Hexapod External Fixator Systems: Principles and Current Practice in Orthopaedic Surgery 3030406660, 9783030406660

Table of contents :
Foreword
Preface
Contents
1: History and Evolution of Hexapod External Fixators
1.1 History of Hexapod External Fixators
1.2 Theoretical Basis: From the Mozzi-Chasles’ Theorem to the “Screw” Theory
1.3 The Hardware: The Beginning of Parallel Manipulators
1.4 Hexapods in Medicine
1.5 Biographic Notes
References
Part I: Mathematical and Physical Principles
2: Mathematics of the Hexapod
2.1 Vectors
2.2 Rotational Matrix
2.3 Six Degrees of Freedom
2.4 Solution of the Forward Kinematics
2.4.1 Practical Example
References
3: Characteristics and Usage Modalities. Main Systems
3.1 Introduction
3.2 Theoretical Basis
3.3 Properties of Hexapod Systems in Orthopaedics
3.4 Octopods
3.5 The Hardware
3.5.1 Operative Instructions
3.5.2 Hexapod Frame Components
3.5.2.1 The Platform
3.5.2.2 The Struts
3.5.2.3 The Strut Joint
3.5.2.4 Strut–Platform Connection
3.5.2.5 Platform–Bone Connection
3.6 The Virtual Hinge
3.7 Additional Fixation Levels (Second Level of Fixation) and Components
3.8 The Software
3.8.1 Software–Frame Relationship
3.8.2 Correction (End of Correction)
3.9 Engage, Conflict, and Impingement
3.10 Future Perspectives
Appendix
References
Recommended Reading
4: Material Properties Related to Requirements of Hexapodalic Systems
4.1 Mathematical Definition of Stress Forces Inside Materials
4.2 Response of Materials Under Mechanical Stress
4.3 Properties of Dia-, Para-, and Ferromagnetic Materials
References
Part II: Clinical Applications of Hexapod External Fixator
5: Hexapod External Fixation for Fractures and Nonunions
5.1 Introduction
5.1.1 Design and Technology
5.1.2 Biomechanics and Application
5.2 Acute Fractures
5.2.1 Fracture Reduction
5.2.2 Open Fractures
5.2.3 Soft-Tissue Management
5.3 Nonunion
5.3.1 Metaphyseal Nonunion
5.3.2 Hypertrophic Nonunion
5.3.3 Infected Nonunion
5.3.4 Soft-Tissue Coverage
5.3.5 Economic Burden
5.4 Summary
References
6: Hexapod External Fixators in the Treatment of Axial and Rotation Deformities and Limb Length Discrepancies
6.1 Metaphyseal Case
6.1.1 Deformity Screen
6.1.2 Hardware Screen
6.1.3 AP X-Ray Screen
6.1.4 AP Proximal Joint Line and Proximal Center Point
6.1.5 AP Distal Bone Segment Line
6.1.6 AP Osteotomy and Proposed Pivot Point
6.1.7 AP RDP Bony and Soft and Review
6.1.8 ML X-Ray Screen
6.1.9 ML Proximal Joint Line and Proximal Center Point
6.1.10 ML Distal Bone Segment Line
6.1.11 ML Osteotomy and Proposed Pivot Point
6.1.12 ML RDP Bony and Soft and Review
6.1.13 Corrections Screen
6.1.14 3D Preview and Bone Overlap
6.1.15 Schedule Screen
6.1.16 Residual Revision
6.1.17 Residual Corrections
6.2 Diaphyseal Case
6.2.1 Preoperative X-Rays
6.2.2 Deformity Screen
6.2.3 Hardware Screen
6.2.4 AP X-Ray Screen
6.2.5 AP Proximal and Distal Bone Segment Lines
6.2.6 AP Osteotomy and Proposed Pivot Point
6.2.7 AP RDP Bony and Soft and Review
6.2.8 ML X-Ray Screen
6.2.9 ML Proximal and Distal Bone Segment Lines
6.2.10 ML Osteotomy and Proposed Pivot Point
6.2.11 ML RDP Bony and Soft and Review
6.2.12 Corrections Screen
6.2.13 3D Preview and Bone Overlap
6.2.14 Schedule Screen
6.2.15 Final X-Rays (Fig. 6.47)
6.2.16 Foot Case
6.2.17 Deformity Screen
6.2.18 Hardware Screen
6.2.19 ML X-Ray Distal Ring Screen
6.2.20 ML Midline of Talus and First Metatarsal Line
6.2.21 ML Osteotomy and Proposed Pivot Point
6.2.22 ML RDP Bony and Soft and Review
6.2.23 Dorsal X-Ray Distal Ring
6.2.24 Dorsal Midline of Talus and First Metatarsal Line
6.2.25 Dorsal Osteotomy and Proposed Pivot Point
6.2.26 Dorsal RDP Bony and Soft and Review
6.2.27 Corrections Screen
6.2.28 3D Preview and Bone Overlap
6.2.29 Schedule
6.2.30 Final X-Rays After Foot Correction and Frame Removal (Fig. 6.67)
References
7: Hexapod External Fixators in Bone Defect Treatment
7.1 Definition and Classification of Bone Defects
7.2 Phases of Bone Transport Performed with Circular External Fixation: Clinical and Biological Features
7.2.1 Surgery (Initial Phase)
7.2.2 Latency Phase
7.2.3 Transportation Phase (Distraction Phase)
7.2.4 Consolidation Phase
7.2.5 Final Phase (External Fixation Removal)
7.3 Complications
7.4 Indications and Contraindications
7.4.1 Indications in Trauma Situations
7.4.2 Indications in Osteomyelitis Management
7.4.3 Indications in Bone Tumors Management
7.4.4 Contraindications for Bone Transport
7.5 Bone Fixation Devices
7.5.1 Classic Circular External Fixators
7.5.2 Hexapod External Fixators
7.6 Alternatives to Bone Transport with Circular External Fixation
7.7 Techniques of Bone Transport
7.7.1 Bone Transport in Acute Trauma Situations (Emergency Procedure)
7.7.1.1 Open Fractures
7.7.2 Bone Transport in Chronic Trauma Situations (Planned Elective Procedure)
7.7.3 Third Type: Atrophic Infected Nonunions
7.7.4 Fourth Type: Infected Nonunions with Bone and Soft-Tissue Loss
7.8 Bone Transport in Osteomyelitis
7.9 Bone Transport in Bone Tumors
7.10 Conversion from External to Internal Fixation
7.11 Observations on Advantages and Disadvantages of Hexapod External Fixation in Segmental Bone Defects Management
7.12 Discussion
References
8: Hexapod External Fixators in Paediatric Deformities
8.1 Introduction
8.2 Preoperative Planning
8.3 Frame Setup
8.4 Postoperative Management
8.5 Specific Clinical Conditions
8.5.1 Physeal Injuries
8.5.1.1 Clinical Case (Fig. 8.1)
8.5.1.2 Surgical Procedure
8.5.1.3 Key Points
8.5.2 Hereditary Multiple Exostoses (HME)
8.5.2.1 Clinical Case (Fig. 8.2)
8.5.2.2 Surgical Procedure
8.5.2.3 Key Points
8.5.3 Ollier’s Disease
8.5.3.1 Clinical Case (Fig. 8.3)
8.5.3.2 Surgical Procedure
8.5.3.3 Femur
8.5.3.4 Tibia
8.5.3.5 Key Points
8.5.4 Congenital Deformities
8.5.4.1 Clinical Case (Fig. 8.4)
8.5.4.2 Surgical Procedure
8.5.4.3 Femur
8.5.4.4 Tibia
8.5.4.5 Key Points
8.5.5 Clubfoot
8.6 Limitations of the Use of Hexapod External Fixator in Paediatric Patients
References
Introduction
Physeal Injuries
Hereditary Multiple Exostoses (HME)
Ollier’s Disease
Congenital Deformities
Clubfoot
9: Hexapod External Fixators in Ankle and Foot Deformity Correction
9.1 Introduction
9.2 Ilizarov Frame and Orthopaedic Hexapods in Ankle and Foot Deformity Correction: General Principles
9.3 Orthopaedic Hexapod “Ortho-SUV Frame” (OSF): Main Peculiarities
9.4 Planning of Distal Tibia Deformity Correction
9.5 OSF Ankle Hardware and Software
9.5.1 OSF Ankle Hardware
9.5.2 OSF Ankle Software
9.6 Planning of Midfoot and Hindfoot Deformity Correction
9.6.1 RLA and Midfoot Planning of Deformity Correction
9.6.2 RLA and Hindfoot Planning of Deformity Correction
9.7 OSF Midfoot Hardware and Software
9.7.1 OSF Midfoot Hardware
9.7.2 OSF Midfoot Software
9.8 OSF Hindfoot Hardware and Software
9.8.1 OSF Hindfoot Hardware
9.8.2 OSF Hindfoot Software
9.9 Postoperative Care
9.10 Contributions
References
10: Hexapod External Fixators in Articular Stiffness Treatment
10.1 Introduction
10.2 Ilizarov Frame and Orthopaedic Hexapods in Articular Stiffness Surgery: General Principles
10.3 “Multi Total Residual” OSF Software Option
10.4 OSF Knee Hardware and Software
10.4.1 OSF Knee Hardware
10.4.2 OSF Knee Software
10.5 OSF Ankle Joint Hardware and Software
10.5.1 OSF Ankle Hardware
10.5.2 OSF Ankle Software
10.6 Postoperative Care
10.7 Contributions
References
11: Problems, Challenge, Complications in Hexapod External Fixation Systems. Contraindications
11.1 Introduction
11.2 Complications
11.2.1 Intraoperative Complications
11.2.2 Postoperative Complications
11.3 Indications and Contraindications to the Use of Hexapod External Fixation
11.3.1 Indications
11.3.2 Contraindications
11.4 The Problem of Conversion
11.5 Discussion
11.6 Conclusion
References
Part III: Special Applications, Biological and Economical Aspects of Hexapod External Fixators
12: Ancillary Usage of Hexapod External Fixators
12.1 Consecutive Method
12.1.1 FAN and FALP (Fixator-Assisted Nailing and Fixator-Assisted Locking Plate)
12.1.1.1 Advantages and Disadvantages
12.1.1.2 Accuracy and Results of the Technique
12.1.1.3 Indications and Contraindications
12.1.1.4 Complications
12.1.1.5 FAN vs FALP
12.1.2 LATN (Lengthening And Then Nailing)
12.1.2.1 Indications and Contraindications
12.1.2.2 Surgical Technique [25]
12.2 Simultaneous Method
12.2.1 LON (Lengthening Over a Nail)
12.2.1.1 Indications and Contraindications
12.2.1.2 Surgical Technique [27, 28, 31]
12.2.1.3 Advantages and Disadvantages
12.2.1.4 Complications
12.2.2 BTON (Bone Transport Over a Nail)
12.2.2.1 Indications and Contraindications
12.2.2.2 Surgical Technique [23]
12.2.3 Comparison of Alternative Lengthening Techniques
12.3 Computer-Assisted Method, Hexapod Fixators, and Internal Fixation
12.3.1 General Aspects
12.3.2 CHAOS (Computer Hexapod-Assisted Orthopaedic Surgery)
12.3.3 CHATS (Computer Hexapod-Assisted Trauma Surgery)
References
13: External to Internal Fixation Conversion Timing: Infectivologist’s Perspectives
13.1 Introduction
13.2 Pin-Tract Infection
13.3 Conversion
13.4 Surgical Technique
13.5 Pin-Site Care
13.6 Bacterial Agents and Antibiotic Therapy
13.7 Conclusion
References
14: Ionizing Radiation Exposure
14.1 Ionizing Radiation
14.1.1 Charged Particles
14.1.2 Photons
14.1.3 Neutrons
14.2 Generation of Ionizing Radiation
14.3 Radiography and CT
14.3.1 Radiological Image Quality and Optimization
14.4 Biological Effects and Dosimetry
14.5 Radiation Exposure
14.5.1 Radiation Dose in Diagnostic Imaging
References
15: Economic Burden and Practical Considerations
15.1 Introduction
15.2 Economic Burden of the Management with Hexapod External Fixators
15.3 Discussion
References
Part IV: Principles of Deformity’s Geometry
16: Geometry of Deformities
16.1 Upper Limb
16.1.1 Anatomical and Mechanical Axis of the Upper Limb
16.1.2 Upper Limb Angles
16.1.2.1 Proximal Humeral Angle
16.1.2.2 Distal Humeral Angle
16.1.3 Forearm
16.2 Lower Limb
16.2.1 The Femoral Axes
16.2.2 Femoral Angles
16.2.2.1 Proximal Femur
16.2.2.2 Distal Femur
16.2.3 The Tibial Axes
16.2.4 The Tibial Angles
16.2.4.1 Proximal Tibia
16.2.4.2 Distal Tibia
16.2.5 MAD (Mechanical Axis Deviation)
16.2.6 CORA (Center of Rotation of Angulation)
16.2.7 ACA (Angulation Correction Axis)
16.3 Canal Flare Index
16.4 Insall–Salvati Ratio
References
Nomenclature

Citation preview

Hexapod External Fixator Systems Principles and Current Practice in Orthopaedic Surgery Marco Massobrio Redento Mora Editors

123

Hexapod External Fixator Systems

Marco Massobrio  •  Redento Mora Editors

Hexapod External Fixator Systems Principles and Current Practice in Orthopaedic Surgery

Editors Marco Massobrio Department of Orthopaedics and Traumatology “Sapienza” - University of Rome Rome Italy

Redento Mora Division of Orthopaedics and Traumatology, Department of Surgical, Diagnostic and Pediatric Sciences University of Pavia, “Città di Pavia” Institute University Hospital, School of Medicine

Pavia Italy

ISBN 978-3-030-40666-0    ISBN 978-3-030-40667-7 (eBook) https://doi.org/10.1007/978-3-030-40667-7 © Springer Nature Switzerland AG 2021 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Foreword

I have known Professor Massobrio and Professor Mora for many years. I met Marco Massobrio, a young resident, in the 1980s, in the Orthopedic Institute at the University of Rome where I was Associate Professor. Twenty years later I was invited two times by Dror Paley to give a lecture on “knee osteotomies” in one of his Instructional Courses. In those occasions I renewed my fascination with the techniques of external fixation. When Marco invited me to write the Foreword on this book, conceived together with Professor Redento Mora, I was not only honored but it was for me like a return to the past! Since a normal life is impossible without proper joint function and since joint function cannot be proper without a proper axial alignment, the orthopaedic surgeons need and now have a very special tool to recover joint function: hexapod external fixators. The expansion of treatment options with external fixators for fractures, nonunions, axial and rotational deformities, limb length discrepancies, and articular stiffness introduces challenging problems to the practicing surgeons and to the Orthopaedic residents in training. Most importantly, this knowledge provides the basis upon which an Orthopaedic surgeon counsels a patient regarding the risks and benefits of every operative treatment. Many patients before or after the medical examination go to the internet to try to understand if the suggestions of the treating surgeon are the same suggested by the “opinion leaders.” They often get confused and frightened by the very different suggestions and proposals from different orthopaedic surgeons. These patients have high expectations for overcoming their complaints and ability to return to their previous activity level. The text of this book is comprehensive and covers all surgical aspects of the mechanics, biomechanics, and generally the use of hexapod external fixators. Basic science, characteristics, planning, and surgical techniques are clearly reported and illustrated in a didactic fashion. Despite the huge number of textbooks, journals, and instructional courses dedicated to the external fixators, there are still enormous areas of controversies within the Orthopaedic community. This is why a multicontinental team of experts has been invited to define and present their own vision and handson experience. One lesson that can be drawn from this book is that none of us can accomplish much by ourselves and that only through cooperation in groups and v

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across national boundaries we can achieve real progress in term of improved patient care. For the future, much remains to be improved and basic research needs to be further refined. With its comprehensive, up-to-date summary of the knowledge of the hexapods, this book, thanks to the organization and knowledge of the editors, will be a very valuable aid in furthering our understanding and management of the patient. Wishing a great success to Marco Massobrio, Redento Mora, and all the authors, I would like to present three quotations. The first is from William Harvey: “I would say with Fabricius, let all reasoning be silent when experience gain says its conclusion. The too familiar vice of the present age is to obtrude as manifest truths, mere fancies, born of conjecture and superficial reasoning, altogether unsupported by the testimony of sense.” The second is from Robert Leach: “Enjoy the book, absorb the material so assiduously collected by the editors and use that material to the benefit of your patients.” The third quotation is from my mentor Jack C. Hughston: “To readers I would say, let the experience presented by this book speak for itself.”

Giancarlo Puddu Private Practice, Rome, Italy

Foreword

Preface

The spread of computer assistance in all fields of medical science has led to the development of new technologies that have deeply changed both the medical research and the clinical approach, by ensuring a different insight into physical and biological phenomena and the design and construction of new equipment and their routine use. In this textbook, the basic principles underlying the hexapod systems applied in Orthopaedic and Trauma surgery are outlined, and the contribution of some institutions and authors, who firstly used this method in Western Europe, Russia, and the United States, is presented. The different lengths of the chapters are explained by the will of the editors to provide a broader and deeper description of particular topics, even with the help of original iconographic material. Circular external fixation developed by Ilizarov has been widespread now for several decades. Today, the application of computer assistance to circular external fixators, lying on the parallel manipulators kinematics, opens up a new digital era based on the simultaneous correction of deformity on all space axes. Deformities and fractures cause anatomical alterations or interruption of the continuity of a long bone, resulting in displacements into the three axes of space. Deformities and fractures, therefore, can be considered as a set of axes that have lost their natural relationships with respect to the main limb axis. When a reduction or correction is performed on one plane only, the risk of malalignment/malunion on non-assessed planes cannot be excluded; the correct reduction can only take place when separate maneuvers for each plane are performed. The use of hexapod systems allows to apply the correction vector resulting from the sum of the deformities on the three orthogonal planes and hence to obtain the correction with a single controlled movement. This textbook consists of five sections. The first one (corresponding to the first chapter) includes the history and the description of the proceedings on the kinematics of rigid bodies developed over several centuries, to give rise, in the mid-twentieth century, to the robotic era, from which the hexapod systems are derived. The second section illustrates the trigonometric calculation procedure dealing with vectors, rotation matrices, and the six degrees of freedom of the system, managed by the software: this allows the correct alignment of the bone segments. The most significant characteristics of the main systems are vii

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also analyzed, as well as the properties and requirements of the hardware that constitutes the hexapod fixator. In the third section the clinical applications of the hexapod systems are described. They can be employed for the treatment of different adulthood and childhood diseases and are especially suitable in the management of fractures, nonunions, long bone defects, multi-axial, complex or rotational deformities, and in joint stiffness treatment. Challenges, complications, and contraindications in the use of hexapod fixation are also largely discussed. The fourth section covers the special applications of the hexapod systems. The use of external to internal fixation conversion (so-called ancillary or auxiliary use of the external fixation) has recently become more common: it depends on the different clinical scenarios and it can suggest many reasons to reflect on the infective complications, on the risk of exposure to ionizing radiations, and also on the economic burden. It is now well recognized that infections of the surgical site are not exclusively caused by the pathogenic agents but they are also related to the degree of soft tissue injury and to the kind of surgical procedure performed. The gradual correction of the position of the bone fragments, allowed by the hexapod system, involves limited surgical trauma and it can simplify the possible application of internal osteosynthesis. The reduction of the use of ionizing radiation both in the operating room and in the medical follow-up represents an additional advantage offered by hexapod fixation, even in case of association with internal fixation. The economic aspects of the external to internal conversion rely on the use of two different types of fixation implants in the same patient and for the same pathology. However, an economic assessment of this conversion procedure should not only be based on the costs of the single device but should also consider that the early removal of the external fixator allows a shorter period of work inability and an earlier return to social life. When considering the cost difference between the hexapod and the circular external devices, it should be noted that a decrease in this disparity, due to the gradual spreading of hexapod fixation systems, could be expected, together with a decrease of the indirect costs actually representing the most important component of the whole procedure cost. Finally, the fifth section of the textbook is a description of the main axes and skeletal relationships of the upper and lower limbs that are the subject of study of the geometry of long bone deformities. Further characteristics and advantages of the hexapod systems (for which it is already possible to obtain automation and remote control) are simulation of the corrective maneuvers, simultaneity of the movement according to the resulting vector in the three planes of the space, calculation of the parameter correction time, re-establishment of the initial conditions, and recalculation. It is noteworthy to emphasize that, after applying the frame to the patient, all stresses of the hardware on the limb do not require any kind of anesthesia. Unlike robotic and computer-assisted surgery, used in other orthopaedic fields, hexapod systems do not conclude their function at the end of the surgi-

Preface

Preface

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cal procedure: they allow to maintain functionality and control as well as to change device configuration during the entire period of application. The technological evolution of the last decades led to the introduction in our specialty of study methods and applications that require basic knowledge regarding not only biology, anatomy, and physiology but also mathematical and physical sciences. We cannot accept being users of technological systems without a deep understanding of the fundamental concepts that govern them. This is the reason why we have dedicated some chapters to the aspects of mathematics and physics behind the use of hexapod systems in orthopaedics, and to the clinical, operational, and economic implications involved in their adoption. We would like to thank all the colleagues who from different Orthopaedic institutes in the world have made available their experience in the drafting of the chapters of this textbook. We also wish to express a special thanks to the colleagues of the Department of Physics of the Sapienza University of Rome, who wrote in an educational form the chapters on mathematics, materials, and risk of exposure to ionizing radiation. Finally, we would like to thank Springer for the full collaboration and all those who, close to us for professional or family reasons, have offered their support in the realization of this textbook.

Marco MassobrioRedento Mora Rome, Italy Pavia, Italy

Contents

1 History and Evolution of Hexapod External Fixators������������������   1 Pasquale Sessa, Giulia Biancucci, Annamaria Dell’Unto, and Marco Massobrio Part I Mathematical and Physical Principles 2 Mathematics of the Hexapod����������������������������������������������������������  13 Giancarlo Ruocco and Alfonso Alessandro Tanga 3 Characteristics and Usage Modalities. Main Systems������������������  19 Marco Massobrio, Pasquale Sessa, Giovanni Pellicanò, and Pasquale Farsetti 4 Material Properties Related to Requirements of Hexapodalic Systems ������������������������������������������������������������������  35 Michele Ortolani and Alessandro Alfonso Tanga Part II Clinical Applications of Hexapod External Fixator 5 Hexapod External Fixation for Fractures and Nonunions����������  43 Gerard A. Sheridan, Austin T. Fragomen, and S. Robert Rozbruch 6 Hexapod External Fixators in the Treatment of Axial and Rotation Deformities and Limb Length Discrepancies����������������������������������������������������������������������  57 Dror Paley and Craig Robbins 7 Hexapod External Fixators in Bone Defect Treatment���������������� 111 Redento Mora, Luisella Pedrotti, Barbara Bertani, Gabriella Tuvo, and Anna Maccabruni 8 Hexapod External Fixators in Paediatric Deformities ���������������� 133 Silvio Boero, Simone Riganti, Giulio Marrè Brunenghi, and Luigi Aurelio Nasto 9 Hexapod External Fixators in Ankle and Foot Deformity Correction ���������������������������������������������������������������������������������������� 153 Leonid Nikolaevich Solomin

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10 Hexapod External Fixators in Articular Stiffness Treatment������ 199 Leonid Nikolaevich Solomin 11 Problems, Challenge, Complications in Hexapod External Fixation Systems. Contraindications������������������������������ 239 Redento Mora, Luisella Pedrotti, Barbara Bertani, Gabriella Tuvo, and Anna Maccabruni Part III Special Applications, Biological and Economical Aspects of Hexapod External Fixators 12 Ancillary Usage of Hexapod External Fixators���������������������������� 249 Marco Massobrio, Giovanni Pellicanò, Pasquale Sessa, and Pasquale Farsetti 13 External to Internal Fixation Conversion Timing: Infectivologist’s Perspectives���������������������������������������������������������� 269 Anna Maccabruni, Redento Mora, Luisella Pedrotti, Barbara Bertani, and Gabriella Tuvo 14 Ionizing Radiation Exposure���������������������������������������������������������� 273 Francesco Collamati, Riccardo Faccini, Carlo Mancini-Terracciano, and Elena Solfaroli Camillocci 15 Economic Burden and Practical Considerations�������������������������� 285 Redento Mora, Luisella Pedrotti, Anna Maccabruni, Barbara Bertani, and Gabriella Tuvo Part IV Principles of Deformity’s Geometry 16 Geometry of Deformities ���������������������������������������������������������������� 293 Giulia Biancucci, Annamaria Dell’Unto, Paolo Martini, and Marco Massobrio Nomenclature ������������������������������������������������������������������������������������������ 309

Contents

1

History and Evolution of Hexapod External Fixators Pasquale Sessa, Giulia Biancucci, Annamaria Dell’Unto, and Marco Massobrio

Nomenclature 6-DOF MAST SUV TSF US

1.1

six degrees of freedom multi-axis simulator table Solomin Utekhin Vilensky Taylor Spatial Frame United States

 istory of Hexapod External H Fixators

The Hexapod external fixator is, nowdays, the most technologically advanced Orthopaedic device for the correction of primary and secondary limb deformities. The history of the hexapod fixator can be considered as closely linked to two main aspects: the search for overcoming the limits of traditional external fixator devices (i.e., Ilizarov’s ring fixator) in the correction of complex limb deformities and the innovations of modern Orthopaedics, that is, computer assistance for the Orthopaedic surgeon in planning and performing surgical interventions. P. Sessa (*) · G. Biancucci · A. Dell’Unto M. Massobrio Department of Orthopaedics and Traumatology, “Sapienza” - University of Rome, Rome, Italy

Hexapod fixators are nothing more than the medical application of parallel manipulators whose invention can be dated back to the beginnings of the twenty-first century for industrial purposes. However, the theoretical basis behind such devices had been known since the fifteenth century, when English and French mathematicians and philosophers started studying the properties of polyhedra and, consequently, created the basis for the study of the kinematics of a rigid body in space.

1.2

Theoretical Basis: From the Mozzi-Chasles’ Theorem to the “Screw” Theory

The theoretical origins of rigid body kinematics study are commonly referred to the studies of Giulio Mozzi and Michel Chasles. These two mathematicians created the funding theorem whose application would become of paramount importance in the development of hexapod devices. In 1763, Giulio Mozzi, an Italian astronomer and mathematician, became the first to describe the motion of rigid bodies (Fig. 1.1) [1]. Mozzi hypothesized that a rigid body firstly undergoes a rotation about an axis passing through the center of mass and then a translation of “X”

© Springer Nature Switzerland AG 2021 M. Massobrio, R. Mora (eds.), Hexapod External Fixator Systems, https://doi.org/10.1007/978-3-030-40667-7_1

1

P. Sessa et al.

2

1.3

Fig. 1.1  The original front page of Giulio Mozzi’s work on the theory of rigid body motion

displacement in an arbitrary direction. The Euler theorem on the existence of an axis of rotation for rigid bodies supports this hypothesis. The displacement “X” of the center of mass can be divided into vectors parallel to and perpendicular to the axis and acting on all points of the rigid body. According to Mozzi, for some points, the previous rotation acts with an opposite displacement leading to a parallel translation of these points to the axis of rotation. Such points lie on Mozzi’s axis through which the rigid motion can be accomplished through a screw motion. Similar conclusions were later obtained by Michel Chasles in 1830 [2] and Louis Poinsot in 1834 [3]. These theorems were fundamental to Sir Robert Ball’s “screw theory” [4], a systematic algebric and calculus method of the pairs of vectors (forces, moments, angular, and linear velocity) arising in rigid body kinematics and dynamics. This theory has become an important tool in robot mechanics [5, 6], in particular for parallel manipulators [7, 8].

The Hardware: The Beginning of Parallel Manipulators

The first attempts to create parallel manipulators dates back to the first decades of twenty-first century: the first prototypes, however, were not designed for academic research; as in most cases, they were meant to automate industrial production and were not based on mathematical calculus. Their importance lies in that they are the far ancestors of modern industrial robots and that they provided the technical basis for the development of more advanced systems such as modern hexapods. The cardan joint (developed by G.  Cardano in 1557) was an important component of such devices. The first patented parallel manipulator to be projected was an automated spray painter. It was created by Willard L.G. Pollard Jr. and patented in 1942 (Fig. 1.2) [9, 10]. This manipulator represents five degrees of freedom (DOF) three-­ branched parallel robot. The robot consisted of three proximal arms connected to a fixed base and pivoted by rotary motors and three distal arms connected to the three proximal arms via universal joints. Ball joints connected the distal arms to additional arms or tool heads. Three motors determined the position of the tool head, and its orientation was controlled by two other motors fixed at the base and transmitting the motion to the tool head via flexible rotary cables. The project was never realized by Pollard, although a similar parallel robot was created by Harold Roselund in 1944 for the DeVilbiss company [10]. The two previous projects highlight two important aspects to be later find in hexapods: –– The idea of a fixed base articulating with a distal mobile platform; –– The use of hinged joints for articulating parts of parallel manipulators. In 1949, V.E.  Gough came up with a new parallel manipulator: the variable length strut

1  History and Evolution of Hexapod External Fixators

3

Fig. 1.2  The project of the “position-controlling apparatus” patented in 1942 (US Patent No. 2,286,571) by W.L.V. Pollard

octahedral hexapod [11]. This device greatly changed industry and led to numerous replicas. It was meant to test tyres at the Dunlop Rubber Company industries in England, where Gough worked as an engineer, and was called the “Universal Tyre-Testing Machine” or “Universal Rig” (Fig.  1.3). This machine had to test tyres under different loads to simulate aero-landing loads. Surprisingly, the same Gough wrote in his papers that systems with six axis, i.e., hexapods, already existed, albeit the configuration of the six axis was different and made up of three horizontal and three vertical axis. These systems are known as MAST (Multi-Axis Simulator Table) and are still manufactured by many companies [10]. Gough needed to arrange the six axis in a octahedral hexapod configuration in

order to test different loads on different space planes. The calculations of loads acting on tyres at different configurations of the hexapod were done by hand and reported in tables in a predigital era. The success of the octahedral configuration for hexapods was based on its intrinsic stability and, consequently, it became the preferred configuration for several testing machines. Indeed, the less known American Engineer Klaus Cappel, in 1962, adopted this six-axis arrangement for the project of his motion simulator commissioned by the Franklin Institute Research Laboratories in Philadelphia [10, 12]. Klaus Cappel was asked to improve on an existing conventional 6-DOF vibration system based on a hexapod (the abovementioned MAST machines)

P. Sessa et al.

4

foundation work in theory and in actual applications. The octahedral configuration of six-axis manipulators (i.e., the hexapod) rapidly spread after Stewart’s publication, and, from 1970, it became the basic setting of parallel actuators. It is worth noting how the calculation of rigid body movements caused by the manipulators was manual and only gross movements were assessed.

1.4

Fig. 1.3 The “Universal Tyre-Testing Machine” or “Universal Rig” invented by V.E. Gough in 1949 to test tyres at the Dunlop Rubber Company industries in England

consisting of four actuators arranged in a cyclic pattern in order to reduce the required horizontal reaction masses. However the problem was the redundancy of the seven-strut configuration causing poor control and high antagonistic forces leading to the fracture of the base platform. Cappel solved the problem by adopting the octahedral configuration of the six struts as proposed by Gough. The p­ rototype (Fig.  1.4) was made and a patent request was filed in 1967 (US patent n° 3.295.224). In 1965, D.  Stewart published a paper on the Institution of Mechanical Engineering (English) describing the project of a flight simulator consisting of a six degrees of freedom motion platform with parallel manipulators [13]. The original project did not have an octahedral configuration of hexapods differently from Gough’s and Cappel’s machine (Fig. 1.5.). Since then, almost every type of parallel mechanisms has been commonly referred to as “Stewart platforms” even though Gough, Cappel, and many others had laid the

Hexapods in Medicine

The introduction of the hexapod in Orthopaedic surgery for the treatment of complex limb deformities is closely connected with the name of the American Surgeon J.  C. Taylor albeit independently the German Surgeons K.  Seide and D. Wolter also made and clinically applied their hexapod fixator. Although they were not the first to understand and apply the potential of hexapod frames to deformity correction, they certainly were, however, the first to use mathematics to solve the equations of six-axis bone correction devices and to use digital assistance for mathematical calculus thanks to the contemporary development of modern personal computers. Prior to the work of J.C. Taylor and Seide and Wolter, many surgeons had tried to overcome the limitations of conventional external fixation with the Ilizarov devices, i.e., the need for frequent frame configuration changes to obtain serial corrections of the deformity due to the impossibility of its correction in the different space planes. In Europe, the French aeronautic engineer Philippe Moniot in 1985 patented a six telescopic struts external fixator for surgical purposes (Fig.  1.6). As Moniot explained in his patent request [14], he started from the conventional external fixator of Ilizarov and, on this frame, he applied telescopic rods in order to obtain a controlled three-dimensional movement of two affronted bones. Perhaps, Moniot meant to create a simulator for bone displacement in order to facilitate the planning of deformity correction,

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Fig. 1.4  The construction phases of Cappel’s prototype of the “motion simulator” and the octahedral hexapod original project drawings presented in 1967 (US patent No. 3,295,224)

by calculating and observing in an “on-table” model the necessary adjustments to be done. The graduated rods were meant to visually quantify the necessary three-dimensional displacements (in degrees and mm) to obtain a correction being linked to two parallel rings with their center perpendicular to the long bone axis. Moreover,

Moniot was, probably, the first to clearly state that adjustment calculations of the telescopic rods could be performed with computer assistance, although in his opinion this was an “expensive” option. To the best of our knowledge, Moniot never built such device and no clinical applications were recorded.

6

Fig. 1.5.  Schematic drawing of the “Stewart platform” from the original article by Stewart et al. [13]

P. Sessa et al.

According to Paley [15] and Solomin [16], two further patented hexapod external fixators for bone deformity corrections were invented, by S.I. Pisler and Y.N. Kostin in 1989 and Shevtov et al. in the early 1990s. The two above-­mentioned devices had no mathematical support for the ­calculus of deformity correction due to the lack of a dedicated software and had a limited clinical use. Several attempts to improve on the existing external fixators were made in Italy, too. The need for stable configurations of the external fixators and for multidirectional corrections of deformities led Dr. Giulio Gentile, an Orthopaedic

Fig. 1.6  The hexapod external fixator designed by P. Moniot in 1985; the figure shows original drawings from the patent file

1  History and Evolution of Hexapod External Fixators

7

Fig. 1.7  The axial external fixator designed by Dr. Giulio Gentile. The picture shows the external fixator (left) and the pluri-directional correction of deformities the fixator could perform (right)

Fig. 1.8  Comparison between the oblique arrangement of the rods of a Monticelli-Spinelli (“MS”) circular external frame performed by Dr. Marco Massobrio in the late

80s (left) and the oblique arrangement of modern struts of the TSF hexapod external frame (right)

Surgeon from “Sapienza” University of Rome, to create an external fixator frame able to generate a concomitant pluri-directional correction of bone deformities in three dimensions (1978) (Fig. 1.7). In fact, up to now, this is the only example of a non-hexapod external fixator allowing for a ­controlled deformity correction in all the space planes. Since 1989, Dr. Marco Massobrio, an Orthopaedic Surgeon form the same Department of Orthopaedics and Traumatology, started using

an oblique arrangement of the rods connecting the rings of the circular external fixators available at that time (the Monticelli-Spinelli, “MS”, external ring fixator) in order to correct translations and rotations by using the spherical morphology of the rod to ring connection (Fig.  1.8). It was possible, however, to obtain an individual correction of the deformity in all space planes. The advent of personal computers as readily available home devices and the development of

P. Sessa et al.

8

the internet are the premise for the modern computer-­assisted hexapods. The software-based calculus for the resolution of Chasles’ equations for predicting rigid body kinematics in the space allowed for an easier and faster spread of six-axis hexapods for the correction of bone deformities. J.C.  Taylor with the help of his brother H.S.  Taylor, an engineer, designed a computer-­ assisted hexapod frame in which the problem of bone deformity correction was transformed into a geometrical problem. They created a six-axis device based on Gough’s platform and used Mozzi-Chasles’ theory on rigid body kinematics. Once the deformity geometry for each assessed case was known, they used a web-based software to solve the Chasles’ equation necessary to obtain the strut length changes to modify the hexapod frame, in order to correct the deformity itself. That is, geometric principles are applied to the initial and final position of the strut ends to calculate the final strut length. The device was named the “Taylor Spatial Frame” (“T.S.F.”) and patented in 1997 [17]. The first clinical application was in 1995. The device passed from a web-based program to a PC-based program in 2002. One characteristic of the “T.S.F.” is that the struts (i.e., telescopic rods) are anchored to the supports in a fixed position with no possibility of changing strut position on the support ring. Independently from JC Taylor, in 1996, K Seide and D Wolters built and patented in Hamburg (Germany) a hexapod named “Lithos” [18]. This device differed from that of Taylor’s in several aspects, although it was also a computer-­ based external fixator. The position of the telescopic rods on the rigid supports is flexible and struts can be positioned anywhere on the support; this is because the “Lithos” hexapod is made up of telescopic rods mounted on a classic Ilizarov external fixator. A different resolution modality of Mozzi-Chasles’ theorem was used, and the “Lithos” hexapod could account for a 0.1  mm adjustment of telescopic rods. A new computer-assisted hexapod device not based on the Gough-Stewart platform was patented by Leonid Solomin, Igor Utekhin, and Victor Vilensky in 2009. The device, named “S.U.V.”

after the three inventors, presented only three telescopic rod attached to the rigid supports in a nonobligated position on the support itself. The other three telescopic rods (i.e., struts) connected to support anchored telescopic rods. The final configuration is that of a triangle in both the supports and between the struts. To solve the equations, the software needs the input of the measure of the distance of the triangle sides created by telescopic rods attachments on the proximal and distal rigid supports and the length of each telescopic rod. Every kind of rigid support can be used for the “S.U.V.” struts [19]. Interestingly, the “S.U.V.” frame solves the problem of strut changes due to the achievement of maximal length by using a “reverse” modality that allows for further lengthening by reverting the screw direction. The possibility of a remote control on automated hexapods is the new frontier in the latest research in the computer-assisted external fixators, and new devices with these characteristics have recently been approved for use.

1.5

Biographic Notes

Giulio Giuseppe Mozzi (Florence, Italy, 23 February 1730–Florence, Italy, 16 April 1830) was an Italian politician, humanist, and poet. Born into an aristocratic family, he received a humanistic education. Versatile genius, he developed a particular interest in mathematics and attended the University of Pisa where Paolo Frisi, an eminent contemporary Italian mathematician, worked. In 1763, Giulio Giuseppe Mozzi wrote his most important work: “Discorso matematico sopra il rotamento momentaneo dei corpi (Naples, 1763).” Although not appreciated by Mozzi’s contemporaries, this work later became famous: according to Mozzi, rigid body instant movement can be considered as helicoidal due to a combination of translation and rotation along an axis he defined as a “spontaneous axis of rotation” and later named Mozzi’s axis. Gerolamo Cardano (Pavia, Italy, 24 September 1501–Rome, Italy, 21 September 1576) was an Italian medicine doctor,

1  History and Evolution of Hexapod External Fixators

9

mathematician, philosopher, and astronomer. Cardano is considered the main founder of the probability calculus theories, writing several works on ­binomial coefficients and developing the binomial calculus theory. Besides, Cardano improved the combination lock mechanism and invented the cardan suspension. Although the cardan joint was credited to be a Cardano’s invention due to its description in his work “De rerum varietate (1557),” it had been known since the third century B.C. and clearly described by Greek engineers such as Filone of Byzantium in his work “Belopoiika.” Michel Chasles (Épernon, France, 15 November 1793–Paris, France, 18 December 1880) was a French mathematician and scientist. Professor of Mathematics at the Sorbonne University in Paris from 1841, he was a member of the French Academy of Sciences (1851) and foreign member of the Royal Society (1854). He was awarded with the Copley medal in 1865 for his Academic works in projective geometry. In 1837, Chasles published his work: “Aperçu historique sur l’origine et le développement des méthodes en géométrie - Historical dissertation on the origin and development of methods in geometry” and in 1852, published the “Traité de géométrie supérieure - Essay on superior geometry” (1852). Michel Chasles formulated several theorems; one of the most famous being the theorem on rigid body kinematics, generically named Chasles’ theorem. The theorem confirms Mozzi’s previous work stating that the most general rigid body displacement can be produced by a translation along a line called screw axis followed (or preceded) by a rotation about an axis parallel to that line. Robert Stawell Ball (Dublin, Ireland, 1 July 1840–Cambridge, England, 25 November 1913) was an Irish mathematician and astronomer. In 1867, he became Professor of Applied Mathematics at the Royal College of Science in Dublin and in 1874, he was nominated Royal Astronomer of Ireland and Andrews Professor of Astronomy at the University of Dublin. In 1892, he was appointed Lowndean Professor of Astronomy and Geometry at Cambridge University. The main contribution of

Robert Stawell Ball to the science of kinematics was the “screw theory” described in the treatise “The theory of screws” (1876) that earned him the Cunningham Medal of the Royal Irish Academy in 1879. Louis Poinsot (Paris, France, 3 January 1777– Paris, France, 5 December 1859) was a French mathematician and physicist. He is considered the founder of geometrical mechanics and his greatest merit was to demonstrate that the systems of forces acting on the motion of a rigid body can be resolved into a single force and coupled by a graphical method. This was later known as Poinsot’s construction. Poinsot’s theories were published in several journals: “The general theory of equilibrium and of movements in systems” (1806) and “Theorie nouvelle de la rotation des corps- New theories on rigid bodies rotation” (1834). Leonhard Euler (Basel, Switzerland, 15 April 1717–St Petersburg, Russia, 18 September 1783) was a Swiss mathematician and physicist. Euler is considered the most eminent mathematician of the eighteenth century and the most prolific mathematician of all times, publishing 92 books on mathematics. Euler was Bernoulli’s most talented pupil. He spent his academic life between Saint Petersburg (1727– 1741; 1760–1787) and Berlin (1741–1760). “Introductio in analysin infinitorum” (1748) and “Institutiones calculus differentialis” (1755) are considered his masterpieces. Euler is also known for the “Euler’s formula,” a mathematical formula in complex analysis that establishes the fundamental relationship between the trigonometric functions and the complex exponential function (eix = cos x + i sin x).

References 1. Mozzi G.  Discorso matematico sopra il rotamento momentaneo dei corpi (in Italian). Napoli: Stamperia di Donato Campo; 1763. 2. Chasles M. Note sur les propriétés générales du système de deux corps semblables entr’eux. Bulletin des Sciences Mathématiques, Astronomiques, Physiques et Chemiques (in French). 1830;14:321–6.

10 3. Poinsot. Theorie Nouvelle de la Rotation des Corps. Paris: Bachelier; 1834. 4. Ball RS. The theory of screws: a study in the dynamics of a rigid body. Foster: Hodges; 1876. 5. Featherstone R. Robot dynamics algorithms. Boston: Kluwer Academic; 1987. isbn:978-0-89838-230-3. 6. Featherstone R.  Robot dynamics algorithms. New York: Springer; 2008. isbn:978-0-387-74315-8. 7. Selig JM.  Rational interpolation of rigid body motions. In: Advances in the theory of control, signals and systems with physical modeling, lecture notes in control and information sciences, vol. 407. New York: Springer; 2011. p. 213–24. 8. Kong X, Gosselin C.  Type synthesis of parallel mechanisms. New  York: Springer; 2007. isbn:978-3-540-71990-8. 9. Pollard WLG. Spray painting machine. US Patent No. 2,213,108; 26 Aug1940. 10. Bonev I. The true origins of parallel robots. www.parallemic.org. 11. Gough VE, Whitehall SG.  Universal Tyre test machine. In: Proceedings of the FISITA ninth international technical congress, May 1962. p. 117–37. 12. Cappel KL.  Motion simulator. US Patent No. 3,295,224, 3 Jan 1967.

P. Sessa et al. 13. Stewart D.  A platform with six degrees of freedom. In: Proceedings of the IMechE, Vol. 180, Pt. 1, No. 15, 1965–1966. p. 371–85 14. Moniot P.  Dispositif de positionnement tridimen sionel de deux piéces quelconques, en particulier de deux parties d’os, et permettant de modifier ledit positionnement. 1985. https://bases-­brevets.inpi.fr/ en/resultats-­de-­recherche-­simpleen/1535879200927/ result.html. 15. Paley D. History and science behind the six-axis correction external fixation devices in orthopedic surgery. Oper Tech Orthop. 2011;21:125–8. 16. Solomin LN. The basic principles of external skeletal fixation using the Ilizarov and other devices. 2nd ed. Milan: Springer; 2012. p. 1593. 17. Taylor JC. The Taylor Spatial Frame fixator. U.S. Pat. No. 5,702,389; 1995. 18. Seide K, Wolter D.  Universal 3-dimensional correction and reposition with the ring fixator using the hexapod configuration. Unfallchirurg. 1996;99(6):422–4. (German). 19. Solomin L, Vilensky V, Utekhin A.  Deformity сorrection and fracture treatment by software-based ortho-SUV frame: user manual. 2013. http://ortho-­ suv.org. Accessed 12 March 2013.

Part I Mathematical and Physical Principles

2

Mathematics of the Hexapod Giancarlo Ruocco and Alfonso Alessandro Tanga

Nomenclature B-frame  orthogonal reference system in the base bi the vector defining the coordinates of the lower anchor point of the leg ci  number of constraints that a joint imposes D interval of positional variables DoF degrees of freedom fi degrees of freedom of the joint i number of the leg (1, …, 6) j number of joints in a system J Jacobian matrix li the vector representing the ith leg mb the translation vector in M-Bar M mobility M-BAR  the segment that connects the two platforms’ center (O and O′ of the M and M′ frame) M′-frame  orthogonal reference system in the platform M-frame  orthogonal reference system in the base n number of connected rigid bodies in a system

G. Ruocco (*) · A. A. Tanga Department of Physics, “Sapienza” - University of Rome, Rome, Italy e-mail: [email protected]

qi the vector that connects the origin on the base to the end of the leg Pi end of the leg Pi the vector that represents the position of the end of the leg on the platform in the T-frame P RB rotational matrix T-frame  orthogonal reference system in the Platform

The hexapod can be described as two non-regular hexagons (Fig.  2.1), whose vertices are connected by six segments. The geometry of the hexapod can be schematized as a structure composed of three different parts. First, one fixed plate, referred to as the Base. Second, a moving plate, named the Platform, which can reach a great variety of positions and orientations, depending on the specific location of the vertices. Last, the six segments of variable length, denominated the Legs of the hexapod. From this point forward, we will consider the center of the Base as the origin of the reference framework, the B-frame with orthogonal axes x, y, and z. The Platform has its own orthogonal coordinates x′, y′, and z′, the T-frame. In addition, two other coordinate frames, the M-frame and the M′-frame are introduced (x″; y″; z″). The origin of M-frame is at O and the z″-axis is in the centerline of M-bar, namely the segment that connects the two

© Springer Nature Switzerland AG 2021 M. Massobrio, R. Mora (eds.), Hexapod External Fixator Systems, https://doi.org/10.1007/978-3-030-40667-7_2

13

G. Ruocco and A. A. Tanga

14 T-frame(–)

platforms’ centers. The M′-frame axes are the same of the M-frame but they are translated to Platform, so that its origin is O′. The M-frame and the M′-frame will be used for a practical example at the end of the chapter. The Platform here defined has six degrees of freedom. This means that it can reach any position with any orientation in the space. Therefore, it can be moved along the three linear axes x, y, and z (lateral, longitudinal, and vertical movements), and rotate around them (pitch, roll, and yaw). Obviously in the case of the hexapod this is not real, because of physics limitations, like the length of the legs that connect the two plates. Another limitation is that the two plates cannot be superimposed one on the other.

2.1

Vectors

The legs of the hexapod can be mathematically thought as vectors. The vectors are mathematical object that describe a quantity that can be well characterized by an intensity, a direction, and a verse. In this case, the intensity is the length the of the leg, the direction is given by the three rotation angles, and the verse is always positive, because it is always in the z  >  0 half-space. In Fig. 2.1, the vector that describes the i-th leg that connects the origin and the point Pi is qi. To obtain this vector, the position of the platform in the B-frame must be known. This information is inside the translation vector M-Bar (mb) that gives the positional linear displacement of the origin of the platform frame with respect to the Base reference framework. Another information needed is the position of the end of the leg on the platform in the T-frame, and this is the vector (pi). It must be multiplied by the rotational matrix PRB (described in the next paragraph) to obtain its coordinates in the B-frame. The sum of these two vectors gives the vector qi, which connects the end of the leg to the origin on the base qi = mb + P R B · pi

The vector representing the i-th leg is finally given by:

z"

M'-frame(---)

Platform

z'

x"

y'

x' O'

Pi

y"

M-bar (mb) li

qi z x" x

z"

O y"

y

Bi

bi

B-frame(–)

Base

M-frame(---)

Fig. 2.1  Illustration of the hexapod with the reference frame of the Base (x y, z) (B-frame), that is fixed, the Platform reference frame (x′, y′, z′) (T-frame), mobile relatively to the base. The frame rotated compared to the Base frame, the M-frame (x″, y″, z″), will be used in an example at the end of the chapter



li = mb + P R B · pi - bi

where bi is the vector defining the coordinates of the lower anchor point of the leg. These six equations (i = 1, …, 6) give the lengths of the six legs to achieve the desired position and attitude of the platform.

2.2

Rotational Matrix

A rotational matrix is a mathematical object that changes the coordinates of a point in a frame of reference to another. If the rotation is in 2D, then it will be a 2 × 2 matrix; if in 3D, a 3 × 3 matrix. A 2D rotation around the origin of the axes changes the coordinates of a point P in the plane, like shown in Fig. 2.2, where there is a rotation of an angle ψ. where

P = i ¢x ¢ + j ¢y¢ = ix + jy x = OA - BC = x ¢ cosy - y¢ siny

2  Mathematics of the Hexapod

15

y



P y'

x' ψ C

éxù é x ¢ù ê y ú = R y ê y¢ú z ( )ê ú ê ú êë z úû êë z ¢ úû

A

x

Fig. 2.2  Geometric derivation of the coordinates after rotating the axes by an angle ψ

y = AB + PC = x ¢ siny + y¢ cosy



where the rotation ψ can be thought around the z-axis. The rotation matrix Rz(ψ) is then defined as:

B

ψ O

P = i ¢x ¢ + j ¢y¢ + k ¢z ¢ = ix + jy + kz



æ cosy ç R z (y ) = ç siny ç 0 è



æ cosy R (y ) = ç è siny



- siny ö ÷ cosy ø

This 2D case can be expanded to the 3D case by adding the variable z, and so two further rotations. The coordinates of point P can now be written as:

p



æ cosy cos q ç R B = ç siny cos q ç - sin q è

2.3

æ cos q ç R y (q ) = ç 0 ç - sin q è





0

To define the degrees of freedom, or mobility, of the hexapod, it is schematized as a kinematic chain. It is a mathematical model for an assembly of rigid bodies used to find the number of parameters that define the configuration of the chain. A



0 æ1 ç R x (f ) = ç 0 cos f ç 0 sin f è

0 sin q ö ÷ 1 0 ÷ 0 cos q ÷ø 0 ö ÷ - sin f ÷ cos f ÷ø

The full rotation matrix of the Platform relative to the Base is then given by the vector product of the three rotational matrices:

P



R B = R x (f ) ´ R y (q ) ´ R z (y )

- siny cos f + cosy sin q sin f siny sin f + cosy sin q cos f ö ÷ cosy cos f + siny sin q sin f - cosy sin f + siny sin q cos f ÷ ÷ cos q sin f cos q cos f ø

Six Degrees of Freedom

0ö ÷ 0÷ 1 ÷ø

The same result can be obtained for the other rotation around the x- and y-axis of an angle θ and φ, respectively.

The rotation matrix R(ψ) is then defined as: é x ¢ù éxù ê y ú = R (y ) ê y¢ ú ë û ë û

- siny cosy





single object in the space, if it is completely free to move, has six degrees of freedom, three translational, and three rotational, so it means that it can reach any position with any orientation in space, as shown in Fig. 2.3. When it is considered a system of n connected rigid bodies, it has M = 6n degrees of freedom,

G. Ruocco and A. A. Tanga

16 Up

Leg length Yaw

Roll

Piston rod

Back

Left

Rod seals

Piston and seals

Fig. 2.4  Linear hydraulic actuators offer two DoF: one translation and one rotation

Yaw Forward

Roll

Right Pitch

Pitch

Down

Fig. 2.3  The six degrees of freedom: forward/back, up/ down, left/right, yaw, pitch, roll

but it has also constraints due to the links that connect these bodies, which decrease the degrees of freedom of the system. The whole structure must be considered as another body of the system, in order to be independent by its position in the fixed frame. This means that N = n + 1 is the number of rigid bodies in the system. The number of constraints ci that a joint imposes in terms of the joint’s degrees of freedom is ci  =  6  −  fi, where fi is the degrees of freedom of the joint. The resulting mobility given by these two components, the n rigid bodies and the j joints, is:



j

j

i =1

i =1

M = 6 n - å ( 6 - fi ) = 6 ( N - 1 - j ) + å fi



In the hexapod case, where the Base is fixed and is not counted among the moving bodies, n = 13, namely the platform and the two ends that compose each of the six legs. In fact, every leg has to be considered as two structures that slide one inside the other, in order to modify the length of the leg itself. The joint between the two parts, a linear hydraulic actuator shown in Fig. 2.4, has only two degrees of freedom, the translational

Fig. 2.5  Universal Joints offer two rotational DoF

one along the direction of the leg and the rotational one around that axis. Thus, for the joints between the two ends of the legs, fi = 2. The joints that connect the legs to the base and the platform are universal joints, shown in Fig. 2.5, that have two rotational degrees of freedom and no translational. The rotational degrees of freedom of the universal joint are ­complementary to the one of the actuator of the connected leg. Also, in this case, the fi = 2. So fi = 2 for all the j joints, where j = 18, given the three joints (the linear actuator and the two universal joints) for all six legs. Using these values in the previous equation, the mobility of the hexapod M = 6.

2.4

Solution of the Forward Kinematics

To find the poses of the moving platform for a given set of leg lengths, the forward kinematics of the Stewart-Gough platform is used. It is the use of the kinematic equations of a machine composed of a chain of components to compute the position of the end-effector from specified values for the joint parameters. In the case of the general

2  Mathematics of the Hexapod

17

Stewart-Gough platform, the formulation of necessary kinematic conditions generates a set of nonlinear equations that has 40 solutions in the complex domain. Numerical iterative schemes with relevant initial estimates are applicable to this problem, but they do not guarantee the convergence to the actual solution of the current pose. Another approach is to find all the possible configurations of the moving platform and then to select the actual solution out of them by proper criteria, such as the current assembly mode or the pose of the latest sampling time. As a method to obtain all the solutions of a nonlinear system, algebraic elimination method is a useful tool. It usually changes the initial set of equations into a univariate polynomial equation that can be readily solved by various efficient and available numerical algorithms. Since the existence of 40 configurations of the general Stewart-Gough platform had been first demonstrated numerically by Raghavan [1], many researchers have applied elimination method to find all the solutions of the problem. An example of a possible numerical solution through a minimization will be shown.

2.4.1 Practical Example



(

)

2

= li2 ( i = 1,¼,6 )

é pù é pù a1 Î ê0, ú , a 2 Î [ 0,2p ] , a 3 Î ê0, ú , ë 4û ë 4û é p pù a 4 Î [ 0,2p ] , a 5 Î ê - , ú , mb Î [1.5a,2 a ] ë 6 6û



0.7a £ li £ 3a

( i = 1,2,¼,6 )

where a is an arbitrary length. The radii of the two platforms are a and t = 0.7a, respectively, and the coordinates of the joints are equidistant in pairs on the same platform and rotated of π/6 between one platform and another (classical configuration).



In this example [2], we define a set of six variables and define their correlation with the length of the six legs (l1, …, l6). The set of new variables [1] (α1, α2, α3, α4, α5, mb) is used as positional variables to express the position and orientation of the mobile platform relative to the base platform. mb is the already defined length of the M-bar (shown in Fig.  2.1); (α1, α2) denote the transformation angles (θ, ψ) from B-frame (x; y; z) to M-frame (x″; y″; z″); (α3, α4, α5) denote the transformation angles (θ, ψ, φ) from M′-frame to T-frame, where M′-frame is translated from M-frame by moving the origin of M-frame to the origin of T-frame. The positional variables of the mobile platform may be calculated by solving the following equation: Rbm wT + Rmt ti - bi

where w = (0, 0, mb), Rbm = R(α1, α2, 0), Rmt = R(α3, α4, α5), bi  =  (bi1, bi2, bi3)T, and ti  =  (ti1, ti2, ti3)T denote coordinates of the joints of the ith leg on the base and on the mobile platform, respectively, (i  =  1, 2, …, 6). The requirement is that the mobile platform can make turning in any direction, but the degree of turning is not more than π/2 during one step of movement. So, the geometric parameters of the Stewart platform in this study are as follows:

p p ö æ b1 = ( a,0,0 ) ; b2 = ç a cos ,a sin ,0 ÷ 6 6 ø è



4p 4p ö æ b3 = ç a cos ,B sin ,0 ; 6 6 ÷ø è 5p 5p ö æ b4 = ç a cos ,a sin ,0 6 6 ÷ø è



8p 8p ö æ b5 = ç a cos ,B sin ,0 ; 6 6 ÷ø è 9p 9p ö æ b6 = ç a cos ,a sin ,0 6 6 ÷ø è



11p 11p ö æ t1 = ç t cos ,70 sin ,0 ÷ ; 6 6 è ø 2p 2p ö æ t2 = ç t cos ,70 sin ,0 6 6 ÷ø è





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3p 3p ö æ t3 = ç t cos ,70 sin ,0 ; 6 6 ÷ø è 6p 6p ö æ t 4 = ç t cos ,70 sin ,0 6 6 ÷ø è



7p 7p ö æ t5 = ç t cos ,70 sin ,0 ; 6 6 ÷ø è 10p 10p ö æ t6 = ç t cos ,70 sin ,0 ÷ 6 6 è ø

One of the limitations of Stewart platform is that they may lead to singular configurations in which the stiffness of mechanism is lost. We now introduce the Jacobian matrix J that defines the relationship between the velocity of links in joint space and the velocity of moving platform in workspace and may be determined by differentiating the equation previously defined with respect to time, that is:



é ¶l1 / ¶a1 ê¶l / ¶a 1 J=ê 2 ê M ê ë¶l6 / ¶a1

¶l1 / ¶a 2 ¶l2 / ¶a 2 M ¶l6 / ¶a 2

L ¶l1 / ¶mb ù L ¶l2 / ¶mb úú ú O M ú L ¶l6 / ¶mb û

Singularity occurs when the Jacobian matrix J of Stewart platform is singular, i.e., when det(J) = 0. The purpose of this singularity analysis is to confirm whether any singular points are

included in a particular interval (D) of positional variables. So, the singularity may be analyzed by minimizing the objective function f(x), which is defined as follows:

min f ( x ) = det ( J × J ¢ ) xÎD



where x = [α1, α2, …, lm] and ì ü é pù ïï x | a1 , a 3 Î ê0, 4 ú ; a 2 a 4 ïï ë û D=í ý ïÎ [ 0, 2p ]; a Î é - p , p ù ; mb Î [1.5 a, 2 a ]ï 5 ê 6 6ú ïî ïþ ë û If the solution of minimization problem is zero, there is at least one singular point, otherwise, the Stewart platform used in this chapter is singularity-free in range D of positional variables. In the range D here defined, it has been calculated that the Stewart platform is singularity-free.

References 1. Raghavan M.  The Stewart platform of general geometry has 40 configurations. J Mech Des. 1993;115(2):277–2822. 2. Wang, et al. Forward kinematics analysis of a six-DOF Stewart platform using PCA and NM algorithm. Ind Robot. 2009;36(5):448–60.

3

Characteristics and Usage Modalities. Main Systems Marco Massobrio, Pasquale Sessa, Giovanni Pellicanò, and Pasquale Farsetti

Nomenclature CAOS computer-assisted orthopaedic surgery CORA center of rotation of angulation SUV Solomin Utekhin Vilensky

3.1

Introduction

The hexapod fixator is an external fixation device consisting of two rings, “fixed” and “mobile”, connected to each other by means of six telescopic rods. Such telescopic rods are arranged in a parallel configuration and are called “struts” and through an internal mechanism, struts can modify their length and, consequently, can change the position of the “mobile” ring (and of the bone segment connected to the ring itself) in the different space planes respect to the “fixed” ring (reference ring) and to the reference bone

M. Massobrio (*) · P. Sessa · G. Pellicanò Department of Orthopaedics and Traumatology, “Sapienza” - University of Rome, Rome, Italy e-mail: [email protected] P. Farsetti Department of Orthopaedics and Traumatology A“Tor Vergata”, University of Rome, Rome, Italy

segment (“nonmobile” segment). Hexapod external fixators have six degrees of freedom, i.e., they can modify the position of a rigid body in the space on six axis (three rotational axes and three translational axes). The six-axis (hexapod) configuration guarantees a high intrinsic stability and a peculiar resistance to the mechanical stresses applied to the rigid system by the external forces. A dedicated software is available for each hexapod external fixator, allowing the simultaneous correction of the deformity in the different space planes by realizing a correction plan with an “acute” or “gradual” correction modality. Such corrections should consider variables related both to the hexapod frame configuration and the deformity parameters (i.e., degree of angular deviation from reference axes, shortening). The computer devises a program with a series of consecutive changes in the length of each telescopic rod so allowing for the simultaneous and progressive correction in the different space planes. This configures the computer-­ assisted hexapod external fixator (computer-­ assisted orthopaedic surgery—CAOS). The hexapod external fixator is actually a powerful correction tool for the complex limb deformities (multiaxial deformity) and it can be used for the treatment of both primary (congenital or developmental deformities) and secondary (post-traumatic) complex limb deformities [1–6].

© Springer Nature Switzerland AG 2021 M. Massobrio, R. Mora (eds.), Hexapod External Fixator Systems, https://doi.org/10.1007/978-3-030-40667-7_3

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Moreover, hexapod fixators overcome the “classic” limitations of standard external fixator systems (i.e., the Ilizarov external fixator) such as the need for frequent frame configuration changes and enhance the theoretical precision of deformity correction [7].

3.2

Theoretical Basis

Hexapod systems are based on the application of Chasles’ theorem and refer to the laws of the kinematic of a rigid body. Chasles’ theorem postulates a nondeformable (i.e., rigid) body could change its shape only due to rotation or translation [8]. In a rigid body where the distance between the particles of the body is constant, the most common act of motion consists of a rotation and of a translation, that is, a rototranslation. The position of a rigid body has two components, linear and angular (also known as orientation). The linear position can be represented by a vector with its tail at an arbitrary reference point in space (the origin of a chosen coordinate system) and its tip at an arbitrary point of interest on the rigid body, typically coinciding with its center of mass or “centroid.” This reference point may define the origin of a coordinate system fixed to the body. The orientation of the rigid body can be described both by the three Euler angles or by a rotation matrix, and define the orientation of a basis set (or coordinate system) which has a fixed orientation relative to the body (i.e., rotates together with the body), relative to another basis set (or coordinate system), from which the motion of the rigid body is observed. The appropriate combination of the rotation matrix along the reference axes for understanding the final position of a rigid body when a rotation occurs. The translation of the “centroid” of the rigid body can be divided into perpendicular and parallel components passing through the center of mass. Such components act on all the points of a rigid body, but for some points of rotation it acts in the opposite way, that is, a contrary dislocation occurs. Such points are translated parallel to the

rotation axis and lie on the Mozzi axis along which the motion of the rigid body has an helicoidal pattern. A solid consisting of eight plane faces is defined octahedron. Each face has a triangular shape. The hexapod external fixator frame consists of an octahedron whose two triangular opposed faces have no modifiable sides (Fig. 3.1), while, instead, the remaining six triangular faces and the respective angles can be modified. The six telescopic rods (struts) realize the sides of each triangle, with an adjustable length, and they are joined by cardan joints to the two nonadjacent, nonmodifiable, and opposite triangles. The sum of a triangle’s interior angle is 180°. Changes in the values of a single angle modify the remaining interior angles and the length of the two adjacent sides. Assuming that the two parallel and opposite triangular faces of the octahedron are fixed, i.e., no changes in the interior angle or side values occur, then a hexapod frame is obtained. Actually, this frame applies Mozzi-­ Chasles’ theorem where a rigid body deformation can be possible only by rotation or translation movements. According to what was reported in Chap. 2, it has to be considered that the actual

Fig. 3.1  The figure shows the two triangles in the opposite surfaces of the hexapod external fixator

3  Characteristics and Usage Modalities. Main Systems

21

translation of a rigid body (the bone) caused by the hexapod frame does not exactly coincident with that planned in the preoperative setting but has to be adjusted by a constant correction (usually performed by the software itself). The application of Chasles’ theorem is possible through the hexapod systems where adjacent triangular faces consisting of rigid rods connected to mobile strut joints can modify their length and thus change their angles. The fundamental criterion is that the connection points of the rods on the platform are able to rotate along their own axis. The two fixed nonmodifiable triangles create two opposite platforms that undergo modifications in their spatial position caused by the length and angular changes of one or several struts. Due to the intrinsic rigidity of the system, strut length and angular variations are fully transmitted by the strut joints to the platform, causing a change in its position into the space. The system creates a closed kinetic chain where changes in the length of one or more struts cause the spatial relocation of the plane passing through the two opposite surfaces, i.e., the platforms of the hexapod system. This system allows for movements of the platform, consisting of a ring, for all the spatial planes, by changing the strut length. We define a ring as the “static,” basic support, and the other opposite ring as the “mobile support.” Bone segments anchored to the abovementioned rings are defined as a “basic bone segment” and “mobile bone segment,” respectively. Therefore whatever point of the platform surface, that is the hexapod ring, can be aligned with a corresponding point on the opposite surface. Consequently, it is possible to align a straight line passing through a selected point on the plane (platform) and perpendicular to it, with a point and a line passing through the opposite plane (platform) of the hexapod system. The motion generated on the opposite platforms occurs at the strut insertion. The lengthening or shortening of the struts allows for the motion of one of the two platforms (the mobile ring), so that the selected point and the axis passing through it coincide.

The characteristics of the hexapod systems are the rigidity of the frame and the possibility to adjust strut length with a micrometric system. Starting from the input data, the software calculates the necessary adjustments to the triangles’ sides to align the selected points on the opposite platforms. The hardware transmits the adjustments calculated by the software to both struts and rings and, consequently, to the bone through wires and screws, without loss of correction. The bending of the frame or of the units of connection with the bone reduces the precision of the alignment due to a defect in the transmission of the guided motion from the external fixator to the bone segment.

3.3

Properties of Hexapod Systems in Orthopaedics

Hexapod systems allow for a gradual correction of the deformity with no need for an anesthesia due to the highly stable and controlled motion generated by the hexapod system. They act simultaneously on all the axes and allow for the onset of a bone regenerate together with deformity correction without injury to the regenerate itself. The concomitant action in all the space plane reduces the correction time, and the bone regenerate appears simultaneously to the correction. On the contrary, the correction of a deformity after the onset of the bone regenerate causes a damage to it that is inversely proportional to the length and more severe when the correction of a rotational deformity is desired. The software is able to calculate the detailed program necessary for the correction of the deformity in all the space planes and to display the amount of the daily adjustments of the struts required to correct the assessed deformity according to the planned time of correction. Therefore, it is possible to add a time parameter, the time necessary to end the planned correction, to the geometrical parameters of the deformity according to the deformity characteristics themselves and the selected correction parameters.

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3.4

Octopods

External fixators consisting of eight struts (octopods) are a further development of the hexapod external fixator system. The increase in the number of the struts for having four vertical struts perpendicular to the platform and four oblique struts that join the vertical struts at their e­ xtremity. The vertical strut pair define four correction planes for the reference ring. Only for vertical struts, can the space plane be easisly identified where the bone deformity correction should be performed without the aid of software. As well, rotational and translational deformity correction could be performed without software calculations. However the external fixation system, can be managed by using the dedicated software when data on both the deformity to be corrected and the external fixator are acquired and correctly inserted in the software. It should be noted that only with software assistance, can a simultaneous correction of the deformity in all the space planes be obtained. A non-software-based correction by the hexapod

a

external fixator allows for the deformity correction (distraction, translation, compression) in a single space plane per time, and could be considered a disadvantage or not according to the applied clinical criteria. When a sequential spatial correction is performed by the external fixator, less precision in the distraction effect and a higher traumatism on the bone regenerate are expected.

3.5

The Hardware

Hexapod external fixation systems could be considered as circular external fixation systems. However, such systems differ from the circular ones due to: –– The need for a structural rigidity in all the elements of the frame with the removal of only one strut causing a collapse in the hexapod system (Fig. 3.2); –– Geometrical arrangement of the struts; –– The presence of a “virtual hinge”;

b

Fig. 3.2 (a) The tightened strut–hexapod connection guarantees the rigidity of the system; (b) The removal of only one strut causes the collapse of the hexapod system due to the loss of the rigidity of the system

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–– The simultaneous correction of the deformity in the three different space planes (space parameter/criteria); –– Time-dependent deformity correction (temporal parameter/criteria); –– The need for a software to plan the deformity correction according to the input data on bone segment and frame (external fixator, i.e., the frame).

–– “Total residual” or “deformity correction”: The bone deformity correction is planned with the support of the software according to the input data of the bone deformity parameters and the mounting frame parameters. An X-ray examination of the bone-frame complex is performed in two views. –– “Recalculate”: Starting from the last frame configuration representing the end of the planned correction, residual deformities can be addressed by recalculating both the actual deformity and the mounting parameters and selecting the needed correction adjustments. The software will recalculate a new correction plan.

3.5.1 Operative Instructions Several applications of hexapod external fixators are described when addressing bone deformity. Although named differently, they can be summarized into three main applications: –– “Acute”: The correction modality with fluoroscopic assistance where the deformity is corrected in one-step, with, the surgeon manipulating the hexapod fixator connected to the bone segments with non fixed struts until a satisfactory deformity correction is obtained.

a

b

Fig. 3.3 (a–c) Different types of support platforms

3.5.2 Hexapod Frame Components 3.5.2.1 The Platform The platform is what the rigid support telescopic threaded rods (“struts”) hold on to (Fig.  3.3). Platforms are defined proximal or distal and basic or mobile, according to the reference bone segment. They can be full rings, three quarter rings, c

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a

b

Fig. 3.4  Different types of hexapod frame construct: (a) proximal three quarter ring with posterior opening allowing knee flexion; (b) dedicated foot platform (“U” ring)

to the type of support ring used or according to the input data. In hexapod systems where all kinds of supports can be used  (SUV) with no need for a specific ring, struts can connect to the support platform everywhere, with no site restrictions. Consequently, in this scenario, it is necessary to input data regarding the distance of the strut connection point on the platform, both proximally and distally obtained by manual measurements.

Fig. 3.5  The figure shows the intercalary distance, i.e., the distance between the two support rings of the hexapod frame

or plate foots of different size. Rings possess one, or two, pierced concentric lines to allow for strut connection (Fig. 3.4). Intercalary ring distance is the distance between the two rings measured along the longitudinal axis (Fig. 3.5). The increase in the intercalary distance between the two rings (or platforms) enhances the potential for deformity correction but, at the same time, reduces the patient’s tolerance according to the patient’s anatomical characteristics [10]. Several hexapod external fixators offer a default position for the strut connection to the support rings. The software, consequently, identifies the strut/platform connection point according

3.5.2.2 The Struts The strut is the mobile and adjustable element of the system (Fig. 3.6). It can either consist of one threaded rod linked to mobile joints and adjusted by blocking nuts or made up of coaxial telescopic rods forming the real strut and cardan joints at each extremity. The strut length can be read on a graduated scale applied on the strut itself, otherwise, the strut length can be directly measured by a meter applied between the two strut connection points on the supporting platforms. Strut length parameters must be inserted in the software. Struts are always arranged counterclockwise for the support platform and numbered from 1 to 6 and marked with different colors. In the SUV hexapod, struts are joined in pairs (“near the top”) before being connected to the support platform (ring). Three connection points are present on each platform (three proximal + three distal). Struts linked to the proximal support platform are numbered 1,3,5 while struts linked

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Fig. 3.7  The figure shows the reduced “strut to platform” angle (i.e., strut slope). The decrease of the strut slope  0; the magnetic moment M induced by the presence of an external field B is parallel and concordant with B and is substantially due to the orientation of the magnetic moments proper to the atoms or molecules of the material. The magnetic susceptibility of paramagnetic materials varies with the temperature according to the Curie law [2]: Cr T where T is the temperature (measured in kelvins), ρ the density of the material, and C is a characteristic constant of the material. As the temperature drops, the magnetic susceptibility of paramagnetic materials increases rapidly.

cm =

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However, under standard conditions (room temperature), the observation (already made for diamagnetic materials) generally valid is that paramagnetic materials usually perturb the magnetic field configuration to a negligible extent. Substances with paramagnetic properties include aluminum, oxygen, titanium, iron oxide (FeO), calcium, and tungsten. Ferromagnetic materials. The ferromagnetism is the property of the ferromagnetic materials to magnetize very intensively under the action of an external magnetic field and to remain magnetized for a long time when the field is annulled, thus becoming magnets. This property remains only below a certain temperature called Curie temperature (Tc), above which the material behaves like a paramagnetic material. For iron, for example, this temperature is about 770  °C.  The susceptibility can be expressed as a function of temperature according to the Curie-Weiss law [2]:

cm =

Cr T - Tc

In ferromagnetic materials, the relative magnetic permeability of the material is not constant as the fields change, as instead occurs in diamagnetic materials and paramagnetic materials; the relationship between the magnetic induction field and the magnetic field is therefore not linear, nor even unique. The method of finding the relationships between these vectors is a graphical method, and the law followed by the course of the magnetic field follows the hysteresis cycle (Fig. 4.4). Ferromagnetic materials include magnetite, iron, cobalt, nickel, numerous transition metals, and their respective alloys. In Table  4.1 are shown some materials and their magnetic properties.

M Mmax Mr – Hmax

– Hc O

Hmax

H

Fig. 4.4  Hysteresis cycle: magnetization field M of a ferromagnetic material as the magnetic field H is first increased, starting from M = 0, then decreased and finally increased again. The curves form a hysteresis loop Table 4.1  Magnetic properties of some materials Material Ag H2O C (graphite) H2 Al Cr O2 Ti Fe Carbon steel Ni Co

Magnetism Diamagnetic Diamagnetic Diamagnetic Diamagnetic Paramagnetic Paramagnetic Paramagnetic Paramagnetic Ferromagnetic Ferromagnetic Ferromagnetic Ferromagnetic

χm −26.4·10−6 −8.0·10−6 −99·10−6 −2.1·10−9 22·10−6 312·10−6 1.9·10−6 153·10−6 150–5000 50–100 100–600 70–250

Tc 770 °C 724 °C 347 °C 1117 °C

References 1. Mencuccini C, Silvestrini V.  Fisica: Meccanica e Termodinamica. Bologna: Zanichelli. 2016. ISBN: 9788808186492. 2. Mencuccini C, Silvestrini V. Fisica: Elettromagnetismo ed Ottica. Bologna: Zanichelli. 2017. ISBN: 9788808186614.

Part II Clinical Applications of Hexapod External Fixator

5

Hexapod External Fixation for Fractures and Nonunions Gerard A. Sheridan, Austin T. Fragomen, and S. Robert Rozbruch

Nomenclature HA hydroxyapatite IM intramedullary N/mm Newton/millimeter, unit of measurement of rigidity TSF Taylor Spatial Frame

5.1

Introduction

Since its introduction in the orthopaedic practice for the treatment of fracture, nonunions and deformity correction [1–3], the external fixator revealed to be an efficient and safe surgical device. However, a steep learning curve was required, especially in the surgery of deformity correction where frequent frame changes and complex mounting rules were required [3]. In response to the need for more pragmatic technology in this field, the Taylor brothers designed their computer-aided circular frame in 1994: The Taylor Spatial Frame (Smith & Nephew, Memphis, TN) (Fig. 5.1) [4].

Fig. 5.1  TSF clinical photograph

5.1.1 Design and Technology G. A. Sheridan (*) · A. T. Fragomen · S. R. Rozbruch Limb Lengthening and Complex Reconstruction Service, Hospital for Special Surgery, New York, NY, USA e-mail: [email protected]

The hexapod frame consists of six telescopic struts connected to two full or partial rings via ball joints. The premise of this technology relies on projective geometry where adjustment of a single strut length will have an effect on the

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position of the two rings in space [4]. As the external fixator is manipulated in space, so too can fracture fragments or osteotomy sites be manipulated in relation to each other. An internet-based software program for the hexapod can be used to correct along six axes simultaneously (sagittal angulation and translation, coronal angulation and translation, and axial shortening and rotation). The TSF is based on the GoughStewart platform technology [5] and on the mathematical model proposed by Seide et al. for the description of three-dimensional movements [6]. However, with new technology comes an increasingly complex set of technical skills that must be accessible to the operating surgeon. The TSF is only one of many hexapod models available and it is known that variation exists between these specific models regarding radiographic analysis and other practical elements [7]. The surgeon must therefore be very familiar with the specific hexapod model they are using as fundamental software differences do exist and these must be appreciated before use of these systems. The hexapod rationale is not completely dependent on computer though. Techniques have been described where fracture reduction and frame manipulation may be performed intraoperatively without the need for any software input. Heidari et  al. report on a technique whereby meticulous strut adjustment in a specific sequence, dependent on the outcome desired, may allow for correction through lengthening, shortening, angulation, rotation and translation without the input of any computer-based system [8].

5.1.2 Biomechanics and Application Regarding the role of the Taylor Spatial frame in modern orthopaedic reconstructive surgery, it was clear that osteotomy surgery for the correction of multiplanar congenital and post-traumatic deformities could now be considered as a fluid, one-step process. Its role in fracture care however was less well defined. The Ilizarov circular fixator requires surgeons to closely follow a prescription for mounting a stable frame, adhering to recommendations for the number of rings, fixation elements per ring and the number of connec-

tions among other stringent criteria. With the implementation of the TSF consisting of 12 wobbling universal hinges and larger rings, the biomechanics at the fracture site had now completely changed. The TSF required the rings to be spaced further apart and discouraged the use of fixation across the fracture site. Oblique fractures raised the question of how the TSF would perform without axial compression. The Ilizarov apparatus had proven to be very effective at healing fracture nonunions [9], but it was not clear if the TSF would be able to match the former’s perfect combination of stability with axial flexibility. Furthermore, the hexapod would also need to outperform the classic Ilizarov in order to justify its increased cost. Henderson et al. set out to describe the difference between the TSF and Ilizarov circular frame from a biomechanical perspective using an acrylic pipe fracture model [10]. When comparing a four-ring TSF with an Ilizarov frame, it was found that the TSF had lower axial rigidity than the Ilizarov frame (645 ± 57 versus 1269 ± 256 N/ mm). However, the TSF was deemed to be superior to the Ilizarov frame under bending loads (42  ±  9  Nm/degree) and torsional loads (16  ±  2  Nm/degree) [10]. Other sources have claimed equivocal axial rigidity outcomes between hexapod and Ilizarov frames with a superior TSF performance under torsional and translational forces [11]. After years of use, it is clear that the hexapod and Ilizarov frames accomplish the same goals, and the decision to use one over the other is now primarily based on availability and surgeon comfort and familiarity. Even when focussing on practical applications of the TSF such as high energy fracture management, the TSF construct has been shown to equal Ilizarov frame outcomes [12]. This chapter will focus on two elements of orthopaedic pathology commonly managed with the hexapod frame: acute fractures and nonunion care.

5.2

Acute Fractures

Fractures are classically managed using an array of surgical options: closed reduction and stabilisation in cast, open reduction and internal

5  Hexapod External Fixation for Fractures and Nonunions

fixation, monolateral external fixation and also circular frames. Circular frames can be used for definitive fracture treatment offering several advantages over linear frames and internal fixation [13, 14]. They have been invaluable in the management of tibial fractures with significant soft-tissue compromise, severe open injuries, bone loss and deformity. Union rates of up to 91% have been reported with this method. Functional outcomes based on the Association for the Study and Application of the Method of Ilizarov criteria confirm that up to 74% of patients report an “excellent” outcome with the TSF and up to 88% of patients treated with this mode will return to their preinjury work activities [15]. The preferred method for frame application in a fracture setting is surgeon dependent, but certain principles should be followed. The key to successful external fixation is frame stability. This starts with fixation to the bone. The pins should be predrilled to prevent damage to the bone during insertion. Hydroxyapatite (HA)coated pins have been shown to provide many advantages over non-coated pins with respect to initial fixation, infection prevention and loosening [16, 17] (Fig. 5.2). Based on histological and biomechanical analyses, Moroni et  al. demonstrated that the presence of a HA-coating was even more important for optimal pin fixation than the combination of design parameters used in each pin type [18]. Wires are tensioned to 130 kg

45

except in certain situations including drop wires and open rings. Much of the data available for circular frame biomechanics was performed with Ilizarov stainless steel rings and not with the larger aluminium hexapod rings which are fundamentally different. We recommend to err on the side of increased stability. Large segments are best fixated with two rings, and small segments need 4–5 points of fixation off of one ring [19]. Soft-tissue safe corridors need to be followed at all times, and fixation should avoid hematoma and fracture sites. The universal joints at either end of the hexapod struts are very different from the connection elements in the classic Ilizarov frame and have generated much attention. Many surgeons feel that this increased motion may suppress bone healing. Others feel it may enhance endochondral ossification. The concept of reverse dynamization (increasing frame stability as the fracture heals commonly called “locking the frame down”) has been practiced for some time and has recently been studied more formally [20]. Allowing less stability initially drives early callus formation. This callus then leads to a subsequent rigidity which allows for improved consolidation [21]. Newer strut designs have reduced the wobble at the ring connection as well, changing the biomechanical environment yet again. Placing pins and wires away from the zone of injury naturally helps to prevent deep infection and preserve the soft-tissue envelope from further surgical trauma that would be required for plate or intramedullary (IM) nail insertion. Determining which open fractures require circular fixation and which can be safely treated with internal fixation is the subject of some debate and the impetus for the FIXIT study [22]. This trial is still ongoing and will report on 1 year outcomes for severe open tibial fractures treated in modern external fixators versus internal fixation. Those that could have undergone internal fixation would have to suffer the drawbacks of external fixator treatment including prolonged discomfort, pin infections and the awkwardness of frame life [23]. Fig. 5.2  Tapered 5–6 mm stainless-steel hydroxyapatite-­ There are many considerations regarding the coated pin. (Orthofix Medical Inc., Lewisville, Texas, specific clinical presentations that may be USA)

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encountered. Fractures with bone defects may benefit from early circular fixation in preparation for bone transport. Fractures that have very small metaphyseal segments are ideally suited for fine-­ wire fixation. Osteopaenic bone can be securely stabilised with the multiplanar, fixed-angle fixation afforded by circular frames. A subset of tibial plateau fractures with missed compartment syndrome of the leg are excellent cases for external fixation where the surgery is percutaneous and the wires can be placed away from the affected compartments. In these cases, internal fixation would expose the necrotic tissues and greatly increase the risk of infection. Anatomic reduction of the articular surface is often not possible in these rare cases. Cases with defects of bone and soft tissue are well suited for intentional deformity at the fracture site to obtain a tension-­ free skin closure with delayed reduction of the bone once the skin has healed [24]. The most common induced deformities that assist with wound closure are rotation, varus and recurvatum. The hexapod frame makes the gradual movement over time to reduce the fracture ends a simple task. Paediatric fractures are also amenable to these techniques, and good results have been widely reported [25, 26]. Neglected fractures in children may also be treated in this way but some sources suggest that neglected tibial fractures may respond more favourably than neglected femoral fractures [27].

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treatment process. Translations as great as 40 mm and rotational deformities as large as 35° were accurately reduced in a series reported by Seide et al. [3]. In 2004, Seide proceeds to develop the reduction capabilities of the hexapod by applying computer software which converts the manual reduction device into an “intelligent fixator” or “fracture reduction robot” [29]. Since then, highly precise, flexible and detachable modular reduction systems with upgraded computer software have also been designed, achieving reported maximum residual deviations of up to only 2 mm [30]. We see again here how the computer-based features of this technology can improve treatment precision and clinical outcomes in patients with acute displaced fractures. It is generally accepted that a two block, four-­ ring construct with each block being applied orthogonally to the fragment it is fixed to, provides optimal stability [31]. Pins and wires are used to achieve this fixation to bone after which six FastFix™ struts are applied in an unlocked sliding mode. Olive wires based on the second and third rings can be utilised to reduce any butterfly fragments present [31]. Fine-tensioned wire fixation is also beneficial in the context of minimal bone stock (Fig. 5.3). These wires may capture smaller fragments that would otherwise be very challenging to control. Acute reduction is performed in theatre, and the frame is locked. Further adjustments can then be made using the total residual deformity correction program. Specific considerations apart from butterfly 5.2.1 Fracture Reduction fragments include the fracture’s obliquity among others. Above 30° of fracture obliquity, inherent Hexapods have significant advantages in the frame stability (defined as less than 2 mm of fracreduction of acute fractures relative to open ture line migration with loading) is not satisfacreduction techniques. Reduced operative times tory. This challenge, however, may be overcome and significantly lower blood losses can be using a number of techniques: Arced wires proachieved through closed reduction and post-­ vide stability up to 40° of obliquity whereas a operative computer-assisted reduction compared formal steerage pin construct has been shown to to open reduction techniques [28]. Due to the provide fracture stability for an obliquity angle of gradual rate of correction and reduction that is up to 60° under axial loading of 1000  N [32]. achieved using a hexapod frame, significant Steerage pins are recommended to prevent some translational and rotational deformities can be shear stress at the fracture site for oblique fracreduced with ease over a period of time allowing tures. The pins are angled parallel to the obliquity the patient to fully weight bear in the frame expe- of the fracture fragments resulting in an arc riencing relatively little discomfort during the motion rather than axial motion during axial

5  Hexapod External Fixation for Fractures and Nonunions

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Fig. 5.3  This 42-year-old male presented with a proximal tibial nonunion post military rifle shot injury. Sagittal view CT (left) shows minimal bone stock (21 mm), reinforcing the need for fine-tensioned wire fixation. The

post-operative radiograph (right) shows the use of six wires to gain adequate stability on the proximal fragment. Four opposing olives wires are employed to prevent medial–lateral instability

loading. The arcs of motion of the two fragments will push them against each other converting a shear force into an oblique compressive force. Alternatively, oblique compression can be exerted on the oblique fracture by manipulating the frame to provide a compression vector. Classic rods can only compress axially, but hexapod struts can simultaneously translate and compress the fracture resulting in an oblique load at the fracture site [2]. Notably, the addition of added proximal and distal perpendicular half-­ pins provides little benefit.

deep infection, osteomyelitis and osteonecrosis— complications that may all be managed with the induced membrane technique described by Masquelet in 2000 [33]. This ingenious development in the field of orthopaedic trauma care relies on the formation of a pseudomembrane which surrounds a cement spacer at the core. After pseudomembrane formation is complete, the central spacer may be removed and replaced by autogenous bone graft. This process and the stability of the entire biomechanical environment is reliant on fixators such as circular frames and hexapods. In this way, through the implementation of the induced membrane technique, hexapods can play a pivotal role in an array of pathologies including long bone infection, post-traumatic reconstruction and even congenital pseudoarthrosis management and reconstruction [34–36] (Fig. 5.4). The use of hexapod systems in open fracture management has been well described. Advantages include early mobilisation, restoration of bone loss, easy application and improved union rates [37]. Studies have shown that using a hexapod in place of an IM nail can reduce infection rates from 14.3 to 8% also [38].

5.2.2 Open Fractures Open fractures pose a significant challenge in modern-day trauma care. Hexapod external fixators are well placed to treat these injuries for a number of reasons. The use of transcutaneous pins and wires through small stab incisions negates the need for long incisions which are known to be associated with an increased risk of wound infection and deep-tissue contamination. Open fractures are also associated with a higher incidence of

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48 Fig. 5.4  Case: bone graft supported by a frame for the treatment of infected nonunion. (a) This 30-year-old male sustained a crush injury of the proximal tibial with multiple attempts at reduction and fixation resulting in an infected nonunion with a metaphyseal defect as seen on this coronal and sagittal CT of the injured area. (b) The defect was sterilised with a local antibiotic depot and then bone grafted with autograft and fixed externally. The hexapod allowed for post-operative adjustability. (c) CT images 3 months later showing graft incorporation. (d) Final AP and lateral radiographs after removal of the external fixator. The bone will hypertrophy over time with use of the limb

a

b

5  Hexapod External Fixation for Fractures and Nonunions Fig. 5.4 (continued)

49

c

d

The seminal work published by Gustilo and Anderson in 1976 was a landmark paper that contributes to the effective management of open fractures in the current orthopaedic trauma context [39]. Expanding on the findings of this work,

in 1984, Gustilo et  al. proceeded to refine the natural history of type 3 fractures in this classification [40]. The critical endpoints in this study were amputation and infection. The rates of amputation increased from 0% in grade 3A to

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16% in grade 3B and 42% in grade 3C. The infection rates noted in this cohort did not replicate this same increasing trend. It was reported in this series that grade 3B open fractures had the highest rate of deep infection at 52% [40]. This exceeded the rate of infection in grade 3C patients by 10%. This may seem counterintuitive at first but when consideration is given to the nature of these injuries, it becomes clear why type 3B fractures traditionally had such poor outcomes—soft tissue. Type 3C injuries have neurovascular compromise and so this threaten the limbs viability. Type 3B injuries on the other hand pose less of a risk to the limbs survival but pose an even greater risk to the limb’s infection status due to the involvement of the essential structure that is the surrounding soft tissue.

5.2.3 Soft-Tissue Management The soft-tissue component to open fractures is perhaps the most important determinant in predicting deep infection complications and chronic infectious sequelae in these patients. Current orthopaedic and plastic surgeon cooperation in this field has forged strong interspeciality relations and advanced care in all open fractures with soft-tissue compromise [41]. Common techniques for achieving soft-tissue coverage include split thickness skin graft, full thickness grafts, localised rotational flaps and finally distant free flaps raised on a vascular pedicle which is then anastomosed to a supplier vessel at the recipient open fracture site. These procedures are challenging and can have high failure rates. Reoperations are common and flap failure can be demoralising for patients and surgeons alike. In order to provide an alternative option to these techniques, hexapod frames have successfully been adapted to treat significant soft-tissue loss without the need for free flap construction. In certain cases, with soft tissue and bone loss, the hexapod can be applied as a definitive management device (Fig.  5.5). The viable bone fragments may then be shortened to eliminate the bone deficit while concurrently reducing the soft-­

tissue deficit to a manageable size [42]. The frame may then be used to lengthen the limb and restore the soft tissues through distraction histiogenesis. Many techniques have been described which include intentional angulation of the fracture to accommodate an eccentric soft-tissue deficit. Once the soft tissue has healed in these cases, the induced bony deformity can then be corrected with ease using the hexapod programming system. Lahoti et al. report on seven consecutive cases using the TSF to induce deformation for soft-tissue closure which was then followed by deformity correction [43]. A two-ring TSF was used in this case series and successful soft-tissue closure with restoration of the tibial alignment was reported in all cases involved. It is also possible to shorten and lengthen without the need for any intentional deformity formation at the fracture site. The bayonet method of wound closure is an example of such a technique [44]. These technical applications of hexapod frames illustrate the ingenuity and inventiveness of a technology that has truly revolutionised our ability to manage challenging fractures with significant soft-tissue components to them. Robbins describes the case of an effective-­ induced angular deformity for primary wound closure in a IIIB open proximal tibial fracture [24]. The treatment strategy in this case involved acute shortening and angulation of the tibia which was then stabilised using the TSF construct. The proximal frame was statically locked for 4 weeks to allow primary wound healing after which slow distraction and angular correction in the TSF was commenced. Robbins describes how the initial frame applied was an Ilizarov frame. This was then changed to a more versatile frame that was lighter weight and felt to be a more appropriate option for this patient—the TSF.

5.3

Nonunion

The hexapod fixator has found its place in the treatment of fracture nonunions as well as acute fractures. Circular fixation provides the

5  Hexapod External Fixation for Fractures and Nonunions

a

c

51

b

d

Fig. 5.5  Case: hexapod applied over an extensive soft-­ tissue injury. (a) This 18-year-old female sustained a diaphyseal tibia fracture with soft-tissue degloving. The circular fixator allowed for plastic surgical access while providing bony stability. (b) A vacuum-assisted dressing

was used to optimise the tissue health yielding improved granulation. (c) Split thickness skin grafting was performed. (d) The hexapod fixator was re-assembled, alignment fine-tuned and the skin responded with excellent healing

optimal solution in cases of infection where surgeons strive to keep fracture sites clear of foreign bodies including internal fixation. Since all nonunions are considered infected until proven otherwise, these frames offer peace of mind in knowing that internal fixation was not placed into an infected site. The lack of metal hardware at the nonunion site also allows for a more cavalier approach to softtissue management. Many wounds that might have required a local or free tissue flap can be allowed to granulate with little intervention. Hexapod fixators are readily adjustable and can be used to apply compression throughout the post-operative period. This s­ ustained compression has been very successful at uniting nonunions [45]. Circular fixation provides a strong foundation for bone shortening and

bone transport. Its modularity makes spanning across the ankle (or knee) joint simple. Spanning the joint with a ring will control joint instability and will also provide better control of very small metaphyseal fragments.

5.3.1 Metaphyseal Nonunion Small metaphyseal fragments are difficult to stabilise with plates and close to impossible with nails. Fine-wire fixation will capture these elusive segments controlling them during compression and docking [31]. Often metaphyseal bone is osteopaenic in nonunion cases due to prolonged protective weight bearing. Circular fixators are unmatched in their ability to pass fixed-angle tensioned wires in multiple planes in order to

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optimise purchase in this weak bone. These wires easily bypass large holes left by locking screws and provide the option of olive wires to prevent the bone from sliding along the wire. Managing metaphyseal bone nonunions can be challenging. Hutson describes his technique of callus distraction using a six-axis frame to manage a distal tibial metaphyseal nonunion [46]. One of the most challenging aspects of this operation is attaining fixation in the often very small periarticular fragment. If the pins are too large, it is suggested that additional smooth wires (in this case passed from posterolateral to anteromedial) are added up to a total of four to achieve control of this challenging fragment.

5.3.2 Hypertrophic Nonunion Nonunions develop when either the biological environment of the fracture site is compromised (e.g. vascular insufficiency, devitalisation) or the mechanical environment of the fracture is inadequate to induce osseous tissue formation by local mesenchymal stem cells. Stephan M.  Perren’s influential studies have described the impact that the degree of strain exerted on a tissue may have on its final type of differentiation [47]. Low strain environments are essential for hard bony callus formation in fracture healing. If a fracture of the tibia were to be well vascularised with preservation of the nourishing periosteum, but there was a strain rate across the site that exceeded the threshold acceptable for bone formation, in this case a fracture would not heal and the fracture ends would produce callus leading to a picture of a hypertrophic nonunion. Hexapod constructs have been highly effective in treating these hypertrophic nonunion cases in both the femur and tibia [48]. Impressive rates of union may be achieved with the application of a TSF alone [49]. Closed distraction techniques utilising the hexapod construct can produce healing rates of 97.8% in a cohort of 46 consecutive stiff tibial nonunions [49]. Bernstein et  al. describe the case of a 46-year-old male with a hypertrophied tibial nonunion. This was subsequently treated by placing a TSF construct, application of distraction and then deformity correction

G. A. Sheridan et al.

using the TSF [50]. The pertinent points to learn from the case were as follows: • Exclude an oligotrophic nonunion first. • Excessive motion is present if fracture site mobility increases by >5°. • Distraction of the hypertrophic nonunion then occurs in sequence. Hypertrophic nonunions may be further complicated by deformity at the nonunion site. In this situation, the hexapod is particularly well poised to manage all of these problems. Seybold et  al. describe the application of the TSF to this clinical scenario. In five hypertrophic and five atrophic nonunions with simultaneous multiplanar deformities, the TSF was able to achieve correction in all cases [51]. The mean time for the gradual correction was 23.1 days with the frame worn by all patients for an average of 158.5  days. In this series, only one patient experienced a residual deformity and this a 5° valgus deformity.

5.3.3 Infected Nonunion Infection is the driver behind a significant proportion of fracture nonunions. With the passing of time, increasingly obscure microorganisms manifest as problematic due to the prevalence of antibiotic usage and concurrent antibiotic resistance accelerating on a worldwide scale. The hexapod is a useful tool in the ongoing struggle against these infective organisms [52]. Assessing 38 tibial nonunions, half of which were infected, surgeons achieved bony union after initial treatment in 71% of patients [45]. The presence of bone infection in this cohort was predictive of initial failure and persistent nonunion (p = 0.03). After further operative intervention, a final union rate of 95% was achieved with significant improvements in functional outcome scores also. Calhoun describes the case of a 54-year-old female presenting with a hypertrophic infected tibial nonunion after insertion of depot antibiotics in a resorbable (CaSO4) carrier [53]. This technique of using a resorbable carrier is very beneficial as it reduces the need for a revision procedure solely to remove a nonresorbable carrier. Although

5  Hexapod External Fixation for Fractures and Nonunions

the fixator used in this instance was an adjustable strut fixator and not a hexapod, this principle is applicable to all infected tibial nonunions managed with hexapod fixators.

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5.3.5 Economic Burden

The progression of a tibial fracture to a nonunion has numerous implications for the treating institution regarding the financial burden. Many of these patients will undergo numerous 5.3.4 Soft-Tissue Coverage surgical procedures, often requiring the use of expensive osteoinductive factors and bone subAs discussed in the acute fracture section, soft-­ stitutes as well as other compounds. The protissue coverage is equally if not more problem- gression of a tibial shaft fracture to a tibial atic in nonunion cases. One of the main reasons nonunion has been shown to double the institufor this is that the soft tissue in the region of the tional economic burden. Antonova et al. report nonunion site has often been violated numerous the cost of tibial fracture management to be times in an attempt to achieve initial stability and $11,686 per patient [55]. For those patients healing. Many after failing initial management who progressed on to nonunion, the median will proceed to nonunion site grafting on more total cost of treatment was as high as $25,556. than one occasion. All of these surgical incisions A review of 40 complex tibial nonunions treated create a suboptimal biological environment for with a TSF in the United Kingdom demontissue that is attempting to heal and so soft-tissue strated an average treatment cost of £26,000 per consideration and possible reconstruction is patient [56]. The expense incurred by instituimperative in these cases. tions treating these complex injuries is signifiBernstein reports on the management of a cant and may have a significant impact on the 22-year-old male who suffered a type IIIB open ability of certain institutions to provide this tibial fracture post motor vehicle accident [54]. highly specialised standard of care. Initial IM nailing became infected. Subsequent hardware removal and unilateral frame application failed to control the process, and so at this 5.4 Summary point, more advanced care was instigated at the complex reconstruction and limb lengthening Hexapod frames have proven to be essential in department. Five basic principles are detailed in the management of complex acute fracture and the case which can be applied to all tibial non- nonunion management. They allow the orthopaeunions with a soft-tissue deficit: dic reconstructive community to manage the most complex of conditions including open frac 1. Removal of all nonviable tissue is imperative tures, infected nonunions and soft-tissue defiat initial debridement. ciency which may be managed now with 2. Reduced wound tension can increase the like- intentional deformity through manipulation of lihood of wound healing. the hexapod’s versatility. 3. Allow at least 3  weeks for wound healing We are observing the evolution of external before proceeding with primary deformity frame technology in real time over recent years. resolution. Ilizarov began with a philosophy that is now rap4. Flaps may be avoided through the use of idly developing into one of the most exciting intentional deformity to close bone and soft-­ areas of innovation in modern surgery. Computer-­ tissue defects—the TSF is then essential in based, multiplanar, minimally invasive dynamic correcting this deformity (Fig. 5.6). fixation is only the latest release with further 5. This technique works best if the soft tissue progress being made constantly in this ever-­ and bone defects are of a similar size. expanding field.

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a

b

c

Fig. 5.6  Case: intentional deformity with pre- and post-­ treatment imaging. (a) This 56-year-old male presented with an infected open fracture with a soft-tissue defect that was unable to be closed. The external fixator was applied and intentionally deformed into recurvatum to approximate the skin edges. (b) A lateral radiograph

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mental defects in the rat femur by reverse dynamization in the presence of bone morphogenetic protein-2. J Bone Joint Surg Am. 2012;94(22):2063. 22. O’Toole RV, Gary JL, Reider L, Bosse MJ, Gordon WT, Hutson J, et  al. A prospective randomized trial to assess fixation strategies for severe open tibia fractures: modern ring external fixators versus internal fixation (FIXIT study). J Orthop Trauma. 2017;31(Suppl 1):S10–S7. 23. Paley D, Herzenberg JE.  Applications of external fixation to foot and ankle reconstruction. In: Myerson M, editor. Foot and ankle disorders, vol. 34. 2nd ed. Philadelphia: WB Saunders; 1984. p.  131–8. (2000. p. 1135–88). 24. Robbins CA. Case 27: induced angular deformity and acute shortening for primary wound closure in a IIIB open proximal tibial fracture. In: Rozbruch SR, editor. Limb lengthening and reconstruction surgery case atlas. New York: Springer; 2015. 25. Al-Sayyad MJ. Taylor Spatial Frame in the treatment of pediatric and adolescent tibial shaft fractures. J Pediatr Orthop. 2006;26(2):164–70. 26. Zenios M. The use of the Taylor spatial frame for the treatment of unstable tibial fractures in children. J Orthop Trauma. 2013;27(10):563–8. 27. Al-Sayyad MJ.  Taylor spatial frame in the treat ment of neglected fractures. J Child Orthop. 2011;5(2):135–41. 28. Ge Q, Wan C, Shao X, Zhang T, Jia P, Mei X, et al. [Application of Taylor spatial frame combined with computer-assisted closed reduction in the treatment of tibiofibular fractures]. Zhongguo Xiu Fu Chong Jian Wai Ke Za Zhi. 2019;33(2):144–8. 29. Seide K, Faschingbauer M, Wenzl ME, Weinrich N, Juergens C. A hexapod robot external fixator for computer assisted fracture reduction and deformity correction. Int J Med Robot. 2004;1(1):64–9. 30. Du H, Hu L, Li C, Wang T, Zhao L, Li Y, et  al. Advancing computer-assisted orthopaedic surgery using a hexapod device for closed diaphyseal fracture reduction. Int J Med Robot. 2015;11(3):348–59. 31. Tellisi N, Ilizarov S, Rozbruch SR. Tibial diaphyseal fractures. In: Limb lengthening and reconstruction surgery. Boca Raton: CRC Press; 2006. p. 123–34. 32. Lowenberg DW, Nork S, Abruzzo FM. Correlation of shear to compression for progressive fracture obliquity. Clin Orthop Relat Res. 2008;466(12):2947–54. 33. Masquelet AC.  Induced membrane technique: pearls and pitfalls. J Orthop Trauma. 2017;31(Suppl 5):S36–S8. 34. Mauffrey C, Hake ME, Chadayammuri V, Masquelet AC.  Reconstruction of long bone infections using the induced membrane technique: tips and tricks. J Orthop Trauma. 2016;30(6):e188–93. 35. Masquelet AC, Kishi T, Benko PE.  Very long-term results of post-traumatic bone defect reconstruction by the induced membrane technique. Orthop Traumatol Surg Res. 2019;105(1):159–66. 36. Pannier S, Pejin Z, Dana C, Masquelet AC, Glorion C.  Induced membrane technique for the treatment

56 of congenital pseudarthrosis of the tibia: preliminary results of five cases. J Child Orthop. 2013;7(6):477–85. 37. Sala F, Thabet AM, Capitani P, Bove F, Abdelgawad AA, Lovisetti G.  Open supracondylar-intercondylar fractures of the femur treatment with Taylor Spatial Frame. J Orthop Trauma. 2017;31(10):546–53. 38. Murray CK, Hsu JR, Solomkin JS, Keeling JJ, Andersen RC, Ficke JR, et  al. Prevention and management of infections associated with combat-­ related extremity injuries. J Trauma. 2008;64(3 Suppl):S239–51. 39. Gustilo RB, Anderson JT. Prevention of infection in the treatment of one thousand and twenty-five open fractures of long bones: retrospective and prospective analyses. J Bone Joint Surg Am. 1976;58(4):453–8. 40. Gustilo RB, Mendoza RM, Williams DN. Problems in the management of type III (severe) open fractures: a new classification of type III open fractures. J Trauma. 1984;24(8):742–6. 41. British Orthopaedic Association. 2020. https://www. boa.ac.uk/standards-­guidance/boasts.html. 42. Pierrie SN, Hsu JR. Shortening and angulation strategies to address composite bone and soft tissue defects. J Orthop Trauma. 2017;31(Suppl 5):S32–S5. 43. Lahoti O, Findlay I, Shetty S, Abhishetty N. Intentional deformation and closure of soft tissue defect in open tibial fractures with a Taylor spatial frame--a simple technique. J Orthop Trauma. 2013;27(8):451–6. 44. O’Farrell P, Barnard AC, Birkholtz F. The tibial bayonet method of wound closure. Strategies Trauma Limb Reconstr. 2018;13(2):103–8. 45. Rozbruch SR, Pugsley JS, Fragomen AT, Ilizarov S.  Repair of tibial nonunions and bone defects with the Taylor Spatial Frame. J Orthop Trauma. 2008;22(2):88–95. 46. Hutson JJ.  Case 37: hypertrophic nonunion distal periarticular tibia. Treatment with callus distraction using a spatial frame. In: Rozbruch S, Hamdy R, editors. Limb lengthening and reconstruction surgery case atlas. Cham: Springer; 2015. 47. Perren SM.  Evolution of the internal fixation of long bone fractures: the scientific basis of biological internal fixation: choosing a new balance

G. A. Sheridan et al. between stability and biology. J Bone Joint Surg Br. 2002;84(8):1093–110. 48. Ferreira N, Marais LC. Femoral locking plate failure salvaged with hexapod circular external fixation: a report of two cases. Strategies Trauma Limb Reconstr. 2016;11(2):123–7. 49. Ferreira N, Marais LC, Aldous C.  Hexapod external fixator closed distraction in the management of stiff hypertrophic tibial nonunions. Bone Joint J. 2015;97-B(10):1417–22. 50. Bernstein M, Rozbruch SR.  Case 19: hypertrophic Tibial nonunion with oblique plane deformity treated with TSF.  In: Rozbruch S, Hamdy R, editors. Limb lengthening and reconstruction surgery case atlas. Cham: Springer; 2015. 51. Seybold D, Gessmann J, Ozokyay L, et al. [Deformity correction of post-traumatic tibial non-unions using the Taylor spatial frame]. Zeitschrift fur Orthopadie und Unfallchirurgie. 2009;147(1):26–31. https://doi. org/10.1055/s-­2008-­1038978. 52. Siebenburger G, Grabein B, Schenck T, Kammerlander C, Bocker W, Zeckey C. Eradication of Acinetobacter baumannii/Enterobacter cloacae complex in an open proximal tibial fracture and closed drop foot correction with a multidisciplinary approach using the Taylor Spatial Frame((R)): a case report. Eur J Med Res. 2019;24(1):2. 53. Calhoun JH, Sullivan AC. Case 10: infected nonunion of the tibia. In: Rozbruch S, Hamdy R, editors. Limb lengthening and reconstruction surgery case atlas. Cham: Springer; 2015. 54. Bernstein M, Rozbruch SR.  Case 29: infected nonunion tibia with bone and soft-tissue defect: treatment with TSF, intentional temporary deformation and bone transport. In: Rozbruch S, Hamdy R, editors. Limb lengthening and reconstruction surgery case atlas. Cham: Springer; 2015. 55. Antonova E, Le TK, Burge R, Mershon J.  Tibia shaft fractures: costly burden of nonunions. BMC Musculoskelet Disord. 2013;14:42. 56. Khunda A, Al-Maiyah M, Eardley WG, Montgomery R.  The management of tibial fracture nonunion using the Taylor Spatial Frame. J Orthop. 2016;13(4):360–3.

6

Hexapod External Fixators in the Treatment of Axial and Rotation Deformities and Limb Length Discrepancies Dror Paley and Craig Robbins

Nomenclature ACA CORA JOAL MPTA RDP TSF

angulation correction axis center of rotation of angulation joint orientation angle line medial proximal tibial angle rate determining points Taylor Spatial Frame

Deformity correction with Ilizarov external fixation was planned using the CORA method by drawing lines and measuring angles on printed X-rays. The device utilized different mechanical constructs to correct angulation (hinges), rotation (tangential transverse rods), translation (parallel transverse rods), and leg length discrepancy (parallel longitudinal rods). Each deformity parameter was corrected independently with its particular construct and multiple parameters required multiple time-consuming modifications of the apparatus in the sequence of correction. Notwithstanding this requirement, the Ilizarov method was a powerful analog tool for six-axis deformity correction and remained the mainstay for several decades [1–4].

D. Paley (*) · C. Robbins Paley Orthopedic and Spine Institute, St Mary’s Medical Institute, West Palm Beach, FL, USA e-mail: [email protected]

In 1996, the Taylor Spatial Frame (TSF) changed the landscape of limb deformity correction [5]. This device heralded the transition from analog to digital deformity correction analysis. Coincident with the advent of digital radiography, analog planning on printed X-rays with the CORA method was augmented by digital planning using the same CORA and osteotomy rules and principles [6]. This technology started as a computer-­based program and evolved by 2002 to web-based software [7]. As with the Ilizarov system before it, the Taylor Spatial Frame system was a powerful tool that had a steep learning curve. The nonsurgical aspects of TSF such as deformity analysis, fixator mounting parameters, and data entry into the nonintuitive software were impediments to new users. They were challenged with understanding and using CORAgin and CORAsponding point deformity planning but embraced the TSF’s ability to correct multiple deformities simultaneously [8]. In 2013, the TSF patent lapsed and many orthopaedic companies developed their own hexapod deformity correction systems. In 2016, the Orthex hexapod fixator, now marketed by Orthopediatrics, was developed with the aim to overcome some practical challenges in the routine management of deformity correction surgery. The Orthex hardware and software were designed to integrate seamlessly to allow the user to easily analyze and treat complex and simple deformities [9].

© Springer Nature Switzerland AG 2021 M. Massobrio, R. Mora (eds.), Hexapod External Fixator Systems, https://doi.org/10.1007/978-3-030-40667-7_6

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For purposes of instruction, as well as to keep which extend the reach of a strut above or below this chapter from becoming dated too quickly, we a ring depending on where it is positioned. have chosen to use the software and hardware of The Orthex system has aluminum rings conthe Orthex fixator as the basis for discussion. structed with two concentric rows. The outer row Orthex is the first point-and-click software that has slots connecting the six standard hexapod was FDA approved for six-axis deformity correc- tabs to provide additional bending strength and tion. This software is, in our opinion, user-­ options for hardware mounting. Foot rings can be friendly but also a sophisticated and powerful completed with low-profile arches. Z-plates tool. A defining characteristic of this system is extend strut mounting above or below the rings to that all aspects of deformity analysis, localizing allow extreme deformity corrections that would the frame to the bone, and deformity planning are cause “submarining” of struts or not be possible performed online via the Orthex software. It uses in other systems. Double-column cubes diminish the CORA method as its guiding principles and cantilever half-pin bending and can be secured to demonstrates how software can be used to facili- both rows of the ring to prevent rotation. The tate deformity planning and correction [10]. struts are telescopic with a patient-adjustable “A” The Orthex system is user-friendly and intui- portion that moves in one-fourth turn increments tive for both the novice and advanced deformity for each 0.25 mm of correction. The telescoping surgeon alike. The software follows standard “B” portion can be quickly positioned and then deformity correction principles with proximal locked to maximize the amount of threaded “A” and distal axis lines and automatically identifies rod available for gradual correction. The telethe CORA and its transverse bisector line. The scoping struts require fewer strut changes than user defines a specific pivot point on the axis of competitor hexapod systems. correction of angulation (ACA) around which the The Orthex hardware and software integrate deformity will hinge during the correction. The by the use of metal spheres temporarily attached software recognizes the relationships between to cardinal points on the outer edge of the preferthe osteotomy, CORA, and the pivot point. It then ence ring prior to taking planning X-rays calculates and displays translations in all three (Fig. 6.1). The X-rays are digitally imported into planes (medial/lateral, anterior/posterior, lengthen/shorten) that occur at the midpoint of the osteotomy during correction around the pivot point. The user has the option to accept or modify these calculated parameters and add rotational deformity. Another powerful feature of the Orthex software is the ability to separate a deformity correction into as many as four consecutive steps. For example, the surgeon may choose to initially perform some of the desired lengthening and all of the angular deformity correction in step 1. Then perform translation in step 2. And finally perform derotation and the remainder lengthening in step 3. The Orthex software provides three-­ dimensional animation of the correction that can be rotated to any point of view and models the cross-sectional area of the osteotomy during the deformity correction. The software can also Fig. 6.1  Metal spheres are temporarily attached to cardiaccommodate for struts placed out of their stan- nal points on the outer edge of the preference ring prior to dard position and for struts placed on Z-plates taking X-rays for software calibration

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the patient case, and the software calibrates the size of the ring and extrapolates its rotation, inclination, and location. Due to the relatively wide diameter of the rings and distance between the X-ray spheres, the Orthex calibration is extremely accurate. The initial steps of the Orthex software have the user define the major deformity in the frontal and sagittal planes and select the fixator hardware and preference ring alignment on consecutive screens through simple drop-down menus. These create a representative bony model of the deformity and fixator. The user then imports anterior-­ to-­posterior and medial-to-lateral X-rays (taken with the X-ray marker spheres on the preference ring) via a Click & Paste or Upload option. The user is then prompted to analyze these X-rays with a simple point-and-click interface using CORA planning methodology. For metaphyseal deformities, the user can select either joint orientation angle line (JOAL) or mid-diaphyseal line planning. The user then selects the center points of the X-ray calibration spheres on the preference ring. This allows the software to calibrate the X-ray measurements and interpret the ring’s orientation. The user then defines the proximal and distal axes of the bone segments. The software draws the transverse bisector at the intersection of these lines which marks the CORA.  The user defines a specific pivot point around which the deformity will hinge during the correction. The pivot point can be placed at the CORA or may be placed at a different level, such as the osteotomy site, depending on the type of correction desired according to the osteotomy rules. The software recognizes the relationships between the osteotomy, CORA, and the pivot point. In addition to defining the CORA, the proximal and distal bone axis lines define the axes of lengthening and rotation. For long bones, the axis of lengthening occurs by default along the preference ring bone axis line. Therefore, for a proximal preference ring, it is along the proximal axis line of the bone and for a distal preference ring, it is along the distal axis of the bone. By contrast in the TSF system, the axis of lengthening is always perpendicular to its reference ring. As well, the

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TSF system requires the reference ring to be mounted perpendicular to its bone segment and that X-rays are taken perpendicular to the reference ring. In the Orthex system, the ring does not have to be mounted perpendicular to the bone and the X-rays do not have to be perpendicular to the ring. The advanced user has the option of drawing an axis of lengthening independent from the bone axis lines. Another important consideration for the surgeon is the axis of rotation. By convention, this has been set to be along the distal bone axis line—regardless of which is the preference segment. As with the axis of lengthening, the user has the option of drawing an axis of rotation independent from the bone axis lines. The Orthex system has powerful software dedicated to foot deformity correction. The hardware screen for foot or axial correction has an intuitive point-and-click interface that allows rings and tabs to be rotated into their representative position for ease of planning (Fig.  6.2). As with the long bone planning, the user has the ability to draw independent axes of lengthening and

Fig. 6.2  The Orthex software user’s interface hardware page allows the user to select ring type and size and rotate the rings and strut-connection tabs to their clinical locations

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rotation for foot correction. These unique abilities exemplify how software can be used to customize the deformity correction to each patient’s specific needs. The Orthex software automatically measures and displays the angular deformities in the frontal and sagittal planes based on the axis lines drawn by the user. It calculates and displays the translations that occur through deformity correction at the midpoint of the osteotomy in three planes (medial/lateral, anterior/posterior, lengthen/shorten). The cross-sectional overlap at the osteotomy during correction is displayed as well. This data informs the surgeon about length gained by an opening wedge osteotomy and potential loss of bone contact at the osteotomy by secondary translations. By contrast, in the TSF system, the user is required to perform the deformity analysis and correction planning extrinsic to the TSF software and manually enter this data. The TSF software requires the reference ring to be mounted orthogonal to its bone segment and planning X-rays to be taken orthogonal to the reference ring. As well, the user must measure postoperative X-rays and enter data to inform the software of the relative position of the external fixator to a user-­ defined point on a bone segment (this is called the Mounting Parameters in the TSF software). These steps may introduce measurement errors and are avoided in the Orthex system. The rate of deformity correction is determined based on two user-defined rate determining points (RDP), one for bone and one for soft tissues. Each step of a correction has its own RDPs. The software will limit the duration of correction based on the slower of the calculated rates for each RDP. Conversely, the software can calculate and display the daily rate of correction at each RDP based on a user-selected duration of correction. The surgeon has the ability to alter the duration of correction or the correction rate at each RDP to customize a correction program. After finalizing the deformity correction parameters and RDPs, the software generates 3D animations showing the correction that can be rotated and viewed from any orientation. The software also displays and

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quantifies the cross-sectional overlap at the osteotomy level at the end of correction. The Orthex system provides several options for displaying the deformity correction schedule. The accuracy of this schedule has been improved from the one-full-turn capability of TSF.  The Orthex struts and software allow corrections in the original Ilizarov 0.25  mm increments. The schedule can be printed in the traditional Millimeters format or a Clicks format. The Millimeters format displays the six strut “A” settings in columnar form in 0.25  mm increments with consecutive days in rows. The Clicks format provides positive or negative integers corresponding to the amount and direction of one-­fourth turns per strut. Each format can be broken up into as many as four adjustment periods per day. Each color coordinated column corresponds to its numbered strut and highlighted date ranges signify the overlap between required B-value strut adjustments, strut changes, or Z-plate modifications. The ease and accuracy of residual deformity correction is one of the most important features of any hexapod system. During the distraction phase, changes to the schedule may be needed for a variety of indications. The most common is to alter the rate of distraction. Other indications are to add or change angulation, length, rotation, or translation parameters. All of these require what is called a residual schedule. The Orthex system offers two ways to generate a residual schedule: without new X-rays or with new X-rays. Generating a residual schedule without X-rays is appropriate for corrections that do not require changes in the level of the CORA or alterations in the lengthening or rotation axis. Therefore, change in rate, length, rotation, or translation can be done very quickly without inputting new X-rays. Only with a change in angulation, with a new CORA, or change in lengthening or rotation axes does one need to perform a residual schedule with new X-rays (with calibration spheres attached to the preference ring). In either instance the residual planning is quick and easy because the software automatically populates data about the hardware and strut lengths on the date of the residual program. The residual program will also

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inform the user of the initial deformity parameters, the current amount of deformity remaining, and allow for deformity parameters to be individually adjusted. Hardware Advances: • Low-profile arches to enclose foot rings. • Double-column half-pin cubes improve drill guide accuracy and better prevent half-pin deformation. • Telescoping struts require fewer sizes and strut changes and have standard and rapidadjust capabilities. • Struts allow one-fourth  mm increment adjustments. Software Advances: • Point-and-click interface. • Deformity analysis and frame mounting performed online. • Identify separate soft tissue and bony rate determining points (RDPs). • Software will calculate a rate of correction at each RDP based on a chosen duration of correction. • User can custom select axis of lengthening. • User can custom select axis of rotation. • Select up to four consecutive correction steps each with its own rate of correction. • Cross-sectional overlap at the osteotomy level is calculated and displayed.

6.1

Metaphyseal Case

SM is a ten-year-old male with cystinosis with multiple lower extremity deformities. His previous orthopaedic surgeries include bilateral medial distal femur hemi-epiphysiodeses and proximal femur osteotomies (Fig. 6.3). Tibia x-rays before and after correction are shown at the end of this section in Figs. 6.23 and 6.24. His problem list includes cystinosis/diminished kidney function and bilateral: 1. Femoral retroversion 2. Anterolateral diaphyseal femoral bow

3 . Distal femur valgus (with hardware) 4. Internal tibial torsion 5. Proximal tibia procurvatum 6. Proximal tibial valgus

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retained

To address the multiple deformities, the reconstructive plan is for surgery on the left side followed by the same procedures on the right side 3 weeks later: 1 . Removal of hardware distal femur 2. Acute femur correction with double-level osteotomy with fixator assisted antegrade nailing (Fig. 6.4a, b) 3. Peroneal nerve decompression 4. Soft-tissue lengthening of the knee (IT band, biceps) 5. Proximal tibia and fibula osteotomy with gradual multiplanar deformity correction 6. Application of Orthex hexapod (Fig. 6.5a, b) 7. Proximal and distal tibio-fibula joint capture

6.1.1 Deformity Screen On the first screen of the Orthex patient case, the user selects the preference segment (Fig. 6.6) and the location and direction of the major deformities in the frontal and sagittal planes. For each long bone, the user has choices of metaphyseal or diaphyseal locations for the deformity. For metaphyseal locations, the user has the option of performing joint line-based CORA planning or mid-diaphyseal CORA planning. In this case, the user selects the proximal preference segment and apex medial (valgus) and apex anterior (procurvatum) and the left tibia proximal metaphyseal location with the point-­ and-­click interface. The software creates representative models of the deformity based on these selections. The user presses “Save and Continue” on the bottom right to save the selections and continue to the next screen. Numbered yellow dots on the top menu bar indicate the working screen.

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Fig. 6.3  SM preoperative X-rays. Right lateral (left), standing AP (center), left lateral (right)

6.1.2 Hardware Screen On this screen the user inputs information regarding the hardware attached to the patient (Fig. 6.7). Through point-and-click drop-down menus and rotating ring icons on the left side of the screen (also see Fig. 6.2), the ring shape, size, orientation, and A-tab position are selected. The top right section denotes the size and mounting position of the struts. “Standard Outer Mount” is the default for struts attached in their standard positions. If one or more struts were placed in nonstandard positions, or Z-plate(s) were used, “Non-Standard Mount” would be selected from the drop-down menu and the appropriate data

entered in a pop-up screen. The user enters the adjustable A and fixed B scale lengths for all six struts in the bottom right and presses “Save and Continue” to move to the next screen. After selecting “Save and Continue,” a new screen opens and the user chooses which X-ray to plan first (Fig. 6.8). In general, the X-ray with the largest deformity is selected because the same axial levels of the pivot point, bone RDP, and soft-tissue RDP will be used on the orthogonal X-ray planning page. In this case, the user selected “AP.” The user is now able to upload or copy and paste X-ray images to the patient case. It is important to remember that planning X-rays

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Fig. 6.4  SM postoperative AP (left) and lateral (right) of left femur after fixator-assisted double-level osteotomy and nailing

require attachment of X-ray calibration spheres in designated positions on the preference ring for both X-rays and the Orthex software requires the traditional “Lateral” X-ray be taken from medial to lateral for measurement calibration purposes. The consecutive steps on this and the following

page allow the user to systematically and simultaneously perform measurement calibration, frame positioning, and deformity analysis and correction planning within the patient case. Axial rotation and limb length discrepancy can be added later in the case. Although each step has

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Fig. 6.5  SM postoperative AP (left) and medial-to-lateral (right) X-rays taken with calibration spheres

Fig. 6.6  Deformity screen of the Orthex patient case: the user selects the preference segment, major deformities in frontal and sagittal planes, and location of the deformity.

The yellow dots at the top of the screen indicate the working screen. The user presses “Save and Continue” at the bottom right to advance to the next screen

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Fig. 6.7  Hardware screen: the user enters data about the hexapod rings and their orientation, strut attachment locations and orientation, and strut lengths

Fig. 6.8  The user chooses the initial X-ray view to plan the deformity correction. In general, the X-ray with the largest deformity is selected because the same axial levels

clear instructions, the software is intuitive and user-friendly and follows standard CORA-based principles.

of the pivot point, bone RDP, and soft-tissue RDP will be used on the orthogonal X-ray planning page

For this case, the user selected JOAL (Fig. 6.9). Tools at the bottom of the screen (Fig. 6.10) allow the user to reorient and crop the X-ray. The first step is to select the center points of the three X-ray spheres from left to right on the 6.1.3 AP X-Ray Screen preference ring (Fig.  6.10). The software calibrates the X-ray measurements and accurately In metaphyseal cases, after selecting which X-ray identifies the orientation of the preference ring. to use first for planning, the user will select which The user then follows sequential CORA-method method of CORA planning to use: Mid-­ steps for deformity analysis and can redo a step diaphyseal or joint orientation angle line (JOAL). by selecting it on the left side of the screen.

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Fig. 6.9  Joint orientation angle line (JOAL) is selected as the method of CORA planning in the metaphyseal case presented

Fig. 6.10  AP X-ray screen: This image demonstrates completion of step 1. The center points of the three X-ray spheres were selected from left to right on the preference

ring (red lines). Tools at the bottom of the screen allow the user to reorient and crop the X-ray

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6.1.4 A  P Proximal Joint Line and Proximal Center Point For joint orientation angle line (JOAL) metaphyseal planning, the user draws a proximal joint line (aqua) in step 2. In step 3, the user selects a proximal center point on the joint line and the software draws a perpendicular line (blue) and a proximal reference line (black) for the preference segment (Fig. 6.11). The default MPTA (medial proximal tibial angle) for the proximal reference line is 87°. The location along the aqua joint line and angle of the black proximal reference line can be adjusted using the tools below the imported X-ray image.

Fig. 6.11  AP X-ray deformity planning: After the proximal joint line is drawn (aqua) in step 2, the user then selects a proximal center point (step 3), and the software draws a perpendicular line (blue) and a proximal refer-

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6.1.5 AP Distal Bone Segment Line After the user selects the distal bone segment line (step 4), the bisector line (green) is drawn at the level of the CORA, and the measured deformity direction and degree are displayed above the X-ray (Fig.  6.12). By default, lengthening will occur along the axis of the preference segment, and rotation will occur along the axis of the distal segment. The advanced user can draw independent axes for lengthening and rotation in the Frame Options drop-down box above the imported X-ray image.

ence line (black) representing the MPTA for the preference segment. The location and angle can be adjusted in the tool box below the X-ray image

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Fig. 6.12  The bisector line (green) is automatically drawn at the level of the CORA, and the measured deformity direction and degree are displayed above the X-ray

6.1.6 A  P Osteotomy and Proposed Pivot Point

6.1.7 A  P RDP Bony and Soft and Review

In step 5, the user denotes the level and width of the osteotomy or correction location (red line), and the location of the proposed pivot point (yellow X) is selected in step 6. The software uses the width of the osteotomy line indicated on AP and ML X-rays to animate and quantify cross-sectional bone overlap during the correction later in the program. The proposed pivot point defines the axis of correction of angulation (ACA) and is the virtual point around which the deformity will hinge during the correction (Fig. 6.13). The software calculates and displays translations in all three planes (medial/ lateral, anterior/posterior, lengthen/shorten) that occur at the midpoint of the osteotomy line during correction around the pivot point.

The user then selects a bony (step 7) and soft-­ tissue (step 8) rate-determining point (RDP) for the correction (Fig. 6.14). In this case, the RDP bony (orange X) is set at the concave border of the osteotomy. The RDP soft (lavender X) is set over the peroneal nerve. The software will limit the speed of correction to the slower of the calculated rates for each RDP.  Conversely, the software can calculate and display the daily rate of correction at each RDP based on a user-selected duration of correction. Step 9 prompts the user to review their selections. Any step can be redone by reselecting it on the left-hand column and completing the remaining steps. When the review is complete, the user selects “Save and Continue”

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Fig. 6.13  The proposed pivot point (yellow X) defines the axis of correction of angulation (ACA) and is the virtual point around which the deformity will hinge during the correction

and will then upload or paste the orthogonal X-ray and follow similar steps.

6.1.8 ML X-Ray Screen Tools at the bottom of the screen allow the user to reorient and crop the X-ray. The ML X-ray must be taken from medial to lateral with the X-ray spheres attached to the preference ring in their correct positions. As with the planning on the first X-ray, the first step is to select the center points of the X-ray spheres from left to right on the preference ring (Fig. 6.15). The software calibrates the X-ray measurements and accurately identifies the orientation of the preference ring.

The user then follows sequential CORA-method steps for deformity analysis and can redo a step by selecting it on the left side of the screen.

6.1.9 M  L Proximal Joint Line and Proximal Center Point As with the first X-ray, for joint orientation angle line (JOAL) metaphyseal planning, the user draws a proximal joint line (aqua) in step 2. In step 3, the user selects a proximal center point, and the software draws a perpendicular line (blue) and a proximal reference line (black) for the preference segment (Fig.  6.16). The default PPTA (posterior proximal tibial angle) for the

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Fig. 6.14  Bony (orange X) and soft-tissue (lavender X) rate-determining points (RDPs) for the correction are selected

proximal reference line is 80°. The location along the joint line and angle of the proximal reference line can be adjusted using the tools below the imported X-ray image.

6.1.10 ML Distal Bone Segment Line After the user selects the distal bone segment line in step 4, the bisector line (green) is drawn at the level of the CORA, and the measured deformity direction and degree are displayed above the X-ray (Fig.  6.17). By default, lengthening will occur along the axis of the preference segment, and rotation will occur along the axis of the distal segment. The advanced user can draw independent axes for

lengthening and rotation in the Frame Options drop-down box above the imported X-ray image.

6.1.11 ML Osteotomy and Proposed Pivot Point In step 5, the user denotes the level and width of the osteotomy (red line). The software uses the width of the osteotomy indicated on AP and ML X-rays to animate and quantify cross-sectional bone overlap during the correction later in the program. After the user denotes the location of the osteotomy line, the software will automatically draw a yellow line at the same axial level the user selected for the pivot point on the first X-ray

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Fig. 6.15  As with the planning on the AP X-ray, the first step is to select the center points of the X-ray spheres from left to right on the preference ring

(Fig. 6.18). The user can adjust the location of the pivot point along the yellow line.

6.1.12 ML RDP Bony and Soft and Review The user then selects a bony (step 7) and soft tissue (step 8) rate-determining point (RDP) for the correction (Fig. 6.19). As with the proposed pivot point, the software will draw an orange line at the same axial level of the bony RDP and lavender line at the same axial level

of the soft RDP on the initial X-ray. The user can adjust the location of the RDP along their respective lines. The software will limit the speed of correction to the slower of the calculated rates for each RDP. Conversely, the software can calculate and display the daily rate of correction at each RDP based on a user-selected duration of correction. Step 9 prompts the user to review their selections. Any step can be redone by reselecting it on the left-hand column and completing the remaining steps. When the review is complete, the user selects “Save and Continue.”

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Fig. 6.16  ML X-Ray deformity planning: After the proximal joint line is drawn (aqua) in step 2, the user then selects a proximal center point in step 3, and the software draws a perpendicular line (blue) and a proximal refer-

ence line (black) representing the PPTA for the preference segment. The location and angle can be adjusted in the tool box below the X-ray image

6.1.13 Corrections Screen

8.9 mm of length. The default is for 0 axial rotation. The user has the ability to accept or override these computed values and add rotation or additional axial discrepancy in the Revised Correction column. In addition to the computed angular corrections, the surgeon wanted to gain 10  mm total length, correct 10° of internal to external rotation and did not want any AP or LM secondary translation at the osteotomy site. These values were entered in the Revised Correction column. If no changes were made, the Computed Correction

The measured angular deformities and calculated translations in all three planes (medial/lateral, anterior/posterior, lengthen/shorten) are displayed in tabular form in the Computed Correction column (Fig.  6.20). In this case, the software calculated 28.2° of valgus to varus and 10.2° of pro to recurvatum angular corrections. At the midpoint of the osteotomy, it calculated secondary translations of 20.3  mm of lateral to medial, 6.4  mm of posterior to anterior, and

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Fig. 6.17  The bisector line (green) is drawn at the level of the CORA, and the measured deformity direction and degree are displayed above the X-ray

values default to the Revised Correction values. The user has the ability to separate and correct deformity parameters in as many as four consecutive steps. In this case, the surgeon wanted to correct all of the nonrotational deformities simultaneously in step 1 and then correct the axial rotation independently in step 2. Bony and soft RDP values must be set for each step. The software displays the calculated duration of correction based on the slower of the user-determined rates for each RDP. Conversely, the software can calculate and display the daily rate of correction at each RDP based on a user-­ selected duration of correction. This allows the

surgeon to adjust RDPs or duration of correction as needed to safely correct the deformities. In this case, the surgeon selected 0.75  mm/day at the bony and soft RDP for step 1 and 1 mm/day for the RDPs in step 2. The software calculated a 48-day and 10-day correction for each step. After entering the values, the user selects “Save and Update” to continue.

6.1.14 3D Preview and Bone Overlap At the bottom of the Correction screen in the 3D Preview tab (Fig. 6.21a, b), the user can select

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Fig. 6.18  After the user denotes the location of the osteotomy (red line), the software will automatically draw a yellow line at the same axial level the user selected for the pivot point on the first X-ray

any cardinal orientation to watch animations of the correction in consecutive step order. The animation itself can be rotated in any direction. The Bone Overlap tab (Fig.  6.21c) shows the bone overlap at the osteotomy site at the end of correction. The cross-sectional area of each bone segment is determined from the width of the osteotomy lines as drawn on AP and ML X-rays.

6.1.15 Schedule Screen The schedule (Fig.  6.22) starts on the userdefined Correction Start Date. Each color coor-

dinated column corresponds to its numbered strut and highlighted date ranges signify the overlap between required B-value strut adjustments, strut changes, or Z-plate modifications. The default schedule is in Millimeters, and the user also has the option of displaying the schedule in Clicks format. The Clicks format provides positive or negative integers corresponding to the amount and direction of one-fourth turns per strut per adjustment period. For example, a change from 123.75 to 123.25 would be indicated as “−2” in Clicks format because two quarter turns of shortening are required to decrease the strut length by 0.5 mm. The schedule can be broken up into as many as four adjust-

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Fig. 6.19  Bony (orange X) and soft (lavender X) tissue rate-determining points (RDPs) for the correction are selected

ment periods per day. Figure 6.23 show the x-rays the day of surgery and Fig. 6.24 shows the x-rays on the final day of the schedule.

6.1.16 Residual Revision Residual corrections can easily be performed by selecting the blue Residual Revision box on the far right of any day on the Schedule screen (Fig. 6.25). Pressing the Residual Revision box automatically creates a new case and adds “residual” to the saved case name. All of the data from the original program are carried over to the new residual program. In the Residual pop-up

window, the user has the option of creating a “Standard” residual based on the original program and X-rays without new X-rays or a “New X-Ray” residual where the user performs an analysis on newly imported images with attached X-ray spheres. Changes in rate, length, and rotation with the original CORA do not need new X-rays. New X-rays are needed if there is a change in the CORA or length or r­ otation axes. In this case, the surgeon wanted to perform additional deformity corrections on the initial program without changing the CORA or rotation axes and selected “Standard.” The surgeon verified or amended incorrect strut settings and pressed “confirm.”

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Fig. 6.20  The measured angular deformities and calculated translations in all three planes (medial/lateral, anterior/posterior, lengthen/shorten) are displayed in tabular form in the Computed Correction column. The user has

a

the option to accept or change each parameter in the Revised Correction column. The user can separate the correction into as many as four consecutive steps

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Fig. 6.21 (a, b) 3D animation of correction. (c) Bone Overlap tab

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Fig. 6.22  Correction Schedule: The MM format (left) shows the A scale readings for each of the six-numbered struts in color-matched columns. Highlighted date ranges indicate when B-scale, struts, or Z plates must be changed.

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The Clicks format (right) provides positive or negative integers corresponding to the amount and direction of one-fourth turns per strut per day

b

Fig. 6.23  SM anteroposterior (a) and medial to lateral (b) X-ray view of the left tibia and fibula the day of surgery

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Fig. 6.24  SM anteroposterior (left) and lateral (right) X-ray view of the left tibia and fibula at the end of correction Fig. 6.25 Residual Revision box screen

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Fig. 6.26  Residual 1 tab. The deformity parameters from the original program are listed in the Desired column. The corrections completed until the day of the residual program are listed in the Completed column. The desired

residual deformity corrections are entered in the Total Residual column. The surgeon chose to correct all of the total residual deformities in a single step

6.1.17 Residual Corrections

make changes to the RDPs or duration of correction. As with the original program, the schedule (Fig.  6.27) can be printed in Millimeters or Clicks (Fig. 6.28). The final results for SM are presented in Figs. 6.29 and 6.30.

The Corrections page opens to the Residual 1 tab (Fig. 6.26). The deformity parameters from the original program are listed in the Desired column. The corrections completed until the day of the Residual program are listed in the Completed column. In this case, the residual was performed after the entire initial program had been completed. The surgeon desired 10° of additional internal to external rotation, 10 mm of additional lateral to medial translation, and 10 mm of additional length and entered this data in the Total Residual column. As with the initial program, the surgeon could separate residual deformities into as many as four consecutive steps. In this case, the surgeon wanted to correct this over 10  days and entered this in the Days column under step 1. After pressing “Save and Update,” the software then calculated and displayed the rates of RDP bony and soft as 1.57 and 2.05 mm/ day, respectively. The surgeon could accept or

6.2

Diaphyseal Case

SR is an 8-year-old child with Paley 5B Fibular hemimelia who has had previous reconstructive surgeries to her left lower extremity. She has a limb length discrepancy, proximal tibia deformity, and a dysplastic ankle (Fig. 6.31). The surgical plan is gradual correction of the proximal tibial deformity with lengthening and an acute ankle fusion (Fig. 6.32). Problem list: 1. Fibular hemimelia 2. Limb length discrepancy

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Fig. 6.27  Residual correction MM schedule generated by the software

3 . Proximal tibia valgus 4. Proximal tibia procurvatum 5. Dysplastic ankle

6.2.1 Preoperative X-Rays

Surgical plan: 1. Proximal tibia osteotomy for gradual deformity correction and lengthening 2. Acute ankle fusion 3. Application of Orthex hexapod

On the first screen of the Orthex patient case, the user selects the preference segment (Fig.  6.33) and the location and direction of the major deformities in the frontal and sagittal planes. For each long bone, the user has choices of metaphyseal or

6.2.2 Deformity Screen

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Fig. 6.28  Residual correction Clicks schedule generated by the software

diaphyseal locations for the deformity. For metaphyseal locations, the user has the option of performing joint line-based CORA planning or mid-diaphyseal CORA planning. In this case, the user selects the proximal preference segment and apex medial (valgus) and

apex anterior (procurvatum) and the left tibia proximal diaphyseal location with the point-and-­ click interface. The software creates representative models of the deformity based on these selections. The user presses “Save and Continue” on the bottom right to save the selections and

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a

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Fig. 6.29  SM at the end of consolidation: Full-length standing AP X-ray (a); AP (b) and lateral (c) left tibia and fibula

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Fig. 6.30  SM comparison of AP pre (a) and post frame-removal (b) standing X-rays. Comparison of pre (c) and post frame-removal (d) lateral views of both legs

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Fig. 6.31  SR Preoperative X-rays. Full-length standing AP (left) and long-lateral (right) of left lower extremity in maximal knee extension. Clinical problems include: fibu-

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lar hemimelia, limb length discrepancy, proximal tibia valgus, proximal tibia procurvatum, and a dysplastic ankle

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Fig. 6.32  SR postoperative AP (left) and medial-to-­ to the medial and lateral sides of the proximal ring mark lateral (right) X-rays taken parallel to proximal (prefer- the knee center of rotation and will be attached to hinges ence) ring with X-ray spheres. The threaded rods attached across the knee

Fig. 6.33  Deformity screen of the Orthex patient case: The user selects the preference segment, major deformities in frontal and sagittal planes, and location of the deformity

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Fig. 6.34  Hardware screen: The user enters data about the hexapod rings and their orientation, strut attachment locations and orientation, and strut lengths

Fig. 6.35  The software interface allows the user to choose the initial X-ray view to plan the deformity correction

continue to the next screen. Numbered yellow dots on the top menu bar indicate the working screen.

6.2.3 Hardware Screen On this screen, the user inputs information regarding the hardware attached to the patient (Fig.  6.34). Through point-and-click drop-down menus and rotating ring icons on the left side of the screen, the ring shape, size, orientation, and A-tab position are selected. The top right section denotes the size and mounting position of the struts. “Standard Outer Mount” is the default for struts attached in their standard positions. If one

or more struts were placed in nonstandard positions, or Z-plate(s) were used, “Non-Standard Mount” would be selected from the drop-down menu and the appropriate data entered in a pop­up screen. The user enters the adjustable A and fixed B scale lengths for all six struts in the bottom right and presses “Save and Continue” to move to the next screen. After selecting “Save and Continue,” a new screen opens and the user chooses which X-ray to plan first (Fig.  6.35). In general, the X-ray with the largest deformity is selected. The same axial levels of the pivot point, bone RDP, and soft-­tissue RDP will be used on the orthogonal X-ray planning page. In this case, the user selected “AP.”

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Fig. 6.36  AP X-ray screen: This image demonstrates completion of step 1.The center points of the three X-ray spheres were selected from left to right on the preference

ring (red lines). Tools at the bottom of the screen allow the user to reorient and crop the X-ray

The user is now able to upload or copy and paste X-ray images to the patient case. It is important to remember that planning X-rays require attachment of X-ray calibration spheres in designated positions on the preference ring for both X-rays and the Orthex software requires the traditional “Lateral” X-ray be taken from medial to lateral for measurement ­calibration purposes. The consecutive steps on this and the following page allow the user to systematically and simultaneously perform measurement calibration, frame positioning, and deformity analysis and correction ­planning within the patient case. Axial rotation and limb length discrepancy can be added later in the case. Although each step has clear instructions, the software is intuitive and userfriendly and follows standard CORA-based principles.

6.2.4 AP X-Ray Screen Tools at the bottom of the screen allow the user to reorient and crop the X-ray. The first step is to select the center points of the three X-ray spheres from left to right on the preference ring. (Fig.  6.36) The software calibrates the X-ray measurements and accurately identifies the orientation of the preference ring. The user then follows sequential CORA-method steps for deformity analysis and can redo a step by selecting it on the left side of the screen.

6.2.5 A  P Proximal and Distal Bone Segment Lines The user then selects the midpoints of the proximal (step 2) and distal (step 3) bone segments.

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Fig. 6.37  The user then selects the midpoints of the proximal (step 2) and distal (step 3) bone segments. The bisector line (green) is drawn at the level of the CORA,

and the measured deformity direction and degree are displayed above the X-ray

The bisector line (green) is drawn at the level of the CORA, and the measured deformity direction and degree are displayed above the X-ray (Fig.  6.37). By default, lengthening will occur along the axis of the preference segment, and rotation will occur along the axis of the distal segment. The advanced user can draw independent axes for lengthening and rotation.

during the correction later in the program. The proposed pivot point defines the axis of correction of angulation (ACA) and is the virtual point around which the deformity will hinge during the correction (Fig. 6.38). The software calculates and displays translations in all three planes (medial/ lateral, anterior/posterior, lengthen/shorten) that occur at the midpoint of the osteotomy line during correction around the pivot point.

6.2.6 A  P Osteotomy and Proposed Pivot Point In step 4, the user denotes the level and width of the osteotomy or correction location (red line), and the location of the proposed pivot point (yellow X) is selected in step 5. The software uses the width of the osteotomy line indicated on AP and ML X-rays to animate and quantify cross-sectional overlap

6.2.7 A  P RDP Bony and Soft and Review The user then selects a bony (step 6) and soft-­ tissue (step 7) rate-determining point (RDP) for the correction (Fig. 6.39). In this case, the bony RDP (orange X) is set at the concave border of the osteotomy. The soft RDP (lavender X) is set

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Fig. 6.38  The proposed pivot point (yellow X) defines the axis of correction of angulation (ACA) and is the virtual point around which the deformity will hinge during the correction

Fig. 6.39  Bony (orange X) and soft-tissue (lavender X) rate-determining points (RDPs) for the correction are selected

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Fig. 6.40  As with the planning on the AP X-ray, the first step is to select the center points of the X-ray spheres from left to right on the preference ring

over the peroneal nerve. The software will limit the speed of correction to the slower of the calculated rates for each RDP.  Conversely, the software can calculate and display the daily rate of correction at each RDP based on a user-selected duration of correction. Step 9 prompts the user to review their selections. Any step can be redone by reselecting it on the left-hand column and completing the remaining steps. When the review is complete, the user selects “Save and Continue” and will then upload or paste the orthogonal X-ray and follow similar steps.

6.2.8 ML X-Ray Screen Tools at the bottom of the screen allow the user to reorient and crop the X-ray. The ML X-ray must be taken from medial to lateral with the X-ray spheres attached to the preference ring in their

correct positions. As with the planning on the first X-ray, the first step is to select the center points of the X-ray spheres from left to right on the preference ring (Fig. 6.40). The software calibrates the X-ray measurements and accurately identifies the orientation of the preference ring. The user then follows sequential CORA-method steps for deformity analysis and can redo a step by selecting it on the left side of the screen.

6.2.9 M  L Proximal and Distal Bone Segment Lines The user then selects the midpoints of the proximal (step 2) and distal (step 3) bone segments (Fig. 6.41). The bisector line (green) is drawn at the level of the CORA, and the measured deformity direction and degree are displayed above the X-ray. By default, lengthening will occur along

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Fig. 6.41  The bisector line (green) is drawn at the level of the CORA, and the measured deformity direction and degree are displayed above the X-ray

the axis of the preference segment, and rotation will occur along the axis of the distal segment. The advanced user can draw independent axes for lengthening and rotation.

6.2.10 ML Osteotomy and Proposed Pivot Point In step 4, the user denotes the level and width of the osteotomy (red line). The software uses the width of the osteotomy indicated on AP and ML X-rays to animate cross-sectional bone overlap during the correction later in the program. After the user denotes the location of the osteotomy, the software will automatically draw a yellow line at the same axial level the user selected for the pivot point on the first X-ray (Fig. 6.42). The user can adjust the location of the pivot point along the yellow line.

6.2.11 ML RDP Bony and Soft and Review The user then selects a bony (step 6) and soft-­ tissue (step 7) rate-determining point (RDP) for the correction (Fig. 6.43). As with the proposed pivot point, the software will draw an orange line at the same axial level of the bony RDP and lavender line at the same axial level of the soft RDP on the initial X-ray. The user can adjust the location of the RDPs along their respective lines. The software will limit the speed of correction to the slower of the calculated rates for each RDP. Conversely, the software can calculate and display the daily rate of correction at each RDP based on a user-selected duration of correction. Step 9 prompts the user to review their selections. Any step can be redone by reselecting it on the left-hand column and completing the remaining steps. When the review is

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Fig. 6.42  After the user denotes the location of the osteotomy, the software will automatically draw a yellow line at the same axial level the user selected for the pivot point on the first X-ray

Fig. 6.43  Bony (orange X) and Soft (lavender X) tissue rate-determining points (RDPs) for the correction are selected

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complete, the user selects “Save and Continue” and will then upload or paste the orthogonal X-ray and follow similar steps.

6.2.12 Corrections Screen The measured angular deformities and calculated translations in all three planes (medial/lateral, anterior/posterior, lengthen/shorten) are displayed in tabular form in the Computed Correction column (Fig.  6.44). In this case, the software calculated 11.3° of valgus to varus and 35.9° of pro to recurvatum angular corrections. At the midpoint of the osteotomy, it calculated secondary translations of 1.5  mm of lateral to medial, 2.9  mm of posterior to anterior, and 6.2 mm of length. The default is for 0 axial rotation. The user has the ability to accept or override these computed values and add rotation or addi-

Fig. 6.44  The measured angular deformities and calculated translations in all three planes (medial/lateral, anterior/posterior, lengthen/shorten) are displayed in tabular form in the Computed Correction column. The user has

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tional length discrepancy in the Revised Correction column. In addition to the computed angular corrections the surgeon wanted to gain 50  mm total length and did not want any AP or LM secondary translation at the osteotomy site. These values were entered in the Revised Correction column. If no changes were made the Computed Correction value defaults to the Revised Correction value. The user has the ability to separate and correct deformity parameters in as many as four consecutive steps, each with its own bony and soft-­tissue RDP. In this case, the surgeon wanted to correct all of the deformities simultaneously in step 1. The software displays the calculated duration of correction based on the slower of the user-­ determined rates for each RDP.  Conversely, the software can calculate and display the daily rate of correction at each RDP based on a user-­

the option to accept or change each parameter in the Revised Correction column. The user can separate the correction into as many as four consecutive steps

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selected duration of correction. This allows the surgeon to adjust RDPs or duration of correction as needed to safely correct the measured deformities. In this case, the surgeon selected 0.75 mm/ day at the bony and soft RDP for step 1 and the software calculated an 85 day correction. After entering the values, the user selects “Save and Update” to continue.

6.2.13 3D Preview and Bone Overlap At the bottom of the Correction screen in the 3D Preview tab (Fig. 6.45a, b), the user can select any cardinal orientation to watch animations of the correction in consecutive step order. The animation itself can be rotated in any direction. The Bone Overlap tab (Fig.  6.45c) shows the bone overlap at the osteotomy site at the end of correction. The cross-sectional area of each bone segment is determined from the width of the osteotomy lines as drawn on AP and ML X-rays.

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6.2.15 Final X-Rays (Fig. 6.47) 6.2.16 Foot Case MC is a 6-year old who had neonatal sepsis and septic emboli to multiple physes. He has multiple deformities to his right lower extremity (Fig. 6.48). Problem list: 1. Distal femur deformity 2. Limb length discrepancy 3. Cavus foot 4. Rigid foot and ankle with partial ray amputations Surgical plan (Fig 6.49): 1. Acute deformity correction of distal femur with internal fixation 2. Proximal tibia and fibula osteoplasty for gradual lengthening 3. Gradual correction of cavus foot deformity 4. Application of Orthex hexapod for tibia/fibula lengthening and cavus foot correction

6.2.14 Schedule Screen

6.2.17 Deformity Screen

The schedule (Fig. 6.46) starts on the user-defined Correction Start Date. Each color coordinated column corresponds to its numbered strut and highlighted date ranges signify the overlap between required B-value adjustments, strut changes, or Z plate adjustments. The default schedule is in Millimeters but the user also has the option of displaying the schedule in Clicks format. The Clicks format provides positive or negative integers corresponding to the amount and direction of one-fourth turns per strut per day. For example, a change from 123.75 to 123.25 would be indicated as “−2” in Clicks format because two quarter turns of shortening are required to decrease the strut length by 0.5 mm. The Clicks format can be broken up into as many as four adjustment periods per day.

On the first screen of the Orthex midfoot or ankle frame, the user enters the location and direction of the major deformities in the frontal and sagittal planes then hovers the cursor over the appropriate side and selects one of two frame options: ankle or midfoot (Fig. 6.50). For midfoot corrections, the preference segment must always be the distal segment because this is the only ring capable of having the X-ray spheres attached and having orthogonal X-rays. For ankle corrections, the preference segment must always be the proximal segment because the foot ring does not allow for placement of X-ray spheres. After selecting the frame type (ankle or midfoot), an overlay screen appears where the user selects the appropriate level for the osteotomy or correction (Fig.  6.51). In this case, the user

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Fig. 6.45 (a, b) 3D animation of correction, Bone Overlap tab (c)

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Fig. 6.46  The correction schedule generated by the software: The MM format (left) shows the A scale readings for each of the six numbered struts in color-matched columns. Highlighted date ranges indicate when B-scale,

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struts, or Z plates must be changed. The Clicks format (right) provides positive or negative integers corresponding to the amount and direction of one-fourth turns per strut per adjustment period

Fig. 6.47  SR Final X-rays: Full-length standing (left); lateral (center) and AP (right) left tibia

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d

Fig. 6.48  MC preoperative X-rays showing distal femur deformity, limb length discrepancy, cavus foot with partial amputations: Full-length standing (a), lateral foot and tibia (b), AP foot (c), and long-axial hindfoot view (d)

Fig. 6.49  MC postoperative AP (left) and lateral (right) X-rays of the right lower extremity taken orthogonal to the foot ring with X-ray spheres

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Fig. 6.50  The user hovers over the appropriate side and selects ankle or midfoot frame

Fig. 6.51  After selecting the frame type (ankle or midfoot), an overlay screen appears where the user selects the appropriate level for the osteotomy or correction

selects Cuboid-Cuneiform and presses “Done.” The software creates representative models of the deformity. In this case, there is only a midfoot cavus deformity so the user selects “None” for the dorsal view, and “Apex Dorsal” for the lateral view deformity (Fig. 6.52). The user presses “Save and Continue” on the bottom right to continue to the next screen (yellow dots on top menu bar) in the patient case.

6.2.18 Hardware Screen On this screen the user inputs information regarding the hardware attached to the patient (Fig.  6.53). Through point-and-click drop-down menus and rotating ring icons on the left side of the screen, the ring shape, size, orientation, and A-tab position are selected. The top right section denotes the size and mounting position of the struts. “Standard Outer Mount” is the default for struts attached in their standard positions. If one

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Fig. 6.52  On the midfoot or ankle deformity page, the user selects the frame type and major deformities. For midfoot corrections, the preference segment must always be the distal segment because this is the only ring capable

of having the X-ray spheres attached and having orthogonal X-rays. For ankle corrections, the preference segment must always be the proximal segment because the foot ring does not allow for placement of X-ray spheres

or more struts were placed in nonstandard positions, or Z-plate(s) were used, “Non-Standard Mount” would be selected from the drop-down menu and the appropriate data entered in a pop­up screen. The user enters the adjustable A and fixed B scale lengths for all six struts in the bottom right and presses “Save and Continue” to move to the next screen. Foot and ankle cases have some notable differences from extremity cases. When the user selects a proximal foot ring, the standard strut positions and tab attachments automatically change. In contrast to the typical default, struts 1 and 2 attach to the same tab on the distal ring when a proximal foot ring is selected. The animations reflect these changes. In this case, the user selected a proximal foot ring and distal full ring. Because Z plates and nonstandard strut mounting positions were

employed, the user selected the “Non-Standard” strut selection. The user then selected the appropriate size, direction, and location for each Z plate under its corresponding strut column. The user then pressed “Launch Custom Strut Selection”to place each strut or Z-plate attachment point (Fig. 6.54). After selecting “Save and Continue,” a new screen opens and the user chooses which X-ray to plan first (Fig. 6.55). In general, the X-ray with the largest deformity is selected because the same axial levels of the pivot point, bone RDP, and soft-tissue RDP will be used on the orthogonal X-ray planning page. In this case, the user selected “Lateral.” The user is now able to upload or copy and paste X-ray images to the patient case. It is important to remember that planning X-rays require attachment of X-ray calibration spheres

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Fig. 6.53  Hardware screen: The user enters data about the hexapod rings and their orientation, strut attachment locations and orientation, and strut lengths. Foot and ankle cases have some notable differences from extremity cases. When the user selects a proximal foot ring, the stan-

dard strut positions and tab attachments automatically change. In contrast to the typical default, struts 1 and 2 attach to the same tab on the distal ring when a proximal foot ring is selected

in designated positions on the preference ring for both X-rays and the Orthex software require the traditional “Lateral” X-ray be taken from medial to lateral for measurement calibration purposes. The consecutive steps on this and the following page allow the user to systematically and simultaneously perform measurement calibration, frame positioning, and deformity analysis and correction planning within the patient case. Axial rotation and limb length discrepancy can be added later in the case. Although each step has clear instructions, the software is intuitive and user-friendly and follows standard CORA-based principles.

(preference) ring in their correct positions. Tools at the bottom of the screen allow the user to reorient and crop the X-ray. The first step is to select the center points of the three X-ray spheres from top to bottom on the preference ring (Fig. 6.56). Because this is a midfoot deformity correction the preference ring is always the distal ring. The software calibrates the X-ray measurements and accurately identifies the orientation of the preference ring. The user then follows CORA-method steps for deformity analysis and can redo a step by selecting it on the left side of the screen.

6.2.19 ML X-Ray Distal Ring Screen The ML X-ray must be taken from medial to lateral with the X-ray spheres attached to the distal

6.2.20 ML Midline of Talus and First Metatarsal Line For a midfoot correction, the user then selects the midpoints of the Talus (step 2) and first metatarsal (step 3). The software automatically draws the

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Fig. 6.54  The user pressed “Launch Custom Strut Selection” and selected the attachment point of each strut or Z-plate attachment site on the proximal and distal rings

Fig. 6.55 The software interface allows the user to choose the initial X-ray view to plan the deformity correction. In general, the X-ray with the largest deformity is

selected. The same axial levels of the pivot point, bone RDP, and soft-tissue RDP will be used on the orthogonal X-ray planning page

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Fig. 6.56  The first step is to select the center points of the three X-ray spheres from top to bottom on the preference ring (Fig. 6.56). Because this is a midfoot deformity cor-

rection, the preference ring is always the distal ring. The software calibrates the X-ray measurements and accurately identifies the orientation of the preference ring

bisector line (green) at the CORA, and the measured Meary’s angle and direction is displayed above the X-ray. (Fig. 6.57) By default, lengthening will occur along the axis of the preference segment, and rotation will occur along the axis of the distal segment. The advanced user can draw independent axes for lengthening and rotation.

later in the program. The proposed pivot point defines the axis of correction of angulation (ACA) and is the virtual point around which the deformity will hinge during the correction (Fig.  6.58). The software calculates and displays translations in all three  planes (medial/ lateral, anterior/posterior, lengthen/shorten) that occur at the midpoint of the osteotomy line during correction around the pivot point.

6.2.21 ML Osteotomy and Proposed Pivot Point In step 4, the user denotes the level and width of the osteotomy or correction location (red line), and the location of the proposed pivot point (yellow X) is selected in step 5. The software uses the width of the osteotomy line indicated on AP and ML X-rays to animate and quantify cross-sectional overlap during the correction

6.2.22 ML RDP Bony and Soft and Review The user then selects a bony (step 6) and soft-­ tissue (step 7) rate-determining point (RDP) for the correction (Fig. 6.59). In this case, the bony RDP (orange X) is set at the concave border of the osteotomy line. The soft RDP (lavender X) is

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Fig. 6.57  For a midfoot correction, the user selects the midpoints of the Talus (step 2) and first metatarsal (step 3). The software automatically draws the bisector line

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(green) at the CORA, and the measured Meary’s angle and direction is displayed above the X-ray

Fig. 6.58  The proposed pivot point (yellow X) defines the axis of correction of angulation (ACA) and is the virtual point around which the deformity will hinge during the correction

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Fig. 6.59  Bony (orange X) and soft-tissue (lavender X) rate-determining points (RDPs) for the correction are selected

set over the tibial nerve. The software will limit the speed of correction to the slower of the calculated rates for each RDP.  Conversely, the software can calculate and display the daily rate of correction at each RDP based on a user-selected duration of correction. Step 9 prompts the user to review their selections. Any step can be redone by reselecting it on the left-hand column and completing the remaining steps. When the review is complete, the user selects “Save and Continue” and will then upload or paste the orthogonal X-ray and follow similar steps.

6.2.23 Dorsal X-Ray Distal Ring Tools at the bottom of the screen allow the user to reorient and crop the X-ray. As with the planning on the first X-ray, the first step is to select the center points of the X-ray spheres from left to right on the preference ring (Fig. 6.60). The software calibrates the X-ray measurements and accurately identities the orientation of the preference ring.

6.2.24 Dorsal Midline of Talus and First Metatarsal Line The user then selects the midpoints of the Talus (step 2) and first metatarsal (step 3). The software automatically draws the bisector line (green) at the CORA, and the measured angle is displayed above the X-ray (Fig.  6.61). By default, lengthening will occur along the axis of the preference segment, and rotation will occur along the axis of the distal segment. The advanced user can draw independent axes for lengthening and rotation. For instance, if the patient had a midfoot pronation deformity an independent rotation axis could be drawn along the third metatarsal.

6.2.25 Dorsal Osteotomy and Proposed Pivot Point In step 4, the user denotes the level and width of the osteotomy or correction location (red line). The software uses the width of the osteotomy line

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Fig. 6.60  As with the planning on the ML X-ray, the first step is to select the center points of the X-ray spheres from left to right on the preference ring

Fig. 6.61  The software automatically draws the bisector line (green) at the CORA, and the measured angle is displayed above the X-ray

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Fig. 6.62  After the user denotes the location of the osteotomy line, the software will automatically draw a yellow line at the same axial level the user selected for the pivot point on the first X-ray

indicated on ML and dorsal X-rays to animate and quantify cross-­sectional overlap during the correction later in the program. After the user denotes the location of the osteotomy line, the software will automatically draw a yellow line at the same axial level the user selected for the pivot point on the first X-ray (Fig.  6.62). The user can adjust the location of the pivot point along the yellow line.

can calculate and display the daily rate of correction at each RDP based on a user-selected duration of correction. Step 9 prompts the user to review their selections. Any step can be redone by reselecting it on the left-hand column and completing the remaining steps. When the review is complete, the user selects “Save and Continue” and will then upload or paste the orthogonal X-ray and follow similar steps.

6.2.26 Dorsal RDP Bony and Soft and Review

6.2.27 Corrections Screen

The user then selects a bony (step 6) and soft-­tissue (step 7) rate-determining point (RDP) for the correction (Fig.  6.63). As with the proposed pivot point, the software will draw an orange line at the same axial level of the bony RDP and lavender line at the same axial level of the soft RDP on the initial X-ray. The user can adjust the location of the RDP along their respective lines. The software will limit the speed of correction to the slower of the calculated rates for each RDP. Conversely, the software

The measured angular deformities and translations in all three planes (medial/lateral, plantar/ dorsal, lengthen/shorten) are displayed in tabular form in the Computed Correction column (Fig. 6.64). In this case, the software calculated 17.9° of abduction to adduction and 45.5 degrees of cavus to rockerbottom angular corrections. At the midpoint of the correction location (osteotomy line), it calculated secondary translations of 1.1 mm of medial to lateral, 0.5 mm of dorsal to

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Fig. 6.63  Bony (orange X) and soft-tissue (lavender X) rate-determining points (RDPs) for the correction are selected

plantar, and 7.8 mm of length. The default is for 0 of axial rotation. These are listed in the Computed Correction column. The user has the ability to accept or override these computed ­values and add rotation or additional length discrepancy in the Revised Correction column. In addition to the computed angular corrections, the surgeon wanted to only gain 5 mm total length, 0.1 mm of medial to lateral, and 0.3 mm of dorsal to plantar translation. These values were entered in the Revised Correction column. If no changes were made, the Computed Correction value defaults to the Revised Correction value. The user has the ability to separate and correct deformity parameters in as many as four consecutive steps, each with its own bony and soft-­tissue RDP. In this case, the surgeon wanted to correct all of the deformities simultaneously in step 1. The software displays the calculated duration of correction based on the slower of the user-­

determined rates for each RDP.  Conversely, the software can calculate and display the daily rate of correction at each RDP based on a user-­ selected duration of correction. This allows the surgeon to adjust RDPs or duration of correction as needed to safely correct the measured deformities. In this case, the surgeon selected 0.75 mm/ day at the bony and soft RDP for step 1 and the software calculated a 43 day correction. After entering the values, the user selects “Save and Update” to continue.

6.2.28 3D Preview and Bone Overlap At the bottom of the Correction screen in the 3D Preview tab (Fig.  6.65a, b), the user can select any cardinal orientation to watch animations of the correction in consecutive step order. The animation itself can be rotated in any direction. The

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Fig. 6.64  The measured angular deformities and calculated translations in all three planes (medial/lateral, anterior/posterior, lengthen/shorten) are displayed in tabular form in the Computed Correction column. The user has

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the option to accept or change each parameter in the Revised Correction column. The user can separate the correction into as many as four consecutive steps

Fig. 6.65 (a, b) 3D animation of correction; (c) Bone Overlap tab

Bone Overlap tab (Fig.  6.65c) shows the cross-­ sectional overlap at the osteotomy site or correction location at the end of correction. This is calculated based on the width of the osteotomy lines as drawn on AP and ML X-rays.

6.2.29 Schedule The schedule (Fig. 6.66) starts on the user-defined Correction Start Date. Each color coordinated column corresponds to its numbered strut and

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Fig. 6.66  The correction schedule generated by the software: The MM format (left) shows the A scale readings for each of the six numbered struts in color-matched columns. Highlighted date ranges indicate when B-scale adjustment, strut change, or Z plate adjustment must be

performed. The Clicks format (right) provides positive or negative integers corresponding to the amount and direction of one-fourth turns per strut per adjustment period. In this case, the schedule was broken up into three adjustment periods per day

highlighted date ranges signify the overlap between required B-value adjustments, strut changes, or Z plate adjustments. The default schedule is in Millimeters but the user also has the option of displaying the schedule in Clicks format. The Clicks format provides positive or negative integers corresponding to the amount and direction of one-fourth turns per strut per adjustment period. For example, a change from 123.75 to 123.25 would be indicated as “−2” in

Clicks format because two quarter turns of shortening are required to decrease the strut length by 0.5 mm. The schedules can be broken up into as many as four adjustment periods per day.

6.2.30 Final X-Rays After Foot Correction and Frame Removal (Fig. 6.67)

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Fig. 6.67  Lateral (left) and AP (right) X-rays of the foot and ankle after correction

References 1. Paley D. The principles of deformity correction by the Ilizarov technique: technical aspects. Tech Orthop. 1989;4(1):15–29. 2. Green SA.  Ilizarov method. Clin Orthop. 1992;280:2–6.

3. Paley D, Tetsworth K.  Mechanical axis deviation of the lower limbs: preoperative planning of multiapical frontal plane angular and bowing deformities of the femur and tibia. Clin Orthop Relat Res. 1992;280:65–71. 4. Tetsworth K, Paley D.  Accuracy of correction of complex lower-extremity deformities by the Ilizarov method. Clin Orthop. 1994;301:102–10.

110 5. Feldman DS, Madan SS, Koval KJ, van Bosse HJP, Bazzi J, Lehman WB.  Correction of tibia vara with six-axis deformity analysis and the Taylor Spatial Frame. J Pediatr Orthop. 2003;23(3):387–91. 6. Paley D.  Principles of deformity correction. 1st ed. Berlin: Springer; 2002. 7. Paley D. History and science behind the six-axis correction external fixation devices in orthopaedic surgery. Oper Tech Orthop. 2011;21(2):125–8. https:// doi.org/10.1053/j.oto.2011.01.011. 8. Hughes A, Heidari N, Mitchell S, et  al. Computer hexapod-assisted orthopaedic surgery provides a pre-

D. Paley and C. Robbins dictable and safe method of femoral deformity correction. Bone Joint J. 2017;99-B(2):283–8. https://doi. org/10.1302/0301-­620X.99B2.BJJ-­2016-­0271.R1. 9. Orthex hexapod fixator. www.orthex.net. 10. Hankemeier S, Gosling T, Richter M, Hufner T, Hochhausen C, Krettek C.  Computer-assisted analysis of lower limb geometry: higher intraobserver reliability compared to conventional method. Comput Aided Surg. 2006;11(2):81–6. https://doi. org/10.3109/10929080600628985.

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Hexapod External Fixators in Bone Defect Treatment Redento Mora, Luisella Pedrotti, Barbara Bertani, Gabriella Tuvo, and Anna Maccabruni

Nomenclature BMAC BMP-7 (or OP-1, Osteogenic Protein-1) BMP-2

BMPs bone marrow aspiration concentrate kinds of rhBMPs used in recalcitrant nonunions kinds of rhBMPs used for acute open tibial fractures

R. Mora (*) Full Professor of Orthopaedic Surgery, Division of Orthopaedics and Traumatology, Department of Surgical, Diagnostic and Pediatric Sciences, University of Pavia, “Città di Pavia” Institute University Hospital, School of Medicine, Pavia, Italy L. Pedrotti Associate Professor of Orthopaedic Surgery, Division of Orthopaedics and Traumatology, Department of Surgical, Diagnostic and Pediatric Sciences, University of Pavia, “Città di Pavia” Institute University Hospital, School of Medicine, Pavia, Italy B. Bertani · G. Tuvo Assistant Surgeon, Division of Orthopaedics and Traumatology, Department of Surgical, Diagnostic and Pediatric Sciences, University of Pavia, “Città di Pavia” Institute University Hospital, School of Medicine, Pavia, Italy A. Maccabruni Associate Professor of Infectious Diseases, Consultant in Infectious Diseases, University of Pavia, “Città di Pavia” Institute University Hospital, School of Medicine, Pavia, Italy

bone morphogenetic proteins b-TCP b-tricalcium phosphate DBM demineralized bone matrix FIZ fibrous interzone interposed between the two extremities of the mineralization front during the distraction HA hydroxyapatite hBMP purified human BMP LATN lengthening and then nailing LATP lengthening and then plating LON lengthening over nail LOP lengthening over plate MCF micro column formation zone are areas that gradually increase during bone lengthening MRSA methicillin-resistant S. aureus MSCs mesenchymal stem cells MSSA methicillin-sensitive S. aureus PMF primary mineralization front, that is the transition zone that separate FIZ and MCF areas PRP platelet-rich plasma R1 region region adjacent to the basic segment R2 region region in the central area of the regenerate R3 region region adjacent to the transported segment rhBMPs recombinant human BMPs

© Springer Nature Switzerland AG 2021 M. Massobrio, R. Mora (eds.), Hexapod External Fixator Systems, https://doi.org/10.1007/978-3-030-40667-7_7

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SUV TL-Hex

Solomin Utekhin Vilenski TrueLok Hexapod System, developed by Samchukov and Cherkasin TSF Taylor Spatial Frame VISA strains with intermediate sensitivity to vancomycin VRE vancomycin-resistant enterococci VRSA vancomycin-resistant S. aureus

7.1

Definition and Classification of Bone Defects

Long bone defect can be observed as a result of acute trauma or chronic conditions (nonunions, infection, tumor, or prosthetic replacement) within the upper or lower limbs and represents a complex surgical problem. A definition of “critical-sized bone defect” was recently introduced; this kind of defect would generally be the one that would not heal spontaneously within a patient’s lifetime [1, 2]. General guidelines suggested in literature include defect size length greater than 2 cm and loss of bone circumference greater than 50%  [3], although rare cases of spontaneous healing of large bone defects have been described [4, 5]. Bone defect may be classified not only on the basis of their size (partial defect; segmentary or intercalary defect) but also on the basis of location (diaphyseal; metaphyseal; articular defect), and, in case of bone fracture, on the basis of type (“true” defect; “in situ” defect) [6, 7]. Bone defect caused by extrusion of a fragment during trauma or by removal of devitalized fragments during debridement is defined as “true” [3]; in cases of fracture with large avascular bone segment, definition of bone defect “in situ” is employed, even if a real bone loss caused by trauma or debridement [8] is not demonstrated. In cases of intercalary bone defects, special surgical techniques, based on the theory of “tension stress” described by Ilizarov [9] and on principles of “distraction osteogenesis” (“bone transport” or “bifocal or multifocal compression– distraction osteosynthesis” or “internal lengthening” or “BTDO: bone transport distraction

osteogenesis”) allow to gradually regenerate bone tissue and to fill a gap of missing bone. Distraction osteogenesis is defined as a process of healing that takes place between two bone segments separated by a corticotomy and gradually spaced from each other. This process is different from “transformation osteogenesis,” defined as the result of alternate cycles of distraction and compression performed with the aim of stimulating consolidation. Umiarov [6] and Liow and Montgomery [8] suggested to manage also the bone defect in situ with resection and early bone transport, with the aim of not to lose months of waiting, and Arslan et al. [7] called fractures with avascular, devitalized bone segment as anticipated nonunion, and early management of such conditions with bone transport technique as early bone transport. The main advantages of bone transport consist of lack of morbidity at the sample site, lack of limits related to the dimensions of bone defect and width of regenerated bone (which does not need to become hypertrophic). According to the type of stabilization employed, these techniques may be divided into three main groups: external, internal (intraosseal), and combined (mixed). The most employed technique is based on the use of a dynamic circular external fixation system, which also allows early functional weight-bearing on the limb and includes a series of phases.

7.2

Phases of Bone Transport Performed with Circular External Fixation: Clinical and Biological Features

7.2.1 Surgery (Initial Phase) It consists of: bone regularization at both ends of the defect; stabilization of the long bone with a circular external fixation device; and preparation of the bone transport segment by corticotomy (cortical osteotomy) performed at the proximal or distal metaphyseal zone, keeping the periosteum and the endosteum intact.

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When a classic circular fixator is employed, bone fragment can be transported using fixation elements (pins or wires) transversely oriented, obliquely oriented, or longitudinally oriented and connected to a system of gradual traction. Transport by means of transverse pins or wires directly connected to the rings is simple, but troublesome for the patient. The oblique wires technique shows a good compromise between functionality and tolerability and is more frequently employed in tibial bone transport. The use of longitudinal wires or cables technique was proposed by many authors [6, 10]; the discomfort of this system in the early stages of treatment is balanced by the accuracy of the movement of the transported fragment. If a hexapod fixator is used, bone fragment is transported by means of bone fixation elements transversely oriented and connected to the rings. In particular cases, a special kind of distraction, performed at two or more sites within the long bone, can reduce the duration of treatment. In the “contralateral” bone transport, a corticotomy is performed both proximally and distally and two bone segments are transported centripetally; in case of “ipsilateral” bone transport, the segment is divided in two or more parts and each part is transported towards the next one [11–13]. Corticotomy and bone transport have another important effect, described by the authors who studied experimentally and clinically bone transport techniques [14]; vascularization of the whole limb increases greatly, enabling a good quality of regenerating bone at the distraction site, enhancing the development of bone callus at the docking site, and stimulating the reconstruction of surrounding soft tissues. With regard to the ideal shape of bone defect ends, in most cases segmental excision technique with transversal proximal and distal sections is the best choice in order to achieve a wide area of bone contact on both bone ends. In particular cases, bone contact may be improved by modifying the bone ends, by means of the invagination technique (fitting one fragment into the other), or by means of the reshaping technique (surgically molding the two fragments in complementary shapes) [6, 15].

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About the maximum length limit of the bone defect, management protocols based on the length of the post-traumatic bone defect have been proposed by some authors [16, 17]. According to these protocols, the bone transport technique is indicated for bone defects no more than 10–12 cm in length, but in our series gradual transport allowed to obtain a good-quality bone regenerate even for defects 18 cm in length.

7.2.2 Latency Phase A delay of 5–10  days before distraction allows osteogenesis to begin. The latency phase is biologically identical to the initial phase of fracture healing (inflammatory phase), with formation of a hematoma. The inflammatory response induced by the trauma of corticotomy causes release of cytokines and recruitment and differentiation of mesenchymal stem cells. Following a quite different method of lengthening (named “callotasis”), described in the 80s, a longer delay (about two weeks) before distraction is employed [18], thus performing a distraction of the newly formed callus.

7.2.3 Transportation Phase (Distraction Phase) Distraction at the corticotomy site creates a new defect, which gradually fills with new bone (bone regenerate). Distraction of the segment is performed approximately 1  mm per day (in just one daily session or regularly spaced over 24 h) [19]. In our opinion, subdivision of the distraction of 1 mm/day into several steps does not represent a real advantage for the speed of formation and consolidation of regenerating bone, because even distraction of 1  mm a day in one step is transferred to the bone gradually, due to the viscosity of soft tissues. A clinical study based on tibial lengthenings showed that even using a motorized system with which the distraction of 1 mm a day is subdivided

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in 1440 steps, the new bone formation does not seem to improve [20]. Histologic features of distraction osteogenesis are different from those of fracture healing and are similar to those found in the embryonic growth. Their temporal evolution has been thoroughly studied in clinical and experimental researches [21, 22]. With the progression of distraction, hematoma organizes in fibrous tissue, with cells longitudinally oriented according to the force of distraction. After about three weeks, the presence of osteoblasts with deposition of osteoid substance begins to appear; formation of new bone proceeds from the corticotomy surfaces towards the center, with a fibrous interzone (“FIZ”) interposed between the two extremities of the mineralization front. Bone tissue organizes in micro columns (“MCF”: micro column formation zone) that gradually increase their length, overcome the interzone, and complete the regenerate consolidation. FIZ and MCF are separated by a transition zone (PMF: primary mineralization front) [23]. Experimental researches on long bones [24] show that mineralization progresses from the extremities towards the hypodense central zone. On the basis of experimental studies on distraction osteogenesis in the mandible, Karp et al. [25] distinguished five histomorphologic zones: central zone, two paracentral zones, two zones at the proximal and distal extremities. A histological research performed on sheep [26] shows different results. It highlights the presence of three different regions (R1 region: adjacent to the basic segment; R2 region: in the central area of the regenerate; R3 region: adjacent to the transported segment) in bone regenerate, with gradual decreasing of ossification from the basis to the transported segment. These observations, in contrast to other, would seem to demonstrate that regenerate ossification progresses only in one direction, “accompanying” the transported segment.

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During the formation of new bone tissue, also the surrounding tissues are stimulated by distraction (including skin, muscle tissue, connective tissue, vessels, and nerves) [27]. Bone regeneration takes place through mechanotransduction (conversion from mechanical forces produced by distraction of bone segments to a cascade of molecular signals) with temporal and spatial expression of cytokines, “growth factors,” matrix proteins and metalloproteinases, which in turn activate cellular events that conduct to new bone formation [24, 28]. Distraction osteogenesis is strictly associated with angiogenesis; in the distraction zone, an increased expression of vascular “growth factors” is observed [14, 24], and histologically gradual increase of vessels oriented parallel to the bone columns can be seen [29]. About the type of regenerate ossification, in many experimental studies, ossification is described as mainly membranous, with the presence of limited foci of endochondral ossification [9, 22]. In some studies, however, prevalence of endochondral ossification is observed [30], while in other [31, 29], the presence of a combination of two types of ossification is showed. A third type of ossification of the regenerate, defined as “transchondroid,” has been described [32]. A prevalence of endochondral ossification in the initial stages of distraction and of membranous ossification in the successive stages has been observed; moreover, a further type of ossification, defined as transchondroid, was described. An intermediate tissue between bone and cartilage was observed, defined as “chondroid bone,” directly formed by cells similar to chondrocytes, with gradual transition from fibrous tissue to bone tissue without capillary invasion. It should be stressed that different factors may play a role in determining the predominant type of ossification of bone regenerate: device stability, vascularization of the surrounding tissues, size and rhythm of distraction, and even animal species may influence the relative contribution of membranous and endochondral ossification.

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7.2.4 Consolidation Phase

7.3

Consolidation of the regenerate: during this phase of distraction osteogenesis, active remodeling takes over. Intermittent mechanical stimulation plays a role in this phase. Keeping patients mobile and weight-bearing is effective in promoting the evolution and in maintaining bone mass of the regenerate bone, and it was also observed that continuation of the tension effect (by means of distraction of 1  mm every fortnight) during the consolidation phase contributes to completion of regenerate consolidation [6, 12]. At the docking site bone healing is obtained by interfragmentary compression between the transported segment and the bone end at the resection site. Just few researches have explored the features of bone consolidation within this area, which appears not rarely poor, with frequent delay or in some cases absence of bone callus formation. A recent study highlights that ossification is mainly intramembranous with some areas of endochondral ossification [33].

Complications such as delay in ossification or angular deformities of the regenerated bone, and delayed consolidation or lack of consolidation of docking site, can occur due to inadequate configuration of the external device, imperfect management of the phases of treatment, and obstacles on bone transport [34, 36, 37]. In cases of delayed consolidation, some cycles of “gymnastics” of the regenerate (consisting in alternating phases of compression and distraction, generally performed with a period of gradual compression of 4–5 mm at the rate of 1 mm per day in only one session, followed by a period of gradual distraction of 4–5 mm and a rest period of 4–5  days, repeated two or three times) can enhance, in most cases, the osteogenic capacity. If this technique is without result, bone grafting is needed. Other methods to stimulate the maturation of regenerated bone have been employed: association with internal osteosynthesis, bone marrow injections, electric or magnetic stimulation, ultrasound stimulation, and use of bone growth stimulating factors or osteoblast cells cultures [38, 39]. At the docking site, opening the nonunion site and once again reshaping the bone ends or bone grafting at the site of the delayed consolidation is sometimes necessary [40]. Other possible complications can be observed during treatment: inflammation or infection, breaking of the bone fixation elements at the site of application of the external device, functional impairment (joint stiffness), and defects of skin coverage during the management of bone defects combined with soft-tissue loss (due to an improper rate of bone and soft-tissue transport) [41]. Respect of precise rules in the preoperative, intraoperative, and postoperative management of these difficult cases is of great importance in order to reduce number and severity of complications [34].

7.2.5 F  inal Phase (External Fixation Removal) The fixator removal is decided on the basis of the clinical conditions and X-ray (and if necessary extensimetric) periodical controls, performed in order to evaluate maturity of callus at the docking site and presence of a bridging callus on at least three cortices at the bone regenerate. Further X-ray dynamic controls under image intensifier, after loosening of connections of the fixator, allow to confirm the achievement of complete stability before definitive device removal [34, 35]. An alternative method consists of a period of dynamization of the external device (by loosening its connections) and direct loading, with the aim to confirm the maturity of bone regenerate, before the device removal.

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7.4

Indications and Contraindications

7.4.1 Indications in Trauma Situations

7.4.3 Indications in Bone Tumors Management In the field of neoplastic bone diseases, main indications to the use of circular external fixation are represented by stable fixation of grafts after bone resection, correction of limb deformities in patients previously treated with radiotherapy, and reconstruction of large bone segments. In case of reconstruction after resection of tumor, bone transport techniques may have indication [46, 47].

There are two main kinds of indications for bone transport according to types of bone defects: segmental defects following acute trauma situations and segmental defects in chronic trauma situations [42]; therefore, bone transport techniques may be classified as immediate (contemporaneous with the injury) or secondary (in cases of nonunions requiring bone resection). The bone defect results in the first case from 7.4.4 Contraindications for Bone Transport acute trauma with loss of bone substance or from surgical debridement after open fractures; in the second case, it is caused by a range of post-­ Multiple systemic or local adverse factors, alone traumatic situations such as noninfected and or in combination, may represent relative contrainfected nonunions. Moreover, severe open indications for bone transport: systemic factors fractures with bone loss, atrophic noninfected (age, metabolic bone diseases) and local factors ­ nonunions, atrophic infected nonunions, and (vascular lesions, immobilization, local radiation infected nonunions with bone loss are often asso- therapy) [48, 49]. ciated with very poor soft-tissue coverage at the site of injury, and a very accurate debridement of soft tissues is mandatory in these cases. 7.5 Bone Fixation Devices Since the favorable result of both bone regeneration and solid docking involve well-­ Bone transport requires a stable mechanical vascularized segments of bone and soft tissue, it environment, which may facilitate gradual is also essential to consider which kind of envi- bone regeneration at the distraction site and ronment is present or can be achieved at both the union at the docking site. Different systems for site of the corticotomy and the docking site [43]. bone transport, such as external fixation or internal fixation (distraction over a nail), were reported, but our preferred technique is the transport with circular external fixators, due to 7.4.2 Indications in Osteomyelitis Management the advantages of external over internal fixation and of circular and hexapod devices over A long bone infection can occur spontaneously axial systems, including early functional loador more often after trauma or after management ing, possibility of displacement correction on every point of the bone circumference, and in of fracture with internal fixation. Infection is often associated with bone defect, every phase of the treatment, easy removal at caused by infection itself, debridement, previous the end of treatment [50]. Circular external devices may be divided in surgeries, or previous traumas [44, 45]. In these cases, the technique of bone transport is two main groups: “classic” (or “conventional”) systems and “hexapod” systems. indicated.

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7.5.1 C  lassic Circular External Fixators Classic systems are composed by a few basic elements: bone fixation elements, rings which encircle the bone segment, rods connecting the rings, connecting elements between rods and rings, and connecting elements between rings and bone fixation elements. Many other secondary elements, which differ in importance and number in various systems, can be added [9, 50, 51]. Ilizarov system is the most well-known [9]. It originally consisted of flat half-rings, which are connected in pairs and compose the apparatus rings. On the surface of the rings, longitudinally threaded rods (fixed by nuts and used to connect the rings) can be passed through holes displaced by 10°. The bone fixation elements are thin metallic wires (1.5 or 1.8 mm in diameter) fixed to the rings by dedicated buckles or special cannulated or slotted bolts and put under tension with a specific tensioner. Then other elements were developed: lighter and radiotransparent composite half-rings as alternatives to the classic steel half-ring; graduated telescopic rods, to promote the execution and the control of compression or distraction through the simple rotation of the head of the rod; and half-pins fixed to the rings through special buckles called “Rancho Cubes” at any level of fixation instead of wires, in order to improve patient compliance and reduce the risk of inflammation and infection [36, 37]. The main problem of “classic systems” in the management of trauma situations or of complex deformities is that they are unable to perform a simultaneous correction of the displacements or deformities, with a consequent need for a sequential correction.

7.5.2 Hexapod External Fixators From the 1980s, a second generation of circular external fixators (hexapod systems or six-axis correction external fixation devices) was developed, linked to computer planning software that processes data provided by X-rays. Hexapod systems ensure a high accuracy in the simultaneous

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correction of all kinds of deformities or fracture displacements of the long bones [52, 53]. These systems are based on the six degrees of freedom mechanism known as Stewart platform, designed by Stewart [54] to simulate flight conditions. Gough and Whitehall [55] augmented from 3 to 6 the number of the linear actuators, so the new mechanism, consisting of a base and a platform connected through six extensible legs, is called the Stewart–Gough platform. The first software-based hexapod circular external fixator in order to perform long bone simultaneous correction of complex deformities was the Taylor Spatial Frame (TSF) [56]. The basic unit consists of two full rings, connected by six diagonally oriented telescopic and adjustable struts. Fixation to the bone is achieved by wires, half-pins, or a combination of the two elements. The accuracy of deformity correction is dependent on analysis of the radiograms. Parameters describing the fixator, displacement or deformity, and position of the fixator with respect to the bone are entered into a computer, and then a software provides the proper adjustments of the six modular struts needed to obtain reduction or correction. Adjusting the struts changes the orientation of one ring to the other, and this results in a spatial change of one bone fragment to the other one. Adjustments during the postoperative period are also possible by changing the strut length and can be done by the patient, according to a special schedule, always generated by the software. This system is today largely employed in the world. New systems of hexapod external fixation were presented later, such as SUV frame system, TL-Hex system, and others. In 2009, Solomin, Utekhin, and Vilenski proposed a new system called SUV frame (from the names of authors) with features different from previous hexapod systems [57, 58]. Each ring is connected to three struts, and the other three struts are connected to the side of another strut. Mathematical calculations of the computer program are based on the length of struts and on the length of the sides of the triangle formed at each ring by the strut connection. This kind of mounting makes the system light and the program simple to use.

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TL-Hex hexapod system is an evolution of the “classic” circular fixator TrueLok, developed by Samchukov and Cherkasin, and was presented in 2012. In this system, the oblique struts are fixed in pairs on tabs positioned on the edge of the rings [59]. An associated software performs the mathematical calculations on the basis of information supplied by measurements.

7.6

Alternatives to Bone Transport with Circular External Fixation

There are various methods other than bone transport proposed for the reconstruction of diaphyseal bone loss. Bone grafting. Autologous bone is considered as the “gold standard” bone grafting material, as it combines all properties required in a bone graft material: osteoinduction (bone morphogenetic proteins and other growth factors), osteogenesis (osteoprogenitor cells), and osteoconduction (scaffold) [60]. Autologous bone graft is most often taken from the iliac crest or, sometimes, from femoral great trochanter, femoral distal metaphysis, or tibial proximal metaphysis. It has been observed that bone of membranous origin (iliac bone) shows better osteoinductive activity than bone of endochondral origin (tibia and femur) [61]. Quantity of bone tissue needed, long time of immobilization, long period to achieve graft hypertrophy, possible morbidity and pain at the donor site, absence of healing and fractures at the graft site, and frequent need for many operations are concerns [16]. The microvascularized autologous bone graft [62] is based on the employment of rib, ipsilateral or contralateral fibula, or, more rarely, the iliac crest with soft-tissue coverage (composite graft). The procedure is technically difficult and requires long operation times; the risks in cases where there is only one vascular axis should moreover be considered [42]. Good outcomes were also described with the use of homoplastic (allogenic) bone grafts to reconstruct large skeletal defects [63, 64]. These grafts are generally stored by refrigeration and

employed as massive graft or as thin sheets of cortical bone. Allogeneic bone is available in many preparations, including demineralized bone matrix (DBM), morcellized and cancellous chips, cortico-­cancellous and cortical grafts, and osteochondral and whole-bone segments. Most frequent complications in this kind of treatment are slow remodeling, infection, and graft fracture. Induced membrane technique. In cases of chronic post-traumatic long bone defects, the induced membrane technique, proposed by Masquelet, takes advantage of the creation of a vascularized envelope with osteogenic factors that can improve union rates when staged bone grafting is performed [65]. The first step of this technique includes a careful debridement with large excision of nonviable tissue; if necessary, a cover flap is created, then an acrylic cement spacer is placed in the bone defect, after adequate stabilization of the bone. The spacer acts as a foreign body and a membrane is gradually created. This “induced membrane” acts as a “biologic chamber” and will prevent graft resorption by providing vascularization and growth factors. The second step, performed at least 6–8 weeks later, includes removing the spacer and filling the biological space which has been created by autologous cancellous bone graft in small chips of no more than 1–2 mm. Because the harvesting of the graft from the iliac crest may be followed by some complications, such as donor site morbidity and limited availability of bone graft, a recently developed procedure increases the capacity of bone reconstruction, by means of a new device (Reamer— Irrigator—Aspirator: RIA) that allows the use of graft harvested from the medullary cavity of a long bone [66]. This system is associated with risk of complications, such as post-reaming fractures, and requires delayed weight-bearing. Reconstruction by means of induced membrane technique associated to bone transport in a case of tibial segmental bone defect was reported by Uzel et al. [67]. Megaprostheses. The development of special prostheses (so-called megaprostheses) that

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replace many skeletal segments, such as the long bones of the upper and lower limbs and the relative joints [68], offers new opportunities for the management of large bone defects in cases of repeated failures of the reconstructive treatments of nonunions with bone defect, by means of application of the principles of biologic chamber combined with the principles of oncologic surgery [69, 70]. Megaprostheses can be implanted with either one- or two-step technique, depending on the septic conditions of the patient. With the two-step technique, in the first phase, an antibiotic-loaded cement spacer is placed in the bone defect following large debridement of infected and necrotic tissues, after careful stabilization of the bone, in order to create an induced membrane with osteogenic factors. In the second phase, after an interval of 6–8 weeks, if inflammatory markers are normalized and signs of infection are absent, the spacer is removed and a pseudo-synovial ­membrane is observed. In this sterile environment, the special prosthesis is implanted. These special prostheses are modular, and the choice of size and length of the elements allows the surgeon to correct limb length and to restore function of joints. Other techniques have been suggested and applied in order to enhance bone regeneration and shorten the treatment period. Bone shortening. Possible alternatives are based on bone shortening: “isolate shortening” to perform immediate interfragmentary compression between the fragments; “acute shortening” followed by immediate or deferred gradual lengthening by distraction in the nonunion area after a short period of compression; “acute shortening with further lengthening” by means of a distractional corticotomy distant from the fracture site [42, 71]. This technique can produce satisfactory results, but has some disadvantages, including the negative psychological effect on the patient, the possible limitations of articular function, difficult walking in the early stages of treatment (in cases of shortening in the lower limbs), and the possible damage to soft tissue produced by a shortening of many centimeters.

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Bone graft substitutes. Bone graft substitutes consist of scaffolds made of synthetic or natural biomaterials that promote the migration, proliferation, and differentiation of bone cells for bone regeneration. A wide range of biomaterials and synthetic bone substitutes are currently used as scaffolds, including collagen, hydroxyapatite (HA), b-­ tricalcium phosphate (b-TCP) and calcium-­ phosphate cements, and glass ceramics. These are being used as adjuncts or alternatives to autologous bone grafts [60]. Mesh cages. A further alternative for reconstruction of large defects of the long bones is the use of cylindrical metallic or titanium mesh cages as a scaffold containing bone graft material [72]. BMP. Bone morphogenetic proteins (BMPs) are potent osteoinductive factors; they induce the mitogenesis of mesenchymal stem cells and their differentiation towards osteoblasts. After the first studies on the use of BMPs in nonunions using purified human BMP (hBMP), the use of recombinant DNA technology to produce rhBMPs made it possible to extend experimental studies and human applications. In 2001 and 2002, two kinds of rhBMPs were approved by the US Food and Drug Administration for trauma: BMP-7 (or OP-1, Osteogenic Protein-1) for use in recalcitrant nonunions and BMP-2 for acute open tibial fractures [73]. However, clinical evidence on BMPs’ use for the treatment of fractures or nonunions is still controversial [74]. PRP. A current approach to enhance bone regeneration and soft-tissue healing by local application of growth factors is represented by the use of platelet-rich plasma (PRP), a volume of the plasma fraction of autologous blood with platelet concentrations above baseline, which is rich in many of the aforementioned molecules [75]. MSC. Mesenchymal stem cells (MSCs) are effective agents of bone regeneration. A minimally invasive procedure is based on the use of bone marrow aspiration concentrate (BMAC), which includes bone marrow aspiration from the iliac crest, further concentration, and delivering mesenchymal osteogenic cells directly to the regeneration site. BMAC is considered to be a

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useful product to augment bone grafting and support bone regeneration [76]. Bone tissue engineering. Bone tissue engineering combines in composite grafts progenitor cells (for osteogenesis), biocompatible scaffolds (for osteoconduction and vascular ingrowth), and growth factors (for osteoinduction), in order to generate bone tissue [77, 78]. Gene therapy. The application of gene therapy [79, 80] involves the transfer of genetic material into the genome of the target cell, using a viral (transfection) or a nonviral (transduction) vector and favoring a prolonged expression of bioactive factors from the cells themselves for skeletal tissue regeneration.

7.7

Techniques of Bone Transport

7.7.1 Bone Transport in Acute Trauma Situations (Emergency Procedure) 7.7.1.1 Open Fractures It has been calculated that 0.4% of all fractures are associated with bone loss and that the most common site of bone loss is the tibia (68%), followed by the femur (22%), with the remaining fractures occurring evenly at different sites [81]. Traumatic segmental bone defects may result from open fractures with bone loss or from surgical debridement after open fracture with comminution. In the last case, it is necessary to decide how much bone to remove, taking into account that an aggressive debridement of bone fragments reduces the risk of infection. Moreover, in open fractures, large skeletal defects are often associated with soft-tissue loss that may result directly from the injury or from delayed wound necrosis. These cases require at the first step to follow the principles of open fracture management, and subsequently the institution of bone transport techniques, taking into account that the greatest problem is the risk of infection [42]. The operative technique follows the rules of bifocal compression–distraction osteosynthesis:

at the proximal or distal metaphysis of the long bone a corticotomy is performed in order to allow a gradual distraction; all the multiple intermediate fragments are removed, if present, and the bone ends are reshaped; when the transported bone fragment comes into contact with the other bone end, interfragmentary compression is performed at the docking site to achieve consolidation.

7.7.2 Bone Transport in Chronic Trauma Situations (Planned Elective Procedure) (a) Atrophic noninfected nonunions In atrophic nonunions, vascularization of the bone ends is almost absent, and the interfragmentary gap is filled with loose connective tissue, without biological activity [34]. Also, in these cases, the operative technique consists of a bifocal compression–distraction osteosynthesis, with reshaping of the bone ends, corticotomy at the proximal or distal metaphysis of the long bone in order to perform gradual distraction; interfragmentary compression at the docking site after the bone transport. (b) Infected nonunions: third and fourth type of Umiarov’s classification Among infected nonunions, our treatments are based on the classification and on the therapeutic principles developed by Umiarov at the Central Institute of Traumatology and Orthopedics (CITO) of Moscow [6, 82–85] (Table 7.1). These kinds of treatment are based on the distraction osteogenesis methods, but also on adequate antibiotic treatment. Ilizarov (1982) optimistically said that “bone infection burns on the fire of the bone regenerate,” but it occurs just rarely, and cases of infection have to be managed with an antibiotic treatment, carefully planned in collaboration with the infectious disease specialist. In this regard, the various types of bone infections require specific therapeutic strategies aimed at the eradication of the infection while preserving bone integrity and function [86, 87].

7  Hexapod External Fixators in Bone Defect Treatment Table 7.1  Classification of infected tibial nonunions and principles of treatment according to Umiarov (1986)

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For treating cases of osteomyelitis caused by MRSA strains with poor response or intolerance Type Treatment to vancomycin, recent antibiotics with high bone Debridement, monofocal Normotrophic penetration such as linezolid, tigecycline, and osteosynthesis nonunion without daptomycin and lipoglycopeptides (dalbavancin) (compression–distraction) shortening are available, but no large randomized trials have Debridement, monofocal Hypertrophic been published on their use for bone infections. osteosynthesis (distraction) nonunion with shortening Rifampicin is effective in bone infections Atrophic nonunion Debridement, bifocal caused by MSSA and MRSA strains, mainly with shortening osteosynthesis because it can penetrate membranes and biofilms (compression–distraction) and kill pathogens in the sessile phase of growth. Debridement, bone resection Nonunion associated Rifampicin use is recommended as adjunctive without soft-tissue coverage, with bone and bone transport soft-tissue loss agent in a combination therapy because the development of resistance is rapid when it is administered in monotherapy and side effects are Parenteral antimicrobial therapies, usually frequent. continued with oral regimens, should be based on Pseudomonas aeruginosa spp., E.coli, and the identification of pathogens from deep bone Klebsiella spp. are the most common Gram-­ cultures effected at the time of bone biopsy or negative organisms responsible of chronic osteodebridement. The antibiotic administration must myelitis and also anaerobic bacteria as be high dose and prolonged (4–6 weeks) because Bacteroides spp., anaerobic cocci, Fusobacterium the rate of relapse is high, mainly in chronic spp., Propionibacterium acnes, and Clostridium forms. The relapses of osteomyelitis are probably spp. have been more and more frequently recogdue to bacterial evasion of host defenses by pen- nized in the bacteriology of bone and joint disetrating intracellularly and/or by persisting eases, mainly in vasculopathic and/or diabetic within biofilm that protects the organisms from subjects. phagocytosis and impedes delivery of the The most important stage in the surgical planantibiotics. ning is an accurate debridement [88], which must Staphylococcus aureus is the most commonly be performed only after bone stabilization and isolated pathogen from both acute and chronic metaphyseal corticotomy. osteomyelitis in all age groups; among The indication for bone stabilization, accord­Gram-­positive bacteria, coagulase-negative ing to most authors [17], is always the external staphylococci (S. epidermidis and others) and osteosynthesis. We always prefer circular exterhemolytic streptococci are also frequently nal fixation due to its intrinsic advantages (stabilresponsible for bone infection. ity, immediate functional weight-bearing, easy Because of the continuous increase in removal at the end of the treatment). methicillin-­resistant S. aureus (MRSA) strains in A circular external fixator is applied; at the the last years, the use of glycopeptides (in par- proximal or distal metaphysis a corticotomy is ticular vancomycin) still represents a useful ther- performed (according to the distal or proximal apeutic strategy against these organisms. resection site) in order to allow a gradual distracNevertheless, true resistance to this antibiotic has tion, and after that, an accurate debridement of already been recognized in U.S.A., and the the infected and necrotic bone tissue at the nonincreased prevalence of strains with intermediate union site is carried out, with bone end resection sensitivity to vancomycin (VISA), vancomycin-­ until healthy bone is observed. Then, the external resistant S. aureus (VRSA), and vancomycin-­ device is completed with a system of gradual disresistant enterococci (VRE) is actually limiting traction applied to the fragment designed to be its usage. transported.

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In the postoperative phase, the patient continues specific antibiotic therapy and daily dressings. After 1  week, the gradual transport of the bone fragment at 1 mm daily causes a progressive distraction with regenerating bone formation at the corticotomy site and a gradual narrowing of the gap between the fragments at the nonunion site. At the end of the transport, a strong interfragmentary compression allows to obtain consolidation. Kinesitherapy and muscle strengthening  are started immediately, and standing and walking start a few days after the operation. Gradual functional weight-bearing is allowed in the first days postoperatively.

Fig. 7.1 (a, b) X-ray of an infected nonunion of the right tibia in a 30-year-old man (as a result of severe trauma of a gunshot wound), previously treated with multiple surgical procedures

a

7.7.3 T  hird Type: Atrophic Infected Nonunions Atrophic infected nonunions are the “infected variety” of the corresponding type of noninfected nonunion. The treatment is similar to that of the atrophic noninfected variety and is based on the distraction osteogenesis methods, but an accurate debridement and adequate specific antibiotic therapy in these cases are needed. The most important stage in the surgical planning is debridement, performed only after bone stabilization and metaphyseal corticotomy (Figs. 7.1a, b and 7.2a, b).

b

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b

Fig. 7.2 (a, b) Same case as in Fig. 7.1 one month after surgery, performed with a combination of a hexapod fixator and a conventional fixator. After mounting of a hexapod SUV frame proximally, connected with an Ilizarov

frame distally, proximal corticotomy and excision of the infected bone and soft tissue were performed, and after 7 days gradual bone transport was started

7.7.4 Fourth Type: Infected Nonunions with Bone and Soft-Tissue Loss

aims of the treatment (represented by: infection healing, soft-tissue reconstruction, and bone consolidation with preservation of the limb length) may be achieved by appropriate surgical management and administration of specific antimicrobial therapy. Soft-tissue reconstruction can be performed by different means [42, 90]. A split thickness skin graft is rarely indicated because it would surely fail if the graft were applied on poorly vascularized soft tissues or bone without periosteum. Therefore, alternative methods are usually employed. A cross-leg flap is also rarely used because of the prolonged period of immobilization and the aesthetic problems that it causes.

In these cases, bone and soft-tissue loss is directly produced by trauma or most often by the wide surgical debridement, usually performed with numerous operations in an attempt to eliminate the necrotic and infected areas [89]. The choice of treatment requires previous evaluation of the possible options (according to the trauma and the features in the individual patient): amputation and prosthesis or reconstruction. If reconstruction is chosen, the problems to deal with are infection, lack of bone continuity, lack of soft-tissue coverage, and the essential

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Local muscle flap offers the advantage of self-­ vascularization; it allows a firm coverage and can also be covered by a skin graft as immediate or delayed procedure; however, distant coverage is often difficult and not rarely impossible to perform because of the extent of the lesion to the whole limb. Free microvascularized grafts [91] can be sampled from areas spared by the trauma. Among the most frequently used microvascularized grafts are the groin flap, the latissimus dorsi flap, and the tensor fasciae latae flap. One particular kind of flap is the composite bone-muscle-skin graft, composed of iliac crest and soft tissues (composite osteocutaneous groin flap) based on the deep circumflex iliac artery, indicated in the treatment of combined defects of both bone and soft tissue. The reestablishment of bone continuity can be achieved with autoplastic bone graft, microvascularized bone graft, and homoplastic bone graft. A particular technique employing autoplastic bone graft is the Papineau method [92], consisting of excision of infected and necrotic bone and soft tissue, stabilization, and reconstruction by cortical spongy bone graft without skin coverage. This procedure has the disadvantages of being performed in many operative stages and requiring prolonged periods of time to heal. The treatment of choice, in our opinion, is based on the distraction osteogenesis methods (bifocal compression–distraction osteosynthesis). In particular, for the management of the most frequent nonunions of this group (Umiarov type 4 infected nonunion of the tibia), an excellent technique is represented by a variant of the bifocal compression–distraction osteosynthesis, employing the method of epidermato-fascio-­osteoplasty. This method, developed by Umiarov, offers the essential advantage of precisely classifying the operative phases and the stages of simultaneous bone and soft-tissue regeneration and eliminating wide tissue losses without previous sterilization of the infected site and closure of the soft tissue or the use of any kind of graft [6, 41]. It must be emphasized that (as in every case of bone infection) using this method it is paramount to follow a very strict order (resection of infected

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bone must be performed only after application of the external device and after corticotomy). A circular fixator is applied. The assembly must be extended to the hindfoot in patients in whom a loss of tissue in the distal tibia requires extensive resection and the expected final length of the distal tibial fragment is only few centimeters in length. After fibular osteotomy, at the proximal or distal tibial metaphysis a corticotomy is performed (according to the distal or proximal resection site) in order to allow a gradual distraction. After that, an accurate debridement of the infected and necrotic bone tissue at the nonunion site is carried out, with bone end resection until healthy bone is observed, and excision of the surrounding infected soft tissues. The softtissue resection level must correspond to the bone resection level; otherwise, a new infection will develop. The wide debridement area is then kept open. Then, a system of gradual distraction is applied to the tibial fragment designed to be transported, which is generally made up of two oblique wires with a support base connected to the apparatus; the transverse wire transport technique should only be employed, in our opinion, when multilevel transport is performed. In Umiarov’s original technique, only one longitudinal wire (only for proximal corticotomy) is employed, whose ends, bent like a hook, are supported on the cortical edge. This wire is passed through the medullary canal, the talus, and the calcaneus, ultimately protruding from the middle of the sole, and is then fixed by a progressive traction device to the distal ring of the apparatus. A similar but different technique is the so-­ called “intramedullary cable bone transport technique,” which tries to prevent docking site troubles and skin problems due to excursion of the K wires [10]. In the postoperative phase, the patient receives specific antibiotic therapy and daily dressings. After two weeks, a granulation tissue covers the bone segment surfaces. From this moment, the transport of the bone fragment at 1 mm daily causes a progressive distraction with regenerating bone formation at the

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corticotomy site and a gradual narrowing of the gap between the fragments at the nonunion site. Simultaneously, the gradual approach of the tibial fragments closes the edges of the soft-­tissue gap until the epidermic and fascial reconstruction is complete because the tibial fragment takes the fascia and the skin, both closely connected to the bone, along during the transport. This is how a true epidermato-fascio-osteoplastic treatment is performed. At this time, the distraction system is removed and the tibial fragment is fixed to an additional ring by two cross transverse wires or by half-­pins, in order to enable a more effective interfragmentary compression and to obtain consolidation. Knee and ankle kinesitherapy and muscle strengthening are started immediately after surgery, and standing and walking start a few days after. Performing this technique by means of hexapod fixators is very similar; some authors used a double-stacked hexapod external fixator (using two hexapod devices) with the aim to maintain high precision in the alignment of bone fragments [93].

7.8

Bone Transport in Osteomyelitis

The dead space created by debridement of osteomyelitis requires an adequate management. Reconstruction of large bone defects with traditional techniques of grafting poses the problem of the defect dimension, and method of bone transport helps to resolve this problem [44, 94–96]. The technique is similar to that employed in the management of bone defect in cases of infected nonunions with bone loss and must be supported by administration of specific antimicrobial therapy.

7.9

Bone Transport in Bone Tumors

Bone transport techniques, after resection of malignant bone tumor, have indication for treatment in selected cases [46, 97].

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In the first phase, circular fixator is used in order to stabilize a temporary spacer in methacrylate, applied to maintain the limb length during the chemotherapic treatment. In the second phase, the spacer is removed and the device is employed to obtain bone regeneration by means of distraction osteogenesis. In this manner, possible damages on bone regenerate induced by simultaneous use of chemotherapy are avoided [98]. Other studies, however, do not report negative effects of chemotherapeutic agent administration contemporary with distraction [99].

7.10 Conversion from External to Internal Fixation In the last decades, new techniques have been developed in trauma surgery with the aim to reduce the possible risks of a prolonged treatment with external fixators, such as loss of stability of the device (with consequent loss of reduction and risk of nonunion), pin tract infection, pin breakage, joint stiffness, psychological pain with inability of patient to tolerate the device for long periods of time, and refracture after external fixator removal [100, 101]. Conversion from femoral external fixation towards nailing, initially performed in multiply injured patients who are critically ill, is generally judged as indicated when the patient condition has been stabilized [102]; conversion from tibial external fixation to intramedullary nailing is taken into account in the light of the supposed high nonunion rate associated with external fixation [103]. In the field of orthopaedic surgery, new techniques of conversion (“combined” or “consecutive” fixation) have been developed in order to achieve similar improvements in cases requiring bone lengthening, bone deformity correction, and bone transport to “correct” bone defects [100]. Lengthening over nail (“LON”), lengthening over plate (“LOP”), lengthening and then nailing (LATN), and lengthening and then plating (“LATP”) are employed in cases of bone lengthening; fixator-assisted nailing and fixator-assisted

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plating are performed for long bone deformity correction (so-called “integrated” techniques for deformity correction). In cases with bone deformity and length discrepancy, correction with external fixation and then insertion of a nail and lengthening is employed. Indications to use of conversion from external to internal fixation in orthopaedic and trauma surgery gradually extended from classic circular external fixation to hexapod external fixation. Moreover, conversion from external to internal fixation was used by some authors also in the management of long bone defects with transport technique [104]. The risks related to all these treatments are loss of stability, occurrence of bone deformity, and mainly cross contamination, depending on pin tract infection. For these reasons, we do not agree with the conversion in these cases and we recommend the greatest caution about these techniques.

7.11 Observations on Advantages and Disadvantages of Hexapod External Fixation in Segmental Bone Defects Management In the evaluation of the pros and cons of the management of bone defects with conventional circular external fixators or hexapod external fixators, it should be considered that the latter devices are an evolution of the first, and since the indications to their use are almost the same, the choice depends also on individual preferences. General advantages of Hexapod fixation. Easy application, precise correction, and possibility of simultaneous and nonsequential action on deformities or displacements are considered the most important general advantages of hexapod fixators. In particular, simultaneous correction of all deformities replaces the need for performing frequent manual changes of the connections of the mounting and makes the daily corrections on the struts much easier for the patient.

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There are, however, some comments to be made. The correct working of different hexapod fixators is completely dependent on the different computer programs. The differences in hardware and software among the available system are often relevant and have to be taken into account. During correction planning, one must always consider not only the three spatial dimensions but also the time factor, because the hexapod fixator configuration changes over time. Struts of the device, getting gradually shorter or longer over time, modify their shape, angle with the rings, and their orientation in the space, and, in the absence of any meticulous planning, a conflict with bone fixation elements could occur. Moreover, the choice of the strut length is limited, so the shortest available distance between the rings must be always taken into account before mounting the device, especially in cases of deformity correction or fracture management in children. A careful planning of the assembly of the device and, after surgery, a precise programming of corrections are therefore requested. Special advantages of Hexapod fixation. Some other special advantages of hexapod fixation in bone defect management should be considered. During bone transport performed with bifocal or also multifocal compression–distraction osteosynthesis, deformities (more often angular deformities) can occur, generally as a consequence of obstacles represented by scar tissue. In these cases, correction with a traditional circular fixator may be difficult, while correction by means of hexapod system is very easy. For the same reason, it may be difficult to obtain a precise contact at docking site at the end of the transport (more often as a consequence of a translational deformity between the fragments), with the risk of delayed consolidation. In this case, correction by means of hexapod system is very easy. Not rarely, during bone transport from proximal to distal level for femoral defects, a gradual appearance of angular varus deformity of the proximal femoral segment is observed, because

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of the strong action of the anterior and medial muscular groups of the thigh and of the insufficient stiffness of the fixator’s rods. Similarly, during bone transport from proximal to distal level for tibial defects, a gradual procurvatus deformity of the proximal meta-­ epiphyseal segment is caused by excessive traction exerted by the quadriceps tendon. In all these cases, the deformity is easily corrected by substitution of the rods of the classic fixator type with the struts of a hexapod fixator and by subsequent correction. General disadvantages of hexapod fixation. As in every other type of use of hexapod fixation, cost of the device and learning curve are the main general disadvantages, as underlined by many authors. With regard to the costs, it should be also noted that in particular cases, a special technique of fixation and treatment of long bone defects is used (so called “stacked” bone transport), which employs a double mounting of hexapod fixators, with a further increasing of costs. Nevertheless, it could be argued that the use of hexapod fixation may result in savings of money, considering the overall benefits of this kind of treatment. The learning curve cannot be underestimated but is not very steep. Moreover, computer program and online help which are provided by the main producers prove to be in practice very useful in order to solve problems in correction programming. Special disadvantages of hexapod fixation. Oblique struts of the hexapod fixator may in particular cases (for example: bone defect with severe injuries of soft tissues) obstruct or prevent an easy management of the lesions. Advantages and disadvantages of bone transport performed with hexapod fixation and followed by conversion to internal fixation. Advantages of the use of hexapod fixation compared with conventional circular fixation in case of bone transport with subsequent conversion to external fixation are summed up in easy application, precise correction, and possibility of simultaneous action on deformities or displacements. These general advantages go along with general disadvantages, in particular high cost (further increased if technique of double hexapod

fixator is employed). Economic burden increases if costs of employed internal devices (nails or plates) and costs of additional surgical procedures and hospitalizations for their application or removal are added. Other possible additional disadvantages in case of conversion are represented by technical problems arising during application and management of internal devices and possible complications (risks of occurrence of length or angular deformities, which are often difficult to treat, risk of bone fracture, risk of infection). Conversion, in our opinion, should be evaluated with extreme caution before making any decision.

7.12 Discussion With the development of gradual distraction techniques and the knowledge of the biology of distraction osteogenesis, in cases of bone defects large bone segments may gradually be regenerated through a metaphyseal corticotomy and further distraction. Many authors limit the bone resection to 3–12  cm, over which this reconstructive technique should not be performed (as reported by Prokuski and Marsh [17]), but we disagree with this opinion. The corticotomy (cortical osteotomy) produces a significant improvement in the vascularization in all the bone segments and has a stimulating effect also on the surrounding soft tissues. The overall treatment time is prolonged and directly depends on the width of the resection. It was quite surprising that in almost all cases, patients well tolerate the external fixator over the entire treatment period, while maintaining good joint function. The stability of the circular external device allows functional weight-bearing on the operated limb from the first few days after the operation; furthermore, during the entire treatment period, the fragments position can be modified and corrected according to therapeutic needs. Morbidity of soft tissues is low, even in cases of bone transport over many centimeters, with the

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use of fine wires and also with the use of transverse screws, which can produce, however, deep lesions in soft tissues during the transport. These advantages can be obtained with all kinds of external circular fixators. The Ilizarov system proved to be the most versatile between the classic systems; the second-generation computer-­ aided circular external fixators (so-­ called hexapod external fixators) add the advantages of easy application, better stability and possibility of performing simultaneous, and extremely precise correction of complex deformities and displacements. An alternative is represented by the acute shortening techniques, but they can have some psychological and practical disadvantages. The multilevel bone transport aims to obtain “multiple” simultaneous distractions by dividing the fragment into many parts in order to shorten the treatment period. The assembly is quite complex, but is generally well tolerated by the patient. In trauma cases, an optimally performed debridement is the most important part of the treatment of open fractures. In the same way, the radical removal of the necrotic and infected parts of both bone and soft tissues represents the most important element for the success of treatment by compression–distraction technique of severe, infected nonunions. This aggressive approach to the problem, which is reminiscent of the guidelines for the surgical therapy of bone tumors, is the key to understanding the effectiveness in the outcomes with these methods. Even if other methods employed to shorten the treatment period have been described and employed (docking site stimulation with autoplastic bone graft, bone marrow injections, decortication, electric or magnetic stimulation, ultrasound stimulation, bone growth stimulating factors, association with internal osteosynthesis by intramedullary nailing, and conversion from external to internal fixation), bifocal or multifocal compression–distraction osteosynthesis techniques proved to be an effective option in the management of cases of acute and chronic situations with segmental bone loss, and, in experienced hands, provide very favorable results.

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7  Hexapod External Fixators in Bone Defect Treatment fixation using the Ilizarov and other devices. 2nd ed. Heidelberg: Springer; 2012. p. 841–93. 90. Weiland AJ, Moore JR, Hotchkiss RN.  Soft tissue procedures for reconstruction of tibial shaft fractures. Clin Orthop Relat Res. 1983;178:42–53. 91. Daniel RK, Taylor G. Distant transfer of an island flap by microvascular anastomoses. Plast Reconstr Surg. 1973;68:73–9. 92. Papineau LJ. L’excision-greffe avec fermeture retardée déliberée dans l’ostéomyélite chronique. Nouv Press Med. 1973;2:2753–5. 93. Mazoochy H, Vris A, Brien J et  al. Double stacked hexapod external fixator for bone transport in tibial segmental bone defect: development of a treatment algorithm and clinical results. Orthop Proc. 2018;100 B (Suppl 8):45. 94. Marsh JL, Prokuski L, Biermann JS. Chronic infected tibial nonunions with bone loss. Conventional techniques versus bone transport. Clin Orthop Relat Res. 1994;301:139–46. 95. Parsons B, Strauss E.  Surgical management of chronic osteomyelitis. Am J Surg. 2004;188(Suppl): 57S–66S. 96. Cruickshank JA, Graham SM, Harrison WJ. Immediate bone transport: a novel technique for the management of bone defects after chronic osteomyelitis in children. Trop Dr. 2018;48:64–6.

131 97. McCoy T, Kim HJ, Cross M, et  al. Bone tumor reconstruction with the Ilizarov method. J Surg Oncol. 2013;107(4):343–52. 98. Friedlander GE, Tross RB, Doganis AC, et al. Effect of chemotherapeutic agents on bone. J Bone Joint Surg. 1984;66-A:602–7. 99. Xu SF, Yu Xc XM, et al. Successful management of a childhood osteosarcoma with epiphysiolysis and distraction osteogenesis. Curr Oncol. 2014;21(4):1–10. 100. Hamdy RC. Evolution in long bone deformity correction in the post-lizarov era. External to internal devices. J Limb Lengthen Reconstr. 2016;2(2):61–7. 101. Hamdy RC, Bernstein M, Fragomen AT, Rozbruch SR. What’s new in limb lengthening and deformity correction. J Bone Joint Surg Am. 2017;99:1408–14. 102. Pairon P, Ossendorf C, Kuhn S, et al. Intramedullary nailing after external fixation of the femur and tibia: a review of advantages and limits. Eur J Trauma Emerg Surg. 2015;41(1):25–38. 103. Nieto H, Baroan C.  Limits of internal fixation in long-bone fracture. Orthop Traumatol Surg Res. 2017;103(1S):S61–6. 104. Bernstein M, Fragomen A, Sabharwal BA, et  al. Does integrated fixation provide benefit in the reconstruction of posttraumatic tibial bone defects? Clin Orthop Relat Res. 2015;473:3143–53.

8

Hexapod External Fixators in Paediatric Deformities Silvio Boero, Simone Riganti, Giulio Marrè Brunenghi, and Luigi Aurelio Nasto

Nomenclature CORA center of rotation of angulation FH fibular hemimelia HME hereditary multiple exostoses LLD limb length discrepancy PFFD proximal focal femoral deficiency PT physical therapy SO supramalleolar osteotomy VO v-osteotomy

8.1

Introduction

Lower limb deformities are a common reason for referral to a paediatric orthopaedic surgeon in children. The etiology can be very diverse and includes congenital abnormalities, trauma, tumor, or postinfectious. Oftentimes, angular deformities are also associated with limb length discrepancy (LLD). Although minor axis deviations are generally well tolerated, the combination of major multiaxial deformities can have serious

S. Boero · S. Riganti · G. Marrè Brunenghi L. A. Nasto (*) Department of Paediatric Orthopaedics, IRCCS Istituto “G. Gaslini”, Children’s Hospital, Genoa, Italy e-mail: [email protected]

biomechanical and functional impact on patients, including gait asymmetry, displacement of the center of gravity, and increase of energy expenditure during gait. While the main goal of treatment is to restore a normal alignment, this often requires treatment of deformities in multiple planes at the same time with or without contemporary limb discrepancy correction. The hexapod fixator is an evolution of the traditional Ilizarov circumferential frame [1, 2]. It consists of two rings connected with six oblique struts in an octahedral configuration. This arrangement allows six degrees of freedom of the external fixator [3]. Specific mathematical formulas allow calculation of strut length adjustments in order to manipulate the orientation of the two rings attached to the bone fragments [4–6]. Traditional Ilizarovtype external fixators require custom-made frames, specifically designed and built to achieve correction of the deformity. This often requires multiple adjustments of the frame construct during treatment of multiplanar deformities [7]. Hexapod external fixators allow creation of a virtual hinge to simultaneously correct complex multiplanar deformities without any need to alter the frame construct during treatment [8–15]. The aim of this chapter is to discuss specific aspects of hexapod external fixator use in paediatric patients. We will be discussing the steps of the frame application and management followed by a dedicated description of hexapod use in specific paediatric conditions.

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8.2

Preoperative Planning

8.3

Frame Setup

similar reasons, posteriorly open 5/8 rings are to be preferred at the distal third of the femur if the A thorough physical examination of both lower surgeon wants to allow complete flexion–extenlimbs in standing position as well as not weight-­ sion mobilization of the knee after surgery. At the bearing is an integral part of the preoperative level of the tibia, closed rings are used making planning. Full-length anteroposterior and lateral sure to leave enough space for calf swelling after lower limb standing X-ray films are executed surgery. If deformity is located at the distal third next. CT and MRI scans can be ordered if needed of the tibia or at the ankle joint it is important to to assess rotational abnormalities. All hexapod include the foot. Reference rings are placed parsystems have an associated software allowing allel to the neighboring joints, while the correcpreoperative planning and external fixator con- tion rings are placed perpendicular to the struct simulation. Regardless of the system used, deformed bone segment. This will reduce tension the software allows uploading of patient’s spe- and stress between the frame and the bone during cific X-rays. The X-rays are used to plan for the the correction and consolidation phases. At least osteotomy site and the desired correction. The two anchors are needed per each level. In femur systems allow virtual preassembly of the external and tibia, 5 mm half-pins are used, while at the fixator so that the surgeon can anticipate any level of the foot or hindfoot 4 mm half-pins are problem during the correction of the deformity preferred. Kirshner wires must be placed accord(e.g., mechanical impingement of the rings). ing to the safety corridors of the anatomical level. Most software also provide a simulation of the If two Kirshner wires are used per ring, it is best correction, and the surgeon can at this stage fine-­ to place one wire above the ring and the other one tune his treating strategy allowing for any hyper- below the ring. Ideally, Kirshner wires must be or hypocorrection if needed. The ability to set up placed at 90° angulation with enough tension to the frame before surgery is of great advantage in increase stability of the frame (90–110  N). All the operating room in terms of speed and ease of anchors (i.e., Kirshner wires or half-pins) should operation. be placed parallel to the rings and perpendicular to the axis of the bone at the fixation point, this will improve stability of the frame.

Frame setup is dependent on the anatomical region of the deformity as well as the desired correction to achieve. The rings have to be chosen according the size of the limb segment to fix. It is important to make sure that the rings are big enough to accommodate for ring movement/ translation during correction. On the other hand, if rings are too big and far from the bone segment to fix this will lead to a decreased tension and unfavorable lever arm for correction. Our rule of thumb is to allow two fingerbreadths distance between skin and the inner surface of the ring. This will also accommodate for any postoperative limb swelling at the osteotomy site. At the proximal third of femur, medially open 5/8 rings are preferred because they allow safe lateral fixation of the femur while avoiding any impingement during gait with the contralateral limb. For

8.4

Postoperative Management

X-Ray. Postoperative X-rays play a pivotal role in achieving a successful correction. X-rays must be performed according to a standard and repeatable protocol to provide meaningful images for postoperative calculations. At our institution, we use a custom-made support attached to the reference rings. This allows perfectly orthogonal views and decreases X-rays exposure of the patients due to repeated images. In addition, in order to accommodate for any magnification artifact, we recommend the use of a calibration template (e.g., a small spherical metal object). Postoperative X-rays are used to confirm preoperative plan. The images are uploaded into the software and used to recalculate the correction plan. This is a very important

8  Hexapod External Fixators in Paediatric Deformities

point because oftentimes small differences are noted between preoperative and postoperative X-rays in terms of rings placement and spacing. As a general rule, we perform a repeat X-ray of the osteotomy site 10 days after beginning of the correction program to make sure there is an adequate opening of the osteotomy site. Physiotherapy. Physical therapy (PT) is a very important aspect of limb deformity correction with external fixator. The role of PT is to prevent muscle contractures and joint stiffness which, if not treated, can lead to join subluxation or dislocation. As the bone segment is corrected or lengthened, muscles, tendons, and blood vessels have to adapt and stretch to accommodate the new position of the limb segment. This leads to a progressive increase in muscle tension which can significantly hamper correction. Another important aspect is to keep the joints adjacent to the fixator as mobile as possible, to facilitate functional recovery once the frame is removed. From this point of view, half-rings are very useful because they permit full range of movement of the joint. Finally, weight-bearing plays a very important role in increasing blood supply to the osteotomy site, thus improving bone healing. Early weight-bearing and walking also improve psychological well-being of the patient and acceptance of the external fixator. During the consolidation phase, it is very important to allow for some elasticity of the external fixator construct so to prevent stress shielding and improve/ accelerate bone healing. Some systems have developed dedicated struts that allow dynamization of the construct during the consolidation stage. Pain therapy. Living with an external fixator is not easy, especially in children or young adult patients. Some days are at times more difficult than others, and pain can have different aspects. It is very important to refer patients to a pain specialist within a multidisciplinary team. The team will support the patient and caregivers throughout the whole process and the different stages of the deformity correction. We cannot emphasize this aspect more as we have found that this is something that families greatly appreciate.

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8.5

Specific Clinical Conditions

Limb deformities in children can be very diverse given the many different etiologies. In this section of the chapter, we will focus on the most common conditions encountered in clinical practice.

8.5.1 Physeal Injuries Physeal injuries represent 18–30% of paediatric fractures, and growth arrest occurs in 5–10% of cases. The incidence of growth arrest is quite variable depending on physeal location, type of injury, and type of treatment [16, 17]. Premature growth arrest is characterized by an unexpected discontinuation of longitudinal and/or appositional bone growth secondary to an insult to the growth plate. Growth arrest is frequently post-­ traumatic, but can also be due to congenital conditions (e.g., Blount’s disease), infection, neoplasm, irradiation, metabolic/ hematologic abnormalities, ischemia, or iatrogenic injury [18]. Deformities resulting from physeal injuries or growth arrest are often multiplanar and combined with lower limb length discrepancy [19]. Hexapodal external fixator appears to be particularly indicated in treatment of these deformities [20].

8.5.1.1 Clinical Case (Fig. 8.1) A 14-year and 8 month-old boy who had undergone 5  years earlier a distal epiphyseal femoral fracture dislocation treated with closed reduction and percutaneous pinning with Kirshner wires and plaster immobilization. The physeal injury resulted in a growth arrest and distal femur deformity (20° external rotation and 45  mm femoral shortening) which required correction. Although the apex of the deformity appeared to be very close to the joint line, careful preoperative planning allowed identification of the CORA in the distal femur. The osteotomy was performed at the same level of the CORA, 22 mm proximal to the reference ring. The construct consisted of two 220 mm full rings with the distal ring functioning as the reference ring.

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8.5.1.2 Surgical Procedure Patient is positioned supine, fluoroscopic guidance is used throughout the procedure. –– Reference ring. Reference ring is placed first at the supracondylar level, the ring should be placed parallel to the distal femoral joint line and perpendicular to the anatomical bone axis. The ring is fixed with two 1.8  mm Kirshner wires tensioned at 110 N and positioned along the safety corridors in a latero-medial and mediolateral direction. The ring is positioned a

b

Fig. 8.1 (a) Preoperative standing lower limb AP X-ray demonstrating a 45  mm femoral shortening on the right side with varus alignment and 20° external rotation malalignment due to physeal growth plate injury from distal femur fracture. (b, c) Standing lower limb AP X-ray obtained during lengthening process demonstrating a progressive improvement of the lower limb length discrep-

slightly posterior to the center of the bone segment to accommodate for any swelling of the posterior compartment. The stability of the ring is reinforced by applying two self-drilling self-tapping half-pins with a diameter of 5 mm positioned along the safety corridors in a latero-medial and mediolateral direction. –– Proximal ring. Exact position of the proximal ring is determined by the anatomy of the deformity and is calculated during preoperative planning. The ring is fixed with two 5 mm self-drilling and self-tapping half-pins in the c

ancy and varus alignment. The osteotomy was performed at the CORA in the distal femur. (d) Lateral view of the osteotomy site confirming opening of the osteotomy. (e) Postoperative standing lower limb AP X-ray confirming equalization of the lower limb length discrepancy and correction of the varus and external rotation deformity

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e

Fig. 8.1 (continued)

latero-medial direction and slightly divergent. The half-pins are placed one proximal and the other distal to the ring, and positioned perpendicularly to the bone segment. –– Proximal half-ring. It is connected to the proximal ring through L-shaped connectors and fixed to the bone through two 5 mm halfpins in a latero-medial direction, slightly divergent and placed perpendicular to the bone segment. –– Osteotomy. In order to perform the osteotomy, it is advisable to temporarily remove the lateral struts of the external fixator. A lateral longitudinal incision is made of about 3  cm length and roughly halfway between the reference and the proximal rings. The osteotomy is performed according to standard percutaneous technique by making several drill holes

into the bone and then connecting the holes with an osteotome. Release of the fascia lata is a key step of the procedure at this stage. This allows a significant reduction of the muscle tension. Postoperative X-Ray execution is performed to confirm correct placement of the osteotomy and to update postoperative correction plan according to ring and osteotomy position. Weight-bearing with two sticks was allowed on postoperative day 2. Correction was started 5  days after the operation and completed in 45 days (correction speed 1 mm per day). At the end of the lengthening program, a residual hypometry of 15 mm was noted, and it was compensated with an additional lengthening of 15  days (correction speed 1  mm per day).

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Physiotherapy was focused on mobilization of the knee, paying particular attention to the stretching of the knee flexors and the lateral ­muscles of the thigh. Walking was encouraged in order to improve circulation and bone healing. The external fixator was completely removed after 195 days, when at least three corticals out of four were visible at the osteotomy sites in the two orthogonal X-rays views. At the end of the treatment, a correct mechanical axis with complete motility in all joints was achieved.

8.5.1.3 Key Points • Often multiplanar deformities. • Apex of the deformity is very close to the joint line, it can be difficult to perform osteotomy at CORA. • Evaluate whether there is a need for associated interventions (e.g., physeal bar resection). • If possible, it is best to wait until physeal growth is completed to decrease risk of deformity relapse. • Good healing can be expected as bones are not metabolically pathological.

8.5.2 Hereditary Multiple Exostoses (HME) Hereditary multiple exostoses is an autosomal dominant heritable disorder, characterized by the formation of multiple osteochondromas, benign cartilage capped bone tumors that grow outward the metaphyses of long bones [21, 22]. These lesions can increase in number and size during skeletal development and stop growing with skeletal maturity, after which no new osteochondromas develop [23]. Exostoses are rarely evident at birth and age of onset is very variable. The disease can manifest clinically with an inhibition of skeletal growth and consequently development of bony deformities, shortened stature, but also restricted joint motion [24–26]. Osteochondromas are located in bones that develop from cartilage, in particular the long bones of the extremities, predominantly around the knee. The rate of knee deformity in

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MHE has been reported to be as high as 84% in ​​ some studies: 50% of those patients have both knees affected. Lesions affecting the distal femur and proximal tibia commonly cause varus or valgus deformity, with valgus being more frequent. Femoral exostoses, in particular proximal ones, can cause antiversion of the femoral head and lead to an impairment of hip flexion [27]. If pain is the only symptom, osteochondroma removal is the procedure of choice; if a clinically significant deformity is present, correction is indicated [28].

8.5.2.1 Clinical Case (Fig. 8.2) A 16-year and two-month-old boy with valgus deformity of the left leg. During preoperative planning, two CORAs were identified at the level of the left tibia (i.e., proximal valgus deformity of 10° and a distal valgus deformity of 15°). There was also a 2 cm shortening of the left leg, so we decided to perform a 5 mm lengthening at both osteotomy sites while the remaining 1 cm shortening was expected to be compensated by angular deformity correction. A double CORA frame was constructed using three 160  mm rings. At both osteotomy levels, the proximal ring was used as reference ring (the distal ring of the proximal CORA worked as reference ring for the distal CORA). Because both CORAs were very close to the joint line, decision was made not to perform the osteotomy at the CORA level but slightly more distal for the proximal CORA and slightly proximal to the distal CORA. This generated a translation during correction of the deformity, which was considered acceptable during preoperative calculations. 8.5.2.2 Surgical Procedure Patient is positioned supine on a radiolucent table, and fluoroscopy is used throughout the procedure. –– Osteotomy of the fibula. A longitudinal incision is made four fingerbreadths proximal to the distal tip of the lateral malleolus. Bone is exposed subperiosteally and an osteotomy of the fibula is made using an oscillating saw.

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Fig. 8.2 (a) Preoperative standing lower limb AP X-ray of a 16 + 2 y/o girl with valgus deformity and 2 cm shortening of the left tibia due to HME. (b) Preoperative planning demonstrates presence of two CORAs with 10° proximal tibia valgus deformity and 15° distal tibia valgus deformity. (c) Intraoperative picture of the frame. (d, e)

Intraoperative X-Ray reproducing the frame setup and showing the two osteotomy sites. (f) Postoperative X-ray showing location of the proximal and distal osteotomy site. Because the distal CORA was very close to the joint line at the ankle, decision was made to perform the osteotomy proximal to the CORA to avoid joint damage

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f

Fig. 8.2 (continued)

–– Proximal reference ring. The reference ring for the proximal CORA is fixed first. The ring is positioned parallel to the proximal tibia joint line and perpendicular to the anatomical axis of the bone. The ring is fixed with two lanceolate Kirshner wires, tensioned at 110 N making sure to fix the ring slightly posterior to accommodate for postoperative calf swelling. Two 5  mm selfdrilling and self-tapping half-­pins are added to further increase stability. The two halfpins are placed in an anteroposterior direction on both sides of the patellar tendon. The two half-pins are very useful in coun-

teracting the mechanical action of the quadriceps during correction. –– Distal reference ring. The distal reference ring is placed in line with distal tibia joint line and perpendicular to the anatomical axis of the bone. The ring is fixed with two Kirshner wires and one 5 mm half-pin placed in anteroposterior direction taking care to protect and avoid transfixion of extensor tendons. –– Osteotomies. The surgeon has to make sure to perform the osteotomies at the exact level as established at preoperative planning. In both cases, a longitudinal 3  cm incision is made and a percutaneous technique is used to perform the two osteotomies. Intraoperative imaging is used to confirm correct placement and execution of both osteotomies. Postoperative X-ray is performed and calculations are updated to accommodate for any discrepancy between preoperative planning and postoperative placement of the rings and/or osteotomies. Weight-bearing with two sticks is allowed on postoperative day 2, and correction is started on postoperative day 6. Correction was completed in 10 and 15 days proximally and distally, respectively (correction speed 1° per day). Physiotherapy was focused on regaining full independence with walking and full range of motion of knee and ankle joints. There were two episodes of superinfection of the pins, in both cases oral antibiotic therapy was given for 10  days. The external fixator was completely removed after 152 days, when at least three corticals out of four were visible at both osteotomy sites. At the end of the treatment, a correct mechanical axis was achieved with full range of motion of all joints with the only exception of 10° loss of ankle dorsiflexion.

8.5.2.3 Key Points • Localizations at knee level are most often progressive. • High risk of deformity relapse if early intervention is performed. • Evaluate whether simultaneous removal of the osteochondroma is needed. • Possible multilevel deformities, even in the same segment.

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8.5.3 Ollier’s Disease Multiple enchondromatosis (i.e., Ollier’s disease) is a benign condition characterized by formation of benign intraosseous cartilaginous tumors (i.e., enchondromas) in close proximity of the growth plate. Ollier’s disease has an estimated prevalence of 1 in 100,000 cases; diagnosis is mainly based on clinical, radiological, and histological evaluation [29]. Involvement of the extremities is asymmetrical, and one side of the skeleton is usually exclusively or predominantly affected. The numerous enchondromas result in growth inhibition. On plain radiographs, long bones are affected with radiolucent longitudinal streaks that involve the metaphysis and extend into the diaphysis. The a

b

Fig. 8.3 (a) Preoperative standing lower limb AP X-ray of a 17 y/o girl with varus deformity and 6 cm shortening of the left lower limb. Preoperative planning demonstrated the presence of three CORAs (i.e., distal femur, proximal tibia, and distal tibia). (b, c) Immediate postoperative X-ray demonstrating external fixator setup. (d–f)

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cortex overlying the enchondroma is usually thin, and calcifications within the lesions are common. The most common deformities encountered in cases of Ollier’s disease are lower limb length discrepancy (LLD) and varus/valgus deformity of the knee. Angular deformities are due to the asymmetrical distribution of the enchondromas and often require surgical treatment [28, 30–33]. The most severe complication is malignant transformation of enchondromas into secondary chondrosarcoma, with a reported incidence of 5–50% in literature [34, 35].

8.5.3.1 Clinical Case (Fig. 8.3) A 17-year-old girl suffering from Ollier’s disease with left side involvement. Clinically, the patient c

Intermediate postoperative X-ray showing lengthening and deformity correction at the three osteotomy sites. Femur was lengthened 4 cm, while proximal tibia and distal tibia were lengthened 7 and 3 mm, respectively. (g–i) Clinical pictures showing final result after lengthening/ correction

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d

g

Fig. 8.3 (continued)

e

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f

i

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had a shortening of the affected limb of 6 cm with angular deformity at multiple levels (total of three CORAs):

direction. To increase the stability of the construct, one pin is fixed above and the other pin is fixed below the ring. –– Proximal safety pin. In order to further increase stability of the construct, an extra 5 mm pin is placed in a lateral to medial direction at the level of the proximal third of the femur. The pin is placed in an intermediate position with respect to the two half-pins fixed to the half-ring. –– Osteotomy. Lateral struts are temporarily removed before performing the osteotomy. A 3 cm skin incision is made on the lateral aspect of the thigh and bone is exposed and a drill and osteotome technique is used to perform the osteotomy using intraoperative imaging. Fascia lata is released next.

–– 10° varus deformity at the distal femur –– 10° varus and 20° internal rotation deformity at the proximal tibia –– 10° valgus and 5° recurvatum deformity at the distal tibia Because the shortening was more prominent at the femoral level, decision was made to lengthen 4 cm at the level of the femoral CORA and 7 and 3  mm at the level of the two tibial CORAs, respectively. The remaining length difference between the two limbs is recovered by angular deformity correction. An hexapodalic frame was constructed using 180  mm femoral rings and 160  mm tibial rings. At the femoral level, because of the thinning of the cortical bone, the frame was reinforced by the addition of a proximal half-ring fixed with two half-pins and an extensor with an extra half-pin in the proximal femur.

8.5.3.2 Surgical Procedure The patient is positioned supine on a radiolucent table, and fluoroscopy is used throughout the procedure. 8.5.3.3 Femur –– Reference ring. Reference ring is placed in the supracondylar region. The ring is positioned parallel to the distal femur joint line and perpendicular to the bone axis. The ring is fixed with one orthogonal lanceolate Kirshner wire, tensioned at 110 N. The stability of the ring is further reinforced with two 5 mm half-pins. –– Proximal ring. The position of the proximal ring is dependent on the CORA and osteotomy location. The proximal ring is fixed with two 5 mm half-pins placed in a latero-medial direction and in a slightly divergent pathway. Care is made to release fascia lata to decrease muscle tension during lengthening/correction. –– Proximal half-ring. The proximal half-ring is joined to the proximal ring with two L-shaped connectors, and it is fixed to the bone with two 5  mm half-pins placed in a latero-medial

8.5.3.4 Tibia –– Osteotomy of the fibula. A longitudinal incision is made four fingerbreadths proximal to the distal tip of the lateral malleolus. Bone is exposed subperiosteally and a complete osteotomy of the fibula is performed with an oscillating saw. –– Proximal reference ring. The proximal reference ring is placed parallel to the proximal tibia joint line and perpendicular to the axis of the bone. The ring is fixed with two lanceolate Kirshner wires tensioned at 110 N. The ring is placed in a slightly eccentric position relative to the center of the tibia to accommodate for any postoperative swelling after surgery. Two 5 mm half-pins are added to the ring to further increase the stability of the construct. The pins are placed on both sides of the patellar tendon and are very helpful in counteracting the mechanical action of the quadriceps muscle after surgery. –– Proximal moving ring. The position of the proximal moving ring is dependent on the anatomy of the deformity and location of the osteotomy. The ring is fixed with a lanceolate Kirshner wire tensioned at 110 N perpendicular to the axis of the bone and a 5 mm half-pin placed in an anteroposterior and slightly mediolateral direction. –– Distal reference ring. The distal reference ring is connected to the proximal moving ring

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through hexagonal bushes. This ring works as the reference ring for the distal CORA.  It is fixed to the bone through two Kirshner wires, tensioned at 110 N and one 5 mm half-pin. –– Distal moving ring. The distal moving ring is placed according to the anatomy of the deformity. The ring is fixed to the bone with two Kirshner wires and one 5 mm half-pin placed in an anteroposterior direction (taking care to protect and avoid transfixion of the extensor tendons). Postoperative X-ray is performed according to the usual protocol, and postoperative calculations are updated according to the final position of the rings and the osteotomies. Weight-bearing is allowed on postoperative day 2, and correction is started on postoperative day 5. Correction is completed in 40  days at the proximal CORA, 20 days at the proximal tibia CORA, and 15 days at the distal tibia CORA. Physiotherapy program is aimed at maintaining full range of motion of the hip, knee, and ankle. There were two cases of pin superficial infection which were treated with oral antibiotic therapy for 10  days. The fixator was completely removed after 272 days, when at least three corticals out of four were visible at the osteotomy sites. At the end of the treatment, a normal mechanical axis alignment was achieved with complete motility of all joints.

8.5.3.5 Key Points • Deformities are unilateral and in general more serious than MHE. • Multilevel deformity on the same limb is common. • Because there is cortical thinning, consider a more stable construct with multiple fixation points into the bone.

8.5.4 Congenital Deformities Congenital lower limb shortening/deformities is a group of relatively rare, heterogeneous disorders. The spectrum of congenital lower extremity shortening is varied and can involve any of the leg bones and joints [36]. The leg length discrepancy associated with these abnormalities can result in severe lifelong morbidity related to abnormal

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weight-bearing and compromised ambulation. Proximal focal femoral deficiency (PFFD) and fibular hemimelia (FH) are the two most common conditions in this disease spectrum. PFFD is characterized by variable shortened femur with proximal femoral deficiency and therefore deficiency of the iliofemoral articulation, leg length discrepancy, limb malrotation, and varus deformity at the subtrochanteric level [37–39]. Affected patients present with a short and bulky thigh which is also flexed, abducted, and externally rotated. Flexion contractures and instability of the hip and knee are frequently present. Treatment of the deformity depends on the severity of the condition and the projected leg discrepancy at maturity [40]. The goals of treatment are to achieve a stable hip, and a straight limb with near normal anatomical alignment. Mild deformities can be managed conservatively. If projected limb length discrepancy is >20– 25  cm, a lengthening procedure can be considered. In more severe deformities, other options include prosthetic fitting, knee arthrodesis, or Van Nes rotationplasty [41]. FH can range from mild hypoplasia to complete absence of the fibula with variable shortening of the tibia. It is the most frequent congenital anomaly of the fibula and the most common long bone agenesis of the body. Approximately 80% of the patients have unilateral involvement and the right side is more frequently affected. FH clinical aspects include equinovalgus foot, shortening of the leg, tibial anterior bowing, and variable knee valgus. On average, affected limb is 19% shorter than contralateral normal limb (25% in the tibia and 13% in the femur). This tends to remain constant with growth. Instability and valgus deformation of the knee usually get worse with growth and ambulation. FH has a strong association with shortening and bowing of the tibia (80% of cases present with anterior bowing, while 33% also show medial bowing), foot deformities (postaxial oligodactyly, tarsal coalitions, ball-and-socket ankle joint, and club foot or equinovalgus), or femoral deformities (femoral shortening, hypoplastic lateral condyle, or PFFD in 15–70% of the cases). There is a strong correlation between the fibular shortening and foot abnormalities, i.e., more severe limb shortening is associated with a greater

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number of metatarsal agenesis [42–45]. The management of FH is individually directed and depends on the severity of the deformity, projection of growth, predicted leg discrepancy at maturity, and the functionality of the foot, knee, and hip. As suggested by several authors, the most important aspect of surgical correction of FH is the achievement of a plantigrade foot and stable ankle joint at the end of treatment. FH leads to a decrease of the lateral buttress at the ankle joint with subsequent valgus deviation, and lateral transla-

tion of the calcaneus. Extra-articular soft tissue releases combined with osteotomy is the best method to obtain a plantigrade stable foot, and some cases will require ankle fusion to maintain this result [46]. Diagnosis and radiologic classification of these abnormalities are imperative for appropriate management and surgical planning.

a

8.5.4.1 Clinical Case (Fig. 8.4) A four and a half-year-old girl with left side FH, equinus foot and femoral shortening of 12 cm with

b

Fig. 8.4 (a) Preoperative standing lower limb AP X-ray of a 4 + 6 y/o girl with 12 cm femoral and tibial shortening due to congenital fibular hemimelia (FH). A valgus deformity is also shown in the midshaft tibia. (b) Lateral preoperative X-ray shows a procurvatus deformity of the proximal tibia. CORAs for valgus and procurvatus deformities do not match. (c, d) Postoperative X-ray demonstrating location of the distal femur osteotomy in both planes. (e, f) Postoperative X-ray demonstrating location of the proximal tibia osteotomy in both planes. (g, h)

Posterior knee subluxation was observed 1  month after starting the lengthening process; the condition was treated by gradually translating anteriorly the distal frame with regard to the proximal frame. (i, j) Pre-removal standing lower limb AP X-ray demonstrating achievement of 10 cm total lengthening and correction of the valgus deformity at the tibia level. (k, l) Final result showing a residual 2.5 cm lower limb length discrepancy and a normalized mechanical axis. The patient underwent a SUPERKNEE procedure for knee stabilization at a later stage

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Fig. 8.4 (continued)

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Fig. 8.4 (continued)

respect to the contralateral leg. Given the patient’s young age and the already important hypometry, we decided to start our correction as early as possible. Due to the very short length of the bone segments at this stage, it was impossible to recover the whole-length discrepancy with a single-stage procedure. We therefore decided to start with a first

lengthening procedure planning a 5 cm lengthening at the femur and tibia level. At preoperative planning two CORAs were identified: –– 10° valgus deformity at the distal femur –– 15° valgus and 10° procurvatus deformity at the proximal tibia

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Analysis of the preoperative imaging showed that the proximal CORA was located at the joint level, whereas the distal CORA was different for the valgus and procurvatus deformity of the tibia. Because of this, we decided to perform the two osteotomies slightly away from the radiographical CORAs. At the tibia level, we decided to perform a single osteotomy halfway between the valgus and the procurvatus CORA.  The frame consisted of two 120  mm rings at the femoral level and two 120 mm rings at the tibia level. The ankle joint was bridged including the foot to prevent late dislocation of the joint during correction/lengthening.

8.5.4.2 Surgical Procedure Patient is positioned supine on a radiolucent table, and fluoroscopy is used throughout the procedure. 8.5.4.3 Femur –– Reference ring. Femur reference ring is placed in the supracondylar region, parallel to the distal femur joint line and perpendicular to the bone axis. The ring is fixed using two Kirshner wires, tensioned at 110 N. The Kirshner wires are placed as orthogonal as possible to further increase stability of the construct. –– Proximal moving ring. The position of this ring is dependent on the anatomy of the deformity and the established location of the osteotomy at preoperative planning. The ring is fixed with two 5  mm half-pin placed in a latero-medial direction. –– Proximal half-ring. The proximal half-ring is joined to the proximal moving ring with two L-shaped connectors. The half-ring is fixed to the bone by using two 5  mm half-pins in a latero-medial direction and a slightly divergent pathway. –– Osteotomy. Before performing the osteotomy, the lateral struts are removed for an easier access to the osteotomy site. A 3 cm long incision is made on the lateral aspect of the thigh. A percutaneous technique is used to perform the osteotomy. Fascia lata is incised at the end of treatment.

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8.5.4.4 Tibia –– Reference ring. The reference ring is positioned in the proximal metaphyseal region, parallel to the proximal tibia joint line and perpendicular to the axis of the bone. The ring is placed slightly eccentrically and more posterior to accommodate for any postoperative swelling of the calf. The ring is fixed with two lanceolate Kirshner wires, both tensioned at 110  N and placed above the ring. The two 5 mm half-pins are used to further stabilize the ring and are placed in anteroposterior direction on both sides of the patellar tendon. The two half-pins are needed to counteract the pull of the quadriceps muscle during correction. –– Moving ring. The position of the moving ring is dependent on the anatomy of the deformity and location of the planned osteotomy. Fixation of the ring is achieved by two Kirshner wires, tensioned at 110 N. The ring is further reinforced by placement of one 5  mm half-pin in anteroposterior direction, slightly medial to the tibial crest. –– Distal half-ring. The distal half-ring is used to stabilize the foot. The half-ring is fixed to the calcaneus by using one 4 mm half-pin and one Kirshner wire with lateral olives. The lateral olive is useful to counteract the tendency to supination of the foot during treatment. Because of the intrinsic instability of the knee joint in these patients, the two frames (i.e., femoral and tibial frame) were connected using three rods with knee locked into extension. The patient was instructed to lock the knee into extension when walking and during rest. The locking rods were removed at multiple times during the day to allow knee range of motion exercises. Postoperative X-rays were obtained as usual and used to update correction program. Weight-­ bearing with two sticks was allowed on postoperative day 2, and correction was started on postoperative day 5. Correction was completed in 50 days (1 mm/day elongation rate) both at femoral and tibial level. The physiotherapy program was mostly aimed at keeping the knee joint mobile and maintaining knee extension during

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the correction. Unfortunately, due to the poor compliance of the patient to the physiotherapy program, she developed a progressive flexion contracture and posterior subluxation of the knee joint in approximately 1 months after the beginning of the correction. The subluxation of the knee joint was corrected in 15 days by translating the distal frame relative to the proximal frame in the sagittal plane. A month after the end of the correction, the foot half-ring was removed and the plantigrade position of the foot was maintained. The fixator was completely removed after 260 days, when at least three cortices out of four were visible at the osteotomy sites. At the end of the treatment, a normal mechanical axis was achieved and foot was plantigrade with slight equinism. At the age of 7, the patient underwent a SUPERKNEE procedure according to Paley which resulted in an improved stability of the knee joint. The patient is now 9 and half-year old, she has an LLD of 4.5 cm but a normally aligned lower limb.

cases, it is an idiopathic deformity, several contributing factors such as genetics, spinal bifida, cerebral palsy, and arthrogryposis have been reported. If left untreated, clubfoot inevitably leads to significant long-term disability, deformity, and pain. The goal of treatment is to achieve a plantigrade, flexible, pain-free foot, with a size similar to the contralateral foot. Nowadays, Ponseti method represents the standard of care for congenital clubfoot [47, 48]. Despite its high success rate, there are situations where correction is insufficient of cases presenting at a later time [49]. The classic approach to the treatment of complex foot deformities involves a single-step surgical correction with multiple osteotomies and/or wedge resections, soft tissue release, and arthrodesis. The main drawback of this approach is the resulting shortening of the foot due to the large bone resection needed for correction. Distraction osteogenesis according to Ilizarov’s principles represents an alternative approach to classic treatment [50–55]. The main advantage of distraction osteogenesis is to allow correction with lengthening rather than shortening. Furthermore, correction forces can be adjusted dynamically during treatment based on the response of the deformity to the correction [56]. In younger patients, correction of the relapsed clubfoot can be achieved with hexapod external fixation using soft-tissue procedures only. The disadvantages are similar to those of any other prolonged treatment with an external fixator, including prolonged discomfort for the patient, pin track infection, and joint contractures/stiffening [57]. Newer hexapod external fixator systems allow simultaneous three-dimensional correction of the deformity using the same frame throughout the whole treatment, making correction easier and more comfortable for the patient. It should be remembered that clubfoot correction with hexapod external fixation should be considered a salvage procedure, and simpler procedures should be considered first. Preoperative planning is mandatory, and a thorough clinical examination is performed in all patients in order to exclude any other associated lower limb deformities. Patients’ gait pattern

8.5.4.5 Key Points • Great variation of clinical presentation. • Correct classification of the deformity guides surgical treatment. • Involvement of many joint components (bones, joints, ligaments, muscles) leads to a greater risk of complications. • Subluxations, rigidity, and further deformity are common, and it is of paramount importance to protect adjacent joints by bridge fixation or stabilizing knee and hip joints according to Paley indications [46]. • Physiotherapy plays a pivotal role in preventing joint-related complications.

8.5.5 Clubfoot Congenital clubfoot is a complex paediatric foot deformity consisting of four complex foot abnormalities with varying degrees of rigidity: midfoot cavus, forefoot adductus, hindfoot varus, and hindfoot equinus. The etiology of clubfoot is poorly understood. Although, in most of the

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must to be analyzed to exclude the presence of any muscle imbalance. A standard standing anteroposterior and lateral X-ray of the feet is used to confirm the diagnosis and assess bone anatomy. In patients older than 11 years and rigid deformity, osteotomy of the midfoot should be performed in order to achieve a satisfactory correction [58–60]. A template of the final external fixator frame is used in clinic before surgery to make sure that there will be no contact areas with skin. It is best to used big rings in order to avoid any risk of contact between different parts of the construct. The most common complications of the procedure include metatarsophalangeal joint subluxations and toes flexion contracture. Some authors recommended temporary arthrodesis of these joints during distraction phase [61]. We do not routinely perform this procedure because not all patients will develop this complication and not all those affected will need surgery. In cases where this happens, surgical treatment of the metatarsophalangeal joint subluxation can be delayed until the removal of the external fixator. A more in-depth discussion on the use of hexapod external fixator for correction of foot deformities can be found in Chap. 9.

8.6

Limitations of the Use of Hexapod External Fixator in Paediatric Patients

There are no absolute contraindications to the use of hexapod external fixator in paediatric patients. The only strict caveat to the use of this system in paediatric patients is to avoid injury and transfixation of the growth plate. Furthermore, the size of the treated segment must be suitable for rings application. As a general rule, we tend to postpone deformity correction with hexapod external fixator after the age of 4 or 5 in order to achieve better collaboration by the patient. However, this cannot be considered a fixed rule as it must be adapted to the severity and type of deformity to be treated.

References Introduction 1. Aronson J.  Limb-lengthening, skeletal reconstruction, and bone transport with the Ilizarov method. J Bone Joint Surg Am. 1997;79:1243–58. https://doi. org/10.2106/00004623-­199708000-­00019. 2. Tsuchiya H, Tomita K, Minematsu K, et al. Limb salvage using distraction osteogenesis. A classification of the technique. J Bone Joint Surg Br. 1997;79:403–11. 3. Ferreira N, Birkholtz F.  Radiographic analysis of hexapod external fixators: fundamental differences between the Taylor Spatial Frame and TrueLok-Hex. J Med Eng Technol. 2015;39:173–6. https://doi.org/1 0.3109/03091902.2015.1025993. 4. Gao X-S, Lei D, Liao Q, Zhang G-F.  Generalized Stewart-Gough platforms and their direct ­kinematics. IEEE Trans Robot. 2005;21:141–51. https://doi. org/10.1109/TRO.2004.835456. 5. Husty ML.  An algorithm for solving the direct kinematics of general Stewart-Gough platforms. Mech Mach Theory. 1996;31:365–79. https://doi. org/10.1016/0094-­114X(95)00091-­C. 6. Docquier P-L, Rodriguez D, Mousny M.  Three-­ dimensional correction of complex leg deformities using a software assisted external fixator. Acta Orthop Belg. 2008;74:816–22. 7. Manner HM, Huebl M, Radler C, et  al. Accuracy of complex lower-limb deformity correction with external fixation: a comparison of the Taylor Spatial Frame with the Ilizarov ring fixator. J Child Orthop. 2007;1:55–61. https://doi.org/10.1007/ s11832-­006-­0005-­1. 8. Pesenti S, Iobst CA, Launay F.  Evaluation of the external fixator TrueLok Hexapod system for tibial deformity correction in children. Orthop Traumatol Surg Res. 2017;103:761–4. https://doi.org/10.1016/j. otsr.2017.03.015. 9. Fadel M, Hosny G.  The Taylor spatial frame for deformity correction in the lower limbs. Int Orthop. 2005;29:125–9. https://doi.org/10.1007/ s00264-­004-­0611-­9. 10. Sluga M, Pfeiffer M, Kotz R, Nehrer S.  Lower limb deformities in children: two-stage correction using the Taylor spatial frame. J Pediatr Orthop B. 2003;12:123–8. https://doi.org/10.1097/01. bpb.0000049578.53117.03. 11. Rozbruch SR, Fragomen AT, Ilizarov S. Correction of tibial deformity with use of the Ilizarov-Taylor spatial frame. J Bone Joint Surg Am. 2006;88(Suppl 4):156– 74. https://doi.org/10.2106/JBJS.F.00745. 12. Eidelman M, Bialik V, Katzman A.  Correction of deformities in children using the Taylor spatial frame. J Pediatr Orthop B. 2006;15:387–95. https://doi. org/10.1097/01.bpb.0000228380.27239.8a.

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13. Rozbruch SR, Segal K, Ilizarov S, et  al. Does the Taylor Spatial Frame accurately correct tibial deformities? Clin Orthop Relat Res. 2010;468:1352–61. https://doi.org/10.1007/s11999-­009-­1161-­7. 14. Koren L, Keren Y, Eidelman M. Multiplanar deformities correction using Taylor Spatial Frame in skeletally immature patients. Open Orthop J. 2016;10:71–9. https://doi.org/10.2174/1874325001610010603. 15. Keshet D, Eidelman M. Clinical utility of the Taylor spatial frame for limb deformities. Orthop Res Rev. 2017;9:51–61. https://doi.org/10.2147/ORR. S113420.

27. Shapiro F, Simon S, Glimcher MJ.  Hereditary multiple exostoses. Anthropometric, roentgenographic, and clinical aspects. J Bone Joint Surg Am. 1979;61:815–24. 28. Eralp L, Bilen FE, Rozbruch SR, et  al. External fixation reconstruction of the residual problems of benign bone tumours. Strategies Trauma Limb Reconstr. 2016;11:37–49. https://doi.org/10.1007/ s11751-­016-­0244-­8.

Physeal Injuries 16. Mann DC, Rajmaira S.  Distribution of physeal and nonphyseal fractures in 2,650 long-bone fractures in children aged 0-16 years. J Pediatr Orthop. 1990;10:713–6. 17. Mizuta T, Benson WM, Foster BK, et  al. Statistical analysis of the incidence of physeal injuries. J Pediatr Orthop. 1987;7:518–23. 18. Ogden JA.  Injury to the growth mechanisms of the immature skeleton. Skelet Radiol. 1981;6:237–53. 19. Caine D, DiFiori J, Maffulli N.  Physeal injuries in children’s and youth sports: reasons for concern? Br J Sports Med. 2006;40:749–60. https://doi.org/10.1136/ bjsm.2005.017822. 20. Dabash S, Prabhakar G, Potter E, et al. Management of growth arrest: current practice and future directions. J Clin Orthop Trauma. 2018;9:S58–66. https:// doi.org/10.1016/j.jcot.2018.01.001.

Hereditary Multiple Exostoses (HME) 21. Peterson HA. Multiple hereditary osteochondromata. Clin Orthop Relat Res. 1989;(239):222–30. 22. Pierz KA, Stieber JR, Kusumi K, Dormans JP.  Hereditary multiple exostoses: one center’s experience and review of etiology. Clin Orthop Relat Res. 2002;(401):49–59. https://doi. org/10.1097/00003086-­200208000-­00008. 23. Porter DE, Lonie L, Fraser M, et al. Severity of disease and risk of malignant change in hereditary multiple exostoses. A genotype-phenotype study. J Bone Joint Surg Br. 2004;86:1041–6. 24. Noonan KJ, Feinberg JR, Levenda A, et  al. Natural history of multiple hereditary osteochondromatosis of the lower extremity and ankle. J Pediatr Orthop. 2002;22:120–4. 25. Wicklund CL, Pauli RM, Johnston D, Hecht JT. Natural history study of hereditary multiple exostoses. Am J Med Genet. 1995;55:43–6. https://doi. org/10.1002/ajmg.1320550113. 26. Schmale GA, Conrad EU, Raskind WH.  The natural history of hereditary multiple exostoses. J Bone Joint Surg Am. 1994;76:986–92. https://doi. org/10.2106/00004623-­199407000-­00005.

Ollier’s Disease 29. Unni KK. Cartilaginous lesions of bone. J Orthop Sci. 2001;6:457–72. 30. Pandey R, White SH, Kenwright J.  Callus dis traction in Ollier’s disease. Acta Orthop Scand. 1995;66:479–80. 31. Baumgart R, Bürklein D, Hinterwimmer S, et al. The management of leg-length discrepancy in Ollier’s disease with a fully implantable lengthening nail. J Bone Joint Surg Br. 2005;87:1000–4. https://doi. org/10.1302/0301-­620X.87B7.16365. 32. Madan SS, Robinson K, Kasliwal PD, et  al. Limb reconstruction in Ollier’s disease. Strategies Trauma Limb Reconstr. 2015;10:49–54. https://doi. org/10.1007/s11751-­015-­0223-­5. 33. Shapiro F.  Ollier’s disease. An assessment of angular deformity, shortening, and pathological fracture in twenty-one patients. J Bone Joint Surg Am. 1982;64:95–103. 34. Schwartz HS, Zimmerman NB, Simon MA, et  al. The malignant potential of enchondromatosis. J Bone Joint Surg Am. 1987;69:269–74. 35. Verdegaal SHM, Bovée JVMG, Pansuriya TC, et  al. Incidence, predictive factors, and prognosis of chondrosarcoma in patients with Ollier disease and Maffucci syndrome: an international multicenter study of 161 patients. Oncologist. 2011;16:1771–9. https://doi.org/10.1634/theoncologist.2011-­0200.

Congenital Deformities 36. Bedoya MA, Chauvin NA, Jaramillo D, et  al. Common patterns of congenital lower extremity shortening: diagnosis, classification, and followup. Radiographics. 2015;35:1191–207. https://doi. ­ org/10.1148/rg.2015140196. 37. Biko DM, Davidson R, Pena A, Jaramillo D. Proximal focal femoral deficiency: evaluation by MR imaging. Pediatr Radiol. 2012;42:50–6. https://doi. org/10.1007/s00247-­011-­2203-­3. 38. Maldjian C, Patel TY, Klein RM, Smith RC. Efficacy of MRI in classifying proximal focal femoral deficiency. Skelet Radiol. 2007;36:215–20. https://doi. org/10.1007/s00256-­006-­0218-­x. 39. Anton CG, Applegate KE, Kuivila TE, Wilkes DC.  Proximal femoral focal deficiency(PFFD): more than an abnormal hip. Semin Musculoskelet

152 Radiol. 1999;3:215–26. https://doi. org/10.1055/s-­2008-­1080067. 40. Hillmann JS, Mesgarzadeh M, Revesz G, et  al. Proximal femoral focal deficiency: radiologic analysis of 49 cases. Radiology. 1987;165:769–73. https:// doi.org/10.1148/radiology.165.3.3685358. 41. Ackman J, Altiok H, Flanagan A, et  al. Long-term follow-up of Van Nes rotationplasty in patients with congenital proximal focal femoral deficiency. Bone Joint J. 2013;95-B:192–8. https://doi. org/10.1302/0301-­620X.95B2.30853. 42. Oberc A, Sułko J. Fibular hemimelia - diagnostic management, principles, and results of treatment. J Pediatr Orthop B. 2013;22:450–6. https://doi.org/10.1097/ BPB.0b013e32836330dd. 43. Achterman C, Kalamchi A. Congenital deficiency of the fibula. J Bone Joint Surg Br. 1979;61-B:133–7. 44. Birch JG, Lincoln TL, Mack PW, Birch CM. Congenital fibular deficiency: a review of thirty years’ experience at one institution and a proposed classification system based on clinical deformity. J Bone Joint Surg Am. 2011;93:1144–51. https://doi. org/10.2106/JBJS.J.00683. 45. Huda S, Sangster G, Pramanik A, et  al. Hemimelia and absence of the peroneal artery. J Perinatol. 2014;34:156–8. https://doi.org/10.1038/jp.2013.137. 46. Paley D.  Surgical reconstruction for fibular hemi melia. J Child Orthop. 2016;10:557–83. https://doi. org/10.1007/s11832-­016-­0790-­0.

Clubfoot 47. Gray K, Pacey V, Gibbons P, et al. Interventions for congenital talipes equinovarus (clubfoot). Cochrane Database Syst Rev. 2014;(8):CD008602. https://doi. org/10.1002/14651858.CD008602.pub3. 48. Liu Y, Zhao D, Zhao L, et  al. Congenital club foot: early recognition and conservative management for preventing late disabilities. Indian J Pediatr. 2016;83:1266–74. https://doi.org/10.1007/ s12098-­015-­1860-­x. 49. Uglow MG, Kurup HV.  Residual clubfoot in children. Foot Ankle Clin. 2010;15:245–64. https://doi. org/10.1016/j.fcl.2010.01.003. 50. Riganti S, Coppa V, Nasto LA, et  al. Treatment of complex foot deformities with hexapod external fixator in growing children and young adult patients.

S. Boero et al. Foot Ankle Surg. 2018; https://doi.org/10.1016/j. fas.2018.07.001. 51. Kocaoğlu M, Eralp L, Atalar AC, Bilen FE. Correction of complex foot deformities using the Ilizarov external fixator. J Foot Ankle Surg. 2002;41:30–9. 52. Khanfour AA.  Ilizarov techniques with limited adjunctive surgical procedures for the treatment of preadolescent recurrent or neglected clubfeet. J Pediatr Orthop B. 2013;22:240–8. https://doi. org/10.1097/BPB.0b013e32835f1f99. 53. Floerkemeier T, Stukenborg-Colsman C, Windhagen H, Waizy H.  Correction of severe foot deformities using the Taylor spatial frame. Foot Ankle Int. 2011;32:176–82. https://doi.org/10.3113/ FAI.2011.0176. 54. Takata M, Vilensky VA, Tsuchiya H, Solomin LN.  Foot deformity correction with hexapod external fixator, the Ortho-SUV FrameTM. J Foot Ankle Surg. 2013;52:324–30. https://doi.org/10.1053/j. jfas.2013.01.013. 55. Eidelman M, Katzman A. Treatment of complex foot deformities in children with the Taylor spatial frame. Orthopedics. 2008;31 56. Ganger R, Radler C, Handlbauer A, Grill F. External fixation in clubfoot treatment - a review of the literature. J Pediatr Orthop B. 2012;21:52–8. https://doi. org/10.1097/BPB.0b013e32834adba7. 57. Slomka R. Complications of ring fixators in the foot and ankle. Clin Orthop Relat Res. 2001;391:115–22. https://doi.org/10.1097/00003086-­200110000-­00012. 58. Shalaby H, Hefny H.  Correction of complex foot deformities using the V-osteotomy and the Ilizarov technique. Strategies Trauma Limb Reconstr. 2007;2:21–30. https://doi.org/10.1007/ s11751-­007-­0015-­7. 59. Waizy H, Windhagen H, Stukenborg-Colsman C, Floerkemeier T.  Taylor spatial frame in severe foot deformities using double osteotomy: technical approach and primary results. Int Orthop. 2011;35:1489–95. https://doi.org/10.1007/ s00264-­011-­1269-­8. 60. Paley D. The correction of complex foot deformities using Ilizarov’s distraction osteotomies. Clin Orthop Relat Res. 1993;(293):97–111. 61. Young JL, Lamm BM, Herzenberg JE. Complex foot deformities: correction with the Taylor Spatial Frame. In: Advanced techniques in limb reconstructiona and surgery. Berlin: Springer; 2015. p. 377–405.

9

Hexapod External Fixators in Ankle and Foot Deformity Correction Leonid Nikolaevich Solomin

Nomenclature 2D two dimensions ADTA anterior distal tibial angle ChJL Chopart joint line LDTA lateral distal tibial angle LHA lateral hindfoot angle MCMA medial Chopart metatarsal angle mLTMA mechanical lateral talo-metatarsal angle MUDEF method of unified designation of external fixation OSF Ortho-SUV frame RLA reference lines and angles RP reference positions SAR structures at risk TL-Hex Truelok hexapod system TJL talus joint line

(including vessels and nerves), significant shortening of the segment, and the high risk of infectious complications. In those cases when there are no contraindications for internal fixation, after gradual correction, external fixation can be substituted by internal fixation. When planning the ankle and foot deformity correction, specific reference lines and angles (RLA) are used. They will be presented in this chapter. Frames assembly must comply with the general biomechanical principle: maximum rigidity with a minimum number of rings, wires and pins [1]. In order to reduce the danger of pin-­induced joint stiffness and pin-tract infection, for the insertion of wires and pins it is necessary to use only Reference Positions (RP) [1].

9.2 9.1

Introduction

Gradual correction by external fixation devices should be used in cases when there are contraindications for acute correction. First of all, it is the threat of traction damage of the soft tissues L. N. Solomin (*) Vreden National Medical Research Center of Traumatology and Orthopaedics, St. Petersburg State University, St. Petersburg, Russia

Ilizarov Frame and Orthopaedic Hexapods in Ankle and Foot Deformity Correction: General Principles

The term “ankle deformities” means deformities with the apex located in the distal tibia. The use of hexapods (Fig.  9.1) is indicated for complex (multiplane and multicomponent) deformations and deformations of medium complexity [1]. The use of Ilizarov hinges is advisable for simple (one-component and one-plane) deformities.

© Springer Nature Switzerland AG 2021 M. Massobrio, R. Mora (eds.), Hexapod External Fixator Systems, https://doi.org/10.1007/978-3-030-40667-7_9

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154 Fig. 9.1  The use of orthopaedic hexapods for distal tibia deformity correction: (a) Taylor Spatial Frame (TSF). (b) True-Lock Hexapod (TL-Hex). (c) Ortho-­ SUV Frame (OSF)

a

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9  Hexapod External Fixators in Ankle and Foot Deformity Correction Fig. 9.2 Procedures used in foot deformity correction (according to Kirienko, unpublished data)

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ExFix in correction of foot deformities

Closed surgery Open surgery

(without osteotomy) 2-12 years

Children after 12 years and adults

• The skeleton is in the active growth phase

Soft tissue procedures

Sometimes “ankle deformities” include ankle joint stiffness. Information on using the hexapod in pes equinus is given in the Chap. 10. The use of external fixation in the foot deformities is also subject to the general rule: it is used when there are contraindications to acute correction and internal fixation. Kirienko classifies procedures on the foot, as shown in Fig. 9.2. It is necessary to emphasize that the use of gradual correction does not exclude the necessity of the associated operations on soft tissues: transposition of muscles and tendons, partial or complete tenotomy, capsulotomy, aponeurotomy, release of nerves, etc. [2–5]. The use of the Ilizarov apparatus and similar circular frames is preferable in the correction of foot deformities [6–10]. However, as in complex long-bone deformity correction, the use of Ilizarov unified reduction units (“Ilizarov hinges”) requires great skill and experience of an orthopaedic surgeon. When complex multiplane deformations, manipulations are sometimes required to be performed almost “intuitively.” Unlike Ilizarov hinges, the use of orthopaedic hexapods allows you to accurately predict the position of the moving fragment. That is why

Ilizarov’s osteotomies

Arthrodesis

they began to be used effectively in the correction of midfoot and hindfoot deformities [11–16]. Currently, Taylor Spatial Frame, TL-Hex, Ortho-­ SUV Frame, Smart Correction are used to correct the deformations of the feet (Fig. 9.3). It is important to understand that orthopaedic hexapods are not more than (and no less than) universal reduction units. That is why the basic principles of external fixation, the rules for performing osteotomies, the postoperative period, including the rate of correction, do not differ from those recommended when using the Ilizarov apparatus [1, 4, 17].

9.3

Orthopaedic Hexapod “Ortho-SUV Frame” (OSF): Main Peculiarities

Please note that this chapter is only an introduction of the OSF. The complete guide and detailed information about the OSF can be found in special sources of information ([1], www.ortho-­suv.org). As it was noted in Chap. 1 “History and evolution of hexapod external fixators” and Chap. 3 “Characteristics and usage modalities. Main

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systems,” currently three hexapod platforms are known. Taking into consideration the number of fixation points of struts to the rings, they can be designated as: 6  +  6 (Gough–Cappel platform), 3 + 6 (Stewart platform) and 3 + 3 (SUV

a

platform) (Chap. 3, Figs. 3.12 and 3.13). The Ortho-­SUV Frame (OSF) is based on the SUV platform: one end of each of the struts is fixed to the ring, and the other end to the adjacent strut (Fig. 9.4).

b

c

d

Fig. 9.3  Assemblies of various orthopaedic hexapods for foot deformities correction: (a) Taylor Spatial Frame (midfoot); (b) Ilizarov Hexapod Apparatus (midfoot and

hindfoot); (c) TL-Hex (ankle and midfoot); (d) Smart Correction (ankle and midfoot); (e) Ortho-SUV Frame (midfoot and hindfoot)

9  Hexapod External Fixators in Ankle and Foot Deformity Correction

e

Fig. 9.3 (continued)

Due to SUV platform, unique features of OSF hardware are (Fig. 9.5): • It is not obligatory to fix the rings orthogonally to the bone, the rings can be fixed with inclination; • It is not obligatory to place the bone in the center of the ring, i.e., the bone can be placed eccentrically; • Struts can be fixed to the rings in three ways, either directly to the rings, or using straight and Z-plates; • It is not obligatory to fix the struts only to the basic (reference) and mobile (corresponding) rings. They can be fixed to stabilizing and dummy rings as well; • There are no fixed points or locations where the struts are fixed to the ring. Any ring hole can be used for this purpose. Ideally, these points (three points on the proximal and distal rings each), should be equidistant to each

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other, thus creating equilateral triangles on each ring, but this is not mandatory; • Multiple sizes strut lengths are not needed (reduced inventory). Changing the length of conventional threaded rods in a strut effectively makes it longer or shorter; • Additionally, acute and gradual deformity correction modes are available. Clickers added to the struts body make the struts length change procedure in gradual mode convenient to the patient due to the clicks that patient hears at each 0.5 mm of the strut’s length change. No one of these “free assembly” parameters require input of additional data into the software. Two sizes of the strut length changing unit are available: standard and short (Fig. 9.6). In addition, the minimized Ortho-SUV Frame (OSFm) is available (Fig. 9.7). Use of SUV platform largely determines the features of OSF software (Fig. 9.8): • A total of 12 simple Steps to calculate the deformity correction. And the 13th step for multitotal residual; • This is image-based software. All the calculations are made on the base of the X-rays loaded to the software. Dicom format is available. The x-ray can be turned and cropped directly in the software; • Standard orthopaedic terminology is used; • It is not obligatory X-ray views to be perfectly orthogonal to each other; • Only 12 parameters are manually measured; • Inbuilt error checking to guard against wrong measurements being input into the software due to user errors. • Possibility to plan deformity correction using both mechanical or anatomic axis; • Complete visualization of deformity correction planning, i.e. simulation of the position of the bone segments, in AP and lateral views after the planned correction.

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b

a

c

Fig. 9.4  SUV platform: (a) “3 + 3” platform. (b, c) Fixing the next strut to the previous one. Published with permission, Ortho-SUV Ltd.

• Possibility to use two structures at risk (SAR): bone- and soft tissue depended; • Depending on surgeon choice, the distraction plan can be made once daily, twice daily, or four times daily distraction at any rate; • Multi total residual option—the ability to ensure the movement of a mobile (corresponding) bone fragment according to any given trajectory. • Each Step has “Help” that describes in detail the current software step.

9.4

Planning of Distal Tibia Deformity Correction

Distal tibia reference lines and angles (RLA) are presented at Fig.  9.9. For AP the mechanical axis identification joint line should be divided into half. From the middle point another line is drawn at an angle of 89 (86–92) degrees to the joint line. It is mechanical axis. Anatomic axis is located 4  mm medial to mechanical axis. This angle named the lateral distal tibia angle— LDTA (Fig. 9.9a). For lateral view anatomical axis identification ankle joint should be divided in half. From the middle point another line is drawn at an angle of 80 (78–82) degrees to the joint line. The angle formed by crossing joint line and anatomical axis

named the anterior distal tibia angle—ADTA (Fig. 9.9b). Planning of distal tibia AP and Lat deformity correction are presented on Figs. 9.10 and 9.11.

9.5

 SF Ankle Hardware O and Software

Leonid Solomin The main information about orthopaedic hexapod “Ortho-SUV Frame” (OSF) hardware and software are in the Sect. 9.3. This chapter is devoted to the features of the use of the OSF for correction of deformities, the apex of which is located at the level of the distal epimetaphysis (“ankle deformities”).

9.5.1 OSF Ankle Hardware Typically, the hexapod assembly includes only two rings: the basic and the mobile (Fig.  9.12). With a severe angular deformation, to facilitate the strut fixation, Z-plates are used. If it is necessary to increase the rigidity of fixation of bone fragments, for example, in case of osteoporosis, instability of the ankle joint, add one or two stabilizing rings.

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Fig. 9.5  Free assembly of OSF. (a) Any ring inclination is possible, bone fragments can be located both in the external support center, and out of the ring center. (b, c) Struts can be fixed to any external supports, even exotic. Any hole can be used for strut fixation. (d) Distance

d

between rings can be “increased” and “decreased” with the help of Z-plates. (e, f) Struts can be fixed to stabilizing and dummy rings as well. None of “free assembly” parameters require inserting a special additional data for the software. Published with permission, Ortho-SUV Ltd.

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e

f

Fig. 9.5 (continued)

Fig. 9.7  Standard Ortho-SUV Frame (OSF) and minimized Ortho-SUV Frame (OSFm). Published with permission, Ortho-SUV Ltd.

Fig. 9.6  Sizes of strut length changing unit and threaded rods: short and standard. Published with permission, Ortho-SUV Ltd.

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Fig. 9.8  Some steps of OSF software. (a) AP and Lat X-ray are input directly into the program. (b, c) Cropping and rotation of the X-ray. (d) X-ray calibration. (e, f) Deformity correction planning on the basis of anatomic and mechanical axes. (g) Yellow bone outline (drawn by user) means initial position of mobile bone fragment. Red bone contour is the final position of mobile bone frag-

ment, proposed by software. (h) Help of the software at Step 11. (i) Program calculated the optimal rate of deformity correction. (j) multi- total residual option provides calculating any path of movement of the mobile fragment. As a joke, the program “wrote” “SUV” with a distal bone fragment, before placing it in the correct position. Published with permission, Ortho-SUV Ltd.

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h

i

Fig. 9.8 (continued)

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j

Fig. 9.8 (continued)

a

b

Fig. 9.9  Distal tibia RLA: (a) AP. (b) Lateral view. Explanations are in the text. Published with permission, Ortho-SUV Ltd.

9.5.2 OSF Ankle Software To calculate the deformity correction, it is necessary to go through 12 steps successively (Fig. 9.13). In Step 1, the lengths of the struts and the sides of the triangles formed by the points of fixation of the struts to the rings are inserted

(Fig. 9.13a). In Steps 2 and 3 AP (Fig. 9.13b) and lateral radiographs are inserted into the program, and cropped, rotated and flipped, if needed. In Steps 4 and 5 radiographs are calibrated with the help of the “pink dumbbell” tool (Fig.  9.13c). This tool should coincide with an object of known length (“ruler”), visible on the radiograph. In this particular example, a piece of wire with a length of 100 mm was used (Fig. 9.13d). Pink dumbbell is coincided with ruler and the value of its length is inserted: 100 mm. In Steps 6 and 7, lines are drawn in the projection of the struts and universal joints (Fig. 9.13e, f). After that, the program analyzes all data inserted at previous steps and creates red lines (Fig. 9.13g). If all data were inserted correctly, the red lines will coincide with the strut projection. Step 8 is very liable: the identification of the anatomical or mechanical axes of the bone fragments. Special tools, so-called “green tree” and “pink tree” provide the possibility to do it extremely precisely. Fig.  9.13h shows how the anatomical axes of the proximal bone fragment are identified using the cortexes. The distal bone fragment is “short”. Therefore, its axes can only be identified by the joint lines (Fig.  9.13i). Reference values of LDTA = 89° and aADTA =

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a

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Fig. 9.10  AP distal tibia planning of deformity correction. (a) Identification of the proximal fragment axis. (b) Identification of distal fragment axis. (c) Apex of the deformity and bisector identification. (d) Osteotomy line identification. (e) Alignment using “open wedge” option

(rotation around point located at external cortex of fibula). (f) Correction using “neutral wedge” option (rotation around CORA). (g) Alignment using “closed wedge” option (rotation around point located at internal cortex of tibia). Published with permission, Ortho-SUV Ltd.

80° were inserted (Fig.  9.13j). In the upper left corner of the screen, you can see the value of angular deformity: AP angle = 1.9° and Lat angle = 24.7°. Step 9 is the notation of the mobile bone fragment initial position. Two, AP and Lat, yellow bone outlines should be done for this purpose (Fig. 9.13k). Red outlines on Step 10 is the calculated by software final position of the mobile bone fragment, i.e. after deformity correction (Fig.  9.13l, m). The orthopaedic surgeon may change the position of the red outline, for example, give a distraction of 11  mm (Fig.  9.13n). Options of angulation, translation, and rotation are also available. When the surgeon is completely satisfied with alignment, he proceeds to Step 11 to identify with the “Green cross” tool the Structures at Risk (SAR) positions

(Fig.  9.13o). Accurate SAR positioning will enable the software to count the correct number of days to correct the deformity (Fig. 9.13l). On Step 12 (Fig.  9.13p) the software calculates the optimal number of days for the deformity correction with the rate was chosen by orthopaedic ­surgeon. This prescription can be printed out. Usually, OSF software calculation takes 5–8 min.

9.6

Planning of Midfoot and Hindfoot Deformity Correction

The methods of analysis and correction of midand hindfoot deformities presented below provide possibility not only to eliminate angulation

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Fig. 9.11  Sagittal plane distal tibia planning of deformity correction (a) identification of the proximal fragment axis. (b) Identification of distal fragment axis. (c) Apex of the deformity and bisector identification. (d) Osteotomy line identification. (e) Alignment using “open wedge”

option (rotation around point located at posterior cortex of fibula). (f) Correction using “neutral wedge” option (rotation around CORA). (g) Alignment using “closed wedge” option (rotation around point located at anterior cortex of tibia). Published with permission, Ortho-SUV Ltd.

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and translation, but also to restore the length of the foot [18–21]. Correction planning for ankle contractures (pes equinus, pes calcaneus) are in the Chap. 10.

9.6.1 R  LA and Midfoot Planning of Deformity Correction Midfoot RLA are shown on Fig. 9.14. Chopard’s joint line (ChJL) |ab| intersects with second metatarsal anatomical axis |cd| at angle 86–94 degrees, forming the Medial Chopart second Metatarsal Anatomical Angle—MCMt2A (Solomin’s-1 angle). (Fig. 9.14a). Point “c” divides ChJL into half (Fig. 9.14b). In order to determine the proper length of the foot, the length of the ChJL is multiplied by the coefficient 2.43 ± 0.23 (Fig. 9.14c). For the lateral view, talus joint line (TJL) |ab| intersects with first metatarsal mechanical axis |ac| at the angle 23.6. This angle ∠bac is called Mechanical Lateral Talo-Metatarsal Angle— mLTMA (Solomin’s-2 angle). In order to ­determine the proper length of the foot, the length of the TJL is multiplied by a coefficient 4.3

(Fig. 9.14b). This is based on previous work from our group [18, 19]. In Fig.  9.15, the planning stages of midfoot deformity correction in frontal plane is shown. Stages of planning midfoot deformity correction in the sagittal plane are shown on Fig. 9.16.

9.6.2 R  LA and Hindfoot Planning of Deformity Correction Hindfoot RLA are shown on Fig. 9.17. The axis of the calcaneus is displaced laterally relative to the axis of the tibia. Valgus is allowed within 6° (Fig. 9.17a). For the lateral view, talus joint line |ab| intersects with calcaneus axis in the point “c” at 15.2, forming lateral hindfoot angle LHA (Solomin’s-4 angle). In normal foot, distance |bc| = |ab| × 2.56, and distance |cd| = |ab| × 4.59 (Fig. 9.17b). This is based on previous work from our group [18, 19]. Stages of planning hindfoot deformity correction in frontal plane are shown on Fig.  9.18. Stages of planning hindfoot deformity correction in sagittal plane are shown on Fig. 9.19.

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Fig. 9.13  OSF software steps. Explanations are in the text. Published with permission, Ortho-SUV Ltd.

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Fig. 9.14 Midfoot RLA: (a) AP. (b) Lateral view. Explanations are in the text. Used with permission, Ortho-SUV Ltd.

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9  Hexapod External Fixators in Ankle and Foot Deformity Correction Fig. 9.15  Planning for midfoot metatarsus adductus deformity in axial plane (AP radiograph) (a) Determination of the idealized mid-diaphyseal line of the second metatarsal and finding the anterior point of its head (d). (b) Construction of the actual mid-diaphyseal line of the second metatarsal. (c) The apex of deformity and osteotomy line identification. (d) Virtual deformity correction is performed. In addition to angular deformity, a shortening of the foot is present, which therefore requires an opening wedge osteotomy, using the Ilizarov method of distraction osteogenesis. Used with permission, Ortho-SUV Ltd.

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Fig. 9.16  Planning of midfoot foot deformity correction in sagittal plane. (a) Talus joint line identification. (b) Ideal mechanical axis of first metatarsal using mLMA identification. (c) Construction of mechanical axis of the first metatarsal. (d) Apex of deformity and osteotomy line

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identification. (e) Virtual angular deformity correction. (f) Virtual identification of ideal foot length using length of TJL (35  mm) and k  =  4.3. (g) Virtual foot lengthening Used with permission, Ortho-SUV Ltd.

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Fig. 9.17  Midfoot RLA: (a) AP. (b)Lateral view. Explanations are in the text. Used with permission, Ortho-SUV Ltd.

Fig. 9.18  AP hindfoot deformity correction planning. (a) Identification of the tibia axis. (b) Identification of calcaneus axis, here found to be in varus. (c) After simulated realignment. The calcaneus has been shifted laterally by 1 cm and made parallel to the tibia. Used with permission, Ortho-SUV Ltd.

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Fig. 9.19  Sagittal plane analysis and planning of hindfoot deformity correction. (a) talus joint line identification. (b) Point “c” identification using coefficient k1 = 2.56. (c) Actual calcaneus axis (using HLA) identification. (d) Proper length of hindfoot identification using

coefficient k2 = 4.59. (e) Actual axis of calcaneus identification. (f) Apex of deformity and osteotomy line identification. (g) Virtual deformity correction. Angular deformity and calcaneus lengthening results in a trapezoid gap. Used with permission, Ortho-SUV Ltd.

9.7

The first step is assembling the basic ring using half-pin inserted into the tibial bone: VI,12,120, and the wire inserted through the talus bone and the tops of the malleolus tal., 8–2 (Fig.  9.20a). After that 2/3 ring is mounted on the base of wire inserted through the calcaneus: calc., 3–9, and connected this ring to the tibial ring (Fig. 9.20b). The next step is mounting the mobile 2/3 ring. To do this, use two wires, inserted through the metatarsal bones: m/ tars.I—m/tars.III and m/ tars.IV—m/tars.II (Fig. 9.20c). If osteotomy is used, in order to avoid metatarsal joints distraction, two stabilizing wires or U-shaped wire must be used (Fig. 9.20d). After osteotomy (Fig. 9.20e), an additional half ring is fixed to the heel two-third ring. This half ring in Fig. 9.20f is indicated by a red arrow. Blue arrows

 SF Midfoot Hardware O and Software

The main information about orthopaedic hexapod “Ortho-SUV Frame” (OSF) hardware and software are in the Sects. 9.3 and 9.5. This chapter is devoted to the features of the use of the OSF for midfoot deformity correction.

9.7.1 OSF Midfoot Hardware For foot deformity correction the short type size of strut should be used. Order of OSF assembly is shown on Fig. 9.20. For frame assembly describing Method of Unified Designation of External Fixation (MUDEF) [1] is used.

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Fig. 9.20  Stages of OSF midfoot assembly. Explanations are in the text. Published with permission, Ortho-SUV Ltd.

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Fig. 9.21 OSF assembly for “dorsiflexion” deformities. Dummy ring noted by arrow. Published with permission, Ortho-SUV Ltd.

indicate Z-plates that use for strut fixation. On Fig. 9.20g, h is represented frame assembly after all strut fixation. In “dorsiflexion” deformities, the distance between the basic and mobile supports is small, which makes strut fixation difficult. Therefore, an additional dummy ring is installed, which is in Fig. 9.21 indicated by an arrow.

9.7.2 OSF Midfoot Software Before inputting AP and Lat radiographs into the software, they should be marked with normal reference lines and angles (Sect. 9.6). In addition, Lat should be rotated 90 (Fig. 9.22). In general, the passage of all the software steps does not have large features (Sect. 9.5.2). After the

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Fig. 9.22  Preparing X-rays: (a) the true axis of the second metatarsal is shown on AP. (b) Lat is rotated by 90. Proper first metatarsal axis is shown. Additionally, by red

dot, proper border of anterior cortex is designated. Published with permission, Ortho-SUV Ltd.

insertion of the all strut lengths and sides of the triangles, AP and Lat X-rays should be inserted into the software (Steps 1–5). On Steps 6 and 7, lines are drawn in the strut projection (Fig. 9.23a, b). In Step 8, green tree and pink tree (bone fragment markers) should coincide with, respectively, the axes of the “proximal bone fragment” and “distal bone fragment” (Fig.  9.23c). Since the proximal AP and Lat axes were marked in advance on radiographs (Fig.  9.22), it is very easy to identify them in Step 8. AP pink tree should be drawn according anatomical axis of 2nd metatarsal bone, Lat pink tree should be drawn according mechanical axis 1st metatarsal bone. At Step 9, a yellow outline is made, i.e. the initial midfoot position, before deformity correction (Fig.  9.23d). A red outline appears at Step 10 (Fig. 9.23e, f): this is calculated by software the midfoot position after deformity correction. However, the program performed only the angular correction. There is a shortening of the foot, since the anterior cortex of the first metatarsal on Lat does not correspond to the red dot, indicated by an arrow. To restore the length of the foot, using the tools of the program, the red contour is moved forward until the front point of the red

contour is aligned with the red reference point. SAR positions are identified by standard (Fig. 9.23g). In this example, the program calculated that it would take 25 days to correct this deformity at a rate of 1 mm/day (Fig.  9.23h). After printing the recommendations, you can proceed to the correction of the deformation.

9.8

 SF Hindfoot Hardware O and Software

The main information about orthopaedic hexapod “Ortho-SUV Frame” (OSF) hardware and software are in the Sects. 9.3 and 9.5. This chapter is devoted to the features of the use of the OSF for hindfoot deformity correction.

9.8.1 OSF Hindfoot Hardware The short type size of strut should be used for foot deformity correction. Order of OSF assembly is shown on Fig.  9.24. For frame assembly describing Method of Unified Designation of External Fixation (MUDEF) [1] is used.

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Fig. 9.23  OSF software steps midfoot peculiarities. Explanations are in the text. Published with permission, Ortho-­ SUV Ltd.

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The first step is mounting the basic ring using two half-pins inserted into the tibia and half-pin inserted into the talus bone: VI,12,120; VII,3,90; talus,2,80. A dummy ring, 1–2 sizes larger, is attached to basic ring. This free ring in Fig. 9.24a is marked by arrows. After that, two-third rings based on two

wires and a half-pin inserted into the calcaneus, is mounted (Fig. 9.24b). Free ring and calcaneus ring are connected by struts. In this case, straight and Z-plates were used (Fig. 9.24c–e). If osteotomy is used, in order to avoid subtalar joint distraction, U-shaped wire should be used (Fig. 9.24f, g).

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Fig. 9.24  Stages of OSF hindfoot assembly. Explanations are in the text. Published with permission, Ortho-SUV Ltd.

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9.8.2 OSF Hindfoot Software Before inputting AP and Lat radiographs into the software, they should be marked with normal reference lines and angles (Sect. 9.6) (Fig. 9.25). In general, the passage of all the software steps does not have big features (Sect. 9.5.2). After insertion of struts and sides of triangles lengths, inserting the AP and Lat X-rays into software and calibration (Steps 1–5), lines in the strut projection are drawn (Fig. 9.26a, b). In Step 8, green tree and pink trees (bone fragment markers) must be coinide with, respectively, the axes of the “proximal bone fragment” and “distal bone fragment.” Since the axis on Lat was designated in advance on radiographs (Fig. 9.25), it is very simple to do this at Step 8: a green tree is drawn over the indicated axis. There is a feature of the proper location of the “yellow dots.” The yellow dot of green tree is placed at the true position of posterior cortex, determined with the help of preliminary planning. The yellow point of the pink tree is located at the initial level of the posterior cortex. After that, the axes of the tibia and the bone of the AP are designated (Fig. 9.26c, d). You cannot change the position of the yellow dots, because the program has already automatically installed them in the correct position based on Lat view. At Step 9, a yellow outline is made—the ini-

Fig. 9.25  Preparing Lat X-ray: hindfoot RLA are applied on the radiograph. The green line shows the proper calcaneus axis. Proper border of posterior cortex showed by red dot. Published with permission, Ortho-SUV Ltd.

tial hindfoot position, before deformity correction (Fig. 9.26e). At Step 10, a red outline appears: calculated by software the hindfoot position after deformity correction. If the yellow points were set correctly, the program determines not only the angular correction, but also the proper length of the foot as well (Fig. 9.26g). It is known that the axis of the calcaneus is lateral to the anatomical axis of the tibia. Therefore, using the capabilities of the program, the red contour is moved 8–10 mm

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Fig. 9.26  OSF software steps midfoot peculiarities. Explanations are in the text. Published with permission, Ortho-­ SUV Ltd.

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laterally (Fig. 9.26h). On lateral view (Fig. 9.26i) if necessary, the red contour is moved backward to achieve the proper hindfoot length. Accurate SAR identification is necessary in order for the software to determine the correct number of days needed for deformity correction (Fig. 9.26j). For this particular case the program calculated that to correct this kind of deformity at a rate of 1 mm/ day, 14 days is necessary (Fig. 9.26k). After printing the strut length change schedule, you can proceed to the deformity correction.

9.9

Postoperative Care

General rules for the management of the postoperative period, including anesthesia, thromboprophylaxis, bandaging, the beginning and the rate of correction, the fixation period, the indications for dismantling the device do not differ from those recommended when using the Ilizarov apparatus [1, 4, 17]. It should only be noted that the correction in case of supramalleolar osteotomies starts at 5–7 days, after osteotomies of the middle and hind part of the foot—on the third day. As the manual has repeatedly pointed out, a significant difference in the use of orthopaedic hexapods is the need to use the “prescriptions” of a computer program for the correction period. It should be noted that after starting gradual correction there is a delay in moving the mobile fragment of 2–4 mm. This is due to the bending of wires and half-pins and the initial instability (backlash) of universal joints (cardans) of struts. In order to avoid this, all the struts 3–4 mm distraction should be done before(!) the X-ray examination. After correction of the deformity, in the absence of contraindications, external fixation can be changed to internal fixation. An alternative is the frame module transformation (Fig.  9.27). The duration of the fixation period also does not differ from that recommended when using the Ilizarov apparatus: from 1 to 2  months with closed correction in children until the complete

ossification of the distraction regenerate after osteotomy in adults. Figure 9.28 presents a clinical example of using OSF in distal lower leg deformity correction; Patient Z., 47 years old, with post-traumatic distal tibia and fibula deformity (Fig.  9.28a–d). OSF was mounted, and a supramalleolar osteotomy was performed (Fig. 9.28e, f). Step 11 of the program on Fig. 9.28g is shown: a yellow outline is the initial position of the distal fragment, a red outline means the position of the distal bone fragment after deformity correction. At Step 13, the software calculated 16 days deformity correction period (Fig.  9.28h). In 16  days OSF hardware provided an accurate alignment (Fig. 9.28i, j): the position of the distal bone fragment corresponds to the red contour. Frame module transformation (MT) was done for fixation period (Fig. 9.28k,l). In 4.5  months the frame was removed (Fig. 9.28m). The 2 years outcome is presented in Fig. 9.28n–p. Here is a clinical example of using OSF in midfoot deformity correction (Fig. 9.29). Patient Sh., 38 years old, as a result of an traffic accident, received traumatic osteomyelitis of the bones of the right tibia and neurogenic equinus deformity of the midfoot (Fig  9.29a–d). Figure  9.29c, d shows the RLA for analyzing and planning the deformation correction. During the operation, OSF was applied and the equinus position of the talus was corrected. After this, the struts were reassembled for midfoot deformity correction (Fig 9.29e, f) and the release of soft tissues was done: aponeurotomy, tenotomy of the short flexor of the fingers. On Fig. 9.29g is shown Step 8 of the program—a yellow outline is formed—the initial position of the “distal fragment.” On Fig. 9.29h, Step 13 of the program is presented: a red outline (calculated correction) and a table with the prescription of struts length change are visible. For 28 calculated days, OSF hardware performed an exact correction. Immediately after the correction, an arthrodesis of the Chopard joint and a cuneo-navicular articulation were performed (Fig. 9.29k–n).

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Fig. 9.27  Initial frames and after module transformation (MT): (a, b) distal tibia. (c, d) midfoot. (e, f) hindfoot. Published with permission, Ortho-SUV Ltd.

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Fig. 9.28  OSF usage in distal tibia deformity correction. Explanations are in the text. Published with permission, Ortho-SUV Ltd.

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A clinical example of using OSF with hindfoot deformity correction is below (Fig. 9.30). Patient T., 28 years old, was hospitalized with complex post-traumatic deformity of the left calcaneus (Fig. 9.30a–d). Figure 9.30c, d shows the RLA for analyzing and planning the deformity correction. During the operation, OSF was applied and an osteotomy of the calcaneus was performed (Fig.  9.30e, f). On Fig.  9.30g is shown Step 8 of the program—a yellow outline

is formed, i.e., the initial position of the distal fragment. At Step 11, the software showed a red ­ outline—the position of the distal bone fragment after correction of the deformity (Fig. 9.30i). For 64 calculated days, OSF hardware performed an exact accurate correction. Next day after the correction, arthrodesis of the subtalar joint with bone grafting and fixation with cannulated screws was performed (Fig. 9.30j–m).

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9.10 Contributions Drs Alexandr Utekhin and Victor Vilensky contributed to the writing of paragraph 9.3: Orthopaedic hexapod “Ortho-Suv Frame (OSF)”: general peculiarities. Drs Konstantin Ukhanov, Alexander Kirienko, John Herzenberg, and Victor Fomichev contributed to the writing of paragraph 9.6: Planning of midfoot and hindfoot deformity correction. Drs Elena Shchepkina and Konstantin Ukhanov contributed to the writing of paragraph 9.7, 9.8 and 9.9: OSF midfoot hardware and software; OSF hindfoot hardware and software; Postoperative care. Dr. Konstantin Korchagin contributed to the writing of paragraph 9.4 Planning of distal tibia deformity correction and 9.5.1 OSF ankle hardware.

References 1. Solomin L.  The basic principles of external skeletal fixation using the Ilizarov and other devices. 2nd edition. Italy: Springer; 2012. 1592p. ISBN: 978-88-470-­ 2618-6. https://doi.org/10.1007/978-­88-­470-­2619-­3.

2. Catagni MA, Guerreschi F, Manzotti A, Knuth A.  Treatment of foot deformities method using the Ilizarov. Foot Ankle Surg. 2000;6(4):207–37. 3. Coughlin MJ, Mann RA, Saltzman CH. Surgery of the foot and ankle. 8th ed. Amsterdam: Elsevier; 2007. 2258p. 4. Shevtsov V, Ismailov G. Transosseous osteosynthesis in foot surgery. Moscow: Medicine; 2008. 360p. 5. Cooper P, Polyzois V, Zgonis T, editors. External fixators of the foot and ankle. Philadelphia: Lippincott Williams & Wilkins; 2013. 419p. ISBN: 978-1-4511-7182-2. 6. Ilizarov GA. Transosseous osteosynthesis. New York: Springer; 1992. ISBN: 978-3-642-84388-4. 7. Wallander H, Hansson G, Tjernstrom B.  Correction of persistent clubfoot deformities with the Ilizarov external fixator. Experience in 10 previously operated feet followed for 2–5 years. Acta Orthop Scand. 1996;67(3):283–7. 8. Gibbons CT, Montgomery RJ.  Management of foot and ankle conditions using Ilizarov technique. Curr Orthop. 2003;17(6):436–46. 9. Paley D, Lamm BM. Correction of the cavus foot using external fixation. Foot Ankle Clin. 2004;9(3):611–24. 10. Wirth SH, Espinosa N, Berli M, Jankauskas L.  Complex reconstruction in Charcot arthropathy using the Ilizarov ring fixator. Orthopade. 2015;44(1):50–7. 11. Seide K, Wolter D, Kortmann HR. Fracture reduction and deformity correction with the hexapod Ilizarov fixator. Clin Orthop Relat Res. 1999;363:186–95. 12. Wukich DK, Belcyzk RJ.  An introduction to the Taylor Spatial Frame for foot and ankle applications. Oper Tech Orthop. 2006;16(1):2–9.

9  Hexapod External Fixators in Ankle and Foot Deformity Correction 13. Eidelman M, Katzman A. Treatment of arthrogrypotic foot deformities with Taylor Spatial Frame. J Pediatr Orthop. 2011;31(4):429–34. 14. Floerkemeier T, Stukenborg-Colsman C, Windhagen H, Waizy H.  Correction of severe foot deformities using the Taylor spatial frame. Foot Ankle Int. 2011;32(2):176–82. 15. Waizy H, Windhagen H, Stukenborg-Colsman C, Floerkemeier T.  Taylor spatial frame in severe foot deformities using double osteotomy technical approach and primary results. Int Orthop. 2011;35(10):1489–95. 16. Young JL, Lamm BM, Herzenberg JE.  Complex foot deformities: correction with the Taylor spatial frame. In: Kocaoğlu M, Tsuchiya H, Eralp L, editors. Advanced techniques in limb reconstruction surgery. Berlin: Springer; 2015. 17. Kirienko A, Villa A, Calhoun JH. Ilizarov technique for complex foot and ankle deformities. New  York: Taylor & Francis; 2004. 459p. ISBN: 0-8247-4789-5.

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18. Solomin LN, Ukhanov КА, Boychenko AV, Herzenberg JE.  Midfoot sagittal plane deformity analysis and correction planning. Vestnik Khirurgii im Grekova. 2017;5:2–8. 19. Solomin LN, Ukhanov КA, Sorokin EP, Herzenberg JE.  Analysis and planning of hindfoot deformity correction in sagittal plane. Traumatol Orthop Russia. 2017;23(1):23–32. https://doi. org/10.21823/2311-­2905-­2017-­23-­1-­23-­32. 20. Solomin LN, Ukhanov K, Kirienko A, Herzenberg J. New Sagittal Plane Reference Parameters for Foot Deformity Correction Planning: The Vitruvian Foot. J Foot Ankle Surg. 2018;58(5):865–869. 21. Solomin LN, Ukhanov K, Kirienko A, Herzenberg J.  Foot Deformity Correction Planning in the Sagittal Plane Based on the Vitruvian Foot First Metatarsal Anatomic Axis. J Foot Ankle Surg. 2020;59(4):774–780.

Hexapod External Fixators in Articular Stiffness Treatment

10

Leonid Nikolaevich Solomin

Nomenclature a ADTA anatomical anterior distal tibial angle EMG electromiography ExFix external fixator MRI magnetic resonance imaging MTR multi total residual ROM range of motion SAR structure at risk

10.1 Introduction It is important to recognize that treatment of joint stiffness is quite a complicated problem, which often couldn’t be solved nonoperatively. In this case, treatment may include soft tissue release procedures, osteotomies (corrective, bone shortening), ExFix applying, and their combination [1–3]. External fixation should be used if after soft tissue release the required result was not achieved. A similar situation occurs at severe old flexion stiffness, when the chronically contracted popliteal vessels and the peroneal nerve exclude the possibility of an acute correction [4–6].

L. N. Solomin (*) Vreden Research Center of Traumatology and Orthopaedics, St. Petersburg State University, St. Petersburg, Russia

This chapter will focus on the treatment of knee and ankle stiffness. However, the principles outlined here can be used in the treatment of contractures of the all large joints.

10.2 Ilizarov Frame and Orthopaedic Hexapods in Articular Stiffness Surgery: General Principles To plan the operation, it is necessary to clearly know the functional and anatomical and topographic characteristics of the muscles that provide movement in the joint, the degree of development of the scar process in the joint and paraarticular tissues. In this regard, in the preoperative examination include EMG, ultrasound, and especially MRI. But even if all the preoperative examination data indicate a possible success of a one-step operation, you should be prepared to use the ExFix [2, 7, 8]. The first requirement for the successful use of an ExFix Frame for treating joint contractures is the use of the atlas of recommended (optimal) positions for wires and half-pins insertion [9]. That are the positions in which, apart from principal vessels and nerves, the displacement of soft tissues relative to the bone during movements in the is considered. If only the “save corridors” are used, bone components will block soft tissues, causing pain, tissue cutting, and pin-­tract infection.

© Springer Nature Switzerland AG 2021 M. Massobrio, R. Mora (eds.), Hexapod External Fixator Systems, https://doi.org/10.1007/978-3-030-40667-7_10

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The second prerequisite is to provide high stability of the proximal (base) and distal (mobile) external fixation modules when using a minimum of rings, wires and half-pins. To do this, knowledge of the biomechanics of rigidity of external fixation are used [9, 10]. All the frames configuration presented below, correspond to these requirements. When frame mounting, special attention must be paid to positioning of Ilizarov hinges ­ accurately to the joint flexion and

extension axis (Fig.  10.1). This is the third requirement. At the same time it is known that movements in the knee joint include sliding, rolling, rotation, and the flexion-extension center is moving. Therefore, a uniaxial hinge cannot match the complex kinematics of the knee joint (Fig. 10.2) [1, 11, 12]. It is also known, the talo-crural joint axis may alter considerably during the arc of motion and differ significantly between individuals. This prompts caution in the use of hinge axes [13, 14].

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Fig. 10.1  The flexion-extension axes. (a) Knee joint: intersection of the posterior cortex and Blumensaat line. (b) Ankle joint: through the tops of the malleolus (similar to [11])

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Fig. 10.2  Schemes explaining the nature of movements in the knee joint: (a) types of movements; (b) evolute (centroid); (c) contact surfaces of the medial and lateral condyles, where 1 - the center of the circumference of the extensor surface of the knee joint, 2  - the center of the

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circumference of the flexor surface of the knee joint, 3 the extensor surface of the condyles, 4 - flexion surface of the condyles, 5 - facet of the anterior horn of the meniscus, 6 - facet of the posterior horn of the meniscus, 7 - (lateral) articular tibial surface (similar to [11])

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Orthopaedic hexapods can potentially provide a trajectory of movement of the articular surfaces, close to physiological. Therefore, they are increasingly used in the treatment of joint stiffness [15, 16]. Some of them are shown on Fig.  10.3. The following sections will provide more detailed information on the use of Ortho-­ SUV Frame (OSF) for this purpose. a

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10.3 “ Multi Total Residual” OSF Software Option As it was repeatedly mentioned in this manual, one of the significant advantages of orthopaedic hexapods is the ability to move a mobile bone fragment along the shortest path, with the simultaneous correction of all components of the deformity.

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Fig. 10.3  Assemblies of various orthopaedic hexapods for foot deformities correction: (a, b) Taylor Spatial Frame; (c, d) TL-Hex; (e, f) Ortho-SUV Frame (OSF)

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However, this property may have negative consequences in some cases. Thus, in “overlapping” of the bone fragments (Fig.  10.4a), the software will calculate the direction of movement of the mobile fragment directly—through the base fragment (Fig.  10.4b). Therefore, we have to do two independent sequential calculations. The first stage is plane-parallel distraction (Fig.  10.4c) and the second stage is alignment (Fig. 10.4d). In order to provide the movement of the mobile bone fragment along any trajectory (Fig.  10.5), OSF software has the “Multi Total Residual” (MTR) option. The basics of standard OSF software work are presented in Sects. 9.3, 9.5, 9.7 and 9.8. To implement the MTR option in Step 12, you need to click the “Total residual” button (Fig.  10.6a). After going to Step 14, click on the “Intermediate position” button (Fig. 10.6b). After that click the “View adjustment panel” button (Fig. 10.6b), as a result of which the tool-

bar appears (Fig.  10.6c). Using this panel, the “new” red outline can be placed in any position. After that, click the “Hide” button (Fig.  10.6d) and we will return to the main window of the Step 14. After that, you must click on the “Calculate” button (Fig.  10.6e) and the software will calculate the number of days required for the last movement of the mobile fragment. For this example, the calculated number of days is 12 (Fig. 10.6f). After that, you must click the “Show” button (Fig. 10.6g) and the program will show the schedule for changing the length of each of the strut for each correction day (Fig. 10.6i). This algorithm can be repeated any number of times, ensuring the calculation of any desired trajectory of the mobile fragment movement. In this case, each of the steps, in order to fully visualize this trajectory, will be displayed in the program with a white contour (Fig. 10.5). In Sect. 10.4 and 10.5, will be explained how to use the MTR option for knee and ankle contractures.

10  Hexapod External Fixators in Articular Stiffness Treatment Fig. 10.4 Hexapod software limitations: (a) there is the overlapping of bone fragments. (b) Software calculates the movement of the mobile fragment through the base. (c) In order to avoid a collision, the first step is to calculate the plane-parallel distraction. (d) After X-ray control, second calculation for alignment is performed. Published with permission, Ortho-SUV Ltd.

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Fig. 10.5  “Multi Total Residual” provides possibility to move the mobile fragment along any trajectory. The yellow contour is the initial position of the mobile fragment. Red contour—calculated by software final position of the mobile fragment, after alignment. White contours are

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step-by-step trajectory from the position of the “yellow contour” to “red contour”. Each step can have personal rate in degress, mm, days. Published with permission, Ortho-SUV Ltd.

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Fig. 10.6 (a) Click “Total residual” button (marked by arrow) to forward to Step 13. (b) Click “View adjustment panel” button (marked by arrow). The toolbar of Step 14 appeared; (d) After you had used the panel and satisfied with the new position of bone fragment click hide (marked by arrow). (e) Click “Calculate” button. (f) The software

had calculated the number of days required for the last movement of the mobile fragment. (g) Click “Show” button. (i) The schedule for changing the length of each of the strut for each correction day that is continuation of the schedule of Step 12 appeared. Published with permission, Ortho-SUV Ltd.

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Fig. 10.6 (continued)

10.4 O  SF Knee Hardware and Software The main information about the orthopaedic hexapod “Ortho-SUV Frame” (OSF) hardware and software are in the Sect. 9.3. The base of

standard OSF software work is presented in Sects. 9.5, 9.7, and 9.8. Section 10.3 explains the features of Step 14—“Multi Total Residual” (MLT). This chapter is devoted to the features of the use of the OSF for knee stiffness treatment.

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10.4.1 OSF Knee Hardware For the insertion of wires and pins, only Reference Positions should be used. The use of “Save corridors,” which do not take into consideration the displacement of soft tissues during movements in the knee joint, is prohibited. Another common, but important, requirement is to ensure the stability of each of the transosseous modules, the femoral and tibial, with a minimum number of wires and pins. It is on these principles that the recommended OSF assembling for treating knee joint contracture are based. When describing the frame assembly used Method of unified designation of external fixation (MUDEF) is used [9]. There are some differences in frame management for flexion and extension knee contractures correction. When treating patients with flexion contractures (cerebral palsy, the effects of traumatic brain injury), the frame is more often used only to ensure extension. To eliminate the “rebound” effect, knee 5–7° hyperextension, and fixation period not less 6–8  weeks should be used. Maximum amplitude flexion-extension cycles are usually not required.

Conversely, in the treatment of extensor contractures, there is almost always a need to provide ROM with the largest amplitude possible. When bending the knee joint more than 90°, the danger of contact of the distal femoral ring and the proximal tibial ring should be excluded. If the treatment of extension contracture requires “full flexion—full extension” cycles, a frame assembly that is for flexion contractures should be used. Steps of OSF assembly for knee joint flexion contractures are presented in Fig. 10.7. In the frontal plane, the rings should be located perpendicular to the mechanical axis of the femur and tibia. However, this is not a requirement, but rather an “aesthetic” request, since the software will calculate the correction for any position of the rings. Usually with OSF knee hardware assembling, Z-plates are required to avoid collision of strut with skin. Due to the low, at the level of VII, the location of the distal femoral ring, knee flexion with this frame arrangement is possible only up to 40–60°. The operation begins with assembling distal femoral ring VII,3-9; VI,8,90 (Fig.  10.7a). Thereafter proximal femoral support III,9,90; IV,8,90 is assembled (Fig. 10.7b). The 3d step is assembling tibial ring III,4-10; II,1,90; IV,12,90

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Fig. 10.7  OSF assembling for flexion contractures. Explanations are in the text. Published with permission, Ortho-­ SUV Ltd.

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Fig. 10.8  OSF assembling for extension contractures: (a) before correction, (b) after correction. Published with permission, Ortho-SUV Ltd.

(Fig. 10.7c). The femoral and tibial modules are connected by struts (Fig. 10.7d, e). Figure  10.8 presents OSF assembly features for knee joint extensor contractures. This arrangement provides maximum flexion—up to 120° without the danger of a collision between the femoral and tibial rings. The distance from the proximal ring to the line of the joint should be 140–150 mm. The distance from the distal ring to the line of the joint should be 160–170 mm. The proximal ring should be applied with inclination of 120° to the anatomical axis of the femur in the sagittal plane. The distal ring is mounted at an inclination of 50° to the anatomical axis of the tibia in the sagittal plane. To increase the fixation stability, additional stabilizing rings can be used. To avoid the collision of the anterior struts with

the patella and soft tissues of distal femur, the dummy sector should be used in the frame assembly (Fig. 10.9).

10.4.2 OSF Knee Software In general, the passage of all the software steps does not have large features (Sect. 9.5.2). On Steps 1–5, the lengths of the struts and sides of the triangles, AP and Lat X-rays, are inserted. On Steps 6 and 7, lines are drawn in the projection of the struts (Fig.  10.10a, b). On Step 8 AP view axis of green tree is placed according to femur mechanical axis. Lat view green tree must coincide with posterior cortex. Pink tree for AP and Lat views should be like a continuation of the

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Fig. 10.9  Using the dummy sector (indicated by arrow) to eliminate collisions of the frontal struts with soft tissues. Published with permission, Ortho-SUV Ltd.

green tree: AP angle = Lat Angle = 0 (Fig. 10.10c). It is very important to place the apex of the blue angle in the center of the flexion-extension of the knee joint (Fig. 10.10d). Yellow dots should be at the level of the join surfaces. At Step 9 the yellow contour is the initial position of tibia (Fig. 10.10e). If at Step 8 trees were set correctly, on Step 10 yellow and red contours will completely coincide (Fig. 10.10f). If there is a mismatching, it must be eliminated using the tools of Step 10. After that, distraction 5–6 mm should be done (Fig. 10.10g) and flexion, for example, 10°. To flex, it is necessary to input the value of flexion in the field “Lat tilt” (Fig. 10.10h). The definition of SAR on Step 11, is done without features (Fig.  10.10i). On Step 12, the software calculates the number of days required for distraction and flexion of 10° (Fig.  10.10j). After that, press the “Total residual” button (Fig. 10.10k) and go to Step 13. After that, using the “View adjustment panel” button, one can access the tools for movement in the knee joint (Fig. 10.10l). In this example, 10° flexion is chosen. Software then shows three contours: yellow (initial position of the lower leg), blue (position of the lower leg after articular distraction and flexion of 10°, and red—after repeated flexion of 10°. Using the “Hide” button, the toolbar is hidden and the “Calculate” button is pressed (Fig. 10.10m). This is the command for the software to calculate the number of days required for the second flexion 10°. However, the user can insert the number of days arbitrarily, for example, 1 day, as in this case. After clicking the

“Show” button, the software displays a schedule for changing на strut lengths to achieve a flexion of 10° (Fig. 10.10n). This schedule is continuation of the schedule of Step 12. This algorithm of the Step 13 should be repeated until the red outline takes the required flexion position in the knee joint (Fig. 10.10o, p). In this case, each of the stages of knee flexion will be rendered by the software as a white outline. In order to follow the proper kinematics of the knee joint, when modeling flexion, the apex of the blue corner must be moved in accordance with the localization of the instantaneous centers of knee joint rotation. After that click on the “Print” button and print out the correction schedule. Thus, as a result, the user has two printouts: for primary distraction and flexion of 10°, and for flexion to 90° (Fig. 10.10q). After that, you can begin to correct the contracture, which will be discussed in more details in the Sect. 10.6 “Postoperative care.”

10.5 O  SF Ankle Joint Hardware and Software The main information about orthopaedic hexapod “Ortho-SUV Frame” (OSF) hardware and software are in the Sect. 9.3. The basics of standard OSF software work are presented in Sect. 9.5, 9.7 and 9.8. Section 9.3 explains the features of Step 14—“Multi Total Residual” (MLT). This chapter is devoted to the features of the use of the OSF for ankle stiffness treatment.

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c Fig. 10.10  OSF software steps knee peculiarities. Explanations are in the text. Published with permission, Ortho-SUV Ltd.

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10.5.1 OSF Ankle Hardware For the insertion of wires and pins, only Reference Positions should be used. The use of “Save corridors,” which do not take into consideration the displacement of soft tissues during movements in the knee joint, is prohibited. Another common, but important, requirement is to ensure the stability of each of the transosseous modules, the tibial and foot, with a minimum number of wires and pins. It is on these principles that the recommended OSF assembling for treating ankle joint contracture are based. When describing the frame assembly Method of unified designation of external fixation (MUDEF) is used [9]. The operation begins with assembling tibial ring V,12,120; VI(8-2)8-2; VII,2,90 (Fig. 10.11a). After that mount horseshoe-shaped foot ring: calc.,8-2; calcl.,4-10; metatas.4-metatars.1 (Fig.  10.11b). Instead of wires, half-pins calc.4,90 and calc., 8,90 can be used, and additional wire is inserted through the metatarsal bones. After this, both rings are connected by struts (Fig. 10.11c, d).

10.5.2 OSF Ankle Software In general, the passage of all the software steps does not have big features (Sect. 9.5.2). After insertion of struts and sides of triangles lengths, inserting the AP and Lat X-rays into software, and calibration (Steps 1–5), lines in the strut projection are drawn (Fig. 10.12a, b). At Step 8, it’s needed to position the green trees so that the AP centrator with the blue angle matches the axis of ankle flexion-extension, i.e., located between the apexes of the malleolus. On Lat view blue angle apex must be in projection of the axis of ankle flexion-extension as well (Fig. 10.1 and 10.12c). Pink trees should be as a continuation of green trees: AP angle = Lat angle = 0. Yellow dots should be located at the level of the ankle joint (Fig.  10.12d). At Step 9, a yellow outline is made—the initial foot position, before equinus deformity correction (Fig. 10.12e). If all the previous steps were done correctly, at Step 10 the yellow and red outlines will coincide (Fig. 10.12f).

After this, a distraction of 5 mm must be given to create the initial distance between the articular surfaces (Fig. 10.12g). The SAR identification on Step 11 has no features (Fig.  10.12h). On Step 12, the software calculates the number of days required for the distraction (Fig.  10.12i). The general algorithm for Step 14 “Multi-total Residual” is discussed in the Sect. 10.3. After clicking “Total residual” button, click the “View adjustment panel” button (Fig.  10.12j). In this example, a dorsiflexion of 5° is selected (indicated by an arrow). Software then shows three contours: yellow (initial position of the foot), blue (position of the foot after articular distraction), and red—after dorsiflexion 5° (Fig. 10.12k). Using the “Hide” button, we return to Step 13. By clicking on “Calculate” we can see calculated by software the number of days for dorsiflexion of 5°. However, the user can insert the number of days arbitrarily, for example, 1 day, as it is in this case (indicated by the arrow) (Fig. 10.12l). This algorithm (“View adjustment panel” – “dorsiflexion 5°” - “Hide” - “Calculate”) should be repeated until the red outline takes the “over dorsiflexion” of 5–10°. Each of the stages of dorsiflexion will be rendered by the software as a white outline (Fig. 10.12m). After that click on the “Print” button and print out the correction prescription.

10.6 Postoperative Care General rules for the management of the postoperative period, including anesthesia, thromboprophylaxis, bandaging, onset and rate of correction, fixation period, indications for dismantling the device generally do not differ from those recommended when using the Ilizarov apparatus [9, 10]. As it was repeatedly pointed out in this manual, a significant difference in hexapods is the need to use the “prescriptions” of software for the correction period. The ability of the hexapod to provide the physiological trajectory of movement of the distal articular surface with a rate degree per day or less allows you to make this procedure more effective and reduce pain.

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Fig. 10.11  OSF ankle assembly. Explanations are in the text. Published with permission. Published with permission, Ortho-SUV Ltd.

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In extension contractures, as a rule, the goal of treatment is to increase the ROM in the knee joint. Therefore it is necessary to follow the standard protocol:

3. Complete cycles of passive “flexion-extension.” 4. Active motion without struts; combination of active and passive motion—if necessary. 5. Frame removal and physical therapy.

1. The latent period. 2. Gradual passive flexion.

The duration of the first period should be kept to a minimum, 1–2 days. The threat of necrosis of

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Fig. 10.12  OSF software steps ankle peculiarities. Explanations are in the text. Published with permission, Ortho-SUV Ltd.

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the edges of the wound is the most common cause of the increase in the duration of the latent period. The second stage is carried out according to the protocol for changing the lengths of the struts, calculated by the software. Usually it is 2–6°/ day. However, if the flexion is painless, the rate can be increased. To do this, one day use the changes in the length of the struts, which the program calculated for 2–3  days. The criterion for the correct pace: the patient must sleep without taking painkillers. The use of a pain reliever (baclofen) pump can be very helpful. Systematic use of analgesics for aggressive therapy “by all means” is unacceptable. A typical mistake is an excessive increase in the rate of correction, which will lead to a pronounced pain syndrome, edema, vascular disorders and, as a result, the correction stops for 1–2 weeks. After flexion of the lower leg to an angle of 120° is achieved (or less if planned preoperatively), extension starts at the same rate. To do this, the same software protocol is used, but in reverse order. When the full flexion-extension cycle is completed, it is repeated. Usually this can be done in a shorter period of time than it was during the first cycle. After 15–20 cycles of passive flexion and extension, the time to complete the cycle is reduced to a few minutes.

After that, active movements should be added to the passive movements. For this, fast struts mode is used. Gradually, within 3–7 days, knee movement should become mostly active. This is a criterion for frame removal. Thus, for 1–4 stages of treatment is spent, depending on the severity of contractures, from 1 to 3 months. There is below an example of using OSF technology in treatment of the patient with the extension contracture of the knee joint (Fig.  10.13). Patient B., 32-years-old, as a result of traffic accident, after multiple surgeries at the femur fracture finally received the rigid extension contracture of the right knee joint (Fig.  10.13a). The operation began with the release of soft tissue. But it provided only 40° flexion. Therefore OSF was applied for gradual correction of knee joint contracture. Figure 10.13b shows the lateral view X-ray after frame assembling before start of the schedule. Figure  10.13c shows calculation in the software. The trajectory of the mobile fragment while flexion-extension procedure is visualized in the software by multiple contours of the distal bone fragment. The flexion procedure duration was 22  days (Fig.  10.13d shows the patient in frame after first circle of flexion) with the following extension during 8 days. The whole flexion-extension period completed 52 days. On Fig. 10.13e, f demonstrated clinical and X-ray result of the procedure in 5 years after frame removal.

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In flexion contractures of the knee joint, which are a consequence of cerebral palsy, stroke, traumatic brain injury, as a rule, the goal of treatment is to ensure the amount of extension, which increases the comfort of the patient’s life. This can be, as a full extension, and flexion in the range of 60–90°—for a comfortable seat.

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As well as with extension contracture, before the frame applying, a soft tissue release, lengthening and transposition of tendons are performed. The postoperative protocol includes four stages: 1. The latent period. 2. Gradual passive extension with overcorrection.

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c Fig. 10.13  OSF application in knee extension deformity. Explanations are in the text. Published with permission, Ortho-SUV Ltd.

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3. Fixation period. 4. Frame removal and vigorous post-removal splinting. Correction is usually started no earlier than 3–5 days after surgery. The second stage is carried out according to the protocol for changing the lengths of the struts, calculated by the software. Usually it is 2–6°/day. However, if the extension is painless, the rate can be increased. To do this, one day use the changes in the length of the struts, which the program calculated for 2–3 days. The criterion for the correct pace: the patient must sleep without taking painkillers. Overcorrection at 5–15° is required to reduce the effect of “rebound.” Early removal of the device and replacing it with splinting increases the risk of recurrence of contracture. Therefore, the external fixation period should last at least 6 weeks. Post-removal splinting can last indefinitely. At high risk of recurrence of contracture, arthrodesis of the knee joint is indicated. There is below an example of using OSF technology in treatment of the patient with flexion contracture of the knee joint and posterior subluxation of the lower leg (Fig. 10.14). The flexion contracture in this case complicated left femur lengthening for pseudoachondroplasia. Figure  10.14a demonstrates X-ray of the left knee just after OSF

application. By the first step calculation of subluxation elimination was performed. To do that we brought the contour of the tibia down (imitation of distraction in the joint): Fig. 10.14b demonstrates this motion: yellow bone contour is initial position, red -final (that we expect to have after distraction). Then in total residual mode of the software we made imitation of the subluxation elimination. On Fig. 10.14c, we see that the contour that was previously red became blue, and the red contour is placed in proper position (subluxation eliminated). In the same total residual mode we made calculation of gradual flexion-extension in the knee (Fig. 10.14d, e). The trajectory of the mobile fragment while flexion-extension procedure is visualized in the software by multiple gray contours of the distal bone fragment. Clinically, we followed the schedule prescribe by the software. Figure 10.14f shows the X-rays of the patient after subluxation elimination that was done during 12 days. After that patient was left in this extended position for 3  weeks. Only after that flexion-­ extension protocol was continued. We reached 90° of flexion in 32 days. The whole period that flexion-extension procedure required in this case was 57 days. On Fig. 10.14f you see the clinical result in 2 months after frame removal. Below (Fig. 10.15) is a case of the 27-year-old patient with cerebral palsy, flexion contractures of both knee joints, nonunion of the left patella, defect of the right hip, flexion contracture of the

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right ankle. Previously patient underwent multiple surgeries. On Fig. 10.15a–d presented preoperative clinical pictures and X-ray views. By the first stage the surgery at the left lower extremity was performed (peroneal neurolysis, z-lengthening of biceps, semimembranosus, sem-

itendinosus tendons, posterior capsulotomy, osteosynthesis of the left patella by tension band wire technique, application of OSF). On Fig.  10.15e presented intraoperation view. On Fig.  10.15f, g presented clinical and X-ray pictures of the patient after the surgery. Then

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Fig. 10.14  OSF usage in knee flexion and subluxation deformity. Explanations are in the text. Published with permission, Ortho-SUV Ltd.

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Fig. 10.15  OSF usage in knee flexion deformity. Explanations are in the text. Published with permission, Ortho-SUV Ltd.

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calculation in the software (Fig. 10.15h) aimed to make gradual extension of the left knee was performed. Yellow outline is initial position of the bone fragment, red—final position, gray—intermediate positions that follow the normal trajectory of motions in the knee. Correction was done according to this calculation during 40 days. The result of correction is shown on Fig.  10.15i. As soon as correction was completely done the rings were connected by Ilizarov details and OSF was removed. Period of fixation was—6 weeks. After that 3 months, the lower extremity was fixed by tutor in knee extension. By the second stage the surgery at the right lower extremity was performed (peroneal neurolysis, z-lengthening of biceps, semimembranosus, semitendinosus tendons, posterior capsulotomy, Achilles tendon lengthening, application of OSF for the knee and Ilizarov hinges for the ankle). On Fig. 10.15k–m presented clinical and X-ray pictures of the patient after the surgery. On Fig. 10.15n presented calculation of the correction in the software. Yellow outline is initial position of the bone fragment, red—final position, gray—intermediate positions that follow the normal trajectory of motions in the knee. Correction was done according to this calculation during 35 days. The result of correction is shown on Fig. 10.15o. Period of fixation was—6 weeks. On Fig. 10.15p presented clinical pictures of the patient in 6 months after frame removal. In flexion contractures of the ankle joint, the postoperative protocol is generally consistent with that given above for the knee joint. However, as a rule, the ankle joint “does not require” 15–20 extension-flexion cycles, 3–5 is sufficient. With a tendency to relapse, it is necessary to use a fixation period in the over dorsiflexion position for up to 6 weeks. In the presence of deforming arthrosis, it is possible to use the technique of arthrodiatasis [17]. At high risk of recurrence of contracture, an arthrodesis of the ankle joint is indicated. The case of OSF technology used in the treatment of the patient with ankle luxation and posttraumatic fibula deformity, is presented on Fig.  10.16. Figure  10.16a demonstrates clinical photos and X-rays films before treatment. The ankle was fixed by OSF, and fibula osteotomy was performed (Fig. 10.16b, c). Multi total resid-

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ual option usage is shown on Fig. 10.16d. Yellow outline is initial position of the foot, red bone contour means its final position. White and blue outlines show intermediate steps of correction. Figure  10.16e, f demonstrates photos and the X-rays after luxation elimination and “hypercorrection”. The next step was lateral malleolus plating and frame removal (Fig.  10.16g). Figure 10.16h demonstrates the 1 year outcome. In 6  years due to arthrosis progression, joint stiffness was formed (Fig.  10.16i). OSF was mounted, joint release was done, and procedure of arthrodiatasis was started (Fig. 10.16j). Software window is shown on Fig. 10.16k, l. Yellow outline is initial position of the foot, red contour means final position, and blue and white contours are intermediate positions of the foot during ankle flexion and extension. Within 12 weeks 8 cycles of flexion-extension were done with a gradual increase in the rate of movement. Twenty degrees of dorsiflexion and 40° of plantar flexion were achieved. Figure  10.16m demonstrates clinical results 6 months after frame removal. Prevention and treatment of complications typical of external fixation, especially pin-tract infection, are carried out in accordance with the general rules [9]. As already mentioned, ROM improvement with external fixation should be carried out in the presence of diastasis between the articular surfaces of 3 mm. In addition to the effect of arthrodiatas, it reduces the risk of collision, if the trajectory of movements is determined incorrectly. Some hexapods allow visualization of the correction protocol. However, to date, all calculations are performed at best with respect to the flexion-extension axis, as with Ilizarov hinges. As soon as possible to calculate the movement based on the evolute (Fig.  10.2), the thesis of “overdistraction” may be revised. Therefore, it should be remembered that due to the bending of transosseous elements, the actual distance between the articular surfaces will be 2–3  mm less. In addition to this, there is a backlash (initial instability) of strut universal joints, which will also reduce the actual distance between the articular surfaces. In order to avoid joint surfaces collision, it’s needed before (!) X-ray examination, to perform

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Fig. 10.16  OSF application in ankle luxation and stiffness. Explanations are in the text. Published with permission, Ortho-SUV Ltd.

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the “distraction tension” of the frame. For this purpose, each of the struts should be elongated to the sensation of light elastic resistance, usually by 3–5  mm. Even in the absence of pain syndrome, radiography or fluoroscopy is necessary every 20–25° of primary flexion (extension). As it was shown above the use of orthopaedic hexapods is justified and promising for realization the technology of arthrodiatasis, “joint distraction” [18–23]. However, this topic detailing is beyond the scope of this chapter.

10.7 Contributions Dr. Saigidula Rokhoev contributed in the writing of paragraph 10.2: “Ilizarov frame and orthopaedic hexapods in articular stiffness surgery: general principles.” Drs Alexandr Utekhin and Victor Vilensky contributed in the writing of paragraph 10.3: “Multi total residual” OSF software option. Drs Victor Vilensky and Saigidula Rokhoev contributed in the writing of paragraph 10.4: “OSF knee hardware and software.” Drs Elena Shchepkina and Dr. Fanil Sabirov contributed in the writing of paragraph 10.6: “Postoperative care.”

References 1. Volkov MV, Oganesyan OV. Restoration of the shape and function of the joints and bones (by authors’ apparatus). Medicine. 1986. 256p. 2. Herzenberg JE, Davis JR, Paley D, et al. Mechanical distraction for treatment of severe knee flexion contractures. Clin Orthop. 1994;301:80–8. 3. Hosny GA, Fadel M.  Managing flexion knee deformity using a circular frame. Clin Orthop Relat Res. 2008;466:2995–3002. 4. Damsin JP, Ghanem I.  Treatment of severe flexion deformity of the knee in children and adolescent using the Ilizarov technique. J Bone Joint Surg Br. 1996;78:140–4. 5. Devalia KL, Fernandes JA, Moras P, Pagdin J, Jones S, Bell MJ.  Joint distraction and reconstruction in complex knee contractures. J Pediatr Orthop. 2007;27(4):402–7. 6. Kocaoglu M. Knee flexion contracture in haemophilia: treatment with circular external fixator. Haemophilia. 2014;20:879–83. https://doi.org/10.1111/hae.12478.

L. N. Solomin 7. Ullmann Y, Fodor L, Soudry M, Lerner A.  The Ilizarov technique in joint contractures and dislocations. Acta Orthop Belg. 2007;73:77–82. 8. Lee D-H, Kim T-H, Jung S-J, Cha E-J, Bin S-I.  Modified Judet quadriceps plasty and Ilizarov frame application for stiff knee after femur fractures. J Orthop Trauma. 2010;24:709–15. 9. Solomin LN, editor. The basic principles of external skeletal fixation using the Ilizarov and other devices. 2nd ed. Italy: Springer; 2012. 1592p. ISBN: 978-88-470-2618-6. https://doi. org/10.1007/978-­88-­470-­2619-­3. 10. Ilizarov GA.  Transosseous osteosynthesis: Springer; 1992. ISBN 978-3-642-84388-4. 11. Paley D.  Principles of deformity correction.  Springer-Verlag, 2002:806 pp. 12. Iwaki H, Pinskerova V, Freeman MA.  Tibiofemoral movement 1: the shapes and relative movements of the femur and tibia in the unloaded cadaver knee. J. Bone Joint Surg. 2000;82-B:1189–95. 13. Sommers M, Fitzpatrick D, Kahn K. Hinged external fixation of the knee. Intrinsic factors influencing passive joint motion. J Orthop Trauma. 2004;18:163–9. 14. Oganesyan OV, Ivannikov SV, Korshunov AV.  The restoration of shape and function of the ankle joint using hinged-distraction apparatus. Moscow: BINOM; 2003. 120p. 15. Lundberg A, Németh G.  The axis of rotation of the ankle joint. Bone Joint J. 1989;71(1):94–9. https:// doi.org/10.1302/0301-­620X.71B1.2915016. 16. Vulcano E, Markowitz JS, Fragomen AT, Rozbruch SR.  Gradual correction of knee flexion contracture using external fixation. J Limb Lengthen Reconstr. 2016;2:102–7. 17. Solomin LN, Korchagin KL. Treatment of Severe Knee Joint Stiffness with Soft Tissue Release and External Fixation. - In: Rozbruch SR, Hamdy RC (Eds.) Limb Lengthening and Reconstruction Surgery Case Atlas. (2015) Adult Deformity-Tumor-Upper Extremity. Springer International Publishing, pp 295–299 https:// doi.org/10.1007/978-­3-­319-­02767-­8_216-­1. 18. Aly T, Hafez K, Amin J.  Arthrodiatasis for man agement of knee osteoarthritis. Orthopedics. 2011;34(8):e338–43. 19. Inda D, Blyakher A, O’Malley M, Rozbruch S.  Distraction arthroplasty for the ankle using the Ilizarov frame. Tech Foot Ankle Surg. 2003;2(4):249– 53. https://doi.org/10.1097/00132587-­20031200000005. 20. Chiodo C, VcGarvey W.  Joint distraction for the treatment of ankle osteoarthritis. Foot Ankle Clin. 2004;9(3):541–53, IX. 21. Paley D, Lamm B. Ankle joint distraction. Foot Ankle Clin. 2005;10(4):685–98, IX. 22. Aly T, Amin O.  Arthrodiatasis for the treatment of Perthes’ disease. Orthopedics. 2009;32(11):817. 23. Smith N, Beaman D, Rozbruch S, Glazebrook M.  Evidence-based indications for distraction ankle arthroplasty. Foot Ankle Int. 2012;33(8):632–6.

Problems, Challenge, Complications in Hexapod External Fixation Systems. Contraindications

11

Redento Mora, Luisella Pedrotti, Barbara Bertani, Gabriella Tuvo, and Anna Maccabruni

Nomenclature

11.1 Introduction

DVT deep vein thrombosis PMMA polymethylmethacrylate SUV Solomin Utekhin Vilenski TSF Taylor Spatial Frame

Possible complications that can arise with the use of conventional or hexapod circular external fixation may be classified as local or systemic, intraoperative or postoperative, early or late. In cases requiring distraction osteogenesis, two additional groups must be considered: during distraction, during fixation. Addressing the complex problem of complications that can arise during limb lengthening, Paley (1990) [1] proposed a classification in three groups, distinguishing between difficulties (divided into “problems” and “obstacles”) and true complications. Problems appear during the treatment and can be solved before it is over, with nonsurgical techniques. Obstacles also appear during the treatment and can be solved before it is over, but with surgical methods. True complications appear during the treatment and remain unsolved at the end of the treatment. These are divided into “minor” and “major” (solvable with nonsurgical or surgical techniques, respectively) and “permanent” (non solvable even after the end of treatment). This classification is adopted worldwide and can be extended also to complications observed during all other kinds of treatments with external fixation. It should be underlined that other classifications of complications of bone lengthening have

R. Mora (*) Full Professor of Orthopaedic Surgery, Division of Orthopaedics and Traumatology, Department of Surgical, Diagnostic and Pediatric Sciences, University of Pavia, “Città di Pavia Institute” University Hospital, School of Medicine, Pavia, Italy L. Pedrotti Associate Professor of Orthopaedic Surgery, Division of Orthopaedics and Traumatology, Department of Surgical, Diagnostic and Pediatric Sciences, University of Pavia, “Città di Pavia Institute” University Hospital, School of Medicine, Pavia, Italy B. Bertani · G. Tuvo Assistant Surgeon, Division of Orthopaedics and Traumatology, Department of Surgical, Diagnostic and Pediatric Sciences, University of Pavia, “Città di Pavia Institute” University Hospital, School of Medicine, Pavia, Italy A. Maccabruni Associate Professor of Infectious Diseases, Consultant in Infectious Diseases, “Città di Pavia Institute” University Hospital, School of Medicine, Pavia, Italy

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been proposed. Caton classification [2] differentiates three categories according to their severity (minor, intermediate, and major). Popkov classification [3] includes osseous, articular, infectious, and neurovascular complications, also distinguished in minor, intermediate, and major according to their severity. Donnan classification [4] includes four grades: according to the significance of functional or anatomic problems after lengthening procedure. Lascombes [5] proposed a classification of complications in four grades, based on a “triple contract,” stipulating the objective to reach in long bone lengthening (planned gain in bone length, duration of treatment, occurrence of sequelae).

11.2 Complications Many intra- and postoperative complications can arise with the use of circular external fixation.

11.2.1 Intraoperative Complications Injuries to vessels or nerves. These potential intraoperative complications must be immediately recognized to be treated successfully [6]. First of all, for the prevention of these complications, full knowledge of the anatomy of the limbs is required. Numerous anatomic-­topographic tables following the lead of the classic atlas of cross-section anatomy [7] are available. Among these atlases, dedicated to the correct insertion of bone fixation elements, the most useful are surely those that also indicate the direction in which the wires or pins are going to be applied [8]. Maximum care must always be taken in pins and wires inserting, and thus one should never hesitate to carry out any investigation that may help to locate the exact position of the principal vessels and nerves of the area of interest (arteriographic study, examination by means of electroneurostimulation). A bleeding during or immediately after inserting a wire can be generally stopped by wire removal and local compression. A vascular lesion after inserting a screw is normally more dangerous and requires removal of the screw itself and

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an arteriographic control performed to actually evaluate the damage and early treat it. A nervous lesion caused by a rotating wire that tears a nerve may often be difficult to treat. Therefore, especially in endangered areas, wires should be inserted through the soft tissues by gradually pushing them or by gentle traction, whereas rotation must be used only when the wire is inserted through the bone. Moreover, the use of pins in these areas is clearly safer, unless a transfixing pin is used.

11.2.2 Postoperative Complications Particular care must be given to treating both immediate or late postoperative problems, without forgetting the importance of prevention in planning and performing the surgical treatment. Injuries to vessels or nerves. Even weeks or months after application of the fixator, bleeding may start, generally due to the erosion of the wall of a vessel caused by a bone fixation element. After removing the wire or the screw, an arteriogram will help to see what kind of damage has occurred and what kind of treatment is indicated. In treatments based on distraction, vascular or nervous injury can appear because of the distraction of the soft tissues. In these cases, interruption of the distraction or even proceeding to temporary compression treatment is generally enough to solve the problem. Injuries to muscles or tendons. Pins inserted through muscles or tendons limit the muscles normal excursion and can lead to muscle fibrosis or tendon rupture, and can also lead to joint stiffness. Inflammatory and infectious conditions. Inflammatory and infectious conditions at the site of insertion of wires or screws represent the most common problems. The reason is simple and has been well explained by Green [9]: “The transfixion of a limb with a wire or a screw violates the principal barrier against the bacterial invasion.” Basically these are superficial problems that can be solved with an adequate treatment (local medications, systemic antibiotic therapy) and only rarely require more radical solutions (removal of the bone fixation element and

11  Problems, Challenge, Complications in Hexapod External Fixation Systems. Contraindications

replacing it at a different site and with a different direction). Deep infections are rare and appear on X-rays as an osteolysis area or as a sequestrum. They require antibiotic therapy, removal of the bone fixation element and surgical cleansing with débridement or in some cases with marginal resection of the infected bone, the same treatment as for chronic osteomyelitis. A correct prevention represents the best treatment, and must be based on two rules: 1. Avoid necrosis of the tissues, which can be caused during the insertion of wires and screws by wrapping of the tissues or by overproduction of heat and, after insertion of the bone fixation element, by excessive tension of the soft tissues (this may be a consequence of a wrong technique of insertion or of an incorrect connection to the external device, followed by straining in flexion of the wire or the screw). 2. Avoid excessive movement of the tissues around the bone fixation element, produced by an unstable mounting. Particular solutions have been studied in attempt to reduce the rate of infections of areas where screws and wires are present: –– Titanium screws [10] that do not interfere with the bactericidal action of the white blood cells (while standard iron screws do). –– Screws covered by hydroxyapatite [11] that allow a more stable fixation on the bone, reducing micro-movements. –– Silver plated screws [12]: the antibacterial properties of silver create a layer that works as a barrier against infections. –– Screws covered with sleeves of PMMA (polymethylmethacrylate) soaked in antibiotic (tobramycin) to prevent local infections [13]. –– Bisphosphonate-coated screws, that demonstrated an action similar to action of HA coated screws [14]. Bad scars or defacing. Scars at the site of previous points of passage of wires or screws are an almost unavoidable inconvenience when dealing with axial or circular external fixation. The risk

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can be reduced by a precise preoperative planning and by correctly performing the operation. Insertion of bone fixation elements should be performed avoiding tension of the soft tissues when no important modifications of the configuration in the postoperative phase are planned, and on the contrary, applying wires or screws by creating a “reserve” of soft tissues in cases of internal or external lengthening of the limb or correction of serious deformities, so avoiding an overload of tension of the soft tissues during the gradual correction period [15]. Joint stiffness. Knee stiffness is often observed when using a circular external fixation device at the level of the femur, while it occurs rarely in other joints. Knee stiffness rate can be reduced in two ways: correct position of the knee when inserting wires or screws (bone fixation elements should go through the flexor muscles with the knee extended and through the extensor muscles with the knee flexed) and using particular techniques in order to reduce soft tissue transfixion. The postoperative treatment is based on kinesitherapy, focusing on both active and passive flexion and extension exercises for the knee, (with the aid of Continuous Passive Motion devices if needed), and using particular spring-­ loaded tensioning braces that help to increase joint range of motion [15]. Deep vein thrombosis (DVT). As in every case of reduced mobility, such as after surgery or an accident, deep vein thrombosis (DVT) can occur, if a blood clot forms in one or more of the deep veins, usually in lower limbs. This complication is not frequent with the use of circular fixation and particularly with the use of hexapod fixation, because in these cases loading starts very early after surgery. Pressure ulcers. Ulcers can be caused by pressure or by shear or friction. In particular, pressure ulcers are observed if the limb swells excessively within the external fixator, with contact of the skin with the parts of the fixator. In cases of moderate swelling, simple elevation of the limb may be useful; partial or complete change of the device is needed if the swelling appears more important. Muscle contractures. These usually result from the tension generated on muscles by

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distraction. Prophylaxis is performed by avoiding transfixion of tendons and maximizing muscle excursion before transfixing muscles, ­physiotherapy and splinting, and, if necessary, fixation across joints [16]. Joint luxation and joint instability. Joint subluxation or luxation may occur during external bone lengthening, due to predisposing factors (such as pre-existing joint instability) or to muscle tension during distraction. Physiotherapy, gradual traction, or extension of the frame across the joint may be needed in order to distract the joint and reduce the subluxation. Axial deviation. Axial deviation may be observed during external or internal bone lengthening, due to imbalance between muscle forces on different sides of the bone, or due to instability, following inadequate construct or loosening of bone fixation elements [16], or, in case of internal lengthening, due to formation of scar tissue as a consequence of severe traumatic lesions of soft tissues. Premature consolidation. During bone lengthening premature consolidation can occur if external fixator regular adjustments are not performed or the rate of distraction is too slow. In this case a new corticotomy is necessary. Delayed consolidation or nonunion. In a study performed by Papaioannou et al. [17] parameters analyzed for their significance for nonunion after tibial fracture included soft tissue damage, energy of injury, method of fracture reduction, type of external fixation frame, supplemental interfragmentary screw fixation, dynamization at the fracture site, and postoperative infection. Nonunion rate was found to be significantly higher in type II and III open fractures, high-­ energy fractures, fractures treated by external fixation using a bilateral frame, and fractures treated with supplemental interfragmentary screw fixation. Delayed consolidation and nonunion can be caused mainly by instability of the frame. On the contrary, a too rigid frame can unload the site of a fracture, with production of an endosteal callus and very little peripheral callus formation and evolution to delayed union or nonunion. Refracture. In case of fracture healing after treatment with a very rigid fixator, union is almost

completely endosteal, and the limb must be protected after fixator removal, in order to prevent possible refracture. Also early fixator removal and forced rehabilitation may increase the risk of bone refracture [18]. Joint infection. When bone fixation elements (pins or wires) are inserted in proximity of joints, the risk of joint infection is significant. Interesting observations, based on anatomical research and instrumental investigations, have been presented about the use of bone fixation elements at the leg in the proximity of the knee and ankle joints [19, 20]. According to these studies, bone fixation elements should not be applied at distances less than 15  mm from the knee joint or less than 12  mm from the ankle joint in order to obtain safe and extracapsular application. Pain. In case of pain not well tolerated by the patient, the rate of gradual fracture reduction or gradual deformity correction must be reduced or temporarily stopped. Depression. In these cases temporary use of antidepressant drugs is useful. High blood pressure. A case of successful management of hypertension in a 13-year-old patient treated with a Taylor Spatial Frame for a tibial fracture due to a road traffic accident was described [21]. The patient received prompt diagnosis and treatment of hypertension with good results. According to Paley [16] hypertension after rapid distraction in bone lengthening may be a manifestation of arterial stretching or may be related to excessive soft tissue stretching.

11.3 Indications and Contraindications to the Use of Hexapod External Fixation In papers dealing with external fixation techniques, generally only a few pages are dedicated to indications that on the contrary are very important. In orthopaedics and traumatology the use of circular external fixation is essentially dynamic and doesn’t end with the application of external frame. A very careful working plan must be

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prepared, and the patient should be followed up closely and using all kinds of tricks during the postoperative course. Indications (and therefore good results of treatment) are strictly dependent on the action of several factors (different circular fixation systems and techniques, pathology to treat, performance of the treatment, features of the patient, psychological attitude and experience of the orthopaedic team) on a single goal: bone segment affected by the pathology.

11.3.1 Indications With regard to the type of disease, indications to adoption of classic circular and hexapod external fixators are the same: bone fractures (including periprosthetic fractures) and their complications, bone deformity correction, bone lengthening. Hexapod frames have several advantages (easier mounting, stronger frame, simultaneous correction of deformities in all planes) and a general disadvantage, especially in developing countries, represented by the cost. Additionally, some special indications for the use of a hexapod instead of a conventional circular fixator may be focused. Achievement of an exact contact at the docking site in bone transport. In these cases hexapod systems higher accuracy (in mono or stacked configuration) helps the gradual approach of fragments during transport, and promotes the achieving of an exact contact at the docking site and the bone callus formation. Correction of deformities appeared during bone lengthening or during bone transport. During femoral lengthening or bone transport performed with conventional circular frame, a gradual varus deformity of the proximal fragment may be observed due to muscular action not sufficiently opposed by the strength of the device. In a similar way, during tibial lengthening or bone transport performed with conventional circular frame, a tendency of the proximal fragment to show gradual procurvatum deformity is often observed, due to the strong action of patellar tendon and to the scarce resistance of the frame rods.

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In both these cases the substitution of the proximal module of the conventional fixator with the correspondent part of a hexapod frame (or simply the substitution of the four rods of the proximal module of the Ilizarov fixator with the six struts of a SUV Frame, since they are fully compatible) may permit an easy correction of the deformity by taking advantage of the opportunities of hexapod fixation. Protection of the growth plate during bone lengthening in pediatric patients. If hexapod fixator is used, the level of application of bone fixation elements may be more distant from epiphyses, thanks to the better stability of the assembly.

11.3.2 Contraindications There are some cases that generally contraindicate the treatment performed with hexapod devices. Patients with mental disorders. Uncooperative or mentally incompetent patients, unable to follow postoperative program, should not be treated with hexapod fixators. Complexity of adjustments. Some patients can consider too hard the daily handling of the struts of the device, in comparison with the action on the rods of conventional circular devices. In our opinion, two additional special contraindications to the use of hexapod devices may be highlighted. Workspace of hexapod fixator. As mentioned above, it was observed that the potential of a frame to correct deformities is limited by its work space [22, 23]. In particular, the minimum frame height of hexapod fixators is higher compared to conventional Ilizarov fixators, and the indication for hexapod constructs in pediatric orthopaedics can be limited, because of their increased minimal frame height. Relapsed or neglected clubfoot. Cases of neglected clubfoot and relapsed clubfoot are frequent, especially in developing countries, and may depend on multiple causes. In these cases, techniques of differentiated distraction, based on the use of circular external

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fixation, can successfully correct severe deformities by means of gradual regeneration and remodeling of soft tissues and bone. According to the majority of Authors, the use of external fixation without any other kind of surgery is only possible until the age of 8 years, but other Authors suggest the threshold age may be significantly higher (16–18 years) [24]. In the last years three particular configurations of TSF hexapod fixator have been proposed for the application at the level of the foot [25]: Standard Frame (a variant of the classic assembly), indicated for the correction of the footdrop; Butt Frame (characterized by the presence of two orthogonal foot-plates connected each other, indicated for the correction of deformities of midfoot and forefoot; Miter Frame (compounded of a proximal ring connected to the tibia, of an intermediate ring connected to the heel and of a distal ring connected to the metatarsal bones It is indicated for the correction of hindfoot and forefoot deformities). Special configurations for correction of foot deformities (4 for application to rearfoot and 5 for application to hindfoot) were studied and proposed even for the Ortho-SUV Frame [26]. According to the most credited theory, the cause of deformity is a stop in the physiologic detorsion of the foot during the intrauterine life. A treatment with gradual detorsion appears therefore indicated, avoiding a simultaneous correction of all deformities, and with a direct control of gradual adjustments, performed by means of conventional circular external fixation. For this reason we generally prefer to use in these cases an Ilizarov fixator with a special configuration, instead of a hexapod fixator, and we perform a program of sequential and controlled corrections of the deformities by means of gradual modifications of the device [27].

11.4 The Problem of Conversion Indications to use of conversion from external to internal fixation gradually extended from classic circular external fixation to hexapod external fixation.

In the last decades new techniques have been developed in trauma surgery with the aim to reduce the possible and supposed risks of a prolonged treatment with external fixators, such as loss of stability, pin tract infection, joint stiffness, psychological pain, refracture after external fixator removal. Conversion from femoral external fixation toward nailing is performed when the patient condition has been stabilized [28]; conversion from tibial external fixation to intramedullary nailing is performed in order to avoid possible nonunion [29]. In the field of orthopaedic surgery, techniques of conversion (“combined” or “consecutive” fixation) have been developed in cases requiring bone lengthening, bone deformity correction, bone transport to eliminate long bone defects [30, 31]. Risks related to these kinds of treatment have to be considered: loss of stability, occurrence of bone deformity, and mainly cross contamination, depending on pin tract infection. For these reasons we do not agree with the conversion in these cases and we recommend the greatest caution about these techniques.

11.5 Discussion The problem concerning the cost of a hexapod frame (considerably higher than the cost of a classic frame) is to be emphasized. This difference is partially balanced by the simplicity of the management and by the reduced number of periodical clinical examinations and radiographic controls. Moreover, features and manner of functioning of “classic” and “hexapod” circular external fixators are similar (although there are “internal differences” within the group of “classic” fixators and within the group of “hexapod” fixators). For this reason, it is impossible to compare the risk of complications related to these two groups of devices; however it is useful to remember some different characteristics. Hexapod frames have several undoubted advantages: mounting is easier, frame is stronger, simultaneous correction of all deformities is

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possible. These devices need adequate stability, which is better granted with the use of pins instead of wires: this means that the risk of lesions to vessels or nerves is lower, because in this case the use of transfixing wires can be avoided. Moreover, considering that the construct is more simple and more stable, there is no strict necessity for insertion of bone fixation elements near to proximal and distal joints of a long bone as is necessary with the use of classic circular fixators, with reduction of articular infection rate. Account should also be taken of the fact that with conventional circular frames, gradual correction of complex deformities may require changes of the frame construct, which may be very time-consuming [23]. Different workspaces of conventional and hexapod frames were studied by some Authors, with consequences for clinical application [22, 23]. TSF frame and Ilizarov frame were compared, in particular with regard to frame heights and potential to correct deformities. It was observed that the potential of a frame to correct deformities is limited by its work space. The geometry of a conventional frame is different from the geometry of a hexapod frame, which is the reason for their different work spaces. The minimal frame height of hexapod fixators is higher in comparison with conventional Ilizarov fixators, and so its indication for hexapod constructs in pediatric orthopaedics can be limited. It should also be considered that hexapod frame is more effective in correcting translation and rotational deformities than a conventional frame, but correction of extensive angulation and shortening deformities almost always needs an exchange of telescopic rods, while conventional frames are usually able to correct these deformities with the primary mounting. Other biomechanical researches were carried out to study maximal deformity correction of hexapod frames potential without impinging on the soft tissues. In particular, studies were performed in order to determine the maximal corrective ability and optimal placement of the Ortho-SUV frame for femoral deformity with respect to the soft tissue envelope [32].

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A comparative study on deformity correction accuracy of a conventional fixator (Ilizarov frame) and a Hexapod fixator (Smart Correction Spatial Frame), performed by Eren et  al. [33], raised the unexpected issue of inferior bone healing index score for Ilizarov fixator, suggesting a possible production of low quality bone regenerate by the use of Hexapod fixator, but this observation requires further deepening.

11.6 Conclusion Management of complications that can arise with the use of conventional or hexapod circular fixation is similar, and always requires a perfect knowledge of anatomy, an understanding of the basic clinical and mechanical principles and a complete evaluation of the potential of the apparatus. Indications and contraindications to adoption of classic circular and hexapod external fixators are essentially the same, but there are some special indications and contraindications to use of hexapod devices that must be well known in order to achieve the best results in these difficult cases.

References 1. Paley D.  Problems, obstacles and complications of limb lengthening by the Ilizarov technique. Clin Orthop Relat Res. 1990;250:81–104. 2. Caton J, Dumont P, Bérard U, et al. Etude des résultats à moyen terme d’une série de 33 allongements des membres inférieurs selon la technique de H. Wagner. Rev Chir Orthop. 1985;71:44–8. 3. Popkov AV.  Errors and complications of operative lengthening of the lower extremities in adults by the Ilizarov method. Vestn Khir. 1991;1:113–6. 4. Donnan LT, Saleh M, Rigby AS. Acute correction of lower limb deformity and simultaneous lengthening with a monolateral fixator. J Bone Joint Surg. 2003;85B:254–60. 5. Lascombes P, Popkov D, Huber H, et al. Classification of complications after progressive long bone lengthening: proposal for a new classification. Orthop Traumatol Surg Res. 2012;98:629–37. 6. Green SA.  Complications of pin and wire external fixation. AAOS Instr Course. 1990;39:219–28.

246 7. Eycleshymer A, Schoemaker D. A cross-section anatomy. New York: Appleton – Century; 1911. 8. Kalnberz VK.  Compression-distraction apparatus. Stress and rigid system. Riga: LNIITO; 1981. 9. Green SA.  External fixation mounting for difficult locations. Tech Orthop. 1996;11:115–24. 10. Paley D, Chaudray M, Pirone AM, et al. Treatment of malunions and malnonunions of the femur and tibia by detailed preoperative planning and the Ilizarov techniques. Orthop Clin North Am. 1990;21:667–91. 11. Caja VL, Moroni A. Hydroxyapatite coated external fixation pins. An experimental study. Clin Orthop Relat Res. 1996;325:269–75. 12. Trace R.  Antimicrobial silver coating reduces external fixation pin-tract infections. Ortop Today. 1997;17:1–2. 13. Voss K, Rosenberg B, Faghri M, et  al. Use of tobramycin-­impregnated polymethylmethacrylate pin sleeve for the prevention of pin-tract infection in goats. J Orthop Trauma. 1998;13:98–101. 14. Toksvig-Larsen S, Aspenberg P.  Bisphosphonate coated external fixation pins appear similar to hydroxyapatite-coated pins in the tibial metaphysis and to uncoated pins in the shaft. Acta Orthop. 2013;84:314–8. 15. Mora R, editor. Nonunion of the long bones. Diagnosis and treatment with compression-distraction techniques. Berlin: Springer; 2006. 16. Paley D.  Problems, obstacles and complications of limb lengthening. In: Bianchi Maiocchi A, Aronson J, editors. Operative principles of Ilizarov. Baltimore: Williams and Wilkins; 1991. p. 352–65. 17. Papaioannou N, Mastrokalos D, Papagelopulos PJ, et  al. Nonunion after primary treatment of tibia fractures with external fixation. Eur J Orthop Surg. 2001;11:231–5. 18. Kesemenli C, Necmioglu S, Kayikci C.  Treatment of refracture occurring after external fixation in paediatric femoral frasctures. Acta Orthop Belg. 2004;70:540–4. 19. DeCoster TA, Crawford WK, Kraut MA. Safe extracapsular placement of proximal tibia transfixation pins. J Orthop Trauma. 1999;13:236–40. 20. Vora AM, Haddad S, Kadakia A, et al. Extracapsular placement of distal tibial transfixation wires. J Bone Joint Surg Am. 2004;86:988–93. 21. Changulani M, Bradbury M, Zenios M. Hyperetension as a complication of Taylor Spatial frame. J Pediatr Orthop B. 2009;18(6):392–3.

R. Mora et al. 22. Rodl R, Leidinger B, Bohm A, et  al. Correction of deformities with conventional and hexapod frames – comparison of methods. Z Ortho. 2003;141(1):92–8. 23. Manner H, Huehl M, Radler C, et  al. Accuracy of complex lower-limb deformity correction with external fixation: a comparison of Taylor Spatial Frame with the Ilizarov Ringfixator. J Child Orthop. 2007;1:55–61. 24. Oganesian OV. Treatment of bone fractures and joint injuries. Moscow: BKL Publishers; 2006. 25. Young J, Lamm B, Herzenberg JE.  Complex foot deformities: correction with the Taylor spatial frame. In: Kocaoglu M, Tsuchiya H, Eralp L, editors. Advanced techniques in limb reconstruction surgery. Berlin: Springer; 2015. 26. Takata M, Vilenski V, Tsuchiya H, Solomin L.  Foot deformity correction with hexapod external fixator, the ortho-SUVFrame™. J Foot Ankle Surg. 2013;52(3):324–30. 27. Mora R, Pedrotti L, Bertani B, et  al. Deformità torsionali del piede. In: Massobrio M, editor. Diagnosi e cura delle deformità rotatorie e torsionali dergli arti. Roma: CIC; 2017. p. 71–8. 28. Pairon P, Ossendorf C, Kuhn S, et al. Intramedullary nailing after external fixation of the femur and tibia: a review of advantages and limits. Eur J Trauma Emerg Surg. 2015;41(1):25–38. 29. Nieto H, Baroan C.  Limits of internal fixation in long-bone fracture. Orthop Traumatol Surg Res. 2017;103(1S):S61–6. 30. Hamdy RC.  Evolution in long bone deformity correction in the post-lizarov era. External to internal devices. JLLR. 2016;2(2):61–7. 31. Hamdy RC, Bernstein M, Fragomen AT, Rozbruch SR.  What’s new in limb lengthening and deformity correction. J Bone Joint Surg Am. 2017;99:1408–14. 32. Skomoroshko PV, Vilenski VA, Hammouda A, et al. Determination of the maximal corrective ability and optimal placement of the Ortho-SUV frame for femoral deformity with respect to the soft tissue envelope, a biomechanical modelling study. Adv Orthop. 2014;2014:1–11. 33. Eren I, Eralp L, Kocaoglu M.  Comparative clinical study on deformity correction accuracy of different external fixators. Int Orthop. 2013;37(11):2247–52.

Part III Special Applications, Biological and Economical Aspects of Hexapod External Fixators

Ancillary Usage of Hexapod External Fixators

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Fixator- Assisted Nailing (FAN), Fixator-­ Assisted Locking Plate (FALP), Computer Hexapod-Assisted Orthopaedic Surgery (CHAOS), Lengthening Over Nail (LON), Bone Transport Over a Nail (BTON) and Lengthening and then Nailing (LATN) Marco Massobrio, Giovanni Pellicanò, Pasquale Sessa, and Pasquale Farsetti

Nomenclature (A)DCO (advanced) damage control orthopaedics (B)HI (bone) healing index BTON bone transport over a nail CHAOS computer hexapod-assisted orthopaedic surgery CHATS computer hexapod-assisted trauma surgery EFI external fixation index ERO endosteal realignment osteostomy FALP fixator-assisted locking plate FAN fixator-assisted nailing FIN flexible intramedullary nails ILN intramedullary lengthening nail

M. Massobrio (*) · G. Pellicanò · P. Sessa Department of Orthopaedics and Traumatology“Sapienza”, University of Rome, Rome, Italy e-mail: [email protected] P. Farsetti Department of Orthopaedics and Traumatology A- “Tor Vergata”, University of Rome, Rome, Italy

LATN LISS LON

lengthening and then nailing less invasive stabilization system lengthening over a nail

The simultaneous use of both external and internal fixation devices is a surgical procedure that combines two different techniques of bone osteosynthesis, with different timing and methods, in order to benefit from the advantages, to eliminate the mutual drawbacks and to reduce treatment time. The external fixator acts as a hardware that allows the orthopaedic surgeon to realign the bone gradually, controllably and reversibly. The internal osteosynthesis protects the biological process of bone healing, maintains the gained correction and allows for an earlier removal of the external fixator. The choice to combine the osteosynthesis always requires a preliminary planning of surgical approaches and the arrangement of screws or wires of the external fixator. The construct of the external fixator must have the same characteristics

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of rigidity and resistance even if combined with internal fixation, which remains an option. Usually, in this kind of surgical intervention, the external fixation can be of greater extension with the concentration of the bone-anchoring elements at the ends of the bone segment. If the fixator screws cannot be spaced from each other so as not to occupy the diaphysis, their position, at the level of the epiphysis must be reciprocally angled to have an adequate hold in a small space. In some locations, or if the bone segment is sufficiently wide, the screws can be applied posterior to the coronal plane and parallel to it in order not to obstruct the intramedullary canal (trochanteric region, femoral, and tibial condylar region). An accurate study of the stability of the fixator, especially if it is unilateral or used for bone lengthening, is of paramount importance here. Therefore the external fixator must combine the characteristics required by its use with the possibility of tolerating, with a dedicated construct, the presence of an internal fixation applied simultaneously or in a second surgical step. The morphology of the intramedullary canal is crucial in the treatment of axial deformities with a combined technique. In these cases, the Endosteal Realignment Osteostomy (ERO) of the canal using an external fixator allows for restoring the anatomical axis of the bone segment, without causing damage to the endosteal canal and can be considered a preliminary treatment to correct the deformity, in order to facilitate a subsequent internal fixation or prosthetic replacement. When a corrective osteotomy is performed in the presence of a closed intramedullary canal or in the case of a failed realignment of the anatomical axis of the assessed bone segment, secondary to a parafocal osteotomy, an intramedullary nail can be used but it can also sometimes be an obstacle to the use of a minimally invasive plate. The preoperative CT scan of the segment, with 3D reconstruction, highlights the structural characteristics of the bone [1]. The application of an internal fixation after the external fixator is not indicated in the following cases: the obstacle of the fixator struc-

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ture to the surgical approach or to the internal fixation and the obstacle of the bone-anchoring elements of the external fixator, screws or wires, to the sliding or to the application of an internal fixation. The indications for the combination of external fixator-internal fixation are also related to the early removal of the external fixator and weight-­ bearing permission. In some external fixation-internal fixation associations, frame removal improves patient tolerance but does not allow for early weight bearing. On the other hand, the early rejection of the external fixator requires a wider internal fixation or an absolute stability between the bone segments being treated. This stability feature is not found in some surgical situations such as bone transport, lengthening or multifragmentary fractures. The associated use of external and internal syntheses on the same bone segment can be consecutive, simultaneous and computer-assisted.

12.1 Consecutive Method The method is consecutive when the external fixator application is followed by the definitive internal fixation and the removal of the external fixator. • Consecutive techniques: FAN, FALP and LATN

12.1.1 FAN and FALP (Fixator-Assisted Nailing and Fixator-Assisted Locking Plate) One of the main disadvantages of external fixation is the fixator’s bulk and encumbrance, which can create discomfort for the patient. To achieve the accuracy and adjustability of the external fixator and reduce the treatment time, the combined use of internal and external fixation has been proposed: Fixator-Assisted Nailing (FAN), first described by Paley in 1997 [2], and Fixator-­Assisted Locking Plate (FALP).

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These two methods combine the advantages of external fixation (accuracy and adjustability) with those of internal fixation (reduction in treatment time). The external fixator is applied temporarily until the desired correction and alignment is achieved and an X-ray exam is performed. Once the desired correction with the external fixator is obtained, an intramedullary nail is applied, in the case of FAN, or a locking plate, in the case of FALP.  Once the internal fixation has been performed, the external fixator is removed before the patient comes out of anesthesia and the osteotomy is stabilized thanks to the intramedullary nail or plate [3, 4].

12.1.1.1 Advantages and Disadvantages FAN and FALP surgical techniques have five main advantages: the possibility of obtaining an extremely precise correction; the convenience of applying the intramedullary nail or the plate while the osteotomy is maintained stable by the external fixator; permanent fixation with a nail or plate that prevents the loss of the achieved correction; the possibility of rehabilitation and early joint mobilization of the patient; lowering of infection risk. The disadvantages of the combination of these two techniques, on the other hand, are primarily related to the surgical steps: firstly, the need for the wires or screws of the external fixator not to interfere with the intramedullary nail or with the plate; the risk of damage at the level of the surgical access; the increased local surgical trauma [1]. 12.1.1.2 Accuracy and Results of the Technique Favorable results are reported in the treatment of axial deviations, nonunions, complex periarticular deformities with complete deformity correction in a high percentage of cases [5–9]. In patients with complex periarticular deformities treated with the FALP technique, Rozbruch [10] reported an earlier functional recovery and lower rate of pin-tract infections, with a correction accuracy similar to the unilateral fixator, but with longer surgical times, higher incidence of postoperative blood transfusions and discomfort

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at the iliotibial band, with the need in some cases for removal of the distal femoral plate. Kocaoglu et  al. [11] demonstrated that the FAN technique has satisfactory results in cases of femoral and tibial deformities, with the foresight to insert the screws of the external fixator at a sufficient distance from the path of the intramedullary nail, especially in the sagittal plane, and to use “poller” screws, to guide the reaming of the canal and to prevent the loss of correction in the proximal or distal area.

12.1.1.3 Indications and Contraindications The FAN and FALP techniques are applicable for the treatment of deformities of all limb long bones, but are mainly used for deformities of the distal femur and those of the tibia at any level [8] (Fig. 12.1). The FAN technique is also indicated for the reconstruction of the distal tibia, associated with ankle arthrodesis [12]. In adults, both FAN and FALP are appropriate, while in children FALP is preferred to FAN because it allows for the integrity of the growth cartilages to be maintained and for less invasiveness [13]. A further indication for the FALP technique is the lengthening in the pediatric population or in patients with a small or obstructed intramedullary canal. The plate is applied percutaneously at the end of the distraction phase and fixed with screws proximally and distally to the bone regenerate site, before the external fixator is removed. The plate can be inserted at the same time as the external fixator. In this case, the length of the plate should be calculated on the basis of the expected lengthening, and fixed in the insertion area. At the end of the distraction, the plate is fixed with screws at the opposite end and the external fixator is removed [14]. In patients with open physis or in adults with a small-diameter intramedullary canal, the lengthening with an external fixator can be associated with Flexible Intramedullary Nails (FIN), with a diameter equal to about 30–40% of the patient’s intramedullary canal, in order to facilitate an early removal of the external fixator and to provide a greater stability of the construct, respecting the bone endosteal biology. The curved subcutaneous

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part of the FIN anchors to the bone and prevents any translation during the lengthening. It has also been demonstrated, in patients treated with this method, a reduction in the healing index (HI). This is the number of days of treatment with the external fixator per centimeter of lengthening. This stimulation of bone formation may be due to the biological effect of the sliding of the FIN curve at the level of the regenerate [15].

a

b

The application of an external fixator to correct intraoperatively an angular deformity ­followed by an immediate internal fixation, FAN or FALP, is contraindicated in the presence of structures at risk that require a slow or gradual correction. This procedure is also contraindicated in cases of bone corrections associated with the need for tendon or capsular distension (e.g. leg deformities combined with ankle and foot deformity).

d

c

e

f

Fig. 12.1  FAN. (a) Distal tibial fracture treated with plate and screws. (b–d) Malunion with rotational deformity (29° external rotation vs controlateral limb). (e) Plate removal and application of unilateral fixator with an angulation of 30° of the distal screw compared to the proximal one. (f) Fibular diaphysis resection and tibial perpendicu-

g

lar osteotomy with Gigli saw. (g) Preparation of the nail insertion (note the posterior position of the proximal screw: no interference with the path of the nail). (h) Nail insertion. (i) Rotational deformity correction, fixator’s screws on the same plane (internal rotation of the distal segment). (j) Final clinical outcome

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i

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j

Fig. 12.1 (continued)

12.1.1.4 Complications Infection of the pin site of the external fixator is the most frequent complication of deformity correction treatment using external fixation, with incidence rates of up to 100% [16]. In most patients, skin infections can be treated with frequent dressings and oral antibiotics, but in some cases pin loosening can occur, with the risk of loss of fixation, alignment and instability of the construct, pain and functional limitation, osteomyelitis (4%), and joint contamination [17, 18]. On the other hand, infection of the intramedullary nail or plate in elective deformity treatments where infection is not present, is a rare occurrence [7, 9]. Pulmonary fat embolism is a serious but rare complication (1–5%) associated with the reaming of the intramedullary canal and the nail insertion [19, 20]. The risk is reduced, but not completely eliminated, by performing the osteotomy before the reaming of the intramedullary canal. The osteotomy creates a decompression of the canal preventing internal pressure increases during reaming and insertion of the intramedullary nail [21, 22].

12.1.1.5 FAN vs FALP The FAN and FALP techniques are comparable, in terms of deformity correction results. In the treatment of femoral deformities, the FALP technique is more advantageous than the FAN technique with a retrograde intramedullary nail. The insertion of the nail, in fact, requires knee flexion, with exposure to the risk of losing the correction obtained with the external fixator. The FALP technique has the advantage of minimizing limb movement on the operating table and, therefore, reducing the risk of loss of correction obtained with the external fixator [23, 24]. The FALP technique, unlike the FAN, has no risk of fat embolism.

12.1.2 LATN (Lengthening And Then Nailing) Distraction osteogenesis is a well-documented and effective surgical technique for performing lower limb lengthening, deformity correction, in the treatment of nonunions or bone reconstruction in the presence of extensive bone gaps. The

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external fixator is used both in the distraction and in the consolidation phase. In 2008 Rozbruch et al. [25] described a new technique (LATN) using an external fixator during the distraction phase to obtain a gradual distraction of the bone fragments. Once the planned length is reached, a reamed intramedullary nail is inserted in order to support the bone segment during the consolidation phase and allow for the early removal of the external fixator. (Fig. 12.2)

12.1.2.1 Indications and Contraindications Indications: 1. limb discrepancies in adults or bilateral hypometries (short stature, deformity); 2. malunions or nonunions (Fig. 12.3); 3. dwarfism; 4. poliomyelitis sequelae; 5. post-traumatic sequelae of epiphyseal damage; 6. fibrous dysplasia (Fig. 12.4). Contraindications: 1. active infection; 2. previous infection at the site of lengthening; 3. open growth cartilages; 4. intramedullary canal diameter