, Nottmeier EW, Acosta FL, Jr, Wang VY, Ames CP. Stabilization of the atlantoaxial complex via C-1 lateral mass and C-2 pedicle screw fixation in a multicenter clinical experience in 102 patients: modification of the Harms and Goel techniques. J Neurosurg Spine. 2008; 8(3):222–229 [69] Madawi AA, Casey AT, Solanki GA, Tuite G, Veres R, Crockard HA. Radiological and anatomical evaluation of the atlantoaxial transarticular screw fixation technique. J Neurosurg. 1997; 86(6):961–968 [70] Neo M, Fujibayashi S, Miyata M, Takemoto M, Nakamura T. Vertebral artery injury during cervical spine surgery: a survey of more than 5600 operations. Spine. 2008; 33(7):779–785 [71] Yeom JS, Buchowski JM, Park KW, Chang BS, Lee CK, Riew KD. Undetected vertebral artery groove and foramen violations during C1 lateral mass and C2 pedicle screw placement. Spine. 2008; 33(25):E942–E949 [72] Hong JT, Lee SW, Son BC, et al. Analysis of anatomical variations of bone and vascular structures around the posterior atlantal arch using three-dimensional computed tomography angiography. J Neurosurg Spine. 2008; 8 (3):230–236 [73] Currier BL, Maus TP, Eck JC, Larson DR, Yaszemski MJ. Relationship of the internal carotid artery to the anterior aspect of the C1 vertebra: implications for C1-C2 transarticular and C1 lateral mass fixation. Spine. 2008; 33(6):635–639

Complications of Static Anterior Cervical Plates

15 Complications of Static Anterior Cervical Plates Barrett I. Woods, Kris E. Radcliff, and Alexander R. Vaccaro

15.1 Introduction Anterior cervical discectomy and fusion (ACDF) is one of the most common and successful spinal procedures performed. The technique for anterior discectomy and fusion was introduced by Smith and Robinson in 1955, with the first published series of 62 patients undergoing this procedure appearing in 1962.1,2 Cloward also contributed to the development of ACDF by publishing his technique in 1958.3 The approach to the anterior cervical spine has changed very little over the past 50 years; however, grafting techniques and anterior cervical instrumentation have evolved significantly. Anterior cervical instrumentation was developed to improve outcomes and decrease complications following anterior cervical fusion procedures. Biomechanically, anterior cervical plates act as a buttress in flexion while tensioning the anterior column in extension.4 Proposed benefits of anterior instrumentation include decreased need for external orthotics, earlier mobilization, superior fusion rates, and decreased graft-related complications.5,6,7 These benefits are more evident following multilevel anterior procedures which are associated with a higher complication rates than those involving a single level.8,9 Perceived designed flaws have inspired the evolution of anterior cervical plate over the past 50 years. The use of anterior cervical plating to stabilize traumatic cervical injuries was first described by Böhler in 1967.10 Following Böhler, in 1971 Orozco and Llovet described stabilization of traumatic anterior cervical injuries with an H-shaped plate.11 In 1989, Caspar et al published a series of 60 consecutive patients who had traumatic cervical injuries stabilized using iliac crest bone grafting and Caspar plating.12 Both the H and Caspar plates had an unrestricted interface and allowed for variable angle screw advancement (▶ Fig. 15.1). This feature allowed for some degree of micromotion and provided flexibility in screw placement, but required bicortical purchase to achieve compression and construct stability. Locking plates were developed to address the issue of screw backout and eliminate the need for bicortical purchase which places

Fig. 15.1 H and Caspar plates, which exhibit nonconstrained plate– screw interface that allows variable-angle screw placement; however, these plates required bicortical purchase to achieve stability.61

the dura and spinal cord at risk of injury. The first plate with a locking mechanism was the Cervical Spine Locking Plate introduced by Synthes (Westchester, PA) in 1991. This was a statically locked plate with a fixed screw–plate interface. Locking plates with variable angle screw trajectories were subsequently developed which again provided more flexibility with plate application. An unintended consequence of static anterior cervical plates was stress shielding due to the rigidity of these constructs. The most recent innovation to plate design has been the development of locked dynamic cervical plates which can allow some degree of micromotion and prevent distraction in the setting of graft settling or resorption (▶ Fig. 15.2). Currently, several options for anterior cervical plating exist with no clear consensus among surgeons as to the optimal plate design. Multilevel anterior cervical fusion poses significantly greater challenges to the surgeon and patient than single-level procedures. In determining which design to use, it is critical for the surgeon to understand the general complications associated with ACDF and design-specific issues. This chapter focuses on complications associated with static locked anterior cervical plating.

15.2 Complications 15.2.1 Dysphagia Some element of dysphagia is one of the most common complications following ACDF. While not significantly appreciated in the older literature, recent series have reported rates of dysphagia as high as 60% following anterior cervical procedures.13,14,15,16 Despite the high frequency of dysphagia following ACDF, most cases resolve without any intervention. Risk factors for the development of dysphagia postoperatively include female sex,

Fig. 15.2 The static plate (ATLANTIS system with fixed-angle screws), the rotationally dynamic plate (ATLANTIS system with variable-angle screws), and the translationally dynamic plate (PREMIER). The designs are licensed under one or more patents (numbers 6,193,721; 6,398,783; and 6,454,771) of G. Karlin Michelson, MD.54

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Cranial procedures involving the upper cervical spine, revisions, and multilevel cases.17,18 Anterior surgical procedures are commonly performed in the setting of kyphosis to restore more normal physiologic sagittal balance. Radcliff et al demonstrated that correction of cervical kyphosis lengthens the anterior column and may tension the anterior soft tissues, which can increase the risk of dysphagia postoperatively.19 There are little data to support that the incidence of dysphagia is influenced by plate design. One specific feature of anterior cervical fixation that may influence the incidence of dysphagia is plate thickness; however, there is no consensus in the literature regarding this issue.20,21

15.2.2 Adjacent Segment Disease A well-documented, however poorly understood, phenomenon observed following anterior cervical fusion is the development of disc degeneration at the cephalad or caudal segment adjacent to the fusion. Hilibrand and Robbins described adjacent segment disease as radiographic degeneration at a level adjacent to a prior fusion which results in new neurological sequelae.22 The estimated incidence of new, symptomatic, adjacent level disease increases approximately 2.9% per year following fusion and is 25% at 10 years.23 Currently, it is unclear if adjacent segment degeneration is a reflection of the natural history of cervical spondylitis or a result of the altered biomechanics that occurs following cervical fusion. Technical factors which may decrease the incidence of adjacent segment degeneration following anterior cervical fusion include limited dissection of the longus coli musculature, localization with a nonpenetrating instruments, and precise plate sizing and placement.24,25,26 Park et al illustrated that the distance of the plate to the adjacent endplate influences the risk of developing adjacent segment degeneration26 (▶ Fig. 15.3). Static places should in theory prevent adjacent level degeneration if positioned appropriately during surgery, at least 5 mm from the adjacent endplate, due to their fixed dimensions. However, plate subsidence does occur regardless of plate used.

Fig. 15.3 X-ray showing grade 2 adjacent segment degeneration at the C3–C4 level (arrow). Notice the proximity of the proximal aspect of the plate to the adjacent endplate.26

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DuBois et al retrospectively reviewed 52 patients undergoing multilevel ACDF with either static or dynamic plates and found no significant difference in the amount of subsidence between the two designs.27 The majority of subsidence which occurred happened within the first month postoperatively. In vitro biomechanical studies have shown that cervical fusion creates a lever arm that increases the intersegmental motion and stress at levels adjacent to the fusion, which may lead to degeneration of discs.28 This concept has led to the development of motion-preserving procedures such as total disc arthroplasty. In Bolhman’s classic series of 122 consecutive patients with ACDF, there was a reported incidence of adjacent segment disease in 11 patients (9%), 9 of which required revision surgery.29 A recent, multicenter, retrospective review found an 81% incidence of radiographic adjacent segment degeneration at 10 years following ACDF; however, revision surgery was required in only 5.9%.30 There is no literature to support the contention that adjacent segment degeneration occurs more frequently with static than dynamic anterior cervical fixation.

15.2.3 Pseudarthrosis/Stress Shielding Pseudarthrosis is a failure to achieve osseous union and is a well-defined complication associated with ACDF regardless of construct used. Although the clinical significance of a pseudoarthrosis following ACDF is often unpredictable, risk factors associated with this complication have been delineated. Technical factors such as meticulous endplate preparation have been effective at increasing fusion rates, most notably in single-level procedures. Bohlman reported a 95% fusion rate following single-level ACDF using this technique.31 This success has not translated to multilevel anterior cervical procedures. Emery et al retrospectively reviewed 16 patients with three-level, noninstrumented ACDF using the modified Smith–Robinson technique and found solid arthrodesis in only 56% of these patients.32 Bolesta et al prospectively evaluated 15 patients undergoing three- or four-level ACDF with tricortical iliac crest autograph and a cervical spine locking plate and found solid arthrodesis in only 47% of the patients.33 Although not supported by the study of Bolesta et al, using of anterior instrumentation following multilevel ACDF is strongly advocated as a means to increase fusion and decrease graft-related complications. Connolly et al prospectively evaluated outcomes following anterior cervical fusion using autograph with and without anterior cervical instrumentation using the Morscher’s screw–plate system.34 This Morscher’s plate was static with unicortical purchase and a locked screw–plate interface. The presence of instrumentation had no effect on fusion rate following a single-level procedure, but did decrease nonunion and graft subsidence following multilevel procedures.34 The biggest theoretical risk with static plate fixation of the anterior cervical column is stress shielding which can compromise micromotion at the graft–host interface and also limit loading of the graft. Distraction across the fusion site can create a suboptimal environment for achieving a solid osseous fusion. The concept of stress shielding has been studied extensively in orthopaedics, particularly germane to total joint arthroplasty and long bone trauma.35,36,37,38,39 Stress shielding occurs when a prosthetic implant removes normal physiologic stress from

Complications of Static Anterior Cervical Plates bone, thereby eliminating the stimuli required by osteoblasts to preserve bone stock. This can ultimately result in focal osteopenia or impaired fracture healing. The clinical implications of stress shielding are illustrated in the evolution of the surgical management of diaphyseal tibia fractures. Unacceptably high rates of delayed or nonunion of tibial shaft fractures following rigid plate fixation with interfragmentary compression led to the development of alternative stabilization methods. In 1985, Goodship and Kenwright evaluated the effect controlled micromotion had on fusion rates of tibial fractures in an animal model.40 They found a significantly higher rate of fusion with fixation that was less rigid and allowed micromotion in the axial plane compared to fractures that where rigidly stabilized. This led to the development of intramedullary devices which allow axial micromotion, callus formation, and fusion rates in the 90th percentile for tibial shaft fractures.41 Static anterior column plating systems are rigid constructs with a set of vertical length. Interbody grafts are press fit to fill the void left by the discectomy or corpectomy. Rigid compression at the graft– host interface is not achieved; in fact, overstuffing the void left by the decompression can compromise the endplates and result in graft settling into the spongy cancellous bone of the vertebral body. Thus static plate constructs can limit the micromotion necessary to achieve bridging body between graft and host, preventing solid osseous fusion. Dynamic anterior cervical instrumentation was developed to combat this theoretical concern. Several designs of dynamic cervical plates exist, which may maintain a locked screw–plate interface, but allow for translation in the axial plate. Nunley et al prospectively evaluated 66 patients over a 4-year period who received an ACDF, half with a static fixation and the other with dynamic anterior cervical instrumentation.42 They found no difference in fusion rates or outcomes using either plate following single-level ACDF; however, patients who had multilevel procedures had better outcomes in regard to visual analog scale (VAS) and Neck Disability Index than those treated with static anterior cervical instrumentation. In this study clinic, outcome was a predictor of solid fusion; however, fusion alone was not a reliable determinate of success. Other studies have failed to show a difference in pseudoarthrosis rates following ACDF procedures stabilized with dynamic or static plating. Pitzen et al performed a prospective randomized control trail which showed no difference in pseudoarthrosis in patients following single- or multilevel ACDF treated with either plate design at 2 years.43 Another strategy to decrease the risk of pseudarthrosis following multilevel anterior cervical procedures is to decrease the number of healing surfaces by performing a corpectomy. Emery et al had a 5% rate of pseudoarthrosis following twolevel corpectomy and anterior plating, which was significantly lower than that seen following three-level ACDF.44 However, the risk of graft-related complications following corpectomy with static plate fixation is significant, proportional to the length of the strut, and can have catastrophic clinical consequence. Vaccaro et al retrospectively reviewed the early postoperative failure rate of long segment anterior cervical fusion and plating after a two- or three-level corpectomy for degenerative, traumatic, and neoplastic diseases of the cervical spine. In the early postoperative period, graft dislodgement occurred in 9% of patients with two-level and 50% of patients following three-level corpectomy and plating.45 The negative

biomechanical consequence of static anterior column fixation may be exacerbated in the setting of a long corpectomy strut. Epstein illustrated a threefold higher incidence of pseudoarthrosis in patients who had a multilevel corpectomy for ossification of the posterior longitudinal ligament (OPLL) fixed with static versus dynamic plate fixation.46 In the setting of a threelevel corpectomy with anterior strut, supplemental posterior fixation is advocated by most surgeons. Pseudoarthrosis following anterior cervical procedures can be diagnosed radiographically by the absence of motion between the spinous processes on dynamic radiographs or by computed tomographic scan.47,48,49 Regardless of the diagnostic method used, the risk of pseudoarthrosis is significantly higher following multilevel anterior cervical procedures. Clinically, about one-third of patients with a pseudoarthrosis will be asymptomatic following ACDF50 (▶ Fig. 15.4). Of the remaining two-thirds who are symptomatic, the majority can be treated conservatively.29 Surgical intervention is typically successful at achieving fusion in the small subset of patients who are symptomatic and fail conservative measures.51,52 The perceived biomechanical risk of static plate fixation has not been consistently illustrated in the literature. However, pseudarthrosis is a very challenging issue to study due to the number of confounding variables which can affect solid arthrodesis following spine surgery. Dynamic plates may be one factor which contributes to solid arthrodesis following multilevel anterior cervical procedures.

15.2.4 Graft Settling (Focal Kyphosis) Endplate preparation using the burr is universally accepted as a means to increase fusion rate following ACDF.29 However, this technique can weaken the endplate and result in graft settling, loss of height, and focal kyphosis. One proposed benefit of static anterior instrumentation is that is can buttress the anterior column, preserving anatomic lordosis. However, the use of static plates may have biomechanical disadvantages at the graft–endplate interface. Appropriately tensioning the graft is challenging when performing anterior cervical fusion procedures. Oversizing the graft can disrupt the endplates and result in settling, which may affect sagittal alignment, foramen decompression, and fusion. Some absorption or settling does commonly occur following anterior fusions.53 Static plates do not accommodate this dynamic process and can result in significant stress shielding in discectomy and corpectomy procedures. The effect graft settling has on the load sharing characteristics of a static construct was illustrated by Brodke et al who illustrated a 70% increase in stress shielding with a 10% graft subsidence in a single-level cadaveric corpectomy model.54 Reidy et al demonstrated that even in the absence of graft settling, static plates significantly shield the host–graft interface through decreased graft loading in a C5 corpectomy model when compared to translational plates.55 Other in vitro cadaveric studies have illustrated the biomechanical disadvantage of static anterior cervical instrumentation following corpectomy, which is exacerbated if the graft is undersized when compare to dynamic fixation. Of particular concern is the reciprocal loading patterns which occur with static fixation of long struts, as flexion unloads the graft, while even slight extension significantly increases graft loading.56 DiAngelo et al evaluated the

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Cranial mismatch of the strut and subchondral endplate can result in graft subsidence. Despite these theoretical concerns and in vitro biomechanical studies, clinical studies have failed to delineate the superior fixation method following anterior cervical corpectomy and spanning strut graft.

15.2.5 Hardware Failure The incidence of screw pullout has been reduced with design modifications that provide a locked screw–plate interface. Preceding designs such as the Caspar system used a variable angle screw which compressed the plate to the anterior vertebral body and required bicortical purchase. Paramore et al retrospectively reviewed 49 patients who had ACDF with Caspar plating and found hardware failure in 22% of patients.58 Severe complications such as esophageal injury from screw back-out in nonconstrained plates has been reported.59 While these issues have been addressed by the development of locked plate–screw interface, static anterior column fixation may facilitate graft dislodgement and catastrophic failure particularly when used to stabilize long struts following corpectomy (▶ Fig. 15.5). As previously discussed, static anterior column fixation results in reciprocal loading of the interbody graft.56 Extension as slight as 5 degrees can result in significant loading, causing the graft to piston and dislodge.57 Hardware failure with graft dislodgement is well documented in the literature following static plating of a corpectomy, with length of the strut increasing the risk of failure44,45,56,57, 58, 60 (▶ Fig. 15.6). Therefore, static plating of a long-strut corpectomy should be performed with caution. Currently, the optimal stabilization of long segment anterior cervical decompression has not been identified in the literature.

15.3 Summary Plate design has evolved significantly over the past 30 years; however, complications persist. It is critical for the surgeon to understand the complications associated with ACDF in general and those associated with specific designs in particular. Despite the biomechanical concerns associated with static plate fixation such as stress shielding and reverse graft loading with plating long struts, the literature has failed to consistently show a difference between static and dynamic plates. There may be an indication for dynamic anterior fixation following multilevel anterior cervical procedures; however, no definite conclusions can be made at this time.

Fig. 15.4 (a,b) A 60-year-old woman 4 years postoperatively following a C3–C7 ACDF with static anterior plate fixation developed an asymptomatic pseudarthrosis at the C6–C7 level. This is clearly illustrated as persistent radiolucency and lack of bridging bone at this level.33

biomechanical implications of static anterior plate fixation following corpectomy in a cadaveric model, and found that resistive strength of the subchondral endplate was reached with only 5 to 15 degrees of cervical extension.57 This supraphysiologic loading with mild extension coupled with the modulus

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15.4 Key Points ●

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●

Static plates are load sharing and limit micromotion at the graft–host interface which may affect osteogenesis. Some degree of graft subsidence is a normal occurrence following ACDF which is not accommodated for when using static anterior cervical instrumentation. Static fixation of strutted corpectomies reverses the loads experienced by the graft as extension significantly increases loading. The phenomenon is influenced by strut length and can result in subsidence or graft dislodgement.

Complications of Static Anterior Cervical Plates

Fig. 15.5 A 54-year-old man with congenital cervical anomalies underwent C3 corpectomy, iliac crest bone graft (ICBG), and static locking anterior plate fixation. Patient improved postoperatively, but returned 8 years later reporting expulsion of a screw from his mouth and difficulty swallowing. Lateral X-ray shows hardware failure with anterior migration of the proximal aspect of the plate (arrows). The plate can be visualized clinically having eroded through the posterior pharynx (arrow).62

15.5 Key References [1] Bohlman HH, Emery SE, Goodfellow DB, Jones PK. Robinson anterior cervical discectomy and arthrodesis for cervical radiculopathy. Long-term follow-up of one hundred and twenty-two patients. J Bone Joint Surg Am. 1993; 75 (9):1298–1307

Classic article, retrospective review of 122 patients who had cervical radiculopathy treated with modified Robinson method of ACDF and instrumented fusion. There was a 13% rate of pseudarthrosis (16 patients) of which only 4 required revision surgery. The risk of pseudoarthrosis following ACDF was found to be significantly associated with number of levels involved. [2] Reidy D, Finkelstein J, Nagpurkar A, Mousavi P, Whyne C. Cervical spine loading characteristics in a cadaveric C5 corpectomy model using a static and dynamic plate. J Spinal Disord Tech. 2004; 17(2):117–122

A cadaveric C5 corpectomy model is used to determine the load transmitted through the graft when a dynamic or a static anterior cervical plate is used. The graft was loaded significantly more when using dynamic plates, indicating the stressshielding properties of static anterior cervical instrumentation. [3] Brodke DS, Klimo P, Jr, Bachus KN, Braun JT, Dailey AT. Anterior cervical fixation: analysis of load-sharing and stability with use of static and dynamic plates. J Bone Joint Surg Am. 2006; 88(7):1566–1573

A cadaveric study which evaluated the load-sharing capabilities of static and dynamic plates after a C5 corpectomy in the presence of graft subsidence. With the full-length interbody spacer, there were no significant differences in load sharing or motion between plate designs. Following shortening of the interbody graft by 10%, the static plate construct lost nearly 70% of its load-sharing capability; this loss was not observed in the dynamic plates. Fig. 15.6 Lateral radiographs of three-level anterior corpectomy reconstruction with early failure of a constrained plate.60

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Dynamic plates were designed to combat the perceived load sharing flaw of static constructs; however, the literature has not clearly delineated the superiority of this modification. Regardless of plate design used, complications following multilevel anterior cervical procedures are significantly higher than observed following single-level surgery.

[4] Pitzen TR, Chrobok J, Stulik J, et al. Implant complications, fusion, loss of lordosis, and outcome after anterior cervical plating with dynamic or rigid plates: two-year results of a multi-centric, randomized, controlled study. Spine (Phila Pa 1976). 2009; 34(7):641–646

Randomized-controlled trial comparing dynamic and static plates. They reported no difference in fusion rates; however, the dynamic plate had less hardware failure, but a greater loss of segmental lordosis. [5] Nunley PD, Jawahar A, Kerr EJ, III, Cavanaugh DA, Howard C, Brandao SM. Choice of plate may affect outcomes for single versus multilevel ACDF: results of a prospective randomized single-blind trial. Spine J. 2009; 9(2):121–127

Single-masked, prospective, randomized study over a 4-year period which evaluated the outcomes for single- and multilevel

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Cranial ACDF using static or dynamic plate designs in 66 patients. There was no difference in fusion rates or outcomes using either plates following single-level ACDF; however, patients who had multilevel procedures had better outcomes in regard to VAS and NDI than those treated with static anterior cervical instrumentation.

References [1] Smith GW, Robinson RA. The treatment of certain cervical-spine disorders by anterior removal of the intervertebral disc and interbody fusion. J Bone Joint Surg Am. 1958; 40-A(3):607–624 [2] Walker AE, Robinson RA. Anterior cervical fusion [in Spanish]. Dia Med. 1962; 34 Spec:894–900 [3] Cloward RB. The anterior approach for removal of ruptured cervical disks. J Neurosurg. 1958; 15(6):602–617 [4] Daffner SD, Wang JC. Anterior cervical fusion: the role of anterior plating. Instr Course Lect. 2009; 58:689–698 [5] Grob D, Peyer JV, Dvorak J. The use of plate fixation in anterior surgery of the degenerative cervical spine: a comparative prospective clinical study. Eur Spine J. 2001; 10(5):408–413 [6] Wang JC, McDonough PW, Endow K, Kanim LE, Delamarter RB. The effect of cervical plating on single-level anterior cervical discectomy and fusion. J Spinal Disord. 1999; 12(6):467–471 [7] McCullen GM, Garfin SR. Spine update: cervical spine internal fixation using screw and screw-plate constructs. Spine. 2000; 25(5):643–652 [8] Wang JC, McDonough PW, Kanim LE, Endow KK, Delamarter RB. Increased fusion rates with cervical plating for three-level anterior cervical discectomy and fusion. Spine. 2001; 26(6):643–646, discussion 646–647 [9] Wang JC, McDonough PW, Endow KK, Delamarter RB. Increased fusion rates with cervical plating for two-level anterior cervical discectomy and fusion. Spine. 2000; 25(1):41–45 [10] Böhler J. Immediate and early treatment of traumatic paraplegias [in German]. Z Orthop Ihre Grenzgeb. 1967; 103(4):512–529 [11] Orozco DR, Llovet TR. Osteosintesis en las lesiones traumaticas y degeneratives de la columna vertebral. Revista Traumatol Chirurg Rehabil. 1971; 1:45–52 [12] Caspar W, Barbier DD, Klara PM. Anterior cervical fusion and Caspar plate stabilization for cervical trauma. Neurosurgery. 1989; 25(4):491–502 [13] Lunsford LD, Bissonette DJ, Zorub DS. Anterior surgery for cervical disc disease. Part 2: Treatment of cervical spondylotic myelopathy in 32 cases. J Neurosurg. 1980; 53(1):12–19 [14] Lunsford LD, Bissonette DJ, Jannetta PJ, Sheptak PE, Zorub DS. Anterior surgery for cervical disc disease. Part 1: Treatment of lateral cervical disc herniation in 253 cases. J Neurosurg. 1980; 53(1):1–11 [15] Winslow CP, Winslow TJ, Wax MK. Dysphonia and dysphagia following the anterior approach to the cervical spine. Arch Otolaryngol Head Neck Surg. 2001; 127(1):51–55 [16] Kalb S, Reis MT, Cowperthwaite MC, et al. Dysphagia after anterior cervical spine surgery: incidence and risk factors. World Neurosurg. 2012; 77 (1):183–187 [17] Riley LH, III, Vaccaro AR, Dettori JR, Hashimoto R. Postoperative dysphagia in anterior cervical spine surgery. Spine. 2010; 35(9) Suppl:S76–S85 [18] Riley LH, III, Skolasky RL, Albert TJ, Vaccaro AR, Heller JG. Dysphagia after anterior cervical decompression and fusion: prevalence and risk factors from a longitudinal cohort study. Spine. 2005; 30(22):2564–2569 [19] Radcliff KE, Bennett J, Stewart RJ, et al. Change in angular alignment is associated with early dysphagia after anterior cervical diskectomy and fusion. Clin Spine Surg. 2016; 29(6):248–254 [20] Lee MJ, Bazaz R, Furey CG, Yoo J. Influence of anterior cervical plate design on Dysphagia: a 2-year prospective longitudinal follow-up study. J Spinal Disord Tech. 2005; 18(5):406–409 [21] Chin KR, Eiszner JR, Adams SB, Jr. Role of plate thickness as a cause of dysphagia after anterior cervical fusion. Spine. 2007; 32(23):2585–2590 [22] Hilibrand AS, Robbins M. Adjacent segment degeneration and adjacent segment disease: the consequences of spinal fusion? Spine J. 2004; 4(6) Suppl:190S–194S [23] Hilibrand AS, Carlson GD, Palumbo MA, Jones PK, Bohlman HH. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am. 1999; 81(4):519–528

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[24] Kettler A, Hartwig E, Schultheiss M, Claes L, Wilke HJ. Mechanically simulated muscle forces strongly stabilize intact and injured upper cervical spine specimens. J Biomech. 2002; 35(3):339–346 [25] Nassr A, Lee JY, Bashir RS, et al. Does incorrect level needle localization during anterior cervical discectomy and fusion lead to accelerated disc degeneration? Spine. 2009; 34(2):189–192 [26] Park JB, Cho YS, Riew KD. Development of adjacent-level ossification in patients with an anterior cervical plate. J Bone Joint Surg Am. 2005; 87 (3):558–563 [27] DuBois CM, Bolt PM, Todd AG, Gupta P, Wetzel FT, Phillips FM. Static versus dynamic plating for multilevel anterior cervical discectomy and fusion. Spine J. 2007; 7(2):188–193 [28] Riew KD, Buchowski JM, Sasso R, Zdeblick T, Metcalf NH, Anderson PA. Cervical disc arthroplasty compared with arthrodesis for the treatment of myelopathy. J Bone Joint Surg Am. 2008; 90(11):2354–2364 [29] Bohlman HH, Emery SE, Goodfellow DB, Jones PK. Robinson anterior cervical discectomy and arthrodesis for cervical radiculopathy. Long-term follow-up of one hundred and twenty-two patients. J Bone Joint Surg Am. 1993; 75 (9):1298–1307 [30] Litrico S, Lonjon N, Riouallon G, et al. French Society of Spine Surgery (SFCR). Adjacent segment disease after anterior cervical interbody fusion: a multicenter retrospective study of 288 patients with long-term follow-up. Orthop Traumatol Surg Res. 2014; 100(6) Suppl:S305–S309 [31] Bohlman H. Robinson anterior cervical discectomy and arthrodesis for cervical radiculopathy. Long-term follow-up of one hundred and twenty-two patients. J Bone Joint Surg Am. 1993; 75(9):1298–1307 [32] Emery SE, Fisher JR, Bohlman HH. Three-level anterior cervical discectomy and fusion: radiographic and clinical results. Spine. 1997; 22(22):2622–2624, discussion 2625 [33] Bolesta MJ, Rechtine GR, II, Chrin AM. Three- and four-level anterior cervical discectomy and fusion with plate fixation: a prospective study. Spine. 2000; 25(16):2040–2044, discussion 2045–2046 [34] Connolly PJ, Esses SI, Kostuik JP. Anterior cervical fusion: outcome analysis of patients fused with and without anterior cervical plates. J Spinal Disord. 1996; 9(3):202–206 [35] Piao C, Wu D, Luo M, Ma H. Stress shielding effects of two prosthetic groups after total hip joint simulation replacement. J Orthop Surg. 2014; 9:71 [36] Nishino T, Mishima H, Kawamura H, Shimizu Y, Miyakawa S, Ochiai N. Follow-up results of 10–12 years after total hip arthroplasty using cementless tapered stem—frequency of severe stress shielding with synergy stem in Japanese patients. J Arthroplasty. 2013; 28(10):1736–1740 [37] Wik TS, Foss OA, Havik S, Persen L, Aamodt A, Witsø E. Periprosthetic fracture caused by stress shielding after implantation of a femoral condyle endoprosthesis in a transfemoral amputee-a case report. Acta Orthop. 2010; 81 (6):765–767 [38] Sathappan SS, Pang HN, Manoj A, Ashwin T, Satku K. Does stress shielding occur with the use of long-stem prosthesis in total knee arthroplasty? Knee Surg Sports Traumatol Arthrosc. 2009; 17(2):179–183 [39] Ren K, Zhang CC, Wang GY, Zhao JN, Sun JW. Effects of swan-like shape memory connector on stress shielding rate and callus development during experimental fracture healing process [in Chinese]. Zhongguo Gu Shang. 2009; 22 (3):202–205 [40] Goodship AE, Kenwright J. The influence of induced micromovement upon the healing of experimental tibial fractures. J Bone Joint Surg Br. 1985; 67 (4):650–655 [41] Jones M, Parry M, Whitehouse M, Mitchell S. Radiologic outcome and patient-reported function after intramedullary nailing: a comparison of the retropatellar and infrapatellar approach. J Orthop Trauma. 2014; 28(5):256–262 [42] Nunley PD, Jawahar A, Kerr EJ, III, Cavanaugh DA, Howard C, Brandao SM. Choice of plate may affect outcomes for single versus multilevel ACDF: results of a prospective randomized single-blind trial. Spine J. 2009; 9(2):121–127 [43] Pitzen TR, Chrobok J, Stulik J, et al. Implant complications, fusion, loss of lordosis, and outcome after anterior cervical plating with dynamic or rigid plates: two-year results of a multi-centric, randomized, controlled study. Spine. 2009; 34(7):641–646 [44] Emery SE, Bohlman HH, Bolesta MJ, Jones PK. Anterior cervical decompression and arthrodesis for the treatment of cervical spondylotic myelopathy. Two to seventeen-year follow-up. J Bone Joint Surg Am. 1998; 80(7):941–951 [45] Vaccaro AR, Falatyn SP, Scuderi GJ, et al. Early failure of long segment anterior cervical plate fixation. J Spinal Disord. 1998; 11(5):410–415 [46] Epstein NE. Fixed vs dynamic plate complications following multilevel anterior cervical corpectomy and fusion with posterior stabilization. Spinal Cord. 2003; 41(7):379–384

Complications of Static Anterior Cervical Plates [47] Kaiser MG, Mummaneni PV, Matz PG, et al. Joint Section on Disorders of the Spine and Peripheral Nerves of the American Association of Neurological Surgeons and Congress of Neurological Surgeons. Radiographic assessment of cervical subaxial fusion. J Neurosurg Spine. 2009; 11(2):221–227 [48] Hipp JA, Reitman CA, Wharton N. Defining pseudoarthrosis in the cervical spine with differing motion thresholds. Spine. 2005; 30(2):209–210 [49] Buchowski JM, Liu G, Bunmaprasert T, Rose PS, Riew KD. Anterior cervical fusion assessment: surgical exploration versus radiographic evaluation. Spine. 2008; 33(11):1185–1191 [50] Kuhns CA, Geck MJ, Wang JC, Delamarter RB. An outcomes analysis of the treatment of cervical pseudarthrosis with posterior fusion. Spine. 2005; 30 (21):2424–2429 [51] Tribus CB, Corteen DP, Zdeblick TA. The efficacy of anterior cervical plating in the management of symptomatic pseudoarthrosis of the cervical spine. Spine. 1999; 24(9):860–864 [52] Zdeblick TA, Hughes SS, Riew KD, Bohlman HH. Failed anterior cervical discectomy and arthrodesis. Analysis and treatment of thirty-five patients. J Bone Joint Surg Am. 1997; 79(4):523–532 [53] Tye GW, Graham RS, Broaddus WC, Young HF. Graft subsidence after instrument-assisted anterior cervical fusion. J Neurosurg. 2002; 97(2) Suppl:186–192 [54] Brodke DS, Klimo P, Jr, Bachus KN, Braun JT, Dailey AT. Anterior cervical fixation: analysis of load-sharing and stability with use of static and dynamic plates. J Bone Joint Surg Am. 2006; 88(7):1566–1573

[55] Reidy D, Finkelstein J, Nagpurkar A, Mousavi P, Whyne C. Cervical spine loading characteristics in a cadaveric C5 corpectomy model using a static and dynamic plate. J Spinal Disord Tech. 2004; 17(2):117–122 [56] Fogel GR, Li Z, Liu W, Liao Z, Wu J, Zhou W. In vitro evaluation of stiffness and load sharing in a two-level corpectomy: comparison of static and dynamic cervical plates. Spine J. 2010; 10(5):417–421 [57] DiAngelo DJ, Foley KT, Vossel KA, Rampersaud YR, Jansen TH. Anterior cervical plating reverses load transfer through multilevel strut-grafts. Spine. 2000; 25(7):783–795 [58] Paramore CG, Dickman CA, Sonntag VK. Radiographic and clinical follow-up review of Caspar plates in 49 patients. J Neurosurg. 1996; 84(6):957–961 [59] Smith MD, Bolesta MJ. Esophageal perforation after anterior cervical plate fixation: a report of two cases. J Spinal Disord. 1992; 5(3):357–362 [60] Sasso RC, Ruggiero RA, Jr, Reilly TM, Hall PV. Early reconstruction failures after multilevel cervical corpectomy. Spine. 2003; 28(2):140–142 [61] Yang S, Wang LW. Biomechanical comparison of the stable efficacy of two anterior plating systems. Clin Biomech (Bristol, Avon). 2003; 18(6):S59–S66 [62] Kapu R, Singh M, Pande A, Vasudevan MC, Ramamurthi R. Delayed anterior cervical plate dislodgement with pharyngeal wall perforation and oral extrusion of cervical plate screw after 8 years: a very rare complication. J Craniovertebr Junction Spine. 2012; 3(1):19–22

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16 Complications of Translational Anterior Cervical Plates Gregory D. Schroeder and Jason W. Savage

16.1 Introduction Anterior cervical discectomy and fusion (ACDF) has become one of the most common and successful operations performed by spine surgeons since being first described by Smith and Robinson in 1958.1 An increase in the understanding of biomechanics and the biology of bone formation has led to significant advances in surgical technique especially with regard to anterior instrumentation. Anterior cervical plates were designed to increase fusion rates, particularly in multilevel fusions, and prevent graft collapse that can lead to postsurgical kyphosis.2,3,4,5,6 Early anterior cervical plates were designed to function as a tension band in cervical extension and a buttress plate in flexion.2 One technical challenge with the early plate design was that bicortical screw fixation was recommended to prevent screw pullout and hardware failure.7,8,9 In an effort to decrease the significant complications from damage to anterior structures associated with hardware failure and to eliminate the risks associated with bicortical screw fixation, constrained plating systems were developed.2,10 The first constrained plating systems were designed similar to locking plates used elsewhere in orthopaedics. They were fully constrained systems in which the screws rigidly locked to the plate to create a fixed-angle device.10 While fully constrained plates solved some of the problems with early anterior cervical plates, biomechanically, these plates do not provide the optimal environment for bone healing. The use of fully constrained plates creates a very stiff construct that often causes stress shielding, which decreases the load experienced by the interbody graft.11,12,13 In an effort to improve the load-sharing properties of anterior cervical plates and increase bone formation at the graft–endplate interface, semiconstrained plates were developed. These plates allow for rotation or translation of the screw in reference to the plate while maintaining a mechanism to prevent screw backout.10 Multiple studies have validated the biomechanical advantages of these plates.12,13,14,15 In a cadaveric C5 corpectomy model, Reidy et al reported that the load transferred through the graft increased from 57 to 80%, and the load transmitted through the plate decreased from 23 to 9% when a dynamic semiconstrained anterior plate was used compared to a static fully constrained plate.12 In similar cadaveric models, Brodke et al initially found similar load sharing capabilities between fully constrained and semiconstrained plates; however, when 10% graft subsidence occurred, the stress shielding increased by 70% in the fully constrained plate.14,15 Semiconstrained plates are divided into two large categories: rotationally semiconstrained plates, which allow for a small amount of motion in the sagittal plane, and translationally semiconstrained plates, or dynamic plates, which allow for axial compression or vertical translation.10 Dynamic plates allow axial translation through either

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slotted/oval screw holes (▶ Fig. 16.1) or a telescoping plate (▶ Fig. 16.2). There are several different types of semiconstrained anterior plates that have been approved by the Food and Drug Administration (FDA) for use in the cervical spine (C2–T1), and complications associated with this plate design will be the focus of this chapter.

Fig. 16.1 The Medtronic Premier Plating System (Medtronic Sofamor Danek, Memphis, TN) is designed as a translational semiconstrained plate with oval holes cephalad, but fully constrained at the caudal end.

Complications of Translational Anterior Cervical Plates

Detection

Fig. 16.2 The Atlantis Plating System (Medtronic Sofamor Danek, Memphis, TN) is a telescoping translational semiconstrained plate.

16.2 Complications 16.2.1 Dysphagia The incidence of dysphagia after an ACDF is a debated topic in the literature. While classic literature failed to report a significant incidence of dysphagia after an ACDF,16,17,18,19 recent literature suggests that at least mild dysphagia may be present in 47 to 60% of patients.20,21,22,23,24,25,26 With these rates, dysphagia is one of the more common complications after an anterior cervical surgery.

Avoidance Because of the high prevalence of dysphagia in recent literature, many studies have been conducted attempting to identify risk factors and methods to avoid this complication. While multiple risk factors have been proposed, in a systematic review of the literature in 2010, it was reported that the only two risk factors that could be definitively identified in high-level studies are multilevel surgeries and female gender.27 However, because of the numerous studies demonstrating increasing dysphagia with longer multilevel26,28,29 or revision surgeries,29 multiple authors conclude that dysphagia is best limited by decreasing the length of the procedure.22,30 While not identified in the systematic review of the literature, other risk factors for dysphagia have been reported. Recently, Radcliff et al demonstrated that a significant lordotic change in spinal alignment increases the risk of dysphagia.30 Additionally, dysphagia may be deceased at 24 hours by decreasing the endotracheal tube cuff pressures to 20 mm Hg.22 Although it has often been postulated that anterior plating may increase the risk of dysphagia, this has not been shown in the literature.21,26,28,29 Research regarding dysphagia specifically with dynamic anterior cervical plating is limited. Telescoping dynamic plates are slightly thicker than other plate designs, and this may increase the risk of dysphagia.31 While Chin et al found no difference in dysphagia scores for patients who had a more prominent plate,32 Lee et al prospectively studied the risk of dysphagia for patients who underwent an ACDF with a thicker, telescoping Atlantis (Medtronic Sofamor Danek, Memphis, TN) plate compared to the thinner Zephir (Medtronic Sofamor Danek) plate, and they reported an increased risk of dysphagia with the thicker dynamic plate at all time points.31

One of the key reasons it is difficult to identify specific risk factors for dysphagia following an ACDF is that many surgeons fail to use an appropriate assessment tool to identify patients with dysphagia. In the studies reporting overall outcomes after an ACDF utilizing dynamic plates, most do not report dysphagia as a complication; of the studies that do report it, an incidence between 0.5 and 4% is present.33,34 However, given that when studies are designed to identify dysphagia in patients after undergoing an ACDF, the incidence ranges between 47 and 60%,20,21,22,23,24,25,26 it is likely that many of the studies evaluating overall efficacy of dynamic plates did not identify many patients with mild dysphagia.33,34 Oftentimes in the literature, dysphagia is recorded only when the patient brings it to the attention of the surgeon; however, recently there have been multiple questionnaires designed to objectively identify patients with this problem. The ideal assessment tool should be patient-reported scores and include global, functional, psychosocial, and physical scores.27 One of the first assessment tools developed to evaluate dysphasia after anterior cervical spine surgery was the Bazaz Dysphagia scale. It is based on telephone interviews, and patients grade their dysphagia as the following: none if they have had no episodes of swallowing difficulty; mild if they experience rare dysphagia that does not cause a significant problem; moderate if they have occasional dysphagia with certain foods; or severe if they have regular dysphagia with most foods.26 In addition, this has been modified to determine early postoperative dysphagia by having the patients rank their dysphagia on postoperative days 0, 1, 3, and 5 using the following point system: mild, 1 to 3 points; moderate, 4 to 6 points; and severe, 7 to 10 points. Patients with 12 or more points are considered to have postoperative dysphagia.35 While the Bazaz scale is commonly used, neither the traditional nor the modified Bazaz scale has been validated in the literature. Other nonvalidated assessment tools include the Dysphagia Disability Index and the World Health Organization Dysphagia Grade. Recently, more comprehensive assessment tools have been developed to evaluate dysphagia. The MD Anderson Dysphagia Inventory is a 20-question survey that asks patients questions about their global swallowing as well as questions regarding emotional, functional, and physical swallowing. It has been validated for cancers of the upper gastrointestinal tract against the SF-36.36 The eating assessment tool 10 (EAT-10) is a simpler, but still validated, 10-question test to identify patients with dysphagia. Patients answer on a scale of 0 to 4, and a score of more than 3 is consistent with dysphagia.37

16.2.2 Eating Assessment Tool 10 1. My swallowing problem has caused me to lose weight. 2. My swallowing problem interferes with my ability to go out for meals. 3. Swallowing liquids takes extra effort. 4. Swallowing solids takes extra effort. 5. Swallowing pills takes extra effort. 6. Swallowing is painful. 7. The pleasure of eating is affected by my swallowing. 8. When I swallow, food sticks in my throat.

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Cranial 9. I cough when I eat. 10. Swallowing is stressful.

Treatment While the development of dysphagia is common immediately after surgery, the prevalence and severity of dysphagia decreases overtime.27,31,38 It is often self-limiting, and it is rare for any further intervention such as a feeding tube or further surgery to be needed.39,40 A recent, prospective, randomized controlled trial found that the placement of steroid (triamcinolone) on a collagen sponge in the retropharyngeal space prior to closure significantly reduces the prevertebral soft-tissue swelling, and the mean visual analog score for odynophagia compared to controls at 2 weeks postoperative.41 This technique may be useful in preventing dysphasia in the early postoperative period.

16.2.3 Adjacent Segment Disease Despite highly predictable and successful outcomes following an ACDF, adjacent segment disease is a potential cause of postoperative disability and pain.42 Hilibrand and Robbins separated adjacent segment changes into two categories: adjacent segment degeneration, which is asymptomatic radiographic changes, and adjacent segment disease, which is new radiculopathy or myelopathy due to degenerative changes at a segment adjacent to a previous fusion.43 Adjacent segment disease is a common complication of cervical spine fusion. The incidence of symptomatic adjacent segment disease is estimated to be 2.9% per year, and 25% at 10-year follow-up.42

Avoidance Limiting this complication begins with precise surgical technique. It has been postulated that excessive stripping of the longus coli muscles, which may act as an important dynamic stabilizer, may increase the rates of adjacent segment disease.44,45 In addition, incorrect level localization with a needle annulotomy can increase the risk of adjacent level degeneration by 300%.46 Regardless of the plate design, encroachment of the plate on adjacent levels can lead to adjacent level changes. Park et al reported that the distance between the end of the plate and the adjacent disc should be greater than 5 mm to limit ossification of the adjacent disc47 (▶ Fig. 16.3). Lee et al reported a decrease in adjacent level degeneration when the cranial and caudal screws are placed at the endplate corners and angled away from the endplates rather than placing the screw perpendicular to the anterior cervical plate just along the endplates.48 This technique allows for the shortest possible plate, leading to less encroachment on adjacent levels. Because dynamic plates with slotted holes allow for the plate to translate toward the adjacent levels, their use may increase the risk of adjacent level ossification. The reported average amount of plate subsidence in the literature ranges from 1.6 to 13.1 mm (▶ Fig. 16.4), with an increase in a corpectomy compared to an ACDF.49,50,51,52 In an effort to limit this complication, some authors recommend using a hybrid construct with fully constrained screws at the caudal end and translational screws

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Fig. 16.3 Adjacent-level ossification due to plate encroachment (arrow).47

at the cephalad end.50 Utilizing the hybrid technique, DuBois et al retrospectively reported equivalent plate subsidence in 21 patients who underwent a multilevel ACDF with a fully constrained plate compared to 31 patients who had a dynamic plate.50 Because of this complication, telescoping dynamic plates were designed, and the use of these plates reduces the risk of plate encroachment on adjacent levels. Another mechanism in which dynamic plates may also accelerate adjacent segment disease is by changing the cervical alignment. Multiple studies have demonstrated that kyphotic malalignment may lead to an increase in adjacent segment disease,53,54 and the postoperative settling that occurs with the use of dynamic plates leads to a decrease in segmental lordosis.55

Diagnosis Park et al designed a grading system for adjacent level ossification on the lateral radiograph: grade 0 is no adjacent level ossification; grade 1 is mild, with ossification of less than 50% of the adjacent disc space; grade 2 is moderate, with ossification between 50 and 100% of the adjacent disc space; and grade 3 is severe, with complete ossification of the adjacent disc space.47 The diagnosis of adjacent level diseases is a combination of clinical and radiographic evidence and is defined as the occurrence of new radicular or myelopathic symptoms present for at least two consecutive visits localized to degenerated adjacent levels.42

Treatment Similar to patients with primary cervical spine radiculopathy, a trial of conservative care for patients who develop adjacent segment disease is warranted. While guidance from the literature is limited, multiple small studies have demonstrated the possible benefits of conservative care.42,56,57 Hilibrand et al reported 2-year follow-up on 46 patients who developed adjacent

Complications of Translational Anterior Cervical Plates

Fig. 16.4 Radiographs demonstrating how a dynamic plate can encroach on adjacent levels and lead to degenerative changes. (a) Immediately postoperative; (b) 3 months postoperative; (c) 6 months postoperative; and (d) 12 months postoperative.49

segment disease, and 13 patients had good or excellent results with the use of soft cervical collar, physiotherapy, and antiinflammatory medications; 6 patients had fair results with nonoperative treatment; and the remaining 27 underwent surgical management.42 When conservative treatment fails, surgery can provide excellent results.58,59,60 Hilibrand et al

retrospectively reported on 38 patients who were treated with either an ACDF or a corpectomy for adjacent segment disease. They found 84% of patients had a good to excellent result with an average of follow-up of more than 5 years; additionally, they found that while the number was limited (14), patients who underwent a corpectomy had a superior outcome.58

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Cranial Recently, some authors have reported on the efficacy of total disk arthroplasty for the treatment of adjacent segment disease.61,62 Phillips et al described the use of a single-level cervical disk replacement for adjacent segment disease after an ACDF in 26 patients, and they compared this cohort with a group of patients undergoing a primary total disk arthroplasty. At a 1-year follow-up, they reported no difference in Neck Disability Index scores, VAS pain scores, and revision rates in the two groups, indicating that a total disk arthroplasty is as efficacious in treating adjacent segment disease as primary pathology in the short term.61 Posterior procedures, such as a laminoplasty or a laminectomy and fusion, are also valid treatment options for patients with adjacent segment disease,63,64 and 360-degree fusions may be needed in patients who have kyphosis and multilevel disease, or patients who are at a high risk for a nonunion.65

16.2.4 Pseudarthrosis Pseudarthrosis, or nonunion, is the absence of solid fusion, and this may or may not cause a patient to be clinically symptomatic. Wolf’s law states that an increase in force across a segment of bone will cause the bone to remodel and become stronger. Because of this, the increased load sharing that occurs with a dynamic plate theoretically should lead to a decrease in the pseudarthrosis rate.12,14,15 However, given the high fusion rate for an ACDF using a fully constrained plate, a statistically significant improved fusion rate with the use of dynamic plates has been difficult to demonstrate in the literature.49,50,55,66 In the only randomized controlled trial comparing translationally semiconstrained and fully constrained plates, Pitzen et al found no difference in pseudarthrosis rate at 2 years in 132 patients.55 In a small retrospective study of 52 patients who underwent a multilevel ACDF, DuBois et al actually reported an increased risk of pseudarthrosis with a dynamic plate (5 vs. 16%, p = 0.05).50 While clinical studies have not been able to demonstrate superior fusion rates with dynamic plates, the overall fusion rates with these plates have been excellent.33,49,50,55,66 In a prospective, multicentered study by Casha and Fehlings of 195 patients who underwent a single- or multilevel ACDF or corpectomy using a dynamic plate, they reported a 93.8% fusion rate.33

extension radiographs has been validated with a mean error of less than 0.5 degrees and 0.5 mm in the cervical spine.68,69 In contrast to the AANS study, multiple studies have reported superior results with a CT scan.70,71 Buchowski et al found that CT imaging has the highest agreement with intraoperative findings70 (▶ Fig. 16.5), and Ploumis et al found that CT was more sensitive for identifying a pseudarthrosis and has a higher interobserver agreement.71

Treatment Approximately 33% of patients with a pseudarthrosis after an ACDF will be asymptomatic and will not require any intervention.72,73,74 In addition, many patients will have only mild symptoms and can be managed conservatively.74 Unfortunately, there is no literature evaluating the best conservative care.72 However, there are multiple studies that have demonstrated excellent outcomes with surgical intervention.72,73,75,76,77 Once the decision has been made to operate, the surgeon has the option to approach the pseudarthrosis anteriorly or posteriorly. The posterior approach eliminates the risk of damaging crucial structures in a revision anterior exposure2 and increases the fusion rate.72,75 Approaching a pseudarthrosis anteriorly allows for the surgeon to take down the painful pseudarthrosis, restore sagittal alignment and intervertebral disc height, and

Diagnosis Cervical arthrodesis can be loosely defined as an absence of motion in flexion/extension radiographs, and the presence of bridging trabecular bone across the vertebral bodies.33 Multiple techniques have been used for assessing a cervical fusion. In 2009, the Joint Section on Disorders of the Spine and Peripheral Nerves of the American Association of Neurological Surgeons (AANS) and Congress of Neurological Surgeons published a systematic review of the literature and concluded that the absence of motion between the spinous processes on dynamic radiographs is the best method for evaluating a fusion in the subaxial cervical spine.67 They reported that the evidence was stronger for this method than for evaluating a fusion with a computed tomographic (CT) scan. When using dynamic radiographs to evaluate a pseudarthrosis, advanced computer programing, such as the use of Quantitative Motion Analysis technology (QMA; MedicalMetrics, Inc., Houston, TX), to evaluate flexion/

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Fig. 16.5 A sagittal image from a CT scan that clearly demonstrates a pseudarthrosis.70

Complications of Translational Anterior Cervical Plates perform a thorough decompression.10 Zdeblick et al reported on 35 patients who underwent an anterior revision for a pseudarthrosis, and they found a 97% fusion rate with 86% of patients reporting good or excellent results.77

16.3 Screw Pullout/Hardware Failure While a constrained plate is designed to limit screw pullout, multiple reports have demonstrated that even with a fully or semiconstrained plate, screw pullout can occur and may lead to significant damage to anterior structures in the neck78,79,80,81 (▶ Fig. 16.6). Casha and Fehlings prospectively reported an 8.2% risk of screw pullout or breakage in 195 patients who underwent an ACDF or corpectomy utilizing a dynamic plate.33 While hardware failure is possible with the use of translational, semiconstrained anterior cervical plates, multiple studies—including a prospective, randomized trial by Pitzen et al of 132 patients, reported less risk of hardware failure with translational semiconstrained plates compared to fully constrained plates.52,55,82 The most common risk factor in the literature for hardware failure is multilevel procedures,33,83 and all patients who have a multilevel corpectomy should have posterior instrumentation to limit this complication.83 Screw trajectory and screw type can also affect the likelihood of hardware failure.84,85 Screws

angled 12 degrees medial and 12 degrees cephalad/caudad have a lower pullout strength compared to screws placed at 90 degrees to the plate,84,85 and variable-angle screws have an increased pullout strength compared to fixed-angle screw.85 Additionally, while a restoration of cervical lordosis is desirable, hyperlordosis can lead to early graft and hardware faiure.86 All patients who have hardware failure should undergo an anterior revision to remove the failed hardware, given that hardware failure can lead to devastating anterior complications including esophageal tears and graft dislodgement.78,86

16.4 Graft Settling and Cervical Alignment The restoration of disc space height and cervical lordosis is an important goal for patients undergoing an ACDF, given restoration of lordosis has been shown to improve rates of neurologic recovery in patients with myelopathy,87 and possibly decrease the rates of adjacent segment degeneration.53,54 While dynamic plating has the benefit of increasing compression and load sharing across the graft, the compression and translation may also lead to a loss of lordosis. Pitzen et al reported patients who underwent an ACDF utilizing a dynamic plate had an average loss of segmental lordosis of 4.3 degrees compared to 0.7 degrees in the static plate group (p = 0.003). Ghahreman et al reported on 55 patients who underwent an ACDF utilizing a dynamic plate and found an average graft subsidence of 1.7 mm at 6 months postoperatively.34 Hong et al reported a statistically significant increase in graft subsidence (2.9 vs. 1.9 mm) when a translationally semiconstrained plate was used compared to a rotationally semiconstrained plate.88

16.5 Summary Dynamic anterior cervical plates were designed to decrease stress shielding, improve load sharing, provide overall resistance to motion, and thereby increase fusion rates. While multiple studies have shown excellent fusion rates with these implants,48,49,54,65 the only randomized controlled trial comparing a translationally semiconstrained plate to a fully constrained plate failed to show any difference in the rate of arthrodesis.55 Additionally, the use of these plates may increase the risk of adjacent segment disease,49,50,51,52 dysphagia,31 and a loss of segmental lordosis.55 Modifications of the plate design have been made to limit some of these complications, such as telescoping plates to limit plate encroachment on adjacent levels49,50,51,52; however, the telescoping plates are slightly thicker, and may lead to an increase in dysphagia.31 The current evidence suggests that excellent results are possible using dynamic anterior cervical plates; however, associated complications have been documented in the literature, with no increased clinical benefit.

16.6 Key Points ●

Fig. 16.6 A lateral radiograph of the cervical spine demonstrates screw pullout after utilization of a dynamic plate.

Dynamic anterior cervical plates were designed to decrease stress shielding, improve load sharing, provide overall resistance to motion, and thereby increase fusion rates.

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Cranial ●

●

●

Dynamic plates have not been shown to lead to an increase in fusion rates compared to static plates. Dynamic plates may be associated with an increase in dysphagia, adjacent segment degeneration, and a loss of segmental lordosis. The use of dynamic plates can lead to high fusion rates, low complications, and good clinical results.

16.7 Key References [1] Reidy D, Finkelstein J, Nagpurkar A, Mousavi P, Whyne C. Cervical spine loading characteristics in a cadaveric C5 corpectomy model using a static and dynamic plate. J Spinal Disord Tech. 2004; 17(2):117–122

A cadaveric C5 corpectomy model is used to determine the load transmitted through the graft when a dynamic or a static anterior cervical plate is used. The load transferred through the graft increased from 57 to 80%, and the load transmitted through the plate decreased from 23 to 9% when a dynamic plate is used. [2] Lee MJ, Bazaz R, Furey CG, Yoo J. Influence of anterior cervical plate design on Dysphagia: a 2-year prospective longitudinal follow-up study. J Spinal Disord Tech. 2005; 18(5):406–409

This is a prospective study of 156 patients who underwent an ACDF designed to determine if plate thickness increases the risk of dysphagia. A total of 126 patients had an ACDF with a thicker, telescoping Atlantis (Medtronic Sofamor Danek, Memphis, TN) plate, and 30 patients had a thinner Zephir (Medtronic Sofamor Danek) plate used. There was an increased risk of dysphagia with the thicker dynamic plate at all time points. [3] Casha S, Fehlings MG. Clinical and radiological evaluation of the Codman semiconstrained load-sharing anterior cervical plate: prospective multicenter trial and independent blinded evaluation of outcome. J Neurosurg. 2003; 99 (3) Suppl:264–270

This was a 10-center, prospective study of 195 patients undergoing an ACDF utilizing a dynamic anterior plate. They reported a 93.8% fusion rate and a low complication rate. [4] DuBois CM, Bolt PM, Todd AG, Gupta P, Wetzel FT, Phillips FM. Static versus dynamic plating for multilevel anterior cervical discectomy and fusion. Spine J. 2007; 7(2):188–193

This study retrospectively looked at 21 patients who underwent a multilevel ACDF with a static plate and 31 who had a dynamic plate used. They found no clinical difference, but there was an increased risk of pseudarthrosis (16 vs. 5%, p = 0.05) in the dynamic plate group. [5] Pitzen TR, Chrobok J, Stulik J, et al. Implant complications, fusion, loss of lordosis, and outcome after anterior cervical plating with dynamic or rigid plates: two-year results of a multi-centric, randomized, controlled study. Spine. 2009; 34(7):641–646

This is the only randomize-controlled trial comparing dynamic and static plates. They reported no difference if fusion rates; however, the dynamic plate had less hardware failure, but a greater loss of segmental lordosis.

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Complications of Translational Anterior Cervical Plates [32] Chin KR, Eiszner JR, Adams SB, Jr. Role of plate thickness as a cause of dysphagia after anterior cervical fusion. Spine. 2007; 32(23):2585–2590 [33] Casha S, Fehlings MG. Clinical and radiological evaluation of the Codman semiconstrained load-sharing anterior cervical plate: prospective multicenter trial and independent blinded evaluation of outcome. J Neurosurg. 2003; 99 (3) Suppl:264–270 [34] Ghahreman A, Rao PJ, Ferch RD. Dynamic plates in anterior cervical fusion surgery: graft settling and cervical alignment. Spine. 2009; 34(15):1567–1571 [35] Papavero L, Heese O, Klotz-Regener V, Buchalla R, Schröder F, Westphal M. The impact of esophagus retraction on early dysphagia after anterior cervical surgery: does a correlation exist? Spine. 2007; 32(10):1089–1093 [36] Chen AY, Frankowski R, Bishop-Leone J, et al. The development and validation of a dysphagia-specific quality-of-life questionnaire for patients with head and neck cancer: the M. D. Anderson dysphagia inventory. Arch Otolaryngol Head Neck Surg. 2001; 127(7):870–876 [37] Belafsky PC, Mouadeb DA, Rees CJ, et al. Validity and reliability of the Eating Assessment Tool (EAT-10). Ann Otol Rhinol Laryngol. 2008; 117(12):919–924 [38] Fountas KN, Kapsalaki EZ, Nikolakakos LG, et al. Anterior cervical discectomy and fusion associated complications. Spine. 2007; 32(21):2310–2317 [39] Martin RE, Neary MA, Diamant NE. Dysphagia following anterior cervical spine surgery. Dysphagia. 1997; 12(1):2–8, discussion 9–10 [40] Stewart M, Johnston RA, Stewart I, Wilson JA. Swallowing performance following anterior cervical spine surgery. Br J Neurosurg. 1995; 9(5):605–609 [41] Lee SH, Kim KT, Suk KS, Park KJ, Oh KI. Effect of retropharyngeal steroid on prevertebral soft tissue swelling following anterior cervical discectomy and fusion: a prospective, randomized study. Spine. 2011; 36(26):2286–2292 [42] Hilibrand AS, Carlson GD, Palumbo MA, Jones PK, Bohlman HH. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am. 1999; 81(4):519–528 [43] Hilibrand AS, Robbins M. Adjacent segment degeneration and adjacent segment disease: the consequences of spinal fusion? Spine J. 2004; 4(6) Suppl:190S–194S [44] Goffin J, van Loon J, Van Calenbergh F, Plets C. Long-term results after anterior cervical fusion and osteosynthetic stabilization for fractures and/or dislocations of the cervical spine. J Spinal Disord. 1995; 8(6):500– 508, discussion 499 [45] Kettler A, Hartwig E, Schultheiss M, Claes L, Wilke HJ. Mechanically simulated muscle forces strongly stabilize intact and injured upper cervical spine specimens. J Biomech. 2002; 35(3):339–346 [46] Nassr A, Lee JY, Bashir RS, et al. Does incorrect level needle localization during anterior cervical discectomy and fusion lead to accelerated disc degeneration? Spine. 2009; 34(2):189–192 [47] Park JB, Cho YS, Riew KD. Development of adjacent-level ossification in patients with an anterior cervical plate. J Bone Joint Surg Am. 2005; 87 (3):558–563 [48] Lee DH, Lee JS, Yi JS, Cho W, Zebala LP, Riew KD. Anterior cervical plating technique to prevent adjacent-level ossification development. Spine J. 2013; 13(7):823–829 [49] Balabhadra RS, Kim DH, Zhang HY. Anterior cervical fusion using dense cancellous allografts and dynamic plating. Neurosurgery. 2004; 54(6):1405– 1411, discussion 1411–1412 [50] DuBois CM, Bolt PM, Todd AG, Gupta P, Wetzel FT, Phillips FM. Static versus dynamic plating for multilevel anterior cervical discectomy and fusion. Spine J. 2007; 7(2):188–193 [51] Epstein NE. Anterior cervical dynamic ABC plating with single level corpectomy and fusion in forty-two patients. Spinal Cord. 2003; 41(3):153–158 [52] Epstein NE. Fixed vs dynamic plate complications following multilevel anterior cervical corpectomy and fusion with posterior stabilization. Spinal Cord. 2003; 41(7):379–384 [53] Katsuura A, Hukuda S, Saruhashi Y, Mori K. Kyphotic malalignment after anterior cervical fusion is one of the factors promoting the degenerative process in adjacent intervertebral levels. Eur Spine J. 2001; 10(4):320–324 [54] Hansen MA, Kim HJ, Van Alstyne EM, Skelly AC, Fehlings MG. Does postsurgical cervical deformity affect the risk of cervical adjacent segment pathology? A systematic review. Spine. 2012; 37(22) Suppl:S75–S84 [55] Pitzen TR, Chrobok J, Stulik J, et al. Implant complications, fusion, loss of lordosis, and outcome after anterior cervical plating with dynamic or rigid plates: two-year results of a multi-centric, randomized, controlled study. Spine. 2009; 34(7):641–646 [56] Elsawaf A, Mastronardi L, Roperto R, Bozzao A, Caroli M, Ferrante L. Effect of cervical dynamics on adjacent segment degeneration after anterior cervical fusion with cages. Neurosurg Rev. 2009; 32(2):215–224, discussion 224

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Ectopic Ossification following ACDF or Disc Replacement

17 Ectopic Ossification following Anterior Cervical Discectomy and Fusion or Disc Replacement Pouya Alijanipour, Gregory D. Schroeder, and Alexander R. Vaccaro

17.1 Introduction Various surgical procedures including instrumented and noninstrumented anterior cervical discectomy and fusion (ACDF) and cervical artificial disc replacement (C-ADR) have been applied to treat degenerative cervical spine disease. The concept of adjacent segment pathology (ASP) consists of postoperative development of degenerative changes in the neighboring functional segments following these surgical procedures. This is an incompletely understood phenomenon and it is unclear whether it is the consequence of the surgery or it is the natural progression of the original degenerative disease. Heterotopic ossification (HO), appearance of ectopic osseous tissue, is a recognized complication following many orthopedic procedures (particularly hip and knee arthroplasty).1 Similarly, HO can happen following surgical procedures of spine, particularly with instrumentation, such as fusion and artificial disc replacement.2,3 However, there are several non-surgery-related factors that can affect its occurrence. These factors include trauma, immobilization, and patient-related risk factors such as demographic factors and genetic predisposition. HO has been postulated to be an unexpected metaplastic tissue that results from deviation of a normal adaptive response for cells with regenerative potential.4 In the presence of triggering factors such as surgical trauma, an interaction between local and systemic signals within an osteoconductive environment facilitates transformation of progenitor stem cells into osteogenic cells, such as osteoblasts. Bone morphogenetic proteins (BMPs) are one of these signals with a role in repair mechanisms in connective, vascular, and osseous tissues,5,6 as well as transcription of genes that lead to osteoblast differentiation of progenitor cells.7 Adjacent level ossification development (ALOD) is a kind of HO and occurs as a postoperative complication following surgical treatment of degenerative cervical disease. It indicates ectopic bone formation in the outer anulus fibrosus and/or anterior longitudinal ligament (ALL) at the neighboring cranial and caudal levels. Nevertheless, HO can also be formed at the level of a prosthetic cervical disc. Both ALOD and HO are postoperative appearance of osseous tissue in the soft tissues at or near the site of surgery where no bone is formed under normal conditions. However, ALOD and same-level HO seem to have different pathophysiology and biomechanical risk factors. Although the degenerative forms of ASP result in bone formation, ALOD is considered as a distinct entity. Patients with degenerative ASP are more likely to have disc protrusion, reduced disc height, facet arthrosis, end-plate sclerosis, spondylolisthesis, and marginal osteophyte formation of the adjacent motion segments, whereas in ALOD, non-marginal bone (such as ALL ossification) is formed and other signs of advanced degeneration are not observed.8 It should be considered that determination of grades of both ALOD and HO is subjective and is based on their morphology.9,10 Nonetheless, the reports of ALOD and HO also depend on the

type of imaging technique (CT scan vs. plain radiography). This may particularly be important in equivocal situations, where residual osteophytes, prosthesis subsidence, asymmetric endplate preparation, and induced bone remodeling could be confused with HO.11 Both ALOD and HO seem to be progressive and do not cease even for years following surgery.12,13 However, their clinical importance is yet to be completely determined. No study has shown that ALOD or HO following an ACDF or cervical disc arthroplasty affects the functional outcome or satisfaction level of the patients. However, there are few studies with long-term follow-up. Progressive ALOD and HO may be concerning and worth scrutiny, particularly in cases of disc replacement surgery, where they can neutralize the original intent of the procedure, which is restoring biomechanical motion.

17.2 Ectopic Ossification in Anterior Cervical Discectomy and Fusion ACDF is a successful surgical treatment for cervical spinal disease associated with radiculopathy and myelopathy refractory to nonoperative management.14 ACDF with plating achieves immediate postoperative stability, resulting in higher fusion rates, resistance to graft subsidence, and shorter immobilization time when compared to noninstrumented fusions.15,16 Despite the advantages of adding a plate, the technique has been associated with increased risk of certain complications, including degenerative changes and HO in the adjacent disc spaces.17,18 ALOD was initially described as incidental degenerative changes at the discs adjacent to the fused levels; yet, subsequent studies demonstrated certain technical details such as improper positioning and oversizing of the plate could considerably influence its appearance.19,20 As mentioned earlier, doubts exist regarding clinical importance of ALOD21 and there is no evidence showing its presence is associated with pain, decreased motion, radiculopathy, myelopathy, cervical instability, or any other discomfort.22 Furthermore, it is unclear whether ALOD increases the risk of reoperation. Therefore, clinical outcome-based studies with long-term follow-up are required to examine the clinical relevance of ALOD.

17.3 Classification ALOD is commonly an exclusively radiographic finding with varying severity. There is no validated classification system for ALOD that correlates with treatment plan or functional outcomes. The classification system proposed by Park et al (▶ Table 17.1) is currently popular in the literature.9 This classification is based on the radiographic morphology and is presented in ▶ Fig. 17.1.

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Cranial Table 17.1 Grading classification for severity of ALOD proposed by Park et al.9 Grading

Description of ALOD

0

Not present

I (mild)

Extends less than 50% of the disc space

II (moderate)

Extends equal to or greater than 50% of the disc space yet does not bridge completely

III (severe)

Complete bridging of the adjacent disc level

Abbreviations: ALOD, adjacent level ossification development

Fig. 17.1 Grades of adjacent level ossification development as proposed by Park et al.9 (Reprinted with permission from Kim et al.8)

17.4 Incidence There is considerable variation in the incidence of ALOD reported by different studies, which could be due to various factors including characteristics of the patients, surgical techniques, follow-up duration, and other reasons. ALOD occurs in both instrumented and noninstrumented ACDFs. However, it has a lower incidence and occurs in milder forms in noninstrumented ACDFs. ALOD can occur within the first 3 months after surgery. It appears in 5% of patients by 6 weeks after anterior cervical plating.23 Nevertheless, the absence of ALOD in the early postoperative period does not preclude the possibility of ALOD development in the future. Patients without ALOD at 3 and 6 months after an ACDF were reported to have an incidence of 23.5% and progression into advanced grade ALOD of 14.9% by

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24 months postoperatively. In patients with mild ALOD by 3, 6, and 12 months after surgery, the incidence of progression to moderate (grade II) or severe (grade III) ALOD in the second year was 87.5, 62.5, and 37.5%, respectively.12 Based on these findings, Park et al suggested that any ALOD appearing in the first year following surgery has substantial likelihood for progression into high-grade ALOD by 2 years.12 In contrast to instrumented ACDF, ALOD in noninstrumented ACDF does not seem to be progressive and studies reported relatively constant rate of 5.5% at 6-, 12-, and 24-month followups.24 Comparative studies to calculate the real odds ratio for occurrence of ALOD in plated and noninstrumented fusion are still missing. Nevertheless, in a post hoc analysis of a level-I investigational device exemption randomized clinical trial study, Garrido et al compared Bryan disc implant with plated ACDF in terms of

Ectopic Ossification following ACDF or Disc Replacement incidence of ALOD within 4 years of postsurgery. They found ACDF had significantly higher ALOD grading scores compared with C-ADR at both 2-year (64 vs 25%, respectively) and 4-year (84 vs. 52%, respectively) follow-ups.2 Considering similarity of surgical approach and technique (including use of Caspar retractors) for both procedures in this study, these findings may indicate that motion preservation and other kinematic changes associated with C-ADR can mitigate or defer the incidence of ALOD.

17.5 Pathophysiology Previous studies showed that following cervical arthrodesis, biomechanical changes in the adjacent disc levels (such as increase in intradiscal pressure and strain along with increased segmental motion) may occur because of elimination of motion at the fused segments and transmission of the load to the adjacent discs.25,26,27 However, it remains controversial whether such changes predispose the adjacent discs to degenerative changes and ALOD. Several mechanisms were suggested for ALOD following instrumented ACDF, with most being focused on surgical technique–related risk factors.8 It is possible that similar to other types of HO, ALOD develops during the healing process of injured soft tissues. Constant irritation of ALL or anterior anulus fibrosus by the anterior plate during flexion–extension movements may aggravate the cycle of physical irritation–inflammation–repair process and contribute to ALOD.8

17.6 Surgical Procedure Implications There is evidence showing that certain modifications in plating technique decrease the incidence of ALOD. The proximity of the plate to the adjacent disc spaces is considered as a major risk determinant for ALOD.9,12 Park et al first proposed this correlation and demonstrated that ALOD occurred at a significantly higher rate and more severe grade in patients with plates within 5 mm of the adjacent disc spaces (odds ratio: 3.3, 95% confidence interval [CI]: 0.8–13.4).9 This observation was consistent for both cephalad and caudal adjacent levels. Interestingly, the risk of progression from no/mild ALOD at the first postoperative year to moderate to severe ALOD at the end of the second postoperative year was 2 to 2.7 times higher when the plates were within 5 mm of the adjacent disc levels.12 Meticulous positioning of the plate may be of particular importance in cases where adequate decompression requires considerable vertebral body resection due to the presence of larger posterior osteophytes or ossification of the posterior longitudinal ligament. Therefore, the appropriate strategy is to use the shortest plate possible and maintaining the caudal and cranial ends of the plate as distant as possible from the neighboring discs.19 To achieve these goals, it has been suggested that the most cranial and caudal screws be positioned immediately next to and with divergent trajectory with respect to their respective operative level end plates on the sagittal plane. This would allow for longer screws and therefore more solid fixation compared to the positioning of screws parallel to the endplates.21,28

Placing angled screws at the corner of operative endplates may have some disadvantages. This technique may pose the risk of breaching the endplate and graft and therefore might jeopardize the fusion. In order to lessen this risk, it has been recommended that the graft be recessed a few millimeters to avoid any contact with the screws.28 Another concern with angled screws at the corner of operative endplate is the risk of loosening and pullout, given that they might not have sufficient cortical bone support. Some authors have postulated that certain technical details such as stripping the ALL, excessive dissection of the anterolateral insertion of longus coli muscles, and use of distractor pins may have role in ALOD, and therefore unnecessary dissection or manipulations should be avoided.19,20,24 Furthermore, it has been postulated that mismatch of modulus of elasticity between the bone and metallic implants, bone debris resulting from bone resection or screw holes, or irritation of ALL by the plate can potentially contribute to ALOD.28 However, no evidence exists to definitively prove these theoretical associations. The overall incidence and severity of ALOD seems to be higher at cephalad compared to caudal disc levels.9,12,24,28 This may be due to the fact that the cranial vertebral body is shorter than the caudal body, and therefore, the plate is likely to be closer to the cephalad disc.9,28 Furthermore, greater bone resection is usually performed at cranial compared with caudal end plates. However, there is also an increased risk of ALOD in noninstrumented ACDFs in the cranial levels compared with caudal levels,24 so it is likely that factors other than the instrumentation are also involved. Moreover, ALOD does not necessarily happen in all patients with plate-to-disc distance of less than 5 mm.2,9

17.7 Ectopic Ossification in Cervical Disc Arthroplasty The original philosophy of cervical disc replacement following anterior decompression was to decrease the incidence of fusion-associated adjacent segment degeneration via preservation of motion in the operated disc space.3 Despite its successful and promising outcomes, subsequent studies with longer follow-up reported an increasing incidence of spontaneous radiographic arthrodesis following C-ADR,29,30,31,32 and furthermore, high-grade HO and spontaneous fusion can occur with both semiconstrained and nonconstrained types of prosthetic discs.3, 29,32,33 HO after C-ADR has similar appearance to an aging osteophyte or fusion mass following interbody fusion.34 However, even its advanced forms do not appear to have clinical implications.33,35 For instance, in one study using Prodisc-C implants, despite 63% of patients demonstrating moderate to severe HO at 4 years of follow-up, 92% would undergo the same procedure again.33 However, complete fusion around prosthetic disc is unfavorable and, similar to ACDF, may theoretically accelerate the risk of degenerative changes in adjacent segments. Additionally, it is important to note that the vast majority of studies performed on cervical artificial discs are industry-sponsored trials in which the authors have significant conflicts of interest. Also patient-reported outcomes in these studies might be biased by the desire of the patients who enrolled to undergo an artificial disc compared to an ACDF.

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Cranial

17.7.1 Classification McAfee et al proposed a morphology-based classification originally for HO following lumber disc arthroplasty (▶ Table 17.2), but the same classification system has been utilized for cervical disc replacement.10 Nevertheless, most studies have shown that the grade of HO is not correlated with clinical outcome parameters such as overall satisfaction and SF-36,35 pain scores, and neck disability index.29,33,36 Although two studies demonstrated a correlation between severity of HO and loss of motion measured on flexion–extension radiographs, the presence of HO did not affect clinical outcomes.35,37

17.7.2 Incidence Significant discrepancy exists in the incidence of HO reported by different studies. The reasons for this discrepancy can be difference in patient characteristics, perioperative care protocols, details of surgical technique, biomechanical characteristics of each type of implant, and sensitivity of method of detection of HO (CT scan vs. simple X-ray imaging).38 A meta-analysis showed that the incidence of overall HO ranged from 17.8 to 72.3% (mean: 44.6%) at 1 year after surgery, and 28.8 to 78.5% (mean: 58.2%) at 2 years after surgery.3 Similarly, the incidence of advanced HO at 1 and 2 years after surgery ranged from 4.2 to 23.1% (mean: 11.1%) and from 8.5 to 32.3% (mean: 16.7%), respectively.3 However, similar to ALOD in instrumented ACDF, the incidence of HO following C-ADR increases over time and the existing reports could be confounded by follow-up duration. In one study, the incidence of high-grade HO following Prodisc-C increased progressively with time being 9 and 63% at 6 months and 4 years of followup, respectively.33 Therefore, the occurrence of HO in C-ADR can be varied based on follow-up duration. The incidence of HO was reported as 21 to 76% for the Bryan Cervical Disc (Medtronic Sofamor Danek, Memphis, TN) at 2 years of follow-up,11, 34,35,39 71 to 79% for Prodisc-C (Synthes Inc., Paoli, PA) at 2 years of follow-up,11,29,33 14 and 17% for Prestige LP (Medtronic Sofamor Danek, Memphis, TN) at 14 and 30 months of follow-up, respectively,34,40 and 0.4% for PCM (Cervitech Inc., Rockaway, NJ) at 1 year of follow-up.41 Moreover, comparative studies showed longer HO-free survival with the Bryan disc (48.4 ± 7.4 months)

compared with Mobi-C (LDR Medical, Troyes, France) (13.7 ± 0.9 months) and Prodisc-C implants (14.4 ± 3.4 months),11 with overall odds ratio for HO being 5.3 and 7.4 for Mobi-C and Prodisc-C compared with Bryan implants.42 Moreover, it has been suggested that the ball-and-socket type disc implants (such as Prodisc-C) tend to alter the biomechanics of the cervical spine more than other implant types and this would lead to increased risk of HO formation.43

17.7.3 Pathophysiology Patient-related conditions, abnormal segmental motion, BMP released in reaction to inflammation or trauma, and chronic irritation of the surrounding soft tissues have been suggested to contribute to HO following C-ADR.33,44 Some authors postulated that mechanical factors contribute to the morphology of HO based on the difference of morphology of anterior and posterior HO, and due to the fact that HO continues to grow even until 4 years following C-ADR.33 Increased age, male gender, presence of preoperative osteophytes including uncovertebral hypertrophy, preoperative ossification of ligamentum nuchae or posterior longitudinal ligament, preoperative chronic kyphosis, limited preoperative range of motion (flexion–extension < 4 degrees), preoperative hard disc disease requiring excessive bone work, multilevel CADRs, certain levels (C3–C4 and C4–C5), type of implant, and hybrid implantation (with cage or artificial disc on the upper adjacent level) have been described as potential risk factors for HO following C-ADR.29,33,34,35,38,42,45,46,47 Unlike reconstructive procedures of peripheral joints, especially hip and knee,1,48 the benefit of perioperative NSAIDs in the prevention of HO is unclear with no available direct evidence and inconsistency of results of the other studies.49 However, some patient-related risk factors such as older age, male gender, and hypertrophic osteoarthritis are general risk factors for HO following all orthopedic procedures.1

17.7.4 Surgical Procedure Implications Various details of the surgical procedure may contribute to formation or prevention of HO in cervical disk replacement. HO could be triggered by surgical trauma to the soft tissue and osseous structures; however, such trauma would likely only be

Table 17.2 Modified McAfee classification for HO following C-ADR.10 Type

Morphologic Description

0

No HO present

I

HO present in islands of bone within soft tissue but not influencing the range of motion of the vertebral motion segment. Bone is not between the planes formed by the two vertebral endplates.

II

HO possibly affecting the vertebral range of motion. HO present between the two planes formed by the vertebral endplates but not blocking or articulating between adjacent vertebral endplates or osteophytes.

III

The range of motion of the vertebral endplates is blocked by the formation of HO and/or postoperative osteophytes on flexion-extension or lateral bending radiographs

IV

HO causing inadvertent arthrodesis. Bony ankylosis. Bridging trabecular bone continuous between adjacent endplates and > 3° of motion of lateral flexion-extension radiographs.

Abbreviations: C-ADR, cervical artificial disc replacement; HO, heterotopic ossification.

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Ectopic Ossification following ACDF or Disc Replacement responsible for early postoperative HO. Comparatively, the unorthodox biomechanical changes associated with implantation of prosthetic discs may be responsible for late-onset progressive HO. However, these different mechanisms may coexist in some instances and therefore increase the risk of HO synergistically. During C-ADR procedure, to obtain adequate exposure of disc space, the bony attachments of the longus colli muscles have to be severed, and this causes release of inflammatory cytokines, including osteogenic proteins, that may lead to HO formation.35 Furthermore, bone particles released during drilling of the endplates (particularly in implants such as Bryan discs where extensive drilling and milling is required), wear debris of the polyethylene, keeling procedure in certain types of prosthetic discs (such as Prodisc-C implants), and stress between the endplate and the implant are considered to have role in the formation of HO following C-ADR procedures.11,35 The influence of marrow exposure (during keeling procedure) on anterior HO remains unclear. Although keeled implants (Prodisc-C) were associated with higher incidence of HO compared with nonkeeled implants such as Mobi-C and Bryan (incidence rates were 90, 65, and 53%, respectively), this finding was limited to the upper vertebral body.33 Despite similar surgical preparation of the superior and inferior endplates, anterior HO rarely occurred in the lower vertebral body, questioning the role of endplate preperation.33 Furthermore, appropriate positioning of the implant and less lordotic segmental angle between the footplates of the prosthetic disc were reported as protective factors for HO following C-ADR,34 while overcorrection of the height of disc space and increase in range of motion (hypermobility) of the implantation segment have been associated with increased risk of HO formation.43 Interestingly and in contrast to the common expectation, Suchomel et al observed less severe HO formation with implants with center of rotation positioned slightly more anteriorly. They also suggested the presence of mismatch between the center of rotation of the implant and measured center of rotation on dynamic radiographs as an association with higher severity of HO.50

17.8 Conclusion The influence of ALOD and HO on clinical outcomes of fusion and disc replacement procedures for cervical degenerative disease is not well understood yet. Both conditions can be progressive and concerns exist regarding their clinical implications in patients with longer follow-up, particularly in patients undergoing C-ADR. Patient-related, surgery-related, and implantrelated factors have been correlated with ectopic bone formation. Further high-quality research would elucidate the real importance of these phenomena and would lead to appropriate strategies for prevention of their occurrence or cessation of their progression in high-risk conditions.

17.9 Key Points ●

HO and ALOD have been described as postoperative complication of C-ADR and ACDF, respectively.

●

●

●

Both conditions seem to be progressive; yet, they have not been shown to influence clinical outcomes or increase the rate of reoperation. Similar to ectopic bone formation in other orthopedic procedures, modifiable and nonmodifiable risk factors have been correlated with these conditions. It seems that surgical technique–related details and implant type can considerably influence the occurrence of both conditions.

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Failure of Anterior Cervical, Low-Profile, Stand-Alone Screw–Plate Devices

18 Failure of Anterior Cervical, Low-Profile, Stand-Alone Screw–Plate Devices Michael P. Kelly and Wilson Z. Ray

18.1 Introduction Low-profile, stand-alone cervical implants have been introduced, in an effort to reduce implant prominence and decrease operative times in anterior cervical discectomy and fusion (ACDF).1,2,3 Recent results are promising, though dysphagia after cervical surgery is multifactorial and not solely related to plate prominence.4,5,6,7,8,9 In fact, dysphagia is not uncommon following posterior cervical surgeries.9,10 The majority of these integrated devices are manufactured from polyetheretherketone (PEEK), which may have a higher risk of pseudarthrosis than autograft or allograft.11 Dysphagia following cervical spine surgery is common.4,5,9 This is not surprising, given the retraction of the esophagus and infrahyoid muscles (i.e., “strap muscles”) with a standard Smith–Robinson approach to the anterior cervical spine. Patient variables associated with postoperative dysphagia include gender, age, and the presence of prior anterior cervical surgeries.4,8, 9 Multilevel surgeries, surgeries performed above C4, and longer retractor times have been associated with postoperative dysphagia.4 Finally, some evidence has implicated plate thickness as a factor associated with postoperative dysphagia. These findings have not been consistent and the effect of implant design and prominence on dysphagia remains undefined.7,9 Dysphagia is often acute and usually does not become a chronic condition, though dysphagia that presents at 1 year postoperatively may not resolve.12 It is important to consider the methods used to detect dysphagia, as prior reports have included clinician-based assessments, patient-reported outcome scores, and barium swallow studies. Of these tests, patient-reported outcome scores are likely the most specific to a clinically relevant dysphagia.13 Too sensitive a test will reveal dysphagia that is of little to no consequence to the patient. Curiously, postoperative dysphagia is not unique to anterior cervical surgeries, given that it is not uncommon after posterior cervical surgery.9,10 Proposed etiologies include postoperative neck pain and stiffness from the arthrodesis altering the mechanics of swallowing. As anterior cervical plating is a variable modifiable by the surgeon, interest in alternative methods of rigid instrumentation, without plating, has grown and has led to the development of low-profile, stand-alone devices. In addition to these fusion devices, cervical disc arthroplasty is another technology that allows for low-profile instrumentation and may reduce postoperative dysphagia.14,15 Anterior cervical plating has been associated with a phenomenon known as adjacent-level ossification development (ALOD).16 This finding is characterized by ossification of the anterior longitudinal ligament (ALL) and anterior annulus at an adjacent segment. While it may cause adjacent-level ankylosis, it is more commonly a nonbridging, nonmarginal syndesmophyte. The clinical implication of ALOD is not known; it may be protective against adjacent segment degeneration or it may predispose to adjacent-level pathology and subsequent repeat surgery. ALOD has been associated with plate creep toward the adjacent-

level disc space, with a critical distance of 5 mm proposed.16 Rates of ALOD are higher if the plate resides within 5 mm of the adjacent disc space. The reasons for ALOD are not known, though disruption of the ALL has been proposed.17 Low-profile, stand-alone devices and cervical disc arthroplasty may minimize rates of ALOD by avoiding anterior plating and minimizing ALL disruption and eliminating creep on the adjacent levels. Adjacent segment pathology (ASP) may require reoperation and is one of the most commonly discussed complications of anterior cervical fusion procedures.18,19 Given that plating of anterior cervical procedures is now routine, management of ASP often requires a wide approach to allow removal of old implants, as well as to allow the ACDF at the subsequent level. Stand-alone, low-profile cervical devices have been designed to allow rigid fixation of the adjacent level, without requiring the removal of instrumentation above or below the pathologic segment.

18.2 Purpose of Instrumentation Low-profile, stand-alone cervical devices are designed to replace anterior cervical plating and interbody graft or device placement. Avoiding anterior cervical plating offers several potential benefits, including reduced incidence of ALOD, reduced dysphagia, and easier arthrodesis instrumentation. These devices may be of particular interest when treating ASP, given the affected segment may be treated without removing any adjacent instrumentation in most cases. Rigid instrumentation minimizes risks of postoperative kyphosis.20 In our practice, we have found these devices to be useful in circumferential (anterior and posterior) surgeries performed for cervical deformities (▶ Fig. 18.1a, b).21 They allow for interbody fusion over multiple levels, without requiring the use of an anterior plate. In cases where the anterior procedure does not provide sufficient sagittal plane correction, we place one screw through the low-profile device, fixing it in the disc space without fixing the sagittal alignment. Further sagittal plane correction is obtained via positioning, Smith–Petersen osteotomies, and compression through posterior instrumentation. If one places screws into both the cranial and caudal endplates, the sagittal plane is locked and no further correction is possible. These devices are FDA approved for anterior cervical instrumentation.

18.3 Relevant Anatomy These devices are placed following a standard Smith–Robinson approach to the cervical spine. This approach exploits the plane between the sternocleidomastoid and the medial strap muscles. Structures at risk during this approach include the esophagus medially and the contents of the carotid sheath (the carotid artery, jugular vein, and vagus nerve) laterally. We prefer to use an appendiceal retractor during the approach to the anterior spine, to protect the medial structures. After removing the

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Cranial longus colli will minimize risk of injury to the sympathetic chain, with a resultant Horner’s syndrome.22 To minimize risk of postoperative dysphagia, we will dissect proximally and distally to have access to the disc spaces above and below the level of interest. This mobilizes the strap muscles and other neck contents more than a confined approach, decreasing stretch and strain on the muscles. Often the omohyoid will cross the surgical field at around C6. In our practice, we routinely sacrifice the most proximal fibers transversely. As the fibers retract, they will move out of the surgical field. In our experience, this has not been associated with complaints of dysphagia. If one chooses not to sacrifice the omohyoid, then it should be retracted medially at C5 and above, laterally when below C5.23 The course of the vertebral artery should be studied prior to any anterior cervical approach for discectomy/vertebrectomy.24 In the majority of cases, the vertebral artery will enter the cervical spine at C6, with the foramen transversarium at C7 containing some small veins. In some cases, however, the artery will enter at C7 or above C6. This should be known before elevating the longus colli. In some cases, the vertebral artery will run a medial course, putting it at risk with discectomy/vertebrectomy.

18.4 Complications 18.4.1 Pseudarthrosis

Fig. 18.1 (a) Preoperative lateral radiograph of a 62-year-old woman with cervical scoliosis. (Used with permission, courtesy K. Daniel Riew.) (b) Postoperative lateral radiograph, after anterior cervical osteotomies with low-profile, stand-alone devices and posterior instrumentation. (Used with permission, courtesy K. Daniel Riew.)

prevertebral fascia, the longus colli is dissected off the medial insertion. This muscle should be dissected off in a subperiosteal fashion, moving distal to proximal. There are veins running with the muscle fibers, so we prefer to use bipolar electrocautery with blunt elevation using a Penfield no. 2 to raise the muscle. A radiolucent retractor is placed underneath the longus colli after elevation. Care not to dissect within the muscle fibers of the

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Our primary concern with stand-alone, low-profile devices stems from their composition and design. These products are entirely, or almost entirely, made from PEEK, a hydrophobic, biologically inert material.25,26 As such, bone and surrounding tissues are unable to bond to PEEK, unlike titanium or other orthopaedic metals. This lack of stability at the bone–implant interface, we believe, raises the risk for pseudarthrosis. These devices rely on bridging bone, passing through the lumen of the device. This is further complicated by the design because most have a relatively small lumen and this lumen is, in part, occupied by the screws used to fix the device. By decreasing the volume of space available for bridging bone, the risk of pseudarthrosis is again raised. To minimize the risk of pseudarthrosis, we often use standalone, low-profile devices when we plan a circumferential surgery and perform anterior interbody fusions for anterior column support and deformity correction. While small case series reporting the results of these devices claim pseudarthrosis rates similar to ACDF, pseudarthrosis after stand-alone devices remains a reason for reoperation in our practices (▶ Fig. 18.2).2, 27,28 In most cases of pseudarthrosis, no revision anterior surgery is needed/performed, and an instrumented, posterior surgery is performed to rigidly fix the level.

18.4.2 Implant Malposition/Screw Placement Stand-alone, low-profile devices have been advocated for use in ASP. In these cases, the potential benefit is the ability to perform the adjacent segment surgery, without exposure and removal of the previous instrumentation. However, one must note the amount of creep upon the adjacent disc space by the plate. If the plate encroaches too much then it may not be

Failure of Anterior Cervical, Low-Profile, Stand-Alone Screw–Plate Devices

Fig. 18.2 Lateral radiograph of a 50-year-old man treated for singlelevel myeloradiculopathy with a low-profile, stand-alone cervical device. He presented with persistent pain and worsening symptoms; workup revealed pseudarthrosis. He was managed with a posterior cervical decompression and instrumented fusion. (Used with permission, courtesy Wilson Z. Ray.)

possible to obtain the appropriate cranial/caudal angle to insert the screws through the stand-alone device (▶ Fig. 18.3). This may cause the screws to deflect off the endplate, rather than engage it, distracting the interspace (▶ Fig. 18.4). This would almost certainly lead to pseudarthrosis.

18.4.3 Lag Effect/Screw Placement Another risk with screw placement is the possibility of a “lag effect” through the integrated device. While some implants are designed to prevent this, there is a risk, when screws are placed, that the implant will lag into the disc space and encroach upon the spinal canal. When placing screws, one should ensure that the implant does not recess into the disc space and the final position must be checked on a lateral radiograph. If intraoperative, neurophysiologic monitoring is used, the neurophysiologist should know when screws are placed to ensure no data changes ensue.

18.4.4 Adjacent-Level Ossification Development This pathology is seen with the ossification of the ALL and/or annulus at cervical levels adjacent to anterior instrumentation.

Fig. 18.3 Preoperative lateral radiograph of a 49-year-old woman with adjacent segment pathology causing radiculopathy above a two-level anterior cervical discectomy and fusion. Plan was low-profile, standalone device at C4–C5, without removal of instrumentation. (Used with permission, courtesy Michael P. Kelly.)

It has been shown to be most frequent when anterior plates are placed within 5 mm of the adjacent disc space. ALOD is less frequently observed in cervical disc arthroplasty, a procedure associated with less disruption of the ALL at the level of surgery and an implant with no anterior instrumentation. Stand-alone, low-profile devices have an exposure more similar to arthroplasty than anterior plating and it stands to reason that the rates of ALOD with stand-alone devices will be similar to cervical disc arthroplasty. The risk of ALOD can be minimized by exposing/debriding only the disc space necessary, with only the endplates of the vertebral bodies exposed. There is no reason to debride the ALL beyond the borders of the disc space, so this should be avoided.

18.4.5 Dysphagia Stand-alone, low-profile devices may decrease rates of postoperative dysphagia, as some believe anterior plating, particularly at higher (C4 or higher) cervical levels, increases dysphagia. Despite this potential benefit, dysphagia is common and can be minimized with surgical technique during the exposure. There is some evidence that retractors, in combination with an inflated endotracheal tube (ETT), may cause nerve and/or muscle injury during surgery.29 To minimize these pressureinduced injuries, one can deflate and reinflate the ETT after retractor placement. This has not been shown to decrease dysphagia, though the intervention carries little risk and it may be

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Fig. 18.4 Intraoperative fluoroscopic image showing malposition of the cranial low-profile screw, causing distraction of the interspace. Note the cranial creep of the prior instrumentation makes appropriate angulation of the cranial screw impossible. She was treated with removal of instrumentation and anterior cervical discectomy and fusion, with anterior plating. (Used with permission, courtesy Michael P. Kelly.)

employed in high-risk patients.30 A wide release of the interval between the medial strap muscles and the sternocleidomastoid, so that the disc space above and below the level of interest can be reached, will minimize stretch on these muscles. This is particularly true of revision procedures, where scar tissue may act as an impediment to a wide exposure. Local and intravenous steroids may decrease rates of dysphagia and appear to be safe, in terms of union and infection rates.31,32

noninferiority with respect to pseudarthrosis rates. Similarly, more research is needed to show improvements in rates of clinically important dysphagia following stand-alone devices relative to ACDF with a plate and bone graft.

18.7 Key Points ●

18.5 Summary Stand-alone, low-profile cervical devices offer a fast and relatively easy way to perform an instrumented ACDF. This is particularly true when the surgery is performed adjacent to prior anterior cervical instrumentation, given the stand-alone device does not require removal of the previous instrumentation. These devices are also useful in cervical deformity surgeries, when anterior column support, sometimes in conjunction with anterior cervical osteotomies, is required prior to posterior instrumentation and deformity correction. In these cases, place one screw only, either into the cranial or caudal endplate, so that lordosis can be achieved with prone positioning, extension, and compression. Published results with these devices are good and comparable to ACDF with allograft. Nevertheless, concern for pseudarthrosis exists due to the PEEK material and relatively small surface area available for fusion. Surgical technique cannot be supplanted by implant design; careful planning and performance will minimize the risk of complications when using these devices.

18.6 Future Directions Larger series, comparing stand-alone, low-profile devices to plated ACDF with autograft/allograft are required to show

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Low-profile, stand-alone cervical instrumentation may decrease postoperative dysphagia, though other variables, including age, gender, and levels treated, are associated with dysphagia as well. Pseudarthrosis is a concern with these devices given that they are made from polyetheretherketone (PEEK) and have relatively small surfaces for bony union. These devices may be used cranial/caudal to previous instrumentation in the treatment of ASPs. One must be sure that the previous instrumentation does not block appropriate screw placement through the stand-alone device. Low-profile devices may decrease rates of adjacent-level ossification development (ALOD), though the clinical implications of this are undefined. Careful surgical planning and performance will minimize the risk of complications following any anterior cervical procedure.

References [1] Njoku I, Jr, Alimi M, Leng LZ, et al. Anterior cervical discectomy and fusion with a zero-profile integrated plate and spacer device: a clinical and radiological study: clinical article. J Neurosurg Spine. 2014; 21(4):529–537 [2] Scholz M, Schnake KJ, Pingel A, Hoffmann R, Kandziora F. A new zero-profile implant for stand-alone anterior cervical interbody fusion. Clin Orthop Relat Res. 2011; 469(3):666–673 [3] Hofstetter CC, Kesavabhotla K, Boockvar JA. Zero-profile anchored spacer reduces rate of dysphagia compared to ACDF with anterior plating. J Spinal Disord Tech. 2015; 28(5):E284–E290

Failure of Anterior Cervical, Low-Profile, Stand-Alone Screw–Plate Devices [4] Bazaz R, Lee MJ, Yoo JU. Incidence of dysphagia after anterior cervical spine surgery: a prospective study. Spine. 2002; 27(22):2453–2458 [5] Frempong-Boadu A, Houten JK, Osborn B, et al. Swallowing and speech dysfunction in patients undergoing anterior cervical discectomy and fusion: a prospective, objective preoperative and postoperative assessment. J Spinal Disord Tech. 2002; 15(5):362–368 [6] Kepler CK, Rihn JA, Bennett JD, et al. Dysphagia and soft-tissue swelling after anterior cervical surgery: a radiographic analysis. Spine J. 2012; 12 (8):639–644 [7] Lee MJ, Bazaz R, Furey CG, Yoo J. Influence of anterior cervical plate design on Dysphagia: a 2-year prospective longitudinal follow-up study. J Spinal Disord Tech. 2005; 18(5):406–409 [8] Lee MJ, Bazaz R, Furey CG, Yoo J. Risk factors for dysphagia after anterior cervical spine surgery: a two-year prospective cohort study. Spine J. 2007; 7 (2):141–147 [9] Smith-Hammond CA, New KC, Pietrobon R, Curtis DJ, Scharver CH, Turner DA. Prospective analysis of incidence and risk factors of dysphagia in spine surgery patients: comparison of anterior cervical, posterior cervical, and lumbar procedures. Spine. 2004; 29(13):1441–1446 [10] Radcliff KE, Koyonos L, Clyde C, et al. What is the incidence of dysphagia after posterior cervical surgery? Spine. 2013; 38(13):1082–1088 [11] Schimmel JJ, Poeschmann MS, Horsting PP, Schönfeld DH, van Limbeek J, Pavlov PW. PEEK cages in lumbar fusion: mid-term clinical outcome and radiological fusion. Clin Spine Surg. 2016; 29(5):E252–E258 [12] Yue WM, Brodner W, Highland TR. Persistent swallowing and voice problems after anterior cervical discectomy and fusion with allograft and plating: a 5to 11-year follow-up study. Eur Spine J. 2005; 14(7):677–682 [13] Riley LH, III, Vaccaro AR, Dettori JR, Hashimoto R. Postoperative dysphagia in anterior cervical spine surgery. Spine. 2010; 35(9) Suppl:S76–S85 [14] McAfee PC, Cappuccino A, Cunningham BW, et al. Lower incidence of dysphagia with cervical arthroplasty compared with ACDF in a prospective randomized clinical trial. J Spinal Disord Tech. 2010; 23(1):1–8 [15] Skeppholm M, Olerud C. Comparison of dysphagia between cervical artificial disc replacement and fusion: data from a randomized controlled study with two years of follow-up. Spine. 2013; 38(24):E1507–E1510 [16] Park JB, Cho YS, Riew KD. Development of adjacent-level ossification in patients with an anterior cervical plate. J Bone Joint Surg Am. 2005; 87 (3):558–563 [17] Yang JY, Song HS, Lee M, Bohlman HH, Riew KD. Adjacent level ossification development after anterior cervical fusion without plate fixation. Spine. 2009; 34(1):30–33 [18] Helgeson MD, Bevevino AJ, Hilibrand AS. Update on the evidence for adjacent segment degeneration and disease. Spine J. 2013; 13(3):342–351

[19] Hilibrand AS, Carlson GD, Palumbo MA, Jones PK, Bohlman HH. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am. 1999; 81(4):519–528 [20] Samartzis D, Shen FH, Lyon C, Phillips M, Goldberg EJ, An HS. Does rigid instrumentation increase the fusion rate in one-level anterior cervical discectomy and fusion? Spine J. 2004; 4(6):636–643 [21] Kim HJ, Piyaskulkaew C, Riew KD. Anterior cervical osteotomy for fixed cervical deformities. Spine. 2014; 39(21):1751–1757 [22] Civelek E, Karasu A, Cansever T, et al. Surgical anatomy of the cervical sympathetic trunk during anterolateral approach to cervical spine. Eur Spine J. 2008; 17(8):991–995 [23] Fengbin Y, Xinwei W, Haisong Y, Yu C, Xiaowei L, Deyu C. Dysphagia after anterior cervical discectomy and fusion: a prospective study comparing two anterior surgical approaches. Eur Spine J. 2013; 22(5):1147–1151 [24] Eskander MS, Drew JM, Aubin ME, et al. Vertebral artery anatomy: a review of two hundred fifty magnetic resonance imaging scans. Spine. 2010; 35 (23):2035–2040 [25] Ma R, Tang T. Current strategies to improve the bioactivity of PEEK. Int J Mol Sci. 2014; 15(4):5426–5445 [26] Nemoto O, Asazuma T, Yato Y, Imabayashi H, Yasuoka H, Fujikawa A. Comparison of fusion rates following transforaminal lumbar interbody fusion using polyetheretherketone cages or titanium cages with transpedicular instrumentation. Eur Spine J. 2014; 23(10):2150–2155 [27] Kasliwal MK, O’toole JE. Integrated intervertebral device for anterior cervical fusion: an initial experience. J Craniovertebr Junction Spine. 2012; 3 (2):52–57 [28] Nemoto O, Kitada A, Naitou S, Tachibana A, Ito Y, Fujikawa A. Stand-alone anchored cage versus cage with plating for single-level anterior cervical discectomy and fusion: a prospective, randomized, controlled study with a 2year follow-up. Eur J Orthop Surg Traumatol. 2015; 25 Suppl 1:S127–S134 [29] Apfelbaum RI, Kriskovich MD, Haller JR. On the incidence, cause, and prevention of recurrent laryngeal nerve palsies during anterior cervical spine surgery. Spine. 2000; 25(22):2906–2912 [30] Kowalczyk I, Ryu WH, Rabin D, Arango M, Duggal N. Reduced endotracheal tube cuff pressure to assess dysphagia after anterior cervical spine surgery. J Spinal Disord Tech. 2015; 28(10):E552–E558 [31] Song KJ, Lee SK, Ko JH, Yoo MJ, Kim DY, Lee KB. The clinical efficacy of shortterm steroid treatment in multilevel anterior cervical arthrodesis. Spine J. 2014; 14(12):2954–2958 [32] Lee SH, Kim KT, Suk KS, Park KJ, Oh KI. Effect of retropharyngeal steroid on prevertebral soft tissue swelling following anterior cervical discectomy and fusion: a prospective, randomized study. Spine. 2011; 36 (26):2286–2292

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19 Complications of Buttress Plating Multilevel Anterior Cervical Corpectomies Christoph P. Hofstetter and Michael Y. Wang

19.1 Introduction The aging cervical spine suffers from joint degeneration, connective tissue hypertrophy, and bone spur growth which lead to narrowing of the spinal canal. Compression and stretching of the cervical spinal cord may cause myelopathy. The prevalence of cervical myelopathy increases with age from approximately 13% in the third decade of life to nearly 100% by the age of 70 years.1 It is generally accepted that anterior decompression is associated with an improvement of the natural history of cervical spondylosis.2,3 Cervical corpectomies are one strategy for the surgical treatment of multilevel cervical degenerative osteoarthritis. Removal of the central vertebral body allows for satisfactory decompression of the spinal cord. Following decompression, strut grafts are used to reconstruct the bony defect.2,4,5 Recently, anterior plates have been utilized for internal stabilization of multilevel cervical corpectomies.6,7,8,9,10,11,12, 13,14,15 The rationale for performing internal fixation of the spine can be summarized as follows: to restore the stability to the structurally compromised spine; to enhance fusion by minimizing motion; to maintain alignment after correction of a deformity; to prevent progression of a deformity; and to alleviate pain with immediate rigid fixation.16 Moreover, internal stabilization functions to optimize the environment for osseous union by providing immediate rigid fixation across the span of the desired arthrodesis.

19.2 Multilevel Cervical Corpectomy Cervical corpectomies utilizing multilevel strut graft techniques have been reported in the literature since the early 1980s.17 This procedure poses an effective method for treating multilevel cervical spondylotic disease. Reported fusion rates are high and excellent improvement in myelopathy has been reported.2, 18,19,20,21 The rate of complications increases with the number of segments involved.22,23 Thus, multilevel reconstructions carry a high risk for graft dislodgement (one-level: 4.2%, two-level: 5.3%, and three-level: 9.9%),23 graft fracture, graft extrusion, pistoning of the graft, pseudoarthrosis, dysphagia, respiratory compromise, and neurological deficits.2,3,24,25,26,27 To counteract these complications, more rigid forms of immobilization have be added, such as halo vests or addition of anterior and/or posterior instrumentation. While halo vests may be an effective means of immobilization in certain clinical scenarios, their use is associated with discomfort as well as minor and major complications for the patient. Complications, such as pin tract infections, skull osteomyelitis, and skull penetration with subsequent cerebrospinal fluid leakage and the possibility of abscess formation, have been described. Moreover, elderly patients tolerate halo immobilization poorly due to the vest`s large profile and weight. These factors limit the applicability of halo vest immobilization in modern clinical practice.

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Fortunately, the last two decades have seen numerous advances in internal fixation options. Anterior cervical plates were introduced by Caspar28 in 1989. Utilization of anterior plates in single-level anterior cervical discectomy and fusions (ACDFs) has been proposed to decrease the amount of graft collapse and segmental kyphosis.29 While several individual studies failed to reveal a statistically significant benefit from anterior plating in single-level ACDFs,29,30,31 a recent meta-analysis suggested that addition of an anterior plate increases fusion rates in one-level ACDFs.32 Thus, the addition of anterior cervical plates reduces the need for postoperative immobilization and may improve quality of life and cost-effectiveness by allowing early rehabilitation and return to work.30,33 In a prospective randomized study by Grob and colleagues, at total of 50 patients were included who underwent one- or two-level ACDF with or without anterior plate.30 The improvement of pain or recovery of function did not statistically differ between patients who underwent ACDF with or without anterior plate. Strikingly, at a mean follow-up of 34 months, 9 out of 26 patients (34.6%) with ACDF without plate were out of the work force, compared to only 3 out of 24 patients (12.5%) with ACDF with plate. It is interesting to note that the authors of this study concluded that “results do not support the general use of anterior plates in degenerative conditions” and the higher rate of return to work in patients who received an anterior plate was not further discussed. Given the high failure rates of multilevel anterior fusions, the use of anterior plating was extended to this indication. Anterior plates were thus included in multilevel strut grafts in order to add immediate stability to the construct. This was based on the experienced gained with anterior plating in ACDFs. It was hypothesized that addition of anterior plates to multilevel corpectomies might increase union rates, decrease graft collapse and associated kyphotic deformity, reduce the need for postoperative immobilization, and be cost-effective by allowing early mobilization and return to work.6,7,8,9,10,11,12,13,14,15 However, these potential advantages of anterior plating seen with ACDF and short-segment corpectomies (two or fewer levels) were not as apparent with long-segment strut-graft cervical corpectomies. In that setting, the addition of an anterior plate failed to lead to an obvious reduction of construct failures. Failure rates of multilevel corpectomies without anterior plating range from 2 to 7.7% (2%,23 7.7%,2 6.8%,25 and 6.6%26). The number of levels has been clearly shown to impact construct failure rate in multilevel corpectomies.22,23,25 Many patients in these studies had additional posterior instrumentation for internal stabilization. Moreover, patients with cervical kyphosis due to previous destabilizing laminectomy surgeries also appear to carry higher risk of construct failure.25 A major problem with a multilevel corpectomy treated with a long strut and plate has been that significant translational force is applied to a twopoint fixation construct, leading to high rates of screw/plate backout. For these patients, either adjuvant halo fixation12 or supplemental posterior stabilization has been proposed.34,35

Complications of Buttress Plating Multilevel Anterior Cervical Corpectomies Sasso and colleagues reported a 6% failure rate in two-level constructs (2 out of 33 patients) and 71% failure rate in three-level constructs (5 out of 7 patients).22 Vaccaro and colleagues revealed a similar impact of the construct length on instrumentation failure (9% failure rate in two-level corpectomies, 50% failure rate in three-level corpectomies).36 Thus, the overall failure rate in multilevel corpectomies with anterior cervical plates ranges from 0 to 20% (11.1%,15 8.2%,5 20%,36 17.5%,22 and 0%24). While the aforementioned limitations of these studies certainly do not allow for direct comparison. It appears obvious that the addition of an anterior plate did not adequately reduce the incidence of complications or instrumentation failures. Furthermore, the addition of an anterior plate may be associated with its own array of complications, such as dysphagia from implant prominence, hardware failure, and the alteration of biomechanical forces on the strut grafts. The rate of postoperative dysphagia lasting for longer than 3 months ranges from 0 to 8.2% in patients who undergo multilevel cervical corpectomies with anterior plating (5.5%,15 8.2%,5 transient dysphagia in 52.9 and 0% at 3 months24). While the causes of dysphagia following anterior cervical procedures are not well understood, several physiological mechanisms have been proposed.37 The anterior cervical locking plate is placed directly posterior to the esophagus and may impinge or irritate the esophagus.38,39,40,41,42 It has been demonstrated that design and thickness of anterior locking plates correlate with postoperative dysphagia.40 Lee and colleagues showed that reduction of plate thickness from 2.5 to 1.6 mm combined with a smoother surface design led to decrease of dysphagia from 22.5 to 14% at 6-month follow-up and from 14 to 0% at 24-month follow-up.40 Moreover, there are several studies that suggest that addition of anterior locking plates is associated with a higher rate of postoperative dysphagia.38,40,41,42 Mobbs and colleagues analyzed 242 cases with ACDF.41 They found a significantly higher rate of dysphagia in patients who received an anterior locking plate (4.5%, 5/112 patients) compared to constructs without anterior plating (0.8%, 1/130 patients). Lee and colleagues observed a similar trend toward a lower rate of dysphagia (14.1%) in 104 patients without anterior plating compared to a 21.1% of dysphagia in patients who received a construct including an anterior locking plate.40 Similarly, lower rates of dysphagia have been reported following implantation of zero-profile implants.42,43 Increased pressure on the esophagus during implantation of an anterior plate has also been suggested to contribute to dysphagia in patients who undergo ACDF with anterior plating.37 Addition of an anterior plate also adds hardware as an additional mode of complications. Screw backout, screw fractures, and plate fractures have been described. The rate of hardwarerelated complications in multilevel corpectomies with anterior plating ranges from 0 to 20% (11.1%,15 8.2%,5 20%,36 17.5%,22 and 0%24). Anterior cervical plates aim to assist with maintaining graft position as well as providing semirigid immobilization of the construct to promote fusion. However, addition of an anterior plate has two important biomechanical consequences. It counteracts settling of the graft and it reverses loading patterns during flexion/extension of the neck. First, it is thought that anterior plating may act to unload and prevent normal settling of the graft into the end plates.44,45 In a cohort of 39 patients who had undergone multilevel cervical corpectomies combined with anterior plate fixation, plate/graft

displacement was observed in approximately 10%.46 A similar rate of plate/graft displacement was reported by Macdonald and colleagues.15 In a patient cohort of 36 patients, who underwent multilevel anterior cervical corpectomies and stabilization using fibular allograft and an anterior plate, displacement of the graft was detected in 6 out of 31 patients (19.4%) in whom follow-up was available. A total of three patients (8.3%) required repeat surgery for graft displacement. Second, biomechanical studies have revealed that the addition of anterior plates to multisegmental corpectomies reverses load transfer through multilevel strut-grafts during flexion and extension. As expected, multisegmental stand-alone strutgrafts are loaded with neck flexion and unloaded with neck extension in a cadaveric model.47 In these studies, addition of an anterior plate decreased local motion and increased stiffness. Importantly, the addition of an anterior plate reversed strutgraft loading mechanics. Thus, extension of approximately 10 degrees gives rise to extensive loads (> 200 N). Endplate loads of this magnitude have been associated with subchondral bone failure. The authors concluded that application of an anterior plate in multilevel strut grafts creates supraphysiological loading that may exacerbate graft pistoning. Graft pistoning occurs as the graft and the vertebral bodies settle during the initial phase of healing. If the amount of pistoning becomes severe, screws pullout or breakage may ensue. Several clinical studies have corroborated this finding.15 Macdonald and colleagues estimated that pistoning of the strut-graft was observed in 2 out of 36 cases (5.5%).15 Paramore and colleagues found that the amount of pistoning was associated with the length of the plate.5 Moreover, the amount of pistoning was less in patients with non-failed constructs (2 ± 1.6 mm) compared to constructs (6 ± 3.1 mm) that had failed. The addition of a posterior tension band combined with anterior stabilization allows for a further increase in the stiffness of the construct.48 Moreover, addition of posterior instrumentation to a multilevel corpectomy with anterior plate counteracts excessive the loading patterns seen with the strut-grafts supplemented with either anterior plate or posterior instrumentation alone.48 However, the loading of the strut-graft remained reversed in a 360-degree construct compared to a stand-alone strut graft. Load fluctuations between flexion and extension are most effectively minimized by anterior and posterior instrumentation in multilevel strut-grafts, which may decrease the rate of subsequent construct failure. Accordingly, Schultz and colleagues report no clinically significant construct failures in 32 patients who underwent either two- or three-level corpectomies.49 However, this approach obviously adds an additional surgical approach and instrumentation, with attendant consequences.

19.3 Buttress Plating The use of a short-segment anterior junctional plate, also known as buttress plate, was developed to decrease the risk of multisegment plate fixation failure and at the same time to counteract graft migration and extrusion. It is less technically challenging to place a buttress plate than a plate spanning the entire graft. Moreover, anterior plates that span the entire construct have been hypothesized to prevent graft settling as the

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Cranial graft heals, and therefore promote graft migration and extrusion. In contrast, a buttress plate, only fixed at one end of the graft, would allow for normal settling which then would counteract graft extrusion. As in most cases of multilevel corpectomies graft dislodgment occurs in the caudal end usually at C6, C7, or T1, buttress plates are typically placed at the caudal end.50 Buttress plates were first mentioned in a report by MacDonald and colleagues who used buttress plates in 2 out of 36 patients who had multilevel corpectomies reconstructed with strut grafts.15 They found that both of these patients suffered from graft and plate displacement. One of these patients required revision surgery, while the other patient was treated expectantly. The initial report focusing on the use of buttress plates by Vanichkachorn and colleagues was promising.51 Eleven patients with cervical myelopathy and cervical kyphosis underwent two- to four-segment cervical corpectomies. For reconstruction, a fibular strut graft was used in 10 patients and a corticocancellous iliac crest bone graft in the remaining patient. Buttress plates were in the majority of patients placed at the caudal end of the graft. All constructs were supplemented with posterior instrumentation. The authors reported no instances of graft extrusion or dislodgement. In one patient, a graft fracture occurred. In this patient, the junctional plate was secured with a locking screw penetrating the fibular strut graft. This patient suffered from no sequelae but required revision of his anterior construct. Interestingly, the authors in this first report warned “that multilevel corpectomies graft and plate constructs are at risk for early failure when not supplemented with a posterior segmental stabilization procedures.” The authors also concluded that “a buttress plate in combination with proper graft selection and preparation can minimize the risk of graft and plate dislodgement when used in combination with a posterior cervical stabilization procedure.” The biomechanical importance of additional posterior fixation proposed in this first report was even more evident in a subsequent publication. Riew and colleagues reported their experience using buttress plates in multilevel cervical corpectomies in 14 patients.52 In their series, 2 patients underwent two-level corpectomies and 12 patients underwent three-level corpectomies that were reconstructed with a fibula strut graft and a buttress plate at the caudal end of the construct. Importantly, 11 out of 14 constructs were stand-alone and not backed up by additional posterior instrumentation. In this patient cohort, graft extrusion was detected in two patients. The first patient had undergone a two-level stand-alone corpectomy. On postoperative day 3, he had a panic attack during which he was combative and removed his external fixation (Philadelphia collar). This patient decompensated and eventually expired. A radiograph revealed that the graft had extruded at the caudal end and had kicked out the cephalad end of the buttress plate, causing compromise of the retrotracheal space. Another patient in this cohort who had undergone a three-level corpectomy with posterior instrumentation also suffered from partial graft extrusion with anteropulsion of the buttress plate. However, this patient remained asymptomatic. Riew and colleagues reported a 23% pseudoarthrosis rate (3 out of 13 patients). Two of these patients were treated with addition of a posterior fusion construct. The third patient remained asymptomatic and was treated expectantly.

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Given the catastrophic outcome of one patient, this group abandoned buttress plates. In their report, they stated that “it is reasonable to use buttress plates to secure the graft when one is performing a circumferential arthrodesis,” and they concluded that “Surgeons who utilize such fixation without additional posterior instrumentation should be aware of the potential complications of buttress plating. The use of buttress plates may have their most ideal indication in settings where a multistage anterior and posterior surgery will require a destabilizing operation followed by realignment and fixation. In this situation, a three-stage operation may be changed to a two-stage operation. For example, if a front–back–front is planned, the third stage is necessary for anterior plating after realignment has been performed in the second operation. Using a buttress plate in the first stage allows the spine to translate and retain the graft and obviates the need of the third (anterior) stage. Similarly, for a back–front–back approach, the use of a buttress as opposed to a fully spanning plate is that the spine can still be mobilized in the final (third) stage of the surgery, given the plate does not constrain spinal motion (▶ Fig. 19.1, ▶ Fig. 19.2, ▶ Fig. 19.3, ▶ Fig. 19.4, ▶ Fig. 19.5).

19.4 Surgical Technique 19.4.1 Preoperative Preparation and Positioning Prior to surgery, careful study of X-rays, flexion/extension films, computed tomography (CT) and magnetic resonance imaging (MRI) is essential. The surgeon should determine the position of the vertebral arteries on CT or MRI. The incidence of anatomic variations of the vertebral artery of the V2 segments is high.53 In a recent study on the anatomic variation of the V2 segment of 500 vertebral arteries, two main anatomic variations were detected. First, while the vertebral artery normally enters the C6 transverse foramen, an abnormal level of entrance is observed in 7% of specimens. In these specimens, it enters the

Fig. 19.1 Case example of a patient with a chin-on-chest deformity plus myelopathy from ankylosing spondylitis.

Complications of Buttress Plating Multilevel Anterior Cervical Corpectomies

Fig. 19.2 The patient’s deformity was relatively rigid, and he was treated with a two-stage approach.

Fig. 19.4 These procedures were followed on the same day by posterior fixation and correction of kyphosis.

Fig. 19.3 The first stage was an anterior cervical corpectomy at C7 to decompress the spinal cord and mobilize the spine anteriorly. A buttress plate was used to obviate the need for a third surgical stage. The plate allowed deformity correction during the second stage by retaining the position of the anterior fibula graft, pulling it posteriorly during correction. This method is acceptable for short-segment corpectomies but would be more hazardous with long-segment fibula struts unless the vertebral endplates are very carefully machined to prevent posterior graft migration.

C7, C5, C4, or C3 foramens. Thus, in case of a more cephalad entry level, the vertebral artery is not protected of a bony structure at C6 and is found just beneath the longus colli muscle. The second anatomic variation is a tortuous course with medial loops of the vertebral artery. These loops are detected in 2% of specimens and are located either in enlarged transverse foramina (1.2%) or within the intervertebral foramina (0.8%). In terms of graft, for the gross majority of cases, we use fibular allograft rather than autograft. While allograft may be

Fig. 19.5 The patient was maintained in a halo vest for 6 weeks after surgery.

associated with a slightly lower rate of anterior cervical fusion, its use circumvents complications associated with harvesting autologous bone. Alternatively, polyetheretherketone (PEEK) implants or expandable titanium cages may be used as graft. For positioning, the patient is placed supine onto the table with roll under neck to promote cervical lordosis. Gardner–

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Cranial Wells tongs are in place to exert axial traction during placement of strut graft. Generally, the procedure is started with 10 lb of traction. During insertion of the graft, the traction is increased and then discontinued during placement of the anterior plate.

19.4.2 Procedure The operation is usually performed from the side that is most comfortable for the surgeon. While the right recurrent laryngeal nerve may be more susceptible to injury, given its location anterior and lateral to the esophagotracheal groove,54 injury to the thoracic duct has been reported as a complication of approaching the caudal cervical spine from the left side.55 Moreover, clinical studies have shown that there is no difference in the incidence of recurrent laryngeal nerve injury between right-and left-sided surgeries.56,57 If the patient had previous cervical procedures, we typically obtain access from the ipsilateral side. If a contralateral approach is chosen, previous injury to vagal nerve branches needs to be excluded by preoperative examination of the vocal cords by an otolaryngologist in order to avoid debilitating bilateral injury to vagal nerve branches. Preoperative lateral fluoroscopy is employed to define the most rostral and most caudal levels of exposure. For up to two-level corpectomies, we chose transverse incisions located within a skin crease. This type of incision is cosmetically superior to a longitudinal incision along the medial border of the sternocleidomastoid muscle. Following sharp incision of the skin, the platysma is approached using meticulous hemostasis with electrocauterization. The platysma is split in a transverse fashion and the cephalad and caudal ends are generously undermined in a maneuver which greatly enhances the cosmetic appearance of the wound closure. Subsequently, the sternocleidomastoid muscle and the tracheoesophageal bundle are identified. At this point, the carotid artery is palpated. The middle cervical fascia is then cut in a longitudinal fashion in the crease between the sternocleidomastoid muscle and the tracheoesophageal bundle. Great care is taken to dissect traversing arteries, veins, and nerves. Using a Cloward hand-held retractor, the tracheoesophageal bundle is retracted medially. Remaining connective tissue and bridging vessels and nerves are dissected. Once the prevertebral fascia, esophagus, and carotid artery are identified, a bipolar electrocauterization may be used to open the prevertebral fascia in order to approach the vertebral column. A Pennfield 4 is placed onto a disc space and a localization X-ray is obtained. Electrocautery is then utilized to undercut bilateral longus colli muscles in order to expose the anterior vertebral column as well as provide a cuff for the blades of the self-retaining retractor. Under microscopic visualization, the appropriate discs are removed using a combination of curettes, rongeurs, and high-speed drill. Vertebral bodies are then removed with a combination of highspeed drill, Leksell-Rongeurs, Kerrison-Rongeurs, and curettes. Remaining posterior vertebral cortex, osteophytes, and/or ossified posterior longitudinal ligament are thinned out with a high-speed drill and remaining fragments removed with a curette. Wide decompression of the spinal cord is further facilitated by undercutting the remaining vertebral body bilaterally. The width of the corpectomy is

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adjusted for the dimensions of the vertebral bodies and the precise area of compression. The average width of the spinal cord is approximately 13.7, 13.8, and 13.3 mm at C4, C5, and C6, respectively.58 Thus, the standard width of decompression is approximately 15 to 18 mm. The endplates of the cephalad and caudal vertebrae are shaped with 0.5- to 1-cm dowel holes to accept the end of the bone graft. Both a posterior and an anterior ledge are left intact in the cephalad vertebra. In the caudal vertebra, a posterior ledge is left to prevent graft intrusion into the spinal cord. Moreover, in the caudal vertebra, which typically shows a downward slope of its endplate, more bone is removed posteriorly to generate a horizontal surface. This maneuver is thought to counteract forward sliding of the graft. The graft is generally machined from a fibula allograft. Prior to insertion, the graft is packed with corpectomy bone. Under 30 to 50 lb of axial skull traction, the graft is tamped into place. Remaining corpectomy bone is then packed around the fibula graft into the uncovertebral spaces. A short buttress plate is then fixed to the caudal vertebra. In some instances, the surgeon will leave the caudal level as a discectomy with fusion instead of incorporating it into the corpectomy. This “Hybrid” (discectomy and corpectomy) has certain advantages. First, it allows the surgeon to have four (instead of two) fixation points for the buttress plate. Second, it reduces the corpectomy strut length without inordinately increasing the number of fusion interfaces between graft and host. Typically, the rostral end of the plate is slightly bent so that it would contact the anterior surface of the strut graft. Additional posterior fusion is always performed in two- or multilevel corpectomies.

19.4.3 Postoperative Care External immobilization, such as a Miami J collar, is typically left in place for 3 months. Clinical follow-up is performed at 2 weeks, 3 months, 6 months, and then every 6 months postoperatively. Plain lateral and anteroposterior cervical X-rays and flexion/extension films are obtained routinely until solid arthrodesis is documented. CT or MRI scanning is typically performed if there is progression of neurological symptoms, pain, inability to determine union of the graft on plain radiographs, or complication of graft placement, such as displacement or fractures.

19.5 Alternative Anterior “Hybrid” Constructs Given the high complication/failure rate of stand-alone anterior multilevel corpectomies, alternative approaches have been proposed. As an alternative ventral approach to three-level corpectomies, Rhee and Riew proposed multilevel ACDF, a singlecorpectomy combined with additional ACDFs, or two singlelevel corpectomies separated by an intact intervening vertebra.59 This approach, if utilized with a plate that spans the entire construct, allows for three- or four-point fixation as opposed to the two-point fixation with screws only at the top and bottom of the construct. Having intermediate points of fixation helps resist translational forces and screw/plate backout.

Complications of Buttress Plating Multilevel Anterior Cervical Corpectomies

19.6 Conclusion Multilevel cervical corpectomy with strut-grafting is an effective means to achieve decompression of the cervical cord in complex clinical scenarios. In multilevel cases (> 2 levels), anterior instrumentation should be supplemented with posterior fixation in order to counteract supraphysiological loads on the strut graft and associated graft failure. Buttress plates do not compensate for poorly placed strut grafts and have been associated with catastrophic complications. In case of poor placement of the strut graft, additional modes of immobilization should be considered. Whenever possible, alternative constructs such as multilevel ACDFs or skip corpectomies should be utilized. However, buttress plates may have a role in multistage surgeries to minimize the number of operative steps in select cases.

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[20] Emery SE, Bohlman HH, Bolesta MJ, Jones PK. Anterior cervical decompression and arthrodesis for the treatment of cervical spondylotic myelopathy. Two to seventeen-year follow-up. J Bone Joint Surg Am. 1998; 80(7):941–951 [21] Saunders RL, Bernini PM, Shirreffs TG, Jr, Reeves AG. Central corpectomy for cervical spondylotic myelopathy: a consecutive series with long-term followup evaluation. J Neurosurg. 1991; 74(2):163–170 [22] Sasso RC, Ruggiero RA, Jr, Reilly TM, Hall PV. Early reconstruction failures after multilevel cervical corpectomy. Spine. 2003; 28(2):140–142 [23] Wang JC, Hart RA, Emery SE, Bohlman HH. Graft migration or displacement after multilevel cervical corpectomy and strut grafting. Spine. 2003; 28 (10):1016–1021, discussion 1021–1022 [24] Cheng NS, Lau PY, Sun LK, Wong NM. Fusion rate of anterior cervical plating after corpectomy. J Orthop Surg (Hong Kong). 2005; 13(3):223–227 [25] Hilibrand AS, Fye MA, Emery SE, Palumbo MA, Bohlman HH. Increased rate of arthrodesis with strut grafting after multilevel anterior cervical decompression. Spine. 2002; 27(2):146–151 [26] Kojima T, Waga S, Kubo Y, Kanamaru K, Shimosaka S, Shimizu T. Anterior cervical vertebrectomy and interbody fusion for multi-level spondylosis and ossification of the posterior longitudinal ligament. Neurosurgery. 1989; 24 (6):864–872 [27] Okada K, Shirasaki N, Hayashi H, Oka S, Hosoya T. Treatment of cervical spondylotic myelopathy by enlargement of the spinal canal anteriorly, followed by arthrodesis. J Bone Joint Surg Am. 1991; 73(3):352–364 [28] Caspar W, Barbier DD, Klara PM. Anterior cervical fusion and Caspar plate stabilization for cervical trauma. Neurosurgery. 1989; 25(4):491–502 [29] Wang JC, McDonough PW, Endow K, Kanim LE, Delamarter RB. The effect of cervical plating on single-level anterior cervical discectomy and fusion. J Spinal Disord. 1999; 12(6):467–471 [30] Grob D, Peyer JV, Dvorak J. The use of plate fixation in anterior surgery of the degenerative cervical spine: a comparative prospective clinical study. Eur Spine J. 2001; 10(5):408–413 [31] Samartzis D, Shen FH, Lyon C, Phillips M, Goldberg EJ, An HS. Does rigid instrumentation increase the fusion rate in one-level anterior cervical discectomy and fusion? Spine J. 2004; 4(6):636–643 [32] Fraser JF, Härtl R. Anterior approaches to fusion of the cervical spine: a metaanalysis of fusion rates. J Neurosurg Spine. 2007; 6(4):298–303 [33] McLaughlin MR, Purighalla V, Pizzi FJ. Cost advantages of two-level anterior cervical fusion with rigid internal fixation for radiculopathy and degenerative disease. Surg Neurol. 1997; 48(6):560–565 [34] Albert TJ, Vacarro A. Postlaminectomy kyphosis. Spine. 1998; 23 (24):2738–2745 [35] Riew KD, Hilibrand AS, Palumbo MA, Bohlman HH. Anterior cervical corpectomy in patients previously managed with a laminectomy: short-term complications. J Bone Joint Surg Am. 1999; 81(7):950–957 [36] Vaccaro AR, Falatyn SP, Scuderi GJ, et al. Early failure of long segment anterior cervical plate fixation. J Spinal Disord. 1998; 11(5):410–415 [37] Tortolani PJ, Cunningham BW, Vigna F, Hu N, Zorn CM, McAfee PC. A comparison of retraction pressure during anterior cervical plate surgery and cervical disc replacement: a cadaveric study. J Spinal Disord Tech. 2006; 19(5):312–317 [38] Bazaz R, Lee MJ, Yoo JU. Incidence of dysphagia after anterior cervical spine surgery: a prospective study. Spine. 2002; 27(22):2453–2458 [39] Hodges SD, Humphreys SC, Eck JC, Covington LA, Van Horn ER, Peterson JE. A modified technique for anterior multilevel cervical fusion. J Orthop Sci. 2002; 7(3):313–316 [40] Lee MJ, Bazaz R, Furey CG, Yoo J. Influence of anterior cervical plate design on Dysphagia: a 2-year prospective longitudinal follow-up study. J Spinal Disord Tech. 2005; 18(5):406–409 [41] Mobbs RJ, Rao P, Chandran NK. Anterior cervical discectomy and fusion: analysis of surgical outcome with and without plating. J Clin Neurosci. 2007; 14 (7):639–642 [42] Scholz M, Schnake KJ, Pingel A, Hoffmann R, Kandziora F. A new zero-profile implant for stand-alone anterior cervical interbody fusion. Clin Orthop Relat Res. 2011; 469(3):666–673 [43] Hofstetter CC, Kesavabhotla K, Boockvar JA. Zero-profile anchored spacer reduces rate of dysphagia compared to ACDF with anterior plating. J Spinal Disord Tech. 2015; 28(5):E284–E290 [44] Doh ES, Heller JG. Multi-level anterior cervical reconstructions: comparison of surgical techniques and results. Paper presented at the Cervical Spine Research Society, 26th Annual Meeting booklet; December 28–29, 1998; Atlanta, Georgia [45] Curtin SL, Heller JG. Multilevel anterior cervical reconstructions: pseudoarthrosis and complication rates. AAOS Annual Meeting; February 23, 1996, 1996

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Complications of Cervical Arthroplasty

20 Complications of Cervical Arthroplasty Amir M. Abtahi and Brandon D. Lawrence

20.1 Introduction Anterior cervical discectomy and fusion (ACDF) is the mainstay of treatment for degenerative conditions of the cervical spine. It is effective, technically simple, and has a relatively low incidence of complications. The problem of adjacent segment degeneration (ASD), however, has generated interest in cervical disc replacement as an alternative for the treatment of degenerative cervical conditions. Up to 25.6% of patients who have undergone ACDF develop symptomatic ASD by 10 years.1 Cervical disc replacement has the theoretical advantage of maintaining intervertebral motion, which, in theory, decreases stress at adjacent levels and may possibly slow or prevent the development of adjacent segment disease.

20.2 History of Cervical Disc Arthroplasty The first cervical arthroplasty device, which utilized a stainless steel ball bearing design, was implanted by Ulf Fernstrom in the 1960s. His results, published in 1966, reported high rates of subsidence, migration, and adjacent segment hypermobility.2 In 1989, B.H. Cummins designed a two-piece stainless steel implant utilizing a metal-on-metal, ball-andsocket articulation with anterior screws fixing the superior and inferior components of the device to their respective vertebral bodies. Initial clinical results of the Cummins– Bristol implant demonstrated high rates of hardware failure, screw pullout, and dysphagia.3 After undergoing several design modifications, the Cummins–Bristol arthroplasty device was reintroduced as the Frenchay disc. The Frenchay disc demonstrated improved clinical outcomes and lower complication rates at 2-year follow-up. Complications included screw breakage in one patient and prosthetic loosening in another patient requiring device removal.4 In 2007, the first prospective, randomized clinical trial in the United States was published comparing outcomes of the Prestige ST (Medtronic, Memphis, TN) cervical disc arthroplasty versus ACDF.5 Results from prospective, randomized clinical FDA IDE trials of several other cervical arthroplasty devices with 24-month follow-up have since been published.6,7,8,9,10 Several studies have subsequently been published with longerterm (up to 8 years) follow-up of these patients.11,12,13,14

frequency and in type to complications previously and concurrently reported for ACDF (▶ Table 20.1).5,6,7,8,9,10 The rate of surgery- or implant-related adverse events or serious adverse events reported in these studies ranges from 2.9 to 6.2% for patients undergoing cervical disc replacement. These rates do not differ significantly from rates concurrently reported for ACDF which ranged from 4.2 to 11.4%.5,6, 7,8,9,10 The majority of complications associated with cervical disc replacement are associated with the anterior cervical approach and are therefore similar to those reported for ACDF. Other complications, however, are only seen in association with cervical disc replacement. Because cervical disc arthroplasty devices vary widely in their design and biomechanical function, many complications seen with these devices are unique not only to cervical arthroplasty in general but to certain device designs and even to specific devices. The goal of this chapter is to comprehensively review the complications of cervical disc arthroplasty.

20.4 Complications Related to the Anterior Cervical Approach All cervical disc arthroplasty devices utilize the anterior cervical approach for exposure, decompression, and implant placement. Complications related to the anterior cervical approach are listed and then described below: ● Dysphagia. ● Dysphonia. ● Hematoma. ● Dural tear. ● Esophageal injury. ● Airway compromise. ● Vertebral artery injury. ● Carotid or internal jugular injury. ● Neurologic injury—nerve root injury, spinal cord injury. ● Horner’s syndrome. ● Infection. ● Other complications.

Table 20.1 Adverse events Study

Cervical disc arthroplasty

ACDF

20.3 Adverse Events Associated with Cervical Disc Arthroplasty

Mummaneni et al (2007)

6.2%

4.2%

Heller et al (2009)

AE, 2.9%; SAE, 1.7%

AE, 5.4%; SAE, 3.2%

The primary goal of the FDA IDE trials was to establish the safety and efficacy of various cervical arthroplasty devices. Therefore, in addition to reporting on the clinical outcomes of cervical disc arthroplasty versus ACDF, these trials also reported on the adverse events observed in association with both cervical arthroplasty and ACDF. Adverse events reported for cervical arthroplasty appear to be similar in

Murrey et al (2009)

2.9%

6.6%

Coric et al (2011)

5.1%

11.4%

Phillips et al (2013)

5.6%

7.4%

Abbreviations: ACDF, anterior cervical discectomy and fusion; AE, adverse events; SAE, serious adverse events.

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Cranial

20.5 Dysphagia Dysphagia is one of the most common complications of anterior cervical spine surgery. Reported rates of dysphagia after anterior cervical spine surgery range from 3 to 60%.15,16,17 Initial clinical results of the Cummins–Bristol cervical arthroplasty device demonstrated persistent dysphagia in all patients.3 This high incidence of dysphagia was attributed to hardware prominence. Reported rates of dysphagia have improved with newer device designs and surgical techniques. Reports of the incidence of dysphagia with currently available cervical disc arthroplasty devices range from 0.0 to 9.9%.5,6,7,8,9 Other studies have reported combined rates of dysphagia and dysphonia up to 10.7%.10 In most studies of cervical disc replacement, rates of dysphagia have been shown to be less than or equivalent to those observed for ACDF.5,6,7,8,9,10 Soft-tissue swelling is the most common cause of transient postoperative dysphagia; however, a number of other factors may contribute to or cause dysphagia, including postoperative fluid collections (hematoma, CSFoma, or abscess); direct or indirect injury to the esophageal neural plexus or to the vagus, superior laryngeal, or recurrent laryngeal nerves (RLNs); implant prominence; and failure or migration of the implanted device.18 When dysphagia is persistent or severe, the possibility of implant migration or failure must be considered and radiographs and/or more advanced imaging studies should be obtained to evaluate for this potential complication, as devices with a polyethylene core may not be visible on routine radiography.

20.6 Dysphonia Dysphonia is also a common complication of anterior cervical spine surgery, although it is less common than dysphagia. Reported rates of dysphonia after anterior cervical spine surgery range from 1 to 51%.15,16,19 The incidence of dysphonia after cervical disc arthroplasty was reported in one study to be 0.4%.5 Other studies have reported combined rates of dysphagia and dysphonia ranging from 1.7 to 10.7%.9,10 Multiple factors may contribute to the development of postoperative dysphonia including laryngeal injury during intubation, laryngeal edema occurring secondary to intraoperative retraction, and RLN injury.16 Injury to the RLN may be caused by stretch, pressure between the endotracheal tube and retractor, or by direct injury to the nerve.20,21,22,23,24,25 Symptoms of RLN injury may include hoarseness, vocal fatigue, coughing, aspiration, and/or dysphagia; however, some cases of RLN injury may be clinically silent.26 A recent study reported that after anterior cervical surgery, the rate of clinically symptomatic RLN palsy was 8.3%, while the incidence of asymptomatic palsy was 15.9% (overall rate of 24.2%). At 3-month follow-up, the rate of persistently symptomatic RLN palsy was 2.5%, while the incidence of asymptomatic palsy was 10.8% (overall rate of 13.3%).25 Although most RLN injuries resolve with time, permanent paralysis has been reported in up to 3.5% of patients after anterior cervical surgery.24 Bilateral RLN palsy may manifest as dyspnea and inspiratory stridor and can lead to life-threatening airway compromise.16,27,28 For this reason, use of a contralateral surgical approach is not

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recommended in patients who have had previous anterior cervical surgery in order to minimize the risk of bilateral RLN injury, unless direct laryngoscopy is performed portraying normal function of the ipsilateral vocal cords. The RLNs are not directly visualized during the anterior cervical approach. The right RLN loops around the right subclavian artery before ascending in the tracheoesophageal groove, whereas the left RLN follows a somewhat longer course looping around the aortic arch before ascending in the tracheoesophageal groove. In approximately 1% of individuals, the right RLN follows a nonrecurrent course.29,30 Anatomic studies have shown that the right RLN approaches the tracheoesophageal groove at a more oblique angle compared to the left and that the RLN on the right side travels within the tracheoesophageal groove more anteriorly and laterally than on the left side.31,32 It has been proposed that these anatomic differences place the right RLN at greater risk of injury during the anterior cervical approach.23 Recent anatomic studies, however, have shown that the RLNs follow a similar course within the tracheoesophageal groove.33,34 There are also conflicting clinical studies regarding RLN injury. Although some studies have shown increased rates of RLN palsy with right-sided approaches, other studies have shown no difference in injury rates between the two approaches.26,35,36 Apart from the potential role of the side of the approach, other potential risk factors for RLN palsy include prolonged operative time, multilevel surgery, previous anterior cervical surgery, and low cervical exposure.37 The risk of RLN injury and other retraction-induced injuries can usually be minimized by placing retractors underneath the longus colli muscles so as to minimize retractor pressure and tension on adjacent structures.

20.7 Hematoma Postoperative hematoma formation is a well-recognized potential complication of anterior cervical spine surgery. Hematoma formation after cervical disc arthroplasty has a reported incidence of 0.7 to 0.8%, which is consistent with previously and concurrently reported rates of hematoma formation after ACDF.5,6,7,8,9,10 Signs and symptoms of hematoma formation may include pain or pressure in the neck, dysphagia, dysphonia, and/or significant swelling at the operative site. Hematomas may lead to wound complications or infection and, when large, may result in life-threatening airway compromise requiring emergency hematoma evacuation. Meticulous intraoperative hemostasis and judicious use of postoperative anticoagulation are recommended to minimize the incidence of postoperative hematoma formation.

20.8 Epidural Hematoma Epidural hematoma formation after anterior cervical spine surgery is rare but can cause progressive spinal cord compression and neurologic dysfunction. A 0.3% incidence of symptomatic epidural hematoma formation has been reported after anterior cervical spine surgery.38 An increased incidence of epidural hematoma has not been reported after cervical total disc arthroplasty, as compared to ACDF. When an epidural hematoma is suspected due to a progressive neurologic deficit,

Complications of Cervical Arthroplasty advanced imaging consisting of CT or MRI is recommended and immediate surgical intervention is required if an epidural hematoma is determined to be the cause.

20.9 Dural Tear Dural tears are an uncommon complication of anterior cervical spine surgery and are far less common than dural tears occurring during posterior lumbar surgery.39 Dural tears have been reported in 1.8 to 3.7% of patients during anterior cervical spine surgery.22,40 The reported incidence of dural tears during cervical disc arthroplasty ranges from 0 to 1% and does not differ significantly from rates concurrently reported for ACDF.5,6,7,8,9,10 A persistent CSF leak may lead to wound complications including spinocutaneous fistula or secondary airway compromise.41,42 When a dural tear is recognized intraoperatively, repair should be attempted, although it is often not possible and consideration should be given to lumbar drain placement. The patient should also be positioned upright postoperatively to decrease the CSF pressure and allow for healing of the dural tear.43

20.11 Airway Compromise Postoperative airway compromise is an uncommon but lifethreatening complication of anterior cervical spine surgery. In a recent retrospective review, 6.1% of patients undergoing anterior cervical spine surgery experienced postoperative airway complications.53 On average, symptoms of airway compromise developed 36 hours postoperatively in this study. In previous studies, a 1.7 to 2.8% incidence of reintubation has been reported following anterior cervical spine surgery.42,53,54 In a study of adverse events following cervical disc arthroplasty, 0.8% of arthroplasty patients experienced postoperative airway compromise requiring reintubation compared to 1.4% of patients who underwent ACDF.10 Postoperative airway obstruction is most commonly a result of significant laryngeal or prevertebral soft-tissue edema; however, other factors may play a role including fluid collections (hematoma, CSFoma, or abscess) or hardware migration/displacement. Additional risk factors for postoperative airway obstruction include obesity, a history of obstructive sleep apnea or asthma, prolonged surgical times, revision surgery, high cervical surgery, and multilevel surgery.53,54

20.10 Esophageal Perforation Esophageal perforation is a rare but life-threatening complication of anterior cervical spine surgery. The risk of esophageal perforation during anterior cervical spine surgery is very low with a reported incidence of 0.1 to 0.7%; however, an increased incidence of esophageal perforation has not been reported after cervical TDA compared with ACDF .5,6,7,8, 9,10,22,23,44,45,46 Esophageal injury usually occurs intraoperatively secondary to malpositioning of retractors, excessively forceful retraction, or direct trauma from an operative instrument; however, delayed esophageal perforation has been reported secondary to displacement of hardware resulting in esophageal erosion.47 A recent cadaveric study demonstrated that cervical disc arthroplasty requires less esophageal retraction compared to anterior cervical plating, which may reduce the incidence of both esophageal perforation and dysphagia after cervical arthroplasty surgery.48 Esophageal perforation may be recognized either intraoperatively or during the early postoperative period. Symptoms may include neck pain and/or swelling, dysphagia, odynophagia, dysphonia, dyspnea or airway compromise, and aspiration, as well as fever and tachycardia.49 Esophageal perforation may cause severe, life-threatening cervical and/ or mediastinal infection.46,49,50 Evidence of early postoperative infection should raise concern for esophageal injury. The mortality rate of esophageal perforation can be as high as 20% when identified within the first 24 hours and increases to up to 50% thereafter—making early diagnosis and treatment of esophageal injuries extremely important.44,51 When an esophageal perforation is suspected, consultation with a general or thoracic surgeon is recommended. Flexible fiberoptic endoscopy may be performed by a trained specialist to evaluate for an esophageal perforation if the diagnosis is not clear intraoperatively. Lateral cervical spine radiographs may show subcutaneous or prevertebral air and/or widening of the prevertebral soft tissues.52 Fluoroscopic contrast swallowing studies or CT may also aid in the diagnosis.

20.12 Vertebral Artery Injury Vertebral artery injury is a rare but very serious complication of anterior cervical spine surgery with a reported incidence of 0.3 to 0.5%.55,56,57 Vertebral artery injury may result in uncontrollable hemorrhage resulting in hemodynamic compromise and intraoperative cardiac arrest or death (0–16.7%) or vertebrobasilar infarction (0–30%).55,56,57 The vertebral artery lies in the costotransverse foramen on the lateral portion of the transverse processes and should not be visible during the anterior cervical approach, unless the operation strays significantly away from midline. The vertebral artery at the level of the disc space is protected during anterior cervical discectomy by the uncovertebral joint. Risk factors for vertebral artery injury, therefore, include excessively wide decompression, soft lateral bone from tumor or infection, and anatomic abnormalities in the course of the vertebral artery.55 Management of vertebral artery injuries when they occur may consist of repair, ligation, or tamponade. No cases of vertebral artery injury resulting from cervical disc arthroplasty have been reported in the literature.

20.13 Neurological Complications Neurological success rates following cervical disc arthroplasty range from 90.9 to 95% and are either equivalent or superior to neurological success rates concurrently reported for ACDF.5,6,7,8,9 One study reported adverse neurologic events in 3.3 and 3.2% of cervical arthroplasty and ACDF patients, respectively.10 Neurological complications after cervical disc arthroplasty may include persistent or progressive radiculopathy or myelopathy, as well as iatrogenic nerve root or spinal cord injury. Spinal cord injury is an infrequent but devastating complication of anterior cervical spine surgery with a reported incidence of 0.2 to 0.9%.23,42,43,58 A recent case report described two cases of spinal cord injury resulting from cervical disc arthroplasty. Both patients experienced paralysis and sensory disturbances

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Cranial in both their upper and lower extremities, as well as urinary/ fecal incontinence immediately after surgery. Surgical intervention was delayed in both patients. Both were eventually revised to ACDF and experienced partial neurological recovery.59 When persistent neck pain or persistent or worsening myelopathy or radiculopathy are present postoperatively with symptoms referable to the index level, multiple authors have reported good results with removal of the arthroplasty device and conversion to ACDF.5,6,7,8,9

20.14 Horner’s Syndrome Horner’s syndrome is a rare complication of anterior cervical spine surgery that occurs secondary to injury to the cervical sympathetic trunk. Symptoms of Horner’s syndrome include the classic triad of ptosis, miosis, and anhydrosis. During the anterior cervical approach, the cervical sympathetic trunk lies at an average distance of 11.6 mm from the medial border of the longus colli muscle at the level of C6.60 It is at risk for both retractor-induced stretch injury and direct injury from operative instruments. The incidence of Horner’s syndrome after anterior cervical spine surgery varies in the literature from 0.2 to 4%.23,43,61,62,63 Most cases of Horner’s syndrome resolve spontaneously, although in some cases symptoms may be permanent.

20.15 Infection Infection is relatively rare following anterior cervical spine surgery, with an estimated incidence of 0.2 to 1.6%.23,43 The incidence of postoperative infection after cervical disc arthroplasty has been reported at a rate of up to 2.9%, although most infections reported in this study were superficial and treated with oral antibiotics alone.10 In most studies, rates of infection did not differ significantly from rates reported for ACDF.5,6,7,8,9 As mentioned earlier, early wound infection should raise concern for esophageal perforation and appropriate imaging studies and/or consultations should be ordered if the index of suspicion is high. Acute wound infection following anterior cervical spine surgery is treated with irrigation, debridement, and intravenous antibiotics. If infection persists, hardware removal should be considered with conversion to ACDF versus posterior instrumented fusion.

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20.17 Subsidence and Migration There are few cases of revision reported in the literature for implant subsidence or migration at up to 24-month follow-up. One study reported a 0.5% incidence of implant migration at 24 months.8 A recently published study with 5-year follow-up demonstrated that subsidence was present in 2.6% of patients at 24 months and 2.8% of patients at 60 months.13 No implant migration was observed. A recently published European study with up to 8-year follow-up demonstrated no cases of anteroposterior migration greater than 3 mm or subsidence greater than 2 mm at any time point.11 The results of these and other studies indicate that rates of subsidence and migration after cervical disc arthroplasty are very low.

20.18 Fracture Vertebral body split fractures have been reported after singleand multilevel cervical disc arthroplasty with prosthetic designs utilizing a central keel.64,65 Implantation of devices utilizing this design requires cutting a slot for the keel into the vertebral endplate. This may weaken the vertebral body and can cause a fracture to propagate from the keel in the prosthesis through the vertebral body. Multilevel cervical disc arthroplasty increases the risk of vertebral body split fracture even further because slots must be cut in both the superior and inferior endplates of the central vertebral body, which weakens the vertebral body to an even greater degree. The primary concerns raised when a vertebral body fracture occurs are fracture progression or displacement and prosthesis stability. In the cases that have been published to date describing this complication, fractures have been successfully managed conservatively with cervical immobilization in a collar and retention of the prosthesis.64,65 Posterior avulsion fractures of the superior and inferior vertebral bodies occurring during endplate preparation for a keeled prosthesis have also been described.66 In the case that has been reported in the literature, treatment consisted of excision of the fractured fragments and implantation of the prosthesis as planned. Patient factors that may be associated with an increased risk of vertebral body fracture include osteoporosis, lower vertebral body height, and significant endplate sclerosis. Intraoperative risk factors may include dull keel osteotomes requiring forceful mallet impaction and use of Caspar retraction pins in the same sagittal plane as the keels in the prosthesis.64,65,66

20.16 Implant-Related Complications

20.19 Implant Malposition

Early cervical disc arthroplasty devices demonstrated high rates of subsidence, migration, and hardware failure.2,3 Most currently available devices, however, have relatively low reported rates of implant-related complications. Reported rates of secondary surgery at the index level following cervical disc arthroplasty at 2-year follow-up range from 1.8 to 5.0%.5,6,7,8,9 The majority of these secondary surgeries have been performed for persistent pain rather than for implant subsidence, migration, failure, or other implant-related complications.

The incidence of initial implant malposition is very low based on published data. One study reported implant malposition in 1 out of 242 (0.4%) patients.10 Similarly, a number of studies have evaluated the effect of cervical arthroplasty with specific disc designs on sagittal alignment and have shown that there is a tendency for kyphotic alignment through the functional spinal unit in which the prosthesis is placed with minimal to no effects on overall sagittal alignment of the cervical spine.67,68,69

Complications of Cervical Arthroplasty

20.20 Implant Failure and Related Complications There are many cervical artificial disc designs utilizing a variety of materials including ultra-high-molecular-weight polyethylene, polyurethane, cobalt chromium alloy (CoCr alloy), stainless steel, titanium, titanium alloys, and ceramics.70 Studies have shown that polyethylene wear debris is present following lumbar disc arthroplasty and tissue specimens have demonstrated the presence of inflammatory infiltrates associated with polyethylene wear debris.71,72,73,74,75,76 Despite periprosthetic particle loads comparable to hip arthroplasty in some patients, osteolysis has rarely been seen in association with disc arthroplasty-generated polyethylene wear debris.71,72,73 Similarly, studies have demonstrated evidence of polyurethane wear debris in association with the Bryan (Medtronic) artificial disc and tissue specimens have shown that inflammatory infiltrates are associated with polyurethane wear debris.70 No evidence of osteolysis has been observed in tissue specimens from explanted discs; however, unpublished cases of osteolysis and adverse local tissue reactions have been described. There have been two known cases of aseptic osteolysis; one case was in an asymptomatic patient in whom osteolysis of the adjacent vertebral bodies was detected during routine follow-up radiographs 3 years postoperatively, and the second case was in a patient who developed a recurrent radiculopathy 5 years postoperatively secondary to osteolysis with associated reactive hypertrophic bone formation that resulted in nerve root compression. In both cases, the prosthesis was removed with conversion to ACDF.70 One study demonstrated that oxidative degradation of the polyurethane sheath was present in 27% of explanted devices. Interestingly, the presence of oxidative degradation did not appear to be associated with implantation time.70 Oxidative degradation was associated in some cases with fissuring and/or full-thickness cracking of the polyurethane sheath. Metal-on-metal articulations utilizing stainless steel as well as CoCr alloy have also been utilized in disc arthroplasty devices. The hip arthroplasty literature has reported a high rate of revision related to metal hypersensitivity, osteolysis, and pseudotumor formation in association with metal-on-metal implants.77,78 Two case reports have been published on complications of cervical arthroplasty devices attributed to metal wear debris—one case of idiopathic vertebral body osteolysis and one case describing an inflammatory soft-tissue mass associated with metal-on-metal disc replacements. In both cases, the salvage operation consisted of implant removal and conversion to ACDF. Histological studies of explanted CoCr alloy metal-onmetal lumbar devices show tissue necrosis and lymphocytedominated inflammatory responses with no evidence of osteolysis.70 Histological analysis of periprosthetic tissues surrounding explanted Prestige ST (stainless steel metal-on-metal) cervical artificial discs have shown both focal and diffuse patterns of metallosis. Histologically, the tissue response is characterized by a mononuclear chronic inflammatory response similar to that observed with other stainless steel surgical devices and has not been associated with tissue necrosis, osteolysis, or tissue degeneration.70

Endplate impingement has also been described with certain devices including the Prestige ST and Bryan implants with observed impingement rates of up to 30%.70 In some cases, endplate impingement has resulted in metal wear debris, cracking of polyurethane sheath, and third body wear involving the polyurethane core. A case report has been published describing rupture of the polyurethane sheath 8 years after implantation of a Bryan cervical disc. The patient presented with neck pain, stiffness, and a soft-tissues mass in the anterior neck. MRI imaging revealed a cystic mass anterior to the disc. When this was explored surgically, a crack was found in the polyurethane sheath and metal debris was present in the surrounding tissues along with significant soft-tissue inflammation. The patient was successfully converted to ACDF.79 Implant failure of cervical disc arthroplasty devices has been infrequently reported in the literature. Earlier cervical disc arthroplasty designs demonstrated high rates of screw pullout and breakage; however, as the technology has progressed, reports of device failure have become increasingly rare. Reports of implant failure, even with longer-term follow-up, are rare. One case report describes fracture of the ceramic bearing surface in a patient with a semiconstrained ceramic-on-ceramic prosthesis who presented with persistent pain and radiculopathy 1 month following cervical disc arthroplasty. The patient was successfully converted to ACDF.80 Polyethylene extrusion has been observed after lumbar disc arthroplasty.81,82 Posterior extrusion of the polyethylene insert in lumbar arthroplasty devices has been associated with neurologic compromise. There have been no reports of polyethylene extrusion following cervical artificial disk replacement; however, a number of implants have designs utilizing polyethylene inserts. Therefore, this is one possible mode of failure for these devices. Implant failures may not be evident or easily recognizable on standard cervical spine radiographs; therefore, a high index of suspicion is required. Advanced imaging studies, such as CT or MRI, may be helpful. If a patient has persistent postoperative pain referable to the operative level, revision to ACDF is recommended.

20.21 Heterotopic Ossification Heterotopic ossification (HO) is a known complication of cervical and lumbar disc arthroplasty. The incidence of HO after cervical disc arthroplasty devices varies from 0 to 15.9%; however, significantly higher rates up to 76.2% have been reported.5,6,7,8,9, 10,83 This discrepancy in reported HO rates may be partially attributable to differences in the method of HO determination as well as significant interobserver variability; however, some of the observed differences may be related to specific factors involving the design and function of different implants and different techniques for endplate preparation and implantation which create bone debris that may precipitate HO formation. It has also been hypothesized that prostheses with a greater degree of constraint lead to increased stress at the bone–prosthesis interface which may lead to a greater propensity for HO formation.84,85 Despite potential differences related to different prostheses and their implantation, the rate of HO has been noted to vary

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Cranial Table 20.2 Grading criteria for heterotopic ossification Grade

Criteria

0

No heterotopic ossification present

1

Heterotopic ossification detectable in front of the vertebral body but not in the disc space

2

Heterotopic ossification present in the disk space; may affect the function of the prosthesis

3

Bridging ossification that allows some movement of the prosthesis

4

Complete fusion with no movement in flexion/extension at the involved level

from study to study using the same prosthesis. For the Bryan disc, for example, the reported rate of HO has varied from 0 to 76.2% in published studies.9,83 This may be related to a number of factors, including operative technique, patient-specific factors, use of nonsteroidal anti-inflammatory drugs (NSAIDs), and single- versus multilevel surgery.9,84,85,86,87 Soft-tissue trauma is a known cause of HO formation; therefore, careful handling of the soft tissues is recommended to reduce the likelihood of HO formation. A recent study evaluated predisposing factors for HO formation and found that the only patient-specific factor predisposing to the development of HO was male gender. Neither age nor degree of preexisting disc degeneration was shown to affect the incidence of HO.84 NSAIDs are thought to play a protective role in the development of HO. In the only study that included NSAID use as a routine part of the postoperative protocol, a 0% rate of HO was reported.9 Finally, there is evidence that multilevel disc arthroplasty is associated with a higher rate of HO than that observed for single-level surgery despite similar clinical outcomes.86,87 Despite a number of studies reporting rates of HO following cervical disc arthroplasty, few studies have evaluated its clinical significance. In a study comparing single- and multilevel disc arthroplasty, it was noted that despite the formation of HO, 97.7% of artificial discs remained mobile.86,87 The classification system proposed by McAfee et al for HO associated with lumbar disc replacements has been modified and applied to cervical arthroplasty (▶ Table 20.2).88,89,90 Grade 4 HO, which completely eliminates the mobility of the implant, is seen infrequently. A recent study with long-term follow-up demonstrated that at 4-year follow-up, 5% of patients had grade 4 HO and at both 6- and 8-year follow-ups, 8% of patients had grade 4 HO.11 Most patients in whom HO is noted have experienced no clinically evident adverse effects, but individuals in whom HO develops may experience a greater rate of ASD with long-term follow-up due to decreased mobility at the operative level.

20.22 Conclusion Complications arising after anterior cervical disc arthroplasty, although rare, may have devastating effects. The majority of complications that occur, similar to those seen after ACDF, are related to the surgical approach. With that said, cervical disc arthroplasty has specific complications inherent to the design

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of these implants that warrant special attention. Studies of up to 8-year follow-up show an overall low rate of complications including implant failure, but longer-term follow-up is needed to determine the long-term durability of these implants, as well as the ultimate question which is whether cervical arthroplasty decreases the rate of ASD. When complications do occur with cervical disc arthroplasty, many of them can be managed successfully by salvaging a failed device with ACDF, a feat that is much more difficult after failed lumbar disc arthroplasty.

References [1] Hilibrand AS, Carlson GD, Palumbo MA, Jones PK, Bohlman HH. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am. 1999; 81(4):519–528 [2] Fernström U. Arthroplasty with intercorporal endoprosthesis in herniated disc and in painful disc. Acta Chir Scand Suppl. 1966; 357:154–159 [3] Cummins BH, Robertson JT, Gill SS. Surgical experience with an implanted artificial cervical joint. J Neurosurg. 1998; 88(6):943–948 [4] Wigfield CC, Gill SS, Nelson RJ, Metcalf NH, Robertson JT. The new Frenchay artificial cervical joint: results from a two-year pilot study. Spine. 2002; 27 (22):2446–2452 [5] Mummaneni PV, Burkus JK, Haid RW, Traynelis VC, Zdeblick TA. Clinical and radiographic analysis of cervical disc arthroplasty compared with allograft fusion: a randomized controlled clinical trial. J Neurosurg Spine. 2007; 6 (3):198–209 [6] Heller JG, Sasso RC, Papadopoulos SM, et al. Comparison of BRYAN cervical disc arthroplasty with anterior cervical decompression and fusion: clinical and radiographic results of a randomized, controlled, clinical trial. Spine. 2009; 34(2):101–107 [7] Murrey D, Janssen M, Delamarter R, et al. Results of the prospective, randomized, controlled multicenter Food and Drug Administration investigational device exemption study of the ProDisc-C total disc replacement versus anterior discectomy and fusion for the treatment of 1-level symptomatic cervical disc disease. Spine J. 2009; 9(4):275–286 [8] Phillips FM, Lee JY, Geisler FH, et al. A prospective, randomized, controlled clinical investigation comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion. 2-year results from the US FDA IDE clinical trial. Spine. 2013; 38(15):E907–E918 [9] Coric D, Nunley PD, Guyer RD, et al. Prospective, randomized, multicenter study of cervical arthroplasty: 269 patients from the Kineflex|C artificial disc investigational device exemption study with a minimum 2-year follow-up: clinical article. J Neurosurg Spine. 2011; 15(4):348–358 [10] Anderson PA, Sasso RC, Riew KD. Comparison of adverse events between the Bryan artificial cervical disc and anterior cervical arthrodesis. Spine. 2008; 33 (12):1305–1312 [11] Walraevens J, Demaerel P, Suetens P, et al. Longitudinal prospective longterm radiographic follow-up after treatment of single-level cervical disk disease with the Bryan Cervical Disc. Neurosurgery. 2010; 67(3):679– 687, discussion 687 [12] Goffin J, van Loon J, Van Calenbergh F, Lipscomb B. A clinical analysis of 4and 6-year follow-up results after cervical disc replacement surgery using the Bryan Cervical Disc Prosthesis. J Neurosurg Spine. 2010; 12(3):261–269 [13] Burkus JK, Haid RW, Traynelis VC, Mummaneni PV. Long-term clinical and radiographic outcomes of cervical disc replacement with the Prestige disc: results from a prospective randomized controlled clinical trial. J Neurosurg Spine. 2010; 13(3):308–318 [14] Sasso RC, Anderson PA, Riew KD, Heller JG. Results of cervical arthroplasty compared with anterior discectomy and fusion: four-year clinical outcomes in a prospective, randomized controlled trial. J Bone Joint Surg Am. 2011; 93 (18):1684–1692 [15] Edwards CC, II, Karpitskaya Y, Cha C, et al. Accurate identification of adverse outcomes after cervical spine surgery. J Bone Joint Surg Am. 2004; 86-A (2):251–256 [16] Winslow CP, Winslow TJ, Wax MK. Dysphonia and dysphagia following the anterior approach to the cervical spine. Arch Otolaryngol Head Neck Surg. 2001; 127(1):51–55 [17] Wilson DH, Campbell DD. Anterior cervical discectomy without bone graft. Report of 71 cases. J Neurosurg. 1977; 47(4):551–555

Complications of Cervical Arthroplasty [18] Frempong-Boadu A, Houten JK, Osborn B, et al. Swallowing and speech dysfunction in patients undergoing anterior cervical discectomy and fusion: a prospective, objective preoperative and postoperative assessment. J Spinal Disord Tech. 2002; 15(5):362–368 [19] Grisoli F, Graziani N, Fabrizi AP, Peragut JC, Vincentelli F, Diaz-Vasquez P. Anterior discectomy without fusion for treatment of cervical lateral soft disc extrusion: a follow-up of 120 cases. Neurosurgery. 1989; 24(6):853–859 [20] Fountas KN, Kapsalaki EZ, Nikolakakos LG, et al. Anterior cervical discectomy and fusion associated complications. Spine. 2007; 32(21):2310–2317 [21] Robinson RA, Walker E, Ferlic DC, et al. The results of anterior interbody fusion of the cervical spine. J Bone Joint Surg Am. 1962; 44:1569–1586 [22] Bertalanffy H, Eggert HR. Complications of anterior cervical discectomy without fusion in 450 consecutive patients. Acta Neurochir (Wien). 1989; 99(1– 2):41–50 [23] Tew JM, Jr, Mayfield FH. Complications of surgery of the anterior cervical spine. Clin Neurosurg. 1976; 23:424–434 [24] Heeneman H. Vocal cord paralysis following approaches to the anterior cervical spine. Laryngoscope. 1973; 83(1):17–21 [25] Jung A, Schramm J, Lehnerdt K, Herberhold C. Recurrent laryngeal nerve palsy during anterior cervical spine surgery: a prospective study. J Neurosurg Spine. 2005; 2(2):123–127 [26] Netterville JL, Koriwchak MJ, Winkle M, Courey MS, Ossoff RH. Vocal fold paralysis following the anterior approach to the cervical spine. Ann Otol Rhinol Laryngol. 1996; 105(2):85–91 [27] Manski TJ, Wood MD, Dunsker SB. Bilateral vocal cord paralysis following anterior cervical discectomy and fusion. Case report. J Neurosurg. 1998; 89 (5):839–843 [28] Muzumdar DP, Deopujari CE, Bhojraj SY. Bilateral vocal cord paralysis after anterior discoidectomy and fusion in a case of whiplash spine injury: a case report. Surg Neurol. 2000; 53(6):586–588 [29] Sanders G, Uyeda RY, Karlan MS. Nonrecurrent inferior laryngeal nerves and their association with a recurrent branch. Am J Surg. 1983; 146(4):501–503 [30] Cannon CR. The anomaly of nonrecurrent laryngeal nerve: identification and management. Otolaryngol Head Neck Surg. 1999; 120(5):769–771 [31] Ebraheim NA, Lu J, Skie M, Heck BE, Yeasting RA. Vulnerability of the recurrent laryngeal nerve in the anterior approach to the lower cervical spine. Spine. 1997; 22(22):2664–2667 [32] Weisberg NK, Spengler DM, Netterville JL. Stretch-induced nerve injury as a cause of paralysis secondary to the anterior cervical approach. Otolaryngol Head Neck Surg. 1997; 116(3):317–326 [33] Monfared A, Kim D, Jaikumar S, Gorti G, Kam A. Microsurgical anatomy of the superior and recurrent laryngeal nerves. Neurosurgery. 2001; 49(4):925– 932, discussion 932–933 [34] Haller JM, Iwanik M, Shen FH. Clinically relevant anatomy of recurrent laryngeal nerve. Spine. 2012; 37(2):97–100 [35] Kilburg C, Sullivan HG, Mathiason MA. Effect of approach side during anterior cervical discectomy and fusion on the incidence of recurrent laryngeal nerve injury. J Neurosurg Spine. 2006; 4(4):273–277 [36] Beutler WJ, Sweeney CA, Connolly PJ. Recurrent laryngeal nerve injury with anterior cervical spine surgery risk with laterality of surgical approach. Spine. 2001; 26(12):1337–1342 [37] Apfelbaum RI, Kriskovich MD, Haller JR. On the incidence, cause, and prevention of recurrent laryngeal nerve palsies during anterior cervical spine surgery. Spine. 2000; 25(22):2906–2912 [38] Song XH, Xu RM, Sun SH, Zhao LJ, Ma WH. [Analysis of epidural hematoma formative reason and its preventive measure after anterior cervical operation]. Zhongguo Gu Shang. 2013; 26(3):197–200 [39] Guerin P, El Fegoun AB, Obeid I, et al. Incidental durotomy during spine surgery: incidence, management and complications. A retrospective review. Injury. 2012; 43(4):397–401 [40] Emery SE, Bohlman HH, Bolesta MJ, Jones PK. Anterior cervical decompression and arthrodesis for the treatment of cervical spondylotic myelopathy. Two to seventeen-year follow-up. J Bone Joint Surg Am. 1998; 80(7):941–951 [41] Chang HS, Kondo S, Mizuno J, Nakagawa H. Airway obstruction caused by cerebrospinal fluid leakage after anterior cervical spine surgery. A report of two cases. J Bone Joint Surg Am. 2004; 86-A(2):370–372 [42] Fountas KN, Kapsalaki EZ, Johnston KW. Cerebrospinal fluid fistula secondary to dural tear in anterior cervical discectomy and fusion: case report. Spine. 2005; 30(10):E277–E280 [43] Hannallah D, Lee J, Khan M, Donaldson WF, Kang JD. Cerebrospinal fluid leaks following cervical spine surgery. J Bone Joint Surg Am. 2008; 90(5):1101– 1105

[44] Orlando ER, Caroli E, Ferrante L. Management of the cervical esophagus and hypofarinx perforations complicating anterior cervical spine surgery. Spine. 2003; 28(15):E290–E295 [45] Lu X, Guo Q, Ni B. Esophagus perforation complicating anterior cervical spine surgery. Eur Spine J. 2012; 21(1):172–177 [46] van Berge Henegouwen DP, Roukema JA, de Nie JC, vd Werken C. Esophageal perforation during surgery on the cervical spine. Neurosurgery. 1991; 29 (5):766–768 [47] Kelly MF, Spiegel J, Rizzo KA, Zwillenberg D. Delayed pharyngoesophageal perforation: a complication of anterior spine surgery. Ann Otol Rhinol Laryngol. 1991; 100(3):201–205 [48] Tortolani PJ, Cunningham BW, Vigna F, Hu N, Zorn CM, McAfee PC. A comparison of retraction pressure during anterior cervical plate surgery and cervical disc replacement: a cadaveric study. J Spinal Disord Tech. 2006; 19(5):312–317 [49] Gaudinez RF, English GM, Gebhard JS, Brugman JL, Donaldson DH, Brown CW. Esophageal perforations after anterior cervical surgery. J Spinal Disord. 2000; 13(1):77–84 [50] Michel L, Grillo HC, Malt RA. Esophageal perforation. Ann Thorac Surg. 1982; 33(2):203–210 [51] Shockley WW, Tate JL, Stucker FJ, Shreveport LA. Management of perforations of the hypopharynx and cervical esophagus. Laryngoscope. 1985; 95(8):939–941 [52] Cloward RB. Complications of anterior cervical disc operation and their treatment. Surgery. 1971; 69(2):175–182 [53] Sagi HC, Beutler W, Carroll E, Connolly PJ. Airway complications associated with surgery on the anterior cervical spine. Spine. 2002; 27(9):949–953 [54] Epstein NE, Hollingsworth R, Nardi D, Singer J. Can airway complications following multilevel anterior cervical surgery be avoided? J Neurosurg. 2001; 94(2) Suppl:185–188 [55] Burke JP, Gerszten PC, Welch WC. Iatrogenic vertebral artery injury during anterior cervical spine surgery. Spine J. 2005; 5(5):508–514, discussion 514 [56] Smith MD, Emery SE, Dudley A, Murray KJ, Leventhal M. Vertebral artery injury during anterior decompression of the cervical spine. A retrospective review of ten patients. J Bone Joint Surg Br. 1993; 75(3):410–415 [57] Golfinos JG, Dickman CA, Zabramski JM, Sonntag VK, Spetzler RF. Repair of vertebral artery injury during anterior cervical decompression. Spine. 1994; 19(22):2552–2556 [58] Hilibrand AS, Schwartz DM, Sethuraman V, Vaccaro AR, Albert TJ. Comparison of transcranial electric motor and somatosensory evoked potential monitoring during cervical spine surgery. J Bone Joint Surg Am. 2004; 86-A(6):1248–1253 [59] Chen J, Wang X, Yuan W, Tang Y, Zhang Y, Wan M. Cervical myelopathy after cervical total disc arthroplasty: case report and literature review. Spine. 2012; 37(10):E624–E628 [60] Civelek E, Karasu A, Cansever T, et al. Surgical anatomy of the cervical sympathetic trunk during anterolateral approach to cervical spine. Eur Spine J. 2008; 17(8):991–995 [61] Cuatico W. Anterior cervical discectomy without interbody fusion: an analysis of 81 cases. Acta Neurochir (Wien). 1981; 57(3–4):269–274 [62] Dohn DF. Anterior interbody fusion for treatment of cervical-disk conditions. JAMA. 1966; 197(11):897–900 [63] Hankinson HL, Wilson CB. Use of the operating microscope in anterior cervical discectomy without fusion. J Neurosurg. 1975; 43(4):452–456 [64] Tu TH, Wu JC, Fay LY, Ko CC, Huang WC, Cheng H. Vertebral body split fracture after a single-level cervical total disc replacement. J Neurosurg Spine. 2012; 16(3):231–235 [65] Datta JC, Janssen ME, Beckham R, Ponce C. Sagittal split fractures in multilevel cervical arthroplasty using a keeled prosthesis. J Spinal Disord Tech. 2007; 20 (1):89–92 [66] Shim CS, Shin HD, Lee SH. Posterior avulsion fracture at adjacent vertebral body during cervical disc replacement with ProDisc-C: a case report. J Spinal Disord Tech. 2007; 20(6):468–472 [67] Sasso RC, Metcalf NH, Hipp JA, Wharton ND, Anderson PA. Sagittal alignment after Bryan cervical arthroplasty. Spine. 2011; 36(13):991–996 [68] Sears WR, Sekhon LH, Duggal N, Williamson OD. Segmental malalignment with the Bryan Cervical Disc prosthesis—does it occur? J Spinal Disord Tech. 2007; 20(1):1–6 [69] Kim SW, Shin JH, Arbatin JJ, Park MS, Chung YK, McAfee PC. Effects of a cervical disc prosthesis on maintaining sagittal alignment of the functional spinal unit and overall sagittal balance of the cervical spine. Eur Spine J. 2008; 17 (1):20–29

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Cranial [70] Kurtz SM, Toth JM, Siskey R, et al. The latest lessons learned from retrieval analyses of ultra-high molecular weight polyethylene, metal-on-metal, and alternative bearing total disc replacements. Semin Spine Surg. 2012; 24 (1):57–70 [71] van Ooij A, Oner FC, Verbout AJ. Complications of artificial disc replacement: a report of 27 patients with the SB Charité disc. J Spinal Disord Tech. 2003; 16(4):369–383 [72] van Ooij A, Kurtz SM, Stessels F, Noten H, van Rhijn L. Polyethylene wear debris and long-term clinical failure of the Charité disc prosthesis: a study of 4 patients. Spine. 2007; 32(2):223–229 [73] Punt IM, Visser VM, van Rhijn LW, et al. Complications and reoperations of the SB Charité lumbar disc prosthesis: experience in 75 patients. Eur Spine J. 2008; 17(1):36–43 [74] Punt IM, Austen S, Cleutjens JP, et al. Are periprosthetic tissue reactions observed after revision of total disc replacement comparable to the reactions observed after total hip or knee revision surgery? Spine. 2012; 37(2):150–159 [75] Punt I, Baxter R, van Ooij A, et al. Submicron sized ultra-high molecular weight polyethylene wear particle analysis from revised SB Charité III total disc replacements. Acta Biomater. 2011; 7(9):3404–3411 [76] Punt IM, Cleutjens JP, de Bruin T, et al. Periprosthetic tissue reactions observed at revision of total intervertebral disc arthroplasty. Biomaterials. 2009; 30(11):2079–2084 [77] Langton DJ, Jameson SS, Joyce TJ, Hallab NJ, Natu S, Nargol AV. Early failure of metal-on-metal bearings in hip resurfacing and large-diameter total hip replacement: a consequence of excess wear. J Bone Joint Surg Br. 2010; 92 (1):38–46 [78] Glyn-Jones S, Pandit H, Kwon YM, Doll H, Gill HS, Murray DW. Risk factors for inflammatory pseudotumour formation following hip resurfacing. J Bone Joint Surg Br. 2009; 91(12):1566–1574 [79] Fan H, Wu S, Wu Z, Wang Z, Guo Z. Implant failure of Bryan cervical disc due to broken polyurethane sheath: a case report. Spine. 2012; 37(13): E814–E816

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[80] Nguyen NQ, Kafle D, Buchowski JM, et al. Ceramic fracture following cervical disc arthroplasty: a case report. J Bone Joint Surg Am. 2011; 93 (22):e132–(1–4) [81] Eskander MS, Onyedika II, Eskander JP, Connolly PJ, Eck JC, Lapinsky A. Revision strategy for posterior extrusion of the CHARITÉ polyethylene core. Spine. 2010; 35(24):E1430–E1434 [82] McAfee PC, Geisler FH, Saiedy SS, et al. Revisability of the CHARITE artificial disc replacement: analysis of 688 patients enrolled in the U.S. IDE study of the CHARITE Artificial Disc. Spine. 2006; 31(11):1217–1226 [83] Sola S, Hebecker R, Knoop M. Bryan cervical disc prosthesis -three years followup. Eur Spine J. 2005; 14 Suppl 1:38 [84] Yi S, Shin DA, Kim KN, et al. The predisposing factors for the heterotopic ossification after cervical artificial disc replacement. Spine J. 2013; 13 (9):1048–1054 [85] Yi S, Kim KN, Yang MS, et al. Difference in occurrence of heterotopic ossification according to prosthesis type in the cervical artificial disc replacement. Spine. 2010; 35(16):1556–1561 [86] Wu JC, Huang WC, Tsai HW, et al. Differences between 1- and 2-level cervical arthroplasty: more heterotopic ossification in 2-level disc replacement: clinical article. J Neurosurg Spine. 2012; 16(6):594–600 [87] Wu JC, Huang WC, Tsai TY, et al. Multilevel arthroplasty for cervical spondylosis: more heterotopic ossification at 3 years of follow-up. Spine. 2012; 37 (20):E1251–E1259 [88] McAfee PC, Cunningham BW, Devine J, Williams E, Yu-Yahiro J. Classification of heterotopic ossification (HO) in artificial disk replacement. J Spinal Disord Tech. 2003; 16(4):384–389 [89] Mehren C, Suchomel P, Grochulla F, et al. Heterotopic ossification in total cervical artificial disc replacement. Spine. 2006; 31(24):2802–2806 [90] Leung C, Casey AT, Goffin J, et al. Clinical significance of heterotopic ossification in cervical disc replacement: a prospective multicenter clinical trial. Neurosurgery. 2005; 57(4):759–763, discussion 759–763

Part 2 Thoracolumbar

21 Lumbar Pedicle Screw Complications

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22 Junctional Breakdown in Pedicle Screw Constructs

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23 Hook Complications in the Thoracic and Lumbar Spine

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24 Sublaminar Wiring Complications

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25 Complications of Percutaneous Vertebral Cement Augmentation

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2 26 Complications of Vertebral Body Implants Introduced through the Posterolateral Approach

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27 Complications of Vertebral Body Replacement Cages

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28 Complications of Anterior Thoracic Instrumentation Systems

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29 Interspinous Spinous Process Fusion Plate Complications

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30 Complications of Cortical Screw Fixation 188 31 Complications of Posterior Screw Fixation in Spine Surgery

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32 Interspinous Spacer Complications

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33 Complications of PresacralApproach–Based Fusion Devices

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34 Complications of Posterior and Transforaminal Lumbar Interbody Fusion 214 35 Complications of Open Transforaminal Lumbar Interbody Fusion

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36 Complications of Instrumentation in Minimally Invasive Transforaminal Lumbar Interbody Fusion

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37 Complications of Percutaneous Pedicle Screw Fixation

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38 Complications of Lateral Lumbar Interbody Fusion Cages

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39 Complications of Lateral Lumbar Fusion Plates

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40 Complications of Lateral Lumbar Arthroplasty Devices

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41 Complications of Lumbar Interbody Fusion with Femoral Ring Allograft

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42 Complications of Anterior Lumbar Interbody Fusion with Polyether Ether Ketone Spacers

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43 Complications of Stand-Alone Anterior Lumbar Interbody Fusion

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44 Complications of Anterior Lumbar Disc Replacement

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45 Complications of Iliac Screw Fixation

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46 Complications of Sacral Alar Iliac Screw Technique

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47 Complications of Sacropelvic Reconstruction for Tumor

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48 Complications of Instrumentation in Cervical Spondyloarthropathy

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49 Thoracolumbar Osteoporosis

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50 Complications of Thoracolumbar Instrumentation in Patients with Spondyloarthropathies

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51 Infection

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52 Instrumentation Complications following Spinal Tumor Surgery

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53 Cervical Kyphosis

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54 Instrumentation Complications Occurring from Thoracic Hyperkyphosis

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55 Flatback

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56 Lumbar High-Grade Spondylolisthesis

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57 Complications Related to Spinal Instrumentation and Surgical Approaches

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58 Complications of Osteobiologics in Spine Surgery 394 59 Removal and Revision of Broken Thoracolumbar Screws

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60 How to Remove/Revise Thoracolumbar Interbody Devices (TLIF Cages/ALIF Cages)

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Thoracolumbar

21 Lumbar Pedicle Screw Complications Barrett I. Woods, Kris E. Radcliff, and Alexander R. Vaccaro

21.1 Introduction The evolution of lumbar stabilization techniques and associated orthopaedic instrumentation has revolutionized the surgical treatment of various spinal pathologies. In 1969, Harrington and Tullos were the first to report pedicle screw fixation as a means to stabilize lumbar spondylolisthesis.1 Implant design and insertion technique were continually revised by numerous surgeons, resulting in acceptance of this fixation method in the United States in the 1980s.2,3,4,5 The North American Spine Society first openly endorsed pedicle screw fixation for the stabilization of the lumbar spine in 1993. Currently, polyaxial pedicle screw fixation is the “gold standard” for treating unstable lumbar disorders with the frequency of these procedures continuing to surge. In 2001, a total of 122,000 lumbar fusions were performed in the United States,6 which represented a 220% increase in number of fusion per 100,000 in 1990. The number of instrumented lumbar fusion has doubled again over the past decade.7 The efficacy of instrumented fusion facilitating solid fusion and improving patient outcomes has been established in the literature.8,9,10,11 However, as the frequency of instrumented lumbar fusion continues to rise, so do the number of complications associated with pedicle screw fixation. This chapter will review the relevant lumbar anatomy, techniques for screw insertion, and complications associated with their placement.

21.2 Technique for Insertion of Lumbar Pedicle Screws The osseous anatomy of the lumbar spine has been studied extensively across a wide variety of demographics.12,13,14,15 The pedicle can be found at the intersection of the transverse process and the superior articular facet. The pars interarticularis is an important osseous landmark, as the lateral pars provide a rough estimate to the medial wall of the corresponding pedicle. The inner diameter of the pedicle can vary significantly from L1 to L5, with diameter typically increasing from proximal to distal.16 Additionally, the medial angulation of the pedicles typically increases from around 12 degrees at L1 to 30 degrees at L5. Lumbar alignment in the sagittal and coronal planes in addition to any rotation of the vertebral bodies must also be taken into account when evaluating the pedicles. Normal lumbar lordosis is approximately 60 degrees with L3 at the apex. The technique for the safe and reliable placement of pedicle screws is dependent on the patient’s pedicle anatomy, screw starting point, and trajectory. Different starting points have been suggested since the advent of transpedicular lumbar fixation. Roy-Camille et al identified the starting point as the intersection of the middle portions of the transverse process and facet joint.3 Other proposed starting points include the junction of the lateral edge of the superior facet and the midline of the transverse process or the native upslope where the transverse process joins the superior articular process.17,18 Optimal entrance point to start transpedicular fixation may vary from proximally to distally in the lumbar spine. Ebraheim et al evaluated 50 cadaveric

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specimens (250 vertebrae) and found that the starting point for transpedicular fixation relative to the midline of the transverse process along the lateral border of the superior articular facet changed consistently from L1 to L5.14 Above the fourth lumbar vertebrae, the starting point was typically cephalad to the midline of the transverse process (average: 3.9 mm for L1, 2.8 mm for L2, and 1.4 mm for L3); however, at the fourth and fifth lumbar vertebrae, the starting point was typically caudal to the midpoint of the transverse process (0.5 mm for L4, 1.5 mm for L5). In addition to the external osseous landmarks which can be used to triangulate the position of the pedicle, transpedicular fixation can be further aided by direct palpation of the pedicle through a laminoforaminotomy or laminectomy. Image-guided pedicle screw techniques have also emerged as a means for accurate placement of instrumentation in the lumbar spine. Computed tomography (CT) and fluoroscopic techniques have been described in the literature.19,20,21,22,23

21.3 Complications Complications associated with lumbar pedicle screw instrumentation can occur intraoperatively or develop over time. Complications can arise from inaccurate screw placement resulting in dural or neurologic injury, screw breakage, back out, rod disengagement, or infection. These complications, management options, and methods for avoidance will be discussed.

21.4 Inaccurate Screw Placement Placement of lumbar pedicle screws is technically challenging and requires a thorough understanding of the three-dimensional anatomy of the lumbar spine. Variations in pedicle morphology, obesity, degenerative changes, and three-dimensional deformity can all complicate pedicle screw placement. Despite improvements in surgical technique, pedicle screw malposition is a relatively common occurrence even in the hands of experienced surgeons. Reported rates of screw malposition vary considerably in the in vitro cadaveric versus the in vivo clinical setting ranging from 5.5 to 39.9%.24,25,26,27 Tian and Xu performed a meta-analysis of the literature regarding pedicle screw insertion accuracy in the cervical, thoracic, and lumbar regions with both in vivo and in vitro studies included.20 A total of 7,533 pedicle screws were evaluated of which 6,721 were accurately placed within the pedicle (89.2%). The relative risk of screw malposition was statistically higher with anatomic insertion techniques when compared to image-guided methods. Gelalis et al performed another systematic review of all the prospective evidence regarding pedicle screw insertion techniques with similar conclusions.19 Imageguided techniques have improved the accuracy of transpedicular fixation, with CT-guided techniques resulting in the highest percentage of proper screw placement in the pedicle. There are currently a total of five prospective in vivo studies evaluating the accuracy of pedicle screw placement in the lumbar spine.19,

Lumbar Pedicle Screw Complications 21,22,28,29

Laine et al prospectively evaluated the accuracy of lumbar pedicle screw placement in 30 consecutive patients using a computer-assisted navigation technique.28 A total of 174 pedicle screws were placed with postoperative CT scans obtained postoperatively. A total of 139 screws were placed using the computer-assisted navigation technique of which 133 (95.7%) were accurately placed in the pedicle. The other 35 screws were placed using a freehand anatomic technique with an accuracy of 85.7% (30). All of the pedicle perforations using the computer-assisted technique were lateral, while freehand screw placement resulted in three medial perforations, one lateral, and one inferior. This finding is consistent with that of Gelalis et al, who reported a tendency toward medial breach with freehand techniques compared to lateral breach with image-guided methods.19 This study is confounded by the fact that the 35 screws placed freehand were done because the computer-assisted method could not be performed due to alterations of the anatomy or equipment malfunction. No surprise that the most difficult screws to place had a higher rate of cortical breach. Laine et al conducted another prospective randomized in vivo control trial, evaluating the accuracy of pedicle screw insertion with and without computer-assisted navigation in a consecutive series of 91 patients.22 A total of 496 screws were placed, 277 using the conventional freehand technique and 219 using computer-assisted navigation. The accuracy of screw placement was 95.4% using navigation and 86.6% using the freehand technique. Of the 37 screws that were misplaced using the freehand technique, 21 (56.8%) screws were medial, 9 were lateral, and 7 were inferior to the pedicle. This contrasts the 10 misplaced screws using the computer-assisted technique with 9 screws lateral (90%) and 1 medial breach. Castro et al prospectively evaluated 30 consecutive patients who received instrumented lumbar fusion.29 Of the 123 lumbar pedicle screws placed using two-dimensional fluoroscopy, only 74 (60%) were accurately placed in the pedicle as determined by postoperative CT scan. Schizas et al prospectively evaluated 15 patients using a CT-guided percutaneous method and found screw misplacement in 30%, with 3.3% having a severe pedicle penetration (> 5 mm).21 One outlier published by Girardi et al used CT-guided navigation for lumbar pedicle screw placement and reported 100% accuracy on 330 screws.30 Cortical breach during transpedicular fixation is a common occurrence regardless of the technique employed. Image-guided techniques do consistently exhibit a lower rate of misplaced screws when compared to freehand conventional techniques. The direction of screw misplacement may be technique dependent, with screws placed freehand more likely to result in a medial cortical breach, although this is not consistent with the authors’ experience.19 In addition to image guidance, stimulus-evoked EMG monitoring intraoperatively is a reliable method for determining if pedicle breach has occurred, allowing the surgeon to redirect or remove the offending screw.31,32,33 The consequence of pedicle breach is quite broad and ranges from benign to resulting in serious neurologic or vascular injury. Violation of the pedicle cortex can also have biomechanical implications compromising construct integrity. Factors that influence the clinical consequence of screw misplacement include pedicle location, direction, and degree of cortical violation.

21.5 Neurologic Injury Neurologic injury is one of the most feared complications of transpedicular instrumentation. Direction of the cortical breach influences the likelihood of neurologic injury with medial violation, placing the neural elements at highest risk.34 Medial breach can have significant morbidity at cord level pedicles; however, canal encroachment below the conus can also result in neurologic injury.35 Degree of cortical violation may also play a role in neural injury following screw misplacement.27 A significant portion of pedicle screws exhibits some degree of cortical breach, with less than 2 mm of violation proposed as safe, although this assertion is not proven by any literature.36,37 Of the prospective in vivo literature comparing pedicle insertion techniques in the lumbar spine, the incidence of neurologic injury ranged from 0 to 16.6%.21,22,28,29,30 From these studies, a total of eight patients with neural injury were identified, seven of who (87.5%) had a medial breach of greater than 5 mm. Both Castro et al and Laine et al identified four patients with medial breaches of at least 4 mm who did not have neurological complications. There were no reports of lateral, inferior, or superior breach causing neural injury in the lumbar spine, although inferior or superior breach could result in neural impingement of the exiting nerve root. Large meta-analysis have not shown any significant difference in neurologic complications between insertion techniques, although free-hand insertion most commonly resulted in a medial breach.19 Thus, the use of image guidance has yet to decrease the neurologic complication rate despite improving the accuracy of pedicle screw placement.38 Cortical breach of less than 2 mm has been proposed safe by multiple authors, with few proven cases in which this degree of medial encroachment has resulted in neurologic injury in the lumbar spine.21,22,28,29,30,37,38

21.6 Dural Injury Iatrogenic dural injury is a relatively common complication associated with lumbar spine surgery with reported incidence ranging from 1 to 17%.35,39,40,41 Although generally considered benign if identified and repaired, dural tear can have significant medical legal implications, as it is one of the most common reason spine surgeons are sued by their patients.42 In addition to the potential legal implications, serious complications associated with durotomy such as pseudomeningocele, fistula, meningitis, and even chronic back pain have been reported.43 Dural injury can result from misplaced pedicle cannulation in the superior medial, medial, or inferior medial direction. Dural injury may go unnoticed; however, cerebrospinal fluid extravasation during probing or screw placement should alert the surgeon of this potential complication. Direct dural repair in this setting may be challenging due to the ventral lateral location of the durotomy. Direct repair can be performed by a number of techniques with no one particular method proven superior. Fat grafts and hydrogel sealant can be used to augment the repair. If a hydrogel sealant is applied, it should be focal to the injured dura and not applied liberally, as reports of expansion and resultant neural compression have been published.44,45 The need for a period of bed rest for 24 to 48 hours has not been proven conclusively in the literature but is advocated by some

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Thoracolumbar authors.46 Lumbar drains can be placed if patients fail bed rest, with irrigation debridement and attempted repair recommended for patients with persistent drainage, symptoms, or pain.

21.7 Screw Pullout/Breakage Construct stability is influenced by patient-specific factors, screw characteristics, and insertion technique.38 Bone mineral density and pedicle size are two intrinsic variables which can influence pullout strength.47,48,49,50 The largest screw diameter possible to fill the isthmus of the pedicle utilizing a convergent trajectory into the vertebral body are technical factors which significantly influence the construct stability.51,52,53,54,55,56 These factors all contribute to the insertional torque required for transpedicular screw placement which is directly proportional to pullout strength.57 Screw misplacement will result in suboptimal isthmic fit, thus decreasing the pullout strength of that fixation point. Cortical breach can occasionally be detected intraoperatively by the decreased insertional torque required for screw placement. The effect that cortical violation due to pedicle misplacement has on the biomechanical stability of screw-based constructs has been evaluated in vivo. Kothe et al determined that iatrogenic disruption of the pedicle resulted in significant decreases in axial rotation and lateral bending stability provided by the instrumentation.58 Although this study was performed on thoracic specimens, similar conclusions can be drawn in the lumber spine. The frequency of screw breakage ranges considerably in the literature from 2.6% to as high as 60%.59,60,61 The highest rates of screw breakage have occurred in situations where the anterior column is compromised such as in burst fractures and no supplemental anterior column support provided. Jutte and Castelein performed a retrospective analysis on 105 consecutive patients who had lumbosacral fusion procedures for degenerative conditions and found an overall complication rate of 54%.62 In 13 patients (12.1%), one or more screws were broken, and 12 of these patients had a subsequent loss of correction in the sagittal and coronal planes. The risk of screw breakage was increased by fusion across the sacrum or in the presence of a spondylolisthesis treated posteriorly without anterior column support. An additional three patients (2.8%) had failure at the screw–rod interface, which resulted in rod migration and loss of correction. Pihlajämaki et al performed a retrospective review on 102 patients who had posterior lateral lumbosacral fusion and found 76 complications in 48 patients.63 Screw breakage occurred in 21 patients (20.1%), with the majority occurring in multilevel fusions that crossed the lumbosacral junction. Failure at the screw–bone and screw–rod interface has been reported in other series as well.8,64 Nonunion and osteoporosis were found to significantly influence the rate of hardware failure. The insertion of methylmethacrylate into the vertebral body has been described as a means to increase pedicle screw purchase in osteoporotic patients. Concerns regarding cement extravasation and the nonbiologic metal– cement interface have waned enthusiasm in this technique.65,66, 67,68,69 These concerns would only be magnified in the setting of cortical breach, particularly in the medial direction which further limits the applications of the technique.

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Our understanding of the biomechanics of transpedicular fixation and advances in instrumentation have decreased the incidence of construct failures, although not eliminated this issue. Improvement in the locking mechanisms at the screw–rod interface has resulted in less rod migration. Technically, the surgeon must remember to finally tighten the screws using an anti-torque device. Larger diameter screws and anterior column support are two other factors surgeons should consider when performing multilevel fusion procedures, especially when crossing the lumbosacral junction. The use of a cortical trajectory for posterior instrumentation has also be advocated as a method to increase pullout strength in osteoporotic patients.70,71

21.8 Infection Infection following posterior lumbar procedures that involve instrumentation is a challenge to the surgeon and can result in significant morbidity to the patient. In addition, the socioeconomic burden imparted by postoperative infections following lumbar spine surgery cannot be overstated. Although instrumented fusion can improve outcomes following the surgical management of spinal infections, the presence of metal in the lumbar spine significantly increases the rate of infection following decompression or deformity correction.72 The reported incidence of infection following instrumented lumbar procedures ranges from 2.6 to 12%.73,74,75 Accurate diagnosis of postoperative infection can be challenging and is typically predicated on physical examination findings. Multiple risk factors for infection have been identified.76 Collins et al performed a 10-year retrospective study on 1,980 instrumented lumbar fusions of which 74 (3.7%) were diagnosed with a postoperative infection.77 The diagnosis of infection was made in 76% of patients less than 2 years after the index procedure; however, only 8% of the patients were diagnosed within 30 days of surgery. In 16 patients, the diagnosis of infection was made only after removal of hardware for pain or implant prominence. Propionibacteria and Staphylococcus were the two most commonly isolated pathogens, with back pain the most common presenting finding. In this retrospective series, normal lab findings were common in those who developed infection with 17% of C-reactive protein, 45% of erythrocyte sedimentation rate, and 95% of white blood cell counts within normal limits. Chaichana et al published a retrospective series of 817 consecutive instrumented lumbar fusions and found an infection rate of 4.5% with mean diagnosis at 0.6 months.78 Management of postoperative infection can be challenging with no clear consensus on the optimal treatment algorithm. Typically, early irrigation and debridement of the wound bed is required with intravenous antibiotics and nutritional optimization if a deep infection is suspected.79 Removal of the spinal instrumentation has been advocated by some authors to adequately eradicate infection; however, resultant instability and pseudoarthrosis are major concerns.80,81,82,83 As in the joint literature, there are studies that suggest deep wound infections may persist despite debridement and antibiotics in the presence of contaminated hardware.84 Early and aggressive irrigation and debridement of suspected infections may allow for successful treatment with preservation of hardware.85,86

Lumbar Pedicle Screw Complications Meticulous hemostasis is paramount during instrumented lumbar procedures, as allogenic transfusion in this setting has been identified as any independent risk factor for infection.87,88,89 The use of vancomycin powder in the lumbar wound following instrumented procedures is a measure which has significantly decreased the incidence of postoperative wound infection.90,91

21.9 Summary The use of pedicle screws is relatively safe and improves fusion rates following cervical, thoracic, and lumbar procedures. Screw placement is technically challenging with a high rate of misplacement resulting in cortical breach. Screw misplacement can result in neurologic injury and compromise construct stability. Medial breach of the pedicle of greater than 2 mm places the neural elements at risk and should not be accepted. Imageguided techniques have improved the accuracy of screw placement but not resulted in lower rates of neurologic injury. Using the largest diameter screw to fill the isthmus while utilizing a convergent path into the vertebral body optimizes the biomechanical stability of the construct. Infection is a major concern following instrumented lumbar surgery. Meticulous hemostasis and the use of intraoperative vancomycin have resulted in lower infection rates postoperatively. Postoperative infection can be difficult to diagnose and should be treated aggressively with early irrigation and debridement which typically allows for preservation of the hardware.

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Thoracolumbar

22 Junctional Breakdown in Pedicle Screw Constructs Ivan Cheng and Michael Stauff

22.1 Introduction Spine surgeons have employed pedicle screw fixation in the thoracolumbar spine for over 30 years to achieve fixation in the setting of degenerative pathology, spine trauma, deformity, infection, and tumor. It is generally accepted that pedicle screw fixation provides the strongest multiplanar fixation of the vertebrae. For this reason, pedicle screw fixation has gained widespread use in the thoracolumbar spine by surgeons worldwide. With this extensive use, most experienced surgeons have noted pathology or breakdown at the adjacent segment above and below fusions with pedicle screws. Theories abound to explain the breakdown at an adjacent level, including progression of spinal degeneration, extent of deformity correction, patient factors, and also pedicle screw fixation. In this chapter, we will focus on adjacent segment pathology (ASP) and the impact of pedicle screw instrumentation. Breakdown or degeneration at a level adjacent to a pedicle screw construct is well recognized and its etiology is a heavily researched topic in the literature. To a certain extent, the research effort has been stymied because of the ambiguity associated with the terms that are used to describe adjacentlevel problems. In a recent systematic review, Kraemer et al1 failed to find consistent terms or classification systems used to describe adjacent segment problems. In order to address this ambiguity in the literature, Riew et al2 proposed a set of three simple descriptive terms that we will utilize throughout this chapter. ASP is a general descriptive term for pathology located proximal or distal to a pedicle screw construct. ASP consists of radiographic ASP, which is used to describe pathologic changes found at an adjacent level on radiographs/magnetic resonance imaging (MRI), and clinical ASP, which is used to describe clinical symptoms that arise from ASP.2 These terms have not been validated, but they serve as a “common ground,” where researchers can clearly define the salient issues and design relevant studies. One specific type of ASP is proximal and distal junctional kyphosis (DJK). Junctional kyphosis is defined as kyphosis at the segment adjacent to a long construct. This phenomenon has been extensively studied in adolescent and adult spinal deformity patients who are frequently treated with long, instrumented fusions. Proximal junctional kyphosis (PJK) typically occurs at a thoracic level above a long, instrumented fusion. The precise definition of PJK has been a topic of debate. In a retrospective review of 81 adult deformity patients, Glattes et al3 used 10 degrees of focal kyphosis above a long construct as the threshold for defining PJK. Using this definition, they demonstrated an incidence of 26% at an average follow-up of 2 years but found no significant difference in Scoliosis Research Society24 patient questionnaire (SRS-24) outcomes with or without PJK. In a series of adolescent scoliosis patients, Helgeson et al4 defined PJK as greater than 15 degrees of focal kyphosis. In this retrospective series, the authors compared the incidence of PJK between different instrumentation techniques and found that all pedicle screw constructs had a higher incidence of PJK. Despite the difference in incidence of PJK, the authors of this study found

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no difference in the SRS-22 scores.4 Recently, Bridwell et al5 defined the “critical angle” for PJK as 20 degrees in another retrospective analysis of adult deformity patients. In this series, the incidence of PJK was 27.8% at 3.5 years. Although one patient with a proximal junctional fracture required revision surgery in this analysis, overall they found no significant difference in outcome scores between patients with or without PJK.5 Junctional kyphosis can also happen at the distal end of long constructs. DJK occurs at the segment distal to a long construct. The precise angular threshold for DJK, like PJK, has been somewhat elusive. Some investigators have attempted to characterize specific thresholds for DJK. Lowe et al6 examined DJK in a multicenter retrospective analysis of 375 patients with selective thoracic fusions for adolescent idiopathic scoliosis. Comparing patients who had either all anterior or all posterior instrumentation, the authors examined the incidence of preoperative and postoperative DJK. With a definition of 10 degrees, the authors reported preoperative DJK in 4.2% of the anterior group and 5.0% in the posterior instrumentation group. They also reported postoperative DJK in 7.1% of the anterior group and 14.6% in the posterior instrumentation group. The authors concluded that when preoperative DJK was present, the construct must include the junctional level. In a study on patients with Scheuermann’s kyphosis who were treated with instrumented fusion, Denis et al7 reported the risk factors for developing DJK. Using a definition of 10 degrees, they reported an incidence of DJK of 12%. They concluded that for patients with Scheuermann’s kyphosis, the construct must include the first lordotic segment distally to prevent DJK. The two studies discussed earlier provide important information regarding the incidence of DJK and risk factors for developing DJK in patients who are treated with long, instrumented thoracic fusions. It should be noted, however, that these small, retrospective studies represent the largest series to date in the literature. DJK has a lower incidence than PJK and as a result, there are fewer studies that provide guidance on its incidence and risk factors. Also, the effect of DJK on clinical outcomes has not been well defined.

22.2 Epidemiology Breakdown at the segment adjacent to a pedicle screw construct was recognized as a phenomenon soon after spine surgeons started to employ pedicle screw fixation on a regular basis. Multiple investigators have sought to define the incidence of ASP in patients who have had pedicle screw-based fusions. When reviewing the literature, it is important to carefully consider the definitions of ASP.8,9,10,11 Many studies consider the need for additional surgery as an indicator for the presence of ASP.12,13 Other studies also consider patients who have radiographic changes and/or clinical symptoms as having adjacent segment disease or pathology and include these patients in the incidence rates and survivorship analysis. These definitions will invariably impact the results of the studies that investigate ASP. Multiple studies in the literature have investigated ASP after pedicle screw fusions8,9,10,11,12,13. The vast majority of these

Junctional Breakdown in Pedicle Screw Constructs studies are based on patients who have undergone lumbar fusions. Ghiselli et al8 published one of the earliest investigations on lumbar ASP. The authors of this study performed a retrospective study of 215 patients who underwent a posterior lumbar fusion and reported that the rate of clinical ASP requiring additional surgery was 16.5% at 5 years and 36.1% at 10 years postoperatively. Lee et al9 reported on 1,069 patients who underwent lumbar fusion and reported a 2.62% incidence of clinical ASP, defined as pathology that required an additional surgery. It should be noted that the low incidence might be related to the short follow-up for many of the patients, as the authors chose to include all patients with at least 1-year followup. In another large, retrospective review of 3,188 patients with thoracic, lumbar, and thoracolumbar fusions for a wide range of spinal pathologies, Ahn et al10 demonstrated clinical ASP rates of 3% at 5 years and 6% at 10 years. In this study, patients were deemed to have clinical ASP if they underwent a second surgical procedure.10 Sears et al11 also defined clinical ASP as that which required an additional surgery. In this retrospective series, the authors reported a 22.2% predicted rate of additional surgery at 10 years for ASP after lumbar fusion using a Kaplan– Meier survivorship analysis of 1,000 consecutive patients undergoing lumbar fusion. These studies are important because they have helped define the number of patients who will require additional surgery after a pedicle screw-based fusion. But, the reported rates of clinical ASP are most likely less than the true rate of ASP because patients who have radiographic changes and/or clinical symptoms were not included. Other investigators have included patients with radiographic ASP as well as symptomatic ASP. Kaito et al12 investigated a series of 85 patients who underwent L4–L5 fusions using a posterior interbody technique with an average 3-year follow-up period. In this analysis, the authors defined radiographic ASP in 14 out of 85 patients and clinical ASP (symptomatic but not necessarily requiring a second surgery) in 13 out of 85 patients. In a study of 188 patients who underwent lumbar and thoracolumbar fusions, Cheh et al13 reported radiographic ASP in 42.6% and clinical ASP in 30.3% at 5 years. The rates of ASP are higher in these two studies12,13 than that of other studies which used additional surgery as the definition for clinical ASP.8,9,10,11 In an effort to consolidate the existing data on ASP, Lawrence et al14 performed a systematic review. They identified 162 citations and focused the analysis on 5 studies based on their inclusion criteria. These studies are detailed earlier.8,9,10,11,12 The authors appropriately focused their analysis on the incidence of clinical ASP. Using the data extracted from the included studies, they reported a mean annual incidence of 0.6 to 3.9% for clinical ASP. The synthesis of the existing literature is helpful because it can be used to counsel patients who are considering a fusion. Future prospective studies would be beneficial to further validate the reported incidence of ASP in the lumbar spine. The rates of junctional problems are intimately related to the natural history of disc degeneration. In many ways, any discussion on ASP is incomplete without a discussion on the natural history of disc degeneration and how this compares to the rates of ASP and then to a pedicle screw-based fusion. The natural history of radiographic disc degeneration has been well studied in the lumbar spine. Classic data from the Framingham Heart Study cohort have been used to look at radiographic disc degeneration in the lumbar spine. Kauppila et al15 evaluated lumbar

radiographs over a 25-year period and reported that 2 out of 617 patients (average age: 54 years) had a degenerative spondylolisthesis of at least 3 mm at baseline imaging, while 123 patients had spondylolisthesis at final follow-up (average age: 79 years). In another study, Aono et al16 followed up 123 female patients without degenerative spondylolisthesis. After 8 years, 12.3% of patients developed a degenerative spondylolisthesis. Other, subtler findings of lumbar disc degeneration, such as herniation, anular tears, and Schmorl’s nodes, have been investigated as well. A more recent article by Cheung et al17 examined MRIs from 1,043 volunteers between 18 and 55 years of age. They discovered that 40% of patients younger than 30 years and 90% of patients older than 50 years had MRI findings of lumbar disc degeneration. Summation of the literature evidence demonstrates that lumbar disc degeneration starts early in some patients, but progresses with age and is very common in patients older than 50 years. For disc degeneration adjacent to a pedicle screw construct, the data are limited to retrospective investigations. The most important studies were summarized in a systematic review by Lawrence et al14 who demonstrated a mean annual incidence of clinical ASP of 0.6 to 3.9%. It is challenging to compare the rates of clinical ASP to the rates of disc degeneration in the lumbar spine, however, because the vast majority of the natural history studies have examined only radiographic changes associated with disc degeneration. Some investigators have performed systematic reviews18 in order to address the issue of whether ASP is secondary to advanced disc degeneration that has been perpetuated by pedicle screw fusions, but further research is necessary before we can make firm conclusions regarding this issue. One specific type of ASP, PJK, is relevant to patients who undergo long pedicle screw constructs. The incidence of PJK has been well studied in patients with spinal deformity. Kim et al19 recently performed a systematic review of all patients with spinal deformity. They included eight studies in their review. For patients with adolescent or adult scoliosis, they found that the risk of developing PJK was 17 to 39%. Furthermore, they reported no significant difference in clinical outcomes associated with the development of PJK.19 More recently, Kim et al20 performed a retrospective comparative study in adult deformity patients and reported an incidence rate of 39.5% in 364 patients. This is one of the few studies that demonstrated poorer postoperative functional outcome scores in patients with PJK based on the SRS postoperative pain subscore. Ha et al21 performed a retrospective review on 89 adult deformity patients who had long constructs that ended at the proximal thoracic and distal thoracic levels. In the proximal thoracic group, they found radiographic PJK and surgically treated PJK rates of 27 and 9.1%, respectively. The authors also found radiographic PJK and surgically treated PJK rates of 34 and 11.9%, respectively, in the distal thoracic group. Overall, the authors found no difference in the incidence of radiographic or surgically treated PJK in constructs where the upper instrumented vertebra is in the proximal versus distal thoracic location.21 There are few studies that have investigated the rates of DJK. One reason for the lower number of studies on DJK is the fact that patients with adult degenerative scoliosis rarely have mobile segments distal to the pedicle screw construct because of the inherent nature and pathophysiology of this condition. In

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Thoracolumbar a similar way, some patients with adolescent idiopathic scoliosis have curve types that mandate fixation to the sacrum and/or pelvis. For these reasons, the few studies on DJK have been in patients with primary thoracic deformities. In one study of patients with Scheuerman’s kyphosis, Denis et al7 reported a DJK rate of 12%. An earlier study on 375 patients with thoracic adolescent idiopathic scoliosis compared the rates of DJK in those who had anterior or posterior instrumentation.6 The authors reported a postoperative DJK rate of 7.1% in the anterior group and 14.6% in the posterior group. Although there are a few studies that help characterize the rates and risk factors associated with DJK, the dearth of well-designed studies leaves more questions than answers. Junctional fractures can also occur in patients with long pedicle screw constructs. These types of failures can sometimes lead to catastrophic neurologic injury, especially when they occur in the thoracic spine. Watanabe et al22 reported on 10 patients who had proximal junctional fracture after surgery for adult degenerative scoliosis. These 10 patients occurred among 428 patients who had undergone long, instrumented fusions for scoliosis. Of the 10 patients who had fractures, 5 patients also had subluxation at the fracture level and 2 of these patients had severe neurologic injury. The authors noted the following risk factors for fracture: old age, osteopenia, comorbidities, and severe preoperative global sagittal imbalance.22 In another retrospective study on PJK, Kim et al23 noted compression fractures at the level above the fusion in 4 out of 99 patients (4%). Hostin et al24 published a large retrospective study examining acute proximal junctional failure, which they defined as subluxation and kyphosis from ligamentous failure or fracture above a scoliosis construct. They reported a rate of 5.6% of acute proximal junctional failure in 1,218 patients. The authors noted that fracture was more common in the lower thoracic spine, whereas subluxation from soft-tissue failure was more common in the upper thoracic spine. Although proximal junctional fractures are rare, it is important to recognize the risk factors for this complication in the preoperative setting in order to allow for preoperative patient counseling.

22.3 Risk Factors In order to minimize the issues related to ASP, it is important to recognize potential risk factors for its development. Many risk factors for ASP are related to technical aspects of the surgical procedure, but some are also related to the patient. These patient factors have been discussed earlier: old age, osteopenia, and comorbidities. In this section, we will focus on modifiable risk factors for junctional problems adjacent to pedicle screw constructs. When performing a pedicle screw-based fusion, especially in the setting of a deformity, it is important to consider the overall stiffness of the construct and how it impacts the rest of the patient’s spine. The stiffness of the construct is related to multiple factors. As a modality for fixation in the spine, pedicle screws have demonstrated superior fixation strength to other means of fixation. The literature that best demonstrates this point is derived from the deformity literature that compares the correction and maintenance of correction in patients who have pedicle screw constructs versus hook or hybrid constructs.

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Hackenberg et al25 demonstrated the superiority of thoracic pedicle screw fixation compared with supralaminar/pedicle hooks in a cadaveric model. Multiple clinical studies on adolescents26,27 as well as adults28,29,30 have demonstrated greater curve correction and better maintenance of curve correction over time with pedicle screw fixation versus hook or hybrid instrumentation. The improved fixation strength provided by pedicle screws over hooks clearly has helped with the amount of deformity correction, but most studies have not demonstrated superior clinical outcomes in patients who have pedicle screw versus hook or hybrid constructs. Despite the greater correction afforded by the fixation strength and stiffness of pedicle screw instrumentation, it is possible that patients may be at a higher risk for junctional problems. Rods are a critical component to pedicle screw constructs as they are in hook and hybrid constructs. The size and composition of the rods is an important factor in the overall stiffness of the pedicle screw construct. Historically, spine surgeons used stainless steel because of its strength. More modern constructs generally utilize cobalt chromium, which has characteristics of excellent strength and stiffness without causing artifact in CT/ MRI scans like stainless steel. Titanium rods are generally utilized for degenerative conditions because the significant notch sensitivity and lower stiffness make them less than ideal for deformity. Most spinal deformity surgeons favor the stiffer metals like stainless steel or cobalt chromium because of the need to achieve correction and to maintain the correction over time. The impact of stiffer rod composition on junctional problems is not well defined in the literature, but the higher overall construct stiffness might lead to more stress at the adjacent level. Another important factor in the construct stiffness is the diameter of the rod. In general, thicker rods allow for greater construct stiffness. Patients who have adolescent scoliosis are generally treated with 5.5-mm rods made out of cobalt chromium, while adults are generally treated with 5.5- to 6.35-mm rods in either cobalt chromium or stainless steel.31 The larger rods are utilized to facilitate and maintain curve correction. Although larger diameter cobalt–chromium or stainless steel rods will allow for significant strength and stiffness, the surgeon must consider how this rigidity will impact the proximal and/or distal junctional zones. Currently, further research is needed in order to elucidate the impact of rod composition and diameter on construct stiffness and how this affects the incidence of junctional failures. Another purported risk factor for junctional problems adjacent to pedicle screw constructs is violation of the structures that stabilize the adjacent level next to the pedicle screw construct, including the facet joints and the supraspinous/ interspinous ligament (SSL/ISL) complex. Efforts to preserve the tissue that stabilizes the segment adjacent to a pedicle screw construct were born out of the need to decrease the incidence of PJK as well as ASP in general. In the lumbar spine, it is important to maintain the integrity of the facet joint capsule as well as the bony structure of the facet joint while placing pedicle screws at the uppermost level of the construct. In addition, some investigators have demonstrated the importance of maintaining the integrity of the SSL/ISL complex.32 In thoracic spine, many surgeons assert the importance of the facet joint and the SSL/ISL complex in preventing PJK. Anderson et al33 performed a cadaveric study that tested the stiffness of the supra-adjacent

Junctional Breakdown in Pedicle Screw Constructs segment next to a pedicle screw construct and demonstrated sequential loss of stiffness with hook instrumentation and interspinous ligament sectioning. Using a finite element analysis, Cahill et al34 also demonstrated the importance of the interspinous ligament as a tether to prevent excessive kyphosis and/ or forward translation. The preservation of the facet joint complex and SSL/ISL complex is important based on these in vitro studies, but clinical data that prove the importance of these structures in preventing ASP are lacking. One of the central tenants in adult spinal deformity surgery is correction of sagittal balance. The use of pedicle screw instrumentation and modern techniques have allowed for dramatic correction of a patient’s sagittal balance. Some investigators have reported that the extent of sagittal realignment is an independent risk factor for PJK after adult deformity surgery. Kim et al23 found that preoperative sagittal imbalance greater than 5 cm was a risk factor for developing sagittal decompensation following adult deformity surgery. Watanabe et al22 also reported that marked correction of sagittal imbalance was a potential risk factor for fracture at the proximal adjacent level. Knowing that the extent of sagittal realignment can be a risk factor for PJK can be important for spinal deformity surgeons

when discussing the likelihood of this complication in the postoperative period (▶ Fig. 22.1). It is important for spine surgeons to understand the risk factors for ASP because this can directly impact postoperative outcomes. The current literature has demonstrated the impact of construct stiffness, facet joint and SSL/ISL integrity, and sagittal realignment on ASP. Future prospective studies on ASP near pedicle screw constructs will help more clearly delineate these risk factors.

22.4 Treatment Options and Prevention The prospect of developing ASP has led to various efforts that decrease the risk of developing clinical ASP. These efforts are related to specific techniques for pedicle screw insertion as well as adjuncts to the surgical procedure. ASP is challenging to study because of the need to have long clinical follow-up. For this reason, studying the effects of specific techniques intended to decrease the risk of clinical ASP is even more difficult. Nevertheless, clinicians should continue to be cognizant of how

Fig. 22.1 Proximal junctional kyphosis (PJK) after adult scoliosis correction. (a) Immediate postoperative lateral image on a 62-year-old woman who underwent L3–S1 anterior lumbar interbody fusion (ALIF) and T10–ilium correction and fusion for adult scoliosis, demonstrating excellent correction with the start of PJK at the T9–T10 disc space. (b) Flexion lateral radiograph 3 months after initial surgery demonstrating proximal junctional kyphosis through the disc space at T9–T10. (c) Standing postoperative lateral radiograph after PJK correction and extension of her instrumented fusion to T4.

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Thoracolumbar interventions, such as pedicle screw-based fusions, will affect adjacent segments in the long term. The stiffness of pedicle screw constructs can impact the local biomechanics of the spine, but the technique for pedicle screw insertion can also impact the adjacent segments. This is most relevant to the proximal adjacent level because the facet joint is in close proximity to the starting point for the upper level’s pedicle screw. In the thoracic spine, various techniques have been described to place pedicle screws. The anatomic technique involves placing the thoracic pedicle screw in line with the axis of the pedicle. In comparison, the straightforward technique involves placing the pedicle screw parallel to the superior endplate. Because of this trajectory, the starting point for the straightforward technique is lower than the starting point for the anatomical technique for placing thoracic pedicle screws.35 The lower starting point is more likely to avoid disruption of the facet joint capsule, cartilage, or bone. In the lumbar spine, there is a similar concern for violation of the facet joint cranial to the construct because of the proximity of the proximal adjacent level’s facet joint to the uppermost-instrumented pedicle start point.36 Surgeon’s awareness of this relationship is vital to avoiding violation of the facet joint capsule, cartilage, or bone when placing this pedicle screw. Avoiding these structures should decrease the likelihood of proximal ASP in patients who undergo pedicle screw-based fusions, but the literature support for this theoretical concern is weak. In addition, it can be very difficult to avoid the facet joint in the setting of the degenerative lumbar spine where overgrown, hypertrophic facet joints might block the pedicle start point. While the technique for placing pedicle screws is important for the incidence of clinical ASP, adjuncts to the surgical procedure can also help decrease the rate of clinical ASP. For patients who undergo surgical treatment for adult deformity, PJK and fracture can lead to additional surgery, neurologic deficit, and poor outcome.22 In order to prevent this complication, some authors have advocated for vertebral augmentation. In a cadaveric study, Kebaish et al37 loaded instrumented spines that had no augmentation, vertebroplasty of the uppermost-instrumented level, or vertebroplasty of the uppermost-instrumented level and the proximal adjacent level. They showed that the rate of proximal junctional failure was significantly higher in the control group and the one-level vertebroplasty group compared to the two-level vertebroplasty group. Hart et al38 performed a retrospective investigation of elderly females who underwent long lumber fusions. They demonstrated a higher rate of proximal junctional failure in the group that did not have vertebroplasty at the proximal adjacent level to the instrumented fusion. These studies provided some evidence that vertebral augmentation with cement can decrease the risk of proximal junctional fracture in adult deformity, but further research is needed to confirm its efficacy. Another technique for preventing junctional problems at an adjacent level is dynamic stabilization. Proponents of dynamic stabilization advocate for dynamic stabilization at adjacent levels near an instrumented fusion in order to allow for a graduated change in stiffness at the proximal or distal junctional level. In theory, this graduated change in stiffness could prevent early disc degeneration at the adjacent level, hence decreasing the rate of ASP. Currently, there are no well-designed clinical studies with data to support this notion. There are cadaveric

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studies that demonstrate effectiveness in decreasing intradiscal pressure39 and motion40 with dynamic stabilization adjacent to an instrumented fusion. These in vitro studies provide some promise that dynamic stabilization can help prevent adjacent segment problems, but its usefulness must be demonstrated in clinical studies before it can be used regularly. Treatment options and strategies to prevent ASP are important, given that many patients are treated with pedicle screwbased fusions. At a minimum, surgeons should endeavor to preserve the anatomy of the adjacent levels when performing pedicle screw instrumentation. Currently, the level of evidence that supports the use of other surgical adjuncts is low, but further research may illuminate techniques to decrease the incidence of ASP.

22.5 Conclusion When surgically treating spinal pathology, surgeons should be cognizant of an intervention’s effect on the biomechanics of the spine. Pedicle screw instrumentation has become the standard for spinal fixation because of their inherent strength. The strength is important for correcting deformities, providing stability, and allowing for fusion. Surgeons need to be cognizant of the potential downside related to the biomechanical strength of pedicle screw fixation: accelerated adjacent level disc degeneration and failure. Current research has defined the incidence of ASP for lumbar degenerative disorders as well as adult and adolescent deformity. Further research is needed to further define the role of pedicle screw instrumentation in ASP, both clinical and radiographic. The additional information regarding the relative contribution of pedicle screw instrumentation to ASP will allow the spine community to more effectively prevent and treat clinical ASP.

References [1] Kraemer P, Fehlings MG, Hashimoto R, et al. A systematic review of definitions and classification systems of adjacent segment pathology. Spine. 2012; 37(22) Suppl:S31–S39 [2] Riew KD, Norvell DC, Chapman JR, Skelly AC, Dettori JR. Introduction/ Summary statement: adjacent segment pathology. Spine. 2012; 37(22) Suppl:S1–S7 [3] Glattes RC, Bridwell KH, Lenke LG, Kim YJ, Rinella A, Edwards C, II. Proximal junctional kyphosis in adult spinal deformity following long instrumented posterior spinal fusion: incidence, outcomes, and risk factor analysis. Spine. 2005; 30(14):1643–1649 [4] Helgeson MD, Shah SA, Newton PO, et al. Harms Study Group. Evaluation of proximal junctional kyphosis in adolescent idiopathic scoliosis following pedicle screw, hook, or hybrid instrumentation. Spine. 2010; 35(2):177–181 [5] Bridwell KH, Lenke LG, Cho SK, et al. Proximal junctional kyphosis in primary adult deformity surgery: evaluation of 20 degrees as a critical angle. Neurosurgery. 2013; 72(6):899–906 [6] Lowe TG, Lenke L, Betz R, et al. Distal junctional kyphosis of adolescent idiopathic thoracic curves following anterior or posterior instrumented fusion: incidence, risk factors, and prevention. Spine. 2006; 31(3):299–302 [7] Denis F, Sun E, Winter RB. Incidence and risk factors for proximal and distal kyphosis following surgical treatment for Scheuermann kyphosis. Spine. 2009; 34:E729–E734 [8] Ghiselli G, Wang JC, Bhatia NN, Hsu WK, Dawson EG. Adjacent segment degeneration in the lumbar spine. J Bone Joint Surg Am. 2004; 86-A (7):1497–1503 [9] Lee CS, Hwang CJ, Lee SW, et al. Risk factors for adjacent segment disease after lumbar fusion. Eur Spine J. 2009; 18(11):1637–1643

Junctional Breakdown in Pedicle Screw Constructs [10] Ahn DK, Park HS, Choi DJ, Kim KS, Yang SJ. Survival and prognostic analysis of adjacent segments after spinal fusion. Clin Orthop Surg. 2010; 2(3):140–147 [11] Sears WR, Sergides IG, Kazemi N, Smith M, White GJ, Osburg B. Incidence and prevalence of surgery at segments adjacent to a previous posterior lumbar arthrodesis. Spine J. 2011; 11(1):11–20 [12] Kaito T, Hosono N, Mukai Y, Makino T, Fuji T, Yonenobu K. Induction of early degeneration of the adjacent segment after posterior lumbar interbody fusion by excessive distraction of lumbar disc space. J Neurosurg Spine. 2010; 12(6):671–679 [13] Cheh G, Bridwell KH, Lenke LG, et al. Adjacent segment disease following lumbar/thoracolumbar fusion with pedicle screw instrumentation: a minimum 5-year follow-up. Spine. 2007; 32(20):2253–2257 [14] Lawrence BD, Wang J, Arnold PM, Hermsmeyer J, Norvell DC, Brodke DS. Predicting the risk of adjacent segment pathology after lumbar fusion: a systematic review. Spine. 2012; 37(22) Suppl:S123–S132 [15] Kauppila LI, Eustace S, Kiel DP, Felson DT, Wright AM. Degenerative displacement of lumbar vertebrae. A 25-year follow-up study in Framingham. Spine. 1998; 23(17):1868–1873, discussion 1873–1874 [16] Aono K, Kobayashi T, Jimbo S, Atsuta Y, Matsuno T. Radiographic analysis of newly developed degenerative spondylolisthesis in a mean twelve-year prospective study. Spine. 2010; 35(8):887–891 [17] Cheung KM, Karppinen J, Chan D, et al. Prevalence and pattern of lumbar magnetic resonance imaging changes in a population study of one thousand forty-three individuals. Spine. 2009; 34(9):934–940 [18] Lee MJ, Dettori JR, Standaert CJ, Brodt ED, Chapman JR. The natural history of degeneration of the lumbar and cervical spines: a systematic review. Spine. 2012; 37(22) Suppl:S18–S30 [19] Kim HJ, Lenke LG, Shaffrey CI, Van Alstyne EM, Skelly AC. Proximal junctional kyphosis as a distinct form of adjacent segment pathology after spinal deformity surgery: a systematic review. Spine. 2012; 37(22) Suppl:S144–S164 [20] Kim HJ, Bridwell KH, Lenke LG, et al. Proximal junctional kyphosis results in inferior SRS pain subscores in adult deformity patients. Spine. 2013; 38 (11):896–901 [21] Ha Y, Maruo K, Racine L, et al. Proximal junctional kyphosis and clinical outcomes in adult spinal deformity surgery with fusion from the thoracic spine to the sacrum: a comparison of proximal and distal upper instrumented vertebrae. J Neurosurg Spine. 2013; 19(3):360–369 [22] Watanabe K, Lenke LG, Bridwell KH, Kim YJ, Koester L, Hensley M. Proximal junctional vertebral fracture in adults after spinal deformity surgery using pedicle screw constructs: analysis of morphological features. Spine. 2010; 35 (2):138–145 [23] Kim YJ, Bridwell KH, Lenke LG, Rhim S, Cheh G. Sagittal thoracic decompensation following long adult lumbar spinal instrumentation and fusion to L5 or S1: causes, prevalence, and risk factor analysis. Spine. 2006; 31 (20):2359–2366 [24] Hostin R, McCarthy I, O'Brien M, et al. International Spine Study Group. Incidence, mode, and location of acute proximal junctional failures following surgical treatment for adult spinal deformity. Spine. 2013; 38(12):1008–1015 [25] Hackenberg L, Link T, Liljenqvist U. Axial and tangential fixation strength of pedicle screws versus hooks in the thoracic spine in relation to bone mineral density. Spine. 2002; 27(9):937–942

[26] Kim YJ, Lenke LG, Cho SK, Bridwell KH, Sides B, Blanke K. Comparative analysis of pedicle screw vs hook instrumentation in posterior spinal fusion of adolescent idiopathic scoliosis. Spine. 2004; 29:2040–2048 [27] Kim YJ, Lenke LG, Kim J, et al. Comparative analysis of pedicle screw versus hybrid instrumentation in posterior spinal fusion of adolescent idiopathic scoliosis. Spine. 2006; 31(3):291–298 [28] Yilmaz G, Borkhuu B, Dhawale AA, et al. Comparative analysis of hook, hybrid, and pedicle screw instrumentation in the posterior treatment of adolescent idiopathic scoliosis. J Pediatr Orthop. 2012; 32(5):490–499 [29] Di Silvestre M, Bakaloudis G, Lolli F, Vommaro F, Martikos K, Parisini P. Posterior fusion only for thoracic adolescent idiopathic scoliosis of more than 80 degrees: pedicle screws versus hybrid instrumentation. Eur Spine J. 2008; 17 (10):1336–1349 [30] Rose PS, Lenke LG, Bridwell KH, et al. Pedicle screw instrumentation for adult idiopathic scoliosis: an improvement over hook/hybrid fixation. Spine. 2009; 34(8):852–857, discussion 858 [31] O'Shaughnessy BA, Lenke L. Posterior spinal deformity correction techniques. In: Bridwell KH, DeWald RL, eds. The Textbook of Spinal Surgery. 3rd ed. Philadelphia, PA: Wolters Kluwer; 2011:823–847 [32] Chen LH, Lai PL, Tai CL, Niu CC, Fu TS, Chen WJ. The effect of interspinous ligament integrity on adjacent segment instability after lumbar instrumentation and laminectomy—an experimental study in porcine model. Biomed Mater Eng. 2006; 16(4):261–267 [33] Anderson AL, McIff TE, Asher MA, Burton DC, Glattes RC. The effect of posterior thoracic spine anatomical structures on motion segment flexion stiffness. Spine. 2009; 34(5):441–446 [34] Cahill PJ, Wang W, Asghar J, et al. The use of a transition rod may prevent proximal junctional kyphosis in the thoracic spine after scoliosis surgery: a finite element analysis. Spine. 2012; 37(12):E687–E695 [35] Lehman RA, Jr, Polly DW, Jr, Kuklo TR, Cunningham B, Kirk KL, Belmont PJ, Jr. Straight-forward versus anatomic trajectory technique of thoracic pedicle screw fixation: a biomechanical analysis. Spine. 2003; 28(18):2058–2065 [36] Chen Z, Zhao J, Xu H, Liu A, Yuan J, Wang C. Technical factors related to the incidence of adjacent superior segment facet joint violation after transpedicular instrumentation in the lumbar spine. Eur Spine J. 2008; 17(11):1476–1480 [37] Kebaish KM, Martin CT, O’Brien JR, LaMotta IE, Voros GD, Belkoff SM. Use of vertebroplasty to prevent proximal junctional fractures in adult deformity surgery: a biomechanical cadaveric study. Spine J. 2013; 13(12):1897–1903 [38] Hart RA, Prendergast MA, Roberts WG, Nesbit GM, Barnwell SL. Proximal junctional acute collapse cranial to multi-level lumbar fusion: a cost analysis of prophylactic vertebral augmentation. Spine J. 2008; 8(6):875–881 [39] Cabello J, Cavanilles-Walker JM, Iborra M, Ubierna MT, Covaro A, Roca J. The protective role of dynamic stabilization on the adjacent disc to a rigid instrumented level. An in vitro biomechanical analysis. Arch Orthop Trauma Surg. 2013; 133(4):443–448 [40] Durrani A, Jain V, Desai R, et al. Could junctional problems at the end of a long construct be addressed by providing a graduated reduction in stiffness? A biomechanical investigation. Spine. 2012; 37(1):E16–E22

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23 Hook Complications in the Thoracic and Lumbar Spine Adam J. Bevevino

23.1 Introduction

23.1.1 Hook Dislodgement

Hook instrumentation has been employed during spinal surgery since the first half of the 20th century. The implants offer several advantageous features. Hooks can be placed in multiple locations throughout the posterior elements of the spinal column, such as the pedicle, lamina, and transverse process. Furthermore, the indications for their use range widely from deformity correction to stabilization of spine fractures to degenerative fusion procedures. The general protocol for placing hooks varies depending on the intended anatomic location of the hook. The technique for placement of pedicle, laminar, and transverse process hooks is outlined in the study of Cotrel et al, describing their universal spinal instrumentation system.1 Placement of a thoracic pedicle hook first requires removal of a portion of the inferior articular facet to expose the medial aspect of the superior articular facet. Once this is accomplished, a pedicle finder tool is placed between the facets and onto the pedicle cephalad to the joint so that the central notch of the hook fits around the inferior wall of the pedicle. Placement of a thoracic or lumbar laminar hook begins with removal of the ligamentum flavum to access the spinal canal. Additionally, in the thoracic spine, the medial portion of the inferior articular facet and the cephalad lamina must be removed to make enough room for the hook. Once a sufficient space has been made, the hook can be placed into the canal over the caudal lamina to apply a downward pressure or under the cephalad lamina for application of an upward pressure. Transverse process hooks are placed in either upward or downward direction after subperiosteal dissection is complete. It should be noted that transverse process hooks are significantly weaker than either a pedicle hook or laminar hook and supplemental fixation is typically recommended.1 While there are clear benefits of using hook instrumentation, like any other spinal implant there are complications associated with their use. Common complications observed with hook instrumentation include hook dislodgement, bony fracture, bony erosion, pseudarthrosis/loss of correction, and neurologic injury. The following subsection will outline the major complications that occur when using hook instrumentation and discuss methods for avoidance and treatment (▶ Table 23.1).

Probably the most common complication, or difficulty, associated with the use of hook implantation is hook dislodgement. In Harrington’s classic 1962 article describing scoliosis correction using compression and distraction rods, dislodgement of the hooks that anchored the rods to the spine was a recognized postoperative problem.2 Cotrel et al additionally noted that hook dislodgement was one of the more common complications associated with hook instrumentation. In their series of 250 patients, there were 6 patients who had hook dislodgement during follow-up. The dislodgements occurred at the hooks at the upper end of the construct.1 More recent series reporting on scoliosis correction with hooks have further documented the problem with hook dislodgement. Classically, dislodgement occurs at either the cephalad or caudal end of the construct, where the hook–bone interface is subjected to the largest amount of force. The cause of dislodgement is usually secondary to one or a combination of the following: inadequate seating of the hook at the time of placement, unrecognized displacement of the hook during corrective maneuvers, inadequate tensioning of the hook during final tightening to the rod construct, excessive bending by the patient in the immediate postoperative period, or poor bone quality at the site of hook attachment. When dislodgement occurs, it is often asymptomatic but can result in pain, loss of correction/reduction, or, in worst case scenario, neurologic injury. Additionally, dislodgment can happen in the acute postoperative period or it can occur as a late complication.3,4 Understanding that hook dislodgement is an inherent complication associated with their use, there are several factors that can decrease the incidence. First and foremost is ensuring that the initial hook placement is accurate and secure. This is accomplished by a careful dissection to visualize the intended hook placement site and meticulous attention to seating of the hook. When done correctly, the hook should sit squarely at the attachment site. During placement of transverse process or laminar hook, the blade of the hooks should fit snuggly around the bony edge, whereas a pedicle hook must be placed so that central notch aligns with the pedicle to prevent dislodgement. An inherent problem with the hook design is that the hook does not provide immediate stability at the hook–bone interface in the same way that a pedicle screw does. Because of this, the hook must be appropriately tensioned through either distraction or compression of the rod to create a stable construct. The task becomes difficult during deformity correction maneuvers, given the hooks must remain somewhat loose to allow correction to take place before they are finally tightened. Because of this, appropriate tensioning of hooks is critical to prevent subsequent dislodgement. As a general rule, the greater the distraction or compression that is placed on the hook toward the bony surface to which it is attached, the lower the chance that it will dislodge. However, if too much force is applied to the hook, bony failure can occur, a fact that is especially important in those patients with osteoporosis. To achieve an appropriate amount of stability, a careful balance must be achieved between too much and too little tension against the bony surface.

Table 23.1 Complications of spinal hooks

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Complication

Timing (early/late)

Dislodgement

Both

Fracture

Both

Bony erosion

Late

Neurologic injury

Both

Pseudarthrosis

Late

Correction loss

Both

Hook Complications in the Thoracic and Lumbar Spine The stability of hooks that are at higher risk of dislodgement, such as those at the cephalad or caudal ends of the construct, can be improved by altering the hook configuration. Hook configurations in which an upward and downward facing hook is placed on the same or adjacent lamina, otherwise known as a “claw configuration,” can create immediate stability without relying on distraction or compression against a single hook. This configuration additionally allows smaller distraction/compression forces to be applied because the hook stability is not solely dependent on this maneuver, and therefore may lessen the chance of fracture at the bony interface. Biomechanical data exist indicating that the strength of this claw configuration is superior to that of a single upward or downward facing laminar hook.5 Stability of transverse process and pedicle hooks can also be augmented by adjusting the configuration of the hooks. Because transverse process hooks are in themselves weaker then pedicle hooks, they are frequently combined with another anchor rather than being placed in isolation. Combining a downward going transverse process hook with an upward going pedicle hook creates a claw-type configuration between the transverse process and pedicle and markedly improves fixation strength. Treatment of hook dislodgement depends on the timing of the dislodgement and the symptoms that are associated with it. Hook dislodgement that is recognized in the acute postoperative period before fusion has occurred may present with the acute onset of pain, a newly recognized deformity, or in worst case scenario a neurologic injury. Any of these listed symptoms or other acute changes in the patient’s clinical status should prompt radiographic examination to focus on the position of the hook implants. If hook dislodgement is recognized and is creating a clinical problem, strong consideration should be made for surgical revision of the construct. Obviously, a neurologic injury from dislodgement must be treated with greater urgency than isolated pain, but both scenarios likely warrant revision. On the other hand, the decision to treat a hook dislodgement that occurs outside of the acute postoperative period becomes less clear. If solid fusion is not achieved, the algorithm should be similar to that of an acute dislodgement. However, if fusion is complete, isolated hook dislodgement without obvious clinical symptoms should be observed, given that the morbidity of surgically revising the construct outweighs the benefit of correcting the displaced hook. Displaced hooks that are causing pain or are protruding on the skin can be removed on an elective basis.3 During revision, in the majority of instances, only the offending dislodged hook needs to be removed and the remainder of the construct can be left intact. It should be noted that displaced hooks can result in neurologic injury years after the index surgery,6 and secondary to this new onset, neurologic symptoms necessitate close evaluation of hook position regardless of how far out from surgery the patient may be.

23.1.2 Fracture Bony fracture at the site of hook attachment is another clinical complication associated with the use of spinal hooks. Fracture typically occurs in one of two scenarios: intraoperatively at the time of hook tensioning or in the postoperative period before fusion has occurred. As mentioned in the earlier section, after

the hook has been seated in its intended position, it must be tensioned through either compression or distraction against the hook. This tensioning maneuver places considerable force on the attachment site and can cause fracture if the mechanical failure point of the bone is exceeded. To prevent fracture, the amount of tension that can be placed against the hook depends on the hook location and the quality of the host bone. Pedicle and lamina hooks can be tensioned to a much greater force than transverse process hooks because the bone is mechanically stronger in these anatomic locations. Additionally, caution must be used when tensioning hooks in osteoporotic patients because their bone quality is compromised. In these patients, the surgeon should err on the side of less tension against a single hook and instead place multiple anchors to dissipate the force on any one hook. If a fracture at the hook site is recognized during tensioning, treatment is dependent on the location of the fracture. Transverse process hooks that result in fracture do not require any additional treatment, given there is no risk of neurologic injury or spinal column destabilization. On the other hand, a fracture that occurs during placement of a lamina hook can result in neurologic injury if either the fracture displaces or the hook protrudes into the spinal canal. Intuitively, the risk of neurologic injury following lamina fracture is higher in the thoracic spine at spinal cord level than in the lumbar spine. When recognized, the hook should be immediately removed and careful inspection of the fracture site should be undertaken. If intraoperative neurologic monitoring is being performed, sensory and motor potentials can be evaluated to check for injury to the spinal cord. Otherwise, if there appears to be displacement of the fracture or the spinal canal has somehow been compromised, consideration should be made to performing a decompressive laminectomy at the fracture level. If the fracture is truly nondisplaced, hook removal and replacement of the hook at a supra-adjacent level is satisfactory. Pedicle fractures resulting from pedicle hooks can cause either neurologic injury or spinal column destabilization. Similar to laminar hooks, neurologic injury can occur if the hook displaces into the canal following fracture or if the fracture itself displaces into either the neural foramen or spinal canal. Furthermore, unlike the transverse process and lamina, the pedicle is a major contributor to the structural stability of the spinal segment. Because of this, a pedicle fracture during hook placement requires the construct to be extended to bridge the level with the fractured pedicle. Fractures that are recognized in the postoperative period typically happen before fusion has occurred and are located mainly at the ends of the constructs, where the highest amount of stress is placed on the hooks. The treatment algorithm for the fracture itself is similar to what was described for intraoperative fractures; transverse process fractures pose little risk of neurologic injury or iatrogenic instability, whereas lamina fractures may result in neurologic injury and pedicle fracture can cause spinal instability. Therefore, pedicle and lamina fractures in the early postoperative period may warrant surgical revision, whereas transverse process fractures, in themselves, do not. A potential risk following fracture at a hook site is subsequent loss of intraoperative deformity correction. Because of this, fractures at hook sites critical for stability of the construct, such as the ends or the deformity apex, prompt more aggressive treatment to prevent correction loss.

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23.1.3 Loss of Correction A primary goal of deformity correction surgery is not only to achieve correction but also to maintain it during the postoperative period. A percentage of loss of the initial postoperative correction is associated with the use of every spinal instrumentation system, and spinal hook constructs are not different in that respect. In the 1988 article by Cotrel et al, the authors reported that loss of correction with hook constructs during treatment for adolescent idiopathic scoliosis was approximately 2 degrees after initial average correction of 60 degrees of the major curve.1 However, more recent series have suggested that loss of correction is greater than what was initially reported. Helenius et al reported on long-term results of scoliosis correction with Harrington and Cotrel–Doubousett (CD) instrumentation.7 Mean follow-up time of patients in the Harrington group was 20 years and approximately 14 years in the CD group. Initial correction of the major curve was 27% in the Harrington group and 55% in the CD group, and at the time of last follow-up, both groups had lost a statistically significant amount of this initial correction. Patients in the Harrington group lost approximately 50% of the initial correction and those in the CD group lost about 25% of the initial correction.7 This study highlighted two points about loss of correction with hook instrumentation: first the amount of correction over time is not insignificant and second that the segmental hook constructs used with CD instrumentation achieved and maintained deformity correction to a greater extent than the nonsegmental Harrington instrumentation. More recently, the use of hook constructs for deformity correction has been compared to segmental pedicle screw instrumentation, which is being increasingly widespread for scoliosis correction surgery. In 2004, a comparative analysis was done between a cohort of patients treated with all pedicle screw constructs and another cohort of patients treated with all-hook constructs. At 2-year follow-up, deformity correction was greater in the pedicle screw group and the percentage loss of correction was also less, 4% compared to 8% in the hook cohort (p < 0.05).8 This previous study was followed up by the same authors with a 2006 study comparing pedicle screw constructs to hybrid construct which were composed of lumbar pedicle screws and thoracic segmental hooks. Results were similar to the 2004 study in that initial correction was greater with all pedicle screws and loss of correction over the 2-year follow-up period was greater in the hybrid group. Ten degrees of correction was lost in the hybrid group compared to only 5 degrees in the pedicle screw group.9 Similar results have been reported in more recent studies, highlighting the superior power of pedicle screws to achieve and maintain correction compared to hooks during scoliosis correction.10,11 A clinical question that remains unanswered is whether the statistically higher correction loss that is observed in hook constructs over time has any impact on patient clinical outcomes.

23.1.4 Neurologic Injury Neurologic complications related to hooks are likely the most feared complication associated with their use. Fortunately, the incidence of neurologic injury with spinal hook instrumentation is relatively low. In a large survey study by the Scoliosis

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Research Society, the incidence of neurologic injury with hook instrumentation during correction of scoliosis was estimated at 0.72%.12 In the original series of Cotrel et al, 2 neurologic injuries were documented in 250 patients both of who were recognized within hours of surgery and resolved completely after removal of the hook.1 By far and away, the highest incidence of neurologic problems associated with the use of hooks is related to laminar hooks. Transverse process hooks pose little risk of neurologic injury and while pedicle hooks can cause an injury if they displace or fracture a pedicle, the likelihood is much lower compared to laminar hooks. Similar to the other complications, neurologic injury with hooks can occur intraoperatively or in the early postoperative period, but can also occur several years out from implantation. Intraoperatively, placement of thoracic laminar hooks poses the greatest risk of neurologic injury. The hooks are space-occupying objects and introducing them into the spinal canal narrows the space available for the spinal cord which is physiologically the smallest within the midthoracic spine. Secondary to this fact, intraoperative neuromonitoring is imperative during hook insertion and if the intention is to place hooks on either side of the lamina at the same level, smaller hooks (4 mm wide) should be used as opposed to larger (5 mm wide) implants.13 Any changes to motor- or sensory-evoked potentials during placement of the hooks should prompt immediate removal. In the lumbar spine, there is no risk of spinal cord injury but nerve root injury can occur, particularly if placed into a segment with preexisting spinal stenosis. EMG activity on neuromonitoring during placement of a lumbar laminar hook would suggest irritation to a lumbar nerve root and can result in postoperative radiculitis or deficit in the distribution of the affected nerve if the hook position is not changed. Special care should be exercised when placing lumbar laminar hooks on the concave side of the deformity because case reports have demonstrated that placement in this location is associated with an increased risk of neurologic injury.14 In the immediate postoperative period, any neurologic deficits not present on the preoperative exam warrants immediate investigation with advanced imaging via CT or MRI scan. Implants that have migrated or are simply impinging on neurologic structures should be emergently revised. Despite prompt recognition when neurologic injury has been recognized either intraoperatively or in the immediate postoperative period, complete neurologic recovery is not guaranteed.12,14 As mentioned earlier, neurologic complications from hook placement can also occur outside of the perioperative period. In 1989, a series was published by Hales et al6 that documented late neurologic complications secondary to hooks in patients with Harrington rod instrumentation. In the series, patients presented between 2 and 32 months after the index surgery and most commonly endorsed increasing back pain or newonset radicular symptoms. The etiology of the neurologic symptoms in these patients was migration of the caudal-most hook into the lumbar spinal canal. The hook migration occurred secondary to erosion of the lamina and was observed most frequently when the fusion was extended down to L5. All patients in the series had resolution of their symptoms following instrumentation revision and hook removal.6 A subsequent series published in 1989 described radicular pain in patients following hook instrumentation. In this series, symptoms were secondary

Hook Complications in the Thoracic and Lumbar Spine to bone overgrowth at the hook attachment site with hook protrusion into the spinal canal. Symptoms resolved in all patients after the offending hook was removed from the canal. Additionally, late cauda equina syndrome from hook impingement has even been documented 8 years following the index scoliosis procedure.15 In addition to these reports, several others have documented neurologic deficits ranging from paralysis to increasing axial pain in patients with hook instrumentation that was impinging on neurologic structures outside of the perioperative period.16,17

23.2 Conclusion Spinal hooks have been successfully used for the better part of the past century. The versatility of the implants allows for a variety of indications, including trauma, degenerative, and deformity diagnoses. The safety record associated with their use is positive, in part, because the rate of complications with hooks is relatively low. When complications do occur, it can happen intraoperatively, during the immediate postoperative period, or several years after the index operation. Successful management of the complication is dependent on a high degree of suspicion by the treating surgeon to make a timely diagnosis and treatment is then dictated by the type of complication and the timing that it occurred. With quick recognition, most complications can be managed without long-term sequela.

References [1] Cotrel Y, Dubousset J, Guillaumat M. New universal instrumentation in spinal surgery. Clin Orthop Relat Res. 1988; 227(227):10–23 [2] Harrington PR. Treatment of scoliosis. Correction and internal fixation by spine instrumentation. J Bone Joint Surg Am. 1962; 44-A:591–610 [3] Shem KL. Late complications of displaced thoracolumbar fusion instrumentation presenting as new pain in individuals with spinal cord injury. J Spinal Cord Med. 2005; 28(4):326–329

[4] Erwin WD, Dickson JH, Harrington PR. Clinical review of patients with broken Harrington rods. J Bone Joint Surg Am. 1980; 62(8):1302–1307 [5] van Laar W, Meester RJ, Smit TH, van Royen BJ. A biomechanical analysis of the self-retaining pedicle hook device in posterior spinal fixation. Eur Spine J. 2007; 16(8):1209–1214 [6] Hales DD, Dawson EG, Delamarter R. Late neurological complications of Harrington-rod instrumentation. J Bone Joint Surg Am. 1989; 71(7):1053–1057 [7] Helenius I, Remes V, Yrjönen T, et al. Harrington and Cotrel-Dubousset instrumentation in adolescent idiopathic scoliosis. Long-term functional and radiographic outcomes. J Bone Joint Surg Am. 2003; 85-A(12):2303–2309 [8] Kim YJ, Lenke LG, Cho SK, Bridwell KH, Sides B, Blanke K. Comparative analysis of pedicle screw versus hook instrumentation in posterior spinal fusion of adolescent idiopathic scoliosis. Spine. 2004; 29(18):2040–2048 [9] Kim YJ, Lenke LG, Kim J, et al. Comparative analysis of pedicle screw versus hybrid instrumentation in posterior spinal fusion of adolescent idiopathic scoliosis. Spine. 2006; 31(3):291–298 [10] Yilmaz G, Borkhuu B, Dhawale AA, et al. Comparative analysis of hook, hybrid, and pedicle screw instrumentation in the posterior treatment of adolescent idiopathic scoliosis. J Pediatr Orthop. 2012; 32(5):490–499 [11] Crawford AH, Lykissas MG, Gao X, Eismann E, Anadio J. All-pedicle screw versus hybrid instrumentation in adolescent idiopathic scoliosis surgery: a comparative radiographical study with a minimum 2-Year follow-up. Spine. 2013; 38(14):1199–1208 [12] MacEwen GD, Bunnell WP, Sriram K. Acute neurological complications in the treatment of scoliosis. A report of the Scoliosis Research Society. J Bone Joint Surg Am. 1975; 57(3):404–408 [13] Chopin D. Cotrel-Dubousset instrumentation (CDI) for adolescent and pediatric scoliosis. In: Bridwell KH, Dewald RL, eds. The Textbook of Spinal Surgery. Philadelphia, PA: JB Lippincott Company; 1991:183–212 [14] Been HD, Kalkman CJ, Traast HS, Ongerboer de Visser BW. Neurologic injury after insertion of laminar hooks during Cotrel-Dubousset instrumentation. Spine. 1994; 19(12):1402–1405 [15] Rittmeister M, Leyendecker K, Kurth A, Schmitt E. Cauda equina compression due to a laminar hook: a late complication of posterior instrumentation in scoliosis surgery. Eur Spine J. 1999; 8(5):417–420 [16] Eismont FJ, Simeone FA. Bone overgrowth (hypertrophy) as a cause of late paraparesis after scoliosis fusion. A case report. J Bone Joint Surg Am. 1981; 63(6):1016–1019 [17] Kornberg M, Herndon WA, Rechtine GR. Lumbar nerve root compression at the site of hook insertion. Late complication of Harrington rod instrumentation for scoliosis. Spine. 1985; 10(9):853–855

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24 Sublaminar Wiring Complications Gurpreet S. Gandhoke, David O. Okonkwo, and Adam S. Kanter

24.1 Introduction Sublaminar wiring was first used as a technique for segmental spinal instrumentation in the beginning of the 20th century.1 Its advantages included rigid internal fixation often obviating the need for postoperative immobilization, and the possibility of significant deformity correction. Perioperative problems included an increased risk of neural injury and morbidity from prolonged operative exposure.2 Over the years, this technique has been supplanted by the use of pedicle screws. In this chapter, we outline the evolution of sublaminar wiring with a stress on the reported complications.

24.2 History Lange (1902) was the first surgeon to wire a rod to the spine in case of spondylitis.1 Resina and Ferreira Alves3 from Portugal, in 1963, wired flexible metal rods to the base of the spinous processes with reinforcing wires passing around either the transverse process or laminae. They reported on 100 patients who underwent treatment for scoliosis with this technique and described no instances of neural injury, with a 14% rate of pseudoarthrosis at 2 years which they attributed to imperfect wirefixation technique.3 Luque developed the technique of using stainless-steel L-shaped rods secured with sublaminar wiring for the treatment of postpolio spinal deformities in populations of low socioeconomic status.4,5,6 The application of this method was then expanded to treat patients with neuromuscular scoliosis,7,8,9,10 myelodysplastic spinal deformities,11 idiopathic scoliosis,2,4,5,12 postural curves,13 and fractures.14,15 The method of sublaminar wiring was tested and found to be superior to the Harrington’s instrumentation in maintaining the correction of spinal deformities because of the multiple fixation points provided by the sublaminar wires.16 Segmental spinal instrumentation, done by sublaminar wiring and Hartshill’s loop rectangle, fell out of favor in comparison to the third-generation implants.17 The main reasons were (1) fear of long-term effects of wires within the spinal canal and high incidence of neurologic complications because of the wires17; (2) inadequate corrective forces, especially rotatory control in the instrumented segment was also a deficiency claimed; and (3) sagittal profile correction and disputed maintenance.

24.3 Complications Perioperative nerve injury has been reported in 5 to 15% of patients undergoing segmental wiring procedures with 4% of injuries being major paraparesis and the remainder being dysesthetic sensory changes that resolved without treatment.18 The mechanism could be stretching and ischemia to the nerve roots and the spinal cord from the corrective forces that may be applied to the spine, which is made possible by the transverse loading at each segment of the spine. Direct dural contusion occurring during wire passage and

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manipulation is also reported.2 Authors have reported late complications of wire fatigue without pseudoarthrosis or neural symptoms.4,9,10 In vitro corrosion is known to occur with stainless-steel implants.19,20,21,22,23 It is seen less commonly with cobalt–chromium alloys,19,22 and rarely with titanium.23 Corrosion may weaken metal, and the late failure of segmental wires may be caused by a combination of repeated cyclical loading and fretting corrosion at the rod–wire junction.19,20,21,22,23 The potential for epidural fibrosis with passing the sublaminar wires in the canal may occur. In their experience of more than 10 years with sublaminar, stainless steel wires, Lea Plaza et al24 described the development of layers of fibrous tissue that isolate metal from dura. This, they believe, acts like a protective shield, when occasionally the wires have to be removed and as a barrier to prevent spread of infection from bone or soft tissue to meninges. There have been interesting studies that reported the dimensions of the human spinal canal at various levels specifically looking at the safety of passing a sublaminar wire in the vicinity of the spinal cord and nerve roots.25,26 The results of an anatomic study done by Pampliega et al26 suggested that there exists in humans a sufficiently ample “safety zone” that permits wire insertion without risking injury to neurologic structures. Such a “safety zone” is nonexistent in lambs and pigs unless an extensive laminectomy is performed to decrease the depth of wire penetration. In another anatomic study done on rabbits, Nixon25 reported that sublaminar wiring induced laminar overgrowth over a 2-year period. Most new bones were formed outside the spinal canal and although the radius of the canal reduced, it was not sufficient to result in spinal stenosis during the period of the study. He explains this phenomenon by quoting Larsen27,28 in that the contents of the spinal canal may in some way inhibit new bone formation within the spinal canal during growth. Lonstein et al29 reported on the results and complications after using sublaminar wiring fixation in 93 patients to treat neuromuscular scoliosis in cerebral palsy and static encephalopathy using Luque–Galveston instrumentation. They found a complication rate of 58% in the study. Their late complication rate was 47%, and 7.5% of patients had a pseudoarthrosis. Dove30 reported the results from a questionnaire circulated among members of the British Scoliotic Society in order to establish the morbidity of surgery for spinal deformities in the years 1983 and 1984 in Great Britain. Surgeons were asked to report the complications relating to all types of surgery for spinal deformity in order to establish the relative morbidity of segmental spinal wiring. Of the 1,121 patients reported, 469 (41%) had segmental wiring. The only neurologic complication that they found to be peculiar to segmental wiring was hyperesthesia. In one nerve-root distribution, 3.2% of cases were complicated by hyperesthesia. These were not associated with any weakness, and resolved within 10 days of the surgery.

Sublaminar Wiring Complications

24.4 Current Trends and the Future There are few surgeons who still prefer the use of sublaminar wires/cables for segmental spinal fixation for correction of spinal deformity and for occiput-cervical, atlantoaxial fixations to treat pathology at the craniocervical junction.31,32,33 Early reports of sublaminar wiring have evolved into modern-day pedicle screw/translaminar constructs, with excellent results.

References [1] Lange F. Support for the spondylitic spine by means of buried steel bars attached to the vertebrae. Am J Orthop Surg. 1910; 1910(8):344–361 [2] Herring JA, Wenger DR. Segmental spinal instrumentation: a preliminary report of 40 consecutive cases. Spine. 1982; 7(3):285–298 [3] Resina J, Alves AF. A technique of correction and internal fixation for scoliosis. J Bone Joint Surg Br. 1977; 59(2):159–165 [4] Luque ER. The anatomic basis and development of segmental spinal instrumentation. Spine. 1982; 7(3):256–259 [5] Luque ER. Segmental spinal instrumentation for correction of scoliosis. Clin Orthop Relat Res. 1982(163):192–198 [6] Luque ER. [Segmental spinal instrumentation in neuromuscular scolioses]. Orthopade. 1989; 18(2):128–133 [7] Allen BL, Jr, Ferguson RL. L-rod instrumentation for scoliosis in cerebral palsy. J Pediatr Orthop. 1982; 2(1):87–96 [8] Luque ER. Paralytic scoliosis in growing children. Clin Orthop Relat Res. 1982 (163):202–209 [9] Sullivan JA, Conner SB. Comparison of Harrington instrumentation and segmental spinal instrumentation in the management of neuromuscular spinal deformity. Spine. 1982; 7(3):299–304 [10] Taddonio RF. Segmental spinal instrumentation in the management of neuromuscular spinal deformity. Spine. 1982; 7(3):305–311 [11] Allen BL, Jr, Ferguson RL. The operative treatment of myelomeningocele spinal deformity—1979. Orthop Clin North Am. 1979; 10(4):845–862 [12] Allen BL, Jr, Ferguson RL. The Galveston technique for L rod instrumentation of the scoliotic spine. Spine. 1982; 7(3):276–284 [13] Luque ER. The correction of postural curves of the spine. Spine. 1982; 7 (3):270–275 [14] Bernard TN, Jr, Whitecloud TS, III, Rodriguez RP, Haddad RJ, Jr. Segmental spinal instrumentation in the management of fractures of the thoracic and lumbar spine. South Med J. 1983; 76(10):1232–1236 [15] Luque ER, Cassis N, Ramírez-Wiella G. Segmental spinal instrumentation in the treatment of fractures of the thoracolumbar spine. Spine. 1982; 7 (3):312–317

[16] Wenger DR, Carollo JJ, Wilkerson JA, Jr, Wauters K, Herring JA. Laboratory testing of segmental spinal instrumentation versus traditional Harrington instrumentation for scoliosis treatment. Spine. 1982; 7(3):265–269 [17] Wilber RG, Thompson GH, Shaffer JW, Brown RH, Nash CL, Jr. Postoperative neurological deficits in segmental spinal instrumentation. A study using spinal cord monitoring. J Bone Joint Surg Am. 1984; 66(8):1178–1187 [18] Herring JA, Fitch R, Wenger DR, Roach J, Cook J, Frith C. Segmental spinal instrumentation - a review of early results and complications. Paper presented at the Annual Meeting of the Scoliosis Research Society, New Orleans, Louisiana; 1983 [19] Aulisa L, di Benedetto A, Vinciguerra A, Lorini G, Tranquilli-Leali P. Corrosion of the Harrington’s instrumentation and biological behaviour of the rodhuman spine system. Biomaterials. 1982; 3(4):246–248 [20] Mayor MB, Merritt K, Brown SA. Metal allergy and the surgical patient. Am J Surg. 1980; 139(4):477–479 [21] Merritt K, Brown SA. Tissue reaction and metal sensitivity. An animal study. Acta Orthop Scand. 1980; 51(3):403–411 [22] Scales JT, Winter GD, Shirley HT. Corrosion of orthopaedic implants. SmithPetersen type hip nails. BMJ. 1961; 2(5250):478–482 [23] Uhthoff HK, Bardos DI, Liskova-Kiar M. The advantages of titanium alloy over stainless steel plates for the internal fixation of fractures. An experimental study in dogs. J Bone Joint Surg Br. 1981; 63-B(3):427–484 [24] Lea Plaza C, Vin Vivo E, Silveri A, Bermudez W, Santo J, Carreras O. Surgical correction of scoliosis with a new three-dimensional device, the “Lea Plaza Frame”. A preliminary report. Spine. 1992; 17(3):365–372 [25] Nixon JE. Does sublaminar wiring produce spinal stenosis? J Bone Joint Surg Br. 1989; 71(1):92–93 [26] Pampliega T, Beguiristain JL, Artieda J. Neurologic complications after sublaminar wiring. An experimental study in lambs. Spine. 1992; 17(4):441–445 [27] Larsen JL. The lumbar spinal canal in children. Part II: the interpedicular distance and its relation to the sagittal diameter and transverse pedicular width. Eur J Radiol. 1981; 1(4):312–321 [28] Larsen JL, Smith D. The lumbar spinal canal in children. Part I: The sagittal diameter. Eur J Radiol. 1981; 1(2):163–170 [29] Lonstein JE, Koop SE, Novachek TF, Perra JH. Results and complications after spinal fusion for neuromuscular scoliosis in cerebral palsy and static encephalopathy using Luque Galveston instrumentation: experience in 93 patients. Spine. 2012; 37(7):583–591 [30] Dove J. Segmental wiring for spinal deformity. A morbidity report. Spine. 1989; 14(2):229–231 [31] Jain VK. Atlantoaxial dislocation. Neurol India. 2012; 60(1):9–17 [32] Kirankumar MV, Behari S, Salunke P, Banerji D, Chhabra DK, Jain VK. Surgical management of remote, isolated type II odontoid fractures with atlantoaxial dislocation causing cervical compressive myelopathy. Neurosurgery. 2005; 56 (5):1004–1012, discussion 1004–1012 [33] Jain VK, Takayasu M, Singh S, Chharbra DK, Sugita K. Occipital-axis posterior wiring and fusion for atlantoaxial dislocation associated with occipitalization of the atlas. Technical note. J Neurosurg. 1993; 79(1):142–144

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Thoracolumbar

25 Complications of Percutaneous Vertebral Cement Augmentation Dennis S. Meredith and Alexander R. Vaccaro

25.1 Introduction Percutaneous techniques for cement augmentation are currently used for the treatment of symptomatic vertebral compression fractures (VCFs—both osteoporotic and pathologic), augmentation of pedicle screw purchase in osteoporotic bone, and prophylaxis against fracture adjacent to the terminal ends of fusion constructs. Percutaneous vertebroplasty (VP) was introduced in France in 1984. Kyphoplasty (KP) was introduced in 2001 and is a modification of the VP technique. In VP, polymethylmethacrylate (PMMA) cement is injected directly into the cancellous bone of the vertebral body (▶ Fig. 25.1), while in KP, the cement is injected into a void created by the pressurization of a balloon device (▶ Fig. 25.2). Recent studies have also utilized calcium–phosphate cement products rather than PMMA with mixed results.1,2,3,4,5,6,7 The epidemiological data for compression fractures is impressive. Osteoporosis is the most common cause of VCF. Studies estimate that the lifetime risk of VCF in postmenopausal women ranges from 20 to 32%.8,9 Currently, more than 10 million Americans older than 50 years have osteoporosis and that number is expected to exceed 14 million by 2020.10 The spinal column is also the most-frequent site of bony metastases. Autopsy studies show that more than 30% of cancer patients have spinal metastases, which predispose them to VCF.11,12 VCFs are associated with significant morbidity and mortality. VCF is associated with chronic back pain in 84% of patients13 along with increased rates of additional VCF, loss of height, loss of mobility, depression, and pulmonary dysfunction.14,15,16,17,18,19,20,21 Mortality is

also increased with thoracic or lumbar VCF, as the 4- to 5-year mortality rates exceed those for patients with hip fractures.22,23, 24 In light of these statistics, it is no surprise that treatment of VCF places a huge economic burden (> 13.8 billion dollars annually) on the U.S. health care system.25 In this chapter, we will touch briefly on the ongoing debate regarding the efficacy of percutaneous vertebral cement augmentation. This is, however, an extensive topic worthy of its own chapter. Our discussion of efficacy will serve only to frame our discussion of complications following percutaneous vertebral cement augmentation. Complications of percutaneous vertebral cement augmentation generally relate to the incidence and effects of cement, escaping beyond the confines of the vertebral body locally, the potential for embolization within the circulation, and finally technical error. Finally, we will address the biomechanical and clinical risks of percutaneous vertebral cement augmentation on the risk of further VCF at levels adjacent to the operative site.

25.2 Overview of the Efficacy of Vertebroplasty and Kyphoplasty 25.2.1 Vertebroplasty Pain relief continues to be a primary goal of both KP and VP. VP was originally introduced as an interventional radiology procedure to address painful vertebral hemangiomas.26 It was subsequently adapted for a wider indication of procedures and

Fig. 25.1 Illustration of vertebroplasty technique.

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25.2.2 Kyphoplasty Kyphoplasty has shown more consistently good results in level I studies. The FREE study enrolled 300 patients with osteoporotic VCF across eight countries and randomized them to KP versus conservative treatment.55,56 KP demonstrated significantly decreased pain, improved function, and improved quality of life at 12 months with the improvements in disability and physical function continuing till 24 months of follow-up. The CAFÉ study was also an international multicenter RCT comparing KP to conservative treatment of VCF in patients with cancer.57 Patients treated with KP had statistically significant improvements in function, quality of life, and pain out to 12 months of follow-up. These results are supported by more than 35 lesser-quality studies.51 When compared, KP tends to demonstrate more favorable results than VP. Eck et al published a meta-analysis of all reports on VP and KP up to 2006.58 They found statistically significant improvements in pain favoring KP without significant differences in overall function. Studies also showed a greater improvement in kyphotic wedge angle with KP relative to VP.59 Although both studies demonstrated a benefit compared to conservative treatment, the clinical relevance of this finding is unclear.

Fig. 25.2 Illustration of balloon kyphoplasty technique.

gained rapid acceptance based on studies with a low level of evidence demonstrating consistently good results.27,28,29,30,31,32, 33,34 Initial studies comparing VP and optimal medical management were limited by low enrollment (INVEST)35 and a high crossover rate from medical management to VP (VERTOS I).36 Non-randomized trials in 2006 and 2010 found a short-term benefit for VP with respect to pain relief but no difference was found at the 1-year follow-up.37,38,39 Two landmark, randomized controlled trials (RCTs) published in the New England Journal of Medicine in 2009 received attention from the lay media and sparked heated debate within the spine care community.40 Kallmes et al randomized 131 patients with osteoporotic VCF to VP or a sham procedure.41 Similarly, Buchbinder et al randomized 71 patients also with osteoporotic VCF to VP or sham procedure.42 Surprisingly, neither study found a benefit for VP at any time point during clinical follow-up. Moreover, a pooled meta-analysis from both studies similarly failed to show any benefit.43 The conclusions from both studies have been called into question becuase of methodological issues.44,45 The use of lidocaine for the sham procedure may have represented a flawed control.46,47,48,49,50 The study by Kallmes et al had a high crossover rate at 3 months (43% of control patients at 3 months). Also a large portion of the patients in the study of Kallmes et al were able to correctly guess the nature of their procedure at 2 weeks potentially biasing their outcomes.41 Both the interventional or control groups in these studies demonstrated a lesser magnitude of improvement than those seen in previous studies.51 Subsequent level I studies using conservative management as a control have demonstrated a benefit for VP with respect to early pain relief.52,53 Certainly, the efficacy of VP for osteoporotic compression fracture treatment is questionable and it is not currently endorsed by the American Academy of Orthopedic Surgeons.54

25.3 Complications from Percutaneous Vertebral Cement Augmentation 25.3.1 Overview of Complications Perioperative complications related to percutaneous cement augmentation of VCF are generally rare. However, when they do occur they have the potential for devastating consequences to the patient.60,61 Perioperative complications can be divided into medical complications, which are unfortunately common even for a minimally invasive procedure when dealing with a geriatric population, and those related to the procedure itself. Procedure-related complications include bleeding around the neural elements and the escape of cement beyond the vertebral body either through local spread or embolization to organs such as the lung or brain. Additionally, biomechanical alterations to the spine from cement augmentation may alter the patients risk for further VCF. Based on the relatively high level of current evidence looking at both VP and KP, several recent meta-analyses have provided a good overview of the risk of complications following the procedure. Eck et al compared complication rates across 42 VP studies and 10 KP studies comprising more than 10,000 patients.58 The overall prevalence of cement leakage was 19.7% in VP compared to 7.0% in KP. However, such leaks were symptomatic in only 1.6 and 0.3% of patients, respectively. New compression fractures were noted in 17.9% of patients after VP versus 14% after KP. Cement embolization to the lung occurred in 0.9% of patients after VP and 0.4% after KP. Medical complications such as myocardial infarction occurred 0.05% of the time in VP patients versus 0.5% in KP patients. Other medical complications noted include hematoma, rib fracture, infection, transient hypotension and tachycardia, hypoxia, and pneumonia. Lee et al performed a more extensive meta-analysis of 121 studies using either VP or KP for both osteoporotic and

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Thoracolumbar pathologic VCFs.62 Their results generally support the findings of Eck et al. The overall rates of medical complications were 0.4% for VP versus 1.6% for KP. The rate of asymptomatic cement leakage was 75% for VP versus 14% for KP. Symptomatic cement leakage rates were 1.48% after VP versus 0.04% after KP. The overall incidence of new fracture after treatment was 18% after VP and 17% after KP. However, the fractures in the KP group were more focused at the adjacent vertebral level with 74.8% of fractures at the adjacent level after KP versus 51.6% after VP. In summary, overall complication rates following percutaneous cement augmentation of VCF are generally lower for KP than for VP with the exception of general medical complications and the risk of adjacent segment fracture.

25.3.2 Local Cement Leakage and Neurological Injury As demonstrated by recent meta-analyses, the rate of cement leakage after treatment of VCF is quite high (▶ Fig. 25.3). However, the vast majority of cement leakage is asymptomatic.

Fig. 25.3 83F treated with vertebroplasty for thoracolumbar burst fracture with extensive extravasation of cement into the perivertebral soft tissue.

Consequently, some authors have argued that asymptomatic cement leakage should not be considered a complication.63,64 Becuase of the proximity of the vertebral body to vital vascular and neurological structures, however, when leakages are symptomatic the potential effects are devastating.65 Reports have included symptomatic radiculopathy and canal stenosis causing pain but no deficit.66,67 Mechanisms of neurological injury include direct spread of PMMA into the neural elements, retropulsion of fracture fragments into the canal, and embolization of local vascular structures supplying the spinal cord. Patel et al have published the largest series on this subject.68 Their series of 14 patients treated at a tertiary referral center for spinal cord injuries includes six cases of immediate neurological deficit becuase of PMMA extravasation, of which, five received surgical decompression. The patient who was not treated surgically was too medically unstable for surgical intervention and ultimately expired from complications related to hematogenous embolization of PMMA. In five patients, the injury occurred from bony retropulsion at the procedural level ranging from 3 to 112 days after the initial procedure. All of these patients were treated with surgical decompression and fusion. Three patients developed injuries related to fracture retropulsion at adjacent levels to the index procedure, which were also addressed surgically. An important point of this series is that though rare, institutions performing these procedures should have a plan to deal with potential complications that will require open surgical intervention. Cement leakage into the basivertebral vein and anterior internal venous plexus leads to the epidural space. Leakage in this pattern has been reported to have an incidence of more than 20%.63,69,70,71 This can lead to catastrophic neurological injury including anterior spinal artery syndrome and paralysis.60,61,72,73 Recently, we have also encountered a case of KP causing a compressive epidural hematoma which led to catastrophic neurological injury. Leakage of cement into the intervertebral disc has been associated with an increased risk of adjacent level fracture.74 Risk for leakage can be predicted based on fracture severity,25,75 the presence of an intravertebral cleft on preoperative MRI scans71, 76,77,78 (▶ Fig. 25.4), and cortical disruption on preoperative CT scans79,80 (▶ Fig. 25.5). The use of higher viscosity PMMA universally decreases the risk for both intradiscal leakage and intravascular complications; however, there is less

Fig. 25.4 Fractured vertebra with an intervertebral cleft (left and middle) with subsequent leakage of cement into the disc (right).

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Fig. 25.5 Cortical disruption of the vertebrae (left and middle) with subsequent leakage of cement into the disc through the disruption (right).

interdigitation into the cancellous bone.63,81 Viscosity of PMMA at the time of injection should have a doughy consistency and not dissociate from the syringe under its own weight when tested in “open air.”63,82,83

25.3.3 Hematogenous Embolization of Cement Much like local spread of cement, the majority of cement embolization events are asymptomatic. However, the incidence occurs at a strikingly high rate (26% in the VERTOS II study).84 When embolization does occur, it can have devastating consequences for the patient. Cement embolization from VP has caused injuries to the lungs,85,86,87 kidneys,88 great vessels,89 heart,90,91 and brain.68 Biomechanical studies suggest that the relatively decreased incidence of cement embolization after KP relative to VP is becuase of the inflation of the balloon, compacting the surrounding cancellous bone creating a barrier for cement and allowing for cement injection at lower pressure.92,93 Cement embolization is limited by higher viscosity, limited dose (current recommendations are to use < 5 mL per level) and low pressure.71,94 Risk of embolization is also dependent on fracture severity with more severe fractures having a higher risk likely becuase of the disruption of the venous system.63 As with neurological injury, facilities performing these procedures should have protocols in place to deal with potentially life-threatening hemodynamic and respiratory instability.

25.3.4 Adjacent Segment Vertebral Fracture The clinical implications of the biomechanical effects caused by cement augmentation continue to be a subject of scientific debate. Biomechanical studies have demonstrated that augmentation reduces compliance within that segment in both neutral and bending modes, thus leading to greater force transmission to the adjacent levels.95 Both the choice of cement and the dose significantly influence this effect.96 This increased mechanical pressure which exceeds that seen in an intact spine is especially important for patients who increase their daily physical activity in response to the pain relief of cement augmentation.97 However, these potential effects have not been evident in clinical studies. Taylor et al performed a systematic

review of studies published prior to 2006 and found a low incidence of subsequent VCF after both VP and KP.98 Other studies have found that the incidence of new VCF is lower in patients treated with VP or KP than those undergoing optimal medical management.53,99 Overall, the reasons behind the observed discrepancy between biomechanical and clinical studies is unclear and remains a topic of further investigation.100

25.3.5 Medical Complications The reasons behind the increase rate of medical complications observed with KP in the recent meta-analyses remain unclear. Authors have suggested that this may be becuase of increased use of general anesthesia in the KP studies.62 However, these studies are not well designed to address this issue and consequently, the current literature cannot address whether this is an incidental or significant finding.

25.3.6 Infection Infection after either VP or KP is exceedingly rare, in large part, becuase of the minimally invasive nature of the procedure. In the rare instances where postprocedural infection has been reported, it has been in immunocompromised hosts.66,101 Consequently, the addition of antibiotics to PMMA used for injection is not recommended for most procedures.

25.4 Conclusion In summary, the use of percutaneous cement augmentation techniques is well supported in the literature with multiple level I studies and meta-analyses available for review. The efficacy of KP is perhaps better supported than VP, given the studies of Kallmes et al and Buchbinder et al that were published in the New England Journal of Medicine. We acknowledge, however, that there are no trials comparing KP to sham surgery and the methodology of the aforementioned studies has been called into question. Multiple meta-analyses suggest that KP has a superior side effect profile with respect to procedural complications. Key technical considerations include using higher viscosity cement and minimizing injection pressure. Although these procedures are minimally invasive and often performed by specialists other an spinal

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Thoracolumbar surgeons, the potentially devastating side effects that can occur require a treatment plan both for intensive medical management and open surgical intervention should the need arise.

References [1] Schmelzer-Schmied N, Cartens C, Meeder PJ, Dafonseca K. Comparison of kyphoplasty with use of a calcium phosphate cement and non-operative therapy in patients with traumatic non-osteoporotic vertebral fractures. Eur Spine J. 2009; 18(5):624–629 [2] Teyssédou S, Saget M, Prébet R, Leclercq N, Vendeuvre T, Pries P. Evaluation of percutaneous surgery in the treatment of thoracolumbar fractures. Preliminary results of a prospective study on 65 patients. Orthop Traumatol Surg Res. 2012; 98(1):39–47 [3] Robinson Y, Heyde CE, Försth P, Olerud C. Kyphoplasty in osteoporotic vertebral compression fractures—guidelines and technical considerations. J Orthop Surg. 2011; 6:43 [4] Zhu X, Chen X, Chen C, et al. Evaluation of calcium phosphate and calcium sulfate as injectable bone cements in sheep vertebrae. J Spinal Disord Tech. 2012; 25(6):333–337 [5] Pizzoli AL, Brivio LR, Caudana R, Vittorini E. Percutaneous CT-guided vertebroplasty in the management of osteoporotic fractures and dorsolumbar metastases. Orthop Clin North Am. 2009; 40(4):449–458, vii [6] Ryu KS, Shim JH, Heo HY, Park CK. Therapeutic efficacy of injectable calcium phosphate cement in osteoporotic vertebral compression fractures: prospective nonrandomized controlled study at 6-month follow-up. World Neurosurg. 2010; 73(4):408–411 [7] Yang H, Zou J. Filling materials used in kyphoplasty and vertebroplasty for vertebral compression fracture: a literature review. Artif Cells Blood Substit Immobil Biotechnol. 2011; 39(2):87–91 [8] Delmas PD, van de Langerijt L, Watts NB, et al. IMPACT Study Group. Underdiagnosis of vertebral fractures is a worldwide problem: the IMPACT study. J Bone Miner Res. 2005; 20(4):557–563 [9] Eastell R, Cedel SL, Wahner HW, Riggs BL, Melton LJ, III. Classification of vertebral fractures. J Bone Miner Res. 1991; 6(3):207–215 [10] America’s Bone Health: The State of Osteoporosis and Low Bone Mass in Our Nation. Washington, DC: National Osteoporosis Foundation; 2002 [11] Wong DA, Fornasier VL, MacNab I. Spinal metastases: the obvious, the occult, and the impostors. Spine. 1990; 15(1):1–4 [12] Ortiz Gómez JA. The incidence of vertebral body metastases. Int Orthop. 1995; 19(5):309–311 [13] Cooper C, Atkinson EJ, O’Fallon WM, Melton LJ, III. Incidence of clinically diagnosed vertebral fractures: a population-based study in Rochester, Minnesota, 1985–1989. J Bone Miner Res. 1992; 7(2):221–227 [14] Ensrud KE, Thompson DE, Cauley JA, et al. Fracture Intervention Trial Research Group. Prevalent vertebral deformities predict mortality and hospitalization in older women with low bone mass. J Am Geriatr Soc. 2000; 48 (3):241–249 [15] Kado DM, Browner WS, Palermo L, Nevitt MC, Genant HK, Cummings SR, Study of Osteoporotic Fractures Research Group. Vertebral fractures and mortality in older women: a prospective study. Arch Intern Med. 1999; 159 (11):1215–1220 [16] Klotzbuecher CM, Ross PD, Landsman PB, Abbott TA, III, Berger M. Patients with prior fractures have an increased risk of future fractures: a summary of the literature and statistical synthesis. J Bone Miner Res. 2000; 15(4):721–739 [17] Lindsay R, Silverman SL, Cooper C, et al. Risk of new vertebral fracture in the year following a fracture. JAMA. 2001; 285(3):320–323 [18] Nevitt MC, Ettinger B, Black DM, et al. The association of radiographically detected vertebral fractures with back pain and function: a prospective study. Ann Intern Med. 1998; 128(10):793–800 [19] Nevitt MC, Thompson DE, Black DM, et al. Fracture Intervention Trial Research Group. Effect of alendronate on limited-activity days and bed-disability days caused by back pain in postmenopausal women with existing vertebral fractures. Arch Intern Med. 2000; 160(1):77–85 [20] Silverman SL. The clinical consequences of vertebral compression fracture. Bone. 1992; 13 Suppl 2:S27–S31 [21] Schlaich C, Minne HW, Bruckner T, et al. Reduced pulmonary function in patients with spinal osteoporotic fractures. Osteoporos Int. 1998; 8 (3):261–267

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Complications of Vertebral Body Implants

26 Complications of Vertebral Body Implants Introduced through the Posterolateral Approach David B. McConda, Jonathan M. Karnes, and Scott D. Daffner

26.1 Introduction Anterior decompression through a vertebral body resection is indicated for a variety of pathologies including primary or metastatic lesions to the spine, infection, and certain fractures. Historically, vertebral body resections in the thoracolumbar spine were performed through an anterior approach with the addition of posterior augmentation through a separate approach, and sometimes in a staged manner. Alternate techniques have emerged that utilize a posterolateral approach that allows access to the anterior and posterior structures through a single posterior incision. With the development of expandable cages, the surgeon can provide anterior stabilization and fusion through this approach as well. This approach can be technically demanding and certain complications can result from increased traction on the nerve roots and poor positioning of the implant, which can lead to neurologic deficits and subsidence. Less invasive techniques are emerging which can result in decreased blood loss, less postoperative pain, and shorter hospital stays.

26.2 Indications for Thoracolumbar Vertebral Body Resection Traumatic injuries, metastatic or primary tumors of the vertebral bodies, infection, and deformity can compromise the sagittal stability of the spine and anteriorly compress the spinal cord. These cases may require resection of one or more vertebral bodies to decompress the spinal canal and stabilize the spine at the affected level, which can be effectively accomplished through the posterolateral approach. Patients presenting with primary and metastatic lesions of the anterior spine are surgical candidates if they have a 50% loss of vertebral height, progressive neurologic decline consistent with the level of the affected spine, or severe pain and an approximate life expectancy of 3 months.1,2,3 Indications for surgical management of anterior spine infections include sepsis, rapid neurologic decline, instability, the inability to perform a computed tomography (CT) guided biopsy/culture, and failure of medical management. Patients with unstable burst fractures that have canal compromise greater than 50%, local kyphosis greater than 30 degrees, loss of vertebral body height of greater than 50%,4,5 or neurologic compromise are also considered candidates for surgical management. As the majority of these oncologic, infectious, and traumatic processes involve the vertebral body, its resection with subsequent reconstruction is commonly required for definitive management. In these situations, the posterolateral approach can be utilized to access the anterior column, especially in the thoracic spine.6

26.3 Posterolateral Approach to the Thoracolumbar Spine and Relevant Anatomy The patient is positioned prone and a midline incision is extended from a point two levels proximal and two levels distal to the vertebral body or bodies to be resected. The superficial dissection is carried down to the level of the spinous process and the paraspinal muscles stripped away to expose the lamina on both sides. Pedicle screw instrumentation is inserted above and below the vertebra to be resected and connected with a rod on the side contralateral to the anterior access point to prevent deformity progression while performing the subsequent laminectomy and vertebral column resection. A posterior decompression is then typically performed by removing the lamina and the ligamentum flavum, exposing the dura (▶ Fig. 26.1a). To access the anterior column, the pedicle of the pathologic vertebra is resected along with the inferior facet and transverse process. The superior facet of the caudal segment is removed down to the pedicle to provide access to the disk space for insertion of the implant. In the thoracic spine, it may be necessary to resect one or two nerve roots in order to provide better access to the anterior column; this approach is contraindicated at T1 or lumbar levels becuase of the risk of neurologic injury and profound motor deficit.7 Metcalfe et al demonstrated that the posterolateral approach could be successfully implemented with reduced complications compared to costotransversectomy or transcavitary approaches. Dissection is carried along the lateral aspect of the vertebral body in a subperiosteal fashion, moving anteriorly until the anterior aspect of the vertebral body is palpable. Depending on the goals of surgery, the contralateral side may also be exposed. Placement of small malleable retractors, hooked around the anterior vertebral body, will help protect adjacent soft tissue structures and facilitate adequate visualization. After a plane is developed between the posterior longitudinal ligament and the dura, the vertebral body is removed in a piecemeal fashion, until an adequate decompression is achieved and there is enough room to accommodate the expandable cage. The adjacent bony endplates are exposed by removal of the vertebral disks and cartilaginous endplates. An expandable cage or other implant is then inserted using an oblique trajectory in the compressed form and maneuvered into an optimal position in the midline (▶ Fig. 26.1b). It is extended to secure it snugly to the superior and inferior bony endplates (▶ Fig. 26.1c). The ipsilateral pedicle screw and rod construct is placed and compression is created to appropriately tension the construct (▶ Fig. 26.1d).7 Minimally invasive approaches for access to a thoracic vertebral body have been proposed to reduce blood loss and minimize postoperative pain and immobility as well as the length of hospitalization following the classic lateral extracavitary

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Fig. 26.1 Surgical technique. (a) A wide laminectomy is performed, the pedicles are resected, and a vertebral body resection is performed. Placement of pedicle screws and a rod on the side contralateral to the vertebrectomy approach helps prevent collapse and inadvertent spinal cord compression during the resection. (b) After preparing the endplates, an expandable cage filled with bone graft is inserted in its collapsed state using an oblique trajectory. (c) After confirming the position of the implant with biplanar fluoroscopy, the implant is expanded, impacting the ends of the implant into the vertebral endplates. (d) The final construct, as viewed posteriorly, with an expanded cage occupying the vertebrectomy site and bilateral pedicle screw–rod instrumentation.

approach. Kim et al described a technique utilizing tubular retractors to access the thoracic vertebral column through a smaller posterolateral incision.8 They utilized this technique on six cadaver specimens and in four clinical cases, reporting adequate resection of the vertebral body and decompression of the ventral canal with minimal resection of the paraspinal musculature and good outcomes in all four patients.8 Likewise, Smith et al9 reported that a similar strategy was able to provide a 72% vertebral body resection and a 48% circumferential volumetric decompression as measured by CT analysis with minimal complications. For this minimally invasive approach, a 4-cm incision is made lateral to the midline and a Kirschner wire is introduced lateral to the facet and held near the pedicle at the target thoracic level. A series of progressively larger diameter dilators are inserted and a retractor is placed over the largest one. The transverse process, facets, and lamina are exposed, and blunt dissection is carried down subperiosteally to expose the lateral portion of the vertebral body; the pedicle is removed and the dura is protected, if needed, with gentle medial retraction. The vertebral body resection is then performed and a compacted expandable cage is inserted through the portal and into the interbody space and subsequently extended. The anterior construct is then augmented posteriorly by the insertion of percutaneous pedicle screws.

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26.4 Purpose of Instrumentation Regardless of the pathology requiring the vertebral body resection, removal of the anterior bony structures destabilizes the spine and requires augmentation for structural support. This reinforcement can be accomplished with a variety of implants, including structural autograft or allograft bone, methylmethacrylate cement, static mesh or polyether ether ketone (PEEK) cages, or expandable cages. Each option has advantages and disadvantages. Because of adjacent anatomic structures, posterolateral approaches offer a smaller window through which to work anteriorly. Placement of a static cage or strut graft through this approach is problematic in that it may require vertebral body distraction or traction on the nerve roots and it is difficult to manipulate a fixed-length cage or graft into optimal position through the limited exposure. An expandable cage, on the other hand, is inserted in the collapsed position with subsequent expansion in situ, facilitating placement into the anterior column through a posterolateral approach. This method of cage placement is particularly important in the lumbar spine because it avoids the need to sacrifice nerve roots in order to insert the device.10 Shen et al examined the use of expandable cages during a posterolateral approach for surgical management of vertebral body tumors. Reports of thoracic and lumbar metastases managed with vertebral body resection through a posterior approach with

Complications of Vertebral Body Implants implantation of an expandable cage reported satisfactory results with minimal complications.10,11,12 In a retrospective review of 95 patients with metastatic lesions to the spine undergoing vertebral body resection with implantation of an expandable titanium cage, Viswanathan et al reported satisfactory results with minimal complications. Overall, they found a very low incidence of cage-related construct failures and no significant issues with subsidence.11 They demonstrated low complication rates using an expandable cage for surgical management of vertebral body tumors. Similarly in a retrospective review of 24 patients with metastatic lesions to the thoracolumbar spine treated with expandable cages, Jeyamohan et al reported a 54% improvement in overall neurological status with no patients showing a decline in neurological status.12 In a multicenter case series of 21 prospectively followed patients with vertebral body tumors treated with vertebral body resection through a posterior only approach, Shen et al reported a 14.3% complication rate, which is similar to reported rates for anterior and staged procedures.10 Expandable cages offer the ability to restore sagittal alignment, vertebral height, and mechanical stability while requiring less surgical dissection for insertion becuase of their expandable nature.

26.5 Complications The traditional approach to vertebral column resection involves combined anterior and posterior incisions. When applied to the thoracic spine, this approach predisposes patients to pulmonary complications and significant blood loss; in the lumbar spine, there is also an increased risk of vascular injury, abdominal hernias, and retrograde ejaculation.13 Hofstetter et al demonstrated that the posterolateral approach to the vertebral body had good results across multiple spine pathologies with

the exception of traumatic injuries, which had an 18% revision rate, likely due to compromised bone within the intervertebral space. Lubelski et al14 reported a complication rate of 39, 17, and 15%, respectively, for the transthoracic thoracotomy, lateral extracavitary, and costotransversectomy approaches to the thoracic spine, suggesting that the traditional approach presents greater risks to patients undergoing vertebral body resection procedures when compared to the single-incision posterolateral approach. Vertebral column resection through a single posterior approach is technically demanding as the narrow working portal into the anterior column limits direct visualization and makes implant positioning more difficult than an anterior approach. These challenges may lead to nerve root injuries from overzealous retraction of the nerve roots or the dura, suboptimal corpectomy site preparation, poor positioning of the implant, and difficulty correcting sagittal alignment (▶ Fig. 26.2). Increased operative time may lead to increased blood loss. In a multicenter case series of 21 patients undergoing vertebral body resection for tumor with placement of an expandable cage through a posterolateral approach, Shen et al10 reported a complication rate of 14.3%. Complications included migration of an interbody cage during the immediate postoperative period which required revision, subsidence of a cage on radiographs that did not necessitate revision, and development of an incomplete motor deficit of a single lower extremity in one patient who remained ambulatory. Metcalfe et al7 presented a report of 50 patients who underwent vertebral body resection and three-column stabilization through a posterior transpedicular approach for tumors in the thoracic and lumbar spine. Complications in this series included one death from postoperative pneumonia, two patients with rapidly progressive paraparesis becuase of epidural hematoma,

Fig. 26.2 A 65-year-old man with a history of metastatic papillary thyroid carcinoma underwent T8 vertebrectomy with posterior spinal fusion from T6 to T10 due to progressive paraparesis from a metastatic lesion. (a) Intraoperative fluoroscopic images show an expandable intervertebral cage with well-maintained sagittal alignment. (b) Postoperative axial CT image shows the cage centered in the vertebrectomy defect. Note the resection of the proximal portion of the eighth rib on the right side as part of the surgical approach. (c) Upright radiographs 2 weeks postoperatively demonstrate settling of the cage into the T7 and T9 endplates with kyphotic angulation. Also, note a small persistent pleural effusion.

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Thoracolumbar and one patient with transient lower extremity weakness due to ischemic changes in the spinal cord. The three patients with neurologic complications went on to a full recovery. Other minor complications from this series included a case of uncomplicated pneumonia and one lower extremity deep venous thrombosis. In a retrospective review of 67 patients undergoing vertebral body resection and reconstruction with an expandable cage (for tumor, infection, or traumatic injury of the thoracic and lumbar spine), Hofstetter et al reported eight complications requiring five revisions.13 Three patients developed significant epidural hematomas postoperatively and five patients required revision surgery for interbody implant subsidence. Interestingly, of the subsided implants, three were placed for traumatic burst fractures, one for osteomyelitis, and one for a pathologic fracture. The authors postulated that the 14% subsidence rate seen in traumatic fractures was caused by endplate defects of the involved vertebral body, ligamentous laxity, and insufficient length of the posterolateral instrumentation.

26.6 Summary Overall the posterolateral approach to vertebral body resection and circumferential reconstruction avoids the morbidity associated with an anterior approach. This one-incision technique avoids the added morbidity and complications associated with anterior and anterior/posterior staged procedures. An expandable cage is well suited for reconstruction using this approach, given that it can be inserted through a relatively small access point collapsed, then expanded in situ. The most common complications related to the surgical approach include neurologic injury and pulmonary complications (pneumonia, pneumothorax, pulmonary effusion). Device-related complications include settling or shifting of the intervertebral device (occasionally leading to neural impingement), device failure (e.g., collapse of an expanded cage), failure of correction of sagittal balance, or endplate fracture and subsequent instability. It is important for the surgeon to weigh the risks and benefits of this technique compared to a staged anterior and posterior approach.

26.7 Key Points ●

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Vertebral body resection through a posterolateral approach is typically indicated for infection, tumor, and trauma involving the anterior spine.

●

●

This technique provides access to the vertebral body through a single posterior incision, which avoids additional morbidity and complications associated with anterior and anterior/posterior staged procedures. Complications with this approach typically involve traction on the nerve roots, subsidence of the implant, or loss of deformity correction.

References [1] Dimar JR, II, Voor MJ, Zhang YM, Glassman SD. A human cadaver model for determination of pathologic fracture threshold resulting from tumorous destruction of the vertebral body. Spine. 1998; 23(11):1209–1214 [2] Kostuik JP, Errico TJ, Gleason TF, Errico CC. Spinal stabilization of vertebral column tumors. Spine. 1988; 13(3):250–256 [3] White AP, Kwon BK, Lindskog DM, Friedlaender GE, Grauer JN. Metastatic disease of the spine. J Am Acad Orthop Surg. 2006; 14(11):587–598 [4] Cantor JB, Lebwohl NH, Garvey T, Eismont FJ. Nonoperative management of stable thoracolumbar burst fractures with early ambulation and bracing. Spine. 1993; 18(8):971–976 [5] Krompinger WJ, Fredrickson BE, Mino DE, Yuan HA. Conservative treatment of fractures of the thoracic and lumbar spine. Orthop Clin North Am. 1986; 17(1):161–170 [6] Tay BK, Deckey J, Hu SS. Spinal infections. J Am Acad Orthop Surg. 2002; 10 (3):188–197 [7] Metcalfe S, Gbejuade H, Patel NR. The posterior transpedicular approach for circumferential decompression and instrumented stabilization with titanium cage vertebrectomy reconstruction for spinal tumors: consecutive case series of 50 patients. Spine. 2012; 37(16):1375–1383 [8] Kim DH, O’Toole JE, Ogden AT, et al. Minimally invasive posterolateral thoracic corpectomy: cadaveric feasibility study and report of four clinical cases. Neurosurgery. 2009; 64(4):746–752, discussion 752–753 [9] Smith ZA, Li Z, Chen NF, Raphael D, Khoo LT. Minimally invasive lateral extracavitary corpectomy: cadaveric evaluation model and report of 3 clinical cases. J Neurosurg Spine. 2012; 16(5):463–470 [10] Shen FH, Marks I, Shaffrey C, Ouellet J, Arlet V. The use of an expandable cage for corpectomy reconstruction of vertebral body tumors through a posterior extracavitary approach: a multicenter consecutive case series of prospectively followed patients. Spine J. 2008; 8(2):329–339 [11] Viswanathan A, Abd-El-Barr MM, Doppenberg E, et al. Initial experience with the use of an expandable titanium cage as a vertebral body replacement in patients with tumors of the spinal column: a report of 95 patients. Eur Spine J. 2012; 21(1):84–92 [12] Jeyamohan S, Vaccaro A, Harrop JS. Use of expandable cages in metastasis to the spine. JHN Journal. 2009; 4:5–7 [13] Hofstetter CP, Chou D, Newman CB, Aryan HE, Girardi FP, Härtl R. Posterior approach for thoracolumbar corpectomies with expandable cage placement and circumferential arthrodesis: a multicenter case series of 67 patients. J Neurosurg Spine. 2011; 14(3):388–397 [14] Lubelski D, Abdullah KG, Steinmetz MP, et al. Lateral extracavitary, costotransversectomy, and transthoracic thoracotomy approaches to the thoracic spine: review of techniques and complications. J Spinal Disord Tech. 2013; 26 (4):222–232

Complications of Vertebral Body Replacement Cages

27 Complications of Vertebral Body Replacement Cages Adam Wollowick, Allison Fillar, Jason Wong, and Woojin Cho

27.1 Introduction

27.2 Cages Available in the Market

An ideal vertebral body replacement system should be stable to resist axial load bearing, have a large interbody–bone interface to facilitate fusion, prevent migration, and restore height and sagittal alignment.1 The anterior column bears 80% of the axial loads in the spine. Ani et al2 first discussed the importance of the anterior column and this has been supported by Lowery and Harms.3 Since the advent of spinal fusion for the treatment of tuberculous spondylitis in 1911 by Hibbs4 and Albee,5 the broadening of application of spinal fusion has grown to be utilized to treat various kinds of spinal diseases. Spinal diseases such as spinal tumors, infection, trauma, and deformity frequently involve the vertebral bodies. The destruction of the vertebral bodies caused by these diseases might compromise neurological stability. Corpectomy has therefore become a common procedure to provide complete decompression of neural elements when the vertebral bodies are involved.6,7,8 Autogenous structural bone grafts such as iliac crest or fibula have been traditionally used to reconstruct the anterior column despite various complications such as donor site morbidity, pseudarthrosis, and graft collapse, which precipitates fatigue and subsequent failure of the construct.9 Also, autogenous bone grafts do not have an ideal shape for anterior column reconstruction, and they also lack intrinsic stability. The development of titanium cages eliminates the need for autogenous structural bone graft. Multiple cages with varying diameters and heights are available and can be filled with autogenous bone graft that enables to provide osteoinductivity and osteoconductivity. Among different types of cages, threaded cylindrical carbon and titanium fiber mesh cages have been the most popular options. Titanium mesh cages are of interest as they are available in different diameters and can be readily adjusted to the needs of the surgeons and provide custom reconstruction property. The mesh cages also allow anchoring by bone with its spikes at their tips. Initially, it was found to be technically demanding to place the nonexpendable spacer in an optimal position. However, the development of expandable cages allows the adjustment of intervertebral body height possible in situ and hence easier insertion than previous designs. We will look at complications associated with vertebral body replacement cages in different perspectives. First, we will illustrate cages available in the market for vertebral corpectomy or total vertebrectomy. Second, general complications associated with vertebral body replacement cages will be discussed, and complications of static cage will be compared with those of expandable cage. Finally, we will also look at specific complications related with the specific disease entities that include tumor, infection, fracture, and deformity.

Structural allografts and the traditional titanium mesh cages are still available. In addition to those traditional options, there are also expandable titanium cages available in the market which are expandable in situ and allow the incorporation of bone grafts with an open architecture (VLIFT, Stryker, MI). Another variation to the aforementioned design is titanium cages that come with a modular cap that renders the implant compatible with various approaches to the spine (T2 Altitude; Medtronic, Memphis, TN). Another material that is used for cages is polyether ether ketone (PEEK) that is radiolucent and offers better imaging after the placement of the cage to monitor pathological progress such as recurrence of tumor. The expandable component also allows the cage to be expanded in situ and therefore more accurate for spinal reconstruction (ECD, Synthes). Other cages that are made of PEEK also come with a modular endcap and the implants are inserted and expanded with the same implant holder, which simplifies the operating technique (Fortify, Globus). Globus also offers vertebral replacement cages that enhance anterior column fixation by titanium screws.

27.3 Most Common Complications Encountered with Vertebral Body Replacement Cages 27.3.1 Cage Migration In cages used for intervertebral spaces, especially with posterior fixations, migration of cages is not usually a problem.10 However, because of a long lever arm, migration of vertebral cages can result in catastrophic failure if it occurs in the spinal cord. In the study by Arts et al,11 it was found that hardware migration was the most common complication encountered when corpectomy cages were used for different disease entities. The authors suggested that different designs of cages and experience of surgeon were related to hardware migration. Shen et al12 also reported on two cases of cage migration, and the authors thought it is approach related. Robertson et al also reported on hardware migration in patients with vertebral body fractures as they believed that cage migration happened as the cage was placed in a tilted position.13 Dai et al14 also had a patient with hardware migration with progressive deformity after using titanium cage for burst fracture.15 They believed that it happened because the posterior column was not stable and the patient should have undergone a circumferential fixation. Another paper by Dvorak et al16 found two patients with cage subsidence after being treated with corpectomy cages for deformity and fractures, respectively. The subsidence was likely caused by breaching of the cage–bone interface as the authors

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Thoracolumbar have pointed out. This phenomenon was also reported in the cervical spine, showing one-level corpectomy is more related with subsidence than two-level anterior cervical discectomy and fusion.15

Neurological Deficit According to the study by Arts et al,11 the second most prevalent complication was neurological deficits. Shen et al12 also reported on a complication with iatrogenic nerve deficits on a patient with vertebral body tumors, which happened during the expansion of the cage. They attributed the complication to the fact that the cage that was used was designed for anterior approach, and it was used for the posterior approach in their case.

Progressive Angulation Arts el at 11 reported progressive kyphosis as one of the other common complications related to vertebral body replacement cages. However, it appeared to be related more to degenerative changes rather than as a direct complication of using cages.

27.4 Complications in Each Disease Entity 27.4.1 Complications Associated with Fusion Cages Used for Tumor Spine column is the most common site of bone metastasis.17 There are also various primary tumors in the spine. Surgical treatment might be beneficial for patients with spinal tumors for reducing pain and local control of tumors with mechanical stabilization of the spine. In a study conducted by Thongtrangan et al,17 they found no hardware-related complications in a case series of 15 patients with an average of 12.6 months’ follow-up. There were two cases of disease recurrence, but they were not related with the titanium mesh cage. Another study that looked at expandable cages usage on vertebral body tumors revealed three implantrelated complications.12 The complications include iatrogenic nerve injury, early post-op repositioning of cage and late post-op cage subsidence. The authors believed that all these complications were technique related: iatrogenic nerve injury was secondary to overdistraction and anterior settling of cage was likely caused by insufficient stabilization of the lumbar spine. In a study by Dvorak et al,16 two patients with spinal tumor, one with plasmacytoma and the other with osteogenic sarcoma, treated with titanium mesh cage experienced deep wound infection. The patient with plasmacytoma developed a pseudomeningocele as well. A study by Arts et al11 has found that half of the patients treated with titanium mesh cage for spinal metastasis developed various kinds of complications and recommended the surgeons to be aware of patient’s life expectancy given the extensive spinal surgery might pose increased risks to these patients secondary to their medical history such as steroid use and radiotherapy.

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27.4.2 Complications Associated with Fusion Cages Used for Infection Although some patients with pyogenic vertebral osteomyelitis can be treated with intravenous antibiotics, usually majority of patient population are indicated for spinal reconstruction, especially for patients who have significant bone destruction, progressive deformity, neurological impairment, or antibioticresistant sepsis. Implantation of metallic instrumentation into an infected area has been a concern; however, some studies have shown that it might be safe with titanium cylindrical mesh cages. In a study by Fayazi et al,18 seven out of eleven patients who underwent fusion with titanium mesh cages experienced perioperative complications. One of them had complications related to anterior approach itself. Two patients experienced superficial wound dehiscence that was treated conservatively. Another patient experienced hardware failure who subsequently developed vertebral body collapse that required a revision procedure. Also, one of the patients presented with screw cutout. Interestingly, none of the patients developed a recurrence of infection. Chen et al19 suggested that a combination of the anterior and posterior approaches had less complications compared to using a single approach. Another study that looked at 24 patients who were treated with titanium mesh cage for septic spondylitis found no hardware-related complications. They had one patient with abdominal hernia, which was approach related.20 Korovessis et al also studied 14 patients with thoracolumbar spondylitis who were treated with titanium mesh cage and found that there was no implant-related complication, but one patient presented with wound infection and another patient with abdominal hernia that was approach related.21

27.4.3 Complications Associated with Fusion Cages Used for Trauma Management of thoracolumbar fracture has been controversial in terms of a single approach, that is, anterior versus posterior or a combined approach should be adopted. It is, however, generally accepted that for unstable burst fracture a combined approach is more biomechanically favorable than a single approach. Dai et al looked at 33 patients who received titanium mesh cage for thoracolumbar burst fractures and they found that there were no major perioperative complications associated with the hardware. In particular, none of the patients lost their postoperative surgical alignment.14 A study by Dvorak et al16 has shown that 2 out of 28 patients with burst fracture who underwent titanium mesh cage implantation experienced cage migration. A radiographic analysis of titanium mesh cages used for burst fractures in 26 patients found that 6 patients in that series experienced loss of correction, and the problem is more prominent in the lumbar region.22 Robertson et al studied 31 patients treated with titanium mesh cage for various indications, with majority being burst fractures, and they found three implant-related complications. The complications included a case with rod breakage, another case with subsidence of cage with encroachment of the spinal canal, and an incidental finding of “case fracture” at 4-year follow-

Complications of Vertebral Body Replacement Cages up. They recommended closer attention on utilization of Harms cage as they had a thinner mesh and may cause nonfusion in certain cases. Payer investigated the outcomes of 22 patients who were treated with titanium cages for thoracolumbar unstable burst fractures and found that only one patient had a complication of malpositioned pedicle screw from the posterior approach.23 On the other hand, the anterior approach was associated with a transient paralytic ileus and in another patient with ilioinguinal hypesthesia. The authors suggested that compression of the ilioinguinal nerve from retraction of the psoas muscle was likely responsible for the complication.

27.4.4 Complications Associated with Fusion Cages Used for Deformity Vertebral body resection (VCR) for spinal deformity was first described by MacLeannan24 in 1922, which consisted of a posterior approach with an apical resection of the vertebral body. In 1991, Bradford25 reported on 16 patients on whom they performed VCR via a combined anterior and posterior approach. Suk was the first one to report on posterior-only approach for VCR with two complete cord injuries26 and Lenke subsequently reported on 43 patients who underwent posterior-only VCR with no complications.27 It was suggested implantation of biological cages into the anterior column provides correction of existing deformity, segmental stabilization, and enlargement of neural foramen by restoration of disc height.28 Cylindrical metallic cages are out of favor given that they have suboptimal contact with the vertebral endplates that might affect the fusion rates and their radiopaque property renders them difficult to be assessed for fusion. Carbon box cages are radiolucent and as a result are more efficient in assessing fusion rate. However, carbon fiber implants may induce inflammatory response with possible foreign body reactions.29 Eck et al28 did not find any radiographic complications with their group of patients who underwent fusion with titanium mesh cage fusion for spinal deformity; however, the study only had 2-year follow-up. A different study that was carried out by Dvorak et al16 found that 3 of 10 patients in whom they placed titanium mesh cages developed complications: rod fractures in 2 patients and cage and hook subsidence that resulted in sagittal misalignment. The authors suggested that the interface between bone and cage that serves to anchor the cage in place might contribute to subsidence because the sharp edges of the cage may breach the surface of the endplate.13 In the study mentioned earlier, two hardware failures were experienced when titanium mesh cages were used for posttraumatic deformity and the authors recommended more aggressive surgeries such as radical bone resection or total vertebrectomy might be required to ensure correct alignment of adjacent vertebral bodies.13 Since current trend of vertebral column resection is through posterior approaches only, many surgeons prefer using expandable cage to maximize the anterior opening. Cho and Lenke suggested the formula to determine how big a cage should be used after posterior vertebral column resection.30,31

References [1] Benzel EC. Biomechanics of Spine Stabilization: Principles and Clinical Practice. New York, NY: McGraw-Hill; 1995 [2] Ani N, Keppler L, Biscup RS, Steffee AD. Reduction of high-grade slips (grades III-V) with VSP instrumentation. Report of a series of 41 cases. Spine. 1991; 16(6) Suppl:S302–S310 [3] Lowery GI, Harms J. Principles of load sharing. In: Bridwell KH, De Wald RL, eds. Textbook of Spinal Surgery. 2nd ed. Philadelphia, PA: Lippincott-Raven; 1997:155–165 [4] Hibbs RA. An operation for progressive spinal deformities: a preliminary report of three cases from the service of the orthopaedic hospital. Clin Orthop Relat Res. 1911; 35:4–8 [5] Transplantation of a portion of the tibia into the spine for Pott's disease. A preliminary report. Clin Orthop Relat Res. 2007; 460:14–16 [6] Alleyne CH, Jr, Rodts GE, Jr, Haid RW. Corpectomy and stabilization with methylmethacrylate in patients with metastatic disease of the spine: a technical note. J Spinal Disord. 1995; 8(6):439–443 [7] Gokaslan ZL, York JE, Walsh GL, et al. Transthoracic vertebrectomy for metastatic spinal tumors. J Neurosurg. 1998; 89(4):599–609 [8] McDonough PW, Davis R, Tribus C, Zdeblick TA. The management of acute thoracolumbar burst fractures with anterior corpectomy and Z-plate fixation. Spine. 2004; 29(17):1901–1908, discussion 1909 [9] Pollock R, Alcelik I, Bhatia C, et al. Donor site morbidity following iliac crest bone harvesting for cervical fusion: a comparison between minimally invasive and open techniques. Eur Spine J. 2008; 17(6):845–852 [10] Cho W, Wu C, Mehbod AA, Transfeldt EE. Comparison of cage designs for transforaminal lumbar interbody fusion: a biomechanical study. Clin Biomech (Bristol, Avon). 2008; 23(8):979–985 [11] Arts MP, Peul WC. Vertebral body replacement systems with expandable cages in the treatment of various spinal pathologies: a prospectively followed case series of 60 patients. Neurosurgery. 2008; 63(3):537–544, discussion 544–545 [12] Shen FH, Marks I, Shaffrey C, Ouellet J, Arlet V. The use of an expandable cage for corpectomy reconstruction of vertebral body tumors through a posterior extracavitary approach: a multicenter consecutive case series of prospectively followed patients. Spine J. 2008; 8(2):329–339 [13] Robertson PA, Rawlinson HJ, Hadlow AT. Radiologic stability of titanium mesh cages for anterior spinal reconstruction following thoracolumbar corpectomy. J Spinal Disord Tech. 2004; 17(1):44–52 [14] Dai LY, Jiang LS, Jiang SD. Anterior-only stabilization using plating with bone structural autograft versus titanium mesh cages for two- or three-column thoracolumbar burst fractures: a prospective randomized study. Spine. 2009; 34(14):1429–1435 [15] Park Y, Maeda T, Cho W, Riew KD. Comparison of anterior cervical fusion after two-level discectomy or single-level corpectomy: sagittal alignment, cervical lordosis, graft collapse, and adjacent-level ossification. Spine J. 2010; 10(3):193–199 [16] Dvorak MF, Kwon BK, Fisher CG, Eiserloh HL, III, Boyd M, Wing PC. Effectiveness of titanium mesh cylindrical cages in anterior column reconstruction after thoracic and lumbar vertebral body resection. Spine. 2003; 28(9):902–908 [17] Thongtrangan I, Balabhadra RS, Le H, Park J, Kim DH. Vertebral body replacement with an expandable cage for reconstruction after spinal tumor resection. Neurosurg Focus. 2003; 15(5):E8 [18] Fayazi AH, Ludwig SC, Dabbah M, Bryan Butler R, Gelb DE. Preliminary results of staged anterior debridement and reconstruction using titanium mesh cages in the treatment of thoracolumbar vertebral osteomyelitis. Spine J. 2004; 4(4):388–395 [19] Chen WH, Jiang LS, Dai LY. Surgical treatment of pyogenic vertebral osteomyelitis with spinal instrumentation. Eur Spine J. 2007; 16(9):1307–1316 [20] Korovessis P, Repantis T, Iliopoulos P, Hadjipavlou A. Beneficial influence of titanium mesh cage on infection healing and spinal reconstruction in hematogenous septic spondylitis: a retrospective analysis of surgical outcome of twenty-five consecutive cases and review of literature. Spine. 2008; 33(21): E759–E767 [21] Korovessis P, Petsinis G, Koureas G, Iliopoulos P, Zacharatos S. Anterior surgery with insertion of titanium mesh cage and posterior instrumented fusion performed sequentially on the same day under one anesthesia for septic spondylitis of thoracolumbar spine: is the use of titanium mesh cages safe? Spine. 2006; 31(9):1014–1019

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Thoracolumbar [22] Karaeminogullari O, Tezer M, Ozturk C, Bilen FE, Talu U, Hamzaoglu A. Radiological analysis of titanium mesh cages used after corpectomy in the thoracic and lumbar spine: minimum 3 years’ follow-up. Acta Orthop Belg. 2005; 71 (6):726–731 [23] Payer M. Unstable burst fractures of the thoraco-lumbar junction: treatment by posterior bisegmental correction/fixation and staged anterior corpectomy and titanium cage implantation. Acta Neurochir (Wien). 2006; 148(3):299– 306, discussion 306 [24] MacLennan A. Scoliosis. BMJ. 1922; 2:864–866 [25] Bradford DS. Vertebral column resection. –Orthop Trans 1987; 11:502 [26] Suk SI, Kim JH, Kim WJ, Lee SM, Chung ER, Nah KH. Posterior vertebral column resection for severe spinal deformities. Spine. 2002; 27(21):2374–2382

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[27] Lenke LG, Sides BA, Koester LA, Hensley M, Blanke KM. Vertebral column resection for the treatment of severe spinal deformity. Clin Orthop Relat Res. 2010; 468(3):687–699 [28] Eck KR, Bridwell KH, Ungacta FF, Lapp MA, Lenke LG, Riew KD. Mesh cages for spinal deformity in adults. Clin Orthop Relat Res. 2002(394):92–97 [29] Jockisch KA, Brown SA, Bauer TW, Merritt K. Biological response to choppedcarbon-fiber-reinforced peek. J Biomed Mater Res. 1992; 26(2):133–146 [30] Cho W. Vertebral osteotomies: review of current concept. Eur Musculoskelet Rev . 2010; 5:45–49 [31] Cho W, Lenke L G, Blanke, KM, et al. Predicting kyphosis correction during posterior-only vertebral column resection by the amount of spinal column shortening. Spine Deformity. 2015; 3(1):65–72

Complications of Anterior Thoracic Instrumentation Systems

28 Complications of Anterior Thoracic Instrumentation Systems Michael Silverstein, Daniel Lubelski, and Thomas E. Mroz

28.1 Introduction ●

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There are a variety of instrumentation systems available for reconstruction and stabilization of the anterior thoracic spine. Knowledge of the thoracic spine anatomy and surrounding neurovascular supply, appropriate instrumentation system selection, and proficient surgical technique all help in limiting complications. Complications should be evaluated and managed on an individual basis.

28.2 Anterior Thoracic Instrumentation: Some History Approximately 80% of the axial loading is through the ventral spine (i.e., vertebral bodies and discs). Anterior thoracic instrumentation must withstand substantial forces during physiologic loading, and this underscores the necessity to optimize the union rate through a thoughtful reconstruction and biological substrate.1 There is a lengthy history of attempts to reconstruct the ventral thoracic spine. Reconstruction of the anterior thoracic spine has evolved greatly since Vincent and Menard first attempted the approach in the late 19th century for Pott’s disease.2,3 The early inception of the transthoracic approach had a high rate of failure,4 and substantial limitations continued into the 20th century. Humphries and Hawk, in 1958, published reports on anterior thoracic spine stabilization with a plate– screw system.5,6 However, their systems failed to provide adequate biomechanical support, and similarly experienced unacceptable failure rates. Further advances occurred in the 1970s when Dwyer et al,7,8 Zielke et al,9 Dunn et al,10 and others developed additional anterior approach systems to the thoracic spine. Dwyer et al introduced the screw–cable system to treat deformity, while Zielke et al9 developed a screw–rod system. Both systems, however, had limited success. Following these attempts, Dunn and colleagues developed the double screw–rod system, which provided adequate stabilization to the anterior thoracic spine. Within several years, however, the Dunn system was abandoned because of reports of great vessel erosion.5 Today, spine surgeons have numerous options to successfully navigate and stabilize the anterior thoracic spine. The complications learned from historical failures have paved the way to better instrumentation design and materials. This has led to an expansion in possible applications to various pathologies. In addition to instrumentation advances, our understanding of the spine, its biomechanics, the changes that occur during the transition from a healthy to a diseased spine, and the selection of appropriate treatments have improved greatly in recent decades.1 The purpose of this chapter is to describe the complications for anterior thoracic spine instrumentation, as well as avoidance and management of the complications.

Comprehensive understanding of the anterior thoracic spinal implants and their associated complications will lead to reduced morbidity and improved outcomes.

28.3 Indications Anterior instrumentation of the thoracic spine has evolved to accommodate numerous disease states.11 The main indications for instrumentation include trauma, deformity and degenerative conditions, infection, and neoplasm. While there are a variety of indications for ventral reconstruction, any implant used must be safe and provide adequate and durable stability until osseous union occurs. Approaches to the ventral thoracic spine have evolved over the past decades, and the use of the costotransversectomy (CTE) and extracavitary approaches has increased. Almost in parallel, implants such as expandable cages that can be placed and deployed through these posterior routes have also gained popularity. Regardless of the type of approach used to access the ventral thoracic spine, a careful selection of proper reconstructive implants is critical. Modern implants have improved mechanisms and designs that help prevent screw back-out, cage collapse, facilitate easier deployment, and minimize pistoning by maximizing surface area contact. Despite these recent advances, it remains crucial to understand the anatomy and the relevant pitfalls, and the merits and limitations of the various types of reconstructive options.

28.4 Food and Drug Administration Approval Status of Instrumentation Various instrumentation systems are available for anterior thoracic spine stabilization (▶ Table 28.1). They include dual-rod–screw systems (▶ Fig. 28.1), single-rod–screw (▶ Fig. 28.2), and plate–screw (▶ Fig. 28.3). Both rigid and semirigid instrumentation systems are approved for their own particular indications. Anterior plates are designed with a low-profile system to minimize damage to surrounding tissues and vessels. Examples of plate–screw and rod–screw systems include V2F™ Anterior fixation system (Zimmer Spine, Minneapolis, MN), Expedium Anterior Spine System (Depuy-Synthes, Raynham, MA), CD Horizon Legacy Anterior Construct (Medtronic, Minneapolis, MN), Gateway Construct (Globus, Audubon, PA), Profile Anterior Fixation System (Depuy-Synthes, Raynham, MA), and Kaneda SP Spine System (Depuy-Synthes, Raynham, MA). The plate and rod systems are combined with vertebral body replacement devices for supplemental stabilization. Vertebral body replacement devices are used to reconstruct the anterior and middle columns and promote fusion (▶ Fig. 28.4). Vertebral body reconstructive options include

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Thoracolumbar Table 28.1 Example of available anterior thoracic spine instrumentation systems Single rod

Dual rod

Anterior ISOLA spine system CD Horizon Legacy Anterior (Depuy-Synthes, Raynham, Construct (Medtronic, MA) Minneapolis, MN) Expedium Anterior Spine System (Depuy-Synthes, Raynham, MA) Kaneda SP Spine System (Depuy-Synthes, Raynham, MA)

Plate

Expandable cage

Stackable cage

Gateway Construct (Globus, Audubon, PA) V2F™ Anterior Fixation system (Zimmer Spine, Minneapolis, MN) Profile Anterior Fixation System (Depuy-Synthes, Raynham, MA)

XPand (Globus, Audubon, PA) FortifyI Corpectomy Spacer System (Globus, Audubon, PA) Synex (Synthes, West Chester, PA)

Bengal (Depuy-Synthes, Raynham, MA) Ocelot Stackable cage system (Depuy-Synthes, Raynham, MA)

synthetic and metallic cages, as well as autogenous or allogeneic structural bone grafts. Modern cages can be stacked, cut, or expanded to the appropriate height, and most cages have a variety of endplate caps that maximize surface area contact and desired angle, and help to prevent dislodgement (i.e., spiked). Examples include XPand (Globus, Audubon, PA), FortifyI Corpectomy Spacer System (Globus, Audubon, PA), Synex (Synthes, West Chester, PA), and Bengal and Ocelot Stackable cage system (Depuy-Synthes, Raynham, MA). Cages are designed to be packed with bone graft substrate for interbody fusion.5 These devices are intended for use with supplemental anterior fixation systems that include screw– plate and screw–rod systems, or to be backed up by posterior pedicle screw–rod constructs.

28.5 Relevant Anatomy 28.5.1 Ribs The ribs and their associated costovertebral facet joints and costotransverse joints limit accessibility for implant placement (▶ Fig. 28.5). The rib head is often resected to afford access to the disc, pedicle, foramen, and the spinal canal.

Vascular Instrumentation is frequently in close proximity to vessels. The great vessels are in close proximity to the thoracic spine.12 The thoracic aorta is located on the left anterolateral aspect of the thoracic spine (▶ Fig. 28.6), while the relatively thin-walled vena cava and azygos veins are located on the right side of the thoracic spine.13 Arterial injuries are rare.14 In a retrospective study of 1,223 anterior spine surgery (T1– S1) patients requiring instrumentation, Faciszewski et al15 reported only one aortic artery injury. The thoracic duct lies anterior to the vertebral bodies of T6–T12 between the aorta and azygos veins.

Fig. 28.1 Dual-rod system.

Spinal Cord and Nerves The right recurrent laryngeal nerve originates from the vagus nerve, and loops under the right subclavian artery and ascends into the neck. A left recurrent laryngeal nerve branches from the vagus nerve between T1 and T3, loops around the aorta, and then travels into the tracheoesophageal groove. Injury could cause mild dysphagia and dysphonia.11 Intercostal nerves lie near the head of the rib, and run distally within the

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neurovascular bundle along the inferior border of their respective rib. Knowledge of this relationship is important to help minimize injury during an approach, retraction, and/or during decompression. The spinal cord location lies within the spinal canal, posterior to the vertebral bodies and discs. Obviously, it is critical to understand its location and functional status in the various pathological states.

Complications of Anterior Thoracic Instrumentation Systems

Fig. 28.2 Single-rod system.

28.6 Complications While some complications occur despite sound preoperative and operative efforts, most complications associated with anterior reconstruction and instrumentation are because of (1) errors in planning and (2) errors in surgical technique (Box 1 (p. 175)). The various surgical approaches also have unique challenges and associated complications, and can be considered separately.

Fig. 28.3 Plate–screw system.

Box 1 Anterior thoracic spine instrumentation complication types Complications of anterior thoracic spine instrumentation systems ● Spinal cord and nerve damage ● Vascular injury ● Secondary deformity ● Pseudoarthrosis ● Spinal instability

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Thoracolumbar

Fig. 28.4 Vertebral cage replacement.

28.6.1 Errors in Planning The easiest way to avoid anterior thoracic complications is to properly plan out the surgery that is required to treat a specific disease. Such preoperative deliberations are equally important, if not more important than the actual surgical procedure when it comes to avoidance of complications and achievement of successful outcomes. The ultimate goals of any thoracic reconstruction are to provide stability and to promote fusion. Without adequate stability, the chance of successful union decreases regardless of the biological substrate that is used. If fusion across the surgically treated levels does not occur, the instrumentation invariably will loosen, fatigue, and fail over time. This can result in loss of spinal alignment and/or dislodgement of implants, which can result in substantial patient morbidity considering the anatomical structures in the vicinity.

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Fig. 28.5 Spinal column.

There are several avoidable errors in surgical planning that can result in a higher complication rate. First, it is important for each surgeon to know his/her own limitation and abilities. Many anterior thoracic complications can be traced back to inexperience or unfamiliarity with a surgical approach or the

Complications of Anterior Thoracic Instrumentation Systems

Fig. 28.6 Thoracic aorta.

ventral anatomy, the underlying bone quality, the instrumentation, spinal biomechanics, and biologic substrates. This can translate into inadequate decompressions, aberrant placement of instrumentation, higher rates of visceral or neurovascular injury, and postoperative construct failure. Second, it is important to understand the disease process and its impact on the structural integrity of the spine. For example, a destructive metastatic lesion involving most of a vertebral body, but confined to the body, is much different than a metastatic lesion that has destroyed 80% of the vertebral body, in addition to a unilateral pedicle and facet joint. While both are metastatic processes, both require a different reconstruction and stabilization; they require distinct preoperative plans. Therefore, it is critical to understand what portion of the anatomy is or is not intact, the pathology of the disease being treated, what surgery is necessary to access and resect the pathology, what will remain intact after the resection, and what reconstructive options are optimal to promote both stability and union. Hence, a single surgical approach, or a single type of cage, a single biological substrate, etc., simply will not be appropriate for all pathology a surgeon encounters. Therefore, it is paramount to understand each disease process and its implications on stability and treatment, and the surgery that is required to treat that disease well in advance of the actual procedure. A third error in planning is lack of familiarity with the various reconstructive options. The latter have evolved substantially over the past several decades, and they can vary substantially in terms of materials, sizes and dimensions, suitability for postoperative imaging, user “friendliness,” and their ability to promote fusion. It is critical to choose the proper implant(s) and construct that is best suited for a specific disease process and patient. Failure to do so can result in complications in either an acute, subacute, or delayed manner. To do this, one must first recognize what is required technically for disease treatment (e.g., reconstruction following a corpectomy for fracture, a ventral debridement of discitis or osteomyelitis, spondylectomy for an osteosarcoma). When planning a ventral thoracic

surgery, one must carefully consider preoperatively any necessary postoperative treatment regimens (e.g., adjunctive radiation), magnetic resonance imaging (MRI) surveillance of tumor recurrence, the operative level(s) of the thoracic spine and its implications(s) on stability, global sagittal and coronal alignment, bone quality, and host risks for nonunion (e.g., steroid use, smoking, radiation, antimetabolite medications). All of these aspects will influence the selection of implant(s) and reconstruction. As an example, consider a T7 vertebral body fracture because of a solitary thyroid carcinoma metastatic lesion with epidural compression that is treated with a ventral corpectomy. If postoperative MRI surveillance is required, using an autogenous or allogeneic bone graft or nonmetallic cage is a wiser choice over a titanium or other metallic alloy because metals result in substantial artifact on MRI, rendering the study almost useless. Similarly, considering that this same patient will likely have some form of radiotherapy postoperatively, it is paramount to consider adding a plate and/or posterior instrumentation given the risk of ventral nonunion is very high. Failure to plan for this can quite likely result in failure of the interbody construct over time. A fourth error in planning is failure to preoperatively study the dimensions of the operative levels of the thoracic spine. This can have serious implications on cage or graft/endplate mismatch, as well as plate and screw placement. Interbody cage subsidence and/or dislodgment can be associated with serious morbidity. It is critical to place appropriately sized screws given the vital surrounding anatomy in the thoracic spine.

28.6.2 Errors in Surgical Technique There are several notable technique pitfalls that can lead to complications when instrumenting in the thoracic spine. While one can instrument the anterior thoracic spine using either the transthoracic or posterior approaches (i.e., CTE, extracavitary), there are complications that are unique to both. As such, each will be considered separately.

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Thoracolumbar

Transthoracic Approach Any of the vascular or neurological anatomy is at risk while placing interbody cages and screw–plate/rod constructs. It is important to optimize the exposure and line of sight to the surgical levels for these cases, and this can be challenging at higher thoracic levels and in larger patients. If the angle of approach is compromised (e.g., incision too low or too high), the delivery of interbody devices, plates, and screws can become exceedingly difficult because they almost invariably require use of longer extensions that are meant to be applied perpendicular to the long axis of the spine. Attempts to force these instruments into the desirable position can result in disastrous slips into vital anatomy or suboptimal instrumentation placement. It is equally critical to understand any rotation of the patient; failure to do so can result in incomplete or improper decompression and malpositioning of cages, grafts, and/or screws, resulting in vascular or neural injury. Another error in technique is suboptimal screw placement. This can result in inadequate stability and hardware prominence (▶ Fig. 28.7). Unicortical screw placement is a prime example, and this results from either improper planning or intraoperative failure to drill/tap bicortically. This is more pertinent for ventral-only constructs that rely on the excellent initial rigid stability. Screw placement that is angled too far ventrally can injure the great vessels, too long can cause a contralateral vascular or pulmonary injury, and an excessive posterior trajectory can cause catastrophic spinal cord penetration. Finally, it is best to choose an implant that has a locking mechanism to prevent screw back-out, which can result in injury to the lungs or great vessels. A third error in surgical technique relates to interbody cage or graft deployment. There are several types of expandable interbody cages, and many have unique mechanisms of expansion. It is important to avoid fracturing the endplates during the surgery, to optimize placement along the long axis of the ventral spine, and to maximize surface area contact of the implant endcap/endplate interface. This will improve the ability to expand the device, to correct kyphotic deformity, and to decrease postoperative subsidence.

Costotransversectomy and Extracavitary Approaches Anterior thoracic instrumentation that is placed via a posterior approach (CTE and extracavitary) is limited mainly to interbody cages and/or structural grafts. The angle of approach limits the deployment of anterior plate/rod and screws constructs. In order to place an interbody cage or structural graft from a posterior approach, it is mandatory to have enough clearance between the lateral dura and the medial tissues (i.e., paraspinal muscles, parietal pleura). This requires a careful and complete resection of the transverse process and rib section to afford the appropriate access to the ventral space. For example, in the case of a CTE a common error is leaving a portion of the lateral cortex of the rib intact, and this limits one’s ability (1) to clear the spinal cord while moving the cage from posterior to anterior past the cord and (2) to medialize the cage enough for proper placement of the device in the center of the vertebral column. The lateral extracavitary approach (LECA) provides a greater ventral exposure, but with more muscle and rib dissection compared with the CTE. The LECA’s greater exposure (i.e., greater rib dissection), along with its trajectory that is lateral to the paraspinal muscles, allows for placement of a cage or graft after decompression. If a ventral cage/graft needs to be placed with a CTE, it is important to resect the entire proximal rib,16 so that the parietal pleura is exposed and easily depressed. This provides access for the cage/graft and minimized potential pulmonary complications. Strategic ligation of nerve roots is also important to avoid tearing or avulsing the root(s) while trying to deliver the cage to the ventral space. Finally, it is very important to understand the techniques and tools used to deliver a specific device. This is especially pertinent while working from a posterior approach because once the cage is deployed, it may very difficult to re-engage the cage with the extender if the placement needs revision. Key points about a particular interbody implant to know prior to surgery are (1) the dimensions of the tools and cage (to deliver it past the spinal cord), (2) the process to re-engage the delivery extender once the cage is placed if the cage is misplaced and needs revision, (3) the reliability of the locking mechanism that

Fig. 28.7 Anteroposterior (a) and lateral (b) Xrays after anterior corpectomy and instrumentation revealing hardware prominence. (Reprinted with permission from Chaudhary et al.43)

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Complications of Anterior Thoracic Instrumentation Systems prevents cage collapse, (4) the difficulty of unlocking the locking mechanism once the cage is placed in the ventral space, (5) the mechanism of expansion (early generations of nonmetal rotatory mechanism were fraught with problems related to stripping), and (6) the ergonomic design of the extender. The latter point is important and is not entirely intuitive during preoperative planning. Some of the extenders by design engage the cage toward its end, and this can make it more difficult to deliver the device at the necessary or ideal angle. This is particularly true during a CTE because the terminal ends of the exposure are often bordered by bone. This type of cage/extender configuration can make it difficult to safely, or appropriately, steer the device into proper position. All of the nuances of instrumented design can impact the complication profile (i.e., neurological injury, spinal fluid leaks, implant migration or malposition) of the procedure. However, such complications are typically avoided by proper preoperative planning and technique.

28.6.3 General Instrumentation Complications

can result from unequal implant–bone contact leading to failure and increased complication risk. This can be prevented by complete removal of associated costovertebral articulation and osteophytes, and contouring the plate to the vertebral body to ensure maximum surface contact. Spinal canal violation can occur during screw placement in approximately 1.5% of patients.23 The dorsal wall of the vertebral body has a concave surface requiring the posterior screw that is placed at the lateral insertion site to be angulated anteriorly to avoid canal penetration. In a cadaveric analysis, Ebraheim et al24 found that the ideal placement of the posterior screw is 4 to 5 mm anterior to posterior wall with slight ventral angulation (10 degrees). Anterior screws should be placed perpendicular to the posterior wall or with a slight dorsal trajectory. This positioning allows for triangulation of the screws, which increases resistance to screw pullout. Frequent intraoperative imaging helps assist with safe screw placement. Vertebral body replacement complications are rare (▶ Fig. 28.9). When they occur, however, they can be severe, including spinal cord or arterial injuries. Subsidence of vertebral

Stability of instrumentation is provided with the use of lowprofile plate–screw implants and by maximizing the implant– bone contact. low-profile plates and screws are utilized to decrease the risk of vessel and soft tissue injury when they are in close proximity to the instrumentation. While rare, several case reports have identified chronic aortic erosion and screw penetration as complications of the anterior thoracic surgery instrumentation systems17,18,19,20,21,22 (▶ Fig. 28.8). Life-threatening injury would require emergent surgical exploration, repair of vascular injury and/or nerve compromise, and possible need for instrumentation removal.14 Increased implant stress

Fig. 28.8 3D computed tomography (CT) scan reveals a loose screw next to the descending aorta. (Reprinted with permission from Chaudhary et al.43)

Fig. 28.9 CT sagittal view of the thoracic spine showing failed anterior instrumentation with cage subsidence and kyphotic progression. (Reprinted with permission from Chaudhary et al.43)

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Thoracolumbar cages can lead to instability, instrument dislodgement, secondary deformity, and neurological symptoms. The current incidence or subsidence is variable, with some studies reporting less than 10%25,26 and others as high as 80%.27 The range is likely due to the wide variety of hosts, pathologies, and surgical techniques (i.e., implants and biologics). Lau and colleagues28 found that expandable cages have a higher rate and risk of subsidence compared to static cages. In a retrospective study, Heary et al29 reported that 39 of 40 patients that had thoracolumbar reconstruction with stackable cages had successful fusion. One patient had cage settling which led to kyphosis and required posterior stabilization. Vertebral body instrumentation following corpectomy requires preparation of the associated endplates.5 Residual cartilaginous endplates are excised except for a small shelf at the posterior border to help prevent posterior graft displacement into the spinal canal. Avoid aggressive removal of endplate because this can cause telescoping of the strut system, a risk for instrumentation failure. Nonexpandable cages should be slightly longer than the size of the relaxed corpectomy site given that retraction of the distracted ligaments will hold the graft in place. Excessive distraction with expandable cages should also be avoided because it can lead to cord and nerve-root injury, arterial injury, and excessive stress on adjacent vertebrae.

28.7 Tips for Avoiding Complications and Their Management ●

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The selection of suitable surgical approach during preoperative planning helps prevent complications resulting from an adequate approach. Use a double lumen endotracheal tube to help with selective lung deflation to limit lung injury during surgery. Make the initial incision into the avascular parietal pleura at the disc space, which is safer from a neurovascular standpoint. Postoperative attention to pain management, aggressive pulmonary toilet (i.e., incentive spirometry, coughing, and bronchodilators), and ambulation, when safe, all help to prevent atelectasis and pneumonia.30,31 Dual-rod versus single-rod systems should be used in patients greater than 60 kg as there is a greater load on the single-rod system. When applicable, the use of spiked vertebral plates (with rod systems) helps limit screw migration and resists axial loads. These staples should be placed straight laterally to prevent misdirected screw insertion. Blunt-tipped screws should penetrate beyond the contralateral cortex by 2 mm to ensure secure purchased. The anterior vertebral screw should be parallel to the posterior border of the vertebral body and the posterior screw should be slightly anterior. This prevents screw penetration into the spinal canal. Vertebral body replacement systems should not be used as a stand-alone system as they should have additional stabilization by plate or rod instrumentation systems. Templates should be used to determine the appropriate cage size.

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Each instrumentation system has their own nuisances, and product technique guides should be reviewed prior to their use. Injury to major blood vessels may require the assistance from a vascular surgeon for repair. Dislodgement of implants, particularly with nerve impingement, requires emergent surgical exploration. Implant failure may require revision surgery, in which case instrumented levels are increased to provide greater support and stability.

28.8 Future Directions In recent years, newer minimally invasive procedures have been described to surgically treat pathology in the thoracic spine. These include the minimally invasive LECA, miniopen transpedicular approach,32 minimally invasive transthoracic transpleural approach,33 and the minimally invasive transpsoas approach. Small cohort reports have shown that these approaches lead to reduced blood loss, smaller exposure and associated muscle dissection, decreased perioperative pain and morbidity, as well as earlier mobility.34, 35,36,37 Randomized controlled trials that validate these results are still needed before there will be wider adoption of these techniques. Advances in thoracic spine instrumentation and surgical approaches will lead to further reduction in associated morbidity/mortality and improve outcomes.

28.9 Summary Anterior thoracic spine surgery has greatly advanced in terms of instrumentation and surgical approaches that are now available in the spine surgeon’s armamentarium. Indications for anterior thoracic spine surgery include trauma, deformity and degenerative changes, infection, and neoplasm. There are a variety of stabilization and vertebral reconstruction systems available. The instrumentation system and surgical approach chosen should be based on a thorough assessment of patient presentation, medical comorbidities, radiographic findings, and the surgeon’s technical proficiency with each approach. Respiratory problems are the most common complication in up to 50% of patients and less frequently occurring complications include cardiac, vascular, gastrointestinal, and infection, which occur in 10 to 30% of patients.38,39,40 Instrumentation complications can occur during the perioperative setting or many years after initial implantation.41 They include implant fracture, pullout, dislodgement, and can lead to vascular and respiratory injuries. Instrumentation complications occur in up to 15% of patients.42 The mortality rate from anterior spine exposures is less than 1%.41 Each complication should be evaluated on an individual basis and may require the need for surgical exploration and possible revision.

28.10 Key Points ●

A variety of instrumentation systems are available for reconstruction and stabilization of the anterior thoracic spine.

Complications of Anterior Thoracic Instrumentation Systems ●

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Complications occur in up to 50% of patients, with higher rates of complications associated with pulmonary issues and lower rates with poor screw and vertebral cage placement. Complication risk can be reduced with a thorough assessment of patient history and medical comorbidities, radiographic findings, surgeon proficiency with the surgical approach, and instrumentation system selection. Possible instrument complications include implant fracture, pullout, and dislodgement, and can cause cardiac, vascular, and respiratory injuries. Complications should be evaluated and managed on an individual basis.

28.11 Key References [1] O'Leary PT, Ghanayem AJ. Instrumentation complications. In: Herkowitz HN, Garfin SR, Eismont FJ, eds. Rothman-Simeone: The Spine. Vol II. 6th ed. Philadelphia, PA: Saunders; 2011:1777–1788

O’Leary and Ghanayem broke down instrumentation complications into different categories. They included biologic failure (related to infection, osteoporosis, and patient-specific issues), biomechanical failure, error in thought process, and error in application. The authors described complication avoidance for each mechanism of failure. [2] Ikard RW. Methods and complications of anterior exposure of the thoracic and lumbar spine. Arch Surg. 2006; 141(10):1025–1034

Ikard did an excellent job describing the anterior thoracic spine exposure, the relevant anatomy associated with surgery, and tips to know in order to avoid exposure complications. The mortality rate of anterior thoracic spine exposure is less than 1%. [3] Syed ON, McCormick PC, Kaiser MG. Anterior thoracic instrumentation. In: Winn HR, ed. Youmans Neurological Surgery. Vol II. 6th ed. Philadelphia, Pa: Saunders; 2011:3051–3060

Syed et al discussed the use of instrumentation systems and general principles of implantation. For example, a translational deformity can result from an intrinsic bending moment between the rods, which can be avoided by cross-fixation of the dual rods and triangulation of the screws within the body. The posterior vertebral body screw should be placed 4 to 5 mm anterior to posterior vertebral wall with a slightly angulated trajectory (~10 degrees). [4] Ebraheim NA, Xu R, Ahmad M, Yeasting RA. Anatomic considerations of anterior instrumentation of the thoracic spine. Am J Orthop. 1997; 26(6):419– 424

Ebraheim et al analyzed 47 thoracic spine specimens from T2 to T12 for their vertebral body dimensions and proper screw placement. They recommend screw placement in the anterior or middle portion of the vertebral body. From T3 to T12, the maximum posterior angle of the vertebral body relative to the frontal plane increases as you descend the spine. Thus, canal violation can be avoided by placing the posterior screw slightly anterior. [5] Kibuule LK, Herkowitz HN. Thoracic spine: surgical approaches. In: Herkowitz HN, Garfan SR, Eismont FJ, eds. Rothman-Simeone: The Spine. Vol I. 6th ed., Philadelphia, PA: Saunders; 2011:318–338

Kibuule and Herkowitz presented data and pearls on each of the surgical approaches for anterior thoracic instrumentation. The pearls and tips assist the surgeon with a global picture, given that limiting complication risk for instrumentation failure includes the need to understand both anatomy and approach information.

References [1] O’Leary PT, Ghanayem AJ. Instrumentation complications. In: Herkowitz HN, Garfin SR, Eismont FJ, eds. Rothman-Simeone: The Spine. Vol II. 6th ed. Philadelphia: Saunders; 2011:1777–1788 [2] Hodgson AR, Stock FE, Fang HS, Ong GB. Anterior spinal fusion. The operative approach and pathological findings in 412 patients with Pott’s disease of the spine. Br J Surg. 1960; 48:172–178 [3] Winter RB, Garamella JJ. Development and growth of anterior spine surgery in Minnesota. Minn Med. 2010; 93(3):53–55 [4] Nadir A. Anterior approaches to thoracic and thoraco-lumbar spine. In: Chung KJ, ed. Spine Surgery. Shanghai: InTech Press; 2012:99–109 [5] Syed ON, McCormick PC, Kaiser MG. Anterior thoracic instrumentation. In: Winn HR, ed. Youmans Neurological Surgery. Vol II. 6th ed. Philadelphia, PA: Saunders; 2011:3051–3060 [6] Humphries AW, Hawk WA. Anterior fusion of the lumbar spine using an internal fixative device. Surg Forum. 1958; 9:770–773 [7] Dwyer AF, Schafer MF. Anterior approach to scoliosis. Results of treatment in fifty-one cases. J Bone Joint Surg Br. 1974; 56(2):218–224 [8] Dwyer AF, Newton NC, Sherwood AA. An anterior approach to scoliosis. A preliminary report. Clin Orthop Relat Res. 1969; 62(62):192–202 [9] Zielke K, Stunkat R, Beaujean F. [Ventrale derotations-spondylodesis (author’s transl)]. Arch Orthop Unfallchir. 1976; 85(3):257–277 [10] Dunn R, Zondagh I, Candy S. Spinal tuberculosis: magnetic resonance imaging and neurological impairment. Spine. 2011; 36(6):469–473 [11] Kibuule LK, Herkowitz HN. Thoracic spine: surgical approaches. In: Herkowitz HN, Garfan SR, Eismont FJ, eds. Rothman-Simeone: The Spine. Vol I. 6 ed. Philadelphia, PA: Saunders; 2011:318–338 [12] Christie SD, Song J, Fessler RG. Fractures of the Upper Thoracic Spine: Approaches and Surgical Management. CNS Annual Meeting; 2005 [13] Radcliff K, Limthongkul W, Gruskay J. Surgical planning for the treatment of thoracolumbar fractures: anterior, posterior, or combined approach? Semin Spine Surg. 2012; 24(4):244–251 [14] Lavigne F, Mascard E, Laurian C, Dubousset J, Wicart P. Delayed-iatrogenic injury of the thoracic aorta by an anterior spinal instrumentation. Eur Spine J. 2009; 18 Suppl 2:265–268 [15] Faciszewski T, Winter RB, Lonstein JE, Denis F, Johnson L. The surgical and medical perioperative complications of anterior spinal fusion surgery in the thoracic and lumbar spine in adults. A review of 1223 procedures. Spine. 1995; 20(14):1592–1599 [16] Lubelski D, Abdullah KG, Mroz TE, et al. Lateral extracavitary vs. costotransversectomy approaches to the thoracic spine: reflections on lessons learned. Neurosurgery. 2012; 71(6):1096–1102 [17] Been HD, Kerkhoffs GM, Balm R. Endovascular graft for late iatrogenic vascular complication after anterior spinal instrumentation: a case report. Spine. 2006; 31(22):E856–E858 [18] Higashino K, Katoh S, Sairyo K, et al. Pseudoaneurysm of the thoracoabdominal aorta caused by a severe migration of an anterior spinal device. Spine J. 2008; 8(4):696–699 [19] Hsieh PH, Chen WJ, Chen LH, Niu CC. An unusual complication of anterior spinal instrumentation: hemothorax contralateral to the side of the incision. A case report. J Bone Joint Surg Am. 1999; 81(7):998–1001 [20] Ohnishi T, Neo M, Matsushita M, Komeda M, Koyama T, Nakamura T. Delayed aortic rupture caused by an implanted anterior spinal device. Case report. J Neurosurg. 2001; 95(2) Suppl:253–256 [21] Matsuzaki H, Tokuhashi Y, Wakabayashi K, Kitamura S. Penetration of a screw into the thoracic aorta in anterior spinal instrumentation. A case report. Spine. 1993; 18(15):2327–2331 [22] Minor ME, Morrissey NJ, Peress R, et al. Endovascular treatment of an iatrogenic thoracic aortic injury after spinal instrumentation: case report. J Vasc Surg. 2004; 39(4):893–896 [23] Suk SI, Kim WJ, Lee SM, Kim JH, Chung ER. Thoracic pedicle screw fixation in spinal deformities: are they really safe? Spine. 2001; 26(18):2049–2057 [24] Ebraheim NA, Xu R, Ahmad M, Yeasting RA. Anatomic considerations of anterior instrumentation of the thoracic spine. Am J Orthop. 1997; 26 (6):419–424 [25] Burkett CJ, Baaj AA, Dakwar E, Uribe JS. Use of titanium expandable vertebral cages in cervical corpectomy. J Clin Neurosci. 2012; 19(3):402–405 [26] Woiciechowsky C. Distractable vertebral cages for reconstruction after cervical corpectomy. Spine. 2005; 30(15):1736–1741 [27] Auguste KI, Chin C, Acosta FL, Ames CP. Expandable cylindrical cages in the cervical spine: a review of 22 cases. J Neurosurg Spine. 2006; 4(4):285–291

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Thoracolumbar [28] Lau D, Song Y, Guan Z, La Marca F, Park P. Radiological outcomes of static vs expandable titanium cages after corpectomy: a retrospective cohort analysis of subsidence. Neurosurgery. 2013; 72(4):529–539, discussion 528–529 [29] Heary RF, Kheterpal A, Mammis A, Kumar S. Stackable carbon fiber cages for thoracolumbar interbody fusion after corpectomy: long-term outcome analysis. Neurosurgery. 2011; 68(3):810–818, discussion 818–819 [30] Ofluoglu O. Minimally invasive management of spinal metastases. Orthop Clin North Am. 2009; 40(1):155–168, viii [31] McCullen GM, Criscitiello AA, Yuan HA. Principles of endoscopic techniques to the thoracic and lumbar spine. In: Mayer HM, ed. Minimally Invasive Spine Surgery. Berlin: Springer-Verlag; 2006:149–156 [32] Chi JH, Dhall SS, Kanter AS, Mummaneni PV. The Mini-Open transpedicular thoracic discectomy: surgical technique and assessment. Neurosurg Focus. 2008; 25(2):E5 [33] Deviren V, Kuelling FA, Poulter G, Pekmezci M. Minimal invasive anterolateral transthoracic transpleural approach: a novel technique for thoracic disc herniation. A review of the literature, description of a new surgical technique and experience with first 12 consecutive patients. J Spinal Disord Tech. 2011; 24(5):E40–E48 [34] Smith JS, Ogden AT, Fessler RG. Minimally invasive posterior thoracic fusion. Neurosurg Focus. 2008; 25(2):E9 [35] Houten JK, Alexandre LC, Nasser R, Wollowick AL. Nerve injury during the transpsoas approach for lumbar fusion. J Neurosurg Spine. 2011; 15(3):280–284

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[36] Lidar Z, Lifshutz J, Bhattacharjee S, Kurpad SN, Maiman DJ. Minimally invasive, extracavitary approach for thoracic disc herniation: technical report and preliminary results. Spine J. 2006; 6(2):157–163 [37] Khoo LT, Smith ZA, Asgarzadie F, et al. Minimally invasive extracavitary approach for thoracic discectomy and interbody fusion: 1-year clinical and radiographic outcomes in 13 patients compared with a cohort of traditional anterior transthoracic approaches. J Neurosurg Spine. 2011; 14(2):250–260 [38] Anand N, Regan JJ. Video-assisted thoracoscopic surgery for thoracic disc disease: Classification and outcome study of 100 consecutive cases with a 2-year minimum follow-up period. Spine. 2002; 27(8):871–879 [39] McDonald WI, Compston A, Edan G, et al. Recommended diagnostic criteria for multiple sclerosis: guidelines from the International Panel on the diagnosis of multiple sclerosis. Ann Neurol. 2001; 50(1):121–127 [40] De Giacomo T, Francioni F, Diso D, et al. Anterior approach to the thoracic spine. Interact Cardiovasc Thorac Surg. 2011; 12(5):692–695 [41] Ikard RW. Methods and complications of anterior exposure of the thoracic and lumbar spine. Arch Surg. 2006; 141(10):1025–1034 [42] McLain RF, Burkus JK, Benson DR. Segmental instrumentation for thoracic and thoracolumbar fractures: prospective analysis of construct survival and five-year follow-up. Spine J. 2001; 1(5):310–323 [43] Chaudhary S, Mroz TE. Thoracic aortic dissection and mycotic pseudoaneurysm in the setting of an unstable upper thoracic type B2 fracture case report. Global Spine J. 2012; 2(3):175–182

Interspinous Spinous Process Fusion Plate Complications

29 Interspinous Spinous Process Fusion Plate Complications Andrew H. Milby, Douglas J. Nestorovski, and Harvey E. Smith

29.1 Introduction Fusion of the posterior elements by means of decortication and bone grafting with internal fixation is a potential method of achieving intervertebral fusion. The relative lack of resistance to rotation and side bending with posterior element-based constructs has motivated the widespread use of pedicle screw fixation with rod constructs for segmental stabilization. Advances in materials and minimally invasive surgical techniques have renewed interest in implantable devices for interspinous fusion. When used as a supplement to anterior column reconstruction, interspinous fusion devices (IFDs) may produce equivalent biomechanical stability in flexion–extension to pedicle screw–rod constructs while affording the potential for indirect neural decompression via interspinous distraction. However, IFDs require intact posterior elements to achieve stability, thereby limiting their indications and yielding a distinct set of complications associated with their use. Limited clinical data are available thus far regarding long-term safety and efficacy of these devices, and further studies will help refine the most appropriate indications for their use.

comparative clinical efficacy and complication rates are unknown, and the precise indications for IFD implantation continue to evolve. In contrast to the relative paucity of data specific to IFD use, the complications associated with the use of dynamic interspinous spacers have been well documented. These devices are commonly grouped because of their biomechanical similarities, though long-term complications with dynamic spacer use, such as device migration, are theoretically obviated by the achievement of segmental stability following successful fusion. Both devices function in a similar capacity to achieve indirect decompression via interspinous distraction, and as such, have similar limitations as to the precise pathoanatomy suitable for their use. While early research showed promise for treatment of neurogenic intermittent claudication, dynamic interspinous spacers have been shown to be associated with relatively high rates of spinous process fractures, especially in patients with osteoporosis and/or spondylolisthesis.2,3 Nonetheless, in properly selected patients, interspinous spacers may provide a less invasive treatment option for neurogenic intermittent claudication.

29.2 IFDs and Interspinous Fusion

29.3 Purpose of Instrumentation

IFDs may be implanted for stabilization of the spinous processes to facilitate interspinous fusion. When compared to traditional posterior spinal instrumentation, such as pedicle screw–rod constructs, IFDs offer the theoretical benefit of minimizing surgical dissection while allowing indirect decompression of the neural elements via interspinous distraction. When used in conjunction with an interbody reconstruction or pedicle screw–rod fixation, IFDs are Food and Drug Administration (FDA) approved as supplemental fixation to achieve the stability needed for intervertebral fusion.1 In patients with suitable pathoanatomy, IFDs allow for indirect decompression of the canal and neural foramina without the risks and exposure of a direct decompression. While clinical experience with IFDs is limited at this time, certain characteristic complications have been observed with their use, such as spinous process fracture, that may negate the benefits and convenience of IFD implantation over conventional posterior segmental fixation. Long-term

Interspinous fixation techniques have evolved alongside other means of segmental fixation over the past 60 years. Early descriptions of interspinous wiring and plate–screw constructs were primarily in the setting of traumatic injuries to the thoracolumbar spine (▶ Fig. 29.1).4,5,6,7,8 Advocates of these techniques espoused the potential benefits of early mobilization to permit nursing care and to avoid complications associated with prolonged cast immobilization. The technique of tunneling wires through the base of the spinous process to increase pullout strength was later described by Drummond et al, thereby broadening its applications to spinal deformity correction when used in conjunction with Harrington and Luque–Galveston rod constructs.9 While theoretically minimizing the risk of neurologic injury by avoiding the passage of wires through the spinal canal, trans-spinous wires ultimately demonstrated inferior pullout strength in comparison to sublaminar wires

Fig. 29.1 Historical techniques for interspinous fusion. (a) Spinous process wiring. (Adapted from Kaufer and Hayes.6) (b) Wilson plating. (Adapted from Cobey.7) (c) Daab plating. (Adapted from Böstman et al.8)

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Thoracolumbar and lower loads to failure than laminar hooks in cadaveric biomechanical testing.10,11 These findings in conjunction with the rapid evolution of segmental pedicle screw–rod systems decreased the utilization of interspinous instrumentation techniques. Pedicle screw–rod constructs are currently the most common means of posterior spinal instrumentation used to achieve intervertebral fusion. Such constructs may be used alone to facilitate posterolateral fusion or may be used in conjunction with interbody techniques for achievement of anterior and posterior fusion. Pedicle screw placement is technically demanding, but it has been demonstrated to be a safe and reproducible technique with appropriate training. A systematic review by Hicks et al noted a 4.2% rate of radiographic pedicle screw malposition in patients undergoing posterior fusion for deformity correction, with less than 1% of patients requiring reoperation for screw removal or revision.12 However, pedicle screw malposition has the potential for serious complications, including cerebrospinal fluid (CSF) leakage, vascular injury, or neurologic injury. In contrast, the interspinous space for IFD implantation is superficial to the lamina and neural elements, minimizing the risk of incidental durotomy or neurologic injury. In addition, the midline paraspinal aponeurosis is a relatively avascular plane that decreases the likelihood of significant blood loss or vascular injury during the procedure. Therefore, an appealing aspect of IFDs is the possibility of achieving posterior stabilization and fusion without the invasiveness and potential complications of pedicle screw placement. Stabilization of segmental motion is essential to create a microenvironment suitable for osseous intervertebral fusion to occur. In contrast to pedicle screw–rod systems, IFDs require the presence of intact and robust posterior elements to achieve mechanical stability. The positioning of IFDs between the spinous processes allows them to effectively resist segmental flexion–extension moments from the posterior end of the osseous lever arm. Cadaveric biomechanical studies indicate that IFD constructs may have equivalent stiffness in flexion–extension to bilateral pedicle screw–rod constructs.13,14,15 The combination of an IFD with an anterior lumbar interbody fusion (ALIF) device may produce equivalent limitation of flexion–extension to an ALIF and bilateral pedicle screw–rod construct.16,17 IFD designs differ with regard to their means of resisting axial or torsional forces, and cadaveric biomechanical testing suggests that, in general, they are not as effective at reducing torsional or lateral bending range of motion as pedicle screw–rod constructs.13, 15 Because of their posterior location, they are also unable to effectively share axial loads transmitted through the vertebral bodies; this factor must be considered when contemplating interbody implant insertion in patients with osteoporosis or incompetent vertebral endplates. Owing to their reliance upon intact posterior elements, direct visualization and decompression of the spinal canal via laminectomy cannot be performed with IFD placement. However, IFDs afford the potential for indirect decompression of the canal and neural foramina by reducing segmental lordosis and increasing foraminal height in a manner similar to that employed by dynamic interspinous spacers.18,19 In selected patients with segmental hyperlordosis or canal

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stenosis because of redundant ligamentum flavum, these indirect reduction techniques alone may be sufficient to arrest or relieve symptomatic neurogenic claudication. A number of other potential benefits to interspinous distraction have been posited, including increased disc space height and reduced facet contact pressure.20,21 These biomechanical findings may have broad implications in the treatment of axial back pain, but little clinical data exist at this time to support the specific role of IFDs in the surgical treatment of this challenging patient population. The reliance on interspinous distraction and reduction of lordosis to achieve indirect reduction is also contrary to the goal of restoring or maintaining overall sagittal balance, and restricts the application of IFDs to shorter fusion constructs.

29.3.1 FDA Approval Status ●

IFDs may be used as supplemental fixation in addition to interbody reconstruction or pedicle screw–rod constructs to limit segmental range of motion and promote intervertebral fusion.

29.3.2 Relative Indications ●

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IFDs are an option for posterior stabilization in patients with abnormal pedicle anatomy that precludes the safe implantation of pedicle screws. IFDs may allow for indirect decompression of a stenotic spinal canal or neural foramina via spinous process distraction and a reduced segmental lordosis.

29.3.3 Contraindications ●

●

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IFDs are contraindicated in patients with defects in the pars interarticularis or any incompetence in the bone between anterior and posterior spinal elements, including advanced degenerative spondylolisthesis (grade II and above). IFDs are relatively contraindicated in the setting of regional or systemic osteoporosis that may increase the risk of spinous process fracture and/or interbody graft subsidence because of the lack of axial load sharing by the posterior instrumentation. IFDs are not intended for stand-alone use.

29.4 Relevant Anatomy and Surgical Technique The patient is placed in the prone position. The spinous processes of the affected levels are identified through manual palpation and the use of intraoperative imaging. A midline incision is made to expose the spinous processes at the correct level. The spinous processes and medial borders of the facet joints are exposed and decorticated. The interspinous ligament may either be removed or dilated without complete removal. The appropriately sized IFD is selected. The IFD is placed as anteriorly as possible and correct placement is confirmed by lateral imaging. The IFD is implanted securely into the spinous processes and manual and visual inspection of the implant is performed to confirm secure fixation.

Interspinous Spinous Process Fusion Plate Complications

29.5 Complications There have been few long-term clinical trials to date that have addressed the efficacy and safety of IFDs. Thus, true observed complication rates have yet to be established for IFD use. Risk factors for certain potential complications may be extrapolated from biomechanical testing data, such as the potential for acute fracture during implantation. To harness the potential for interspinous distraction with device implantation, a variable amount of resistance is encountered during device insertion and seating. Shepherd et al created a cadaveric model of spinous process loading in which hooks were placed through the spinous process and a tensile load to failure was applied.22 The mean load to failure was 339 N, and these loads were significantly correlated with bone mineral density as assessed by dual-energy X-ray absorptiometry. A similar trend toward increased rates of spinous fracture in patients with low bone mineral density has also been observed clinically following interspinous spacer implantation.3 Of note, failure at the junction of the spinous process and lamina was not uniformly observed, and other modes of failure included fractures of the pedicles and vertebral body. Thus, loading of the spinous processes may result in a variety of failure patterns that should be considered during IFD implantation. Due to the supraphysiological loads required to achieve interspinous process distraction, questions have been raised regarding the potential for IFDs to contribute to accelerated adjacent segment degeneration. Lindsey et al found that dynamic interspinous spacer implantation produced an isolated reduction of flexion–extension at the instrumented level without significant effects on range of motion at the cranial or caudal adjacent levels.23 In contrast, Hartmann et al found a significant increase in cranial and caudal adjacent segment range of motion following implantation of both a dynamic interspinous spacer and a rigid IFD.24 On the basis of these limited and conflicting findings, no conclusions can be drawn regarding the biomechanical effects of IFDs on the adjacent motion segments, or whether these may result in accelerated adjacent segment degeneration. There is currently insufficient data to support the proposed role of flexible IFDs for dynamic stabilization adjacent to long fusion constructs in an effort to prevent rapid adjacent segment degeneration following deformity correction. The largest reported series to date of IFD use as an adjunct to interbody fusion was published by Kim et al in 2012.25 The authors reported comparative outcomes between two nonrandomized groups either undergoing (1) posterior lumbar interbody fusion (PLIF) with CD HORIZON SPIRE (Medtronic Sofamor Danek, Memphis, TN) IFD implantation (n = 40) or (2) PLIF with pedicle screw fixation (n = 36). The indications for the PLIF + IFD group included spinal stenosis, degenerative spondylolisthesis, and disc herniation, with a mean follow-up period of 14 months (range: 12–22 months). An equivalent and statistically significant improvement in clinical outcome measures was seen in both groups at the final follow-up. Operative time (136 vs. 171 min) and estimated blood loss (479 vs. 1,131 mL) were both significantly lower in the PLIF + IFD group. Using measures of translation and segmental instability on plain flexion–extension radiography, the authors reported a significantly higher rate of adjacent segment degeneration in the PLIF + pedicle screw group (13/36, 36%) when compared to the PLIF +

IFD group (5/40, 13%). The authors also reported deep infection (3/36), dural tear with CSF leakage (2/36), epidural hematoma requiring evacuation (1/36) in the PLIF + pedicle screw group. None of these complications occurred in the PLIF + IFD group; however, a distinct set of complications including interbody graft retropulsion requiring reoperation (2/40) and inferior articular process fracture (1/40) were noted in this group. Definitive management of these complications, specifically whether or not the IFD was retained, was not discussed in detail. The next largest clinical series to date was published by Wang et al in 2006, retrospectively comparing (1) ALIF and CD HORIZON SPIRE IFD constructs (n = 21) and (2) ALIF with bilateral pedicle screw constructs (n = 11).26 Importantly, ALIF implants were augmented with bone morphogenetic proteins, and pedicle screws were placed with a mix of open (n = 3) and minimally invasive (n = 8) approaches. Consistent with the previous series, the authors again noted lower operative times and blood loss in the ALIF + IFD group. Both techniques had an excellent safety profile, as no cases of major surgical complications, implant failure, or pseudoarthrosis occurred in either group over the 1- to 12-month follow-up period. The authors concluded that IFDs are a viable substitute for pedicle screws that yielded an equivalent fusion rate when used in conjunction with a biologically augmented ALIF implant, but acknowledge that additional long-term, prospective data are needed to confirm these findings. Limited data have been published regarding the off-label use of IFDs as stand-alone devices for interspinous distraction or posterior-only fusion. Kim et al reported on eight cases of implantation of the Aspen (Lanx, Broomfield, CO) IFD for lumbar spinal stenosis as part of a larger series of 38 patients, with the remainder undergoing dynamic interspinous spacer implantation.2 Overall, 11 cases of atraumatic, radiographically occult spinous process fracture were identified in the series on subsequent computed tomography scanning. Three of these fractures were noted to heal spontaneously at 1 year, and three necessitated implant removal and laminectomy. The authors note that radiographically occult spinous process fractures may be only mildly symptomatic, but are likely responsible for a greaterthan-previously-considered proportion of suboptimal outcomes following interspinous spacer implantation. Management options for complications associated with IFD implantation vary considerably based upon the patient’s predominant symptoms, underlying indication, and presence of any associated instrumentation. For an isolated asymptomatic spinous process fracture identified incidentally on follow-up imaging without evidence of device migration or impending failure, no immediate intervention is required. Close radiographic follow-up is necessary to ensure that there are no further sequelae of the fracture, and activity modification should be encouraged until healing has occurred to prevent worsening injury or catastrophic device failure. Painful fractures of the posterior elements may benefit from initial treatment with analgesia and bracing as needed for comfort, as a significant proportion of such fractures will heal spontaneously. For painful nonunions of the posterior elements, surgical options range from fragment excision to device removal and revision instrumentation as needed to achieve sufficient stability to permit fusion. In patients with an underlying diagnosis of spinal

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Fig. 29.2 (a–e) Interspinous device implantation associated with spondylolisthesis and progressive spinal stenosis. An interspinous fusion device (IFD) was utilized in the setting of spondylolisthesis (a,b) with subsequent continued symptoms and loss of lumbar lordosis. Postoperative MRI demonstrated continued severe stenosis (c). The patient was revised with an anteroposterior (AP) instrumented fusion with correction of deformity and subsequent complete relief of neurogenic claudicatory symptoms (d,e).

stenosis, laminectomy and/or foraminotomy will also be required to achieve decompression of the neural elements in the absence of indirect decompression from interspinous distraction (▶ Fig. 29.2). Any progressive neurologic deficit prompts immediate evaluation and urgent decompression with instrumentation and fusion as needed to restore stability. Painful segmental pseudoarthroses without neurologic compromise present a therapeutic dilemma, as the risks of reoperation and potentially extensive revision instrumentation must be balanced against the patient’s willingness to attempt additional nonoperative optimization of fracture healing (including smoking cessation, nutritional supplementation, and/or bone stimulator use). Such scenarios require a thorough dialog between physician and patient to ensure informed consent prior to proceeding with an extensive revision procedure.

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29.6 Summary Interspinous spinous process fusion devices offer a less invasive alternative to pedicle screw–rod constructs for supplemental posterior fixation to achieve lumbar intervertebral fusion. Despite their relative ease of use and favorable perioperative safety profile, long-term data regarding fusion rates and clinical outcomes following IFD use are still limited.

29.7 Future Directions Well-designed prospective randomized trials comparing constructs including IFDs to other forms of spinal fixation for lumbar intervertebral fusion will continue to refine the appropriate indications for IFD use.

Interspinous Spinous Process Fusion Plate Complications

29.8 Key Points ●

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Interspinous decortication and bone grafting with or without instrumentation is a well-described technique for achieving fusion of an intervertebral motion segment. Historic approaches to interspinous process fusion have been surpassed in popularity by the availability of posterior pedicle screw–rod instrumentation. Advances in materials and minimally invasive surgical techniques have led to the development of a new generation of implantable devices for interspinous fusion. When used in combination with anterior column reconstruction, IFDs may produce equivalent biomechanical stability in flexion–extension to pedicle screw–rod constructs. The role of IFDs remains controversial, as they require intact posterior elements to achieve stability and have limited clinical data thus far regarding fusion rates and long-term outcomes.

References [1] CD HORIZON Spinal System: Summary of Safety and Effectiveness August 2003, Food and Drug Administration. Available at: http://www.accessdata. fda.gov/cdrh_docs/pdf3/K032037.pdf. Accessed July 15, 2015 [2] Kim DH, Tantorski M, Shaw J, et al. Occult spinous process fractures associated with interspinous process spacers. Spine. 2011; 36(16):E1080–E1085 [3] Kim DH, Shanti N, Tantorski ME, et al. Association between degenerative spondylolisthesis and spinous process fracture after interspinous process spacer surgery. Spine J. 2012; 12(6):466–472 [4] Wilson PD, Straub LR. Lumbosacral fusion with metallic plate fixation. Instr Course Lect. 1952; 9:52–57 [5] Holdsworth FW, Hardy A. Early treatment of paraplegia from fractures of the thoraco-lumbar spine. J Bone Joint Surg Br. 1953; 35-B(4):540–550 [6] Kaufer H, Hayes JT. Lumbar fracture-dislocation. A study of twenty-one cases. J Bone Joint Surg Am. 1966; 48(4):712–730 [7] Cobey MC. The value of the Wilson plate in spinal fusion. Clin Orthop Relat Res. 1971; 76(76):138–140 [8] Böstman O, Myllynen P, Riska EB. Posterior spinal fusion using internal fixation with the Daab plate. Acta Orthop Scand. 1984; 55(3):310–314 [9] Drummond D, Guadagni J, Keene JS, Breed A, Narechania R. Interspinous process segmental spinal instrumentation. J Pediatr Orthop. 1984; 4 (4):397–404 [10] Coe JD, Warden KE, Herzig MA, McAfee PC. Influence of bone mineral density on the fixation of thoracolumbar implants. A comparative study of transpedicular screws, laminar hooks, and spinous process wires. Spine. 1990; 15 (9):902–907

[11] Heller KD, Prescher A, Schneider T, Block FR, Forst R. Stability of different wiring techniques in segmental spinal instrumentation. An experimental study. Arch Orthop Trauma Surg. 1998; 117(1–2):96–99 [12] Hicks JM, Singla A, Shen FH, Arlet V. Complications of pedicle screw fixation in scoliosis surgery: a systematic review. Spine. 2010; 35(11):E465–E470 [13] Kaibara T, Karahalios DG, Porter RW, et al. Biomechanics of a lumbar interspinous anchor with transforaminal lumbar interbody fixation. World Neurosurg. 2010; 73(5):572–577 [14] Hartmann F, Dietz SO, Hely H, Rommens PM, Gercek E. Biomechanical effect of different interspinous devices on lumbar spinal range of motion under preload conditions. Arch Orthop Trauma Surg. 2011; 131(7):917–926 [15] Kasai Y, Inaba T, Akeda K, Uchida A. Tadpole system as new lumbar spinal instrumentation. J Orthop Surg. 2008; 3:41 [16] Karahalios DG, Kaibara T, Porter RW, et al. Biomechanics of a lumbar interspinous anchor with anterior lumbar interbody fusion. J Neurosurg Spine. 2010; 12(4):372–380 [17] Wang JC, Spenciner D, Robinson JC. SPIRE spinous process stabilization plate: biomechanical evaluation of a novel technology. Invited submission from the Joint Section Meeting on Disorders of the Spine and Peripheral Nerves, March 2005. J Neurosurg Spine. 2006; 4(2):160–164 [18] Richards JC, Majumdar S, Lindsey DP, Beaupré GS, Yerby SA. The treatment mechanism of an interspinous process implant for lumbar neurogenic intermittent claudication. Spine. 2005; 30(7):744–749 [19] Siddiqui M, Nicol M, Karadimas E, Smith F, Wardlaw D. The positional magnetic resonance imaging changes in the lumbar spine following insertion of a novel interspinous process distraction device. Spine. 2005; 30(23):2677–2682 [20] Lee J, Hida K, Seki T, Iwasaki Y, Minoru A. An interspinous process distractor (X STOP) for lumbar spinal stenosis in elderly patients: preliminary experiences in 10 consecutive cases. J Spinal Disord Tech. 2004; 17(1):72–77, discussion 78 [21] Wiseman CM, Lindsey DP, Fredrick AD, Yerby SA. The effect of an interspinous process implant on facet loading during extension. Spine. 2005; 30(8):903–907 [22] Shepherd DE, Leahy JC, Mathias KJ, Wilkinson SJ, Hukins DW. Spinous process strength. Spine. 2000; 25(3):319–323 [23] Lindsey DP, Swanson KE, Fuchs P, Hsu KY, Zucherman JF, Yerby SA. The effects of an interspinous implant on the kinematics of the instrumented and adjacent levels in the lumbar spine. Spine. 2003; 28(19):2192–2197 [24] Hartmann F, Dietz SO, Kuhn S, Hely H, Rommens PM, Gercek E. Biomechanical comparison of an interspinous device and a rigid stabilization on lumbar adjacent segment range of motion. Acta Chir Orthop Traumatol Cech. 2011; 78(5):404–409 [25] Kim HJ, Bak KH, Chun HJ, Oh SJ, Kang TH, Yang MS. Posterior interspinous fusion device for one-level fusion in degenerative lumbar spine disease: comparison with pedicle screw fixation - preliminary report of at least one year follow up. J Korean Neurosurg Soc. 2012; 52(4):359–364 [26] Wang JC, Haid RW, Jr, Miller JS, Robinson JC. Comparison of CD HORIZON SPIRE spinous process plate stabilization and pedicle screw fixation after anterior lumbar interbody fusion. Invited submission from the Joint Section Meeting On Disorders of the Spine and Peripheral Nerves, March 2005. J Neurosurg Spine. 2006; 4(2):132–136

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30 Complications of Cortical Screw Fixation Andrew Zhang and Peter G. Whang

30.1 Introduction 30.1.1 Purpose of Instrumentation Lumbar instrumentation is routinely employed as an adjunct to fusion to enhance arthrodesis rates, facilitate early mobilization, and minimize the need for prolonged postoperative immobilization. Transpedicular screws are still largely considered to be the “gold standard” technique for this purpose because they achieve fixation across all three columns and therefore represent a powerful tool for maintaining segmental stability which is well suited for applications such as deformity correction, trauma, and tumor/infection. Nevertheless, the use of pedicle screws is not without its challenges and the incidence of complications has been reported to be as high as > 50%.1,2,3,4 Su et al, in their cadaveric study, defined the “mid-lateral pars” as an area of dense cortical bone which is easily identifiable during a posterior approach to the lumbar spine even in the setting of significant degenerative disease. Because the starting point for cortical screws is located within this space, the anatomic landmarks for cortical screws are generally more consistent than those used for pedicle screws, particularly in patients with significant facet hypertrophy. With their lateral-to-medial angulation, pedicle screws inserted through an open approach require an extensile exposure, which produces a significant iatrogenic insult to the surrounding soft tissues, increases blood loss, and prolongs the operative time such that these individuals may often experience severe postoperative pain and functional disability. There is also an inherent risk of neurologic injury with misdirected implants, particularly since their trajectory places them in close proximity to both the nerve roots in the foramina as well as the thecal sac within the central canal. Furthermore, because the most superior implant of a pedicle screw construct abuts a facet joint that is not being fused, this strategy may predispose patients to the development of adjacent segment degeneration. Osteoporosis currently affects over 40 million individuals in the United States alone and is expected to become even more prevalent in the future as the elderly population continues to grow.5 Since these screws capture primarily cancellous bone in the pedicle and vertebral body, they may provide suboptimal fixation in these patients and may be susceptible to loosening over time.6,7,8,9,10,11 For this reason, various measures have been advocated to improve the purchase of pedicle screws in osteoporotic bone including incorporating more levels into the fusion, augmenting the tracts with cement or allograft, and modifying their design.12,13,14,15,16,17,18,19,20 In an attempt to avoid many of the disadvantages associated with transpedicular instrumentation, an alternative method of fixation in the lumbar spine known as “cortical” screws has also been described.21,22 The purpose of the human cadaveric study by Santoni et al was to compare the respective biomechanical profiles of cortical and transpedicular instrumentation. The authors demonstrated that cortical screws exhibited greater pullout strength which they attributed to the higher density of the bone surrounding these implants. Mobbs et al, in a clinical review of cortical screws, detailed the less invasive nature of this surgical

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technique which utilizes a novel medial-to-lateral trajectory through the vertebra. This report also included an in-depth discussion of the various benefits as well as the potential pitfalls associated with this method of segmental instrumentation. This technique utilizes a caudal–cephalad and medial–lateral trajectory in the sagittal and coronal planes, respectively, which allows the screws to secure greater purchase within the vertebra by engaging the hard cortical bone of the “force nucleus,” a term that has been used to describe the convergence point of the posterior elements (▶ Fig. 30.1 and ▶ Fig. 30.2).23 The study by Steffee et al is of historical interest because the authors describe the “force nucleus” of the vertebra which represents the “keystone” of the posterior elements and is in close proximity to the entry point for cortical screws. Because it is subjected to significant biomechanical forces, this structure is composed of hard cortical bone which is captured by these implants. Although they are shorter and smaller than pedicle screws, these implants incorporate a greater number of deeper threads, a unique design feature which maximizes the contact area at the bone–metal interface so that they may be less prone to loosening (▶ Fig. 30.3). The biomechanical characteristics of cortical instrumentation has been elucidated by multiple in vitro cadaveric studies and their greater pullout strength relative to pedicle screws was attributed to the higher mineral density of the surrounding cortical bone around the implants.21,24 As part of the investigation in Inceoğlu et al, human lumbar vertebral specimens were instrumented with both pedicle and cortical screws which were subsequently subjected to biomechanical testing. The pullout strength of the cortical implants was found to be significantly higher, which the authors suggested could be related to their medial starting point and their unique thread design which allow them to acquire greater bony purchase. Cortical screws may also confer a number of other benefits as a result of their unique trajectory. For instance, the superolateral angulation of these screws away from the thecal sac and exiting nerve root likely reduces the risk of neural injury compared to the use of transpedicular fixation. With their more inferior starting point, most cephalad screws may be positioned so their heads do not abut the facet joints which are not going to be fused, possibly decreasing the incidence of adjacent segment degeneration (▶ Fig. 30.4); similarly, the construct is not situated in the posterolateral gutters which facilitates placement of the rods and permits more graft material to be placed in this area to promote bone formation between the transverse processes. Finally, because the posterior elements do not need to be exposed lateral to the facet joints, cortical screws may be introduced in a less invasive fashion through a smaller skin incision and with less damage to the paraspinal musculature which collectively may decrease the surgical time, blood loss, and postoperative pain (▶ Fig. 30.5).

30.2 Relevant Anatomy and Surgical Technique As part of a standard posterior approach to the lumbar spine, the skin, subcutaneous tissues, and fascia are split so that a

Complications of Cortical Screw Fixation

Fig. 30.1 (a) AP and (b) lateral radiographs of a patient with an L4-L5 degenerative spondylolisthesis who was treated with cortical screws and an interbody fusion.

Fig. 30.2 Illustration of the trajectory of (a) traditional and (b) cortical pedicle fixation. A traditional pedicle screw trajectory (a) exploits a cancellous channel and terminates in cancellous bone. The cortical pedicle fixation (b) utilizes a caudal to cranial upward angulation to optimize purchase in the dense cortical bone of the pars, inferior pedicle, and vertebral endplate.

subperiosteal dissection may be performed. Using a specialized retractor, it is possible to retain many of the muscle attachments and protect the neurovascular bundle adjacent to the facet joints while still achieving clear visualization of the

critical anatomic landmarks. The typical starting point for cortical screws is at the intersection of a horizontal line along the inferior border of the transverse process and a vertical line bisecting the pars interarticularis, no more than 3 mm from its

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Fig. 30.3 Magnified view of the thread pattern of (a) cortical and (b) traditional pedicle screws. The cortical screws (a) have a unique pitch, thread design, and tapered root diameter taper to maximize cortical bone purchase at the posterior aspect of the screw and cancellous purchase at the distal tip of the screw. A traditional pedicle screw (b) has a standard root diameter and standard pitch.

Fig. 30.4 Intraoperative view demonstrating that a cortical screw tulip head is a safe distance away from the adjacent, (unfused) facet joint. Cranial is left and medial is at the top of the screen.

lateral edge (▶ Fig. 30.6). An initial pilot hole is created with a high-speed burr and its angulation may be adjusted appropriately using fluoroscopy or some other type of intraoperative imaging modality such as surgical navigation so that it is directed approximately 20 degrees laterally and 30 to 45 degrees cephalad (▶ Fig. 30.7). Once the trajectory has been verified in multiple planes, the drill is advanced through the posterior elements in a superior and lateral direction until it reaches the proper depth within the cancellous bone of the vertebral body, immediately below the level of the endplate. Because these screws must traverse dense cortical bone, it is recommended that the holes be tapped “line to line” (e.g., 5.0mm tap for a 5.0-mm-diameter screw). The tracts are palpated to ensure that there are no bony defects, the instrumentation is placed under fluoroscopic guidance after the fusion, and any decompressive procedures have been completed. In the majority of cases, the diameter of cortical bone screws is either 5.0 or 5.5 mm with lengths between 25 and 35 mm.

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30.3 Complications Inherent to any type of spinal instrumentation is the risk of malpositioned hardware which could potentially result in a neurologic injury. While this technique may be relatively safer than transpedicular fixation because the implants are directed away from the thecal sac and nerve roots, the drill, tap, or screws may still extend beyond the margins of the vertebra so that they are in continuity with the central canal, foramina, disc space, or psoas muscle. Given the location of the starting point for these implants along the lateral aspect of the pars interarticularis, it is also possible for an iatrogenic fracture to occur while the screw is being introduced into the dense cortical bone, especially if the hole is “under-tapped.”24 As with all surgical procedures, patients undergoing the placement of cortical screws as part of a lumbar fusion may develop postoperative infections or other wound complications although the incidence of these adverse events may be

Complications of Cortical Screw Fixation

Fig. 30.5 Representative example of the surgical exposure for cortical screws. In general, less exposure of the lateral compartment and intertransverse region is required with cortical screws compared to traditional pedicle screws.

Fig. 30.6 Starting points (a) and (b) trajectory of cortical screws.

Fig. 30.7 (a-c) Cadaveric anatomical model comparing the trajectory of cortical pedicle screws compared to traditional pedicle screws.

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Thoracolumbar somewhat lower because of the less extensile exposure required for their insertion. The favorable biomechanical profile of cortical fixation has been established by multiple studies, but these constructs may still be subject to implant loosening or catastrophic failure indicative of a pseudarthrosis.21,24

30.4 Diagnosis Intraoperative imaging modalities such as fluoroscopy are critical to the safety of this fixation technique and the “real-time” position of the instruments and screws should be assessed in multiple planes to minimize the risk of misdirected implants or other hardware complications. After the screw holes have been created, they should be manually probed to identify the presence of any pars fractures or cortical defects within the pedicles or vertebral bodies; in particular, it is important to recognize any loss of integrity of the medial and inferior walls in order to avoid injuries to the thecal sac and nerve roots, respectively. Neuromonitoring is another diagnostic tool that is frequently utilized during surgery to evaluate for any electrophysiologic evidence of iatrogenic nerve dysfunction resulting from screw malpositioning. For triggered electromyographic testing, a threshold of 8 mA is commonly employed, above which it is likely that the implant is safely within bone.25 However, this value was derived from normative data acquired solely from lumbar pedicle screws, so it may not necessarily be applicable to cortical fixation. Nevertheless, even if the sensitivity and specificity of adjunctive neuromonitoring for this specific method of instrumentation remains unknown, surgeons may still find it beneficial to stimulate cortical screws in an effort to detect any occult osseous violations. Anteroposterior and lateral plain radiographs are generally sufficient for routine postoperative imaging since they will show the trajectory and location of the screws, so any significant issues such as screw migration or malalignment should be readily apparent. However, if clinically warranted (e.g., worsening axial pain or new onset radiculopathy), computed tomography or magnetic resonance imaging studies may be useful for evaluating the position of the screws in multiple planes, assessing for bone formation, and identifying any fractures of the pars interarticularis. As with all spinal procedures, most cases of infection or other wound complications will be evident upon inspection of the incision, but in the absence of any obvious signs or symptoms, laboratory testing or further imaging may also serve to establish the diagnosis.

30.5 Management If a bony breach is noted intraoperatively using manual palpation, fluoroscopy, or triggered electromyogram, it is usually feasible to create another tract for a cortical screw by selecting a new starting point and adjusting the angulation of the drill appropriately. Medial and inferior defects are obviously of greatest concern because of the risk to the neural elements; however, implants that are inserted a few millimeters past the lateral cortex of the vertebral body into the psoas muscle are unlikely to give rise to a significant neurovascular injury and may therefore be safe to retain in many instances (▶ Fig. 30.8). If a cortical screw cannot reliably be placed or if a fracture of

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Fig. 30.8 (a) AP radiograph and (b) axial CT scan demonstrating lateral breach of the tip of a right L5 cortical screw. The tip of the screw lies in the iliopsoas muscle.

the pars is encountered, conventional transpedicular instrumentation may be employed as an alternative method of fixation at this level. Other postoperative complications such as surgical site infections should be addressed in the usual fashion (e.g., antibiotic therapy, irrigation, and debridement). Likewise, patients who develop clinical or radiographic findings consistent with a symptomatic nonunion may be candidates for revision fusion procedures with removal of the loose hardware, replacement

Complications of Cortical Screw Fixation with pedicle screws, and possibly even supplementation of the construct with anterior column support or other stabilizing techniques if indicated.

30.6 Summary Cortical screws may represent a less invasive method of stabilizing the lumbar spine which may also avoid many of the complications associated with transpedicular instrumentation. With their unique medial–lateral trajectory, these implants may be inserted through a less extensive exposure while achieving equivalent or possibly even superior bony fixation compared to pedicle screws, especially in the setting of osteoporosis. Even though cortical screws are still subject to various hazards, adherence to meticulous surgical technique and the proper use of diagnostic tools including intraoperative imaging modalities and neuromonitoring would be expected to minimize the risk of serious adverse events. Whenever necessary, appropriate revision strategies may be initiated to manage complications such as hardware malpositioning, neurologic injury, or construct loosening.

30.7 Future Directions Given that the utility of cortical screws is currently based largely upon in vitro biomechanical data as well as extensive clinical experience, Level 1 evidence from prospective, randomized, controlled investigations will ultimately be required to definitively establish the safety and efficacy of cortical fixation as well its proper indications; in particular, comparative studies should be performed to elucidate the salient differences between cortical and pedicle screws. In the meantime, further refinements in this surgical technique in conjunction with the more widespread implementation of intraoperative navigation systems will hopefully allow these implants to be placed in a truly percutaneous fashion.

30.8 Key Points ●

●

●

●

●

Lumbar pedicle screws are associated with a number of complications including iatrogenic injury to the surrounding soft tissues and suboptimal fixation in osteoporotic bone. Cortical screws utilize a unique caudal–cephalad and medial– lateral trajectory which allows them to engage more cortical bone and secure greater purchase within the vertebra, which has been confirmed by biomechanical testing. Because the instruments and implants are directed away from the thecal sac and nerve roots, the safety profile of cortical screws may be improved relative to that of transpedicular instrumentation. Standard techniques for identifying cortical breaches such as manual palpation, intraoperative imaging, and neuromonitoring should be routinely employed to decrease the incidence of neural injury. It may not be necessary to reposition cortical screws that extend a few millimeters past the lateral border of the vertebral body into the psoas muscle because they are unlikely to give rise to a significant neurovascular injury.

References [1] Davne SH, Myers DL. Complications of lumbar spinal fusion with transpedicular instrumentation. Spine. 1992; 17(6) Suppl:S184–S189 [2] Esses SI, Sachs BL, Dreyzin V. Complications associated with the technique of pedicle screw fixation. A selected survey of ABS members. Spine. 1993; 18 (15):2231–2238, discussion 2238–2239 [3] Su BW, Kim PD, Cha TD, et al. An anatomical study of the mid-lateral pars relative to the pedicle footprint in the lower lumbar spine. Spine. 2009; 34 (13):1355–1362 [4] Gautschi OP, Schatlo B, Schaller K, Tessitore E. Clinically relevant complications related to pedicle screw placement in thoracolumbar surgery and their management: a literature review of 35,630 pedicle screws. Neurosurg Focus. 2011; 31(4):E8 [5] Anderson GF, Hussey PS. Population aging: a comparison among industrialized countries. Health Aff (Millwood). 2000; 19(3):191–203 [6] Misenhimer GR, Peek RD, Wiltse LL, Rothman SL, Widell EH, Jr. Anatomic analysis of pedicle cortical and cancellous diameter as related to screw size. Spine. 1989; 14(4):367–372 [7] Wittenberg RH, Shea M, Swartz DE, Lee KS, White AA, III, Hayes WC. Importance of bone mineral density in instrumented spine fusions. Spine. 1991; 16 (6):647–652 [8] Okuyama K, Sato K, Abe E, Inaba H, Shimada Y, Murai H. Stability of transpedicle screwing for the osteoporotic spine. An in vitro study of the mechanical stability. Spine. 1993; 18(15):2240–2245 [9] Halvorson TL, Kelley LA, Thomas KA, Whitecloud TS, III, Cook SD. Effects of bone mineral density on pedicle screw fixation. Spine. 1994; 19(21):2415–2420 [10] Hirano T, Hasegawa K, Takahashi HE, et al. Structural characteristics of the pedicle and its role in screw stability. Spine. 1997; 22(21):2504–2509, discussion 2510 [11] Cook SD, Salkeld SL, Stanley T, Faciane A, Miller SD. Biomechanical study of pedicle screw fixation in severely osteoporotic bone. Spine J. 2004; 4(4):402–408 [12] Moore DC, Maitra RS, Farjo LA, Graziano GP, Goldstein SA. Restoration of pedicle screw fixation with an in situ setting calcium phosphate cement. Spine. 1997; 22(15):1696–1705 [13] Bai B, Kummer FJ, Spivak J. Augmentation of anterior vertebral body screw fixation by an injectable, biodegradable calcium phosphate bone substitute. Spine. 2001; 26(24):2679–2683 [14] Renner SM, Lim TH, Kim WJ, Katolik L, An HS, Andersson GB. Augmentation of pedicle screw fixation strength using an injectable calcium phosphate cement as a function of injection timing and method. Spine. 2004; 29(11):E212–E216 [15] Burval DJ, McLain RF, Milks R, Inceoglu S. Primary pedicle screw augmentation in osteoporotic lumbar vertebrae: biomechanical analysis of pedicle fixation strength. Spine. 2007; 32(10):1077–1083 [16] Pfeifer BA, Krag MH, Johnson C. Repair of failed transpedicle screw fixation. A biomechanical study comparing polymethylmethacrylate, milled bone, and matchstick bone reconstruction. Spine. 1994; 19(3):350–353 [17] Cook SD, Salkeld SL, Whitecloud TS, III, Barbera J. Biomechanical evaluation and preliminary clinical experience with an expansive pedicle screw design. J Spinal Disord. 2000; 13(3):230–236 [18] Cook SD, Barbera J, Rubi M, Salkeld SL, Whitecloud TS, III. Lumbosacral fixation using expandable pedicle screws. an alternative in reoperation and osteoporosis. Spine J. 2001; 1(2):109–114 [19] Sandén B, Olerud C, Johansson C, Larsson S. Improved bone-screw interface with hydroxyapatite coating: an in vivo study of loaded pedicle screws in sheep. Spine. 2001; 26(24):2673–2678 [20] Aldini NN, Fini M, Giavaresi G, Giardino R, Greggi T, Parisini P. Pedicular fixation in the osteoporotic spine: a pilot in vivo study on long-term ovariectomized sheep. J Orthop Res. 2002; 20(6):1217–1224 [21] Santoni BG, Hynes RA, McGilvray KC, et al. Cortical bone trajectory for lumbar pedicle screws. Spine J. 2009; 9(5):366–373 [22] Mobbs RJ. The “medio-latero-superior trajectory technique”: an alternative cortical trajectory for pedicle fixation. Orthop Surg. 2013; 5(1):56–59 [23] Steffee AD, Biscup RS, Sitkowski DJ. Segmental spine plates with pedicle screw fixation. A new internal fixation device for disorders of the lumbar and thoracolumbar spine. Clin Orthop Relat Res. 1986(203):45–53 [24] Inceoğlu S, Montgomery WH, Jr, St Clair S, McLain RF. Pedicle screw insertion angle and pullout strength: comparison of 2 proposed strategies. J Neurosurg Spine. 2011; 14(5):670–676 [25] Raynor BL, Lenke LG, Bridwell KH, Taylor BA, Padberg AM. Correlation between low triggered electromyographic thresholds and lumbar pedicle screw malposition: analysis of 4857 screws. Spine. 2007; 32(24):2673–2678

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31 Complications of Posterior Screw Fixation in Spine Surgery Pouya Alijanipour, Gregory D. Schroeder, Christie E. Stawicki, and Alexander R. Vaccaro

31.1 Introduction In modern spine surgery, the posterior approach with screwbased fixation in combination with other instrumentation, such as rods, plates, wires, and hooks is the most common fixation techniques. Screws provide rigid constructs with the advantage of early mobilization, fast healing, and high fusion rates, while obviating the need for external bracing during postoperative recovery. The use of pedicle screws (PS) provides superior biomechanical properties allowing for intraoperative manipulations in pathologies such as deformities and traumatic lesions. Depending on the regional anatomy of the spine, different options are available for posterior screw fixation. The options can vary based on the targeted fixation points in the vertebrae and also the technique of screw insertion. Therefore, numerous choices are available which can considerably differ in terms of biomechanical strength, risk of damage to osseous or soft tissue anatomic elements and long-term complication profile. Therefore, use of each type of screw should be based on considerate risk–benefit analysis along with the expertise and experience level of the spine surgeon. Use of screw-based fixation methods, like any other surgical instrumentation technique, is associated with complications, and spine surgeons should have adequate knowledge about the nature of those complications, how to prevent them, and how to deal with and manage them should they occur. The complications related to screws can be intraoperative or postoperative. Intraoperative complications can occur during surgical dissection or as a result of inappropriate hardware positioning. They consist of screw malposition, dural tears, violation of the integrity of the osseous structure in which the screws were placed, and damage to surrounding anatomical structures such as arteries, nerve roots, and the spinal cord. Late complications include loosening, pullout, breakage of the screw or rod/plate, loss of reduction, pseudarthrosis, and adjacent segment disease. This chapter consists of a review of the available literature with major focus on the potential complications of different types of screw-based fixation methods performed via posterior approach to the spine. Although most of the complications have low incidence based on the literature, the reader should have in mind the possibility of publication bias because complications are not reported as frequently as successful outcomes. Moreover, highly experienced surgeons have higher chance of publishing their results and hence the literature may not represent the reality for less experienced surgeons.

31.2 Atlantoaxial Fixation Atlantoaxial fixation can be done with traditional wiring and bone graft method or via more recent polyaxial screw fixation methods such as transarticular fixation and use of screw–plate or screw–rod constructs. The modern transarticular C1–C2

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fixation and screw–rod/plate constructs (C1 lateral mass and C2 pars or PS) have considerably improved the surgical treatment for stabilization of atlantoaxial instability with successful rates of arthrodesis (95 and 98% for transarticular and screw–rod constructs, respectively1) without requiring external immobilization with halo vest.2 These techniques provide rigid constructs with high resistance to pullout and translational and rotational forces.3 However, they are technically demanding and require precise understanding of three-dimensional anatomy of individual patients on preoperative imaging.

31.3 Malposition Malposition is the most common technical problem in screwbased fixation methods. A recent meta-analysis reported 7.1% prevalence for clinically significant malposition of transarticular C1–C2 screws with 4.1% incidence of vertebral artery injury (VAI).4 However, a separate meta-analysis on screw–rod fixation found an incidence of 2.4 and 2% for malposition and VAI, respectively.5 There is no direct prospective comparative study for these techniques. Anatomic constraints, especially high-riding VA (exists in 10–20% of the patients6,7) and narrow C2 isthmus, can influence ideal positioning of transarticular screws. Suboptimal alignment can affect positioning of the screws and this is particularly important in cases where optimal atlantoaxial alignment can be challenging, such as in obese patients.1

31.4 Vertebral Artery Injury Atlantoaxial instrumentation is challenging because of the risk of injury to several vital neurovascular structures, namely the spinal cord, VA, and the venous plexus surrounding the greater occipital and C2 nerve roots. Moreover, considerable anatomical variation can exist. Perhaps, the most serious complication is VAI, which can be asymptomatic or cause vertebrobasilar insufficiency, stroke (involving brain stem and posterior fossa regions), or even death. VAI may be acute, resulting in hemorrhage or occlusion, or lead to subacute or chronic processes such as arteriovenous fistula. A recent meta-analysis reported an incidence of 2% for VAI following screw–rod C1–C2 constructs.5 Although screw trajectory preparation or insertion (malposition) can lead to VAI (▶ Fig. 31.1), it can also occur during soft tissue dissection. Although not supported by evidence, atlantoaxial screw–rod/plate techniques and C2 PS are generally assumed to be safer than transarticular screws in terms of VAI because the insertion site and direction of the screws can be moved superiorly and medially, respectively, to avoid the course of VA.6,7,8 Anatomic variations such as high-riding VA and narrow C2 pedicles are also associated with increased risk of VAI by atlantoaxial transarticular and C2 PS.7 These variations can coexist as shown by Yeom et al who found narrow pedicles are commonly associated with high-riding VA (82%) and therefore have considerably higher risk of VA groove violation with both

Complications of Posterior Screw Fixation in Spine Surgery postsurgical angiography should be done. If intraoperative bleeding cannot be controlled, the artery should be dissected free and either repaired or ligated.

31.5 Neurologic Damage Neuropathic pain or paresthesia of C2 can occur with both screw–plate and screw–rod atlantoaxial fixation. Although the original technique of Goel and Laheri for screw–plate constructs required sectioning of C2 nerve root,16 in the modified technique (screw–rod construct) sectioning the C2 nerve is optional. Numbness is more common (6.3%) with intentional nerve sectioning but with nerve preservation and caudal retraction of C1, neuropathic pain can also occur (1.2%).5

31.6 Subaxial Cervical Spine 31.6.1 Transfacet Screws

Fig. 31.1 Misplaced left pedicle screw at C6 level invading vertebral artery canal.

transarticular and PS (71 and 76%, respectively).7 The anatomical pattern of VA groove violation depends on the screw techniques considering their difference in insertion and orientation. PS tend to violate the lateral wall of the pedicle, which is the inferomedial portion of the VA groove. Transarticular pedicles, however, tend to breach the superoposterior part of the groove.7 C1 and C2 screw techniques may need to be modified in the presence of certain challenges such as anatomical variations of the VA. For instance, if a persistent first intersegmental artery, a fenestrated VA, or a VA with abnormal course (below C1) exist, C1 lateral mass pedicle should be disregarded or the insertion point and direction should be modified accordingly.9 Another important variation for C1 lateral mass screw (LMS) placement is the presence of an arcuate foramen (ponticulus posticus) which can be mistaken as part of lamina and therefore misguide the screw insertion too superiorly and cause VAI.10 Similarly, hypoplastic pedicles or aberrant VA prevents the use of PS in C2 in at least 5 to 9% of the patients.1,11,12 A meta-analysis showed lower risk of VAI and malposition with C2 pars screws compared to PS; however, bilateral PS had a slightly better rate of arthrodesis compared with bilateral pars or pedicle–pars hybrid screws (99.8 vs. 95.6%).13 Female sex, small pedicle size, presence of C1–C2 fracture, and surgeons with inadequate experience were risk factors for misplacement of C2 PS.1,14 If the anatomical constrains do not allow for safe placement of C2 screws, short pars or intralaminar screws can be used, or the construct may bridge C2 and be extended to C3.2,5,15 If VAI occurs, the hole should be packed with absorbable hemostat material such as cellulose or with bone wax, and

Quadricortical transfacet fixation provides equal or advantageous biomechanical strength compared to LMS.17,18 Compared to PS, transfacet screws are shorter and therefore their pullout resistance may be less than PS’s. If properly placed, there is minimal risk of damage to the cord. Cadaver studies report an increased risk of inferior facet fracture (26%) during transfacet screw insertion, especially if the starting point is positioned more than 2 mm caudal to the midpoint of the lateral mass.18 A more cephalad starting point can avoid an inferior facet fracture.19 The occipital bone protuberance may physically impede proper drill orientation and more aggressive exposure of the cephalad portion of the surgical wound may be needed. If bony impingement does not allow for acceptable drill positioning, tricortical screw fixation is an option to avoid nerve-root damage, but some stability may be sacrificed.19,20 The mechanical strength of tricortical and quadricortical screws has not been compared to date. The penetration of the ventral cortex of the inferior articular facet (the last cortex penetrated) can be associated with nerveroot injury. Both tactile sensation and imaging control can help avoid drill overpenetration. If the drill and screw are directed toward the juncture of the transverse process and the lateral mass, accidental overpenetration does not cause nerve-root injury. Nevertheless, the instruments (drill bit, gauge, tap, or screw) should not pass beyond the posterior margin of the vertebral body on the lateral imaging. One pitch (2-mm) penetration beyond the most ventral cortex has been described as the safety limit for transfacet screws.21

31.6.2 Cervical Lateral Mass Screws22 Lateral mass screw technique has commonly been utilized as a standard method of posterior fixation for the subaxial cervical spine in recent years.23 LMS placement is technically simple, safe, and effective, and does not require intraoperative X-ray for screw insertion.24 It has successfully been used in combination with plates or rods to achieve stability in various pathologies of the subaxial cervical spine including degenerative conditions, inflammatory diseases, traumatic lesions, malignant conditions, and deformities.25,26

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Thoracolumbar Studies reporting the outcome of LMS techniques report high fusion rates (97%) and resolution of symptoms during short- to mid-term follow-up.23 The frequency of complications directly related to LMS instrumentation has been reported to be generally low. Based on two comparative studies,25,26 the overall intraoperative complication rate of LMS placement was comparable to wiring techniques (up to 7.1 vs. up to 6.3%, respectively).23 ▶ Table 31.1 presents the complications profile for LMS instrumentation (data have been adapted from a recent systematic review23). The prevalence of suboptimal screw placement without clinical consequences can vary (up to 42–73%) depending on the technique and radiographic assessment method.27,28 However, screw malposition requiring revision or removal is much less common and was reported as 0.38% per screw and 2.64% per

Table 31.1 The rate of complications related to cervical lateral mass screw (LMS) and pedicle screw (PS) fusion Complication

Prevalence (%) LMS

Superficial infection

3

Local hematoma/seroma

1

Dysphagia

0.6

Deep infection

0.6

Nerve-root injuries (radiculopathy, palsy, and pain)

1 (0.14 per screw)

Dural tear

1.9

Cerebrospinal fluid leakage

1.4

Cerebrovascular accidents

0

Vertebral artery damage

0

0.61 (0.15 per screw)

Lateral mass fracture

1.9

1.62

Screw or rod pullout

0.2

0.24

Screw or plate breakage

0.2

1.76 (0 plate breakage)

1.24 (0.31 per screw)

Loosening

0.8

1.73 (0.45 per screw)

Violation of facet joint

0.6

0.62

Violation of vertebral artery foramen

1.5

Pseudoarthrosis

2.67

0.87

Adjacent segment disorder requir- 0.74 ing surgery

1.19

Revision procedure (to modify or adjust the implant)

2.3

1.03

Implant removal (malposition, breakout, or loosening)

1.2

Need for supplemental fixation Source: Adapted from Coe et

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PS

al23

1.3 and Yoshihara et al.29

patient in a meta-analysis.29 The safe placement of an LMS is the superior-lateral quadrant of the lateral mass with the tip of the screw ideally positioned in the superior-lateral-ventral part of lateral mass for safety and adequate bone purchase.30,31 Precise positioning of screws is a key element in preventing complications. In fact, many studies showed the screw trajectory is the most critical factor correlating with clinical complications.24,27 For instance, violation of vertebral foramen and articular facets has been linked to lack of adequate lateralized angulation in the axial plane and low trajectory angulation in the sagittal plane, respectively.27 The spatial relationship between the posterior midpoint of the lateral mass and VA foramen can be different between cervical vertebrae as shown by Ebraheim et al. The vertebral foramen is located directly in front of posterior midpoint of lateral mass at C6, whereas at the C3– C5 vertebrae, it had a more medial position.32 These anatomical considerations may demand technique modification based on the cervical level. Several different techniques have been described for LMS and some studies suggested the complication rate is technique-dependent. Xu et al33 found the risk of nerveroot violation is lower in the An technique compared to the Magerl and Anderson techniques and Barrey et al34 recommended use of the Roy-Camille technique for C3 and C4 and the Magerl technique for C5 and C6. For C7, because of the thinness and cephalad–caudal orientation of the lateral mass, PS fixation may be more appropriate. If an LMS is going to be used at C7, shorter screws are recommendable to avoid irritation of the C8 nerve root. Furthermore, Heller et al reported the risk of facet violation was higher in the Roy-Camille technique (22.5%) compared with the Magerl technique (2.4%).28 LMS technique is generally safe in terms of VAI, although anecdotal cases of VAI and brain stem infarction were reported because of poor surgical technique.35 Bicortical bone purchase can increase the rigidity of LMS constructs by 20% compared to unicortical screws.36 However, this improvement of rigidity may clinically be negligible, and some studies recommended unicortical screws because they provide acceptable pullout resistance while avoiding the potential risk of VAI and nerve-root injury with bicortical screws.37,38

31.7 Cervical Pedicle Screws Throughout the vertebral column, the pedicles are considered the strongest part of the vertebrae. CPS provides superior biomechanical properties with higher load-to-failure resistance, lower rate of loosening at the bone–screw interface, and a higher resistance to fatigue testing compared to LMS and other internal fixation procedures.39,40 The indications of CPS have been expanded to a variety of traumatic and nontraumatic conditions with instability including kyphotic deformities, metastatic tumors, and inflammatory arthropathies.41,42,43 CPS is indicated for postdecompression instability and salvage procedures, especially when other types of internal fixation such as laminar screws, LMS, or posterior wiring are not expected to provide adequate stability.44 As shown in ▶ Table 17.1, the general safety profile for LMS and CPS screws in subaxial cervical vertebrae is similar with the majority of complications being infrequent. However, the two major complications of concern for CPS are pedicle

Complications of Posterior Screw Fixation in Spine Surgery perforation and VAI. Studies reported pedicle perforation occurs up to 30% although it usually does not have any clinical adverse effect.45 Moreover, VAI occurs infrequently, with the overall incidence being 0.15% per screw and 0.61% per patient.29 Imaging-assisted techniques, such as navigation can improve the accuracy of positioning and the safety profile of CPS.46,47 Preoperative assessment of the VA anatomy is essential. If a dominant VA exists, CPS can be substituted by other fixation techniques, such as LMS on the side of dominant artery. Nevertheless, the nondominant side may be considered for CPS if obtaining rigid fixation is a priority.48 Morphometric differences between the pedicles of cervical vertebrae have technical implications for CPS, with some studies showing that the surgery level is the most important determinant of correct positioning.45 The risk of CPS misplacement and neurovascular injury increases in smaller pedicles.29,45 Considering the smaller size of pedicles of the C3–C6 vertebrae, some surgeons recommend using CPS in C2 and C7 vertebrae and LMS in C3–C6. CPS method is technically demanding and requires considerable training experience.49 In a study of 52 consecutive cases, postoperative computed tomography (CT) evaluation revealed perforations in 12, 7, and 1% of screws during three consecutive periods of the learning experience.49 Most of the publications reflect outcomes of highly experienced surgeons who have reached the plateau in their learning curve.

31.8 Thoracolumbar Spine 31.8.1 Pedicle Screws Pedicle screw fixation is the most common technique in posterior thoracolumbar instrumentation. PS fixation achieves threecolumn fixation with superior biomechanical properties at multiple vertebrae.50,51 Therefore, considering the rigid constructs and the versatility of the technique for all spine regions, PS has gained considerable popularity in the recent decades and its indications have been expanded to numerous pathologic conditions including fractures, degenerative disorders, deformities, infections, tumors, and iatrogenic instabilities.

31.8.2 Malposition Correct positioning of PS is essential to avoid encroachment of the spinal canal (▶ Fig. 31.2) and its content or injury to the extracanal neurovascular structures. Misplaced PS does not

achieve the expected fixation and therefore may not contribute sufficiently to construct stability. Misplacement is the most common complication of PS with an overall incidence of 8.7% according to the meta-analysis by Kosmopoulos et al.52 However, malposition can vary with the surgical technique. The accumulative incidence of screw malposition in studies on computer-assisted technology is lower than (0–11% for CT guided navigation and 8–19% for fluoroscopy guided navigation) those using freehand techniques (6–31%) and fluoroscopy (15–72%).53 The malposition pattern can be different between freehand and navigation-based techniques. Freehand techniques tend to misplace PS medially. In the navigation-based techniques, lateral malposition is more common.53 Comparative studies reported improved accuracy, with intraoperative image-guidance technologies reporting malposition rates of 31.9, 15.7, and 4.5% for conventional fluoroscopy, two-dimensional, and three-dimensional fluoroscopic navigation, respectively.54 Nevertheless, sophisticated technologies can be technically challenging, and highly successful outcomes were achieved with freehand techniques by experienced surgeons.55,56 Despite relatively high incidence rates of misplaced PS reported by some studies, the incidence of PS malposition causing clinical consequences does not seem to be as high. A single institutional retrospective study of patients undergoing thoracic PS insertion using freehand technique showed an incidence of 6.2% of moderate cortical perforation (defined as central line of the pedicle being out of the outer cortex of the pedicle wall) and 1.7% of the screws breeched the medial wall. However, there was no incidence of neurovascular or visceral complications during the 10-year follow-up period.55 Satisfactory outcomes can be obtained with suboptimal PS positioning depending on the direction of misplacement. Moreover, the impact of a breech depends on the direction of the breech and also the spinal region. Suboptimal positioning of screws in a lateral or superior direction is expected to have less chance of causing clinical consequences outside of the cervical region compared to medial or inferior breeches, which may encroach on the spinal cord and nerve roots, respectively. Intraoperative electromyogram monitoring can serve as a sensitive screening tool for detection of screw malposition that jeopardizes the integrity of nerve roots or the spinal cord. Adequate knowledge of the regional anatomy and morphometric parameters of the vertebrae, thorough preoperative imaging assessment, respect of anatomical landmarks during screw application, and orderly performance of all steps of the

Fig. 31.2 Malposition of left lumbar pedicle screw at L4 level with invasion of the spinal canal.

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Thoracolumbar surgical technique are key elements in safe PS placement. It is important to consider that characteristics of the pedicle such as its thickness, length, cross-sectional shape, level of projection in the sagittal plane (with respect to the height of vertebral body), and angle of projection in the coronal, sagittal, and axial planes (with respect to the axes of vertebral body/spinous process) depend on the region of the spine. Once the initial trajectory is prepared, the boundaries of the trajectory should be carefully inspected using a tactile probe. This step should be repeated after tapping and before screw insertion. However, it may still not detect all pedicle wall breeches and therefore confirmation of PS position should also be performed radiographically. The probe position can be directly visualized during surgery in cases of open laminoforaminotomy. Firm screw torque during insertion, gentle movement of the vertebra with progression of the screw, and no change of the screw direction during insertion are indirect clues that the screw is within the pedicle wall boundaries. Real-time intraoperative neuromonitoring has considerably improved recently and is now common for PS insertion particularly in severe spinal disorders and deformities.57 Somatosensory evoked potentials (SEP) and motor evoked potentials (MEP) monitor the integrity of sensory pathways (posterior column) and motor pathways (anterior column), respectively, allowing for continuous neural monitoring. SEP is a sensitive method, but false negative results may happen in anterior spinal artery injuries because it is relatively less sensitive to anterior cord injuries.58 Modern multimodal intraoperative neuromonitoring protocols consist of a combination of SEP, MEP, transcranial (tcMEP), and electromyography monitoring. Breech of the medial pedicle wall at the level of the spinal cord does not necessarily lead to spinal cord injury (SCI) depending on the spinal region. A safety zone can be defined in which the possibility of a symptomatic injury to the dura mater or spinal cord is still low following a medial pedicle wall breech. This explains why a misplaced PS does not always lead to clinically relevant adverse consequences. Although Gertzbein and Robbins considered a mediolateral safe zone of ±2 mm surrounding the borders of the pedicle in the thoracic region,59 recent publications have extended this safety zone up to 2 and 4 mm on the medial and lateral border of the thoracic pedicles, respectively.60 Revision surgery for misplaced surgery should be meticulously planned. The surgeon may consider application of more sophisticated image-guidance techniques such as navigation or intraoperative CT scan. A revised PS may require a new screw starting site and new trajectory, which should be planned preoperatively. The surgeon should anticipate inadequate bone purchase for which solutions need to be available. The rescue procedures include use of a larger size screw, skipping a level, extension of the fusion length, augmentation techniques using poly methylmethacrylate (PMMA; either preinsertion injection of PMMA or use of perforated screws) and recently introduced self-expanding screws.

31.9 Neurological Complications Neurological complications can occur because of direct injury during instrumentation or indirectly as a consequence of

198

manipulation maneuvers (such as reduction of fractures, correction of deformities, or overdistraction of spine). The incidence of clinically relevant nerve-root impingement because of PS misplacement was reported to be 0.19% per PS in a meta-analysis, with only 0.6% patients requiring revision surgery because of neurological consequences.61 SCI is rare and none of the recent studies have reported SCI although there is high possibility for SCI being underreported in the literature.61 Nerve-root injury may lead to self-limiting transient neurapraxia (more common) or permanent nerve dysfunction. Newonset postoperative pain or neurologic deficit warrants thorough clinical and radiologic assessment for hardware-related impingement. Nerve-root injuries in the thoracic spine are most commonly unremarkable and compared to the lumbar region, revision of thoracic PS because of thoracic nerve-root impingement is less commonly reported. Neurological damage may be recognized intraoperatively by neuromonitoring techniques. If noticed postoperatively, especially a progressive neurological deficit, immediate imaging (magnetic resonance imaging, CT, or CT myelogram) should be done to identify the presence of misplaced instrumentation.

31.10 Dural Tear and Cerebrospinal Fluid Leak Inadvertent lacerations of dura mater can happen during screw trajectory preparation or insertion. According to the recent meta-analysis by Gautschi et al, dural lesions had an incidence of 0.18% (0–2%) per PS although not all dural tears were clinically symptomatic.61 Dural tears usually happen if a PS is misplaced too inferiorly or too medially. If a dural tear does occur, a primary repair of the tear is preferred, and meticulous watertight closure of the fascia is required. If the durotomy is irreparable, fibrin sealants and patches may be used.

31.11 Vascular Complications Because of the proximity of critical vascular structures to the thoracolumbar spine, inadvertent vessel damage during or after the surgery can potentially occur. Despite some small case series and anecdotal reports, vascular complications following PS insertion are uncommon.61,62 These lesions include perforation, rupture, thrombosis, and occlusion. They may be asymptomatic, cause acute symptoms, or lead to late manifestations as part of an erosive process with aneurysm or pseudoaneurysm formation, especially with regard to pulsatile arterial vessels. The azygos vein and inferior vena cava are on the right side, the aorta (thoracic and upper lumbar area) and hemiazygos vein are on the left side, and the common iliac vessels (lumbar area) are within 5 mm of the anterior vertebral cortex. If intraoperative vascular injury occurs, emergent surgical exploration with repair or embolization is often required. The management of asymptomatic patients with screws in contact with the vascular structures identified postoperatively is often unclear. A few publications reported early and late postoperative erosion of arterial vessels by misplaced screws61,64,65 however, another publication reported that

Complications of Posterior Screw Fixation in Spine Surgery 4.9% (33/686) of all thoracolumbar PS are in contact with great vessels, and one-third of these screws had no clinical consequences (mean follow-up of 44 months).66 The authors stated that revision of asymptomatic screws in contact with, but not penetrating or deforming major vessels, is not crucial and the risks of revision procedure should be verified against its potential benefits.66 To avoid PS overpenetration, several technical details should be respected. Preparation of the pilot trajectory (drilling or probing) should be limited to slightly longer than the pedicle length to avoid violation of anterior vertebral cortex. Biomechanically, if the screw purchases the inner cortex of the pedicle, increasing its length will not increase its stability.67 The optimal screw length should stop at a distance of 20% of the anteroposterior diameter of the vertebral body from the anterior vertebral body cortex.67

31.12 Pedicle Fracture The incidence of pedicle fracture during screw insertion is quite low (less than 0.5%68) and can vary with the technique, experience level of the surgeon, and patient population. Violation of pedicle or vertebral body may occur with oversized drills or taps during trajectory preparation, application of excessive torque force, or change of screw direction during insertion of a PS. Low-quality bone (metabolic bone diseases and osteoporosis) can lead to loss of tactile feedback at the time of screw insertion. Pediatric PS can be oversized up to 20% because plastic expansion of the pedicles is expected. If PS purchase seems robust enough even though fracture has been noted, the screw can be maintained and incorporated into the final construct. Excessive forces during reduction maneuvers or rod connection should be avoided because it may cause screw pullout, construct failure, or vertebral body fracture. Other intraoperative mechanical complications such as loosening, pullout, screw breakage, and construct failure (such as rod–screw disconnection) are uncommon but can potentially occur. In a review of recent literature reporting results of 6,972 PS, loosening occurred in 0.54%68 and pullout was reported to occur in up to 0.7%.69 Others reported screw breakage of up to 2.8%,70 but based on the recent literature it seems that the incidence is decreasing considerably.68 Undersized PS or failure to insert the screw in the prepared track can lead to intraoperative screw loosening. Screw breakage may happen because of nonunion or because of inadequate anterior column support leading to fatigue of the implant. If the broken screw jeopardizes neurovascular structures, removal with specific instruments, osteotomy, or even an anterior approach in cases of migration might be required.

31.13 Infection Use of implants is associated with potential risk of intraoperative bacterial colonization and biofilm formation, which in vulnerable hosts with an insufficiently competent local or systemic defense system can progress into a true infection. Complex interaction of multiple risk factors including patient-related, procedure-related, and

perioperative care–related elements determines the risk of infection. Patient-related risk factors include, but are not limited to, age, underlying medical conditions (such as diabetes, nephropathies, immunodeficiency), comorbidity indices (such as American Society of Anesthesiology or Charlson Comorbidity Index), obesity, smoking, previous surgery, history of infection in the same area, and chronic skin diseases (such as psoriasis). However, modifiable risk factors should be optimized before surgery. Adherence to strict intraoperative and perioperative preventive protocols such as skin preparation, draping techniques, strict sterility, antibiotic prophylaxis, wound irrigation, and appropriate postoperative wound care can considerably decrease the risk of infection. Major recognized surgery-related risk factors are the posterior approach, presence of instrumentation, blood loss especially associated with blood transfusion, longer duration of surgery, and concomitant autologous bone graft harvest procedure. According to a recent review, irrigation with dilute betadine was the only intraoperative intervention shown to be able to decrease the risk of spine surgical infection based on evidence of moderate strength.71 However, many other common intraoperative preventive strategies are not based on robust evidence.

31.14 Cortical Bone Trajectory Pedicle Screws This is a recently introduced technique consisting of using small diameter screws into the lumbar pedicles starting from the medial part of pars interarticularis with an inferomedial to superolateral direction. Cadaver studies demonstrated cortical bone trajectory (CBT) has strong bone–screw interface and high pullout resistance because of cortical bone purchase at the pars interarticularis and the base of pedicle.72 However, little clinical evidence regarding cortical bone trajectory pedicle screws (CBT-PS) exists. A randomized trial on patients undergoing single-level posterior lumbar interbody fusion found a similar nonunion rate for CBTPS and simple PS based on dynamic radiographs (11 and 13%, respectively) and CT (8 and 13%, respectively) at 1-year follow-up. No complications happened during this study.73 A small-size case series with 6-month follow-up used CBT-PS to treat single-level symptomatic adjacent segment lumbar disease without removal of prior hardware (simple PS) and reported no complications at 6-month follow-up.74 Nevertheless, another small-size case series of eight patients undergoing primary degenerative lumbar fusion found a high rate of complications including loosening (60%), and loss of reduction (50%) especially in patients without interbody support and revision surgery (38%).75 Based on cadaver studies, the stiffness of CBT-PS to axial loading is inferior to PS with an intact disc, but stiffness of both screw types was equal when a transforaminal interbody fusion device was added.76 Loosening may be because of stiff and oblique constructs with shorter screws (CBT-PS is usually shorter than traditional PS), which increase the shear bending stress.75 Nevertheless, large-scale studies with long-term follow-up are required for better understanding of this recent technique.

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31.15 Pedicle Screws in Pediatric Scoliosis Surgery Use of PS in pediatric deformity correction merits specific considerations. First, pedicle dimensions are smaller in immature spine, but the orientation remains unchanged throughout life. Second, pediatric deformities commonly involve the thoracic spine with small endosteal pedicle width. However, pedicles can expand during screw insertion (plastic deformation) and their growth occurs mostly on the lateral side.77 Third, moderate to severe curves consist of dysmorphic vertebrae with distorted anatomy in which the pedicles on the concave side are thinner, sclerotic, and dysplastic. Lastly, the spinal cord is in close proximity to the medial wall of the pedicles on the concave side of the curve.68,78 Therefore, misplaced screws on the concave side of the apical vertebrae of thoracic curves have higher possibility for clinical consequences (such as epidural hematoma, dural tear, or cord encroachment) than those on the convex side of nonapical vertebrae in lumbar curves. Despite technical challenges of PS placement in the pediatric spine, a recent review of literature shows that the accumulative reported accuracy of PS in the pediatric population is comparable to the adult population (94.6 vs. 91.3%, respectively).52,79 The incidence of screw-related complications is generally low in the adolescent scoliosis.68 Malposition varies between 1 and 20% depending on its definition and the postoperative imaging surveillance protocol. Low threshold for acquisition of postoperative CT scan leads to detection of many misplaced screws with no clinical consequences. Protocols consisting of universal postoperative CT scanning demonstrate a 15.7 versus 1.8% malposition rate if the CT was ordered only when abnormal findings were perceived on the postoperative plain radiographs. However, the rate of revision surgery in the same study because of screw malposition was only 0.6%.68 In a multicenter report of pediatric scoliosis cases of the Scoliosis Research Society Morbidity and Mortality database, Reames et al found the rate of new neurologic deficits following thoracic and lumbar PS was similar (0.5 vs. 0.6%, respectively), but the new deficits associated with thoracic and lumbar screws occurred at different levels (spinal cord and nerve roots, respectively).80 The use of PS-only constructs in this study was associated with half the risk of new neurologic deficits compared with surgical instrumentation using anterior screw-only and posterior wire–only constructs. The surgical complication rates in neuromuscular scoliosis are generally higher than adolescent scoliosis.80 This could be because of the complexity of the procedure and severity of comorbidities in these patients. A meta-analysis reported the following screw-related complications for neuromuscular scoliosis: revision surgery because of removal or extension 7.9%, misplacement 4.8%, implant breakage 4.6%, loosening 2.4%, and cutout/pullout/migration 2.4%.81 The pooled risk of neurologic complications was 3%, yet screw-related neurologic deficits were not specified. Patient-related factors such as age, type, and severity of neuromuscular disorders (e.g., spastic nonambulatory cerebral palsy, severe myelomeningocele associated with paralysis) and surgery-related factors (such as adequacy of stabilization and spino-pelvic fixation) interact to determine the risk of postinstrumentation complications such as infection, fractures, pseudoarthrosis, and construct failure.81,82,83,84

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31.16 Facet Screws Facet screws can be placed via two methods. The translaminar facet screw (TLFS) was described by Magerl and is inserted from the contralateral side of the spinous process of the cephalad vertebra, passing through the lamina and the facet joints and ending at the base of the ipsilateral transverse process of the caudal vertebra.85 The transfacetopedicular screws (TFPS) are inserted at the transitional zone between the pars interarticularis and the inferior articular process of the cranial vertebra and are directed toward the medial root of the pedicle of the caudal vertebra (Boucher technique86). Biomechanical studies show similar stability with both TLFS and TFPS types of facet screws.87 TLFS and TFPS (alone or in combination with PS) provide constructs with similar or slightly lower rigidity compared to PS fixation only.87,88,89 However, with the TLFS technique, the screw may violate the inner lamina cortex (11% based on postoperative CT90), which is asymptomatic most of the times but has the potential risk of injury to the neural elements. The published studies report a 4 to 11% incidence of a neurologic deficit with TLFS91,92,93. Moreover, late displacement of the screw with violation of the inner lamina requiring screw removal can occur especially in patients with low bone quality.94 The nonunion rate ranges from 2 to 9% with various interbody fusion techniques.95 Complications such as loosening and infection are similar to other screw fixation methods and occur infrequently (1–2%).91,95 A prospective study comparing long-term outcomes of 40 patients with TLFS and 37 patients with PS found an increased risk of nonunion (18 vs. 3%, respectively) and reoperation (32.5 vs. 27%, respectively) for TLFS. Moreover the revision surgery for translaminar screws was generally performed earlier than PS fixation (3.5 vs. 6.3 years, respectively).96 Nevertheless, in a prospective observational study of patients with limited degenerative lumbar spine disease, patient-rated outcomes at 2-year follow-up, the complication rates, and the requirement for revision surgery were similar between both groups.97 The study, however, reported a statistically insignificant higher incidence of pseudarthrosis for translaminar screws and a higher incidence of adjacent segment disease in the PS group. In a retrospective study with more than 5 years of follow-up, the nonunion and loosening rate of posterior fixation with translaminar screws were 6 and 3%, respectively.98 In this case series, revision surgery for painful pseudarthrosis was performed in 5% of the patients. Painful root irritation was reported in 2% of the patients, whereas neurologic deficit and dural tear occurred in less than 1%.

31.17 Conclusion Screw-fixation techniques are the most commonly applied instrumentation for modern posterior spine surgeries. For each spine region, various options are available, which are selected depending on the anatomy of the patient, the pathology, the availability of resources, and surgeon experience. The spine surgeon should be cognizant of the potential intraoperative and postoperative complications of the screwrelated techniques and have deep familiarity with several alternative strategies for prevention and management of those complications.

Complications of Posterior Screw Fixation in Spine Surgery

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pedicles for adjacent-segment lumbar disease using CT image-guided navigation. Neurosurg Focus. 2014; 36(3):E9 Glennie RA, Dea N, Kwon BK, Street JT. Early clinical results with cortically based pedicle screw trajectory for fusion of the degenerative lumbar spine. J Clin Neurosci. 2015; 22(6):972–975 Perez-Orribo L, Kalb S, Reyes PM, Chang SW, Crawford NR. Biomechanics of lumbar cortical screw-rod fixation versus pedicle screw-rod fixation with and without interbody support. Spine. 2013; 38(8):635–641 Zindrick MR, Knight GW, Sartori MJ, Carnevale TJ, Patwardhan AG, Lorenz MA. Pedicle morphology of the immature thoracolumbar spine. Spine. 2000; 25(21):2726–2735 Liljenqvist UR, Link TM, Halm HF. Morphometric analysis of thoracic and lumbar vertebrae in idiopathic scoliosis. Spine. 2000; 25(10):1247–1253 Ledonio CG, Polly DW, Jr, Vitale MG, Wang Q, Richards BS. Pediatric pedicle screws: comparative effectiveness and safety: a systematic literature review from the Scoliosis Research Society and the Pediatric Orthopaedic Society of North America task force. J Bone Joint Surg Am. 2011; 93(13):1227–1234 Reames DL, Smith JS, Fu K-MG, et al. Scoliosis Research Society Morbidity and Mortality Committee. Complications in the surgical treatment of 19,360 cases of pediatric scoliosis: a review of the Scoliosis Research Society Morbidity and Mortality database. Spine. 2011; 36(18):1484–1491 Sharma S, Wu C, Andersen T, Wang Y, Hansen ES, Bünger CE. Prevalence of complications in neuromuscular scoliosis surgery: a literature meta-analysis from the past 15 years. Eur Spine J. 2013; 22(6):1230–1249 Nectoux E, Giacomelli MC, Karger C, Herbaux B, Clavert JM. Complications of the Luque-Galveston scoliosis correction technique in paediatric cerebral palsy. Orthop Traumatol Surg Res. 2010; 96(4):354–361 Phillips JH, Gutheil JP, Knapp DR, Jr. Iliac screw fixation in neuromuscular scoliosis. Spine. 2007; 32(14):1566–1570 Parsch D, Geiger F, Brocai DR, Lang RD, Carstens C. Surgical management of paralytic scoliosis in myelomeningocele. J Pediatr Orthop B. 2001; 10 (1):10–17 Magerl FP. Stabilization of the lower thoracic and lumbar spine with external skeletal fixation. Clin Orthop Relat Res. 1984(189):125–141 Boucher HH. A method of spinal fusion. J Bone Joint Surg Br. 1959; 41-B (2):248–259 Kim S-M, Lim TJ, Paterno J, Kim DH. A biomechanical comparison of supplementary posterior translaminar facet and transfacetopedicular screw fixation after anterior lumbar interbody fusion. J Neurosurg Spine. 2004; 1(1):101–107 Ferrara LA, Secor JL, Jin B-H, Wakefield A, Inceoglu S, Benzel EC. A biomechanical comparison of facet screw fixation and pedicle screw fixation: effects of short-term and long-term repetitive cycling. Spine. 2003; 28(12):1226–1234 Slucky AV, Brodke DS, Bachus KN, Droge JA, Braun JT. Less invasive posterior fixation method following transforaminal lumbar interbody fusion: a biomechanical analysis. Spine J. 2006; 6(1):78–85 Shim CS, Lee S-H, Jung B, Sivasabaapathi P, Park S-H, Shin S-W. Fluoroscopically assisted percutaneous translaminar facet screw fixation following anterior lumbar interbody fusion: technical report. Spine. 2005; 30(7):838–843 Aepli M, Mannion AF, Grob D. Translaminar screw fixation of the lumbar spine: long-term outcome. Spine. 2009; 34(14):1492–1498 Montesano PX, Magerl F, Jacobs RR, Jackson RP, Rauschning W. Translaminar facet joint screws. Orthopedics. 1988; 11(10):1393–1397 Jacobs RR, Montesano PX, Jackson RP. Enhancement of lumbar spine fusion by use of translaminar facet joint screws. Spine. 1989; 14(1):12–15 Park SH, Park WM, Park CW, Kang KS, Lee YK, Lim SR. Minimally invasive anterior lumbar interbody fusion followed by percutaneous translaminar facet screw fixation in elderly patients. J Neurosurg Spine. 2009; 10 (6):610–616 Best NM, Sasso RC. Efficacy of translaminar facet screw fixation in circumferential interbody fusions as compared to pedicle screw fixation. J Spinal Disord Tech. 2006; 19(2):98–103 Tuli J, Tuli S, Eichler ME, Woodard EJ. A comparison of long-term outcomes of translaminar facet screw fixation and pedicle screw fixation: a prospective study. J Neurosurg Spine. 2007; 7(3):287–292 Grob D, Bartanusz V, Jeszenszky D, et al. A prospective, cohort study comparing translaminar screw fixation with transforaminal lumbar interbody fusion and pedicle screw fixation for fusion of the degenerative lumbar spine. J Bone Joint Surg Br. 2009; 91(10):1347–1353 Humke T, Grob D, Dvorak J, Messikommer A. Translaminar screw fixation of the lumbar and lumbosacral spine. A 5-year follow-up. Spine. 1998; 23 (10):1180–1184

Interspinous Spacer Complications

32 Interspinous Spacer Complications William Ryan Spiker and Alan S. Hilibrand

32.1 Introduction

32.3 Anatomic Considerations

Degenerative lumbar spinal stenosis is a common and disabling condition in the elderly population. Symptoms include leg and or back pain and dysfunction that is worse with standing or walking and improved with flexion. Diagnosis requires both clinical symptoms and evidence of narrowing of the lumbar spinal canal on imaging studies. In the absence of a progressive neurologic deficit or cauda equina syndrome, treatment usually begins with nonoperative modalities, such as nonsteroidal antiinflammatory drugs, physical therapy, and/or epidural steroid injections. Surgery is indicated in patients that fail appropriate nonsurgical management. Surgery is performed with the goal of reducing positional buttock and leg pain (neurogenic claudication) but may not reduce back pain because of degenerative disease. Surgical options for neurogenic claudication caused by spinal stenosis without significant instability or deformity include open laminectomy, open laminotomy, microendoscopic laminotomy, and interspinous spacer placement or so-called “interlaminar stabilization.” Although laminectomy (with fusion for instability) remains the gold standard treatment, a desire to reduce the amount of tissue destruction, minimize blood loss, decrease recovery time, and minimize adjacent level pathology has propelled further research into less invasive surgical treatments. Interspinous spacers are a less-invasive surgical treatment option for patients with intermittent neurogenic claudication caused by spinal stenosis. Interspinous spacers are placed between the spinous processes at the level of stenosis to limit extension and provide interlaminar stabilization. This local kyphosis/flexion enlarges the spinal canal at that level and mimics the symptomatic relief of flexion in this patient population. In this review, we will discuss the indications, techniques, and outcome data of interspinous spacers in an attempt to better understand and avoid the complications of this relatively new surgical option.

Lumbar spinal stenosis is often the result of a degenerative process that involves the intervertebral disk, facet joints, and ligamentum flavum (see ▶ Fig. 32.2 and ▶ Fig. 32.3). This process can lead to nerve compression in the central spinal canal, the lateral recess, and the neuroforamina at one or multiple levels. The symptoms of neurogenic claudication are usually because of central stenosis, but coexisting radicular complaints may be caused by lateral recess stenosis or compression of the exiting nerve root in the neural foramen. Interspinous spacers are placed through a posterior incision with the patient in a prone or lateral decubitus position. Some data suggest that lateral positioning during insertion avoids the extension moment of prone positioning and allows more focal kyphosis at the instrumented level. After skin incision, the supraspinous and interspinous ligaments are exposed; for some devices, such as the X-Stop, the supraspinous and interspinous ligaments are preserved. For others, like the Coflex, they are excised at the involved level for appropriate placement. The devices are then secured to the spinous process(es), limiting local extension by resisting compression of the posterior elements. The ability of the spacer to resist compression is dependent on the bone quality of the spinous process. Thus, conditions that may predispose to fracture of the spinous process, such as osteoporosis, must be considered prior to implant placement.

32.2 Food and Drug Administration Approval Status Several different interspinous spacers have been approved for use in the United States to treat intermittent neurogenic claudication caused by lumbar spinal stenosis at one or two levels. Interspinous spacers are generally not approved for use in cases with significant instability (fracture or unstable spondylolisthesis), deformity (scoliosis > 25 degrees), ankylosis or previous fusion of the affected level, severe osteoporosis, stenosis at greater than two levels, or cauda equina syndrome. Interspinous devices currently in clinical use in the United States and Europe include the Wallis device, Device for Intervertebral Assisted Motion (DIAM), Coflex, Extensure H2, Aperius, and X-Stop (see ▶ Fig. 32.1). Proposed indications for these devices include treatment of lumbar spinal stenosis in patients with grade I degenerative spondylolisthesis, mild scoliosis, discogenic low back pain, recurrent lumbar disc herniation, and facet syndrome.1,2

32.4 Mechanism Interspinous spacers obtain the local kyphosis through several different designs. Static spacers are noncompressible and act as a posterior extension block. The Wallis device is secured to the adjacent spinous processes by synthetic straps, whereas the Extensure H2 is secured only to the cranial spinous process. Dynamic spacers allow motion preservation through implant design (U-shaped spring mechanism of Coflex) or material properties (elastomeric DIAM device). Some devices like the Coflex require more ventral placement to take advantage of the strong laminar bone to limit extension and providing an opportunity for a central decompression. The details of the surgical technique for any interspinous device must be reviewed in detail prior to implantation to limit complications. It is important to note that interspinous spacers do not prevent all motion at the treated level,3 allowing rotation and lateral bending of the spine.4 They create focal flexion at the level of stenosis,4 mimicking the symptomatic relief that flexion provides to patients with neurogenic claudication. Studies have shown that by maintaining segmental flexion, spacers increase the spinal canal area by 18% and the foraminal area by 25%.5 This indirect decompression has been confirmed in clinic studies with 6-month follow-up.6 Biomechanical studies have also noted at least two other possible mechanisms of pain relief from interspinous spacers, decreasing compressive forces across the intervertebral disc

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Fig. 32.1 (a-d) Illustrations of different interspinous spacers.

and the facet joints. Placement of an interspinous spacer has been shown to decrease intradiscal pressure by approximately 50% in extension, 40% in a neutral position, and 30% in flexion.7 Although interspinous spacer placement has not been shown to have any significant effect on disc height,8 animal models have showed that intervertebral distraction can reverse the degenerative changes caused by compression. Facet joints are common pain generators that have been historically difficult to treat. By decreasing the load across the facet joint up to 55%, interspinous spacers address facet joint pathology without the need for spinal fusion.

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32.5 Interspinous Spacer Outcomes and Complications Interspinous spacers have risks common to all posterior lumbar spine surgeries and unique complications because of the biomechanical function of the spacer. Adverse events common to all posterior lumbar spine surgery include the following: wound infections, medical complications (blood clots, heart attack, stroke), need for blood transfusion, neurologic injury, need for revision surgery, and worsening of leg and back symptoms.

Interspinous Spacer Complications Because spacer placement can be performed through a small incision with minimal soft tissue dissection and relatively short operative times, some complications (such as wound infections and blood clots) may be less frequent with spacer placement than with classic open decompression techniques. Further, surgical placement of most interspinous spacers does not require direct decompression of the spinal canal, and the risk of cerebral spinal fluid leak or nerve damage from direct nerve root injury is minimal in these cases. Unique complications associated with interspinous spacer insertion include spinous process fracture and device dislocation. However, to fully understand the risk profile of any surgical intervention, a thorough understanding of the outcomes data is paramount. The X-stop was the first interspinous device to be approved by the Food and Drug Administration (FDA) and has been extensively studied. In the first prospective randomized trial on the device, Zucherman et al9 compared 100 patients treated with an X-Stop to 91 patients treated with nonoperative modalities. Strict inclusion criteria were used for the study, including age > 50 years, intermittent neurogenic claudication resolved by sitting, radiographic spinal stenosis, and failure of 6 months of

Fig. 32.2 Lumbar spinal stenosis. Illustration of spondylolisthesis with disc bulge, hypertrophic ligamentum, etc.

nonoperative treatment. At 2-year follow-up, they found that the operatively treated patients had superior outcomes to the nonoperatively treated patients that were statistically significant. Using the Zurich Claudication Questionnaire (ZCQ), they reported that 60% of patients treated with an X-Stop had improvement in symptom severity and physical function. In another prospective randomized trial, Anderson et al10 evaluated the X-Stop in patients with grade I degenerative spondylolisthesis and spinal stenosis. Using the ZCQ and SF-36, they found clinical improvement in 63% of X-Stop patients and only 13% of nonoperatively treated patients. Importantly, the procedure was not associated with progression of spondylolisthesis in this study. With an understanding that interspinous spacers are likely more effective than nonoperative modalities for patients with neurogenic claudication, a recent prospective, randomized controlled trial compared the Coflex interspinous spacer with the “current standard of care”—a posterior decompression and instrumented fusion.11 This study focused on one- and twolevel lumbar spinal stenoses with neurogenic claudication in patients that failed nonoperative treatment. In total, 322 patients were included in the study and 96% of participants completed 2-year follow-up. The study revealed expected perioperative findings of decreased length of surgery, decreased blood loss, and decreased length of hospitalization in patients treated with the Coflex device. Clinical outcomes such as improvements in functional outcomes scores and need for further spine interventions trended to be superior in the Coflex group, but did not reach statistical significance. Patient satisfaction scores and radiographic preservation of adjacent level biomechanics were both found to be statistically superior to fusion. A similar prospective randomized study compared the Coflex device to lumbar decompression in the setting of lumbar stenosis.12 With 2-year follow-up on 62 patients, they were unable to show any significant improvement in clinical outcomes in patients treated with Coflex placement over decompression alone. Taken together, these studies suggest that the Coflex device has similar outcomes to traditional surgical decompression with some measurable benefits over instrumented fusion for patients with stenosis also requiring surgery, at least at short-term follow-up. Data on the effectiveness of other interspinous spacers have failed to show superiority to traditional surgical decompression. Multiple studies13,14 report good to excellent outcomes with DIAM device insertion, but fail to prove any improvement beyond what would be expected from the decompression Fig. 32.3 Lumbar spinal stenosis—illustrations of (a) sagittal and (b) axial cuts.

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Thoracolumbar alone. Similarly, a prospective study of 36 patients compared patients with lumbar stenosis treated with the Aperius device to those treated with a traditional decompression. At 2-year follow-up, outcomes assessed with the ZCQ and Oswestry Disability Index (ODI) showed consistently worse results in the Aperius cohort with revision surgery necessary in approximately 20% of patients.15 With most studies showing similar clinical outcomes to traditional surgical interventions, one of the advantages of interspinous spacers is their minimally invasive insertion. Interspinous spacers consistently have been shown to have shorter operative times, less blood loss, and shorter hospitalizations. All of these perioperative findings likely contribute to a decreased risk of major medical complications in the postoperative period. A recent review of approximately 100,000 Medicare patients treated surgically for lumbar spinal stenosis revealed that despite being used in an older population, spacers result in less medical complications than laminectomy or fusion (1.2 vs. 1.8% and 3.3%, respectively).16 However, this same study noted that at 2-year follow-up, the reoperation rate was over 16% in patients treated with spacers and approximately 9% in patients treated with a traditional decompression with or without fusion. Beyond the risks associated with any spine surgery such as persistent symptoms, infection, blood clots, etc., the placement of interspinous spacers also carries unique risks based on their design and function in the spine. Although some studies have suggested complication rates up to 20% with interspinous spacer insertion, in the largest randomized controlled trials the complication rates have been found to be similar to traditional surgical techniques with total complication rates at 2 years of approximately 8 to 10%.9,11 It is important to remember that these results were obtained in a strictly defined patient population. Studies have found that only approximately 17% of patients with neurogenic claudication meet these strict inclusion criteria and would be appropriate for interspinous spacer insertion.17 Device-related complications include spinous process fracture, device dislocation, and bone changes at the device interface. Spinous process fractures are thought to occur because of the repetitive compressive loading of the implant against the bone in an elderly population with relatively poor bone quality (see ▶ Fig. 32.4). Implantation of the X-Stop device requires 11 to 150 N of force and the spinous process fractures with between 95 and 786 N of force depending on bone mineral density.18 It is thus not surprising that clinical studies have published rates of spinous process fracture range from 419 to 23%.20 This large range is likely partially because of variance in surgical technique, but it also depends on the method of postoperative evaluation as computed tomography–based studies will show a higher incidence of fractures than plain radiographs. Because of this potential complication, most patients undergoing interspinous spacer placement have postoperative restrictions placed on their extension range of motion. Interspinous device dislocation rates are likely unique to each implant given there is significant variability in their method of attachment to the spine. The X-Stop device has reported rates of dislocation between 19 and 6%.19 However, other devices such as the Wallis device and the Aperius have shown at longterm follow-up (> 10 y) to have rates of device removal of 1821 and 17%,22 respectively. When device dislocation does occur,

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surgical treatment commonly includes removal of the interspinous device with revision decompression and instrumented fusion of the involved spinal segments. Another unique complication of interspinous spacers is progressive changes in the bone at the site of device attachment. The repetitive compression loading of the spinous processes and preserved rotational and lateral bending motion can lead to bone erosion or heterotopic ossification. Bone erosion of the spinous processes has been reported in several patients leading to recurrent symptoms necessitating implant removal and decompressive procedures.23 Heterotopic ossification (HO) can occur in the interspinous space leading to recurrent stenosis and neurogenic claudication.24 Although the mechanism for HO is unclear, it is likely related to tissue damage and exposure of cancellous bone at the time of surgery, as well as residual motion in the interspinous space.

32.6 Summary Lumbar spinal stenosis with neurogenic claudication is a common and disabling condition that responds well to surgical

Fig. 32.4 Illustration of spinous process fracture.

Interspinous Spacer Complications interventions in a well-selected patient population. Interspinous spacers provide a minimally invasive surgical treatment option with similar clinical outcomes to more traditional surgical decompression and fusion techniques. Spacer insertion may lead to decreased medical complications in the perioperative period, although some studies suggest increased revision rates at 2-year follow-up. Beyond the risks associated with all posterior lumbar spinal operations, interspinous spacers carry the additional risks of spinous process fracture and device displacement. Further studies are needed to determine if the biomechanical advantages of spacers result in significant differences in long-term clinical outcomes. Until then, they remain a viable option in treatment of lumbar spinal stenosis with similar expected outcomes to traditional surgical interventions.

32.7 Future Directions Future research will likely continue to compare the clinical outcomes of different interspinous spacers to traditional surgical treatment. Longer term follow-up will reveal any effect on adjacent level disease formation and the survivorship of the implants themselves. Further studies will also guide patient selection by identifying individual characteristics (age, gender, DEXA scores, etc.) that are linked to particularly good or poor outcomes. As total disc arthroplasty technology continues to improve, posterior interspinous spacers may also have a role as part of arthroplasty of the functional spinal unit (replacement of the disc, facet joints, and interspinous space).

32.8 Key Points ●

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Interspinous spacers can be safe and effective in well-selected patients. Patients must be educated about the risk profile of these devices. Each spacer design is unique, with individual risk/benefit profiles that must be understood by the surgeon and discussed with the patient. The mechanism of decompression of these devices vary, with some allowing for direct decompression, and providing some degree of interlaminar stabilization. Although interspinous spacers minimize traditional surgical risks through less invasive and shorter surgeries, they carry unique risks including spinous process fracture and implant migration.

References [1] Kabir SMR, Gupta SR, Casey ATH. Lumbar interspinous spacers: a systematic review of clinical and biomechanical evidence. Spine. 2010; 35(25):E1499– E1506 [2] Bono CM, Vaccaro AR. Interspinous process devices in the lumbar spine. J Spinal Disord Tech. 2007; 20(3):255–261 [3] Wilke HJ, Drumm J, Häussler K, Mack C, Steudel WI, Kettler A. Biomechanical effect of different lumbar interspinous implants on flexibility and intradiscal pressure. Eur Spine J. 2008; 17(8):1049–1056 [4] Lindsey DP, Swanson KE, Fuchs P, Hsu KY, Zucherman JF, Yerby SA. The effects of an interspinous implant on the kinematics of the instrumented and adjacent levels in the lumbar spine. Spine. 2003; 28(19):2192–2197

[5] Richards JC, Majumdar S, Lindsey DP, Beaupré GS, Yerby SA. The treatment mechanism of an interspinous process implant for lumbar neurogenic intermittent claudication. Spine. 2005; 30(7):744–749 [6] Siddiqui M, Karadimas E, Nicol M, Smith FW, Wardlaw D. Influence of X Stop on neural foramina and spinal canal area in spinal stenosis. Spine. 2006; 31 (25):2958–2962 [7] Swanson KE, Lindsey DP, Hsu KY, Zucherman JF, Yerby SA. The effects of an interspinous implant on intervertebral disc pressures. Spine. 2003; 28(1):26– 32 [8] Lee J, Hida K, Seki T, Iwasaki Y, Minoru A. An interspinous process distractor (X STOP) for lumbar spinal stenosis in elderly patients: preliminary experiences in 10 consecutive cases. J Spinal Disord Tech. 2004; 17(1):72–77, discussion 78 [9] Zucherman JF, Hsu KY, Hartjen CA, et al. A multicenter, prospective, randomized trial evaluating the X STOP interspinous process decompression system for the treatment of neurogenic intermittent claudication: two-year followup results. Spine. 2005; 30(12):1351–1358 [10] Anderson PA, Tribus CB, Kitchel SH. Treatment of neurogenic claudication by interspinous decompression: application of the X STOP device in patients with lumbar degenerative spondylolisthesis. J Neurosurg Spine. 2006; 4 (6):463–471 [11] Davis R, Errico T, Bae H, et al. Decompression and Coflex interlaminar stabilization compared with decompression and instrumented spinal fusion for spinal stenosis and low-grade degenerative spondylolisthesis: two-year results from the prospective, randomized, multicenter, Food and Drug Administration Investigational Device Exemption trial. Spine. 2013; 38(8):1529–1539 [12] Richter A, Halm HFH, Hauck M, Quante M. Two-year follow-up after decompressive surgery with and without implantation of an interspinous device for lumbar spinal stenosis: a prospective controlled study. J Spinal Disord Tech. 2014; 27(6):336–341 [13] Mariottini A, Pieri S, Giachi S, et al. Preliminary results of a soft novel lumbar intervertebral prosthesis (DIAM) in the degenerative spinal pathology. Acta Neurochir Suppl (Wien). 2005; 92:129–131 [14] Fabrizi AP, Maina R, Schiabello L. Interspinous spacers in the treatment of degenerative lumbar spinal disease: our experience with DIAM and Aperius devices. Eur Spine J. 2011; 20 Suppl 1:S20–S26 [15] Postacchini R, Ferrari E, Cinotti G, Menchetti PP, Postacchini F. Aperius interspinous implant versus open surgical decompression in lumbar spinal stenosis. Spine J. 2011; 11(10):933–939 [16] Deyo RA, Martin BI, Ching A, et al. Interspinous spacers compared with decompression or fusion for lumbar stenosis: complications and repeat operations in the Medicare population. Spine. 2013; 38(10):865–872 [17] Sobottke R, Schlüter-Brust K, Kaulhausen T, et al. Interspinous implants (X Stop, Wallis, Diam) for the treatment of LSS: is there a correlation between radiological parameters and clinical outcome? Eur Spine J. 2009; 18 (10):1494–1503 [18] Talwar V, Lindsey DP, Fredrick A, Hsu KY, Zucherman JF, Yerby SA. Insertion loads of the X STOP interspinous process distraction system designed to treat neurogenic intermittent claudication. Eur Spine J. 2006; 15(6):908–912 [19] Barbagallo GM, Olindo G, Corbino L, Albanese V. Analysis of complications in patients treated with the X-Stop Interspinous Process Decompression System: proposal for a novel anatomic scoring system for patient selection and review of the literature. Neurosurgery. 2009; 65(1):111–119, discussion 119– 120 [20] Bowers C, Amini A, Dailey AT, Schmidt MH. Dynamic interspinous process stabilization: review of complications associated with the X-Stop device. Neurosurg Focus. 2010; 28(6):E8 [21] Sénégas J, Vital JM, Pointillart V, Mangione P. Clinical evaluation of a lumbar interspinous dynamic stabilization device (the Wallis system) with a 13-year mean follow-up. Neurosurg Rev. 2009; 32(3):335–341, discussion 341–342 [22] Postacchini R, Ferrari E, Cinotti G, Menchetti PP, Postacchini F. Aperius interspinous implant versus open surgical decompression in lumbar spinal stenosis. Spine J. 2011; 11(10):933–939 [23] Miller JD, Miller MC, Lucas MG. Erosion of the spinous process: a potential cause of interspinous process spacer failure. J Neurosurg Spine. 2010; 12 (2):210–213 [24] Maida G, Marcati E, Sarubbo S. Heterotopic ossification in vertebral interlaminar/interspinous instrumentation: report of a case. Case Rep Surg. 2012; 2012:970642

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33 Complications of Presacral-Approach–Based Fusion Devices Michael Vives, Saad Chaudhary, and John Koerner

33.1 Introduction and Rationale for the Presacral Approach

33.3 Anatomy of the Presacral Space

Arthrodesis of the lower lumbar spine is frequently utilized to treat symptomatic disorders involving this region of the spinal column. Symptomatic disc degeneration, spondylolisthesis, and scoliosis are among the most common indications for fusion involving the lumbosacral junction. Interbody fusion is often a component of this technique, and this can be accomplished using an anterior lumbar interbody fusion (ALIF), posterior lumbar interbody fusion (PLIF), or transforaminal lumbar interbody fusion (TLIF) approach. The ALIF technique involves transperitoneal or retroperitoneal approach to the lower lumbar spine with disruption of the musculofascial layer of the abdominal wall and risk of injury to the abdominal viscera, ureters, and great vessels intraoperatively.1,2,3 Postoperative sequela may include abdominal wall hernia and retrograde ejaculation (in males) because of disruption of the hypogastric parasympathetic plexus.4,5 The PLIF and TLIF techniques require disruption of the posterior paraspinal musculature and some degree of removal of the lamina and facet complex and manipulation of the neurologic elements. This may be associated with tractionrelated neurologic injury, dural tear, wound infection, and arachnoiditis.6 All of the aforementioned approaches require disruption of the annulus and typically some sectioning of either the anterior or the posterior longitudinal ligaments. More recently, a novel approach has been developed to overcome the potential downsides of the conventional approaches. This approach utilizes the collection of loose connective tissue anterior to the sacrum. This space has been referred to as the retrorectal space, but in recent years it is more commonly termed the presacral space. Utilizing this approach, anterior column fusion involving L4–S1 can be achieved using the axial lumbar interbody fusion (AxiaLIF) procedure (TranS1, Inc., Wilmington, NC). In addition to its minimally invasive nature, other purported advantages include its ability to be accomplished without disruption of the facets, anterior or posterior longitudinal ligaments, or annulus. When combined with a posterior stabilization procedure (which can be performed percutaneously), advocates of this approach have suggested that the initial stability achieved surpasses the traditional constructs because the surrounding stabilizing structures of the motion segment are left undisturbed.7,8

Several authors have undertaken anatomic study of the presacral space and its relation to the anatomy of the pelvis.9,10,11 Yuan et al utilized cadaveric dissection, computed tomography (CT), and magnetic resonance imaging (MRI) data to establish “safe zones” for surgical guidance during the presacral approach. The compartments of the pelvis are delineated by defined fascial planes. The sacrum and rectum are separated by the mesorectum, a layer of adipose tissue containing blood vessels, lymphatics, and rectal lymph nodes. The posterior aspect of the mesorectum is covered by visceral fascia. The adjacent sacrum and coccyx are covered by parietal fascia. The region between these two fascial layers is known as the presacral space, which consists primarily of loose connective tissue. The width of the presacral space was studied by Oto and colleagues, utilizing MRI in a series of 193 patients.12 They found the presacral width to be significantly larger in males than in females at the S1, S2, and S3 levels. Average widths in males and females were measured to be 16.2 and 11.9 mm for S1, 14.9 and 11.2 mm for S2, and 13.0 and 10.6 mm for S3, respectively. The smaller width in females was suggested to be because of the volume occupied by the uterus. Dixon reported that men have more fat within the abdominal cavity, possibly accounting for the larger width of the presacral space.13 The vascular anatomy at the L5–S1 disc space and along the anterior aspect of the sacrum should also be considered. Tribus and Belanger studied the variability of the vascular anatomy at the L5–S1 disc space.14 They found the middle sacral artery to have a range of variability greater than 2 cm from the midline in both the top and the bottom of the disc. Parke, upon anatomic study, found the middle sacral artery to be only a minor contributor to significant segmental arteries, through bilateral segmental branches.15 It was found to be entirely absent in some cases. At the lumbosacral junction, the total distance between the left common iliac vein and the right common iliac artery measured an average of 33.5 mm with a range of 12 to 50 mm.14 More recently, with the specific technique of percutaneous axial presacral lumbar interbody fusion in mind, Yuan and colleagues undertook study of the safe corridor for such an approach utilizing cadaveric, CT, and MRI-derived measurements.11 Distances from the midline trajectory of the approach to surrounding vascular structures were determined. A “safe zone” was determined utilizing the sagittal length of the presacral space and the distance between the most medial internal iliac vessel on the right and left, respectively. At the typical guide wire entry point (S1–S2), the coronal safe zone averaged 6.9 and 6.0 cm on MRI and CT, respectively. The average distance from the anterior sacral margin to the rectum at the

33.2 Food and Drug Administration Status The TranS1 Axialif procedure is approved by the U.S. Food and Drug Administration for anterior supplemental fixation at L5– S1 in conjunction with posterior stabilization.

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Complications of Presacral-Approach–Based Fusion Devices S3–S4 level was 1.2 and 1.3 cm on MRI and CT, respectively. The sacral nerve roots are positioned more laterally and typically would not be disturbed with an appropriately targeted approach. The low entry point for the trocar at S1–S2 should also avoid injury to the hypogastric plexus.

33.4 Overview of the Surgical Technique for Presacral Fusion Preoperative bowel preparation has been recommended 24 hours prior to the surgery to empty the colon and rectum and mitigate the effects of accidental bowel perforation. Gram-negative, in addition to standard gram-positive coverage, should also be considered for prophylactic antibiotics. The patient is positioned prone on a radiolucent table and high-quality fluoroscopy is essential. A small skin incision (≤ 2 cm) is made just lateral to the sacrococcygeal junction below the paracoccygeal notch. After division of the subcutaneous tissues, the presacral space is accessed in a retroperitoneal manner by puncturing the anorectal fascia/ligament. Finger dissection in the presacral space anterior to the coccyx and lower sacrum mobilizes the retroperitoneal fat anteriorly. A blunt introducer assembly is then slowly advanced along the anterior midline of the sacrum under frequent biplanar fluoroscopic control. A starting point at the anterior cortex is usually selected and appropriate trajectory is determined prior to advancing a sharp guide pin through S1, across the L5–S1 disk space, and into L5. A modification of this trajectory is used when both L4–L5 and L5–S1 is to be included in the construct.16,17 A series of dilators are then introduced, with the last sheath left intraosseously and used as a working channel for the remainder of the procedure. A threaded reamer is used to create the body channel in S1 and into the L5–S1 disc. A discectomy is then performed using a series of radial disc cutters. The endplates are prepared and the disc/cartilaginous fragments are captured with a wire-brush device. The outer annulus and adjacent longitudinal ligaments are left intact. The desired bone graft material is then introduced into the prepared disc space with a funnel-type cannula. Next, a slightly smaller drill is used to develop the channel in the L5 vertebral body. The threaded dowel (TranS1 screw) is then inserted axially across the disc space to provide anterior column support and maintain or restore disc height. Implants with differential thread counts on each end can be used to distract the disc space using a reverse Herbert screw effect.18 To achieve greater initial stability, posteriorly placed pedicle or facet screws are recommended.

33.5 Complications 33.5.1 Approach Based Rectal Injury Perforation of the wall of the rectum can occur because of its proximity to the starting point for the transsacral implant. Such an injury is more likely to occur if the presacral space is inadequately developed. Risk factors for such injury have been offered. As previously described, males have significantly larger presacral spaces than females. The width of the presacral space

in women averages 10.6 mm at S3 and 11.9 mm at S1.11 By comparison, the width of the presacral space in males averages 13.0 mm at S3 and 16.2 mm at S1. This discrepancy may be because of the volume occupied by the uterus in a female pelvis and the greater amount of visceral fat in men. Given these considerations, women may be at higher risk for rectal injury than men. Previous surgery or inflammation in the presacral space is another risk factor for rectal injury. Intra-abdominal adhesions between viscera and the abdominal or pelvic wall can occur secondary to infections, appendicitis, diverticulitis, or pelvic inflammatory disease.19,20,21 Prior surgery has been suggested as the most common cause of problematic intraabdominal adhesions, accounting for 43 to 85% of cases.22,23 As such, preoperative imaging studies must be carefully scrutinized and some have suggested that previous surgery near the presacral space is a specific contraindication to this procedure.24 In a recent clinical article, Lindley and colleagues described two cases that were complicated by rectal injury in their series of 68 patients undergoing AxiaLIF.25 One of the patients was a 44-year-old female who had a history of previous anterior and posterior spinal surgeries, pelvic inflammatory disease, and nondisclosed prior diverticulitis. There was no recognition of bowel injury intraoperatively, and she presented on postoperative day 4 with low-grade fever, nausea, vomiting, and mild hypogastric pain. A CT scan with oral and intravenously administered contrast demonstrated presacral soft tissue density with fat stranding and extraluminal rectal contrast. These findings were deemed consistent with high rectal perforation. This was treated by an emergent diverting ileostomy and 6 weeks of intravenous antibiotics, followed by later reversal. The patient recovered normal bowel function and went on to a solid fusion. The second case presented was a 57-year-old man undergoing Axialif at L4–L5 and L5–S1. The rectal injury was detected intraoperatively and a general surgeon was consulted who identified two rectal perforations by intraoperative colonoscopy. This patient also underwent temporary diversion and antibiotic treatment. Whereas no residual of the rectal injury occurred, the patient ultimately went on to develop a painful pseudoarthrosis and underwent a subsequent posterior fusion with iliac fixation.

Pelvic Hematoma Given the anatomic considerations described above, significant blood loss is not typically associated with the presacral approach. In Tobler and Ferrara’s series of 26 patients, the mean blood loss reported for single-level cases was 137 mL (50–275) and 363 mL (50–600) for two-level procedures.24 They attributed the majority of their recorded blood losses to associated posterior procedures done under the same anesthesia and not separately measured. They felt that bleeding observed during their presacral procedure was typically bony bleeding from the intraosseous tunnel drilled. In a series on 27 patients undergoing L4–L5, L5–S1 AxiaLIFs, Marchi et al reported an average blood loss of 82 mL (50–300), with no clinical issues related to perioperative bleeding.26 They also reported high rates of pseudoarthrosis and peri-implant radiolucencies at 24-month follow-up.

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Thoracolumbar In one of the largest series of patients reported, Lindley described the complications observed in 68 patients undergoing AxiaLIF.25 They described two cases of pelvic hematoma, for an incidence of 2.9%. In one case, the patient became tachycardic postoperatively, and required transfusion of packed red blood cells totaling 5 units given over the first four postoperative days. In the second case, the patient reported worsening abdominal pain on the third postoperative day, and CT scan of the abdomen demonstrated a hematoma measuring 7.6 × 7.34 × 4.4 cm. This was observed and later noted to have resorbed. These authors speculated that the hematomas were a result of injury to presacral or middle sacral vasculature, although the precise etiologies were never determined. They offered that those patients might have benefitted from the application of hemostatic agents in the presacral space and at the opening of the intraosseous tunnel through the sacrum. Additionally they emphasized preoperative assessment for hemorrhagic risk factors such as the use of anticoagulants (and antiplatelets). A final suggestion they presented was to perform the axial lumbar procedure later in a combined procedure when being done concurrently with another lengthy procedure such as TLIF at the adjacent level. This would theoretically allow sooner “recompression” of the presacral space after the patient is returned to the supine position. To our knowledge, these are the only such events of this kind reported. It is important to entertain these possibilities, however, if such a procedure is being considered for an outpatient or surgery center setting.

Nerve Root Injury Because the ventral foramina housing the sacral nerve roots exit lateral to the midline, an appropriately targeted approach should theoretically minimize risk to these structures. One case of transient S1 nerve root irritation has been reported.25 The surgeons retrospectively recognized that the starting point for the implant was right of the midline and speculated that the implant was in mild contact with the nerve root based on postoperative CT scan. The patient’s symptoms resolved over time, so it is not clear whether the implant itself was producing the irritation versus localized edema immediately adjacent to the nerve root. The authors observed that some patients have quite large ventral S1 foramina; therefore, great effort should be taken to obtain a starting point as close to the midline as possible.

Wound Infection The close proximity of the skin incision to the anus might suggest that the presacral technique might have a high rate of postoperative contamination and subsequent wound infection. Two of the relatively large series, however, did not report any wound infections in their experiences involving 26 and 27 patients, respectively.24,26 Conversely, the Lindley study reported a 5.9% rate of superficial wound infection postoperatively. These cases were diagnosed from approximately 1 to 2 weeks postoperatively. Two of the four cases were successfully treated with empiric antibiotics (ertapenem or moxifloxacin). The other two cases were treated with operative irrigation and drainage of the wound area. All of the cases in this series responded well to treatment with no infectious sequelae. All also achieved

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successful union and showed no evidence of late implant loosening at long-term follow-up. Careful attention to preoperative preparation with isolation of the anus out of the prepared field, along with a meticulous closure, seems paramount to minimize the frequency of such events.

33.5.2 Fixation-Related Complications Sacral Fracture Whereas infrequently reported, sacral fracture is a theoretic risk given the resultant forces across the lumbosacral junction and their transfer across an implant of this design. Lindley reported two cases of sacral fracture in their series of 68 cases for a rate of approximately 3%.25 Both patients were noted to have preexisting osteoporosis, and one of the two occurred in the setting of a pseudoarthrosis. One patient opted against further surgery and developed progressive kyphosis. The other patient was treated with long iliac bolts that stabilized the sacral fracture and led to resolution of associated L5 nerve root pain. Given the above, such a development should be considered in patients with osteoporosis. Some surgeons have also championed the merits of AxiaLIF at the bottom of long constructs for adult degenerative deformity, reporting good outcomes with this less invasive approach.27 Despite the theoretically increased initial stability of an AxiaLIF construct, extension of the posterior fixation to the ilium may still be warranted in situations where it would be traditionally applied.

Pseudoarthrosis The rates of successful union for axial lumbar fusion have generally been similar or favorable to traditional approaches.28 Gerszten and colleagues studied the use of AxiaLIF with posterior percutaneous fixation for the treatment of lumbosacral isthmic spondylolisthesis.17 In a series of 26 consecutive patients with 2-year follow-up, they reported a 100% successful union rate as judged by radiographs and CT scan. Aryan and associates reported the outcomes of 35 patients undergoing AxiaLIF for diagnoses including degenerative disc disease, degenerative scoliosis, and lytic spondylolisthesis.29 They reported three patients went on to develop pseudoarthroses (9%). Two of these had undergone stand-alone AxiaLIF without posterior supplemental fixation. Tobler and Ferrara’s study of 26 patients undergoing one- or two-level AxiaLIF reported a 4% rate of nonunion at 24 months.24 Lindley’s study reported the results of 68 patients undergoing AxiaLIF with average follow-up of 34 months.25 They reported an 8.8% rate of pseudoarthrosis. The pseudoarthrosis rate in two-level (L4–L5 and L5–S1) axial interbody procedures is more discouraging. Marchi and colleagues reported the results of 27 patients undergoing twolevel AxiaLIF at a single center.26 At their 24-month CT and radiographic evaluations, only 8% of patients showed solid fusion at both L4–L5 and L5–S1. Interbody fusion at L4–L5 was only successful in 20%, and at L5–S1 it was successful in only 24% of these patients. The authors also noted that while disc space distraction was noted on 1-week radiographic follow-up, it was lost at both levels at 24 months. Moreover, the disc heights at 24 months were noted diminished compared to the

Complications of Presacral-Approach–Based Fusion Devices preoperative state. This questions the procedure’s ability to provide durable indirect foraminal decompression for two-level cases.

biomechanical results were previously demonstrated7,8 their results suggest that such a construct is not sufficient to routinely promote fusion across both L4–L5 and L5–S1.

33.6 Device Loosening, Migration, and Failure

33.7 Salvage Strategies

Radiolucencies around the axial implant were reported in 8.6% of the cases studied in Tobler and Ferrara’s series of 26 patients.24 One of these went on to fail as part of a multilevel construct. The other two patients had bridging bone across the implanted levels by 12 months, suggesting fusion was achieved despite persistent radiolucency and resorption around the implants. The authors postulated that the causes of bone resorption and radiolucency in those cases could be because of the load-sharing environment and micromotion at the implant–bone interface, possibly because of osteolysis caused by the use of bone morphogenetic protein. In contrast, the aforementioned study of two-level axial lumbar interbody procedures (by Marchi et al) reported alarmingly high levels of implant-related problems.26 They reported malpositioning of the implant in three cases because of difficulty establishing an adequate route for double-level placement. In one of those cases, the axial implant progressively migrated caudally and eventually perforated the bowel 14 months postoperatively. This resulted in septicemia and required bowel repair and prolonged antibiotic therapy. In their discussion pertinent to this complication, the authors cited a study establishing safety criteria for two-level axial interbody procedures.30 These included the following: insertion of the implant more than 6 mm from the anterior and posterior walls of L4 and L5 and more than 7 mm from the posterior boarder of S1; additionally the route should lie between the sacrococcygeal junction and the coccygeal tip. They concluded that lines frequently traversed the edges of the L4–L5 disc and that 50% of patients would not have a suitable route for the two-level presacral approach. Five patients (18.5%) in Marchi et al’s series of 27 patients underwent additional surgeries because of issues of the axial implant.26 There were two cases of malpositioned axial implants and one case each of posterior broken screw, simultaneous failure of posterior construct and the anterior implant, and collapse of the spine levels involved. One of these cases required axial implant retrieval, and four cases needed posterior direct decompression. These authors also reported that three cases (11.1%) developed some degree of detachment at the point at which the distal and proximal segments of the axial implant joined (at the L5–S1 disc space). In this same study, radiologic evaluation at 24 months demonstrated high rates of observed radiolucencies at 84%.26 These peri-implant radiolucencies generally appeared earlier and more frequently at L4 than L5. At the 24-month evaluation, radiolucency was seen at L5 in 32% and at L4 in 72% of cases. In 24% of cases, disc space collapse accompanied by cephalic implant migration into the adjacent L3–L4 disc space was reported. In three of these cases (12%), the implant caused damage to the inferior endplate of L3. Infection was excluded in all of these cases by gallium scintigraphy. Assessing their own “disastrous” results, the authors concluded that whereas favorable

There are several options for revising a failed AxiaLIF. Concomitant infection should be excluded utilizing appropriate bloodwork and nuclear studies if indicated. If the implant has migrated, or appears to be migrating, in a direction that would injure adjacent structures, then retrieval must be considered. If significant migration has not occurred or seems unlikely to occur, then one option would be to perform an open posterolateral fusion and revision of loose or broken posteriorly placed implants. This may be a reasonable strategy when the index surgery involved percutaneously placed posterior implants and there is favorable posterior/posterolateral anatomy to promote a fusion. Patients who had undergone previous wide laminectomy, have extremely small L5 transverse processed, or failed previous attempted posterolateral fusion seem less suitable candidates. Such a procedure can be combined with an interbody fusion from a posterior or transforaminal approach.31 Careful evaluation of the position of the axial implant should be done to determine suitable location for placement of interbody devices that can help distribute axial forces over a larger footprint and transfer load to a larger endplate surface. Patients who have significant symptoms because of associated compression of the neurologic elements may benefit from the direct decompression associated with such an approach. Patients who have significant scarring in the lumbosacral epidural space may present more significant challenges. In such patients, an anterior retroperitoneal approach can be considered. After removal of the remaining disc and removal of fibrous tissue and unincorporated bone graft or graft substitute, revision interbody fusion can be performed. Again, interbody devices should be selected and strategically oriented around the retained axial implant or any deficiencies of the bony endplates. If removal of the axial implant is deemed warranted, then two strategies have been described. One is to retrieve the implant through the same presacral access corridor. Given reports of rectal injury in patients who have had previous surgery or inflammation in the retrorectal region, this strategy may not seem inviting to some. Successful removal using the same presacral access corridor, however, has been described by Manjila et al. This study details two cases requiring removal of axial lumbar interbody implants. The authors detail the technique in which the rods were removed through the previous access corridor.31,32 These authors reported uncomplicated use of the previous access corridor. They noted that the dense planes of fascia, along the posterior aspect of the mesorectum anteriorly and the ventral sacrum posteriorly, can be redeveloped through careful blunt dissection. Manjila and colleagues described their technique for axial rod removal.32 After redeveloping the presacral corridor, a blunt obturator probe is advanced along the sacral surface under fluoroscopic guidance. The probe can be docked with the distal end of the AxiaLIF rod under the sacral promontory. Bony overgrowth may be present, making it difficult to initially dock. Hofstetter described advancing a guide wire into the hollow core of the implant to maintain alignment until an exchange cannula can be positioned.31

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Thoracolumbar Following this, a Retrieval Expanding Hex Screwdriver (TranS1, Inc.) can be inserted into the back end of the rod. Both groups found that once the retrieval device was securely engaged, the implant could be backed out without difficulty. The hex tip of the retrieval device is 6 mm (0.236 in) between flats to mate with the single-level implant. The screwdriver can expand to engage and provide the necessary torque to remove the AxiaLIF two-level implant, which has a 0.250-in hex. Once the axial implant has been removed, the interbody space can be addressed by either the posterior or the anterior retroperitoneal approach mentioned above. Utilization of an anterior approach facilitates the use of a large ALIF spacer, the margins of which extend beyond the defect created by the axial device. This promotes better postoperative stress distribution between the cage and corresponding endplates. Surgeons who are unfamiliar with the presacral approach, or who are reticent to attempt a revision presacral approach, may consider other options. Aryan et al described removal of an AxiaLif implant through an anterior retroperitoneal approach similar to that used for standard ALIF.29 The sacral promontory was exposed and a tract of bone anterior to the implant was removed to allow retrieval of the device. DeVine et al described removal of an AxiaLIF implant through a standard paramedian retroperitoneal approach centered on the L5–S1 disc space.33 The dissection was carefully extended along the sacral promontory to identify the original insertion site of the axial implant. A burr and curved curettes were used to remove osseous overgrowth. A discectomy was performed and the portion of the rod traversing the disc space was isolated. A large, heavy needle driver was then used to manipulate the rod and back it out through its original entry site. A standard ALIF, through the same exposure, was then performed using an impacted polyetheretherketone spacer.

33.8 Future Directions and Summary The presacral approach for AxiaLIF is a novel technique for addressing lumbosacral pathology. Whereas early reports are promising, complications have also been noted in relatively small numbers overall. As with all emerging technology, further evaluation of complications and suboptimal outcomes will promote refinement of the indications for this technique and possible modifications. Particular attention is warranted to the relatively higher failure rate of two-level procedures, and further study is necessary to clarify its ongoing role as a valid treatment option.

33.9 Key Points ●

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The presacral approach is a minimally invasive technique for anterior column stabilization across the L5–S1 and L4–L5 levels. The approach utilizes the retrorectal or presacral space, the plane between the visceral fascia of the mesorectum and the parietal fascia covering the anterior aspect of the coccyx and sacrum

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●

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Previous surgery or inflammation in the perirectal or pelvic area may increase the risk of injury to the rectum. Complications including pseudoarthroses, radiolucencies, and device migration are more common in two-level (L4–L5 and L5–S1) constructs. If implant retrieval is necessary, both the previous presacral corridor and standard anterior retroperitoneal approached have been described.

References [1] Quraishi NA, Konig M, Booker SJ, et al. Access related complications in anterior lumbar surgery performed by spinal surgeons. Eur Spine J. 2013; 22 Suppl 1:S16–S20 [2] Sasso RC, Best NM, Mummaneni PV, Reilly TM, Hussain SM. Analysis of operative complications in a series of 471 anterior lumbar interbody fusion procedures. Spine. 2005; 30(6):670–674 [3] Gumbs AA, Hanan S, Yue JJ, Shah RV, Sumpio B. Revision open anterior approaches for spine procedures. Spine J. 2007; 7(3):280–285 [4] Comer GC, Smith MW, Hurwitz EL, Mitsunaga KA, Kessler R, Carragee EJ. Retrograde ejaculation after anterior lumbar interbody fusion with and without bone morphogenetic protein-2 augmentation: a 10-year cohort controlled study. Spine J. 2012; 12(10):881–890 [5] Lubelski D, Abdullah KG, Nowacki AS, et al. Urological complications following use of recombinant human bone morphogenetic protein-2 in anterior lumbar interbody fusion: presented at the 2012 Joint Spine Section Meeting: clinical article. J Neurosurg Spine. 2013; 18(2):126–131 [6] Chrastil J, Patel AA. Complications associated with posterior and transforaminal lumbar interbody fusion. J Am Acad Orthop Surg. 2012; 20(5):283–291 [7] Ledet EH, Tymeson MP, Salerno S, Carl AL, Cragg A. Biomechanical evaluation of a novel lumbosacral axial fixation device. J Biomech Eng. 2005; 127 (6):929–933 [8] Akesen B, Wu C, Mehbod AA, Transfeldt EE. Biomechanical evaluation of paracoccygeal transsacral fixation. J Spinal Disord Tech. 2008; 21(1):39–44 [9] Havenga K, Maas CP, DeRuiter MC, Welvaart K, Trimbos JB. Avoiding longterm disturbance to bladder and sexual function in pelvic surgery, particularly with rectal cancer. Semin Surg Oncol. 2000; 18(3):235–243 [10] Kaiser AM, Ortega AE. Anorectal anatomy. Surg Clin North Am. 2002; 82 (6):1125–1138, v [11] Yuan PS, Day TF, Albert TJ, et al. Anatomy of the percutaneous presacral space for a novel fusion technique. J Spinal Disord Tech. 2006; 19(4):237–241 [12] Oto A, Peynircioglu B, Eryilmaz M, Besim A, Sürücü HS, Celik HH. Determination of the width of the presacral space on magnetic resonance imaging. Clin Anat. 2004; 17(1):14–16 [13] Dixon AK. Abdominal fat assessed by computed tomography: sex difference in distribution. Clin Radiol. 1983; 34(2):189–191 [14] Tribus CB, Belanger T. The vascular anatomy anterior to the L5-S1 disk space. Spine. 2001; 26(11):1205–1208 [15] Parke WW, Whalen JL, Van Demark RE, Kambin P. The infra-aortic arteries of the spine: their variability and clinical significance. Spine. 1994; 19(1):1–5 [16] Smith ZA, Cosar M, Johnson IT, et al. Minimally invasive presacral retroperitoneal approach for lumbosacral axial instrumentation. In: Vaccaro AR and Baron EM, eds. Operative Techniques: Spine Surgery. 2nd ed. Philadelphia, PA: Elsevier-Saunders; 2012:373–389 [17] Gerszten PC, Tobler W, Raley TJ, Miller LE, Block JE, Nasca RJ. Axial presacral lumbar interbody fusion and percutaneous posterior fixation for stabilization of lumbosacral isthmic spondylolisthesis. J Spinal Disord Tech. 2012; 25(2): E36–E40 [18] Herbert TJ, Fisher WE. Management of the fractured scaphoid using a new bone screw. J Bone Joint Surg Br. 1984; 66(1):114–123 [19] Frantzides CT, Zeni TM, Phillips FM, et al. L5-S1 laparoscopic anterior interbody fusion. JSLS. 2006; 10(4):488–492 [20] Perry JF, Jr, Smith GA, Yonehiro EG. Intestinal obstruction caused by adhesions; a review of 388 cases. Ann Surg. 1955; 142(5):810–816 [21] Räf LE. Causes of abdominal adhesions in cases of intestinal obstruction. Acta Chir Scand. 1969; 135(1):73–76 [22] Hammoud A, Gago LA, Diamond MP. Adhesions in patients with chronic pelvic pain: a role for adhesiolysis? Fertil Steril. 2004; 82(6):1483–1491

Complications of Presacral-Approach–Based Fusion Devices [23] Peters AA, Van den Tillaart SA. The difficult patient in gastroenterology: chronic pelvic pain, adhesions, and sub occlusive episodes. Best Pract Res Clin Gastroenterol. 2007; 21(3):445–463 [24] Tobler WD, Ferrara LA. The presacral retroperitoneal approach for axial lumbar interbody fusion: a prospective study of clinical outcomes, complications and fusion rates at a follow-up of two years in 26 patients. J Bone Joint Surg Br. 2011; 93(7):955–960 [25] Lindley EM, McCullough MA, Burger EL, Brown CW, Patel VV. Complications of axial lumbar interbody fusion. J Neurosurg Spine. 2011; 15(3):273–279 [26] Marchi L, Oliveira L, Coutinho E, Pimenta L. Results and complications after 2level axial lumbar interbody fusion with a minimum 2-year follow-up. J Neurosurg Spine. 2012; 17(3):187–192 [27] Anand N, Baron EM. Minimally invasive approaches for the correction of adult spinal deformity. Eur Spine J. 2013; 22 Suppl 2:S232–S241 [28] Bono CM, Lee CK. Critical analysis of trends in fusion for degenerative disc disease over the past 20 years: influence of technique on fusion rate and clinical outcome. Spine. 2004; 29(4):455–463, discussion Z5

[29] Aryan HE, Newman CB, Gold JJ, Acosta FL, Jr, Coover C, Ames CP. Percutaneous axial lumbar interbody fusion (AxiaLIF) of the L5-S1 segment: initial clinical and radiographic experience. Minim Invasive Neurosurg. 2008; 51(4):225– 230 [30] Liu BF, Zhang LG, Liu YB, et al. Is the transsacral axial interbody fusion a candidate surgical approach for fusing both L5/S1 and L4/5? Chin Med J (Engl). 2011; 124(2):215–217 [31] Hofstetter CP, James AR, Härtl R. Revision strategies for AxiaLIF. Neurosurg Focus. 2011; 31(4):E17 [32] Manjila S, Singer J, Knudson K, Tomac AC, Hart DJ. Minimally invasive presacral retrieval of a failed AxiaLIF rod implant: technical note and illustrative cases. Spine J. 2012; 12(10):940–948 [33] DeVine JG, Gloystein D, Singh N. A novel alternative for removal of the AxiaLif (TranS1) in the setting of pseudarthrosis of L5-S1. Spine J. 2009; 9(11):910– 915

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Thoracolumbar

34 Complications of Posterior and Transforaminal Lumbar Interbody Fusion Jonathan Duncan and Ahmad Nassr

34.1 Introduction Posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) are important techniques in modern spine surgery. They are commonly utilized in the treatment of most major types of adult spinal pathology including degenerative disc disease (DDD), recurrent lumbar disc herniation, lumbar spinal stenosis, adult and adolescent spine deformity including both low- and high-grade spondylolistheses, trauma, infection, tumor, revision spine surgery including pseudoarthrosis, as well as minimally invasive lumbar fusion. Popularized by Cloward,1 PLIF in its simplest form entails a posterior approach to the anterior intervertebral space with laminectomy, medial facetectomy, retraction and decompression of thecal sac and nerve roots, complete discectomy, and subsequent interbody placement of bone graft material for fusion. This allowed for maintenance or restoration of the intervertebral space for decompression of the neural elements after previous discectomy or decompression as well as anterior support and fusion surface. Initially unpopular secondary to concerns of excessive risk of neurological injury, increased adoption of PLIF occurred after the advent of pedicle screw and rod instrumentation and interbody structural cages capable of containing bone graft. These increased stability of the constructs and fusion rates. In conjunction with a posterolateral fusion (PLF), PLIF allows a circumferential spine fusion from an all posterior approach, negating the risk and morbidity of traditional anterior lumber interbody fusion (ALIF). Out of concern for risk of neurological injury during retraction of the cauda equina and nerve roots during PLIF, Harms2 popularized the TLIF technique using a more lateral, transforaminal approach with unilateral laminectomy and inferior facetectomy followed by retraction of the dural sac, total discectomy, and interbody bone graft or cage placement as in PLIF. Both PLIF and TLIF have had numerous variations, additions, and changes to their surgical techniques over time with various forms of instrumentation, bilateral applications, different interbody cages, and use in conjunction with other fusion procedures, although the core principles remain the same.

34.2 Purpose of PLIF/TLIF The purpose of PLIF/TLIF instrumentation is to indirectly decompress the thecal sac and nerve roots by restoration and maintenance of the intervertebral space, restore sagittal alignment, and increase spine stability through anterior column support and anterior interbody fusion from a posterior spine approach.

34.3 Food and Drug Administration Approval Status of PLIF/TLIF The U.S. Food and Drug Administration (FDA) has defined interbody fusion devices as “an implanted single or multiple

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component spinal devices made from a variety of materials, including titanium and polymers. The device is inserted into the intervertebral body space of the lumbosacral spine, and is intended for intervertebral body fusion. It is intended to stabilize the spinal segment to promote fusion to restrict motion and decrease pain using bone graft.”3 Most PLIF/TLIF devices fall under FDA Class II jurisdiction for intervertebral body fusion devices that contain bone grafting material as opposed to Class III devices that contain any therapeutic biologic (bone morphogenetic protein) and require a more rigorous premarket approval (PMA) process. Original devices without a predecessor to form a basis of approval must undergo PMA as well. Once a device gains PMA, similar devices may apply for 510(K) approval by demonstration to the FDA that the device is at least as safe and effective (substantially equivalent) as a legally marketed device.4 Most PLIF/TLIF cages rely on 510(K) approval demonstrating substantial equivalence and under such provisions hundreds of lumbar interbody fusion cages have been FDA approved and can be accessed under product code MAX.3 The original lumbar interbody cages that underwent more extensive PMA process include the BAK lumbar interbody fusion instrumentation system (Zimmer Spine) for anterior approaches and the RAY Threaded Fusion Cage (TFC; Stryker Spine) threaded titanium hollow cylinder for posterior approaches, both of which were FDA approved in 1996. The Brantigan I/F Cage (Depuy Spine) interbody fusion device used with posterior pedicle screw fixation was approved in 1999. Interbody cages of various metals, carbon fiber, and polyether ether ketone (PEEK) have all been approved.5 A multitude of pedicle screw systems exist which are FDA approved and often used in conjunction with PLIF/TLIF instrumentation. Indications for FDA-approved PLIF/TLIF cages are3 for use in an open posterior approach using autogenous bone graft in patients with DDD at one or two spinal levels from L2 to S1 whose condition requires the use of interbody fusion combined with PLF (360-degrees fusion) and posterior pedicle screw fixation. Other approved indications include use in spondylolisthesis. In 2002,5 the FDA approved Infuse Bone Graft/LT-cage (Medtronic Sofamor Danek) lumbar tapered fusion device as a Class III device under its own PMA (product code NEK), given its combination with recombinant human bone morphogenic protein2 (rhbmp-2) on an absorbable collagen sponge carrier. The original indication was for L4–S1 single-level anterior fusions in patients who had failed a minimum of 6 months of nonoperative treatment. Later approval was extended for L2–S1 levels and inclusion of spondylolisthesis. In 2008, the FDA issued a public health notification regarding life-threatening complications of swelling when bone morphogenetic protein (BMP) was used in the cervical spine. A higher dose BMP product for PLF of single L2–S1 levels for DDD was denied approval. Additional FDA approvals5 of BMP for use in the spine were OP-1 Putty (rhBMP-7, Stryker Biotech) under a Humanitarian

Complications of Posterior and Transforaminal Lumbar Interbody Fusion Device Exemption (HDE) for use as an alternative to autograft in compromised patients requiring revision posterolateral lumbar spinal fusion, for whom autologous bone and bone marrow harvest were not feasible or there was high risk of failure of fusion (osteoporosis, smoking, diabetes). Subsequent expansion of approval for uninstrumented posterolateral lumbar spinal fusion for spondylolisthesis was denied. OP-1 is no longer commercially available in the United States. Importantly, the use of BMP is not FDA approved for use in any PLIF or TLIF instrumentation device.

34.4 Complications 34.4.1 Osseous Complications Whereas neurological complications certainly are serious and potentially devastating, the osseous complications related to PLIF/TLIF can have an enormous impact on the ultimate outcome of a surgery. As evident in the name of the procedure, interbody fusion between the targeted contiguous vertebrae is a necessity to the optimal outcome. As opposed to neurological complications which often present in the immediate to short-term perioperative time frame, osseous complications typically present with a more protracted course. This further complicates their reporting, given that it requires longer term follow-up with high patient retention, seemingly simple, yet difficult challenges encountered in clinical spine research. Commonly reported osseous complications of PLIF/ TLIF include insufficient bony healing with failure of fusion and pseudoarthrosis, and BMP-associated overproduction of bone with heterotopic ossification (HO), and excessive bony resorption with osteolysis and interbody spacer/cage subsidence (▶ Table 34.1).

34.4.2 Osseous Complications: Pseudoarthrosis One of the initial motivations for the development of PLIF/TLIFs was to enhance posterior lumbar fusion rates and avoid the complication of pseudoarthrosis. Yet, PLIF/TLIFs are not exempt from failure to fuse, and achieving a solid bony interbody fusion remains one of the primary goals with treatment. The benefits of interbody fusion include decreased instability and motion of degenerative, pathologic, or pain-generating motion segments. Fusion halts further collapse of the motion segment and associated height loss of the neural foramen with subsequent neurological compromise. Any component of disc-related pathology or pain is theoretically removed as near-complete discectomy is involved in the PLIF/TLIF procedure.

There are many factors related to achieving fusion in the lumbar spine, most of which are not unique to PLIF/TLIF and will not be directly addressed. Generally, these factors can be categorized into mechanical and biological factors, both intrinsic and extrinsic to the patient. Cited benefits of the PLIF/TLIF procedure to achieve spine fusion include increased mechanical stability via anterior interbody support and restoration of vertebral height indirectly restoring ligamentous tension. Intrinsic biological factors vital to fusion are theoretically increased given the additional surface area of the interbody fusion region. By gaining access to the anterior spine through the posterior approach, the associated risks and complications of anterior lumbar interbody fusions are avoided, while gaining the benefits of both an anterior and posterior fusion. Avoidance of pseudoarthrosis is the best form of nonunion management. In the setting of degenerative lumbar spondylolisthesis with instability, recent guidelines state that interbody fusion has a higher fusion rate than PLF, although no specific interbody technique was shown to be clinically or radiographically superior. When adding a PLF as an adjunct to a primary interbody fusion in hopes of preventing pseudoarthrosis, there was no demonstrated clinical benefit and in fact it was not recommended because of increased cost and complications.6 When comparing instrumented fusions, a recent meta-analysis showed that instrumented PLIF was more successful in solid arthrodesis than instrumented PLF, although global outcomes and complications were similar.7 A subgroup analysis of fusion methods of degenerative spondylolisthesis the Spine Patient Outcomes Research Trial (SPORT) favored a posterolateral plus interbody (circumferential 360-degree) instrumented fusion in SF-36 and Oswestry Disability Index (ODI) measures at 2-year follow-up, although the improved outcomes did not persist between 360-degree fusion and the uninstrumented or PLF fusion groups at 3 or 4 years.8 One study showed the benefit of bilateral pedicle screw instrumentation with TLIF demonstrating a superior rate of nonunion over unilateral constructs by a sevenfold difference.9 Iliac crest autograft has historically been the standard of comparison for bone graft, and many advocate its use to prevent nonunion in lumbar spine fusion. Ito et al reported nearly identical fusion rates (94.5 versus 95.8%) at over 2-year follow-up using local autograft from laminectomy bone to load singlelevel carbon PLIF cages. They concluded local autograft was as efficacious as iliac crest autograft for single-level PLIF, citing the complications and donor site pain at the iliac crest harvest site.10 Good evidence exists that freeze-dried allograft has a higher rate of radiographic pseudoarthrosis and subsequent revision surgery for pseudoarthrosis repair than frozen allograft during ALIF with femoral ring allografts, although no such evidence has been shown in PLIF/TLIF.11

Table 34.1 Calculated complication rates with pooled data in two recent systematic reviews24,73 Calculated average rates

No. of studies used in analysis

Ranges in literature

Chrastil (2013)24

Singh (2014)73

Chrastil (2013)24

Singh (2014)73

Pseudoarthrosis

6.8%

6.3%

17

2

0–23%

Osteolysis

46.7%

15.7%

5

4

0–100%

Heterotopic Ossification

17.6%

6.5%

3

3

0–45%

215

Thoracolumbar Biological adjuncts have been proposed to support fusion, with BMP being the most commonly used which will be discussed separately. Others have proposed using bone marrow aspirate and bone dust collection at the time of surgery as means to harvest mesenchymal stem cells to supplement fusion.12 A platelet concentrated growth factor gel added to TLIF showed decreased fusion rates as opposed to hopes it would increase fusion consolidation.13 Avoiding nonsteroidal antiinflammatory drugs (NSAIDs) in the immediate postoperative period as well has been shown to aid in spine fusion. Specifically in PLIFs with local autograft, diclofenac sodium showed a dose-dependent negative effect on fusion rates as well as time to union.14 Pseudoarthrosis in the setting of PLIF/TLIF often presents with continued pain or lack of radiographic solid arthrodesis on routine follow-up, similar to other lumbar pseudoarthroses. Diagnosis of pseudoarthrosis remains one of the purposes of follow-up, although some have questioned its importance given that direct correlation between pseudoarthrosis and worse clinical outcomes has been difficult to prove in lumbar fusions. Recent guidelines demonstrate increased evidence to suggest improved clinical outcomes with radiographic fusion, although they were not specific to fusion technique.15 Specific to TLIF/ PLIF nonunion, Makino et al reported significantly worse patient reported outcomes 6 months after surgery for the radiographic nonunion group, especially in walking and social life function.16 Most literature regarding the diagnosis of pseudoarthrosis of lumbar fusion is not specific to PLIF/TLIF, so the primary evidence to guide decision-making is often inferred from pooled lumbar fusion data. Choudhri et al nicely summarize the best evidence which suggests that plain static radiographs are only accurate in diagnosis of pseudoarthrosis approximately two-thirds of the time. Adding a lateral flexion– extension view can add to the sensitivity and specificity, but only in the absence of instrumentation. Difficulty arises because the majority of PLIF/TLIF cases have posterior instrumentation present. Therefore, fine-cut computed tomography (CT) imaging is routinely used with axial and multiplanar views. Specific CT predictors of nonunion during PLF are bilateral absence of facet fusions, whereas bilateral and unilateral PL fusion masses are good predictors of fusion. Some inference can also be made from ALIF studies assessing bridging bone anterior and posterior to the interbody graft.17 Multiple studies show superiority of CT imaging compared to plain imaging for PLIF/TLIF, although these are of lower quality evidence given their lack of comparison to intraoperative confirmation of pseudoarthrosis. Technetium-99 m bone scan is not recommended because of poor reliability. Other potential but unproven modalities of diagnosis include invasive Roentgen stereophotogrammetric analysis (RSA), ultrasonography, single-photon emission computed tomography (SPECT) fused with CT (SPECT/CT), and magnetic resonance imaging (MRI). Other radiographic findings used in assessment of pseudoarthrosis are radiolucent clear zones around pedicle screws and endplate cyst formation. If the lucency around the pedicle screws remains present at 2 years or longer after surgery, it is highly suggestive of nonunion,18 and alternatively the presence of endplate cysts in the early postsurgical time period is an early predictor of nonunion.19 The management of PLIF-/TLIF-associated pseudoarthrosis presents a difficult challenge with minimal literature directly

216

addressing the problem. One option is to continue careful observation.20 Tokuhashi et al described a set of patients who went on to fusion more than 2 years from the time of surgery, although that subset of patients included, but was not limited to, PLIF/TLIF. Conservative treatment remains an option, similar to prior to the index procedure. Likewise, this includes pharmacological, therapy-based, bracing, electrical stimulation, alternative nontraditional measures, and diagnostic and therapeutic injections. Careful attention should be paid to surgical patient selection with precise diagnosis of pain-generating segments, adjacent-level pathology, global spine balance and or deformity, and overall patient goals and expectations. Modifiable host risk factors should be addressed including nicotine usage, diabetes, osteoporosis and bone mineral density, endocrine or bone metabolism disorders, BMI, nutrition, medications including corticosteroids, immune modifying medications, NSAIDs, and narcotics. Consideration of infectious etiology is always important in the setting of revision spine surgery. Selection of bone graft may be altered based on the previous procedure and availability of both local and iliac crest autograft may be limited. Femoral reaming has been shown to be a safe alternative source of autograft used in combination with TLIF.21 Surgical planning should consider the augmentation of the biological milieu with possible use of biologics and/or bone graft extenders. Preoperative discussion of risks and benefits of any off-label use of products including use of BMP is essential. Choice of instrumentation, approach or approaches, and fusion levels should be planned. Early revision strategies often involved explantation of the device, at times for migration of the interbody device. Although that remains an option, one consecutive series of 38 TLIF nonunion revisions compared a direct anterior fusion with an anterior fusion plus posterior nonunion repair and showed no differences in clinical or radiographic outcomes.22 Patients who had pseudoarthrosis of stand-alone threaded titanium PLIF cages were successfully revised with PL fusion with iliac crest autograft and pedicle screw instrumentation, going on to 94% fusion, although fusion did not always correspond to improved clinical outcome.23 Given the multitude of variables affecting nonspecific lumbar pseudoarthrosis in combination with limited evidence directly addressing management of PLIF/TLIF nonunion, there is no consensus as to the optimal revision strategy for PLIF-/TLIF-associated pseudoarthrosis. Avoidance and prevention of nonunion remain the optimal strategy. The general principle of revision spine surgery should be kept in mind—if you want to change the outcome, you must do something different than you did the first time.

34.4.3 Osseus Complications: BMP-Related Complications Concurrent with the rising popularity of the PLIF/TLIF technique was the 2002 approval of recombinant human bone morphogenic protein 2 (rhBMP-2; INFUSE, Medtronic Sofamor Danek, Memphis, TN) by the FDA for L4–S1 single-level anterior fusions when used in conjunction with the Lumbar Tapered Fusion Device (LT-Cage, Medtronic Sofamor Danek, Memphis, TN). This was the first FDA-approved use of BMP in the spine after previously approving rhBMP-7 (OP-1 Implant, Stryker Biotech, Hopkinton, MA) for long bone fracture nonunion under a

Complications of Posterior and Transforaminal Lumbar Interbody Fusion HDE.24 Despite approval for ALIF, multiple off-label spine practices evolved well documented by Ong et al.25 Between 2003 and 2007, an over fourfold increase in annual BMP usage occurred with over 85% of indications being off-label. Spine fusions were the predominant driver of off-label BMP practice, totaling nearly 93% of all BMP-related procedures. BMP usage in conjunction with PLIF or TLIF comprised the largest subgroup of spine procedures at 30%. Subsequent to the widespread increase in BMP usage with PLIF/TLIF were increasingly recognized associated complications. Along with BMP’s purported benefit of increasing fusion rates and decreasing pseudoarthrosis, commonly cited complications include osseous manifestations of both HO and osteolysis with subsequent subsidence of the interbody graft. Neurological sequelae related to BMP with PLIF/TLIF have primarily been reported as radiculitis or compression by heterotopic bone.24 Other BMP-related complications including retrograde ejaculation, possible oncogenic potential, swelling, and wound complications not specific to use with PLIF/ TLIF are outside the scope of this text. BMP usage has been justified by attempting to prove its superiority or equivalence to other methods of fusion, most notably iliac crest autograft, given the morbidity, operative time, and associated complications of an additional surgical procedure. The risk-to-benefit ratio of BMP usage should be assessed for individual patients.

34.4.4 Osseous Complications: BMP-Related Heterotopic Ossification In relation to PLIF/TLIF, HO (ectopic bone, heterotopic bone) specifically refers to the bony overgrowth outside of the intended fusion region within the interbody disc space and its posterior encroachment on the neural elements into the spinal canal and neuroforamina. Whereas HO has previously been reported in relation to injury and surgery of the spine for decades, its relation to PLIF/TLIF when not in conjunction with the use of BMP is relatively rare as illustrated by Wagner et al25 with their recent publication of its occurrence as a case report. Therefore, avoidance of BMP usage is quite simply the most direct method of eluding the complication of HO when PLIF/ TLIF is the technique of fusion. Reported rates of HO in PLIF/TLIF vary along with rates of associated symptomatic radiculopathy, despite nearly uniform fusion rates and varying dosages of BMP (▶ Table 34.2). Haid et al27 initiated a well-designed, prospective, controlled, multicenter trial in 1999 using PLIF with either BMP or iliac crest bone graft (ICBG) intent on recruiting hundreds of patients, but terminated recruitment early as they discovered a disproportionate percentage (75 vs. 13%) of BMP patients with HO compared to the control group based on CT scans at the 6month interval. Despite this finding, they did not find any correlation to leg pain, radiculopathy, or clinical sequelae. They concluded “bone formation in the spinal canal does not appear to have a discernable effect on patient outcomes. Therefore, bone formation in the spinal canal after the PLIF procedure with stand-alone cylindrical interbody fusion cages appears to be primarily just a radiographic finding that is not associated with any clinical outcome.” They postulated that leaving less than 3 mm between the posterior vertebral endplate and the posterior interbody device as well as residual sagittal

spondylolisthesis created a triangular region anterior to the posterior longitudinal ligament and posterior to the unrecessed interbody device that filled with HO. In sharp contrast, shortly thereafter Mummaneni et al28 reported no HO in a similarly designed study, although several key differences were cited for the disparate findings including use of radiographs instead of CT scan to evaluate HO. In addition, their surgical technique placed BMP anterior in the disk space adjacent to the anterior ligament and packed multiple layers of iliac and local autograft posteriorly as a barrier between the BMP and neural elements. Villavicencio et al29 likewise used a barrier technique and despite utilizing CT scan for follow-up imaging reported no increased HO, although they were criticized for a less thorough quantification of the definition of HO. Joseph and Rampersaud30 used a more quantitative assessment of HO with grading schema on CT scan and predictably reported higher rates of HO (21 vs. 8%) between BMP and the control group, despite not using a barrier technique. They likewise denied finding any clinical sequelae. This was again sharply contrasted with reports of postoperative cases of TLIF with BMP with clear evidence of HO on imaging and correlating increased radicular symptoms which resolved with revision decompression of the HO.31,32 Further postulated mechanisms of HO were irrigation of the wounds after BMP placement, drain placement, and hematoma/seroma formation at the interbody device space, all theoretically increasing the potential of BMP forming bone in a different location than its original deliberate interbody surgical placement, specifically into the spinal canal or neuroforamen. Other suggestions for prevention of HO were the lowering of the BMP dosage per intervertebral level and use of fibrin glue to seal the annulotomy prior to closure.31,32

Avoidance of BMP-Related Heterotopic Ossification ●

●

●

●

●

●

●

●

●

Anterior interbody placement of BMP and/or inside cage with anterior cage placement. Use a “barrier technique” of bone or bone graft extenders packed posterior to the anteriorly placed BMP to form a barrier/seal between BMP and neural elements. Barrier of fibrin glue or hydrogel sealant posterior to interbody device to seal annulotomy. Avoidance of irrigation with exposed BMP to avoid dispersion to ectopic locations. Once BMP is sealed anteriorly, irrigation of any residual hematoma overlying neural elements to dilute any inadvertently remaining BMP. If cage is placed more posterior, recess cage > 3 to 5 mm from posterior vertebral body endplate. Some authors recommend avoidance of drain placement which theoretically pulls BMP throughout surgical wound. Other authors promote drain usage to prevent seromas/ hematomas theoretically caused by BMP and when seromas/ hematomas form, they disperse BMP over the neural elements. Decreasing doses of BMP, use lowest dose possible per level; some authors promote 4 mg per level.

217

Thoracolumbar Table 34.2 Evidence-based BMP-associated heterotopic bone formation in posterior lumbar interbody fusion/transforaminal lumbar interbody fusion Reference

Year

Procedure

No. Of Pts.

rhBMP-2 (mg per level)

Fusion rate (%)

Presence heterotopic bone (%)

Presence radiculop- Barrier athy (%) technique

2008

PLIF/TLIF + BMP

5

4.2–10.5

Na

100

100

2/5 Yes

2010

TLIF + BMP

4

12

100

100

100

no

Case reports Wong et al32 Chen et

al31

Retroprospective uncontrolled Villavicencio et al29

2005

TLIF + BMP

74

4.2–12

100

0

0

Yes

Crandall et al44

2013

TLIF + BMP

509

2–12 mean 7.3

98.4

0.6 symptomatic

1

Yes

2008

PLIF + BMP

17

12

100

6

0

No

2011

PLIF/TLIF + BMP

30

1.4

97

6.7

3.3

Yes

2009

TLIF + BMP

86

8.4

97

2.3

14

Yes

TLIF + ICBG

33

0

97

0

3

PLIF + BMP

34

4–8

92.3

75 (CT scan)

0*

PLIF + ICBG

33

0

77.8

13 (CT scan)

0*

TLIF + BMP

21

8.4

95.2

0 (X-ray)

0

TLIF + ICBG

19

0

94.7

0 (X-ray)

0

PLIF/TLIF + BMP

23

4.2

100

21 (CT scan)

0

PLIF or TLIF

10

0

90

8 (CT scan)

0

Prospective uncontrolled Meisel et al37 Mannion et

al42

Retrospective controlled Rihn et al40

Prospective controlled Haid et al27

Mummaneni et

2004

al28

Joseph and Rampersaud30

2004

2007

No

Yes

No

Abbreviations: BMP, bone morphogenetic protein; rhBMP-2, recombinant human bone morphogenetic protein 2; PLIF, posterior lumbar interbody fusion; TLIF, transforaminal lumbar interbody fusion; ICBG, iliac crest bone graft; CT, computed tomography. Source: Adapted from Chrastil et al.24 aTwenty-nine

percent (BMP) and 36% (ICBG) of patients had a minimum of 1 point increased leg pain (of 20 point maximum) at some postoperative period, but did not correlate to heterotopic bone formation according to the authors.

Spurred on by consistently excellent fusion rates despite early reports of complications, larger series were reported including one in which a polyethylene glycol hydrogel sealant (Duraseal, Confluent Surgical Inc., Waltham, MA) was used as an adjunct to a barrier technique with ensuing decrease in reported radiculitis from approximately 20 to 5%40. Longer term follow-up also emerged when Crandall et al44 reported their series of 509 patients at nearly 5-year follow-up with varying dosages of BMP. Their conclusions were the lowest dosage per level of BMP that reliably produced fusion with minimal complications was 4 mg, although with the overall low complications they reported, including only 0.6% symptomatic HO, their study may have not been adequately powered to detect difference in dosage response. There are no specific studies addressing the diagnosis of HO after PLIF/TLIF, although arguably CT scan is better able to detect and characterize the location of any HO as opposed to plain radiographs. Several grading schemes have been proposed to quantify and better define HO, although none have been

218

widely accepted or shown to have any clinical relevance. Perhaps the most important factor in the diagnosis of HO is having a clinical suspicion in the setting of persistent or new radicular pain postoperatively, given the time course of presentation has varied greatly. Conversely, not all radiographically evident HO has shown to be clinically relevant. Management of truly clinically significant HO offers a unique challenge as revision surgery has not always showed clinical improvement, and the HO is often described as very adherent to the neural structures.

34.4.5 Osseous Complications: BMP-Related Osteolysis In contrast to the overabundance of bone formation in HO, basic science studies have demonstrated dose-dependent BMPrelated activation of osteoclasts with resultant bone resorption and osteolysis, and in an animal fracture model, resultant failure of fixation.24 Reported rates of PLIF-/TLIF-related osteolysis vary greatly, although nearly universally they have involved the

Complications of Posterior and Transforaminal Lumbar Interbody Fusion Table 34.3 BMP-associated osteolysis in posterior lumbar interbody fusion and transforaminal lumbar interbody fusion: citations in review articles Review articles

Singh et al73 Chrastil Chrastil et al24 and Patel33

Calculated rate osteolysis (%)

15.7

Reference

46.7

Details of study

NA

Year published

Lewandrowski et

al35

2007

McClellan et

al34

2006

Balseiro and

Nottmeier36

2010

X

100%

5 cases with back pain

69% levels

Only 26 of 198 patients had CT scans at 3 mo

100%

2 cases of preoperative subchondral endplate cysts

al37

2008

X

100%

17 patients. All had CT scans at 3 mo and high-dose (12-mg) BMP

Vaidya et al38

2007

X

53% BMP 12% DBM

Allograft spacers

Vaidya et al39

2008

82%

PEEK cages, 35% migration, 8 of 9 patients with migration requiring revision with worse outcomes

Rihn et al40

2009

5.8%

2 of 5 cases of osteolysis eventually diagnosed as infection

Owens et al41

2011

0.5%

1 symptomatic case

Knox et al42

2011

X

30%

Migration 25%, CT scans on all patients immediate and average 4-mo postoperative, no revisions

Helgeson et al45

2011

X

54% early 41% late

CT scans on all patients at 3–6 mo and 1–2 y

Mannion et al42

2011

X

3.3%

CT scans on all patients 6–12 mo postoperative

Crandall et al44

2013

0% symptomatic

No routine CT scans

Meisel et

X

X

X

Abbreviations: CT, computed tomography; BMP, bone morphogenetic protein; DBM, demineralized bone matrix; PEEK, polyether ether ketone; X, articles included in the analysis.

use of BMP. As previously stated, avoidance of BMP is the simplest form of prevention of osteolysis, but the entire patient scenario must be kept in context because the clinical significance of osteolysis is not fully understood. In their 2012 general review article, Chrastil et al used five previous studies to calculate an average rate of osteolysis of 46.7%.33 More recently, Singh et al73 reported a 15.7% (31/197 pooled patients) rate from four studies meeting their inclusion criteria in a systematic review. They excluded outcomes not reported on the basis of BMP utilization, although they did not report individual specific exclusions of commonly cited publications reporting osteolysis. The sharp contrast in rates obviously relates to which studies are included in the analysis (▶ Table 34.3). The earliest reported BMP-related osteolysis in relation to PLIF/TLIF came from McClellan et al34 in their 2006 retrospective review of 26 of their 198 patients who had TLIF with BMP. Included patients had 3 months’ CT scans; although imaging indications were not directly described, it was inferred that this subset of patients was not clinically improving as well as those without CT scans, because they did not routinely CT scan at 3 months after surgery. They noted osteolysis in 69% of levels in their included patients. Furthermore, “bone resorption within the vertebral body led to graft subsidence and lack of radiographic evidence of progression toward fusion in multiple cases.”34 The authors acknowledged their own selection bias as

well as their lack of standardized implantation techniques, implant types, and BMP dosing between many surgeons and therefore inability to comment on clinical implications. The question raised was whether osteolysis may be important in the early postoperative period in patients with new or continued pain. They changed their practice by decreasing the dosages of BMP used and renewed focus on placement of the interbody cages at the periphery of the intervertebral spaces. Shortly thereafter, a case series of five patients who exhibited severe new onset of low back pain without radiculopathy between 4 weeks and 3 months after TLIF with BMP (4.2-mg dose/level) at the L5–S1 level was published.35 No comment was made on the remaining 63 patients in their patient series for clinical or radiographic comparison. Histopathology of one of the patients revised for symptomatic posterior instrumentation showed granulation tissue next to trabecular bone with suggestion of inflammation at the site of osteolysis. They hypothesized that violation of the subchondral endplates with dilators and shavers may have exposed more bleeding cancellous bone to the interbody BMP, especially the less confined BMP placed with other bone graft outside the tight confines of the PEEK cage. The increased inclination of the L5–S1 interspace as compared to other levels may have contributed to excessive decortication at those levels. They also raised the possibility of dose-dependent osteolysis with their 4.2-mg dosing. Despite their patients’ increased postoperative pain, they reported

219

Thoracolumbar resolution of symptoms with nonoperative care at 3 months after symptom onset. In addition, Balseiro and Nottheimer36 reported two cases of postoperative pain that showed evidence of osteolysis seemingly originating from their preexisting subchondral endplate cysts, citing their preoperative existence as a possible risk factor for subsequent osteolysis. Avoidance of PLIF/ TLIF in this clinical scenario may be warranted. These early reports seemed to suggest association of osteolysis with early unfavorable results with variable longer term implications. On the contrary, Meisel et al37 performed CT scans of all of their 17 patients who had TLIF with BMP and reported 100% presence of osteolysis at 3 months with all progressing to fusion and good clinical outcomes at 6 months. They reported minimal associated cage migration or subsidence, although not quantified, and suggested the posterior instrumentation stabilized and negated any potential resultant instability. Given their exclusive use of high-dose (12 mg/level) BMP, they suggested better investigation into the effects of dosage variability. The question remained whether BMP-associated osteolysis was perhaps inherent to the remodeling process of fusion with BMP and its long-term clinical relevance. Two prospective studies published by Vaidya et al38,39 furthered our understanding of the topic. Their first study used machined allograft spacers with either BMP or demineralized bone matrix and found higher rates of early osteolysis and spacer subsidence in 53% (9 of 17) versus 12% (3 of 25) of fused levels in the BMP group. They calculated mean subsidence as 24% (13–40%) versus 12% (11–14%) in the two groups, respectively.38 They postulated the subsidence was the result of increased bone turnover of the allograft spacer in the BMP group as well as osteolysis of the adjacent endplates. The resultant loss of intrinsic strength of the graft and endplates was followed by subsidence of the graft and loss of intervertebral height. Clinical outcomes did not differ between groups despite the increased osteolysis and subsidence in the BMP group and notably the anterior subsidence with measurable radiographic collapse occurred despite their use of posterior stabilizing instrumentation. They cautioned against using allograft spacers as a structural support with BMP. This same group39 transitioned to PEEK cages, attempting to maintain stability of the implant in the presence of BMP. They used identical dosages to their previous technique (2 mg/level), and now placed the BMP within the PEEK cage as opposed to anterior to the allograft spacers. They reported 82% (31/38) of levels with evidence of osteolysis and endplate resorption, but more importantly 35% (9/26) of patients who had PLIF/TLIF showed evidence of cage migration on plain radiograph at 6 weeks postoperative or earlier, again despite using posterior stabilizing instrumentation. Eight of the nine (88%) patients with cage migration required revision secondary to neurological symptoms. Earlier revisions found extensive bone resorption and loose cages necessitating much larger cages to fill the intervertebral space. Later revisions found the cages fused in their posteriorly migrated position with both cage and heterotopic bone impingement on neural structures. They pointed out the lack of plate placement in PLIF/TLIF to prevent cage migration as opposed to ALIF or anterior cervical discectomy and fusion (ACDF). Of significance, their revision patients with cage migration were the first documented evidence of BMP-related osteolysis resulting in comparatively worse clinical outcomes.

220

Rihn et al40 published a rate of 5.8% (5/86 patients) of symptomatic osteolysis in single-level TLIF, which presented at between 1 and 5 months postoperative as back pain and was diagnosed by CT scan. Of the five cases, two resolved with fusion after 1 year, one progressed to nonunion, and two were diagnosed as osteomyelitis and required revision. In 2011, two series reported very low levels of osteolysis at 0.5 and 3.3%.41,42 This was despite differing standard BMP dosages of 4 and 1.4 mg per level, respectively. Rates in both series resulted from one patient who presented with radicular pain, and in one case mild retropulsion of the cage and nonunion that was treated conservatively.

BMP-Related Osteolysis in PLIF and TLIF Avoidance ● PLIF- and TLIF-associated osteolysis is extremely rare without the use of BMP. ● Decreasing BMP dosage to the minimum necessary may minimize osteolysis. ● Placement of cages/spacers at peripheral locations of interbody space is possibly less susceptible to subsidence if osteolysis occurs. ● Avoid excessive decortication or violation of the subchondral endplates during discectomy and interspace preparation. ● Allograft spacers with BMP exhibit increased osteolysis and subsidence. ● Preexistence of subchondral endplate cysts may be a risk factor for developing adjacent osteolysis. Diagnosis The differential diagnosis of early back pain after PLIF/TLIF should include BMP-associated osteolysis as well as infection. ● Osteolysis with associated cage migration can be evident at or before 6 weeks postoperative on plain radiographs. ● Routine and earlier postoperative CT scans seem to show higher rates of osteolysis, although no clinical benefit has been shown to routine imaging. ● Cage subsidence and migration usually occur in the setting of osteolysis. Maintaining an increased awareness of these potential complications when osteolysis is present is necessary. ●

Management In the absence of infection, subsidence, or cage migration, BMP-related osteolysis can resolve without intervention. Variable rates of resolution exist. Over the long term, osteolytic defects tend to decrease but usually do not completely resolve. ● Symptomatic osteolysis often resolves near the time of fusion, often by 6 months, but possibly 1 year or longer. ● Cage migration with ensuing radicular pain often, but not always, requires revision surgery with worse clinical outcomes. Asymptomatic migration can often be managed with observation. ● Posterior instrumentation contributes to overall construct stability, but does not guarantee prevention of subsidence or migration of PLIF/TLIF grafts in the setting of osteolysis. ●

Complications of Posterior and Transforaminal Lumbar Interbody Fusion One difficulty in comparing results of osteolysis is the differing postoperative imaging protocols. As pointed out by Knox et al,43 most studies employ selective postoperative imaging without routine CT scans as illustrated by the recent reporting of no symptomatic osteolysis in 509 consecutive patients by Crandall et al,44 all of whom had postoperative CT scans and high-dose BMP. In 2011, publications of two groups, both using routine postoperative CT scans on all patients, reported their results. Mannion et al42 performed CT scans at 6 and 12 months on patients to arrive at their 3.3% rate. In contrast, Knox et al43 acquired CT scans immediately postoperative and at an average of 4-month follow-up and interestingly found nearly one-third (16 of 58 [27.6%]) of patients and one-quarter (19 of 77 [24.7%]) levels treated exhibited osteolysis with no difference found between one- and two-level PLIF/TLIF. Nearly one-third (31.6%) of those with osteolysis demonstrated graft subsidence, all of whom had severe osteolytic defects. Cage migration was found in 8.8% (5/57) of patients, with moderate osteolysis in four of the five patients, and severe osteolysis in the other. No patients required revisions for osteolysis, subsidence, or migration, although no clinical outcomes were described. Helgeson et al45 also used routing CT imaging and reported a postoperative rate of 54% at 3 to 6 months and 41% at 1 to 2 years with corresponding decrease in osteolysis volume, but nearly three-quarters never completely resolved.

34.4.6 Neurologic Complications of PLIF/TLIF Of all the complications relevant to PLIF and TLIF, neurologic complications are arguably the most potentially devastating. Historically, the slow adoption of the earliest PLIF techniques was partially the result of high reported rates of neurologic complications. Over time, the trend toward TLIF has decreased those risks, as opposed to PLIF, although anytime a posteriorbased lumbar interbody fusion is performed, the risk of neurologic injury remains. Thus, the potential benefit of an additional region of fusion with PLIF/TLIF must be considered in light of these inherent risks. In their review, Chrastil et al33 report a range of intraoperative neurologic injury of 0 to 7%, and from their references calculated a 4.9% average rate. Common symptoms from neurologic complications include radiculopathy, numbness, or weakness with a wide range in the clinical severity of each, although most are typically transient and do not require revision surgery.

34.4.7 Neurologic Complications: Incidental Durotomy Although frequently reported in the literature as a complication of both PLIF and TLIF, rates of incidental durotomy (ID) are typically low, resulting in no large series specifically addressing this complication in PLIF/TLIF. A recent review article reported a range of 2 to 14% drawn from smaller studies including PLIF, TLIF, and minimally invasive surgery TLIF (MIS-TLIF), and calculated an average rate of 7.3% from their selected studies. They also found a range of 0 to 14% in MIS-TLIFs.33 Several large series and database studies report a much tighter range of ID in spine surgery with rates ranging from 2.7 to 4.0%,46,47,48,49 although these are not specific to PLIF/TLIF.

One such study, not specific to PLIF/TLIF, evaluated risk factors for unintended durotomy in lumbar spine surgery and identified female sex, older age, preoperative diagnosis of degenerative spondylolisthesis, and juxtafacet cysts. The authors identified four high-risk anatomical zones for dural tears which included adjacent to medial facet joint, adjacent to the disc or disc space, at facet cysts, and near the cranial and caudal borders of the decompression.47 Another general spine study showed increased hospital costs, length of stay, overall complications, and decreased rate of discharge to home after ID.46 One analysis stressed the identification and immediate primary repair of ID and found no longterm sequelae at over 3 years after surgery when dural tears were recognized and treated.48 Multivariate analysis of a large prospective registry found revision surgery, degenerative lumbar diagnosis, and increased surgical invasiveness as significant risk factors for ID.49 Although not specific to PLIF/TLIF, we can infer that many of these general trends and risk factors persist when dealing with PLIF/TLIF. Direct comparisons of PLIF versus TLIF show TLIF has a lower rate of ID. Although not statistically significant, durotomy rates of 17% (PLIF) versus 9% (TLIF) were reported in one study.50 A recent meta-analysis found that PLIF had increased rates of ID with an odds ratio of greater than 3.0 compared to TLIF.51 MIS-TLIF creates a unique challenge when dealing with ID as standard repair instrumentation is often not feasible. Multiple adjuncts to primary repair have been utilized including sealants, dural grafts, and fibrin glue,33 as well as some proponents that repair is unnecessary given the decreased postoperative dead space compared to open procedures. Nonpenetrating titanium clips originally designed for vascular surgery have been described for treatment of ID in the setting of MIS-PLIF/TLIF.52 Regarding treatment of ID in PLIF/TLIF, no specific studies show superiority of any single recommendation and therefore management conclusions are drawn from the general spine surgery literature. Options include limited bed rest and flat positioning for a period of time prior to mobilization, low suction or gravity drains, or, in more difficult or irreparable tears, placement of a diverting lumbar cerebrospinal fluid (CSF) drain to decrease back pressure on the healing site of dural injury. Extreme caution should be used with placement of CSF drains as devastating consequences including death have been reported when used incorrectly and with inexperienced hospital support staff. Incidental durotomy is an undesirable complication with data suggestive that TLIF has decreased risk compared to PLIF and open TLIF has decreased risk compared to MIS-TLIF.

34.4.8 Neurologic Complications: Battered Root Syndrome Dr. Gilles Bertrand, a neurosurgeon from McGill University, first termed the “battered root” problem in 1975.53 He defines a subset of patients who are a “core of unhappy cripples who haunt neurosurgical, orthopedic, and compensation clinics [which] constitute an endless source of frustration to all concerned.” He goes on to describe them as patients that have failed previous surgical lumbar decompression, typically a discectomy, who present with persistent, worsened, or new-onset radiculopathy and paresthesia. The typical clinical sequence is

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Thoracolumbar sciatica, followed by surgery with relief of pain but accompanied by severe numbness. Subsequently, reappearance of the pain and incomplete improvement of the numbness occur. The “chronic traumatic radiculopathy” is often constant, burning, aching, or ice cold. He felt strongly the cause was a traumatic result of overzealous retraction of the nerve roots because of inadequate surgical exposure and advocated a wider exposure with partial facetectomy during nerve root decompression. Often at re-exploration, only scarring, adhesions, and a “cheloid-like mass surrounding the dorsolateral dura” were found. He reported a small series of dorsal sensory root rhizotomies as a salvage-only procedure for the “battered root” and estimated a 40% improvement rate with little risk of worsening if a localized and preexisting neurologic deficit is present. Pheasant and Dyck54 in their 1982 article on failed lumbar disc surgery, attribute the “battered root” and the resulting arachnoiditis as one cause of failure. They likewise cite the cause as inadequate interlaminar exposure with excessive retraction of the neural elements, often in the setting of isolated discectomy with concomitant or unrecognized spinal canal stenosis. Soon thereafter in 1985, a German group reported successful treatment of the “battered root syndrome” with indwelling spinal cord stimulators.55 Their definition included patients with severe, intractable radicular pain after previous spine surgery who upon workup revealed complete nerve root block on myelogram, surrounding scar tissue on CT, and pathologic changes on electromyographic and somatosensory evoked potential studies. One potential method of specifically decreasing battered root syndrome was recently reported56 with a neurophysiological monitoring technique to avoid excessive force and duration of nerve root retraction, allowing safer dynamic nerve root retraction, which could certainly be applicable to PLIF/TLIF. More recently in an analysis of immediate failed back surgery syndrome (iFBSS) after lumbar microdiscectomy,57 13 of 1,546 (0.8%) patients were diagnosed with “battered root syndrome” after no abnormality was found at revision decompression. They attributed it to “nerve root swelling because of excessive surgical manipulation.” The diagnosis of iFBSS was made in patients experiencing worsening or recurrent radicular pain accompanied by sensorimotor or sphincter disturbances while still hospitalized after the primary procedure, despite the absence of complications reported by the surgeon. Certainly, the diagnosis of iFBSS, as previously described, could be made in select cases of failed or unsuccessful PLIF/TLIF. The “battered root syndrome” seems to represent a poorly understood and underreported, yet distinct clinical entity that represents a challenge to both patient and surgeon and not only is applicable in the setting of lumbar discectomy as previously reported, but also highly relevant to the surgical techniques of PLIF and TLIF. Battered root syndrome warrants further investigation into the incidence, mechanism, prevention, and treatment.

34.4.9 Neurologic Complications: Radiculopathy and Radiculitis Of all neurologic complications, the most commonly reported is radiculopathy. This seemingly straightforward complication

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illustrates the difficulty in comparing the literature. The definition of radiculopathy as a reportable complication is not uniform between studies and often baseline rates of preoperative symptoms are not reported. Many patients indicated for PLIF/ TLIF surgery have preexisting radiculopathy, yet most studies do not adequately report or differentiate the preoperative versus postoperative or new radiculopathy. In addition, “radiculopathy” is often combined with “radiculitis” in many studies, although frequently the two terms are referred to as distinct clinical entities. This challenge is well illustrated by Chrastil et al24 in their 2013 review of BMP-associated complications of PLIF/TLIFs in which they analyzed 22 studies with designs ranging from case reports to prospective randomized multicenter trials. Ten of 22 studies had no data reported regarding postoperative radiculopathy. Of the five case reports, three reported 100% of patients having radiculopathy, two implicating HO, and the other citing BMP-associated radiculitis. The other two case reports described 100% rates of osteolysis without resultant radiculopathy, with similar findings in one other small series. On the contrary, one prospective series similarly reported very high rates of osteolysis, but differed in that cage migration with resultant radiculopathy was also found at a high rate. Four observational studies lacking non-BMP control groups included three large retrospective series which reported postoperative radiculopathy rates of 1, 6.4, and 18.8% (8% new) and one small prospective series reporting 3.3%. Two retrospective cohort studies added control groups with direct comparisons of BMP and non-BMP cohorts and both reported higher rates of radiculopathy in the BMP groups (14 and 11.4%) than in the control groups (3 and 0%), respectively. Excluding case reports and preexisting radicular pain, the resultant range of new or worsened postoperative radiculopathy in PLIF/TLIF with BMP is 1 to 14% in the studies cited in their analysis.24 Severe leg pain 20 months after TLIF revealed a calcified perineural cyst seen on imaging and in revision excision which on histopathology revealed connective and bone tissue suggestive of BMP-induced cyst formation.58 Another group also reported perineural cyst formation requiring revision after MIS-TLIF despite using low-dose BMP (1.4 mg/level) with local autograft.42 Fluid collections causing compressive radiculopathy beginning 4 weeks after bilateral PEEK TLIFs with intermediatedose (8.4 mg) BMP required revision at nearly 4 months (right side) and 8 months (left side) after index surgery. Both revisions found a discrete inflammatory mass at time of decompression that exhibited histopathology of “diffuse osteoid and woven bone amidst a fibrovascular stroma densely populated by lymphocytes and eosinophils.” Another case report involved development of a rapidly progressive cauda equina syndrome 2 days after surgery involving TLIF with BMP. MRI and postexcision pathology suggested edematous epidural fat consistent with an intense inflammatory reaction suggesting a possible relation to BMP.59 An additional study comparing various lumbar fusion methods that utilized BMP showed increased risk of radiculitis after revision surgeries and patients who were smokers at the time of surgery. No difference between the PLIF/TLIF group and the PLF or ALIF groups was seen regarding radiculitis when using BMP. In addition, their nearly 9% rate of new-onset radiculitis after PLIF/TLIF with BMP is reported as similar to historical

Complications of Posterior and Transforaminal Lumbar Interbody Fusion controls without BMP.60 Another large series of TLIF/PLIF comparing various BMP dosages between 2- and 12-mg BMP per level published a much lower rate of postoperative radiculitis (1%). No correlation between specific dosages of BMP and radiculitis or other potential etiologies of radiculopathy, including HO and seroma, was found.44 A small retrospective series reported rates of immediate postoperative (within 72 h of surgery) leg pain doubled from 10 to 21% when BMP was utilized with PLIF/TLIF cages. The difference between groups was attributed to BMP-associated radiculitis without nerve root compression as MRI was utilized to exclude cases with other compressive etiologies of leg pain. The small size and differences between the BMP and control group, which included a much higher rate of previous surgery, limited the study.61 A larger series of TLIFs with BMP41 reported an overall rate of 6.4% of new or worsened postoperative radiculopathy corresponding to the same side and dermatome of the TLIF window. Their literature review found rates of postoperative radiculitis with TLIF using autograft from 2 to 7% compared to 7 to 14% with BMP. Subanalysis of their 6.4% of patients with radiculopathy characterized 2.5% with a compressive foraminal seroma or hematoma, which presented on average 2 months after surgery, all required revision, and symptomatically resolved at a mean of 4 months after revision decompression. Their diagnosis was “rhBMP-2-induced compression.” The remaining 4% of patients with radiculopathy had no clear etiology on repeat imaging and resolved without revision on average 4 months after treatment with oral steroids, gabapentin and pregabalin. They concluded that this 4% rate was similar to a baseline rate of radiculopathy in another group of TLIFs with autograft (without BMP). This contrasted with Rowan et al,61 who would have classified these 4% as “BMP associated radiculitis” and excluded compressive etiologies such as seromas from association with BMP. Another small series of MIS-TLIFs compared postoperative rates of radiculopathy not attributable to structural cause and found 11% in the BMP group compared to 0% in the control group.62 Clearly, there is an association between BMP utilization and radiculopathy/radiculitis in PLIF/TLIF and therefore the balance between the added benefit for increased rate of fusion and the associated complication must be weighed. Consequently, multiple studies have theorized the importance of confining BMP away from the neurological structures as indirectly evidenced by the lack of similar patterns of radiculopathy after ALIF surgeries utilizing BMP. The intact posterior annulus and posterior longitudinal ligament theoretically prevent posterior BMP migration. Multiple authors describe techniques to place the BMP anterior in the disk space during PLIF/TLIF, packing various combinations of cages and bone graft and creating a posterior bone graft barrier to BMP outflow. Rihn et al40 reported an overall 14% BMP-associated radiculitis rate, significantly higher than the 3% of a comparison autograft group. They described using a hydrogel sealant, Duraseal (Coviden, Waltham, MA) after TLIF placement to seal the annulotomy window and coat the adjacent exiting and traversing nerve roots. They noted a resulting decrease in the rate of radiculitis from 20 to 5% with use of the sealant. Many surgeons adopted or modified this technique, although the same group subsequently published a cautionary case

report61 of cauda equina syndrome related to this technique. On postoperative day 3 after TLIF, they attributed the expansion of Duraseal to the patient’s clinical decline and urgent revision for cauda equine syndrome. They had sealed the TLIF annulotomy with hydrogel sealant according to their previously published technique as well as over a separate ID. The area of sealant application covered approximately one-half the circumference of the cauda equina. Because of its hydrophilic properties, Duraseal is known to have expansile properties, but has been relatively safe when used in this “off-label” fashion in the spine with only isolated case reports of such dramatic complications. The authors’ recommendations cautioned against filling the residual posterior interbody void as this region could accommodate a high volume of hydrogel sealant and expand posteriorly. They also recommended using no more than 2 mL per level, applying only a very fine layer using the MicroMist applicator, and not applying in multiple contiguous regions encompassing the thecal sac if used to reinforce a durotomy repair in addition to the TLIF window.63

34.4.10 Neurologic Complications: General Considerations One important factor in avoidance of neurologic injury during PLIF/TLIF is recognition of abnormal anatomic variants. Neidre and Macnab64 developed a classification system for lumbosacral nerve root anomalies. The three major categories of variants in order of most common occurrence include conjoined, anastomotic, and redundant nerve roots. Burke et al65 suggest intraoperative signs of a nerve root abnormality include an unusual root location, an abnormal exiting angle from the dural tube, difficulty freeing up a nerve root despite adequate decompression, and a lack of normal ligamentum flavum. Recognition of the anomaly is the most important factor in dealing with these anatomic variants and often necessitates abandonment or modification of the original surgical plan, as these are often not recognized on preoperative imaging findings. Higher rates of postoperative radiculopathy were found after PLIF in a subtotal facetectomy group (9.7%) as opposed to a total facetectomy group (4.9%). Although not reaching statistical significance, this suggests the wider exposure with total facetectomy allows for better nerve root decompression as well as decreased necessity for nerve root retraction.66 Radiculopathy on the contralateral, asymptomatic side after TLIF has been reported and decompression of the opposite, asymptomatic foramen may be warranted if preoperative MRI demonstrates stenosis.67 Appropriate visualization and decompression of the traversing and exiting nerve root are necessary regardless of specific techniques used. Maintenance of hemostasis is an important component of anatomic visualization and avoidance of electrocautery in close proximity to neurologic structures with the judicious use of hemostatic agents and bipolar cautery is preferred to achieve hemostasis. A cadaveric study of a novel spine shaver device used to prepare the interbody space noted the number of insertions needed to prepare the disc space was six times higher using conventional manual instruments, and the device could potentially decrease the risk of inadvertent neurologic injury from

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Thoracolumbar repeated entries into the interbody space. In addition, they report higher volume of disk removed, increased area of cartilage removal, and decreased endplate damage with the spine shaver device.68

Avoidance of Neurologic Complications ●

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● ●

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Recognize increased risk with revision surgery and more invasive surgeries. Consider avoidance of nicotine during perioperative time period. Recognition and awareness of anatomic nerve root variants before and during surgery. Consider complete facetectomy to facilitate wider exposure and less retraction. Minimize duration, force, and frequency of retraction of nerve roots and thecal sac. Avoid thermal electrocautery near neurologic structures. Use bipolar and hemostatic agents to attain hemostasis. Minimize frequency of unnecessary instrument passages into interbody space. Consider TLIF over PLIF in avoidance of neurologic injury. If using BMP, consider a barrier or sealant between BMP and neurologic structures. If using a hydrogel sealant, use a thin layer and avoid filling the posterior interbody space.

Recognition of neurologic complications is essential for successful outcomes in PLIF/TLIF. Often diagnosis can be made intraoperatively with direct injuries or ID and the key is acknowledgment and treatment even if inconvenient. The timing of onset of symptoms is often a key component to diagnosis of neurologic complications if no intraoperative complications are noted. Advanced imaging including CT scan or MRI is the most common means of diagnosis of neurologic complications in the postoperative period. Assessment of compressive pathologies including pedicle screws, cages, bone graft, or hematoma/ seromas is important to recognize and manage, and ruling out these distinct causes of compression is vital prior to arriving at other diagnoses of exclusion. Failure of surgical success because of neurological compression often requires direct management with revision decompression, regardless of timing of onset of symptoms. In contrast, when noncompressive etiologies are diagnosed, treatment is often nonsurgical. Medications mentioned by multiple authors include oral corticosteroids or neuropathic agents such as gabapentin or pregabalin. There is some evidence that NSAIDS are detrimental to fusion rates in PLIF when used in the immediate postoperative time frame.69 Prophylaxis with routine placement of intraoperative local corticosteroids near the exposed neurologic elements is an option, although no widely accepted protocol or technique exists. Often a last resort involves postoperative nerve root blocks or corticosteroid injections if confident that the postoperative symptoms are truly transient as failure of these injections is often one of the original indications for the surgery. Expectant management with regularly scheduled follow-up remains a mainstay of treating patients with a more protracted recovery and exclusion of complications (▶ Table 34.4).

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34.4.11 Infection As with all spine surgery, infection is a dreaded complication. Few studies look directly at infection directly associated with PLIF/TLIF, and the reported rates vary dramatically. Chrastil et al report a 0 to 9% range of infection rates from seven studies of both PLIF and TLIF and calculated an overall average of 3.7%.33 Over 108,000 spine surgery cases were analyzed from the Scoliosis Research Society (SRS) morbidity and mortality (M&M) database and an overall TLIF/PLIF infection rate of 2.3% (superficial 0.8 vs. deep 1.5%) was found from over 12,000 cases, mirroring the 2.1% rate for all cases.70 Another large database analysis calculated a 5.6% overall PLIF-/TLIF-associated surgical site infection (SSI) with a mean direct cost of $15,817 per SSI.71 One large, retrospective, single-institution study found differing SSI rates between posterior or PLF (0.3%, 3/974 cases) and PLIF (1.37%, 29/2110 cases), although the comparison groups were not controlled or homogeneous. Interestingly though, when further classifying SSI, the PLIF group had approximately one-third wound infections and two-thirds osteomyelitis, whereas the comparison group had the opposite trend with nearly two-thirds wound infections and one-third osteomyelitis. The authors attributed the increased PLIF infections to multiple factors, although admittedly without supportive evidence. Those most identifiable to PLIF included increased burden of foreign material with cages, and avascularity and difficulty in irrigation of the disk space.72 Singh et al,73 in their systematic review of BMP-related PLIF/ TLIF complications, pooled data from three included studies to arrive at a rate of 2.4% (7 of 290 patients) in BMP-related PLIF/ TLIF infections versus 9.1% (3 of 33 patients) in controls, although not statistically significant and arguably much greater numbers of patients are needed to adequately power such an analysis. Crandall et al44 published a 2.6% deep infection rate and slightly lower in the strictly degenerative group of 1.7% when deformity or spondylolisthesis groups were separated out. The overall range in these analyses of PLIF-/TLIF-associated infection is 0.8 to 5.6%.

34.4.12 Infection: Avoidance Many principles in avoidance of infection in PLIF/TLIF are not unique to these procedures. Standard measures to prevent spine SSI include optimization of patient and surgical factors. Modifiable patient factors can include patient selection, preoperative decolonization of nares, medical and nutritional optimization, and management of immune-modulating, blood glucose, and anticoagulation medications, as well as risk factors for thrombophilia.74 Surgical factors associated with prevention of spine infection are numerous, heavily debated, often lack high-quality evidence, and most are beyond the scope of this chapter. Only those with some specific evidence relating to avoidance of PLIF-/TLIF-associated infection are discussed. Prophylactic intraoperative powdered vancomycin applied to the wound prior to closure has been proposed as one method of preventing or decreasing postoperative spine infection. Using this technique with a 1-g dose, one series by a single surgeon documented a 1.37% (1/73 cases) rate of SSI within a subgroup of open PLIFs drawn from over 1,500 consecutive cases of various spinal fusions without a comparison group.75 A second

Complications of Posterior and Transforaminal Lumbar Interbody Fusion Table 34.4 Etiologies and onset of radiculopathy/radiculitis associated with posterior lumbar interbody fusion/transforaminal lumbar interbody fusion Postoperative time period of symptom onset

Compressive

Immediate

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Early

● ● ● ● ● ● ● ● ●

Subacute

● ● ● ● ● ● ● ●

Late

● ● ●

Noncompressive

Screw/implant/cage malposition Hematoma/seroma Disc herniation/reherniation Bone graft migration Lamina/pars fracture with impingement Hydrogel sealant expansion Inadequate surgical decompression Undersized cage

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Infection Hematoma/seroma Disc herniation/reherniation Bone graft migration Cage migration Edematous epidural fat Hydrogel sealant expansion Inadequate surgical decompression Undersized cage

●

BMP associated Heterotopic bone formation Osteolysis with cage migration Osteolysis with cage subsidence/foraminal collapse Perineural cyst/inflammatory mass formation Non-BMP associated Scar formation Inadequate surgical decompression

●

Pseudoarthrosis: instability, dynamic nerve root impingement Pseudoarthrosis: osteophyte formation Heterotopic bone formation

●

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● ●

●

●

Neuropraxia/direct injury Retraction injury/battered root syndrome Traction injury Excessive cage height/overdistraction Excessive electrocautery

Infection BMP-associated radiculitis Battered root syndrome

Arachnoiditis Adjacent segment disease

Arachnoiditis Adjacent segment disease

Abbreviation: BMP, bone morphogenetic protein.

retrospective, consecutive, single-surgeon cohort of posterior instrumented thoracolumbar spine fusions used a consecutive historical comparison group that had no difference in operative times, estimated blood loss, or patient demographics. In both groups, the most common procedure performed was a onelevel (48 vs. 42%) or two-level (31 vs. 34%) TLIF/PLIF. They demonstrated a decreased rate of postoperative deep spine SSI (2.6%, [21/821] vs. 0.2% [2/911]) using a 2-g intraoperative vancomycin powder dose divided into 1 g mixed with the autogenous ICBG and 1 g in the wound. In addition, local levels of vancomycin drawn from drain output showed levels greater than minimal inhibitory concentration for both methicillinresistant Staphylococcus aureus (MRSA) and methicillin-resistant S. aureus (MSSA), with minimal simultaneous serum concentrations in only 20% of patients, avoiding systemically known complications of hypotension, renal toxicity, and antibiotic resistance.76 Similar to most infection studies, these lack prospective randomization and are underpowered to reveal other possible complications, such as pseudoarthrosis. Easily the most published and debated method of infection prevention related to PLIF/TLIF is MIS versus traditional open procedures. The SRS M&M database was used to specifically evaluate the TLIF subset and found MIS-TLIF (n = 848) infection rates were significantly lower (1.3 vs. 2.9%) than open TLIF (n = 6,241). More importantly, this difference was most evident in the deep infection rate (0.4 vs. 1.9%).70

A large multihospital database study of PLIF/TLIF found significant differences in perioperative SSI between MIS and open two-level fusions only (4.6 vs 7.0%). There was no difference for single-level PLIF/TLIF (4.5 vs. 4.8%). In addition, for two-level PLIF/TLIF procedures, they calculated a mean SSI-associated cost ($756 vs. $1,140), significantly lower in the MIS than in the open group. This correlated with a direct cost savings of nearly $40,000 per 100 PLIF/TLIF procedures in two-level fusions.71 A systematic review by Parker et al showed SSI rates between 0 and 15% in 30 cohorts of TLIFs, the largest of which was 130 patients. They compared SSI rates of 10 MIS-TLIF (0–2.7%) versus 20 open TLIF (0–15%) cohorts, with 362 and 1,133 patients, respectively. Subsequently they calculated a cumulative TLIF SSI incidence of 0.6% (MIS) versus 4.0% (open), or nearly sevenfold difference, although each individual study was small and arguably underpowered. The 3.4% overall decrease in SSI incidence for MIS versus open TLIF was estimated to save nearly $100,000 per 100 MIS-TLIFs in direct cost with a mean hospital treatment cost of approximately $29,000.77 Further discussion of MIS versus open PLIF/TLIF is continued in a separate section.

34.4.13 Infection: Diagnosis Beyond standard diagnostic techniques for spine infection, little evidence is specific to diagnosis of PLIF-/TLIF-associated infections. BMP-related osteolysis may confound the postoperative

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Thoracolumbar imaging as illustrated in two of five cases originally thought to be BMP-related osteolysis that were eventually diagnosed as infection requiring revision surgery.40 Kraft et al78 reported preoperative and postoperative C-reactive protein (CRP) and white blood cell (WBC) values in groups of PLIF and endoscopic discectomy patients. Both groups exhibited CRP peak at postoperative days 2 to 3, followed by a rapid decrease at 4 to 6 days, and nearly normal values at postoperative day 14. Maximum CRP level was significantly higher after PLIF (mean: 127 vs. 75), and longer surgery duration and BMI > 25 also exhibited higher peak CRP values. The WBC was unpredictable and its kinetic profile therefore unreliable. They suggested a preoperative CRP and repeating on postoperative days 2 to 3 and 4 to 6 to aid in early postoperative infection, although there are no clinical data to show this protocol actually aids in early diagnosis and improves outcome. Furthermore, no cost analysis was discussed in relation to the overall value of such a protocol. Similarly, postoperative serum CRP and amyloid A (SAA) were prospectively evaluated in a cohort of PLIF patients.79 In noninfected patients, peak levels of both lab values were reached on postoperative day 3 and significantly decreased by days 7 and 13. Levels of SAA decreased to more normal levels faster than CRP and therefore were more primed to reveal a postoperative increase suggestive of infection. In the infected subgroup, the SAA was more sensitive than CRP in early diagnosis. In addition, SAA does not show significant fluctuation with steroid administration as opposed to CRP and they concluded SAA was a better marker of postoperative inflammation than CRP in spine surgery.

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crest PLIF in the setting of known infection.82,83 Various types of spinal fusion including TLIF (3 of 20 cases) were successfully treated without implant or instrumentation removal using vacuum-assisted wound closure (VAC) as an adjunct in between irrigation and debridement procedures prior to definitive closure of infected deep spinal wounds with exposed instrumentation.84

Key Points: PLIF- and TLIF-Associated Infections ●

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34.4.14 Infection: Management

●

Early case reports and small series reported successful treatment of PLIF-associated infections with surgical debridement of both retained and explanted interbody cages, anterior and/or posterior approaches, and even conservative treatment with intravenous (IV) antibiotics. Large well-controlled series are lacking and there is no consensus protocol. One series of 10 patients who underwent revision for deep postoperative SSI after PLIF with cages reported 90% fusion rates after anterior radical debridement, removal of all implants, and autogenous ICBG interbody fusion. MRSA was the organism cultured in 50% of cases. Despite the revision with autograft interbody support, complete collapse of the disc space occurred with a mean loss of both height (12.7 mm) and lordosis (5.6 degrees),80 questioning the necessity or benefit of interbody removal. Another series of eight patients had successful posterior treatment of deep PLIF-associated SSI without removal of interbody cages. The protocol was surgical debridement, 4 to 6 weeks of susceptibility-guided IV antibiotics, with subsequent 6 to 9 weeks of oral antibiotics. At 2 years, no recurrent infection was noted, although only 50% reported clinical improvement from prior to index procedure, with 6-year telephone follow-up reported as mild to moderate disability on ODI.81 Indirect support of the ability to successfully treat PLIFassociated infection with maintenance of interbody support are two small series by Lee et al who report the effective treatment of known primary pyogenic spondylodiscitis and tuberculous spondylitis with implantation of stabilizing autogenous iliac

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High-quality, randomized, well-controlled studies examining the avoidance, diagnosis, and management of PLIF-/TLIFassociated infections are lacking. Better prevention protocols, earlier diagnostic capabilities, and less morbid treatment strategies are needed. PLIF-/TLIF-associated infections result in suboptimal clinical outcomes and are costly. Most reported rates of PLIF-/TLIF-associated infections are less than 5%. Some evidence suggests MIS-TLIF may have lower rates of infection than open TLIF. PLIF-/TLIF-associated infections may involve higher rates of osteomyelitis than other posterior spine fusion techniques. Intraoperative local vancomycin powder in the wound and/or bone graft may decrease infection rates. Perioperative CRP has a predictable profile with peak at postoperative days 2 to 3, fall at days 4 to 6, and normalization at day 14. Perioperative serum amyloid A (SAA) is perhaps a better marker of early postoperative infection than CRP. Perioperative trending of CRP and/or SAA may aid in early diagnosis of subclinical infection. Both BMP-related osteolysis and infection should be in the differential diagnosis of new or continued back pain after PLIF/TLIF, and can be confused on diagnostic imaging. Management of infection in the setting of PLIF/TLIF often requires surgical debridement. Successful treatment is possible with both explantation and retention of the interbody device at time of surgical debridement. Long-term IV antibiotics are required with consideration of continued oral antibiotics. VAC is a possible adjunct to surgery in difficult wound closure with exposed instrumentation.

34.4.15 Rare Catastrophic Complications Other rare reported complications in prone posterior spine surgery which can occur with PLIF/TLIF are plunging of instruments through the intertransverse space causing ureteral injury, lateral femoral cutaneous neuropathy/meralgia paresthetica, and lumbar plexopathy from erroneous retractor placement. Several case reports of rare but disastrous complications associated with PLIF/TLIF are worth mentioning. Massive hemorrhage after anterior dislodgment of a TLIF cage for treatment

Complications of Posterior and Transforaminal Lumbar Interbody Fusion of infectious L3–L4 spondylodiscitis occurred with resultant migration to the left pulmonary artery.85 Despite this catastrophic complication, the patient survived and had a good outcome at 6 months after surgery. On postoperative day 2 after an L5–S1 PLIF, massive unilateral lower extremity swelling was because of anterior migration of bone graft causing occlusion of the left common iliac vein by a large deep vein thrombosis,86 once again warning against overly aggressive bone graft/cage impaction. A misplaced K-wire during an L4–5 MIS-TLIF was the source of a large hematoma extending from T12-sacrum causing postoperative paraplegia.87 As more MIS-TLIF cases are carried out in the ambulatory setting, the importance of thorough preoperative evaluation is illustrated by the case of a woman who remained on oral contraceptives and was an active smoker at the time of her TLIF surgery and developed cardiac arrest in the postanesthesia care unit because of a massive pulmonary embolism.88

34.5 Summary Posterior-based lumbar interbody fusions, including PLIF and TLIF are some of the many tools that modern-day spine surgeons have in their current armamentarium in treating spinal pathology. These techniques allow circumferential lumbar fusion without accessing anterior approaches to the spine and have evolved over time, decreasing many of the complications which initially limited their acceptance. Newer technologies have significantly increased the utilization of PLIF/TLIF, which are now some of the most common spine fusion procedures performed. Despite being a useful and generally safe procedure, numerous possible complications exist and represent real challenges to both surgeon and patient. The benefits of utilizing these techniques must always be evaluated in context of keeping the best interest of the patient in mind. Understanding and recognition of the multiple associated complications with PLIF/ TLIF will assist surgeons in achieving the best clinical outcomes for their patients, as well as drive future research to continuously improve upon the art and science of modern-day spine surgery.

Key Points: Complications of Posterior and Transforaminal Lumbar Interbody Fusion ●

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Posterior-based lumbar interbody fusions, including PLIF and TLIF, allow for circumferential (360-degree) lumbar fusion while eliminating risks associated with anterior-based surgeries and the often required coordination with an access surgeon. Evolution of the TLIF technique has decreased associated neurologic complications compared to earlier PLIF techniques while maintaining the benefit of high rates of fusion. The advent of rhBMP-2 in conjunction with improved instrumentation and interbody devices has significantly increased the utilization of PLIF/TLIF, but with a significant set of unique complications that must be balanced. Advantages of using rhBMP-2 with PLIF/TLIF include higher fusion rates, avoidance of morbidity and risk of iliac crest autograft harvest, and high fusion rates in MIS-based surgeries with minimal dissection and bone grafting. These

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benefits must be weighed against the increased risks of osteolysis with and without interbody graft subsidence, HO, and radiculitis as well as others. Future high-quality investigations are needed to clarify many aspects of PLIF/TLIF surgery to maximize benefit and minimize complications including ideal types of interbody devices, the best bone grafting techniques and ingredients, indications for usage and optimal dosages of BMP, the minimal necessary supplementary instrumentation, and indications and best practices for MIS techniques.

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Thoracolumbar

35 Complications of Open Transforaminal Lumbar Interbody Fusion Louis F. Amorosa, Jeffrey A. Rihn, and Todd J. Albert

35.1 Introduction Interbody devices are used as adjuncts to promoting spinal fusion in the setting of spondylolisthesis, scoliosis, and other conditions. A 360-degree fusion with interbody cage and posterior instrumentation offers very high fusion rates. Interbody devices also aid in restoring segmental sagittal and coronal alignment. The indications for interbody fusion versus posterolateral fusion alone are still a topic of intense debate by experienced spine surgeons. Removing the disc not only takes compression off the dural sac, but also removes one of the potential pain generators of low back pain. With the increased concerns about health care costs, we generally reserve interbody operations for patients with significant disc space collapse which may contribute to foraminal stenosis. Also, if the disc space is collapsed asymmetrically, the interbody can be placed asymmetrically to prop open the collapsed disc space and restore the normal coronal plane of the spine. Placement of the interbody cage in the anterior one-third of the intervertebral space has the ability to restore a collapsed or kyphotic segment to a more lordotic angle.

35.2 Open Transforaminal Lumbar Interbody Fusion Compared with the Alternatives Open transforaminal lumbar interbody fusion (TLIF) offers many advantages over the standard anterior lumbar interbody fusion (ALIF). Comparative studies have shown advantages including less blood loss, shorter operative time, less likelihood of intensive care unit (ICU) level care, and shorter hospital stay.1 Studies have shown a significant cost savings of performing open TLIF versus ALIF given the added cost of two procedures, longer ICU stay, and longer operative time associated with the ALIF.2 Open TLIF gives the surgeon the ability to perform a 360degree fusion with one surgical incision while at the same time placing pedicle screw instrumentation with direct palpation of the bridging pedicles. Furthermore, studies have shown it has a lower complication rate than the ALIF procedure 1.1,3 In the setting of deformity surgery, TLIF and ALIF have been compared. In a prospectively enrolled, retrospectively matched cohort analysis, 42 patients who underwent TLIF at the caudal end of a long construct were compared with 42 matched controls who underwent ALIF at the end of the construct.4 At 2 years postoperatively, the study found no difference in overall or neurologic complication rates between the two procedures and one pseudoarthrosis in an ALIF patient versus none in the TLIF patients. Patients who underwent TLIF had shorter operative time and had better correction of coronal plane deformity, whereas ALIF did provide better lordotic correction. When to use open TLIF as opposed to other interbody fusion techniques is also open to debate. ALIF is a better alternative

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when the surgeon intends to place interbodies at multiple levels, because with single anterior retroperitoneal approach by an experienced approach surgeon, it is relatively easy to access multiple lower lumbar disc spaces. However, when only one level is involved, TLIF offers the ability to place the interbody graft at the same time as the posterior instrumentation, thus obviating the need for a separate anterior abdominal surgery. Few studies have compared TLIF to posterior lumbar interbody fusion (PLIF). PLIF is a much older procedure than TLIF and is described in detail in another chapter of this text.5,6 Whereas the TLIF utilizes a transforaminal approach via osteotomy of the pars interarticularis, the PLIF is a more direct posterior approach in which the dura and nerve roots require more retraction to access the disc space to perform the procedure. One Level III retrospective comparative review examined outcomes of TLIF in 40 patients to PLIF in 34 patients.7 The study found similar rates of fusion, blood loss, operative time, and hospital stay; however, whereas no complications were reported with the TLIF procedures, several complications with PLIF were reported including four cases of radiculitis. Another retrospective study comparing PLIF to TLIF also found trends toward a higher rate of nerve root injury and durotomy with the PLIF procedure than the TLIF procedure.8 These studies illustrate that the main distinguishing feature between PLIF and TLIF: TLIF requires very little retraction of neural elements, whereas PLIF requires significant retraction on the dura and nerve roots. Biomechanical studies have shown that the amount of endplate area that should be fused for an interbody device to promote fusion as opposed to graft subsidence is at least 30% of endplate area.9 A unilateral TLIF has the capability to remove 69% of the volume of the disk space and 56% of the area of the disk space.10 Therefore, a unilateral TLIF offers all of the fusion capability as the PLIF without as much concern regarding dural sac and nerve root retraction. Other notable advantages of the TLIF over PLIF include the following: it does not remove as much of the posterior longitudinal ligament and therefore the posterior tension band remains intact; less bone is resected in unilateral cases and therefore the contralateral lamina and facets provide more surface area for fusion; if a revision is needed, it can be performed easily from the contralateral untouched side very easily.11 Another interbody fusion technique which has gained popularity over the past several years is the transpsoas extreme lateral interbody fusion, sometimes referred to as XLIF. XLIF is an alternative to TLIF at higher lumbar levels, such as L1–L2, L2–3, and L3-4 especially in those patients with a conus medullaris that terminates in the lumbar spine. The XLIF offers the advantage that it does not require manipulation of the dural sac or nerve roots. However, it offers its own disadvantages such as a separate surgical procedure and risk of genitofemoral nerve injury, which will be discussed in more detail in another chapter. It also does not allow access to

Complications of Open Transforaminal Lumbar Interbody Fusion L5–S1, as the iliac crests do not allow access to the disc space from the lateral approach. An alternative to open TLIF is minimally invasive TLIF (MISTLIF), to which another section of this text is devoted. MIS-TLIF is performed with a smaller incision and requires much more fluoroscopy. We typically prefer an open TLIF given that the incision is relatively small, radiation exposure to patient and surgeon is less, and outcomes are similar in terms of functional outcomes, fusion rates, and complications. Furthermore, the open procedure allows direct visualization of traversing nerve roots, which we feel is safer. One retrospective comparative study comparing open TLIF in 63 patients to MIS-TLIF in 76 patients found a postoperative neurologic deficit rate of 1.6 versus 10.5% in the MIS group (p = 0.02), suggesting that the open procedure may be safer from a neurologic standpoint.12

35.3 Unilateral versus Bilateral TLIF We typically do perform a unilateral TLIF with bilateral pedicle screw instrumentation. We feel this is a more stable construct than unilateral TLIF and unilateral pedicle screw instrumentation. A Level II prospective randomized study compared unilateral TLIF with unilateral pedicle screw instrumentation to bilateral TLIF and bilateral pedicle screw instrumentation and showed trends toward higher rates of fusion with bilateral TLIF and better relief of back pain and leg pain.13 Typically we perform a unilateral TLIF either on the side in which the leg pain is more symptomatic or on the side that is more collapsed, with concomitant bilateral pedicle screw instrumentation and posterolateral bone grafting.

35.4 Purpose of Instrumentation TLIF is a technique used to place an interbody cage/bone graft in the disc space of the lumbar spine to promote stability and fusion, and in some cases to correct deformity. This technique is typically used in conjunction with and during the same surgical procedure as posterolateral fusion with pedicle screw instrumentation.14 Standing TLIF alone is, generally, not indicated because it does not promote the biomechanical stability to promote fusion without concomitant use of pedicle screw fixation.15,16 TLIF can be performed bilaterally, from one side with the purpose of making it symmetric or it can be performed asymmetrically with the purpose of correcting an asymmetrically collapsed disc space or lateral listhesis. The question of when to use an interbody versus posterolateral fusion alone often arises and it is certainly open to debate based on the available evidence in the literature. Interbody fusion is useful to use for local deformity correction, as well as conditions where it is advantageous to widen the disc space, such as in a symptomatic spondylolisthesis, where disc space collapse contributes to nerve root compression (▶ Fig. 35.1). Independently of spondylolisthesis and deformity correction, interbody fusion is a useful definitive treatment for recurrent disc herniation.

35.5 Food and Drug Administration Approval Status TLIF is a Food and Drug Administration (FDA)-approved procedure for interbody placement in the intervertebral space.

35.5.1 Relevant Anatomy The anatomy relevant to performing the open TLIF procedure begins with the surgical approach. A standard midline incision is used. The fascia is dissected off the midline and the paraspinal muscles subperiosteally elevated off the bony elements of the posterior spine with a Cobb elevator. If only one level is being fused, then it is extremely important not to violate uninvolved facet joints, including the adjacent facet joint of the superior level being fused. This can be avoided by taking a localizing lateral radiograph prior to dissecting past the facets. Once the proper level has been identified, the superior facet joint of the levels to be instrumented should not be violated, although it needs to be adequately exposed to properly place instrumentation. Therefore, the fascia should be opened longitudinally one level above this level to allow for proper identification of the facet joint and transverse process. The caudal facet joint of the fusion level can, however, safely be exposed and violated. For instance, if a TLIF is being performed at L4–L5, then the facet capsule of L3–L4 should be exposed and preserved for pedicle screw instrumentation, but the capsule should not be penetrated or removed. The L4–L5 facet joint can be exposed and the joint capsule freely removed. The transverse processes of both levels should be completely exposed, as well as the intertransverse membrane between them. This will provide a posterolateral fusion bed in addition to the intervertebral disc space fusion provided by the TLIF. The pars interarticularis of the superior level (L4 in this example) should be completely exposed. The above exposure should be performed bilaterally. Once the level is exposed, it is important to understand the topographical anatomy. Starting with the superior level, we begin with the pedicle. Traveling just medial to and below the superior pedicle is its corresponding nerve root out laterally through the neuroforamen between the superior and the inferior pedicles. The lateral recess is often compressed by the undersurface of the superior articular facet of the inferior level. More laterally, in the neuroforamen, the lateral aspect of a hypertrophied superior articular facet of the inferior level may also impinge on the exiting nerve root, in addition to far lateral disk herniations. The intervertebral disc space of the level planned for TLIF should be identified. The superior exiting nerve root has already exited above and is not typically involved with pathology from the disc unless a far lateral disc herniation in the neuroforamen impinges upon it. The nerve root that is impinged upon is the inferior nerve root, which is still in the spinal canal and is impinged upon by disc herniation, or disc-osteophyte complex commonly present in degenerative spondylolisthesis or scoliosis. Caudal to the disc space is the pedicle of the inferior vertebrae. The nerve root passes just medial and then turns out laterally just below the pedicle.

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Fig. 35.1 The TLIF is indicated to aid reduction of spondylolisthesis and restore disc height, which decompresses the foramina. This 55-year-old male presented with back and leg pain. Radiographs (a,b), including flexion and extension films (c,d), showed a degenerative spondylolisthesis of L4–L5 (continued).

35.5.2 Surgical Technique The surgical technique once the exposure is performed begins with entry into the spinal canal (▶ Fig. 35.2). A lamina spreader can be placed between the involved spinous processes once the supraspinous and infraspinous ligaments are removed at this level. Alternatively, if the surgeon chooses to perform a midline decompressive complete laminectomy before performing TLIF, the lamina spreader can be placed between the facet joints to effectively distract the level once facetectomy has been performed. An osteotome is used to remove the inferior articular facet and most of the pars interarticularis of the upper level. The osteotomy is directed inferolaterally toward the facet joint. This is the safest direction as it is directed away from the spinal canal and an obvious pitch change will be felt and heard once the osteotome enters the facet joint. Typically, supination of the wrist with the osteotome still in the facet joint will unroof the facet joint and expose the superior articular facet of the caudad level. It is important with this osteotomy not to cut into the pedicle of the lower level to be fused. This can be avoided by using a Woodson elevator to palpate the pedicle from within

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the spinal canal and estimate how far inferior the osteotomy can be safely performed. At this point, ligamentum flavum can be removed with a Kerrison rongeur and the dural sac exposed. The traversing superior exiting nerve root should be visualized traveling underneath the pedicle above and the traversing inferior nerve root still in the spinal canal should both be visible. Epidural bleeding can be controlled with bipolar coagulation under direct visualization as well as various anticoagulant agents. Once hemostasis is achieved, the disc space can be exposed by gently retracting the inferior nerve root medially toward the dural sac. The inferior pedicle should be skeletonized with a Kerrison rongeur to increase visualization of the disk space. The disc space can also be distracted with a laminar spreader between the spinous processes or the facet joints. We do not recommend using pedicle screws instrumentation to distract the disc space, especially in older individuals where it may add undue stress to the screws, increasing the risk of screw cutout. Often the disc space will be covered with a leash of epidural vessels, which should be bipolared and swept away. Once the disc space is exposed and dural sac and nerve roots protected,

Complications of Open Transforaminal Lumbar Interbody Fusion

Fig. 35.1 (continued) Postoperative radiographs showed excellent reduction of the spondylolisthesis and restoration of disc height (e,f).

an annulotomy is performed with a 15-blade scalpel, directed in line with the nerve root, because this is least likely to cause dural tear or nerve root injury. A box cut or crosscut is made. A pituitary rongeur is then used to remove the incised annulus. A Kerrison rongeur can be used to remove any disc osteophyte complex. Once the annulotomy is opened, a pituitary is placed to remove as much disc material as possible. It is important not to penetrate too far ventrally with the pituitary. If the anterior disc space is not well visualized, then a safe depth for the pituitary and all other instruments is approximately 30 mm at the midline. Deeper than this risks great vessel injury. An alternative to this is examining the preoperative magnetic resonance imaging (MRI) or computed tomography (CT) scan to measure the posterior to anterior diameter of the disc space in order not to violate the anterior longitudinal ligament (ALL) and great vessel injury. Endplate shavers and various angled curettes should be used to remove the cartilage from the superior and inferior endplates. It is important to remove as much cartilage as possible to promote fusion, while at the same time care should be taken to not violate the endplate and expose cancellous bone of the vertebral body, which may contribute to subsidence of the interbody. Finally, trials are used. Placement of a lamina spreader between the lamina of the involved levels can allow distraction of the interspace and can facilitate disc space preparation and cage placement. Most instrumentation systems also have distractors that attach to the pedicle screws and can be used to distract the interspace. It is important while passing

instruments that both the dural sac and the nerve root are protected to prevent injury. The proper trial height should have a snug fit and should not move when in the disc space. Having to back hammer the trial out of the disc space is a good sign it is a snug fit. This is important because a less than tight fit may result in interbody migration posteriorly into the spinal canal. It is also important not to overstuff or overdistract the disc space with too large an implant, as this risks subsidence. Once the trial is removed, the TLIF can be placed. Bone graft material can be placed in the interspace directly and can be packed into the cage itself prior to insertion. If attempting to correct an asymmetrically collapsed disc space, the TLIF can be placed asymmetrically to prop up the collapsed portion of the disc space (▶ Fig. 35.3). A bullet-shaped cage works well in this situation, as it is easier to insert into the collapsed space. Alternatively, if the disc space is evenly collapsed, the TLIF can be placed across the disc space from one side to the other. If doing this, it needs to be aimed medially while tapping it in from one side. A banana-shaped cage works well in this situation, given it can be positioned in the anterior one-third of the interspace. Another alternative to this is to use bilateral TLIFs, which will increase surface area for fusion but need to be weighed against the risks of longer operative time, more blood loss, and higher likelihood of complication. Once the TLIF is performed, instrumentation with pedicle screws can now be performed.

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Fig. 35.2 The TLIF technique at L4-5. (a) The facet joint is exposed. (b) Osteotomy performed being sure to not break pedicle. (c) Traversing nerve root identified and disc space cleared of epidural leash. (d) Annulotomy and discectomy performed. (e) Interbody placed.

35.6 Complications 35.6.1 Adjacent Segment Degeneration Adjacent segment degeneration is defined as degeneration at adjacent spinal segments that occur after the fusion surgery (▶ Fig. 35.4). Adjacent segment degeneration can have solely radiographic consequences or can result in clinical symptoms. A Medline review of the literature found that radiographic evidence of adjacent segment degeneration occurs 8 to 100% of the time after lumbar fusion surgery and clinical evidence of adjacent segment degeneration 5.2 to 18.5% after lumbar fusion surgery.17 The study also suggested that PLIF may be a risk factor for adjacent segment degeneration. Others have suggested that the addition of PLIF to a posterolateral fusion alone construct may accelerate adjacent segment degeneration as it increases the rigidity of the motion segment, creating greater stress loads at adjacent levels.18 A more recent systematic review of the literature found only five Level I or II articles related to the topic of adjacent segment degeneration after

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fusion.19 Based on this higher level of evidence, the authors found an annual incidence of clinically relevant adjacent segment degeneration to be 0.6 to 3.9%, and did not find the addition of lumbar interbody fusion to be an independent risk factor. Excessive disc height distraction when interbody fusion is performed was found to be a risk factor for its development in one high-level study.20 Whereas these studies specifically were addressing risk factors related to PLIF, there is very little evidence specifically for TLIF although the risk for TLIF can be inferred to be similar to PLIF. In modern spine fusion surgery, instrumented fusion with pedicle screws and a rigid rod construct is almost always indicated because of the unacceptably higher incidence of pseudoarthrosis in uninstrumented fusion operations compared to instrumented fusions.21,22 The interbody device itself does not confer biomechanical stability to the level being fused and therefore pedicle screw fixation along with it is required to promote fusion.15 The rigidity that is conferred which is inherent within the posterolateral fusion procedure itself is thought to contribute to the risk of adjacent segment degeneration based

Complications of Open Transforaminal Lumbar Interbody Fusion

Fig. 35.3 (a,b) A 69-year-old man presented with recurrent left leg symptoms and a recurrent foraminal disc herniation at L4–L5 several years after a previous decompression (magnetic resonance imaging). (c,d) Radiographs showed L-sided asymmetric collapse of the L4–L5 disc space. He was indicated for revision decompression with asymmetric TLIF and posterolateral fusion (post-op X-rays). (e,f) Restoration of coronal alignment was obtained and his symptoms resolved.

on biomechanical data which shows increased disc pressures and facet motion in the presence of a fusion at an adjacent levels.23 However, other technical factors related to pedicle screw insertion may also have a role in the development of adjacent segment degeneration. Adjacent segment degeneration more commonly occurs at the suprajacent level than the infrajacent level and this is thought to occur at least partially because of pedicle screw instrumentation.24 The incidence of pedicle screw malposition

has been reported to be 2.1% when used in conjunction with the open TLIF procedure.25 Pedicle screws may be malpositioned in multiple ways—this will be discussed in greater detail in another chapter—and only some of these malpositions relate to adjacent segment degeneration. The two ways in which pedicle screws placement can influence the development of adjacent segment degeneration are by violation of the superior facet joint and by violation of the adjacent endplate and disc space.

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Fig. 35.4 Adjacent segment degeneration after a TLIF procedure. A 60-year-old female presented with back and leg symptoms, and was found to have a degenerative spondylolisthesis at L4–L5 (a–d) (continued).

Violation of the superior facet joint uninvolved with the fusion increases the risk of adjacent segment degeneration.16 This can be avoided by first preserving the facet joint of the superior level during exposure and also during osteotomy of the pars and inferior articular facet of the superior fusion level. Whereas the entire transverse process and facet capsule should be exposed for proper posterolateral pedicle screw instrumentation and fusion, neither the facet capsule nor the facet joint should be violated with during pedicle screw cannulation or placement.24 Avoiding facet capsule and joint violation might entail having a starting point slightly more lateral than usual and aiming more medially. Pedicle screws should not violate the adjacent endplate or disk space, which will increase the risk of adjacent disk degeneration. The surgeon should pay close attention to the trajectory of pedicle screw cannulation and insertion in the sagittal plane to avoid this. Lateral fluoroscopy

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can be used to assist in this. Furthermore, whereas the pars should be removed with the TLIF procedure, once the par begins to curve superolaterally, it should be preserved so as not to allow the osteotome to violate the facet.

35.6.2 Infection In the study of Tormenti et al, infection was the second most common complication after durotomy, occurring in 3.8% of patients who underwent the procedure.25 Nine of the 20 patients with an infection had had a prior surgery (i.e., it was a revision case) and in 10 cases a multilevel fusion was performed. All 20 patients were treated with intravenous antibiotics, 19 of 20 patients underwent irrigation and debridement, and 2 patients underwent removal of pedicle screw and rod constructs, but no patient underwent removal of the interbody.

Complications of Open Transforaminal Lumbar Interbody Fusion

Fig. 35.4 (continued) She was indicated for the TLIF procedure and symptoms soon resolved (e,f) (continued).

Fig. 35.4 (continued) However, 4 years postoperatively she began developing increasing back pain and was found to have adjacent segment degeneration at L3–L4 (g-i).

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Thoracolumbar Another retrospective study examined a series of 10 patients referred to the authors’ institution with spondylitis after PLIF, an interbody technique quite similar to TLIF.26 Several of the patients had already had irrigation and debridements prior to referral. The authors reported that they first tried to remove the implants from the posterior approach, but epidural scarring and difficulty grasping the interbodies forced them in all cases to perform a separate anterior retroperitoneal approach, at which time, the interbody was removed, a thorough irrigation and debridement of disc space and infected bone performed, followed by placement of iliac crest bone graft. Posterior pedicle screws were also removed. Debate exists regarding treating deep infected TLIFs and no high-level evidence exists for one form of treatment over another. We typically first perform a thorough irrigation and debridement. In the early postoperative period (< 20 weeks postoperatively), we tend to try to keep implants retained in the patient. Spinal wound infections in the setting of fusion surgery require stability to heal not only the fusion but also the infection. Removing implants prior to fusion risks continued infection and pseudoarthrosis. With late infection (> 20 weeks postoperatively) or if the fusion has healed, we typically remove the instrumentation. However, if the graft has healed, we leave it in place. Whether or not osteomyelitis is present, irrigation and debridement should be performed, as well as 6 weeks of antibiotics tailored to intraoperative cultures. Typically, if concomitant osteomyelitis develops, all implants should be removed, one or multiple irrigation and debridements should be performed until clinical resolution of infection is resolved, followed by combined anterior and posterior reconstruction. The anterior reconstruction may use iliac crest structural autograft. Whether or not the incidence of infection related to TLIF is any different than stand-alone posterolateral fusion with posterior pedicle instrumentation is open to debate. That is, it is unclear if TLIF increases the risk of postoperative infection. Another question is whether or not open TLIF has a higher rate of infection than MIS-TLIF. These are questions which are open to debate and evidence for is lacking.

35.6.3 Great Vessel Injury/ Retroperitoneal Injury Great vessel injury is a catastrophic complication that occurs with overly aggressive diskectomy. The goal of the diskectomy portion of the procedure should be to remove as much disk material as possible and removing as much cartilage as possible from the endplates. However, overaggressive diskectomy with violation of the ALL may risk injury to the great vessels anteriorly. One study reported the incidence of retroperitoneal injury to be 0.4%.25 Based on MRI studies of normal living human beings, the most common location of the aortic bifurcation and the most common location of the confluence of the iliac vessels are both at L4.27 Preoperative MRI should be examined closely prior to the procedure to measure the depth from the posterior annulus to the anterior annulus as well as the relationship and proximity of the large veins and arteries anteriorly to the anterior

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annulus. The ALL is a thick ligamentous structure anteriorly and should not be disrupted. In general, one should not use disk removal instruments deeper than 30 mm. Many open TLIF instrumentation systems are marked so that the surgeon can easily ascertain the depth of the instrument. If the patient becomes hemodynamically unstable during or soon after the diskectomy, or if a rush of blood begins to pool in the wound from deep in the disk space, great vessel injury should be considered. Anesthesia should be notified. An emergent vascular surgery consultation should be performed. The wound should be packed and quickly closed. Depending on how stable the patient is, and after consultation with the anesthesia and vascular surgery teams, the next step may be advanced imaging in the form of an emergent CT angiogram with venous run-through, or the patient can be turned to the supine position, and an emergent laparotomy performed to repair the bleeding vessel.

35.6.4 Postoperative Epidural Hematoma Postoperative epidural hematoma is a rare but serious complication that can result in permanent disabling neurologic deficit if not evacuated within 6 to 12 hours of the onset of symptoms.28,29 One study of 86 patients who underwent open TLIF had one postoperative epidural hematoma, a rate of 1.2%, in which urgent evacuation of the hematoma relieved the developing motor weakness in the patient.30 Oftentimes, to adequately expose the disc space, a leash of epidural vessels needs to be coagulated and bleeding can be significant with the TLIF procedure. In addition to bipolar cautery, other methods of obtaining hemostasis include Gelfoam, floseal, and other procoagulants, which can be placed onto the bleeding vessel for one or more minutes, followed by reevaluation. It is important at the end of the procedure to ensure adequate hemostasis has been achieved. If there is a significant amount of active bleeding emanating from the epidural space, this should be reinspected and procoagulants used if no specific bleeder is found. Postoperative epidural hematoma is a potential surgical emergency if the patient develops neurologic deficit, bowel or bladder changes, or other symptoms or signs of cauda equina syndrome. If this develops, an emergent MRI should be obtained and surgical decompression performed. If MRI cannot be obtained emergently, then the patient should proceed to the operating room emergently for surgical decompression and bleeding control. The evidence for drain usage is equivocal, and drains may increase the rate of blood transfusion and length of hospital stay.31 However, for open TLIF procedures, because bleeding can be substantial and the epidural space has been disrupted, we feel the potential benefit of a drain in preventing this devastating complication outweighs its risks, and therefore we do use a drain. It is typically removed on postoperative day 1 if output is less than 100 mL over 24 hours as prolonged use of postoperative drains has been associated with increased risk of surgical site infection.32 One clinical challenge in the postoperative patient is distinguishing postoperative epidural hematoma from pseudomeningocele or spinal fluid leak versus postoperative infection. MRI findings postoperatively can be difficult to interpret. A recent

Complications of Open Transforaminal Lumbar Interbody Fusion study found that postoperative epidural hematoma has a mass effect on the dural sac.33 Pseudomeningocele directly communicates with and has the same signal intensity as spinal fluid within the dural sac and does not have a mass effect. Infection has osseous involvement and in some cases destruction.

35.6.5 Interbody Dislodgement/Cage Migration Cage migration is a rare but potentially serious complication of the TLIF procedure. If it occurs immediately postoperatively, it suggests a technical error. If it occurs at a later time, it suggests failure of fusion. In one series of 531 patients who underwent TLIF, cage migration occurred 1.9% of the time, and in all cases the cage migrated posteriorly through the same path in which it was inserted.25 In another series of 125 patients with 144 disc levels, cage migration occurred in four cases, all posteriorly.34 In three of the four cases, unilateral pedicle screw instrumentation was used and in only one was bilateral pedicle screw instrumentation used, although the incidence of cage migration between unilateral fixation was 8.3% (3 of 36) versus 2.1% (1 of 48), which was not statistically significant. In all cases, cage migration occurred within the first 3 months postoperatively and in all cases a bullet-shaped cage migrated. The study also found that higher posterior disc height (greater than or equal to 6 mm) significantly increased the incidence of cage migration. In one of the four cases, it was found at revision surgery that the caudal pedicle of the instrumented TLIF had fractured and the pedicle screw had no purchase. Another series of 86 patients found cage migration to occur in one osteoporotic individual after she sustained a fall in the early postoperative period.30 She refused a revision procedure because she was asymptomatic, had no neurologic deficit, and went on to fuse uneventfully. To avoid this complication, the interbody should be placed in the anterior half of the disk space. This not only restores segmental lordosis better, but also allows the posterior disc height to collapse down, making it more difficult for the TLIF to migrate posteriorly. The interbody should fit tightly into the disk space and should not be loose at all on inspection. The interbody is not in danger of anterior migration as long as the ALL is left intact. When cage migration does occur, multiple options should be considered. If the patient is symptomatic because of the cage impinging upon the dural sac or nerve roots, then it must be removed and revised. However, if cage migration does not result in any symptoms or signs and it is solely a radiographic finding, then the surgeon may consider observation after discussing the risks of this with the patient. Migrated cages have been left in place in asymptomatic patients who have then gone on to successfully heal their fusion without any residual side effects.30,34 If observation in the early postoperative period is decided, the patient should understand that later revision will likely be more complex with a higher risk of complications. This is because of the fact that epidural scarring on fibrosis may make revision challenging and risk injury to neural elements. We, therefore, recommend revision in the early postoperative period even if migration is merely a radiographic finding because it suggests construct instability and higher probability of fusion failure.

Cage migration that occurs later than in the postoperative period is rare and suggests pseudoarthrosis. Advanced imaging with CT should be obtained to evaluate the fusion. If the fusion has failed at a late period, authors have suggested revision through an anterior approach primarily to avoid injury to neural elements. In one series of 14 patients who had revision anterior surgery for pseudoarthrosis and cage migration, in 5 of the patients a TLIF was initially performed, 4 had prior PLIF, and 5 had a prior ALIF.35

35.6.6 Postoperative Radiculitis When performed with good surgical technique, the incidence of postoperative radiculitis or nerve root injury is very low with the open TLIF procedure. Postoperative radiculitis is considered to be worsening of leg pain after surgery in a dermatomal distribution and most often occurs in the early postoperative period, within 2 weeks of surgery.36 One study of 119 patients who underwent TLIF found a rate of postoperative radiculitis of 10.9%; however, when broken down into those who had received bone morphogenetic protein 2 (BMP2) in the interbody device and those who had not, the rate of radiculitis was 14 versus 3%, respectively (p = 0.08).36 Because the open TLIF technique provides complete visualization of the traversing nerve roots from both cephalad and caudal vertebrae, injury to either of these nerve roots should be avoided with proper visualization and protection. Excessive nerve root or dural sac retraction should be avoided to prevent this complication. When radiculitis occurs postoperatively, advanced imaging studies should be obtained to rule out a source of compression on the nerve root, such as epidural hematoma, misplaced pedicle screw, migrated interbody, or ectopic bone formation. If an etiology for the radiculitis can be identified, it should be addressed surgically. If no source of radiculitis is identified, as was the case in 9 of 13 patients in the study of Rihn et al, the patient should be followed closely and treated symptomatically.36

35.6.7 Neurologic Injury The incidence of postoperative neurologic deficit with the open TLIF procedure is uncommon, reported to be 2%3,8 and as low as 0.4%.25 Neurologic injury may be in the form of weakness or numbness postoperatively, which is new. Without a source of compression, it is likely related to excessive retraction during the TLIF procedure. It can also be caused by excessive electrocauterization in the vicinity of the ganglion or nerve root. There is very little evidence to prove that the natural history of neurologic injury to the nerve root may be because of transient retraction, and it may or may not improve with time. Neurologic injury, while rare with the open TLIF, is a devastating complication. It is best to avoid this complication by retracting on the nerve root for as short a time as possible.

35.6.8 Durotomy The incidence of durotomy has been reported to be as high as 14.3 to 19.6%, and increases when the TLIF is used as part of a revision procedure.3,25 A meta-analysis of 668 open TLIF procedures revealed an incidence of durotomy of 4.8%.25

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Thoracolumbar Durotomy during the decompression portion of the procedure prior to open TLIF can be managed with dural repair and the TLIF performed as planned. The question of whether or not to keep the patient on flat bedrest for 24 hours or more depends on the size of the tear and the integrity of the repair. There are various techniques of dural repair, which are beyond the scope of this chapter. However, most often durotomies which are repaired appropriately have low likelihood of longterm complications. Complications of an unrecognized or inadequately repaired durotomy include spinal headache, pseudomeningocele, meningitis, and brain herniation. Therefore, whereas durotomies can sometimes be difficult to prevent, especially in revision situations with scarring and fibrosis, recognizing them when they do occur and performing an adequate repair may be the best method of preventing long-term consequences.

35.7 Use of rhBMP-2 in TLIF The use of recombinant human bone morphogenetic protein 2 (rhBMP2) is not recommended to be placed into the TLIF interbody device because of the fact that use of rhBMP2 in this setting has been associated with higher rates of postoperative radiculitis, ectopic bone formation, and osteolysis. Postoperative radiculitis with the use of rhBMP2 for use in TLIF has an incidence of up to 14.0%.36 The reasons for postoperative radiculitis in the setting of rhBMP2 usage are unclear but are believed to be because of inflammatory changes near the nerve root, including heterotopic bone formation. In addition to radiculitis, the same study found a 5.8% incidence of vertebral body osteolysis, 2.3% rate of ectopic bone formation, and 3.5% incidence of wound infection. An earlier study examining the use of rhBMP2 in PLIF found a 75% incidence of extradiscal ectopic bone formation versus 12.9% of the control non-rhBMP2 group (p < 0.0001).37 Furthermore, whereas rhBMP-2 is believed to promote spine fusion, based on a reanalysis of the published Level I and II evidence, others have suggested that the rate of complications with rhBMP-2 is 10 to 50 times higher than was originally reported in earlier industry-sponsored studies.38 Given the complications of radiculitis, ectopic bone formation and vertebral endplate osteolysis, as well as the high rate of complications associated with it in posterior spinal fusion surgery, we do not routinely use rhBMP2 for open TLIF. Instead, we pack the interbody device with local autograft. High-dose rhBMP2 (40-mg rhBMP-2 per level) for use in posterolateral fusion has been found to increase the carcinogenic risk to the patient as well.38 When used in TLIF, a retrospective study showed a 54% rate of adjacent vertebral osteolysis at 3 to 6 months postoperatively, which was still as high as 41% by 1 to 2 years postoperatively.39 Another retrospective study of rhBMP-2 use with TLIF found a 27.6% rate of osteolysis, and 31.6% of patients with osteolysis; there was significant graft subsidence, related to the severity of the osteolytic defect.40 Therefore, rhBMP-2 is to be avoided in the open TLIF procedure.

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35.8 Key Points ●

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Open TLIF offers the surgeon the ability to directly decompress the nerve root while at the same time providing anterior column support to promote fusion in conjunction with a posterolateral fusion, all with one surgical approach. Successful fusion is aided by circumferential techniques, including the TLIF. Open TLIF is indicated for degenerative spondylolisthesis, scoliosis, and far lateral disc herniation at all lumbar levels. With proper indications and good surgical technique, complication rates of open TLIF are acceptably low. The use of RhBMP-2 with the TLIF is generally not indicated as it increases the rate of osteolysis, radiculitis, and heterotopic bone formation.

35.9 Key References 4:

This was a prospectively enrolled, retrospectively matched cohort analysis comparing 42 patients who underwent TLIF to 42 matched patients who underwent ALIF in the setting of deformity surgery. The study found no difference in overall or neurologic complication rates between the two and one pseudoarthrosis in an ALIF patient versus none in the TLIF patients. The TLIF group had shorter operative time and better correction of coronal plane deformity, whereas ALIF group had better lordotic correction. 13: This was a prospective randomized study comparing unilateral TLIF with unilateral pedicle screw instrumentation to bilateral TLIF and bilateral pedicle screw instrumentation. It showed trends toward higher rates of fusion with bilateral TLIF (not significantly different) with significantly less blood loss and shorter operative time in the unilateral group but significantly better relief of back pain and leg pain based on VAS scores as well as better relief of leg numbness with the bilateral TLIF/bilateral pedicle screw group. 36: Retrospective comparative study of 130 patients who underwent single level TLIF procedure comparing 33 patients who received iliac crest autograft versus 86 patients who received rhBMP-2. Whereas the autograft group had a higher complication rate, it was not statistically significant. The rhBMP-2 group had a higher incidence of postoperative radiculitis (14 vs. 3%) though this was not significant (p = 0.08). Fusion rates were also not significantly different. 15: Cadaveric biomechanical study comparing four different L4–L5 reconstruction techniques following TLIF procedure of the spinal motion segment in terms of segmental flexibility using five cadavers. The study found that TLIF with bilateral pedicle screws most closely approximated the L4–L5 segmental flexibility of the intact spine. It confirms the original Harms and Jeszenszky recommendations that the TLIF be performed with bilateral pedicle screw instrumentation. 25: This is a large retrospective study that examined the incidence of the most common complications with the TLIF procedure, as well as risk factors for complications in a group of 531 consecutive TLIF procedures at a single institution. Durotomy and infection were the most common complications of the TLIF procedure. Complications were more common in revision procedures and multilevel interbody fusions.

Complications of Open Transforaminal Lumbar Interbody Fusion

References [1] Hee HT, Castro FP, Jr, Majd ME, Holt RT, Myers L. Anterior/posterior lumbar fusion versus transforaminal lumbar interbody fusion: analysis of complications and predictive factors. J Spinal Disord. 2001; 14(6):533–540 [2] Whitecloud TS, III, Roesch WW, Ricciardi JE. Transforaminal interbody fusion versus anterior-posterior interbody fusion of the lumbar spine: a financial analysis. J Spinal Disord. 2001; 14(2):100–103 [3] Villavicencio AT, Burneikiene S, Bulsara KR, Thramann JJ. Perioperative complications in transforaminal lumbar interbody fusion versus anterior-posterior reconstruction for lumbar disc degeneration and instability. J Spinal Disord Tech. 2006; 19(2):92–97 [4] Dorward IG, Lenke LG, Bridwell KH, et al. Transforaminal versus anterior lumbar interbody fusion in long deformity constructs: a matched cohort analysis. Spine. 2013; 38(12):E755–E762 [5] Cloward RB. The treatment of ruptured lumbar intervertebral discs by vertebral body fusion. I. Indications, operative technique, after care. J Neurosurg. 1953; 10(2):154–168 [6] Lin PM. A technical modification of Cloward’s posterior lumbar interbody fusion. Neurosurgery. 1977; 1(2):118–124 [7] Humphreys SC, Hodges SD, Patwardhan AG, Eck JC, Murphy RB, Covington LA. Comparison of posterior and transforaminal approaches to lumbar interbody fusion. Spine. 2001; 26(5):567–571 [8] Mehta VA, McGirt MJ, Garcés Ambrossi GL, et al. Trans-foraminal versus posterior lumbar interbody fusion: comparison of surgical morbidity. Neurol Res. 2011; 33(1):38–42 [9] Closkey RF, Parsons JR, Lee CK, Blacksin MF, Zimmerman MC. Mechanics of interbody spinal fusion. Analysis of critical bone graft area. Spine. 1993; 18 (8):1011–1015 [10] Javernick MA, Kuklo TR, Polly DW, Jr. Transforaminal lumbar interbody fusion: unilateral versus bilateral disk removal—an in vivo study. Am J Orthop. 2003; 32(7):344–348, discussion 348 [11] Potter BK, Freedman BA, Verwiebe EG, Hall JM, Polly DW, Jr, Kuklo TR. Transforaminal lumbar interbody fusion: clinical and radiographic results and complications in 100 consecutive patients. J Spinal Disord Tech. 2005; 18 (4):337–346 [12] Villavicencio AT, Burneikiene S, Roeca CM, Nelson EL, Mason A. Minimally invasive versus open transforaminal lumbar interbody fusion. Surg Neurol Int. 2010; 1:12 [13] Aoki Y, Yamagata M, Ikeda Y, et al. A prospective randomized controlled study comparing transforaminal lumbar interbody fusion techniques for degenerative spondylolisthesis: unilateral pedicle screw and 1 cage versus bilateral pedicle screws and 2 cages. J Neurosurg Spine. 2012; 17(2):153–159 [14] Harms JG, Jeszenszky D. Die posteriore, lumbale, interkorporelle Fusion in unilateraler transforaminaler Technik. Oper Orthop Traumatol. 1998; 10 (2):90–102 [15] Harris BM, Hilibrand AS, Savas PE, et al. Transforaminal lumbar interbody fusion: the effect of various instrumentation techniques on the flexibility of the lumbar spine. Spine. 2004; 29(4):E65–E70 [16] Ames CP, Acosta FL, Jr, Chi J, et al. Biomechanical comparison of posterior lumbar interbody fusion and transforaminal lumbar interbody fusion performed at 1 and 2 levels. Spine. 2005; 30(19):E562–E566 [17] Park P, Garton HJ, Gala VC, Hoff JT, McGillicuddy JE. Adjacent segment disease after lumbar or lumbosacral fusion: review of the literature. Spine. 2004; 29 (17):1938–1944 [18] Rahm MD, Hall BB. Adjacent-segment degeneration after lumbar fusion with instrumentation: a retrospective study. J Spinal Disord. 1996; 9(5):392–400 [19] Lawrence BD, Wang J, Arnold PM, Hermsmeyer J, Norvell DC, Brodke DS. Predicting the risk of adjacent segment pathology after lumbar fusion: a systematic review. Spine. 2012; 37(22) Suppl:S123–S132

[20] Kaito T, Hosono N, Fuji T, Makino T, Yonenobu K. Disc space distraction is a potent risk factor for adjacent disc disease after PLIF. Arch Orthop Trauma Surg. 2011; 131(11):1499–1507 [21] Lorenz M, Zindrick M, Schwaegler P, et al. A comparison of single-level fusions with and without hardware. Spine. 1991; 16(8) Suppl:S455–S458 [22] Zdeblick TA. A prospective, randomized study of lumbar fusion. Preliminary results. Spine. 1993; 18(8):983–991 [23] Ha KY, Schendel MJ, Lewis JL, Ogilvie JW. Effect of immobilization and configuration on lumbar adjacent-segment biomechanics. J Spinal Disord. 1993; 6 (2):99–105 [24] Aota Y, Kumano K, Hirabayashi S. Postfusion instability at the adjacent segments after rigid pedicle screw fixation for degenerative lumbar spinal disorders. J Spinal Disord. 1995; 8(6):464–473 [25] Tormenti MJ, Maserati MB, Bonfield CM, et al. Perioperative surgical complications of transforaminal lumbar interbody fusion: a single-center experience. J Neurosurg Spine. 2012; 16(1):44–50 [26] Ha KY, Kim YH. Postoperative spondylitis after posterior lumbar interbody fusion using cages. Eur Spine J. 2004; 13(5):419–424 [27] Vaccaro AR, Kepler CK, Rihn JA, et al. Anatomical relationships of the anterior blood vessels to the lower lumbar intervertebral discs: analysis based on magnetic resonance imaging of patients in the prone position. J Bone Joint Surg Am. 2012; 94(12):1088–1094 [28] Lawton MT, Porter RW, Heiserman JE, Jacobowitz R, Sonntag VK, Dickman CA. Surgical management of spinal epidural hematoma: relationship between surgical timing and neurological outcome. J Neurosurg. 1995; 83(1):1–7 [29] Amiri AR, Fouyas IP, Cro S, Casey AT. Postoperative spinal epidural hematoma (SEH): incidence, risk factors, onset, and management. Spine J. 2013; 13 (2):134–140 [30] Taneichi H, Suda K, Kajino T, Matsumura A, Moridaira H, Kaneda K. Unilateral transforaminal lumbar interbody fusion and bilateral anterior-column fixation with two Brantigan I/F cages per level: clinical outcomes during a minimum 2-year follow-up period. J Neurosurg Spine. 2006; 4(3):198–205 [31] Walid MS, Abbara M, Tolaymat A, et al. The role of drains in lumbar spine fusion. World Neurosurg. 2012; 77(3–4):564–568 [32] Rao SB, Vasquez G, Harrop J, et al. Risk factors for surgical site infections following spinal fusion procedures: a case-control study. Clin Infect Dis. 2011; 53(7):686–692 [33] Radcliff KE, Morrison WB, Kepler C, et al. Distinguishing pseudomeningocele, epidural hematoma, and postoperative infection on postoperative MRI. Clin Spine Surg. 2016 (e-pub ahead of print). DOI: 10.1097/BSD.0b013e31828f9 203 [34] Aoki Y, Yamagata M, Nakajima F, et al. Examining risk factors for posterior migration of fusion cages following transforaminal lumbar interbody fusion: a possible limitation of unilateral pedicle screw fixation. J Neurosurg Spine. 2010; 13(3):381–387 [35] Nguyen HV, Akbarnia BA, van Dam BE, et al. Anterior exposure of the spine for removal of lumbar interbody devices and implants. Spine. 2006; 31 (21):2449–2453 [36] Rihn JA, Patel R, Makda J, et al. Complications associated with single-level transforaminal lumbar interbody fusion. Spine J. 2009; 9(8):623–629 [37] Haid RW, Jr, Branch CL, Jr, Alexander JT, Burkus JK. Posterior lumbar interbody fusion using recombinant human bone morphogenetic protein type 2 with cylindrical interbody cages. Spine J. 2004; 4(5):527–538, discussion 538–539 [38] Carragee EJ, Hurwitz EL, Weiner BK. A critical review of recombinant human bone morphogenetic protein-2 trials in spinal surgery: emerging safety concerns and lessons learned. Spine J. 2011; 11(6):471–491 [39] Helgeson MD, Lehman RA, Jr, Patzkowski JC, Dmitriev AE, Rosner MK, Mack AW. Adjacent vertebral body osteolysis with bone morphogenetic protein use in transforaminal lumbar interbody fusion. Spine J. 2011; 11(6):507–510 [40] Knox JB, Dai JM, III, Orchowski J. Osteolysis in transforaminal lumbar interbody fusion with bone morphogenetic protein-2. Spine. 2011; 36(8):672–676

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36 Complications of Instrumentation in Minimally Invasive Transforaminal Lumbar Interbody Fusion Steven J. Fineberg, Matthew Oglesby, and Kern Singh

36.1 Introduction Significant advances have been made in lumbar fusion techniques since Cloward first introduced the posterior lumbar interbody fusion (PLIF) more than 50 years ago. In 1982, Harms and Rolinger developed the transforaminal lumbar interbody fusion (TLIF), a modification of the PLIF approach.1 Although PLIF is still commonly performed,2,3,4,5 many surgeons now prefer the TLIF procedure in the management of spinal disorders requiring lumbar arthrodesis.6,7,8 Compared to the PLIF, distinct advantages of the TLIF include unilateral exposure, decreased neural retraction, and a more lateral angle of approach that facilitates revision surgery. Innovations in spinal instrumentation have taken place along with the advancements in surgical techniques. Pedicle screw instrumentation was first utilized by Boucher in the 1950s and later popularized by Roy-Camille et al in the 1980s.9,10,11 Today, pedicle screws and interconnecting rods are frequently utilized for various procedures to improve stability, including the TLIF. Additionally, interbody implants are utilized in TLIF procedures in order to restore disc height, provide stability, and to potentially eliminate discogenic sources of pain. In recent years, minimally invasive spine surgery has gained considerable momentum and increased acceptance among spine surgeons. Minimally invasive surgical (MIS) approaches to the spine utilize specialized retraction systems to minimize the exposure of the spine. In a MIS TLIF, decompression and fusion may be performed with smaller incisions, minimal muscle trauma, decreased intraoperative blood loss, reduced postoperative pain, and earlier rehabilitation.12,13,14 Complications of MIS TLIF instrumentation are similar to those of the open approach, including pedicle screw misplacement, improper endplate preparation, subsidence or migration of an interbody implant, and pseudarthrosis. The risk of these complications may be increased in the MIS approach if the surgeon does not take the appropriate measures to prevent them. This chapter discusses potential complications related to spinal instrumentation in an MIS TLIF and techniques to avoid them.

36.2 Purpose of Instrumentation The spinal column provides structural support to the body. The biomechanics of the spinal column can be described simply by the three-column classification proposed by Denis, the anterior, middle, and posterior columns.15 Biomechanical analysis of the spine demonstrates that approximately 80% of axial loads are transmitted through the anterior and middle columns, while the remaining 20% are transferred through the posterior column. Two of the three columns must be intact for spinal stability.15 Therefore, spinal instrumentation is often required when more than one column is disrupted, such as the iatrogenic instability introduced from the unilateral facetectomy and discectomy in a TLIF. The purpose of instrumentation in a TLIF is to

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stabilize the spine until fusion takes place. TLIF instrumentation typically involves the use of an interbody cage to stabilize the anterior column as well as pedicle screws and rods that provide stabilization across all three columns. Interbody cages are utilized in a TLIF to provide structural support to the anterior column, maintain disc height, and restore physiologic lordosis. Implants are made from iliac crest autograft, allograft bone, metals, carbon fiber, or polyetherether-ketone (PEEK). Cages may also be filled with local autograft, allograft bone chips, and/or a biologic agent such as bone morphogenetic protein (BMP) to enhance fusion rates. Interbody implants come in various shapes and sizes; however, in a TLIF, a rectangular, curved, or bullet-shaped cage is typically preferred. Pedicle screw fixation is generally used in lumbar fusion procedures to provide more rigid fixation that may enhance fusion rates.16 Currently, pedicle screws are approved by the Food and Drug Administration for use in the lumbar spine for the treatment of degenerative spondylolisthesis with neurologic impairment, fracture, dislocation, scoliosis, kyphosis, spinal tumors, or pseudarthrosis following a failed previous fusion.17 Pedicle screws may be placed before or after the decompression and disc space preparation. Placement of pedicle screws prior to disc space preparation may assist in distraction, allowing easier access. Interconnecting rods are placed at the end of the case, and compression is applied to restore sagittal alignment.

36.3 Relevant Anatomy An in-depth knowledge of the three-dimensional surgical anatomy is critical when using the MIS approach, considering the limited exposure. Due to the steep learning curve associated with MIS procedures, the surgeon should be familiar with the open approach before attempting MIS TLIF. In the MIS technique, the surgeon must become proficient in maneuvering longer bayoneted instruments through the tubular retractors. Retractor placement is an important step to assure that the relevant anatomy can be identified in the surgical field. The approach for retractor placement begins with an incision approximately 4 cm from the midline. A guide pin, serial tubular dilators, and finally the tubular retractor are placed with a medial trajectory toward the medial portion of the facet complex (▶ Fig. 36.1). The retractor trajectory must also be in line with the disc space. Once the retractor is in place, the visible anatomy within the working channel should include the facet complex laterally, the inferior portion of the cephalad lamina superiorly, and the ligamentum flavum medially. After retractor placement, the next step is to perform the facetectomy. A laminectomy may be performed as well if there is stenosis. If bilateral stenosis is present, the retractor may be angulated in a more medial direction to undercut the spinous process and perform a contralateral laminectomy and medial facetectomy. The disc space should be visible in the center of the surgical field after the facet is removed. At this point, the

Complications of Instrumentation in Minimally Invasive TLIF

Fig. 36.2 Intraoperative photograph of a minimally invasive surgical transforaminal lumbar interbody fusion. The facet complex has been removed. The suction tip is located in the disc space. The thecal sac and traversing nerve root are visible in the center of the surgical field. The exiting nerve root is seen laterally, just cranial to the disc space.

Fig. 36.1 Lateral fluoroscopic image demonstrating tubular retractor placement directly in line with the disc space.

thecal sac and traversing nerve root are visible in the medial aspect of the portal. The exiting nerve root hugs the medial and inferior borders of the pedicle as it enters the neuroforamen and it may be seen in the superolateral aspect of the portal (▶ Fig. 36.2). Compared to the PLIF approach, minimal medial retraction of the thecal sac and traversing nerve root are required for intervertebral disc space preparation in a TLIF. Knowledge of pedicle anatomy is also important when placing pedicle screws using minimally invasive techniques. Although intraoperative fluoroscopy is helpful in locating the pedicles, the surgeon must be familiar with the three-dimensional orientation of the pedicles to minimize complications related to pedicle screw misplacement. The entry site for pedicle screws in the lumbar spine is at the junction of the transverse process and the lateral facet, which is located at the 10- or 2-o’clock position on the pedicle on anteroposterior (AP) fluoroscopy (▶ Fig. 36.3).18 The lordotic curve of the lumbar spine requires a rostral inclination of screws at upper lumbar segments and a caudal inclination at lower levels.19 In general, the sagittal angle approximates 0° at the L4 vertebra.19 Pedicle screws also must be placed with a medial trajectory on the coronal plane. The coronal angle increases 5° per level from L1 to the sacrum, with L4–S1 levels typically requiring approximately 20° to 30° of medial angulation.19 Preoperative planning on computed tomographic (CT) scans or magnetic resonance imaging may assist the surgeon in assessing the pedicle orientation and diameter.

36.4 Complications of Instrumentation 36.4.1 Pedicle Screw Misplacement Misplacement is one of the most frequent complications of pedicle screws.20,21,22 Lonstein et al retrospectively reviewed

Fig. 36.3 Anteroposterior fluoroscopic image demonstrating the Jamshidi needle located at the starting point (2-o'clock position) which correlates to the junction between the transverse process and facet complex.

4,790 pedicle screws and found that 242 (5.1%) were not located entirely within the pedicle and vertebral body.20 The most common type of misplacement was penetration of the anterior cortex of the vertebral body (2.8%), followed by the lateral cortex of the pedicle (1.0%), the inferior cortex (0.6%), the medial cortex (0.4%), and the inferior cortex (0.2%).20 Unlike the open pedicle screw placement, it is impossible to visualize the walls of the pedicle to assess orientation prior to screw placement. Therefore, the risk of pedicle screw misplacement can be exaggerated in an MIS TLIF.

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Fig. 36.4 Medially placed pedicle screw violating the pedicle and encroaching upon the spinal canal. (With kind permission from Springer Science + Business Media: Fig. 2 of Modi et al.21)

Medial and inferior pedicle wall breaches have the potential for disastrous outcomes due to the proximity of the nerve root as it exits the neuroforamen just inferior to the pedicle. When placed too medially, the pedicle screw may enter the spinal canal (▶ Fig. 36.4). Violation of the medial or inferior wall may result in new-onset radicular pain or motor weakness.20 Symptoms of nerve irritation typically present early in the postoperative period and warrant a CT scan to assess placement of the pedicle screw. Intraoperative electromyography (EMG) is recommended after pedicle screw placement in a MIS TLIF to assure the nerve is not affected by the screw.23 If there is a positive response on intraoperative EMG (< 11 milliamps), a pedicle breach has likely occurred and the screw should be redirected in more lateral trajectory.24 Several authors have demonstrated that anterior penetration of the vertebral body cortex is the most common type of perforation, with most occurring in the sacrum.20,22 Pedicle screws placed too anteriorly have the potential to injure neurovascular structures depending on the level (▶ Fig. 36.5). Lateral screw misplacement is also a common complication of pedicle screws. When placed too far laterally, the screw may be located outside of the vertebral body and impinge on the neuroforamen (▶ Fig. 36.6). In addition to nerve irritation, a laterally placed screw may decrease stability leading to pseudarthrosis due to instability. In a MIS TLIF, the risk of screw misplacement may be increased by the limited surgical exposure and difficulty in visualizing anatomic structures. Therefore, a working knowledge of the three-dimensional anatomy and utilization of imaging to assist in pedicle screw placement become even more critical in a MIS case. Fluoroscopy is frequently utilized intraoperatively to assist in pedicle screw placement. In the fluoroscopic technique, biplanar fluoroscopy with perfect AP and lateral images

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Fig. 36.5 Pedicle screw penetrating the anterior vertebral cortex. Contralateral pedicle screw with medial wall violation. (With kind permission from Springer Science + Business Media: Fig. 5 of Modi et al.21)

Fig. 36.6 Laterally displaced pedicle screw that does not enter the vertebral body. (With kind permission from Springer Science + Business Media: Fig. 3 of Modi et al.21)

are essential for safe pedicle screw placement.25 With the endplates and pedicles clearly visualized on AP fluoroscopy, a Jamshidi needle is advanced to the 10- or 2-o'clock position on the pedicle which corresponds to the junction of the transverse process and facet complex. The Jamshidi is slowly advanced 15 to 20 mm into the pedicle, using AP fluoroscopy to assure the medial wall has not been breached. A K-wire is then advanced through the Jamshidi until it passes the posterior vertebral

Complications of Instrumentation in Minimally Invasive TLIF

Fig. 36.7 Anteroposterior fluoroscopic image demonstrating pedicle screws placed safely in the L4 and L5 pedicles. Radiopaque markers from the interbody cage are also visualized confirming central placement of the cage in the disc space.

cortex on lateral fluoroscopy without crossing the medial pedicle wall on AP fluoroscopy. To place the screw, the pedicle is tapped over the K-wire. The tap can be stimulated with EMG monitoring to identify if a pedicle breach has occurred. When tapping and placing the pedicle screw, it is important to obtain lateral fluoroscopic images to confirm that the guide wire does not inadvertently penetrate the anterior cortex of the vertebral body.25,26,27 Fluoroscopy-guided pedicle screw placement has been demonstrated to be safe and effective (▶ Fig. 36.7)22; however, it carries the limitation of increased operative time and radiation exposure to the surgical staff and patient.28 Computer-assisted navigation represents another imaging modality for placing pedicle screws safely while decreasing radiation exposure to surgical staff. Navigation allows the surgeon to view the three-dimensional orientation of the pedicle during placement. Smith et al demonstrated a 6.2% incidence of pedicle breach identified on CT scan in 601 percutaneously placed pedicle screws in 151 patients, with only 2 of the 37 breaches being symptomatic.29 Additional studies have found mixed results when comparing the accuracy of computer-navigated and fluoroscopic techniques. Schizas et al performed a prospective study comparing the accuracy of pedicle screw placement with a three-dimensional computer-navigated technique and a two-dimensional fluoroscopic technique3031,32. The authors demonstrated a 4.7% rate of screw misplacement using the computer-navigated technique and a 7.8% rate of screw misplacement with the fluoroscopic technique, although this was not statistically different (p = 0.71).32

36.4.2 Improper Disc Space Preparation Preparation of the disc space is a critical step in the MIS TLIF procedure. The surgeon must remove as much of the

Fig. 36.8 Lateral fluoroscopic image demonstrating endplate preparation with a paddle distractor.

intervertebral disc as possible and meticulously prepare the endplate to create a healthy bleeding bed of bone in order for fusion to occur. An incomplete discectomy may result in pseudarthrosis due to the decreased surface area of the fusion bed. Similarly, failure to remove the cartilaginous endplate will also impede arthrodesis. On the other hand, overly aggressive endplate removal may lead to violation of the endplate, thus decreasing its structural integrity (▶ Fig. 36.8). The biomechanical load-sharing ability of an interbody graft necessitates that the endplate is intact.33 Endplate violation may lead to subsidence of the graft into the vertebral body.33 Therefore, if a significant violation occurs, the surgeon should consider aborting the interbody portion of the procedure.33 Visualization of the disc space is essential to perform an adequate discectomy; therefore, significant care should be taken to assure accurate placement of the tubular retractor.34 The correct position of the retractor is centered over the facet joint with a trajectory parallel to the disc space, angled toward the midline. Once the facet is removed, the disc space should be clearly visible. Incomplete resection of the pars interarticularis results in a small vertical window and potential medialization of the working portal. In cases of extreme disc space collapse, the PLL may be released as far to the contralateral side as possible. There are a variety of instruments surgeons may use to prepare the disc space, including curettes, rongeurs, paddle distractors, and shavers. It is important that the surgeon become experienced at using these tools. Pumberger et al demonstrated that a surgeon’s experience plays a role in the adequacy of disc space preparation, with attending surgeons having significantly increased total areas of discectomy compared to those discectomies performed by fellows.35 The authors also demonstrated that attending surgeons performed more thorough discectomies compared to fellows. Regardless of experience, both attendings and fellows performed more thorough discectomies

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Fig. 36.9 (a,b) Coronal and sagittal CT images following minimally invasive surgical transforaminal lumbar interbody fusion with utilization of bone morphogenetic protein. The interbody cage (arrows) has migrated posteriorly into the neuroforamen.

using powered discectomy instruments compared to manual instruments.35 The authors also demonstrated that an increased area of discectomy was performed when using powered tools compared to conventional instruments, regardless of training.35 These findings highlight the importance of being experienced in the open approach before performing a MIS TLIF.

36.4.3 Interbody Cage Migration and Subsidence The purpose of the interbody cage in a MIS TLIF is to maintain disc height and decompression of the neuroforamen, and to provide mechanical support to the vertebral column until a solid fusion is obtained. Cages may be filled or surrounded by bone graft that promotes fusion. Ideally, load is distributed between the implant and the bone graft.36 Although typically wedged tightly into the disc space, interbody cages are not secured in place and, therefore, have the potential to migrate. After a TLIF, a cage that is too small or placed posteriorly in the intervertebral space may migrate into the spinal canal or neuroforamen, causing nerve compression (▶ Fig. 36.9). Additionally, if the adjacent endplates do not have the structural integrity to support the interbody cage, the cage may subside into the vertebral bodies. Proper disc space preparation and careful selection of interbody implants may help reduce the frequency of cage migration and subsidence. Rates of posterior cage migration range from 1.1 to 23% in the literature.37,38,39,40 Zhao et al reviewed 512 patients who underwent TLIF to assess risk factors for interbody cage migration. The authors demonstrated significant differences in the rate of cage migration depending on cage shape, size, endplate morphology, and the number of levels fused.37 When migration does occur, it is typically within the first several months following surgery.37 Aoki et al reported three case reports of posterior cage migration in the neuroforamen due to undersized, bulletshaped cages.41 Two of the three patients were asymptomatic and went on to fuse without complications.41 The third patient developed nerve root irritation and had a revision to a larger cage. The authors concluded that cage migration after TLIF does not always cause nerve compression and that revision surgery for cage migration is relatively safe given the posterolateral location of the cage.41 In a retrospective review of 512 patients

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Fig. 36.10 Postoperative CT scan demonstrating interbody cage subsidence and pseudarthrosis.

undergoing TLIF by Zhao et al, only 1.1% of patients were found to have posterior cage migration.37 The authors demonstrated the rate of cage migration to be significantly increased with rectangular cages versus kidney-shaped (3.1 vs. 0.3%, p < 0.05), small cages versus large cages (5.1 vs. 0.5%, p < 0.05), two-level TLIFs versus single-level TLIFs (5.7 vs. 0.2%, p < 0.05), and among patients with flat endplates versus concave endplates (3.5 vs. 0.3%, p < 0.05).37 Additional risk factors for cage migration have been reported, including bioabsorbable cages, osteolysis secondary to BMP use, and unilateral pedicle screw fixation.38,39,40,42 A small amount of subsidence is not uncommon after an interbody fusion; however, excessive loss of disc height may lead to collapse of the neuroforamen and compression of the nerve root.43 The majority of cage subsidence occurs within the first year following surgery (▶ Fig. 36.10).44 Fukuta et al identified that older age and cage placement in the center of the intervertebral disc space were risk factors for subsidence due to decreased structural integrity of the endplates.45 Matsumura et al demonstrated that use of cylindrical cages also increased the rate of subsidence over box-shaped cages.43 Increased rates of subsidence have also been attributed to osteolysis associated with BMP utilization.39

Complications of Instrumentation in Minimally Invasive TLIF

36.5 Summary The MIS TLIF allows for bilateral decompression and fusion through a unilateral approach, decreasing the amount of neural retraction. Compared to an open TLIF, the MIS approach is associated with decreased blood loss, postoperative pain, and hospitalizations.12,13,14 Despite the advantages, complications related to spinal instrumentation in a MIS TLIF do still occur. Misplacement of pedicle screws, interbody cage migration, subsidence, and pseudarthrosis are some of the many complications that may occur if caution is not emphasized in the MIS approach. To prevent these complications, spine surgeons must appreciate the technical subtleties required to perform MIS spine surgery before implementing these procedures into their practice.

36.6 Key Points ●

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The MIS TLIF technique can be performed safely for lumbar decompression and fusion through a muscle-sparing approach, leading to decreased blood loss, decreased postoperative pain, and earlier rehabilitation compared to the open approach. Screw misplacement is a common complication of pedicle screws and may lead to neurovascular injury. Pedicle screw misplacement may be avoided with careful technique, utilization of fluoroscopy or computer navigation, and a working knowledge of the pedicle anatomy. Meticulous disc space preparation is essential to maximize the potential for arthrodesis. Selection of interbody cage shape, size, and materials plays an important role in preventing cage migration.

References [1] Harms J, Rolinger H. [A one-stager procedure in operative treatment of spondylolistheses: dorsal traction-reposition and anterior fusion (author’s transl)]. Z Orthop Ihre Grenzgeb. 1982; 120(3):343–347 [2] Fraser RD. Interbody, posterior, and combined lumbar fusions. Spine. 1995; 20(24) Suppl:167S–177S [3] Branch CL, Jr. The case for posterior lumbar interbody fusion. Clin Neurosurg. 1996; 43:252–267 [4] McLaughlin MR, Haid RW, Jr, Rodts GE, Jr, Subach BR. Posterior lumbar interbody fusion: indications, techniques, and results. Clin Neurosurg. 2000; 47:514–527 [5] Stonecipher T, Wright S. Posterior lumbar interbody fusion with facet-screw fixation. Spine. 1989; 14(4):468–471 [6] Lowe TG, Tahernia AD, O’Brien MF, Smith DA. Unilateral transforaminal posterior lumbar interbody fusion (TLIF): indications, technique, and 2-year results. J Spinal Disord Tech. 2002; 15(1):31–38 [7] Moskowitz A. Transforaminal lumbar interbody fusion. Orthop Clin North Am. 2002; 33(2):359–366 [8] Rosenberg WS, Mummaneni PV. Transforaminal lumbar interbody fusion: technique, complications, and early results. Neurosurgery. 2001; 48(3):569– 574, discussion 574–575 [9] Boucher HH. A method of spinal fusion. J Bone Joint Surg Br. 1959; 41-B (2):248–259 [10] Roy-Camille R, Saillant G, Mazel C. Internal fixation of the lumbar spine with pedicle screw plating. Clin Orthop Relat Res. 1986(203):7–17 [11] Roy-Camille R, Saillant G, Mazel C. Plating of thoracic, thoracolumbar, and lumbar injuries with pedicle screw plates. Orthop Clin North Am. 1986; 17 (1):147–159 [12] Kim CW, Siemionow K, Anderson DG, Phillips FM. The current state of minimally invasive spine surgery. J Bone Joint Surg Am. 2011; 93(6):582–596

[13] Park P, Foley KT. Minimally invasive transforaminal lumbar interbody fusion with reduction of spondylolisthesis: technique and outcomes after a minimum of 2 years’ follow-up. Neurosurg Focus. 2008; 25(2):E16 [14] McAfee PC, Phillips FM, Andersson G, et al. Minimally invasive spine surgery. Spine. 2010; 35(26) Suppl:S271–S273 [15] Denis F. The three column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine. 1983; 8(8):817–831 [16] Brodke DS, Bachus KN, Mohr RA, Nguyen BK. Segmental pedicle screw fixation or cross-links in multilevel lumbar constructs. a biomechanical analysis. Spine J. 2001; 1(5):373–379 [17] Friedman MA, Shalala DE. Orthopedic Devices: Classification and Reclassification of Pedicle Screw Spinal Systems. Washington, DC: Food and Drug Administration; 1998 [18] Singh K, Vaccaro, AR. Pocket Atlas of Spine Surgery. New York, NY: Thieme; 2012 [19] Awashti D, Thomas N. Pedicle Screw Placement. Available at: http://www. medschool.lsuhsc.edu/neurosurgery/nervecenter/tlscrew.html. Accessed April 19, 2013 [20] Lonstein JE, Denis F, Perra JH, Pinto MR, Smith MD, Winter RB. Complications associated with pedicle screws. J Bone Joint Surg Am. 1999; 81(11):1519– 1528 [21] Modi HN, Suh SW, Fernandez H, Yang JH, Song HR. Accuracy and safety of pedicle screw placement in neuromuscular scoliosis with free-hand technique. Eur Spine J. 2008; 17(12):1686–1696 [22] Sethi A, Lee A, Vaidya R. Lumbar pedicle screw placement: using only AP plane imaging. Indian J Orthop. 2012; 46(4):434–438 [23] Luo W, Zhang F, Liu T, Du XL, Chen AM, Li F. Minimally invasive transforaminal lumbar interbody fusion aided with computer-assisted spinal navigation system combined with electromyography monitoring. Chin Med J (Engl). 2012; 125(22):3947–3951 [24] Clements DH, Morledge DE, Martin WH, Betz RR. Evoked and spontaneous electromyography to evaluate lumbosacral pedicle screw placement. Spine. 1996; 21(5):600–604 [25] Fassett DR, Brodke DS. Percutaneous lumbar pedicle screws. In: Vaccaro AR, Bono CM, eds. Minimally Invasive Spine Surgery. New York, NY: MarcelDecker; 2007:229–235 [26] Karikari IO, Isaacs RE. Minimally invasive transforaminal lumbar interbody fusion: a review of techniques and outcomes. Spine. 2010; 35(26) Suppl: S294–S301 [27] Gala VC, Haid RW Jr. Minimally invasive transforaminal lumbar interbody fusion. In: Sandhu FA, Voyadzis JM, Fessler RG, eds. Decision Making for Minimally Invasive Spine Surgery. New York, NY: Thieme; 2011:90–102 [28] Rampersaud YR, Foley KT, Shen AC, Williams S, Solomito M. Radiation exposure to the spine surgeon during fluoroscopically assisted pedicle screw insertion. Spine. 2000; 25(20):2637–2645 [29] Smith ZA, Sugimoto K, Lawton CD, et al. Incidence of lumbar spine pedicle breach following percutaneous screw fixation: a radiographic evaluation of 601 screws in 151 patients. J Spinal Disord Tech. 2014; 27(7):358–363 [30] Waschke A, Walter J, Duenisch P, Reichart R, Kalff R, Ewald C. CT-navigation versus fluoroscopy-guided placement of pedicle screws at the thoracolumbar spine: single center experience of 4,500 screws. Eur Spine J. 2013; 22 (3):654–660 [31] Yang BP, Wahl MM, Idler CS. Percutaneous lumbar pedicle screw placement aided by computer-assisted fluoroscopy-based navigation: perioperative results of a prospective, comparative, multicenter study. Spine. 2012; 37 (24):2055–2060 [32] Schizas C, Thein E, Kwiatkowski B, Kulik G. Pedicle screw insertion: robotic assistance versus conventional C-arm fluoroscopy. Acta Orthop Belg. 2012; 78(2):240–245 [33] Hilibrand AS, Smith HE. Transforaminal lumbar interbody fusion. In: Herkowitz HN, Garfin SR, Eismont FJ, et al. eds. Rothman-Simeone: The Spine. 6th ed. Philadelphia, PA: Elsevier; 2011 [34] Ozgur BM, Yoo K, Rodriguez G, Taylor WR. Minimally-invasive technique for transforaminal lumbar interbody fusion (TLIF). Eur Spine J. 2005; 14(9):887– 894 [35] Pumberger M, Hughes AP, Girardi FP, et al. Influence of surgical experience on the efficiency of discectomy in TLIF: a cadaveric testing in 40 levels. J Spinal Disord Tech. 2012; 25(8):E254–E258 [36] Kowalski RJ, Ferrara LA, Benzel EC. Biomechanics of bone fusion. Neurosurg Focus. 2001; 10(4):E2 [37] Zhao FD, Yang W, Shan Z, et al. Cage migration after transforaminal lumbar interbody fusion and factors related to it. Orthop Surg. 2012; 4(4):227–232

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Thoracolumbar [38] Smith AJ, Arginteanu M, Moore F, Steinberger A, Camins M. Increased incidence of cage migration and nonunion in instrumented transforaminal lumbar interbody fusion with bioabsorbable cages. J Neurosurg Spine. 2010; 13 (3):388–393 [39] Knox JB, Dai JM, III, Orchowski J. Osteolysis in transforaminal lumbar interbody fusion with bone morphogenetic protein-2. Spine. 2011; 36(8):672–676 [40] Duncan JW, Bailey RA. An analysis of fusion cage migration in unilateral and bilateral fixation with transforaminal lumbar interbody fusion. Eur Spine J. 2013; 22(2):439–445 [41] Aoki Y, Yamagata M, Nakajima F, Ikeda Y, Takahashi K. Posterior migration of fusion cages in degenerative lumbar disease treated with transforaminal lumbar interbody fusion: a report of three patients. Spine. 2009; 34(1):E54–E58 [42] Aoki Y, Yamagata M, Nakajima F, et al. Examining risk factors for posterior migration of fusion cages following transforaminal lumbar interbody fusion:

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a possible limitation of unilateral pedicle screw fixation. J Neurosurg Spine. 2010; 13(3):381–387 [43] Matsumura A, Taneichi H, Suda K, Kajino T, Moridaira H, Kaneda K. Comparative study of radiographic disc height changes using two different interbody devices for transforaminal lumbar interbody fusion: open box vs. fenestrated tube interbody cage. Spine. 2006; 31(23):E871–E876 [44] Kim MC, Chung HT, Cho JL, Kim DJ, Chung NS. Subsidence of polyetheretherketone cage after minimally invasive transforaminal lumbar interbody fusion. J Spinal Disord Tech. 2013; 26(2):87–92 [45] Fukuta S, Miyamoto K, Hosoe H, Shimizu K. Kidney-type intervertebral spacers should be located anteriorly in cantilever transforaminal lumbar interbody fusion: analyses of risk factors for spacer subsidence for a minimum of 2 years. J Spinal Disord Tech. 2011; 24(3):189–195

Complications of Percutaneous Pedicle Screw Fixation

37 Complications of Percutaneous Pedicle Screw Fixation Brandon P. Hirsch and Seth K. Williams

37.1 Introduction Minimally invasive spinal instrumentation has gained popularity during the past decade with the evolution of implant systems and refinement of surgical technique. Minimally invasive spine surgery aims to accomplish the same degree of neurological decompression and spinal stabilization as with open surgery, while limiting procedural morbidity. Percutaneous pedicle screw fixation is used to treat instability associated with degenerative, oncologic, infectious, and traumatic conditions of the thoracic, lumbar, and sacral spine. Traditional open and mini-open approaches for pedicle screw placement involve either a midline dissection or paramedian intermuscular approaches with direct visualization of the anatomic screw starting point. Percutaneous pedicle screw fixation relies on cannulation of the pedicle with an introducer needle and guidewire using image guidance, without direct visualization of the screw starting point. The rationale for the percutaneous technique is avoidance of retraction crush injury to the paraspinal muscles, preservation of musculotendinous attachments, and limitation of the surgical corridor to the area necessary for delivery of the implant.1 Several clinical studies have demonstrated the ability of percutaneous approaches to decrease blood loss, hospital length of stay, and postoperative pain.2,3,4 While minimally invasive posterior instrumentation may decrease postoperative morbidity, the degree of technical difficulty associated with the technique can potentially increase the risk of complication. The surgeon accustomed to traditional open posterior approaches may encounter a steep learning curve in using percutaneous pedicle screw systems. A thorough understanding of the fluoroscopic anatomy as it relates to screw placement is crucial to avoiding complications.

37.2 Relevant Anatomy Spinal position is actively controlled by two major muscle groups invested within the dorsolumbar fascia, the erector spinae and the deep paramedian musculature. The multifidus, contained in the deep paramedian group, is the largest and most medial of the paraspinal muscles and provides the primary dynamic posterior stability to the spine. It contains multiple bands forming tendinous attachments to the spinous processes and lamina of lumbar spine. Innervation of the multifidus is derived from the medial branch of the dorsal rami. Upon exiting the neural foramina, the medial branch curves and courses posteroinferior to the mammillary body before entering the overlying multifidus. Traditional posterior open approaches to the thoracolumbar spine involve extensive dissection and forceful retraction of these midline soft-tissue structures. The posterolateral fusion exposure typically extends to the lateral extent of the transverse processes, disrupting the osseous attachments and neurovascular supply of the paraspinal muscles. Dissection must extend caudal and cephalad to the area of direct interest in order to gain enough exposure to place the screws. The physiologic consequences of this dissection on

paraspinal muscular atrophy and performance has been documented.5,6 To avoid these consequences, percutaneous pedicle instrumentation uses paramedian incisions that are just big enough to accommodate the screws, thus minimizing collateral damage. The percutaneous approach also theoretically lowers the risk of injury to the medial branch nerve to the multifidus, given exposure of the facet capsule and transverse processes is not necessary. Denervation of the multifidus can lead to atrophy and altered spinal biomechanics and is thought to negatively affect clinical outcome.7 A surgeon performing percutaneous pedicle screw instrumentation must have thorough knowledge of the bony anatomy as it relates to the fluoroscopic images. Pedicle size and orientation with respect to the vertebral body varies throughout the thoracic, lumbar, and sacral spine. Facet joints exhibit similar variation. Thoracic pedicles are usually smaller in diameter than lumbar pedicles. Thoracic pedicles tend to be wider in the superior-inferior plane than they are in the medial-lateral plane. The medial cortical wall is two to three times thicker than the lateral wall at all levels. Thoracic pedicle angulation in the axial (transverse) plane decreases (i.e., becomes more anterior to posterior) as one progresses from T1 (25–30°) to T12 (5–10°).8 The superior and inferior articular processes arise from the pars interarticularis at the junction of the pedicle and the transverse process. Initially oriented in a coronal plane, facet orientation becomes more sagittal when progressing distally in the thoracic spine. In patients with degenerative spinal conditions, facet joints may be hypertrophic and sclerotic. The pedicle morphology of the upper lumbar vertebrae (L1–L3) is similar to that of the lower thoracic spine. The pedicles retain their oblong shape but increase their angulation in the transverse plane to approximately 15° to 20° with respect to the midline. Pedicle size is relatively similar at L1 and L2, with L3 approximately 1 mm2 greater in cross-sectional area. Pedicle angulation with respect to the midline increases in the lower lumbar vertebrae to approximately 15° to 25°. Pedicle size also increases with L5 pedicles having nearly twice the cross-sectional area of those at L1 and L2.9 The articular processes of the lumbar vertebrae are larger than that of the thoracic vertebrae and maintain a nearly direct sagittal orientation. Osteophytes resulting from degenerative arthrosis are much more common at the lumbar facets and can obscure entry to the pedicle.

37.3 Pitfalls of Percutaneous Pedicle Screw Fixation Surgeons new to percutaneous pedicle screw instrumentation need to be aware of potential pitfalls. Lack of proper imaging is the most common cause of errors in screw placement. Highquality, “true” anteroposterior (AP), and lateral fluoroscopic images are critical for proper screw placement. On the AP image, the vertebral endplates should be parallel and the pedicle should be inferolateral to the superior articulating facet. The spinous process usually lies directly in the midline of the vertebral body, equidistant from each pedicle, although at times

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Thoracolumbar the spinous process is not exactly in the midline and can be misleading. Symmetrical pedicles are the most reliable fluoroscopic landmarks. In the lateral projection, the superior endplate should be parallel to the fluoroscopy beam and the pedicles should overlap and appear as one. Small errors in beam orientation can lead to large variance in screw trajectory due to the extended length of instruments used for percutaneous pedicle fixation. If CT navigation is used, accuracy must be regularly confirmed with known landmarks such as the spinous process or posterior superior iliac spine. Whenever the accuracy of a navigated instrument is in doubt, a fluoroscopic image should be used for verification. As with any procedure, proper patient selection is paramount. Obese patients represent a unique challenge in percutaneous posterior instrumentation. In general, high-quality fluoroscopic views are more difficult to obtain in obese patients because of image degradation by adipose tissue. A large soft-tissue envelope can also hamper palpation of bony landmarks and hence the ability to locate the correct starting point with the introducer needle. The increased working length required in obese patients can also magnify the effect of small changes in hand position on screw trajectory. In larger patients, the surgeon must ensure that the length of the instruments being used can accommodate the depth of the wound. One author suggests making a measurement of soft-tissue depth on the preoperative sagittal magnetic resonance image (MRI) as an estimate of the required length of the instrument.10 The literature regarding the effect of obesity on screw malposition is mixed. In a study of 89 patients, Park et al found no statistical evidence that patients’ body mass index (BMI) affected rates of pedicle wall violation.11 However, two subsequent studies did find that patients with increased BMI had an increased risk of facet joint violation when undergoing percutaneous pedicle instrumentation.12,13 Overall, obesity is not a contraindication to the use of percutaneous techniques, and with experience may be considered a relative indication because of the reduction in surgical cavity size and potential dead space. Surgeon’s radiation exposure during percutaneous pedicle screw instrumentation is higher than that of traditional open methods given the reliance on fluoroscopy.14 Exposure to the solid organs is generally inconsequential with the use of a lead apron, but the hands, thyroid, and eyes are at risk if left unprotected. In a cadaveric study, Mroz et al calculated that a surgeon could place as many as 4,854 and 6,396 percutaneous screws without exceeding the National Council on Radiation Protection’s yearly recommended exposure limits to the hands and eyes, respectively.15 Nevertheless, use of a proper lead apron, thyroid shield, and perhaps leaded eyewear is strongly recommended. Radiation exposure to the hands can be significantly reduced by distancing the hands from the source beam during image acquisition or by using leaded gloves. Percutaneous pedicle screw placement relies on a skill set different from that of open instrumentation. Fluoroscopy or CT guidance is mandatory, given anatomic landmarks are not visualized. Those unfamiliar with the technique may encounter a significant learning curve when attempting to master these skills. Cadaver training is a good introductory step. This may be followed by using all aspects of the percutaneous technique during open surgery, which allows the surgeon to become more comfortable with the correlation of anatomic landmarks to

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fluoroscopic images and allows for familiarization with the equipment. It is recommended that surgeons new to percutaneous pedicle instrumentation begin with single-level procedures before attempting to instrument multiple levels, especially in cases requiring significant deformity correction. Postoperative CT scans will help with self-assessment of screw placement skill and facilitate technique modification as technical deficiencies are discovered.

37.4 Specific Complications and Methods of Avoidance Percutaneous pedicle instrumentation is generally safe when performed by an experienced surgeon. While wound complications and deep infection are of concern as with any procedure, they are relatively rare occurrences. The most common complications of percutaneous pedicle screw placement are due to screw malposition. Screw malposition can involve pedicle wall breach, facet joint disruption, or violation of the vertebral body cortex. Another potentially serious complication can result from guidewire insertion beyond the anterior vertebral body wall, placing vital structures in the thorax or abdominal cavity at risk. Breach of the pedicle wall can cause pedicle fracture, radicular pain, and/or neurologic injury, given the proximity of nerve roots exiting the neural foramina. In most large series of percutaneous pedicle screw placement, breach rates range between 5 and 15%.16,17,18,19,20 While no randomized studies exist, retrospective cohort studies have found the risk of pedicle violation to be similar when comparing open to percutaneous techniques. In a study comparing 162 patients undergoing anterior lumbar interbody fusion followed by either open or percutaneous pedicle screw placement, Kepler et al found a 4.9% incidence of screw malposition in each group.21 Oh et al retrospectively studied the rates of screw malposition in 237 patients undergoing anterior or transforaminal interbody fusion followed by either open or percutaneous instrumentation.22 The severity of pedicle breach was graded as mild (< 3 mm), moderate (3–6 mm), or severe (> 6 mm) based on the amount of screw located outside of the pedicle on postoperative CT scan. In the open group, 75 screws (13.4%) were misplaced with 54 (9.7%) minor, 13 (2.3%) moderate, and 8 (1.4%) severe grade malposition. The percutaneous group had 71 (14.3%) misplaced screws with 53 (10.6%) having minor grade malposition, 13 (2.6%) moderate, and 5 (1.1%) severe.22 While pedicle breach can cause a range of neurological symptoms including radicular pain, sensory disturbances, and lower extremity motor weakness, not all patients with pedicle screw malposition are symptomatic. Breach severity tends to influence the likelihood of developing symptoms. Pedicle breach up to 2 mm is generally well tolerated, with no reports of neurologic sequelae in the available literature. Patients reported to have motor deficits resulting from misplaced pedicle screws typically have cortical wall violation greater than 3 mm.16,18,20,22,23 Pedicle wall violation can occur in multiple directions (medial, lateral, superior, inferior) depending on the accuracy of the starting point and screw trajectory. The direction in which the screw is misplaced also appears to influence the probability of neurologic injury with medial wall violation more likely to cause radicular

Complications of Percutaneous Pedicle Screw Fixation symptoms.16,20,22,24 This is explained by the anatomic relationship of the nerve roots with the inferomedial aspect of the pedicle.25 The available data are conflicting on the most common direction of misplacement and whether or not the vertebral level being instrumented affects the likelihood of screw malposition.18,22 The most important aspects to avoiding pedicle breach are planning the screw placement by studying preoperative imaging and accurate intraoperative imaging. Pedicle size and orientation can usually be discerned on MRI, but if there is any question, a CT scan will clearly show the anatomy. Particular attention should be paid to the proper screw trajectory for L5 and S1, which tend to have a more oblique lateral-to-medial orientation and carry a greater risk of medial pedicle screw breach. Small or dysplastic pedicles in the thoracic and occasionally the lumbar spine should be noted and either skipped or managed with a small screw diameter. Screw malposition can lead to facet joint disruption. This is primarily of concern at the facet joint superior to the most cephalad instrumented level, because this joint is in close proximity to the cephalad-most screw and is not included in the instrumentation construct. If the facet joints within the construct are violated, this is typically not an issue because these joints are included in the fusion. In trauma cases, where instrumentation may be performed without fusion, all the facet joints in the construct are at risk. Trauma cases may be particularly problematic when the facet joint is disrupted. The screw shaft, the screw head, or the rod may violate the facet joint (▶ Fig. 37.1 and ▶ Fig. 37.2). In an open approach, the facets are directly visualized and can be more easily preserved. The percutaneous technique, however, relies on a combination of

palpation with the introducer needle and fluoroscopic localization to cannulate the pedicle and avoid nearby structures. Multiple authors have looked specifically at this complication, finding facet joint disruption rates of 2 to 14% during percutaneous pedicle screw instrumentation.12,13,26,27 The available literature suggests that the percutaneous technique does carry a higher risk of facet joint violation than does open instrumentation. Jones-Quaidoo et al retrospectively reviewed 132 patients undergoing open or minimally invasive single-level transforaminal lumbar interbody fusion (TLIF), finding a facet joint violation rate of 13.6% in the percutaneous cohort compared with a rate of 6.1% in patients undergoing open pedicle screw placement.26 This difference was statistically significant. A separate retrospective review of 179 patients by Babu et al found similar results when comparing rates of facet joint violation between patients undergoing percutaneous screw placement as compared with open instrumentation.12 Obesity appears to influence the rate of facet joint violation in percutaneous pedicle screw instrumentation. In the same retrospective study by Babu et al, a BMI greater than 30 kg/m2 was found to be a risk factor for facet joint disruption in logistic regression analysis. Lau et al also found an increased risk of facet violation with increasing BMI in a series of 282 patients undergoing one-, two-, or threelevel minimally invasive TLIF.13 At present, violation of the facet joints at the end vertebrae of an instrumentation construct is thought to play a role in adjacent segment degeneration. This theoretical long-term risk is still unproven, given that no studies with long-term follow-up exist. Novice surgeons employing the percutaneous technique should pay careful attention to palpation of the bony landmarks of the posterior elements during

Fig. 37.1 Left L5 pedicle screw shaft preventing reduction of a traumatic L4/L5 facet subluxation.

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Thoracolumbar

Fig. 37.2 Right L1/L2 articular facet joint violation by pedicle screw head.

approach with the introducer needle. It may also be wise to postpone using percutaneous instrumentation on obese patients until more experience has been gained with the procedure. Structures within the thoracic or abdominal cavities, especially the great vessels, are at risk when the guidewire or screw violates the vertebral body cortex (▶ Fig. 37.3). Accurate intraoperative imaging is the key to proper guidewire placement, screw size selection, and screw positioning. Careful technique is the key to avoiding inadvertent guidewire passage into the thoracic or abdominal cavity. The introducer needle should be advanced no more than 5 to 10 mm into the vertebral body, which allows for sufficient room anteriorly to place the guidewire through the cannula and anchor it in bone. If the introducer needle is placed too anteriorly in the vertebral body, the guidewire may be more easily passed beyond the anterior vertebral body cortex. The greatest risk is in patients with poor bone quality. The surgeon must always have control of the guidewire and pay constant attention to its depth to avoid misplacement. Newer guidewires with split tips are being developed to try to minimize the risk of anterior vertebral body cortex violation28. While potentially dangerous, anterior vertebral body perforation appears to be rare, given only one study reported on this particular complication. In a recent review of 525 percutaneously placed pedicle screws, Mobbs and Raley recorded seven (1.4%) instances of anterior vertebral body breach.29 Of these patients, two were symptomatic in the form of a postoperative ileus. Both patients were found to have a small retroperitoneal hemorrhage that did not require intervention or transfusion.

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Facet, pedicle, and vertebral body sclerosis can make passage of the introducer needle difficult and can even result in instrument failure. This degree of sclerosis occurs most commonly in patients with degenerative scoliosis on the concave side of the curve and is usually limited to one or two pedicles. CT scans are particularly useful in evaluating sclerosis, and the decision can be made either preoperatively or intraoperatively to skip the involved areas. There are several pitfalls that may accompany sclerotic bone. The most common is difficulty in passing the introducer needle through the pedicle. The area of sclerosis may prevent the introducer needle from passing at all, or it may misdirect the needle into areas that are less sclerotic. The most difficult scenario occurs when the introducer needle can be passed through a sclerotic pedicle but not removed, in which case the cannula may break off within the pedicle. Extraction of the broken instrument is difficult. It may be possible to engage the cannula with a tap and then forcibly remove it. If this is not successful, direct extraction is an option. A table-mounted tubular retractor system can be used to visualize the pedicle entry site, and then a high-speed burr used to remove bone from around the cannula, taking care to avoid violating the pedicle wall. A universal screw extraction system with a broken screw extractor attachment that is just big enough to fit around the cannula may be used to remove enough pedicular bone until the cannula is freed.

37.5 Summary During the past decade, minimally invasive spine surgery has become increasingly popular, given its potential for reduced

Complications of Percutaneous Pedicle Screw Fixation

Fig. 37.3 Breach of the anterior vertebral body by percutaneous pedicle screws placed at T6.

morbidity compared to traditional open techniques. Percutaneous pedicle screw instrumentation is a key component of most minimally invasive thoracic and lumbar procedures and can serve as a powerful tool in the treatment of instability and deformity. Percutaneous procedures rely on a set of skills different from that of open surgery in order to ensure safe pedicle cannulation. Potential complications of percutaneous pedicle screw placement involve pedicle breach, facet violation, and perforation of the anterior vertebral body. These pitfalls can be avoided with careful preoperative planning/patient selection, use of accurate fluoroscopic views of the spine, and vigilant positioning of the introducer needle and/or guidewire prior to screw insertion. Caution should be used when attempting percutaneous instrumentation of patients who have sclerotic or osteoporotic bone or who are obese. The learning curve associated with percutaneous pedicle screw instrumentation requires that surgeons new to the technique begin with less complex single-level procedures and advance to more complex procedures as their comfort with percutaneous techniques increases.

37.6 Future Directions Research continues on methods of decreasing complication rates associated with percutaneous pedicle screw placement. Electrophysiologic stimulation of pedicle screws has gained widespread acceptance in open procedures as a reliable method of detecting screw misplacement. Pedicle screw stimulation is generally not used in percutaneous procedures, as the surrounding soft-tissue envelope precludes access to screw heads. Wang et al evaluated the feasibility of stimulation of pedicle

taps surrounded by insulation sleeves as a method of predicting screw malposition during percutaneous pedicle screw instrumentation.30 The authors found that the standard threshold used to detect pedicle breach in pedicle screws placed with open techniques was inadequate to detect screw malposition in percutaneous cases, with a high rate of false-positive and falsenegative results. Further improvements in cannula design may allow for more reliable use of pedicle stimulation during percutaneous pedicle screw instrumentation in the future, but its use is not currently recommended. New instrument and guidewire systems continue to be developed, making cannulation of the pedicle easier and more accurate. New types of guidewires employing Y-shaped tips are designed to increase resistance to forward progression of the guidewire in the pedicle and vertebral body. This design type has the potential to reduce the risk of unintended perforation of the anterior vertebral body. Peer-reviewed studies have yet to establish the efficacy of this type of guidewire.

37.7 Key Points ●

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Percutaneous pedicle screw placement is commonplace in minimally invasive spine surgery. The percutaneous technique employs a different skill set than that of traditional open pedicle screw placement and involves a significant learning curve. Risks associated with the technique result primarily from screw and/or guidewire malposition and include pedicle wall breach, facet joint violation, and perforation of the anterior vertebral body.

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Complications of percutaneous pedicle screw placement can be avoided by obtaining high-quality fluoroscopic views of the level being instrumented and by choosing an appropriate starting point/screw trajectory. Surgeons new to the technique should begin with less complex procedures and advance to more complex procedures as their comfort with percutaneous cases increases.

References [1] Herkowitz HN, Garfin SR, Eismont FJ, Bell GR. Rothman-Simeone, The Spine. 6th ed. Philadelphia, PA: Saunders Elsevier; 2011 [2] Kotani Y, Abumi K, Ito M, Sudo H, Abe Y, Minami A. Mid-term clinical results of minimally invasive decompression and posterolateral fusion with percutaneous pedicle screws versus conventional approach for degenerative spondylolisthesis with spinal stenosis. Eur Spine J. 2012; 21(6):1171–1177 [3] Peng CW, Yue WM, Poh SY, Yeo W, Tan SB. Clinical and radiological outcomes of minimally invasive versus open transforaminal lumbar interbody fusion. Spine. 2009; 34(13):1385–1389 [4] Wang J, Zhou Y, Zhang ZF, Li CQ, Zheng WJ, Liu J. Comparison of one-level minimally invasive and open transforaminal lumbar interbody fusion in degenerative and isthmic spondylolisthesis grades 1 and 2. Eur Spine J. 2010; 19(10):1780–1784 [5] Kim DY, Lee SH, Chung SK, Lee HY. Comparison of multifidus muscle atrophy and trunk extension muscle strength: percutaneous versus open pedicle screw fixation. Spine. 2005; 30(1):123–129 [6] Gejo R, Matsui H, Kawaguchi Y, Ishihara H, Tsuji H. Serial changes in trunk muscle performance after posterior lumbar surgery. Spine. 1999; 24 (10):1023–1028 [7] Sihvonen T, Herno A, Paljärvi L, Airaksinen O, Partanen J, Tapaninaho A. Local denervation atrophy of paraspinal muscles in postoperative failed back syndrome. Spine. 1993; 18(5):575–581 [8] Kothe R, O’Holleran JD, Liu W, Panjabi MM. Internal architecture of the thoracic pedicle. An anatomic study. Spine. 1996; 21(3):264–270 [9] Panjabi MM, Goel V, Oxland T, et al. Human lumbar vertebrae. Quantitative three-dimensional anatomy. Spine. 1992; 17(3):299–306 [10] Mobbs RJ, Sivabalan P, Li J. Technique, challenges and indications for percutaneous pedicle screw fixation. J Clin Neurosci. 2011; 18(6):741–749 [11] Park Y, Ha JW, Lee YT, Sung NY. Percutaneous placement of pedicle screws in overweight and obese patients. Spine J. 2011; 11(10):919–924 [12] Babu R, Park JG, Mehta AI, et al. Comparison of superior-level facet joint violations during open and percutaneous pedicle screw placement. Neurosurgery. 2012; 71(5):962–970 [13] Lau D, Terman SW, Patel R, La Marca F, Park P. Incidence of and risk factors for superior facet violation in minimally invasive versus open pedicle screw placement during transforaminal lumbar interbody fusion: a comparative analysis. J Neurosurg Spine. 2013; 18(4):356–361

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[14] Lehmann W, Ushmaev A, Ruecker A, et al. Comparison of open versus percutaneous pedicle screw insertion in a sheep model. Eur Spine J. 2008; 17 (6):857–863 [15] Mroz TE, Abdullah KG, Steinmetz MP, Klineberg EO, Lieberman IH. Radiation exposure to the surgeon during percutaneous pedicle screw placement. J Spinal Disord Tech. 2011; 24(4):264–267 [16] Kim MC, Chung HT, Cho JL, Kim DJ, Chung NS. Factors affecting the accurate placement of percutaneous pedicle screws during minimally invasive transforaminal lumbar interbody fusion. Eur Spine J. 2011; 20(10):1635–1643 [17] Lee SH, Choi WG, Lim SR, Kang HY, Shin SW. Minimally invasive anterior lumbar interbody fusion followed by percutaneous pedicle screw fixation for isthmic spondylolisthesis. Spine J. 2004; 4(6):644–649 [18] Raley DA, Mobbs RJ. Retrospective computed tomography scan analysis of percutaneously inserted pedicle screws for posterior transpedicular stabilization of the thoracic and lumbar spine: accuracy and complication rates. Spine. 2012; 37(12):1092–1100 [19] Ringel F, Stoffel M, Stüer C, Meyer B. Minimally invasive transmuscular pedicle screw fixation of the thoracic and lumbar spine. Neurosurgery. 2006; 59(4) Suppl 2:ONS361–ONS366, discussion ONS366–ONS367 [20] Smith ZA, Sugimoto K, Lawton CD, Fessler RG. Incidence of lumbar spine pedicle breach following percutaneous screw fixation: a radiographic evaluation of 601 screws in 151 patients. J Spinal Disord Tech. 2014; 27(7):358–363 [21] Kepler CK, Yu AL, Gruskay JA, et al. Comparison of open and minimally invasive techniques for posterior lumbar instrumentation and fusion after open anterior lumbar interbody fusion. Spine J. 2013; 13(5):489–497 [22] Oh HS, Kim JS, Lee SH, Liu WC, Hong SW. Comparison between the accuracy of percutaneous and open pedicle screw fixations in lumbosacral fusion. Spine J. 2013; 13(12):1751–1757 [23] Schizas C, Michel J, Kosmopoulos V, Theumann N. Computer tomography assessment of pedicle screw insertion in percutaneous posterior transpedicular stabilization. Eur Spine J. 2007; 16(5):613–617 [24] Wang MY. Improvement of sagittal balance and lumbar lordosis following less invasive adult spinal deformity surgery with expandable cages and percutaneous instrumentation. J Neurosurg Spine. 2013; 18(1):4–12 [25] Attar A, Ugur HC, Uz A, Tekdemir I, Egemen N, Genc Y. Lumbar pedicle: surgical anatomic evaluation and relationships. Eur Spine J. 2001; 10(1):10–15 [26] Jones-Quaidoo SM, Djurasovic M, Owens RK, II, Carreon LY. Superior articulating facet violation: percutaneous versus open techniques. J Neurosurg Spine. 2013; 18(6):593–597 [27] Knox JB, Dai JM, III, Orchowski JR. Superior segment facet joint violation and cortical violation after minimally invasive pedicle screw placement. Spine J. 2011; 11(3):213–217 [28] Ishii K, et al. A novel percutaneous guide wire (S-wire) for percutaneous pedicle screw insertion: its development, efficacy, and safety. Surg Innov. 2015; 22(5):469–73 [29] Mobbs RJ, Raley DA. Complications with K-wire insertion for percutaneous pedicle screws. J Spinal Disord Tech. 2014; 27(7):390–394 [30] Wang MY, Pineiro G, Mummaneni PV. Stimulus-evoked electromyography testing of percutaneous pedicle screws for the detection of pedicle breaches: a clinical study of 409 screws in 93 patients. J Neurosurg Spine. 2010; 13 (5):600–605

Complications of Lateral Lumbar Interbody Fusion Cages

38 Complications of Lateral Lumbar Interbody Fusion Cages Mohammed A. Khaleel and Andrew P. White

38.1 Introduction

38.4 Relevant Anatomy

Lateral lumbar interbody fusion cages provide excellent interbody reconstruction by traversing the lateral aspects of the ring apophysis and marginal cortex of the vertebral body. This advantageous reconstruction provides great potential for indirect neural decompression as well as powerful deformity correction. The surgical approach and the placement of these cages can be associated with complications; however, that must be avoided for successful fusion and favorable patient outcomes.

The direct lateral approach avoids specific risks inherent to other approaches to the disc space. The mobilization of the abdominal contents and vasculature required for anterior exposure of the spine is avoided. This may lead to decreased rates of postoperative ileus and vascular complications.5 The lateral approach may avoid the potential neurologic complications of posterior lumbar interbody fusion and transforaminal lumbar interbody fusion procedures that require passing instruments and implants adjacent to the neural elements. The portal of entry is a 3- to 4-cm incision at the flank. After traversing subcutaneous fat, the external oblique, internal oblique, and transversalis muscles are sequentially dissected in line with their respective fibers. The transversalis fascia is penetrated with blunt dissection to reveal retroperitoneal fat which is swept forward by finger dissection. The quadratus lumborum and transverse process can be palpated posteriorly. The psoas can be palpated overlying the disc space. One lateral approach technique utilizes only fluoroscopy for the placement of the initial dilator through the psoas. We do not advise this approach. Alternatively, direct visualization (▶ Fig. 38.1) of the psoas is advocated to reduce the potential for peritoneal, vascular, urologic, and neurologic injury.6 Wylie vein retractors can be used very effectively to directly visualize the lateral surface of the psoas and any adjacent or overlying structures potentially at risk. Level and laterality (▶ Fig. 38.2) may influence the risk of injury to neurovascular structures. The percentage of patients with vascular structures at risk with right-sided approaches is greater than with left-sided approaches, largely due to the relatively posterior vasculature on the right side. Risk of injury to lumbar plexus significantly rises with more caudal level, and the overwhelming majority of neurologic injuries occur with surgery at L4–L5.7 From the L1 to L5 levels, the lumbar plexus travels from a dorsal to ventral position, making the L4–L5 level high risk for neural injury.8 Intraoperative neuromonitoring with free run EMG and dynamic triggered EMG will provide real-time assessment of the proximity to nerves, allowing the surgeon to replace the retractor and minimize neurologic insult. We have also found motor-evoked potential (MEP) to be more helpful than EMG in detecting nerve injuries related to prolonged retraction and prolonged nerve compression (▶ Fig. 38.3). The L5–S1 level is typically too low to consider a lateral approach. The L4–L5 level may also prove challenging to access laterally if the iliac crests are high on a lateral radiograph. More superiorly, the ribs may limit access to thoracolumbar levels. However, the thoracic cavity may be successfully accessed to treat thoracic and thoracolumbar spine pathology. If the iliac crest or rib cage do not allow expansion of the retractor, bending of the patient in the lateral position may be helpful. Osteotomies of the rib or iliac crest may be performed to gain access. To access the L2–L3 disc space, the 12th rib may need to be retracted, and to access L1–L2, an intercostal approach between the 11th and 12th ribs may be necessary.

38.2 Purpose of Instrumentation Like any interbody device, the primary goal of the lateral lumbar interbody cage is to maintain stability and provide a favorable environment to obtain interbody fusion. Fusion rates of up to 97% have been reported with lateral interbody procedures.1 All mechanical intervertebral devices may provide the additional benefit of indirect neural decompression by increasing foramen height. Even central stenosis may be improved, given distraction of the disc space may serve to reduce a posterior disc protrusion and reduce ligamentum flavum redundancy. The large, strong cage provides certain advantages in the setting of deformity. Preservation of the strong posterior and even stronger anterior longitudinal ligament (ALL)2 allows ligamentotaxis to be employed in reducing low-grade spondylolisthesis with the interbody cage. This is often employed in cases of degenerative spondylolisthesis. Even with isthmic spondylolisthesis, however, the indirect central and foraminal decompression achieved with distraction of the interbody space may obviate the need for wide posterior decompression and removal of the Gill fragment. This may allow for the use of minimally invasive percutaneous posterior instrumentation without the need for an open decompression.

38.3 FDA-Approval Status Several different lateral interbody device systems have obtained FDA approval. These devices are considered analogous to anterior lumbar interbody devices. The intended use is for intervertebral fusion at one level or two contiguous levels in the lumbar spine to treat degenerative disc disease with up to Grade 1 spondylolisthesis. Patients are to have failed 6 months of nonoperative treatment. Supplemental FDA-approved internal spinal fixation systems are intended to be used concurrently.3 The FDA has allowed several lateral interbody devices to be used with integrated lateral plates or lateral fixation devices.4 Despite the conditions of the FDA-approval letters, the interbody spacers are variably used in an off-label fashion without the use of supplemental instrumentation. This use is often seen in the setting of adjacent segment degeneration, where the surgeon may forego posterior supplemental fixation so as to avoid exposure of present fixation.

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Fig. 38.1 Images supporting the discussion of recommending direct visualization for the surgical approach, particularly our recommendation to use Wylie vein retractors (shown in photo and in radiographs) to facilitate direct visualization.

Severe rotational deformities of more than 30° may represent a relative contraindication to lateral access, given that there may be aberrant anatomy or anomalous vasculature that may impede access. Thorough review of preoperative imaging is imperative. The magnetic resonance imaging will also allow evaluation of the shape and size of the psoas. Risk of neural injury at the plexus is higher if the psoas has atypical anterior position. Posterior retraction can also pose a risk to the plexus because it may become trapped between the posterior retractor blade and the transverse process. In cases of coronal plane deformity, the surgeon must choose to approach the spine from the concavity or the convexity of the curve. Approach from the convexity may present easier access to the disc and is particularly useful in single-level fusion. In multilevel fusions, however, approach from the concavity may allow multiple levels to be addressed through a single incision. Obliquity of the L4–L5 disc space must be noted, as this may affect the side of approach depending on the obstruction caused by the iliac crest. Plain films and CT may also provide an assessment of bridging osteophytes, which may affect the approach from either side.

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38.5 Complications 38.5.1 Positioning Potential complications exist at each stage of the direct lateral interbody fusion procedure. Careful review of preoperative imaging for relevant anatomic considerations is imperative. Intraoperative measures are taken to avoid potential complications of placement of the lateral interbody cage (▶ Fig. 38.4). Patient positioning is one of the most important factors in a successful approach. The patient is placed in true lateral position, confirmed by fluoroscopy, on a radiolucent articulating table. The hips and knees must be flexed to ease tension on the psoas, the lumbar plexus, and the sciatic and femoral nerves. Appropriate padding must be ensured to prevent positioningrelated complications. Padding under the leg closest to the table is necessary to prevent peroneal palsy. Nonelastic tape is used to secure the patient to the table (▶ Fig. 38.5) and to prevent any motion because any inadvertent change in the position intraoperatively can have catastrophic consequences. The iliac crest is placed near the “break” in the

Complications of Lateral Lumbar Interbody Fusion Cages to maintain a direct vertical approach to the lateral disc space and decrease the risk of inadvertently traversing posteriorly toward the spinal canal or anteriorly toward the retroperitoneal vasculature and other structures.

38.5.2 Exposure

Fig. 38.2 Radiographs supporting the discussion of “level and laterality” in coronal plane deformity.

table and the pelvis is secured to the table by bringing tape across the patient below the crest. Tape is then placed from the greater trochanter over the lateral femoral condyle to the edge of the table; another band of tape is placed from the lateral femoral condyle over the lateral malleolus to the other edge of the table. The peroneal nerve of this leg is protected by careful placement of the tape to avoid compression at the proximal fibula. The table may be gently flexed to allow expansion of the space between the iliac crest and the rib cage. Aggressive bending of the table should be avoided; this may increase the rate of thigh dysesthesia, and may put the psoas and lumbar plexus under tension. It is imperative that the table be moved and not the C-arm to obtain true anteroposterior and lateral imaging of the operative disc level, with the X-ray beam remaining orthogonal to the walls and floor of the operating room. This allows the surgeon

Expedient and efficient surgery is important. A prolonged lateral position itself may increase risk of thigh dysesthesias. With prolonged retractor placement, the nerves of the lumbar plexus may experience prolonged compression between the retractor and the transverse process, and may become injured. A detailed preoperative plan and an experienced team favor efficient surgery. Exposure-related complications range from minor to severe. The lateral abdominal muscles are typically split in line with their respective fibers. This should prevent the cosmetic complications of a muscle hernia and may reduce bleeding and tissue injury. Blunt finger dissection into the retroperitoneal space is important to ensure that the peritoneum is not entered. Finger dissection also is helpful to palpate for any anomalous anatomy that may impede access, such as renal abnormalities. Injury to the retroperitoneal structures or entry into the peritoneum would require prompt vascular or general surgical consultation. The placement of the initial dilator should be just anterior to the center of the disc. Anterior bias favors lordosis and posterior bias may favor foramen height restoration (▶ Fig. 38.6). Anterior bias may reduce the risk of nerve complications by decreasing direct injury to the nerves of the lumbar plexus9 as well as by decreasing risk of posterior placement of the cage. Careful placement of the dilators and the retractor directly affect the final position of the cage, given the portal of entry is just wide enough for discectomy and implant placement. Wide expansion of the retractor as well as prolonged retraction time may increase risk of neurologic complications. While most postoperative weakness, numbness, and dysesthesia are transient,10 permanent nerve injury has been reported.11 Even transient quadriceps weakness is significantly limiting to a patient’s mobility postoperatively. Neurologic injury may occur with direct injury to a traversing nerve of the lumbar plexus through the psoas. Most iatrogenic injuries, however, are probably not direct injuries. Most are probably related to prolonged nerve compression or tension induced by the retractor displacing and compressing the nerves against the transverse process, as discussed later. Spontaneous or triggered EMG is sensitive for the direct mechanism of injury, as uninjured nerves will reliably depolarize on stimulation by the dilator or handheld probe eliciting an EMG response. Triggered EMG leads are clipped on the sequential dilators, which are turned 360° to allow directional monitoring of nerves within proximity. The second mechanism of neurologic injury, which is more common, involves indirect and prolonged compression or tension of the nerves between the posterior retractor blade and the transverse process. This compression may be related to the increased rates of injury with longer surgical times.12 Spontaneous EMG is less sensitive for this mechanism of injury,13 and this is likely the reason that most cases of clinically significant neurologic injury were not detected by traditional EMG

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Fig. 38.3 Image supports the text describing the mechanism of nerve injury caused by prolonged nerve compression.

Fig. 38.4 Images from a patient who had lateral interbody placed in Florida; the cage was impinging on the exiting nerve root, on the side contralateral to the surgical approach, causing radiculitis.

monitoring. MEPs are capable of detecting prolonged compression injuries that do not elicit an EMG depolarization. This has been very helpful in our practice. In response to an MEP alert, the opportunity to relax or reposition the retractor may limit the severity of the neurologic injury or even reverse it.

38.5.3 Endplate Preparation and Device Insertion After adequate exposure is obtained, box annulotomy is performed, and a series of instruments may be used for discectomy, including curettes, pituitary and Kerrison Rongeurs, and rasps. A Cobb elevator is advanced along the endplate under fluoroscopy to separate the Sharpey’s fibers from the cranial and caudal endplates, as well as to perform contralateral annulotomy. This bilateral release is important to create a stable and

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balanced interbody space, which may also reduce the risk of postoperative cage migration. Fluoroscopic control is imperative given that contralateral neurovascular injury has been reported with catastrophic consequences. Just as in the placement of any intervertebral device, compromise of the endplates may represent potential complications of subsidence and loss of reduction or height. This may be manifested intraoperatively or it may be evident as a postoperative finding. Iatrogenic coronal plane deformities are a risk. Osteoporosis may represent a significant risk factor for such complications. In the setting of deformity, several surgeons will recommend medical treatment of osteoporosis with improvement in bone mineral density prior to surgical intervention. Trial implants are placed sequentially to size the implant and to symmetrically distract the disc space. Endplate fracture is again a significant risk at this stage of the procedure. Placement of too short an implant that does not fully traverse

Complications of Lateral Lumbar Interbody Fusion Cages

Fig. 38.5 Secure pelvis and leg to lower half of table. Use 3-in. cloth tape directly on skin. Beware the fibular head. Some technique guides have it wrong (bottom left).

the strong lateral apophyseal ring will increase the risk of subsidence. Aggressive anterior discectomy or overdistraction of the disc space with large implants can violate the integrity of the ALL. Rupture of the ALL may compromise the integrity of the construct and may lead to anterior extrusion of the cage. In these cases, supplemental instrumentation is typically required with the use of a lateral plate or an implant with integrated instrumentation. Catastrophic pedicle fracture has been reported with overdistraction, specifically in the setting of ankylosis of the posterior elements. Preoperative imaging review is advised to ensure that fusion does not already exist at the surgically treated segment. As with any intervertebral cage, the purpose of the lateral cage is to obtain fusion. Nonunion is a potential (but relatively infrequent) complication. Nonunion may be less frequently recognized (and less often symptomatic) with the lateral cages because they may not subside, even in the setting of failure of fusion, since they typically rest on the rather robust marginal cortex and apophyseal ring. Patient factors such as smoking

status and diabetes play a significant role. Inadequate endplate preparation may also contribute to this delayed complication. Bone graft may consist of autograft, allograft, or bone graft substitutes. Bone morphogenetic protein has been used off label, and the known risks of osteolysis and heterotopic bone formation must be considered (▶ Fig. 38.7). As with any implanted device, infection is a risk. Fortunately, the minimally invasive approach is expected to be at significantly lower risk of infection.14

38.6 Summary Lateral lumbar interbody fusion has a unique set of complications associated with positioning, approach, and placement of the cage. Nonetheless, the procedure has been associated with shorter operative times, shorter hospital stays, and lowered complication rates. Although minimally invasive techniques may not provide as significant a magnitude of deformity correction as open techniques, they have demonstrated a 12% rate of major complication, which favors well against the overall

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Fig. 38.6 Overstuffing causes traction radiculitis—an oversized cage can be placed because the endplates will allow it—lesson is to not overshoot the goal of restoring interbody height.

Fig. 38.7 Heterotopic ossification in the psoas ipsilateral to the surgical approach.

complication rate of up to 37% and 20% major complication rate seen with traditional open techniques in the elderly.15 The lateral cage traverses the strong apophyseal ring of the vertebral body, allowing for powerful deformity correction and indirect neural decompression. Complications, though rare, can have catastrophic consequences associated with significant morbidity and mortality. Great care must be employed to avoid the anatomical structures at risk, while proceeding expeditiously to avoid neurologic complications associated with traversing the psoas muscle adjacent to the lumbar plexus.

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38.7 Future Directions The increasing popularity of the lateral interbody technique has led to significant evolution of the technology. Systems for direct visualization of the psoas have evolved, as this technique has been associated with decreased neurologic complications.6 As more surgeons adopt the use of MEP, the frequency of indirect nerve injuries may decrease. Implants with integrated fixation have developed in response to the potential for ALL disruption. Such fixation is now

Complications of Lateral Lumbar Interbody Fusion Cages employed with hyperlordotic cages with intentional release of the ALL for sagittal plane correction. We recognize that this method of obtaining lordosis carries significant risk, however, and anticipate that case reports will bear that out in the future. The risk is to the (frequently calcified) vascular structures of the retroperitoneum, which are tethered to the vertebrae by segmental vessels. When lengthening the anterior aspect of the anterior column, these vessels may be injured, given that they may not be able to adequately lengthen in conjunction with the spine. They may also become stenotic or have intimal injury leading to thrombosis. The lengthening of the spine may cause significant bleeding that may be hard to control from the lateral approach. Expandable cages with torque-limiting mechanisms have been introduced with the intended goal of decreasing risks of endplate fracture and subsidence. Disc arthroplasty implants also have been designed for introduction through a direct lateral approach.

References [1] Rodgers WB, Gerber EJ, Patterson J. Intraoperative and early postoperative complications in extreme lateral interbody fusion: an analysis of 600 cases. Spine. 2011; 36(1):26–32 [2] Oliveira L, Marchi L, Coutinho E, Pimenta L. A radiographic assessment of the ability of the extreme lateral interbody fusion procedure to indirectly decompress the neural elements. Spine. 2010; 35(26) Suppl:S331–S337 [3] U.S. Food and Drug Administration, Center for Devices and Radiological Health NuVasive CoRoent System K071795 Approval Letter, November 21, 2007

[4] U.S. Food and Drug Administration, Center for Devices and Radiological Health Globus Intercontinental Plate Spacer K103382 Approval Letter, May 20, 2011 [5] Knight RQ, Schwaegler P, Hanscom D, Roh J. Direct lateral lumbar interbody fusion for degenerative conditions: early complication profile. J Spinal Disord Tech. 2009; 22(1):34–37 [6] Yuan PS, Rowshan K, Verma RB, Miller LE, Block JE. Minimally invasive lateral lumbar interbody fusion with direct psoas visualization. J Orthop Surg. 2014; 9:20 [7] Kepler CK, Bogner EA, Herzog RJ, Huang RC. Anatomy of the psoas muscle and lumbar plexus with respect to the surgical approach for lateral transpsoas interbody fusion. Eur Spine J. 2011; 20(4):550–556 [8] Benglis DM, Vanni S, Levi AD. An anatomical study of the lumbosacral plexus as related to the minimally invasive transpsoas approach to the lumbar spine. J Neurosurg Spine. 2009; 10(2):139–144 [9] Uribe JS, Arredondo N, Dakwar E, Vale FL. Defining the safe working zones using the minimally invasive lateral retroperitoneal transpsoas approach: an anatomical study. J Neurosurg Spine. 2010; 13(2):260–266 [10] Le TV, Burkett CJ, Deukmedjian AR, Uribe JS. Postoperative lumbar plexus injury after lumbar retroperitoneal transpsoas minimally invasive lateral interbody fusion. Spine. 2013; 38(1):E13–E20 [11] Cahill KS, Martinez JL, Wang MY, Vanni S, Levi AD. Motor nerve injuries following the minimally invasive lateral transpsoas approach. J Neurosurg Spine. 2012; 17(3):227–231 [12] Wang MY, Mummaneni PV. Minimally invasive surgery for thoracolumbar spinal deformity: initial clinical experience with clinical and radiographic outcomes. Neurosurg Focus. 2010; 28(3):E9 [13] Houten JK, Alexandre LC, Nasser R, Wollowick AL. Nerve injury during the transpsoas approach for lumbar fusion. J Neurosurg Spine. 2011; 15(3):280– 284 [14] O’Toole JE, Eichholz KM, Fessler RG. Surgical site infection rates after minimally invasive spinal surgery. J Neurosurg Spine. 2009; 11(4):471–476 [15] Daubs MD, Lenke LG, Cheh G, Stobbs G, Bridwell KH. Adult spinal deformity surgery: complications and outcomes in patients over age 60. Spine. 2007; 32 (20):2238–2244

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39 Complications of Lateral Lumbar Fusion Plates Justin K. Scheer, Alejandro J. Lopez, Alpesh A. Patel, and Zachary A. Smith

39.1 Introduction 39.1.1 Purpose of Instrumentation Lateral lumbar interbody fusion is a minimally invasive surgical technique for anterior column fusion. It has the potential to reduce surgical approach morbidity, length of hospitalization, blood loss, tissue trauma, and postoperative pain when compared to traditional open fusions.1,2,3 Originally described in 2001, the lateral transpsoas approach4 also allows for the placement of larger instruments of fixation, such as lateral vertebral body plates,5 allowing the surgeon to avoid patient repositioning and secondary posterior exposure.6 Proprietary names for the transpsoas approach include direct lateral lumbar interbody fusion (DLIF) and extreme lateral lumbar interbody fusion (XLIF).7 The lateral approach is currently indicated for the treatment of degenerative disc disease, spinal stenosis, degenerative scoliosis, nonunion, trauma, infection, and grade I–II spondylolisthesis.8 A lateral plate may be used to supplement the interbody cage that is placed during the lateral interbody procedure. This plate is usually a metal alloy that spans the disc space and has a superior and inferior screw hole. It is held in place by two screws that are placed across the width of the vertebral body parallel to the adjacent endplate with bicortical purchase. Ex vivo studies have found that plates added to pedicle screw instrumentation result in greater rigidity than lateral plates alone.5 However, when considering only the lumbar spine (L1–S1), a single lateral plate fixation was found to reduce flexion–extension by 49.5%, lateral bending by 67.3%, and axial rotation by 48.2%.6 Other ex vivo analyses found decreased lateral bending up to 84.1%.5 However, lateral plates alone have been shown to be not as rigid as bilateral pedicle screws.9 Complication rates for this approach have been reported to vary from 2 to 22.4%, depending on the surgical indications and level of fusion,7,10 whereas lateral plate-associated complications have been reported to range from 5.9 to 15%.2,8 This chapter focuses specifically on the complications associated with the use of these lateral interbody plates.

39.2 FDA-Approval Status of Instrumentation 39.2.1 Relevant Anatomy The lateral aspect of the vertebral body is approached by the placement of blunt serial dilators through the psoas muscle. The psoas muscle ensconced branches from the lumbar plexus and is bounded anteriorly by the femoral nerve, genitourinary nerve, iliac artery, and vein. Anatomic studies have found that 20% of left-sided and 44% of right-sided lateral fusions contain important neurovascular structures within the standard 20mm operative corridor.11 However, in general, the most critical “at-risk” structures are the nerves of the lumbar plexus. Anatomic studies have demonstrated that the safe corridor of

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approach exists between the lumbar plexus and the great vessels. This corridor narrows as the surgeon descends in the lumbar spine and is most constricted at L4/L5. Traditionally, this procedure is not done below the L4/L5 level given the anatomy of the pelvis, as the iliac crest often will block surgical access at the L5/S1 level.

39.3 Complications 39.3.1 Vertebral Fracture Vertebral fractures have been associated with the lateral plates. Dua and colleagues2 reviewed 13 patients who underwent XLIF supplemented by a lateral plate and unilateral pedicle screws. The authors found two patients who sustained coronal plane vertebral fractures. In each of these patients, there was a history of osteopenia or osteoporosis. Another study by Le and colleagues8 specifically investigated complications from lateral plating during the minimally invasive lateral transpsoas approach. The authors studied 101 patients and found 3 patients who had coronal vertebral body fractures. All were atraumatic. Kepler and colleagues reported postoperative atraumatic vertebral body fractures through the anterolateral plate screw holes in two patients with osteoporosis diagnosed by dual-energy X-ray absorptiometry. Both fractures occurred in the coronal plane within 6 weeks of surgery and one required a secondary procedure (kyphoplasty) due to pain.12 Two potential mechanisms for this complication have been proposed.2 The first includes a stress riser being formed above and below the interbody cage at the site of plate fixation. Stress is also increased at the site that the cage contacts the endplates, especially when large height restoration is accomplished.10 This combination may result in failure of the bone between the screw/plate and the endplate and allow for a fracture to occur. The second mechanism begins with interbody cage migration through the endplates. This could occur due to endplate preparation, overstuffing of the disc space, or endplate resorption perioperatively. A loss of endplate integrity places additional strain on the bone–screw interface, leading to failure and fracture.

39.3.2 Hardware Failure Plate failure has been reported as well. In the study by Le and colleagues, three patients also sustained lateral plate failure by a dislodged lock nut and plate. This complication may occur because the osseous anatomy of the lumbar vertebral body does not provide the same purchase as a multicortical pedicle screw. Furthermore, in all circumstances of lateral plating, there is only unilateral anatomic fixation.

39.3.3 Approach-Related Complications Approach-related complications from lateral interbody fusion are well documented in the spine literature. These include lumbar plexus injury as well as injury to more superficial nerves

Complications of Lateral Lumbar Fusion Plates that run through and on the psoas muscle. This can lead to proximal leg weakness and medial thigh numbness. Furthermore, rare complications of vascular injury (arterial or venous) as well as injury to the ureters have been reported. It should be noted that the placement of a lateral plate increases the area of exposure as well as the operative time. Placing additional hardware, including screw fixation, has the potential to increase approach-related injury by widening the exposure corridor as well as placing screws with only partial visual guidance. Furthermore, it is widely held that retraction time on the plexus may be a factor in lumbar plexus injury during the lateral approach. The placement of a lateral plate may add to retraction time and has the potential to increase the incidence of this type of injury.

39.4 Summary Lateral plate fixation is an alternative means of fixation for lateral transpsoas approaches for lateral interbody fusion, such as DLIF and XLIF. The complications associated with lateral plate fixation include vertebral fractures and hardware failure. The addition of a lateral plate to an interbody cage does increase the rigidity of the construct, however not as much as posterior pedicle screws. In addition, the increased exposure and dissection required for this approach and the use of the plate may place the patient at an increased risk for both neurological and vascular injury.

39.5 Future Directions There currently exists no high-quality or strong evidence clinical studies investigating the clinical safety and efficacy of lateral plates in the setting of transpsoas interbody fusions. A prospective study with a large number of patients and an appropriate matched control group (posterior pedicle screw fixation) is needed and would help determine the value of these devices.

References [1] Matsuzaki H, Tokuhashi Y, Matsumoto F, Hoshino M, Kiuchi T, Toriyama S. Problems and solutions of pedicle screw plate fixation of lumbar spine. Spine. 1990; 15(11):1159–1165 [2] Dua K, Kepler CK, Huang RC, Marchenko A. Vertebral body fracture after anterolateral instrumentation and interbody fusion in two osteoporotic patients. Spine J. 2010; 10(9):e11–e15 [3] Tender GC. Caudal vertebral body fractures following lateral interbody fusion in nonosteoporotic patients. Ochsner J. 2014; 14(1):123–130 [4] Marchi L, Abdala N, Oliveira L, Amaral R, Coutinho E, Pimenta L. Stand-alone lateral interbody fusion for the treatment of low-grade degenerative spondylolisthesis. ScientificWorldJournal. 2012; 2012:456346 [5] Cappuccino A, Cornwall GB, Turner AW, et al. Biomechanical analysis and review of lateral lumbar fusion constructs. Spine. 2010; 35(26) Suppl:S361– S367 [6] Nayak AN, Gutierrez S, Billys JB, Santoni BG, Castellvi AE. Biomechanics of lateral plate and pedicle screw constructs in lumbar spines instrumented at two levels with laterally placed interbody cages. Spine J. 2013; 13(10):1331–1338 [7] Lehman RA, Jr, Kang DG. Commentary: an increasing awareness of the complications after transpsoas lumbar interbody fusion procedure. Spine J. 2011; 11(11):1073–1075 [8] Le TV, Smith DA, Greenberg MS, Dakwar E, Baaj AA, Uribe JS. Complications of lateral plating in the minimally invasive lateral transpsoas approach. J Neurosurg Spine. 2012; 16(3):302–307 [9] Fogel GR, Turner AW, Dooley ZA, Cornwall GB. Biomechanical stability of lateral interbody implants and supplemental fixation in a cadaveric degenerative spondylolisthesis model. Spine. 2014; 39(19):E1138–E1146 [10] Palm WJ, IV, Rosenberg WS, Keaveny TM. Load transfer mechanisms in cylindrical interbody cage constructs. Spine. 2002; 27(19):2101–2107 [11] Kepler CK, Bogner EA, Herzog RJ, Huang RC. Anatomy of the psoas muscle and lumbar plexus with respect to the surgical approach for lateral transpsoas interbody fusion. Eur Spine J. 2011; 20(4):550–556 [12] Kepler CK, Sharma AK, Huang RC. Lateral transpsoas interbody fusion (LTIF) with plate fixation and unilateral pedicle screws: a preliminary report. J Spinal Disord Tech. 2011; 24(6):363–367 [13] Knight RQ, Schwaegler P, Hanscom D, Roh J. Direct lateral lumbar interbody fusion for degenerative conditions: early complication profile. J Spinal Disord Tech. 2009; 22(1):34–37

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40 Complications of Lateral Lumbar Arthroplasty Devices Nicholas Schroeder and Rakesh D. Patel

40.1 Complications of Lateral Lumbar Arthroplasty Devices Total disc replacement (TDR) has been used for the treatment of low back pain as an alternative to fusion surgery. Among the assumed benefits of motion preservation surgery are better functional outcomes and decreased adjacent segment degeneration compared to spinal fusions. Unlike fusion surgery, which can be performed via an anterior, extreme lateral or posterior approach, disc arthroplasty is traditionally performed only via an anterior approach. Owing to the technical drawbacks of the anterior approach, a TDR has been recently developed that can be performed from an extreme lateral approach. The anterior approach to the lumbar spine has been performed traditionally for the purpose of anterior lumbar interbody fusion. Although generally deemed safe, anterior open approaches to the spine for a fusion have reported complication rates of up to 38.3%.1 Approach-related complications include vascular injury, bowel injury, sexual dysfunction, ileus, sympathetic dysfunction, and somatic neural injury.1,2,3,4,5,6 Similar complications have been reported in the U.S. Food and Drug Administration Investigational Device Exemption trial of the Charite TDR that is placed via the anterior approach. In addition to the approach-related complications, there is evidence that resecting the anterior longitudinal ligament (ALL), as must be done during a TDR performed via an anterior approach, leads to hypermobility in extension and axial rotation. A biomechanical study demonstrated an increase in extension motion by 35% with the placement of an anterior TDR.7 This is believed to lead to premature facet arthrosis, pain, and possibly premature failure of the implant. Proper positioning of a TDR is requisite to a successful clinical outcome. It must be placed midline in the coronal plane and posteriorly in the sagittal plane for ideal load sharing with the facets and appropriate range of motion. Studies have demonstrated up to a 40% incidence of malposition of TDR performed via the anterior approach.8 Coronal malpositioning can be partially attributed to difficulty obtaining anteroposterior (AP) images of good quality while implanting a TDR anteriorly. Extreme lateral interbody TDR sought to improve upon traditional anterior TDR by decreasing anterior approach-related complications, implanting the device without sacrificing the ALL, and improving coronal positioning secondary to the ease of obtaining AP images of the spine during implantation. The use of the extreme lateral approach was initially described as a revision technique for an anterior approach to TDR.9 Revision via an anterior approach led to a high rate of vascular injury due to scarring from the previous surgery.10 This was avoided by a retroperitoneal extreme lateral approach. Additionally, explanation and fusion via a cage were performed in one stage with the implantation of a lateral fusion device. Extreme lateral lumbar TDR is not commonly performed. An extensive literature search yielded one case series of 36 patients with a minimum of 2-year follow-up. An inherent limitation to a TDR performed via the extreme lateral approach is that it

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cannot be performed at the L5–S1 level due to the presence of the iliac wing. It also has its own approach-related complications that have been reported in the literature for lateral interbody fusions. The extreme lateral approach is most commonly performed with the patient in the lateral position. A skin incision is made in line with the disc space, being approached spanning from the anterior to posterior aspects of the vertebral body as determined by fluoroscopy. Dissection is carried through the external and internal oblique muscles and the retroperitoneal plane is entered bluntly. Once in the retroperitoneal space, the abdominal contents are swept anteriorly with finger dissection. The psoas muscle is palpated. Within the psoas muscle lies the lumbar plexus (▶ Fig. 40.1), which is formed by the anterior divisions of the L1–L4 nerve roots. The nerves of the lumbar plexus lie within the posterior half of the psoas muscle belly with the exception of the genitofemoral nerve, which passes anteriorly through the muscle belly and exits anteriorly at the level of L3.11,12,13 The abdominal aorta and inferior vena cava lie anterior to vertebral bodies, after which they divide into common iliac branches. Blood supply flows through segmental arteries and veins located midway between the superior and inferior endplates. Sympathetic nerves travel along the surface of the aorta and may be injured by aggressive dissection, retraction, or damage to the aorta.11,14 The initial dilator is connected to an electromyographic (EMG) monitoring system that alerts the surgeon to the

Fig. 40.1 Diagram of lumbar plexus.

Complications of Lateral Lumbar Arthroplasty Devices proximity of the nearby lumbar plexus and nerves, which are located within the posterior substance of the psoas muscle. “Safe zones”13 for each disc level have been described, generally between the anterior third and posterior two-thirds of the psoas muscle. The dilator is advanced through the psoas muscle under EMG guidance. Alternatively, the surgeon can place his finger around the anterior aspect of the psoas muscle and sweep it posteriorly. This allows docking into the disc space without piercing the psoas muscle, but may place the great vessels at increased risk. Once an initial path is forged and confirmed with fluoroscopy, sequentially larger dilators are inserted to eventually make way for a tubular retractor.15,16,17 There is a large discrepancy in the rate of complications from the extreme lateral approach, ranging from 6.2 to 52%. Much of this is due to inconsistencies in the definition of complications. Several complications are specific to the extremely lateral approach as described. An uncommon, however, potentially fatal complication is bowel injury. This can occur due to the blind docking of the initial dilator on the psoas muscle, at which point the bowel may be entrapped and injured. This complication of the approach may present acute or delayed. In the setting of a delayed presentation, patients complain of severe abdominal pain. Chest and abdomen radiographs may demonstrate free air. Computed tomography demonstrates intraperitoneal air. Treatment includes emergent exploration, bowel resection, and a diverting colostomy. Another complication specific to this approach is injury to the neural elements during the transpsoas approach. Nerve injuries can be divided into those superficial to the psoas and those within the psoas. Superficial nerves include the ilioinguinal, iliohypogastric, and lateral femoral cutaneous nerves. The genitofemoral nerve is also at risk of injury and it is found along the anterior border of the iliopsoas. Injury to these nerves typically results in numbness in their respective distributions without a significant motor disturbance. Dilating through the psoas can lead to an injury to the lumbar plexus particularly at L4–L5 due to the narrow safe zone anterior to the lumbar plexus. These deficits may be temporary or permanent, with some studies reporting transient weakness and others reporting persistent weakness at last follow-up.18,19,20,21 Postoperative hip flexor weakness can be attributed to nerve injury or psoas trauma/hematoma. In 2009, Knight et al20 reported complications of 58 patients who underwent minimally invasive extreme lateral lumbar interbody fusions for treatment of degenerative conditions. While 13 patients (22.4%) experienced mild or major complications, 9 (15.5%) patients experienced approach-related complications. These included ipsilateral L4 nerve root injury (two), meralgia paresthetica (six), and psoas muscle spasm resulting in extended hospital stay (one). In 2010, Dakwar et al22 retrospectively reviewed 25 patients who underwent lateral interbody fusion for degenerative deformity. Approach-related complications were limited to transient lateral thigh numbness (three). Similarly, Tormenti et al21 reviewed eight patients who underwent similar procedures. Six patients had postoperative radiculopathy and one experienced a bowel perforation. The aforementioned studies all involved patients undergoing interbody fusions through the lateral minimally invasive surgical approach. Only one prospective nonrandomized study has investigated the outcomes of TDR placed via an extreme lateral

approach.16 Theoretically, the risk of injury to the lumbar plexus should be greater with lateral TDR than fusion due to the more posterior positioning of the implant within the vertebral body. In 2011, Pimenta et al16 reported on 36 patients at 2year follow-up. Postoperatively, five patients (13.8%) had psoas weakness and three (8.3%) had anterior thigh numbness, all of which resolved by 2 weeks. Presumably, these transient complications were secondary to trauma to the psoas and injury to the lateral femoral cutaneous nerves. Surprisingly, only one patient (2.8%) was found to have weakness on the ipsilateral side of the approach, likely due to an injury of the lumbar plexus during the transpsoas approach. This weakness was transient and resolved by the 6-month visit. One patient (2.8%) developed hypertrophy of the ipsilateral quadriceps muscle, thought to be related to psoas weakness, which had resolved at 2-year followup. The authors attributed the lowest rate of lumbar plexus injury to the use of real-time, stimulus-evoked, discrete-threshold EMG.16 The authors reported two patients (5.6%) needing revision surgery and conversion from a TDR to a fusion.16 In both cases, the implant positioning was not ideal and may have been a contributing factor to the need for revision surgery. No separate radiographic analysis was reported detailing implant position of all devices placed, except a statement that “postoperative radiographs showed good device placement.”16 Placement of TDR from an anterior approach reports less than ideal positioning in 17 to 40% of devices.5,8,23

40.2 Conclusion There are very limited data on TDR performed through an extreme lateral approach. Complications of placing a TDR via this approach may be approach related, placement related, or device related. The approach-related complications can be predicted from the literature on extreme lateral interbody fusions. It is difficult to ascertain the placement-related complications because the literature reports only one case series of 36 implants of a lateral TDR. Although placement was not specifically addressed in the study, the two patients who underwent revision surgery had what appears to be less than ideal placement. Similarly, due to the small number of cases of lateral TDR in the literature, conclusions cannot be made regarding the implant itself, except to note that no catastrophic failures have been reported. In summary, lateral TDR is a promising alternative to traditional anterior TDR. Further higher level studies are needed to assess the efficacy and safety of lateral TDR.

References [1] Rajaraman V, Vingan R, Roth P, Heary RF, Conklin L, Jacobs GB. Visceral and vascular complications resulting from anterior lumbar interbody fusion. J Neurosurg. 1999; 91(1) Suppl:60–64 [2] Blumenthal S, McAfee PC, Guyer RD, et al. A prospective, randomized, multicenter Food and Drug Administration investigational device exemptions study of lumbar total disc replacement with the CHARITE artificial disc versus lumbar fusion: part I: evaluation of clinical outcomes. Spine (Phila Pa 1976). 2005; 30(14):1565–1575, discussion E387–E391 [3] Delamarter R, Zigler JE, Balderston RA, Cammisa FP, Goldstein JA, Spivak JM. Prospective, randomized, multicenter Food and Drug Administration investigational device exemption study of the ProDisc-L total disc replacement compared with circumferential arthrodesis for the treatment of two-level lumbar

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degenerative disc disease: results at twenty-four months. J Bone Joint Surg Am. 2011; 93(8):705–715 Geisler FH, Blumenthal SL, Guyer RD, et al. Neurological complications of lumbar artificial disc replacement and comparison of clinical results with those related to lumbar arthrodesis in the literature: results of a multicenter, prospective, randomized investigational device exemption study of Charité intervertebral disc. Invited submission from the Joint Section Meeting on Disorders of the Spine and Peripheral Nerves, March 2004. J Neurosurg Spine. 2004; 1(2):143–154 McAfee PC, Cunningham B, Holsapple G, et al. A prospective, randomized, multicenter Food and Drug Administration investigational device exemption study of lumbar total disc replacement with the CHARITE artificial disc versus lumbar fusion: part II: evaluation of radiographic outcomes and correlation of surgical technique accuracy with clinical outcomes. Spine (Phila Pa 1976). 2005; 30(14):1576–1583, discussion E388–E390 van den Eerenbeemt KD, Ostelo RW, van Royen BJ, Peul WC, van Tulder MW. Total disc replacement surgery for symptomatic degenerative lumbar disc disease: a systematic review of the literature. Eur Spine J. 2010; 19(8):1262– 1280 Erkan S, Rivera Y, Wu C, Mehbod AA, Transfeldt EE. Biomechanical comparison of a two-level Maverick disc replacement with a hybrid one-level disc replacement and one-level anterior lumbar interbody fusion. Spine J. 2009; 9 (10):830–835 Lemaire JP, Carrier H, Sariali H, Skalli W, Lavaste F. Clinical and radiological outcomes with the Charité artificial disc: a 10-year minimum follow-up. J Spinal Disord Tech. 2005; 18(4):353–359 Pimenta L, Díaz RC, Guerrero LG. Charité lumbar artificial disc retrieval: use of a lateral minimally invasive technique. Technical note. J Neurosurg Spine. 2006; 5(6):556–561 Bertagnoli R, Zigler J, Karg A, Voigt S. Complications and strategies for revision surgery in total disc replacement. Orthop Clin North Am. 2005; 36 (3):389–395 Moses KP. Atlas of Clinical Gross Anatomy. Philadelphia, PA: Elsevier/Saunders; 2013

[12] Netter FH. Atlas of Human Anatomy. Philadelphia, PA: Saunders/Elsevier; 2010 [13] Uribe JS, Arredondo N, Dakwar E, Vale FL. Defining the safe working zones using the minimally invasive lateral retroperitoneal transpsoas approach: an anatomical study. J Neurosurg Spine. 2010; 13(2):260–266 [14] Vaccaro AR. Spine: Core Knowledge in Orthopaedics. St. Louis, MO: Mosby; 2005 [15] Ozgur BM, Aryan HE, Pimenta L, Taylor WR. Extreme lateral interbody fusion (XLIF): a novel surgical technique for anterior lumbar interbody fusion. Spine J. 2006; 6(4):435–443 [16] Pimenta L, Oliveira L, Schaffa T, Coutinho E, Marchi L. Lumbar total disc replacement from an extreme lateral approach: clinical experience with a minimum of 2 years’ follow-up. J Neurosurg Spine. 2011; 14(1):38–45 [17] Rodgers WB, Cox CS, Gerber EJ. Early complications of extreme lateral interbody fusion in the obese. J Spinal Disord Tech. 2010; 23(6):393–397 [18] Sofianos DA, Briseño MR, Abrams J, Patel AA. Complications of the lateral transpsoas approach for lumbar interbody arthrodesis: a case series and literature review. Clin Orthop Relat Res. 2012; 470(6):1621–1632 [19] Houten JK, Alexandre LC, Nasser R, Wollowick AL. Nerve injury during the transpsoas approach for lumbar fusion. J Neurosurg Spine. 2011; 15(3):280– 284 [20] Knight RQ, Schwaegler P, Hanscom D, Roh J. Direct lateral lumbar interbody fusion for degenerative conditions: early complication profile. J Spinal Disord Tech. 2009; 22(1):34–37 [21] Tormenti MJ, Maserati MB, Bonfield CM, Okonkwo DO, Kanter AS. Complications and radiographic correction in adult scoliosis following combined transpsoas extreme lateral interbody fusion and posterior pedicle screw instrumentation. Neurosurg Focus. 2010; 28(3):E7 [22] Dakwar E, Cardona RF, Smith DA, Uribe JS. Early outcomes and safety of the minimally invasive, lateral retroperitoneal transpsoas approach for adult degenerative scoliosis. Neurosurg Focus. 2010; 28(3):E8 [23] Rundell SA, Auerbach JD, Balderston RA, Kurtz SM. Total disc replacement positioning affects facet contact forces and vertebral body strains. Spine. 2008; 33(23):2510–2517

Complications of Lumbar Interbody Fusion with Femoral Ring Allograft

41 Complications of Lumbar Interbody Fusion with Femoral Ring Allograft Adam J. Bevevino and Tristan Fried

41.1 Introduction

41.2 Complications/Limitations

Interbody structural grafts are a mainstay of lumbar spine reconstruction and fusion procedures. There are a variety of interbody graft choices including synthetics (polyether ether ketone [PEEK]), metal alloys (titanium), structural autograft, and allograft, each of which is associated with advantages and disadvantages. Of the available allograft options, femoral ring allograft is the most common structural graft utilized for lumbar interbody fusions. The graft has long track record and has compared favorably to other graft options. Advantages of femoral ring allograft over some of the other options include an abundant supply versus the relatively limited supply of structural autograft and low cost versus the more expensive synthetic and metal alloy options. Prospective randomized data comparing femoral ring allograft to titanium cages have illustrated that the graft compares favorably to titanium cages in terms of both clinical outcome and cost effectiveness. McKenna et al conducted a prospective randomized controlled trial (RCT) comparing femoral ring allograft to titanium cages. Results suggested that patients undergoing lumbar interbody fusion with femoral ring allograft had superior clinical results to those undergoing the same procedure with a titanium cage. Freeman et al conducted a prospective RCT comparing the cost of lumbar interbody fusion with femoral ring allograft to that of a titanium cage. They concluded that the femoral ring allograft was more cost-effective while also yielding greater quality of life improvements.1,2 Furthermore, the compressive strength of femoral ring allograft has been found superior to other allograft options such as tricortical iliac crest.3 When employed for interbody fusion, the intention of a femoral ring allograft is to restore lost disc height of the interbody space, provide immediate structural support, and foster an environment that promotes healing at the host/graft interface. Femoral ring allograft is produced through machining of harvested human cadaveric femurs and is then sterilized to remove communicable diseases and processed to decrease the amount of immunogenicity. The graft serves as a mainly osteoconductive interbody device, thereby lacking the osteoinductive or osteogenic properties of autograft or bone morphogenic protein (BMP) and demineralized bone matrix. Despite this, the design of femoral ring allograft, with a central hole, allows the surgeon to pack the center of graft with autograft or other biologic to improve the overall potency of the graft. While the graft clearly has many advantages for interbody fusions, like any implant, there are disadvantages and complications associated with its use. The following will outline and review the literature concerning complications associated with the use of femoral ring allograft.

41.2.1 Pseudarthrosis Pseudoarthrosis is defined by the absence of solid fusion and remains a paramount concern for all spinal fusion procedures, regardless of the method or device that is used for fusion. In the case of lumbar interbody fusion with femoral ring allograft, pseudarthrosis is defined by a lack of bony integration between the graft and the lumbar vertebral endplates despite allowing a sufficient time for healing. As a cortical bone graft, femoral ring allograft incorporates into the endplates via a fairly reproducible process. Incorporation is initiated by a host inflammatory response that increases blood flow to the graft interface that is then followed by revascularization of the graft beginning when host capillary buds sprout into the graft. The next step that occurs is partial resorption, mediated by osteoclastic activity, of the allograft. During this time period at 6 to 8 months post implantation, as much as 50% of the graft’s structural strength can be lost.4 The resorption phase is followed by osteoblast mediated bony deposition which creates an external and internal bridging callous that attaches the host bone to the graft and then remodels over time. Even when graft incorporation proceeds as anticipated, a substantial amount of necrotic allograft bone remains present within the allograft once remodeling, and thereby final healing, is complete. Intuitively, if any of the incorporation steps are disrupted, the risk of pseudarthrosis increases. Several modifiable patient and surgical related factors can influence the rate of pseudarthrosis by interrupting one or more steps in the process of incorporation. Classically, patient factors that decrease the chance of successful fusion include smoking, chronic steroid (or other immunosuppressant drug) use, nonsteroidal anti-inflammatory drugs, and bisphosphonates. Surgical factors that increase the chance of pseudoarthrosis with femoral ring allograft include inadequate preparation of the bony endplates, poor graft sizing leading to decreased contact at the endplate, and lack of posterior fixation. Fortunately, rates of pseudoarthrosis with femoral ring allograft are relatively low. In a retrospective study done by Chotivichit et al,5 59 patients who had a femoral ring allograft were studied. They found complete incorporation of the graft in 24.3% of patients at 6 months, 94.9% at 18 months, and 97% at 24 months. The remaining 3% still had the graft intact but not fully incorporated, and none of the grafts showed any resorption. In 1997, a study by Buttermann et al6 reported on pseudarthrosis among 26 patients with 64 cortical allografts and published a rate of 6%. On the other hand, not all results have been as encouraging as the previous two listed studies. Thalgott et al conducted a prospective randomized clinical trial

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Thoracolumbar comparing the results of fresh-frozen femoral ring allograft to freeze-dried femoral ring allograft. The study found that freezedried femoral ring allograft was associated with higher rate of intraoperative fracture and a higher rate of pseudarthrosis requiring surgical revision.7 They also documented a 17% reoperation rate secondary to pseudarthrosis in a series of lumbar fusion patients implanted with femoral ring allograft. The use of BMPs in spine surgery has become increasingly common with a primary goal of increasing fusion rates. In fact, one of the only Food and Drug Administration (FDA) approved uses for BMP in the spine is during anterior lumbar interbody fusions, and positive results with BMP and femoral ring allograft have been reported. A study by Slosar et al8 published in 2007 documented a fusion rate of 100% with the use of BMP combined in femoral ring allograft. However, these results have not been echoed universally as was the case in the findings of Pradhan et al9 who suggested an increase in pseudoarthrosis rate from 37 to 56% when BMP was employed. The authors found that 40% of grafts had evidence of resorption and concluded that when BMP is combined with femoral ring allograft, resorption should be considered a normal part of the healing process. Another potential reason for the high pseudarthrosis rate in the Pradhan study is the fact that the femoral ring allografts in the study were used in a stand-alone fashion. This last detail highlights the importance of supplementing femoral ring allografts with posterior fixation.

41.3 Disease Transmission

The presence of a pseudoarthrosis in the setting of femoral ring allograft can be identified clinically and/or radiographically. Clinical symptoms suggestive of pseudoarthrosis following interbody fusion with femoral ring allograft include continued pain or the recurrence of pain after symptoms had initially abated. As such, the possibility of a pseudarthrosis should be considered in any patient that continues to have pain despite allowing an adequate time for postoperative recovery. Radiographically pseudarthrosis can be identified on plain X-ray by the presence of persistent lucencies at the interface between the femoral ring allograft and the vertebral endplates. Additionally, flexion/extension films may demonstrate continued motion across the spinal segment that is attempting to fuse. If pseudarthrosis is suspected either from clinical symptoms or by plain film radiography, advanced imaging with computed tomography (CT) can assist to confirm the presence or absence of bridging callous between the host endplate and the femoral ring allograft.

An inherent risk of procedures that employ human cadaveric tissue is the transmission of communicable disease from the graft to the host. Femoral ring allograft is no different and likewise carries a risk of disease transmission. Viral illnesses such as HIV, Hepatitis C, and Hepatitis B are the most commonly implicated pathogens for disease transmission; however, bacterial illnesses can be transmitted and be potentially fatal.10 Fortunately, this risk is exceedingly low, particularly with femoral ring allograft, and often considered in the modern day to be theoretical. All femoral ring allografts undergo a rigorous screening process which begins at the time of tissue harvest. Initially a thorough history is obtained to identify the presence of any communicable diseases (HIV, Hepatitis B or C, sexually transmitted disease, systemic illnesses) or high-risk behavior that could increase the chances of the donor carrying a disease. During tissue harvest, the specimen is thoroughly inspected for the appearance of any disease and serologic screening tests mandated by the Federal FDA and American Association of Tissue Banks are performed to rule out the presence of the more common communicable diseases.4 Further sterilization techniques are employed depending on how the graft is intended to be used and include antibiotic washing, low-dose radiation and/or chemical treatments. Bone allografts can be employed as a fresh allograft, a fresh-frozen graft, or a freeze-dried graft. According to the Centers for Disease Control and Prevention, there have been no case reports of disease transmission in the past 30 years when using freeze-dried allograft. Four cases of HIV transmission have been documented over that time period with the use of fresh allografts.11 Fortunately, for lumbar interbody fusion, femoral ring allograft is not used as a fresh allograft and is most commonly prepared via fresh-frozen or freeze techniques drying with the addition of radiation treatment and/or chemical washing.

41.2.3 Treatment

41.3.1 Diagnosis and Treatment

Pseudarthroses can be clinically symptomatic or clinically silent, and this distinction is largely what dictates treatment. If an asymptomatic pseudarthrosis is identified during routine radiographic follow-up and the femoral ring allograft is maintaining its position within the interbody space, treatment is observation. In contradistinction, if a femoral ring allograft fails to heal and is resulting in clinical symptoms despite conservative measures, treatment is warranted. Prior to proceeding with surgical revision, the etiology of the pseudarthrosis should be established. The workup for pseudarthrosis extends beyond the

Diagnosis of a communicable disease that has been transferred from a tissue donation starts with a high degree of suspicion. In the hypothetical scenario of a disease being transmitted from a femoral ring allograft, an affected patient would most likely present with symptoms related to the specific disease that had been contracted. If and when suspected, the diagnosis is made with screening blood tests—most commonly for HIV, Hepatitis B, and Hepatitis C as these are the common diseases that are at risk of being transferred. In the event of a bacterial contamination, acute symptoms such as fever, wound problems, and/or

41.2.2 Diagnosis

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scope of this chapter, but most often, if infection is ruled out, the lack of healing is a result of insufficient biology or insufficient mechanical stability. Assuming this to be the case, increasing the biologic potency during revision of a femoral ring allograft can be accomplished through use of autograft or other osteoinductive/osteogenic substances. If mechanical stability is the cause of the pseudarthrosis revision discectomy with resizing of the graft and re-preparation of the endplates may be indicated. Alternately, revision of posterior instrumentation with fusion may increase mechanical stability sufficiently to allow complete bony union.

Complications of Lumbar Interbody Fusion with Femoral Ring Allograft bacteremia may be predominant, and trigger a workup for a deep surgical infection. Once a diagnosis is made or further workup is needed, early involvement of infectious disease specialists is essential for management of the acquired disease. Additionally, the tissue bank from which the donated graft was derived should be contacted so that any specimens from the same host can be further tested. Finally, strong consideration should be made into removing the infected femoral ring allograft, as this represents the source of infection and removal will likely improve the chances of successful medical management.

41.4 Graft Fracture The true incidence for femoral ring allograft fracture is largely unknown given that most events are probably not documented in the literature. One study that documented the rate of fracture was a 2005 randomized controlled trial by McKenna et al1 comparing femoral ring allograft to titanium cages. In this study, the authors reported a 2.7% revision rate secondary to femoral ring allograft fracture. In all likelihood, the rate of femoral ring allograft fracture is likely higher but it is managed at the time that it is diagnosed and not further investigated. The graft shares similar biomechanical properties of cortical bone and likewise fails under similar loads. A caveat to this statement is that processed femoral ring allograft, particularly that has been freeze-dried or irradiated, is more brittle and weaker than native cortical bone.4,12,13 Because of this, manipulating the graft or inserting at loads that are near the mechanical failure point of cortical bone may result in fractures of a femoral ring allograft. When a femoral ring allograft fractures, it occurs in two different scenarios—at time of insertion or following implantation during incorporation. Femoral ring allograft is typically implanted by way of an inserter device along with a bone tamp and mallet. Intuitively, if the femoral ring allograft is oversized or the disc space is collapsed so that overly aggressive insertion techniques are required, fracture can occur. Alternatively, after insertion if the graft is subjected to excessive stress from either severe instability or compression at the interbody space, fracture can result. Other variables that are potentially linked to graft fracture include donor bone quality and, as mentioned above, graft processing techniques. Both factors will be discussed in a subsequent session, but in short both can affect the mechanical strength of the femoral ring allograft and increase the chance of graft fracture.

41.4.1 Diagnosis and Treatment Diagnosis of femoral ring allograft fracture is either made at the time of graft insertion or on follow-up radiographs, if the fracture is unnoticed at the time of insertion or occurs during incorporation. Fractures that occur during insertion are observed under direct visualization or, occasionally, may not be noticed until postoperative X-rays are obtained if the fracture is small and/or nondisplaced. If/when the diagnosis is made either at the time of the operation or in the immediate postoperative period, revision of the graft is typically indicated. One of the primary goals of the femoral ring allograft is to provide immediate structural support and, therefore if the integrity of the

graft is compromised by fracture, this cannot be accomplished. In the acute period, revision of the graft can be completed by removal of the fractured femoral ring allograft with re-preparation of the interbody space and replacement of a new graft. If the fracture occurs during the process of incorporation further out from the operation, the decision to revise the graft is slightly more difficult. Strong consideration should be made for graft revision; however, observation may be an option if enough healing has occurred, the graft remains seated within the interbody space, and the overall stability of the construct is maintained. In this scenario, the morbidity of re-exposing and exploring the femoral ring allograft may outweigh the benefits.

41.5 Graft Subsidence/Resorption As described earlier, the initial phase of femoral ring allograft incorporation into the vertebral endplates involves an inflammatory process. This process increases vascularity to the bone graft interface and is responsible for carrying the osteoprogenitor cells that will eventually bridge the bone between the graft and the host. A byproduct of this reaction is that the graft loses a percentage of its mechanical strength as a portion of the graft undergoes resorption. This process is an anticipated normal part of the healing cascade; however, excessive graft resorption can weaken the graft and/or result in subsidence. Particularly with the increased use of BMP to enhance the osteoinductive activity of the femoral ring allograft, graft resorption is being observed at a fairly significant rate. The etiology of this phenomenon is not fully understood, but potential causes include inadvertent endplate violation, BMP-2 overdosing, and excessive osteoclastic response to BMP.9,14,15 A 2006 study by Pradhan et al9 examined the effects of BMP in combination with femoral ring allograft for lumbar interbody fusion. In the report, a cohort of patients that received femoral ring allograft with iliac crest autograft was compared to a cohort of femoral ring allograft with BMP patients. The authors reported an elevated rate of pseudarthrosis, 59%, in patients that were implanted with a femoral ring allograft combined with BMP. The study was aborted secondary to this finding, with the authors citing that an aggressive resorptive response mediated by BMP results in an unacceptably high rate of pseudoarthrosis with stand-alone femoral ring allograft. A more recent study in 2014 by Kayanja et al14 specifically examined subsidence in femoral ring allografts with recombinant human bone morphogenetic protein-2 (rhBMP-2). In the study, 60 patients were included and 40% had early graft absorption. In addition, the intensity of this subsidence varied by spinal level. The lower spinal levels (L5–S1) had 67% resorption, while the upper levels (L3–L4, L4–L5) had resorption only 33% of the time. The authors determined that the dosage of the rhBMP-2 was not related to the presence or absence of femoral ring allograft resorption. Furthermore, in contradistinction to the previously cited study, Kayanja et al14 concluded that BMP-mediated femoral ring allograft resorption is an expected part of femoral ring graft incorporation and should not preclude the use of BMP for lumbar interbody fusion. The excessive resorptive response of femoral ring allograft in the presence of BMP has also been cited as a cause for other graft-related complications. A case report published in 2006

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Thoracolumbar describes BMP-mediated femoral ring allograft resorption as mimicking an acute postoperative infection.16 In the presented case, the patient had an initial relief of symptoms but then had a recurrence of back and buttock pain. Advanced imaging studies (CT and MRI) were suggestive of osteomyelitis at the vertebral bodies adjacent to the femoral ring allograft with associated graft resorption; however, infectious blood markers remained within normal ranges. The symptoms eventually resolved more than 15 months postoperatively with the assistance of sacroiliac joint injections. In another case, BMPinduced femoral ring allograft resorption was cited as a cause of acute graft displacement. The case presented describes a patient who began to have femoral ring allograft subsidence at 3 months post-op following a fall and the complete graft displacement at a 6-month follow-up. At time of revision, the graft was not incorporated into the interbody space and had the consistency of cancellous bone. Histologic analysis did not reveal excessive resorption of the femoral ring allograft itself, but the graft host interface was not examined.17

41.5.1 Diagnosis and Treatment Femoral ring allograft resorption is diagnosed most commonly on routine postoperative radiographs. In some less common scenarios, graft resorption may result in clinical symptoms such as back pain that may trigger a radiographic workup and reveal the presence of resorption. Assuming the femoral ring allograft is maintaining its position within the interbody space and there is no gross instability at the spinal segment, observation is warranted. Patients with persistent pain and evidence of endplate osteolysis should be worked up for the possibility of osteomyelitis and any patient with signs of significant femoral ring allograft subsidence should be considered for surgical revision. If, after allowing sufficient time for radiographic union, there is still evidence of resorption with lack of bony bridging across the host graft interface, the patient should be treated for pseudoarthrosis accordingly.

41.6 Graft Variability Femoral ring allograft is derived from human tissue and because of this fact, there is variability in the composition of the graft just as there is variability in the composition of living bone between persons. Of particular concern is that variables between femoral ring allograft donors, as well as graft sterilization and processing techniques exist that can decrease the biomechanical strength of the graft. This is in contradistinction to synthetic allografts such as those made from titanium or PEEK, which are manufactured in a uniform fashion and, therefore, do not have biomechanical properties that differ from graft to graft.

41.7 Donor Variables Bone mineral density (BMD) of living femoral cortical bone varies with age, sex, and overall health. This factor is taken into account when selecting donors for femoral ring allografts as

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one could surmise that the compressive strength of a graft from an osteoporotic elderly female would be less than one derived from a young male.18 Because of this assumption, several tissue banks have implemented age and BMD limits for donors prior to manufacturing femoral ring allograft.19 However, not all of the literature entirely supports this logic. A biomechanical study published in 2011 by Hart et al20 sought to identify donor variables that affect the compressive strength of femoral ring allograft. The study found that cortical thickness was the strongest predictor of graft compressive strength. Donor age, BMD, and graft diameter were much weaker correlators to femoral ring allograft strength.20 A subsequent study in 2014 by Krishnamoorthy et al21 found that age and BMD did not play a role in determining the strength of the femoral ring allograft. The authors suggested that performing DEXA scans to appreciate bone density may be unnecessary and costly. In addition, the allograft strength was not statistically different in the young and old donors, suggesting that the age restrictions for allografts may be too stringent.21 While these biomechanical studies argue that age and BMD of donors may not affect graft material properties, they do not evaluate the graft under repetitive loading or on their ability to create solid union. Clearly variability in donor femoral graft dimensions will result in some variability with the mechanical strength of femoral ring allografts; however, with appropriate graft selection, these effects can be minimized.

41.8 Processing Variables There is not a standardized protocol in place for processing femoral ring allograft. However, generally speaking, those grafts that are used as fresh allografts or even fresh-frozen grafts are packaged in a fairly uniform manner with similar biomechanical properties. On the other hand, femoral ring allografts that are processed as freeze dried have been consistently shown to be biomechanically weaker than fresh and fresh-frozen grafts. After being washed with an antibiotic solution, freeze-dried grafts are frozen to –70 °C and the water is decreased to approximately 5% via lyophilization. The deleterious effects of decreasing the water content for freeze-dried allograft have been well documented4,22; however, it is somewhat required to allow the graft to be stored at room temperature. Furthermore, fresh-frozen and freeze-dried graft are often terminally sterilized with either radiation or cleansing in ethylene oxide, both of which can weaken the graft.13 Low dose of radiation (less than 3 MRAD) is believed to be safe in that it does not affect the mechanical strength of the graft.12 However, terminal sterilization with radiation followed by freeze drying leads to the weakest femoral ring allograft preparation.4,13 In a prospective clinical trial, Thalgott et al7 randomized 50 patients who underwent an anterior lumbar interbody fusion with femoral ring allograft into two groups: a fresh-frozen group and a freeze-dried group. At final follow-up, clinical outcomes were not significantly different between the two groups. However, the freeze-dried group had a higher incidence of graft fracture and approximately 85% of revisions secondary to pseudarthrosis were in patients with a freeze-dried femoral ring.

Complications of Lumbar Interbody Fusion with Femoral Ring Allograft

41.9 Summary Femoral ring allograft as an interbody device is a cornerstone of spinal reconstructive procedures. It is in abundant supply, costeffective, and associated with a successful clinical track record. However, like any medical device there are complications that are connected to its use. Pseudarthrosis, graft fracture, and subsidence are complications that are not unique to femoral ring allograft and are observed in nearly all interbody graft devices. On the other hand, the risk of disease transmission, BMPrelated resorption, and graft biomechanical variability are complications more specific to femoral ring allograft. Intricate knowledge and awareness of these potential complications are essential to maximizing the chances of successful clinical outcome and effectiveness of femoral ring allograft.

41.10 Key Points ●

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Femoral ring allograft is a reliable and cost-effective graft for lumbar interbody fusions. Pseudarthrosis rates of lumbar interbody fusion with femoral ring allograft vary but are generally low. Reported rates in the literature range from 0 to 15% when supplemental posterior fixation is used. The risk of disease transmission from femoral ring allograft is exceedingly low. Fresh allografts carry the highest risk of transmission; however, femoral ring allografts for lumbar interbody fusion are rarely used in this fashion. No cases of disease transmission have ever been documented with use of a freeze-dried graft As the graft incorporates into the vertebral endplates, partial resorption of the femoral ring allograft occurs and this phenomenon appears to be increased when BMP is used to supplement the graft. Assuming that the construct and graft remain in stable position, observation is warranted. Variability in femoral ring allograft mechanical strength can occur as a result of donor bone variability. However, donor age and BMD do not appear to be predictive of graft strength. Freeze-dried femoral ring allograft shows inferior biomechanical properties compared to fresh and fresh-frozen grafts. Additionally, literature suggests that they may also result in a higher rate of pseudoarthrosis.

References [1] McKenna PJ, Freeman BJ, Mulholland RC, Grevitt MP, Webb JK, Mehdian SH. A prospective, randomised controlled trial of femoral ring allograft versus a titanium cage in circumferential lumbar spinal fusion with minimum 2-year clinical results. Eur Spine J. 2005; 14(8):727–737

[2] Freeman BJ, Steele NA, Sach TH, Hegarty J, Soegaard R. ISSLS prize winner: cost-effectiveness of two forms of circumferential lumbar fusion: a prospective randomized controlled trial. Spine. 2007; 32(25):2891–2897 [3] Kozak JA, Heilman AE, O’Brien JP. Anterior lumbar fusion options. Technique and graft materials. Clin Orthop Relat Res. 1994(300):45–51 [4] Ehrler DM, Vaccaro AR. The use of allograft bone in lumbar spine surgery. Clin Orthop Relat Res. 2000(371):38–45 [5] Chotivichit A, Fujita T, Wong TH, Kostuik JP, Sieber AN. Role of femoral ring allograft in anterior interbody fusion of the spine. J Orthop Surg (Hong Kong). 2001; 9(2):1–5 [6] Buttermann GR, Glazer PA, Hu SS, Bradford DS. Revision of failed lumbar fusions. A comparison of anterior autograft and allograft. Spine. 1997; 22 (23):2748–2755 [7] Thalgott JS, Fogarty ME, Giuffre JM, Christenson SD, Epstein AK, Aprill C. A prospective, randomized, blinded, single-site study to evaluate the clinical and radiographic differences between frozen and freeze-dried allograft when used as part of a circumferential anterior lumbar interbody fusion procedure. Spine. 2009; 34(12):1251–1256 [8] Slosar PJ, Josey R, Reynolds J. Accelerating lumbar fusions by combining rhBMP-2 with allograft bone: a prospective analysis of interbody fusion rates and clinical outcomes. Spine J. 2007; 7(3):301–307 [9] Pradhan BB, Bae HW, Dawson EG, Patel VV, Delamarter RB. Graft resorption with the use of bone morphogenetic protein: lessons from anterior lumbar interbody fusion using femoral ring allografts and recombinant human bone morphogenetic protein-2. Spine (Phila Pa 1976). 2006; 31(10):E277–E284 [10] Delloye C, Cornu O, Druez V, Barbier O. Bone allografts: What they can offer and what they cannot. J Bone Joint Surg Br. 2007; 89(5):574–579 [11] Centers for Disease Control (CDC). Bone Allografts. Available at: http://www. cdc.gov/oralhealth/infectioncontrol/faq/allografts.htm. Accessed February 12, 2014 [12] Pelker RR, Friedlaender GE, Markham TC. Biomechanical properties of bone allografts. Clin Orthop Relat Res. 1983(174):54–57 [13] Triantafyllou N, Sotiropoulos E, Triantafyllou JN. The mechanical properties of the lyophylized and irradiated bone grafts. Acta Orthop Belg. 1975; 41 Suppl 1:35–44 [14] Kayanja M, Orr RD. Incidence and outcome of graft resorption in anterior lumbar interbody fusion: using femoral ring allografts and recombinant human bone morphogenetic protein-2. Spine. 2014; 39(5):374–380 [15] Poynton AR, Lane JM. Safety profile for the clinical use of bone morphogenetic proteins in the spine. Spine. 2002; 27(16) Suppl 1:S40–S48 [16] Hansen SM, Sasso RC. Resorptive response of rhBMP2 simulating infection in an anterior lumbar interbody fusion with a femoral ring. J Spinal Disord Tech. 2006; 19(2):130–134 [17] Lee JY, Zeiller S, Voltaggio L, et al. Histological analysis of a displaced femoral ring allograft spacer filled with a recombinant human bone morphogenetic protein-2-soaked collagen sponge. A case report. J Bone Joint Surg Am. 2005; 87(10):2318–2322 [18] Martin B. Aging and strength of bone as a structural material. Calcif Tissue Int. 1993; 53 Suppl 1:S34–S39, discussion S39–S40 [19] Jurgensmeier D, Hart R. Variability in tissue bank practices regarding donor and tissue screening of structural allograft bone. Spine. 2010; 35(15):E702– E707 [20] Hart RA, Daniels AH, Bahney T, Tesar J, Sales JR, Bay B. Relationship of donor variables and graft dimension on biomechanical performance of femoral ring allograft. J Orthop Res. 2011; 29(12):1840–1845 [21] Krishnamoorthy B, Bay BK, Hart RA. Bone mineral density and donor age are not predictive of femoral ring allograft bone mechanical strength. J Orthop Res. 2014; 32(10):1271–1276 [22] Kleinstueck FS, Hu SS, Bradford DS. Use of allograft femoral rings for spinal deformity in adults. Clin Orthop Relat Res. 2002(394):84–91

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Thoracolumbar

42 Complications of Anterior Lumbar Interbody Fusion with Polyether Ether Ketone Spacers Peter G. Passias, Carrie Poorman, Sun Yang, and Matthew Nalbandian

42.1 Introduction Anterior lumbar interbody fusion (ALIF) was introduced in the early 20th century as an approach to the lumbar spine for the treatment of spondylolisthesis. The earliest documented spinal surgery via the anterior transperitoneal approach was performed in 1933 by Burns,1 and the retroperitoneal approach was first introduced in 1944 by Iwahara.2 Since its introduction, it has become a popular treatment for deformity and degenerative conditions affecting the lumbar spine because of an increased understanding of the significant biomechanical properties of the anterior column and the direct access it provides to the intervertebral disc and vertebral body. In ALIF, a variety of different spacers, as well as structural grafts have been introduced to maximize the goal of obtaining a solid interbody fusion while at the same time minimizing the occurrence of possible adverse events associated with the procedure itself and implanted biomechanical device. The polyether ether ketone (PEEK) spacer was first introduced as an alternative to titanium (Ti) and allograft implants as a result of its very similar elastic modulus to subchondral vertebral body bone and its radiolucent characteristic. These advantages were thought to potentially facilitate higher fusion rates, decrease graft subsidence, and allow for better visualization of the healing process on radiographs as well as avoid the complications that have been associated with allograft spacers.

42.2 ALIF Surgical Approach— Spine Surgeon’s Perspective The patient is positioned supine on the table and the location of the incision varies depending on the lumbar level being treated. For ALIF, optimal positioning usually involves placing the lumbar spine in a lordotic position by reversing the flex on the table and when necessary placing a support under the lower back at the apex of the lordosis. This positioning helps open the ventral interspaces to facilitate discectomy. Although placement of the patient in lumbar hyperlordosis can facilitate the discectomy portion of the procedure, it may negatively impact an ideal working angle for the surgeon. For this reason, placing the operating table in a slight reverse Trendelenburg position can be beneficial, particularly in the lower lumbar levels, to facilitate working in a less cephalad-oriented direction. We generally flex the hips and thighs with padded support in order to relax the iliopsoas musculature to facilitate the approach and potentially allow for wider lateral retraction and anterior exposure of the lumbar spine. Finally, it is important for the surgeon to be cognizant of the operating table available as older models and nonradiolucent beds may complicate intraoperative fluoroscopy. We generally reverse the position of older models to avoid interference of the base of the bed with imaging. Newer models have options that allow for sliding the bed in relation to the base.

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Incision is typically based on preoperative imaging to assess the location of the spine in relation to the pelvis and on palpation of anatomical landmarks. For isolated L5–S1 approaches, a Pfannenstiel transverse incision is used except in larger or muscular patients, or in certain revision settings. We generally prefer midline vertical incisions for more proximal or multiple levels. Generally, the incision for levels L4 and below can end inferior to the umbilicus although revision procedures and patient characteristics do affect this. ALIF refers to two particular approaches, transperitoneal and retroperitoneal, which differ in several respects despite their common endpoint with direct access to the anterior lumbar spine. Generally, the retroperitoneal approach involves blunt dissection and mobilization of the peritoneum to the side, while the transperitoneal approach involves incision into the anterior parietal peritoneum and then through the posterior peritoneum to expose the prevertebral area. In addition to transperitoneal and retroperitoneal approaches, there are laparoscopic approaches to ALIF, but they have been used less frequently lately because of the prolonged operative time, a steep learning curve, and lack of long-term follow-up data supporting their usage.3 Most commonly, patients undergo a left-sided retroperitoneal approach because it involves a safer retraction of the infrarenal aorta compared to the inferior vena cava on the right side and helps avoid vascular complications. One exception to this may be for an initial L5–S1 approach in a younger patient, where a right-sided retroperitoneal approach may be done in anticipation of future potential surgery for superior adjacent disease that can be treated with a left-sided retroperitoneal with native tissue planes.

42.3 ALIF Surgical Approach— Vascular Surgeon’s Perspective A transverse skin incision is made just above the symphysis pubis. Subcutaneous flaps are then created superiorly and inferiorly to expose more of the rectus fascia. This will allow for a smaller, more cosmetic incision, while maximizing the extent of the exposure. A left or right paramedian incision is made throughout the length of the fascial exposure depending on whether a right- or left-sided retroperitoneal approach is desired. Again, right-sided approaches are usually reserved for an isolated L5–S1 exposure. A left-sided approach will be described for the purposes of this chapter. Next, the medial border of the left rectus muscle is dissected bluntly off the linea alba. This muscle sparing technique allows for less pain and faster recovery. A plane is then developed underneath the rectus muscle but above the posterior rectus fascia in a lateral direction. This will allow the peritoneal contents along with the left ureter to be swept in an anteromedial direction. A retractor system is then used to retract these structures so that dissection around the iliac vessels may be performed. We prefer to

Complications of ALIF with PEEK Spacers use renal vein retractors because they are fairly narrow and useful for small incision. In addition to providing gentle retraction, they will also protect structures because of their steel component. The peritoneum and ureter are usually retracted toward the patient’s midline with two renal vein retractors. The left rectus muscle is retracted laterally with two separate renal vein retractors. Now dissection of the iliac vessels may be accomplished. For an L5–S1 ALIF, the dissection is usually carried out medial to the left iliac artery and vein. The middle sacral artery and vein will need to be ligated and divided in order to retract the left and right iliac arteries and veins to their respective sides. Gentle blunt dissection is usually required to free up the soft tissue surrounding the vessels over the disc space after division of the middle sacral vessels. Once the disc is free, two renal vein retractors may be repositioned to retract the left iliac artery and vein to the left. Two separate renal vein retractors will be used to retract the peritoneum, left ureter, right iliac artery, and right iliac vein to the patient’s right. In addition, the retractors will serve to protect these structures as well as the sympathetic chain during the discectomy and fusion. A confirmatory X-ray is then taken to ensure that the proper level has been exposed, prior to commencing with the discectomy and fusion. To expose the L4–L5 disc space, a similar technique to the exposure described above may be utilized. Since the L4–L5 disc is usually located just below the umbilicus, we have found that a vertical skin incision is most optimal, as well as cosmetically appealing. Because most patients will wear their pants closer to their umbilicus than their pubis, a vertical incision from the umbilicus downward will be hidden by the patient’s pants. A transverse incision just below the umbilicus has the risk of being seen in its entirety. Once the skin incision has been made, the same steps to access the retroperitoneum are utilized as described above for an L5–S1 exposure. Once the retroperitoneum is exposed, the next step is to dissect the iliac vessels on their lateral side in order to disconnect any lateral vascular attachments. This will allow for mobilization of the iliac vessels in a medial direction exposing the L4–L5 disc space. The main lateral attachment for an L4–L5 exposure is the iliolumbar vein. This vessel usually comes off the lateral side of the left common iliac vein and traverses posteriorly into the psoas muscle. The location and number of lateral veins may vary widely. Great care must be taken to identify all of these veins. If the lateral venous attachments are not divided, inadvertent avulsion of the iliac vein may occur, which can lead to significant hemorrhage and possibly death. The iliolumbar vein is dissected and ligated proximally and distally along with any other lateral venous branches in the vicinity of the L4–L5 disc space. This may include the segmental artery and vein from L3–L4, which can sometimes be low down closer to the L4–L5 disc space. Once the vessels are ligated and divided, the left iliac artery, left iliac vein, and perhaps the lower aorta are mobilized in a medial direction, allowing visualization of the L4–L5 disc space. Once the vessels have been mobilized across the spine, the renal vein retractors are once again positioned to retract the structures and provide protection. The two medial retractors are used to retract the left iliac artery, left iliac vein, peritoneum, and left ureter medially. Two separate renal vein retractors are used to retract the left rectus muscle laterally. Once again, the renal vein retractors will serve to protect these structures as well as

the sympathetic chain. Once a confirmatory X-ray has been taken, the spine surgeon is now able to perform the discectomy and fusion at L4–L5. When exposure of L4–L5 and L5–S1 disc spaces are required during the same operation, we will perform the initial exposure of both levels, as described above. This is done through a midline incision. Once both levels are dissected, we will expose the L4–L5 level first and have the spine surgeon perform the discectomy and fusion at that level first and then reposition the retractors at L5–S1 to complete the procedure. Once the spine surgeon has completed his portion of the procedure, closure may begin. The renal vein retractors are removed and the iliac vessels along with all of the surrounding structures are inspected. The peritoneal contents and left ureter are returned to their normal anatomic position. The anterior rectus fascia, subcutaneous tissue, and skin are then closed. Discectomy is carried out with long-handled curettes and rongeurs. First, an annulotomy is performed to open a window in the annulus through which the inner annulus and nucleus pulposus can be removed. Rongeurs will be used to remove large pieces of disc, and curettes to scrape the cartilage off the vertebral endplates and expose the bleeding bone. A successful discectomy removes the disc to the proper dorsal depth without penetrating the annulus laterally or dorsally because this could injure surrounding vascular and nerve structures. Throughout the discectomy, care should be taken to orient the blade of the rongeur away from vascular structures, which may move around or slip beneath the edges of the retractors. Exposing bleeding surfaces is necessary for bone graft fusion to occur. This is routinely performed with a puncture of the subchondral endplate surface with either a curette or a burr, with care taken to not harm the overall structural integrity of the endplate. Once the disc is removed, distraction is performed to restore the proper disc height and a trial implant is used to determine the appropriate size. The implant is packed with bone graft and inserted using an insertion device that maintains distraction as the implant is placed from the anterior. In some cases, additional anterior instrumentation is fixated onto the ventral surface of the vertebral bodies or through the implanted cage itself. Intraoperative imaging should be performed to confirm proper interbody placement.

42.4 Complications of ALIF Due to the proximity of major vascular structures and the viscera, the potential for major complications is high. Fortunately, the actual incidence of sustaining a complication specific to the ALIF approach is low. The major complications in ALIF are due to injury to vascular, urologic, neurological or gastrointestinal structures, and/or the abdominal wall.4 To minimize the risk of complications, an experienced vascular or general surgeon provides assistance during the approach based on how comfortable the spinal surgeon is with relevant anatomy. To avoid excessive bleeding and vascular injury, proper ligation of vessels is required based upon the access level. For instance, failure to properly identify and ligate median sacral vessels or the iliolumbar vein for L5–S1 and L4–L5 approaches, respectively, can result in inadvertent rupture of the vessels during the course of the procedure. The most common vascular structure injury is to the left common iliac vein because of its

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Thoracolumbar dorsal location.4 Major blood vessel injuries occur in 2 to 6% of ALIF operations, but minor vessel injuries (usually defined as those that do not require direct repair) have been reported with incidence as high as 18%.5,6 Presence of a vascular surgeon, avoidance of self-retaining retractor usage, and the use of vessel loops to control major vessels will help avoid vessel injury. Handheld retractors for major vascular structures should be released regularly at intervals of no longer than 15 min in order to avoid loss of normal elasticity or plaque fracture.4 One major urologic complication is retrograde ejaculation (RE). RE occurs in approximately 0.5 to 22% of men undergoing ALIF, and the incidence is about 10-fold in the transperitoneal procedure.7,8,9 Additional risk factors for RE include the use of monopolar electrocautery and potentially the use of bone morphogenetic protein (BMP).9,10 Monopolar electrocautery is used during exposure, but it can damage the presacral sympathetic plexus to cause RE and must be used minimally or with great care in the prevertebral space. RE seems to be increased in patients treated with BMP, with an incidence of 6 to 7% compared to 0 to 1% in non-BMP patients,9,10 potentially due to the high rates of ectopic bone formation and osteolysis causing persistent radiculitis from exposure of BMP-2 to lumbar roots and dorsal root ganglion demonstrated in other interbody fusion studies with BMP-2 use.10,11 During the approach, violation of the peritoneum is not uncommon, but it is usually repaired immediately to minimize risk to patients.5 Violation of the peritoneum can cause postoperative hernia if left untreated, which may lead to bowel obstruction, and therefore, further complications are avoided by direct repair. Occasionally, larger defects in the peritoneum are left unrepaired because of a low risk of strangulation. Direct injury of the bowel is rare and should be treated with immediate irrigation, prophylactic antibiotics, and termination of the procedure. In thin patients, it is possible to inadvertently dissect dorsal to the psoas muscle rather than ventral, which could result in excessive fluid collections, blood loss, and nerve injury. Finally, neurological injuries are possible but are rare in properly performed ALIF. Neurological injury can be caused by violation of the dural sac or inadvertent injury of neural elements.3 However, because decompression is not performed in the anterior procedure, direct injury of nerve structures is relatively uncommon. During the transperitoneal ALIF procedure, additional complications (e.g., prolonged postoperative ileus, problems with fluid management, and “third spacing” secondary to fluid shift from an edematous bowel) can occur. This technique is used less commonly due to these additional complications. Compared to posterior lumbar interbody fusion (PLIF), ALIF carries a slightly lower risk of complications, increased fusion rate, and decreased operative time.12 Moreover, there are biomechanical studies that suggest that the cages inserted anteriorly provide better stabilization in axial rotation and lateral bending compared to cages from a posterior approach.13 Transforaminal lumbar interbody fusion (TLIF), on the other hand, is associated with shorter operative times, fewer complications, and decreased blood loss compared to ALIF.14 Lateral-based approaches to the lumbar spine nearly eliminate the occurrence of major vessel injury by avoiding the prevertebral space although the ascending iliolumbar vein is still a concern and may require ligation and division during this procedure.4

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42.4.1 Indications ALIF is indicated for patients with degenerative disc disease suffering from long-term pain and/or neurological symptoms as a result. ALIF provides stability through the anterior column and also facilitates restoration of lumbar lordosis. Therefore, it is commonly used to treat high-grade spondylolisthesis. A patient should not be considered for ALIF surgery until they have completed 6 months of conservative care unless they have a neurological deficit. There are a few contraindications, but the only absolute contraindication is advanced osteoporosis that would prevent the vertebrae from maintaining a bone graft. Other contraindications that may complicate but not completely rule out ALIF are prior retroperitoneal surgery, disc space infection, severe peripheral vascular disease, anomalous genitourinary system, infrarenal aortic aneurysm, neoplasm, and neural compression, for which a posterior approach may be safer. ALIF is often used to revise posterior surgeries complicated by pseudarthrosis because it adds additional stability to the construct and another site for arthrosis.

42.4.2 Interbody Spacers A variety of spacers currently exist as options for interbody support, such as structural grafts, graft adjuncts, and various cages. Cages come in many shapes (i.e., tapered, circular, and rectangular) with and without curvature15 and are made with different materials. The most successful ALIF cage should allow for sufficient structural support to preserve the restoration of the disc height achieved during surgery. At the same time, ALIF cage should not be excessively rigid relative to the modulus of elasticity of the vertebral body so as to not increase the risk of subsidence. In addition, many surgeons prefer to use radiolucent material for clear visualization of graft incorporation. A successful ALIF cage should also have ample space to allow for maximum bone graft placement and prevent migration of the cage via translation, either anteriorly toward the retroperitoneum or posteriorly toward the spinal canal. Mechanisms to minimize risk of migration include incorporating ridges or teeth projecting into the subchondral bone or creating more rigid designs incorporated into the cage, including screws or blades, which can be advanced into the cancellous bone of the vertebral body. A cage with these characteristics will maximize fusion, alignment correction, and visualization of fusion, and avoid complications such as nonunion, adjacent segment degeneration, and loss of deformity correction. Ti and other metallic cages have been used for a long time, but some concerns exist over stressshielding forces resulting from the rigidity of the motion segment.16,17 Although threading may decrease some stress-shielding forces, it can also compromise the endplate, negating this effect and preventing Ti cages from reaching maximal levels of success due to subsidence.16,18 Some spacers are approved for use as stand-alone, but often surgeons will supplement them with additional anterior and/or posterior instrumentation because incidence of nonunion is lower with additional stabilization.19,20 Biomechanical studies have shown that stand-alone interbody implants have decreased strength in extension or rotation compared to flexion and lateral bending,21 and clinical studies reflect the same trend.22 Many surgeons use anterior plates, which can increase

Complications of ALIF with PEEK Spacers stability, protect against graft migration, increase healing rates, and potentially obviate the need for posterior fixation,13,21 performed to further stabilize the construct. Thus, some surgeons advocate anterior-only surgery as a viable way to avoid more extensive surgery and adjacent level stress from posterior instrumentation. However, ALIF is widely used today with supplemental posterior fixation to provide the most stable construct.23 The addition of interbody support in these procedures restores disc height and lordosis, supports load transmission, and addresses discogenic pain.23

42.4.3 The PEEK Spacer Biomechanical Development and Characteristics of PEEK ALIF Devices The PEEK spacer, introduced in the late 1990s to a market that was largely composed of Ti cages and structural grafts, was the first radiolucent cage material. PEEK is a semicrystalline aromatic, hydrophobic polymer with an elastic modulus of approximately 3.5 GPa (▶ Fig. 42.1).24 The elastic modulus is theoretically favorable to that of Ti, 100 to 110 GPa, because it is a closer match with cancellous bone at about 1 GPa and cortical bone at 12 to 20 GPa.24 Biomechanical studies suggest that the stiffness of a cage influences fusion rates19 and that the materials with a similar elastic modulus to bone are less likely to cause subsidence at the endplate. This effect was first studied by comparing Ti and poly-(L-lactic acid) (PLLA) in goats, which revealed enhanced fusion in PLLA cages.19,25 Namely, the PLLA group fused earlier had overall coarser and more homogeneous bone structure, indicating a more mature fusion.25 Moreover, exams of bone makeup near Ti hip implants have demonstrated bone loss from elastic modulus mismatch due to altered loading, stress shielding, and periprosthetic bone remodeling.26 A finite-element analysis comparing PEEK spacers to Ti revealed increased stress forces in the bone graft of the PEEK spacer, thereby inducing fusion, paired with decreased stress forces in the endplates, reducing subsidence.27 The stiffness of the spacer was not found

Fig. 42.1 Fortitude Vue Spacer (Zummer, Minneapolis, MN)—a PEEK implant.

to affect the relative motion, or stability, of the instrumented segment. Thus, PEEK spacers theoretically provide similar segmental stability to Ti but also reduce stress in the endplates and increase load transfer through the graft.27 Another important attribute of PEEK is its radiolucency, which allows for better visualization of trabecular bone formation to assess fusion after surgery. Therefore, the PEEK spacer was thought to be a step up from Ti, allowing improved visualization of fusion and potentially higher fusion rates with decreased subsidence. The PEEK cage also has theoretical advantages over structural grafts and allografts, which carry a number of complications despite some reports of fusion rates over 90% and clinical success.28,29 Namely, allograft may cause prolonged healing time or time to fuse, failure to maintain disc space height, collapse of the interbody graft, graft retropulsion, graft resorption, and increased incidence of pseudarthrosis.30,31,32 Some studies suggest that allograft cannot adequately maintain disc space height, with graft subsidence rates up to 34% reported due to both resorption and graft protrusion.30,33,34 This problem is not as commonly seen with PEEK in comparison, and multiple studies have reported its successful maintenance of disc space height and lordosis correction.34,35 Thus, the PEEK cage theoretically fulfills the biological and mechanical functions required of a successful interbody spacer by incorporating allograft, as well as providing the right amount of mechanical support.30

Biomechanical Concerns with the Use of PEEK Spacer Biomechanical studies suggest that PEEK may be less successful at decreasing range of motion and resisting pullout compared to Ti,17 and the clinical implications of this finding are unclear. There is mixed evidence of the fusion rates with PEEK, and these biomechanical properties could indicate that, in some cage designs, the PEEK cage does not provide enough initial stability for successful fusion.36,37 Other studies, however, have not detected this effect when comparing PEEK and Ti.18,38 One inherent problem with nonorganic spacers is that they generally cannot integrate into the fusion mass and thus rely on autograft growth through hollow compartments for success. Thus the design of the cage is important and can greatly alter the fusion rates.24,39 Cages must provide necessary stability and also allow ample bone to graft contact. As a result, PEEK and Ti spacers have often been supplemented with BMP to increase the osteoinductive nature of the fusion.23 However, recent reanalysis of the clinical data concerning BMP suggests increased risk of certain ALIF-related complications including RE and others.9,10 Therefore, there may be increased risk as well as unnecessary increase in cost when using PEEK spacers (e.g., recombinant human bone morphogenetic protein 2 [rhBMP-2] costs up to $7,000 per case).23 However, health care costs include more than just the outright material and instruments cost. Operating time, hospital stay, lost productivity, reoperation rate, and quality of life comprise a much larger portion of the total health care cost, and therefore, studying clinical and radiological outcomes of PEEK plus allograft versus Ti and other allograft implants could be more consequential. Also, it is conceivable that the clinical success of PEEK implants for ALIF procedures may be adversely affected by changing practice patterns among spine surgeons.

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Thoracolumbar A specific concern about the PEEK cage is its hydrophobic nature, which may limit the amount of bone contact and decrease fusion rates.36 The hydrophobic material does not absorb proteins or encourage cell adhesion.40 One study used scanning electron microscopy to examine the percentage of the implant that was in contact with bone. Results showed that the best bone contact occurred in plasma-treated Ti cages (42%), followed by PEEK (12%) and polished Ti (5.6%).24 Previous studies have shown that the best bone ingrowth occurs in a Ti osteochondral composite material compared to plasma spraycoated Ti and smooth-sided Ti, reiterating that the ideal fusion material may require a scaffold for ingrowth.40 Thus, PEEK cages may be disadvantageous for fusion with respect to graft contact and osteoconduction, but the practical implications are unclear and therefore requires a further study of the healing process. Although there is some evidence to support the idea that the lower elastic modulus of the PEEK spacer decreases the risk for subsidence,38,41 subsidence still occurs to some degree with PEEK spacers.42 Moreover, it is unclear whether or not the rate of subsidence should be a major determinant because it has not been strongly correlated with fusion success.42,43,44,45 Although subsidence may cause loss of lumbar lordosis or disc space height, it does not have a clear clinical impact.42 Another biomechanical study compared large and small footprint PEEK cages (differing by surface area) to Ti cages of a similar design and found decreased stability in the PEEK cages, based on increased range of motion and decreased pullout strength.17 This was true of the stand-alone cages and cages with translaminar screws. The larger PEEK implant did not succeed in providing segmental stability equal to the Ti cage in terms of decreasing range of motion adequately.17 Moreover, the PEEK cage teeth, which facilitate secure fixation to the vertebral endplates, were not as sharp as those in the Ti cage due to the nature of the materials.17 This probably contributes to decreased pullout strength in PEEK cages.

Clinical Concerns with the Use of PEEK Spacer Although many initial studies have shown encouraging results with the PEEK cage, there have also been some questions concerning fusion rates, ease of evaluating radiological fusion, subsidence, and the need for posterior instrumentation. The PEEK spacer packed with autograft has been reported to facilitate faster fusion than allograft spacers.30,31 However, fusion rates with PEEK in additional studies have not been consistent. In fact, some have reported very low fusion rates, resulting in high numbers of reoperation.36,37,42 The same study also reported lower fusion rates on computed tomography (CT) scans, ranging between 70.6 and 75.9% compared to previously reported 82.4 and 89.7%. Although the authors could not iterate the reason for the difference in fusion rates on CT scans and found no significant correlation between clinical outcome and fusion rates, the radiolucency of PEEK can become questionable and its major advantage of using PEEK over Ti implant, that is its radiolucency, can potentially become invalidated.36 One study involving a posterior/anterior procedure with rigid posterior instrumentation reported an overall fusion rate of 98% and excellent or good clinical outcomes in 86% of patients.42 However, lumbar lordosis decreased at ultimate follow-up in 13 patients (23%), particularly in older patients with

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high cages and a rigid primary posterior instrumentation, and at more caudal levels.42 Patients who initially achieved lordosis correction reverted back to their preoperative sagittal balance by final follow-up, indicating that there was some subsidence of the cages. The clinical implications of this study are not clear. However, it suggests that posterior surgery and pedicle screws may be necessary to sufficiently stabilize the spine when using the PEEK spacer, which could negate the advantages of ALIF over other posterior procedures due to the muscle stripping necessary during the posterior surgery. Some of the most concerning outcomes to date were reported in studies of the stand-alone Synfix-integrated spacer-plate system. Stand-alone interbody cages are used for gaining access anteriorly and to avoid any posterior involvement. The Synfix is a stand-alone PEEK device that has an integrated anterior Ti plate and four divergent locking screws. Several studies have examined clinical outcomes of a specific PEEK spacer, the Synfix-LR™ device (Synthes), and have reported differing outcomes. One randomized trial compared the interspace collapse of the Synfix to a Ti implant and found that disc and intervertebral foraminal (IVF) height increased about 6 and 7 mm, respectively, and was maintained at ultimate follow-up with the Synfix; however, with the Ti device, disc and IVF height returned to preoperative value.41 This study demonstrated fusion rates of 85 and 87% in PEEK and Ti, respectively,41 with significantly improved Visual Analogue Score (VAS) and Oswestry Disability Index (ODI) scores in both groups. This study provides some clinical evidence that the PEEK spacer may be better for avoiding subsidence, but the clinical effect is unclear. Another study found that ODI and VAS scores were better with a stand-alone Synfix compared to a group with a PEEK ALIF implant plus translaminar screws, but fusion rates for the study were very low in both groups (71 and 69%, respectively).37 On the other hand, Schimmel et al reported a series of ALIF procedures using Synfix cages, in which 26 of 95 patients underwent reoperation (27%), with 24% as a result of pseudarthrosis (▶ Fig. 42.2).36 The concern over fusion rates with this device was confirmed in other studies, reporting variable

Fig. 42.2 SynFix-LR (Synthes Bettlach, Switzerland)—two distinct parts; polyether ether ketone frame and Ti anterior plate with diverging locking screws that penetrate the vertebral body close to the anterior rim for stability.

Complications of ALIF with PEEK Spacers

Fig. 42.3 Stabilis (Stryker, Kalamazoo, MI)—a Ti implant with an anatomically friendly frame and a bone graft delivery unit.

rates of a successful fusion, ranging from 63 to 98%,36,37,41 several of which were much lower than typically expected using traditional stand-alone ALIF procedures with fusion rates approaching 90%.36,46,47 Factors that could have contributed to the high rate of pseudarthrosis in these studies are low initial instability with the stand-alone device and hydrophobic characteristics of PEEK. Overall, the results from these studies suggest that stand-alone cages may not maximize the chance of achieving solid fusion and that the integrated anterior plate may require more careful monitoring or patient selection. A particular concern for the use of PEEK implants regarding the treatment of spondylolisthesis has been raised. Lastfogel et al published a small case series concluding that ALIF with PEEK stand-alone spacers may be contraindicated for patients with this diagnosis. This study describes three consecutive L5–S1 spondylolisthesis patients who were treated with ALIF and stand-alone spacers with an integrated system for internal fixation into the vertebral bodies (▶ Fig. 42.3).48 All three patients suffered from anterior sacral fractures 10 to 40 days after their surgery and had to undergo reoperations.48 Additionally, one patient from another study suffered from a Synfix cage dislocation 7 days postoperatively, and reevaluation of preoperative radiographs revealed bilateral spondylolysis that likely contributed to the implant failure and postoperative spondylolisthesis.37 These studies alert us to a complication of stand-alone PEEK spacers with integrated screws in treating patients with spondylolysis and spondylolisthesis and highlight the fact that the Synfix cannot sufficiently stabilize the shear stress and axial loads present among spondylolisthesis. This can potentially result in dislocation of the spacer or fracture of the sacrum, presenting a significant danger with the PEEK stand-alone spacer.

42.5 Conclusion The complications associated with the PEEK spacer were initially thought to be, in many respects, similar to those of other spacers with slight variations in frequency and severity. Despite the initial excitement regarding the biomechanical advantages of PEEK ALIF devices and potentially improved clinical effects, there have been several significant discrepancies between PEEK and other spacers that have been detected in more recent literature in various subsets of patients. We recommend caution with the use of PEEK devices, particularly as a stand-alone device or in the setting of spondylolisthesis.

References [1] Burns B. An operation for spondylolisthesis. Lancet. 1933; 221(5728):1233 [2] Iwahara T. A new method of vertebral body fusion. Surgery (Japan). 1944; 8:271–287

[3] Heary RF, Yanni DS, Benzel EC. Anterior lumbar interbody fusion. In: Benzel EC, ed. Spine Surgery: Techniques, Complication Avoidance, and Management. Vol. 1. 3rd ed. Philadelphia, PA: Elsevier Saunders; 2012:523–534 [4] Fantini GA, Pawar AY. Access related complications during anterior exposure of the lumbar spine. World J Orthod. 2013; 4(1):19–23 [5] Rajaraman V, Vingan R, Roth P, Heary RF, Conklin L, Jacobs GB. Visceral and vascular complications resulting from anterior lumbar interbody fusion. J Neurosurg. 1999; 91(1) Suppl:60–64 [6] Baker JK, Reardon PR, Reardon MJ, Heggeness MH. Vascular injury in anterior lumbar surgery. Spine. 1993; 18(15):2227–2230 [7] Christensen FB, Bünger CE. Retrograde ejaculation after retroperitoneal lower lumbar interbody fusion. Int Orthop. 1997; 21(3):176–180 [8] Peng CW, Bendo JA, Goldstein JA, Nalbandian MM. Perioperative outcomes of anterior lumbar surgery in obese versus non-obese patients. Spine J. 2009; 9 (9):715–720 [9] Carragee EJ, Mitsunaga KA, Hurwitz EL, Scuderi GJ. Retrograde ejaculation after anterior lumbar interbody fusion using rhBMP-2: a cohort controlled study. Spine J. 2011; 11(6):511–516 [10] Comer GC, Smith MW, Hurwitz EL, Mitsunaga KA, Kessler R, Carragee EJ. Retrograde ejaculation after anterior lumbar interbody fusion with and without bone morphogenetic protein-2 augmentation: a 10-year cohort controlled study. Spine J. 2012; 12(10):881–890 [11] Rihn JA, Patel R, Makda J, et al. Complications associated with single-level transforaminal lumbar interbody fusion. Spine J. 2009; 9(8):623–629 [12] Freudenberger C, Lindley EM, Beard DW, et al. Posterior versus anterior lumbar interbody fusion with anterior tension band plating: retrospective analysis. Orthopedics. 2009; 32(7):492 [13] Oxland TR, Lund T. Biomechanics of stand-alone cages and cages in combination with posterior fixation: a literature review. Eur Spine J. 2000; 9(7) Suppl 1:S95–S101 [14] Hee HT, Castro FP, Jr, Majd ME, Holt RT, Myers L. Anterior/posterior lumbar fusion versus transforaminal lumbar interbody fusion: analysis of complications and predictive factors. J Spinal Disord. 2001; 14(6):533–540 [15] Agabegi SS, Conelly C, Fischgrund JS. Lumbar interbody cages. In: Benzel EC, ed. Spine Surgery: Techniques, Complication Avoidance, and Management. Vol. 1. 3rd ed. Philadelphia, PA: Elsevier Saunders; 2012:535–540 [16] Kanayama M, Cunningham BW, Haggerty CJ, Abumi K, Kaneda K, McAfee PC. In vitro biomechanical investigation of the stability and stress-shielding effect of lumbar interbody fusion devices. J Neurosurg. 2000; 93(2) Suppl:259–265 [17] Spruit M, Falk RG, Beckmann L, Steffen T, Castelein RM. The in vitro stabilising effect of polyetheretherketone cages versus a titanium cage of similar design for anterior lumbar interbody fusion. Eur Spine J. 2005; 14(8):752–758 [18] Niu C-C, Liao J-C, Chen W-J, Chen L-H. Outcomes of interbody fusion cages used in 1 and 2-levels anterior cervical discectomy and fusion: titanium cages versus polyetheretherketone (PEEK) cages. J Spinal Disord Tech. 2010; 23 (5):310–316 [19] van Dijk M, Smit TH, Sugihara S, Burger EH, Wuisman PI. The effect of cage stiffness on the rate of lumbar interbody fusion: an in vivo model using poly (l-lactic Acid) and titanium cages. Spine. 2002; 27(7):682–688 [20] Madan SS, Harley JM, Boeree NR. Anterior lumbar interbody fusion: does stable anterior fixation matter? Eur Spine J. 2003; 12(4):386–392 [21] Tzermiadianos MN, Mekhail A, Voronov LI, et al. Enhancing the stability of anterior lumbar interbody fusion: a biomechanical comparison of anterior plate versus posterior transpedicular instrumentation. Spine. 2008; 33(2): E38–E43 [22] Aryan HE, Lu DC, Acosta FL, Jr, Ames CP. Stand-alone anterior lumbar discectomy and fusion with plate: initial experience. Commentary Surg Neurol. 2007; 68(1):7–13, discussion 13 [23] Chau AM, Xu LL, Wong JH, Mobbs RJ. Current status of bone graft options for anterior interbody fusion of the cervical and lumbar spine. Neurosurg Rev. 2014; 37(1):23–37

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Thoracolumbar [24] Pelletier MH, Cordaro N, Punjabi VM, Waites M, Lau A, Walsh WR. PEEK versus Ti interbody fusion devices: resultant fusion, bone apposition, initial and 26 week biomechanics. Clin Spine Surg. 2016; 29(4):E208–E214 [25] Smit TH, Müller R, van Dijk M, Wuisman PI. Changes in bone architecture during spinal fusion: three years follow-up and the role of cage stiffness. Spine. 2003; 28(16):1802–1808, discussion 1809 [26] Bryan JM, Sumner DR, Hurwitz DE, Tompkins GS, Andriacchi TP, Galante JO. Altered load history affects periprosthetic bone loss following cementless total hip arthroplasty. J Orthop Res. 1996; 14(5):762–768 [27] Vadapalli S, Sairyo K, Goel VK, et al. Biomechanical rationale for using polyetheretherketone (PEEK) spacers for lumbar interbody fusion-A finite element study. Spine. 2006; 31(26):E992–E998 [28] Cloward RB. Posterior lumbar interbody fusion updated. Clin Orthop Relat Res. 1985(193):16–19 [29] Hanson DS, Bridwell KH, Rhee JM, Lenke LG. Dowel fibular strut grafts for high-grade dysplastic isthmic spondylolisthesis. Spine. 2002; 27(18):1982– 1988 [30] Brantigan JW, Steffee AD. A carbon fiber implant to aid interbody lumbar fusion. Two-year clinical results in the first 26 patients. Spine. 1993; 18 (14):2106–2107 [31] Brantigan JW, McAfee PC, Cunningham BW, Wang H, Orbegoso CM. Interbody lumbar fusion using a carbon fiber cage implant versus allograft bone. An investigational study in the Spanish goat. Spine. 1994; 19(13):1436–1444 [32] Brantigan JW. Pseudarthrosis rate after allograft posterior lumbar interbody fusion with pedicle screw and plate fixation. Spine. 1994; 19(11):1271–1279, discussion 1280 [33] Liljenqvist U, O’Brien JP, Renton P. Simultaneous combined anterior and posterior lumbar fusion with femoral cortical allograft. Eur Spine J. 1998; 7 (2):125–131 [34] Cutler AR, Siddiqui S, Mohan AL, Hillard VH, Cerabona F, Das K. Comparison of polyetheretherketone cages with femoral cortical bone allograft as a single-piece interbody spacer in transforaminal lumbar interbody fusion. J Neurosurg Spine. 2006; 5(6):534–539 [35] McAfee PC, DeVine JG, Chaput CD, et al. The indications for interbody fusion cages in the treatment of spondylolisthesis: analysis of 120 cases. Spine. 2005; 30(6) Suppl:S60–S65

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[36] Schimmel JJ, Poeschmann MS, Horsting PP, Schönfeld DH, van Limbeek J, Pavlov PW. PEEK cages in lumbar fusion: mid-term clinical outcome and radiological fusion. J Spinal Disord Tech. 2012 [37] Strube P, Hoff E, Hartwig T, Perka CF, Gross C, Putzier M. Stand-alone anterior versus anteroposterior lumbar interbody single-level fusion after a mean follow-up of 41 months. J Spinal Disord Tech. 2012; 25(7):362–369 [38] Wan Z, Dai M, Miao J, Li G, Wood KB. Radiographic Analysis of PEEK Cage and FRA in Adult Spinal Deformity Fused to Sacrum. J Spinal Disord Tech. 2014; 27(6):327–335 [39] Schleicher P, Gerlach R, Schär B, et al. Biomechanical comparison of two different concepts for stand alone anterior lumbar interbody fusion. Eur Spine J. 2008; 17(12):1757–1765 [40] Chang Y-S, Gu H-O, Kobayashi M, Oka M. Influence of various structure treatments on histological fixation of titanium implants. J Arthroplasty. 1998; 13 (7):816–825 [41] Cho C-B, Ryu K-S, Park C-K. Anterior lumbar interbody fusion with standalone interbody cage in treatment of lumbar intervertebral foraminal stenosis : comparative study of two different types of cages. J Korean Neurosurg Soc. 2010; 47(5):352–357 [42] Rousseau M-A, Lazennec J-Y, Saillant G. Circumferential arthrodesis using PEEK cages at the lumbar spine. J Spinal Disord Tech. 2007; 20(4):278–281 [43] Choi JY, Sung KH. Subsidence after anterior lumbar interbody fusion using paired stand-alone rectangular cages. Eur Spine J. 2006; 15(1):16–22 [44] Pavlov PW, Meijers H, van Limbeek J, et al. Good outcome and restoration of lordosis after anterior lumbar interbody fusion with additional posterior fixation. Spine. 2004; 29(17):1893–1899, discussion 1900 [45] Crandall DG, Revella J. Transforaminal lumbar interbody fusion versus anterior lumbar interbody fusion as an adjunct to posterior instrumented correction of degenerative lumbar scoliosis: three year clinical and radiographic outcomes. Spine. 2009; 34(20):2126–2133 [46] Lee CS, Hwang CJ, Lee D-H, Kim Y-T, Lee HS. Fusion rates of instrumented lumbar spinal arthrodesis according to surgical approach: a systematic review of randomized trials. Clin Orthop Surg. 2011; 3(1):39–47 [47] Than KD, Wang AC, Rahman SU, et al. Complication avoidance and management in anterior lumbar interbody fusion. Neurosurg Focus. 2011; 31(4):E6 [48] Lastfogel JF, Altstadt TJ, Rodgers RB, Horn EM. Sacral fractures following stand-alone L5-S1 anterior lumbar interbody fusion for isthmic spondylolisthesis. J Neurosurg Spine. 2010; 13(2):288–293

Complications of Stand-Alone Anterior Lumbar Interbody Fusion

43 Complications of Stand-Alone Anterior Lumbar Interbody Fusion Branko Skovrlj, John M. Caridi, Vikas Varma, and Samuel K. Cho

43.1 Introduction 43.1.1 Historical Background Anterior lumbar interbody fusion (ALIF) was first described in 1932 when it was used in the treatment of tuberculosis and lumbar spondylolisthesis.1,2,3 The initial approach to the anterior lumbar spine was achieved through the transperitoneal approach and was later replaced by the retroperitoneal approach in the mid-1940s.4,5 In 1948, ALIF was first reported as a treatment modality for lumbar degenerative disc disease (DDD).6 In the initial technique described, corticocancellous blocks of autogenous bone were placed in the disc space defect following discectomy. In 1953, the dowel technique was described which employed the use of cylindrically shaped corticocancellous dowels.7,8 In the early 1960s, a cylindrical allograft was developed followed by the use of trapezoid bone blocks for the treatment of lumbar discogenic pain.9 Shortly thereafter, a hybrid interbody graft using a biologic femoral cortical allograft ring fusion cage packed with autologous iliac crest bone graft was developed. This hybrid construct allowed for rapid incorporation and vascularization of the bone graft coupled with acute stability of the construct and a compatible framework for host bone ingrowth.10 Despite the success and safety of the approach to the anterior lumbar spine, the stand-alone ALIF was not an acceptable procedure due to exceedingly high rates of pseudoarthrosis. A landmark study by the Mayo Clinic in 1972 showed a pseudoarthrosis rate of 44% in a group of 83 patients followed over 8 years.11 In response to low fusion rates, a technique combining ALIF with posterior instrumentation and fusion became commonly used. The addition of the posterior instrumentation increased stability across the fusion segment. However, it led to increased morbidity secondary to the circumferential fusion. In 1961, a slotted contoured plate was developed that was placed over the anterior lumbar spine in an attempt to enhance arthrodesis sparing the need for posterior instrumentation.12 In the mid-1970s, the cylindrical cage was first developed and following significant improvements in design and physical properties of cylindrical cages, the Bagby and Kuslich (BAK) titanium cage was first implanted in humans in 1992.13,14,15 This cage was threaded and screwed into the endplates for increased stabilization and fusion. Metal cages were later replaced by machined bone dowels which allow for greater osteoconductivity, incorporation over time, and easier radiographic interpretation and revision. In the late 1990s, tapered cages were developed. These cages provided further benefits over the cylindrical cages by allowing symmetrical reaming of the endplates which prepared the endplates for fusion while preserving strength and restoration of lordosis. The latest interbody devices to be developed were the trapezoidal cages, which are made from various materials and have a large footprint for maximal endplate coverage and a large inner volume for biologic substrate placement and future fusion maturation (▶ Fig. 43.8).16

43.2 Approach and Relevant Anatomy The surgical approach used for ALIF procedures can be either transperitoneal or retroperitoneal. Both the transperitoneal and retroperitoneal approaches allow for excellent exposure and visualization, as well as adequate space to perform surgery while preserving the paravertebral muscles and ligaments. The transperitoneal approach relies on the surgeon passing through the abdominal cavity and has a higher rate of associated retrograde ejaculation and bladder injury. It is more commonly associated with postoperative ileus and more difficult to perform in patients who have had prior abdominal surgeries.17,18 As such, this approach is uncommonly performed and has been largely replaced with the retroperitoneal approach. The retroperitoneal approach is performed through a paramedian incision and avoids the need to enter the peritoneal cavity. The incision is preferably performed on the left side as the arterial structures can more easily withstand retraction and mobilization than the venous structures encountered with a right-sided approach. A longitudinal incision is most commonly made halfway between the umbilicus and lateral border of the rectus sheath at the level identified by preoperative radiography (▶ Fig. 43.1). The anterior rectus sheath is incised and the rectus muscle is retracted laterally to allow exposure of the peritoneum and to protect the nerve supply to the rectus muscle. The ureter and peritoneum together with its contents are mobilized away from the psoas muscle allowing for deep retractors to be inserted (▶ Fig. 43.2). Mobilization of the

Fig. 43.1 Location of skin incision.

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Thoracolumbar

Fig. 43.2 Retroperitoneal approach.

common iliac vein/artery and/or vena cava and aorta are performed depending on the disc space of interest. For L5/S1 exposure, the middle sacral artery should be identified and ligated as it intersects perpendicularly across this disc space. At this level, the great vessels have already bifurcated and are not in the operative corridor. For procedures involving the L4/L5 interspace, the iliolumbar vein must be identified and ligated in order to avoid unintentional avulsion. The left-sided L4 segmental vessels should also be ligated prior to mobilization. For procedures involving the L3/L4 disc space, the segmental leftsided vessels adjacent to the L3/L4 vertebral bodies should be

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ligated prior to mobilization of the great vessels. A self-retaining retractor should be used to retract the great vessels and abdominal structures in a safe fashion for the remainder of the procedure. The disc space of interest is then identified and this is confirmed using intraoperative radiography (▶ Fig. 43.3). In the early 1990s, laparoscopic ALIF showed early success with its pioneers and was reported to be less invasive with less blood loss and faster recovery times.19 However, later studies contraindicated earlier findings, noting no identifiable advantages, added technical challenges, and increased retrograde ejaculation.15,20,21

Complications of Stand-Alone Anterior Lumbar Interbody Fusion

Fig. 43.3 Final exposure.

43.3 Patient Selection ALIF is indicated primarily for the treatment of symptomatic DDD. Other indications for ALIF include treatment of scoliosis, tumors, fractures, low-grade spondylolisthesis, failed posterior spinal fusion, and other degenerative lumbar disorders.21,22,23,24 In the treatment of symptomatic DDD, indications for an interbody fusion include DDD of one or two adjacent levels with severe, chronic, disabling, low back pain lasting longer than 6 months that is unresponsive to nonoperative management. Contraindications to ALIF include morbid obesity complicating access to the lumbar spine, severe atherosclerosis or calcification of the great vessels hindering mobilization, retroperitoneal scarring caused by prior abdominal surgery, and active infection. To maximize the predictive value of ALIF outcome, the patient’s history should be consistent with mechanical back pain and radiographic studies should show disc degeneration at particular levels. Multiple socioeconomic and psychosocial factors affect outcomes, and these confounding variables must be accounted for prior to the decision to undergo surgical treatment. Patients with a significant psychosocial component to their pain should be considered poor surgical candidates.

43.3.1 Biomechanics The ultimate goal of the ALIF procedure is achieving a stable fusion. In the early stages after the introduction of the ALIF, a number of studies documented that autogenous and allogenic cortical and cancellous bone grafts had insufficient strength to support the weight of the body and that tridimensional interbody stability was crucial for future fusion.25,26,27 This led to the development of the modern interbody cages. Studies have shown that a larger contact area between endplate and cage produced a lower stress distribution pattern and that bone grafts covering greater than 30% of the endplate area were able to carry significantly greater loads.1,28 The

characteristics of the vertebral endplate are not uniform throughout its surface. Studies have shown that the greatest strength of the vertebral body is in the peripheral, posterolateral subchondral bone of the cortical endplate, just anterior to the pedicle.29,30 The central portion of the endplate was found to have a thin cortex and provided little resistance to compressive loads. It is also known that the superior endplate is significantly weaker than the inferior endplate, thus more prone to subsidence. This fact alone impacts the positioning and design of the cage used when performing an ALIF. In biomechanical tests, the modern-day implants are able to withstand maximum loads without failure, and failure most commonly occurs at the endplate.31 As such, failures generally result in implant subsidence or cavitation. Failure of the endplate leads to implant migration into the vertebral body and subsequent segment collapse. Implant design affects how the load is transmitted to the adjacent vertebra and may contribute to adjacent level disc degeneration and pain.1 Studies show that greater implant contact areas transmit load to the adjacent segment in a more physiologic manner and that smaller surface areas transmit loads in a similar manner to a degenerative disc.1 Furthermore, physiologic stress patterns are better recreated when the patient’s lordotic curve is restored.

43.4 Implant Selection 43.4.1 Cage A successful implant must be mechanically strong to withstand compressive loads while producing an osteogenic, osteoinductive, and osteoconductive environment. Modern-day implants differ in the materials from which they are made and also in their shape and biological properties. Biologic cages, such as bone dowels and femoral rings are threaded pieces of femoral allograft. They comprise a cortical ring of bone with a hollow center allowing for placement of a bone graft and/or bone graft substitute. The main advantages of using biologic cages include placement of a completely biologic device as well as absence of radiographic artifact. The disadvantages of these devices include risk of disease transmission and the potential for fracture during insertion into the interspace.32 A concern with biologic cages is with their use with recombinant human bone morphogenetic protein 2 (rhBMP-2) as the bone graft substitute or supplement. A study evaluating the use of rhBMP-2 in standalone ALIF with femoral ring allograft found a trend toward a higher nonunion rate with the use of rhBMP-2.33 It is believed that the robust inflammatory response created by the local rhBMP-2 causes ring absorption before fusion formation, destabilizing the segment before fusion matures. Metal alloy cages are made from titanium alloys which provide the necessary strength to withstand a wide range of loading forces. Metal cages come in various shapes and are usually threaded and fenestrated which increases their pullout strength and decreases radiographic artifact formation, respectively.34 However, metal cages lack the environment necessary for fusion maturation. To compensate for this deficiency, metal implants provide a large space for placement of bone graft and/ or bone graft substitute. Although metal implants can provide an environment that is conducive to fusion, they are limited by the specific design and subsequent volume available for the

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Thoracolumbar fusion to penetrate through the implant. As such, the fusion area must be maximized by exposing the entire endplate and choosing an implant that provides the most volume for the biologic substrate and future fusion block. The first- and secondgeneration metal cages were cylindrical in shape, thicker than newer cages allowing for less bone graft placement, and also produced more artifacts on imaging studies.35,36 Third-generation metal cages have a trapezoidal configuration and are tapered.37 This shape allows for increased surface area for bone growth and facilitates restoration of lordosis.38 Trabecular metal cages, made from porous tantalum biomaterial with structure and mechanical properties similar to trabecular bone, have been shown to have a very high osteoconductive potential. Composite cages are made from plastic polymers with biomechanical properties similar to those of cortical bone.34 Composite cages are most commonly made from polyether ether ketone (PEEK). PEEK cages exhibit a modulus of elasticity similar to bone, enhancing load transfer to tissue in the cage, resulting in potentially lower rates of subsidence. PEEK cages are radiolucent and enable postoperative radiographic evaluation of fusion. One disadvantage with PEEK cages is their relative density and bio-inertness, limiting incorporation into the fusion mass and subsequent implant instability. Another disadvantage of PEEK cages is the fact that bio-inert materials are coated with a layer of fibrous tissue when implanted into the human body. As such, it is not clear as to the amount of fusion mass necessary around the PEEK implant to achieve a solid fusion.

43.4.2 Graft Selection Successful arthrodesis depends on numerous surgical and host factors, including selection of bone graft with elements critical for bone regeneration and subsequent fusion.39 With the development of interbody cages, bone grafts are now no longer needed for structural support and are used as cage fillers to create an environment more conducive to bone formation and fusion. Autograft harvested from iliac crest remains the “gold-standard” because of its potent biological properties.40 Autograft provides a natural environment rich in stem cells, osteoblasts, as well as osteoinductive factors such as BMPs which stimulate new bone formation. Autograft provides an optimal osteoconductive scaffold which facilitates neovascularization crucial for new bone formation.39 Allograft can be obtained from cadaveric femora or iliac crests and has been the traditional alternative to autograft use. Allograft bone is biologically inferior to autologous bone because of its lack of osteoinductivity and osteogenic strength.39 However, allograft bone has a long shelf life, is readily available, and prevents the need for iliac crest harvest which increases blood loss, operative time, and postoperative morbidity. Disadvantages to allograft bone include host rejection, bacterial contamination, and transfer of infection. Demineralized bone matrices (DBMs) are made by acid extraction of allograft bone which isolates type I collagen as well as multiple other growth factors. DBMs possess osteoconductive, as well as osteoinductive, properties and are effective bone graft extenders.

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BMPs are currently considered the most successful autograft alternatives and have been demonstrated to be as effective as iliac crest autograft without the potential pain and complications associated with an iliac crest bone harvest procedure.39 BMPs induce bone growth by triggering the differentiation of pluripotent mesenchymal cells into osteoblasts to generate a bony lattice.39 Disadvantages to BMPs include their high cost, complication risks, and the potential association with cancer. Other bone graft substitutes such as ceramics appear to have ideal properties as graft extenders or substitutes but lack clinical trials to support their use at this time.

43.5 Supplemental Fixation The initial favorable outcome of ALIF as a stand-alone procedure later became contraindicated by a high incidence of pseudoarthrosis. Initial fusion rates were inconsistent, with various authors reporting rates between 1 and 94%.6,41,42 Multiple biomechanical human cadaveric studies assessing three-dimensional stability following ALIF showed that in flexion, mobility was reduced by 40%, while in extension no stabilizing effect was reached.43 This paradoxical effect was thought to result from the resection of the anterior longitudinal ligament, as well as anterior annulus fibrosus. However, biomechanical studies of interbody fusions comparing anterior versus posterior approach showed similar biomechanical results in flexion and extension in both groups even though in the posterior group the annulus fibrosus and anterior longitudinal ligament was left intact.43 It was postulated that this finding was due to the facet destruction which occurs in the posterior approach. These same studies also showed a reduction in lateral bending and axial rotation after ALIF. In light of these studies, inadequate immobilization of the intervertebral joint during the process of bone healing has been accepted as the main mechanical reason for the development of pseudoarthrosis. On account of the high rate of pseudoarthrosis, it was suggested to combine anterior cage interbody fusion with an additional posterior stabilization to reach sufficient primary stability.44,45,46,47 Fusion rates were reported highest following intervertebral fusion combined with transpedicular fixation because of high primary stability and large bony area for consolidation.2 Despite having a very high fusion rate, circumferential fusion carries significantly greater morbidity such as approach-dependent damage to the posterior muscles attributed to persistent or recurrent low back pain postoperatively, increased rate of screw displacement–related neural complication, and increase rate of adjacent segment degeneration.48,49,50 For this reason, several types of supplementary fixation techniques have been developed to improve segmental stability. These include anterior plates, cages screwed into endplates, pedicle screw systems, and translaminar screws. The initial stability of a stand-alone ALIF cage depends mainly on the compressive forces produced by the tension on the remaining annulus fibrosus.25 However, these compressive forces reduce in magnitude by more than 20% in the first 15 minutes after cage insertion due to relaxation of the soft tissue.51 A biomechanical comparison of anterior plate versus posterior transpedicular augmentation in human cadaveric specimens reported that compared to the anterior plate, transpedicular

Complications of Stand-Alone Anterior Lumbar Interbody Fusion instrumentation resulted in significantly less range of motion in flexion–extension and lateral bending but not in rotation.52 The result of another biomechanical study showed that the results were biomechanically similar between anterior plate fixation and pedicle screw fixation.53 Biomechanical studies comparing supplemental fixation with pedicle screw versus translaminar screw found similar increases in rigidity as long as the anterior annulus was intact.54 When the anterior annulus was excised, as is the case in ALIF, translaminar fixation was not as strong as pedicle screw fixation. Biomechanical studies assessing some of the newer technologies such as composite cages screwed into endplates are currently lacking. The above biomechanical studies suggest that stand-alone ALIF does not provide adequate stability. However, there is a lack of evidence to support the contention that ALIF with supplementary fixation results in better fusion rates or clinical outcome. Currently, the precise mechanism of fusion in ALIF and the amount of micromotion needed for bone healing remain poorly understood.

43.6 Complications 43.6.1 Immediate/Short Term Vascular Injury Vascular injury is the most common complication of ALIF, reported to occur in 0.5 to 6.7% of ALIF procedures.55,56,57,58 The structures at risk include the great vessels, segmental vessels, and numerous veins. The abdominal aorta most commonly bifurcates at the level of the L4 vertebral body, while the confluence of the inferior vena cava is most commonly located at the level of the L5 vertebral body (▶ Fig. 43.4).59 For this reason, vascular injury most often occurs when operating at the L4/L5 level.60 Venous laceration is the most common vascular injury. The veins most commonly lacerated include the left common iliac vein, inferior vena cava, and iliolumbar vein.15

Whereas venous injury is the most common, arterial injury is the most serious. The most common arterial injury is left iliac artery thrombosis, which is thought to occur following prolonged retraction of the common iliac arteries to the right, causing diminished arterial flow and subsequent left-sided thrombosis.60 Multiple studies have shown that vascular injury to the great vessels occurs more commonly while the discectomy is being performed and not during the initial approach.24,61,62 Vascular injury is reported to occur more commonly with the use of threaded cages compared to nonthreaded cages and is attributed to the added instrumentation needed to place threaded devices.63 There is also a significantly increased risk of vascular injury when two spinal levels are instrumented.5

Urologic Injury Retrograde ejaculation, which results in male sterility, is a serious complication following ALIF. This complication results from injury to the superior hypogastric sympathetic plexus. This plexus can exist as either a bundle of nerves or a single presacral nerve located just anterior to the L5–S1 disc space (▶ Fig. 43.5).64 Reports of retrograde ejaculation following ALIF vary widely in the literature and range from 0 to 10% in different series.3,65,66,67,68,69 Various causative factors have been postulated as the cause of an increased risk for retrograde ejaculation and include lack of experience, laparoscopic technique, use of monopolar electrocautery, and transperitoneal approach.64 Recently, the use of rhBMP-2 in ALIF has been associated with an increased risk of retrograde ejaculation following ALIF surgery.18 Bladder injury is infrequently seen with ALIF and is thought to occur during peritoneal mobilization or psoas muscle mobilization. Efferent parasympathetic fibers arising from the second to fourth sacral vertebral segments convey motor fibers to the detrusor muscle and inhibitory fibers to the sphincter vesicae. When these nerves are damaged, either from prolonged

Fig. 43.4 Vascular anatomy.

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Fig. 43.5 Superior hypogastric sympathetic plexus.

Fig. 43.6 Ureters.

retraction of the bladder or ligation, normal micturition cannot occur and patients develop postoperative bladder dysfuntion.65 Ureteral injury during open ALIF is extremely rare and has only been described in a case report in the literature (▶ Fig. 43.6).70 Ureteral laceration during laparoscopic-assisted ALIF also has been reported.71

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Gastrointestinal Complications The most common gastrointestinal complaint complicating postoperative recovery after ALIF is postoperative ileus, with reported incidence ranging from 0.6 to 5.6%.22 Postoperative ileus is more likely after transperitoneal procedures than retroperitoneal procedures, and ileus is often associated with

Complications of Stand-Alone Anterior Lumbar Interbody Fusion multiple previous abdominal surgeries, extensive procedures, significant fluid shifts, retroperitoneal hematoma, and excessive narcotic use.72 Intraoperative bowel injury is a rare complication of ALIF, with reported incidence ranging from 0.2 to 1.9%.73,74,75 Bowel injuries are more common in the transperitoneal approach; however, they have also been documented during retroperitoneal approaches following peritoneal violations. Bowel injuries are most likely to occur during revision surgery. A rare but serious complication following ALIF surgery is acute colonic pseudoobstruction which can result in cecal perforation in as many as 20% of cases with an associated mortality rate of 25 to 60%.15

literature.77,78,79,80,81 Two lumbar lymphatic trunks together with a network of smaller regional ducts travel along the anterior lumbar spine to become the cisterna chyli, which arises anterior to L2 and can be seen as an enlarged sac (▶ Fig. 43.7).82 This close network of lymphatic vessels surrounding the anterior lumbar spine is at an increased risk of laceration during ALIF. Fortunately, multiple lymphatic collaterals and anastomoses exist in the lymphatic network and complications occur in very few cases. In one study of 1,000 ALIF procedures, the lymphatic trunks and/or cisterna chyli was identified in only 12 cases, with complications occurring in three patients.64

Abdominal Wall Complications

Deep venous thrombosis occurs in 7.5% of patients following abdominal surgery performed in the vicinity of major blood vessels.83 The vessels most commonly affected are the inferior vena cava and common iliac veins.72 This complication is thought to arise from prolonged retraction of the veins during the surgery and must be taken seriously because fatal pulmonary embolism is a possible sequela.

Deep Venous Thrombosis

Abdominal asymmetry, manifested as a change in the contour of the abdominal wall is a recognized potential complication of anterior spinal surgery. The resultant bulging of the abdomen is not a true hernia and no risk of bowel incarceration exists.76 This occurs with denervation of the oblique musculature of the abdomen and is more commonly seen with incisions above the umbilicus. The internal oblique and transversus abdominis muscles are innervated by the iliohypogastric and ilioinguinal nerves. Distal branches of these nerves perforate the rectus sheath and terminate as anterior cutaneous branches of the abdomen.4 Development of an incisional hernia is a complication of abdominal surgery that has been previously reported with ALIF and is a risk with any abdominal surgery that disrupts the anterior abdominal musculature.

There are a wide variety of neurologic complications from ALIF resulting either from the initial approach or the procedure itself.84 Iatrogenic nerve root injury resulting in neurologic deficit is rare with ALIF. Iatrogenic nerve root injury can occur as a result of herniated nucleus pulposus from incomplete disc removal, overdistraction of the disc space, or foraminal intrusion of the interbody device.

Lymphatic Injury

Other Complications

Postoperative chyloperitoneum, or lymphocele, is a rare complication of ALIF with only limited cases reported in the

The lumbar sympathetic trunks, coursing on the lateral aspects of the vertebral bodies from T12–L4 are at risk of injury during

Nerve Root Injury

Fig. 43.7 Lymphatic drainage.

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Fig. 43.8 ALIF case example.

the anterior approach.72 Injury to these structures leads to unopposed parasympathetic vasodilation or loss of sympathetic vasoconstriction on the ipsilateral foot. Symptoms are usually temporary, but in some patients long-term dysesthesia persists.

43.6.2 Long Term Pseudoarthrosis Pseudoarthrosis, or nonunion, is a universal complication of fusion surgery (▶ Fig. 43.9). A systematic review of the literature found pseudoarthrosis rates ranging between 10 and 53% for ALIF, with most reported rates nearing 10%.85 Several studies have identified factors that may decrease the incidence of pseudoarthrosis, including graft/cage preparation and usage, the use of biologics, and addition of supplemental instrumentation.15 Inadequate immobilization of the intervertebral joint during the process of bone healing has been accepted as the main mechanical reason for nonfusion.

Subsidence

Fig. 43.9 Pseudoarthrosis.

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Subsidence is defined as a decrease in the height of the disc space prior to complete incorporation of the fusion mass (▶ Fig. 43.10).86 The benefits of lumbar interbody surgery stem from the increase in disc height and neural foraminal caliber, both of which are negatively affected by subsidence. A high rate of subsidence is reported in the literature. Early reports of ALIF using autografts and allografts reported a 100% subsidence rate.4,87,88,89 With the advent of cages, the subsidence rate decreased, with reported subsidence rates for femoral ring allograft and metallic implants of 85 and 50%, respectively.87,89 The reported median time for cage subsidence is 2.75 months with ranges varying widely from 0.2 to 8 months postoperatively.16,87,90 The etiology of subsidence of intervertebral cages

Complications of Stand-Alone Anterior Lumbar Interbody Fusion

Fig. 43.10 Subsidence.

is not fully understood. However, many factors associated with cages and endplate anatomy influence the extent and time of onset of subsidence following ALIF.

Graft Malposition and Migration Malposition of the interbody cage is a complication that most commonly occurs as a result of the surgeon failing to accurately identify the anterior vertebral anatomic midline.91 Laterally positioned cages or threaded cortical bone dowels can cause direct foraminal nerve root compression and radiculopathy. Similarly, lateral placement of interbody devices can result in a far lateral disc herniation with subsequent neurologic complication. ALIF implant migration has been reported in 2.3% of patients, with 1.2% of the total requiring reoperation (▶ Fig. 43.11).92 Graft migration and/or malposition can also result in poor alignment, subsidence, inadequate fusion, and subsequent pseudoarthrosis.

cage migration.30 Vertebral body osteolysis and ectopic bone formation leading to neurologic complications have also been described with the use of rhBMP-2 in ALIF.93

43.7 Summary ALIF is indicated primarily for the treatment of symptomatic DDD, it but can also be used in the treatment of other degenerative lumbar disorders as well as scoliosis, tumors, and fractures. Stand-alone ALIF with interbody cage without supplemental fixation does not confer sufficient biomechanical fixation in human cadaveric studies. Supplemental fixation with either posterior or anterior techniques has been recommended and should be performed with ALIF. The choice of approach for supplemental fixation should be tailored to each patient based on body habitus, comorbidities, psychosocial factors as well as surgeon proficiency, and outcomes with each particular technique.

Other Complications The use of rhBMP-2 in ALIF has led to a subset of complications specific to the use of this product. In 2002, the Food and Drug Administration approved the use of Infuse bone graft (Medtronic Sofamor Danek, Minneapolis, MN) in patients with DDD undergoing anterior lumbar surgery at one level using a tapered titanium cage. However, rhBMP-2 has been mostly used “offlabel” in lumbar spine surgery. A review of the literature regarding the use of rhBMP-2 in the lumbar spine revealed that its “off-label” use with the interbody cage contributed to a 44% resorption rate, a 25% subsidence rate, and a 27% incidence of

43.8 Future Directions Advances in minimally invasive surgical techniques as well as instrumentation have had great success in spine surgery. Potential for improved fixation techniques through minimally invasive approaches could be of great benefit in ALIF. Improved graft options to substitute and/or enhance rhBMP-2 are being developed and currently used. For example, allograft of cancellous bone containing viable adult stem cells and osteoprogenitor cells are showing promising results.

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Fig. 43.11 Cage migration.

43.9 Key References [1] Resnick DK, Choudhri TF, Dailey AT, et al. American Association of Neurological Surgeons/Congress of Neurological Surgeons. Guidelines for the performance of fusion procedures for degenerative disease of the lumbar spine. Part 11: interbody techniques for lumbar fusion. J Neurosurg Spine. 2005; 2 (6):692–699

This study was a systematic review of the literature evaluating the available medical evidence for the use of various interbody techniques compared with posterolateral fusion applied to patients with low back pain due to degenerative disc disease limited to one or two levels. [2] Oxland TR, Lund T. Biomechanics of stand-alone cages and cages in combination with posterior fixation: a literature review. Eur Spine J. 2000; 9 Suppl 1: S95–S101

The objective of this literature review was to address the mechanics of interbody cage fixation in the lumbar spine with respect to three-dimensional stabilization and the strength of the cage–vertebra interface. [3] Sasso RC, Best NM, Mummaneni PV, Reilly TM, Hussain SM. Analysis of operative complications in a series of 471 anterior lumbar interbody fusion procedures. Spine. 2005; 30(6):670–674

This study was a retrospective review comparing the intraoperative and perioperative complications associated with the placement of threaded devices and nonthreaded devices used in anterior lumbar interbody fusions. [4] Czerwein JK, Jr, Thakur N, Migliori SJ, Lucas P, Palumbo M. Complications of anterior lumbar surgery. J Am Acad Orthop Surg. 2011; 19(5):251–258

This review article focused on immediate intraoperative adverse events that occur during the exposure or the procedure itself as well as adverse events that occur between 1 and 6 weeks postoperatively.

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[5] Than KD, Wang AC, Rahman SU, et al. Complication avoidance and management in anterior lumbar interbody fusion. Neurosurg Focus. 2011; 31(4):E6

This study reviewed the literature and compared strategies for avoiding and treating complications from anterior lumbar interbody fusion (ALIF), and thus providing a comprehensive aid for spine surgeons.

References [1] Resnick DK, Choudhri TF, Dailey AT, et al. American Association of Neurological Surgeons/Congress of Neurological Surgeons. Guidelines for the performance of fusion procedures for degenerative disease of the lumbar spine. Part 11: interbody techniques for lumbar fusion. J Neurosurg Spine. 2005; 2 (6):692–699 [2] Oxland TR, Lund T. Biomechanics of stand-alone cages and cages in combination with posterior fixation: a literature review. Eur Spine J. 2000; 9 Suppl 1: S95–S101 [3] Sasso RC, Best NM, Mummaneni PV, Reilly TM, Hussain SM. Analysis of operative complications in a series of 471 anterior lumbar interbody fusion procedures. Spine. 2005; 30(6):670–674 [4] Czerwein JK, Jr, Thakur N, Migliori SJ, Lucas P, Palumbo M. Complications of anterior lumbar surgery. J Am Acad Orthop Surg. 2011; 19(5):251–258 [5] Than KD, Wang AC, Rahman SU, et al. Complication avoidance and management in anterior lumbar interbody fusion. Neurosurg Focus. 2011; 31(4):E6 [6] Ito H, Suchiya J, Asami G. A new radical operation for Pott's disease: report of ten cases. J Bone Joint Surg Am. 1934; 16:499–515 [7] Burns B. An operation for spondylolisthesis. Lancet. 1933; 224:1233–1239 [8] Mercer W. Spondylolisthesis with a description of a new method of operative treatment and notes of ten cases. Edinburgh Med J. 1936; 43:545–572 [9] Muller W. Transperitoneale freilegung der wirbelsaule bei tuberkuloser spondylitis. Dtsch Z Chirop. 1906; 85:128–137 [10] Iwahara T. A new method of vertebral body fusion. Surgery. 1944; 8:271–287 [11] Lane JD, Jr, Moore ES, Jr. Transperitoneal approach to the intervertebral disc in the lumbar area. Ann Surg. 1948; 127(3):537–551

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[39] Williams AL, Gornet MF, Burkus JK. CT evaluation of lumbar interbody fusion: current concepts. AJNR Am J Neuroradiol. 2005; 26(8):2057–2066 [40] Cheung KM, Zhang YG, Lu DS, Luk KD, Leong JC. Reduction of disc space distraction after anterior lumbar interbody fusion with autologous iliac crest graft. Spine. 2003; 28(13):1385–1389 [41] Hacker RJ. Comparison of interbody fusion approaches for disabling low back pain. Spine. 1997; 22(6):660–665, discussion 665–666 [42] Kuslich SD, Danielson G, Dowdle JD, et al. Four-year follow-up results of lumbar spine arthrodesis using the Bagby and Kuslich lumbar fusion cage. Spine. 2000; 25(20):2656–2662 [43] Ray CD. Threaded fusion cages for lumbar interbody fusions. An economic comparison with 360 degrees fusions. Spine. 1997; 22(6):681–685 [44] Burkus JK, Gornet MF, Dickman CA, Zdeblick TA. Anterior lumbar interbody fusion using rhBMP-2 with tapered interbody cages. J Spinal Disord Tech. 2002; 15(5):337–349 [45] Mobbs RJ, Chung M, Rao PJ. Bone graft substitutes for anterior lumbar interbody fusion. Orthop Surg. 2013; 5(2):77–85 [46] Adkins EWO. Lumbo-sacral arthrodesis after laminectomy. J Bone Joint Surg Br. 1955; 37-B(2):208–223 [47] Nilsson LT, Geijer M, Neumann P, et al. The Brantigan anterior lumbar I/F cage: two years radiological results. Eur Spine J. 2001; 10 Suppl 1:S26 [48] Button G, Gupta M, Barrett C, Cammack P, Benson D. Three- to six-year follow-up of stand-alone BAK cages implanted by a single surgeon. Spine J. 2005; 5(2):155–160 [49] Glazer PA, Colliou O, Klisch SM, Bradfore DS, Bueff HU, Lotz JC. Biomechanical analysis of multilevel fixation methods in the lumbar spine. Spine. 1997; 22 (2):171–182 [50] Kandziora F, Pflugmacher R, Kleemann R, et al. Biomechanical analysis of biodegradable interbody fusion cages augmented With poly(propylene glycolco-fumaric acid). Spine. 2002; 27(15):1644–1651 [51] Videbaek TS, Christensen FB, Soegaard R, et al. Circumferential fusion improves outcome in comparison with instrumented posterolateral fusion: long-term results of a randomized clinical trial. Spine. 2006; 31(25):2875– 2880 [52] Christensen FB. Lumbar spinal fusion. Outcome in relation to surgical methods, choice of implant and postoperative rehabilitation. Acta Orthop Scand Suppl. 2004; 75(313):2–43 [53] Park P, Garton HJ, Gala VC, Hoff JT, McGillicuddy JE. Adjacent segment disease after lumbar or lumbosacral fusion: review of the literature. Spine. 2004; 29 (17):1938–1944 [54] Amato V, Giannachi L, Irace C, Corona C. Accuracy of pedicle screw placement in the lumbosacral spine using conventional technique: computed tomography postoperative assessment in 102 consecutive patients. J Neurosurg Spine. 2010; 12(3):306–313 [55] Fan S, Hu Z, Zhao F, Zhao X, Huang Y, Fang X. Multifidus muscle changes and clinical effects of one-level posterior lumbar interbody fusion: minimally invasive procedure versus conventional open approach. Eur Spine J. 2010; 19 (2):316–324 [56] Havey RM, Voronov LI, Gaitanis I, et al. Relaxation response of lumbar spine Segments Undergoing Annular Distraction: Implication to Anterior Lumbar Interbody Implant Stability. San Francisco, CA: Orthopedic Research Society; 2004 [57] Tzermiadianos MN, Mekhail A, Voronov LI, et al. Enhancing the stability of anterior lumbar interbody fusion: a biomechanical comparison of anterior plate versus posterior transpedicular instrumentation. Spine. 2008; 33(2): E38–E43 [58] Nichols TA, Yantzer BK, Alameda S, Johnson WM, Guiot BH. Augmentation of an anterior lumbar interbody fusion with an anterior plate or pedicle screw fixation: a comparative biomechanical in vitro study. J Neurosurg Spine. 2007; 6(3):267–271 [59] Humke T, Grob D, Dvorak J, Messikommer A. Translaminar screw fixation of the lumbar and lumbosacral spine. A 5-year follow-up. Spine. 1998; 23 (10):1180–1184 [60] Kozak JA, Heilman AE, O’Brien JP. Anterior lumbar fusion options. Technique and graft materials. Clin Orthop Relat Res. 1994(300):45–51 [61] Ray CD. Threaded titanium cages for lumbar interbody fusions. Spine. 1997; 22(6):667–679, discussion 679–680 [62] Inamasu J, Kim DH, Logan L. Three-dimensional computed tomographic anatomy of the abdominal great vessels pertinent to L4-L5 anterior lumbar interbody fusion. Minim Invasive Neurosurg. 2005; 48(3):127–131 [63] Inamasu J, Guiot BH. Vascular injury and complication in neurosurgical spine surgery. Acta Neurochir (Wien). 2006; 148(4):375–387

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Thoracolumbar [64] Rajaraman V, Vingan R, Roth P, Heary RF, Conklin L, Jacobs GB. Visceral and vascular complications resulting from anterior lumbar interbody fusion. J Neurosurg. 1999; 91(1) Suppl:60–64 [65] Baker JK, Reardon PR, Reardon MJ, Heggeness MH. Vascular injury in anterior lumbar surgery. Spine. 1993; 18(15):2227–2230 [66] Harmon PH. A simplified surgical technic for anterior lumbar diskectomy and fusion; avoidance of complications; anatomy of the retroperitoneal veins. Clin Orthop Relat Res. 1964; 37(37):130–144 [67] Holscher EC. Vascular and visceral injuries during lumbar-disc surgery. J Bone Joint Surg Am. 1968; 50(2):383–393 [68] Garg J, Woo K, Hirsch J, Bruffey JD, Dilley RB. Vascular complications of exposure for anterior lumbar interbody fusion. J Vasc Surg. 2010; 51(4):946–950, discussion 950 [69] Flynn JC, Price CT. Sexual complications of anterior fusion of the lumbar spine. Spine. 1984; 9(5):489–492 [70] Regan JJ, Yuan H, McAfee PC. Laparoscopic fusion of the lumbar spine: minimally invasive spine surgery. A prospective multicenter study evaluating open and laparoscopic lumbar fusion. Spine. 1999; 24(4):402–411 [71] Slosar PJ, Reynolds JB, Schofferman J, Goldthwaite N, White AH, Keaney D. Patient satisfaction after circumferential lumbar fusion. Spine. 2000; 25 (6):722–726 [72] Isiklar ZU, Lindsey RW, Coburn M. Ureteral injury after anterior lumbar interbody fusion. A case report. Spine. 1996; 21(20):2379–2382 [73] Guingrich JA, McDermott JC. Ureteral injury during laparoscopy-assisted anterior lumbar fusion. Spine. 2000; 25(12):1586–1588 [74] Carragee EJ, Mitsunaga KA, Hurwitz EL, Scuderi GJ. Retrograde ejaculation after anterior lumbar interbody fusion using rhBMP-2: a cohort controlled study. Spine J. 2011; 11(6):511–516 [75] Faraj AA, Webb JK, Lemberger RJ. Urinary bladder dysfunction following anterior lumbosacral spine fusion: case report and review of the literature. Eur Spine J. 1996; 5(2):121–124 [76] Santos ER, Pinto MR, Lonstein JE, et al. Revision lumbar arthrodesis for the treatment of lumbar cage pseudoarthrosis: complications. J Spinal Disord Tech. 2008; 21(6):418–421 [77] Bianchi C, Ballard JL, Abou-Zamzam AM, Teruya TH, Abu-Assal ML. Anterior retroperitoneal lumbosacral spine exposure: operative technique and results. Ann Vasc Surg. 2003; 17(2):137–142 [78] Gardner GP, Josephs LG, Rosca M, Rich J, Woodson J, Menzoian JO. The retroperitoneal incision. An evaluation of postoperative flank ‘bulge’. Arch Surg. 1994; 129(7):753–756 [79] Fantini GA, Pawar AY. Access related complications during anterior exposure of the lumbar spine. World J Orthod. 2013; 4(1):19–23

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[80] Gary H, Williams P, Warwick R. Gray’s Anatomy. Philadelphia, PA: Churchill Livingstone; 1965 [81] Propst-Proctor SL, Rinsky LA, Bleck EE. The cisterna chyli in orthopaedic surgery. Spine. 1983; 8(7):787–792 [82] Kang BU, Choi WC, Lee SH, et al. An analysis of general surgery-related complications in a series of 412 minilaparotomic anterior lumbosacral procedures. J Neurosurg Spine. 2009; 10(1):60–65 [83] Hart AK, Greinwald JH, Jr, Shaffrey CI, Postma GN. Thoracic duct injury during anterior cervical discectomy: a rare complication. Case report. J Neurosurg. 1998; 88(1):151–154 [84] Faciszewski T, Winter RB, Lonstein JE, Denis F, Johnson L. The surgical and medical perioperative complications of anterior spinal fusion surgery in the thoracic and lumbar spine in adults. A review of 1223 procedures. Spine. 1995; 20(14):1592–1599 [85] Tropiano P, Huang RC, Girardi FP, Cammisa FP, Jr, Marnay T. Lumbar total disc replacement. Seven to eleven-year follow-up. J Bone Joint Surg Am. 2005; 87 (3):490–496 [86] Levi AD. Treatment of a retroperitoneal lymphocele after lumbar fusion surgery with intralesional povidone iodine: technical case report. Neurosurgery. 1999; 45(3):658–660, discussion 660–661 [87] Patel AA, Spiker WR, Daubs MD, Brodke DS, Cheng I, Glasgow RE. Retroperitoneal lymphocele after anterior spinal surgery. Spine. 2008; 33(18):E648– E652 [88] Farkas JC, Chapuis C, Combe S, et al. A randomised controlled trial of a lowmolecular-weight heparin (Enoxaparin) to prevent deep-vein thrombosis in patients undergoing vascular surgery. Eur J Vasc Surg. 1993; 7(5):554–560 [89] Jacobs WC, Vreeling A, De Kleuver M. Fusion for low-grade adult isthmic spondylolisthesis: a systematic review of the literature. Eur Spine J. 2006; 15 (4):391–402 [90] Kumar A, Kozak JA, Doherty BJ, Dickson JH. Interspace distraction and graft subsidence after anterior lumbar fusion with femoral strut allograft. Spine. 1993; 18(16):2393–2400 [91] Weiner BK, Fraser RD. Spine update lumbar interbody cages. Spine. 1998; 23 (5):634–640 [92] Soini J. Lumbar disc space heights after external fixation and anterior interbody fusion: a prospective 2-year follow-up of clinical and radiographic results. J Spinal Disord. 1994; 7(6):487–494 [93] Mroz TE, Wang JC, Hashimoto R, Norvell DC. Complications related to osteobiologics use in spine surgery: a systematic review. Spine. 2010; 35(9) Suppl: S86–S104

Complications of Anterior Lumbar Disc Replacement

44 Complications of Anterior Lumbar Disc Replacement Jason Pittman, Anthony Degiacomo, Dan Plev, Tony Tannoury, and Chadi Tannoury

44.1 Introduction The treatment of discogenic back pain with spinal arthrodesis may result in less-than-satisfactory outcomes. For instance, the rate of pseudoarthrosis and postoperative pain are estimated to be 14 and 9%, respectively.1 Additionally, adjacent segment pathology, in the forms of facet arthropathy, segmental instability, spinal stenosis, and disc collapse, develops due to the increased load and stress proximal and distal to the fused segments, and often warrants further medical and/or surgical interventions. Total disc replacement (TDR) was developed as an alternative to spinal arthrodesis addressing the discogenic back pain while preserving the mobility across the diseased lumbar segments and potentially preventing the development of adjacent segment disease.2 Initially developed in the 1950s, the first prostheses provided initial pain relief, but failed relatively early on due to subsidence into the vertebral body.3 Generally, there are two categories of disc arthroplasty: the TDR and the nuclear replacement.3 This chapter will cover the complications associated with TDR. The most common indications for total disc arthroplasty are discogenic low back pain with a single-level degenerative disc disease confirmed by magnetic resonance imaging (MRI) or computed tomography (CT) scan, in patients18 to 60 years of age, following a minimum of 6 months of unsuccessful conservative therapy and back pain greater than leg pain.4 On the other hand, this technology does not benefit patients with lumbar stenosis (central or subarticular), facet arthropathy, spondylolysis/ spondylolisthesis, scoliosis, posttraumatic degenerative segments, postoperative segment (excluding postdiscectomy), metabolic bone disease, metal allergy, pregnancy, autoimmune disorders, morbid obesity (body mass index > 40), tumor, or infection.3,4 The successful treatment of the discogenic back pain patient with TDR requires adherence to strict patient selection criteria, which are discussed in the previous chapters. Additionally, a significant surgical learning curve and appropriate additional surgical training are keys to successful outcomes. However, long-term follow-up data and revision rates, whether due to polyethylene wear or adjacent segment disease, have not been well established yet. Complications with disc arthroplasty implantation can occur during the anterior surgical exposure of the spine, following the surgery, or can be related to the implant itself. This chapter will go over the most commonly reported complications as follows: ● Exposure-related complications: ○ Vascular (i.e., direct injury, compartment syndrome, deep vessel thrombosis). ○ Dural injury. ○ Visceral injury (i.e., direct injury, ileus). ○ Sympathetic plexus injury (i.e., retrograde ejaculation, anhidrosis). ○ Lymphatic injury. ● Perioperative-/implant-related complications: ○ Implant malpositioning.

Implant subluxation. Implant subsidence. ○ Implant failure. Postoperative complications: ○ Infection. ○ Granuloma formation. ○ Radicular pain. ○ Heterotopic ossification. ○ ○

●

44.2 Exposure-Related Complications Complications occurring during the surgical approach and the placement of a TDR include and are not limited to vascular injury, retrograde ejaculation, incisional hernia, ileus, clinically significant blood loss, epidural hematoma, dural tear, deep vein thrombosis, and arterial thrombosis.1,5,6,7,8,9,10,11 These complications are not unique to TDR and are shared with anterior lumbar interbody fusion (ALIF) whether the approach be transperitoneal or retroperitoneal. Regan endorses the use of an experienced vascular or general surgeon familiar with the anterior approach to the lumbar spine as the greatest method to minimize the risk of intraoperative- or approach-related complications.5 Quraishi et al reported a 20% incidence of complications when an experienced spine surgeon performed the surgical approach, which was felt to be consistent with published complication rates.11

44.2.1 Vascular Injury The most common intraoperative complication encountered during the anterior approach for total lumbar disc replacement is vascular in nature and has a reported incidence of 1.8 to 7.8%.1,7,8,9,10,11 Delamarter et al reported a single patient with an iliac artery tear resulting in a blood loss of > 1,500 mL.7 No discussion of the treatment or outcome following this injury was presented. Tropiano et al reported that out of 64 patients who underwent single-level or multilevel TDRs, 5 (9%) patients had surgical complications.1 One of these patients had a laceration of the iliac vein that was repaired primarily during the procedure. Quraishi et al, in a retrospective review of 304 consecutive patients undergoing anterior lumbar spinal surgery with the approach performed by the spinal surgeon, reported venous injury at a rate of 6.3% (n = 19).11 Of the 19 patients who had a venous injury during the procedure, 14 required repair (4.6%) with the remainder treated with conservative measures (i.e., hemostatic agents or tamponade). Arterial injuries were far less common with an incidence of 1.2% (n = 5), three requiring repair and two undergoing thrombolysis.11 Rajaraman et al, in a retrospective review of 60 patients undergoing ALIF, reported a vascular injury rate of 6.66% despite the surgical exposure being performed by an experienced general or vascular surgeon.9 In this series, three instances of venous injury occurred in patients undergoing single-level

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Thoracolumbar fusion and one instance during a two-level fusion. In one additional instance, during revision of poorly positioned fusion cage from a previously performed ALIF, adhesions present between the posterior vessel wall and the previously placed instrumentation resulted in a significant venous injury and cessation of the operative procedure due to excessive blood loss. Brau et al retrospectively reviewed 1,310 patients undergoing anterior lumbar procedures and reported an incidence of vascular injury of 1.9%.10 The risk of vascular injury is increased in women and in patients undergoing procedures at the L4–L5 level. Nineteen patients (1.4%) had lacerations to venous structures, 16 to the left common iliac vein, 2 to the lumbar veins arising from the right side of the inferior vena cava, and 1 to the “crotch” of the inferior vena cava. In 10 of the patients who had lacerations to the left common iliac vein, the injury took place during the surgical exposure. The remaining 6 lacerations to the common iliac vein took place either during the arthrodesis or during the removal of the insertion instrumentation. All of the lacerations were repaired and the procedure completed.10 The tear at the crotch of the inferior vena cava required ligation of the vena cava and bilateral iliac veins. There was significant blood loss at the time of this injury and the planned procedure aborted. The two patients with tears to the right lumbar veins required control of bleeding with thrombin-soaked sponges followed by aborting the planned procedure due to an inability to mobilize the vena cava without continued bleeding. The aforementioned injuries are not common and are minimized when the procedure is performed by a well-trained surgeon (i.e., general surgeon, vascular surgeon, spine surgeon, etc.).5,11 Protection of the vessels with blunt retractors following dissection is critical and knowledge of the vessels’ location during the remainder of the procedure is key to minimizing injury. Mayer et al described using preoperative MRI of the lumbar spine in combination with three-dimensional CT to delineate the retroperitoneal vascular topography and help planning the surgical access.4

44.2.2 Compartment Syndrome Although a rare complication of spinal surgery, lower extremity compartment syndrome has been reported in the literature.12 In a case report by Magaji et al, lower limb compartment syndrome occurred in a woman following total lumbar disc replacement through a supine, anterior approach. During an anterior retroperitoneal approach for placement of a lumbar total disc device, the patient sustained an iliac vein injury, with unsuccessful surgical repair. Bleeding was controlled with temporary cross-clamping of the aorta and packing of the abdomen and pelvis. Over the next 48 hours following the surgical procedure, the patient developed compartment syndrome of the left lower limb that was successfully treated with expedited surgical decompression of the lateral thigh and four-compartment fasciotomies of the leg.12

44.2.3 Deep Vessel Thrombosis Thrombosis of the iliac vessels during the anterior approach to the lumbar spine or as a postoperative complication of anterior lumbar surgery has been documented as 0.45 to 8%.1,5,7,9,10 Brau et al stated that 6 of 1,310 (0.45%) consecutive patients were

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diagnosed with left iliac artery thrombosis.10 It was hypothesized that the thrombosis was a result of prolonged retraction of the vessel during the approach to the L4–L5 level. The authors routinely monitored the SaO2 of the left lower extremity by placing a pulse oximeter on one of the toes of the foot. In the six affected patients, four were treated with immediate thrombectomy. In addition to requiring a thrombectomy, one of the four patients developed a compartment syndrome of the left lower extremity and required fasciotomies. The authors did not feel that the chance of iliac artery thrombosis warranted a large, preoperative vascular evaluation beyond that of palpating the distal pulses of bilateral lower extremities unless the patient was known to have a complicated vascular history.10 Delamarter et al reported that 2 of 165 (1.2%) TDR patients had a deep venous thrombosis in the postoperative period.7 This is similar to the 2 of 72 (2.8%) arthrodesis patients. Each of the patients with deep venous thrombosis was successfully treated without further operative intervention. Rajaraman et al stated that the incidence of deep venous thrombosis in patients undergoing an abdominal procedure is 7 to 8%.9 They recommend that handheld, malleable retractors be used for the retraction of the iliac vessels in the vicinity of the operative level. Use of a handheld retractor versus a Steinmann pin allows the periodic release of pressure on the vessel when work is not actively being done near the vein or artery.

44.2.4 Durotomy Incidental durotomy is defined as an unintended tear of the dura during surgery or other invasive extradural procedure.13 The true rate of intraoperative dural tears is difficult to establish due to the lack of morbidity or mortality associated with the unintended injury.13,14,15,16 Cammisa et al reviewed 2,144 patients, 69 of who underwent anterior lumbosacral surgery.13 An incidence of 3.1% was reported for incidental durotomy in all patients presented (n = 66). Of the 66 durotomies that occurred during surgery, 63 occurred during lumbar procedures. The incidence of durotomy during anterior procedures was not separated from those that occurred during all lumbar procedures. Sixty of these durotomies were recognized at the time of surgery and repaired. Repair of incidental durotomies is accomplished with 5–0, nonabsorbable, monofilament suture in either an interrupted or a running suture with a watertight repair.13,14,15 Depending on the quality of the surrounding tissues and of the repair, it can be augmented with fibrin patches, fibrin glue, or gelfoam.13 Following the repair, a Valsalva maneuver is performed with the assistance of the anesthesiologist to evaluate for further leakage through the repair.13,14,15,16 Following surgery, patients are monitored for severe postural headache, nausea, or vomiting.15 If wound drainage is suspected to be composed of cerebral spinal fluid, some of the fluid should be sent for immunofixation electrophoresis for β-2-transferrin, a protein produced by cerebral neuraminidase.15

44.2.5 Visceral Injury The rate of peritoneal injury is not well documented in the literature and is difficult to truly estimate.9 In the literature reviewed for this chapter, the incidence of peritoneal injury

Complications of Anterior Lumbar Disc Replacement ranged from 1.7 to 3.9%.9,11 It is very important to recognize the presence of bowel perforation at the time of surgery. The enterotomy should be repaired immediately. If the wound becomes contaminated with the contents of the perforated bowel, the planned spinal procedure should be aborted, the bowel repaired, and the abdomen closed.9 It is not always possible to predict the level of adhesion of the peritoneal contents with the retroperitoneal structures, but it should be anticipated in patients with a history of abdominal surgery, malignancy, intraabdominal sepsis, or previous radiation therapy.9

44.2.6 Ileus Ileus occurs postoperatively with anterior lumbar spine surgery using the retroperitoneal or transperitoneal approach. Although higher in incidence with the transperitoneal approach, postoperative ileus can still occur with the retroperitoneal approach even without defilement of the peritoneal tissue. The rate of ileus following placement of a lumbar total disc is not significantly different than the rate of ileus following other anterior lumbar surgical procedures. Prolonged ileus is often related to previous abdominal procedures, formation of a retroperitoneal hematoma, postoperative fluid shifts, extensive intraabdominal dissection, and increased narcotic usage.9 Patients suffering from prolonged, postoperative ileus are treated with complete bowel rest including nasogastric suction, intravenous hydration, mobilization, and working toward decreased narcotics use.

44.2.7 Retrograde Ejaculation Retrograde ejaculation is an inability of the internal vesical sphincter to contract during ejaculation. In a normal ejaculation, the internal vesical sphincter at the base of the bladder constricts and prevents the ejaculatory bolus from entering the bladder as it enters the prostatic urethra from the seminal vesicles.17 The incidence of retrograde ejaculation following anterior lumbar spine procedures is reported as 0.49 to 5.9% and is a risk for all male patients undergoing an intra-abdominal lumbar procedure.17,18 Sasso et al investigated whether or not a transperitoneal versus retroperitoneal exposure altered the incidence of retrograde ejaculation.17 In a prospective study of 146 male patients who underwent a single-level procedure at L4–L5 or L5–S1, 2/116 patients (1.7%) in the retroperitoneal approach group and 4/30 patients (13.3%) in the transperitoneal group developed retrograde ejaculation.17 This was found to be statistically significant in favor of a decreased incidence in the retroperitoneal approach group; however, no power analysis was performed to determine the number of patients necessary to show a true effect. Tiusanen et al retrospectively reviewed 40 male patients who underwent ALIF between 1982 and 1990 for the incidence of retrograde ejaculation.18 Out of the 40 patients included in the study, nine patients (22.5%) developed retrograde ejaculation. Eight of these nine patients had been previously operated on and all of the patients developing retrograde ejaculation underwent a transabdominal approach for their surgery.18

44.2.8 Anhidrosis The common approach used for surgical placement of total disc arthroplasty is an anterior retroperitoneal approach. With this

approach, many structures are at risk, such as the sympathetic nervous system. The most commonly recognized presentation of injury to the sympathetic nervous system during anterior lumbar spinal surgery is retrograde ejaculation. However, after injury to this sympathetic chain, other more subtle signs may manifest such as temperature variation, dysesthesias, discoloration, and/or swelling of the lower limb.19 In a case report by Kasliwal and Deutsch, a woman sustaining injury to the sympathetic nervous system during an anterior retroperitoneal approach for L4–L5 artificial disc replacement presented with anhidrosis.19 As a result, she noticed dryness of her left lower limb along with visible fissuring of the left foot that required an increased use of skin lubricants to prevent skin breakdown. Despite some improvement, the anhidrosis persisted at the 1year follow-up.

44.2.9 Lymphatic Injury During exposure with the retroperitoneal approach, the lymphatic channels, among other structures, are at risk of injury. The cisterna chyli, a secular dilation of lymph vessels that drain the lower extremities, is located posteromedial to the abdominal aorta, dorsal to the vena cava, and anterior to the first and second lumbar vertebra.20 Damage to the lymphatic channels can lead to an accumulation of chyle in the peritoneal cavity, which is known as chylous ascites.21 Although abdominal aortic surgery remains the most common surgical procedure causing chylous ascites, there have been a few reported cases following anterior spinal surgery.21 Given the rarity of the complication, the overall incidence of lymphatic injury following anterior spinal surgery, and more specifically TDR, remains unclear. Persistent chylous leakage can lead to nutritional deficits, electrolyte imbalance/depletion, and lymphocytopenia. The goals of treatment are to prevent accumulation of the chylous ascites and the resulting complications from increased abdominal pressure as well as to provide adequate nutritional supplementation.20 Leibovitch et al described a management algorithm in which a diagnostic and therapeutic paracentesis is performed to decrease the volume of the ascites as well as to confirm the origin of the fluid collection.21 The first step in treatment is to place the patient on a low-fat, medium-chain triglyceride diet. If the clinical response is not adequate, total parenteral nutrition is initiated. If the ascites continues to recollect despite total parenteral nutrition, subcutaneous somatostatin is administered in an attempt to close the lymphatic fistula. Conservative treatment should be pursued for 6 to 8 weeks before concluding that it has failed and considering surgical intervention. The next step in intervention is exploration and direct ligation of the leaking lymphatic glands.21

44.3 Perioperative- and Implant-Related Complications 44.3.1 Implant Malpositioning Malpositioning of the TDR may lead to foraminal narrowing resulting in dorsal root ganglion or nerve root compromise.22 Error in surgical technique or devices that require extensive distraction of the intervertebral space with placement are at risk

293

Thoracolumbar for malpositioning. Ideally, the implant should be positioned in the center of the vertebral body in both the coronal and sagittal plane. For this reason, incorrect selection of implant size can make proper placement difficult and often off-centered.

44.3.2 Implant Subluxation/Subsidence The most common device-related complication with total disc arthroplasty is subsidence.22 Bone quality, the main determinant of subsidence, affects the stable location of the device within the vertebral body. Most commonly, subsidence into the vertebral body occurs within the first 3 months after implantation (▶ Fig. 44.1). Likewise, implant migration is dependent on device fixation, which occurs through osteointegration with coated endplates or by fixation into the vertebral body, such as with the keel of the implant into the vertebral body. Additionally, confirming parallel placement of the implant onto the endplates safeguards against violation of the endplate, which aids in preventing implant subsidence. Poor implant placement coupled with patient noncompliance of postoperative hyperextension restrictions can contribute to implant subluxation, dislocation, or extrusion (▶ Fig. 44.2).5 Consequently, implant subsidence or subluxation results in activity-related back pain. Le Huec et al reported on the 2-year follow-up of 64 patients who underwent lumbar TDA.23 From

follow-up of this cohort, 5 patients were noted to have migration of the implant axially 3 to 5 mm into the superior endplate, yet at 1 year, the subsidence was stable and 3 of these 5 patients had satisfactory outcomes.23 In a European case series, Griffith et al reported a rate of implant subsidence/subluxation of 4.3%, which was attributed to inappropriate choice of prosthetic size.24 Likewise, Blumenthal et al, in a randomized study of lumbar TDR versus lumbar fusion, reported a rate of implant subsidence of 3.4%.8 Other less common modes of implant displacement have been noted as case reports in the literature. In a case report by Eskander et al, the posterior extrusion of the polyethylene core of a total disc arthroplasty device was found in a patient who presented with symptoms of radiculopathy.25

44.3.3 Implant Failure Implant failure has been reported in long-term follow-up results following TDR. In a case report by Devin, chronic failure of a lumbar TDR with osteolysis was noted at 19 years’ followup.26 In this case, the radiographs demonstrated the metallic endplates in contact with one another after complete loss of the polyolefin spacer. With this collapse, there was a significant amount of metal debris noted in the adjacent vertebral bodies. Given the failure of the device, the patient underwent surgery

Fig. 44.1 Computed tomographic scan of a patient who underwent placement of a ProDisc prosthesis at the L4–L5 disc level for adjacent segment disease (a,b: coronal cuts) and had subsequent subsidence of the implant into the inferior endplate and resultant collapse of the disc space (c–g) (continued).

294

Complications of Anterior Lumbar Disc Replacement

Fig. 44.1 (continued) Subsequent subsidence of the implant into the inferior endplate and resultant collapse of the disc space (c–g).

that required a subtotal corpectomy at the involved level to adequately remove the large amount of black rubber and metal wear debris. Furthermore, histology of the surgical specimens showed chronic inflammatory cells and reactive fibrosis of the vertebral tissue.27,28,29,30 Kurtz et al analyzed 21 implants removed from 18 patients due to intractable pain following placement of the SB Charité III implant.27 At the time of revision surgery, the mean time of implantation was 7.8 years (1.8–16.0 years). The pain was associated with subsidence, anterior migration, core dislocation, lateral subluxation, endplate loosening, and osteolysis.27 At the time of implant analysis, the central dome of the polyethylene was noted to have a wear pattern similar to that seen in total hip prostheses where a crossing-shear pattern of wear was present. Around the rim, plastic deformation and fracture was noted, which was more consistent with the wear pattern noted in total knee arthroplasties. Due to the patterns of wear noted, the authors recommended that all patients implanted with a TDR be regularly followed.27 The impact of polyethelene wear particles was not felt to be as important in TDR compared to total hip and knee replacements due to the fact that the intervertebral joint is not a synovial joint.28,29,30 Punt et al, in 2009, identified 83 patients who underwent revision surgery for persistent back and leg pain following implantation of a SB Charité III disc prosthesis.29 Upon review of the tissues obtained at the time of revision surgery, a

correlation was noted between the mean number of particles per square millimeter and the length of time that the implant was in place as well as the number of macrophages and giant cells present. Another mode of failure that has been reported in two patients by Shim et al is fracture of the vertebral body by the placement of a ProDisc arthroplasty.31 The authors hypothesized that the keel design of the ProDisc prosthesis can lead to a vertical split fracture of the vertebral body in some patients. In these two patients, the only complaint was continued pain at the 3-month follow-up visit. No serious clinical consequences were reported.31

44.4 Postoperative Complications 44.4.1 Infection Infection after TDR is very uncommon. In a randomized study of lumbar disc replacement versus fusion, superficial wound infection occurred in 12.7% of patients in the investigational group of disc replacement.32 Still, there was no significant difference in both, superficial or deep wound infection, between the TDR group and the control fusion group.32 However, there have been case reports of infection following treatment with TDR. Flouzat-Lachaniette et al reported a case of Mycoplasma hominis infection after TDR.33 In this case, a woman underwent

295

Thoracolumbar

Fig. 44.2 Radiographs and computed tomographic scan of a patient that underwent placement of a ProDisc implant at the L4–L5 (a,b) level who subsequently had anterior extrusion of the polyethylene component (c–g).

a MobiDisc TDR at L4–L5 for discogenic pain. One month postoperatively, CT scan showed a left psoas-based retroperitoneal abscess with cultures growing out M. hominis after 7 days. Following a 2-month course of antibiotic therapy, the infection was eradicated.

296

44.4.2 Granuloma Formation Within the lumbar spine, at the level of a total disc prosthesis, granuloma formation has been shown to follow implantation of the device.34 Depending on the size of the granuloma

Complications of Anterior Lumbar Disc Replacement formation, subsequent ramifications can manifest from this complication. In a case report by Berry et al, 3 years following implantation of a TDR, a granulomatous mass developed at the level of the implant, which resulted in spinal stenosis and iliac vein occlusion. Similarly, Cabraja et al, in a case report, noted the development of a granulomatous necrotizing inflammatory mass, as identified on histopathological analysis, occurring 11 months after the placement of a lumbar total disc device.35 In this case, the granuloma was found to be infiltrating the spinal canal, leading to paraparesis as well as occlusion of the left ureter, common iliac veins, and inferior vena cava. Given the complications arising from the granuloma formation, the patient underwent mass removal along with removal of the TDR device. Following removal of the device, no further granuloma growth was noted.

these advantages are tempered by the limited indications, significant learning curve, and risk of multiple complications. There are multiple series with outcome data at 2 to 11 years.1,5, 7,23,24,40 When compared directly to arthrodesis, total disc arthroplasty offers no clinically significant difference with regard to pain relief and quality of life.2 Therefore, the surgeon is encouraged to be prudent in the adoption of TDR technology over the continued use of arthrodesis for the treatment of patients with degenerative disc disease of the lumbar spine.

44.6 Key Points ●

44.4.3 Neurologic Complications During placement of the total disc arthroplasty device, distraction is often used to provide ample space for placement of the implant. However, this technique of surgical distraction for implant insertion can lead to stretching of the exiting nerve, thus resulting in postoperative radicular pain. Nevertheless, the sequela of radicular pain is often limited and managed with observation.1,36 Geisler et al, in 2004, reviewed the neurologic complications of the Charité lumbar artificial disc replacement and reported that the overall rate of neurologic complications was 16.6%, with 4.9% of those complications being considered major.32,37 Major complications were described as burning or dysesthetic leg pain, motor deficit, or nerve root injury. Zeegers et al, in a prospective review of 50 patients implanted with the SB Charité III device, reported a 20% (10 of 50 patients) rate of neurological complications.38 The most common complication reported within this prospective study was dysesthesia of the leg (7 of 10 patients).

44.4.4 Heterotopic Ossification Following implantation of total disc arthroplasty in animals and humans, heterotopic ossification has been shown to develop around the devices. In a randomized study of 276 patients, Tortolani et al reported the prevalence of heterotopic ossification was 4.3% after lumbar disc replacement with the Charité artificial disc.39 As early as 6 weeks postoperatively, heterotopic ossification was visible on follow-up radiographs, and by 3 months postoperatively, almost all patients who developed heterotopic ossification had excessive bone visible around the devices. Despite the presence of heterotopic ossification, there was no significant difference in range of motion or clinical outcomes in comparison to patients without heterotopic ossification who also underwent lumbar TDR. In a prospective follow-up of 64 patients undergoing lumbar TDR, Le Huec et al reported that 4.7% developed heterotopic ossification that was evident on follow-up radiographs.23

44.5 Conclusion TDR offers theoretical and potential advantages over arthrodesis for the treatment of discogenic low back pain. However,

●

●

●

●

TDR may be indicated in the treatment of patients with single-level discogenic low back pain due to degenerative disc disease confirmed by MRI or CT scan, an age of 18 to 60 years, who failed a minimum of 6 months of unsuccessful conservative therapy and with complains of back pain greater than leg pain. The operative risks of TDR are similar to other anterior retroperitoneal and transperitoneal approaches. The long-term outcome of TDR versus arthrodesis has yet to be fully elucidated, but does not appear to be significantly different. As with all operative procedures, an adequate option for revision must be available before implanting a TDR prosthesis. The effects of polyethylene wear particles appears to be similar to that seen in total knee and hip arthroplasties despite the intervertebral disc not being a synovial joint.

References [1] Tropiano P, Huang RC, Girardi FP, Cammisa FP, Jr, Marnay T. Lumbar total disc replacement. Seven to eleven-year follow-up. J Bone Joint Surg Am. 2005; 87 (3):490–496 [2] Jacobs WCH, van der Gaag NA, Kruyt MC, et al. Total disc replacement for chronic discogenic low back pain: a Cochrane review. Spine. 2013; 38(1):24–36 [3] Lin EL, Wang JC. Total disk arthroplasty. J Am Acad Orthop Surg. 2006; 14 (13):705–714 [4] Mayer HM. Total lumbar disc replacement. J Bone Joint Surg Br. 2005; 87 (8):1029–1037 [5] Regan JJ. Clinical results of charité lumbar total disc replacement. Orthop Clin North Am. 2005; 36(3):323–340 [6] van den Eerenbeemt KD, Ostelo RW, van Royen BJ, Peul WC, van Tulder MW. Total disc replacement surgery for symptomatic degenerative lumbar disc disease: a systematic review of the literature. Eur Spine J. 2010; 19(8):1262– 1280 [7] Delamarter R, Zigler JE, Balderston RA, Cammisa FP, Goldstein JA, Spivak JM. Prospective, randomized, multicenter Food and Drug Administration investigational device exemption study of the ProDisc-L total disc replacement compared with circumferential arthrodesis for the treatment of two-level lumbar degenerative disc disease: results at twenty-four months. J Bone Joint Surg Am. 2011; 93(8):705–715 [8] Blumenthal S, McAfee PC, Guyer RD, et al. A prospective, randomized, multicenter Food and Drug Administration investigational device exemptions study of lumbar total disc replacement with the CHARITE artificial disc versus lumbar fusion: part I: evaluation of clinical outcomes. Spine. 2005; 30 (14):1565–1575, discussion E387–E391 [9] Rajaraman V, Vingan R, Roth P, Heary RF, Conklin L, Jacobs GB. Visceral and vascular complications resulting from anterior lumbar interbody fusion. J Neurosurg. 1999; 91(1) Suppl:60–64 [10] Brau SA, Delamarter RB, Schiffman ML, Williams LA, Watkins RG. Vascular injury during anterior lumbar surgery. Spine J. 2004; 4(4):409–412 [11] Quraishi NA, Konig M, Booker SJ, et al. Access related complications in anterior lumbar surgery performed by spinal surgeons. Eur Spine J. 2013; 22 Suppl 1:S16–S20

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Thoracolumbar [12] Magaji SA, Debnath UK, Mehdian HS. Compartment syndrome of leg following total lumbar disc replacement via anterior retroperitoneal approach: a rare complication of anterior spinal surgery. Spine. 2010; 35(3):E74–E76 [13] Cammisa FP, Jr, Girardi FP, Sangani PK, Parvataneni HK, Cadag S, Sandhu HS. Incidental durotomy in spine surgery. Spine. 2000; 25(20):2663–2667 [14] Hodges SD, Humphreys SC, Eck JC, Covington LA. Management of incidental durotomy without mandatory bed rest. A retrospective review of 20 cases. Spine. 1999; 24(19):2062–2064 [15] Bosacco SJ, Gardner MJ, Guille JT. Evaluation and treatment of dural tears in lumbar spine surgery: a review. Clin Orthop Relat Res. 2001(389):238–247 [16] Wang JC, Bohlman HH, Riew KD. Dural tears secondary to operations on the lumbar spine. Management and results after a two-year-minimum follow-up of eighty-eight patients. J Bone Joint Surg Am. 1998; 80(12):1728–1732 [17] Sasso RC, Kenneth Burkus J, LeHuec J-C. Retrograde ejaculation after anterior lumbar interbody fusion: transperitoneal versus retroperitoneal exposure. Spine. 2003; 28(10):1023–1026 [18] Tiusanen H, Seitsalo S, Osterman K, Soini J. Retrograde ejaculation after anterior interbody lumbar fusion. Eur Spine J. 1995; 4(6):339–342 [19] Kasliwal MK, Deutsch H. Anhidrosis after anterior retroperitoneal approach for L4-L5 artificial disc replacement. J Clin Neurosci. 2011; 18(7):990–991 [20] DeHart MM, Lauerman WC, Conely AH, Roettger RH, West JL, Cain JE. Management of retroperitoneal chylous leakage. Spine. 1994; 19(6):716–718 [21] Leibovitch I, Mor Y, Golomb J, Ramon J. The diagnosis and management of postoperative chylous ascites. J Urol. 2002; 167(2, Pt 1):449–457 [22] Bertagnoli R, Zigler J, Karg A, Voigt S. Complications and strategies for revision surgery in total disc replacement. Orthop Clin North Am. 2005; 36 (3):389–395 [23] Le Huec JC, Mathews H, Basso Y, et al. Clinical results of Maverick lumbar total disc replacement: two-year prospective follow-up. Orthop Clin North Am. 2005; 36(3):315–322 [24] Griffith SL, Shelokov AP, Büttner-Janz K, LeMaire JP, Zeegers WS. A multicenter retrospective study of the clinical results of the LINK SB Charité intervertebral prosthesis. The initial European experience. Spine. 1994; 19(16):1842– 1849 [25] Eskander MS, Onyedika II, Eskander JP, Connolly PJ, Eck JC, Lapinsky A. Revision strategy for posterior extrusion of the CHARITÉ polyethylene core. Spine. 2010; 35(24):E1430–E1434 [26] Devin CJ, Myers TG, Kang JD. Chronic failure of a lumbar total disc replacement with osteolysis. Report of a case with nineteen-year follow-up. J Bone Joint Surg Am. 2008; 90(10):2230–2234 [27] Kurtz SM, van Ooij A, Ross R, et al. Polyethylene wear and rim fracture in total disc arthroplasty. Spine J. 2007; 7(1):12–21

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[28] Punt IM, Austen S, Cleutjens JP, et al. Are periprosthetic tissue reactions observed after revision of total disc replacement comparable to the reactions observed after total hip or knee revision surgery? Spine. 2012; 37(2):150–159 [29] Punt IM, Cleutjens JPM, de Bruin T, et al. Periprosthetic tissue reactions observed at revision of total intervertebral disc arthroplasty. Biomaterials. 2009; 30(11):2079–2084 [30] Punt I, Baxter R, van Ooij A, et al. Submicron sized ultra-high molecular weight polyethylene wear particle analysis from revised SB Charité III total disc replacements. Acta Biomater. 2011; 7(9):3404–3411 [31] Shim CS, Lee S, Maeng DH, Lee SH. Vertical split fracture of the vertebral body following total disc replacement using ProDisc: report of two cases. J Spinal Disord Tech. 2005; 18(5):465–469 [32] Holt RT, Majd ME, Isaza JE, et al. Complications of lumbar artificial disc replacement compared to fusion: results from the prospective, randomized, multicenter US Food and Drug Administration Investigational Device Exemption Study of the Charité Artificial Disc. SAS J. 2007; 1(1):20–27 [33] Flouzat-Lachaniette C-H, Guidon J, Allain J, Poignard A. An uncommon case of Mycoplasma hominis infection after total disc replacement. Eur Spine J. 2013; 22 Suppl 3:S394–S398 [34] Berry MR, Peterson BG, Alander DH. A granulomatous mass surrounding a Maverick total disc replacement causing iliac vein occlusion and spinal stenosis: a case report. J Bone Joint Surg Am. 2010; 92(5):1242–1245 [35] Cabraja M, Schmeding M, Koch A, Podrabsky P, Kroppenstedt S. Delayed formation of a devastating granulomatous process after metal-on-metal lumbar disc arthroplasty. Spine. 2012; 37(13):E809–E813 [36] Mayer HM, Wiechert K, Korge A, Qose I. Minimally invasive total disc replacement: surgical technique and preliminary clinical results. Eur Spine J. 2002; 11 Suppl 2:S124–S130 [37] Geisler FH, Blumenthal SL, Guyer RD, et al. Neurological complications of lumbar artificial disc replacement and comparison of clinical results with those related to lumbar arthrodesis in the literature: results of a multicenter, prospective, randomized investigational device exemption study of Charité intervertebral disc. Invited submission from the Joint Section Meeting on Disorders of the Spine and Peripheral Nerves, March 2004. J Neurosurg Spine. 2004; 1(2):143–154 [38] Zeegers WS, Bohnen LM, Laaper M, Verhaegen MJ. Artificial disc replacement with the modular type SB Charité III: 2-year results in 50 prospectively studied patients. Eur Spine J. 1999; 8(3):210–217 [39] Tortolani PJ, Cunningham BW, Eng M, McAfee PC, Holsapple GA, Adams KA. Prevalence of heterotopic ossification following total disc replacement. A prospective, randomized study of two hundred and seventy-six patients. J Bone Joint Surg Am. 2007; 89(1):82–88 [40] Cinotti G, David T, Postacchini F. Results of disc prosthesis after a minimum follow-up period of 2 years. Spine. 1996; 21(8):995–1000

Complications of Iliac Screw Fixation

45 Complications of Iliac Screw Fixation Shawn Bifano and John Koerner

45.1 Brief Iliac screws are an evolution from the Galveston technique. The screws have biomechanical and clinical advantages over the unthreaded rods. The main indication for iliac screws is distal fixation to the pelvis after long spinal fusions to reduce failure rate. Detailed anatomical knowledge and surgical technique is essential for optimal outcomes. The most common complications arising from iliac screw placement are (1) screw prominence/pain, (2) rod breakage/screw loosening, (3) infection, and (4) neurologic injury.

45.2 Introduction The development of iliac screws was a logical evolution from the former Galveston technique for iliac fixation. Studies have shown the increased biomechanical advantages of extending instrumentation into the pelvis.1,2,3,4,5 Recent biomechanical studies looked at different iliac screw lengths, locations of lateral connectors, augmentation with bone cement, the use of sacral screws, and the number of iliac screws and the resultant amount of force on the screws.6,7,8,9 In theory, reducing the forces on the iliac screws will clinically reduce rates of failure and screw pullout. Iliac screws have been shown to be clinically superior to unthreaded rods (the Galveston technique) placed in the sacrum.10 Iliac screws lead to decreased rates of rod breakage, better correction of pelvic obliquity, and decreased halo formation around the instrumentation on radiographic studies.10

attached to each hemipelvis via the sacroiliac joint. The sacroiliac joint functions to offload axial forces from the spinal column to each hemipelvis. The internal iliac artery and vein, middle sacral artery and vein, sympathetic trunk, lumbosacral trunk, and sigmoid colon all cross the sacrum at some point.23 Care must be taken to avoid any injuries to these structures. Historically, two paths of iliac screw placement have been described.24 Path A has a trajectory from the posterior superior iliac spine (PSIS) toward the superior rim of the acetabulum, and Path B has a trajectory from the PSIS toward the anterior inferior iliac spine (▶ Fig. 45.1). Both paths begin at the PSIS above the greater sciatic notch. The superior prominence of the PSIS is located directly lateral to the S2 pedicle. Optimal placement is 1.5 to 2.0 cm above the greater sciatic notch. The greater sciatic notch may be palpated during surgery to confirm location. Intraoperative fluoroscopy or plain radiographs can be used during the procedure to confirm accurate screw placement.25 To view the sciatic notch, hip joint, and medial wall, use the obturator oblique view, the pelvic inlet and outlet views, and the iliac oblique views, respectively.25 A “modified

45.3 Purpose of Instrumentation The purpose of iliac screws is to achieve secure distal fixation of long constructs. The goal is to achieve a stable base and maintain the surgical correction until a solid fusion of the deformity is formed. Pelvic fixation may be indicated for long fusions to the sacrum, high-grade spondylolisthesis, decompression caudad to a long fusion, flat back syndrome requiring osteotomy, and correction of pelvic obliquity, after resection of sacral tumors and sacral fractures.11 One of the most common reasons to use iliac screws includes surgery for adult spinal deformities.10,11,12,13,14,15,16,17,18,19,20,21 In the pediatric population, one of the most common indications for pelvic fixation is correction of pelvic obliquity due to neuromuscular scoliosis.22 Iliac screws decrease bending strain and are effective in increasing the load to catastrophic failure when concomitantly using sacral fixation in spinal fusions.2 Combined bilateral iliac screws and bilateral S1 screws demonstrated fusions rates up to 95.1% in long fusions extending to the sacrum.12,14

45.4 Relevant Anatomy Detailed anatomic knowledge of the sacropelvic region is essential for placement of iliac screws. The sacrum consists of five fused vertebrae with fused transverse processes. The sacrum is

Fig. 45.1 Path A has a trajectory from the posterior superior iliac spine (PSIS) toward the superior rim of the acetabulum, and Path B has a trajectory from the PSIS toward the anterior inferior iliac spine.

299

Thoracolumbar approach” was developed by Harrop et al.26 The iliac screw entry point is located along the medial border of the posterior superior iliac crest. The “modified approach” does not use the adjunctive offset or slotted connector that the traditional approach requires.26 For both approaches, surgical dissection of the erector spinae muscles from a medial to lateral direction to the medial border of the iliac crest and dissection of the gluteal muscle attachments on the lateral iliac crest is needed to allow sufficient surgical exposure to insert the iliac screws.

45.5 Food and Drug Administration Status Multiple spinal fixation devices are Food and Drug Administration approved for fixation to the ilium as an adjunct to fusion for indications not limited to scoliosis, trauma, tumor, and pseudarthrosis.

45.6 Complications Although iliac screw placement has been shown to be a safe and effective method of pelvic fixation, the placement of iliac screws is still a major surgical procedure with the potential for substantial morbidity. The technique to allow for placement of the iliac screws requires extensive surgical exposure as described above. The most common complications from iliac screw placement include but are not limited to (1) screw prominence/pain, (2) rod breakage/screw loosening/instrument failure, (3) infection, and (4) neurologic injury (▶ Table 45.1).

45.6.1 Screw Prominence/Pain Given the nature of the dissection and the anatomical location of the iliac screws, residual screw prominence or pain is fairly common after iliac screw placement. Pain/tenderness perceived by the patient is usually in the buttock, directly overlying the iliac screw head. Prominence of the screw head may or may not be appreciated on physical exam of the patient. Hip/buttock pain is the most common reason patients seek elective removal of iliac screws. Pain may be unilateral or bilateral. In a retrospective study comparing differing techniques of fixation after long fusion to the pelvis, 8 of 39 patients (20.5%) had iliac screw removal due to hardware prominence and pain.13 There was a trend toward statistical significance for the hardware removal in the iliac screw group (p = 0.08) compared to the Luque–Galveston and sacral screw groups. In one series after a minimum of 2-year follow-up, 18% (12 of 65 patients) of patients reported moderate buttock/sacral pain.12 In a

Table 45.1 Incidence of complications of iliac screws

300

Complication

Incidence (%)

Prominence/pain

6–5412,13,14,27,28,29,30

Breakage of iliac screw

5–2410,14,15,21,29

Infection

4–21.415,16,28,29,31,32,33

Pseudoarthrosis

0–12.810,13,14,15,16,20,28,29,31,34,35

follow-up questionnaire, 30 of 65 patients (47%) reported screw prominence. Pain of any kind was most reported with increased activity (78%, 51 of 65 patients) or with sitting greater than 1 hour (49%, 32 of 65).12 In the same patient population after a minimum of 5-year follow-up, 23 of 67 patients (34.3%) had elective removal of iliac screw hardware due to pain, prominence, or surgeon choice.14 There was an increase in buttock pain from 18% of patients to 54% of patients from the minimum 2-year follow-up to the minimum of 5-year follow-up.12,14 Unilateral iliac screw placement is an option that should be considered to limit morbidity. Studies have shown unilateral and bilateral iliac screw placement leads to a similar biomechanical construct.27 In addition to offering similar construct biomechanics, unilateral iliac screw placement decreases the intraoperative time and the risk of implant prominence.27 In a study comparing unilateral versus bilateral iliac screw placement, there is less pain postoperatively when using unilateral iliac screws as compared to bilateral iliac screws.28 The decision to use unilateral versus bilateral iliac screws may be made on a patient-to-patient basis. Pain may take time to develop into clinical significance. In one study, the average time to presentation of adults with pain was 11.8 months and the average time of pediatrics with pain was 21.2 months for iliac screws alone and 19.9 months with iliac screws and a unit rod.29 When placing bilateral iliac screws, delayed postoperative pain may be unilateral or bilateral, although unilateral is more common.29 Inquiring about pain at follow-up visits for patients who have iliac screws is warranted given the high incidence. The pain may not significantly improve with narcotic or anti-inflammatory pain medication. As high as 78.1% of patients reported their pain level as “much improved” and 8.7% of patients as “somewhat improved” after removal of symptomatic iliac screws.30 Some patients may have no pain, but may have screw prominence. Given the location of the screw, the most common complaint is screw prominence while sitting. Overall, the decision to electively remove iliac screws is patient and surgeon choice. Complications may arise from this procedure, but the removal of the iliac screws has good outcomes.

45.6.2 Screw Loosening/Rod Breakage/ Instrument Failure One of the most feared complications is failure of the instrumentation that might require reoperation. Given the complexity of not only iliac screw placement but also stabilizing a long fusion to the pelvis, there have been many studies assessing the biomechanical viability of iliac screws to reduce instrument failure.1,2,3,4,5,6,7,8,9 Although many studies have reported no incidences of pseudarthrosis,10, 14, 15, 16, 20, 21, 29, 31, 34, 35 the complication has been reported in the literature after placement of iliac screws. A minimum of 2-year analysis of sacropelvic fixation and L5–S1 fusion using S1 and iliac screws in high-grade spondylolisthesis reported 4 out of 81 patients (4.9%) experienced pseudarthrosis.12 A follow-up by the same authors after 5 years noted no new incidences of pseudarthrosis in 67 of the 81 original patient population.14 Emami et al compared three different fixation techniques to the pelvis in a 2002 study. Five of 36 patients (13.8%) experienced pseudoarthrosis. Four of these were at the

Complications of Iliac Screw Fixation lumbosacral junction and one was at the thoracolumbar junction.13 Bilateral iliac screws were not better when compared to unilateral screws to reduce the rate of pseudarthosis.28 Another complication related directly to the iliac screw is breakage of the iliac screws.10,14,15,21,29 The incidence of screw breakage can range from 5 to 24% in patients with sacropelvic fixation using iliac screws.10,21 In pediatric neuromuscular scoliosis patients, the use of two screws in each side may lead to fewer complications related to implants.15 Even after a minimum of 5-year follow-up, the complication of breakage of the iliac screws can be as low as 10%.14 When comparing screw breakage in pediatric against an adult population, pediatric patients generally present with screw breakage on average longer after the initial surgery compared to an adult population.29 Screw loosening as demonstrated by a radiographic “halo” sign around the iliac screw can be considered a complication after placement of iliac screws (▶ Fig. 45.2).14,15,16,20,28,29,31 Whether or not radiographic loosening can eventually lead to clinical symptoms (i.e., pain/prominence, increased risk of screw breakage, increase risk of pseudoarthrosis) is yet to be

determined. The decision to remove the iliac screws is determined clinically on a patient-by-patient basis. Radiographic evidence of fusion, patient comorbidities, age of the patient, and complexity of the patient’s diagnosis will influence a surgeon’s decision to remove a loose screw seen on radiographs. Other complications after iliac screw placement can be related indirectly to the iliac screw. In a 2013 study involving 67 patients, 8 (11.9%) had major failure (defined by the authors as rod breakage between L4 and S1, failure of the S1 screws, or prominent iliac screws requiring removal) and 15 (22.4%) had minor failure (defined by the authors as rod breakage between S1 and iliac screws and failure of iliac screws).34 Separation of the rod connector/lateral connector can also occur.35 Distal anchor breakage, broken wires, and rod disengagement can occur after placement of iliac screws.21 Overall, there seems to be no difference in instrument complications when comparing bilateral and unilateral iliac screws.28 Close follow-up is recommended to uncover any instrumentation complications before the patient becomes symptomatic. The main goal of spinal fusion must be kept in mind when

Fig. 45.2 Screw loosening as demonstrated by a radiographic “halo” sign around the iliac screw can be considered a complication after placement of iliac screws.

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Thoracolumbar reviewing radiographs and when considering removing asymptomatic loose screws based on radiographs. Although the techniques to enhance the reliability of iliac screws as well as long spinal fusion systems have progressed throughout the years, careful surgical technique and placement of all instrumentation is required to minimize the complications.

45.6.3 Infection Given the extensive dissection required placing iliac screws as outlined above and the introduction of a foreign body, infection is always possible. The exact incidence of infection involving iliac screws is hard to ascertain from the literature given iliac screws are usually placed in conjunction with other hardware, as well as the diverse patient populations requiring the procedure. In a minimum 2-year follow-up study, an infection rate of 4% (3 of 81 patients) was found. All three required iliac screw implant removal. If infection persists, hardware removal is generally recommended.36 Many other studies report patients who experienced infections after implantation of iliac screws.10,15,16, 20,28,29,31,32,36 Infections can be either superficial or deep wound infections. Depending on the clinical picture, surgical irrigation and debridement can be used in conjunction with hardware removal. Few studies document the nature of the organisms involved in postoperative infections after instrumentation with iliac screws. In a prospective series of 60 patients, 11 patients developed postoperative infections.32 Five of those patients had Staphylococcus aureus infections. The remaining infectious organisms identified were two Escherichia coli, one Klebsiella pneumonia, one Pseudomonas aeruginosa, and two species of Enterococcus. One death occurred in the patient who developed a Klebsiella infection. As in all wound infections, cultures and local resistance patterns are recommended to guide the appropriate antibiotic therapy. Generally, acute infections are defined as infections occurring within 90 days (3 months) of the operation. Delayed infections are infections occurring after 90 days (3 months).29,36 A recent study looking at spinal correction and fusion for spinal deformities in childhood and adolescence recommended waiting until radiographic evidence of fusion was documented before removing any anchoring hardware.36 The authors found aggressive early irrigation and debridement lead to favorable outcomes in patients who experienced deep wound infections. Careful perioperative sterile technique should be followed to minimize the risk of infection given the extensive exposure during placement of iliac screws. A high index of suspicion must be exercised when a patient presents clinically with a possible wound infection considering the complications that may arise from an infection that is not aggressively managed. Aggressive irrigation and debridement should be used liberally to minimize long-term complications.

45.6.4 Neurological/Vessel Injury Although the risk of neurological/vessel injury is relatively low in iliac screw placement, the possibility needs to be taken into consideration. The internal iliac artery and vein, middle sacral artery and vein, sympathetic trunk, lumbosacral trunk, and

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sigmoid colon all cross the sacrum at some point.23 Placement of the iliac screw 1.5 to 2.0 cm above the greater sciatic notch puts the structures (superior and inferior gluteal vessels and nerves, the sciatic and posterior femoral cutaneous nerve, the internal pudendal vessels, and the nerves to the obturator internus and quadratus femoris) at risk for injury. Given the low incidence of neurologic injury in iliac screw placement, the exact incidence is unknown. In a 2014 study by Finger et al, 13% (3 of 23) of patients who had iliac screws placed experienced neurological deficits.20 One patient still experienced symptoms of bowel and bladder incontinence after 1-year follow-up.20 The authors attributed neurological injury to the development of a hematoma postoperatively. Disruption of the greater sciatic notch may also happen during placement of iliac screws.31 One of 13 patients in a 2010 study experienced disruption of the greater sciatic notch during the placement of the iliac screw.31 The patient remained asymptomatic throughout the follow-up period. No studies have demonstrated any symptomatic injuries to the structures of the greater sciatic notch; however, great care must be taken while placing iliac screws. Neurological/vessel injury during iliac screw placement is a relatively rare postoperative complication. Although most studies do not report any neurological/vessel injury after placement of iliac screws, the possibility of injury still exists given the trajectory of the iliac screw. The neurological injuries can range from muscle palsy to bowel/bladder incontinence.20 Theoretically, paresthesias due to damage to the posterior femoral cutaneous nerve, and muscle atrophy/palsy due to injury to motor nerves are realistic complications that may occur. A thorough understanding of the anatomy and experience with the surgical technique of placement of iliac screws is recommended to decrease the risk of injury to surrounding structures.

45.7 Future Directions Advancement of surgical techniques may lead to the decrease in iliac screw complications. Percutaneous placement, computed tomography (CT) guidance placement, and freehand placement of iliac screws have all been described.33, 37, 38, 39, 40, 41 The three different surgical techniques have also been found to be a safe alternative to the “classical” extensive dissection while placing iliac screws in small stuides.33,37,38,39,40,41 The obturator outlet view via X-ray imaging is used in the percutaneous placement technique of placement of iliac screws.38,39,40 Only 1 patient in a study of 24 developed pseudoarthrosis upon follow-up.39 The patient was later found to have metastatic adenocarcinoma. One study demonstrated no hardware complications,39 while another study demonstrated 2 out of 10 patients had a complication.40 One complication was an asymptomatic medial screw break of T10 and L1 and the other was the development of a symptomatic epidural hematoma on postoperative day 6. CT-guided placement of iliac screws has been described in a 2011 study and a 2012 study.37,42 The studies demonstrated CTguided placement of iliac screws facilitates both traditional and anatomic approaches to iliac screws, eliminates fluoroscopic exposure and extensive soft-tissue dissection, and is a safe procedure.37,42

Complications of Iliac Screw Fixation The newest surgical technique described is freehand placement of iliac screws.33 A total of 20 screws were placed in 10 patients over a 1-year period. The greater sciatic notch was not dissected or palpated, nor was fluoroscopy used in any of the cases. At the end of the follow-up period (range of 24 to 40 months), there were no postoperative complications to be reported related to iliac screw placement.33 Although newer techniques of iliac screw placement have been described, there have been no larger scale trials demonstrating the effectiveness or safety of the newer techniques. To truly determine the effectiveness and safety of the techniques described above for iliac screw placement, multiple larger scale studies demonstrating the same results seen in the small studies need to be undertaken. Although not mentioned in the CTand X-ray-guided iliac screw placement, radiation exposure needs to be taken into account.

References [1] McCord DH, Cunningham BW, Shono Y, Myers JJ, McAfee PC. Biomechanical analysis of lumbosacral fixation. Spine. 1992; 17(8) Suppl:S235–S243 [2] Lebwohl NH, Cunningham BW, Dmitriev A, et al. Biomechanical comparison of lumbosacral fixation techniques in a calf spine model. Spine. 2002; 27 (21):2312–2320 [3] Schwend RM, Sluyters R, Najdzionek J. The pylon concept of pelvic anchorage for spinal instrumentation in the human cadaver. Spine. 2003; 28(6):542– 547 [4] Erickson MA, Oliver T, Baldini T, Bach J. Biomechanical assessment of conventional unit rod fixation versus a unit rod pedicle screw construct: a human cadaver study. Spine. 2004; 29(12):1314–1319 [5] Tis JE, Helgeson M, Lehman RA, Dmitriev AE. A biomechanical comparison of different types of lumbopelvic fixation. Spine. 2009; 34(24):E866–E872 [6] Zheng ZM, Zhang KB, Zhang JF, Yu BS, Liu H, Zhuang XM. The effect of screw length and bone cement augmentation on the fixation strength of iliac screws: a biomechanical study. J Spinal Disord Tech. 2009; 22(8):545–550 [7] Yu BS, Zhuang XM, Zheng ZM, Li ZM, Wang TP, Lu WW. Biomechanical advantages of dual over single iliac screws in lumbo-iliac fixation construct. Eur Spine J. 2010; 19(7):1121–1128 [8] Perrault FD, Aubin CE, Wang X, Schwend RM. Biomechanical analysis of forces sustained by iliac screws in spinal instrumentation for deformity treatment: preliminary results. Stud Health Technol Inform. 2012; 176:307–310 [9] Desrochers-Perrault F, Aubin CE, Wang X, Schwend RM. Biomechanical analysis of iliac screw fixation in spinal deformity instrumentation. Clin Biomech (Bristol, Avon). 2014; 29(6):614–621 [10] Peelle MW, Lenke LG, Bridwell KH, Sides B. Comparison of pelvic fixation techniques in neuromuscular spinal deformity correction: Galveston rod versus iliac and lumbosacral screws. Spine. 2006; 31(20):2392–2398, discussion 2399 [11] Moshirfar A, Rand FF, Sponseller PD, et al. Pelvic fixation in spine surgery. Historical overview, indications, biomechanical relevance, and current techniques. J Bone Joint Surg Am. 2005; 87 Suppl 2:89–106 [12] Kuklo TR, Bridwell KH, Lewis SJ, et al. Minimum 2-year analysis of sacropelvic fixation and L5-S1 fusion using S1 and iliac screws. Spine. 2001; 26 (18):1976–1983 [13] Emami A, Deviren V, Berven S, Smith JA, Hu SS, Bradford DS. Outcome and complications of long fusions to the sacrum in adult spine deformity: LuqueGalveston, combined iliac and sacral screws, and sacral fixation. Spine. 2002; 27(7):776–786 [14] Tsuchiya K, Bridwell KH, Kuklo TR, Lenke LG, Baldus C. Minimum 5-year analysis of L5-S1 fusion using sacropelvic fixation (bilateral S1 and iliac screws) for spinal deformity. Spine. 2006; 31(3):303–308 [15] Phillips JH, Gutheil JP, Knapp DR, Jr. Iliac screw fixation in neuromuscular scoliosis. Spine. 2007; 32(14):1566–1570 [16] Gitelman A, Joseph SA, Jr, Carrion W, Stephen M. Results and morbidity in a consecutive series of patients undergoing spinal fusion with iliac screws for neuromuscular scoliosis. Orthopedics. 2008; 31(12):31

[17] Kasten MD, Rao LA, Priest B. Long-term results of iliac wing fixation below extensive fusions in ambulatory adult patients with spinal disorders. J Spinal Disord Tech. 2010; 23(7):e37–e42 [18] Modi HN, Suh SW, Song HR, Yang JH, Jajodia N. Evaluation of pelvic fixation in neuromuscular scoliosis: a retrospective study in 55 patients. Int Orthop. 2010; 34(1):89–96 [19] Shen FH, Mason JR, Shimer AL, Arlet VM. Pelvic fixation for adult scoliosis. Eur Spine J. 2013; 22 Suppl 2:S265–S275 [20] Finger T, Bayerl S, Onken J, Czabanka M, Woitzik J, Vajkoczy P. Sacropelvic fixation versus fusion to the sacrum for spondylodesis in multilevel degenerative spine disease. Eur Spine J. 2014; 23(5):1013–1020 [21] Sponseller PD, Yang JS, Thompson GH, et al. Pelvic fixation of growing rods: comparison of constructs. Spine. 2009; 34(16):1706–1710 [22] Dayer R, Ouellet JA, Saran N. Pelvic fixation for neuromuscular scoliosis deformity correction. Curr Rev Musculoskelet Med. 2012; 5(2):91–101 [23] Mirkovic S, Abitbol JJ, Steinman J, et al. Anatomic consideration for sacral screw placement. Spine. 1991; 16(6) Suppl:S289–S294 [24] Berry JL, Stahurski T, Asher MA. Morphometry of the supra sciatic notch intrailiac implant anchor passage. Spine. 2001; 26(7):E143–E148 [25] Orchowski JR, Polly DW, Jr, Kuklo TR, Klemme WR, Schroeder TM. Use of fluoroscopy to evaluate iliac screw position. Am J Orthop. 2006; 35(3):144–146 [26] Harrop JS, Jeyamohan SB, Sharan A, Ratliff J, Vaccaro AR. Iliac bolt fixation: an anatomic approach. J Spinal Disord Tech. 2009; 22(8):541–544 [27] Tomlinson T, Chen J, Upasani V, Mahar A. Unilateral and bilateral sacropelvic fixation result in similar construct biomechanics. Spine. 2008; 33(20):2127– 2133 [28] Saigal R, Lau D, Wadhwa R, et al. Unilateral versus bilateral iliac screws for spinopelvic fixation: are two screws better than one? Neurosurg Focus. 2014; 36(5):E10 [29] Ilyas H, Place H, Puryear A. A Comparison of early clinical and radiographic complications of iliac screw fixation versus S2 alar iliac (S2AI) fixation in the adult and pediatric populations. J Spinal Disord Tech. 2015; 28(4):E199–E205 [30] O’Shaughnessy BA, Lenke LG, Bridwell KH, et al. Should symptomatic iliac screws be electively removed in adult spinal deformity patients fused to the sacrum? Spine. 2012; 37:1175–1181 [31] Hyun SJ, Rhim SC, Kim YJ, Kim YB. A mid-term follow-up result of spinopelvic fixation using iliac screws for lumbosacral fusion. J Korean Neurosurg Soc. 2010; 48(4):347–353 [32] Bouyer B, Bachy M, Zahi R, Thévenin-Lemoine C, Mary P, Vialle R. Correction of pelvic obliquity in neuromuscular spinal deformities using the “T construct”: results and complications in a prospective series of 60 patients. Eur Spine J. 2014; 23(1):163–171 [33] Ould-Slimane M, Miladi L, Rousseau MA, et al. Sacropelvic fixation with iliosacral screws: applications and results in adult spinal deformities. J Spinal Disord Tech. 2013; 26(4):212–217 [34] Cho W, Mason JR, Smith JS, et al. Failure of lumbopelvic fixation after long construct fusions in patients with adult spinal deformity: clinical and radiographic risk factors: clinical article. J Neurosurg Spine. 2013; 19(4):445–453 [35] Guler UO, Cetin E, Yaman O, et al. Sacropelvic fixation in adult spinal deformity (ASD); a very high rate of mechanical failure. Eur Spine J. 2015; 24 (5):1085–1091 [36] Bachy M, Bouyer B, Vialle R. Infections after spinal correction and fusion for spinal deformities in childhood and adolescence. Int Orthop. 2012; 36 (2):465–469 [37] Shin JH, Hoh DJ, Kalfas IH. Iliac screw fixation using computer-assisted computer tomographic image guidance: technical note. Neurosurgery. 2012; 70 (1) Suppl Operative:16–20, discussion 20 [38] Wang MY, Ludwig SC, Anderson DG, Mummaneni PV. Percutaneous iliac screw placement: description of a new minimally invasive technique. Neurosurg Focus. 2008; 25(2):E17 [39] Wang MY, Williams S, Mummaneni PV, Sherman JD. Minimally invasive percutaneous iliac screws: initial 24 case experience with CT confirmation. J Spinal Disord Tech. 2012 [40] Wang MY. Percutaneous iliac screws for minimally invasive spinal deformity surgery. Minim Invasive Surg. 2012; 2012:173685 [41] Fridley J, Fahim D, Navarro J, Wolinsky JP, Omeis I. Free-hand placement of iliac screws for spinopelvic fixation based on anatomical landmarks: technical note. Int J Spine Surg. 2014; 8 [42] Garrido BJ, Wood KE. Navigated placement of iliac bolts: description of a new technique. Spine J. 2011; 11(4):331–335

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46 Complications of Sacral Alar Iliac Screw Technique Vidyadhar V. Upasani and Richard T. Allen

46.1 Introduction Pelvic fixation in posterior spinal surgery has evolved over the past few decades. Secure pelvic fixation is necessary in a variety of conditions to overcome the significant biomechanical forces across the lumbosacral junction, as well as the sacral anatomical complexities and poor bone quality. In this chapter, we describe the indications for pelvic fixation, review the current most commonly used techniques, and present the short-term clinical outcomes and complications of the sacral alar iliac screw technique.

46.2 Purpose of Instrumentation Indications for pelvic fixation include correction of pelvic obliquity associated with scoliotic deformity,1 reduction of high-grade

spondylolisthesis,2 treatment of lumbosacral pseudarthrosis,3 sacroiliac dislocations, and high-energy lumbosacral trauma,4 congenital conditions such as failures of formation/segmentation (▶ Fig. 46.1) or lumbosacral agenesis,5 and pathologic conditions such as metastatic disease or primary sacropelvic involvement.6 Despite recent advances in surgical techniques and spinal instrumentation, controversy exists on how to best achieve a solid arthrodesis and minimize complications because of implant failure, coronal or sagittal imbalance, and neurovascular compromise. The two most commonly used pelvic fixation strategies prior to 2010 were the Galveston technique7 as developed by Allen and Ferguson in the 1980s and iliac screw fixation.8 Although both techniques have been shown to be clinically successful,9,10 a number of biomechanical studies have found the iliac screws to

Fig. 46.1 Posteroanterior (a) and lateral (b) radiographs of a 9-year-old girl with right L4 hemivertebra and progressive deformity. 3D reconstruction (c) demonstrating deformity. Posteroanterior (d) and lateral (e) radiographs after she underwent excision of hemivertebra with posterior instrumented fusion from L3 to S2.

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Complications of Sacral Alar Iliac Screw Technique offer better pull-out strength11 and simplified instrumentation because of modular components.12 The iliac screws, however, also have some limitations. For example, a substantial dissection of the paraspinal musculature and adjacent skin is required to place these screws,8 implant prominence over the posterior superior iliac spine (PSIS) can be symptomatic,13 and screw integrity can be compromised by harvesting iliac crest bone graft.

46.3 Relevant Anatomy The sacrum consists of five fused vertebrae with transverse processes that merge to form a single continuous lateral mass. A majority of the sacrum has cancellous osseous architecture with two areas of increased bone density in the sacral alae and sacral promontory.14 The sacrum acts as a keystone to unite the two hemipelves and is supported by strong interosseous, dorsal, ventral, and accessory ligaments.15 Four pairs of foramen allow passage of the ventral and dorsal rami of the sacral nerves. The dorsal foramens are smaller and lie more medial than the ventral foramens. The first three ventral sacral roots contribute to the sacral plexus and innervate intrapelvic visceral structures. The dorsal rami provide sensory feedback from the skin overlying the sacrum and are often sacrificed during the dorsal sacral dissection. The obturator nerve, fifth lumbar root, lumbosacral trunk, and sympathetic chain are closely adherent to the ventral surface of the sacrum. The middle sacral artery originates just proximal to the bifurcation of the aorta. It travels along the midline over the fifth lumbar vertebra, sacrum, and coccyx and runs posterior to the venous system to anastomose with the lateral sacral arteries. The lateral sacral arteries are branches off the internal iliac arteries.15 These vessels cross the sacroiliac joint near the first or second ventral sacral foramen and run caudally lateral to the foraminal margin. The common and internal iliac veins are dorsal to its corresponding arteries and lie in the connective tissue immediately ventral to the sacral alae medial to the sacroiliac joints.16 The sigmoid colon and mesentery descend on the left and lie ventral to the neurovascular structures described earlier. The length and position of the sigmoid colon are variable and the colon is quite mobile at the level of the first two sacral vertebral bodies. The rectosigmoid junction occurs at the level of third sacral vertebra and lies midline and directly on the ventral sacral surface.

46.4 Sacral Alar-Iliac Screw Surgical Technique The sacral alar-iliac (S2AI) screw technique was described by Chang, Kebaish, and Sponseller in 2009.17 Its primary advantages as described by the authors include decreased implant prominence, decreased need for soft tissue dissection, improved position of the screw head in relation to a long spinal construct, and obviating the need for connectors. Based on CT data, the recommended starting point for this screw is approximately 25 mm caudal to the superior endplate of S1 and 22 mm lateral to the midline.17 The screw is angled about 40 degrees laterally and 40 degrees caudally (▶ Fig. 46.2). Fluoroscopic or intraoperative CT guidance is used to ensure that the screw does not violate the sciatic notch or the hip joint18 (▶ Fig. 46.3). The maximal mean length of the S2AI screw, based on the ideal trajectory, was slightly more than 100 mm and screw traversed approximately 35 mm of sacral bone prior to crossing the sacroiliac joint.

46.5 Clinical Outcomes and Complications Clinical outcomes with minimum 2-year follow-up were presented in 2010.19 Twenty-six pediatric patients with S2AI pelvic fixation were reviewed and compared to 27 patients with traditional PSIS iliac screw fixation. No statistically

Fig. 46.2 Starting point and trajectory of S2 alar-iliac screws demonstrated on 3D reconstruction of pelvis.

Fig. 46.3 Intraoperative fluoroscopic images (a,b) demonstrating position of screw track in relation to the sciatic notch and hip joint.

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Fig. 46.4 Posteroanterior (a) and lateral (b) preoperative and posteroanterior (c) and lateral (d) postoperative radiographs of a 15-year-old female with cerebral palsy and significant thoracolumbar deformity with pelvic obliquity status post a T2-pelvis posterior instrumented spinal fusion.

significant difference was found in the magnitude of deformity or pelvic obliquity correction (▶ Fig. 46.4). Both groups had no vascular or neurologic complications. Four patients in the S2AI group experienced superficial wound infection or partial wound dehiscence, whereas three patients in the traditional group had deep wound infection and two had superficial wound infections. There were no cases of implant prominence, late skin breakdown, or anchor migration in the S2AI group, compared with one instance of each in the iliac screw patients. Postoperative CT scans were obtained on 18 S2AI patients. There were no instances of screw intrusion into the pelvis and one screw was found to protrude laterally into the gluteus musculature. Radiographic lucency was observed around two screws in each group, but was not found to be clinically relevant. One of the S2AI screws fractured at the neck; however, the patient has not required a revision procedure. One patient in each group required revision surgery. One patient in the S2AI group reported

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sacroiliac joint pain and was revised with bilaterally longer screws. One patient in the iliac screw group required revision surgery for failure of fixation and pain at the implant site. Because this technique was described relatively recently no midterm or long-term data currently exist. However, a number of potential complications can be considered. The most serious would occur from a ventral breach into the pelvis causing neurologic or vascular compromise or damage to the visceral organs.20 Additionally, inferior breach of the sciatic notch could injure the superior gluteal artery or sciatic nerve.21 Preoperative planning with computed tomography is extremely useful to approximate the appropriate screw length/trajectory, and intraoperative image guidance is critical to optimize safe screw placement. Posterior lateral breach of the iliac wing is relatively well tolerated and may provide improved cortical fixation, although this has not been proven with biomechanical data.

Complications of Sacral Alar Iliac Screw Technique

Fig. 46.5 A 12-year-old female with cerebral palsy status post–scoliosis correction with a windswept pelvis and left hip subluxation. The position of the left sacral alar-iliac screw limits acetabular correction options for this patient.

Screw length is also an important factor given the trajectory of this screw is directed toward the ipsilateral hip joint. Orthogonal fluoroscopic images have to be obtained to ensure that the screw tip does not violate the articular surface. Although the dense bone superior to the roof of the acetabulum provides strong fixation for these screws, its position may interfere with future procedures for hip preservation (▶ Fig. 46.5). Coordination between the hip and spine surgeons is important especially in the neuromuscular population that requires hip reduction and acetabular reorientation surgery, as well as spinal stabilization. Another important consideration in the neuromuscular patient population is the effect of transverse-plane pelvic asymmetry22 on pelvic fixation. Ko et al described significant pelvic asymmetry in patients with windswept hips requiring a more lateral starting point for the S2AI screw.22 Depending of the severity of the inward iliac rotation, the screw should start lateral to the sacroiliac joint and enter directly into the ilium to achieve an optimal trajectory (▶ Fig. 46.6). Lastly, the implications of crossing the sacroiliac joint should be considered. This may be better tolerated in severely debilitated patients with neuromuscular conditions and minimal baseline function. However, in ambulatory patients, implants across the sacroiliac joint could become symptomatic. The

lucency observed around the S2AI screws and implant fractures at the neck of the screw as described by Sponseller et al19 are likely caused by continued motion through the sacroiliac joint. While this may be asymptomatic or not require revision surgery in the short term, the long-term implications are as yet unknown. Some authors recommend the abundant use of bone graft dorsally around the sacroiliac joint in an attempt to obtain an arthrodesis.23 The clinical success of this technique to actually arthrodese the sacroiliac joint, however, is unclear.

46.6 Summary Sacral alar iliac screws provide low-profile, biomechanically stable sacropelvic fixation. In the short term, this technique appears to be safe in a diverse patient population and effective at correcting pelvic obliquity. It facilitates rod assembly in long spinal constructs and minimizes the risk of implant prominence and wound breakdown by preserving the paraspinal muscle envelope. The surgical technique is feasible with appropriate preoperative planning and intraoperative image guidance. No long-term data exist, however, and the long-term implications of crossing the sacroiliac joint in ambulatory patients are unknown.

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Thoracolumbar Fig. 46.6 Posteroanterior (a) and lateral (b) preoperative and posteroanterior (c) and lateral (d) postoperative radiographs of a 19-year-old male with cerebral palsy and significant thoracolumbar deformity. Because of the pelvic deformity, an iliac screw was used on the right side of this construct.

References [1] Gau YL, Lonstein JE, Winter RB, Koop S, Denis F. Luque-Galveston procedure for correction and stabilization of neuromuscular scoliosis and pelvic obliquity: a review of 68 patients. J Spinal Disord. 1991; 4(4):399–410 [2] Cunningham BW, Lewis SJ, Long J, Dmitriev AE, Linville DA, Bridwell KH. Biomechanical evaluation of lumbosacral reconstruction techniques for spondylolisthesis: an in vitro porcine model. Spine. 2002; 27(21):2321–2327 [3] Bridwell KH. Utilization of iliac screws and structural interbody grafting for revision spondylolisthesis surgery. Spine. 2005; 30(6) Suppl:S88–S96 [4] Abumi K, Saita M, Iida T, Kaneda K. Reduction and fixation of sacroiliac joint dislocation by the combined use of S1 pedicle screws and the Galveston technique. Spine. 2000; 25(15):1977–1983 [5] Dumont CE, Damsin JP, Forin V, Carlioz H. Lumbosacral agenesis. Three cases of reconstruction using Cotrel-Dubousset or L-rod instrumentation. Spine. 1993; 18(9):1229–1235 [6] Doita M, Harada T, Iguchi T, et al. Total sacrectomy and reconstruction for sacral tumors. Spine. 2003; 28(15):E296–E301 [7] Allen BL, Jr, Ferguson RL. The Galveston technique of pelvic fixation with Lrod instrumentation of the spine. Spine. 1984; 9(4):388–394 [8] Moshirfar A, Rand FF, Sponseller PD, et al. Pelvic fixation in spine surgery. Historical overview, indications, biomechanical relevance, and current techniques. J Bone Joint Surg Am. 2005; 87 Suppl 2:89–106 [9] Kuklo TR, Bridwell KH, Lewis SJ, et al. Minimum 2-year analysis of sacropelvic fixation and L5-S1 fusion using S1 and iliac screws. Spine. 2001; 26 (18):1976–1983 [10] Nectoux E, Giacomelli MC, Karger C, Herbaux B, Clavert JM. Complications of the Luque-Galveston scoliosis correction technique in paediatric cerebral palsy. Orthop Traumatol Surg Res. 2010; 96(4):354–361 [11] Tis JE, Helgeson M, Lehman RA, Dmitriev AE. A biomechanical comparison of different types of lumbopelvic fixation. Spine. 2009; 34(24):E866–E872

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[12] Peelle MW, Lenke LG, Bridwell KH, Sides B. Comparison of pelvic fixation techniques in neuromuscular spinal deformity correction: Galveston rod versus iliac and lumbosacral screws. Spine. 2006; 31(20):2392–2398, discussion 2399 [13] Stevens DB, Beard C. Segmental spinal instrumentation for neuromuscular spinal deformity. Clin Orthop Relat Res. 1989(242):164–168 [14] Peretz AM, Hipp JA, Heggeness MH. The internal bony architecture of the sacrum. Spine. 1998; 23(9):971–974 [15] Esses SI, Botsford DJ, Huler RJ, Rauschning W. Surgical anatomy of the sacrum. A guide for rational screw fixation. Spine. 1991; 16(6) Suppl:S283–S288 [16] Mirkovic S, Abitbol JJ, Steinman J, et al. Anatomic consideration for sacral screw placement. Spine. 1991; 16(6) Suppl:S289–S294 [17] Chang TL, Sponseller PD, Kebaish KM, Fishman EK. Low profile pelvic fixation: anatomic parameters for sacral alar-iliac fixation versus traditional iliac fixation. Spine. 2009; 34(5):436–440 [18] Mattei TA, Fassett DR. Low-profile pelvic fixation with sacral alar-iliac screws. Acta Neurochir (Wien). 2013; 155(2):293–297 [19] Sponseller PD, Zimmerman RM, Ko PS, et al. Low profile pelvic fixation with the sacral alar iliac technique in the pediatric population improves results at two-year minimum follow-up. Spine. 2010; 35(20):1887–1892 [20] O’Brien JR, Yu WD, Bhatnagar R, Sponseller P, Kebaish KM. An anatomic study of the S2 iliac technique for lumbopelvic screw placement. Spine. 2009; 34 (12):E439–E442 [21] Lanzieri CF, Hilal SK. Computed tomography of the sacral plexus and sciatic nerve in the greater sciatic foramen. AJR Am J Roentgenol. 1984; 143 (1):165–168 [22] Ko PS, Jameson PG, II, Chang TL, Sponseller PD. Transverse-plane pelvic asymmetry in patients with cerebral palsy and scoliosis. J Pediatr Orthop. 2011; 31 (3):277–283 [23] Zhu F, Bao HD, Yuan S, et al. Posterior second sacral alar iliac screw insertion: anatomic study in a Chinese population. Eur Spine J. 2013; 22(7):1683–1689

Complications of Sacropelvic Reconstruction for Tumor

47 Complications of Sacropelvic Reconstruction for Tumor Eitan Kohan, Kushagra Verma, and John A. Abraham

47.1 Introduction Sacropelvic reconstruction for tumor resection is a technically challenging procedure. Patients are often medically complex requiring careful coordination with medical oncologists, radiation oncologists, and family support systems. Outcome from surgery is largely dependent on the timing of surgery, as well as the underlying histology of the tumor. Over the last 30 years, incredible advancements have been made both medically and surgically, leading to improvements in overall survival. This is particularly true for those patients with primary osseous spinal neoplasms, as malignant primary tumors in this region come with significant morbidity and mortality. There are approximately 2,400 new cases of primary osseous malignancy each year, of which 5% involve the spine.1 Survival is histologically specific for the four most common primary osseous spinal tumors (osteosarcoma: 11 months, Ewing sarcoma: 26 months, chondrosarcoma: 37 months, chordoma: 50 months).1 In a recent review of data spanning 30 years in the U.S. population-based cancer registry (Surveillance, Epidemiology, and End Results [SEER]), patients with osseous spinal osteosarcoma and Ewing sarcoma were three times more likely to be diagnosed with metastasis than those with chondrosarcoma or chordoma. Surgeons managing sacropelvic reconstructions must be mindful of the underlying diagnosis and tumor grade as surgical outcome is most dependent on these factors. This chapter will first review the common tumors affecting the sacrum and pelvis. Subsequently, we will provide a brief overview of resection types. Sacropelvic reconstruction techniques will be discussed as well as the most common complications associated with reconstruction. Lastly, the chapter will discuss emerging technologies and directions for future study.

47.2 Common Tumors in the Pelvis Sacral chordomas are malignant neoplasms that occur most commonly in the axial skeleton, with the sacrum being the most common site. Chemotherapy and radiation therapy have not been successful treatment options, leaving surgical resection with wide margins the mainstay of surgical treatment. This is associated with significant morbidity to bowel, bladder, and sexual function in up to 75% of patients, and with wound complications in almost half of all patients. Overall 5-year diseasefree survival is 77%, with local recurrence in 40% and metastasis in 31% of patients.2 In one series of 42 patients, wide resection did not reduce local recurrence as compared to marginal resection. However, intralesional resections were associated with 100% recurrence, metastasis, and eventual mortality. As noted by the authors, the series was likely underpowered to detect differences in outcome between wide and marginal resection.2 Adjuvant cryosurgery or radiation may be considered, but outcome data are limited.

For neurogenic tumors, patients with benign tumors have a mean Musculoskeletal Tumor Society (MSTS) score of 94% at 2 years’ follow-up, while those with malignant tumors at presentation had 40% recurrence and 50% survival at 5 years.3 Another group reported 5-year local recurrence rates of 35.9% for benign and 35% malignant tumors. Five-year survival was 25.9% for malignant neurogenic tumors.4 Osteosarcoma of the pelvis typically is associated with poor 5-year survival rates of 38 and 33% at 2 years if metastasis is identified at the time of initial diagnosis. Fuchs et al identified tumor size above 10 cm and location in the ilium to be independent risk factors for recurrence and mortality.5 Chondrosarcoma, in contrast, can have 69% disease-free survival for an average of 12 years after wide surgical resection. Overall 10-year survival rates were dependent on the tumor grade (97% for grade 1, 75% for grade 2, and 14% for dedifferentiated chondrosarcoma).6 Recurrent chondrosarcoma is associated with a 71% second recurrence rate and 24% distant metastasis. With aggressive secondary surgical intervention, 48% of patients had disease-free survival in one report. Complications were mostly wound related, occurring in 38% of patients.7 Although rare, desmoid tumors are soft tissue neoplasms that may be identified in the female pelvis. The tumors are characterized by abundant fibroblasts without cytologic evidence of malignancy. Surgical resection in conjunction with radiation and hormonal therapy is the mainstay of treatment.8 Giant cell tumors (GCT) are commonly treated with intralesional curettage, but lesions in the pelvis and sacrum have a high rate of recurrence and distant metastasis. Authors of one series advocated for marginal or wide excision.9 Aneurysmal bone cysts are benign, nonneoplastic, highly vascular bone lesions of unknown origin that can affect the pelvis and sacrum. Ninety-five percent of patients present with pain as their initial symptom, and treatment recommendations include selective arterial embolization, excision curettage, and bone grafting. Surgical reconstruction for large destructive lesions of the pelvis and sacrum must be individualized, but in almost all cases complete intralesional resection is recommended. In a series of 40 patients from 1921 to 1996, all patients were disease free at final follow-up and 70% were asymptomatic.10 Other primary tumors may be diagnosed in the sacrum or pelvis including GCT, malignant fibrous histiocytoma, osteoblastoma, hemangioma, and rare sarcomas not mentioned above. Prognosis is often guided by the histology and the quality of the tumor resection. While many options exist for sacropelvic reconstruction after tumor resection, these have to be tailored to the individual patient. In the absence of the impending neurological demise, surgical treatment should be cautiously approached and carefully planned. The medical oncologist and radiation oncologist should be involved early in the care of these patients so that the surgeon and patient can accurately weigh the benefits of surgical versus nonsurgical treatment. In addition, the surgical treatment—if appropriate—should fall in line with the patient’s long-term prognosis.

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Fig. 47.1 Pelvic resection classification. (Adapted from Pring et al.6)

47.3 Resection Techniques Pelvic resection is generally described according to the system of Enneking and Dunham (▶ Fig. 47.1).11 Type 1 resection involves only the ilium, while type 1A involves the ilium and gluteal muscles. For type 1S, the ilium and part of the sacrum are resected. Type 2 is a periacetabular resection and type 2A is a resection that involves the hip joint. Type 3 is a resection of all or a portion of the ischium and pubis. Surgery is commonly individualized to the patient, with a combination of these resections being utilized depending on tumor location.6 Partial or complete sacral resections are referred to as type 4 resections. These can be grouped as (1) transverse partial sacrectomy, (2) sagittal hemisacrectomy, or (3) combined type (▶ Fig. 47.2). The sacrum acts to transmit forces between the lower limbs and the vertebral column. The sacroiliac joint has intrinsic stability given it is wedged between the iliac bones and is further stabilized by strong sacroiliac, sacrotuberous, sacrospinous, and lumbosacral ligaments. Patients that undergo a partial transverse sacrectomy may continue to have intrinsic stability, but the biomechanics of this are poorly understood. It remains unclear the amount of sacrum that can be safely removed with a transverse partial sacrectomy without an iliolumbar arthrodesis. Patients that undergo a sagittal hemisacrectomy, however, require reconstruction to reconstitute the pelvic ring.12 Total sacrectomy is rare, but necessitates pelvic and lumbar fixation.

47.4 Methods for Reconstruction Sacropelvic reconstruction is challenging because stabilization is often required through the lumbosacral junction. It is challenging to achieve a solid fusion in this region because of the large loads and the lumbo-pelvic anatomy. This region is a transition from the mobile lumbar spine to the fixed pelvis.13 Increasing the number of spinal segments fused (length of lever arm) increases the magnitude of the forces at the lumbosacral

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Fig. 47.2 (a-c) Type 4 resections. (Adapted from Hugate and Sim.12)

junction, which can lead to loss of fixation. With longer spinopelvic constructs, the Galveston’s technique may be utilized. This technique was originally described by Allen and Ferguson for scoliosis.14,15 In this technique, the distal limb of the spinal fixation rod is angled and inserted into the posterior iliac bones, just above the sciatic notch (▶ Fig. 47.3). In a series of 13 patients by Jackson et al, this technique offered significant pain relief, stabilization, and preservation of ambulatory ability although long-term follow-up regarding radiographic outcomes and hardware complications was lacking.16 Although the Galveston’s technique was successful in obtaining rigid fixation across the lumbosacral junction, difficulty with loosening, rod contouring, and attachment promoted use of iliac screws instead (modified Galveston’s technique [MGT]; ▶ Fig. 47.4). The iliac screws are linked to the spinal rod using a cross-linked bar to create a more rigid and stable construct. In a series of 20 patients with neuromuscular deformity with 2-year follow-up, use of iliac screws resulted in equivalent radiographic outcomes with fewer hardware complications and increased ease of use.17 The addition of a biologic component to the reconstruction aids in establishing a bony union to bridge the large defects following resection. Early methods utilized both autologous iliac crest and allogenic corticocancellous bone for this purpose.18 The use of a double- or triple-barrel fibular autograft has been reported, with the goal of producing less stress and less displacement across the bone graft (▶ Fig. 47.5).19 When combined with a plate or a pedicle screw–rod system, this combines the short-term stability of metal with the long-term stability of bony union. This has been shown to have improved functional outcomes without increasing the risk of complications when

Complications of Sacropelvic Reconstruction for Tumor

Fig. 47.3 Galveston’s technique. (Adapted from Varga et al.46)

Fig. 47.4 Modified Galveston’s technique. (Adapted from Varga et al.46)

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Fig. 47.5 Double-barrel fibula reconstruction. (Adapted from Hubert et al.20)

compared to patients who did not undergo any reconstruction.19,20 Although these techniques address the problems of bony union, they disrupt the muscular attachments of the gluteus medius and can often be technically challenging. A simpler method of reconstruction was developed that allows for reconstitution of the pelvic ring using the host bone while leaving the muscular attachments intact.21 This technique utilizes two screws for stabilization: one at the level of S1 vertebral body and another in the posterior column. A rod is then used to connect the screws and compression is applied across the construct. Of the six patients who received this procedure, there was one death within 6 months. In the surviving patients, all posterior column graft sites healed, but four of the five proximal sacral sites showed a stable pseudarthrosis. All four patients who did not have complete bony healing progressed to have a complication that required surgical intervention. A careful balance must be maintained between providing primary stability using implants, while minimizing implant

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material to reduce infection risk. Using these principles, a reconstruction method was developed using only polyaxial screws, titanium rods, and antibiotic-containing bone cement (▶ Fig. 47.6).22 This compound osteosynthesis technique entirely dispensed with allografts or large metal implants. While the functional outcomes, hardware failures, and complication rates are comparable to existing techniques, there has been a decreased rate of deep infection that necessitated a revision surgery (14 vs. up to 43%). This principle of minimizing instrumentation to reduce infection risk may be useful in selecting what reconstruction method to utilize. While the topic falls outside the scope of a typical spine practice, attempts have been made to restore anatomy, joint function, and loading capacity using custom-made pelvic prostheses. While in some cases these prostheses have been effective, revisions have been required in up to 52.6% of cases.23,24 The most common complication necessitating revision was deep infection, but local recurrence, aseptic loosening, recurrent hip dislocation, and postoperative bleeding have been cited as well.

Complications of Sacropelvic Reconstruction for Tumor

Fig. 47.6 Reconstruction using only screws, rods, and bone cement. (Adapted from Gebert et al.22)

47.5 Complications Encountered with Reconstruction Because of the lengthy and complex surgical techniques required for sacropelvic reconstruction, complication rates are often extraordinarily high. Here we classify complications into five categories: biologic, neurologic, deformity, hardware failure, and disease progression.

47.5.1 Biologic The sacropelvic junction serves as the transition zone from the mobile spine to the relatively fixed pelvis. Long-term stability, therefore, of sacropelvic reconstruction is dependent on bony union.16 This bony bridge is necessary to provide reinforcement to the construct in the face of the large loads and biomechanical forces acting in this region. Aside from painful nonunions, complications directly related to pseudarthroses have not been reported in articles describing spinopelvic reconstruction for tumor. However, there remains a high incidence of lumbosacral pseudarthroses in the spinal deformity literature and these have been associated with loss of fixation, fracture, and failure of instrumentation.25 Using recently developed techniques, fusion rates have been reported to be over 90%.19,20,25,26 However, there is no uniform classification system for defining sacropelvic fusion, making direct comparisons across literature difficult. In monitoring L5– S1 fusion for spondylolisthesis, Kuklo et al assigned grades of A (definite fusion) through D (definite pseudarthroses) based on the radiographic appearance of the bony union (▶ Fig. 47.7).25 This grading system, originally described by Lenke et al,27 may be utilized to provide a standard definition of fusion rates for sacropelvic reconstruction. In addition to bony healing, there is a significant amount of soft tissue healing that is necessary following the resection of

sacropelvic tumors. The significant soft tissue stripping needed for surgical exposure can hinder the ability to heal and, along with the proximity to the rectum, increases the risk of infection.28 Flaps are typically used to close the large defects following resection, the most common being the vertical rectus abdominis myocutaneous flap and the gluteus maximus adipomuscular flap.29,30 Complications of flap healing include delayed wound healing, surgical site infections, wound dehiscence, fistula formation, and flap necrosis. Wound dehiscence and surgical site infections have been the most heavily investigated (albeit often following sacrectomy without reconstruction) and complications have been reported between 15 and 50%.21,22,24,30,31 Significant risk factors for wound complications include preoperative radiation, rectum rupture, age less than 40, diabetes mellitus, tumor size greater than 10 cm, and increased instrumentation.28 Deep infection, the final biologic complication, is much more devastating than superficial wound complications and commonly necessitates surgical debridement in addition to antibiotics, if not a revision surgery.32,33 In a review of 43 patients who underwent spinopelvic reconstruction, deep infections were reported in 7% of patients, each of whom were reconstructed using pedicle screws connected to iliac screws or an iliac plate.34 The remaining cases consisted of a variety of reconstruction methods, but it should be noted that complications were not recorded in 20 (46%) of the cases reviewed. One series has examined deep infection rates and risk factors in resection of sacral tumors without reconstruction, specifically GCT and sacral chordomas. These authors found that the type of surgery performed was the greatest risk factor for infection. Intralesional excision for sacral GCT was not considered a significant risk for infection. In contrast, while wide excision for sacral chordomas improves survival, there was a 44% incidence of infection.31 The most common infectious agents were Enterococcus, Escherichia coli,

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Fig. 47.7 Fusion grades. (Adapted from Kuklo et al.25)

and Pseudomonas aeruginosa, although most infections were polymicrobial. In this series, all infections healed with surgical debridement and culture-directed antibiotics.

47.5.2 Neurologic Sacral nerves have previously been shown to be closely associated with ability to ambulate as well as bowel and bladder continence.35 Given the proximity of sacral tumors to these nerves, urinary dysfunction, rectal dysfunction, and sciatic nerve palsies are commonly reported complications. It is important to obtain a good baseline neurologic exam in these patients because tumors may compress the nerves and cause dysfunction preoperatively.22 Additionally, the location of the neoplasm oftentimes necessitates unilateral or bilateral sacral nerve resection as a planned part of the procedure.19,22 In patients with a normal neurologic baseline, it is important for the surgeon to carefully consider what neural structures will be sacrificed and the clinical implications. These should be discussed in advance with the patient. Literature has shown that a progressively larger and more proximal level of sacrectomy is associated with worse functional outcomes.36,37 S4 and S5 nerve roots may be excised with minimal clinical effect on ambulatory status, or bowel and bladder function. Sacrifice of the S3, however, appears to be the key level that has the highest association with both bowel and bladder incontinence. Unilateral and bilateral resection of the S3 nerves have shown a 37.5 and 75% incidence, respectively, of loss of bowel and bladder control.35 When bilateral S3 nerves are spared, incontinence rates drop below 25%, and some authors have shown that bowel and bladder function will remain completely intact.35,36,37 Ambulatory status does not appear to be affected until resection reaches the S1 and S2 nerve levels. Resection of the S1 nerve roots has been shown to decrease the chances of postoperative ambulation to 50 versus 76% or up to 100% when the highest level sacrificed is S2 or S3, respectively.35,37 These planned consequences of surgery should be discussed in detail with the patient and

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attempts should be made to tailor postoperative rehabilitation accordingly.

47.5.3 Deformity Sacropelvic resection and reconstruction greatly disrupts the anatomy of the sacrum as well as the surrounding soft tissues. These defects can lead to significant alterations in the pelvic incidence (PI) and limb length discrepancy. Most concerning to the patient, however, may be the deformity created by the soft tissue injury (▶ Fig. 47.8).26 PI is defined as the angle between a line perpendicular to the S1 endplate at its midpoint and the line connecting this point to the center of the femoral head (▶ Fig. 47.9).38 When sacropelvic resection includes a total sacrectomy, the PI is altered because of complete disarticulation of the sacroiliac joint.39 Combined with nerve root resection that often accompanies total sacrectomy, this may lead to significant gait difficulties. However, the clinical implications of PI alterations on sagittal balance, pain, and ambulation following sacrectomy and reconstruction have not been well described. Of note, when only partial resection of the SI joint (partial sacrectomy) is performed, there is no alteration in the PI.39 Even if the SI joint is preserved, there may be a significant leg length discrepancy (LLD). In a case series of 22 patients, iliosacral resection without any reconstruction caused an LLD of 2 to 4.3 cm in 57% of patients.19 The addition of spinopelvic reconstruction reduced both the size and the incidence of LLD (1– 1.3 cm, 25% incidence), though this did not reach statistical significance. Functional outcomes, however, were significantly improved with reconstruction as measured by the MSTS score.

47.5.4 Hardware The hardware of spinopelvic reconstructions are under large loads given they transfer the body weight from the axial skeleton to the lower extremities. When choosing a reconstruction

Complications of Sacropelvic Reconstruction for Tumor

Fig. 47.8 Visible deformity seen following hemipelvectomy. (Adapted from Chang et al.26)

the compressive load at either of these points can lead to aseptic loosening or failure of the instrumentation. While these biomechanical analyses have not been performed on every reconstruction type, all have shown evidence of hardware failure regardless of the amount of instrumentation. Of the patients receiving the screw–rod–antibiotic cement method, six patients (17%) showed evidence of broken screws.22 Aseptic implant failures developed in 5% of the patients with the large, custom-made pelvic prosthesis.24 However, hardware failure does not indicate definitive surgical failure given that successful bony fusion has been shown following screws failure.25 In these situations, it is reasonable to delay revision surgery and closely follow the patient radiographically. Revision surgery should be offered if the patient is experiencing progressive deformity or pain. At the time of revision, surgery should address the original cause of hardware failure.

47.5.5 Disease Process and Management Fig. 47.9 Pelvic incidence. (Adapted from Legaye et al.38)

method, it is important to account for the biomechanical forces that will be placed across the construct. In response to axial loading, the MGT has been shown to place excessive stress on the spinal rod connecting the L5 pedicle screw to the iliac screw (▶ Fig. 47.10).40 Using the triangular frame reconstruction (TFR) method, these forces have been shifted from the construct to the surrounding iliac bone (▶ Fig. 47.11). The concentration of

Resection and reconstruction of sacropelvic tumors should aim to provide the patient a disease-free state with the hope of a functional outcome. Minimizing the risk of local recurrence is therefore a key aspect in selecting the proper surgical management. En bloc resection, in which the tumor is not violated during the procedure, has proven to be a technique that can decrease the risk of recurrence.41 Despite these approaches, however, recurrence rates have still been reported as high as 15%.23 While it is likely that the rate of recurrence is dependent on the primary tumor type, the majority of research to date has been isolated case reports or case series. The larger studies that

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Fig. 47.10 Analysis of the modified Galveston’s technique. Maximum stress is observed at a point on the spinal rod between the pedicle screw of the fifth lumbar vertebra and the iliac screw (I). (Adapted from Kawahara et al.40)

have been done consist of a heterogeneous group of tumors, making analysis difficult. In recent years, multiple institutions from around the globe developed a database of nearly 1,500 patients with primary tumors of the spine.42 As this database grows, it may be used to identify trends of tumor recurrence based on specific pathologic diagnoses. There is conflicting data on the extent that adjuvant chemotherapy and radiotherapy contribute to the rate of complications. While specific complications were not mentioned, Ji et al found that in 45 patients who developed complications, adjuvant chemotherapy was associated with a significantly increased risk.24 Fourney et al found that preoperative radiation therapy was the only factor associated with an increase in complications.43 Others have found that while postoperative chemotherapy prolonged the time to fusion (3–4 vs. 2 months), neither the overall complication rate nor the infection rate was increased and fusion was still eventually achieved.20,22,26

47.6 New Technologies Some of the difficulty with sacropelvic reconstruction stems from the fact that there is no strong consensus on reconstruction methods. This may be due to the paucity of patients and

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the high rate of complications with any technique. In recent years, several innovative methods of sacropelvic reconstruction have been developed to improve upon the biomechanical limitations of existing systems. Early methods of spinopelvic reconstruction utilized extensive bone grafting to obtain an adequate fusion.18 However, the bone graft did not add any additional structural support between the spine and the pelvis until bony fusion occurred. The addition of triangular fibular strut (TFS) grafting was developed at the Mayo Clinic to place a structural graft along the force vectors between the base of the remaining vertebrae and the hip joints bilaterally.32 TFS grafting consists of bridging fibular grafts from a docking site in the inferior aspect of L5 proximally into iliopectineal docking sites distally (▶ Fig. 47.12). The forces transmitted across the construct compress the proximal and distal docking sites of the fibular grafts, providing a loading condition that is more favorable for bony healing. The published case series regarding TFS grafting reports nine sacrectomies with reconstruction.32 Seven of the nine patients were able to ambulate and none complained of pain. While all patients lost bowel and bladder control, this was because of planned resection of the sacral nerves rather than a complication of the surgery. The reported complications included one pseudarthrosis and hardware failure, one wound infection, two local recurrences, and two distant metastases. The closed-loop technique was developed in an effort to avoid the points of stress identified in the earlier techniques.40,44 The advantage lies in that it uses a single U-shaped rod anchored to the pelvis with multiple iliac screws (▶ Fig. 47.13). Although no biomechanical analyses of this technique have been published, this single-rod technique theoretically allows the forces to be distributed more symmetrically across the construct.44 This rod-and-screw construct provides improved rotational stability and better anchoring to the pelvis, while allowing the option of additional lumbopelvic screws to improve stability in flexion– extension. The Johns Hopkins University method is an extensive reconstruction method that was developed based on the MGT.45 Additional stabilization is provided utilizing three additional side-to-side connections: a connector between the spinal rods, a horizontal rod connecting the iliac screws, and a transiliac bar across the iliac crests. These rods are then attached using connectors and a femoral shaft graft is placed between the ilia (▶ Fig. 47.14). This construct allows the axial load to be transmitted to the pelvis at two separate fixation points, through the transiliac bar, as well as the rod connecting the iliac screws. While dispersing the load transmitted to the pelvis is beneficial, increased instrumentation is needed for this procedure, whereas decreasing the amount of instrumentation has been associated with decreased risk of infection, as noted earlier.22 The novel reconstruction (NR) method was also developed based on the MGT.40 This method adds anterior column support using two pedicle screws in the inferior endplate of L5 attached to a sacral rod that connects the two ilia (▶ Fig. 47.15). Under the same biomechanical testing used for the MGT and TFR, no excessive stress concentrations were detected using NR, indicating it has low risk of instrument failure or loosening. An additional benefit of this technique is the minimal amount of instrumentation needed to provide the additional stability.

Complications of Sacropelvic Reconstruction for Tumor

Fig. 47.11 Analysis of triangular frame technique. Excessive stress greater than the yield stress of cortical bone occurs at the interface between the pelvis and the upper sacral rod (P). (Adapted from Kawahara et al.40)

Fig. 47.12 Triangular fibular strut grafting. (Adapted from Dickey et al.32)

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Fig. 47.13 Closed-loop technique. (Adapted from Varga et al.44)

Fig. 47.14 Johns Hopkins University method. (Adapted from Gallia et al.45)

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Fig. 47.15 Novel reconstruction method. (Adapted from Kawahara et al.40)

47.7 Summary Reconstruction of the spinopelvic junction following resection can be extremely difficult and technically challenging. Though many techniques have been described, there remains no consensus on the best reconstruction method because all have had high complication rates. Determining the type of reconstruction to be utilized should be a multidisciplinary effort based on surgeon experience and tailored to the individual patient. Complications can be classified into five different categories: biologic, neurologic, deformity, hardware failure, and disease progression. In the published literature, complication rates have been reported in up to 50% regardless of reconstruction type. Newer reconstruction techniques developed have been targeted toward decreasing the failures of the constructs and minimizing instrumentation. Early theories have provided hope that the outcomes may improve and complication rates may decline using these methods, but further research is needed. Lastly, because of the rarity of these tumors, the majority of the published research is limited to case repots and case series providing preliminary levels of evidence only for ideal treatment methods. An international database has recently been developed to provide larger datasets regarding the management of these rare conditions.42 Future research utilizing this database can better define complications and rates, and hopefully identify an ideal method to guide treatment of these challenging problems.

References [1] Mukherjee D, Chaichana KL, Gokaslan ZL, Aaronson O, Cheng JS, McGirt MJ. Survival of patients with malignant primary osseous spinal neoplasms: results from the Surveillance, Epidemiology, and End Results (SEER) database from 1973 to 2003. J Neurosurg Spine. 2011; 14(2):143–150 [2] Schwab JH, Healey JH, Rose P, Casas-Ganem J, Boland PJ. The surgical management of sacral chordomas. Spine. 2009; 34(24):2700–2704 [3] Alderete J, Novais EN, Dozois EJ, Rose PS, Sim FF. Morbidity and functional status of patients with pelvic neurogenic tumors after wide excision. Clin Orthop Relat Res. 2010; 468(11):2948–2953 [4] Dozois EJ, Wall JC, Spinner RJ, et al. Neurogenic tumors of the pelvis: clinicopathologic features and surgical outcomes using a multidisciplinary team. Ann Surg Oncol. 2009; 16(4):1010–1016 [5] Fuchs B, Hoekzema N, Larson DR, Inwards CY, Sim FH. Osteosarcoma of the pelvis: outcome analysis of surgical treatment. Clin Orthop Relat Res. 2009; 467(2):510–518 [6] Pring ME, Weber KL, Unni KK, Sim FH. Chondrosarcoma of the pelvis. A review of sixty-four cases. J Bone Joint Surg Am. 2001; 83-A(11):1630–1642 [7] Weber KL, Pring ME, Sim FH. Treatment and outcome of recurrent pelvic chondrosarcoma. Clin Orthop Relat Res. 2002(397):19–28 [8] Mariani A, Nascimento AG, Webb MJ, Sim FH, Podratz KC. Surgical management of desmoid tumors of the female pelvis. J Am Coll Surg. 2000; 191 (2):175–183 [9] Guo W, Tang XD, Li X, Ji T, Sun X. The analysis of the treatment of giant cell tumor of the pelvis and sacrum [in Chinese]. Zhonghua Wai Ke Za Zhi. 2008; 46(7):501–505 [10] Papagelopoulos PJ, Choudhury SN, Frassica FJ, Bond JR, Unni KK, Sim FH. Treatment of aneurysmal bone cysts of the pelvis and sacrum. J Bone Joint Surg Am. 2001; 83-A(11):1674–1681 [11] Enneking WF, Dunham WK. Resection and reconstruction for primary neoplasms involving the innominate bone. J Bone Joint Surg Am. 1978; 60 (6):731–746

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Thoracolumbar [12] Hugate R, Jr, Sim FH. Pelvic reconstruction techniques. Orthop Clin North Am. 2006; 37(1):85–97 [13] Fourney DR, Prabhu SS, Cohen ZR, Rhines LD, Gokaslan ZL. Thoracolumbopelvic stabilization for the treatment of instability caused by recurrent myxopapillary ependymoma. J Spinal Disord Tech. 2003; 16(1):108–111 [14] Allen BL, Jr, Ferguson RL. The Galveston technique for L rod instrumentation of the scoliotic spine. Spine. 1982; 7(3):276–284 [15] Allen BL, Jr, Ferguson RL. The Galveston technique of pelvic fixation with Lrod instrumentation of the spine. Spine. 1984; 9(4):388–394 [16] Jackson RJ, Gokaslan ZL. Spinal-pelvic fixation in patients with lumbosacral neoplasms. J Neurosurg. 2000; 92(1) Suppl:61–70 [17] Peelle MW, Lenke LG, Bridwell KH, Sides B. Comparison of pelvic fixation techniques in neuromuscular spinal deformity correction: Galveston rod versus iliac and lumbosacral screws. Spine. 2006; 31(20):2392–2398, discussion 2399 [18] Gokaslan ZL, Romsdahl MM, Kroll SS, et al. Total sacrectomy and Galveston Lrod reconstruction for malignant neoplasms. Technical note. J Neurosurg. 1997; 87(5):781–787 [19] Wang J, Tang Q, Xie X, et al. Iliosacral resections of pelvic malignant tumors and reconstruction with nonvascular bilateral fibular autografts. Ann Surg Oncol. 2012; 19(13):4043–4051 [20] Hubert DM, Low DW, Serletti JM, Chang B, Dormans JP. Fibula free flap reconstruction of the pelvis in children after limb-sparing internal hemipelvectomy for bone sarcoma. Plast Reconstr Surg. 2010; 125(1):195–200 [21] Nassif NA, Buchowski JM, Osterman K, McDonald DJ. Surgical technique: Iliosacral reconstruction with minimal spinal instrumentation. Clin Orthop Relat Res. 2013; 471(3):947–955 [22] Gebert C, Wessling M, Gosheger G, et al. Pelvic reconstruction with compound osteosynthesis following hemipelvectomy: a clinical study. Bone Joint J. 2013; 95-B(10):1410–1416 [23] Rudert M, Holzapfel BM, Pilge H, Rechl H, Gradinger R. Partial pelvic resection (internal hemipelvectomy) and endoprosthetic replacement in periacetabular tumors [in German]. Oper Orthop Traumatol. 2012; 24(3):196–214 [24] Ji T, Guo W, Yang RL, Tang XD, Wang YF. Modular hemipelvic endoprosthesis reconstruction—experience in 100 patients with mid-term follow-up results. Eur J Surg Oncol. 2013; 39(1):53–60 [25] Kuklo TR, Bridwell KH, Lewis SJ, et al. Minimum 2-year analysis of sacropelvic fixation and L5-S1 fusion using S1 and iliac screws. Spine. 2001; 26 (18):1976–1983 [26] Chang DW, Fortin AJ, Oates SD, Lewis VO. Reconstruction of the pelvic ring with vascularized double-strut fibular flap following internal hemipelvectomy. Plast Reconstr Surg. 2008; 121(6):1993–2000 [27] Lenke LG, Bridwell KH, Bullis D, Betz RR, Baldus C, Schoenecker PL. Results of in situ fusion for isthmic spondylolisthesis. J Spinal Disord. 1992; 5(4):433– 442 [28] Li D, Guo W, Qu H, et al. Experience with wound complications after surgery for sacral tumors. Eur Spine J. 2013; 22(9):2069–2076 [29] Miles WK, Chang DW, Kroll SS, et al. Reconstruction of large sacral defects following total sacrectomy. Plast Reconstr Surg. 2000; 105(7):2387–2394

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[30] Garvey PB, Rhines LD, Feng L, Gu X, Butler CE. Reconstructive strategies for partial sacrectomy defects based on surgical outcomes. Plast Reconstr Surg. 2011; 127(1):190–199 [31] Ruggieri P, Angelini A, Pala E, Mercuri M. Infections in surgery of primary tumors of the sacrum. Spine. 2012; 37(5):420–428 [32] Dickey ID, Hugate RR, Jr, Fuchs B, Yaszemski MJ, Sim FH. Reconstruction after total sacrectomy: early experience with a new surgical technique. Clin Orthop Relat Res. 2005; 438(438):42–50 [33] Randall RL, Bruckner J, Lloyd C, Pohlman TH, Conrad EU, III. Sacral resection and reconstruction for tumors and tumor-like conditions. Orthopedics. 2005; 28(3):307–313 [34] Bederman SS, Shah KN, Hassan JM, Hoang BH, Kiester PD, Bhatia NN. Surgical techniques for spinopelvic reconstruction following total sacrectomy: a systematic review. Eur Spine J. 2014; 23(2):305–319 [35] Guo Y, Palmer JL, Shen L, et al. Bowel and bladder continence, wound healing, and functional outcomes in patients who underwent sacrectomy. J Neurosurg Spine. 2005; 3(2):106–110 [36] Todd LT, Jr, Yaszemski MJ, Currier BL, Fuchs B, Kim CW, Sim FH. Bowel and bladder function after major sacral resection. Clin Orthop Relat Res. 2002 (397):36–39 [37] Moran D, Zadnik PL, Taylor T, et al. Maintenance of bowel, bladder, and motor functions after sacrectomy. Spine J. 2015; 15(2):222–229 [38] Legaye J, Duval-Beaupère G, Hecquet J, Marty C. Pelvic incidence: a fundamental pelvic parameter for three-dimensional regulation of spinal sagittal curves. Eur Spine J. 1998; 7(2):99–103 [39] Gottfried ON, Omeis I, Mehta VA, Solakoglu C, Gokaslan ZL, Wolinsky JP. Sacral tumor resection and the impact on pelvic incidence. J Neurosurg Spine. 2011; 14(1):78–84 [40] Kawahara N, Murakami H, Yoshida A, Sakamoto J, Oda J, Tomita K. Reconstruction after total sacrectomy using a new instrumentation technique: a biomechanical comparison. Spine. 2003; 28(14):1567–1572 [41] Fisher CG, Saravanja DD, Dvorak MF, et al. Surgical management of primary bone tumors of the spine: validation of an approach to enhance cure and reduce local recurrence. Spine. 2011; 36(10):830–836 [42] Fisher CG, Goldschlager T, Boriani S, et al. An evidence-based medicine model for rare and often neglected neoplastic conditions. J Neurosurg Spine. 2014; 21(5):704–710 [43] Fourney DR, Abi-Said D, Lang FF, McCutcheon IE, Gokaslan ZL. Use of pedicle screw fixation in the management of malignant spinal disease: experience in 100 consecutive procedures. J Neurosurg. 2001; 94(1) Suppl:25–37 [44] Varga PP, Bors I, Lazary A. Sacral tumors and management. Orthop Clin North Am. 2009; 40(1):105–123, vii [45] Gallia GL, Haque R, Garonzik I, et al. Spinal pelvic reconstruction after total sacrectomy for en bloc resection of a giant sacral chordoma. Technical note. J Neurosurg Spine. 2005; 3(6):501–506 [46] Varga PP, Szoverfi Z, Lazary A. Surgical resection and reconstruction after resection of tumors involving the sacropelvic region. Neurol Res. 2014; 36 (6):588–596

Complications of Instrumentation in Cervical Spondyloarthropathy

48 Complications of Instrumentation in Cervical Spondyloarthropathy S. Samuel Bederman, Vu H. Le, and Nitin Bhatia

48.1 Introduction

48.2.3 Diagnosis

Spondyloarthropathy is the result of a systemic inflammatory process that affects the spine. There are two main categories of such inflammatory arthritides—seropositive and seronegative spondyloarthropathies. Rheumatoid arthritis (RA), a seropositive spondyloarthropathy, is characterized by inflammatory synovitis leading to joint destruction and spinal instability that can result in neurological impairment and death. The prototype seronegative spondyloarthropathy, ankylosing spondylitis (AS), manifests as a progressive fusion of the spine leading to stiffness, deformity, and the propensity for fracture. Because of advances in treatment, the burden of this disease has decreased, thus reducing the need for surgical intervention. In the cases that fail medical management, surgery plays a critical role in maintaining neurological function and spinal stability. Surgical complications, however, remain a challenge. Perhaps the most difficult complication is that of instrumentation failure because of poor bone quality and diminished healing potential. The goal of this chapter is to describe common surgical options and their complications for RA and AS patients with cervical spine pathologies.

The diagnosis of RA is based on satisfying at least four of seven major criteria according to the American College of Rheumatology.5 These evaluative criteria include the following: morning stiffness, distribution of joint involvement with respect to arthritis, rheumatoid nodules, rheumatoid factor (RF), and radiographic changes. RF is present in 80% of patients with RA, whereas antinuclear antibodies are present in approximately 30% of patients.6 Radiographic changes that are characteristic of RA involve joint swelling, joint space narrowing without osteophytes, periarticular osteopenia, and bony destruction without reactive sclerosis. Symmetric joint pain and stiffness is a common clinical complaint. Cervical spine symptoms include pain with activities and limited motion. Instability and subsidence of the atlantoaxial joints can lead to occipital headaches that result from impingement of upper cervical nerve roots. If bony erosion is severe enough at the facet joints, the patient can present with tilting of the neck to one side. Patients with atlantoaxial subluxation may report the sensation of the head falling forward during flexion.7 Large pannus formation encroaching the spinal canal can create myelopathy presenting with spasticity, gait disturbance, weakness, nondermatomal paresthesia, bowel or bladder incontinence, fine motor deficits, and upper motor signs such as hyperreflexia and Babinski’s sign. With basilar invagination, brainstem functions can be disrupted, causing vertigo, dysarthria, ataxia, breathing difficulty, visual disturbances, or even sudden death. Subaxial instability can cause myelopathy or radiculopathy based on the severity of the pathology. Overall, neurological symptoms are seen in approximately 7 to 34% of RA patients with cervical spine involvement.8,9 There are several radiographic parameters that facilitate diagnosis and serve as predictive factors for neurological recovery. Boden et al described the posterior atlantodental interval (PADI) as a reliable predictor of neurologic deficits and recovery in patients with atlantoaxial subluxation.10 The PADI is defined as the distance from the posterior dens to the anterior margin of the posterior arch of C1 on the sagittal view and serves as a direct measure of the space available for the spinal cord. Patients with preoperative PADI less than 10 mm did not experience significant neurologic recovery following surgery. Meanwhile, all patients with preoperative PADI greater than 14 mm recovered fully. Moreover, in the presence of subaxial subluxation, a subaxial sagittal canal diameter less than 13 mm was highly associated with severe neurologic deficits. Yonezawa et al defined subaxial subluxation as more than 4 mm or 20% olisthesis of the vertebral body diameter.11 The cervicomedullary angle (CMA) is another radiographic parameter that is prognostic for neurological recovery. This angle is measured on

48.2 Rheumatoid Arthritis 48.2.1 Epidemiology RA is a chronic autoimmune inflammatory disease that affects 0.5 to 1.5% of the U.S. population.1 Women are more likely to be affected compared to men. The cervical spine is the third most common site of skeletal involvement in RA, after the hands and feet.2 It is estimated that 17 to 86% of people with RA have cervical spine disease.3 Of those with cervical spine involvement, the incidence of atlantoaxial subluxation may occur in up to 49%, basilar invagination ranges from 5 to 32%, and subaxial subluxation is seen in 20 to 25% of patients.3,4

48.2.2 Pathogenesis RA typically affects synovial joints by causing a destructive, inflammatory process through a chronic immune-mediated mechanism. The inflammatory process involves the creation of synovitis and pannus formation at synovial joints, resulting in attenuation of the joint capsules with associated instability and canal encroachment. Additionally, the bones adjacent to the inflammation become osteopenic. RA typically affects the atlantoaxial and facet joints, potentially causing atlantoaxial and subaxial instability and basilar invagination, where the dens may settle into the foramen magnum, resulting in brainstem compression.

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Thoracolumbar magnetic resonance imaging (MRI) by drawing two intersecting lines: one along the posterior aspect of C2 and the other along the ventral aspect of the medulla. The angle subtended by these two lines is normally between 135 and 175 degrees. According to one study looking at 15 RA patients with MRIs, all patients who presented with a CMA less than 135 degrees had neurological deficits.12 Therefore, surgery has been recommended in patients who present with a CMA less than 135 degrees.

48.3 Ankylosing Spondylitis 48.3.1 Epidemiology The worldwide prevalence for AS is 0.9%.13 It is closely associated with human leukocyte antigen B27 (HLA-B27) given 90% of patients with AS test positive for this marker. HLA-B27 is a class 1 surface antigen encoded by a locus in the major histocompatibility complex on chromosome 6. Compared to AS patients who are HLA-B27 positive, AS patients who are HLAB27 negative develop the disease at an older age and lack a significant family history. Contrary to RA, males are more affected than women. In females, AS occurs at a later age, and diagnosis is usually delayed.14

48.3.2 Pathogenesis

The goal of nonoperative treatment is to control the symptoms while minimizing the toxicities of medical management. Thus, the regimen in medical management consists of adding drugs with greater toxicities as the disease progresses. For early stages of both diseases, a comprehensive program of treatment including patient education, gentle physical therapy, and nonsteroidal anti-inflammatory drugs (NSAIDs) should be recommended. If NSAIDs fail to control the symptoms, diseasemodifying antirheumatic drugs (DMARDs) and antitumor necrosis factor-alpha inhibitors are successful second-line options for both diseases. Unlike in AS, RA patients who fail NSAIDs can be treated using corticosteroids with good results.16 It has been shown that early aggressive medical management with DMARDs can delay or prevent progression of the disease.6

48.5 Surgical Indications for Rheumatoid Arthritis and Ankylosing Spondylitis

Although the cause of AS is unknown, the hallmark feature consists of inflammation and bony remodeling at the tendon insertion site (enthesis), known as enthesopathy. Abnormal bone formation in response to inflammation around joints leads to a stiffening, or ankylosis, of the respective joints. In addition, this process creates syndesmophytes, or ossification of the ligaments around the vertebrae, leading to the formation of a “bamboo spine.” Whereas the appendicular joints are affected in approximately 30% of patients, AS is largely a disease of synovial and cartilaginous joints of the axial skeleton, including the spine, sacroiliac joints, and symphysis pubis.6 Ankylosis at multiple levels of the spine creates a long and rigid lever arm, especially at the cervicothoracic region, that can lead to fractures. The cervical spine is the most common site of spinal fracture in AS patients.13

Indications for surgical management in RA patients with cervical spine pathology include the presence of neurologic deficits or spinal instability. In the absence of neurological compromise, patterns of spinal instability that warrant surgery include atlantoaxial subluxation with a PADI less than 14 mm, basilar invagination with odontoid migration into the foramen magnum, or subaxial subluxation with a sagittal canal diameter less than 14 mm.10 For AS patients with cervical spine pathologies, surgical treatment is generally considered when nonoperative management fails to control the functional disability caused by sagittal plane imbalance (chin-on-chest deformity or acquired flat back deformity) or in the setting of spinal fractures.17,18

48.3.3 Diagnosis

The two common surgical approaches to the cervical spine include a standard anterior (right or left-sided) Smith–Robinson approach to the subaxial cervical spine and a midline posterior approach. Although both approaches allow decompression, fusion, and stabilization, the posterior approach is generally more extensile compared to the anterior and allows for extension of the surgical incision from the occiput all the way to the pelvis. Posterior stabilization may utilize screw–rod constructs. Specifically, lateral mass screws are commonly used in the subaxial cervical spine. C1 lateral mass screws are also used, but require a different trajectory than the subaxial lateral mass screws to account for the unique anatomy at the atlas. At C2, pars, pedicle, or intralaminar screws are commonly used, and,

Criteria.15

Diagnosis of AS relies on the modified New York Early in the disease, common presentations include low back pain and stiffness of the spine, sacroiliac joints, and hips. Pain is usually worse in the morning and at night, and spinal motion and chest expansion are limited. As the disease progresses, there is a gradual loss of lordosis in the lumbar and cervical spine, which can lead to progressive sagittal plane deformity given the patient is no longer able to stand upright. Cervical kyphosis may develop into a chin-on-chest deformity, thus inhibiting patients from achieving horizontal gaze and causing significant disability if compensatory changes in other joints are inadequate.

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48.4 Nonoperative Treatment in Rheumatoid Arthritis and Ankylosing Spondylitis

48.6 Surgical Approaches

Complications of Instrumentation in Cervical Spondyloarthropathy because the pedicle is larger at C7 versus the other levels of the subaxial spine and the vertebral artery is usually not within the foramen transversarium at that level, pedicle screws are often used at C7 as well. For additional stability, posterior wiring can be added to augment fixation, particularly in the upper cervical spine. Unique to atlantoaxial fixation, transarticular, or Magerl, screws are alternatives to a screw–rod technique utilizing C1 lateral mass screw fixation and one of the various forms of C2 screw fixation. Anteriorly, two procedures, anterior cervical discectomy and fusion and anterior cervical corpectomy and fusion, are commonly performed for decompression, stabilization, or correction of kyphosis. Cages or allograft bones are generally used to replace the resected disc or vertebral body and to reconstruct the anterior column. Additionally, anterior plates may be used to stabilize the fusion site and prevent cage or graft displacement.

48.7 Surgical Management 48.7.1 Rheumatoid Arthritis Historically, atlantoaxial subluxation was treated surgically with posterior wiring techniques around the posterior arches of C1 and C2 with an intervening structural bone graft. Because these procedures lacked rigid fixation, however, patients were often placed in halo-vest immobilization postoperatively which was associated with significant morbidity. Today, posterior wiring is commonly used as adjunct with other types of internal fixation. Transarticular C1–C2 screws were introduced by Magerl to provide more rigid fixation while minimizing proud instrumentation. Transarticular screw fixation is technically challenging because the location of the vertebral artery can vary, requiring meticulous scrutiny of preoperative imaging to avoid arterial injury. A high-riding or anomalous vertebral artery is a contraindication to placing transarticular screws. Another option for rigid fixation is a screw–rod construct between C1 and C2 (Harms technique). This technique involves C1 lateral mass screws and C2 pedicle, or pars screws connected by bilateral rods. In an attempt to avoid the risk to the vertebral artery associated with other screw techniques, Wright introduced an alternative form of fixation for C2 that involves placement of intralaminar screws instead of pars or pedicle screws. Both transarticular screws and C1–C2 screw–rod constructs obviate the need for postoperative halo-vest immobilization.19 Mild to moderate basilar invagination causing neurologic deficits and radiographic spinal cord compression may be treated with posterior C1 laminectomy and occipitocervical fusion. A stable arthrodesis usually leads to spontaneous resorption of the pannus following fusion.20 In the setting of severe cord or brainstem impingement by the pannus or the cranially migrating dens, a transoral odontoid resection or suboccipital craniectomy may be warranted as an adjunct to a posterior stabilization procedure with or without traction. Subaxial subluxation can be addressed through an anterior, posterior, or combined approach. For fixed subluxation at less than three motion segments, anterior decompression and fusion is usually recommended.21,22 On the other hand, reducible subluxation can be treated with a posterior instrumented fusion, with or without decompression based on neurological

deficits. Typically, however, the location of neurologic impingement requiring decompression will usually dictate the surgical approach. Supplemental posterior instrumentation should be considered when multilevel anterior procedures are done to avoid the risk of pseudarthrosis.

48.7.2 Ankylosing Spondylitis Neck pain in the setting of any type of trauma in a patient with AS should raise a high suspicion for fracture. Computed tomography (CT) scans or MRIs are recommended because the diffuse ankylosis of the spine can obscure subtle fracture findings on standard radiographs. Fractures in patients with AS are generally unstable because of the long functional lever arms from the ankylosed spinal segments and extension of the fractures through the ossified soft tissues. These injuries are associated with a high rate of neurological deficits. Attention to the preinjured alignment of the neck is important given these patients tend to be kyphotic. Placing the neck in neutral or excessive extension might produce further neurological compromise and relative malalignment. Stabilization may be performed with long posterior constructs, unless the source of neurological compression is anterior. In general, long instrumented constructs are recommended because of the high biomechanical forces from the long lever arms and the osteopenia seen in these patients. Cervical deformity can create difficulties with horizontal gaze, dysphagia, and poor oral intake in the AS patient. When the deformity is rigid in the subaxial spine, correction using a posterior-based closing osteotomy, an anterior-based opening wedge osteotomy, or a combined approach can be attempted. For rigid chin-on-chest deformity stemming from cervicothoracic kyphosis, single-stage opening or closing wedge osteotomies have been described. Both of these extension osteotomy procedures are commonly performed at C7 because the transverse foramina do not contain the vertebral arteries at this level. Simmons, one of the first pioneers to introduce the single-stage opening wedge posterior osteotomy for kyphotic deformity in AS, described the opening-wedge osteotomy whereby the entire posterior elements of C7 are removed along with parts of C6 and T1, followed by a controlled osteoclasis resulting in a rupture of the anterior longitudinal ligament to achieve lordotic correction.23 Deviren et al later described a pure closing-wedge osteotomy of C7, similar to a typical pedicle subtraction osteotomy used in the thoracolumbar spine, with good results.24 In a 540-degree combined approach, the first step is to apply posterior screws and perform multilevel posterior decompression and Smith–Peterson osteotomies while in the prone position.25 The patient is then turned supine, and anterior column height is restored at multiple levels with discectomies and osteotomies with reconstruction using anterior grafts and a plate. Finally, the patient is placed prone again to insert the rods and prepare for fusion.

48.8 Complications Surgical treatment of cervical spine pathologies in RA and AS poses a challenge for the treating spinal surgeon. Susceptibility to infection from prolonged medical management and a high propensity for neurological deficits are of high concern. Poor

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Thoracolumbar bone quality caused by the inflammatory process and prolonged medication use challenges the ability to obtain adequate stable fixation needed to achieve a successful fusion. Because of this, it is not uncommon to perform long constructs or combined anterior–posterior fusions to reduce the risks of instrumentation failure and nonunion. Additional stability and long constructs, however, are not without complications. Common complications encountered after cervical spine surgery in AS and RA patients include infection, wound dehiscence, pseudarthrosis, and failure of fixation. This is compounded by the inherent danger of instrumentation in the cervical spine because of the proximity of important anatomic structures (e.g., vertebral artery, nerve roots, spinal cord, esophagus, recurrent laryngeal nerve, sympathetic chain, etc.). Complications can be because of the associated medical comorbidities and deconditioning encountered in patients with AS and RA, especially those with long-standing disease and complicated medical treatment. Osteoporosis and malnutrition in this population can compromise the strength of fixation, leading to increased rates of instrumentation failure and pseudarthrosis.26 To reduce the risks of such complications, patients should be adequately optimized preoperatively. Ideally, serum albumin should be more than 3.5 mg/dL, prealbumin higher than 15 mg/dL, and total lymphocyte count above 1,500/mm3. Surgically, patients at high risk for pseudarthrosis should be considered for circumferential fusion or immobilized adequately postoperatively. Additional forms of fixation, such as posterior interspinous wiring, should be considered as an adjunct to screw–rod fixation. Complications may also arise from the surgical approach used. A posterior cervical approach may yield a more extensile exposure than the anterior approach. Dissection of the posterior cervical musculature, however, can lead to prolonged postoperative neck pain and tends to be more prone to wound infection than anterior-only approaches, specifically when longer operative time is involved.27 Infection risk can be minimized by the addition of intrawound vancomycin powder. Pahys and colleagues have shown its effectiveness in decreasing postoperative cervical spine infections by 100% in 195 patients.28 Posterior instrumentation may also be prominent and result in irritation particularly in patients who have atrophic soft tissue from chronic steroid use. Lower profile implants are beneficial to minimize discomfort. Anterior approaches also have their inherent risks and can result in dysphagia, recurrent laryngeal nerve dysfunction leading to dysphonia, and direct esophageal and tracheal injuries. The surgical exposure can injure the sympathetic chain if the longus colli muscles are not elevated from midline. Similarly, vertebral artery injuries can result from aggressive dissection lateral to the uncinate processes. In general, however, these approaches are well tolerated and most approach-related complications are mild. Complications may also arise from direct placement of the instrumentation. Implant malpositioning can occur because of the erosive changes of once-normal anatomical structures. Careful scrutiny of the cervical anatomy on preoperative imaging is essential. The proximity of the vertebral artery and nerve root directly anterior, spinal cord directly medially, and adjacent facet joints superiorly and inferiorly make precise placement of posterior lateral mass screws in the cervical spine

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challenging. Care should be taken when C1 lateral mass screws are placed so as not to injure the internal carotid artery and hypoglossal nerve anterior to the anterior arch of the atlas. While the spinal cord is medial, the vertebral artery traverses C1 laterally and then comes medially on the superior surface of the posterior arch. Unlike subaxial lateral mass screws, C1 lateral mass screws require a medial, instead of lateral, trajectory to avoid the vertebral arteries. With transarticular atlantoaxial screws or C2 pars or pedicle screws, careful analysis of the course of the vertebral arteries must be scrutinized to avoid injury, particularly in patients with rheumatoid destruction of the C1 and C2 lateral masses. As in posterior instrumentation, the surrounding vital structures adjacent to the anterior instrumentation can be damaged. Complications of anterior instrumentation include screw violation of the spinal cord or vertebral artery. Apart from the location of instrumentation, the selection of levels is important to avoid failures of fixation. Because of the progressive nature of RA and its ongoing tendency to affect mobile joints, balancing the risks of more extensive surgery with that of less extensive surgery that maintains motion and minimizes the morbidity of surgery is critical. Clarke et al showed that at an average 8.3-year follow-up, 39% of patients who originally underwent C1–C2 fusion developed caudal instability in the subaxial spine. Of the 39%, half of these patients required extension of fusion.29 Interestingly, secondary subluxation at C3–C4 occurred in more than half of the patients requiring additional surgery. In addition, patients who initially underwent long posterior fusions from C1 to C6–T1 did not require revision surgery for adjacent segment instability. Therefore, to reduce the risk of secondary procedures and to preserve motion, it is recommended that dynamic radiographic flexion– extension views be obtained to rule out multisegment instability so that the appropriate levels can be incorporated in the initial procedure. If short segment constructs are performed adjacent to stable segments, long-term follow-up is necessary to monitor for new instability patterns causing neurological symptoms. In the setting of both atlantoaxial and subaxial instabilities, a long posterior fusion should be strongly considered. In the absence of basilar invagination, it appears that prophylactic extension to the occiput is unnecessary as the likelihood of basilar invagination after atlantoaxial fusion is reduced when not initially present.30,31 Finally, although instrumentation plays a pivotal role in deformity correction, the method of correction determines the complications encountered.32,33 For patients with AS and chinon-chest deformity, the two most common surgical strategies include a combined posterior–anterior–posterior (540-degree) approach and a posterior extension osteotomy via an opening or closing wedge technique. Both procedures entail higher risks for complications compared to standard posterior- or anteriorbased decompression and fusion. The combined approach may result in a greater degree of correction than the anterioralone procedure, but it carries a higher rate of postoperative neurological deterioration, complications, revision surgery, and mortality. Etame et al reported a complication rate of 26.9 to 87.5% for a posterior-based opening wedge osteotomy of C7 with a mortality rate of 2.6% and a permanent neurologic complication rate of 4.3%.34 Deviren et al recently introduced a closing wedge osteotomy of C7, akin to a thoracic or

Complications of Instrumentation in Cervical Spondyloarthropathy lumbar pedicle subtraction osteotomy.24 In their series of 11 patients, the authors found it to be relatively safe with no intraoperative complications or neurological deterioration. Two patients (18%) developed benign pneumonia, one developed postoperative dysphagia, and one had fatigue-related rod fracture needing revision surgery. Scheer et al studied the effect of rod material and diameter in a biomechanical model of posterior opening wedge osteotomies.35 They found that in comparison with 3.2-mm titanium rods, 3.5-mm cobalt-chromium (CoCr) rods provided significantly more rigidity. The authors concluded that the use of 3.5-mm CoCr rods in posterior cervical osteotomies may minimize instrumentation failure. In another biomechanical study, Scheer et al discovered that closing wedge osteotomy led to greater stiffness in flexion and extension, compared to the opening wedge osteotomy model.36 However, because there are few large series in the literature describing these techniques and most are small case series, there are no direct clinical comparisons between these techniques.

48.9 Case Examples 48.9.1 Case 1 A 78-year-old woman with a history of RA presented with increasing neck pain for about 2 years. She described associated “clunking” with neck flexion and bilateral hand deformities. On examination, she was neurologically intact without any long tract signs. Her preoperative CT scans showed a posterior atlantodens interval of 12 mm and anterior atlantodens interval of greater than 5 mm, signifying severe instability at the atlantoaxial articulation with decreased canal space for the spinal cord (▶ Fig. 48.1). The parasagittal CT images showed that the right atlantoaxial facet joint was disrupted, making transarticular screw placement on that side high risk (▶ Fig. 48.2). After the appropriate workup, she underwent surgery to stabilize the atlantoaxial joint to preserve neurologic function and to alleviate the “clunking” neck pain. Unilateral transarticular screw was placed on the left side and posterior interspinous wiring was performed to augment the fixation (▶ Fig. 48.3).

48.9.2 Case 2 A 48-year-old man with a history of AS presented with increasing neck pain and difficulty with looking straight ahead over many years. On examination, he was found to have a rigid chinon-chest deformity with difficulty with horizontal gaze. His neurological examination was significant for mild weakness (grade 4/5) in the left deltoid, biceps, and triceps, and diminished sensation in the C5, C6, and C7 dermatome on the ipsilateral side. His preoperative radiographs showed positive sagittal imbalance, with significant kyphosis in the lower cervical spine (▶ Fig. 48.4). Because of the dysfunction caused by the rigid kyphotic deformity, surgery was recommended to correct the sagittal imbalance with simultaneous neurological decompression. An opening wedge osteotomy was performed at C7, and bilateral pedicle screws and rods were placed in the cervical and thoracic spine to stabilize the osteotomy and to preserve the correction (▶ Fig. 48.5).

48.10 Summary Fig. 48.1 Midsagittal CT view showing decreased posterior and increased anterior atlantodens intervals.

Patients with cervical spondyloarthropathy pose challenging problems for the treating spinal surgeon. Accounting for anatomical and physiological differences in these patients is critical to avoid complications of instrumentation. These complications

Fig. 48.2 Parasagittal CT views displaying marked destruction of the right atlantoaxial joint (arrows).

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Thoracolumbar

Fig. 48.3 Lateral and anteroposterior radiographs depicting unilateral transarticular screw placement with posterior spinous wiring.

can arise from the surgical approach, insertion of spinal instrumentation, the extent of fusion, deformity correction techniques, diminished healing potential, and poor bone quality. With a thorough understanding of the challenges seen in the surgical treatment of this patient population, spine surgeons can provide better outcomes with avoidance of some of these complications.

48.11 Key Points ●

●

●

●

Fig. 48.4 Lateral radiograph showing severe cervical kyphosis, mainly at the lower cervical segments.

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●

AS and RA patients are at increased risk for surgical complications compared to the normal population. Proper patient assessment, medical optimization, and scrutiny of the local anatomy are essential. Poor bone quality predisposes this population to instrumentation failure and pseudarthrosis; thus, longer constructs or combined approaches may be necessary to achieve more stability. Correction of cervical deformities is associated with significant risks; however, newer techniques of closing wedge osteotomies with more rigid instrumentation may reduce complications. Because of the natural history of RA, long-term follow-up is recommended to monitor adjacent segment instability from chronic joint destruction.

Complications of Instrumentation in Cervical Spondyloarthropathy

Fig. 48.5 Lateral and anteroposterior radiographs showing an opening wedge osteotomy at C7 and posterior instrumented fusion with pedicle screws and dual rods.

References [1] Lawrence RC, Helmick CG, Arnett FC, et al. Estimates of the prevalence of arthritis and selected musculoskeletal disorders in the United States. Arthritis Rheum. 1998; 41(5):778–799 [2] Crockard HA. Surgical management of cervical rheumatoid problems. Spine. 1995; 20(23):2584–2590 [3] Rawlins BA, Girardi FP, Boachie-Adjei O. Rheumatoid arthritis of the cervical spine. Rheum Dis Clin North Am. 1998; 24(1):55–65 [4] Neva MH, Kaarela K, Kauppi M. Prevalence of radiological changes in the cervical spine—a cross sectional study after 20 years from presentation of rheumatoid arthritis. J Rheumatol. 2000; 27(1):90–93 [5] Arnett FC, Edworthy SM, Bloch DA, et al. The American Rheumatism Association 1987 revised criteria for the classification of rheumatoid arthritis. Arthritis Rheum. 1988; 31(3):315–324 [6] Borenstein DG. Arthritic disorders. In: Herkowitz HN, Garfin SR, Eismont FJ, Bell GR, Balderson RA, eds. Rothman-Simeone: The Spine. Philadelphia, PA: Elsevier; 2011:632–650 [7] Dreyer SJ, Boden SD. Natural history of rheumatoid arthritis of the cervical spine. Clin Orthop Relat Res. 1999(366):98–106 [8] Pellicci PM, Ranawat CS, Tsairis P, Bryan WJ. A prospective study of the progression of rheumatoid arthritis of the cervical spine. J Bone Joint Surg Am. 1981; 63(3):342–350 [9] Conlon PW, Isdale IC, Rose BS. Rheumatoid arthritis of the cervical spine. An analysis of 333 cases. Ann Rheum Dis. 1966; 25(2):120–126 [10] Boden SD, Dodge LD, Bohlman HH, Rechtine GR. Rheumatoid arthritis of the cervical spine. A long-term analysis with predictors of paralysis and recovery. J Bone Joint Surg Am. 1993; 75(9):1282–1297 [11] Yonezawa T, Tsuji H, Matsui H, Hirano N. Subaxial lesions in rheumatoid arthritis. Radiographic factors suggestive of lower cervical myelopathy. Spine. 1995; 20(2):208–215 [12] Bundschuh C, Modic MT, Kearney F, Morris R, Deal C. Rheumatoid arthritis of the cervical spine: surface-coil MR imaging. AJR Am J Roentgenol. 1988; 151 (1):181–187 [13] Kubiak EN, Moskovich R, Errico TJ, Di Cesare PE. Orthopaedic management of ankylosing spondylitis. J Am Acad Orthop Surg. 2005; 13(4):267–278 [14] Khan MA. Epidemiology of HLA-B27 and arthritis. Clin Rheumatol. 1996; 15 Suppl 1:10–12 [15] van der Linden S, Valkenburg HA, Cats A. Evaluation of diagnostic criteria for ankylosing spondylitis. A proposal for modification of the New York criteria. Arthritis Rheum. 1984; 27(4):361–368

[16] van Everdingen AA, Jacobs JW, Siewertsz Van Reesema DR, Bijlsma JW. Lowdose prednisone therapy for patients with early active rheumatoid arthritis: clinical efficacy, disease-modifying properties, and side effects: a randomized, double-blind, placebo-controlled clinical trial. Ann Intern Med. 2002; 136(1):1–12 [17] Colterjohn NR, Bednar DA. Identifiable risk factors for secondary neurologic deterioration in the cervical spine-injured patient. Spine. 1995; 20 (21):2293–2297 [18] Trent G, Armstrong GW, O’Neil J. Thoracolumbar fractures in ankylosing spondylitis. High-risk injuries. Clin Orthop Relat Res. 1988; 227(227):61–66 [19] Wright NM. Posterior C2 fixation using bilateral, crossing C2 laminar screws: case series and technical note. J Spinal Disord Tech. 2004; 17(2):158–162 [20] Larsson E-M, Holtås S, Zygmunt S. Pre- and postoperative MR imaging of the craniocervical junction in rheumatoid arthritis. AJR Am J Roentgenol. 1989; 152(3):561–566 [21] Hopkins JS. Lower cervical rheumatoid subluxation with tetraplegia. J Bone Joint Surg Br. 1967; 49(1):46–51 [22] Ranawat CS, O’Leary P, Pellicci P, Tsairis P, Marchisello P, Dorr L. Cervical spine fusion in rheumatoid arthritis. J Bone Joint Surg Am. 1979; 61(7):1003–1010 [23] Simmons EH. Kyphotic deformity of the spine in ankylosing spondylitis. Clin Orthop Relat Res. 1977(128):65–77 [24] Deviren V, Scheer JK, Ames CP. Technique of cervicothoracic junction pedicle subtraction osteotomy for cervical sagittal imbalance: report of 11 cases. J Neurosurg Spine. 2011; 15(2):174–181 [25] Chi JH, Tay B, Stahl D, Lee R. Complex deformities of the cervical spine. Neurosurg Clin N Am. 2007; 18(2):295–304 [26] Olerud C, Larsson BE, Rodriguez M. Subaxial cervical spine subluxation in rheumatoid arthritis. A retrospective analysis of 16 operated patients after 1– 5 years. Acta Orthop Scand. 1997; 68(2):109–115 [27] Fehlings MG, Smith JS, Kopjar B, et al. Perioperative and delayed complications associated with the surgical treatment of cervical spondylotic myelopathy based on 302 patients from the AOSpine North America Cervical Spondylotic Myelopathy Study. J Neurosurg Spine. 2012; 16(5):425–432 [28] Pahys JM, Pahys JR, Cho SK, et al. Methods to decrease postoperative infections following posterior cervical spine surgery. J Bone Joint Surg Am. 2013; 95(6):549–554 [29] Clarke MJ, Cohen-Gadol AA, Ebersold MJ, Cabanela ME. Long-term incidence of subaxial cervical spine instability following cervical arthrodesis surgery in patients with rheumatoid arthritis. Surg Neurol. 2006; 66(2):136–140, discussion 140

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Thoracolumbar [30] Agarwal AK, Peppelman WC, Kraus DR, et al. Recurrence of cervical spine instability in rheumatoid arthritis following previous fusion: can disease progression be prevented by early surgery? J Rheumatol. 1992; 19(9):1364– 1370 [31] Werle S, Ezzati A, ElSaghir H, Boehm H. Is inclusion of the occiput necessary in fusion for C1–2 instability in rheumatoid arthritis? J Neurosurg Spine. 2013; 18(1):50–56 [32] Koller H, Meier O, Zenner J, Mayer M, Hitzl W. Non-instrumented correction of cervicothoracic kyphosis in ankylosing spondylitis: a critical analysis on the results of open-wedge osteotomy C7-T1 with gradual Halo-Thoracic-Cast based correction. Eur Spine J. 2013; 22(4):819–832

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[33] Han K, Lu C, Li J, et al. Surgical treatment of cervical kyphosis. Eur Spine J. 2011; 20(4):523–536 [34] Etame AB, Than KD, Wang AC, La Marca F, Park P. Surgical management of symptomatic cervical or cervicothoracic kyphosis due to ankylosing spondylitis. Spine. 2008; 33(16):E559–E564 [35] Scheer JK, Tang JA, Deviren V, et al. Biomechanical analysis of cervicothoracic junction osteotomy in cadaveric model of ankylosing spondylitis: effect of rod material and diameter. J Neurosurg Spine. 2011; 14(3):330–335 [36] Scheer JK, Tang JA, Buckley JM, et al. Biomechanical analysis of osteotomy type and rod diameter for treatment of cervicothoracic kyphosis. Spine. 2011; 36(8):E519–E523

Thoracolumbar Osteoporosis

49 Thoracolumbar Osteoporosis Namath Syed Hussain, Mick J. Perez-Cruet, and Rod J. Oskouian Jr.

49.1 Osteoporosis The clinical definition of osteoporosis is low bone mineral density (BMD). Approximately 10 million Americans have this condition.1 Spinal instrumentation integrity depends not only on device integrity but also, more importantly, on integrity and strength of the bone–instrument interface. Bone fragility can lead to instrumentation failure and progressive deformity or pain with or without loss of function. A thorough medical workup for causes of osteoporosis should be undertaken before surgery is planned. Unrecognized medical conditions such as hypercortisolism, hyperparathyroidism, or multiple myeloma should all be considered as possible causes of accelerated osteoporosis and thoracolumbar fractures.2 There are three types of osteoporosis. Type I, or postmenopausal, occurs in women because of a decrease in estrogen levels. The fractures generally occur in patients between 50 and 60 years of age, predominantly in the distal radius and spine. Type II or senile osteoporosis occurs in men and women around 70 years of age. Type III or secondary osteoporosis occurs because of other medical conditions or treatments, most commonly steroid-induced osteoporosis (▶ Table 49.1). The basic pathology involves an imbalance between bone formation and resorption. Although adults lose bone mass at 0.5% per year, not every individual develops osteoporosis. The cause is multifactorial, involving environment, lifestyle, genetic, hormonal, medications, nutrition, and other disease processes. Not only does osteoporosis place a patient at risk of fracture, but also, once a fracture occurs, surgical fixation can be difficult. Laboratory tests such as complete blood count, comprehensive metabolic panel, erythrocyte sedimentation rate, serum and urine electrophoresis, and serum 25-hydroxy-vitamin D can clue the practitioner into underlying infectious and metabolic processes. Table 49.1 Causes of secondary osteoporosis Men and women

Hyperparathyroidism Thyroid disease Chronic lung disease Chronic glucocorticoid use Alcohol abuse Tobacco use Vitamin D insufficiency Low calcium intake Immobilization Diabetes mellitus (types 1 and 2) Adrenal insufficiency Malabsorptive gastrointestinal disease Rheumatoid arthritis Systemic lupus erythematosus Ankylosing spondylitis

Men

Hypogonadism Gonadotropin-releasing hormone agonist treatment

Women

Ovarian failure Amenorrhea

Dual energy X-ray absorptiometry is the most popular and well-validated method of measuring BMD.3,4 It directs X-ray energy from two different alternating sources toward the bone being examined at a set frequency. It is reported in the form of a T-score which indicates the number of standard deviations the measured results differ from a normative mean of young healthy women. A T-score of –2.5 or lower indicates osteoporosis. A Z-score is similar in that it compares bone density with a matched age, gender, and race cohort. The measurement is typically taken from the lumbar spine, femur, or radius.

49.2 Compression Fractures Patients with osteoporosis are at risk for vertebral compression fractures (VCFs). The annual incidence of new VCFs is 750,000. The cost of these fractures to the U.S. health system was $17 billion in 2005 and should exceed $25 billion by 2025.5 A past history of VCF greatly increases the risk for a second fracture. Patients usually present with severe pain, deformity, and loss of height. These fractures more commonly occur in the lower thoracic or upper lumbar spine. In people with severe osteoporosis, a VCF may be caused by simple daily activities, such as lifting a heavy object. Pain from thoracolumbar osteoporotic fractures often radiates to the posterosuperior iliac spine. On physical exam, the patient may resist assuming the supine position. Focal spinous process tenderness to palpation can also be present.

49.3 Symptoms The following is a brief list of symptoms of VCFs: ● Sudden onset of back pain. ● Increase of pain intensity while standing or lifting. ● Spinal height loss. ● Spinal kyphotic deformity. Spinal instability can produce pain and impair normal daily activities. The instability can cause accelerated degeneration of the spine in the affected and adjacent areas. This can result in vertebral body height loss and development of a kyphosis where the vertebra takes on a wedge shape because of anterior collapse (▶ Fig. 49.1). Severe multilevel kyphosis can cause pain and may even result in respiratory compromise.1 If the fracture impinges on the spinal cord or nerve roots, neurological deficits may develop.5 This lack of space can also lower the supply of blood to the spinal cord leading to tissue ischemia with pain and spinal cord infarction.

49.4 Diagnostic Tests The initial suspicion of a compression fracture can be made with an accurate clinical history and physical examination. Confirmatory imaging with plain X-rays, computed tomography, or magnetic resonance imaging is then undertaken. X-rays will also show bony alignment, disc degeneration, and osteophytes,

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Thoracolumbar bone healing and regeneration of the intervertebral disc, but human studies are still lacking. Adequate intake of calcium, phosphorus, and vitamin D is essential for normal fracture repair. Recommended daily intake is 1,200 mg of calcium and 800 IU of vitamin D. Systemic steroids can have deleterious effects on fracture healing.

49.6 Percutaneous Techniques When nonsurgical care does not improve symptoms or progressive deformity results, there are certain new minimally invasive percutaneous procedures that can help reduce pain and restore vertebral body height. These procedures are used for fractures that have been present for more than 2 weeks and have failed nonoperative care.

49.6.1 Vertebroplasty Fig. 49.1 Computed tomography (CT) image of L1 wedge compression fracture.

which may irritate nerve roots. Computed tomography can show the shape and size of the vertebral bodies along with the spinal canal and foramina. This can be supplemented with a myelogram to provide additional information. This diagnostic study is ideal for showing bone detail including stenosis. Magnetic resonance imaging provides better soft tissue detail and can also reveal marrow edema and endplate changes or microfractures.

49.5 Nonsurgical Treatment Pain from VCFs can be treated with rest, medications, or bracing. The pain generator is often vertebral instability at the fracture site, which leads to micromotion and irritation. Healing of these fractures can take 3 to 6 months. Tylenol and nonsteroidal anti-inflammatory drugs are used for symptomatic treatment. Muscle relaxants can also decrease motion-induced spasms. Bracing with a corset of thoracolumbar orthosis can limit the motion of fractured vertebrae. Patients with fractures are at risk for subsequent new fractures. Bisphosphonate therapy has been shown in multiple trials to be helpful in reducing the incidence of VCFs by 50 to 70%.5 Denosumab, a human monoclonal antibody, has been shown to inhibit bone remodeling more potently than even the bisphosphonates. Its effects on implant stability are unknown, but its effect on fracture healing is similar to alendronate.6,7,8 Bone morphogenic protein (BMP) is another drug class long used in spinal surgery for fusion. It is a member of the transforming growth factor-beta family that regulates osteogenesis through transcription factor signaling. Teriparatide is the only Food and Drug Administration–approved skeletal anabolic agent for severe osteoporosis. It has been shown to accelerate fracture repair. The final class of medical treatment for VCFs is stem cell therapy. Several animal studies have shown promise with respect to

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Vertebroplasty for VCFs was first introduced in 1987 and became popular in the 1990s. Using X-ray guidance, a Jamshidi needle is advanced along the pedicle into the vertebral body. Acrylic bone cement is then injected into the collapsed vertebra. The cement hardens within minutes, stabilizing the fractured vertebra. The hardening of the cement occurs via an exothermic reaction, which cauterizes small pain fibers in the bone trabeculae.9,10,11,12

49.6.2 Kyphoplasty A newer procedure, called kyphoplasty, involves inflation of a balloon called a bone tamp in the vertebral body. The balloon is then inflated with contrast medium, which is visualized using X-rays until they expand to the desired height and then removed. The spaces created by the balloons are then filled with the acrylic bone cement.10 Kyphoplasty, thus, can correct deformity. Complication rates for vertebroplasty and kyphoplasty have been estimated at less than 2% for osteoporotic VCFs.13,14 Although a large percentage of patients report significant pain relief, there is no guarantee that surgery will help every individual.

49.7 Instrumentation in the Setting of Osteoporosis 49.7.1 Posterior Approaches Osteoporotic spine fractures can manifest as compression fractures, burst fractures, and sacral insufficiency fractures.4 Osteoporotic patients not only have bone disease, but, because of the advanced age of this population, they also often have additional comorbid conditions that increase their overall operative risk. Transforaminal lumbar interbody fusion (TLIF) has in recent years become the workhorse of the spinal surgeon with respect to management of osteoporotic VCFs. Minimally invasive TLIFs provide similar results with reduced morbidity and patient hospital stay (▶ Fig. 49.2 and ▶ Fig. 49.3). In addition, BMD next to a fusion has been found to be higher. At one, two, and three levels away from a fusion construct,

Thoracolumbar Osteoporosis

Fig. 49.2 Lateral X-ray of METRx approach for transforaminal lumbar interbody fusion (TLIF).

Fig. 49.3 Pedicle cannulation for minimally invasive screw placement.

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Fig. 49.4 Mini-thoracotomy approach for spinal fusion.

there was a 14.8, 10.8, and 9.5% increase, respectively, in normalized BMD when compared with the mean 4-year fusion values (p < 0.05).7

49.7.2 Anterior Approaches Severe deformity can often preclude the use of posterior approaches. Anterior surgical methods can provide immediate vertebral body height restoration and correct deformity. It provides a powerful option for the spinal surgeon with the correct training and experience. Access issues are the main cause of morbidity in this class of surgical procedures, but these have been minimized with newer minimally invasive techniques like the mini-thoracotomy approach (▶ Fig. 49.4).15 Anterior lumbar approaches also carry morbidity because of the proximity of vascular and lymphatic structures (▶ Fig. 49.5).16 Because of the access issues with these approaches, lateral approaches have been developed, providing a powerful option for deformity correction and fusion (▶ Fig. 49.6).17,18,19,20

49.8 Operative Adjuncts Fusion can be a problem with osteoporotic spines. Several companies have developed multiple products with different

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combinations of osteoconductive, osteoinductive, and osteogenic properties. The only graft that has all three properties is autograft. Owing to cost issues along with a realization that collection of autograft does not have to be a cumbersome process, a renewed interest into local autograft collection has emerged. Products and methods have been developed to more easily collect autograft bone and use it in the fusion construct (▶ Fig. 49.7).21

49.9 Conclusion Likely due in large part to its high percentage of trabecular bone, the spine is an important and often critically affected site when it comes to osteoporosis. Although osteoporosis is a systemic disease process, localized factors and the special role the spine plays in electrolyte homeostasis along with the functional loads it bears make a working understanding of thoracolumbar osteoporosis vital for any spine surgeon. Knowledge of normal anatomy and physiology and how this disease process affects the spine can clue the practitioner into better methods of treating this often debilitating and chronic disease process. New research into drugs that reduce bone loss coupled with surgical methods and instrumentation that can shore up and stabilize diseased segments can help improve patients’ quality of life and restore function.

Thoracolumbar Osteoporosis

Fig. 49.5 Anterior lumbar approach showing vascular, urinary, nerve, and lymphatic structures at risk.

Fig. 49.6 Lateral interbody fusion.

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Fig. 49.7 BoneBac Press for autograft collection.

References [1] Body JJ, Bergmann P, Boonen S, et al. Evidence-based guidelines for the pharmacological treatment of postmenopausal osteoporosis: a consensus document by the Belgian Bone Club. Osteoporos Int. 2010; 21(10):1657–1680 [2] Wong P, Anpalahan M. Osteoporotic fractures and vitamin D deficiency. Aust Fam Physician. 2006; 35(7):519–520, 522 [3] Okano K, Ito M, Aoyagi K, Osaki M, Enomoto H, Yamaguchi K. Discrepancy in bone mineral densities at different skeletal sites in hip osteoarthritis patients. Mod Rheumatol. 2013 [4] Meredith DS, Taher F, Cammisa FP, Jr, Girardi FP. Incidence, diagnosis, and management of sacral fractures following multilevel spinal arthrodesis. Spine J. 2013; 13(11):1464–1469 [5] Dodwad SM, Khan SN. Surgical stabilization of the spine in the osteoporotic patient. Orthop Clin North Am. 2013; 44(2):243–249 [6] Cummings SR, San Martin J, McClung MR, et al. FREEDOM Trial. Denosumab for prevention of fractures in postmenopausal women with osteoporosis. N Engl J Med. 2009; 361(8):756–765 [7] Singh K, An HS, Samartzis D, et al. A prospective cohort analysis of adjacent vertebral body bone mineral density in lumbar surgery patients with or without instrumented posterolateral fusion: a 9- to 12-year follow-up. Spine. 2005; 30(15):1750–1755 [8] Gerstenfeld LC, Sacks DJ, Pelis M, et al. Comparison of effects of the bisphosphonate alendronate versus the RANKL inhibitor denosumab on murine fracture healing. J Bone Miner Res. 2009; 24(2):196–208 [9] Gu Y, Zhang F, Jiang X, Jia L, McGuire R. Minimally invasive pedicle screw fixation combined with percutaneous vertebroplasty in the surgical treatment of thoracolumbar osteoporosis fracture. J Neurosurg Spine. 2013; 18(6):634– 640 [10] Hussain NS, Perez-Cruet MJ. Complication management with minimally invasive spine procedures. Neurosurg Focus. 2011; 31(4):E2 [11] Lai PL, Chen LH, Chen WJ, Chu IM. Chemical and physical properties of bone cement for vertebroplasty. Biom J. 2013; 36(4):162–167

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[12] Pneumaticos SG, Triantafyllopoulos GK, Evangelopoulos DS, Hipp JA, Heggeness MH. Effect of vertebroplasty on the compressive strength of vertebral bodies. Spine J. 2013; 13(12):1921–1927 [13] Liu D, Shi L, Lei W, et al. Biomechanical comparison of expansive pedicle screw and polymethylmethacrylate-augmented pedicle screw in osteoporotic synthetic bone in primary implantation: an experimental study. Clin Spine Surg. 2016; 29(7):E351–E357 [14] Kolb JP, Kueny RA, Püschel K, et al. Does the cement stiffness affect fatigue fracture strength of vertebrae after cement augmentation in osteoporotic patients? Eur Spine J. 2013; 22(7):1650–1656 [15] Hussain NS, Perez-Cruet M. Mini-thoracotomy approach. In: Perez-Cruet MJ, Beisse R, Pimenta L, Kim, DH, eds. Minimally Invasive Spine Fusion: Techniques and Operative Nuances. St. Louis, MO: Quality Medical Publishing; 2011:345–367 [16] Hussain NS, Hanscom D, Oskouian RJ, Jr. Chyloretroperitoneum following anterior spinal surgery. J Neurosurg Spine. 2012; 17(5):415–421 [17] Hussain NS, Iqbal O, Oskouian RJ. Clinical outcomes, complications, and deformity correction in lateral transpsoas interbody fusion. Pennsylvania Neurosurgical Society’s 100th Scientific Meeting, July 12–13; 2013 [18] Caputo AM, Michael KW, Chapman TM, et al. Extreme lateral interbody fusion for the treatment of adult degenerative scoliosis. J Clin Neurosci. 2013; 20 (11):1558–1563 [19] Pimenta L, Marchi L, Oliveira L, et al. A prospective, randomized, controlled trial comparing radiographic and clinical outcomes between stand-alone lateral interbody lumbar fusion with either silicate calcium phosphate or rhBMP2. J Neurol Surg A Cent Eur Neurosurg 2013;74(6):343–350 [20] Ahmadian A, Verma S, Mundis GM, Jr, Oskouian RJ, Jr, Smith DA, Uribe JS. Minimally invasive lateral retroperitoneal transpsoas interbody fusion for L4–5 spondylolisthesis: clinical outcomes. J Neurosurg Spine. 2013; 19(3):314–320 [21] Hussain NS, Oskouian RJ, Hanscom D, et al. Initial Clinical Experience of 400 Patients Treated with the BoneBac PressTM: A Novel Autologous Bone Graft Harvesting and Collection Device. CNS Annual Meeting, San Francisco, CA; 2013

Thoracolumbar Instrumentation in Patients with Spondyloarthropathies

50 Complications of Thoracolumbar Instrumentation in Patients with Spondyloarthropathies Heidi Martin Hullinger and Rex A. W. Marco

50.1 Overview of Chapter Thoracolumbar pathology in patients with spondyloarthropathies varies depending on the specific disease. For example, whereas some arthritides, such as rheumatoid arthritis (RA), have primarily erosive and destabilizing effects on the spinal column, others are characterized by the formation of bone. The most common of these latter arthritides is ankylosing spondylitis (AS), which will be a primary focus of this chapter. Another less common spondyloarthropathy affecting the thoracolumbar spine is ossification of the posterior longitudinal ligament, or OPLL. Surgery to the thoracic or lumbar spine may be indicated for patients with either of these conditions. Reasons for surgery in AS patients include traumatic injury, pseudoarthrosis, and fixed kyphotic deformity. Meanwhile, patients with OPLL may be indicated for surgery because of stenosis with resultant myelopathy. Surgical treatment of these conditions is particularly risky in both groups of patients because of the nature of the underlying disease, more so than the particular instrumentation used. There are multiple surgical techniques that can be utilized for the management of these disorders, and each will be discussed here, along with their respective risks. Whereas RA can cause instability throughout the cervical spine, RA patients do not tend to develop thoracolumbar pathology that differs from non-RA patients, and thus RA will not be a focus of this chapter.

50.2 Pathophysiology of Spondyloarthropathies AS is a seronegative inflammatory arthropathy that primarily affects the spinal column and sacroiliac joints. It is associated with the human leukocyte antigen B27 phenotype and most commonly affects males, with an age of onset of between 20 and 40 years.1 It characteristically causes inflammation at the insertion of ligaments or tendons into the bone, termed enthesitis.2,3 Unlike RA, in which inflammation leads to erosion of bone, new bone, in the form of enthesophytes and syndesmophytes, is formed in patients with AS. Syndesmophytes bridge vertebral bodies, as well as zygapophyseal joints, leading to the pathognomonic “bamboo spine” of AS. This bridging of vertebral bodies by syndesmophytes in essence turns the spine into a long bone, making it stiffer and thus less capable of absorbing the shock of even minor trauma. This stiffening of the spine also leads to stress shielding within individual vertebral bodies; the resultant secondary osteoporosis is compounded by bony resorption from the inflammatory component of the disease.3,4,5 In addition, hyperkyphosis and loss of lordosis tend to occur in affected areas of the spinal column, making the spinal column particularly susceptible to extension forces. For all of these reasons, patients with AS are more prone to a hyperextension-type fracture after even mild trauma such as a fall from standing; the lifetime incidence of a

significant spinal fracture in these patients has been estimated at 4 to 18%.2 A less common fracture pattern seen in these patients after acute trauma is a flexion–distraction injury manifesting as a chance fracture, which typically traverses the disc space rather than the vertebral body.1,6 Whereas shearing-type forces can lead to acute traumatic injuries in the ankylosed spine, subacute and chronic lesions in these patients are often secondary to compressive forces. The secondary osteoporosis that can arise in these patients further increases the risk of compression fractures.7 A pre-existing kyphotic deformity can compound the situation because the resulting positive sagittal balance places further stress on the anterior column. Chronic compressive microfractures can lead to fibrosis as a result of the continuous micromotion at the site as well as the large ankylosed lever arms on either side. Occult fractures that go unrecognized can develop into pseudoarthroses because of the inherent instability of many of these fractures. Whereas pseudoarthroses, also termed Andersson lesions or spondylodiscitis, were historically thought to be primarily inflammatory in nature, recent reports have identified a subset of patients whose pseudoarthroses stem from occult fractures and not inflammation.8,9 Whereas inflammatory lesions may be treated medically, traumatic lesions may require surgical management given their potential to cause continued pain and/or instability. The kyphotic deformity that develops in these patients can itself become disabling, particularly as it becomes fixed. When kyphosis occurs in the thoracic and lumbar spine, patients can develop a grossly positive sagittal balance. Positive sagittal balance is increasingly being recognized as a huge detriment to quality of life.10,11 Patients with severe deformities can thus be well served with corrective osteotomies. Options for osteotomies in these patients include an opening-wedge osteotomy such as a traditional Smith–Peterson procedure and closingwedge osteotomies such as a Ponte osteotomy or a pedicle-subtraction osteotomy. OPLL is another spondyloarthropathy characterized by abnormal ossification of soft-tissue structures. Whereas this entity most frequently affects the cervical spine, it may also affect the thoracic spine. It is more frequently seen in Asians, particularly in those of Japanese descent, and there is evidence that genetics do play a role in the development of OPLL, though this has not been fully elucidated. Though, like AS, OPLL can create ankylosis across spinal segments, the most common pathology requiring surgical intervention in these patients is myelopathy resulting from the ossified posterior longitudinal ligament compressing the spinal cord. Compression may be compounded by ossification of the ligamentum flavum. Once patients are frankly myelopathic, surgical decompression confers the most optimal outcome. The options for decompression include posterior decompression, anterior decompression through a posterior approach, and anterior decompression through an anterior approach. Whereas all of these have been associated with some level of success, patients undergoing any of them are at a high

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Thoracolumbar risk of further neurologic compromise given the intimacy of the ossified ligament with the dura, as well as the fragility of an already-compromised spinal cord. Details regarding patient selection for the various surgical options and ways to lessen complication rates will be discussed further in the chapter.

50.3 Acute Trauma in Patients with AS As noted above, patients with AS and other ankylosing disorders are uniquely susceptible to spinal fractures after even minor trauma. Because the spine in these patients acts as a long bone, these fractures nearly always span all three columns of the spine, creating a highly unstable injury. Ossification of many of the stabilizing soft-tissue structures such as the anterior longitudinal ligament and PLL makes them more likely to be disrupted as part of the fracture pattern, further destabilizing the spinal column. Whereas instrumentation of the thoracolumbar spine in any trauma patient can have complications, such as pedicle breakthrough and loss of alignment, the gravest complications in these patients stem either from failure to recognize potential for concomitant injuries or from failure to maintain appropriate alignment at all times. During the initial evaluation of any patient with AS presenting with a thoracolumbar spine fracture, one must maintain a high index of suspicion for concomitant injuries, given that up to 8% of patients can have a noncontiguous fracture.12 It is crucial to fully image the spine, with particular focus on the cervicothoracic junction, which is particularly prone to injury. Because plain radiography cannot adequately visualize the cervicothoracic junction, computed tomography (CT) scanning is the best modality to evaluate for injury in this region. In fact,

some authors recommend CT scanning of the entire spinal column in any AS patient undergoing workup for a spinal fracture.12 Displacement of an undiagnosed contiguous fracture, particularly in the cervicothoracic junction, may lead to a catastrophic neurologic injury. In Caron’s 2010 study, a delay in the diagnosis of a spinal fracture in AS patients was associated with an 81% likelihood of decline in neurologic function.12 For similar reasons, there should be a low threshold for advanced imaging in any patients with AS who have sustained any type of trauma, including patients without a fracture diagnosed on initial imaging (▶ Fig. 50.1). A thorough physical exam is essential to identify any areas of potential injury, and CT scanning can show fractures that may not be seen on plain radiographs. Even if imaging does not show a fracture, the patients should then be followed closely to ensure they do not have continued pain or an evolving neurologic deficit indicative of an occult fracture. Because these patients often have a preexisting kyphotic deformity, after a traumatic injury they should be positioned at all times in a way that closely approximates the pre-injury state, thus keeping the spinal column in its usual alignment. If these patients are laid flat, the rigid spine will not be able to accommodate, so they will compensate by extending through the fracture site, with resultant potential for neurologic decline (▶ Fig. 50.2). Pillows can be used to prop up the trunk when laying patients supine; if patients have difficulty with fitting into a magnetic resonance imaging (MRI) scanner in this position, the hips may be elevated instead to allow the torso to be closer to the gurney.5 Another complication that can arise is the failure to recognize an epidural hematoma, which is significantly more common in these patients than in a standard trauma patient. The syndesmophytes seen in AS consist of immature, poorly organized

Fig. 50.1 Advanced imaging performed on an ankylosing spondylitis patient after a low-energy trauma; attention was paid to compression fractures in the lower lumbar spine, and thus the T10 hyperextension-type fracture, as noted by the white arrows, was not detected. The patient was discharged home, and later presented with neurologic deterioration and displacement of the fracture, as seen in ▶ Fig. 50.2.

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Thoracolumbar Instrumentation in Patients with Spondyloarthropathies

Fig. 50.2 Typical fracture displacement pattern seen in ankylosing spondylitis patients with a three-column injury, with extension– distraction about a dorsal fulcrum point.

bone that have a significant bleeding potential, which is further increased by the presence of inflammatory tissue. Thus, fractures that cross through bridged regions can bleed substantially and lead to the formation of an epidural hematoma. Given that this is seen in 7 to 8% of AS patients with trauma to the spine,6,12 it should be routinely ruled out, and any deterioration of a patient’s neurologic status that is not explained by a change in positioning necessitates immediate MRI to look for this complication.4,13 Patients with fractures that cross all three columns should generally undergo surgery to stabilize the spine unless they have significant medical comorbidities. The most common construct is a long posterior one; short constructs can fail because of stress from the long lever arms on either side of the fracture. In Caron’s study, there were no failed constructs in 58 patients treated with posterior fixation with at least three instrumented

levels above and below the fracture.12 Pedicle screw constructs are ideal for these highly unstable injury patterns as they accomplish three-column fixation. If laminar hooks are used, one must keep in mind the potential for ossification of the ligamentum flavum, which can necessitate thinning of the lamina or modification of the construct.4 Anterior instrumentation is used less commonly, in part because it can compromise pulmonary function in patients already susceptible to pulmonary complications; up to 35% of these patients can have pulmonary complications even without undergoing an anterior approach.12 Circumferential fusion with an anterior–posterior approach may be indicated, however, if anterior bony contact that restores anterior column stability cannot be obtained, as in patients with the “fish-mouth” deformity that can be seen in distraction–extension injuries.6 Rib harvest for autograft bone is generally not recommended if a posterior-only approach is being used, given the theoretical risks of pulmonary compromise.3 An iliac crest bone harvest also may not be advisable in such patients because it can reduce postoperative mobility, thereby worsening pulmonary status and increasing surgical morbidity. An allograft or local bone graft may be the best option in this setting. No matter which approach is undertaken, it is positioning and reduction maneuvers, and not the instrumentation itself, that pose the greatest intraoperative risks in AS patients undergoing surgery for the management of spinal fractures. When positioning a patient, one must keep in mind the preexisting kyphotic deformity, particularly with regard to the cervical spine and cervicothoracic junction. The patient’s neck should not be extended beyond the functional range, and it should be stabilized in line with the preexisting deformity. Reduction maneuvers, meanwhile, should be performed in a controlled fashion, and should avoid any localized stress on other vulnerable areas of the spine. Fluoroscopy can be used to visualize the vulnerable cervicothoracic region during or just after the reduction of a spinal fracture in patients with rigid kyphosis.5 Any postoperative change in alignment or pain at a site distant from the site of the procedure is cause for immediate evaluation for a possible iatrogenic fracture. Even when all proper precautions are taken, these patients remain at an increased risk of complications perioperatively, including pulmonary complications potentiated by preoperative restrictive pulmonary disease.14 Whereas thoracolumbar injuries are not associated with as high a rate of spinal cord injury as cervical fractures in these patients, the rate of spinal cord injury still ranges from 30 to 75%.4,6,12 Of these patients, only 30 to 55% achieve appreciable neurologic recovery following surgical management.4,12 Overall, the mortality rate in these patients is much higher than that in patients without ankylosis who undergo surgery for a spinal fracture. This is especially striking when one considers the, at times, outwardly benign nature of some of their injuries. In studies of AS patients with injuries at any spinal level, mortality rates were as high as 21%,12 which is in stark contrast to mortality rates of less than 0.5% in patients without AS who undergo similar surgeries to manage a spinal fracture.1 Meanwhile, in a small cohort of patients with AS who sustained injuries only in the thoracolumbar region, the mortality rate was 13%.15 Thus, not only must the treating physician be vigilant throughout the perioperative period when caring for AS patients with these injuries,

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Thoracolumbar but they should also counsel patients regarding the serious nature of these injuries and the potential morbidity and mortality associated with them. A late surgical complication is failure of the construct, and this is a particular risk in patients with secondary osteoporosis and in those with a severe kyphotic deformity that places greater stress on the construct. If a patient’s poor bone quality is a concern intraoperatively, measures that can lessen the chance of failure include the use of a larger caliber rod, utilizing stainless steel or cobalt-chrome, or augmenting the screws with polymethyl methacrylate.3 To further prevent construct failure, patients should be maintained in an external orthosis postoperatively.3,6,14 If the hardware fails despite these measures, one must determine the source of the failure to determine how best to proceed. If anterior bone is anticipated or found to be inadequate, support of the anterior column with 360-degree fixation should be strongly considered. Meanwhile, if at the time of the primary surgery, a kyphotic deformity is anticipated to place excessive stress on the construct, an osteotomy with fixation can be done concomitantly. Whereas this is infrequently performed in the thoracolumbar region, there have been brief descriptions of its use in the literature.3,4 Alternatively, if the hardware has already failed because of kyphotic deformity, a correction can be undertaken during revision fixation. However, combining an osteotomy with fracture fixation or construct revision should be undertaken only with extreme caution because it compounds the risks of fracture fixation in these patients with the potential morbidity of deformity correction. Further details regarding the management of kyphotic deformities via osteotomies and the potential complications can be found later in this chapter. While not, strictly speaking, a spondyloarthropathy, diffuse idiopathic skeletal hyperostosis (DISH) can lead to similar injury patterns as those seen in patients with AS following a lowenergy trauma. Unlike the marginal syndesmophytes that are pathognomonic for AS, DISH patients have large flowing osteophytes that extend across at least four vertebral levels. Whereas a spinal fracture in these patients is more likely to pass through the vertebral body than the intervertebral disc, as is seen in AS patients,1,6 DISH patients also commonly sustain a hyperextension-type injury. In comparative case series, the rates of spinal cord injury have been found to be lower in DISH than AS patients, though the rate is still significant at upward of 50%.6 Management of injury in these patients, as in patients with AS, generally consists of a long posterior construct and, if appropriate, anterior augmentation. Special attention to intraoperative positioning and the need to accommodate a previous kyphotic deformity are similarly important in these patients to decrease the risk of catastrophic injury. Finally, even despite all precautions, these patients are also at high risk of morbidity and mortality, with mortality rates upward of 30%.12,16

50.4 Pseudoarthrosis in Patients with AS As noted earlier, whereas pseudoarthroses were once thought to be solely inflammatory lesions, more recently a subset of these lesions has been recognized to be the sequelae of trauma present in a subacute or chronic fashion. Traumatic lesions can

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be differentiated from inflammatory lesions by increased sclerosis and hypertrophy at the edges of the lesion, as may be seen in a nonunion in the appendicular skeleton, and possibly by a history of a remote injury.8,9 Localized kyphosis at the site is also frequently seen in these injuries. Whereas inflammatory lesions can be treated medically by interrupting the inflammatory cycle, traumatic lesions should be treated in a manner similar to that used for acute fractures, with consideration for surgical management. Surgical treatment is especially recommended for unstable posttraumatic lesions.8,9 Neurologically intact patients with a lesion within the thoracic spine are candidates for nonsurgical management consisting of a spinal orthosis, if their habitus is amenable to brace wear.9 However, often these lesions occur about the thoracolumbar junction, and because of the increased motion in this location, surgical management should be strongly considered in these cases. A variety of surgical approaches have been used in the management of a traumatic-type pseudoarthrosis. As in management of acute fractures, posterior instrumentation is key to the restoration of a posterior tension band, particularly in patients with local kyphosis. However, while concomitant correction of a kyphotic deformity is uncommon in the treatment of acute injuries, it is often undertaken during surgical management of pseudoarthroses.8,17,18 In these cases, a long posterior construct, generally consisting of pedicle screws, is utilized to stabilize and maintain the correction during the healing phase. Because the anterior column is already disrupted at the site of the pseudoarthrosis, an opening wedge osteotomy is the usual method of obtaining correction of the local kyphosis. This is at times combined with an additional osteotomy, particularly in the lower lumbar spine, to restore overall sagittal balance. Details of surgical techniques for osteotomies are detailed in the below section. Just as one would manage a nonunion in the appendicular skeleton, some authors advocate for the use of a concomitant anterior approach to remove fibrotic nonunion material and to pack bone graft into the resultant defect. Most authors also recommend placing an interbody graft to support the anterior column when concomitant correction is performed.1,18 Small case series utilizing this technique, including use of an interbody graft, have found greater than 85% fusion rates and high satisfaction rates in the long term.18,19 However, as noted earlier, an anterior approach is associated with a high risk of cardiopulmonary compromise during the perioperative period, in part because of preexisting disease, so this must be taken into consideration when planning treatment in these patients. Because of pulmonary concerns, some authors have advocated for use of posterior-only approaches in these patients, either with or without a corrective osteotomy. Chang et al, having noted high healing rates in AS patients who undergo opening-wedge osteotomies for management of a kyphotic deformity, used the same technique to correct kyphosis in patients with a traumatic pseudoarthrosis. They used a long posterior construct with pedicle screws to support the correction and allow healing, and they did not place an interbody graft. Their results in 30 patients, including neither nonunions nor significant loss of correction, suggest the merits of their approach.17 Dave et al, meanwhile, advocate the use of shortsegment posterior instrumentation without any concomitant

Thoracolumbar Instrumentation in Patients with Spondyloarthropathies osteotomy in these patients because these patients are often older and are at high risk of perioperative complications because of their chronic disease. Their technique focuses solely on healing the pseudoarthrosis to avoid a lengthy procedure, and in their series resulted in low rates of major complications.9 However, one must keep in mind that these patients’ secondary osteoporosis may necessitate adding-on levels to achieve appropriate mechanical stability, and thus one must be prepared for this possibility intraoperatively.

50.5 Surgical Management of Kyphotic Deformity in Patients with AS A fixed kyphotic deformity and positive sagittal balance can be debilitating in patients with AS, particularly given the progressive nature of the disease. Various osteotomies may be used to correct patients’ alignment and restore their sagittal balance; these fall into the broad categories of opening-wedge and closing-wedge osteotomies. The classic opening-wedge osteotomy is the traditional Smith–Peterson osteotomy (SPO). Closingwedge osteotomies include pedicle-subtraction osteotomies and modified Smith–Peterson or Ponte osteotomies.2,20 Ponte osteotomies obtain a less powerful correction, so they are often performed at multiple levels, termed polysegmental-wedge osteotomies. Like the surgical treatment of traumatic injuries in patients with AS, the surgical treatment of kyphotic deformities in these patients can be fraught with complications, and the complications specific to each of the above techniques must be carefully weighed when planning treatment. The traditional SPO was first described for use in patients with AS because of the ability to open the spine anteriorly through the disc space in these patients. The anterior column can potentially be lengthened more than in nonankylosed individuals because the disc, having lost its normal properties because of ankylosis, no longer acts as a constraint. An SPO thus has the potential to powerfully correct a patient’s kyphosis by closing down the posterior column while simultaneously lengthening the anterior column. If the anterior column is fused rigidly by syndesmophytes, an anterior approach must be undertaken to perform osteoclasis and allow the anterior column to lengthen. If anterior osteoclasis is not necessary, fusion can be reliably obtained even without an interbody graft anteriorly. In this case, one can address the deformity from an all-posterior approach utilizing a long, rigid construct.21 Whereas short-segment hook-and-rod systems were used before the advent of pedicle screws, nowadays pedicle screw constructs are the standard, as they rigidly maintain the osteotomized segment while bone forms in the anterior defect.20,22 The potential need to use an anterior approach is a downside of this technique in this patient population, as detailed earlier. However, a greater concern in these patients is the potential for catastrophic injury because of the lengthening of the anterior column and adjacent structures. Patients with arteriosclerosis and hardening of the major vessels evident on preoperative imaging should not undergo this type of osteotomy because of the risk of a tension-induced injury to the vessel walls.22,23,24 Even in patients without arteriosclerosis, adventitial scarring

and tethering of the aorta can occur secondary to the inflammatory disease process, making it vulnerable to injury during lengthening of the anterior column.3 Other potential side effects of anterior lengthening include tension injury to the thecal sac, superior mesenteric artery syndrome, and paralytic ileus.23 Some authors have also cited osteoporosis as a relative contraindication to this correction technique, because there is not a broad base of bony support of the correction as there is in closing-wedge osteotomies.20,22 Pedicle-subtraction osteotomies have the benefits of producing immediate stability from a broad base of bony contact and avoiding anterior column lengthening. However, the blood loss associated with this technique is significantly higher than that associated with an opening-wedge technique, averaging 2,000 to 2,500 mL.20,22,25 As noted in the subsection dealing with fractures in these patients, the very nature of these patients’ tissues puts them at higher risk for bleeding complications; secondary complications seen in tandem with excessive blood loss in AS patients undergoing PSO include myocardial infarction, abdominal compartment syndrome, and a visual field defect because of intraoperative hypotension.25 Whereas in openingwedge osteotomies the neural elements are at risk of injury from a tension injury, in a closing-wedge osteotomy, one must be careful not to damage the neural elements by overshortening the posterior column and causing kinking and compression of the cord or thecal sac. To lessen this risk, it is of utmost importance to ensure thorough removal of any potentially impinging posterior structure such as overhanging lamina or, in particular, ossified ligamentum flavum. In addition, some have recommended that the angular correction in a closing-wedge osteotomy be limited to less than 40 to 45 degrees to decrease the potential for injury.22 Polysegmental wedge osteotomies can be used in patients with AS to obtain a more gradual correction along a region of kyphosis; they can also be created asymmetrically to simultaneously correct any coronal deformity. Blood loss in patients treated with this technique has been noted in some series to be as high as that in patients treated with pedicle-subtraction osteotomies,20 while other series have noted significantly less blood loss in these patients.25 A potential complication of this technique stems from the need to perform osteotomies at multiple sites to achieve a large correction, which heightens the potential for loss of correction and/or decompensation in both the coronal and sagittal planes.25,26 Regardless of the technique chosen, there are important considerations when managing deformity in these patients as compared to a nonankylosed population. For example, because of the large, rigid lever arms on either side of an osteotomy in these patients, once the cuts are fully made, there is an increased risk of translation of one lever arm relative to the other, causing neural or vascular injury. To decrease this risk, relative stability should be maintained as the osteotomy is being created. This can be obtained by placing pedicle screws before performing the osteotomy, and then either maintaining a single rod or two malleable rods while finishing the osteotomy and initiating the corrective maneuver.20,27 In addition, when working near the dura during removal of posterior elements, one must keep in mind that the chronic inflammation in these patients can thin the dura and cause dural adhesions, making these patients more prone to dural tears.23,26 Most

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Thoracolumbar importantly, just as positioning is of utmost importance in AS patients who have sustained trauma, one must be careful to not place undue tension on adjacent regions of the ankylosed spine when obtaining correction through the osteotomy. The safest way to obtain the correction is via external manipulation by means of a change in the bed positioning or careful external manipulation of the torso, instead of relying on compression or cantilevering through the hardware.23,27 If an iatrogenic fracture is suspected postoperatively, further evaluation is mandatory to prevent devastating neurologic injury.

50.6 Surgical Management of Myelopathy in Thoracic OPLL Though OPLL more commonly affects the cervical spine than the thoracic spine, myelopathy secondary to OPLL in the thoracic spine is particularly difficult to manage, with surgical outcomes being less favorable than those seen in patients with cervical OPLL.28,29 When a posterior-only approach is used, the natural kyphosis of the thoracic spine makes it difficult to achieve full decompression. However, because of anatomic constraints, it is more difficult to approach the affected regions via an anterior approach to perform a direct decompression or extirpation.30 The options in these patients include decompression alone from a posterior approach, anterior decompression from a posterior approach, and direct anterior decompression. Anterior decompression can be achieved by either extirpating the compressive lesion or “anterior floating” of the ossified ligament. Despite this multitude of options, all of the above techniques carry a significant risk of neurologic decline in this patient population. However, as the natural history of OPLL is progression of the lesion and further neurologic deterioration, surgical management is nonetheless the treatment of choice for nearly all of these patients once myelopathy develops. Options for sole posterior decompression include laminectomy and laminoplasty. A benefit of the posterior approach is that one can then resect ossified ligament flavum, which can contribute to the spinal cord compression. However, posterior decompression can induce instability and further kyphosis. In turn, neural tissue that has already been compromised as a result of chronic compression may actually be further impinged upon by the ossified PLL anteriorly.30,31 This is of particular risk when performing a laminectomy without instrumentation. For this reason, laminectomy without fusion is generally not recommended, particularly in the middle and lower thoracic spine, which is most prone to further kyphosis. Similarly, when performing a laminectomy and fusion, instrumentation should be placed before the decompression is performed to achieve relative stability and thus lessen the risk of an acute-on-chronic spinal cord injury.29,30 Pedicle screw constructs are used most often to increase the stability and allow use of a shorter construct, though hook-and-rod systems may also be used. Laminoplasty has less potential for instability and worsening kyphosis because of the maintenance of the midline soft-tissue stabilizers, and therefore was traditionally thought to be a safe procedure for patients with thoracic-level OPLL. However, Matsuyama et al reported two cases of neurologic deterioration following laminoplasty for OPLL of the thoracic spine, which they attributed to an increase in instability after the decompression.

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They noted that this only occurred in patients with beaked patterns of ossification, in which the PLL has peaked foci of ossification at the disc spaces instead of maintaining a more flat configuration. Thus, they recommended that neither laminectomy nor laminoplasty be undertaken in patients with this beaked pattern of ossification.29 Direct decompression of the compressive ossification can be obtained using either a direct anterior approach or a posterior approach. The anterior approach, however, requires one to enter the chest cavity, which increases the risk of a pulmonary complication postoperatively. Using an anterior approach can also be more technically difficult in OPLL patients because of their increased kyphosis. One cannot address ligamentum hypertrophy directly from an anterior approach; thus, a circumferential decompression in this setting requires two approaches and patient repositioning, which adds time to an already complex procedure. For this reason, some authors have advocated use of an all-posterior approach for a 360-degree decompression. Multiple techniques of performing an anterior decompression from a posterior approach have been described. A costotransversectomy may be used to directly approach large compressive lesions, but is best used for a focal lesion because of the morbidity associated with the procedure. As this procedure destabilizes the spine, a structural graft such as a rib strut must be placed anteriorly.32 Variations on transpedicular approaches have been described for the surgical management of lesions spanning multiple levels, with some authors leaving the pedicle largely intact if the canal allows and others removing the medial portion of the pedicle, pars, and facet to better approach the anterior aspect of the spinal column. In each of these techniques, one first removes any adherent tissue between the ossified PLL and the dura, after which one may either remove the lesion or leave it to float anteriorly. However, if a lesion extends all the way back from the vertebral body to make contact with the cord, there is no room in which to remove the adhesions without placing excessive pressure on the cord. For this reason, a transpedicular-type technique should not be used in patients in whom this morphology is seen on preoperative imaging. Another disadvantage of a transpedicular technique is the higher rate of dural tears than a posterior-only decompression because of increased manipulation about the fragile, adhesed dura, with rates of tears up to 57% as compared to approximately 20%.28 Patients with lesions that span multiple vertebral levels are at an even higher risk of dural tears when utilizing this type of technique, as the ossified lesions must be broken up into separate fragments to lessen the risk of injury to segmental nerves. When managing a dural tear in these patients, one should have fibrin glue on hand to use as an adjunct, given the dura may be difficult to primarily repair because of chronic inflammatory changes.32 There are a limited number of studies that directly compare the various decompression techniques in patients with thoracic OPLL, but heterogeneous case series have revealed trends that can help one decide on the optimal treatment in a particular patient. Findings from these studies have also better defined the complications more common to each. In general, patients who undergo any type of posterior-only decompression tend to not show as dramatic an improvement in their neurologic status as patients undergoing a 360-degree decompression. This is

Thoracolumbar Instrumentation in Patients with Spondyloarthropathies likely because of the fact that there is still a compressive lesion anteriorly in the kyphotic thoracic spine.28,30,31 Meanwhile, studies are more mixed as to whether neurologic recovery is better after use of an anterior–posterior approach or an all-posterior approach to circumferentially decompress. One caveat is that an extracavitary or anterior–posterior approach, not a transpedicular-type approach, should be used in patients with lesions that directly contact the dura, to lessen the risk of catastrophic injury.31,33 Though rates of neurologic recovery are higher after any type of circumferential decompression than after posterior-only decompression, with 80 versus 45 to 50% of patients experiencing greater than 50% recovery, the rates of postoperative deterioration are also significantly higher after circumferential decompression. Proper patient selection is the best way to mitigate this risk of neurologic deterioration. Most authors recommend that patients who are nonambulatory because of myelopathy should not undergo circumferential decompression, both because this is a sign that the cord is more fragile in these patients and because neuromonitoring is less effective.28,30 In addition, selective circumferential decompression of only the most highly stenosed areas is advised in patients with five or more levels of involvement to lessen the risk of cord ischemia and resultant neurologic compromise.33 Just as in patients with AS, it is of utmost importance to be constantly cognizant of the very high rate of complications in these patients. These include neurologic deterioration, excessive blood loss averaging 2,000 mL and ranging up to 6 L, and the potential for dural tears.31

precautions can be instituted to lessen the risk of catastrophic complications.

50.8 Key Points ●

●

●

●

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Patients with AS are at risk of a hyperextension fracture after even minor trauma, with resultant high rates of spinal cord injury and mortality. Positioning the patient in a way that recreates preexisting kyphosis and recognizing concomitant injuries are crucial to avoid iatrogenic complications. Pseudoarthroses in patients with AS may be sequelae of either trauma or chronic inflammatory lesions; the former can be managed with posterior instrumentation to diminish micromotion and allow healing. Traditional Smith-Peterson osteotomies in AS patients can obtain considerable correction but at the risk of devastating vascular injury, and thus are now rarely undertaken. When performing any osteotomy in AS patients, one should obtain closure of the osteotomy via direct manipulation of the patient and not via maneuvers relying on the instrumentation alone. Myelopathy because of thoracic OPLL will progress if patients are not treated surgically; whereas laminectomy and fusion are associated with lower rates of postoperative deterioration, circumferential decompression leads to more reliable rates of neurologic recovery.

References 50.7 Summary Patients with spondyloarthropathies, in particular AS and OPLL, can be appropriately treated with surgery for a variety of secondary complications. These include traumatic injuries, kyphotic deformity with positive sagittal balance, and myelopathy because of a compressive lesion. However, any surgery in these patients is a serious undertaking, as the perioperative course can be fraught with complications and a high mortality rate. Whereas they are at risk for the same instrumentation-related complications as patients without spondyloarthropathy undergoing similar procedures, the anatomy and pathologic conditions specific to spondyloarthropathies put them at risk for unique complications as well. Patients with AS are at particular risk of a neurologic injury as the result of an iatrogenic fracture, improper positioning leading to neural compromise, or an ascending epidural hematoma, which can cause a devastating progressive neurologic insult. They are also at greater risk of pulmonary complications because of preexisting restrictive lung disease, which is of particular concern after anterior surgical approaches. Whereas patients with thoracic OPLL often gain neurologic improvement after surgical decompression for myelopathy, the tenuous condition of the spinal cord in these patients also puts them at particular risk of neurologic injury after surgical treatment, particularly in those who undergo either posterior decompression without fusion or circumferential decompression. Thus, whereas surgical treatment can greatly enhance the quality of life of patients with spondyloarthropathy, it is vital that one be constantly aware of the unique properties of each disease so that the appropriate

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Thoracolumbar [12] Caron T, Bransford R, Nguyen Q, Agel J, Chapman J, Bellabarba C. Spine fractures in patients with ankylosing spinal disorders. Spine. 2010; 35(11):E458– E464 [13] Elgafy H, Bransford RJ, Chapman JR. Epidural hematoma associated with occult fracture in ankylosing spondylitis patient: a case report and review of the literature. J Spinal Disord Tech. 2011; 24(7):469–473 [14] Sapkas G, Kateros K, Papadakis SA, et al. Surgical outcome after spinal fractures in patients with ankylosing spondylitis. BMC Musculoskelet Disord. 2009; 10:96 [15] Trent G, Armstrong GW, O’Neil J. Thoracolumbar fractures in ankylosing spondylitis. High-risk injuries. Clin Orthop Relat Res. 1988; 227(227):61–66 [16] Meyer PR, Jr. Diffuse idiopathic skeletal hyperostosis in the cervical spine. Clin Orthop Relat Res. 1999(359):49–57 [17] Chang KW, Tu MY, Huang HH, Chen HC, Chen YY, Lin CC. Posterior correction and fixation without anterior fusion for pseudoarthrosis with kyphotic deformity in ankylosing spondylitis. Spine. 2006; 31(13):E408–E413 [18] Kim KT, Lee SH, Suk KS, Lee JH, Im YJ. Spinal pseudarthrosis in advanced ankylosing spondylitis with sagittal plane deformity: clinical characteristics and outcome analysis. Spine. 2007; 32(15):1641–1647 [19] Fang D, Leong JCY, Ho EKW, Chan FL, Chow SP. Spinal pseudarthrosis in ankylosing spondylitis. Clinicopathological correlation and the results of anterior spinal fusion. J Bone Joint Surg Br. 1988; 70(3):443–447 [20] Arun R, Dabke HV, Mehdian H. Comparison of three types of lumbar osteotomy for ankylosing spondylitis: a case series and evolution of a safe technique for instrumented reduction. Eur Spine J. 2011; 20(12):2252–2260 [21] Kim KT, Jo DJ, Lee SH, Park KJ, Sin JH. Does it need to perform anterior column support after Smith-Petersen osteotomy for ankylosing spondylitis? Eur Spine J. 2012; 21(5):985–991 [22] Chang KW, Chen YY, Lin CC, Hsu HL, Pai KC. Closing wedge osteotomy versus opening wedge osteotomy in ankylosing spondylitis with thoracolumbar kyphotic deformity. Spine. 2005; 30(14):1584–1593 [23] Zhu Z, Wang X, Qian B, et al. Loss of correction in the treatment of thoracolumbar kyphosis secondary to ankylosing spondylitis: a comparison between Smith-Petersen osteotomies and pedicle subtraction osteotomy. J Spinal Disord Tech. 2012; 25(7):383–390

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[24] Lazennec JY, Saillant G, Saidi K, et al. Surgery of the deformities in ankylosing spondylitis: our experience of lumbar osteotomies in 31 patients. Eur Spine J. 1997; 6(4):222–232 [25] Cho KJ, Bridwell KH, Lenke LG, Berra A, Baldus C. Comparison of SmithPetersen versus pedicle subtraction osteotomy for the correction of fixed sagittal imbalance. Spine. 2005; 30(18):2030–2037, discussion 2038 [26] Kiaer T, Gehrchen M. Transpedicular closed wedge osteotomy in ankylosing spondylitis: results of surgical treatment and prospective outcome analysis. Eur Spine J. 2010; 19(1):57–64 [27] Qian BP, Wang XH, Qiu Y, et al. The influence of closing-opening wedge osteotomy on sagittal balance in thoracolumbar kyphosis secondary to ankylosing spondylitis: a comparison with closing wedge osteotomy. Spine. 2012; 37(16):1415–1423 [28] Li M, Meng H, Du J, Tao H, Luo Z, Wang Z. Management of thoracic myelopathy caused by ossification of the posterior longitudinal ligament combined with ossification of the ligamentum flavum-a retrospective study. Spine J. 2012; 12(12):1093–1102 [29] Matsuyama Y, Yoshihara H, Tsuji T, et al. Surgical outcome of ossification of the posterior longitudinal ligament (OPLL) of the thoracic spine: implication of the type of ossification and surgical options. J Spinal Disord Tech. 2005; 18 (6):492–497, discussion 498 [30] Yamazaki M, Mochizuki M, Ikeda Y, et al. Clinical results of surgery for thoracic myelopathy caused by ossification of the posterior longitudinal ligament: operative indication of posterior decompression with instrumented fusion. Spine. 2006; 31(13):1452–1460 [31] Matsumoto M, Chiba K, Toyama Y, et al. Surgical results and related factors for ossification of posterior longitudinal ligament of the thoracic spine: a multi-institutional retrospective study. Spine. 2008; 33(9):1034–1041 [32] Yang C, Bi Z, Fu C, Zhang Z. A modified decompression surgery for thoracic myelopathy caused by ossification of posterior longitudinal ligament: a case report and literature review. Spine. 2010; 35(13):E609–E613 [33] Takahata M, Ito M, Abumi K, Kotani Y, Sudo H, Minami A. Clinical results and complications of circumferential spinal cord decompression through a single posterior approach for thoracic myelopathy caused by ossification of posterior longitudinal ligament. Spine. 2008; 33(11):1199–1208

Infection

51 Infection Armen R. Deukmedjian, Yusef I. Mosley, Amir Ahmadian, and Juan S. Uribe

51.1 Introduction In the 1990s, it was estimated that more than 18 million patients underwent surgery in the United States every year.1 Out of these, more than 500,000 surgical site infections (SSIs) occur each year, at a rate of 2.8 per 100 operations.2 Previous studies have shown that SSI prolongs hospitalization from 7 to 19.5 days, and estimated that the mean additional cost per patient hospitalization was $4,500.3 Postoperative SSI is an unfortunately common and potentially devastating complication after spinal instrumentation, and has been estimated to increase health care costs up to fourfold.4 The economic impact of nosocomial infections will play an important role in the future.5 In one study examining all patients with an SSI after an orthopedic procedure at a tertiary referral center, Whitehouse et al6 demonstrated that these patients had an average of 2 weeks longer hospital stay, double rehospitalization rate, and 300% increased health care costs when compared with patients without an SSI. The incidence of postoperative wound infections in patients undergoing spinal instrumentation for all diagnoses is wide ranging, though most large cohort studies proclaim rates between 0.8 and 4.4%,7,8,9,10,11 whereas for pediatric scoliosis correction, it ranges from 0.5 to 41% depending on the diagnosis and complexity of the procedure.12,13,14 In a study spanning 30 years at a single institution, Cahill et al15 examined all cases of fusion for pediatric spinal deformity, and discovered that out of 1,744 patients, infection rate in idiopathic scoliosis was 0.5%, it was 19.2% in myelomeningocele, 4.3% in myopathies, and 11.2% in cerebral palsy. Nearly half of the patients with infection required removal of their instrumentation, and 44% had an average 27-degree progression of their deformity. In their cohort of nearly 2,000 patients with instrumented spinal fusions, Collins et al reported that infection occurred in 5.3% following trauma, 6.7% following deformity correction, and 1.1% following degenerative spinal surgery.7 Traumatic spine injury has a well-documented infection risk especially in patients with concomitant neurological injury with reported rates of up to 10%. Blam et al16 reported an incidence of 9.4% in traumatic spine patients compared with 3.7% of elective spinal operations in the same period. Some of the factors that contribute to the increased risk of infection include soft-tissue injury that leads to tissue hypoxia and also prolonged ICU stay, which exposes patients to antibiotic resistant organisms. Additionally, traumatic patients are in a catabolic state leading to protein–calorie malnutrition. Some of the same issues that are encountered in traumatic spine patients also contribute to the infection rates seen in patients with spinal tumors. Patients with metastatic lesions in the spine often undergo immunosuppressive therapies which can also increase the risk of SSI. The variable incidence of SSI is secondary to the spectrum of spine procedures. It is difficult to assign a specific infection rate to spine surgery in general. However, one can make postulations of the propensity to acquire an SSI given the type of surgery (minimally invasive vs. open), instrumentation versus noninstrumentation, degenerative versus deformity,

adult versus pediatric, presence of trauma or tumor, etc. Finally, there are patient-related risk factors that will be examined that contribute to infection susceptibility and include diabetes mellitus, obesity, smoking, advanced age, and preoperative hospitalization for more than 1 week. The goal of this chapter is to discuss the epidemiology of SSI after spinal instrumentation, the risk factors associated with SSI, the difference in the incidence of SSI given the operative procedure, patient-related risk factors, diagnostic criteria, treatment, and preventative measures. By the end of the chapter, we hope the reader would have gained knowledge that will help prevent and treat SSI.

51.2 Epidemiology The most frequent causative organism for SSIs following spine surgery is Staphylococcus aureus, with a recent increase in the incidence of methicillin-resistant strains of this organism (MRSA). Other reported causative organisms include Staphylococcus epidermidis, Enterococcus faecalis, Pseudomonas species, Enterobacter cloacae, and Proteus mirabilis. Gram-negative bacteria are more common in trauma patients and may result from hematogenous spread in the setting of urosepsis in patients with a neurological injury.17 Collins et al7 performed a retrospective review over a 10-year period of patients diagnosed with an SSI that included 39 females and 35 males. A total of 46 patients had a single organism isolated and 28 patients had polymicrobial infections. Low virulence skin organisms such as Propionibacteria have been reported as a late cause of postoperative infection following posterior spinal fusion.17 Bémer et al18 reported a rate of almost 10% positive cultures to P. acnes in spinal instrumentation in a series of 68 patients. The data presented in the aforementioned study demonstrate the pathogenicity of this organism. Pull ter Gunne and Cohen reported that S. aureus was able to be isolated in 73% of 132 deep wound infections, with 18% demonstrating methicillin resistance.11,17 Most studies examining infection epidemiology agree on the monomicrobial nature of the majority of SSI. However, on average, one-third of all wound infections are polymicrobial. Cahill et al described 61 pediatric patients undergoing deformity correction with a postoperative infection in which 48% of infections are monomicrobial and 34% of infections are polymicrobial. The most common monomicrobial organisms encountered in this study include S. aureus, coagulase-negative staphylococcus, and MRSA, whereas polymicrobial infections usually involved Pseudomonas species, Escherichia coli, E. faecalis, P. mirabilis, and Enterobacter species. Mok et al described the epidemiology of the pathogens in 16 patients with SSI following instrumented posterior spinal fusion.19 Seven patients had a monomicrobial infection, and four out of the seven were infected with S. aureus, whereas nine patients had a polymicrobial infection with the aforementioned organisms. Interestingly in this study, the authors reported that all patients with a monomicrobial infection required only a single irrigation and debridement, whereas six of the nine patients with a polymicrobial infection required more than one

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Thoracolumbar procedure. The most common organisms in patients undergoing multiple debridements were S. epidermidis (six of six) and Enterococcus species (four of six). In the four patients who presented with late infection and underwent removal of implants, the most common organisms were S. epidermidis (four of four) and P. acnes (three of four).19 These data stress the importance of correct identification of infecting pathogens and the insight that this may provide to the treating physician.

51.3 Diagnosis The diagnosis of an SSI after spinal instrumentation can be challenging, and must be made using clinical judgment and taking into account all available information. It increases perioperative morbidity and associated medical resource utilization.20,21 Collins et al reported that the median time to diagnosis of an infection in their cohort was 14 months (range: 7 days to 9 years postoperatively), with 76% diagnosed within a 2-year period, 24% after 2 years, and 8% within 30 days.7 The diagnosis is unclear in many cases and the surgeon often questions whether that small area of erythema, or the small amount of drainage, should be treated. Clinical signs and symptoms, as well as laboratory values, aid the diagnosis of an infection. In select cases, a contrasted MRI or CT scan may be useful. Postoperative infections of the spine are generally classified based on the relationship to the fascia (superficial, deep, or both), as well as the timing with which they present (early, late, and delayed).17 Deep infections indicate that the peri-implant tissues have been compromised, and are present in 1.3% of cases following any spine surgery, versus the 0.8% rate of superficial infections recently reported by the Scoliosis Research Society (SRS).5,8 Superficial incisional infections are defined as occurring within 30 days of surgery, and deep infections of the hardware may occur within 1 year of surgery. This reason alone may act as an incentive for spine surgeons to follow their patients in the long term. Once it has been diagnosed, an SSI will likely need to be irrigated and debrided, at which point cultures should be sent to the microbiology lab from the deepest and most necrotic/ inflammatory region of the wound.

51.3.1 Clinical Signs and Symptoms In the majority of cases, clinical signs and symptoms are periincisional pain, erythema, warmth, edema, tenderness to palpation, abscess/fluctuance, or wound drainage.17 A study by Pull ter Gunne and Cohen demonstrated wound drainage as the most common finding in SSI, being present in nearly 70% of both deep and superficial infections.11 However, in a series of 236 patients undergoing correction of adolescent idiopathic scoliosis (AIS), Rihn et al report that the most common presenting symptoms included back pain (5 of 7 infected patients) and a localized peri-incisional swelling or fullness (4 of 7 infected patients).22 Weinstein et al identified 46 of 2,391 patients (1.9%) who developed a wound infection after spine surgery, and in whom only 30% had a temperature higher than 37.5 °C on presentation.23 In a similar study, examining all spine surgery at one institution over a 4-year period, Olsen et al identified 46 of 2,316 patients (2.0%) with a wound infection, with a median time to diagnosis of 11 days, and of whom 43% were

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classified as deep (involving fascia or muscle).21 Particularly concerning in this group of patients are those demonstrating constitutional symptoms, including fevers/chills. In cases of severe infection requiring immediate medical attention, signs of sepsis may be evident, such as hypotension, confusion, and lethargy. In these cases, emergent medical management is necessary, followed by surgical debridement of the wound and intravenous (IV) antibiotics. Another catastrophic consequence of infection after instrumentation is pseudarthrosis. Cahill et al reported that the incidence of pseudarthrosis in pediatric patients undergoing surgery for spine deformity with an infection is 25% (13 of 51).15 These patients required an average of 1.2 procedures to treat the pseudarthrosis, which was refractory in almost 50% of those cases, and had a progression of their curve an average of 22 degrees.

51.3.2 Laboratory and Radiographic Evaluation As mentioned previously, it is inadvisable to wholly rely on laboratory values in diagnosing an SSI. However, they may be used as an adjunct to clinical judgment in predicting an infection. In the immediate postoperative period, inflammatory markers in the blood such as white blood cell (WBC) count, C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR) are elevated and remain so for some weeks. In a study by Aono et al,24 CRP was found to be the most reliable marker and at 14 days after surgery (posterior lumbar interbody fusion [PLIF]) it returned to its normal level in half of the patients. ESR is generally elevated for a longer period after surgery, reaching its peak 2 weeks postoperative and normalizing around 6 weeks postoperative.25 It is accepted by most authors that CRP is a more sensitive predictor for different types of SSI than either ESR or WBC count, with elevated levels in 97% of superficial SSI and 100% of deep SSI.17,26,27,28 In a study by Takahashi et al, a peak in CRP occurs 2 days after implantation of spinal instrumentation. In the absence of an infection, the CRP level on postoperative day 7 should be lower than the level on postoperative day 2.29 Interestingly, Takahashi et al reported that a low WBC count within 4 days of spinal instrumentation might also be a predictor of an SSI. Median CRP, ESR, and WBC count of infected patients reported in a cohort of 1,980 patients was 37.5, 33.5, and 8.3, respectively, at the time of diagnosis, and in a cohort of 2,391 patients mean WBC was 13.4 and ESR was 71.5 mm/h.7,23 Rihn et al also noted that in the AIS population,22 average WBC count and ESR at the time of diagnosis was 10.5 and 52.5, respectively, whereas CRP was 8. However, of the infected patients in this cohort, normal postoperative values occurred in 17% of CRP results, 45% of ESR results, and 95% of WBC results. Following serial serum markers to evaluate the course of the infection is also recommended, but will likely fall under the auspices of the infectious disease team to decide the course of antibiotics. Imaging in spine infection may be useful as well. A contrasted MRI scan with gadolinium would show enhancement of the subcutaneous tissues in the case of an infection. Visualization of the area surrounding the instrumentation may be difficult secondary to artifact, except in select centers with specialized magnetic resonance software. The MRI may also be useful in

Infection demonstrating a fluid collection, or seroma that needs to be evacuated. Nuclear medicine scans can be used to evaluate osteomyelitis/discitis, but there is a lack of data on utility in diagnosing an infection in the case of spinal instrumentation.

51.4 Risk Factors Although improvements in surgical techniques and instrumentation have allowed for improved patient outcomes, certain variables that have been identified and analyzed continue to increase patient risk for postoperative infection. Interestingly, it has recently been shown that even the season plays a role in infection risk, with a rate of 4.1% in the summer months, 3.9% in the fall, and 2.8% in the spring and winter.30 There is a general consensus that risk of infection is increased in those patients undergoing arthrodesis, versus a simple laminectomy/ discectomy. The reason for this is likely a combination of longer operative time and instrumentation serving as a nidus for infection. Recognition of an individual patient’s risk factors may allow the surgical team to optimize their preoperative condition to minimize the incidence of infection in hopes of improving patient outcome. Identifying risk factors during the periand postoperative period is also of paramount importance to potentially significantly lower incidence of infection. In an attempt to determine if any difference in the rate of infection following spine surgery between neurosurgeon and orthopedic surgeon is secondary to patient factors, Olsen et al published two studies.21,31 In one of the studies (the “neurosurgeon spine population”), they determined that independent risk factors for infection included postoperative urinary incontinence, a posterior surgical approach, tumor surgery, and morbid obesity.31 In the another study (the “orthopedic spine population”), a retrospective review of 2,316 patients showed that independent risk factors for spinal SSI were diabetes (odds ratio: 3.5, 95% confidence interval: 1.2, 10), preoperative serum glucose level of > 125 mg/dL or a postoperative serum glucose level of > 200 mg/ dL, obesity, suboptimal timing of prophylactic antibiotic therapy (either > 60 minutes before the incision or after the incision), and two or more surgical residents participating in the operative procedure.21 Another interesting finding from this study, though only approaching statistical significance (p = 0.07), was the use of a Hemovac drain and its association with SSI. In comparing open to minimally invasive surgery, McGirt et al32 retrospectively evaluated 5,170 patients undergoing one- or two-level P/TLIF (posterior/transforaminal lumbar interbody fusion), and found that in two-level surgery, the minimally invasive technique was associated with a decreased incidence of postoperative SSI, and a direct cost savings of $38,400 per 100 P/ TLIF procedures performed. These findings did not translate to one-level surgery, however. Further studies comparing outcomes and costs of minimally invasive surgery versus traditional open surgery are needed. Specific pre- and perioperative risk factors are examined in the ensuing sections, and, in general, reflect results of multiple studies by many accomplished investigators.

51.4.1 Preoperative Risk Factors Commonly reported patient-related risk factors for SSI include smoking,33 alcohol abuse, obesity/diabetes mellitus,21,33,34,35 advanced age,36,37 malnutrition,37,38 steroid use or NSAIDs,39

revision surgery,33 chronic obstructive pulmonary disease (COPD), coronary artery disease, osteoporosis, and preoperative hospitalization > 1 week.40,41 Pull ter Gunne and Cohen identified 132 of 3,174 patients (4.2%) with an SSI following adult spinal surgery.11 Independent risk factor for infection from this study include obesity, diabetes, increased EBL (estimated blood loss), previous SSI, and longer surgery (> 2 h), whereas an anterior approach reduced risk. In a review of more than 1,500 spinal procedures performed, Fang et al found that statistically significant preoperative risk factors include age > 60 years, smoking, diabetes, previous surgical infection, high body mass index, and alcohol abuse.10 This study found that the most likely procedure to be complicated by an SSI was a combined anterior/posterior spinal fusion performed in a staged manner under separate anesthesia.42 Satake et al attempted to determine which diabetes-related parameters have the strongest influence on SSI after spinal instrumentation surgery and found that preoperative proteinuria is a significant predisposing factor.43 This provides the surgeon a possible target for treatment to minimize infection risk in diabetic patients. Also for those patients, less invasive surgery is recommended. However, in this retrospective study, there was no significant impact of preoperative condition in relation to glycemic control, though good perioperative control of hemoglobin A1c (< 6%) is generally recommended. Neuromuscular scoliosis has been hypothesized to increase the risk of infection secondary to the presence of paralysis, urinary incontinence, and seeding with enteric bacteria given the difficult nature of caring for these patients.44

51.4.2 Perioperative Risk Factors Procedure-related risk factors include more than 10 people in the operating room (OR),41 longer duration of surgery, increased blood loss or need for transfusion,33,45 and incidental durotomy.40 It has been shown previously that an EBL > 1 L during surgery increases the risk of infection, which is consistent with several studies in the field of cardiovascular surgery.46,47 Interestingly and possibly related, immune suppression occurs with transfusion with nonautologous blood products, increasing the risk of all infections.48 Some authors believe that the use of instrumentation in spinal fusion increases the risk of infection, citing reasons such as increased operative time and surgical exposure, bulk of the implants, an inflammatory response to fretting corrosion of the implants, and an allergy to the nickel within the implants.22,49,50,51 Although the use of allograft has not been found to carry an increased infection rate in spinal fusion, Sponseller et al have suggested that its use in neuromuscular scoliosis patients may increase risk of infection.44,52 Abdul-Jabbar et al, in a retrospective review of more than 6,000 patients, demonstrated a strong correlation between SSI and spine surgery involving the sacrum (9.6%), and more than 13 levels of fusion (7.8% for > 7 levels, 10.4% for > 12 levels).9 Cases involving an osteotomy were associated with a 6.5% risk of infection, whereas those longer than 5 h and those associated with blood transfusions were associated with a 5% risk of infection. Although there is an increased incidence of SSI with diabetes (4.2%) and anemia (4.3%), this study interestingly demonstrates that infection is not strongly associated with advanced age, obesity, and a history of smoking, which contradicts data presented by other groups.21,33

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Thoracolumbar In the past decade, there has been a substantial increase in the use of minimally invasive spine surgery. Proponents claim that in addition to reducing hospital stay and patient postoperative pain, it also is associated with a reduced risk of infection.53 Smith et al,54 in reporting data from the SRS morbidity and mortality committee, demonstrated that compared with a traditional open approach, a minimally invasive approach is associated with a lower rate of infection for lumbar discectomy (0.4 vs 1.1%, p < 0.001) and transforaminal lumbar interbody fusion (1.3 vs. 2.9%, p = 0.005). Overall rate of infection with minimally invasive spine surgery was lower when compared with traditional open surgery (0.5 vs. 2.4%, p < 0.001). This database review of 108,419 procedures demonstrated some significant findings. The risk of infection in those cases where arthrodesis was performed (2.4%) was higher than those without arthrodesis (1.8%, p < 0.001). Anterior-only surgery had a significantly lower rate of infection (0.6%) than TLIF/PLIF (2.3%), posterolateral fusion (3%), anterior–posterior (3.2%), interlaminar facet (2.8%), and posterior–anterior–posterior fusions (3.3%). Revision surgeries were also associated with a higher rate of infection than initial surgery (3.3 vs. 2.0%, p < 0.001). Another interesting finding in this study is that rates of SSI are lowest for surgery performed for degenerative spine disease versus that performed for spinal deformity.

51.5 Prevention Although there have been significant advances in surgical techniques and preventive measures, the wider application of spinal instrumentation and ever-increasing risk factors contribute to continued high infection rates. Because of the patient morbidity and associated health care costs associated with SSI following spine instrumentation, it is imperative that health care providers attempt to minimize and altogether prevent infection. Potential devastating sequelae include pseudarthrosis, neurological deficit, osteomyelitis, and even death.55

51.5.1 Preoperative Considerations A consistent risk factor in most studies of SSI after spinal instrumentation is diabetes mellitus, and poor glycemic control. As mentioned previously, preoperative serum glucose levels of > 125 mg/dL or postoperative levels of > 200 mg/dL can increase risk of infection. Dubberke et al56 found that tight preoperative glycemic control may reduce risk of SSI. In the case of a prior infection, some authors recommended attempting to identify the organism that caused the infection and tailor antibiotic prophylaxis to the prior sensitivity.11 It has also been previously shown that an anterior approach for spine fusion may provide a protective effect from infection, though may not always be feasible on operative planning. Preoperative optimization of nutritional status with a specialist may be beneficial to reduce risk of infection. As mentioned previously, attempting to minimize preoperative proteinuria in diabetic patients may play a protective role against infections.

51.5.2 Perioperative Considerations There are a variety of operative maneuvers available in the attempt to decrease risk of SSI following spinal instrumentation,

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but none more important than meticulous aseptic technique in the OR. Thorough scrubbing of the exposed upper extremities with a sterilizing solution as well as nail trimming has previously been proven to reduce microbial burden and thus infection risk. Additionally, simple measures such as reducing OR traffic, wide and thorough prepping of the patient, hospital/OR air handling, and changing gloves with a hole in them have been shown to reduce infection.57 Using an electric clipper to remove hair has also been shown to reduce infection when compared to a razor, which can likely be attributable to fewer micro abrasions. A retrospective cohort study was performed by Rehman et al58 to determine whether changing the surgeon’s outer gloves before handling spine instrumentation during 389 posterior lumbar fusions had an effect on infection risk. They discovered a significant reduction of infection rate from 3.35 to 0.48% with a simple glove change. This is an example of a simple and costeffective method to reduce the burden of postoperative SSI. Studies have shown that preoperative administration of IV antibiotics within 60 minutes of incision reduces risk of infection. In 2002, Barker59 performed a meta-analysis in which he evaluated six randomized controlled trials with a total of 843 patients undergoing spine surgery. Overall infection rate for those having prophylactic antibiotics versus those without was 2.2 versus 5.9%, respectively. Another study by Ho et al12 showed early reduced infection risk when vancomycin and ceftazidime were used in cases of posterior fusion rather than cefazolin, to provide coverage for S. epidermidis, one of the most commonly encountered pathogens in AIS. In addition, they used a pulse lavage of a detergent solution at the conclusion of the case prior to closure. Cheng et al60 performed a prospective randomized trial, testing irrigation of the spinal wound with a dilute Betadine solution, and found no infection in 208 patients versus a 2.9% infection rate in 206 patients without Betadine irrigation. Some surgeons advocate the use of antibiotics for 24 h in the postoperative period, though data on the efficacy of this practice remain elusive. For longer surgeries, it may be beneficial to re-dose the antibiotic to keep serum levels at a useful concentration. One technique with significant promise that has recently been gaining in popularity is the prophylactic local application of vancomycin powder into the surgical wound to prevent infection. In a retrospective manner and over a 5-year period (2005–2010), Molinari et al61 examined 1,512 patients undergoing spine surgery (663 instrumented cases) by a single fellowship trained spine surgeon. One gram of vancomycin powder was placed in all surgical sites prior to wound closure. Of the entire cohort (n = 1,512, instrumented and noninstrumented cases), 15 patients (0.99%) were identified with a deep wound infection. The rate of deep wound infection was 1.2% (8/ 663) for instrumented cases and 0.82% (7/849) for noninstrumented surgeries. Deep infection occurred in only 1.23% of multilevel-instrumented posterior spinal fusions, 1.37% of open PLIF procedures, 1.23% of single-level instrumented posterior fusions, and 0 noninstrumented spinal fusions. No infections were reported out of 146 anterior cervical fusions. There was a relatively low risk of infection in trauma (0.55%) and revision (1.15%) surgeries. No complications from the use of local application of powdered vancomycin were identified.61 Strom et al62 examined 171 patients undergoing posterior cervical fusion by a single spine surgeon, with local application of vancomycin

Infection powder in 79 of them, and found a statistically significant reduction of infection rate from 10.9 to 2.5% with no significant difference in rate of pseudarthrosis and no complications attributable to the vancomycin powder. Further study of locally applied vancomycin powder is needed to optimize dosing, assess long-term safety, and evaluate use in a broad range of spine surgeries. Though all surgeons attempt to minimize intraoperative blood loss, it is especially important in the prevention of infections, given that it has been shown in numerous studies to be an independent risk factor for SSI.11,46,47 Meticulous hemostasis during the course of the procedure is important to accomplish that goal. Nonautologous blood transfusions have been shown to produce immune suppression in patients, increasing the likelihood of an infection, and should be minimized if possible.48 With prolonged use of retractors and rough surgical technique, tissue necrosis may become a problem that can lead to increased dead space and a good medium for pathogen growth. This can be prevented with frequent release of retractors.

51.6 Treatment/Outcomes The treatment for an SSI following spinal instrumentation depends on the location, and in general whether or not it is isolated superficial to the muscular fascia or includes the spine deep to the fascia. Other factors to consider are the infecting organism, the amount of time elapsed from the index procedure, the extent of purulence, and the gross appearance of the fusion mass. Mok et al19 evaluated outcomes in 16 patients with a postoperative SSI after spinal fusion by comparing with a 1:1 matched cohort and found that with early surgical debridement and irrigation, it is possible to retain implants in early postoperative infections. The outcomes in these patients were also similar to the control group when aggressive treatment is undertaken. However, multiple debridements may be associated with polymicrobial infections and later, pseudarthrosis. This should be taken into account when considering a staged infection treatment, with the initial surgery to remove hardware leaving an open wound, with a subsequent debridement and wound closure 3 to 4 days later. This is more commonly done in the case of AIS, where there is a nearly 50% chance that the infection will remain if all spinal implants are not removed and only irrigation and debridement is performed.12 Although the rate of infection is much higher in pediatric patients undergoing scoliosis correction for neuromuscular disease than for AIS, the patients with idiopathic scoliosis do not appear to clear infection better after irrigation and debridement.12 In a 10-year (1993–2003) retrospective study of 1,980 patients having an instrumented spine fusion with stainless steel implants, Collins et al7 reported on their method of managing infection in their cohort, as well as provide an outcome assessment. All patients were given a broad-spectrum prophylactic antibiotic at the time of the index procedure. Management of the infection was undertaken in a dedicated bone infection unit under the care of the infectious diseases team. The treatment algorithm depended on whether the spine had fused at the time of diagnosis of infection. If unfused, each patient was given 6 weeks of IV antibiotics, and then oral antibiotics until the fusion was complete and the implants could be

safely removed. If the spine had fused already, in the case of S. aureus and gram-negative bacteria, the hardware was removed, intraoperative cultures were sent for microbiology, and antibiotic therapy was dictated by sensitivity but generally included 6 weeks of IV antibiotics followed by 6 weeks of oral antibiotics. If the infecting organism was propionibacteria or coagulase-negative Staphylococcus bacteria, patients were treated with 4 weeks of oral antibiotics in total unless they had a poor immune response, when the duration of treatment was extended with implant removal. Reportedly, 46% of the infected cohort had “pain-free, stable spines following successful eradication of their infections.” There were also no reported neurological complications from the treatment management schema.7 Weinstein et al,23 examining 2,391 spine procedures and identifying 46 cases of infection, performed a similar study over a 9-year period at a single institution. All patients underwent operative incision and drainage and had cultures sent from both the superficial and deep layers of the wound. After the cultures were sent, 9 L of a bacitracin solution was used to pulse lavage the wound. Superficial wound infections were closed over a drain, but the deep wound infections were packed with gauze and returned to the OR for repeat irrigation and debridement 48 h later. The wound was then closed over a drain if it appeared to be “healthy,” and if not was packed again and brought back another 48 h later to repeat the process. Instrumentation was removed in only 14% of the population. Superficial infections were treated with 3 weeks of IV antibiotics, whereas deep infections were treated with 6 weeks of sensitivity-directed IV antibiotics. As outcome measures, this group reports that no patient died as a result of infection and pseudarthrosis was documented in only three patients. Three patients also required flap closure of the wound. Vacuum-assisted wound closure (VAC) is another option in the treatment of nonhealing wounds and postoperative wound infections. It exposes the wound bed to negative pressure, resulting in removal of edema fluid, stimulation of cellular proliferation of reparative granulation tissue, and improvement of blood supply.63,64 A retrospective study by Mehbod et al63 examined 20 patients with deep wound infection after spinal fusion treated with irrigation and debridement followed by placement of a wound VAC with subsequent delayed closure of the wound (an average of 7 days after initial placement of the VAC). All patients tolerated the VAC without complication, and no cases of sepsis were discovered. Further analysis of VAC utility with a long-term, prospective, randomized study or a retrospective case–control study is warranted to evaluate if patients with a VAC require fewer operative procedures and a shorter time to recovery.

51.7 Summary Infection following spinal instrumentation, one of the most disastrous complications of spine surgery, will likely continue to play a role in the current spine surgeon’s practice because of the projected increase in number of fusions in an aging population. Sequelae of deep wound infection are potentially catastrophic, and include osteomyelitis, pseudarthrosis, failure of fixation, and significant morbidity in the relative short term, with long-term complications including persistent pain or

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Thoracolumbar deformity, cost, and need for revision surgery or prolonged hospitalization.19

51.7.1 Etiology Preoperative risk factors for infection following spinal instrumentation include a prior SSI, diabetes, obesity, anemia, smoking, alcohol abuse, advanced age, malnutrition, steroid use, use of nonsteroidal anti-inflammatory medications, revision surgery, chronic obstructive pulmonary disease, coronary artery disease, osteoporosis, and preoperative hospitalization.10,11 Perioperative risk factors for an SSI include increased OR traffic and more than 10 people in the OR, longer duration of surgery (> 5 h), incidental durotomy, blood loss of more than 1 L or need for transfusion, surgery involving the sacrum or more than 13 levels of fusion, allograft use, and deformity surgery. Minimally invasive techniques for spinal fusion seem to have a lower rate of infection, as does an anterior approach to the spine. Aggressive treatment of patients undergoing complex or prolonged spinal procedures is essential to prevent and treat infections. Preoperative modification of the patient’s risk factors may help the physician to optimize their preoperative condition as well as improve surgical outcome. For example, strict blood sugar control and maximizing nutritional status may reduce risk of an SSI. Meticulous aseptic technique, prophylactic antibiotics, and intraoperative irrigation can all play an important role during surgery. An emerging technique that shows immense promise is the local application of vancomycin powder to the surgical bed. Changing outer gloves just prior to instrumentation implantation has also been proposed as cheap and effective method of lowering infection risk. In those patients who develop SSI, prompt diagnosis and treatment allow for optimization of patient outcomes. Treatments are varied and depend on many factors, but once the SSI is deemed surgical it should include meticulous surgical debridement of all devitalized tissue along with copious amounts of irrigation of normal saline either with or without antibiotics (bacitracin). Some authors also recommend irrigation with a Betadine solution after aggressive debridement of infected tissue. Intraoperative cultures should be sent for microbiological analysis to guide antibiotic therapy based on pathogen sensitivities. Involvement of the infectious disease team is surgeon dependent, but is reasonable in light of the fact that the patient will need long-term IV antibiotics depending on the pathogen and its drug-sensitivity profile. The IV antibiotics are generally continued for 6 to 8 weeks postoperatively, and further oral antibiotic administration may be an option. Management of the wound may require a wound VAC and multiple debridements, or possibly closure with a muscle flap, in which case assistance from a plastic surgeon is recommended. It is usually possible to clear an early infection while retaining spinal instrumentation, although instrumentation can be removed following fusion if necessary. Certain complex wound infections may require removal of posterior instrumentation if initial debridement is inadequate. The risk of pseudarthrosis increases with infection, especially with hardware removal. Infection may be followed with serial serum markers such as ESR, CRP, and WBC.

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51.8 Future Directions With the potentially severe manifestations of a postoperative wound infection, the importance of prevention guides our future efforts. As discussed earlier, one such possible tool in the prevention of SSI is the use of intraoperative antibiotic powder. Strom et al62 reported a statistically significant decrease in infections in posterior cervical fusions from 10.9 to 2.5% (p = 0.038) when vancomycin powder is spread locally into the wound. Similarly, Molinari et al61 reported a low rate of deep wound infection following instrumented (1.2%) and noninstrumented (0.82%) spine surgery in 1,512 consecutive cases. Although these data are promising for the future of SSI prevention, there still exists a need for a large prospective randomized control trial evaluating the efficacy and risk profile of vancomycin powder. Another intervention requiring further study is the use of perioperative antibiotic usage, which, unlike the administration of preoperative antibiotic, has yet to be shown to reduce overall infection rate. Also, as reported previously, the use of VAC in the intermediate period between subsequent wound washouts has become more popular. Further study of this technique is required. As pathogens become resistant to current antibiotics (vancomycin-resistant enterococci, MRSA), researchers carry the important role of developing newer and stronger antibiotics to be used for SSI prevention/treatment. The use of bone morphogenic protein to aid osseous fusions is a powerful tool when used appropriately. However, recent studies showing the complication profile from BMP use have acted as a deterrent to many surgeons. A literature search provides a recent study by Crandall et al who retrospectively reviewed 509 patients with spine deformity, spondylolisthesis, and degenerative spinal disease and underwent a TLIF with offlabel use of bone morphogenic protein at a single institution. They found the rate of deep infection to be similar to other reports after spinal instrumentation (2.6% overall, 1.7% in degenerative group).65 Further study is warranted in the future use of BMP. Studies, such as that by Rehman et al demonstrating a reduction in infection rate by a simple glove change prior to handling instrumentation, provide hope for cheap and easy prevention of infection following spine instrumentation, and should become implemented in the everyday use of spine surgeons.58

51.9 Key References [1] Pull ter Gunne AF, Cohen DB. Incidence, prevalence, and analysis of risk factors for surgical site infection following adult spinal surgery. Spine. 2009; 34 (13):1422–1428

This is a retrospective cohort study to identify rates and analyze the risk factors for postoperative spinal wound infections. Out of 3,174 patients, 132 (4.2%) were found to have an SSI. Independent risk factors for infection include EBL > 1 L, previous SSI, diabetes, obesity, and longer duration of surgery (> 5 hours). [2] Abdul-Jabbar A, Takemoto S, Weber MH, et al. Surgical site infection in spinal surgery: description of surgical and patient-based risk factors for postoperative infection using administrative claims data. Spine. 2012; 37(15):1340– 1345

Infection Out of 6,628 spine surgery admissions, the cumulative incidence of infection was 2.9%. Procedural risk factors include sacral involvement, fusions greater than 7 levels, transfusions of red blood cells/serum/autologous blood. Patient risk factors include anemia, diabetes, CAD, coagulopathy, and bone or connective tissue neoplasm. [3] Smith JS, Shaffrey CI, Sansur CA, et al. Scoliosis Research Society Morbidity and Mortality Committee. Rates of infection after spine surgery based on 108,419 procedures: a report from the Scoliosis Research Society Morbidity and Mortality Committee. Spine. 2011; 36(7):556–563

Retrospective review of prospectively collected database from the Scoliosis Research Society Committee on morbidity and mortality. The overall rate of infection was 2.1%. Factors associated with increased rate of infection included revision surgery, performance of spinal fusion, and use of implants. Minimally invasive approaches were associated with a lower rate of infection for lumbar discectomy and TLIF. [4] McGirt MJ, Parker SL, Lerner J, Engelhart L, Knight T, Wang MY. Comparative analysis of perioperative surgical site infection after minimally invasive versus open posterior/transforaminal lumbar interbody fusion: analysis of hospital billing and discharge data from 5170 patients. J Neurosurg Spine. 2011; 14(6):771–778

Evaluating 5,170 patients undergoing P/TLIF at one institution, the authors found that a two-level minimally invasive P/ TLIF had a lower rate of infection (4.6%) versus an open P/TLIF (7%), and the mean SSI-associated costs were lower for the MI patients. The MI technique was associated with a decreased incidence of perioperative SSI and a direct cost savings of $38,400 per 100 P/TLIF procedures when used in two-level fusions. [5] Mok JM, Guillaume TJ, Talu U, et al. Clinical outcome of deep wound infection after instrumented posterior spinal fusion: a matched cohort analysis. Spine. 2009; 34(6):578–583

This is a retrospective case–control study that identified 16 patients with an SSI after an instrumented posterior spinal fusion, and matched them with an uninfected control group based on primary or revision status, length of fusion, diagnosis, and age. An aggressive approach to deep wound infection emphasizing early irrigation and debridement allowed preservation of instrumentation and successful fusion in most cases. At the completion of treatment, patients can expect a mediumterm clinical outcome similar to patients in whom the complication did not occur.

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Thoracolumbar [33] Wimmer C, Gluch H, Franzreb M, Ogon M. Predisposing factors for infection in spine surgery: a survey of 850 spinal procedures. J Spinal Disord. 1998; 11 (2):124–128 [34] Capen DA, Calderone RR, Green A. Perioperative risk factors for wound infections after lower back fusions. Orthop Clin North Am. 1996; 27(1):83–86 [35] Ho C, Sucato DJ, Richards BS. Risk factors for the development of delayed infections following posterior spinal fusion and instrumentation in adolescent idiopathic scoliosis patients. Spine. 2007; 32(20):2272–2277 [36] Tenney JH, Vlahov D, Salcman M, Ducker TB. Wide variation in risk of wound infection following clean neurosurgery. Implications for perioperative antibiotic prophylaxis. J Neurosurg. 1985; 62(2):243–247 [37] Klein JD, Hey LA, Yu CS, et al. Perioperative nutrition and postoperative complications in patients undergoing spinal surgery. Spine. 1996; 21(22):2676– 2682 [38] Klein JD, Garfin SR. Nutritional status in the patient with spinal infection. Orthop Clin North Am. 1996; 27(1):33–36 [39] Dahners LE, Mullis BH. Effects of nonsteroidal anti-inflammatory drugs on bone formation and soft-tissue healing. J Am Acad Orthop Surg. 2004; 12 (3):139–143 [40] Meredith DS, Kepler CK, Huang RC, Brause BD, Boachie-Adjei O. Postoperative infections of the lumbar spine: presentation and management. Int Orthop. 2012; 36(2):439–444 [41] Koutsoumbelis S, Hughes AP, Girardi FP, et al. Risk factors for postoperative infection following posterior lumbar instrumented arthrodesis. J Bone Joint Surg Am. 2011; 93(17):1627–1633 [42] Dick J, Boachie-Adjei O, Wilson M. One-stage versus two-stage anterior and posterior spinal reconstruction in adults. Comparison of outcomes including nutritional status, complications rates, hospital costs, and other factors. Spine. 1992; 17(8) Suppl:S310–S316 [43] Satake K, Kanemura T, Matsumoto A, Yamaguchi H, Ishikawa Y. Predisposing factors for surgical site infection of spinal instrumentation surgery for diabetes patients. Eur Spine J. 2013; 22(8):1854–1858 [44] Sponseller PD, LaPorte DM, Hungerford MW, Eck K, Bridwell KH, Lenke LG. Deep wound infections after neuromuscular scoliosis surgery: a multicenter study of risk factors and treatment outcomes. Spine. 2000; 25(19):2461– 2466 [45] McPhee IB, Williams RP, Swanson CE. Factors influencing wound healing after surgery for metastatic disease of the spine. Spine. 1998; 23(6):726–732, discussion 732–733 [46] Banbury MK, Brizzio ME, Rajeswaran J, Lytle BW, Blackstone EH. Transfusion increases the risk of postoperative infection after cardiovascular surgery. J Am Coll Surg. 2006; 202(1):131–138 [47] Taylor RW, O’Brien J, Trottier SJ, et al. Red blood cell transfusions and nosocomial infections in critically ill patients. Crit Care Med. 2006; 34(9):2302– 2308, quiz 2309 [48] Quintiliani L, Pescini A, Di Girolamo M, et al. Relationship of blood transfusion, post-operative infections and immunoreactivity in patients undergoing surgery for gastrointestinal cancer. Haematologica. 1997; 82(3):318–323 [49] Richards BS. Delayed infections following posterior spinal instrumentation for the treatment of idiopathic scoliosis. J Bone Joint Surg Am. 1995; 77 (4):524–529

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[50] Richards BR, Emara KM. Delayed infections after posterior TSRH spinal instrumentation for idiopathic scoliosis: revisited. Spine. 2001; 26(18):1990– 1996 [51] Wimmer C, Gluch H. Aseptic loosening after CD instrumentation in the treatment of scoliosis: a report about eight cases. J Spinal Disord. 1998; 11 (5):440–443 [52] McCarthy RE, Peek RD, Morrissy RT, Hough AJ, Jr. Allograft bone in spinal fusion for paralytic scoliosis. J Bone Joint Surg Am. 1986; 68(3):370–375 [53] O’Toole JE, Eichholz KM, Fessler RG. Surgical site infection rates after minimally invasive spinal surgery. J Neurosurg Spine. 2009; 11(4):471–476 [54] Smith JS, Saulle D, Chen CJ, et al. Rates and causes of mortality associated with spine surgery based on 108,419 procedures: a review of the Scoliosis Research Society Morbidity and Mortality Database. Spine. 2012; 37 (23):1975–1982 [55] Darden BV, II, Duncan J. Postoperative lumbar spine infection. Orthopedics. 2006; 29(5):425–429, quiz 430–431 [56] Dubberke ER, Reske KA, Yan Y, Olsen MA, McDonald LC, Fraser VJ. Clostridium difficile—associated disease in a setting of endemicity: identification of novel risk factors. Clin Infect Dis. 2007; 45(12):1543–1549 [57] Alexander JW, Solomkin JS, Edwards MJ. Updated recommendations for control of surgical site infections. Ann Surg. 2011; 253(6):1082–1093 [58] Rehman A, Rehman AU, Rehman TU, Freeman C. Removing outer gloves as a method to reduce spinal surgery infection. J Spinal Disord Tech. 2015; 28(6): E343–E346 [59] Barker FG, II. Efficacy of prophylactic antibiotic therapy in spinal surgery: a meta-analysis. Neurosurgery. 2002; 51(2):391–400, discussion 400–401 [60] Cheng MT, Chang MC, Wang ST, Yu WK, Liu CL, Chen TH. Efficacy of dilute betadine solution irrigation in the prevention of postoperative infection of spinal surgery. Spine. 2005; 30(15):1689–1693 [61] Molinari RW, Khera OA, Molinari WJ, III. Prophylactic intraoperative powdered vancomycin and postoperative deep spinal wound infection: 1,512 consecutive surgical cases over a 6-year period. Eur Spine J. 2012; 21 Suppl 4: S476–S482 [62] Strom RG, Pacione D, Kalhorn SP, Frempong-Boadu AK. Decreased risk of wound infection after posterior cervical fusion with routine local application of vancomycin powder. Spine. 2013; 38(12):991–994 [63] Mehbod AA, Ogilvie JW, Pinto MR, et al. Postoperative deep wound infections in adults after spinal fusion: management with vacuum-assisted wound closure. J Spinal Disord Tech. 2005; 18(1):14–17 [64] Ploumis A, Mehbod AA, Dressel TD, Dykes DC, Transfeldt EE, Lonstein JE. Therapy of spinal wound infections using vacuum-assisted wound closure: risk factors leading to resistance to treatment. J Spinal Disord Tech. 2008; 21 (5):320–323 [65] Crandall DG, Revella J, Patterson J, Huish E, Chang M, McLemore R. Transforaminal lumbar interbody fusion with rhBMP-2 in spinal deformity, spondylolisthesis, and degenerative disease—part 1: Large series diagnosis related outcomes and complications with 2- to 9-year follow-up. Spine. 2013; 38 (13):1128–1136

Instrumentation Complications following Spinal Tumor Surgery

52 Instrumentation Complications following Spinal Tumor Surgery Addisu Mesfin and Jacob M. Buchowski

52.1 Brief The skeletal system is the third most common site of metastases after the lung and liver. Within the skeletal system, the spine is the most common site of metastases. Metastatic disease can present with epidural spinal cord compression as well as spinal instability because of pathologic fractures. The thoracic spine is most frequently affected by metastatic disease followed by the lumbar spine and cervical spine. Surgical management of metastatic disease of the spine is predominantly palliative. Primary spinal tumors are rare and isolated malignant osseous tumor cases are candidates for en bloc resections. Instrument-related complications in spine tumor surgery can include failure of fixation in osteoporotic or lytic bone, failure of instrumentation across transitional zones of the spine (occipitocervical, cervicothoracic, thoracolumbar, lumbosacral), and instrumentation failure because of pseudarthrosis and because of use of short construct instrumentation following multilevel tumor resection.

52.2 Introduction Oncologic principles in the management of spinal tumors are integral to planning the extent of surgery. Spine tumors can be divided into extradural extramedullary (e.g., metastatic disease or pathology arising from osseous structures), intradural extramedullary (e.g., meningioma or schwannoma), and intradural intramedullary (e.g., ependymoma or astrocytoma).1 Extradural extramedullary is the most common type of spine lesion and specifically metastatic disease is the most common cause. In the United States,2 there were 1.2 million cases of cancer in 2012 and 577,190 deaths from cancer in 2012. The thoracic spine is frequently affected by metastatic disease (68–70%), followed by the lumbar spine (16–22%) and the cervical spine (8–15%).3,4,5 The vertebral body is the most common site of metastases. Anterior body support must be taken into consideration during surgical planning because posterior-only instrumentation in the setting of vertebral body collapse may lead to instrumentation failure. Mechanisms of metastatic spread can include hematogenous, through the valveless vertebral-venous plexus commonly referred to as Baston’s plexus, and seeding through the arterial supply of the vertebral body. Direct extension or invasion of the tumor from adjacent organs is another means of metastatic spread. In palliative cases where prevention of neurologic compromise and spinal stability are the goals, posteriorly based circumferential decompression and reconstruction with instrumentation can be performed. Surgical planning for spine tumor is ideally performed in a multidisciplinary manner. Radiation oncologists, medical oncologists, orthopedic spine surgeons, neurosurgeons, and importantly the patient and family must understand the patient’s prognosis and associated risk and benefits of the planned surgery.

Prognostic scores assist in the surgical planning process and in determining whether or not to operate. The modified Tokuhashi’s score is composed of six components (Karnofsky’s performance status, extraspinal bone metastases, number of metastases in the vertebral body, metastases to major internal organs, primary site of cancer, and the patient’s neurological status). Scoring can range from 0 to 18 with a higher score indicating better prognosis.6 The Tomita’s score is another prognostic score with three components (type of tumor, the presence of visceral metastases, and the presence of bone metastases). The scoring is from 2 to 10 with a lower score indicating better prognosis.7 Life expectancy of less than 3 months is usually the cut-off for nonoperative management. In addition to neurological compromise, spinal instability is a common indication for surgical management. Imaging-based classifications of stability include the Denis’ classification and Kostuik’s classification. The Denis’ classification divides the spine into three columns on the sagittal plane (anterior, middle, and posterior) and involvement of two or more columns is deemed as unstable. Recently, the Spine Instability Neoplastic Score (SINS) was developed to serve as a prognostic score for spinal instability. It is scored from 0 to 18. There are six components: location of tumor (junctional spine, mobile spine), presence of pain, type of lesion (lytic, blastic), radiographic alignment, presence of vertebral collapse, and involvement of posterior elements. A score of 0 to 6 is a stable spine, 7 to 12 is impending instability, and 13 to 18 is an unstable spine. SINS has been validated in a multidisciplinary manner.8 Tumors that commonly metastasize to the spine include thyroid, prostate, breast, lung, and renal cancers. Preoperative embolization must be taken into consideration for lytic vascular lesions such as renal cell cancer, thyroid cancer, and hepatocellular cancer. With newer chemotherapy modalities, cancer patients may be living longer. Thyroid and prostate cancer have the longest average life expectancy (48 months), and breast cancer (24–36 months) and certain types of pancreatic and lung cancers have the least longevity. Nonmetastatic malignant lesions in the spine include lymphoma and multiple myeloma. These are radiosensitive tumors and can be managed primarily with radiation and chemotherapy. However, multiple myeloma can present with unstable pathologic fractures requiring surgical management. Primary malignant lesions of the spine include chondrosarcoma, chordoma, osteosarcoma, and Ewing’s sarcoma. Primary aggressive benign tumors include giant cell tumor, Langerhans’ cell histiocytosis eosinophilic granuloma [EOG], aneurysmal bone cysts, osteoid osteomas, and osteoblastomas. The Weinstein–Boriani– Biagini classification can assist in the surgical planning for primary tumors of the spine.9 For malignant primary tumors, a curative approach such as en bloc spondylectomy or total en bloc spondylectomy (TES) can be attempted.10 These approaches apply the oncologic principles of en bloc resection as used in the extremities to provide marginal or wide margins.

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Thoracolumbar

Fig. 52.1 (a) Preoperative sagittal CT scan reconstruction demonstrating a pathologic C2 fracture in a 63-year-old patient with metastatic breast cancer who presented with severe neck pain. (b) Postoperative lateral plain radiograph demonstrating posterior stabilization from occiput to C5. The patient was treated with postoperative radiation therapy to prevent further destruction of C2.

52.3 Surgical Approaches 52.3.1 Posterior-Based Approaches Posterior-based approaches and instrumentation can be used throughout the spine. In the cervical spine, lateral mass screws and pedicle screws at C2 and C7 are commonly used. An occipital plate and occipitocervical instrumentation can be used to address upper cervical (C1, C2) metastatic disease (▶ Fig. 52.1). Whereas open decompression and pedicle screw stabilization are widely used in the thoracic and lumbar spine, percutaneous-based instrumentation systems are also being used. Posterior-based approaches allow for decompression of metastatic epidural compression. In the thoracic and lumbar spine, transpedicular decompression can provide adequate decompression depending on the extent of compression. If a wider decompression or anterior body support is needed in the thoracic spine, a costotransversectomy or a lateral extracavitary approach can also be used.11,12 Anterior-based support includes mesh cages, expandable cage, strut allograft, or polymethylmethacrylate (PMMA) (▶ Fig. 52.2). In the lumbar spine, the extracavitary approach is starting to be used for decompression and placing anterior column support.13,14 This technique is technically challenging because the nerve roots cannot be sacrificed as can be done in the thoracic spine. Potential advantages of an all-posterior approach include low morbidity and low cost. En bloc spondylectomy for spine tumors was first described by Stener in the 1960s.15,16,17 Tomita et al popularized the technique of TES at the Kanazawa University in Japan.10 With the advent of a fine cutting handheld saw that allowed for precise bone cuts, TES allows for posterior-based en bloc resection of tumors. In the thoracic spine, this is an all-posterior approach.

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The lumbar spine is addressed by combined anterior-posterior approaches. In the cervical spine, posterior-based approaches usually supplement anterior-based instrumentation. Following a corpectomy in metastatic cervical spine disease, it is advisable to supplement the construct with posterior-based instrumentation especially when resecting a lytic lesion. Posterior-based instrumentation is strongly recommended if performing corpectomy at two or more levels because of the higher failure rate of anterior-only instrumentation. En bloc resections of primary spine tumors have also been described in the cervical spine via a combined anterior and posterior approach, albeit en bloc resection is less common in the cervical than other regions.18,19 The vertebral artery may be ligated during these en bloc resections. Although metastasis to the sacrum is not common, chordomas frequently arise in the sacrum. En bloc approaches have been described for the resection of sacral chordomas. These tumors can be approached from an all-posterior approach or a combined anterior–posterior approach. Depending on the location of the chordoma and extent of resection, lumbo-sacro-pelvic fixation is usually needed.20,21

52.3.2 Anterior-Based Approaches Because the vertebral body is the most common site involved in metastatic disease, anterior-based approaches can be performed for direct decompression of the lesion.22 In the thoracic spine, anterior-based decompression is being performed less because of the advent of posterior-based anterior stabilization and decompression via transpedicular, costotransversectomy, and lateral extracavitary approaches. This can avoid the need of chest tubes and complications from the thoracotomy. In the

Instrumentation Complications following Spinal Tumor Surgery

Fig. 52.2 (a) Preoperative T2-weighted sagittal MRI image demonstrating a pathologic fracture of T11 with metastatic epidural spinal cord compression in a 58-year-old patient with metastatic renal cell cancer who presented with back pain and mild leg numbness and weakness. (b,c) Anteroposterior and lateral plain radiographs demonstrating posterior stabilization from T9 to L1 with posterior-based circumferential intralesional T11 tumor resection and reconstruction using polymethylmethacrylate.

cervical spine and lumbar spine, anterior approaches are frequently performed. Vascular surgeons are useful for the lumbar spine and can assist with exposure of the vascular elements. In the sacrum depending on the extent of presacral tumors, a colorectal surgeon is used to help with mobilization of the rectum and sigmoid. Because of high rates of infections associated with sacral wounds, a prophylactic colostomy can be performed.

52.3.3 Lateral-Based Approaches With the advent of lateral interbody fusion technology, some surgeons are using this approach for the management of thoracic and lumbar spine tumors. Especially in the thoracic spine, there is a learning curve associated with this technique.23,24 Larger series are pending on outcomes of this approach for spine tumors. Lateral mass screws are not approved by the Food and Drug Administration for cervical spine use.

52.4 Complications 52.4.1 Posterior-Based Instrumentation Pedicle screws and rod constructs are the standard instrumentation in the thoracic and lumbar spine. In the cervical spine, lateral mass screws are used with the exception of C2 and C7, where pedicle screws can be used. Titanium rods are frequently used because follow-up MRI may be necessary and less scatter is present in comparison to cobalt chrome rods. Posterior-based instrumentation can be placed percutaneously or via an open technique.

If extensive posterior decompression and fusion is performed, there is risk of pseudarthrosis and rod failure. However, the majority of spine tumor surgeries are palliative and pseudarthrosis may not be a significant concern as in other types of spine surgeries. However, patients with certain types of spine tumor are living longer and pseudarthrosis may occur. Pseudarthrosis may manifest with a broken rod (▶ Fig. 52.3). If a life expectancy of greater than 1 year is anticipated, consideration for anterior column support in addition to posterior instrumentation should be considered. When performing a three-column resection such as TES, adding a third or fourth rod to create a stiffer construct may be considered. This technique has been described for spinal deformity cases with three-column osteotomies.25 In cases of TES, instrumentation failure rates of 25 to 40% have been reported.26,27 Pedicle screw failure and pullout, especially with osteoporotic or lytic bone, can be a complication of spine tumor surgery.28 Anabolic agents for osteoporosis such as Forteo (Teriparatide; Eli Lilly Inc., Indianapolis, IN) are contraindicated in patients with malignancy. Supplementing the pedicle screws with PMMA is an option. Postoperative bracing may also be used. In the cervical spine, PMMA supplementation of lateral mass screws is not routinely performed; however, adjuncts to create stiffer constructs can include spine process cabling, anterior column support, and use of third rod. Instrumenting across junctional levels such as the cervicothoracic, thoracolumbar, and lumbosacral spine can lead to instrumentation failure.29 In the cervicothoracic region, the transition from the flexible cervical spine to the rigid thoracic

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Thoracolumbar

Fig. 52.3 Anteroposterior (a) and lateral (b) thoracic radiograph demonstrating bilateral broken rods (open arrow) 64 months following thoracic vertebrectomy and anterior column support for osteosarcoma (Image courtesy of Peter Rose, MD [Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN].)

spine can lead to instrumentation failure, especially if anterior column support is not present (▶ Fig. 52.4). Depending on the patient’s life expectancy and neurological status, revision of the instrumentation including longer constructs or anterior column support can be considered. In the thoracolumbar region, osteoporosis or lytic lesions can lead to proximal junction kyphosis and end-plate subsidence. If proximal junction kyphosis is greater than 20 degrees and the patient is symptomatic, then revision and extension of the construct can be considered. However, supplementing the pedicle screws with PMMA during initial implantation may be the best preventive method.30 When managing low lumbar lesions (L4, L5), sacral instrumentation is often needed. Because of significant forces across the lumbosacral junction, iliac fixation should be considered to avoid failure of the S1 screws. Newer techniques for lumbopelvic fixation, such as the S2-alar-iliac (S2AI) technique, avoid the extradissection required for the placement of traditional iliac screws.31 In addition, patients with metastatic disease can be underweight and because the S2AI screws are not as prominent as traditional iliac screws, there is less prevalence of symptomatic iliac screws.

52.4.2 Anterior Instrumentation In the cervical spine, anterior-based instrumentation such as mesh cages or strut allograft is supplemented with plates and

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screws. Anterior screw and graft dislodgments are complications that can occur following single- or multilevel corpectomy of the cervical spine. Although one or two vertebral bodies sustain pathologic fractures, the adjacent levels also have lytic lesions that can compromise anterior screw fixation (▶ Fig. 52.5). It is advisable to supplement anterior fixation with posterior-based instrumentation if poor bone quality is encountered. There have been descriptions of supplementing anterior cervical screws with PMMA. Multilevel en bloc resections have been described for cervical chordomas. In such cases, custom cage systems can be used that attach to the clivus to minimize instrumentation failure. Supplementation with occipitocervical fixation is also advisable. Anterior instrumentation in the thoracic and lumbar for spine tumors is frequently supplemented with posterior-based instrumentation. Plating of allografts or cages is not frequently performed. Cage subsidence is a concern following corpectomies especially in osteoporotic bone. If using expandable cages, it would be ideal to use the largest footprint available. Material options for expandable cages include titanium and polyether ether ketone (PEEK). The advantage of using a PEEK cage is less metal artifact when obtaining postoperative MRI. In regard to subsidence because of PEEK or titanium cages, the most important factor appears to be the foot print or surface area of the cage against the endplates.32 PEEK cages can be more expensive than titanium cages or strut allograft.

Instrumentation Complications following Spinal Tumor Surgery

Fig. 52.4 A 73-year-old man with renal cell metastasis to T1. (a) Sagittal CT demonstrating the lesion (arrow); (b) Sagittal MRI STIR sequence demonstrating lesion at T1 with some epidural extension. (c) The patient was managed with C5– T4 posterior spinal fusion with C7 and T1 laminectomy. Dominoes were used to connect the cervical 3.5-mm rod to the thoracic 5.5-mm rod. (d) At 8 months postoperatively, the patient had cervical rod pullout from the domino (arrow). (e) CT confirmed the failure was at the cervico– domino junction on the right. The patient opted nonoperative management as his renal cell had progressed and was seeking hospice care.

Fig. 52.5 Preoperative sagittal CT myelogram reconstruction (a) and lateral plain radiograph (b) demonstrating adjacent level destruction at L1 in a 47-year-old patient with giant cell tumor of L2 treated at an outside institution with multiple spinal operations resulting in an anterior spinal fusion from L1 to L3 with an intervertebral expandable cage and laminectomy from L1 to L3. (c) Lateral plain radiograph demonstrating an anterior–posterior tumor resection and reconstruction from T11 to L4 posteriorly and from T12 to L3 anteriorly. Patient was treated postoperatively with stereotactic radiosurgery and denosumab.

52.4.3 Lateral Instrumentation The experience with lateral interbody fusion for thoracic and lumbar tumors consists of case series. However, the principles of poor fixation and risk of implant subsidence in the setting of poor bone quality still apply.33,34 With the larger footprint of lateral interbody cages, there may be less risk of implant subsidence.

52.4.4 Sacral-Tumor–Related Complications Management of sacral tumors can consist of partial sacrectomy or complete sacrectomy. In cases of partial sacrectomy, instrumentation consists of lumbar pedicle screws with sacral instrumentation, if viable bone is present, and iliac instrumentation.

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Thoracolumbar In cases of complete sacrectomy, a construct consisting of femoral allograft and lumbopelvic fixation is used.35,36,37,38,39,40,41,42 As in other regions of the spine, there is risk of instrumentation failure. The benefit of iliac fixation is the option of putting up to three iliac screws if necessary. This has been described for spinal deformity and sacral fractures. The same principles of multiple fixation points in the ilium for sacral tumors can apply. Iliac instrumentation can consist of traditional iliac screws and the newer S2AI screw technique. The start point for the S2AI is in the bone bridge between the S1 and the S2 foramen and would be applicable for partial sacrectomies.31

52.5 Summary Management of patients with spinal tumor is fraught with potential instrumentation complications because of poor bone quality, pseudarthrosis, and large three-column resection that can lead to instrumentation failure. Tumor recurrence may also occur and compromise existing fixation points. Current posterior-based approaches in the thoracic spine allow for resection of the vertebral body and anterior column support. This approach is also starting to be used in the lumbar spine. In the cervical spine, a combined anterior–posterior approach is usually needed, especially with corpectomies and poor bone quality. Sacral tumors are rare, but when partial or complete sacrectomy is performed, appropriate planning for sacropelvic fixation is needed.

52.6 Future Directions Spinal tumor surgery is an area of ongoing innovation. As more vertebral decompressions are being performed from posteriorbased approaches, smaller cages are being developed. The combination of spinal stereotactic radiosurgery (SRS) with surgical decompression may lessen the amount of bone than needs to be resected in the vertebral body and potentially decrease instrumentation-based failure. This concept of “separation surgery” has been introduced by Laufer and colleagues.43 An instrumentation failure rate of 2.8% has been reported with this technique.44 The more precise radiation that is obtained with SRS has also been shown to decrease instrumentation failure as compared to conventional radiation therapy. A small series noted 43% instrumentation failure with conventional radiation therapy versus 0% with SRS. As SRS become more common, it is possible instrumentation failure may be diminished.45 Minimally invasive tumors stabilization and decompression is an area of future growth.46,47,48,49,50 Percutaneous screw fixation combined with open decompression are becoming more common. Tube-based tumor decompression and percutaneous stabilization have also been described. Lateral interbody fusion technique also allows for minimally invasive corpectomies of the thoracic and lumbar spine. If blood loss and patient outcomes are better with the minimally invasive techniques, more adoptions of these techniques may occur.

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References [1] Gebauer GP, Farjoodi P, Sciubba DM, et al. Magnetic resonance imaging of spine tumors: classification, differential diagnosis, and spectrum of disease. J Bone Joint Surg Am. 2008; 90 Suppl 4:146–162 [2] National Cancer Institute: https://seer.cancer.gov. Accessed March 3, 2017 [3] Brihaye J, Ectors P, Lemort M, Van Houtte P. The management of spinal epidural metastases. Adv Tech Stand Neurosurg. 1988; 16:121–176 [4] Constans JP, de Divitiis E, Donzelli R, Spaziante R, Meder JF, Haye C. Spinal metastases with neurological manifestations. Review of 600 cases. J Neurosurg. 1983; 59(1):111–118 [5] Mesfin A, Buchowski JM, Gokaslan ZL, Bird JE. Management of metastatic cervical spine tumors. J Am Acad Orthop Surg. 2015; 23(1):38–46 [6] Tokuhashi Y, Matsuzaki H, Oda H, Oshima M, Ryu J. A revised scoring system for preoperative evaluation of metastatic spine tumor prognosis. Spine. 2005; 30(19):2186–2191 [7] Kawahara N, Tomita K, Murakami H, Demura S. Total en bloc spondylectomy for spinal tumors: surgical techniques and related basic background. Orthop Clin North Am. 2009; 40(1):47–63, vi [8] Fourney DR, Frangou EM, Ryken TC, et al. Spinal instability neoplastic score: an analysis of reliability and validity from the spine oncology study group. J Clin Oncol. 2011; 29(22):3072–3077 [9] Hart RA, Boriani S, Biagini R, Currier B, Weinstein JN. A system for surgical staging and management of spine tumors. A clinical outcome study of giant cell tumors of the spine. Spine. 1997; 22(15):1773–1782, discussion 1783 [10] Tomita K, Kawahara N, Baba H, Tsuchiya H, Fujita T, Toribatake Y. Total en bloc spondylectomy. A new surgical technique for primary malignant vertebral tumors. Spine. 1997; 22(3):324–333 [11] Bilsky MH, Boland P, Lis E, Raizer JJ, Healey JH. Single-stage posterolateral transpedicle approach for spondylectomy, epidural decompression, and circumferential fusion of spinal metastases. Spine. 2000; 25(17):2240–2249, discussion 250 [12] Stoker GE, Buchowski JM, Kelly MP, Meyers BF, Patterson GA. Video-assisted thoracoscopic surgery with posterior spinal reconstruction for the resection of upper lobe lung tumors involving the spine. Spine J. 2013; 13(1):68–76 [13] Jandial R, Kelly B, Chen MY. Posterior-only approach for lumbar vertebral column resection and expandable cage reconstruction for spinal metastases. J Neurosurg Spine. 2013; 19(1):27–33 [14] Shen FH, Marks I, Shaffrey C, Ouellet J, Arlet V. The use of an expandable cage for corpectomy reconstruction of vertebral body tumors through a posterior extracavitary approach: a multicenter consecutive case series of prospectively followed patients. Spine J. 2008; 8(2):329–339 [15] Stener B, Johnsen OE. Complete removal of three vertebrae for giant-cell tumour. J Bone Joint Surg Br. 1971; 53(2):278–287 [16] Stener B. Total spondylectomy in chondrosarcoma arising from the seventh thoracic vertebra. J Bone Joint Surg Br. 1971; 53(2):288–295 [17] Stener B. Complete removal of vertebrae for extirpation of tumors. A 20-year experience. Clin Orthop Relat Res. 1989(245):72–82 [18] Jandial R, Kelly B, Bucklen B, et al. Axial spondylectomy and circumferential reconstruction via a posterior approach. Neurosurgery. 2013; 72(2):300–308, discussion 308–309 [19] Currier BL, Papagelopoulos PJ, Krauss WE, Unni KK, Yaszemski MJ. Total en bloc spondylectomy of C5 vertebra for chordoma. Spine. 2007; 32(9):E294–E299 [20] Arkader A, Yang CH, Tolo VT. High long-term local control with sacrectomy for primary high-grade bone sarcoma in children. Clin Orthop Relat Res. 2012; 470(5):1491–1497 [21] Clarke MJ, Dasenbrock H, Bydon A, et al. Posterior-only approach for en bloc sacrectomy: clinical outcomes in 36 consecutive patients. Neurosurgery. 2012; 71(2):357–364, discussion 364 [22] Sasagawa T, Kawahara N, Murakami H, et al. The route of metastatic vertebral tumors extending to the adjacent vertebral body: a histological study. J Orthop Sci. 2011; 16(2):203–211 [23] Karikari IO, Nimjee SM, Hardin CA, et al. Extreme lateral interbody fusion approach for isolated thoracic and thoracolumbar spine diseases: initial clinical experience and early outcomes. J Spinal Disord Tech. 2011; 24(6):368– 375

Instrumentation Complications following Spinal Tumor Surgery [24] Uribe JS, Dakwar E, Le TV, Christian G, Serrano S, Smith WD. Minimally invasive surgery treatment for thoracic spine tumor removal: a mini-open, lateral approach. Spine. 2010; 35(26) Suppl:S347–S354 [25] Scheer JK, Tang JA, Deviren V, et al. Biomechanical analysis of revision strategies for rod fracture in pedicle subtraction osteotomy. Neurosurgery. 2011; 69(1):164–172, discussion 172 [26] Matsumoto M, Watanabe K, Tsuji T, et al. Late instrumentation failure after total en bloc spondylectomy. J Neurosurg Spine. 2011; 15(3):320–327 [27] Matsumoto M, Tsuji T, Iwanami A, et al. Total en bloc spondylectomy for spinal metastasis of differentiated thyroid cancers: a long-term follow-up. J Spinal Disord Tech. 2013; 26(4):E137–E142 [28] Frankel BM, Jones T, Wang C. Segmental polymethylmethacrylate-augmented pedicle screw fixation in patients with bone softening caused by osteoporosis and metastatic tumor involvement: a clinical evaluation. Neurosurgery. 2007; 61(3):531–537, discussion 537–538 [29] Ramieri A, Domenicucci M, Ciappetta P, Cellocco P, Raco A, Costanzo G. Spine surgery in neurological lesions of the cervicothoracic junction: multicentric experience on 33 consecutive cases. Eur Spine J. 2011; 20 Suppl 1:S13–S19 [30] Kebaish KM, Martin CT, O’Brien JR, LaMotta IE, Voros GD, Belkoff SM. Use of vertebroplasty to prevent proximal junctional fractures in adult deformity surgery: a biomechanical cadaveric study. Spine J. 2013; 13(12):1897–1903 [31] Kebaish KM. Sacropelvic fixation: techniques and complications. Spine. 2010; 35(25):2245–2251 [32] Pekmezci M, McDonald E, Kennedy A, et al. Can a novel rectangular footplate provide higher resistance to subsidence than circular footplates? An ex vivo biomechanical study. Spine. 2012; 37(19):E1177–E1181 [33] Baaj AA, Dakwar E, Le TV, et al. Complications of the mini-open anterolateral approach to the thoracolumbar spine. J Clin Neurosci. 2012; 19(9):1265– 1267 [34] Rodgers WB, Gerber EJ, Patterson J. Intraoperative and early postoperative complications in extreme lateral interbody fusion: an analysis of 600 cases. Spine. 2011; 36(1):26–32 [35] Dickey ID, Hugate RR, Jr, Fuchs B, Yaszemski MJ, Sim FH. Reconstruction after total sacrectomy: early experience with a new surgical technique. Clin Orthop Relat Res. 2005; 438(438):42–50 [36] Kelly BP, Shen FH, Schwab JS, Arlet V, Diangelo DJ. Biomechanical testing of a novel four-rod technique for lumbo-pelvic reconstruction. Spine. 2008; 33 (13):E400–E406 [37] Zhu R, Cheng LM, Yu Y, Zander T, Chen B, Rohlmann A. Comparison of four reconstruction methods after total sacrectomy: a finite element study. Clin Biomech (Bristol, Avon). 2012; 27(8):771–776

[38] Mindea SA, Chinthakunta S, Moldavsky M, Gudipally M, Khalil S. Biomechanical comparison of spinopelvic reconstruction techniques in the setting of total sacrectomy. Spine. 2012; 37(26):E1622–E1627 [39] Guo W, Tang X, Zang J, Ji T. One-stage total en bloc sacrectomy: a novel technique and report of 9 cases. Spine. 2013; 38(10):E626–E631 [40] Bederman SS, Shah KN, Hassan JM, Hoang BH, Kiester PD, Bhatia NN. Surgical techniques for spinopelvic reconstruction following total sacrectomy: asystematic review. Eur Spine J. 2014; 23(2):305–319 [41] Doita M, Harada T, Iguchi T, et al. Total sacrectomy and reconstruction for sacral tumors. Spine. 2003; 28(15):E296–E301 [42] Hulen CA, Temple HT, Fox WP, Sama AA, Green BA, Eismont FJ. Oncologic and functional outcome following sacrectomy for sacral chordoma. J Bone Joint Surg Am. 2006; 88(7):1532–1539 [43] Laufer I, Iorgulescu JB, Chapman T, et al. Local disease control for spinal metastases following “separation surgery” and adjuvant hypofractionated or highdose single-fraction stereotactic radiosurgery: outcome analysis in 186 patients. J Neurosurg Spine. 2013; 18(3):207–214 [44] Amankulor NM, Xu R, Iorgulescu JB, et al. The incidence and patterns of hardware failure after separation surgery in patients with spinal metastatic tumors. Spine J. 2014; 14(9):1850–1859 [45] Harel R, Chao S, Krishnaney A, Emch T, Benzel EC, Angelov L. Spine instrumentation failure after spine tumor resection and radiation: comparing conventional radiotherapy with stereotactic radiosurgery outcomes. World Neurosurg. 2010; 74(4–5):517–522 [46] Massicotte E, Foote M, Reddy R, Sahgal A. Minimal access spine surgery (MASS) for decompression and stabilization performed as an out-patient procedure for metastatic spinal tumours followed by spine stereotactic body radiotherapy (SBRT): first report of technique and preliminary outcomes. Technol Cancer Res Treat. 2012; 11(1):15–25 [47] Schwab JH, Gasbarrini A, Cappuccio M, et al. Minimally invasive posterior stabilization improved ambulation and pain scores in patients with plasmacytomas and/or metastases of the spine. Int J Surg Oncol. 2011; 2011:239230 [48] Rose PS, Clarke MJ, Dekutoski MB. Minimally invasive treatment of spinal metastases: techniques. Int J Surg Oncol. 2011; 2011:494381 [49] Roldan H, Ribas-Nijkerk JC, Perez-Orribo L, Garcia-Marin V. Stabilization of the cervicothoracic junction in tumoral cases with a hybrid less invasiveminimally invasive surgical technique: report of two cases. J Neurol Surg A Cent Eur Neurosurg. 2014; 75(3):236–240 [50] Zairi F, Arikat A, Allaoui M, Marinho P, Assaker R. Minimally invasive decompression and stabilization for the management of thoracolumbar spine metastasis. J Neurosurg Spine. 2012; 17(1):19–23

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53 Cervical Kyphosis Christopher A. Burks, Lauren M. Burke, and Adam L. Shimer

53.1 Introduction Whether iatrogenic, congenital, secondary to degenerative changes, or because of other etiologies, cervical kyphosis (CK) is a difficult problem to address. Avoidance of iatrogenic postoperative malalignment is imperative, but not always predictable. The goal of this chapter is to discuss avoidance, diagnosis, and management of CK.

53.2 CK Background The normal resting posture of a healthy cervical spine is lordotic in nature. CK may develop secondary to degenerative changes in the intervertebral disc, trauma, infection, inflammatory arthritides, or neoplastic disease; however, most commonly CK is iatrogenic. Albert and Vacarro described the etiology, biomechanics, diagnosis, and treatment strategies for postlaminectomy CK.1 Postsurgical CK can occur because of pseudarthrosis and settling of an anterior interbody graft, failure to achieve normal lordosis during surgery, or disruption of stabilizing structures posteriorly. Avoidance of such complications requires careful surgical planning and execution. Postlaminectomy kyphosis is the most common iatrogenic cause of CK with a reported incidence of up to 21% in patients undergoing laminectomy for cervical spondylotic myelopathy.2 Exact incidence varies widely depending on multifactorial influences, such as age, severity of preoperative deformity, and the presence of preoperative spondylolisthesis, as well as the extent of the surgical resection.1,2,3,4,5 Children are at a higher risk of CK as a complication of posterior laminectomy because of their continued growth potential, relative increase in ligamentous laxity, more horizontal facet orientation, and incomplete ossification of vertebrae.6,7,8 Laminectomy in children is most commonly performed to resect an intradural or intramedullary neoplasm and adjuvant external beam radiation therapy may also play a prominent role in the development of postlaminectomy kyphosis. Much of the discussion on CK is out of the scope of this chapter. The focus of this chapter is to review CK as both a complication of and an indication for cervical spine surgery. We will briefly review the complications that occur with the use of cervical instrumentation, specifically as it relates to CK, as subsequent chapters will go into greater detail.

53.3 Relevant Anatomy The cervical spine acts to support and orient the head, and to protect the spinal cord and nerve roots. The cervical load-bearing axis lies posteriorly to the subaxial vertebral bodies. The cervical vertebral bodies are relatively small, bearing the least weight of all the spinal vertebrae. They primarily resist compressive forces, whereas the posterior elements primarily resist tensile forces. Anatomic studies showed that 36% of axial load was through the anterior vertebral bodies, whereas 64% was via the posterior elements including the facet joints. In a classic

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biomechanical study, Pal and Sherk demonstrated the importance of the posterior elements in load sharing in the cervical spine. They utilized five cadaveric cervical spines and applied an axial load. They demonstrated that 36% of the load was transmitted to the vertebral bodies and 64% to the posterior elements.9 The lateral edges of the superior bodies are upturned to form the uncinate processes. The facet joints have a limited gliding motion, with the plane of articulation being more horizontally oriented to allow a greater range of motion in the cervical spine. The superior articular process is anterior and inferior to the inferior articular process of the cephalad vertebra. Flexion and extension of the cervical spine provides a wide arc of motion, averaging 90 degrees. Extension of the neck is limited by the anterior longitudinal ligament, anterior cervical musculature, fascia, and visceral structures. Posterior ligaments and musculature, particularly the interspinous ligaments, ligamentum flavum, and ligamentum nuchae, resist cervical flexion and the development of kyphosis.1 The aged spine cannot withstand the same stress as a juvenile spine. Ligamentous laxity reduces resistance to distractive forces. Disc desiccation and loss of disc height places increased axial load on the anterior vertebral bodies resulting in vertebral wedging, ultimately leading to CK and abnormal shear forces. As the center of gravity moves anterior to the bodies, the posterior spinal musculature must continually contract to keep the head upright, causing fatigue, neck pain, and further decompensation and kyphosis. Although important to review, the anatomy discussed earlier is altered during revision surgery, either anterior or posterior. Thus, detailed preoperative planning is imperative for a revision operation.

53.4 Presentation Axial neck pain and neurologic deficits, including radiculopathy and myelopathy, are common presenting symptoms of CK.1,10 Severe kyphotic deformity may negatively impact forward gaze and swallowing capabilities. This “chin-on-chest” deformity can be debilitating for the patient, and difficult to treat for the surgeon. CK places the posterior cervical musculature at a biomechanical disadvantage, leading to fatigue. Advanced degenerative disc disease and muscle fatigue can both cause axial neck pain. As the deformity progresses, the spinal cord drapes over the posterior vertebral bodies, shifting ventrally in the canal. Neurologic deficits can occur as a result of central or foraminal stenosis, tethering of the nerve roots with anterior positioning of the spinal cord, effacement of the spinal cord on the vertebral bodies, and additionally, repetitive trauma that can occur with normal flexion and extension of the neck in the setting of CK.

53.5 Diagnosis First and foremost, a detailed history, followed by a thorough physical exam, elucidates meaningful information. Ask pertinent questions about symptoms, past surgical history, and prior

Cervical Kyphosis treatments. Treatment of CK relies also on the diagnosis of fixed versus flexible deformity. In most cases, CK is not visible on gross inspection of the patient, but diagnosed radiographically. Standard cervical spine Xray series includes anteroposterior (AP) and lateral, and likely a swimmer’s, view to ensure adequate visualization of the C7–T1 interspace. Dynamic flexion and extension X-rays evaluate flexibility and may reveal instability. Full-length scoliosis films can determine overall sagittal balance. Computed tomography (CT), CT myelogram, and magnetic resonance imaging (MRI) permit the further evaluation of bony anatomy and compression of the spinal cord and nerve roots. When evaluating a postoperative patient, CT is also helpful in evaluating fusion status, existence of a pseudarthrosis, the amount of bony resection, and hardware or graft position. The addition of radiopaque dye for a myelogram aids in the assessment of the decompression or presence of residual compression sites. Multiple methods have been proposed for radiographically measuring cervical sagittal alignment, with the Cobb’s method from C2 to C7 being the most common.11 Studies have addressed normal alignment of the cervical spine, and although there is no standardized value of normal cervical lordosis, reported range is 15 to 40 degrees.12,13

53.6 Treatment CK can be managed conservatively or surgically. Conservative treatments used for the management of symptoms secondary to kyphosis include physical therapy, traction, nonsteroidal anti-inflammatory medicines, steroid injections, and other modalities. Indications for further surgical intervention include intractable pain, neurologic deficits, progressive deformity, or disability, such as dysphagia or difficulty with forward gaze. Principal goals in the management of CK are to correct sagittal profile, decompress neural elements, and stabilize the spine.

In the patient with iatrogenic CK, revision surgery should not be undertaken lightly and careful preoperative planning is imperative. Surgical treatment strategies may be composed of anterior, posterior, or dual approaches. Preoperative cervical traction with cranial tongs may result in slow, gentle, controlled correction of the deformity in an awake patient that can be serially monitored for any neurologic changes. Each strategy must be individualized for the patient, depending on symptoms, previous surgery, and the indication for surgery. Vocal cord function should be analyzed by direct laryngoscopy prior to revision anterior cervical surgery. CK as a result of failed anterior surgery in the setting of graft settling, hardware failure, and pseudarthrosis is best revised through an anterior approach. Reported incidence of pseudarthrosis after anterior cervical discectomy and interbody fusion ranges from 0 to 50%, and up to 30% of these are asymptomatic and may be treated nonoperatively.14,15 Excessive settling of an interbody graft in the setting of a pseudarthrosis and failed hardware can lead to focal kyphosis. The symptomatic patient in this scenario is best treated with revision anterior surgery, removal of hardware, and exploration of fusion, followed by repeat endplate preparation, correction of kyphosis with anterior interbody placement, and anterior cervical plating. The presence of focal kyphosis because of anterior pseudarthrosis and hardware failure is treated differently than a patient with post-laminectomy kyphosis. In addition, decompression of the spinal cord for myelopathy versus root decompression for radiculopathy changes the surgical management in revision anterior surgery. Fixed versus flexible deformity, presence of previous hardware, and previous anterior approach all require additional preoperative planning. Treatment algorithm of postlaminectomy kyphosis centers on fixed versus flexible deformity, area of stenosis, and symptoms. If the sagittal profile corrects to neutral on extension radiographs, this patient most likely can be treated with anterior-only or posterior-only procedure (▶ Fig. 53.1). Multilevel

Fig. 53.1 Lateral radiograph (a) of a 58-year-old woman with cervical myelopathy, who underwent C4–C6 laminectomies and developed postlaminectomy kyphosis 6 months later (b) with junctional stenosis and difficulty maintaining horizontal gaze. She was treated with a C3–C7 anterior cervical discectomy and fusion (c).

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Thoracolumbar anterior discectomy and fusion is preferred because it allows segmental correction of lordosis, increased number of fixation points, and has lower graft dislodgement rates than a long corpectomy.1,15,16 Cervical plating helps prevent graft dislodgment and increases union rates.16,17 A corpectomy should be performed at levels with spinal cord compression, whereas a discectomy can be performed at additional levels, if needed.18 Anterior-only surgical approach to postlaminectomy kyphosis proves to be a safe and effective method of correction while avoiding posterior fusion and instrumentation.19 Posterior-only instrumentation of postlaminectomy kyphosis, utilizing lateral mass and plate or rod fixation, is a good option for those patients with a flexible deformity, and minimal anterior stenosis accounting for the symptoms. A combined anterior and posterior procedure may be indicated in patients with dorsal spinal cord compression requiring posterior decompressive strategies, those with instability, and those with ankylosed facet joints (▶ Fig. 53.2). Posterior instrumentation and arthrodesis is also used to augment anterior procedures in patients requiring three or more corpectomies for kyphosis correction and poor bone quality15,20,21 (▶ Fig. 53.3). The combined approach allows for full decompression of neural

elements, lengthening of the anterior column, shortening of the posterior column, and spinal stabilization.

53.7 Instrumentation Many of the techniques commonly used today, including instrumentation, were only established in the past few decades and have undergone tremendous development since their birth. The first anterior cervical plate and screw system was developed by Orozco Delclos and Llovet Tapies in 1972 for use in cervical trauma.22 Caspar et al refined the plate, using it to stabilize the cervical spine and enhance fusion after trauma.23 The benefit of plate fixation is immediate stabilization, prevention of graft extrusion or subsidence, maintenance of sagittal alignment, and reduction of the need for external immobilization or posterior instrumentation. Numerous anterior cervical plating systems are approved for use by the Food and Drug Administration (FDA) for anterior intervertebral screw fixation of the cervical spine at levels C2–T1. Complications related to the use of anterior cervical instrumentation are vast and can be related to implant limitations, application, and surgical technique. Utilization of the standard

Fig. 53.2 Neutral and extension lateral and sagittal STIR images (a–c) of a 71-year-old man with severe cervical myelopathy and cervical instability. He was treated with preoperative surgical traction and C3–T1 anterior cervical discectomy and fusion and C2–T2 posterior instrumentation with revision decompression (d).

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Cervical Kyphosis

Fig. 53.3 Lateral radiograph (a) of a 64-year-old man with a history of carcinoma of the base of the tongue who presented with severe cervical myelopathy and a fixed cervical kyphosis. He was treated with a C3–C5 corpectomy backed up with posterior instrumentation from C2 to C7. (b) Intraoperative frozen section positive for chronic osteomyelitis.

Smith–Robinson approach to the anterior cervical spine places multiple structures at risk, such as the carotid sheath and its contents, the esophagus, the sympathetic chain, and the recurrent laryngeal nerve among others. In a retrospective review, Fountas et al documented the complications of more than 1,000 consecutive anterior cervical discectomy and fusion (ACDF) procedures. Their complication rate was 19.3% overall, with dysphagia being the most common. Implant-related complications were 0.1%.24 Familiarity with anatomy of the neck and careful surgical technique are imperative in avoiding injury to these structures. Multiple types of anterior cervical plating symptoms exist with much of the variation dealing with the screw mechanism. The devices are classified as class II medical devices subject to 510k premarket notification to the FDA. Their use is recognized and monitored by the FDA under the following product codes: KWQ 21 CFR 888.3050, ODP 21 CFR 888.3080, and OVE 21 CFR 888.3080.25 Static and constrained systems provide the most rigid constructs with resistance to both angular and translational motion. Dynamic and unconstrained systems may allow for both translation and angular motion. Dynamic plates allow for micromotion at the graft site to increase stress seen by the graft to improve fusion rates in accordance to Wolff’s law. Fusion rates with the use of dynamic plating systems are equivocal or slightly higher than the more rigid static systems; however, static systems are associated with less risk of graft subsidence, hardware failure, and better maintenance of lordotic correction. In a systematic review, Campos and Botelho assessed the differences in outcomes and complications between dynamic and rigid fixation systems for anterior cervical instrumentation. They found no significant differences in fusion rates between the systems, though individual studies showed improved fusion rates with the use of dynamic systems. There was a trend toward loss of lordotic correction with the use of dynamic systems when compared to static plate systems.26,27,28,29,30 Most plates incorporate a locking mechanism to prevent screws from backing out, as screw migration into adjacent structures, and even the remote gastrointestinal tract, has been reported.24,31,32 Attention to detail by ensuring these mechanisms are locked can easily lead to avoidance of screw

migration. Standalone interbody cages with integrated screw fixation have recently been introduced with the goals of increasing fusion rates, maintaining sagittal correction, and providing a low profile to minimize implant prominence; however, no long-term comparative studies exist comparing standalone interbody devices versus conventional graft and plate systems.33 There is only a single cleared system approved by the FDA that includes posterior cervical screw fixation (Medtronic Axis Fixation System, Medtronic Sofamor Danek; Memphis, TN; FDA product code NKG). Despite extensive literature on the safety and efficacy for the use of cervical lateral mass and pedicle screws, as well as the strong recommendation of an FDA Advisory Panel in 2012 that they be made class II devices, their use remains unclassified by the FDA.25 Despite this, multiple screw systems exist on the market for lateral mass or pedicle fixation, and despite their off-label use, they are currently the predominant technique for achieving posterior cervical fixation and have largely replaced the use of sublaminar wires and hooks. Currently, the only posterior cervical instrumentation type classified by the FDA is plates for laminoplasty (NQW 21 CFR 888.3050).25 Complications can arise related to the use of posterior cervical instrumentation. Complications associated with the placement of pedicle and lateral mass screws in the subaxial cervical spine include vertebral artery, nerve root, and spinal cord injuries; pedicle and lateral mass fractures; and cerebrospinal fluid leak.34,35,36,37,38 The risk of these complications can be mitigated by a careful review of preoperative imaging for anomalous anatomy, careful surgical technique, and placement of lateral mass screws, as first described by Levine et al,39 as opposed to pedicle screws.38 Implant complications include screw pull out, rod failure, and loss of correction, though this occurs in less than 1% of cases. In a systematic review, Coe et al sought to identify complications associated with the use of lateral mass screws in the subaxial cervical spine. They found lateral mass screw complications to be at worst, equivalent to those associated with wiring techniques. They found a 1% incidence of nerve injury, less than 1% incidence of screw failure, no vertebral artery injuries, and a 97% fusion rate.37 Kyphosis as a result

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Thoracolumbar of the use of posterior instrumentation is rare and is avoidable with careful surgical technique. Proper contouring of the rods, release of ankylosed facet joints, care not to violate the facet joints or release the interspinous ligament at the proximal and distal extent of the instrumentation, and patient positioning are all important steps to prevent a kyphotic postoperative sagittal profile. Furthermore, meticulous soft-tissue handling and closure of the posterior soft tissues is paramount to prevent further alterations to cervical biomechanics.

53.8 Summary Postoperative CK is a fairly avoidable complication of cervical spine surgery, and can be a difficult problem to address when it occurs. Avoidance altogether is the best measure. Posterior facet fusion with or without instrumentation in the setting of laminectomy allows for increased stability and maintenance of the sagittal profile. The use of an anterior plate and screw system when performing anterior discectomy or corpectomy with interbody fusion aides in preventing graft dislodgement and subsidence that would otherwise possibly lead to focal segmental kyphosis. Careful preoperative planning in patients with kyphosis is imperative.

53.9 Key Points ●

●

●

Cervical kyphosis can be both idiopathic and iatrogenic. Careful preoperative planning can mitigate the risk of iatrogenic CK. Dynamic versus static anterior fixation requires additional research, though early research shows a benefit to static or constrained fixation in minimizing post anterior cervical fusion kyphosis. Prevention of cervical kyphosis requires an individualized approach to both the patient’s anatomy and symptomatic imaging findings. There is not a ‘one size fits all’ approach to the prevention and management of cervical kyphosis in the setting of cervical myeloradiculopathy.

References [1] Albert TJ, Vacarro A. Postlaminectomy kyphosis. Spine. 1998; 23(24):2738– 2745 [2] Kaptain GJ, Simmons NE, Replogle RE, Pobereskin L. Incidence and outcome of kyphotic deformity following laminectomy for cervical spondylotic myelopathy. J Neurosurg. 2000; 93(2) Suppl:199–204 [3] Butler JC, Whitecloud TS, III. Postlaminectomy kyphosis. Causes and surgical management. Orthop Clin North Am. 1992; 23(3):505–511 [4] Katsumi Y, Honma T, Nakamura T. Analysis of cervical instability resulting from laminectomies for removal of spinal cord tumor. Spine. 1989; 14 (11):1171–1176 [5] Mikawa Y, Shikata J, Yamamuro T. Spinal deformity and instability after multilevel cervical laminectomy. Spine. 1987; 12(1):6–11 [6] Bell DF, Walker JL, O’Connor G, Tibshirani R. Spinal deformity after multiplelevel cervical laminectomy in children. Spine. 1994; 19(4):406–411 [7] Yasuoka S, Peterson HA, Laws ER, Jr, MacCarty CS. Pathogenesis and prophylaxis of postlaminectomy deformity of the spine after multiple level laminectomy: difference between children and adults. Neurosurgery. 1981; 9 (2):145–152

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[8] Yasuoka S, Peterson HA, MacCarty CS. Incidence of spinal column deformity after multilevel laminectomy in children and adults. J Neurosurg. 1982; 57 (4):441–445 [9] Pal GP, Sherk HH. The vertical stability of the cervical spine. Spine (Phila Pa 1976). 1988; 13(5):447–449 [10] Ferch RD, Shad A, Cadoux-Hudson TA, Teddy PJ. Anterior correction of cervical kyphotic deformity: effects on myelopathy, neck pain, and sagittal alignment. J Neurosurg. 2004; 100(1) Suppl Spine:13–19 [11] Harrison DE, Harrison DD, Cailliet R, Troyanovich SJ, Janik TJ, Holland B. Cobb method or Harrison posterior tangent method: which to choose for lateral cervical radiographic analysis. Spine. 2000; 25(16):2072–2078 [12] Machino M, Yukawa Y, Hida T, et al. Cervical alignment and range of motion after laminoplasty: radiographical data from more than 500 cases with cervical spondylotic myelopathy and a review of the literature. Spine. 2012; 37 (20):E1243–E1250 [13] Han K, Lu C, Li J, et al. Surgical treatment of cervical kyphosis. Eur Spine J. 2011; 20(4):523–536 [14] Bohlman HH, Emery SE, Goodfellow DB, Jones PK. Robinson anterior cervical discectomy and arthrodesis for cervical radiculopathy. Long-term follow-up of one hundred and twenty-two patients. J Bone Joint Surg Am. 1993; 75 (9):1298–1307 [15] Zdeblick TA, Hughes SS, Riew KD, Bohlman HH. Failed anterior cervical discectomy and arthrodesis. Analysis and treatment of thirty-five patients. J Bone Joint Surg Am. 1997; 79(4):523–532 [16] Herman JM, Sonntag VK. Cervical corpectomy and plate fixation for postlaminectomy kyphosis. J Neurosurg. 1994; 80(6):963–970 [17] Ebraheim NA, DeTroye RJ, Rupp RE, Taha J, Brown J, Jackson WT. Osteosynthesis of the cervical spine with an anterior plate. Orthopedics. 1995; 18 (2):141–147 [18] Riew KD, Hilibrand AS, Palumbo MA, Bohlman HH. Anterior cervical corpectomy in patients previously managed with a laminectomy: short-term complications. J Bone Joint Surg Am. 1999; 81(7):950–957 [19] Steinmetz MP, Kager CD, Benzel EC. Ventral correction of postsurgical cervical kyphosis. J Neurosurg. 2003; 98(1) Suppl:1–7 [20] Zdeblick TA, Bohlman HH. Cervical kyphosis and myelopathy. Treatment by anterior corpectomy and strut-grafting. J Bone Joint Surg Am. 1989; 71 (2):170–182 [21] Park Y, Riew KD, Cho W. The long-term results of anterior surgical reconstruction in patients with postlaminectomy cervical kyphosis. Spine J. 2010; 10(5):380–387 [22] Orozco DR, Llovet TR. Osteosintesis en las lesiones traumaticas y degeneratives de la columna vertebral. Revista Traumatol Chirurg Rehabil. 1972; 1:45–52 [23] Caspar W, Barbier DD, Klara PM. Anterior cervical fusion and Caspar plate stabilization for cervical trauma. Neurosurgery. 1989; 25(4):491–502 [24] Fountas KN, Kapsalaki EZ, Nikolakakos LG, et al. Anterior cervical discectomy and fusion associated complications. Spine (Phila Pa 1976). 2007; 32 (21):2310–2317 [25] Food and Drug Administration: http://www.fda.gov/downloads/AdvisoryCommittees/CommitteesMeetingMaterials/MedicalDevices/MedicalDevicesAdvisoryCommittee/OrthopaedicandRehabilitationDevicesPanel/ UCM319946.pdf. Updated 2012. Accessed November 10, 2014 [26] DuBois CM, Bolt PM, Todd AG, Gupta P, Wetzel FT, Phillips FM. Static versus dynamic plating for multilevel anterior cervical discectomy and fusion. Spine J. 2007; 7(2):188–193 [27] Ipsen BJ, Kim DH, Jenis LG, Tromanhauser SG, Banco RJ. Effect of plate position on clinical outcome after anterior cervical spine surgery. Spine J. 2007; 7 (6):637–642 [28] Nunley PD, Jawahar A, Kerr EJ, III, Cavanaugh DA, Howard C, Brandao SM. Choice of plate may affect outcomes for single versus multilevel ACDF: results of a prospective randomized single-blind trial. Spine J. 2009; 9(2):121–127 [29] Campos RR, Botelho RV. Systematic review of the effect of dynamic fixation systems compared with rigid fixation in the anterior cervical spine. Eur Spine J. 2014; 23(2):298–304 [30] Pitzen TR, Chrobok J, Stulik J, et al. Implant complications, fusion, loss of lordosis, and outcome after anterior cervical plating with dynamic or rigid plates: two-year results of a multi-centric, randomized, controlled study. Spine. 2009; 34(7):641–646 [31] Fountas KN, Kapsalaki EZ, Machinis T, Robinson JS. Extrusion of a screw into the gastrointestinal tract after anterior cervical spine plating. J Spinal Disord Tech. 2006; 19(3):199–203

Cervical Kyphosis [32] Gazzeri R, Tamorri M, Faiola A, Gazzeri G. Delayed migration of a screw into the gastrointestinal tract after anterior cervical spine plating. Spine. 2008; 33 (8):E268–E271 [33] Nayak AN, Stein MI, James CR, et al. Biomechanical analysis of an interbody cage with three integrated cancellous lag screws in a two-level cervical spine fusion construct: an in vitro study. Spine J. 2014; 14(12):3002–3010 [34] Stevens QE, Majd ME, Kattner KA, Jones CL, Holt RT. Use of spinous processes to determine the optimal trajectory for placement of lateral mass screws: technical note. J Spinal Disord Tech. 2009; 22(5):347–352 [35] Yukawa Y, Kato F, Ito K, et al. Placement and complications of cervical pedicle screws in 144 cervical trauma patients using pedicle axis view techniques by fluoroscope. Eur Spine J. 2009; 18(9):1293–1299

[36] Abumi K, Shono Y, Ito M, Taneichi H, Kotani Y, Kaneda K. Complications of pedicle screw fixation in reconstructive surgery of the cervical spine. Spine. 2000; 25(8):962–969 [37] Coe JD, Vaccaro AR, Dailey AT, et al. Lateral mass screw fixation in the cervical spine: a systematic literature review. J Bone Joint Surg Am. 2013; 95 (23):2136–2143 [38] Yoshihara H, Passias PG, Errico TJ. Screw-related complications in the subaxial cervical spine with the use of lateral mass versus cervical pedicle screws: a systematic review. J Neurosurg Spine. 2013; 19(5):614–623 [39] Levine AM, Mazel C, Roy-Camille R. Management of fracture separations of the articular mass using posterior cervical plating. Spine. 1992; 17(10) Suppl: S447–S454

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54 Instrumentation Complications Occurring from Thoracic Hyperkyphosis Paul Millhouse, Loren Mead, Christie E. Stawicki, and Kris E. Radcliff

54.1 Introduction Gross deformity of the thoracic curve can drastically increase the rate of surgical complications. If left untreated, the deformity can progress and result in weakened function of the heart and lungs, cord compression, neurologic impairment, and socioeconomic debilitations.1,2 Overall, patients suffering from hyperkyphosis (HK) can have complication rates as high as 15%, with drastically increased risk as patients advance in age.3 HK often requires significant rod contouring which can predispose to rod breakage. Moreover, HK requires advanced corrective osteotomies to obtain appropriate alignment. Osteotomies are associated with their own set of complications such as instrumentation failure, wound infection, damage to the dura, neurological deficits, and pseudarthrosis.4 Even with successful osteotomies, there is an increased risk of kyphosis, particularly proximal junctional kyphosis (PJK).23 Spinal cord injury and other serious injuries can also occur from correcting kyphosis, particularly from anterior column-lengthening procedures. Moreover, positioning patients with HK on the operating table can prove difficult, especially those with ankylosing spondylitis.

54.2 Relevant Anatomy The typical thoracic spine has 12 vertebrae; however, some anatomic variants can have one more or one fewer segments.24 Each of these segments has an osteoligamentous connection to the rib cage.24 Because of the presence of the rib cage, the thoracic spinal motion is limited in comparison to the cervical and lumbar spine.24 The normal curve of the thoracic spine is a projecting kyphosis ranging from 20 to 40 degrees that extends from T2 to T12 with an apex at T7.4,5,6 The curve results from the greater superior-to-inferior measurements of the thoracic vertebral segment’s posterior side.7 The causes of HK include trauma, poor posture, bone degeneration and osteoporosis, scoliosis, Pott’s disease, and Scheuermann’s disease.8 The degree of kyphosis in the thoracic spine can be defined by using a plumb line to determine sagittal imbalance. On the lateral radiograph, a plumb line is placed on the C7 vertebral segment and extended caudally/inferiorly. The patient has sagittal plane imbalance when the plumb line extends on the anterior side of the sacrum. This positive sagittal balance can lead to severe discomfort and handicap.2 The extent of the kyphosis directs the necessary treatment. Curvatures greater than 30 degrees can be considered candidates for surgery. Patients with a kyphosis ranging between 30 and 50 degrees should be assessed for surgery only if they have reached skeletal maturity and the rate of postural degeneration is advanced. Beyond 50 degrees, patients should be strongly considered for surgery because the rate of curvature progression is serious (1 degree or greater annually). Without treatment, the progression of the kyphosis can lead to pain, poor respiratory ability, and disability.2 The standard indication for surgery is a kyphosis associated

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with pain and resistant to conservative treatment; however, some clinicians advise surgical intervention even in cases of deformity without pain.3 Scheuermann’s kyphosis (SK) is one cause of thoracic HK. There is a paucity of literature on the natural history of Scheuermann’s disease contributing to a lack of consensus on surgical indications, with differing accounts of the degree of discomfort, handicap, and deterioration rate of the thoracic curvature.2 Usually, patients suffering from SK progress into a hunched posture with the shoulders and head bent forward. Whereas this appearance is not always associated with pain, affected individuals may have persistent discomfort that classically ceases as the skeleton reaches maturity.7 Typical magnetic resonance imaging (MRI) may demonstrate wedged vertebral segments, malformed vertebral endplates, disk degeneration, and decreased development of the anterior aspect of the vertebrae.2 SK characteristically has a thoracic curvature more than 45 degrees as well as wedging of one or more vertebral segments greater than 5 degrees. The degree of vertebral wedging can be determined on lateral radiographs by measuring the angle formed between lines placed parallel to the vertebra’s bony endplates. Patients suffering from Scheuermann’s disease have malformations of the cartilaginous end plate and the annular apophyses as well as the end plates of the adjoining vertebral bodies. The end plate may also have evidence of increased levels of mucopolysaccharides, reduced collagen, and disorganized endochondral ossification.2 The resultant kyphotic spine is often quite rigid, which can cause biomechanical instrumentation failure at the junction with the more flexible cervical spine.7

54.3 Complications The various complications associated with thoracic HK can be broadly grouped into biological, biomechanical, and surgical approach-related failures. Biological failures are the result of infection, osteoporosis, pseudarthrosis, and various comorbidities. Owing to the complicated nature of the surgical procedures used to treat HK, patients are susceptible to higher wound infection rates. The likelihood of infection increases with longer operative time and the use of hardware, which are standard characteristics of HK surgical correction. Comorbidities, including steroid and tobacco use, history of cancer, radiation treatment, spinal trauma, and vitamin deficiency, are also factors that increase the risk of infection.5 These comorbidities may also have the effect of delaying healing and decreasing bone density. Adequate bone quality is vital for the successful biomechanical integration of hardware within the thoracic spine. Thus, osteoporosis is another biological factor that can increase complications in the treatment of HK. Osteoporotic vertebral endplates can contribute to failure of instrumentation fixation and loosening of implants.5 The

Instrumentation Complications Occurring from Thoracic Hyperkyphosis failure of instrumentation can cause deformity, increase pain, and may require revision procedures. Patients suffering from HK are at increased risk of biomechanical failures. These failures typically occur at either endpoint of instrumentation fixation. For example, the distal fixation point in posterior dual rod constructs can fail at a rate of 0 to 3%.9 Some common biomechanical failures associated with HK include rod breakage and junctional kyphosis, especially PJK. Central rods, sometimes used in pedicle subtraction osteotomy (PSO) and Smith–Petersen osteotomy (SPO), are at greater risk of failure in the presence of preoperative kyphosis.10 With central rod constructs, the degree of rod contouring required by these procedures can lead to overshortening as well as laminar fractures.11 Preexisting kyphosis is also a risk factor for junctional kyphosis due to the increased stresses borne between the rigid thoracic spine and the more flexible lumbar spine. The upper instrumented vertebra becomes strained and progressively weakens, potentially leading to double-digit degrees of deformity and eventually proximal junction breakdown.12 Vertebroplasty is sometimes used to supplement corrective procedures to lessen the chance of proximal junctional kyphosis (PJK).13 To ameliorate the risks of distal junctional kyphosis, one should extend the level of fusion to the sagittal stable vertebra (SSV), which is the most proximal lumbar vertebra that crosses a vertical line drawn from the posterosuperior sacral corner.3 Another biomechanical risk is the distal pullout of instrumentation. This occurs in up to 3% of patients operated on for HK and can be exacerbated by osteoporosis or poor bone density.9 Ideally, surgeons will select the levels of fusion with the utmost care to adequately distribute the stress placed on the proximal and distal instrumentation.2 The three-dimensional nature of the spinal deformity must also be carefully considered when contemplating a surgical approach. Positioning patients with HK on the operating table can prove challenging, and can therefore compound the onus of maintaining spatial orientation. This issue can lead to improper placement of instrumentation, risking damage to surrounding tissues.5 Specifically, pedicle screw insertion can be more difficult if the pedicles are obscured on preoperative imaging due to sagittal plane deformity.14 Frequent intraoperative fluoroscopic imaging is vital to preserving one’s orientation. Moreover, the use of positioning aids underneath the patient may be necessary for stabilization. Correct positioning of patients with ankylosing spondylitis is especially difficult to achieve. The surgical techniques used to treat thoracic HK often require advanced corrective osteotomies. While osteotomies are well-established methods of correcting spinal deformities, such as HK, these procedures are associated with inherent complications, including damage to the dura, pseudarthrosis, and neurological deficits.4 In particular, when osteotomies shorten the thoracic spine by more than 10 mm, significant signal loss (> 80% of motor-evoked potential in one or more muscle groups) is common.15 Spinal cord and vascular injury is also a risk, especially in cases of hemivertebrae excisions and posterior vertebral column resection (PVCR).16,17,18 Gradual kyphotic curvature requires multilevel osteotomies, whereas shorter, pointed malformations should be treated with aggressive osteotomies involving fewer levels. However, there is strong

evidence to suggest that complication rates increase with more aggressive osteotomy procedures.4 Common osteotomy methods used to correct thoracic kyphotic deformity include SPOs (▶ Fig. 54.1 and ▶ Fig. 54.2), PSOs (▶ Fig. 54.3 and ▶ Fig. 54.4), and PVCR (▶ Fig. 54.5). The Smith–Petersen technique involves a laminotomy and detachment of the superior articular processes at each level, typically starting with the vertebra nearest the apex of the kyphosis. Each suprajacent inferior articular process is then connected to the posterior arch (▶ Fig. 54.1 and ▶ Fig. 54.2). This method can yield correction of approximately 10 degrees per level.19 The potential complications of SPOs include neurological deficits and damage to the dura.4 Despite these risks, this technique is associated with lower intraoperative blood loss and reduced rates of neurological deficits in comparison to more complex procedures.20 PVCR and PSOs are aggressive, three-column osteotomy techniques. These are appropriate for cases requiring more than 10 degrees of correction.16 Owing to the increased complexity of these methods, the risks of excessive blood loss and biomechanical failure are exacerbated.16 Both procedures involve the resection of the pedicles. The PSO involves a wedge-shaped resection of the vertebral body and removal of the posterior portions. A new joint is then formed between the facets of the proximal and distal vertebrae (▶ Fig. 54.3).11 In the thoracic spine, PSOs can provide between 10 and 30 degrees of correction. However, these osteotomies have a high rate of complications with reported rates ranging from 39 to 58.5%.4 The relative benefits of the PSO include reduced risk of damage to the vessels anterior to the spine, and correction involving all three columns improves the chance of healing.20

Fig. 54.1 Smith–Petersen osteotomy.11 (a) Resection of posterior vertebral elements and placement of laminar hooks. (b) Closure of the osteotomy through the tightening of a central rod.

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Fig. 54.2 A posterior view of the chevron-shaped Smith–Petersen osteotomy.20

Fig. 54.4 Lateral view of a pedicle subtraction osteotomy.20 The figure on the left shows the location of the osteotomy and the right shows the postoperative correction. Fig. 54.3 Pedicle-subtraction osteotomy.11 (a) Wedge-shaped resection of vertebral body and posterior elements. (b) Closure achieved through the tightening of a central rod.

Similarly, PVCR has the benefit of obtaining a 45 to 68% correction of kyphotic deformity, albeit with an increased rate of complications.4 These complications include spinal cord/nerve root and cauda equina deficits, hardware failure, adjacent-level fractures, and hemo- or pneumothorax. Owing to the severity of these potential complications, three-column osteotomies are usually reserved for sharp, pointed deformities in rigid kyphotic

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spines.16 The complication profiles of these osteotomy techniques are compared in ▶ Table 54.1.

54.4 Key Points ●

●

Surgical management involves advanced corrective osteotomies to obtain appropriate alignment, which are associated with inherent complications. Spinal cord injury can occur from correcting kyphosis, particularly with anterior column-lengthening procedures.

Instrumentation Complications Occurring from Thoracic Hyperkyphosis

Fig. 54.5 Posterior vertebral column resection.20 (a) Segmental insertion of pedicle screws. (b) Resection of vertebrae on one side following placement of stabilizing rod. (c) Stabilizing rod placed on opposite side of the resection is repeated with the remaining portions. (d) Gradual correction of kyphosis through alternating contouring of the rods. (e) Anterior placement of a mesh cage to counteract overshortening and placement of femoral allograft posteriorly along with a last stabilizing compression.

Table 54.1 Comparison of common corrective procedures’ indications and risks Procedure Pedicle subtraction osteotomy

Indications ●

●

Deformity correction

> 10 degrees of correction Sharp, pointed kyphotic curvatures

10–32 degrees per

level4,22

Complication rates

Potential complications

39–58.5%4

Excessive blood loss,16 rod breakage,11 damage to dura, neurological deficits, and pseudarthrosis

Smith–Petersen osteotomy

●

Longer, arcing kyphotic curvatures

9–19 degrees per level16,20,21 25–59%4,21

Posterior vertebral column resection

●

Sharp, pointed kyphotic curvatures > 10 degrees of correction

45–68% improvement at surgical levels16

●

34–61%4

Neurological deficits, damage to dura4 Spinal cord/nerve root and cauda equina deficits, hardware failure, adjacent level fractures, and hemo- and pneumothorax16

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●

●

There is a high risk of postoperative junctional kyphosis, particularly PJK, in patients with HK. HK correction often entails a great deal of rod contouring which can predispose to rod breakage. The surgeon should weigh the benefits of each method of surgical approach against the added risks associated with more complex procedures (e.g., PVCR and PSOs).

References [1] Kibuule LK, Herkowitz HN. Thoracic Spine: Surgical Approaches. In: Herkowitz HN, Garfin SR, Eismont FJ, et al, eds. Rothman-Simeone The Spine: Expert Consult. Philadelphia, PA: Saunders Elsevier; 2011 [2] Schroerlucke SR, Akbarnia BA, Pawelek JB, et al. Growing Spine Study Group. How does thoracic kyphosis affect patient outcomes in growing rod surgery? Spine. 2012; 37(15):1303–1309 [3] Keyoung HM, Kanter AS, Mummaneni PV. Delayed-onset neurological deficit following correction of severe thoracic kyphotic deformity. J Neurosurg Spine. 2008; 8(1):74–79 [4] Kuklo TR, Lenke LG, O’Brien MF, Lehman RA, Jr, Polly DW, Jr, Schroeder TM. Accuracy and efficacy of thoracic pedicle screws in curves more than 90 degrees. Spine. 2005; 30(2):222–226 [5] Weiss HR, Goodall D. Rate of complications in scoliosis surgery - a systematic review of the PubMed literature. Scoliosis. 2008; 3:9 [6] Charles YP, Schuller S, Sfeir G, Steib JP. Vertebral column resection for thoracic hyperkyphosis in Pott’s disease. Eur Spine J. 2014; 23(3):708–710 [7] Chang KW, Chen YY, Leng X, et al. Guan-Din method: a novel surgical technique for selective thoracic fusion to maximize the rate of selective thoracic fusion and compensatory correction. Spine. 2014; 39(4):E284–E293 [8] Papadopoulos EC, Boachie-adjei O, Hess WF, et al. Foundation of Orthopedics and Complex Spine, New York, NY. Early outcomes and complications of posterior vertebral column resection. Spine J. 2015; 15(5):983–991 [9] Chaiyamongkol W, Klineberg EO, Gupta MC. Apical wiring technique in surgical treatment of adolescent idiopathic scoliosis: the intermediate outcomes between Lenke types. J Spinal Disord Tech. 2013; 26(1):E28–E34 [10] Lundine K, Turner P, Johnson M. Thoracic hyperkyphosis: assessment of the distal fusion level. Global Spine J. 2012; 2(2):65–70 [11] Tsutsui S, Pawelek JB, Bastrom TP, Shah SA, Newton PO. Do discs “open” anteriorly with posterior-only correction of Scheuermann’s kyphosis? Spine. 2011; 36(16):E1086–E1092 [12] Geck MJ, Macagno A, Ponte A, Shufflebarger HL. The Ponte procedure: posterior only treatment of Scheuermann’s kyphosis using segmental posterior shortening and pedicle screw instrumentation. J Spinal Disord Tech. 2007; 20 (8):586–593 [13] La Rosa G, Giglio G, Oggiano L. The Universal Clamp hybrid system: a safe technique to correct deformity and restore kyphosis in adolescent idiopathic scoliosis. Eur Spine J. 2013; 22 Suppl 6:S823–S828 [14] Huang MH, Barrett-Connor E, Greendale GA, Kado DM. Hyperkyphotic posture and risk of future osteoporotic fractures: the Rancho Bernardo study. J Bone Miner Res. 2006; 21(3):419–423 [15] Schizas C, Pralong E, Debatisse D, Kulik G. Neurophysiological changes during shortening osteotomies of the spine. Spine J. 2014; 14(1):73–79

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[16] Kim YJ, Otsuka NY, Flynn JM, Hall JE, Emans JB, Hresko MT. Surgical treatment of congenital kyphosis. Spine. 2001; 26(20):2251–2257 [17] Takahashi J, Ebara S, Hashidate H, et al. Computer-assisted hemivertebral resection for congenital spinal deformity. J Orthop Sci. 2011; 16(5):503–509 [18] Yang C, Zheng Z, Liu H, Wang J, Kim YJ, Cho S. Posterior vertebral column resection in spinal deformity: a systematic review. Eur Spine J. 2016; 25 (8):2368–2375 [19] Sun E, Alkalay R, Vader D, Snyder BD. Preventing distal pullout of posterior spine instrumentation in thoracic hyperkyphosis: a biomechanical analysis. J Spinal Disord Tech. 2009; 22(4):270–277 [20] Enercan M, Ozturk C, Kahraman S, Sarıer M, Hamzaoglu A, Alanay A. Osteotomies/spinal column resections in adult deformity. Eur Spine J. 2013; 22 Suppl 2:S254–S264 [21] Xia L, Li P, Wang D, Bao D, Xu J. Spinal osteotomy techniques in management of severe pediatric spinal deformity and analysis of postoperative complications. Spine. 2015; 40(5):E286–E292 [22] Lewis SJ, Goldstein S, Bodrogi A, et al. Comparison of pedicle subtraction and Smith-Petersen osteotomies in correcting thoracic kyphosis when closed with a central hook-rod construct. Spine. 2014; 39(15):1217–1224 [23] Denis F, Sun EC, Winter RB. Incidence and risk factors for proximal and distal junctional kyphosis following surgical treatment for Scheuermann kyphosis: minimum five-year follow-up. Spine. 2009; 34(20):E729–E734 [24] Cramer GD, Darby SA. Clinical Anatomy of the Spine, Spinal Cord, and ANS. St. Louis, MO: Mosby; 2013. https://www.elsevier.com/books/clinical-anatomyof-the-spine-spinal-cord-and-ans/cramer/978-0-323-07954-9 [25] Baaj AA. Handbook of Spine Surgery. Thieme Medical Pub; 2012 [26] Bartleson JD, Deen HG. Spine Disorders: Medical and Surgical Management [electronic resource]. Leiden, The Netherlands: Cambridge University Press; 2009 [27] Kashlan ON, Valdivia JM. Pedicle-sparing transforaminal thoracic spine wedge osteotomy for kyphosis correction. Surg Neurol Int. 2014; 5 Suppl 15:S561– S563 [28] Cecchinato R, Berjano P, Bassani R, Lamartina C. Osteotomies in proximal junctional kyphosis in the cervicothoracic area. Eur Spine J. 2015; 24 Suppl 1: S31–S37 [29] Yanik HS, Ketenci IE, Polat A, et al. Prevention of proximal junctional kyphosis after posterior surgery of Scheuermann kyphosis: an operative technique. J Spinal Disord Tech. 2015; 28(2):E101–E105 [30] Smith JS, Shaffrey E, Klineberg E, et al. International Spine Study Group. Prospective multicenter assessment of risk factors for rod fracture following surgery for adult spinal deformity. J Neurosurg Spine. 2014; 21(6):994–1003 [31] Akazawa T, Kotani T, Sakuma T, Nemoto T, Minami S. Rod fracture after long construct fusion for spinal deformity: clinical and radiographic risk factors. J Orthop Sci. 2013; 18(6):926–931 [32] Pellisé F, Vila-Casademunt A, European Spine Study Group (ESSG). Posterior thoracic osteotomies. Eur J Orthop Surg Traumatol. 2014; 24 Suppl 1:S39– S48 [33] Auerbach JD, Lenke LG, Bridwell KH, et al. Major complications and comparison between 3-column osteotomy techniques in 105 consecutive spinal deformity procedures. Spine .(Phila Pa 1976). 2012; 37(14):1198–1210 [34] Kim SS, Cho BC, Kim JH, et al. Complications of posterior vertebral resection for spinal deformity. Asian Spine J. 2012; 6(4):257–265

Flatback

55 Flatback Jonathan D. Krystal and Alok D. Sharan

55.1 Introduction 55.1.1 Sagittal Balance Achieving proper sagittal balance is becoming an increasingly recognized factor that leads to improved patient outcomes after spinal surgery. A lack of understanding of sagittal balance has resulted in numerous patients experiencing inadvertent outcomes after spine surgery. Spinopelvic balance is essentially an open linear chain in the sagittal plane, extending from the head cranially to the pelvis caudally.1 To maintain a stable posture without unreasonable energy expenditure, each level of the spine must be closely related to its adjacent levels with regard to shape and orientation. Any alteration of the anatomy at one level will have repercussions for subsequent adjacent levels. This relates directly to the concept of the cone of economy for standing sagittal balance (▶ Fig. 55.1).

The cone of economy refers to the standing posture in which a person can maintain standing balance without increased energy expenditure. A cone is drawn starting with a circle around the feet and extending cranially and outward. Within this cone, an individual can maintain standing balance; however, outside of this cone, the individual will require supportive devices to maintain balance. This concept demonstrates the narrow range of sway that is tolerated around the feet and the increased energy expenditure required to maintain balance once the alignment is out of this range; a misalignment often leads to fatigue and pain.2,3,4 It is critical for the spine surgeon to pay close attention to the sagittal alignment whenever operating on the spine to ensure proper balance. The normal sagittal balance in the adult spine is kyphotic from T1 to T12 with an average angulation of 10 to 40 degrees. Lumbar lordosis from T12 to S1 generally measures anywhere from 40 to 60 degrees. Furthermore, there tends to be an overall balance within the spine where pelvic tilt, which tends to be

Fig. 55.1 Cone of economy. (Adapted with permission from Dubousset.4)

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Thoracolumbar posterior in patients with flat back; sacral base angle, normally 35 to 45 degrees; cervical lordosis, normally 30 to 40 degrees; as well as the aforementioned lumbar lordosis and thoracic kyphosis are balanced to give an overall erect posture3,5,6,7 (▶ Fig. 55.2). Early attempts at spinal instrumentation included the use of facet screws, which, despite good initial results, demonstrated poor long-term outcomes related to catastrophic hardware failure when patients were mobilized prior to adequate fusion. In response to deformities associated with the polio epidemic, Harrington developed his instrumentation to provide correction and stabilization of spinal deformity.8 The Harrington’s instrumentation consists of a hook and rod construct with hooks placed around the posterior elements cranially and caudally. Distraction was provided through the rod and hook construct leading to correction of the deformity in the coronal plane. Unfortunately, this often resulted in a loss of lumbar lordosis and the development of flatback. This basic instrument design was later used by Luque, whose instrumentation system

used wires placed under the lamina and multiple points of fixation. With long-term follow-up of both the Harrington’s instrumentation and the Luque’s wires, it was clear that patients developed a loss of lumbar lordosis, leading to symptoms of pain and fatigue known as flatback.8,9,10,11 The loss of lumbar lordosis also results in a forward inclination of the trunk and causes difficulty in standing erect with the knees extended.

55.2 Flatback The most common cause of flatback syndrome is the result of distraction instrumentation in the lumbar spine and sacrum.1,5, 6,12,13,14,15 Early surgical treatment of scoliosis, aimed at halting progression rather than correcting existing deformity, did not lead to the development of iatrogenic flatback deformity as the sagittal balance was not altered. The introduction of distractive forces used to provide curve correction with the Harrington’s technique resulted in the vertical axis translating anteriorly, shifting the patient’s center of gravity.5,16 This led to the loss of lumbar lordosis which was made rigid by the fusion mass. To compensate for this misalignment, the patient must then hyperextend any segments not included in the instrumentation and fusion mass, creating a loss of the normal thoracic kyphosis. The loss of lordosis seen with Harrington’s instrumentation is made more significant with the increase of instrumentation to more caudal levels.14 Whereas there has been an observed radiological anterior shift of the vertical axis at all levels below L1, L3 seems to be the critical level for loss of lordosis and anterior shift, as fusions below this level showed a precipitous loss of lordosis when studied.16 Early attempts to avoid this radiographic shift in the vertebral axis include the use of pre-contoured rods to maintain lumbar lordosis. However, regardless of the contouring, extension distraction instrumentation demonstrated a loss of lumbar lordosis without any significant difference in magnitude when compared to noncontoured rods.17 In addition to the use of Harrington’s technique, other causes of iatrogenic flatback still exist. With the increasing number of posterior instrumented fusions being performed for degenerative spine conditions, there has been an increase in fixed sagittal imbalance related to these procedures.12,18,19 When performing a posterior instrumented fusion for a degenerative spine, special care must be taken to maintain or enhance the lumbar lordosis. If the degenerative spine is fused in a position with inadequate lordosis, there is evidence that adjacent level degeneration and loss of sagittal balance will result.20,21 Additionally, the development of pseudarthrosis after a lumbar fusion for degenerative spine conditions has been shown to contribute to the loss of lordosis and symptomatic flatback.22

55.2.1 Presentation

Fig. 55.2 Normal sagittal orientation of the spine.

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Patients with a flatback will present with complaints of pain and an inability to stand fully erect. One study of patients with iatrogenic flatback reported an inability to stand erect in 95% of patients, whereas 89% of patients reported back pain with activity.22 Hip flexion contractures are often associated with the deformity and the pelvic tilt may be abnormal as well. Patients should be assessed for gait abnormalities and should be examined both prone and supine to assess flexibility of the

Flatback deformity.6 Additionally, a complete neurologic exam should be carried out at the initial presentation.

55.2.2 Imaging Studies Imaging studies should include full-length anteroposterior and lateral radiographs, with the patient standing with the hips and knees at maximum extension. Based on the standing lateral Xray, the sagittal vertical axis (SVA) can be assessed. The SVA is measured by dropping a plumb line from the center of the C7 vertebral body; this line should pass within 25 mm of the posterior–superior corner of S1 (▶ Fig. 55.3). If the C7 plumb line is greater than 2.5 cm from the posterior–superior corner of S1, it is said to be abnormal and the SVA is unbalanced. The lumbar lordosis can be measured from the inferior endplate of T12 to the superior endplate of S1 using the Cobb’s method and should be 30 degrees more than the thoracic kyphosis.3

55.3 Prevention of Iatrogenic Flatback Preoperative planning and selection of implant and technique can have a large impact on the potential to avoid the development of iatrogenic flatback deformity after instrumented fusion. Initial attempts to modify the Harrington’s technique focused on ways to continue using distraction instrumentation without causing a straightening of the lordosis. Initial attempts

to use precontoured rods with built-in lordosis were replaced with square rods to prevent rotation after contouring. Additional modifications included decreasing the number of fusion levels while not shortening the length of the instrumentation.17,23,24 However, none of these modifications were successful in preventing the development of iatrogenic flatback. Advancements in spinal implants have changed the way spinal instrumentation and fusion is performed. Segmental instrumentation was introduced by Luque, whose use of sublaminar wires provided improved fixation, improved rotational control, and resistance to construct failure.5 Other advantages of Luque’s wiring with segmental fusion includes the ability to preserve sagittal curvature and overall balance. Patients who underwent instrumented segmental fusion had better preservation of lumbar lordosis than patients who had undergone surgery using the Harrington’s technique; however, the loss of lumbar lordosis remained a frequent complication.18,25,26 Further advancements in segmental instrumentation include the development of Cotrel–Dubousset instrumentation, which included the segmental hook instrumentation. Several authors have looked at the sagittal balance in patients having undergone scoliosis correction using segmental hook instrumentation and found improved maintenance of lumbar lordosis when compared with prior methods of spinal instrumentation, including both Harrington’s technique and Luque’s wiring.19,27 In one series, more than 97% of patients with normal preoperative lordosis and 94% of patients with preoperative hypolordosis were found to have normal lumbar lordosis postoperatively.28 Recently, pedicle screw fixation has replaced previous generations of spinal instrumentation. This technique has come into favor largely for the ability to achieve three-column fixation and therefore better rotational control. When compared with other modes of fixation, all pedicle screw constructs provide greater curve correction, rotational improvement, and improved sagittal alignment.29,30 Once the fusion levels and instrumentation are selected, there are intraoperative techniques that can be used to further prevent loss of lumbar lordosis and flatback deformity. Surgical positioning is crucial to the maintenance of lordosis with spinal fusion. If the patient is positioned in such a way that will make it difficult to restore lordosis, the spine will be fused in a suboptimal position. Hip flexion causes a flattening of lumbar lordosis, highlighting the importance of careful positioning during spinal fusion.31,32 Patients should be positioned on a table allowing hip extension. When positioned on an open frame which sits atop the operating table, with the hips flexed, there was a significant decrease in lumbar lordosis when compared to patients positioned on the Jackson’s table with hips extended.33

55.4 Treatment of Flatback

Fig. 55.3 (a) Normal sagittal vertical axis using C7 plumb line. (b) Anteriorly displaced sagittal vertical axis.

The nonoperative treatment of flatback consists mainly of hipextension and trunk-stabilizing stretches, supplemented with medical pain management. However, studies have demonstrated a long-term success rate of only 25% in patients treated without realignment surgery.34 Furthermore, those patients who did improve without surgery had at least two unfused disc spaces caudal to the fusion and less than 4 cm of sagittal

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Thoracolumbar malalignment prior to treatment.34 Therefore, only a select group of patients are ideal candidates for nonoperative management. With the lack of success of nonoperative treatment, the treating surgeon must consider surgical options early when seeing a patient with flatback. Preoperative planning involves assessing the flexibility of the deformity. If the deformity is corrected completely while in the supine or prone position, it is considered flexible. Alternatively, it is considered fixed if there is no correction, with some patients demonstrating partial correction. The most important factor in determining surgical approach is the flexibility of the curve35 and this assessment must be made carefully. If the deformity is flexible, it implies that the increased kyphosis is through the disc. For these deformities, sagittal balance can be restored through anterior–posterior or all posterior surgery. Sagittal balance can be restored by structurally grafting the anterior column. The posterior column can then be addressed with appropriate decompression if stenosis is present.3,36 For fixed deformities, posterior-column-shortening procedures can be used to restore sagittal balance. Options include Smith–Petersen osteotomy, pedicle subtraction osteotomy, and vertebral column resection.3

55.4.1 Osteotomies The Smith–Petersen osteotomy provides shortening of the posterior column while lengthening the anterior column. This entails resection of the posterior elements, laminae, superior and inferior facets, as well as undercutting of the adjacent spinous processes (▶ Fig. 55.4). After completion of the osteotomy, the posterior column can be compressed to achieve sagittal correction.37 This procedure can be coupled with an anterior release to achieve more correction of the deformity.38,39 For every millimeter of bone resected, approximately 1 degree of

Fig. 55.4 Smith–Petersen osteotomy. Shaded area represents bony resection.

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correction can be expected.36 Corrections of 25 to 30 degrees have been reported with an average improvement of 6.4 cm and an 86% patient satisfaction.12,37 Owing to the lengthening of the anterior column, there is a risk of vascular injury and over distraction must be avoided. Pedicle subtraction osteotomies are three-column closing wedge osteotomies that are essentially equivalent to performing adjacent Smith–Petersen osteotomies with the resection of the pedicle and a wedge of the vertebral body.3,40 The procedure involves removing all of the posterior elements at the levels to be corrected along with both superior and inferior adjacent facet joints, pedicle, and portions of the vertebral body. The posterior and lateral walls of the vertebral body are also often removed. A closing wedge osteotomy is subsequently performed by applying compression of the instrumentation at the level of the osteotomy. Alternatively, the patient can be extended on the frame to provide the desired correction (▶ Fig. 55.5). The neural elements must not be compressed. The exiting nerve root will now share an enlarged foramen with the more cephalad exiting nerve root.3,5,41 One study of pedicle subtraction osteotomies found that an improvement of the sagittal plumb line of 13.5 cm provided an average of 34 degrees of correction.40 ▶ Fig. 55.6 represents the radiographs of a patient who initially presented with pain and disability related to loss of lumbar lordosis after a previous spinal fusion. The patient’s symptoms have greatly improved after undergoing a pedicle subtraction osteotomy at L3–L4 (▶ Fig. 55.6). More severe deformities of the thoracolumbar spine require more aggressive vertebral resections such as a vertebral column resection. In this procedure, one or more vertebral segments, including the posterior elements, pedicles, and vertebral body along with the discs both caudal and cephalad, are removed35 (▶ Fig. 55.7). The anterior and posterior columns are usually reconstructed using an anterior cage with posterior pedicle screw instrumentation.3

Fig. 55.5 Pedicle subtraction osteotomy.

Flatback

Fig. 55.6 Patient being treated for flatback. (a) Presenting X-ray showing loss of lordosis after previous fusion. (b) Postoperative X-ray showing increased lordosis following pedicle subtraction osteotomy.

Fig. 55.7 Vertebral column resection. (a) Sharp angular kyphosis. (b) Resection of the vertebral segment. (c) Closure of the wedge with instrumentation.

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Thoracolumbar

55.5 Summary Sagittal imbalance and the loss of lumbar lordosis is a potentially serious and debilitating complication of spinal surgery. Whereas the most notable cause of iatrogenic flatback is the use of Harrington’s distraction instrumentation, other causes include failure to maintain lordosis during fusion procedures. It is critical for the surgeon to take the appropriate steps intraoperatively to avoid the development of this complication. Appropriate positioning and minimizing the extent of the lumbar fusion are key in avoiding the loss of lumbar lordosis. In patients who do develop flatback, nonoperative techniques have shown poor results and corrective surgeries with various osteotomies are often required.

55.6 Key References [1] Potter BK, Lenke LG, Kuklo TR. Prevention and management of iatrogenic flatback deformity. J Bone Joint Surg Am. 2004; 86-A(8):1793–1808

This is a very complete review of iatrogenic flatback which includes the causes, treatments, and clinical data. [2] Joseph SA, Jr, Moreno AP, Brandoff J, Casden AC, Kuflik P, Neuwirth MG. Sagittal plane deformity in the adult patient. J Am Acad Orthop Surg. 2009; 17 (6):378–388

A comprehensive review of sagittal balance in the adult spine. This review covers all aspects of sagittal deformity. [3] Mohan AL, Das K. History of surgery for the correction of spinal deformity. Neurosurg Focus. 2003; 14(1):e1

An interesting review of the history of spinal deformity surgery, as well as summary of the history and evolution of deformity surgery. [4] Bridwell KH. Decision making regarding Smith-Petersen vs. pedicle subtraction osteotomy vs. vertebral column resection for spinal deformity. Spine (Phila Pa 1976). 2006; 31(19) Suppl:S171–S178

A good summary of the data and treatment options for flatback deformity. [5] Doherty J. Complications of fusion in lumbar scoliosis: proceedings of the Scoliosis Research Society. J Bone Joint Surg Am. 1973; 55

An original publication noting the existence of iatrogenic flatback after the use of Harrington’s instrumentation.

References [1] Berthonnaud E, Dimnet J, Roussouly P, Labelle H. Analysis of the sagittal balance of the spine and pelvis using shape and orientation parameters. J Spinal Disord Tech. 2005; 18(1):40–47 [2] Schwab F, Lafage V, Boyce R, Skalli W, Farcy JP. Gravity line analysis in adult volunteers: age-related correlation with spinal parameters, pelvic parameters, and foot position. Spine. 2006; 31(25):E959–E967 [3] Joseph SA, Jr, Moreno AP, Brandoff J, Casden AC, Kuflik P, Neuwirth MG. Sagittal plane deformity in the adult patient. J Am Acad Orthop Surg. 2009; 17:378–388 [4] Dubousset J. Three-dimensional analysis of the scoliotic spine. In: Weinstein SL, ed., The Pediatric Spine: Principles and Practices. New York, NY: Raven Press; 1994:479–496 [5] Potter BK, Lenke LG, Kuklo TR. Prevention and management of iatrogenic flatback deformity. J Bone Joint Surg Am. 2004; 86-A(8):1793–1808 [6] Angevine PD, O'Leary PT, Bridwell KH. Fixed sagittal imbalance. In: Herkowitz HN, Garfin SR, Eismont FJ, Bell GR, Balderston RA, eds. Rothman-Simeone The Spine. Philadelphia, PA: Elsevier-Saunders; 2011:1285–1298 [7] Stagnara P, De Mauroy JC, Dran G, et al. Reciprocal angulation of vertebral bodies in a sagittal plane: approach to references for the evaluation of kyphosis and lordosis. Spine. 1982; 7(4):335–342

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[8] Mohan AL, Das K. History of surgery for the correction of spinal deformity. Neurosurg Focus. 2003; 14(1):e1 [9] Harrington PR. Treatment of scoliosis. Correction and internal fixation by spine instrumentation. J Bone Joint Surg Am. 1962; 44-A:591–610 [10] Harrington PR. The history and development of Harrington instrumentation. by Paul R. Harrington, 1973. Clin Orthop Relat Res. 1988; 227(227):3–5 [11] Dickson JH, Harrington PR. The evolution of the Harrington instrumentation technique in scoliosis. J Bone Joint Surg Am. 1973; 55(5):993–1002 [12] Booth KC, Bridwell KH, Lenke LG, Baldus CR, Blanke KM. Complications and predictive factors for the successful treatment of flatback deformity (fixed sagittal imbalance). Spine. 1999; 24(16):1712–1720 [13] Doherty J. Complications of fusion in lumbar scoliosis: proceedings of the Scoliosis Research Society. J Bone Joint Surg Am. 1973; 55 [14] Swank SM, Mauri TM, Brown JC. The lumbar lordosis below Harrington instrumentation for scoliosis. Spine. 1990; 15(3):181–186 [15] Cochran T, Irstam L, Nachemson A. Long-term anatomic and functional changes in patients with adolescent idiopathic scoliosis treated by Harrington rod fusion. Spine. 1983; 8(6):576–584 [16] Aaro S, Ohlén G. The effect of Harrington instrumentation on the sagittal configuration and mobility of the spine in scoliosis. Spine. 1983; 8(6):570–575 [17] Casey MP, Asher MA, Jacobs RR, Orrick JM. The effect of Harrington rod contouring on lumbar lordosis. Spine. 1987; 12(8):750–753 [18] Kostuik JP, Hall BB. Spinal fusions to the sacrum in adults with scoliosis. Spine. 1983; 8(5):489–500 [19] Bridwell KH, Betz R, Capelli AM, Huss G, Harvey C. Sagittal plane analysis in idiopathic scoliosis patients treated with Cotrel-Dubousset instrumentation. Spine. 1990; 15(7):644–649 [20] Yang SH, Chen PQ. Proximal kyphosis after short posterior fusion for thoracolumbar scoliosis. Clin Orthop Relat Res. 2003(411):152–158 [21] Kawakami M, Tamaki T, Ando M, Yamada H, Hashizume H, Yoshida M. Lumbar sagittal balance influences the clinical outcome after decompression and posterolateral spinal fusion for degenerative lumbar spondylolisthesis. Spine. 2002; 27(1):59–64 [22] Lagrone MO, Bradford DS, Moe JH, Lonstein JE, Winter RB, Ogilvie JW. Treatment of symptomatic flatback after spinal fusion. J Bone Joint Surg Am. 1988; 70(4):569–580 [23] van Dam BE, Bradford DS, Lonstein JE, Moe JH, Ogilvie JW, Winter RB. Adult idiopathic scoliosis treated by posterior spinal fusion and Harrington instrumentation. Spine. 1987; 12(1):32–36 [24] Gaines RW, Leatherman KD. Benefits of the Harrington compression system in lumbar and thoracolumbar idiopathic scoliosis in adolescents and adults. Spine. 1981; 6(5):483–488 [25] Wenger DR, Carollo JJ, Wilkerson JA, Jr. Biomechanics of scoliosis correction by segmental spinal instrumentation. Spine. 1982; 7(3):260–264 [26] Luque ER. Segmental spinal instrumentation for correction of scoliosis. Clin Orthop Relat Res. 1982(163):192–198 [27] Takahashi S, Delécrin J, Passuti N. Changes in the unfused lumbar spine in patients with idiopathic scoliosis. A 5- to 9-year assessment after CotrelDubousset instrumentation. Spine. 1997; 22(5):517–523, discussion 524 [28] de Jonge T, Dubousset JF, Illés T. Sagittal plane correction in idiopathic scoliosis. Spine. 2002; 27(7):754–760 [29] Liljenqvist UR, Halm HF, Link TM. Pedicle screw instrumentation of the thoracic spine in idiopathic scoliosis. Spine. 1997; 22(19):2239–2245 [30] Suk SI, Lee CK, Kim WJ, Chung YJ, Park YB. Segmental pedicle screw fixation in the treatment of thoracic idiopathic scoliosis. Spine. 1995; 20(12):1399– 1405 [31] Benfanti PL, Geissele AE. The effect of intraoperative hip position on maintenance of lumbar lordosis: a radiographic study of anesthetized patients and unanesthetized volunteers on the Wilson frame. Spine. 1997; 22(19):2299– 2303 [32] Guanciale AF, Dinsay JM, Watkins RG. Lumbar lordosis in spinal fusion. A comparison of intraoperative results of patient positioning on two different operative table frame types. Spine. 1996; 21(8):964–969 [33] Peterson MD, Nelson LM, McManus AC, Jackson RP. The effect of operative position on lumbar lordosis. A radiographic study of patients under anesthesia in the prone and 90–90 positions. Spine. 1995; 20(12):1419–1424 [34] Farcy JP, Schwab FJ. Management of flatback and related kyphotic decompensation syndromes. Spine. 1997; 22(20):2452–2457 [35] Bridwell KH. Decision making regarding Smith-Petersen vs. pedicle subtraction osteotomy vs. vertebral column resection for spinal deformity. Spine. 2006; 31(19) Suppl:S171–S178

Flatback [36] Bridwell KH, Lenke LG, Lewis SJ. Treatment of spinal stenosis and fixed sagittal imbalance. Clin Orthop Relat Res. 2001(384):35–44 [37] Kostuik JP, Maurais GR, Richardson WJ, Okajima Y. Combined single stage anterior and posterior osteotomy for correction of iatrogenic lumbar kyphosis. Spine. 1988; 13(3):257–266 [38] La CHAPELLE EH. Osteotomy of the lumbar spine for correction of kyphosis in a case of ankylosing spondylarthritis. J Bone Joint Surg Am. 1946; 28(4):851– 858

[39] Camargo FP, Cordeiro EN, Napoli MM. Corrective osteotomy of the spine in ankylosing spondylitis. Experience with 66 cases. Clin Orthop Relat Res. 1986 (208):157–167 [40] Bridwell KH, Lewis SJ, Lenke LG, Baldus C, Blanke K. Pedicle subtraction osteotomy for the treatment of fixed sagittal imbalance. J Bone Joint Surg Am. 2003; 85-A(3):454–463 [41] Bridwell KH, Lewis SJ, Rinella A, Lenke LG, Baldus C, Blanke K. Pedicle subtraction osteotomy for the treatment of fixed sagittal imbalance. Surgical technique. J Bone Joint Surg Am. 2004; 86-A Suppl 1:44–50

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56 Lumbar High-Grade Spondylolisthesis Evan O. Baird and Sheeraz A. Qureshi

56.1 Case Example A 22-year-old woman with no previous medical history presented to the office with complaints of low back pain. She noted that the pain began 7 to 8 years ago and had gradually worsened over the past year; it now prevents her from participating in sports activities. She was most comfortable lying down, whereas her pain increased with standing, sitting, and walking. She also noted pain radiating into her buttocks bilaterally. She denied bowel or bladder habit changes or difficulties. Prior to presentation, she had undergone a course of nonsteroidal antiinflammatory medications and physical therapy, both of which improved her symptoms initially and which at the time of presentation no longer had an effect. On physical exam, the patient was a well-appearing young woman; when standing erect, she exhibited a slight forward tilt of her trunk relative to her pelvis. She had a palpable step-off present at the lumbosacral junction. Her motor strength was full throughout all major muscle groups and her sensory exam was unremarkable. Deep tendon reflexes were normal. She demonstrated bilateral hamstring tightness. Plain X-rays were obtained (▶ Fig. 56.1). Given her high-grade slip, unremitting pain, and diminished quality of life, surgical options as well as risks and benefits of treatment were discussed. The patient ultimately underwent

transsacral fibular strut grafting (▶ Fig. 56.2a,b) for stabilization of the listhesed segment (▶ Fig. 56.3).

56.2 Introduction High-grade spondylolisthesis refers to anterior translation of one vertebra over the subjacent vertebral body of greater than 50%.1 It is an entity encountered most often in the symptomatic adolescent or young adult and is usually associated with some component of developmental spondylolisthesis.2,3,4,5,6 As the surgical treatment of high-grade spondylolisthesis has evolved, instrumentation is being used with greater frequency. Because of the fact that use of instrumentation has become commonplace in the treatment of high-grade spondylolisthesis, it is important to understand potential complications and modes of failure.7,8,9,10,11,12,13,14 Many patients in whom highgrade spondylolisthesis has been identified have been demonstrated to exhibit specific spinal anatomic characteristics (so-called dysplastic/congenital or developmental spondylolisthesis15,16), such as underdeveloped facets and pars interarticularis, an incomplete neural arch, a wedge-shaped L5 body, and a domed sacrum. These compromises to structural integrity of the spine may lead to a propensity for the development of a high-grade slip, which can lead to increased loads being placed on implants placed to treat the condition.

56.3 Classification

Fig. 56.1 Lateral lumbosacral X-ray demonstrating > 50% anterior translation of the L5 vertebra over the sacrum.

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Briefly, there are several methods of etiological classification of spondylolisthesis; the most commonly encountered are those of Wiltse–Newman15 and Marchetti–Bartolozzi.16 Wiltse and Newman classified spondylolisthesis as being one of the following five types: (1) dysplastic/congenital, (2) isthmic, (3) degenerative, (4) traumatic, or (5) pathologic. Dysplastic/congenital implies that there are developmental shortcomings involving the L5–S1 level, as mentioned previously. Isthmic implicates a defect in the pars as the cause. Degenerative occurs with increasing age and is the result of disk degeneration and resultant facet degeneration. Traumatic implies a bilateral fracture of the posterior column that leads to spondylolisthesis. The pathologic form arises as a result of an underlying metabolic bone disorder. The Marchetti–Bartolozzi classification differs in that it divides cases into either developmental or acquired. Developmental is defined as having anatomic abnormalities that predispose the patient to development of a spondylolisthesis and is divided into high and low dysplastic, whereas acquired includes the subclassifications of traumatic, surgical, pathologic, and degenerative. Perceived advantages to this system are the distinction given to iatrogenic slips and a method of defining the amount of dysplasia present. It is useful to note that cases designated as high dysplastic demonstrate a wedged L5 vertebral body, a domed and vertical sacrum, and a significant slip angle, whereas low dysplastic forms demonstrate translation without a component of angulation.

Lumbar High-Grade Spondylolisthesis

Fig. 56.2 Intraoperative lateral lumbosacral X-ray demonstrating (a) placement of the guidewire in a transsacral manner across the L5–S1 intervertebral disc space and into the L5 vertebral body, (b) cannulated reamer passing over the guidewire to prepare channel for placement of fibular strut graft.

56.4 Implants Whereas the natural history of low-grade spondylolisthesis is generally benign and less often requires surgical intervention,17,18 that of high-grade spondylolisthesis is less favorable and its treatment is more often surgical.12,19,20,21 Although now more often corrected with the use of instrumentation,22,23,24,25, 26 some authors have demonstrated success with in situ bone grafting and fusion for treatment of a low-grade slip.27,28 Though this method has been used in the past for the treatment of high-grade disease,29 it has been associated with significant complications, including elevated rates of pseudarthrosis and slip progression19,30 as well as reports of cauda equina syndrome.31,32 Many authors have demonstrated good outcomes including a low pseudarthrosis rate,10,12,20,33,34,35,36 using an instrumented approach for the stabilization (which may include reduction) of the listhesed segment. Implants described for use in the surgical treatment of high-grade spondylolisthesis include pedicle screws, iliac screws, intrasacral rods,35 various interbody devices,37,38,39 transsacral screws, and, though distinct from other implants listed here, fibular strut grafts. Fibular strut grafts have been used in the technique as described by Bohlman and Cook,40 variations of which have been developed.41,42 The purpose of each of these forms of instrumentation is to aid in fusion,10 prevent further displacement, and/or to aid in attaining and maintaining reduction of a spondylolisthesis. Implants, such as intrasacral rods and iliac screws,

provide supplemental fixation to anchor the construct to the pelvis.

56.5 Food and Drug Administration Approval Status of Instrumentation Whereas it is common practice to employ spinal implants in a manner other than that approved by the Food and Drug Administration (FDA), important in the use of any spinal implant is awareness of the FDA-approved indications for its use. As per the FDA, pedicle screw constructs may use plates and/or rods and/or transverse connectors for immobilization and stabilization of spinal segments in skeletally mature patients as an adjunct to fusion in the treatment of the following acute and chronic instabilities or deformities of the thoracic, lumbar, and sacral spine: degenerative spondylolisthesis with objective evidence of neurologic impairment, fracture, dislocation, scoliosis, kyphosis, spinal tumor, and failed previous fusion (pseudarthrosis). Interbody fusion devices are generally approved for spinal fusion at one or two continuous levels from L2 to S1 for the diagnosis of degenerative disc disease and/or Grade I spondylolisthesis, and to be packed with autograft. Iliac screws are approved as an adjunct for fixation for the treatment of the aforementioned indications for pedicle screw fixation.

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Thoracolumbar

Fig. 56.4 Spinopelvic parameters: PT, pelvic tilt, the angle formed by a line from the middle of the sacral vertebral endplate to the center of the coxofemoral axis and the vertical axis; SS, sacral slope, the angle formed by a line along the superior endplate of S1 and the horizontal axis; PI, pelvic incidence, the sum of PT and SS, the angle between a line perpendicular to the sacral plate at its midpoint and a line connecting this point to the coxofemoral axis; SK, sacral kyphosis, the angle formed by a line passing through the middle of the superior and inferior endplates of S1 and a line connecting the inferior endplates of S2 and S4.

Fig. 56.3 Postoperative lateral lumbosacral X-ray showing placement of fibular strut graft.

Intrasacral rods are approved for degenerative disc disease (as defined by chronic back pain of discogenic origin with degeneration of the disc confirmed by history and radiographic studies), idiopathic scoliosis, kyphotic deformities of the spine, paralytic scoliosis and/or pelvic obliquity, lordotic deformities of the spine, neuromuscular scoliosis associated with pelvic obliquity, vertebral fracture or dislocation, tumor, spondylolisthesis, and pseudarthrosis.

56.6 Relevant Anatomy As mentioned previously, spinal and particularly lumbosacral and pelvic anatomy play a significant role in the development of spondylolisthesis; these in turn are necessary to consider when planning to instrument the spine with high-grade spondylolisthesis. Factors to consider include local and global sagittal balance of the patient, as well as intrinsic spinopelvic morphology including radiographic parameters.

56.6.1 Spinopelvic Anatomic Parameters First described by Duval-Beaupère et al43 and later by Legaye et al,44 pelvic incidence (▶ Fig. 56.4) is defined as the angle between the line perpendicular to the sacral plate at its midpoint and the line connecting this point to the axis of the

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femoral heads. It is an anatomic parameter and thus independent of the position of the pelvis. Several other authors2,3,4,45 have further contributed to the study of this anatomic parameter and its role in spondylolisthesis. These studies have shown that increased pelvic incidence is correlated with the development of a spondylolisthesis and that the severity of spondylolisthesis is proportionally correlated to the pelvic incidence; however, though there is a suggestion of relationship between the two, there has not been demonstrated to be a direct correlation between pelvic incidence and progression of spondylolisthesis.45,46 Several of these studies have also demonstrated that overall spinopelvic sagittal balance may have a significant impact on the development of spondylolisthesis,45,47,48 with Wang et al demonstrating that sacral kyphosis (▶ Fig. 56.4) is significant in the development of spondylolisthesis but does not demonstrate a correlation with severity of the slip. Furthermore, Jackson et al49 and others45 have shown relationship between increasing sacral kyphosis and increased lumbar lordosis, thought to be a compensatory balance mechanism. The same has been demonstrated2,44 for the relationship between increasing pelvic incidence and lumbar lordosis. Finally, Hresko et al50 evaluated patients with high-grade spondylolisthesis and divided them into two groups: those with a “balanced” pelvis (low pelvic tilt and high sacral slope) and those with an “unbalanced” pelvis (high pelvic tilt and low sacral slope). The authors suggested that treatment for this entity ought to take into account the differing mechanical forces at work at the spinopelvic junction, and that reduction should be considered in the unbalanced pelvis.

Lumbar High-Grade Spondylolisthesis

56.6.2 Anatomic Features of the Dysplastic Spinal Segment As noted previously, dysplastic or developmental forms of spondylolisthesis, which account for the majority of cases of high-grade spondylolisthesis, demonstrate a number of anatomic features not typically seen in degenerative spondylolisthesis or the normal spine. Among these is the demonstration of an underdeveloped or elongated pars, as well as dysplastic facets, underdeveloped transverse processes,10 a defective neural arch, wedging of the L5 vertebral body, and sacral doming. However, as Ikata et al51 suggested, some of these anatomic aberrations, namely, sacral doming and wedging of the L5 vertebral body, may develop as a response or adaptation to the forces at work in the listhesed segment. These anatomic features lay the groundwork for the development of neural impingement in the patient with a dysplastic spondylolisthesis, as the elongation of the pars and lamina have been shown to elongate but flatten the foramen in an oblique manner52; development of hypertrophic fibrous tissue (if spondylolysis is present) and osteophytes have also been shown to narrow down the neuroforamen.53 Whereas cases of degenerative spondylolisthesis have also been shown to share some mechanisms of neural impingement (such as disc bulges and/or osteophyte encroachment on the neuroforamen), unlike developmental spondylolisthesis, other aspects, such as hypertrophic ligamentum flavum and facet arthrosis, are thought to contribute significantly.

56.6.3 Radiographic Descriptors of Spondylolisthesis Meyerding1 was the first to describe a method of quantifying and classifying the degree to which a vertebral body shifts forward over its subjacent vertebra. This classification system is still widely used; as mentioned previously, a high-grade spondylolisthesis is a Meyerding grade 3 or 4, with spondyloptosis designated grade 5 (▶ Fig. 56.5). In 1979, Boxall et al19 described a method of measurement of the slip angle—that is, the angle formed by the listhesed vertebrae and the sacrum (▶ Fig. 56.5). Initially measured from the inferior endplate of L5 and the perpendicular drawn from the posterior cortex of the sacrum, it is now more often measured using the superior endplate of L5 because of recognition of wedging of the vertebral body encountered in dysplastic spondylolisthesis.

56.7 Implant-Related Complications Complications associated with instrumentation applied to the spine exhibiting a high-grade spondylolisthesis have been documented, with the most prominent of these being implant failure/pullout and neural injury. It is important for the surgeon to keep in mind that treatment of high-grade spondylolisthesis is associated with a significantly increased overall complication rate when compared to low-grade disease. Sansur et al,54 in their review of reported Scoliosis Research Society Morbidity and Mortality database complications associated with more

Fig. 56.5 Measurements of severity of spondylolisthesis. SA, slip angle, the angle formed by a line perpendicular to the posterior sacral cortex and a line parallel to the superior endplate of L5; I–V denotes Meyerding grades of spondylolisthesis, I = < 25%, II = < 50%, III = < 75%, IV = up to 100%, V = > 100% (spondyloptosis).

than 10,000 adult patients treated for spondylolisthesis, showed a 22.9% complication rate in the treatment of highgrade spondylolisthesis, compared with only 8.3% for those in the low-grade group. In this study, they also noted a 0.7% implant complication rate; however, this number was not stratified with respect to Meyerding grade. These data were able to demonstrate, however, that the single factor most associated with the development of a treatment complication was the grade of slip. A note of importance is that the literature has been inconsistent in the reporting of patient functional outcomes based on choice of instrumentation. Whereas the most attractive method of instrumentation would be the one which provides the best patient outcome while minimizing complications risks, the method that provides that is not entirely clear. For instance, Abdu et al,22 in a study analyzing patients with degenerative spondylolisthesis from the SPORT trial,55 were unable to demonstrate a statistically significant difference in patient outcomes (utilizing SF-36 and Oswestry Disability Index scores) at 3 and 4 years postoperatively when comparing in situ fusion, instrumentation with pedicle screws combined with posterolateral fusion, and a third group receiving posterior instrumentation and posterolateral fusion combined with interbody fusion. They did show, however, that 360-degree fusion was associated with more blood loss and longer operative time. Instrumented posterolateral fusion was found to have a statistically higher rate of postoperative blood transfusion than either in situ fusion or 360-degree fusion; the authors attributed this to the lower number of operated levels in the 360-degree fusion group. Instrumentation complications were not reported. A crucial element to keep in mind about this study, however, was that the grade of spondylolisthesis was not reported in the results, as well as the fact that this study dealt with the treatment of degenerative spondylolisthesis rather than developmental/

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Thoracolumbar dysplastic spondylolisthesis, and which tends to be of a lower grade slip. Molinari et al10 demonstrated a higher level of patient function, satisfaction, and fusion rate in the treatment of patients with high-grade spondylolisthesis when utilizing partial reduction of the listhesed segment and an interbody fusion device (circumferential fusion) versus instrumented posterolateral fusion without a reduction maneuver. Of note, some authors38,56 have advocated the use of supplemental iliac fixation in the treatment of high-grade spondylolisthesis because of the large moment acting on the most caudal aspect of the construct.

posterior instrumentation and a 0% incidence of migration in those with instrumentation. In patients without instrumentation and a grade 1 listhesis, 4 of 25 patients demonstrated migration; in patients without instrumentation and grade 2 listhesis, 3 of 14 patients had evidence of migration. Of note, all patients with grade 3 listhesis underwent posterior instrumentation. A similar rate of migration (17%) has been demonstrated when lateral approach stand-alone interbody cages were used to treat low-grade lumbar spondylolisthesis.63

56.7.1 Pedicle Screw Constructs

Treatment of high-grade spondylolisthesis (especially when combined with a reduction maneuver) often requires additional support to prevent implant failure and loss of reduction.10,13 This may come in the form of interbody devices or in the form of a transsacral device, whether a screw or a fibular dowel autograft/allograft. Abdu et al23 described the technique of placement of S1 pedicle screws across the sacral promontory and into the listhesed L5 vertebral body. Their series included three patients, all of whom achieved successful fusion without instrumentation complications. Boachie-Adjei et al64 also reported on their experiences using transsacral screw fixation in conjunction with interbody fusion in the treatment of high-grade spondylolisthesis. All six patients in their series achieved fusion as well as a good functional outcome according to the Scoliosis Research Society outcomes measure, and at an average of 42 months of follow-up, none demonstrated any instrumentationrelated complications. Though not implants in the same sense as pedicle screws and intervertebral cages, the successful use of transsacral fibula dowel graft fixation in the treatment of high-grade spondylolisthesis and spondyloptosis has been documented by several authors.14,39,40,42,64 Bohlman and Cooke40 reported two cases of use of their single-stage technique of transsacral fibula autograft for stabilization of high-grade spondylolisthesis, whereby a guide wire is passed across the sacrum, through the intervertebral disc and into the L5 vertebral body while the dural sac is retracted medially. The fibula is harvested, split longitudinally, and placed into the reamed passages for fixation across the segment. Smith and Bohlman later expanded their series to include 11 patients65 and amended their technique to an undivided fibula graft used in a single, drilled passage in lieu of the previously described technique. All patients achieved fusion, and they did not encounter any implant-related complications. Smith et al14 reported on nine patients undergoing surgery using the Bohlman’s technique, with the modification of use of a fibular allograft (thus avoiding donor-site complications), partial reduction of the listhesed segment prior to insertion of the fibular dowel, and the addition (in seven of nine patients) of posterior pedicle-based instrumentation; this series demonstrated two failures (22%) of the fibula strut, both of which were in the two patients in the series that did not have placement of supplemental posterior instrumentation. Another modification was described by Jones et al,39 in which the approach for placement of the fibula strut was anterior. All four patients in their series of salvage operations for previously failed fusion achieved a successful fusion; there were no implant complications. Sasso et al42 also described their results, with eight patients having bilateral fibular struts placed from a posterior

As the most widely used instrumentation in surgery for highgrade spondylolisthesis, complications associated with pedicle screws are well documented. Ani et al,7 in their review of 20 patients with an average of 40 months of follow-up, demonstrated a 15% (3 out of 20 patients) instrumentation-related complication rate using pedicle screw–plate constructs, posterolateral fusion, reduction, and interbody fusion. Two patients encountered screw breakage and one breakage of the plate. However, in analyzing the short-term follow-up (< 2 years; 41 patients included), there were 3 patients who underwent reduction and instrumented posterolateral fusion only, all of who experienced loss of reduction. Of note, the authors noted no neurologic complications. Hu et al13 showed a 25% (4 patients) instrumentation failure rate performing complete reduction with the Edwards Modular Spinal System, with each patient requiring a revision procedure. The authors highlighted the need for supplemental sacropelvic fixation and the limitation of foregoing an L5–S1 interbody device. Boos et al11 also demonstrated the need for an interbody device in the reporting of their results, in which they noted that five out of six patients treated for high-grade spondylolisthesis with instrumented posterolateral fusion without interbody support had a loss of reduction and instrumentation failure. As further illustration of this point, DeWald et al12 demonstrated 100% fusion rate in patients with high-grade spondylolisthesis undergoing circumferential fusion utilizing pedicle screws, with one case of implant pullout (7.7%) and loss of reduction. Therefore, it has become the recommendation by many authors11,12,13,56,57 that surgical treatment for high-grade spondylolisthesis include the use of an interbody fusion device for anterior column support.

56.7.2 Interbody Devices As mentioned previously, the use of interbody fusion devices is both common and recommended in the treatment of highgrade spondylolisthesis, both to increase fusion rate and maintain reduction.11,12,13,56,57 That being said, there are few reports of interbody cage migration or subsidence in the context of their use in high-grade spondylolisthesis. However, there have been several reports detailing the risk factors for subsidence of interbody cages58,59,60,61; these have been identified as including cage size and shape, disc space size, number of levels fused, bone mineral density, and the use of unilateral fixation. Chen et al,62 in a review of 88 patients with spondylolisthesis treated with posterior interbody fusion, demonstrated a 16.7% incidence of cage migration in the group without supplemental

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56.7.3 Transsacral Screws/Dowels

Lumbar High-Grade Spondylolisthesis approach, whereas seventeen others underwent a combined anterior–posterior approach; both methods utilized supplemental pedicle-based instrumentation. One patient had late implant removal because of subcutaneous prominence; they did not report any implant failures.

56.7.4 Intrasacral Rods Described in 1993, Jackson’s intrasacral rods were originally proposed in a radiographic study as a method of sacral anchoring which may have proven useful in the treatment of neuromuscular scoliosis.66 Ilharreborde and colleagues35 repurposed this instrumentation and described their technique for reduction and fixation of high-grade isthmic spondylolisthesis, but did not include results of treatment in that study. Ilharreborde et al have as of yet not reported their outcomes with the use of this technique for treatment of high-grade spondylolisthesis, but did later36 describe their experience with the technique when employed for the original indication, neuromuscular scoliosis. They included 56 patients with 5 years (average: 10.3) of follow-up; they had no rod breakage at the intrasacral portion, though 2 patients did have rods break in the thoracolumbar region, away from the connection with the intrasacral rods. Molinari et al,10 in their report on 32 patients undergoing one of three procedures (in situ fusion, instrumented posterolateral fusion, or reduction and circumferential fusion), showed a 29% implant complication rate (including loosening, breakage, or pullout which caused partial loss of reduction) in the instrumented posterolateral fusion group, and 11% of those in the reduction and interbody fusion group had partial loss of reduction. The authors noted that all complications occurred with intrasacral rods (2 of 32 or 6.3%) or undersized S2 screws and that no failure occurred with four-point sacro-pelvic fixation utilizing bicortical S1 screws and iliac fixation with screws measuring at least 60 mm in length by 7-mm diameter.

56.7.5 Gaines Vertebrectomy Gaines and Nichols67 described in 1985 a novel technique for a staged procedure for the treatment of spondyloptosis; an L5 vertebrectomy was performed in two patients. They utilized an anterior approach for L5 corpectomy, followed by a second stage for posterior element resection and placement of instrumentation in L4 and S1. A follow-up study in 2005 chronicled the 30 patients treated in this method.68 They noted that 23 of 30 patients (76.7%) had a postoperative L5 neuropraxia, 21 of who recovered completely. Regarding implant complications, they noted that two (6.7%) patients had pedicle screw breakage because of nonunion; both of these patients required a revision procedure.

56.7.6 Neural Injury It is difficult to discuss complications related to instrumentation of high-grade spondylolisthesis without including the entity of neural injury. This is particularly true, as it relates to the topic of reduction during surgical treatment of a high-grade spondylolisthesis, a matter that remains rather controversial for adolescent spondylolisthesis and even more so in adults.69

As mentioned previously, neural injury has been reported even in the context of in situ fusion.31,32 Schoenecker et al32 suggested that a preoperative slip angle greater than 45 degrees was associated with a risk of development of cauda equina syndrome in patients treated with in situ fusion for high-grade spondylolisthesis. Nevertheless, reduction maneuvers are often included in the treatment for high-grade spondylolisthesis when significant sagittal imbalance is present.10,11,12,13,14,19,33,38 Whereas reduction of the slip grade is both aesthetically and biomechanically advantageous, many authors10,12,20,38,64,70 have shown that partial reduction is sufficient and further that reduction of the slip angle is paramount (rather than slip grade) in the restoration of sagittal balance and achievement of fusion and a satisfied patient. It is worth noting, however, that several studies33,34,71 have demonstrated success in treatment without reduction. Boachie-Adjei et al,64 as mentioned previously, reported on six patients who underwent treatment for highgrade spondylolisthesis including partial reduction and placement of transsacral screws. The authors noted that the procedure produced a significant reduction in slip angle without a significant reduction in slip grade, but that they had no neural injuries, no progression of slip, restoration of sagittal balance, and good functional outcome in all patients at an average of 2 years of follow-up. These findings reinforced Bradford and Boachie-Adjei’s70 earlier conclusion that reduction of slip angle is more important than slip grade reduction. Attempts at complete reduction have been associated with higher rates of neurologic injury13,19,72 and, in light of the aforementioned findings, are generally not indicated. Petraco and colleagues,73 in an anatomic study, showed that the amount of strain on the L5 nerve root increased considerably when transitioning from a 50% reduction of a 100% slip to a full reduction maneuver and suggested that this provided a mechanism for increased rates of neurologic deficit encountered with attempts at full reduction. Reduction has further been shown to have benefits other than sagittal realignment such as making available a larger bony surface area on which to obtain a successful arthrodesis12,64,70 and providing additional fixation points by making the L5 pedicles accessible. Though the advantages of reduction are many, the neurologic risks often include nerve root palsies (overwhelmingly the L5 root),7,9,10,54 most of which are temporary. Cauda equina syndrome has also been reported with reduction procedures.9,12 Finally, it has been suggested69 that because of the inflexibility of adult deformity (as compared to the pediatric and adolescent patient), the reduction may be more difficult and therefore brings with it a higher risk of neurologic injury.

56.7.7 Minimally Invasive Surgical Treatment of Spondylolisthesis As minimally invasive spine surgery (MISS) gains popularity, reports of its use in many aspects of spine surgery74,75,76,77,78,79 have surfaced. Though there have been numerous reports of minimally invasive surgical techniques employed for the treatment of low-grade spondylolisthesis,24,80,81,82 at the time of this writing there are few83,84 reports published regarding minimally invasive treatment for high-grade spondylolisthesis. Though both reports demonstrated good outcomes, these

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Thoracolumbar studies were of low statistical power (one a case report and the other a series of three patients) and further studies are warranted to evaluate for the incidence of implant-related complications.

56.8 Summary Operative treatment of high-grade lumbar spondylolisthesis, a disease entity with significant mechanical challenges that must be overcome with the chosen instrumentation construct, is well documented to be associated with risks of neural damage, persistent sagittal imbalance, and implant failure. Understanding of associated anatomic variants and contemporary surgical techniques is key to successful treatment. By acknowledging the risks involved in surgical treatment of this disease and by utilizing current principles of secure implant fixation, which often includes an intervertebral fusion device, supplemental fixation to the pelvis, and/or transsacral implants in addition to partial reduction at the surgeon’s discretion, such complications can be anticipated and minimized.

56.9 Future Directions With better understanding of the pathology and mechanics involved in the treatment of high-grade spondylolisthesis, and the increasingly successful use of MISS techniques, it is likely that more surgeons will pursue these novel treatment strategies. We look forward to the results of such endeavors.

56.10 Key Points ●

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High-grade spondylolisthesis is a disease often necessitating surgical treatment, which has been associated with significantly higher rates of overall complications. Understanding of a given patient’s sagittal balance and the forces that must be counteracted during surgical treatment is paramount to long-term treatment success. Most authors advocate the use of instrumentation as a part of the treatment algorithm and the choices of implants are many; this presents several methods of achieving secure fixation with a relatively low rate of implant-related complications. Reduction of a high-grade slip remains controversial. If the treating surgeon elects to perform a reduction maneuver, it need not be complete; rather, a partial reduction of the slip angle alone is enough to aid in the restoration of sagittal balance. The use of minimally invasive surgical techniques has been described; though only a few reports exist, it is likely that this will be a focus of future research relating to high-grade spondylolisthesis.

56.11 Key References [1] Molinari RW, Bridwell KH, Lenke LG, Ungacta FF, Riew KD. Complications in the surgical treatment of pediatric high-grade, isthmic dysplastic spondylolisthesis. A comparison of three surgical approaches. Spine. 1999; 24(16):1701– 1711

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This study showed the benefits of circumferential fusion and reduction by demonstrating a 100% fusion rate in the circumferential group (45% pseudarthrosis rate in the in situ fusion group and 29% in the instrumented posterolateral fusion group). The study also demonstrated a correlation between L5 transverse process surface area and likelihood of achieving fusion. [2] DeWald RL, Faut MM, Taddonio RF, Neuwirth MG. Severe lumbosacral spondylolisthesis in adolescents and children. Reduction and staged circumferential fusion. J Bone Joint Surg Am. 1981; 63(4):619–626

This study demonstrated that a partial slip reduction was effective in helping to achieve a satisfactory clinical result, and established the benefit of circumferential fusion. This study also documented a case of cauda equina syndrome following a reduction maneuver, with resolution after removal of instrumentation and release of the reduction. [3] Marchetti PG, Bartolozzi P. Classification of spondylolisthesis as guideline for treatment. In: Bridwell KH, ed. The Textbook of Spinal Surgery. 2nd ed. Philadelphia, PA: Lippincott-Raven; 1997:1299–1315

This study established the frequently used eponymous classification of spondylolisthesis, most notably distinguishing between developmental and acquired forms, and further defined the amount of dysplasia present in a developmental case. [4] Bohlman HH, Cook SS. One-stage decompression and posterolateral and interbody fusion for lumbosacral spondyloptosis through a posterior approach. Report of two cases. J Bone Joint Surg Am. 1982; 64(3):415–418

This study described a novel technique for use of fibula autograft as a transsacral fixation method across the L5–S1 intervertebral disc space; it was largely successful and inspired several authors to propose a number of technique variants. [5] Labelle H, Roussouly P, Berthonnaud E, et al. Spondylolisthesis, pelvic incidence, and spinopelvic balance: a correlation study. Spine. 2004; 29 (18):2049–2054

This study described the correlation between spinopelvic radiographic parameters and spondylolisthesis, with the conclusion that increased pelvic incidence is correlated with the development of spondylolisthesis and that the severity of spondylolisthesis may be correlated with the pelvic incidence as well.

References [1] Meyerding H. Spondylolisthesis: surgical treatment and results. Surg Gynecol Obstet. 1932; 54:371–377 [2] Hanson DS, Bridwell KH, Rhee JM, Lenke LG. Correlation of pelvic incidence with low- and high-grade isthmic spondylolisthesis. Spine. 2002; 27 (18):2026–2029 [3] Curylo LJ, Edwards C, DeWald RW. Radiographic markers in spondyloptosis: implications for spondylolisthesis progression. Spine. 2002; 27(18):2021– 2025 [4] Schwab FJ, Farcy JP, Roye DP, Jr. The sagittal pelvic tilt index as a criterion in the evaluation of spondylolisthesis. Preliminary observations. Spine. 1997; 22 (14):1661–1667 [5] Lindholm TS, Ragni P, Ylikoski M, Poussa M. Lumbar isthmic spondylolisthesis in children and adolescents. Radiologic evaluation and results of operative treatment. Spine. 1990; 15(12):1350–1355 [6] Takahashi K, Yamagata M, Takayanagi K, Tauchi T, Hatakeyama K, Moriya H. Changes of the sacrum in severe spondylolisthesis: a possible key pathology of the disorder. J Orthop Sci. 2000; 5(1):18–24 [7] Ani N, Keppler L, Biscup RS, Steffee AD. Reduction of high-grade slips (grades III-V) with VSP instrumentation. Report of a series of 41 cases. Spine. 1991; 16(6) Suppl:S302–S310 [8] Chung JY, Parthasarathy S, Avadhani A, Rajasekaran S. Reduction of high grade listhesis. Eur Spine J. 2010; 19(2):353–354

Lumbar High-Grade Spondylolisthesis [9] Kasliwal MK, Smith JS, Shaffrey CI, et al. Short-term complications associated with surgery for high-grade spondylolisthesis in adults and pediatric patients: a report from the scoliosis research society morbidity and mortality database. Neurosurgery. 2012; 71(1):109–116 [10] Molinari RW, Bridwell KH, Lenke LG, Ungacta FF, Riew KD. Complications in the surgical treatment of pediatric high-grade, isthmic dysplastic spondylolisthesis. A comparison of three surgical approaches. Spine. 1999; 24(16):1701– 1711 [11] Boos N, Marchesi D, Zuber K, Aebi M. Treatment of severe spondylolisthesis by reduction and pedicular fixation. A 4–6-year follow-up study. Spine. 1993; 18(12):1655–1661 [12] DeWald RL, Faut MM, Taddonio RF, Neuwirth MG. Severe lumbosacral spondylolisthesis in adolescents and children. Reduction and staged circumferential fusion. J Bone Joint Surg Am. 1981; 63(4):619–626 [13] Hu SS, Bradford DS, Transfeldt EE, Cohen M. Reduction of high-grade spondylolisthesis using Edwards instrumentation. Spine. 1996; 21(3):367–371 [14] Smith JA, Deviren V, Berven S, Kleinstueck F, Bradford DS. Clinical outcome of trans-sacral interbody fusion after partial reduction for high-grade l5-s1 spondylolisthesis. Spine. 2001; 26(20):2227–2234 [15] Wiltse LL, Newman PH, Macnab I. Classification of spondylolisis and spondylolisthesis. Clin Orthop Relat Res. 1976(117):23–29 [16] Marchetti PG, Bartolozzi P. Classification of spondylolisthesis as guideline for treatment. In: Bridwell KH, ed. The Textbook of Spinal Surgery. 2nd ed. Philadelphia, PA: Lippincott-Raven; 1997:1299–1315 [17] Beutler WJ, Fredrickson BE, Murtland A, Sweeney CA, Grant WD, Baker D. The natural history of spondylolysis and spondylolisthesis: 45-year follow-up evaluation. Spine. 2003; 28(10):1027–1035, discussion 1035 [18] Ishida Y, Ohmori K, Inoue H, Suzuki K. Delayed vertebral slip and adjacent disc degeneration with an isthmic defect of the fifth lumbar vertebra. J Bone Joint Surg Br. 1999; 81(2):240–244 [19] Boxall D, Bradford DS, Winter RB, Moe JH. Management of severe spondylolisthesis in children and adolescents. J Bone Joint Surg Am. 1979; 61(4):479– 495 [20] Muschik M, Zippel H, Perka C. Surgical management of severe spondylolisthesis in children and adolescents. Anterior fusion in situ versus anterior spondylodesis with posterior transpedicular instrumentation and reduction. Spine. 1997; 22(17):2036–2042, discussion 2043 [21] Pizzutillo PD, Mirenda W, MacEwen GD. Posterolateral fusion for spondylolisthesis in adolescence. J Pediatr Orthop. 1986; 6(3):311–316 [22] Abdu WA, Lurie JD, Spratt KF, et al. Degenerative spondylolisthesis: does fusion method influence outcome? Four-year results of the spine patient outcomes research trial. Spine (Phila Pa 1976). 2009; 34(21):2351–2360 [23] Abdu WA, Wilber RG, Emery SE. Pedicular transvertebral screw fixation of the lumbosacral spine in spondylolisthesis. A new technique for stabilization. Spine. 1994; 19(6):710–715 [24] Wang J, Zhou Y, Zhang ZF, Li CQ, Zheng WJ, Liu J. Comparison of one-level minimally invasive and open transforaminal lumbar interbody fusion in degenerative and isthmic spondylolisthesis grades 1 and 2. Eur Spine J. 2010; 19(10):1780–1784 [25] Zagra A, Giudici F, Minoia L, Corriero AS, Zagra L. Long-term results of pediculo-body fixation and posterolateral fusion for lumbar spondylolisthesis. Eur Spine J. 2009; 18 Suppl 1:151–155 [26] Jacobs WC, Vreeling A, De Kleuver M. Fusion for low-grade adult isthmic spondylolisthesis: a systematic review of the literature. Eur Spine J. 2006; 15 (4):391–402 [27] Burkus JK, Lonstein JE, Winter RB, Denis F. Long-term evaluation of adolescents treated operatively for spondylolisthesis. A comparison of in situ arthrodesis only with in situ arthrodesis and reduction followed by immobilization in a cast. J Bone Joint Surg Am. 1992; 74(5):693–704 [28] Lenke LG, Bridwell KH, Bullis D, Betz RR, Baldus C, Schoenecker PL. Results of in situ fusion for isthmic spondylolisthesis. J Spinal Disord. 1992; 5(4):433– 442 [29] Freeman BL, III, Donati NL. Spinal arthrodesis for severe spondylolisthesis in children and adolescents. A long-term follow-up study. J Bone Joint Surg Am. 1989; 71(4):594–598 [30] Transfeldt EE, Dendrinos GK, Bradford DS. Paresis of proximal lumbar roots after reduction of L5-S1 spondylolisthesis. Spine. 1989; 14(8):884–887 [31] Maurice HD, Morley TR. Cauda equina lesions following fusion in situ and decompressive laminectomy for severe spondylolisthesis. Four case reports. Spine. 1989; 14(2):214–216 [32] Schoenecker PL, Cole HO, Herring JA, Capelli AM, Bradford DS. Cauda equina syndrome after in situ arthrodesis for severe spondylolisthesis at the lumbosacral junction. J Bone Joint Surg Am. 1990; 72(3):369–377

[33] Poussa M, Schlenzka D, Seitsalo S, Ylikoski M, Hurri H, Osterman K. Surgical treatment of severe isthmic spondylolisthesis in adolescents. Reduction or fusion in situ. Spine. 1993; 18(7):894–901 [34] Poussa M, Remes V, Lamberg T, et al. Treatment of severe spondylolisthesis in adolescence with reduction or fusion in situ: long-term clinical, radiologic, and functional outcome. Spine. 2006; 31(5):583–590, discussion 591–592 [35] Ilharreborde B, Fitoussi F, Morel E, Bensahel H, Penneçot GF, Mazda K. Jackson’s intrasacral fixation in the management of high-grade isthmic spondylolisthesis. J Pediatr Orthop B. 2007; 16(1):16–18 [36] Ilharreborde B, Hoffmann E, Tavakoli S, et al. Intrasacral rod fixation for pediatric long spinal fusion: results of a prospective study with a minimum 5-year follow-up. J Pediatr Orthop. 2009; 29(6):594–601 [37] Agabegi SS, Fischgrund JS. Contemporary management of isthmic spondylolisthesis: pediatric and adult. Spine J. 2010; 10(6):530–543 [38] Bridwell KH. Surgical treatment of high-grade spondylolisthesis. Neurosurg Clin N Am. 2006; 17(3):331–338, vii [39] Jones AA, McAfee PC, Robinson RA, Zinreich SJ, Wang H. Failed arthrodesis of the spine for severe spondylolisthesis. Salvage by interbody arthrodesis. J Bone Joint Surg Am. 1988; 70(1):25–30 [40] Bohlman HH, Cook SS. One-stage decompression and posterolateral and interbody fusion for lumbosacral spondyloptosis through a posterior approach. Report of two cases. J Bone Joint Surg Am. 1982; 64(3):415–418 [41] Hanson DS, Bridwell KH, Rhee JM, Lenke LG. Dowel fibular strut grafts for high-grade dysplastic isthmic spondylolisthesis. Spine. 2002; 27(18):1982– 1988 [42] Sasso RC, Shively KD, Reilly TM. Transvertebral transsacral strut grafting for high-grade isthmic spondylolisthesis L5-S1 with fibular allograft. J Spinal Disord Tech. 2008; 21(5):328–333 [43] Duval-Beaupère G, Schmidt C, Cosson P. A Barycentremetric study of the sagittal shape of spine and pelvis: the conditions required for an economic standing position. Ann Biomed Eng. 1992; 20(4):451–462 [44] Legaye J, Duval-Beaupère G, Hecquet J, Marty C. Pelvic incidence: a fundamental pelvic parameter for three-dimensional regulation of spinal sagittal curves. Eur Spine J. 1998; 7(2):99–103 [45] Labelle H, Roussouly P, Berthonnaud E, et al. Spondylolisthesis, pelvic incidence, and spinopelvic balance: a correlation study. Spine. 2004; 29 (18):2049–2054 [46] Huang RP, Bohlman HH, Thompson GH, Poe-Kochert C. Predictive value of pelvic incidence in progression of spondylolisthesis. Spine. 2003; 28 (20):2381–2385, discussion 2385 [47] Wang Z, Parent S, Mac-Thiong JM, Petit Y, Labelle H. Influence of sacral morphology in developmental spondylolisthesis. Spine (Phila Pa 1976). 2008; 33 (20):2185–2191 [48] Hresko MT, Hirschfeld R, Buerk AA, Zurakowski D. The effect of reduction and instrumentation of spondylolisthesis on spinopelvic sagittal alignment. J Pediatr Orthop. 2009; 29(2):157–162 [49] Jackson RP, Phipps T, Hales C, Surber J. Pelvic lordosis and alignment in spondylolisthesis. Spine. 2003; 28(2):151–160 [50] Hresko MT, Labelle H, Roussouly P, Berthonnaud E. Classification of highgrade spondylolistheses based on pelvic version and spine balance: possible rationale for reduction. Spine. 2007; 32(20):2208–2213 [51] Ikata T, Miyake R, Katoh S, Morita T, Murase M. Pathogenesis of sports-related spondylolisthesis in adolescents. Radiographic and magnetic resonance imaging study. Am J Sports Med. 1996; 24(1):94–98 [52] Jinkins JR, Matthes JC, Sener RN, Venkatappan S, Rauch R. Spondylolysis, spondylolisthesis, and associated nerve root entrapment in the lumbosacral spine: MR evaluation. AJR Am J Roentgenol. 1992; 159(4):799–803 [53] Kim KW, Chung JW, Park JB, Song SW, Ha KY, An HS. The course of the nerve root in the neural foramen and its relationship with foraminal entrapment or impingement in adult patients with lumbar isthmic spondylolisthesis and radicular pain. J Spinal Disord Tech. 2004; 17(3):220–225 [54] Sansur CA, Reames DL, Smith JS, et al. Morbidity and mortality in the surgical treatment of 10,242 adults with spondylolisthesis. J Neurosurg Spine. 2010; 13(5):589–593 [55] Weinstein JN, Lurie JD, Tosteson TD, et al. Surgical versus nonsurgical treatment for lumbar degenerative spondylolisthesis. N Engl J Med. 2007; 356 (22):2257–2270 [56] DeWald CJ, Vartabedian JE, Rodts MF, Hammerberg KW. Evaluation and management of high-grade spondylolisthesis in adults. Spine. 2005; 30(6) Suppl:S49–S59 [57] Molinari RW, Bridwell KH, Lenke LG, Baldus C. Anterior column support in surgery for high-grade, isthmic spondylolisthesis. Clin Orthop Relat Res. 2002 (394):109–120

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Thoracolumbar [58] Duncan JW, Bailey RA. An analysis of fusion cage migration in unilateral and bilateral fixation with transforaminal lumbar interbody fusion. Eur Spine J. 2013; 22(2):439–445 [59] Zhao FD, Yang W, Shan Z, et al. Cage migration after transforaminal lumbar interbody fusion and factors related to it. Orthop Surg. 2012; 4(4):227–232 [60] Aoki Y, Yamagata M, Nakajima F, et al. Examining risk factors for posterior migration of fusion cages following transforaminal lumbar interbody fusion: a possible limitation of unilateral pedicle screw fixation. J Neurosurg Spine. 2010; 13(3):381–387 [61] Aoki Y, Yamagata M, Nakajima F, Ikeda Y, Takahashi K. Posterior migration of fusion cages in degenerative lumbar disease treated with transforaminal lumbar interbody fusion: a report of three patients. Spine (Phila Pa 1976). 2009; 34(1):E54–E58 [62] Chen L, Yang H, Tang T. Cage migration in spondylolisthesis treated with posterior lumbar interbody fusion using BAK cages. Spine. 2005; 30(19):2171– 2175 [63] Marchi L, Abdala N, Oliveira L, Amaral R, Coutinho E, Pimenta L. Stand-alone lateral interbody fusion for the treatment of low-grade degenerative spondylolisthesis. ScientificWorldJournal. 2012; 2012:456346 [64] Boachie-Adjei O, Do T, Rawlins BA. Partial lumbosacral kyphosis reduction, decompression, and posterior lumbosacral transfixation in high-grade isthmic spondylolisthesis: clinical and radiographic results in six patients. Spine. 2002; 27(6):E161–E168 [65] Smith MD, Bohlman HH. Spondylolisthesis treated by a single-stage operation combining decompression with in situ posterolateral and anterior fusion. An analysis of eleven patients who had long-term follow-up. J Bone Joint Surg Am. 1990; 72(3):415–421 [66] Jackson RP, McManus AC. The iliac buttress. A computed tomographic study of sacral anatomy. Spine. 1993; 18(10):1318–1328 [67] Gaines RW, Nichols WK. Treatment of spondyloptosis by two stage L5 vertebrectomy and reduction of L4 onto S1. Spine. 1985; 10(7):680–686 [68] Gaines RW. L5 vertebrectomy for the surgical treatment of spondyloptosis: thirty cases in 25 years. Spine. 2005; 30(6) Suppl:S66–S70 [69] Lonstein JE. Spondylolisthesis in children. Cause, natural history, and management. Spine. 1999; 24(24):2640–2648 [70] Bradford DS, Boachie-Adjei O. Treatment of severe spondylolisthesis by anterior and posterior reduction and stabilization. A long-term follow-up study. J Bone Joint Surg Am. 1990; 72(7):1060–1066 [71] Lamberg T, Remes V, Helenius I, Schlenzka D, Seitsalo S, Poussa M. Uninstrumented in situ fusion for high-grade childhood and adolescent isthmic

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Complications Related to Spinal Instrumentation and Surgical Approaches

57 Complications Related to Spinal Instrumentation and Surgical Approaches Christopher Klifto and Michael Gerling

57.1 Introduction Within the past 50 years, the introduction and evolution of instrumentation has revolutionized surgical management of scoliosis. Modern spinal implants improve deformity correction, hasten functional recovery, improve fusion rates, and improve maintenance of correction. Though a small proportion of patients require surgical intervention, surgical correction is only considered in select cases with substantial deformity, where pain and disability are refractory to conservative treatment. The surgeon’s decision process is guided by the expected benefits and, to a larger extent, the risks of surgery. Surgical complications are common and potentially catastrophic with significant patient morbidity and a high cost to society. This chapter will review surgical complications of spinal deformity correction in the context of each category of implant and by surgical approach.

57.2 Background Scoliosis can be defined as a helical deformity involving the coronal, transverse, and sagittal planes of the spine. The disorder is classified as congenital, neuromuscular, degenerative, and idiopathic. Congenital scoliosis occurs when vertebrae fail to properly form or when the vertebrae do not separate, otherwise known as failure of formation and failure of segmentation. Neuromuscular scoliosis results from muscle imbalance or weakness as with cerebral palsy, muscular dystrophy, or a spinal column injury. Degenerative scoliosis is a chronic disorder in elderly patients with deterioration of the disc, and spinal elements. Idiopathic scoliosis is the most common spinal deformity and has no known cause.1,2,3 Curve deterioration can present in multiple forms and combinations with variable prevalence of back pain, reduced pulmonary function, neurologic manifestations, and immobilization.4 Goals for surgical management of scoliosis include curve correction and stabilization, minimization of chest deformity, and improved patient mobility.

57.3 Relevant Alignment and Anatomy The most pertinent anatomy pertaining to scoliosis is visualized in the transverse, sagittal, and coronal planes. The three-dimensional alignment is the core concept corrected during scoliosis surgery. Understanding the normal alignment of the spine is the first step in operative scoliosis correction. The coronal plane typically is straight with the exception of a normal variant of a small thoracic convexity. Coronal alignment can be measured by a line extending from the dens inferiorly on the anteroposterior view. All vertebrae should bisect the plumb line. The transverse plane is analyzed by vertebral anatomy. The spinous

processes should point posteriorly and the vertebral bodies anteriorly. Sagittal plane deformity is measured by drawing a plumb line perpendicular to the floor, from the dens. It should fall just posterior to C7, anterior to the thoracic spine, posterior to the lumbar spine, and should intersect S1 at the posterior-superior border. If the plumb line falls in front of the sacrum, it is termed positive sagittal balance. Conversely, if the plumb line falls posteriorly, the condition is termed negative sagittal balance.5,6 A key parameter that needs to be balanced is the spinopelvic alignment. Spinopelvic parameters define the base of the sagittal curve between the immobile sacrum and the mobile lumbar spine. Certain terms describe the spinopelvic alignment, including sacral inclination, pelvic incidence, sacral slope, and pelvic tilt (PT). Sacral inclination is the angle formed between the posterior border of S1 and a horizontal line parallel to the x-axis. The average sacral inclination has a mean of 50 degrees (43–58).7 Pelvic incidence (PI) is also measured because of its importance in size of lumbar lordosis and pelvic orientation, and is viewed on lateral radiographs; the angle is between a line perpendicular to the sacral plate and a line drawn from the midpoint of the sacral plate to the axis of the femoral heads.8 Normal PI is 55 ± 11 degrees and abnormal values are associated with pathologic conditions. Sacral slope is the angle formed between the superior aspect of S1 and the x-axis.8,9 PT is the angle formed between the vertical axis (z-axis) and a line joining the midpoint of the sacral plate to the femoral head axis. PT is positive when the hip axis is in front of the center of the sacral plate.10 PI refers to the sum of the sacral slope and PT.

57.4 Modes of Failure Instrumentation failure can occur from a variety of reasons with surgical treatment of scoliosis. This relatively common complication of scoliosis correction is minimized with surgical technique that emphasizes adequate bone purchase and fixation. Modes of failure include inadequate surgical instrumentation, fracture or malpositioning of the hardware, curvature progression around the fusion site, multiple complications for one patient, neurologic impairment, infection, and lack of surgeon’s experience/skill. The complications can be debilitating. Surgical instrumentation failure of rods, hooks, wires, screws, and cages can damage the spine and surrounding tissues requiring revision surgery to remove and replace the defective instrument. The fractured hardware or the malposition of hardware either by dislodgment or dislocation can cause pseudoarthrosis, and the hardware can be palpable under the skin causing discomfort in need of corrective surgery. The progression of the curvature can result in neurologic deterioration and a cosmetic deformity. After each surgical procedure, possible complications also include paraplegia, blood loss, infection, pulmonary emboli, and neurologic impairment. Scoliosis correction must be

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Thoracolumbar performed by a skilled orthopedic surgeon with experience to avoid potential complications.

57.5 Neuromonitoring and Its Role in Detecting Intraoperative Complications The Stagnara Wake Up Test was developed as the earliest form of monitoring for scoliosis surgery, whereby patients would be awakened intraoperatively to test their ability to move their feet. There are multiple inherent limitations of the technique that include lack of continuous monitoring, loss of positioning, recall by the patient, risk of extubation, and lack of sensory information.11 Somatosensory-evoked potentials (SSEP) measure sensorytract–specific function of the spinal cord in real time intraoperatively. The technique utilizes large diameter, myelinated, fastconducting mixed nerves such as the median, tibial, and ulnar nerve. Surface electrodes are used for stimulation and subdermal needles are considered superior for recording.11 SSEP monitors spinal cord sensory tracts, and can be recorded at various locations along the peripheral nerve, spinal cord, and brain stem, and current guidelines recommend nerves to have multiple monitoring points in the cortical, subcortical, and peripheral regions.11 As SSEP monitors only the sensory aspect of the spinal column and nerves, other tests were developed including descending neurogenic evoked potentials (DNEP). This test directly stimulates the spine, and the response is monitored in the peripheral nerves and muscles.12 DNEPs have the advantage over SSEP in that DNEPs are monosynaptic and SSEPs are polysynaptic. This makes them less affected by anesthetic inhalation. The monosynaptic transmission also makes DNEP more sensitive to ischemic change. A shortcoming of DNEPs is the lack of nerve root monitoring, which became increasingly evident with the use of pedicle screws. This type of testing uses myotomes associated with nerves to monitor nerve roots. Two types exist, mechanical and electrical. Mechanical EMG (spEMG) provides continuous monitoring of nerve roots and is used when nerve roots are being manipulated. Electrical EMG (trEMG) is used during a static phase of monitoring such as with direct nerve stimulation and pedicle screw placement.13,14 Another modality for spinal cord monitoring, motor-evoked potentials, has become mainstream in neuromonitoring. This test involves stimulating the motor cortex of the brain and evaluating the peripheral musculature’s response to the stimulation.13 No single test is 100% sensitive and specific for nerve root/spinal column injury; therefore, multiple monitoring systems are typically utilized.15

57.6 Complications Specific to Instrumentation 57.6.1 Harrington’s Instrumentation In 1962, Paul Harrington developed an instrumentation for a posterior spinal fusion for scoliosis correction for children, adolescents, and adults. His system is a combination of hooks and

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ratcheted rods that provided instrumented spinal distraction and fusion with the rods/hooks placed in a sublaminar manner at the proximal and distal aspect of the deformity.4,16 Harrington’s distraction instrumentation yielded a correction of scoliosis in the coronal plane with flexion in the sagittal plane and a limited effect on the axial plane rotational deformity.4,17 As force is applied to the spine posterior to the sagittal axis, there is elongation of the posterior column. Whereas this corrects thoracic hypokyphosis, there is loss of lumbar lordosis producing the known “flatback deformity” and overall forward pitching of the body. Revision surgery in patients with flatback deformity typically includes pedicle subtraction osteotomy (PSO) to re-create lumbar lordosis and correct global sagittal spinal balance.4 After placement of Harrington’s rods, significant back pain can result from sagittal imbalance. Pain can also result from construct failure, most commonly presenting with hook displacement. Rod breakage, protruding rods through the skin, and rod dislocation and extensions into the sacrum are complications of thoracolumbar/lumbar constructs.18 Hooks enter in the spinal canal, potentially causing canal stenosis or spinal cord injury.19,20 Postsurgical bracing or casting and months of bed rest maintain the position of the rods and hooks.17 Aaro and Ohlén reported late postoperative complications including worsening pain and deformity.21 McMaster’s research noted a 0.5% neurologic deficit rate with the Harrington’s instrumentation.17 When used with a single concave rod technique, the Harrington’s system was associated with high rates of implant failure and pseudarthrosis because of nonsegmental fixation.4 In turn, the necessary radiologic monitoring increases radiation exposure and risk in younger patients.21 Surgical implantation of the Harrington’s rods in young children younger than 10 years was associated with crankshaft syndrome, where anterior column growth continues after restriction of posterior growth because of the tethering action of the posterior fusion. In a study of 23 patients, Terek et al reported seven cases where deformity progressed to ≥ 10 degrees. Six of the seven patients demonstrated increased rotational crankshaft deformity.22 With advanced technology, other instrumentation replaced the Harrington’s rod.

57.6.2 Luque’s Rod Segmental Spinal Instrumentation In the 1970s, Luque subsequently developed an instrumentation system designed to address the limitations of the Harrington’s system. The Luque-rod segmental spinal instrumentation (LSSI) consists of an L-shaped rod adhering to the spine with segmental sublaminar wires designed to have greater control of the sagittal contour of the spine and maintain normal lordosis.23 With a posterior approach, the system was designed to correct idiopathic scoliosis, postural curves, spinal fractures, and primarily neuromuscular scoliosis in children, adolescents, and adult deformities. As McMaster noted, a reported disadvantage and potentially dangerous procedure using the LSSI system was passing the flexible wires within the spinal canal resulting in an increased frequency of intraoperative spinal cord injury (17%) over the Harrington’s system (0.5%).17

Complications Related to Spinal Instrumentation and Surgical Approaches More problems ensue with longer follow-up. Wire fixation of the rod is frequently compromised when rods break, which enables migration of rod sections caudally and cephalically.23 Nectoux et al’s incidences of migration at the proximal and distal ends with postoperative complications involved respiratory, digestive, pulmonary, and wound infections; neurologic injury; and broken hardware.24 The rods or broken hardware can migrate cephaladly, pushing through the spinal canal, or caudally penetrating the sacrum, intestines, and pelvic organs, and projecting through the rectum.23 Repeated microtrauma or cyclic loading may have added to the breakage of the wires or rods causing the migration.23 Loss of sacral fixation and loss of lumbar lordosis add to the risk factors. Increased intraoperative blood loss can occur when there is invasion of the epidural space.24 Furthermore, this system does not allow for axial stability, and when infection or nonunion occurs, removal of the implant is difficult. The correction could be lost.4 The Luque rods are rarely used in modern scoliosis surgery.

57.6.3 The Wisconsin’s Technique To address the shortcomings of its predecessors, the Wisconsin’s system was designed in the 1970s using a posterior surgical approach for segmental fixation of the spine. This system uses hooks and button wires implanted at the base of the spinous process and attached to rods for correction.25 Because the bone is thicker at the base, the interspinous instrumented spine resists compressive loads of failure.26 Complications from this instrumentation consist of flatback syndrome, high rates of pseudarthrosis, postoperative immobilization, extensive fusion needed to balance the spine, and limited deformity correction.4,26 It is believed that these complications originated from relatively weak fixation and control of the vertebrae in all three planes accentuated by the medial location of the instrumentation on the posterior spinous processes and the need for extended bracing postoperatively.26 The Wisconsin’s wires and hook system are no longer the preferred choice by surgeons for correction in scoliosis.

57.6.4 Single- versus Double-Rod Constructs As would be expected, there are more hardware failures using single-rod instrumentation constructs than with double-rod constructs. Reported failures include broken rods, curve progression, and pseudarthrosis. Hooks occasionally unseat in both constructs and dislodge, pulling away from the spine. Following two years after surgery, Wattenbarger et al compared outcomes of scoliosis correction using single- and double-rod constructs in adolescents. Patients treated with singlerod instrumentation (43 patients) were compared with the patients receiving double rods (103 patients).27 There were eight patients (19%) who experienced hardware-related problems with the single rod, compared to four (4%) in the doublerod group, which needed additional surgery. Of the nine patients (21%) in the single-rod group, five had revision surgery for broken rods, whereas no rods broke in the double-rod group. Two patients in the single-rod group required more surgeries because of pseudarthrosis. There were two neurologic

complications: a spinal cord injury prior to surgery and a somatosensory-evoked potential when an over aggressive correction of the lumbar curvature was enforced. The study found two postoperative wound infections in the single-rod group with no late complications, and there were 10 late infections in the double-rod group.27

57.6.5 Growing Rods For children and young adolescents, this surgical, fusionless procedure allows correction of deformity without restricting spinal growth. The paraspinal muscles are dissected with bone grafts to provide a foundational area. Rods are inserted between two established foundations and attached to the vertebrae with hooks, pedicle screws, or both.28 A tandem or sideto-side connector connects the uppermost proximal foundation to the lower, more distal foundations to create a thoracic kyphosis and a lumbar lordosis.29 After surgery, a back brace secures the foundation and the rod lengthening continues with other surgeries until the spine has grown adequately. The growing rods are removed once correction is achieved.29 Postoperative complications reported by Watanabe et al occurred in 22% (119 of 538) of the surgical procedures with 88 implant-related failures, 19 infections, 3 neurologic impairments, 2 respiratory problems, 2 gastrointestinal problems, 2 urinary problems, and 2 decubitus ulcers resulting from protruding implants. Sixty-one patients experienced dislodged implants, rod breakage, and foundation loosening. Most dislodged implants occurred at the proximal foundations (95%).29

57.6.6 Pedicle Screws The development of the pedicle screws opened a new era in the treatment of scoliosis used in both fusion and fusionless instrumentation constructs. It was the first instrumentation to address spinal deformity in the sagittal, coronal, and axial planes to allow powerful correction in three dimensions with improved biomechanical stability.30 Pedicle screws are placed through the posterior column into the body to achieve threecolumn fixation with a better ability to deteriorate the spine and allow for greater correction of the sagittal and coronal plane as compared to other instrumentation types.31,32 Complications associated with pedicle screws most commonly include malpositioning of the screws, followed with loose screws, which may require revision surgery.30 Hicks et al reported that in 16 studies following 1,436 patients, 12 patients (0.83%) experienced reoperation for malpositioned or loose screws.31 A larger diameter of the pedicle screw in the upper thoracic spine provides more reliable stability; however, it can cause a pedicle wall breach posing a potential risk of causing spinal cord and nerve root damage.19 Hicks et al also reported 27 pedicle fractures in a total of 5,370 screws with an incidence of 0.50% per screw inserted. Less common complications with screw insertion included dural tears, epidural hematomas, and pleural effusions.31

57.6.7 Rib-Based Fixation Systems Campbell and Smith developed the vertical expandable prosthetic titanium rib (VEPTR) system for the treatment of thoracic

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Thoracolumbar insufficiency syndrome in skeletally immature patients.33 VEPTR treats children by using a dual sliding sleeve connected by a locking clip that expands as the child grows, enabling ongoing growth of the spine, lung, and chest.28,33 This minimally invasive procedure offers an alternative to surgical fusion that limits thoracic cavity growth.34,35,36 The VEPTR implants attach rib to rib, rib to spine, or rib to ilium to achieve curve correction. They improve thoracic height, and allow spinal growth through serial lengthenings.35 Reported complications include lateral sliding and dislodgment of the pelvic hooks requiring adjustment. Migration upward and downward may require reattachment. Erosion of superior cradles through the ribs may require reattachment during routine expansion. In some cases, wound infection mandates removal. Upper extremity brachial plexopathy may occur and recovers after surgical adjustment of the system. Samdani et al reported 36.7% complications in their study of 11 patients inclusive of migrating hooks and erosion of superior cradles through the rib.35 They documented no neurologic, vascular, or visceral complications in their study. The failure rate of single rods approached 70% and that of the implantation of double rods approached 50%.37 Mersilene tape inserted submuscularly between two pelvic incisions decreased the S-hook migration in the VEPTR.35

57.6.8 Vertebral Body Stapling An alternative to spinal fusion in growing children, vertebral body stapling (VBS) places metal staples between the vertebral bodies on the convex side of the anterior spine, selectively restraining vertebral growth plate activity. Curve progression is halted and often resolves.38 In a study of 11 patients receiving stapling of thoracic and thoracolumbar curves, Betz et al reported complications including a diaphragmatic hernia, one staple overcorrection necessitating staple placement in the other direction, one mesenteric artery syndrome treated with nonoperative measures, one patient with a mucous plug leading to atelectasis, and three broken and dislodged staples. When overcorrection of 10 degrees or more appears on the radiographs, the surgeons remove the staples.39

57.6.9 Interbody Fusion Implants Interbody cages and grafts are often placed during spinal fusion procedures to improve fusion rates and allow for significant deformity correction.40 The cages are made from allograft bone, metal, or PEEK (polyetheretherketone) and can be embedded with a combination of various synthetic bone substitutes, allograft bone, and autograft bone. Approach-related complications are discussed in surgical approaches.

57.7 Surgical Approaches 57.7.1 Interbody Techniques Though the interbody space has historically been used as a site for releasing deformity and enhancing fusion, its popularity for enhanced deformity correction has increased with recent advances in surgical instruments, interbody implants, and

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biologic technologies. Depending on the targeted level of spinal pathology, a wide variety of surgical approach options and modern retraction techniques enable powerful deformity correction and reduced patient morbidity. The vertebral end plates of the interbody space are suited to deformity correction and provide large footprints of opposing surfaces in close proximity to one another, with biomechanical compressive forces that contribute to fusion. Interbody fusion for treatment of deformity is often combined with posterior instrumentation as an adjunct rather than a primary source of correction and stabilization. Nevertheless, approach-related complications associated with interbody implants are significant and must be considered during surgical planning.

57.7.2 Anterior Lumbar Interbody Fusion Anterior lumbar interbody fusion, known as ALIF, is performed through the abdomen with a transperitoneal or retroperitoneal approach. Access is limited by the great vessels, and therefore, it is typically limited to the lower levels of the lumbar spine.41 It can address focal deformity including spondylolisthesis or degenerative disc disease, or it can enhance correction and stability at the bottom of longer instrumentation constructs extending to the sacrum. A cage and graft are inserted into the disc space after the discectomy with biologic enhancement used by many surgeons.42 Trauma to the back muscles and posterior ligamentous structures may be spared when stand-alone, anterior-only technique is used, or ALIF may be combined with percutaneous minimally invasive posterior instrumentation techniques. Typical complications associated with ALIF approaches include injury to abdominal and pelvic blood vessels or viscera. There can be life-threatening blood loss, neurologic injury by laceration, or stretch during deformity correction, incisional hernia, deep venous thrombosis, pulmonary embolus, pulmonary dysfunction, retrograde ejaculation, wound dehiscence, and nonunion. In their extensive research, Jiang et al gathered information and documented complications from ALIF. Fourteen of 218 patients developed a wound infection hematoma and wound dehiscence; 2 of 244 had an incisional hernia; 1 of 32 reported retrograde ejaculation; 2 of 91 suffered with venous injury; and 6 of 96 patients recovered from deep venous thrombosis and pulmonary embolus.41

57.7.3 Posterior Lumbar Interbody Fusion With patients in the prone position, the posterior lumbar interbody fusion (PLIF) procedure employs a laminectomy and disc nucleus removal to fuse the interbody space. The pars interarticularis and facet joints are preserved bilaterally, which necessitates retraction of the neural elements during interbody work. Critics of this technique believe that excessive thecal sac retraction leads to high rates of nerve root irritation and injury.43 Okuda and his colleague reported intraoperative, early postoperative, and late postoperative complications in 251 patients after PLIF.44 Twenty-six intraoperative complications were

Complications Related to Spinal Instrumentation and Surgical Approaches reported with 19 dural tears and 7 pedicle screw malpositioning. Early postoperative complications in 19 patients included 1 brain infarction, 1 infection, and 17 neurologic complications showing 8 patients with slight motor loss improving in 6 weeks, and 9 patients with severe motor loss such as drop foot. Seventeen patients experienced late complications with three hardware failures, 3 with nonunions, and 11 with adjacent-segment degeneration who required additional surgery.44

57.7.4 Transforaminal Lumbar Interbody Fusion A newer posterior interbody technique, transforaminal lumbar interbody fusion (TLIF), can be performed with midline traditional posterior approach to the spine, or through tubular retractors using a minimally invasive (Longer operating time and more fluoroscopic radiation lengthen the surgical procedure.45 A meta-analysis by Habib et al reviewed articles to investigate the complication rates for MIS-TLIF (▶ Table 57.1). The articles showed an infection rate of 6.9%, urinary tract infection of 3.4%, neurologic deficits of 20.7%, screw cage complications of 44.8%, cerebrospinal fluid leak of 10.3%, blood transfusion/coagulation of 3.4%, and 10% other (pseudoarthrosis, ileus, and radiculopathy) after TLIF.45

57.7.5 Minimally Invasive Transforaminal Lumbar Interbody Fusion Schizas et al studied instrumentation-related complications and claimed that inexperience can be associated with inadequate endplate preparation and misplacement of transpedicular screws. Long-term failure of implants could be attributed to nonunion and contributes to poor outcomes.46 Nevertheless, meta-analysis has compared MIS TLIF with open or traditional TLIF and found comparable fusion rates and lower overall complication rates with the MIS technique.47

57.7.6 Lateral Interbody Fusion and Extreme Lateral Interbody Fusion An alternative to anterior and posterior surgery, lateral approach has recently gained popularity for use in deformity

correction and spinal fusion. This procedure is typically performed in the lumbar spine during deformity correction in conjunction with disk removal and, in severe cases, vertebral body resection (VCR), or complete body removal. MIS adaptations of the procedure have recently evolved with reduction in complications, blood loss, and postoperative pain for patients with adult scoliosis and degenerative disease.48,49,50 Fluoroscopic images guide the surgical approach with removal of disk material, preparation of the endplates, and insertion of a structural interbody spacer and graft laterally.49 The approach typically traverses the psoas muscle, though some retractor systems are designed to pass anterior to the psoas. The nerves of the lumbar plexus are carefully monitored during the procedure. The insertion of interbody fusion cages carry a variety of possible complications including misplacement and cage migration. These devices may fracture or perforate the adjacent endplates, or translate anteriorly or laterally into the retroperitoneal space, with loss of reduction, or neurologic impingent in the foramen.48 Posterior instrumentation is a frequent adjunct to lateral interbody implantation techniques, and provides improved stability compared to lateral instrumentation using plate and screw constructs. Vascular complications are less common using the lateral approach when compared to the ALIF approach. Great vessel injuries rarely occur; however, the injuries could happen when retractors or sharp instruments divert anteriorly during the procedure. Local radicular vessel injury rarely results in substantial hemorrhage or hematoma. Neurologic injury is most commonly associated with femoral nerve palsy from damage to the lumbar plexus during retractor placement through the psoas muscle. The lumbar plexus is most vulnerable during L4– L5 procedures where the plexus is more anterior and centrally located in the path of dissection.51 In a case report of 107 patients, two-thirds of patients recorded blood loss over 100 mL, 7 patients experienced motor deficits, 26% of patients had hip flexor weakness correlated to the surgical wound in the psoas muscle, and one patient had kidney laceration.52 A study of the lateral approach conducted by Rodgers et al reviews 710 cases with a low complication rate (▶ Table 57.2).

Table 57.2 Research findings for 710 cases reported by Rodgers et al53 Complication

Number of patients

Table 57.1 Analysis review reported by Habib et al45

Wound infection

3

TLIF complications

MI rate

GI

7

Infection

6.9%

Respiratory

7

UTI

3.4%

Cardiac

7

Neurologic deficits

20.7%

Neurologic

4

Screw/cage complaints

44.8%

Iatrogenic HNP

1

CSF leak

10.3%

Vertebral fractures

14

Blood transfusions

3.4%

Sacral fractures

2

Other

10.5%

Hardware fractures

6

Abbreviations: CSF, cerebrospinal fluid; UTI, urinary tract infection.

Abbreviations: GI, gastrointestinal; HNP, hypoglossal nerve palsy.

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Thoracolumbar Table 57.3 Research findings in 100 cases reported by Tsahtsarlis et al48 Complications

Statistical rate

Pedicle screw misplacement

2.5%

Interbody cage displacement

1.7%

Interbody cage migration

0.8%

Blood transfusion

0.8%

Venous-thrombo embolism

2%

Bone graft protein

3%

There were 49 complications: 3 wound infections, 7 gastrointestinal infections, 7 respiratory complications, 7 cardiac complications, 4 neurologic complications, 12 vertebral fractures, 1 iatrogenic hypoglossal nerve palsy, 2 sacral fractures, and 6 hardware fractures.53

57.7.7 XLIF Surgical Procedure Tsahtsarlis et al documented their observations of 100 patients who underwent lateral interbody fusion with posterior instrumentation (▶ Table 57.3). CT scans demonstrated 2.5% pedicle screw misplacement; 1.7% interbody cage displacement; 0.8% interbody cage migration; 0.8% requiring postoperative blood transfusion; 2% venous thromboembolism; and 3% complications related to biologic enhancement products.48

57.8 Lateral Transpsoas Fusion 57.8.1 Discussion Patients burdened with the curve deterioration of scoliosis live with pain, reduced pulmonary function, and increased mortality rates when not treated. Chronic back pain is higher in untreated scoliotic patients.4 When appropriately indicated, modern scoliosis reconstruction can employ a multitude of alternative techniques and philosophies to minimize suffering and optimize function54 with each option carrying unique complications. The younger the patient and the larger the curve, the more rapid the progression. In younger patients, all treatment measures focus around slowing down the progression until skeletal maturity is reached. In cases where significant growth is still anticipated in the developing spine, nonfusion procedures may be selected. Growing rods allow residual growth in one operation lasting over 3 years with subsequent surgeries to follow.35 Growing rods, VEPRT, and vertebral stapling may require revision surgery for hardware failures, misplacement, erosion of ribs, and realignment. When fusion is selected for treatment of scoliosis deformity, metal implants, such as screws, hooks, and rods, hold the placement in the corrected position until the vertebrae fuse together. Harrington’s instrumentation was riddled with complications including loss of lordosis or flatback syndrome. Patients often develop degenerated adjacent segments, chronic pain, and spinal stenosis, requiring surgeons to rebalance the spine with one or more osteotomies.3,55 The inclusion of the lumbosacral segment is a surgeon’s decision when fusing the thoracolumbar

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spine, because pain most likely will occur from the deterioration, and this may necessitate a future extension to the sacrum.3,56 Rods can break, and hooks and screws can dislodge, requiring another surgical procedure and further evaluation to replace the fractured or malpositioned hardware. A failure of the spine to fuse or the continued progression of the curve often leads to instrumentation failure and may necessitate revision surgery. In patients with osteoporosis, instrumentation may fail because of weakness of the bone. Strategies for fixation include use of polymethylmethacrylate (PMMA) cement injected into the bodies before screw placement, large anterior interbody cages, and larger diameter screws to improve fixation and prevent bony fractures.3,57,58 Other pitfalls in elderly patients include misjudgment of a case, poor patient selection, wrong technical performance, implant failure, a lack of achieving balance in the sagittal and coronal planes, and complications that cannot be explained.59 The age of the patients influences the increased rates of morbidity and mortality during hospitalization.60 MIS for correction of spinal deformity records a shorter recovery, reduces morbidity, decreases hospital stay, decreases pain, and reduces blood loss.61,62 Arnold et al and other groups of researchers reported in their investigation the problematic effects of recombinant human bone morphogenetic protein-2 (rhBMP-2), bone morphogenetic protein use, the incidences of bony overgrowth or heterotopic ossification, graft subsidence, loss of fixation, inflammation, infection, cancer risk, toxicity, neurologic events/deterioration, retrograde ejaculation, radiculitis, and functional loss as the indicated effects.63,64,65 For developmental kyphosis, the recommended instrumentations are pedicle screws and rod implementation, and osteotomy when necessary to correct sagittal plane imbalance. PSOs remove the bone in the back of the vertebra so that the bone pushes backward. Mummaneni et al conducted a study of 10 patients who underwent thoracolumbar PSO and reported two dural tears, one cardiac instability, two coagulopathy, two wound infection, one urinary infection, and two delirium; all patients recovered fully.66 Complications can develop from monitoring instrumentation for treatment of scoliosis. Women who had undergone many radiographs in their youth for scoliosis report the adverse effects of the radiation resulting from early instrumentation. With repeated exposure to the soft tissue, women encountered the risk of breast cancer. As the amount of radiation accumulates in the body, women could be at risk. A study of surveys and telephone interviews investigated by Ronckers and his colleagues67 published a report indicating 68 women affected with breast cancer from a cohort of 3,010. Proximal junctional kyphosis (PJK) is a known complication of posterior spinal fusion with a 10-degree or greater increase in kyphosis at the proximal junction as measured by the Cobb’s angle from the caudal endplate of the uppermost instrumented vertebrae to the cephalic endplate of the vertebrae above. Most cases of PJK are asymptomatic and do not require surgery; however, some do require revision because of pain.68 Cosmetic concerns appear when PJK is greater than 20 degrees. Radiographs and clinical data for 161 patients revealed 62 patients developed PJK postoperative in 7.8 years.69

Complications Related to Spinal Instrumentation and Surgical Approaches A more severe form of PJK that does require revision surgery is termed proximal junctional failure (PJF) that carries an increased risk of neurologic deficit. PJF is defined as a fracture of the vertebrae just above the most superiorly fused vertebral body pedicle screw constructs or the most superiorly fused vertebrae itself with an increase in kyphosis. The failure of the fusion can be because of a fracture of the vertebrae, disruption of the posterior osseoligamentous complex, or pullout of the instrumentation along with 10 degrees of kyphosis. The prevalence is found to be 26 to 39% and progression rarely outside of the postoperative period.69,70 Risk factors for developing PJK include female gender, older than 55 years, and combined anterior/posterior fusion. Preoperative sagittal imbalance is also found to predict PJK. When PJK occurs that is symptomatic, extension of the fusion is the treatment of choice.

57.9 Neurologic Complications A research study of 108,419 cases conducted by the SRS morbidity and mortality database indicated 1,064 as new neurologic deficits (NND; 0.1%); 662 as nerve root deficit; 74 as cauda equina deficits, and 293 as spinal cord deficit, and 353 as nonspecific.71 With the loss of sensation between the legs, buttocks, and bladder resulting from nerve root, cauda equina, and spinal cord damage, a neurologic consult necessitates urgent care of the deficit. Depending on the outcome, neurosurgery and/or medications are the treatments. Revision cases climbed to a 41% higher rate (1.25%) of NND as compared with primary cases, and pediatric cases revealed a 59% higher rate of NND when compared with adult cases. The NND rate in cases with implants rose to more than twice the rate for cases without implants.71 To reduce the risk of neurologic complications that may occur during spine surgery, intraoperative neurophysiological monitoring (IONM) assists in assessing the real-time status of the nervous system. Its high and low sensitivity and specificity reduce the risk of injury, and assesses the neural structures of the neuromuscular junction, peripheral nerve, spinal cord, brainstem, and cortex during surgery.72

57.10 Adjacent-Segmented Degeneration and Disease Adjacent-segmented degeneration (ASD) is the condition in which a patient shows radiographic evidence of accelerated degenerative changes at disks adjacent to a prior surgery. It is considered adjacent segment disease (ASDi) when it becomes symptomatic.73 Though there is significant controversy regarding the etiology of ASD and ASDi, the biomechanical changes in the operated segment and damage to the local environment adjacent to the fusion are felt to contribute. The rigidity imparted by stabilizing instrumentation constructs may increase the wear and tear at adjacent segments and thus cause the damage. In a research study conducted by Choon et al of 1,069 patients who had undergone lumbar or lumbosacral fusion, 28 (2.62%) had revision surgery for ASD.74 These researchers documented degenerative spondylolisthesis as the most common

initial diagnosis. Results included motor weakness in major leg muscles (32.1%) with two improving after revision surgery. All patients with ASD had spinal stenosis with neural encroachment, accompanied by disc herniation in 8 patients, spondylolisthesis in 11 patients, and retrolisthesis in 7 patients. Patients suffered with significant back pain and leg pain. Disk arthroplasty, known as disk replacement, had been proposed to restore natural motion and reduce adjacent segment disease. Though many industry-sponsored studies have demonstrated lower rates of secondary surgery compared to fusion surgery, other independent studies have been less promising.73

57.11 Conclusion In the surgical treatment of scoliosis, surgeons use a variety of instrumentation and approaches to decrease curve progression in juvenile, adolescent, and adult patients. As with all surgeries, patients are at risk and complications occur. In so keeping, substantial strategies are used by surgeons to tailor the instrumentation and surgical approach to benefit each patient. Advances in instrumentation are designed to minimize morbidity and recovery time after surgery, and to optimize function and quality of life.

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[42] Fantini GA, Pawar AY. Access related complications during anterior exposure of the lumbar spine. World J Orthod. 2013; 4(1):19–23 [43] Hey HW, Hee HT. Lumbar degenerative spinal deformity: surgical options of PLIF, TLIF and MI-TLIF. Indian J Orthop. 2010; 44(2):159–162 [44] Okuda S, Miyauchi A, Oda T, Haku T, Yamamoto T, Iwasaki M. Surgical complications of posterior lumbar interbody fusion with total facetectomy in 251 patients. J Neurosurg Spine. 2006; 4(4):304–309 [45] Habib A, Smith ZA, Lawton CD, Fessler RG. Minimally invasive transforaminal lumbar interbody fusion: a perspective on current evidence and clinical knowledge. Minim Invasive Surg. 2012; 2012:657342 [46] Schizas C, Tzinieris N, Tsiridis E, Kosmopoulos V. Minimally invasive versus open transforaminal lumbar interbody fusion: evaluating initial experience. Int Orthop. 2009; 33(6):1683–1688 [47] Wu RH, Fraser JF, Härtl R. Minimal access versus open transforaminal lumbar interbody fusion: meta-analysis of fusion rates. Spine. 2010; 35(26):2273– 2281 [48] Tsahtsarlis A, Efendy JL, Mannion RJ, Wood M. Complications from minimally invasive lumbar interbody fusion. J Clin Neurosci. 2013; 20(6):813–817 [49] Patel VC, Park DK, Herkowitz HN. Lateral transpsoas fusion: indications and outcomes. ScientificWorldJournal. 2012; 2012:893608 [50] Caputo AM, Michael KW, Chapman TM, Jr, et al. Clinical outcomes of extreme lateral interbody fusion in the treatment of adult degenerative scoliosis. ScientificWorldJournal. 2012; 2012:680643 [51] Le TV, Burkett CJ, Deukmedjian AR, Uribe JS. Postoperative lumbar plexus injury after lumbar retroperitoneal transpsoas minimally invasive lateral interbody fusion. Spine. 2013; 38(1):E13–E20 [52] Berjano P, Lamartina C. Far lateral approaches (XLIF) in adult scoliosis. Eur Spine J. 2013; 22(2):S243–S253 [53] Rodgers WB, Gerber EJ, Patterson J. Complications in 710 XLIF surgeries: Sp11. Spine. 2010(Oct):93 [54] Pruijs JE, van Tol MJ, van Kesteren RG, van Nieuwenhuizen O. Neuromuscular scoliosis: clinical evaluation pre-and postoperative. J Pediatr Orthop B. 2000; 9(4):217–220 [55] van Dam BE, Bradford DS, Lonstein JE, Moe JH, Ogilvie JW, Winter RB. Adult idiopathic scoliosis treated by posterior spinal fusion and Harrington instrumentation. Spine. 1987; 12(1):32–36 [56] Bradford DS, Tay BK, Hu SS. Adult scoliosis: surgical indications, operative management, complications, and outcomes. Spine. 1999; 24(24):2617–2629 [57] Ploumis A, Transfledt EE, Denis F. Degenerative lumbar scoliosis associated with spinal stenosis. Spine J. 2007; 7(4):428–436 [58] Postacchini F. Surgical management of lumbar spinal stenosis. Spine. 1999; 24(10):1043–1047 [59] Aebi M. The adult scoliosis. Eur Spine J. 2005; 14(10):925–948 [60] Deyo RA, Cherkin DC, Loeser JD, Bigos SJ, Ciol MA. Morbidity and mortality in association with operations on the lumbar spine. The influence of age, diagnosis, and procedure. J Bone Joint Surg Am. 1992; 74(4):536–543 [61] Anand N, Baron EM. Minimally invasive approaches for the correction of adult spinal deformity. Eur Spine.. 2013; 22(2):S232–S241 [62] Anand N, Baron EM, Khandehroo B, Kahwaty S. Long-term 2- to 5-year clinical and functional outcomes of minimally invasive surgery for adult scoliosis. Spine (Phila Pa 1976). 2013; 38(18):1566–1575 [63] Arnold PM, Anderson KK, McGuire RA, Jr. The lateral transpsoas approach to the lumbar and thoracic spine: a review. Surg Neurol Int. 2012; 3 Suppl 3: S198–S215 [64] Carragee EJ, Hurwitz EL, Weiner BK. A critical review of recombinant human bone morphogenetic protein-2 trials in spinal surgery; emerging safety concerns and lessons learned. Spine. 2011; 111:471–491 [65] Poynton AR, Lane JM. Safety profile for the clinical use of bone morphogenetic proteins in the spine. Spine. 2002; 27(16) Suppl 1:S40–S48 [66] Mummaneni PV, Dhall SS, Ondra SL, Mummaneni VP, Berven S. Pedicle subtraction osteotomy. Neurosurgery. 2008; 63(3) Suppl:171–176 [67] Ronckers CM, Doody MM, Lonstein JE, Stovall M, Land CE. Multiple diagnostic X-rays for spine deformities and risk of breast cancer. Cancer Epidemiol Biomarkers Prev. 2008; 17(3):605–613 [68] McClendon J, Jr, O’Shaughnessy BA, Sugrue PA, et al. Techniques for operative correction of proximal junctional kyphosis of the upper thoracic spine. Spine (Phila Pa 1976). 2012; 37(4):292–303 [69] Kim YJ, Bridwell KH, Lenke LG, Glattes CR, Rhim S, Cheh G. Proximal junctional kyphosis in adult spinal deformity after segmental posterior spinal instrumentation and fusion: minimum five-year follow-up. Spine. 2008; 33 (20):2179–2184

Complications Related to Spinal Instrumentation and Surgical Approaches [70] Kim YJ, Lenke LG, Bridwell KH, et al. Proximal junctional kyphosis in adolescent idiopathic scoliosis after 3 different types of posterior segmental spinal instrumentation and fusions: incidence and risk factor analysis of 410 cases. Spine (Phila Pa 1976). 2007; 32(24):2731–2738 [71] Hamilton DK, Smith JS, Sansur CA, et al. Scoliosis Research Society Morbidity and Mortality Committee. Rates of new neurological deficit associated with spine surgery based on 108,419 procedures: a report of the scoliosis research society morbidity and mortality committee. Spine. 2011; 36(15):1218–1228

[72] Stecker MM. A review of intraoperative monitoring for spinal surgery. Surg Neurol Int. 2012; 3(3) Suppl 3:S174–S187 [73] Bertagnoli R, Yue JJ, Fenk-Mayer A, Eerulkar J, Emerson JW. Treatment of symptomatic adjacent-segment degeneration after lumbar fusion with total disc arthroplasty by using the prodisc prosthesis: a prospective study with 2year minimum follow up. J Neurosurg Spine. 2006; 4(2):91–97 [74] Lee CS, Hwang CJ, Lee SW, et al. Risk factors for adjacent segment disease after lumbar fusion. Eur Spine J. 2009; 18(11):1637–1643

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58 Complications of Osteobiologics in Spine Surgery Jozef Murar, Gregory D. Schroeder, and Wellington K. Hsu

58.1 Introduction

58.2.2 Ectopic Bone Formation

Autogenous bone graft has historically been used in spinal fusion surgery. In an effort to increase fusion rates while decreasing the morbidity associated with harvesting iliac crest bone graft (ICBG), the use of allograft bone, synthetic bone graft substitutes, and recombinant bone morphogenetic protein-2 (rhBMP-2) has increased. However, these osteobiologic replacements are associated with potential complications. This chapter will focus on the complications from osteobiologics.

Heterotopic bone formation has been reported after the use of rhBMP-2 in the lumbar spine in a transforaminal lumbar interbody fusion (TLIF)18 and posterior lumbar interbody fusion (PLIF),10 which can lead to significant clinical sequelae.10,19 In the first clinical study using rhBMP-2 in a PLIF, Haid et al demonstrated ectopic bone formation in 70% of patients as seen on computed tomographic (CT) scans.10 Because these patients were asymptomatic, the authors concluded that the ectopic bone formation was clinically irrelevant. Since then, more recent literature has associated radiculopathy with ectopic bone formation (▶ Fig. 58.1).18,19,20,21 In one such report of 37 patients who underwent a TLIF utilizing rhBMP-2, Chen et al found that 11% of patients had symptomatic neural element compression corresponding to the anatomic location of ectopic bone in the neural foramina18; three of the four patients underwent removal of the heterotopic ossification (HO) with complete resolution of radiculitis.18 Strategies to mitigate HO in posterior interbody fusions include use of lower concentrations of rhBMP-2, placement of sponges away from the dura mater (anterior to the cage), and maintenance of a physical barrier posteriorly to prevent extravasation of BMP outside the intervertebral space.18,22,23 Potential barriers have been investigated such as fibrin glue, sealants, and bone wax.24,25,26

58.2 Recombinant Bone Morphogenetic Protein-2 in the Lumbar Spine 58.2.1 History The use of rhBMP-2 was approved by the Food and Drug Administration (FDA) in an anterior lumbar interbody fusion (ALIF) within the Lumbar Tapered Fusion Device system (LTCage) in skeletally mature patients in 2002.1 Early studies reported that the use of rhBMP-2 led to decreased operating room time, blood loss, and hospital stay with less morbidity than those treated with ICBG.2,3 These promising results led to an increased off-label use of rhBMP-2.1 Although few complications were reported in early clinical trials of rhBMP-2,4 potential adverse reactions were proposed including bony overgrowth; interaction with exposed dura and nerves; carcinogenicity; reproductive toxicity; immunogenicity; and increased osteoclast activity.5 The risk of adverse events with the use of rhBMP-2 has been found to be significantly higher than that originally reported in industry-sponsored trials.2,4,6,7,8,9,10,11,12,13,14,15,16,17

58.2.3 Postoperative Radiculitis Whereas postoperative radiculitis after a posterior interbody fusion can result from nerve root retraction during cage insertion,27 the rates of postoperative radiculitis are significantly increased (7–18%) when rhBMP-2 is used.22,28,29,30,31,32 Some investigators have suggested that radicular symptoms can result

Fig. 58.1 (a) Post-op axial CT scan at L5-S1with ectopic bone adjacent to the transforaminal lumbar interbody fusion entry site and extending posterior into the spinal canal. (b) Post-op saggital CT through the right side of the spinal canal. Ectopic bone in the canal is located opposite the transforaminal lumbar interbody fusion entry site and extending up posterior to the lower L5 vertebral body. (c) Post-op saggital CT more to the right than Fig B, through the entry zone of the L5–S1 foramen. Note a large mass of ectopic bone in the entry zone of the foramen.19

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Fig. 58.2 (a) Post-op saggital MRI demonstrating intraspinal cyst as noted by the white arrow. (b) Axial MRI cut demonstrating intraspinal cyst (large white arrow) and a fluid-fluid level juxtaposed to the interbody cage (double arrows). There is compression of the left L4 nerve root in left lateral recess.35

from a localized inflammatory response that occurs with the use of rhBMP-2.33 Multiple authors have reported increased radicular symptoms 2 to 4 days postoperatively (when the maximum inflammatory response is present) without evidence of a compressive pathology on advanced imaging.26,27,34 Rihn et al noted a 14% (12/86) postoperative radiculitis rate in patients undergoing TLIF with rhBMP-2 compared to just 3% (1/33) without rhBMP-2 which was not statistically significant (p = 0.08).28 However, its incidence was decreased from 20% (10/54) to 5% (2/37) when a hydrogel sealant was injected over the posterior annular defect which was statistically significant (p = 0.047).28 Radiculitis can also occur with fusions in different anatomic areas. Lubelski et al demonstrated a rate of 18% after TLIF/PLIF, 23% after posterolateral lumbar fusion (PLF), 21% after ALIF, and 17% after combine anterior/posterior surgery.29 Additionally, one report of delayed postoperative radiculitis was found to be caused by an intraspinal cyst (▶ Fig. 58.2) encasing the rhBMP-2 collagen sponge compressing the axilla of the left L4 nerve root and the shoulder of the left L5 nerve root.35 One potential mechanism for this complication has been implicated in a preclinical study that demonstrates a systemic elevation of inflammatory cytokines associated with pain in response to localized rhBMP-2 delivery.33

58.2.4 Osteolysis/Graft Subsidence/ Cage Migration Whereas rhBMP-2 is responsible for stimulating bone growth, early bone resorption and osteolysis have been well documented in the literature.27,28,36,37,38,39,40,41,42,43,44 McClellan et al obtained CT scans 3 months after patients underwent a TLIF utilizing rhBMP-2 and noted osteolytic changes in 22 of 33 levels (69%).43 They also reported graft subsidence in five (16%) of those patients (▶ Fig. 58.3 and ▶ Fig. 58.4). This finding was corroborated by Vaidya et al who noted development of osteolysis and subsidence related to rhBMP-2 use in lumbar as well as cervical fusions.45 At 3 months, the subsidence rate in patients who underwent TLIF was 53% (9 of 17 levels) in the rhBMP-2 group compared to 12% (3 of 25 levels) in the control group, and the mean graft height loss was 24% in the study group

Fig. 58.3 (a) Saggital CT scan reconstruction demonstrating osteolysis. (b) Coronal CT scan reconstruction demonstrating osteolysis.43

compared to 12% in controls.45 Similar outcomes were found in patients who underwent an ALIF utilizing rhBMP-2; however, despite collapse in more than half of the levels in which rhBMP2 was utilized, there were no clinical outcome differences between patients who did and did not have rhBMP-2.45 The incidence of osteolysis and cage migrations may be exacerbated by the use of rhBMP-2 with polyetheretherketone (PEEK) cages.41,44 In one report, the use of rhBMP-2 with PEEK

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Fig. 58.5 PEEK cage migration in lumbar spine. Arrows demonstrate the posterior most radiographic marker of the interbody implant, which is shown to be posterior and spun after 3 months compared to 0.5 months.44

soft endplates (▶ Fig. 58.5).44 Importantly, the osteolysis and cage migration appeared to be an early complication, as no cage migration was observed after 6 months.44 Similarly, bony resorption has also been reported with the use of rhBMP-2 and a femoral ring allograft in an anterior lumbar interbody fusion.46 Several mechanisms of action have been hypothesized to contribute to subsidence. The early cell-mediated inflammatory response may lead to a loss of its intrinsic strength in allograft spacers and increase subsidence.44,45 Similarly, the increased cytokine-induced inflammatory process may lead to erosion of adjacent vertebral endplates leading to subsidence of the spacer as well.44,45 Another possible risk factor for rhBMP-2-associated osteolysis is the presence of preexisting subchondral cysts (▶ Fig. 58.6 and ▶ Fig. 58.7).47 Finally, a preclinical study suggests that an osteolytic response may be initially induced by systemic release of macrophage inflammatory protein-1α and monocyte chemotactic protein-1.48 Whereas early osteolysis is often asymptomatic and results in rapid radiographic healing, rhBMP-2-associated osteolysis has been hypothesized to be a source of postoperative low back pain.49 Lewandrowski et al reported five cases of vertebral osteolysis in a study of 68 patients who underwent L5–S1 TLIF, and all five patients with osteolysis presented with significant back pain 6 to 12 weeks postoperatively that resolved without intervention.49

58.2.5 Hematoma/Seroma/Infection

Fig. 58.4 Sagittal (a) and coronal (b) CT scan reconstructions demonstrating severe osteolysis 3 months postoperatively after TLIF with use of recombinant bone morphogenetic protein-2.43

cages led to bone resorption in 80% (30/38) of the operative levels and significant device migration necessitating revision surgery occurred in 31% (8/26) of patients.44 PLIF/TLIF procedures were at the highest risk for cage migration, and at the time of reoperation, the PEEK cages were found to be grossly loose with

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Whereas hematomas and seromas likely occur in the posterolateral lumbar spine at similar rates to the cervical spine, because this anatomic area is more forgiving to localized edema, symptoms are less likely to occur. Garrett et al reported that of 130 patients who underwent a posterior lateral fusion utilizing rhBMP-2, six patients (4.6%) required reoperation for a symptomatic sterile seroma.50 On the other hand, in the PLIF such as a TLIF, case reports have documented localized fluid collection associated with nerve root impingement that requires a reoperation.19,33 The overall rate of symptomatic seromas or hematomas in the lumbar spine does not appear to be increased with the use of rhBMP-2.51 Williams et al reviewed 55,862 cases from the

Complications of Osteobiologics in Spine Surgery

Fig. 58.6 Preoperative and postoperative MRI demonstrating subchondral cyst formation and osteolysis around subchondral cyst postoperatively.47

Fig. 58.7 Preoperative and postoperative MRI demonstrating subchondral cyst formation and osteolysis around subchondral cyst 4 months postoperatively.47

Scoliosis Research Society (SRS) database, of which 11,933 used rhBMP-2.51 They found no significant increase in the reported epidural hematoma/seroma rate in the rhBMP-2 group in the thoracolumbar spine compared to the control group (0.2 vs. 0.2%, p = 0.3).51 Conversely, there does appear to be a marginal increase in the overall infection rate in lumbar spine fusions when rhBMP2 is utilized. In a large review of the original 13 industry-sponsored rhBMP-2 trials of 780 patients, Carragee et al reported an equivalent early infection rate in lumbar fusions when utilizing rhBMP-2 compared to ICBG (both 9.4%); however, there was a trend toward increased delayed infections in the rhBMP-2 group (4.2%) compared to the control group (1.4%) (p = 0.07).6,52 These data were substantiated by SRS database review, which found a statistically significant (p = 0.013) increase in deep wound infections in the thoracolumbar spine when rhBMP-2 was utilized.51 On the other hand, a recent meta-analysis of 11 Medtronic trials comparing adverse events of ICBG with rhBMP-2 did not demonstrate a significant increase in infections when rhBMP-2 was used.53

58.2.6 Retrograde Ejaculation Retrograde ejaculation (RE) is defined as the reflux of semen into the bladder instead of out through the urethra.54 Failure of closure of the bladder neck, which is under sympathetic control, can lead to a low-volume ejaculate and a low/absent sperm count with subsequent subfertility.54 RE has been shown to be a potential inherent complication of an ALIF caused by injury to the autonomic plexus during the approach.55,56,57,58,59,60 The reported rates of RE have varied in the literature (0–45%) and have been reported to be related to many different factors including the technique of dissection around the lumbar plexus, number of levels exposed, and amount of soft-tissue debridement that may be necessary during infection, tumor, or revision surgery.55,56,57,58,59,60 Other factors that have been reported to increase rates of RE include the interbody implant used, surgical approach, surgical technique, and surgeon experience.61,62,63 The association of rhBMP-2 with an increased risk of RE has been controversial.55,60,64,65 The FDA pivotal investigational device exemption trial for INFUSE (Medtronic Sofamor Danek,

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Thoracolumbar Memphis, TN)52 reported 11 RE events (7.9%) in the rhBMP-2 group compared to 1 RE event (1.4%) in the ICBG group, but no statistical analysis was performed. Carragee et al also retrospectively reviewed patients who underwent ALIF with and without rhBMP-2 (69 and 174, respectively).55 Five cases of RE were reported in the rhBMP-2 group (6.7%) compared with 1 in the control group (0.6%) (p = 0.0025).55 One year after the surgery, three of the six patients with RE reported resolution of symptoms (one from control and two from rhBMP-2 group).55 However, an independent review of the individual patient data of industry-sponsored clinical trials concluded that there was no statistically significant risk of RE with the use of rhBMP2.53 Burkus et al also demonstrated no significant differences in RE rate in 508 patients from five multicenter FDA IDE trials2,8,14, 65,66,67,68 that were observed for 2 years (p = 0.242).52 The study did find a statistical increase in the rates of RE with the transperitoneal approaches, which was 8.6% compared to 1.6% in the retroperitoneal approaches (p = 0.007).52 Finally, Tepper et al reported that self-reported RE rates may not correspond to semen analysis.69 As future studies are designed to delineate the true risk of such a complication, semen analysis will likely need to be included to identify its incidence.

58.3 Recombinant Bone Morphogenetic Protein-2 in the Cervical Spine 58.3.1 History Recombinant bone morphogenetic protein-2 is not FDA approved for cervical surgeries. In 2008, the FDA issued a

warning, stating that the use of rhBMP-2 in the anterior cervical spine may contribute to marked dysphagia, hematoma, swelling, and/or the need for intubation/tracheostomy.70 Other adverse events in the cervical spine reported in the literature have included ectopic bone formation, radiculitis, osteolysis, graft subsidence, and cage migration. Cahill et al analyzed complication rates of rhBMP-2 use from the National Inpatient Sample Database from 2002 to 2006 and identified 328,468 patients who underwent spinal fusion procedures.71 In anterior cervical spine surgery, rhBMP-2 was associated with a complication rate of 7.09%, which was more than double the rate of complications when rhBMP-2 was not used (4.68%, p < 0.001).71

58.3.2 Swelling/Hematoma/Seroma Soft-tissue swelling in the cervical spine associated with the use of rhBMP-2 postoperatively is potentially life-threatening.72,73 The FDA has released 28 direct reports of complications over a 4-year period with regard to swelling of the neck and throat leading to airway and or neurologic compression in the neck.70, 74,75,76,77,78

Initial clinical studies of rhBMP-2 use in anterior cervical surgery demonstrated no specific evidence of adverse events specifically related to rhBMP-2.16 In 2006, increased rates of cervical swelling were reported that were thought to be because of rhBMP-2 use (▶ Fig. 58.8, ▶ Fig. 58.9, ▶ Fig. 58.10, ▶ Fig. 58.11).77 In a retrospective review of 234 patients who underwent an ACDF, 69 of who received rhBMP-2, Smucker et al reported a 27.5% rate of cervical swelling in the rhBMP-2 group compared to 3.6% in the control group (p < 0.0001).77 Swelling complications related to rhBMP-2 were often found several days postoperatively after a seemingly uneventful initial

Fig. 58.8 Prevertebral soft-tissue swelling (arrows) 4 days postoperatively after ACDF with utilization of rhBMP-2 and a return to baseline at 6 weeks postoperatively.77

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Complications of Osteobiologics in Spine Surgery postoperative course (▶ Fig. 58.8), whereas swelling related to prolonged surgery or prolonged retraction occurred in the immediate postoperative period.77 Three patients had to be taken to the operating room for exploration and drainage of a swollen neck on postoperative days 4, 5, and 7; however, intraoperatively there was no evidence of acute postoperative hematoma or fluid collection but rather diffuse swelling of the softtissue structures of the anterior neck including the strap muscles and the esophagus.77 In a separate study, Shields et al reported a 9.9% symptomatic hematoma rate (15 of 151 patients) after an anterior fusion using rhBMP-2.76 Of those, 11 were diagnosed on the fourth or fifth postoperative day and eight of them required surgical hematoma evacuation (▶ Fig. 58.12).76 Although systematic reviews have concluded that a dose–response curve to rhBMP-2 does not exist,79 it is likely that the absolute dose of rhBMP-2 plays a significant role in the magnitude of the inflammatory response in soft tissues leading to postoperative swelling and hematomas.72,75,80 Tumialán et al reported excellent clinical and radiographic results in 200 patients who underwent an ACDF using a PEEK spacer filled with rhBMP-2 regardless if 2.1 or 0.7 mg was used per level.81 Similarly, Dickerman et al were able to decrease retropharyngeal swelling as well by using low doses of rhBMP-2 (1.05 mg per level).82 Seroma formation has also been reported in posterior cervical procedures. Shahlaie and Kim reported on a patient who

developed a large symptomatic seroma postoperatively 3 days after a posterior occipitocervical fusion using 12-mg rhBMP2.83 After evacuation of the seroma, the patient’s symptoms including numbness and weakness in her arms and hands resolved. Additionally, Anderson et al reported on two cases where a moderate to large sized seroma resulted in severe compression of the spinal cord after posterior cervical laminectomy and fusion with rhBMP-2.84 Both patients showed immediate improvement after surgical evacuation of the seromas.84

58.3.3 Dysphagia Although the true dysphagia rate after an anterior cervical fusion procedure is high (47–60%),85,86,87,88,89,90,91,92,93,94,95 it is unclear if the use of rhBMP-2 increases this risk. For those patients with life-threatening sequelae, such as diffuse edema and hematoma, dysphagia is also induced. However, in a clinical study in 150 patients who underwent ACDF with and without rhBMP-2, Lu et al demonstrated no significant difference in overall dysphagia incidence between the two groups (40 vs. 44%, respectively, p > 0.05, measured with SWAL-QOL scoring system).96 Furthermore, the severity of dysphagia was lower in the rhBMP-2 group. In the absence of significant swelling causing possible airway compromise, dysphagia rates may not be significantly different with the addition of rhBMP-2 use.

Fig. 58.9 Tracheal deviation, diffuse right-side soft-tissue swelling, and gas within the tissues can be seen at levels above and below the hyoid.75

Fig. 58.10 Right-side soft-tissue swelling, tracheal deviation, and gas within the tissues at the C3–C4 level.75

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Fig. 58.11 Soft-tissue swelling and tracheal deviation caudal to the fusion side.75

surgical levels (▶ Fig. 58.13).97 Despite the radiographic findings, there were no reported clinical sequelae.97

58.3.5 Osteolysis and Graft Subsidence Similarly to the lumbar spine, the inflammatory reaction from rhBMP-2 can lead to osteolysis and graft subsidence in the anterior cervical spine as well.48,49,97 In the aforementioned study by Klimo and Peelle, a 57% rate of moderate to severe osteolysis and endplate resorption leading to implant migration was reported (▶ Fig. 58.14).97 The osteolysis was most extensive at 3 months and led to a loss of sagittal correction and a height of the fused vertebrae.97 Similarly, Vaidya et al reported a 100% rate of osteolysis in 23 patients who underwent an ACDF utilizing rhBMP-2, with subsidence noted in 13 of 32 levels.44

58.3.6 Wound Infection Compared to thoracolumbar surgery, the rate of wound infections in anterior cervical fusions is quite low.51 However, during an analysis of the Scoliosis Research Society Database, Williams et al identified 5,284 anterior cervical fusions and rhBMP-2 was used in 13% of the cases.51 They reported a fivefold increase in wound infections (2.1 vs. 0.4%, p < 0.001) when thBMP-2 was utilized compared to the control.51 Both superficial and deep infections were more frequent in the rhBMP-2 group. Fig. 58.12 CT scan demonstrating a cervical hematoma (outlined by arrowheads) in retropharyngeal space displacing the trachea anteriorly.76

400

58.3.4 Ectopic Bone Formation

58.4 Recombinant Bone Morphogenetic Protein-2 and Antibody Formation

Another possible complication with the use of rhBMP-2 in the cervical spine is HO.9,16,97 Boakye et al postulated that the HO formation may be dose dependent, and demonstrated that reducing the rhBMP-2 dose by half during their trial resulted in no further HO. Before decreasing the dose, three cases of asymptomatic HO were noted; however, no statistical analysis was performed.16 Additionally, Klimo and Peelle performed a radiographic study of 22 patients who underwent an ACDF using a PEEK interbody spacer with rhBMP-2 and noted excessive bone growth into the spinal canal or foramina in 68% of

Recombinant proteins have the potential to elicit a hostimmune response resulting in the production of antibodies in B cells.98,99 The development of immunogenicity to a therapeutic protein may reduce the efficacy of the protein.98,100 The antibody can bind to the active site of the protein and cause inactivation of the protein or it can induce rapid clearance of the protein.98,100 Other antibodies can bind to nonactive regions of a protein and reduce their bioavailability.98,100 Assessment of antibody response to biopharmaceutical products is an essential part of the safety and efficacy profile of such products.98,99,

Complications of Osteobiologics in Spine Surgery

Fig. 58.13 Ectopic bone formation into foramina at C5–C6 and C6–C7 after ACDF.97

Fig. 58.14 Endplate resorption in the cervical spine. Arrows demonstrate the position of the superior and inferior endplate postoperatively. 1.5 months later the arrows are in the same position, however the endplate is now resorbed both superiorly and inferiorly.44

101 Rates of antibody formation to therapeutic proteins vary widely ranging from 0 to 96%.98 The incidence may depend on a multitude of factors such as the delivery method, the residence time of the protein, the purity, and the test methodology used for detection.102,103 Initial clinical studies of BMP included detection of rhBMP-2 antibodies and found them to be very uncommon and without

clinical sequelae (▶ Table 58.1).100 This was later also confirmed by Burkus et al, who analyzed data from three different studies to examine the effect of rhBMP-2 antibodies.98 The authors found the overall incidence rate of rhBMP-2 antibody formation was 3.0% (range: 0.8–6.4%) in rhBMP-2-treated patients and 1.8% (range: 0–2.3%) in ICBG-treated patients (p = 0.297).98 The authors also found that the formation of rhBMP-2 antibodies

401

Thoracolumbar Table 58.1 Summary of studies of the immunogenicity of rhBMP-2a Authors and year

Time point

No. of patients

BMP Group

Antibodies (%)

Control Group

Antibodies (%)

BMP concentration (mg/mL) Dose

Assay

Boden et al (2000)

NS

11

0 (0.0)

None

None

1.5

1.3 mL/ 2.6 mL

NS

Burkus et al (2002)

Pre-op, 3 mo

137

1 (0.7)

124

1 (0.8)

1.5

4.2–8.4 mg

ELISA

Zdeblick et al (2001)

3 mo

136

1 (0.8)

None

None

NS

NS

NS

Govender et al (2002)

Pre-op, 6 wk, 20 wk

300

12 (4.0)

150

1 (0.7)

0.75/1.5

6 mg/12 mg

NS

Boden et al (2002)

NS

22

1 (4.5)

4

0 (0.0)

2.0

20 mg

NS

Baskin et al (2003)

Pre-op, 3 mo

18

0 (0.0)

15

0 (0.0)

1.5

0.4 mL

NS

Haid et al (2004)

Pre-op, 3 mo

34

0 (0.0)

33

0 (0.0)

1.5

4.0–8.0 mg

ELISA

Burkus et al (2005)

Pre-op, 3 mo

78

0 (0.0)

49

0 (0.0)

1.5

8.4–12.0 mg NS

Jones et al (2006)

Pre-op, 6 15 wk, 12 wk, 6 mo

0 (0.0)

15

0 (0.0)

1.5

12.0 mg

ELISA

Abbreviations: NS, not specified; rhBMP, recombinant bone morphogenetic protein-2. Note: Figure of immunogenicity of early BMP studies from Hwang et al.100

peaked within the first 3 months after surgery. The antibodies were present only transiently and 12 months postoperatively and only 3 of 667 rhBMP-2-treated patients (0.4%) had a positive titer for BMP-2 antibodies. Notably, 100% of patients who had a positive antibody response had CT evidence of bone bridging at 6, 12, and 24 months postoperatively, suggesting that the immune response did not impact the efficacy of rhBMP-2.98 Additionally, there was no difference in adverse event rates in patients with and without BMP-2 antibodies, given that similar rates were observed in both populations. Although there does not appear to be specific adverse reactions to rhBMP-2 antibodies, one potential exception may be during pregnancy, in which antibodies to rhBMP-2 could cross the placenta and potentially cause devastating effects in the developing fetus.98 In a preclinical study, rhBMP-2 antibodies have been shown to be capable of crossing the placenta.104 Because the influence of maternal antibody formation against rhBMP-2 on human fetal development is unknown, the use of BMPs is currently not recommended in women of childbearing potential and pregnant women.5,52,100

58.5 Recombinant Bone Morphogenetic Protein-2 and Cancer The clinical effect of rhBMP-2 on carcinogenesis and malignancy is a highly controversial topic despite the extensive in

402

vitro and in vivo research on this topic. BMP receptors are upregulated on cell membrane surfaces of many different cancer cell lines such as osteosarcomas, malignant fibrous histiocytomas, breast and prostate adenocarcinomas, and dedifferentiated chondrosarcomas.104,105,106 Conversely, because BMPs are a part of the TGF-beta superfamily with known tumor suppressor effects, they have been shown to inhibit cell proliferation in breast, ovarian, non-small cell lung, and prostate cancer cells in vitro.107 In the FDA data summary regarding INFUSE, the risk of cancer (0.7%) was the same in the rhBMP-2 and control group at 24month follow-up.52 A separate rhBMP-2 product, AMPLIFY, which contains a substantially higher concentration of growth factor (40 mg/mL) with a compression-resistant ceramic matrix (Medtronic Sofamor Danek, Memphis, TN), was also studied for cancer rates. In patients who received this product, Carragee et al demonstrated a higher cancer risk in the AMPLIFY group compared to control (3.8 vs. 0.9%, respectively [p = 0.064]).11,108 Summaries of the independent review of industry-sponsored data from the Yale Open Access Data Project concluded that although rhBMP-2 may be associated with a slight increased risk of malignancy, the overall absolute risk of cancer remained quite low.53,109 In is important to recognize that the relationship of cancer to a particular exposure such as rhBMP-2 is a complex one that can be studied in many different ways. For example, clinical trials designed to show clinical significance in outcomes are not powered appropriately to detect differences in cancer rates.

Complications of Osteobiologics in Spine Surgery Furthermore, relative risk and annual incidence of new cancers are often more important statistical measures than frequency over a longer time period. Although population-based database studies have their own inherent flaws, available data provide incidence rates to a much larger scale than those seen in prospective trials. In a retrospective study of 35,854 patients who underwent spinal fusion because of spinal stenosis, Lad et al utilized a propensity score-matched cohort of 4,698 patients (2,349 patients in whom rhBMP-2 was used vs. 2,349 patients in whom rhBMP2 was not used) to evaluate whether rhBMP-2 was associated with an increased risk of cancer.110 The authors concluded that BMP-exposed patients had a statistically nonsignificant increase in the rate of cancer diagnosis (9.37 vs. 7.92%, p = 0.08).110 However, patients in whom rhBMP-2 was used were at a 31% increased risk of benign tumor diagnosis (odds ratio: 1.31, p < 0.05), particularly benign nervous system tumors of the spinal meninges.110 Cooper and Kou reviewed more than 146,000 Medicare patients who underwent lumbar spinal fusion between 2003 and 2008 with or without rhBMP-2 and compared the rates of new cancer diagnosis.111 In the cohort, 15.1% of patients received rhBMP-2 and after an average overall follow-up of 4.7 years, 15.4% of rhBMP-2 patients and 17.0% of patients without rhBMP-2 had a new cancer diagnosis. There was no association found between rhBMP-2 and cancer risk in a multivariate proportional hazards model (hazard ratio: 0.99, 95% confidence interval: 0.95–1.02).111 Similarly, Kelly et al presented a review of the Medicare database of more than 467,000 patients who had a lumbar fusion, and found no statistical difference in the cancer risk with or without the use of rhBMP-2 (5.9% with rhBMP-2 vs. 6.5% without rhBMP2).112 The relative risk of developing cancer in the rhBMP-2 group compared to the control group was 0.938 which was statistically significant (95% confidence interval [95% CI]: 0.913 to 0.964).112 The reason for this association is unknown and further investigation is necessary.

58.6 Allograft and Disease Transmission Historically, spinal fusions relied on autogenous bone graft from the iliac crest or locally harvested bone to stimulate bone healing.113,114 However, autograft is not always adequate in volume and has been associated with surgical morbidity.113,114 Allograft bone has been used with increased frequency to help prevent surgical morbidity of obtaining iliac crest autograft.113,114,115 However, allografts also can be associated with complications, the most concerning being disease transmission.115,116,117

58.6.1 HIV and Hepatitis C Virus Approximately 1 million musculoskeletal allografts were distributed for use in the United States in 2004 and the associated infections because of viruses are overall quite uncommon (▶ Table 58.2 and ▶ Table 58.3).117 In 1999, the estimated risk of HIV transmission from an allograft was estimated to be approximately 1 in 1.6 million.118 However, since the advent of new FDA guidelines that mandate nucleic acid testing for HIV and HCV for all new tissue donors,118 no new cases of HIV/HCV transmission have been reported.117 To date, there have been a total of nine cases of HIV infections reported because of the use of fresh frozen bone and/or tendon allograft (▶ Table 58.2).115,119,120,121,122,123 Of these, there has only been one reported case of HIV transmission in a patient undergoing spine surgery in the United States which was contracted after receiving femoral head bone from a seronegative, but infectious donor in 1988.119 There have been 10 reported HCV transmissions from allografts, and all have resulted from the transplantation of frozen or cryopreserved allografts that were not heavily processed or sterilized (▶ Table 58.3).115,124,125, 126,127 The last reported case was in 2002, which led to the implementation of mandatory nucleic acid testing and stringent donor screening.115,117

Table 58.2 Cases of HIV transmission N

Type of allograft

Date

Publication date

Proven

Author (reference)

1

Frozen femoral

heada

1984

1988

+

CDC120

4

Cryopreserved bonea

1984

1996

+

Schratt et al.121

2

Frozen femoral headb

1985

1992

+

Simonds et al119

3

Bone chip, lyophilized bone allografts (not specified)a

1985

1997

±

Karcher122

1

Frozen patella (including patellar ligament and 1986 tendon and a section of tibia)b

1992

+

Simonds et al119

1

Frozen femoral heada

2001

±

Li et al123

1996

Source: From Hinsenkamp et al.115 aNo

anti-HIV test performed on donor.

bAnti-HIV-1

negative, NAT (nucleic acid testing) positive.

403

Thoracolumbar Table 58.3 Reported cases of HCV transmission N

Type of allograft bonea

Date

Publication

Proven

Author (reference)

1986–1990

1993

?

Pereira et al124

1

Frozen

1

Frozen bonea

1990

1992

+

Eggen and Nordbø125

1

Frozen bonea

1991

1995

+

Conrad et al126

3

Cryopreserved soft tissue (fascia, ligaments)a

1991

1995

+

Conrad et al126

3

Frozen bone–tendon–boneb

2000

2005

+

Tugwell et al.127

1

Cryopreserved tendonb

2000

2005

+

Tugwell et al127

Source: From Hinsenkamp et al.115 aNo

anti-HCV test.

bAnti-HCV

negative, no HCV NAT.

It is important to remember that when considering disease transmission in spinal patients, there are numerous potential confounders. It can be very difficult to link an infection to an allograft bone donor. Seroconversion of a patient inoculated by a virally contaminated graft may not occur or be noticed until sometime postoperatively, making it difficult to track back to the allograft. Additionally, if the patient received a perioperative blood transfusion, the tracing becomes further complicated. Nevertheless, given the development of safer sterilization processes and better testing, risk of disease transmission is extremely low with the use of allografts.116

58.7 Summary Autogenous ICBG remains the gold standard for cervical and lumbar spinal fusion surgery; however, many new adjuncts have been developed and used to limit the need to harvest ICBG and to attempt to increase fusion rates. Some of these adjuncts, particularly rhBMP-2, are largely used in an off-label setting and can lead to significant clinical complications, including ectopic bone formation, radiculitis, osteolysis and cage migration, hematoma and seroma formation, RE, and cervical swelling and dysphagia. It is important to be aware of the complications of such adjuncts, as well as the alternatives available, when making an operative decision to provide the best care to the patient and to limit any potential complications of surgery.

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[119] Simonds RJ, Holmberg SD, Hurwitz RL, et al. Transmission of human immunodeficiency virus type 1 from a seronegative organ and tissue donor. N Engl J Med. 1992; 326(11):726–732 [120] Centers for Disease Control (CDC). Transmission of HIV through bone transplantation: case report and public health recommendations. MMWR Morb Mortal Wkly Rep. 1988; 37(39):597–599 [121] Schratt HE, Regel G, Kiesewetter B, Tscherne H. [HIV infection caused by cold preserved bone transplants]. Unfallchirurg. 1996; 99(9):679–684 [122] Karcher HL. HIV transmitted by bone graft. BMJ. 1997; 314(7090):1300 [123] Li CM, Ho YR, Liu YC. Transmission of human immunodeficiency virus through bone transplantation: a case report. J Formos Med Assoc. 2001; 100 (5):350–351 [124] Pereira BJ, Milford EL, Kirkman RL, et al. Low risk of liver disease after tissue transplantation from donors with HCV. Lancet. 1993; 341(8849):903–904 [125] Eggen BM, Nordbø SA. Transmission of HCV by organ transplantation. N Engl J Med. 1992; 326(6):411–, author reply 412–413 [126] Conrad EU, Gretch DR, Obermeyer KR, et al. Transmission of the hepatitis-C virus by tissue transplantation. J Bone Joint Surg Am. 1995; 77(2):214–224 [127] Tugwell BD, Patel PR, Williams IT, et al. Transmission of hepatitis C virus to several organ and tissue recipients from an antibody-negative donor. Ann Intern Med. 2005; 143(9):648–654 [128] Zdeblick TA, Heim SE, Kleeman TJ. Laparoscopic approach with tapered metal cages: rhBMP-2 vs autograft Read at the Annual Meeting of the North American Spine Society; 2001 [129] Govender S, Csimma C, Genant HK, Valentin-Opran A, Amit Y, Arbel R, et al. Recombinant human bone morphogenetic protein-2 for treatment of open tibial fractures: a prospective, controlled, randomized study of four hundred and fifty patients. J Bone Joint Surg Am. 2002; 84-A:2123–2134 [130] Jones AL, Bucholz RW, Bosse MJ, Mirza SK, Lyon TR, Webb LX, et al. Recombinant human BMP-2 and allograft compared with autogenous bone graft for reconstruction of diaphyseal tibial fractures with cortical defects. A randomized, controlled trial. J Bone Joint Surg Am. 2006; 88:1431–1441

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Thoracolumbar

59 Removal and Revision of Broken Thoracolumbar Screws Jay M. Zampini and Andre Jakoi

59.1 Introduction The sophistication and rate of utilization1,2,3,4,5,6,7,8 of metallic implants for spinal stabilization have increased dramatically since the first use of steel bars and silver wires in 1910 by Fritz Lange.9 Even in the past two decades, the development and refinement of modern pedicle screw fixation systems has been accompanied by a doubling of the rate of internal fixation of the spine.10 Although many authors have reported that the use of spinal instrumentation can increase the rate of successful arthrodesis,11,12 it has become clear that patients with spinal implants may fail to achieve that goal and may require revision surgery.6 As many as 13% of all spinal implants will ultimately fail; therefore, as the number of instrumented spine operations continues to increase, so will the need for surgical revision or removal.13,14,15,16,17,18 Of all the modes of implant failure, screw fracture represents one of the more challenging obstacles faced in the process of revision spinal surgery (▶ Fig. 59.1). The purpose of this chapter is to review the process of evaluating patients with fractured thoracolumbar pedicle screws and planning revision surgery for patients with fractured screws.

59.2 Evaluation of Fractured Thoracolumbar Screws Patients with fractured thoracolumbar pedicle screws can present in a manner similar to that of other patients with failed back surgery—with axial pain.19 The causes of postoperative surgical site pain are numerous—infection, implant loosening, pseudarthrosis, adjacent segment degeneration, fracture, additional trauma, to name a few—and, as such, often require a thorough and systematic clinical evaluation to determine the most likely cause or causes of pain. Information elicited from the patient can usually direct the evaluation. The presence of fever, malaise, progressively worsening nonmechanical pain, or wound drainage can alert the surgeon of the possibility of infection. Even in the absence of frank signs of infection, each patient should be evaluated for occult infection with laboratory determination of the leukocyte count, erythrocyte sedimentation rate, and C-reactive protein. A history of trauma or the

occurrence of acute pain or motion deep within the surgical site can be suggestive of acute vertebral fracture or catastrophic failure of the instrumentation. A period of relative relief of the axial pain that led to the index fusion operation followed by a return of similar pain is characteristic of both implant loosening and pseudarthrosis. When all types and designs of spinal instrumentation are considered in a single group, it has been estimated that 3 to 7% of all implants will fail to maintain a stable interface with bone and will loosen.13,14,16,20,21,22 Additionally, there have been various estimates that 5 to 40% of lumbar fusion procedures result in pseudarthrosis.23 Nicotine use is now considered to be one of the most important predictors of the development of pseudarthrosis and is the single most relevant one solely within the patient’s control.24,25 The use of nonsteroidal anti-inflammatory drugs in the early postoperative period has also been clearly associated with the failure to achieve solid arthrodesis.26 The patient’s history of such use should be specifically questioned. Because of the multiplicity of causes of late postoperative pain, a thorough radiographic evaluation is also required. Pseudarthrosis is, very likely, the most important factor contributing to implant fracture and will typically be the primary reason for treating the fractured screws. The diagnosis of pseudarthrosis can be difficult to make, given no single method of evaluation has been accepted for the definitive diagnosis. The radiographic observation of new bone bridging the fused segment either between transverse processes or within the interbody space is highly suggestive of solid arthrodesis. Conversely, changes in implant position and radiolucent lines surrounding spinal implants suggest pseudarthrosis. Zdeblick found that solidly fused motion segments demonstrate no more than two degrees of motion on dynamic radiographs.27 Others have suggested that motion greater than five degrees suggests pseudarthrosis.28,29,30 The inherent difficulty in evaluating the three-dimensional nature of a fusion mass with two-dimensional radiographs has led some to propose fine-section axial computed tomographic (CT) evaluation with sagittal and coronal reconstruction for more accurate preoperative determination of fusion adequacy.23 In reality, both studies should be performed. Thirty-six-inch standing radiographs should be obtained to both evaluate the surgical site and implants and assess sagittal

Fig. 59.1 This is a CT scan in the sagittal (a) and axial (b) planes of a patient who presented for evaluation of back pain 1 year after minimally invasive lateral interbody fusion and posterior unilateral instrumentation. The imaging reveals fracture of the L5 screw with no definitive signs of fusion. Surgical exploration confirmed pseudarthrosis of L3–L4 and L4–L5 and revealed excellent purchase of the tip fragment of the screw.

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Removal and Revision of Broken Thoracolumbar Screws and coronal balance to determine if alterations in either have contributed to implant failure. CT scan should be obtained to assess fusion and to evaluate the stability of the bone–implant interface. In the authors’ experience, fractured implants are seldom seen in the setting of loose screws because, in this situation, the bone–implant interface has failed prior to failure of the implant itself. Fractured screws are more often encountered in patients with adequate bone mineral density and screw purchase and who have persistent motion across the surgical site because of pseudarthrosis (▶ Fig. 59.1). Additionally, CT should be evaluated for bone loss because instrumentation in the spine shields the spine from mechanical stress and can lead to implant-related osteopenia.31,32 Finally, the imaging studies should be evaluated for screws that penetrate a pedicle wall, particularly the medial wall and especially if screws are to be reinserted.

59.3 Removal and Revision of Fractured Thoracolumbar Screws 59.3.1 Preoperative Planning After it has been determined by a thorough clinical and radiographic evaluation that a patient would benefit from revision surgery, an equally thorough plan should be produced with attention to each of the specific surgical goals. This generally involves determining the neurologic, segmental, and global aspects of the patient’s condition. In addition to fractured screws, for example, a patient may have fixed sagittal plane imbalance, pseudarthrosis, and neural compression. Each factor should be considered separately with a preoperative plan to resolve each issue. A thorough discussion of the surgical treatment of these commonly associated pitfalls of revision spinal surgery is beyond the scope of this chapter. Prior operative reports should be obtained to determine the path of previous surgical exposure and complications associated with the index procedure.33,34,35 Specifically, locations of prior decompressive laminectomy, previous inadvertent durotomy, or pedicle fracture would be important information to have to avoid further surgical misadventure. The operative report or hospital record should also be reviewed to determine the manufacturer and model of screws currently implanted. If this information is not available, characteristics of the implants can occasionally be discerned on preoperative imaging to identify the manufacturer. This information allows the surgical team to make accommodations to obtain implant-specific insertion and removal instrumentation or a commercially available universal screw and implant removal systems, such as those manufactured by Innomed, Inc. (Savanah, GA), Symmetry Medical (Warsaw, IN), or Xtract All, Shukla Medical (Piscataway, NJ). A universal implant removal system is critically important for removal of instrumentation that is no longer being manufactured and is a challenge in itself to remove (e.g., the VSP plate and screw system [Acromed DePuy, Raynham, MA] or Cotrel-Dubousset screws and rods [Sofamor Medtronic, Minneapolis, MN]).

59.3.2 Surgical Treatment Removal of fractured thoracolumbar screws first requires exposure of all existing instrumentation to be removed and revised.

Reexposure of posterior instrumentation can be relatively straightforward and can often be performed using minimally invasive techniques.36 Various authors have described using sharp dissection with a scalpel or electrocautery to identify hardware and the prior fusion mass.37 The implant can usually be separated from the soft tissue, fibrous scar, and pseudocapsule with electrocautery, rongeurs, and curettes. Bone is often noted to have grown over the sides of metallic implants. This can be removed with an osteotome, rongeur, or high speed burr. Care should be taken to allow some fibrous scar to cover the dura and neural elements in areas of prior laminectomy. Most spinal instrumentation can be safely exposed with these methods. Once the retained instrumentation has been adequately liberated from the surrounding soft tissue and fibrous scar, removal should begin in reverse order from which it was initially placed. Any cross-linking connectors and set screws should be first removed from the screws, hooks, or rods. Care must be taken to avoid damaging the driver–screw interface. Should this occur, one of the specialized universal devices should be employed to achieve the removal. Next, attention should be given to removing each of the individual screws. The diameter and length of screws should also be determined from the manufacturer’s markings on existing screw or measured individually if reimplantation of new instrumentation is planned. Attention can now be turned to the fractured screws. The decision to remove the fractured screw must be balanced with the need to maintain adequate bone for pedicle and fusion mass integrity as well as for potential reinstrumentation. The optimal method of treatment for a fractured pedicle screw, therefore, depends partly on the ultimate surgical goals. If the intention of the operation is to revise a deformity correction because of adjacent segment disease and points of fixation exist beyond the level of the fractured screw, one option would be to remove only the screw head and dorsal segment of the shaft and leave the remainder of the screw embedded deep in the bone intact. The new instrumentation would then be inserted skipping the level of the fractured screw. This extremely simple technique would, of course, be contraindicated if the surgical site is being reexplored for infection and implant removal. When removal of the screw is desired, a variety of techniques have been described, although the actual removal will typically require some ingenuity to achieve removal without undue damage to the surrounding bone. Miyamoto and colleagues described using a high-speed drill with a 2-mm diamond-tip bit to etch a linear slot in the screw fragment.38 A common flathead screwdriver can then be used to rotate the screw fragment free from the bone. McGuire described a technique that also utilizes a high-speed drill.39 A pilot hole is first drilled into the screw fragment. A reverse-threaded screw extractor can then be inserted into the pilot hole and the fragment rotated out of the bone. Duncan and MacDonald described a technique that takes advantage of the clockwise direction of rotation of the high-speed drill.22 A pilot hole is drilled immediately adjacent to the edge of the fractured screw. The high-speed drill bit can then be inserted into the hole and pressed against the screw thread. By engaging the drill in short bursts, the clockwise rotation of the drill bit rotates the screw fragment in a counterclockwise direction, thereby removing it from the bone. The authors utilized each of these techniques with variable success

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Thoracolumbar and found the following additional technique to be helpful as well. A high-speed drill with a 2-mm diamond-tip bit can be used to remove the dorsal one to two threads of the broken screw that is embedded in bone. A toothed trephine from a universal implant extraction set that has an inner diameter greater than the inner diameter but less than the outer diameter of the broken screw can be attached to a standard power drill or reamer and applied over the broken screw fragment. The drill can then be run on reverse (counter clockwise) while engaging the teeth of the trephine onto the portion of the screw that has been shaved of the threads. A screw that is particularly well fixed in the bone and refractory to these techniques can be loosened by applying a curved gouge of a similar diameter around the screw to break the screw–bone interface. This does, however, remove more bone than the other techniques and will have to be taken into account if reinstrumentation is planned. Other techniques have been described that similarly remove very little bone but require special equipment for broken screw removal. Di Lorenzo and colleagues use a low-speed drill with a conically cored drill bit that has a rough inner surface.40 The bit is pressed against the fractured surface of the screw and the drill engaged in the counterclockwise direction. The bit drills into the bone surrounding the screw fragment for 1 to 2 mm until it engages the fragment within the conical core. The rough inner surface and taper of the cone grasp the screw fragment and rotate it free from the bone. The advantage of each of these techniques is that the removal instruments are generally available in most hospitals or obtainable with preoperative planning and preparation. Additionally, very little bone is removed in the extraction of the screw fragment.

small anatomic size, loss of bone from screw fragment removal, or pedicle fracture may limit the ability to use a larger screw. In this situation, the bone can be left uninstrumented and left empty or filled with a suitable bone graft product, and spanned with instrumentation of the cranial and caudal spinal segments. As an alternative in a small or osteopenic pedicle with intact walls, polymethyl methacrylate can be used to fill the pedicle and adjacent vertebral body to augment the fixation strength.44 Additionally, simple augmentation of posterolateral intertransverse process fusion or unilaterally instrumented fusion with postoperative orthosis immobilization can lead to acceptable outcomes.45,46

59.4 Summary The volume of spinal surgery and utilization of spinal instrumentation have increased steadily over the past few decades. Surgeons who routinely treat patients with spinal instrumentation will inevitably encounter fractured screws. Although screws can be found to have fractured even in patients with successful fusion procedures, the underlying cause of implant failure—infection, pseudarthrosis, sagittal, or coronal imbalance —should be sought out specifically so that these factors can be included in the surgical plan. It is useful to have several options for implant removal and revision available, should one technique fail to achieve the goals. The surgical treatment of fractured screws is challenging and requires thorough preoperative preparation, including evaluation of the patient, review of imaging and prior operative records, and discussion with the operating room staff to ensure that a proper plan can be established before attempting revision surgery.

59.3.3 Pitfalls of Fractured Screw Removal Removal of fractured thoracolumbar pedicle screws presents a significant challenge to the revision surgeon and is associated with certain pitfalls. Specific attention to these pitfalls can help avoid undue complication and make the revision operation proceed more smoothly. Stress-shielding of the bone within an instrumented spine can lead to implant-associated osteopenia. In removing fractured screws, care must be taken to avoid inadvertently advancing or displacing implants as this can introduce a risk of injuring surrounding structures. Vanichkachorn and coworkers described a case in which an instrument designed to grasp and remove a broken screw fragment inadvertently advanced a broken L2 pedicle screw through the anterior cortex of a vertebral body.41 Although no vascular or visceral structures were injured, the patient required an anterior spinal exposure for screw removal. Reinstrumentation following successful fractured screw removal will often be indicated. The simple removal and replacement of a screw of the same size, however, has been found to reduce pullout strength by 34%.42 To overcome this, a screw should be inserted that is 5 to 10 mm longer and 1 to 2 mm wider in diameter (▶ Fig. 59.2).42,43 At times, though,

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Fig. 59.2 This is a radiograph in the lateral (a) anteroposterior (b) projections of the same patient after surgery. The patient was treated with surgical exploration of fusion, removal of posterior instrumentation, excision of screw fragment using a high-speed drill and trephine, revision instrumentation through a new starting point with a larger screw, and posterior fusion.

Removal and Revision of Broken Thoracolumbar Screws

References [1] Dwyer AF, Newton NC, Sherwood AA. An anterior approach to scoliosis. A preliminary report. Clin Orthop Relat Res. 1969; 62(227):192–202 [2] Luque ER. Segmental spinal instrumentation for correction of scoliosis. Clin Orthop Relat Res. 1982(163):192–198 [3] Cotrel Y, Dubousset J, Guillaumat M. New universal instrumentation in spinal surgery. Clin Orthop Relat Res. 1988; 227(227):10–23 [4] Webb JK, Burwell RG, Cole AA, Lieberman I. Posterior instrumentation in scoliosis. Eur Spine J. 1995; 4(1):2–5 [5] Kaneda K, Shono Y, Satoh S, Abumi K. New anterior instrumentation for the management of thoracolumbar and lumbar scoliosis. Application of the Kaneda two-rod system. Spine. 1996; 21(10):1250–1261, discussion 1261– 1262 [6] Mohan AL, Das K. History of surgery for the correction of spinal deformity. Neurosurg Focus. 2004; 16(1):E1 [7] Singh H, Rahimi SY, Yeh DJ, Floyd D. History of posterior thoracic instrumentation. Neurosurg Focus. 2004; 16(1):E11 [8] Bono CM, Garfin SR. History and evolution of disc replacement. Spine J. 2004; 4(6) Suppl:145S–150S [9] Lange F. The classic. Support for the spondylitic spine by means of buried steel bars, attached to the vertebrae. By Fritz Lange. 1910. Clin Orthop Relat Res. 1986(203):3–6 [10] Bono CM, Lee CK. Critical analysis of trends in fusion for degenerative disc disease over the last twenty years: influence of technique on fusion rate and clinical outcome. Presented at the annual meeting of the International Society for the Study of the Lumbar Spine, Vancouver, BC, Canada, May 13–17, 2004 [11] Fischgrund JS, Mackay M, Herkowitz HN, Brower R, Montgomery DM, Kurz LT. 1997 Volvo Award winner in clinical studies. Degenerative lumbar spondylolisthesis with spinal stenosis: a prospective, randomized study comparing decompressive laminectomy and arthrodesis with and without spinal instrumentation. Spine. 1997; 22(24):2807–2812 [12] Connolly PJ, Esses SI, Kostuik JP. Anterior cervical fusion: outcome analysis of patients fused with and without anterior cervical plates. J Spinal Disord. 1996; 9(3):202–206 [13] Esses SI, Sachs BL, Dreyzin V. Complications associated with the technique of pedicle screw fixation. A selected survey of ABS members. Spine. 1993; 18 (15):2231–2238, discussion 2238–2239 [14] Blumenthal S, Gill K. Complications of the Wiltse pedicle screw fixation system. Spine. 1993; 18(13):1867–1871 [15] Connolly PJ, Von Schroeder HP, Johnson GE, Kostuik JP. Adolescent idiopathic scoliosis. Long-term effect of instrumentation extending to the lumbar spine. J Bone Joint Surg Am. 1995; 77(8):1210–1216 [16] Bago J, Ramirez M, Pellise F, Villanueva C. Survivorship analysis of CotrelDubousset instrumentation in idiopathic scoliosis. Eur Spine J. 2003; 12 (4):435–439 [17] Babat LB, McLain RF, Bingaman W, Kalfas I, Young P, Rufo-Smith C. Spinal surgery in patients with Parkinson’s disease: construct failure and progressive deformity. Spine. 2004; 29(18):2006–2012 [18] Greiner-Perth R, Boehm H, Allam Y, Elsaghir H, Franke J. Reoperation rate after instrumented posterior lumbar interbody fusion: a report on 1680 cases. Spine. 2004; 29(22):2516–2520 [19] Lonstein JE, Denis F, Perra JH, Pinto MR, Smith MD, Winter RB. Complications associated with pedicle screws. J Bone Joint Surg Am. 1999; 81(11):1519– 1528 [20] Cook S, Asher M, Lai SM, Shobe J. Reoperation after primary posterior instrumentation and fusion for idiopathic scoliosis. Toward defining late operative site pain of unknown cause. Spine. 2000; 25(4):463–468 [21] Rommens PM, Weyns F, Van Calenbergh F, Goffin J, Broos PL. Mechanical performance of the Dick internal fixator: a clinical study of 75 patients. Eur Spine J. 1995; 4(2):104–109

[22] Duncan JD, MacDonald JD. Extraction of broken pedicle screws: technical note. Neurosurgery. 1998; 42(6):1399–1400 [23] Brown CA, Eismont FJ. Complications in spinal fusion. Orthop Clin North Am. 1998; 29(4):679–699 [24] Daftari TK, Whitesides TE, Jr, Heller JG, Goodrich AC, McCarey BE, Hutton WC. Nicotine on the revascularization of bone graft. An experimental study in rabbits. Spine. 1994; 19(8):904–911 [25] Silcox DH, III, Daftari T, Boden SD, Schimandle JH, Hutton WC, Whitesides TE, Jr. The effect of nicotine on spinal fusion. Spine. 1995; 20(14):1549–1553 [26] Dimar JR, II, Ante WA, Zhang YP, Glassman SD. The effects of nonsteroidal anti-inflammatory drugs on posterior spinal fusions in the rat. Spine. 1996; 21(16):1870–1876 [27] Zdeblick TA. A prospective, randomized study of lumbar fusion. Preliminary results. Spine. 1993; 18(8):983–991 [28] Cannada LK, Scherping SC, Yoo JU, Jones PK, Emery SE. Pseudoarthrosis of the cervical spine: a comparison of radiographic diagnostic measures. Spine. 2003; 28(1):46–51 [29] Lehmann TR, LaRocca HS. Repeat lumbar surgery. A review of patients with failure from previous lumbar surgery treated by spinal canal exploration and lumbar spinal fusion. Spine. 1981; 6(6):615–619 [30] McAfee PC, Boden SD, Brantigan JW, et al. Symposium: a critical discrepancya criteria of successful arthrodesis following interbody spinal fusions. Spine. 2001; 26(3):320–334 [31] McAfee PC, Farey ID, Sutterlin CE, Gurr KR, Warden KE, Cunningham BW. 1989 Volvo Award in basic science. Device-related osteoporosis with spinal instrumentation. Spine. 1989; 14(9):919–926 [32] Myers MA, Casciani T, Whitbeck MG, Jr, Puzas JE. Vertebral body osteopenia associated with posterolateral spine fusion in humans. Spine. 1996; 21 (20):2368–2371 [33] McAfee PC, Cunningham BW, Lee GA, et al. Revision strategies for salvaging or improving failed cylindrical cages. Spine. 1999; 24(20):2147–2153 [34] Wagner WH, Regan JJ, Leary SP, et al. Access strategies for revision or explantation of the Charité lumbar artificial disc replacement. J Vasc Surg. 2006; 44 (6):1266–1272 [35] Gumbs AA, Hanan S, Yue JJ, Shah RV, Sumpio B. Revision open anterior approaches for spine procedures. Spine J. 2007; 7(3):280–285 [36] Salerni AA. Minimally invasive removal or revision of lumbar spinal fixation. Spine J. 2004; 4(6):701–705 [37] Olson SA, Gaines RW, Jr. Removal of sublaminar wires after spinal fusion. J Bone Joint Surg Am. 1987; 69(9):1419–1423 [38] Miyamoto K, Shimizu K, Kouda K, Hosoe H. Removal of broken pedicle screws. Technical note. J Neurosurg (Spine 1). 2001; 95(1) Suppl:150–151 [39] McGuire RA, Jr. A method for removal of broken vertebral screws. Orthop Rev. 1992; 21(6):775–776 [40] Di Lorenzo N, Conti R, Romoli S. Retrieval of broken pedicle screws by “friction” technique. Technical note. J Neurosurg (Spine 1). 2000; 92(1) Suppl:114–116 [41] Vanichkachorn JS, Vaccaro AR, Cohen MJ, Cotler JM. Potential large vessel injury during thoracolumbar pedicle screw removal. A case report. Spine. 1997; 22(1):110–113 [42] Polly DW, Jr, Orchowski JR, Ellenbogen RG. Revision pedicle screws. Bigger, longer shims—what is best? Spine. 1998; 23(12):1374–1379 [43] Klein SA, Glassman SD, Dimar JR, II, Voor MJ. Evaluation of the fixation and strength of a “rescue” revision pedicle screw. J Spinal Disord Tech. 2002; 15 (2):100–104 [44] Wittenberg RH, Lee KS, Shea M, White AA, III, Hayes WC. Effect of screw diameter, insertion technique, and bone cement augmentation of pedicular screw fixation strength. Clin Orthop Relat Res. 1993(296):278–287 [45] Highhouse ME, Schultz RT, Dall BE. Lateral intertransverse process singlelevel fusion for salvage of the unstable failed posterior lumbar interbody fusion. J Spinal Disord. 1996; 9(1):59–63 [46] Suk KS, Lee HM, Kim NH, Ha JW. Unilateral versus bilateral pedicle screw fixation in lumbar spinal fusion. Spine. 2000; 25(14):1843–1847

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60 How to Remove/Revise Thoracolumbar Interbody Devices (TLIF Cages/ALIF Cages) Michael Flippin

60.1 Introduction Interbody cages are used in spine surgery to restore disc height, correct deformity, and to develop a fusion mass in the disc space. Potential downsides of interbody devices include the possibility of nonunion or pseudoarthrosis. In the case of a nonunion, removal or revision of interbody devices can prove to be very difficult. Several factors must be taken into consideration when revising an interbody nonunion. One of the most important decisions is the surgical approach. Access to the implant may be severely limited by adhesions and scar tissue. Surgeons must also consider how to remove the device, as well as how this may affect subsequent reconstruction options. Proper planning is necessary to obtain the best outcome.

60.2 Spinal Instrumentation 60.2.1 Indications The most common indication to remove or revise a thoracolumbar interbody device is nonunion or pseudoarthrosis. Other indications include subsidence with resulting kyphosis, implant migration, malposition, or infection.

60.2.2 Pseudoarthrosis Spinal instrumentation has been shown to improve fusion rates in lumbar surgery. The well-known study by Fischgrund et al1 reported that fusion rates improved from 45 to 82% when treating degenerative spondylolisthesis with noninstrumented versus instrumented fusions. Zdeblick et al showed similar findings when comparing the use of noninstrumented, semirigid, or rigid instrumentation with lumbar fusions. This comparison demonstrated that patients with rigid fixation had the highest fusion rate.2 However, the use of instrumentation has remained controversial. Thomsen et al showed that there was no significant difference in outcomes and patient satisfaction with noninstrumented or instrumented fusions.3 Despite the controversial data, instrumented lumbar fusion continues to be widely performed today. The addition of an interbody graft with pedicle screw instrumentation has been shown to further increase the fusion rate compared to pedicle screws alone.4 Kornblum et al5 demonstrated that patients with a successful fusion have better longterm outcomes.5 Thus, some surgeons believe the usage of interbody devices can improve outcomes by decreasing the risk of nonunion. However, the use of interbody devices remains controversial. Various types of interbody fusions have been described in the literature. The anterior lumbar interbody fusion has historically been considered the “gold standard.” Early reports by Loguidice et al showed an 80% successful fusion rate with anterior lumbar interbody fusions.6 Newman reported successful anterior

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lumbar interbody fusions in 88.9% of patients.7 A review by Jacobs et al showed that the anterior lumbar interbody fusion procedure achieved a range of successful fusions from 47-90%.8 The fusion rate seen with anterior lumbar interbody fusions can be increased with the addition of posterior spinal fixation. Gertzbein et al reported a 97% fusion rate when anterior lumbar interbody fusions were combined with pedicle screw fixation.9 In a study by Christensen et al, patients receiving a circumferential fusion had a higher successful fusion rate, improved clinical outcomes, and improved reoperation rates compared to the patients with only an instrumented posterolateral fusion.10 A review of the literature by Kwon et al11 showed that combined anterior interbody grafting with posterior fixation has the highest fusion rates, but most of the reports available for the review were retrospective. Placing an interbody graft through a posterior approach is accomplished with a posterior or transforaminal lumbar interbody fusion. These posterior fusion techniques have been shown to have high fusion rates when combined with posterior fixation. Suk et al reported a reduction in the nonunion rates seen in posterolateral fusions from 7.5 to 0% with the addition of posterior lumbar interbody grafts.12 Jacobs et al reported successful fusion rates between 80 and 95% with posterior lumbar interbody fusions.8 Similar results have been seen with transforaminal lumbar interbody fusions. Potter et al reported an overall fusion rate of 93% per level in a series of 100 patients.13 In the prospective study by Lauber et al, the fusion rate from transforaminal lumbar interbody fusions was 94.8%.14 Studies comparing anterior and posterior lumbar interbody fusion techniques have shown similar fusion rates between the two techniques. Crandall and Revella reported on a series of patients with similar results and outcomes between the two types of fusions.15 Faundez et al reported statistically equivalent fusion rates with transforaminal lumbar interbody fusions compared to anterior lumbar interbody fusions with posterior fixation. However, the overall nonunion rate in both arms of the study was higher than most other published reports.16 Unsuccessful fusions result in a nonunion or pseudoarthrosis. There are many potential factors that can play a role in developing a nonunion. Tobacco usage is a well-known risk factor for pseudoarthrosis.17 Inadequate correction of sagittal balance or kyphosis has also been shown to play a role in developing a nonunion.18 Another important factor is the type of bone graft utilized in the procedure. Iliac crest autograft remains the “gold standard” for bone graft material. The use of bone morphogenic protein, ceramics, stem cells, and other technologies has led to further variation in fusion rates.

60.2.3 Migration Anterior migration of an interbody graft can lead to vascular impingement and erosion into the great vessels. Posterior migration may lead to encroachment on the nerves and thecal sac. Cage migration has been associated with multilevel fusion

How to Remove/Revise Thoracolumbar Interbody Devices procedures and the physical dimensions of the disc space.19 In posterior lumbar interbody fusion procedures with Bagby and Kuslich cages, the risk factors for graft migration included a total facetectomy and stand-alone cages with no posterior instrumentation.20 The different shapes of interbody implants can also play a role. Graft extrusion has even been described with an expandable transforaminal lumbar interbody fusion cage.21

60.2.4 Impingement/Improper Placement Poor placement of an interbody graft can lead to the encroachment on the nearby nerves and vessels. Malpositioned grafts may result from inadequate intraoperative imaging or failure to correctly identify landmarks. Special care is necessary when using techniques that are highly dependent on good quality images, such as minimally invasive surgeries and lateral interbody fusions. A CT scan may be necessary to determine the exact location of the graft.

60.2.5 Infection Infections are a frustrating source of complications in spine surgery. Fortunately, most infections are superficial and can be treated with surgical debridement and antibiotics. The Scoliosis Research Society Morbidity and Mortality database has been used to evaluate the incidence of infections in spine surgery. The database had a rate of 0.8% deep and 1.3% superficial infections.22 A superficial infection identified in the early postoperative period can be treated with antibiotics and preservation of the surgical implants. A deep infection requires more careful consideration regarding the retention or removal of the implants. Carmouche and Molinari reported a case where the removal of the interbody device was required in order to successfully treat a deep infection.23 The infection was initially treated with surgical debridement and retention of the interbody graft. However, the interbody device required removal 3 weeks later due to a persistent infection. Another case series by Mirovsky et al reported deep infections in 7.2% of their cases.24 Eight patients were treated with intravenous antibiotics, and two of the eight required repositioning of the cage. None of the interbody cages required removal.

60.3 Workup 60.3.1 Relevant History A thorough history and physical examination should be performed on every patient. It is important to note the patient's overall health status, medical comorbidities, and other problems that may have contributed to the initial failed procedure. Important factors to identify include the use of tobacco, nutritional status, and presence of osteoporosis. Decreased bone mineral density has been associated with the decreased pullout strength of pedicle screws.25 There are little data detailing the risk of interbody graft subsidence in relation to osteoporosis. Formby et al showed a higher risk of subsidence, iatrogenic fractures, and radiographic complications in osteoporotic

patients compared to patients without osteoporosis. However, this study showed no significant increase in revisions or clinical outcomes.26 The patient history should include any factors that may affect the revision surgery. Special considerations include identifying prior surgical approaches, the type of implants currently present in the patient, and what type of bone graft material was used. If iliac crest bone graft was used in the prior surgeries, it should be noted from which side the graft was obtained. It is important to determine if bone morphogenic protein (BMP) had been used previously. BMP has been shown to improve the rates in lumbar fusion surgery. Burkus et al reported a 98% fusion rate with the use of BMP-2 and anterior lumbar interbody cages.27 However, the inflammatory reaction generated by BMP during the healing process may have an adverse effect. Side effects such as radiculitis28,29 and osteolysis30,31 have been attributed to the use of BMP. BMP has also been associated with increased fibrosis and scarring around the disc space. Rodgers et al reported excessive fibrosis after BMP use that led to vascular injury, substantial blood loss, and further intraoperative complications during a revision anterior procedure.32

60.3.2 Imaging Routine radiographs should be evaluated for loosening, pseudoarthrosis, or graft migration. Motion seen on flexion and extension films potentially indicates a nonunion. Current images can be compared with prior films to assess for any changes. A CT scan can provide a more detailed assessment of the prior fusion and the location of the surgical implants. Bridging trabecular bone within or around the interbody device indicates a successful fusion. Evidence of a pseudoarthrosis includes halo formation around the implants, sclerotic changes in the end plates, fractured implants or vertebrae, or implant migration. An magnetic resonance imaging (MRI) scan may be of limited benefit in identifying a nonunion. Frequently, the MRI images are distorted by the presence of metallic implants. However, MRI images can still be helpful in identifying adjacent level disease or stenosis that may need to be addressed during the revision surgery. A CT myelogram is also helpful if additional crosssectional imaging is needed to identify stenosis.

60.4 Revision Surgery 60.4.1 Approaches The surgical approach determines access to the interbody device and revision options.

Anterior Approach The anterior approach provides excellent visualization and access to the disc space. This approach can be challenging when fibrous tissue and adhesions form around nearby veins, arteries, ureter, visceral organs, and peritoneum. In the CHARITE IDE study, a 3.6% incidence of vascular injury was reported at the time of the index total disc arthroplasty. Subsequent revision procedures in the CHARITE study had a 16.7% incidence of

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Thoracolumbar vascular injury. In addition, 2 of the 24 revision anterior procedures had to be aborted due to difficulties with vessel mobilization.33 Mobilization of adherent vessels during the revision surgery may lead to iatrogenic injury. A revision approach at L5-S1 typically requires less mobilization of blood vessels than at L4-5. In addition, if a paramedian approach was used in the prior surgery, adhesions may prevent access to the retroperitoneal space and increase the chance of tearing the peritoneum. One option for a revision anterior surgery is using a contralateral paramedian retroperitoneal approach to L5–S1. Another option is a transperitoneal approach if a retroperitoneal approach had been used before.34 In the CHARITE IDE study, the author described using a transperitoneal approach for the revision of L5–S1, and a right-sided retroperitoneal approach to revise the L4–L5 disc space.33 In addition to vascular complications, repeat mobilization of the sacral plexus may lead to retrograde ejaculation. A CT angiogram may help identify tortuous or displaced vessels. A surgeon may also consider placing a urethral stent preoperatively to facilitate intraoperative identification of the ureter. There are few data specifying if a preoperative CT angiogram or urethral stenting is effective in preventing injury.

Lateral Approach The lateral approach, also known as the transpsoas approach, is an alternative option for obtaining anterior access to disc spaces cephalad to the L5–S1 level. The transpsoas approach has been described as a means of reducing risk of injury to the vasculature or other abdominal structures when performing an anterior lumbar fusion.34,35 This approach has been used to remove a total disc prosthesis at the L4–L5 level.36 A variation on the lateral approach is the anterolateral retroperitoneal approach, in which the dissection is kept more anterior to the psoas muscle to minimize nerve dissection and retraction (▶ Fig. 60.1, ▶ Fig. 60.2). There are little published data regarding the use of the lateral approach to revise a prior lateral interbody fusion. Approaching from the contralateral side potentially avoids excessive scar tissue. Iatrogenic injury to the ureter has been reported during an open ipsilateral revision procedure. At the time of the procedure, the surgeon was unable to identify the ureter because of the presence of retroperitoneal scar. Postoperatively, the patient developed a retroperitoneal fluid collection, and the ureter was found to be entrapped by both the instrumentation and periureteral fibrosis.37

Fig. 60.1 Preoperative computed tomography (CT) scan of an L3-L4 nonunion.

approach. McAfee et al described using a posterior approach to remove Bagby and Kuslich cages. The study reported using a curved osteotome to create a cavity lateral to the inserted implant. The cage was then moved laterally within the disc space to permit extraction and to minimize retraction on the nerve roots.39

60.4.2 Device Removal Posterior Approach The presence of epidural fibrosis and adhesions may limit a posterior revision approach. Access to the disc space and the interbody graft may require significant manipulation of the dura and nerve roots. Mobilizing the thecal sac potentially increases the chance of dural tears, nerve traction injuries, and arachnoiditis. Khan et al reported the incidence of dural tears with primary and revision lumbar surgery as 7.6 and 15.9%, respectively.38 Despite the aforementioned risks, successful revision surgery has been described through a posterior

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Obtaining a firm grasp on the implant through a small opening can be very difficult if osteolysis allows the device to “float” around the disc space. Fibrous tissue from the previous nonunion may also hinder removal of the implant. Proper lighting, visualization, and having the correct equipment can be very helpful. Special rongeurs and drills may be necessary to retrieve the interbody graft. Osteotomes may be helpful in removing sclerotic bone and freeing the implant.39 A surgeon must attempt to avoid aggressive bone removal, which may complicate the subsequent reconstruction.

How to Remove/Revise Thoracolumbar Interbody Devices

Fig. 60.2 (a,b) Postoperative films after revision of the L3-L4 nonunion and successful placement of an interbody cage through a lateral approach.

60.4.3 Reconstruction Reconstructing the spine requires restoring the anterior column and utilizing appropriate internal fixation to support the construct. Any fibrous tissue that obstructs the placement of the new interbody device should be removed. In addition, the surgeon must develop a bony surface that is able to support the new implant. In the presence of significant osteolysis and bone loss, a partial or complete corpectomy may be necessary. Preoperative planning is important to restore sagittal balance, obtain a solid fusion, and achieve a good outcome. A detailed discussion of the various interbody grafts and cages available for reconstruction of the spine exceeds the scope of this chapter. However, it is often necessary to increase the size of the implants to accommodate for bone loss from the interbody graft removal. Other options may include a partial or complete corpectomy. Preoperative planning with the goal of restoring sagittal balance would be helpful in achieving a solid fusion and a good outcome. The literature contains several reports on revising interbody grafts. Vargas-Soto et al reported on the revision of failed transforaminal lumbar interbody fusions. This study compared the use of a direct anterior-only approach versus a combined anterior interbody fusion with a posterior decompression and repair of the pseudoarthrosis. The authors found no significant difference in fusion rates between the two groups (81 and 88%, respectively), no difference in outcomes, and little overall functional improvement.40 Santos et al compared a posterior instrumented technique alone versus a combined anterior–posterior surgical technique in revising cylindrical interbody grafts. The anterior–posterior surgeries had a higher fusion rate, 79 versus 37%, and a higher complication rate, but there was no difference in clinical outcome.41 Lebl et al reported a novel technique for

the treatment of an L5–S1 pseudoarthrosis. The technique included transacral reaming for both the interbody device removal and insertion of a Harms cage.42 However, the series was limited to 10 patients. Additional studies are needed before the optimal strategy for removing and revising interbody grafts can be determined.

60.5 Complications Mobilization of the great vessels during a revision anterior approach increases the risk of vascular injury.33 If BMP was utilized within the interbody cage during the index procedure, there is the possibility for adhesions of the great vessels to the disc space.31 Attempts at mobilization can lead to vessel injury and substantial blood loss. Proper preparation may include having an approach surgeon or vascular surgeon available if necessary, and having the appropriate blood products available (▶ Fig. 60.3). Traction and manipulation of the nerve roots may lead to neurologic injury. A posterior approach may be at risk for traction injury because of the epidural fibrosis and adhesions. Neurological injury can also occur through a lateral approach if significant manipulation is needed to access the disc space. Retrograde ejaculation is possible with repeat mobilization of the sacral plexus during a revision anterior approach. Bone loss and endplate erosion may occur if a pseudoarthrosis is present with significant motion. In addition, the use of BMP has been associated with osteolysis when the endplate is compromised during disc preparation.43 The study by Helgeson et al demonstrated that the osteolysis associated with BMP-2 usage had resolved in only 24% of patients by 1 year.31 Excessive bone may be removed during the implant retrieval and

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References

Fig. 60.3 Sagittal MRI showing a nonunion at L4-L5. This patient had subsidence of the interbody graft and significant scarring around the disc space. Initial attempts at an anterior approach had to be aborted due to excessive blood loss.

vertebral body preparation. Preoperative imaging helps prepare for bone loss and reconstruction. Larger interbody cages or a corpectomy may be needed to replace the lost bone and restore the anterior column.

60.6 Summary Revision of an interbody graft requires careful attention to detail. Preoperative planning can be crucial to anticipate challenges and mitigate their effects. Choosing the best surgical approach, successful implant removal, and reconstruction of the spine are critical to a successful surgery.

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How to Remove/Revise Thoracolumbar Interbody Devices [21] Kim PD, Baron EM, Levesque M. Extrusion of expandable stacked interbody device for lumbar fusion: case report of a complication. Spine. 2012; 37(18): E1155–E1158 [22] Smith JS, Shaffrey CI, Sansur CA, et al. Scoliosis Research Society Morbidity and Mortality Committee. Rates of infection after spine surgery based on 108,419 procedures: a report from the Scoliosis Research Society Morbidity and Mortality Committee. Spine. 2011; 36(7):556–563 [23] Carmouche JJ, Molinari RW. Epidural abscess and discitis complicating instrumented posterior lumbar interbody fusion: a case report. Spine. 2004; 29 (23):E542–E546 [24] Mirovsky Y, Floman Y, Smorgick Y, et al. Management of deep wound infection after posterior lumbar interbody fusion with cages. J Spinal Disord Tech. 2007; 20(2):127–131 [25] Soshi S, Shiba R, Kondo H, Murota K. An experimental study on transpedicular screw fixation in relation to osteoporosis of the lumbar spine. Spine. 1991; 16(11):1335–1341 [26] Formby PM, Kang DG, Helgeson MD, Wagner SC. Clinical and radiographic outcomes of transforaminal lumbar interbody fusion in patients with osteoporosis. Global Spine J. 2016; 6(7):660–664 [27] Burkus JK, Gornet MF, Schuler TC, Kleeman TJ, Zdeblick TA. Six-year outcomes of anterior lumbar interbody arthrodesis with use of interbody fusion cages and recombinant human bone morphogenetic protein-2. J Bone Joint Surg Am. 2009; 91(5):1181–1189 [28] Muchow RD, Hsu WK, Anderson PA. Histopathologic inflammatory response induced by recombinant bone morphogenetic protein-2 causing radiculopathy after transforaminal lumbar interbody fusion. Spine J. 2010; 10(9):e1–e6 [29] Rowan FE, O’Malley N, Poynton A. RhBMP-2 use in lumbar fusion surgery is associated with transient immediate post-operative leg pain. Eur Spine J. 2012; 21(7):1331–1337 [30] Knox JB, Dai JM, III, Orchowski J. Osteolysis in transforaminal lumbar interbody fusion with bone morphogenetic protein-2. Spine. 2011; 36(8):672–676 [31] Helgeson MD, Lehman RA, Jr, Patzkowski JC, Dmitriev AE, Rosner MK, Mack AW. Adjacent vertebral body osteolysis with bone morphogenetic protein use in transforaminal lumbar interbody fusion. Spine J. 2011; 11(6):507–510 [32] Rodgers SD, Marascalchi BJ, Grobelny BT, Smith ML, Samadani U. Revision surgery after interbody fusion with rhBMP-2: a cautionary tale for spine surgeons. J Neurosurg Spine. 2013; 18(6):582–587

[33] McAfee PC, Geisler FH, Saiedy SS, et al. Revisability of the CHARITE artificial disc replacement: analysis of 688 patients enrolled in the U.S. IDE study of the CHARITE Artificial Disc. Spine. 2006; 31(11):1217–1226 [34] Wagner WH, Regan JJ, Leary SP, et al. Access strategies for revision or explantation of the Charité lumbar artificial disc replacement. J Vasc Surg. 2006; 44 (6):1266–1272 [35] Ozgur BM, Aryan HE, Pimenta L, Taylor WR. Extreme lateral interbody fusion (XLIF): a novel surgical technique for anterior lumbar interbody fusion. Spine J. 2006; 6(4):435–443 [36] Pimenta L, Díaz RC, Guerrero LG. Charité lumbar artificial disc retrieval: use of a lateral minimally invasive technique. Technical note. J Neurosurg Spine. 2006; 5(6):556–561 [37] Bjurlin MA, Rousseau LA, Vidal PP, Hollowell CM. Iatrogenic ureteral injury secondary to a thoracolumbar lateral revision instrumentation and fusion. Spine J. 2009; 9(6):e13–e15 [38] Khan MH, Rihn J, Steele G, et al. Postoperative management protocol for incidental dural tears during degenerative lumbar spine surgery: a review of 3,183 consecutive degenerative lumbar cases. Spine. 2006; 31(22):2609– 2613 [39] McAfee PC, Cunningham BW, Lee GA, et al. Revision strategies for salvaging or improving failed cylindrical cages. Spine. 1999; 24(20):2147–2153 [40] Vargas-Soto HA, Mehbod A, Mullaney KJ, et al. Salvage procedures for pseudarthrosis after transforaminal lumbar interbody fusion (TLIF)-anterior-only versus anterior-posterior surgery: a clinical and radiological outcome study. J Surg Orthop Adv. 2009; 18(4):200–204 [41] Santos ER, Pinto MR, Lonstein JE, et al. Revision lumbar arthrodesis for the treatment of lumbar cage pseudoarthrosis: complications. J Spinal Disord Tech. 2008; 21(6):418–421 [42] Lebl DR, Sama AA, Pumberger M, Kotwal S, Cammisa FP, Jr, Girardi FP. Reamed transacral interbody fusion for L5–S1 pseudoarthrosis: a novel salvage technique in 10 patients. J Spinal Disord Tech. 2013; 26(6):334–341 [43] Lewandrowski KU, Nanson C, Calderon R. Vertebral osteolysis after posterior interbody lumbar fusion with recombinant human bone morphogenetic protein 2: a report of five cases. Spine J. 2007; 7(5):609–614

417

Index A ACDF, see anterior cervical plating, cervical arthroplasty, cervical corpectomy adenocarcinoma 408 adjacent level ossification development – characterization 117 – classification 111, 112 – in ACDF 111 – incidence 112 – overview 111 – pathophysiology 113 – surgical procedure implications 113 adjacent segment pathology – adjacent structure violation 148 – anterior cervical plating 96, 96 – anterior cervical plating (translational) 104 – avoidance 104, 104, 105 – characterization 117 – construct stiffness impacts 148 – diagnosis 104 – disc degeneration and 147 – epidemiology 146 – interspinous fusion devices 185 – junctional fractures 148 – junctional kyphosis 146–147 – low-profile stand-alone implants 119, 119 – open TLIF 234, 236–237 – ossification development 119 – prevention 149 – risk factors 148 – rod diameter 148 – rod size, composition 148 – scoliosis 397 – scoliosis correction 149, 149 – treatment 104 – treatment options 149 airway compromise 131 ALIF, see anterior lumbar interbody fusion allograft bone 282 ALOD, see adjacent level ossification development Alphatech Solanas Avalon Posterior Fixation System 11 AMPLIFY 408 Andersson lesions 339 aneurysmal bone cysts 312 anhidrosis 293 ankylosing spondylitis – acute trauma in 340, 340, 341 – case studies 329, 330–331 – complications 327 – complications risks 341–342 – deformity correction 328 – diagnosis 326 – epidemiology 326 – epidural hematoma 340 – fractures 341 – hardware failures 328, 342 – imaging 340, 340 – implant malpositioning 328 – kyphotic deformity surgical management 343 – nonoperative treatment 326 – pathogenesis 326, 339 – patient positioning 340–341, 341

418

– pseudoarthrosis 342, 345 – Smith–Petersen osteotomy 343, 345 – surgical approaches 326 – surgical indications for 326 – surgical management 327, 328 – thoracolumbar pathology in 339 anterior C1–C2 fusion – anterior plating 80 – anterior plating, technique 81 – anterior retropharyngeal approach 79, 79 – complications 82 – fixation failure 83 – indications 79 – lateral retropharyngeal approach 80 – nerve injury 82 – operative setup 79 – patient positioning 79 – preoperative evaluation 79 – T-shaped plates 83 – transarticular screws 80 – transarticular screws, technique 80, 81–82 – transoral transpharyngeal approach 79 anterior cervical discectomy and fusion, see anterior cervical plating anterior cervical plating – adjacent segment disease 96, 96 – advantages of 122 – ATLANTIS system 95 – biomechanics 123 – Cervical Spine Locking Plate 95 – complications 95, 123 – dysphagia 95, 123 – graft settling (focal kyphosis) 97 – H, Caspar plates 95, 95 – hardware failure 98, 99, 123 – overview 95 – pseudarthrosis 96, 98 – stress shielding 96 – supplemental fixation vs. 282 anterior cervical plating (translational) – adjacent segment disease 104 – cervical alignment 107 – complications 103 – dysphagia 103 – EAT-10 103 – graft settling 107 – overview 102, 102–103 – plate subsidence 104, 105 – pseudarthrosis 106 – screw pullout, hardware failure 107, 107 anterior lumbar interbody fusion, see stand-alone ALIF – complications 273 – history of 279, 286 – indications 274 – interbody spacers 274 – overview 272 – PEEK spacers, see PEEK spacers – PLLA cages 275 – removal, revision of, see interbody fusion removal, revision – scoliosis 394 – spinal surgical approach 272 – vascular injury 291 – vascular surgical approach 272 anterior thoracic instrumentation

– anatomy 174, 176–177 – aortic erosion, screw penetration 179, 179 – complications 175 – complications, avoidance and management 180 – costotransversectomy complications 178 – dual rod systems 174, 180 – extracavitary approach complications 178 – FDA approval status 173, 174–175 – history of 173 – indications 173 – instrumentational complications 179, 179 – minimally invasive procedures 180 – overview 180 – planning error complications 176 – plate–screw systems 173, 174–175 – single-rod systems 174–175, 180 – spinal canal violation 179 – surgical technique error complications 177 – transthoracic approach complications 178, 178 – vertebral cage replacement 173, 176, 180 –– See also vertebral cage replacement – vertebral cage replacement complications 179, 179 antibody formation, rhBMP-2 and 406, 408 Aperius spacer 203 ASP, see adjacent segment pathology Aspen IFD 185 Atlantis plating system 95, 103, 103 atlantoaxial injuries, see C1 lateral mass screw fixation, C1–C2 transarticular screws, C2 pedicle, pars screws axial neck pain, post-laminoplasty 70 Axis Fixation System 364

B BAK interbody fusion system 214 battered root syndrome 221 Bazaz Dysphagia scale 103 bone morphogenic proteins (BMPs), see rhBMP-2 – femoral ring allografts and 268–269 – in grafts 282 – in open TLIF 239 – infection and 352 – interbody fusion removal, revision and 419 – osteolysis, BMP-related 215, 218, 219 – PEEK spacers and 274–275, 401 – PLIF-related complications 214, 216, 216, 217, 222 – TLIF-related complications 214, 216, 216, 217, 222, 401, 401–402 BoneBac Press 338 Brantigan I/F Cage 214 Bryan implants 133 buttress plating 123, 124–125 – See also cervical corpectomy

C C1 lateral mass screw fixation – anatomy 23 – artificial atlanto-odontoid joint systems 28 – CSF leak 27 – device failure 24 – dural tear 27 – Harms–Melcher technique 23, 27 – hypoglossal nerve injury 27 – ICA injury 25 – imaging in anomaly detection 28 – implant complications 24 – infection 28 – occipital neuralgia, neuropathy 26 – overview 23 – screw malposition 25 – vascular complications 25 – venous plexus injury 26 – vertebral artery injury 25 C1–C2 transarticular screws – anatomy 37, 38 – construct failure 41 – CT imaging 37 – hypoglossal nerve injury 40, 41 – image guidance 40 – indications 37 – insertion angle 39, 41 – instrumentation, purpose of 37 – malpositioned screw 39, 39 – mortality 51 – overview 37 – preoperative imaging 38, 39–40 – vertebral artery injury 39, 195 C1–C2 wiring – anatomy 43 – canal encroachment classification 44, 44 – complications 44 – dural tears 44 – extension malalignment 45 – FDA status 43 – halo bracing 45 – iatrogenic fracture 44 – implant failure 45 – neurologic injury 44 – nonunion 45 – overview 43, 45 – purpose of 43 – techniques, biomechanical comparison 44 – techniques, types of 43 C2 pedicle, pars screws – alternative fixation methods 34, 35 – complications 32 – computer-assisted navigation 33 – construct-related complications 34 – halos 32 – imaging 33 – instrumentation 31, 31, 32, 32 – neurologic injury 33, 34 – nonunion 34 – overview 31 – venous plexus injury 33 – vertebral artery injury 31–32, 32, 34 C2 translaminar screws – anatomy 47, 47 – biomechanics 48 – complications 49

Index – hardware prominence 51 – infection 51 – instrumentation options 48, 48 – mortality 51 – neurologic injury 49, 49 – overview 47, 51 – preoperative imaging 47, 48 – pseudoarthrosis 50, 50 – vertebral artery injury 50, 50 CAFÉ study 159 canal encroachment classification 44, 44 cancer, rhBMP-2 and 408 carbon fiber implants 171 CD HORIZON SPIRE 185 cervical arthroplasty – adverse events 129, 129 – airway compromise 131 – complications, anterior approach-related 129 – dural tears 131 – dysphagia 130 – dysphonia 130 – endplate impingement 133 – epidural hematoma 130 – esophageal perforation 131 – fractures 132 – hematoma 130 – heterotopic ossification 133 – history of 129 – Horner’s syndrome 132 – implant failure-related complications 133 – implant malposition 132 – implant-related complications 132 – infection 132 – metal-on metal implant complications 133 – neurological complications 131 – overview 129 – polyurethane wear debris 133 – recurrent laryngeal nerve injury 130 – spinal cord injury 131 – subsidence, migration 132 – vertebral artery injury 131 cervical corpectomy – buttress plating 123, 124–125 – complications 122 – hybrid constructs 126 – multilevel 122 – overview 122 – postoperative care 126 – surgical technique 124 cervical kyphosis – anatomy 362 – background 362, 367 – cervical plating systems 364 – complications 364 – diagnosis 362 – iatrogenic 363 – instrumentation 364 – pediatric 362 – post-laminectomy 362–363, 363, 364, 365–366 – presentation 362 – pseudarthrosis 363 – treatment 363 Cervical Spine Locking Plate 95 cervical swelling, rhBMP-2 and 404, 404, 405–406 cervicothoracic junction – anatomy 73, 73 – anterior approach complications 75

– – – – – –

anterior instrumentation 74 C7 screw placement 76 FDA approval 76 instrumentation 73 outcomes 76 posterior approach complications 75, 76–77 – posterior instrumentation 74, 74, 75 CHARITE IDE study 413, 414 children, see pediatric patients chondrosarcoma 312, 408 chyloperitoneum, postoperative 285, 285 Coflex spacer 203, 205 compartment syndrome 292 compression fractures – diagnostic tests 333 – epidemiology 333 – kyphoplasty 335 – nonsurgical treatment 334 – symptoms 333, 334 – vertebroplasty 334 cortical bone trajectory pedicle screws 199 cortical screw fixation – anatomy 188 – benefits of 188, 189–191, 193 – complications 190, 193 – diagnosis 192, 193 – management 192, 192 – purpose of 188, 189–190 – surgical technique 188, 191 CSF leak 198

D deep venous thrombosis 285, 292 demineralized bone matrices (DBMs) 282 desmoid tumors 312 diabetes mellitus 350 DIAM spacer 203, 205 diffuse idiopathic skeletal hyperostosis (DISH) 342 direct lateral lumbar interbody fusion 262 DLIF, see direct lateral lumbar interbody fusion dural tears – C1 lateral mass screw fixation 27 – C1–C2 wiring 44 – cervical arthroplasty 131 – lumbar pedicle screws 141 – occipitocervical fusion 10 – pedicle screw fixation 58, 59 – posterior screw fixation 198 – subaxial fusions 62 Duraseal 218 durotomy – open TLIF 239 – repair of 292 – total disc replacement 292 – transforaminal lumbar interbody fusion 221 dysphagia – anterior cervical plating 95, 123 – anterior cervical plating (translational) 103 – avoidance 103 – cervical arthroplasty 130 – detection 103 – EAT-10 103

– low-profile stand-alone implants 117, 119 – rhBMP-2 405 – treatment 104 dysphonia 130

– iatrogenic, C1–C2 wiring 44 – odontoid, see odontoid fractures – sacral 210 – vertebral 262 Framingham Heart Study 147

E

G

EAT-10 103 ectopic ossification, see adjacent level ossification development, heterotopic ossification epidural hematoma – ankylosing spondylitis 340 – cervical arthroplasty 130 – open TLIF 238 – subaxial fusions 62 esophageal perforation 131 esophagus, hypopharynx injury 83 Extensure H2 spacer 203

graft settling (focal kyphosis) 97 granuloma formation 296 great auricular nerve injury 82

F facet screws 200 femoral ring allografts – BMP usage and 268–269 – bone mineral density and 270 – complications 267 – disease transmission 268 – disease transmission diagnosis, treatment 268 – donor variables 270 – graft fracture 269 – graft fracture diagnosis, treatment 269 – graft subsidence, resorption 269 – graft subsidence, resorption diagnosis, treatment 270 – graft variability 270 – limitations 267 – overview 267, 271 – processing variables 270 – pseudoarthrosis 267 – pseudoarthrosis, diagnosis of 268 – pseudoarthrosis, treatment of 268 – purpose of 267 flatback syndrome – causes of 376 – cone of economy 375, 375 – Cotrel–Dubousset instrumentation 377 – imaging studies 377, 377 – instrumentation historically 376 – osteotomies 378 – pedicle screw fixation 377 – pedicle subtraction osteotomies 378, 378–379 – posterior vertebral column resection 378, 379 – presentation 376 – prevention of 377 – sagittal balance 375, 376 – segmental instrumentation 377 – Smith–Petersen osteotomy 378, 378 – treatment of 377 fractures – ankylosing spondylitis 341 – cervical arthroplasty 132 – compression, see compression fractures – hinge 71 – hooks 153

H halo bracing – C1–C2 wiring 45 – complications 87 – contraindications 87 – immobilization 87 – nonunion, risk factors 88 – outcomes 88 Harms cage 171 hematoma – cervical arthroplasty 130 – epidural, see epidural hematoma – pelvic 209 – rhBMP-2-associated 402, 404 hepatitis C, rhBMP-2 and 409, 410 heterotopic ossification – cervical arthroplasty 133 – classification 114, 114, 134 – in cervical disc arthroplasty 113 – incidence 114 – interspinous spacers 206 – NSIADs in prevention of 114, 133 – overview 111 – pathophysiology 114 – PLIF, TLIF 215, 217, 218 – rhBMP-2 400, 400, 406, 407 – surgical procedure implications 113 – total disc replacement 297 high riding vertebral artery 47 high-grade spondylolisthesis, see spondylolisthesis hinge fracture 71 HIV, rhBMP-2 and 409, 409 hooks – complications of 152 – correction, loss of 154 – dislodgement 152 – fracture 153 – neurologic injury 153, 154 – overview 152 – placement protocol 152 Horner’s syndrome 132 hyperkyphosis – anatomy 369 – biomechanical failures 370 – complications 369, 373 – corrective osteotomies 370 – infection 369 – junctional kyphosis 370 – osteoporosis 370 – overview 369, 372 – patient positioning 370 – pedicle-subtraction osteotomy 370– 371, 371–373 – plumb line measurement 369 – posterior vertebral column resection 370–372, 373 – proximal junctional kyphosis 369– 370

419

Index – Smith–Petersen osteotomy 370, 370–371, 373 hypoglossal nerve injury – anatomy 24 – anterior C1–C2 fusion 83 – C1 lateral mass screw fixation 27 – C1–C2 transarticular screws 40, 41 – occipitocervical fusion 14, 17

I ICA injury – anatomy 24 – C1–C2 posterior screw–rod fixation 92, 92 – occipitocervical fusion 17 IFDs, see interspinous fusion devices ileus 293 iliac screw fixation – anatomy 299, 299 – complications 300, 300 – FDA approval status 300 – infection 300, 302 – instrument failure 300 – neurological, vessel injury 302 – overview 299 – pediatric 299 – pseudoarthrosis 300 – purpose of 299 – rod breakage 300 – screw breakage 300 – screw loosening 300, 301 – screw placement 299, 299, 302 – screw prominence, pain 300, 300 immediate failed back surgery syndrome 222 infection – antibiotic management, prophylaxis 350, 352 – avoidance 224 – BMP and 352 – C1 lateral mass screw fixation 28 – C2 translaminar screws 51 – cervical arthroplasty 132 – clinical features 348 – common organisms 347 – diagnosis 225, 348 – epidemiology 347 – etiology 352 – hyperkyphosis 369 – iliac screw fixation 300, 302 – interbody fusion removal, revision 419 – laboratory, radiographic evaluation 348 – laminoplasty 71 – lumbar pedicle screws 142 – management 226 – occipitocervical fusion 9 – open TLIF 236 – outcomes 351, 352 – overview 347 – percutaneous vertebral cement augmentation 161 – perioperative risk factors 349–350 – PLIF, TLIF 224, 226, 349 – posterior screw fixation 199 – preoperative risk factors 349–350, 352 – presacral fusion devices 210 – prevention 350, 352 – rhBMP-2 402, 406 – risk factors 349

420

– sacropelvic reconstruction, tumor resection 316 – spinal cord injury 347 – subaxial fusions 62, 63 – total disc replacement 295 – treatment 351, 352 – vacuum-assisted wound closure 351 INFUSE 408 Infuse Bone Graft/LT-cage 214 interbody fusion, see lateral lumbar interbody fusion cages, posterior lumbar interbody fusion, transforaminal lumbar interbody fusion interbody fusion removal, revision – anterior approach 419 – BMP usage and 419 – complications 421, 422 – device removal 420 – history, physical examination 419 – imaging 419 – impingement, improper placement 419 – indications 418 – infection 419 – lateral approach 420, 420, 421 – migration 418 – overview 418 – posterior approach 420 – pseudoarthrosis 418 – reconstruction 421 – workup 419 interspinous fusion devices – adjacent segment degeneration 185 – ALIF device and 184–185 – anatomy 184 – benefits of 183–184 – biomechanical findings 184 – complications 183, 185 – complications management 185, 186 – contraindications 184 – FDA approval status 184 – indications 184 – outcomes 185 – overview 183 – pedicle screw–rod constructs 184 – purpose of 183, 183 – spinous fracture 185 – spondylolisthesis and 186, 186 – surgical technique 184 interspinous spacers – anatomy 203, 205 – complication rates 206 – complications 204 – complications, device-related 206, 206 – device dislocation 206 – FDA approval status 203, 204 – heterotopic ossification 206 – indications 203 – mechanism 203 – outcomes 204 – overview 203, 206 – spinous process fractures 206, 206 – technique, principles of 203

K kyphoplasty, see percutaneous vertebral cement augmentation – adjacent segment vertebral fracture 161 – complications 159

– compression fractures 335 – efficacy 159 – history of 158

L laminoplasty – axial neck pain 70 – complications 69 – contraindications 67 – French-door technique 67, 68, 69 – hinge fracture 71 – indications 67 – infections 71 – lordosis, loss of 70 – motion, loss of 70 – nerve root palsy 69 – open-door technique 67, 68, 69 – outcomes 69 – overview 67, 71 – procedure 68, 69 – restenosis 71, 71 – spondyloarthropathy 344 – techniques 67, 68 lateral lumbar interbody fusion cages – anatomy 255, 256–258 – complications 256 – concavity, convexity approach 256 – device insertion 258 – EMG monitoring 255, 258 – endplate preparation 258 – exposure 257, 260 – FDA approval status 255 – integrated fixation implants 261 – lateral access 255 – nerve injury 255, 257–258 – neurologic injury 257 – nonunion 259, 260 – overview 255, 259 – patient positioning 256, 258–259 – purpose of 255 – scoliosis 395, 395 – vascular injury 395 lateral lumbar interbody fusion plates – anatomy 262 – approach-related complications 262 – complication rates 262 – complications 262 – hardware failure 262 – purpose of 262 – vertebral fractures 262 lateral lumbar TDR – approach-related complications 264 – bowel injury 265 – complications 265 – nerve injury 265 – overview 264 – positioning of 264 – purpose of 264 – technique, principles of 264, 264 lordosis, loss of post-laminoplasty 70 low-profile stand-alone implants – adjacent level ossification development 119 – adjacent segment disease 119, 119 – anatomy 117 – complications 118 – dysphagia and 117, 119 – implant malposition, screw placement 118, 119–120 – lag effect, screw placement 119 – overview 117 – pseudarthrosis 118, 119

– purpose of 117, 118 lumbar pedicle screws, see pedicle screw fixation – complications 140 – cortical breach 141 – dural tears 141 – inaccurate placement 140 – infection 142 – insertion technique 140 – methylmethacrylate in 142 – neurologic injury 141 – nonunion 142 – overview 140, 143 – pullout, breakage 142 lumbar spinal stenosis 203, 205 lymphatic injury 285, 285, 293 lymphocele 285, 285 lymphoma 355

M Magerl’s technique – neurologic injury 62 – posterior screw fixation 196 – subaxial fusions 61–62 marginal mandibular branch, facial nerve injury 82 McGregor line measurement 8, 8 MD Anderson Dysphagia Inventory 103 Medtronic Premier Plating System 102 minimally invasive TLIF – anatomy 242, 243 – cage migration, subsidence 246, 246 – complications 243 – disc space preparation, improper 245, 245 – overview 242 – pedicle screw misplacement 243, 244–245 – principles of 231 – purpose of 242 – scoliosis 395 MIS-TLIF, see minimally invasive TLIF motion, loss of post-laminoplasty 70 MOUNTAINEER OCT System 11 multilevel cervical corpectomy 122 – See also cervical corpectomy multiple myeloma 355

N narrowest oropharyngeal airway space (nPAS) 8 nerve injury – anterior C1–C2 fusion 82 – lateral lumbar interbody fusion cages 255, 257–258 – lateral lumbar TDR 265 – open TLIF 239 – pedicle screw fixation 58, 59 – posterior screw fixation 196, 198 – presacral fusion devices 210 – sacropelvic reconstruction, tumor resection 317 – spondylolisthesis 387 – stand-alone ALIF 285 – sublaminar wiring 156 – vertebral body replacement cages and 170 nerve root palsy 69 neurogenic tumors 312

Index neurologic injury – C1–C2 wiring 44 – C2 pedicle, pars screws 33, 34 – C2 translaminar screws 49, 49 – hooks 153, 154 – iliac screw fixation 302 – lateral lumbar interbody fusion cages 257 – lumbar pedicle screws 141 – pedicle screw fixation 188 – percutaneous vertebral cement augmentation 160 – posterior screw fixation 195 – scoliosis 397 – subaxial fusions 62 – vertebral body replacement cages 170 nonunion, see pseudoarthrosis – C1–C2 wiring 45 – C2 pedicle, pars screws 34 – lateral lumbar interbody fusion cages 259, 260 – lumbar pedicle screws 142 – occipitocervical fusion 9 – odontoid fractures 85 NuVasive OCT System 11

O occipital fixation 10 occipital neuralgia, neuropathy 26 Occipital Spine System 11 occipitocervical fusion – anatomy 3, 4 – biomechanics 3, 3 – complications 6 – dural tear 10 – hardware failure 10 – hardware, fusion malposition 8, 8 – hypoglossal nerve injury 14, 17 – ICA injury 17 – infection 9 – instrumentation history 4, 5 – longitudinal components 11 – nonunion 9 – occipital fixation 10 – suboccipital fixation 11 – technique 4, 6 – venous sinus injury 6, 6 – vertebral artery injury 7, 7, 8 odontoid fractures – anterior osteosynthesis 89, 90 – C1–C2 posterior screw–rod fixation 91, 92 – classification 85, 85–86 – epidemiology 85 – halo vest immobilization 87 – in elderly patients 88 – nonrigid immobilization 86 – nonunion 85 – operative management 89 – outcomes 85 – posterior fusion 90 – posterior transarticular screws 91 – posterior wiring 91 – treatment principles 85 – treatment selection 86 OP-1 Putty 214 open TLIF – adjacent segment degeneration 234, 236–237 – advantages of 230 – anatomy 231

– – – – – – – – – – – – – – –

BMP usage in 239 cage migration 239 complications 234 durotomy 239 epidural hematoma 238 FDA approval status 231 great vessel injury 238 infection 236 nerve injury 239 overview 230, 240 purpose of 231, 232–233 radiculitis 239, 240 retroperitoneal injury 238 rhBMP-2 usage in 240 surgical technique 232, 232, 233, 234–235 – techniques, comparison of 230 – unilateral vs. bilateral 231 OPLL – characterization 339 – complications 344 – myelopathy, surgical management 344, 345 – outcomes 344 ossification of posterior longitudinal ligament, see OPLL osteolysis – avoidance 220 – BMP-related 215, 218, 219 – rhBMP-2-associated 401 osteomyelitis 170 osteoporosis – anterior lumbar approach 335, 337 – clinical definition 333 – compression fractures 333, 334 – hyperkyphosis 370 – imaging 333 – laboratory testing 333 – lateral interbody fusion 335, 337 – mini-thoracotomy approach 335, 336 – operative adjuncts 335, 338 – pedicle screws for 188 – proximal junctional kyphosis and 75 – scoliosis and 396 – secondary 333, 333 – transforaminal lumbar interbody fusion 335, 335–336 – types 333 osteosarcomas 408 O–C2 angle 8

P pediatric patients – cervical kyphosis 362 – growing rods 393, 396 – iliac screw fixation 299 – pelvic fixation 304, 308–309 – posterior screw fixation 199, 200 – scoliosis 393, 396 pedicle screw fixation, see percutaneous pedicle screw fixation, posterior screw fixation – biomechanics 57 – complications 58, 188, 196 – complications, avoiding 59, 60 – dural tear 58, 59 – flatback syndrome 377 – imaging 60 – junctional kyphosis 147 –– See also adjacent segment pathology

– – – – – – – – – – –

learning curve 59 lumbar, see lumbar pedicle screws nerve injury 58, 59 neurologic injury 188 overview 57, 60, 242 scoliosis 393 screw malposition 59 spondylolisthesis 386 supplemental fixation vs. 282 technique 57, 57, 58, 59 thoracolumbar spine complications 197 – vertebral artery injury 58, 59 pedicle screw removal, revision – fracture 414, 414 – fracture evaluation 414 – pitfalls of 416, 416 – preoperative planning 415 – surgical technique 415 – surgical treatment 415 pedicle-subtraction osteotomy – complications 343 – flatback syndrome 378, 378–379 – hyperkyphosis 370–371, 371–373 PEEK spacers – ALIF complications 273 – ALIF surgical approach, spinal surgeon 272 – ALIF surgical approach, vascular surgeon 272 – biomechanical concerns 275 – biomechanical development 275 – BMP-related complications 274– 275, 401 – bone contact and 276 – cage migration 401, 402 – characteristics of 275, 275 – clinical concerns 276 – indications 274 – interbody spacers 274 – neurological injury 274 – overview 272 – peritoneum violation 274 – PLLA cages vs. 275 – posterior lumbar interbody fusion 220, 222 – pseudarthrosis 276, 276 – retrograde ejaculation 274 – segmental stability 276, 276 – spondylolisthesis as contraindication 277, 277 – stand-alone ALIF 282 – structural grafts, allografts vs. 275 – subsidence risk 276 – transforaminal lumbar interbody fusion 220, 222, 242 – vascular injury 273 pelvic fixation – anatomy 304 – complications 304, 308–310 – outcomes 304, 308 – pediatric 304, 308–309 – purpose of 304, 305–306 – sacral alar-iliac (S2AI) technique 304, 306–307, 359 – sacroiliac joint, crossing 309 – strategies 304 – transverse-plane pelvic asymmetry 309, 310 pelvic hematoma 209 percutaneous pedicle screw fixation – anatomy 249 – complications 250

– – – – – – – – – – –

electrophysiologic stimulation 253 guidewire placement 252 imaging 249, 252 instrument failure 252 learning curve 250 overview 249, 252 patient selection 250 pedicle wall breach 250 pitfalls of 249 radiation exposure 250 sclerosis-associated complications 252 – screw malposition 251, 251–252 – vertebral artery injury 252, 253 percutaneous vertebral cement augmentation – adjacent segment vertebral fracture 161 – cement embolization 161 – cement leakage 160, 160, 161 – complications 159 – fracture epidemiology 158 – infection 161 – neurological injury 160 – overview 158 PITTS score 28 plasmacytoma 170 PLIF, see posterior lumbar interbody fusion polysegmental wedge osteotomies 343 posterior atlantodental interval (PADI) 325 posterior lumbar interbody fusion – battered root syndrome 221 – BMP-related complications 214, 216, 216, 217, 222, 401 – complications 227 – complications, rare catastropic 226 – FDA approval status 214 – heterotopic ossification 215, 217, 218 – heterotopic ossification avoidance 217 – imaging assessment of 216, 224 – incidental durotomy 221 – indications 214 – infection 224, 226, 349 – infection avoidance 224 – infection diagnosis 225 – infection management 226 – neurologic complications 221 – neurologic complications avoidance 224 – neurologic complications management 223 – NSAIDs usage in 216, 224 – osseous complications 215, 215 – osteolysis, avoidance 220 – osteolysis, BMP-related 215, 218, 219 – overview 208, 214, 227 – PEEK spacers 220, 222 – principles of 214 – pseudarthrosis 215, 215 – purpose of 214, 230 – radiculopathy, radiculitis 222, 223, 225 – removal, revision of, see interbody fusion removal, revision – scoliosis 394 – techniques, comparison of 230 posterior screw fixation, see pedicle screw fixation

421

Index – atlantoaxial fixation 194 – cervical lateral mass screws 195, 196 – cervical pedicle screws 196 – complications 194, 196 – continuous neural monitoring 198 – cortical bone trajectory pedicle screws 199 – CSF leak 198 – dural tears 198 – facet screws 200 – infection 199 – malposition 194 – nerve injury 196, 198 – neurologic injury 195 – neurological complications 198 – overview 194 – pediatric 199, 200 – pedicle fracture 199 – scoliosis 200 – screw malposition 196, 197, 197 – spinal cord injury 198 – subaxial cervical spine complications 195 – thoracolumbar spine complications 197 – transfacet screws 195 – vascular complications 198 – vertebral artery injury 194, 195, 196 posterior vertebral column resection – flatback syndrome 378, 379 – hyperkyphosis 370–372, 373 presacral fusion devices – anatomy 208 – complications 209 – device loosening, migration, failure 211 – FDA approval status 208 – infection 210 – nerve injury 210 – pelvic hematoma 209 – pseudoarthrosis 210 – rationale for 208 – rectal injury 209 – sacral fracture 210 – salvage strategies 211 – surgical technique 209 Prestige ST implants 133 proximal junctional failure 397 proximal junctional kyphosis – defined 146 – hyperkyphosis 369 – osteoporosis and 75 – risk factors 370 – scoliosis 149, 396 pseudoarthrosis, see nonunion – ankylosing spondylitis 342, 345 – anterior cervical plating 96, 98 – anterior cervical plating (translational) 106 – C2 translaminar screws 50, 50 – cervical kyphosis 363 – diagnosis 106, 106, 268 – femoral ring allografts 267 – iliac screw fixation 300 – interbody fusion removal, revision 418 – low-profile stand-alone implants 118, 119 – PEEK spacers 276, 276 – PLIF, TLIF 215, 215 – presacral fusion devices 210

422

– sacropelvic reconstruction, tumor resection 316, 317 – spinal tumor surgery 358, 358 – spondylolisthesis 383 – stand-alone ALIF 286, 286 – subaxial fusions 63, 64 – treatment 106, 268

R radiculopathy, radiculitis – open TLIF 239, 240 – rhBMP-2 400, 401 – transforaminal lumbar interbody fusion 222, 223, 225 RAY Threaded Fusion Cage 214 rectal injury 209 recurrent laryngeal nerve injury 130 restenosis, post-laminoplasty 71, 71 Retrieval Expanding Hex Screwdriver 212 retrograde ejaculation – PEEK spacers 274 – rhBMP-2 403 – rhBMP-2 and 283 – stand-alone ALIF 283, 284 – total disc replacement 293 rhBMP-2, see bone morphogenic proteins (BMPs) – absolute dose role in complications 405 – allografts and 409 – antibody formation and 406, 408 – cage migration 401 – cancer and 408 – cervical swelling and 404, 404, 405– 406 – disease transmission and 409 – dysphagia 405 – ectopic bone formation 400, 400, 406, 407 – graft subsidence 401, 406 – hematoma 402, 404 – hepatitis C and 409, 410 – history of 400, 404 – HIV and 409, 409 – in cervical spine 404 – in lumbar spine 400 – in open TLIF 240 – infection 402, 406 – osteolysis 401, 401, 402–403, 406, 407 – radiculitis 400, 401 – retrograde ejaculation and 283, 403 – seroma 402, 404 – stand-alone ALIF and 281, 287 rheumatoid arthritis – case studies 329, 329, 330 – complications 327 – deformity correction 328 – diagnosis 325 – epidemiology 325 – hardware failures 328 – implant malpositioning 328 – nonoperative treatment 326 – pathogenesis 325 – surgical approaches 326 – surgical indications for 326 – surgical management 327, 328 Roy-Camille’s technique – neurologic injury 62 – posterior screw fixation 196 – subaxial fusions 61–62

S S4 Cervical Occipital Plating System 11 sacral alar iliac screw fixation, see pelvic fixation sacral alar-iliac (S2AI) technique 304, 306–307, 359 sacral chordomas 312, 316 sacral fracture 210 sacropelvic reconstruction, tumor resection – classification 313, 313, 322 – closed-loop technique 320, 322 – complications 316 – compound osteosynthesis technique 315, 316 – deformity 317, 318 – disease process, management 318 – fibular autograft 313, 315 – flap healing complications 316 – fusion grading 316, 317 – Galveston’s technique 313, 314 – hardware failure 317, 319 – infection 316 – Johns Hopkins technique 321, 323 – leg length discrepancy 317 – modified Galveston’s technique 313, 314–315, 317, 319 – muscular attachments 315 – nerve damage 317 – neurologic complications 317 – novel reconstruction method 321, 323 – overview 312 – pelvic incidence deformity 317, 318 – pelvis, common tumors in 312 – prostheses 315 – pseudarthrosis 316, 317 – reconstruction methods 313, 314 – resection techniques 313 – triangular frame technique 318– 319, 320–321 sarcoma 170 Scheuermann’s kyphosis 369 scoliosis – adjacent segment pathology 149, 149, 397 – anatomy 391 – anterior lumbar interbody fusion 394 – background 391 – correction 149, 149 – developmental kyphosis treatment 396 – EMG monitoring 392 – failure, modes of 391 – growing rods 393, 396 – Harrington’s instrumentation 392, 396 – interbody fusion implants 394 – interbody techniques 394 – lateral interbody fusion cages 395, 395 – lateral transpsoas fusion 396 – Luque-rod segmental spinal instrumentation 392 – MIS TLIF 395 – neurologic complications 397 – neuromonitoring applications 392 – osteoporosis and 396 – pediatric 393, 396 – pedicle screw fixation 393 – pelvic incidence 391

– pelvic tilt 391 – posterior lumbar interbody fusion 394 – posterior screw fixation 200 – proximal junctional failure 397 – proximal junctional kyphosis 149, 396 – radiation-related complications 396 – rib-based fixation systems 393 – rod constructs, single vs. double 393 – sacral inclination 391 – sacral slope 391 – sagittal balance 391 – somatosensory-evoked potentials 392 – spinal alignment 391 – surgical approaches 394 – transforaminal lumbar interbody fusion 395, 395 – vertebral body stapling 394 – Wisconsin’s technique 393 – XLIF 395 – XLIF procedure 396, 396 seroma 402, 404 Smith–Petersen osteotomy – ankylosing spondylitis 343, 345 – flatback syndrome 378, 378 – hyperkyphosis 370, 370–371, 373 spinal accessory nerve injury 83 spinal cord injury – cervical arthroplasty 131 – infection 347 – posterior screw fixation 198 Spinal Summit SI OCT Spinal System 11 Spinal Synapse System 11 spinal tumor surgery – anterior-based approaches 356 – anterior-based instrumentation 359, 359 – complications 358, 360 – indications 355 – instrumentation failure 358, 359 – lateral-based approaches 357 – lateral-based instrumentation 360 – lymphoma 355 – metastasis 170, 355 – multiple myeloma 355 – overview 355 – posterior-based approaches 356, 356, 357 – posterior-based instrumentation 356, 358, 358 – prognostic scores 355 – pseudarthrosis 358, 358 – stereotactic radiosurgery 360 spinous fracture 185 spondyloarthropathy – ankylosing spondylitis, see ankylosing spondylitis – complications 327 – deformity correction 328 – DISH 342 – hardware failures 328 – implant malpositioning 328 – laminoplasty 344 – nonoperative treatment 326 – OPLL, see OPLL – overview 325, 330, 345 – pathophysiology 339 – rheumatoid arthritis, see rheumatoid arthritis – surgical approaches 326

Index – surgical indications for 326 – surgical management 328 – thoracolumbar pathology in 339 spondylodiscitis 339 spondylolisthesis – anatomy 384 – case study 382, 382–384 – classification 382 – development of 384 – dysplastic spinal segment anatomy 385 – FDA approval status 383 – Gaines vertebrectomy 387 – high-grade 382, 388 – implant-related complications 385 – implants 383 – interbody fusion devices 386 – intrasacral rods 387 – minimally invasive spine surgery 387 – neural injury 387 – pedicle screw fixation 386 – pseudarthrosis 383 – radiographic descriptors of 385, 385 – spinopelvic anatomic parameters 384, 384 – transsacral screws, dowels 386 SPORT trial 215, 385 SSI, see infection Stagnara Wake Up Test 392 stand-alone ALIF – abdominal wall complications 285 – anatomy 279 – biomechanics 281 – bladder, ureter injury 283, 284 – bowel injury 285 – cages 281 – colonic pseudoobstruction 285 – complications 283 – deep venous thrombosis 285 – gastrointestinal complications 284 – graft malposition, migration 287, 288 – graft selection 282 – history of 279, 286 – implant selection 281 – lumbar sympathetic trunk injury 285 – lymphatic injury 285, 285 – metal cages 281 – nerve injury 285 – patient selection 281 – PEEK cages 282 – pseudoarthrosis 286, 286 – retrograde ejaculation 283, 284 – rhBMP-2 and 281, 287 – subsidence 286, 287 – supplemental fixation 282 – surgical approach 279, 279, 280–281 – urologic Injury 283 – vascular injury 283, 283 stand-alone, low-profile devices, see low-profile stand-alone implants stress shielding 96 structured allograft cages, see vertebral cage replacement subaxial fusions – anatomy 61 – complications 61 – dural tear 62 – epidural hematoma 62 – infection 62, 63

– instrumentation, construct failure 63, 65 – instrumentation, purpose of 61 – Magerl’s technique 61–62 – neurologic injury 62 – overview 61, 63 – preoperative imaging 61 – pseudarthrosis (nonunion) 63, 64 – Roy-Camille’s technique 61–62 – vertebral artery injury 62, 62 subaxial lateral mass screw fixation – advantages 53 – An technique 54, 55 – anatomy 53, 54 – complications 55 – history 53 – indications 53 – Magerl technique 54, 54, 55, 55 – overview 53 – Roy-Camille technique 54, 54–55 – surgical technique 54, 54, 55 sublaminar wiring – complications 156 – epidural fibrosis 156 – history 156 – in vitro corrosion 156 – laminar overgrowth 156 – Luque–Galveston 156 – nerve injury 156 – overview 156 – safety zone 156 – spinal deformity surgery complications 156 suboccipital fixation, occipitocervical fusion 11 superior hypogastric sympathetic plexus 283, 284 superior laryngeal nerve injury 82 Synfix, Synfix-LR™ devices 276, 276

T TAS placement, see C1–C2 transarticular screws, cervicothoracic junction thoracolumbar burst fractures 170 thoracolumbar vertebral body resection – anatomy 165 – complications 167, 167 – indications 165 – instrumentation, purpose of 166 – overview 165 – posterolateral approach 165, 166 titanium mesh cages, see vertebral cage replacement TLIF, see minimally invasive TLIF, open TLIF, transforaminal lumbar interbody fusion total disc replacement – anhidrosis 293 – compartment syndrome 292 – complications, list 291 – deep venous thrombosis 292 – durotomy 292 – exposure-related complications 291 – granuloma formation 296 – heterotopic ossification 297 – ileus 293 – implant failure 294 – implant malpositioning 293 – implant subluxation, subsidence 294, 294, 295–296 – indications 291

– infection 295 – lateral lumbar, see lateral lumbar TDR – lymphatic injury 293 – neurologic complications 297 – overview 291, 297 – peritoneal injury 292 – retrograde ejaculation 293 – vascular injury 291 – vertebral fracture 295 – visceral injury 292 TranS1 Axialif procedure, see presacral fusion devices transforaminal lumbar interbody fusion, see minimally invasive TLIF, open TLIF – battered root syndrome 221 – benefits of 274 – BMP-related complications 214, 216, 216, 217, 222, 401, 401–402 – complications 227 – complications, rare catastropic 226 – durotomy 221 – FDA approval status 214 – heterotopic ossification 215, 217, 218 – heterotopic ossification avoidance 217 – imaging assessment of 216, 224 – indications 214 – infection 224, 226, 349 – infection avoidance 224 – infection diagnosis 225 – infection management 226 – neurologic complications 221 – neurologic complications avoidance 224 – neurologic complications management 223 – NSAIDs usage in 216, 224 – osseous complications 215, 215 – osteolysis, avoidance 220 – osteolysis, BMP-related 215, 218, 219 – osteoporosis 335, 335–336 – overview 208, 214, 227 – PEEK spacers 220, 222, 242 – pseudarthrosis 215, 215 – purpose of 214 – radiculopathy, radiculitis 222, 223, 225 – removal, revision of, see interbody fusion removal, revision – scoliosis 395, 395 – techniques, comparison of 230 – unilateral vs. bilateral 231 translaminar facet screws 200 transpsoas extreme lateral interbody fusion – purpose of 262 – scoliosis 395 – scoliosis, procedure 396, 396 – TLIF vs. 230 – vertebral fractures 262 trauma-associated complications 170 tumor-associated complications 170, 170

V vacuum-assisted wound closure 351 vancomycin, intrawound powder 9 vascular injury

– anterior lumbar interbody fusion 291 – iliac screw fixation 302 – lateral lumbar interbody fusion cages 395 – stand-alone ALIF 283, 283 – total disc replacement 291 venous plexus injury 26, 33 venous sinus injury 6, 6 vertebral artery – anatomy 37, 38 – atlantoaxial fixation 14, 15–18 – complications, management 18 – epidemiology 14, 20 – fenestration 16 – fixation techniques 14 – persistent first intersegmental artery 16 – subaxial fixation 17, 19–20 – surgical anatomy 14, 15–16 vertebral artery injury – anterior C1–C2 fusion 83 – C1 lateral mass screw fixation 25 – C1–C2 posterior screw–rod fixation 92, 92 – C1–C2 transarticular screws 39, 195 – C2 pedicle, pars screws 31–32, 32, 34 – C2 translaminar screws 50, 50 – cervical arthroplasty 131 – occipitocervical fusion 7, 7, 8 – pedicle screw fixation 58, 59 – percutaneous pedicle screw fixation 252, 253 – posterior screw fixation 194, 195, 196 – subaxial fusions 62, 62 vertebral cage replacement – cage migration 169 – commercially available 169 – complications 179, 179 – contraindications 180 – deformity-associated complications 171 – infection-associated complications 170 – instrumentation 173, 176 – nerve injury and 170 – neurological injury 170 – overview 169 – progressive angulation 170 – sagittal misalignment 171 – trauma-associated complications 170 – tumor-associated complications 170, 170 vertebral fractures 262 vertebroplasty, see percutaneous vertebral cement augmentation – adjacent segment vertebral fracture 161 – balloon kyphoplasty technique 159 – complications 159 – compression fractures 334 – efficacy 158 – epidemiology 158 – overview 158 – technique 158 Vertex Select Reconstruction System 11 vertical expandable prosthetic titanium rib (VEPTR) 393 VERTOS II study 161

423

Index VLIFT system 169

X

Z

W

X-stop spacer 203, 205–206 XLIF, see transpsoas extreme lateral interbody fusion

Zephir plating system 103

Wallis spacer 203

424