Transforaminal Endoscopy for Lumbar Spine [1st ed. 2023] 9811989702, 9789811989704

Table of contents :
Preface
Contents
Part I: Introduction
Historical Consideration for Transforaminal Endoscopy for Lumbar Spine
1 Introduction
2 The Invention of the Transforaminal Approach (Before the 1990s)
3 The Beginning of the Endoscopic Spine Surgery (the 1990s)
4 Development of Endoscopic Spine Surgery (Since 2000)
5 Summary
References
Anatomical Considerations of the Lumbar Spine for Transforaminal Access
1 Introduction
2 Lumbar Intervertebral Foramen
2.1 Boundaries of the Lumbar Intervertebral Foramen
2.2 Internal Structure of Intervertebral Foramen
2.3 Spinal Nerves in the Intervertebral Foramen
2.4 Vessels in the Intervertebral Foramen
3 Ligaments in the Intervertebral Foramen
4 Kambin’s Triangle
5 Endoscopic Anatomy
6 Summary
References
Setting of Operation Room and Patient Position and Equipment
1 General Operating Room Layout
2 Positioning
3 Equipment
4 Summary
References
Instruments for Transforaminal Endoscopy and Its Handling
1 Introduction
2 Endoscopic Visualization
3 Dilator
4 Working Cannula
5 Endoscopes
6 Fluid
7 Reamer/Drill
8 Radiofrequency Device
9 Laser
10 Hand Instruments
11 Summary
References
Historical Review and Pros and Cons of Different Surgical Approaches: Outside-In Vs. Inside-Out
1 Introduction
2 Inside-Out Technique
3 Outside-In Technique
4 Results
4.1 Disc Herniation Treatment by Inside-Out Technique
4.1.1 Evidence Level 2 Data
4.1.2 Evidence Level 3 Data
4.2 Disc Herniation Treatment by Outside-In Technique
4.2.1 Evidence Level 2 Data
4.2.2 Evidence Level 3 Data
4.3 Foraminal Stenosis Treatment by Inside-Out Technique
4.3.1 Evidence Level 3 Data
4.4 Foraminal Stenosis Treatment by Outside-In Technique
4.4.1 Evidence Level 2 Data
4.4.2 Evidence Level 3 Data
5 Summary
References
Principles of Transforaminal Endoscopic Approach Technique
1 Introduction
2 Indications
2.1 Clinical Considerations
2.2 Radiological Considerations
2.3 Technical Considerations and Accessible Range of the Endoscopic Forceps
3 Surgical Technique
3.1 Preoperative Setting, Positioning of the Patient, and Anesthesia
3.2 Planning for Initial Access (Initial Target Point and Skin Entry Point Determination)
3.2.1 Primary (Initial) Target Point
3.2.2 Skin Entry Point Determination
3.2.3 Inside-Out Tactic or Outside-In Tactic
3.2.4 Pitfalls to Watch Out for
3.3 Needle Insertion and Optimal Trajectory of Approach
3.4 Obturator Insertion Technique and Annulus Entry Point
3.5 Proper Working Cannula Placement
3.6 Full-Visualized Endoscopic Procedure
3.7 Foraminoplasty
3.8 Levering
3.9 Procedure of Discectomy (Subannular Space Decompression, Annular Releasing, and Fragmentectomy)
3.9.1 Decompression of Subannular Space Around the Base of Herniation
3.9.2 Annular Releasing
3.9.3 Fragmentectomy
3.10 Confirmation of Decompression
3.11 Hemostasis and Closing
4 Postoperative Consideration
5 Case Illustration
5.1 Case 1. (TELD for Subarticular Zone Disc Herniation)
5.2 Case 2 (TELD for Central Zone Disc Herniation)
5.3 Case 3 (TELD for Central Zone Disc Herniation, Improper Working Cannula Placement)
5.4 Case 4 (Contralateral Approach of TELD in Case of Conjoined Nerve Root)
5.5 Case 5 (TELD for Sequestrated Disc Herniations Migrated Beyond the Disc Level)
5.6 Case 6 (TELD Without Foraminoplasty for the Treatment of Down-Migrated Disc Herniation)
5.7 Case 7 (Unsuccessful Outcome Case of TELD)
5.8 Case 8 (TELD for Highly Down-Migrated Disc Herniation with Grade 1 Spondylolisthesis)
5.9 Case 9 (TELD for Up-Migrated Disc Herniation)
5.10 Case 10 (TELD for Highly Up-Migrated Disc Herniation)
5.11 Case 11 (TELD for Upper Lumbar Disc Herniation)
6 Summary
References
Part II: Transforaminal Endoscopy for Lumbar Disc Disease
The Paramedian-Contained Disc Herniation
1 Introduction
2 Indications
3 Surgical Instrument
4 Surgical Technique
4.1 Surgical Technique
5 Postoperative Consideration
6 Summary
References
Paramedian Migrated Disc Herniation
1 Low-Grade Down-Migrated Disc Without Foraminoplasty
1.1 Introduction
1.2 Surgical Procedure
1.3 Case Illustration
1.4 Summary
2 Transforaminal Endoscopic Lumbar Discectomy for the Treatment of Highly Down-Migrated Disc Herniation with Foraminoplasty
2.1 Introduction
2.2 Indications
2.2.1 Indications of Foraminoplasty
2.3 Surgical Technique
2.3.1 Positioning of the Patient and Anesthesia
2.3.2 Planning for Initial Access and Needle Insertion
2.3.3 Obturator Insertion Technique and Annulus Entry Point
2.3.4 Proper Working Cannula Placement
2.3.5 Full Visualized Endoscopic Procedure
2.3.6 Foraminoplasty
2.3.7 Levering
2.3.8 Procedure of Discectomy (Subannular Space Decompression and Fragmentectomy)
2.3.9 Confirmation of Decompression
2.3.10 Hemostasis 및 Closing
2.4 Postoperative Consideration
2.5 Clinical Outcomes and Case Illustration
2.5.1 Clinical Outcomes
2.5.2 Case Illustration
Case 1 (Cases Illustration for Technical Learning)
Case 2
Case 3
2.6 Summary
3 High-Grade Down-Migrated Disc Using Transpedicular Approach
3.1 Introduction
3.2 Surgical Technique
3.3 Case Illustration
3.4 Summary
4 High-Grade Down-Migrated Disc at Axillary Portion Using Extreme Lateral Approach
4.1 Introduction
4.2 Indications
4.3 Surgical Technique
4.4 Case Illustration
4.5 Summary
5 Low-Grade Up-Migrated Disc Without Foraminoplasty
5.1 Introduction
5.2 Classification
5.3 Surgical Technique
5.4 Case Review
5.5 Summary
6 Low-Grade Up-Migrated Disc Using Target-Oriented Approach
6.1 Introduction
6.2 Indications
6.3 Surgical Technique
6.4 Case Illustration
6.5 Summary
7 High-Grade Up-Migrated Disc with Foraminoplasty
7.1 Introduction
7.2 Surgical Procedure
7.3 Case Illustration
7.4 Summary
8 High-Grade Up-Migrated Disc Using Isthmus Plasty Approach
8.1 Introduction
8.2 Surgical Technique
8.3 Case Illustration
8.4 Summary
References
Endoscopic Effort to Overcome Anatomical Barriers at L5/S1 Level
1 Preoperative Trajectory Evaluation and Foraminoplastic Ventral Epidural Approach
1.1 Introduction
1.2 Indications
1.3 Evaluation
1.4 Surgical Technique
1.4.1 Foraminoplasty Using a Bone Reamer or Bone Cutter
1.4.2 Foraminoplasty Using an Endoscopic Drill
1.5 Summary
2 Transiliac Approach
2.1 Introduction
2.2 Indications
2.3 Surgical Technique
2.4 Case Illustration
2.5 Summary
3 Anatomical Approach Using the Isthmic Corridor
3.1 Introduction
3.2 Indications
3.3 Surgical Technique
3.3.1 Surgical Technique (Fig. 15)
3.4 Case Illustration
3.5 Summary
References
Foraminal Disc Herniation
1 Inside-Out Technique
1.1 Introduction
1.2 Indications
1.3 Surgical Technique
1.4 Case Illustration
1.5 Summary
2 Outside-In Technique
2.1 Introduction
2.2 Indications
2.3 Surgical Technique
2.4 Postoperative Consideration
2.5 Case Illustration
3 Extraforaminal Disc Herniation: Outside-In Technique
3.1 Introduction
3.2 Indications
3.3 Surgical Technique
3.4 Case Illustration
3.5 Summary
References
Various Other Disc Herniations
1 Recurrent Disc Herniation
1.1 Introduction
1.2 Main Text
1.3 Surgical Technique [28]
1.4 Case Illustration
1.5 Summary
2 Huge Central Disc Herniation
2.1 Presentation of the Patient and Illustrated Cases
2.2 Preoperative Planning
2.3 Surgical Steps
2.4 Commentary
3 Bilateral Disc Herniation
3.1 Presentation of the Patient and Illustrated Cases
3.2 Preoperative Planning
3.3 Surgical Steps
3.4 Commentary
4 Calcified or Hard Disc Herniation
4.1 Presentation of the Patient and Illustrated Cases
4.2 Preoperative Planning
4.2.1 Calcified Disc Herniation
4.2.2 Hard Disc Herniation
4.3 Surgical Steps
4.3.1 Calcified Disc Herniation
4.3.2 Hard Disc Herniation
4.3.3 Foraminal Hard Disc Herniation
4.4 Commentary
5 Double Compartment Herniation
5.1 Introduction
5.2 Indications
5.3 Surgical Technique
5.4 Case Illustration
5.5 Summary
References
Endoscopic Annuloplasty for Discogenic Back Pain
1 Introduction
2 Diagnosis
3 Indications
4 Surgical Technique
4.1 Instrument
5 Techniques
5.1 Position
5.2 Anesthesia
5.3 Provocation Test
5.4 Landing of the Working Sheath (as Shallow as Possible)
5.5 Annuloplasty
6 Complication Avoidance
7 Case Illustration
8 Summary
References
Part III: Transforaminal Endoscopy for Lumbar Spinal Stenosis
Lateral Recess Stenosis
1 Ventral Decompression
1.1 Introduction
1.2 Indications
1.3 Surgical Technique
1.3.1 Patient Preparation
1.3.2 Transforaminal Landing with Local Anesthesia
1.3.3 Foraminoplasty
1.3.4 Ventral Decompression of Lateral Recess
1.4 Case Illustration
1.5 Summary
2 Lateral Recess Stenosis: Dorsal Decompression
2.1 Presentation of the Patient and Illustrated Cases
2.2 Preoperative Planning
2.3 Surgical Steps
2.4 Extreme Lateral Transforaminal Approach with Foraminoplasty
2.5 Partial Upper Pediculectomy of the Lower Pedicle Following Vertical Foraminal Widening
2.6 Removal of the Ligamentum Flavum in the Lateral Portion of the Spinal Canal
2.7 Removal of the Ligamentum Flavum in the Dorsal Portion of the Spinal Canal
2.8 Ventral Decompression (if Necessary)
2.9 Commentary
References
Foraminal Stenosis
1 Foraminal Stenosis Ventral Decompression
1.1 Presentation of the Patient and Illustrated Cases
1.2 Preoperative Planning
1.3 Surgical Steps
1.4 Commentary
2 Dorsal Decompression
2.1 Introduction
2.2 Indications
2.3 Surgical Technique
2.4 Case Illustration
2.5 Summary
References
Lumbar Foraminal Stenosis Combined with Disc Herniation
1 Introduction
2 Indications
2.1 Surgical Technique
2.2 Postoperative Consideration
2.3 Case Illustration
2.4 Summary
References
Part IV: Complication and Its Management
Incomplete Removal of Herniated Disc and Recurred Disc
1 Introduction
2 Clinical Features
2.1 Inappropriate Placement of Working Channel
2.2 Type of Herniated Disc
2.3 Clinical Risk Factors
2.4 Radiological/Biomechanical Risk Factors
3 Clinical Risk Factors
3.1 Smoking
3.2 Obesity
3.3 Heavy Work/Early Ambulation
3.4 High ODI Score without Neurologic Deficit
4 Radiological/Biomechanical Risk Factors
4.1 Modic Changes
4.2 Rupture of Posterior Longitudinal Ligament (PLL)
4.3 Large Disk Height/Disc Height Index
4.4 High Segmental Range of Motion in Dynamic Radiographs
4.5 Lumbosacral Transitional Vertebrae (LSTV)
4.6 Management of Recurrent Herniation
4.7 Future Scope
4.8 Summary
Further Readings
Postoperative Infection After Transforaminal Endoscopic Lumbar Disc Surgeries
1 Introduction
2 Patient Population and Outcome Measurements
3 Demographics and Clinical Courses
4 Clinical Outcomes
5 Discussion
6 Summary
References
Hematoma
1 Introduction
2 Main Text
2.1 Blood Supply of the Lumbar Spine
2.2 Possible Anatomical Focuses of the Bleeding
2.3 Management of the Hemorrhages
3 Summary
References
Dura Tear
1 Introduction
2 Classification
3 Symptoms and Diagnosis
4 Treatment
5 Prognosis and Prevention
Further Reading
Radiation Risks Associated with Transforaminal Endoscopy for Lumbar Spine and Prevention Strategies
1 Introduction/Main Text
2 Scatter Effect in Operating Theater
3 Strategies to Reduce the Radiation Exposure
4 Summary
References
Epidural Steroid Injection
1 Introduction
2 Surgical Technique and Epidural Steroid Application
3 Main Text
References

Citation preview

Transforaminal Endoscopy for Lumbar Spine Sang-Ho Lee Sang-Ha Shin Junseok Bae Sang-Joon Park Editors

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Transforaminal Endoscopy for Lumbar Spine

Sang-Ho Lee  •  Sang-Ha Shin Junseok Bae  •  Sang-Joon Park Editors

Transforaminal Endoscopy for Lumbar Spine

Editors Sang-Ho Lee Wooridul Spine Hospital Seoul, Korea (Republic of)

Sang-Ha Shin Wooridul Spine Hospital Seoul, Korea (Republic of)

Junseok Bae Wooridul Spine Hospital Seoul, Korea (Republic of)

Sang-Joon Park Wooridul Spine Hospital Busan, Korea (Republic of)

ISBN 978-981-19-8970-4    ISBN 978-981-19-8971-1 (eBook) https://doi.org/10.1007/978-981-19-8971-1 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 This work is subject to copyright. All rights are solely and exclusively licensed 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 Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Preface

Transforaminal endoscopy is not just a field in medical science but a patient-centered philosophy. It is a technique of care, endeavoring to alleviate the patients’ back pain, sciatica, and paralysis of the legs and feet, and helping them to become, once again, a healthy person without sequelae. Surgery consisting of big skin incisions and bone cutting can be devastating to patients. If surgeons treat their patients the way they would treat their own body or those of their family, they would shy away from destructive incisional surgeries. After the procedure, patients should be able to return to their work and study as soon as possible. Therefore, surgeons should focus not only on the problem at hand but also on the patient’s life and daily routine to follow. In spinal surgery, safety is as important as a successful outcome. The expansion and brightening of the operation field through the endoscope help prevent post-treatment side effects such as nerve damage and bleeding. The smaller the incision and greater the magnification of the affected area with bright light, the less invasive the treatment can be, allowing for minimal damage to the patient’s body while effectively treating the lesion. These advances work together towards an optimal cure with minimal scarring. In addition, as transforaminal endoscopy does not require general anesthesia, patients tend to experience less anxiety compared to open surgery. Patients with chronic diseases such as diabetes, heart disease, kidney failure, and stroke, as well as older patients, can be treated with this technique. Since it is performed with the patient under conscious sedation, the patient can communicate with the surgeon and feel the resolving pain and numbness right after the procedure. A typical endoscopic lumbar disc herniation procedure performed by a spine specialist takes about 20–30 min. The patient experiences immediate improvement after the procedure and can be discharged on the same day. Since the lesion is approached directly, the typical scar is less than 1 cm in length. Patients with spinal stenosis also show improvement in less than a day after transforaminal endoscopy. The procedure has a small skin incision and brings fast patient recovery since there is minimal damage to the normal tissue.

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Preface

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The one portal endoscopy is a delicate, safe, and effective procedure, and the biportal endoscopy also produces good clinical outcomes. I hope this book can help all spine surgeons who are training and performing procedures via transforaminal endoscopy. Seoul, Korea (Republic of)

Sang-Ho Lee

Contents

Part I Introduction Historical Consideration for Transforaminal Endoscopy for Lumbar Spine������������������������������������������������������������������������������������������   3 Seong Kyun Jeong and Sang-Ho Lee Anatomical Considerations of the Lumbar Spine for Transforaminal Access����������������������������������������������������������������������   9 Dong-Ju Yun Setting of Operation Room and Patient Position and Equipment ����������������������������������������������������������������������������������������  21 Shih Min Lee  Instruments for Transforaminal Endoscopy and Its Handling ����������  27 Shin-Jae Kim Historical Review and Pros and Cons of Different Surgical Approaches: Outside-In Vs. Inside-Out������������������������������������������������  33 Ki-Hyoung Moon Principles of Transforaminal Endoscopic Approach Technique��������������������������������������������������������������������������������������������������  41 Sang-Joon Park Part II Transforaminal Endoscopy for Lumbar Disc Disease  The Paramedian-Contained Disc Herniation����������������������������������������  91 Junseok Bae  Paramedian Migrated Disc Herniation��������������������������������������������������  99 Han Joong Keum, Sang-Joon Park, Yong Soo Choi, Shin-Jae Kim, Sang-Ha Shin, and Shih Min Lee Endoscopic Effort to Overcome Anatomical Barriers at L5/S1 Level ������������������������������������������������������������������������������������������ 163 Ju-Wan Seuk, Hyun Jin Ma, and Junseok Bae Foraminal Disc Herniation���������������������������������������������������������������������� 177 Ju-Wan Seuk, Jisang Kim, Won-Chul Choi, Shin-­Jae Kim, and Sang-Ha Shin vii

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 Various Other Disc Herniations�������������������������������������������������������������� 191 Jeong Hoon Choi, Sang-Ha Shin, and Shin-Jae Kim  Endoscopic Annuloplasty for Discogenic Back Pain���������������������������� 217 Shih Min Lee Part III Transforaminal Endoscopy for Lumbar Spinal Stenosis Lateral Recess Stenosis���������������������������������������������������������������������������� 229 Jiyoung Cho and Sang-Ha Shin Foraminal Stenosis���������������������������������������������������������������������������������� 247 Sang-Ha Shin and Junseok Bae  Lumbar Foraminal Stenosis Combined with Disc Herniation������������ 257 Kang Suk Moon and Minseung Jeong Part IV Complication and Its Management  Incomplete Removal of Herniated Disc and Recurred Disc���������������� 267 Syed Ifthekar and Junseok Bae Postoperative Infection After Transforaminal Endoscopic Lumbar Disc Surgeries���������������������������������������������������������������������������� 277 Seong Kyun Jeong and Sang-Ha Shin Hematoma������������������������������������������������������������������������������������������������ 285 Hyoung Woo Lho and Sang-Ha Shin Dura Tear�������������������������������������������������������������������������������������������������� 293 Ju Hyung Lee and Junseok Bae Radiation Risks Associated with Transforaminal Endoscopy for Lumbar Spine and Prevention Strategies���������������������������������������� 299 Syed Ifthekar and Junseok Bae Epidural Steroid Injection���������������������������������������������������������������������� 305 Sang-Ha Shin

Contents

Part I Introduction

Historical Consideration for Transforaminal Endoscopy for Lumbar Spine Seong Kyun Jeong and Sang-Ho Lee

1 Introduction In today’s various surgical fields, endoscopic therapy plays a prominent role. Numerous surgeries performed with the naked eye in the past have achieved the same or better results using an endoscope. As in other surgical departments, spine surgery has continued to strive for the use of endoscopes for treatment. With the development of optical technology, imaging devices, and surgical instruments, and the passionate dedication of the various spine surgeons, endoscopic spine surgery (ESS) has made many advances over the past half-century. Minimizing damage to normal structures and effectively removing only lesions through spinal endoscopy helps patients recover quickly and return to daily life early while relieving patients from unnecessary worries and anxiety about the sequelae of surgery. Furthermore, it encourages patients not to hesitate to choose the appropriate surgical treatment. The transforaminal approach is historically the most fundamental endoscopic approach among the endoscopic approaches ever been made. It is the most faithful to the minimally S. K. Jeong · S.-H. Lee (*) Department of Neurosurgery, Chungdam Wooridul Spine Hospital, Seoul, Republic of Korea e-mail: [email protected]

invasive principles and has various advantages in removing lesions. The transforaminal approach utilizes the original anatomy of the spine to its fullest extent. It allows direct access to the dorsal root ganglion, the fundamental cause of low back pain and radiating pain, by directly checking the inside of the intervertebral disc, epidural space, nerve tissue, and facet joint area. In this chapter, we will discuss the invention of the transforaminal approach, the development of the transforaminal endoscopic spine surgery, and the spine surgeons who contributed to the ESS.

2 The Invention of the Transforaminal Approach (Before the 1990s) Before endoscopic treatment was invented, there have been attempts to percutaneously examine spinal lesions and treat them nonsurgically using a posterolateral approach such as percutaneous biopsy, discography, and chemonucleolysis. However, after Parviz Kambin’s achievements, proper percutaneous surgical treatment of intervertebral disc was possible. Confirming the concept of an accessible, reproducible, and neurologically safer corridor was a monumental event in the history of endoscopic spinal surgery (ESS).

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 S.-H. Lee et al. (eds.), Transforaminal Endoscopy for Lumbar Spine, https://doi.org/10.1007/978-981-19-8971-1_1

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Open discectomy following laminectomy was the standard treatment for disc herniation before and long after Kambin. The surgery was performed using a midline or paramedian approach. It required damage to paraspinal muscles, laminar, and facet joint structures to secure a field of view to identify and remove the herniated intervertebral discs. In addition, acceleration of disc degeneration by removing the nucleus pulposus was a common concern of spine surgeons performing open disc surgery (Fig. 1). In particular, spine surgery in historically earlier periods targeted patients with more severely degenerated diseases. In contrast, later spine surgery targeted more patients who only complained of pain and did not develop severe neurological deficits. It was essential to have an operation that caused as few sequelae as possible. Several spine surgeons have studied alternative surgical methods that avoid the midline or paramedian approach. In 1951, Hult reported a nucleotomy using an anterolateral abdominal

S. K. Jeong and S.-H. Lee

extraperitoneal approach [1]. In 1975, Hijikata performed nonvisualized percutaneous nucleotomy using a posterolateral approach [2]. Kambin and his colleagues have studied methods and devices to reach the posterior surface of an intervertebral disc through a posterolateral approach since the mid-1970s. He performed the first percutaneous decompression of an intervertebral disc using the Craig cannula in 1973 [3]. In 1982, he performed percutaneous posterolateral discectomy on nine patients and reported the results of suctioning fragments from the dorsal portion of the discs using high negative pressure. Kambin’s research and experience of the posterolateral approach without passing through the central spinal canal led to the first description of “the triangular working zone” in 1988 [4]. It inspired many pioneering spine surgeons to develop new surgical treatments. For spine surgeons seeking new treatments, discovering a safe passage to the intervertebral disc was like Vasco da Gama’s discovery of the sea route to India.

Fig. 1  Preoperative X-ray image of a patient who underwent conventional discectomy on L4–5 level (left). Two years and eight months later, the disc height was significantly decreased to cause lower back pain (right)

Historical Consideration for Transforaminal Endoscopy for Lumbar Spine

3 The Beginning of the Endoscopic Spine Surgery (the 1990s) ESS began in the 1990s. After Parviz Kambin reported on a “safe triangular working zone” on the verge of the 1990s, with the addition of advances in surgical instruments and imaging devices, ESS was finally realized. Early in the history of ESS, the primary attention was focused on the intervertebral disc. Before introducing ESS, percutaneous treatment for intervertebral discs was a blind method rather than directly viewing a fragmented disc. It was an indirect method of decompression of the center of the intervertebral disc. In 1985 Onik performed automated percutaneous nucleotomy [5]. After crushing the inside of the nucleus pulposus by a mechanical method, they were washed with saline. It was difficult to expect a high success rate due to limited indications. Still, it was an alternative treatment modality that provided a percutaneous surgical method without anaphylaxis, which was the significant side effect of chemonucleolysis. The most significant advantage of endoscopic surgery is that lesions can be treated while closely visualizing in the surgical field. It was needed to differentiate between lesions and normal tissues to achieve the goal. As the experience of percutaneous treatment has been accumulated, several ideas have been reported that can lead to the birth of percutaneous endoscopic disc surgery around 1990. Kambin reported intraoperative discoscopic views of herniated nucleus pulposus (HNP) in 1988 [6], and Schriber in 1989 injected indigo carmine, which can stain a normal nucleus and annular fissure into an intervertebral disc [7]. In 1991 Leu and Karl Storz developed a foraminoscope. Their method, called “discoscopy,” introduced an arthroscope from the contralateral side of the lesion, allowing direct visualization of intradiscal operative procedures. Leu’s foraminoscope contributed to the development of early endoscopy for a long time. Mayer and Brock first used the term “percutaneous endoscopic lumbar discectomy

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(PELD)” in 1993 [8]. They used a bilateral biportal approach, similar to the Leu method. They removed the intervertebral disc fragments using an automated nucleotome and rigid or flexible forceps while observing the posterior aspect of the fibrous annulus inside the intervertebral disc. A method of treating the ipsilateral side of the lesion using an endoscope and surgical instruments like the current transforaminal ESS was reported in 1996. Mathews in 1996 and Ditsworth in 1998 performed transforaminal ESS using a working channel scope [9]. In 1996, Kambin and Zhou also reported transforaminal arthroscopic decompression of lateral recess stenosis [10]. From these, transforaminal ESS was initiated. SH Lee, the coauthor of this chapter and the founder of Wooridul Spine Hospital (WSH), also pioneered ESS since 1991. He reported his experiences of the percutaneous endoscopic manual and laser discectomy at the 19th SICOT World Congress in 1993. He published the result in the Orthopade, a surgical journal in Germany, in 1996 [11]. He established the concept of “intra-­ annular subligamentous fragmentectomy” using Ho:YAG laser. With Martin Knight and Anthony Yeung, SH Lee was invited to the American Minimally Invasive Surgery Conference in 2000 and presented his surgical method. He frequently cooperated with Kambin from the beginning and devoted his whole life to expanding ESS fundamentals worldwide (Fig. 2).

Fig. 2  Parviz Kambin and Sang Ho Lee in 1992

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4 Development of Endoscopic Spine Surgery (Since 2000) In the 2000s, two important endoscopic techniques by Anthony Yeung and Thomas Hoogland were reported (Fig. 3). In 2002, Yeung and Tsou reported an endoscopic disc surgery using a rigid rod-lens, integrated, multichannel, and wide-angled endoscope. Anthony Yeung’s surgical method was known as the “inside-out” technique due to the starting position being the inside of the discs. He developed the Yeung Endoscopic Spine System (YESS) with Wolf Company of Illinois [12]. In 2005, Schubert and Thomas Hoogland reported a surgical technique using the Thomas Hoogland Endoscopic Spine System (THESSYS). They performed foraminoplasty using a specialized reamer before removing disc particles, so their surgical method was known as the “outside­in” technique. The two methods have become the most famous endoscopic techniques soon. Many doctors have reproduced their surgical procedures. Each method has strengths in treating prolapsed intervertebral discs through the inside of the intervertebral disc (YESS) and resolution of foraminal stenosis through foraminoplasty (THESSYS). Spine doctors at WSH, including the author SH Lee, used the “half-and-half” technique that improved the “inside-out” technique [13]. This Fig. 4  The participants of the Spine Total Care Conference, 2002. Martin Knight, Sang Ho Lee, and Reuven Gepstein are sitting in the front line (in order from the left)

S. K. Jeong and S.-H. Lee

method was a way to see the inside of the intervertebral disc with half of the field of view and the epidural space with the other half of the field of view. As trained doctors from WSH spread nationally, this method became widely accepted, especially in Korea (Fig. 4). Since 2000, ESS has gradually expanded the scope of decompression surgery. In 2004, Ahn et al. of the WSH group reported the usefulness of ESS for the treatment of recurrent HNP [14]. In 2008, the same group, Choi et al., reported that highly migrated intracanal disc herniations could be treated using a foraminoplastic technique using a rigid working channel endoscope [15]. In addition, transforaminal approach methods have also become more diverse. In 2005, Rutten reported a technique called full endoscopy through extreme lateral access to overcome the

Fig. 3 Martin Knight, Anthony Yeung, and Thomas Hoogland (in order from the left)

Historical Consideration for Transforaminal Endoscopy for Lumbar Spine

usual transforaminal approach, which is associated with problems in reaching the epidural space directly with unhindered vision [16]. Transforaminal ESS has been further developed. The decompression range is now available in various types of HNP, including low- and high-­ grade migrated HNP, huge central HNP, calcified or hard HNP, foraminal HNP, extraforaminal HNP, and recurrent HNP. It also can treat foraminal and lateral recess stenosis. Since the mid-2010s, transforaminal endoscopic fusion surgery has also been reported [17]. In 2018, the U.S. government and academic societies approved medical insurance coverage for endoscopic disc treatment, which Kambin and Leu initiated with the International Society of Minimally Invasive Spinal Surgery (ISMISS). At the University of Miami Hospital and the training hospitals of Yale School of Medicine, endoscopic surgery was included in the regular spine doctor training program. In 2019, the North American Spine Society also had this surgery in the formal educational program.

5 Summary Based on the advances in optical technology, imaging devices, surgical instruments, and the passionate dedication of many spine surgeons, ESS has made much progress. Only a limited portion of the prolapsed intervertebral disc inside the spinal canal could be removed in the earlier period of ESS. For the past half-century, ESS has expanded its indications to treat a broader range of diseases. The transforaminal approach is the most fundamental approach for endoscopic treatment and is most faithful to the minimally invasive principle. It is possible to solve the pain caused by compressive lesions inside and outside the intervertebral foramen. The ESS removes the cause of the disease without tissue damage, helps the patient recover quickly and return early, and encourages the patient to receive the necessary treatment in time without sequelae. It is an approved treatment recognized by the U.S. government, aca-

7

demic societies, and medical t­raining institutes. Spine surgeons must acquire and further develop transforaminal ESS skills for their patients.

References 1. Hult L. Retroperitoneal disc fenestration in low-back pain and sciatica; a preliminary report. Acta Orthop Scand. 1951;20(4):342–8. 2. Hijikata S. Percutaneous nucleotomy. A new concept technique and 12 years’ experience. Clin Orthop Relat Res. 1989;238:9–23. 3. Kambin P.  Arthroscopic microdiscectomy. Arthroscopy. 1992;8(3):287–95. 4. Kambin P, Zhou L. History and current status of percutaneous arthroscopic disc surgery. Spine. 1996;21(24 Suppl):57s–61s. 5. Onik G, Helms CA, Ginsberg L, Hoaglund FT, Morris J. Percutaneous lumbar diskectomy using a new aspiration probe: porcine and cadaver model. Radiology. 1985;155(1):251–2. 6. Kambin P, Nixon JE, Chait A, Schaffer JL. Annular protrusion: pathophysiology and roentgenographic appearance. Spine. 1988;13(6):671–5. 7. Schreiber A, Suezawa Y, Leu H.  Does percutaneous nucleotomy with discoscopy replace conventional discectomy? Eight years of experience and results in treatment of herniated lumbar disc. Clin Orthop Relat Res. 1989;238:35–42. 8. Mayer HM, Brock M.  Percutaneous endoscopic lumbar discectomy (PELD). Neurosurg Rev. 1993;16(2):115–20. 9. Ditsworth DA.  Endoscopic transforaminal lumbar discectomy and reconfiguration: a postero-­ lateral approach into the spinal canal. Surg Neurol. 1998;49(6):588–97; discussion 97–8 10. Kambin P, Casey K, O'Brien E, Zhou L. Transforaminal arthroscopic decompression of lateral recess stenosis. J Neurosurg. 1996;84(3):462–7. 11. Lee SH, Lee SJ, Park KH, Lee IM, Sung KH, Kim JS, et  al. Comparison of percutaneous manual and endoscopic laser diskectomy with chemonucleolysis and automated nucleotomy. Der Orthopade. 1996;25(1):49–55. 12. Yeung AT, Tsou PM. Posterolateral endoscopic excision for lumbar disc herniation: surgical technique, outcome, and complications in 307 consecutive cases. Spine. 2002;27(7):722–31. 13. Lee S, Kim SK, Lee SH, Kim WJ, Choi WC, Choi G, et  al. Percutaneous endoscopic lumbar discectomy for migrated disc herniation: classification of disc migration and surgical approaches. Eur Spine J. 2007;16(3):431–7. 14. Ahn Y, Lee SH, Park WM, Lee HY, Shin SW, Kang HY.  Percutaneous endoscopic lumbar discectomy for recurrent disc herniation: surgical technique, out-

8 come, and prognostic factors of 43 consecutive cases. Spine. 2004;29(16):E326–32. 15. Choi G, Lee SH, Lokhande P, Kong BJ, Shim CS, Jung B, et al. Percutaneous endoscopic approach for highly migrated intracanal disc herniations by foraminoplastic technique using rigid working channel endoscope. Spine. 2008;33(15):E508–15. 16. Ruetten S, Komp M, Godolias G. An extreme lateral access for the surgery of lumbar disc herniations inside

S. K. Jeong and S.-H. Lee the spinal canal using the full-endoscopic uniportal transforaminal approach-technique and prospective results of 463 patients. Spine. 2005;30(22):2570–8. 17. Lee SH, Erken HY, Bae J. Percutaneous transforaminal endoscopic lumbar interbody fusion: clinical and radiological results of mean 46-month follow-up. Biomed Res Int. 2017;2017:3731983.

Anatomical Considerations of the Lumbar Spine for Transforaminal Access Dong-Ju Yun

1 Introduction In this chapter, we will discuss the intervertebral foramen (IVF), Kambin’s triangle, and endoscopic anatomy for a transforaminal endoscopic approach to the lumbar spine.

2 Lumbar Intervertebral Foramen 2.1 Boundaries of the Lumbar Intervertebral Foramen The IVF is the opening between consecutive vertebrae. The inferior notch of the pedicle of the superior vertebra and the superior vertebral notch of the pedicle of the inferior vertebra form the upper and lower boundaries of the IVF. The posterior border of two adjacent vertebral bodies and the intervertebral disc form its anterior border. The superior articular process of the lower vertebra and the inferior articular process of the upper

vertebra, ligamentum flavum, and pars intercularis form the posterior part of the IVF. The dural sac and traversing spinal nerve form its medial part (Fig.  1a). Using MRI scans, Cramer et  al. reported three parameters of the lumbar IVF in normal human subjects. In the lumbar IVF, the supero-inferior dimension (foraminal height) is the largest at L2/3. It gradually decreases and is the smallest at L5/S1. The anteroposterior dimensions are smaller than the supero-inferior dimensions from L1/2 to L4/5. However, at L5/S1, the supero-inferior dimension is greater than the anteroposterior dimension [1]. The transforaminal endoscopic approach at L5/S1 can sometimes pose difficulties for the surgeon with respect to approaching the L5-S1 disc space, owing to the oblique trajectory created by the iliac crest and the narrow foraminal area that is hindered by the transverse process of L5, hypertrophic L5/S1 facet joint, and sacral ala (Fig.  2) [2]. Therefore, an accessible trajectory should be confirmed before undertaking the transforaminal approach at L5/S1.

D.-J. Yun (*) Department of Neurosurgery, Busan Wooridul Spine Hospital, Busan, South Korea e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 S.-H. Lee et al. (eds.), Transforaminal Endoscopy for Lumbar Spine, https://doi.org/10.1007/978-981-19-8971-1_2

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10 Fig. 1  Boundaries of the intervertebral foramen at the lumbar spine. (Reproduced from Kim DH et al. 2011)

D.-J. Yun Pedicle Superior articular process Vertebral body

Transverse process 1

Spinous process

Intervertebral disc Inferior articular process 2

Inferior vertebral notch Intervertebral foramen

3

Superior vertebral notch

4

5

Fig. 2 Transforaminal endoscopic approach at the L5/S1 level. The working channel may be hindered by the iliac crest, transverse process of L5, hypertrophic L5-S1 facet joint, or sacral ala

Anatomical Considerations of the Lumbar Spine for Transforaminal Access

2.2 Internal Structure of Intervertebral Foramen Inside the IVF are the spinal nerve (union of the dorsal and ventral roots), dural root sleeve, the spinal branch of the segmental artery, communicating veins, recurrent meningeal (sinuvertebral) nerves, lymphatic channels, adipose tissue, and accessory ligaments (Fig. 3).

2.3 Spinal Nerves in the Intervertebral Foramen The spinal cord terminates at the L1/2 level in the vertebral canal in most cases. In some cases, it terminates at T12/L1 or L2/3. A pair of spinal nerve roots exit the dural sac just above the IVF.  The dura mater and the arachnoid mater come together while enveloping the spinal nerve roots; this area is called the dural sleeve. Thus, the nerve roots in this area are covered with pia mater and contain CSF (Fig. 4). Immediately before the site where the dorsal and ventral roots merge to form a spinal nerve,

Ventral and dorsal nerve roots within dural root sleeve

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the dorsal root is enlarged and is called the dorsal root ganglion (DRG). The DRG contains cell bodies of the sensory fibers in the dorsal root [3]. Most of the DRGs from L1 to L5 are inside the IVF.  However, the DRG of the upper lumbar region tends to be lateral and that of the lower lumbar region tends to be medial to the center of the IVF [4]. The angle at which the spinal nerve roots leave the dural sac differs at each level. At the upper lumbar level, they leave at an obtuse angle, while the dural sleeves of the lower nerve roots form increasingly acute angles with the dural sac margins. Hasegawa et al. reported the following angles between the spinal nerve root and the dural sac (degrees): L1: 40.9  ±  9.7, L2: 32.9  ±  7.4, L3: 30.8 ± 7.1, L4: 27.6 ± 7.3, L5: 27.7 ± 8.0 [5]. Can et al. also reported similar results (degrees): L1: 41.56 ± 6.89, L2: 37.07 ± 5.76, L3: 34.36 ± 5.67, L4: 33.08 ± 5.12, L5: 28.23 ± 4.51 [6]. The average dimensions of the DRG gradually increase from L1 to L5. Compared with the foraminal height, the height of the DRG is greater in the lower lumbar area. Therefore, the lower lumbar

Epidural adipose tissue

Intervertebral v. Lymphatic channel Recurrent meningeal n.

Spinal branch of lumbar segmental a.

Transforaminal ligament

Fig. 3  Internal structure of the intervertebral foramen

D.-J. Yun

12 Arachnoid Subarachnoid space Dura Pia

Dorsal root Dural sac

Ventral root Dural sleeve Dorsal root ganglion

Cauda equina

Spinal nerve Cut edge of dural sac Ventral ramus Dural sleeve Dorsal ramus

Fig. 4  Dural sac, spinal nerve roots, and spinal nerve

level with a relatively large DRG may be more susceptible to compression than the upper lumbar level [5, 6]. When performing the transforaminal endoscopic approach, the DRG should be manipulated carefully as there is a risk of causing heat injury, which can lead to postoperative dysesthesia [4].

2.4 Vessels in the Intervertebral Foramen The spinal branch of the segmental artery is divided into three branches: (a) the anterior

branch supplies the posterior aspect of the vertebral body, (b) one branch runs posteriorly, supplying the posterior arch, and (c) neural branches supply the spinal nerves. The segmental artery supplying the posterior arch should be approached cautiously as bleeding may occur while manipulating the superior articular process during the transforaminal approach (Fig. 5a). The venous drainage includes the internal and external vertebral venous plexuses. The communicating (intervertebral) veins should also be approached cautiously, as bleeding may occur while manipulating the epidural space during the transforaminal approach (Fig. 5b).

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Anatomical Considerations of the Lumbar Spine for Transforaminal Access Fig. 5 (a) Arteries and segmental branches in the intervertebral foramen and lumbar spine. (b) The anterior internal venous plexus in the vertebral body and intervertebral foramen

a

b pscb dr

ascb vr LA

ia

To lumbar vein

man ppa spa ana

3 Ligaments in the Intervertebral Foramen The ligaments in the IVF are also called transforaminal ligaments (TFL). TFL are narrow bands of collagen fibers that traverse the outer end of the IVF. The reported incidence of the TFL in the lumbar region varies greatly. These structures resemble fascial bands rather than the ligaments that connect bones. TFL do not have a significant effect on endoscopic procedures through the transforaminal approach [3] (Fig. 3).

4 Kambin’s Triangle For safe access to the intervertebral disc through the transforaminal approach, a triangular zone, commonly called Kambin’s triangle, was introduced in 1983 by Dr. Parviz Kambin. It is bor-

dered anteriorly by the exiting root, inferiorly by the endplate of the lower lumbar segment, posteriorly by the superior articular process of the inferior vertebra, and medially by the traversing nerve root and the dural sac (Fig. 6). Can et  al. reported a cadaveric study on the base (superior endplate of the inferior vertebral body between the lateral border of the dural sac and the medial border of the exiting nerve), height (lateral margin of the dura extending from the exiting root axilla superiorly to the lower border of the intervertebral disc inferiorly), and the hypotenuse of the triangular zone. The mean values ​​of the base (millimeters) were L1–2: 12.15, L2–3: 13.24, L3–4: 14.12, L4–5: 15.76, and L5-S1: 17.94. The average height (millimeters) was L1–2: 11.29, L2–3: 12.58, L3–4: 14.33, L4–5: 16.01, and L5-S1: 17.87. The mean values​​ of the hypotenuse (millimeters) were L1–2: 16.69, L2–3: 18.43, L3–4: 20.28, L4–5: 24.54, and L5-S1: 28.03 [6].

D.-J. Yun

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Kambin’s triangle Traversing nerve root and dural sac Exiting nerve root

Superior articular process of the inferior vertebra

Superior endplate of the inferior vertebra

Fig. 6  Kambin’s triangle

5 Endoscopic Anatomy

and the medial side is approached from the lateral side, nuclear fragments trapped in the annular In general, the optical angle of a transforaminal fibers can be seen in many cases (Fig. 10). After endoscope ranges from 20° to 30°. The visible removing the herniated nuclear material, the sursurrounding structures differ during the transfo- geon can see the annular hole leading to the herraminal endoscopic approach depending upon niation posteriorly (Fig. 11). When approaching perpendicular to the disc whether it is started inside the disc space (inside-­ space via the outside-in technique, the superficial out technique) or outside the disc space (outside­in technique). It is also necessary to accurately layer of the annulus fibrosus and posterior longidetermine the structures observed in the tudinal ligament, superior articular process in the ­endoscopic field according to the angle of entry. inferior vertebra, some epidural vessels, and fatty The structures of IVF seen from the endoscope tissue can be seen initially. With some structures may be slightly different when approaching the removed, the traversing nerve root and dural sac perpendicular to disc space, when approaching can be seen when approaching the medial side by the foraminal route with upward inclination, laterally (Fig. 12). Using the foraminal route with upward incliand when approaching with the suprapedicular nation, endoscopy reveals the superior articular route under downward inclination (Fig. 7). When approaching perpendicular to the disc process of the inferior vertebra, vertebral body of space using the inside-out technique, the poste- the superior vertebra, intervertebral disc, and the rior part of the disc can be seen initially (Fig. 8). exiting nerve root (Figs. 13 and 14). Using the suprapedicular route with downThe posterior longitudinal ligament and annulus ward inclination, the endoscopic view shows the fibrosus are seen on the dorsal side, while some superior articular process of the inferior vertebra, nuclear tissue is seen on the ventral side (Fig. 9). superior pedicular notch of the inferior vertebra, When stained with indigo carmine, degenerated acidic nuclear tissue stains blue, which can help vertebral body of the inferior vertebra, intervertedistinguish it from the surrounding structures. bral disc, and the traversing nerve root (Figs. 15 When the annulus fibrosus is partially removed and 16).

Anatomical Considerations of the Lumbar Spine for Transforaminal Access

15

Fig. 7  Three routes to access the intervertebral foramen: foraminal, intervertebral, and suprapedicular

Traversing spinal nerve Intervertebral disc Magnification

Superior articualar process of inferior vertebra

Fig. 8  Schematic anatomy of the intervertebral route. The circular area on the left image is enlarged and shown in the image on the right. Image viewed at eye level, horizontal to the disc space

D.-J. Yun

16 Fig. 9 Endoscopic anatomy: Intervertebral route, inside-out technique. A case with a herniated disc at the L4/5 level. This was the first image that the surgeon beheld when the working cannula entered inside the disc space

Dorsal

Posterior longitudinal ligament and annulus fibrosus Cranial

Caudal

Nuclear tissue

Ventral

Fig. 10 Endoscopic anatomy: Intervertebral route, inside-out technique. A case of a herniated disc at the L4/5 level. In many cases, after removing some of the annulus fibrosus, surgeons see the herniated nuclear material trapped in the annulus fibrosus

Dorsal

Annulus fibrosus: partially removed state Cranial

Caudal

Herniated nucleus material trapped in the annulus fibrosus

Ventral

Fig. 11 Endoscopic anatomy: Intervertebral route, inside-out technique. A case of a herniated disc at the L4/5 level. After removing the herniated nuclear material, the surgeon sees the annular hole posteriorly that has led to the herniation

Dorsal

Caudal

Cranial

Annular hole after removing herniated nucleus material

Ventral

Anatomical Considerations of the Lumbar Spine for Transforaminal Access Fig. 12 Endoscopic anatomy: Intervertebral route, outside-in technique. A case of a herniated disc at the L4/5 level. This is the first image that the surgeon saw when the working cannula moved outside the disc space

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Dorsal

Superior articular process

Cranial

Caudal Epidural fat

Annulus fibrosus

Ventral

Exiting spinal nerve Verterbral body of superior vertebra Magnification

Intervertebral disc

Superior articualar process of inferior vertebra

Fig. 13  Schematic anatomy of the foraminal route with an upward inclination. The circular area on the left image is enlarged and shown in the image on the right. The image is at an angle, looking up at about 30° upward

D.-J. Yun

18 Dorsal

Ligamentum flavum

Superior articular process : partially removed state Caudal

Cranial Posterior aspect of upper vertebral body

Intervertebral disc Ventral

Fig. 14  Endoscopic anatomy of the foraminal route with an upward inclination: A case with a highly upward migrated disc at the L4/5 level. This image depicts the epidural space approach after partially removing the supe-

rior articular process of L5, ligamentum flavum, and fat tissue to approach the upwardly migrated disc particles. The ruptured particles are not yet visible

Intervertebral disc Traversing spinal nerve Verterbral body of inferior vertebra

Magnification

Superior articualar process of inferior vertebra Superior pedicular notch

Fig. 15  Schematic anatomy of the suprapedicular route with a downward inclination. The circular area on the left image is enlarged and shown in the image on the right. The image is at an angle, looking up from about 30° down

Anatomical Considerations of the Lumbar Spine for Transforaminal Access

19

Dorsal Superior articular process : partially removed state Superior pedicular notch: partially removed state

Epidural fat Cranial

Caudal Postero-superior edge of vertebral body

Intervertebral disc

Ventral

Fig. 16  Endoscopic anatomy: Suprapedicular route. A case of a highly downward migrated disc at the L4/5 level. This image depicts the epidural space approach after removing the superior articular process and the superior

pedicular notch of L5 to approach the downwardly migrated disc particles. The ruptured particles are not yet visible

6 Summary

2. Eun SS, Lee S-H, Liu WC, Erken HY.  A novel preoperative trajectory evaluation method for L5-S1 transforaminal percutaneous endoscopic lumbar discectomy. Spine J. 2018;18(7):1286–91. 3. Bogduk N.  Clinical and radiological anatomy of the lumbar spine e-book. Edinburgh, London: Elsevier Health Sciences; 2012. 4. Kim DH, Choi G, Lee S-H Endoscopic spine procedures: Thieme; New York, NY 10001: Thieme Medical Publishers, Inc; 2011. 5. Hasegawa T, Mikawa Y, Watanabe R, An HSJS.  Morphometric analysis of the lumbosacral nerve roots and dorsal root ganglia by magnetic resonance imaging. Spine. 1996;21(9):1005–9. 6. Can H, Unal TC, Dolas I, Guclu G, Diren F, Dolen D, et al. Comprehensive anatomic and morphometric analyses of triangular working zone for transforaminal endoscopic approach in lumbar spine: a fresh cadaveric study. World Neurosurg. 2020;138:e486–91.

Familiarity with the anatomy of the intervertebral foramen, its surrounding structures, and endoscopic anatomy will help in performing transforaminal endoscopic procedures successfully.

References 1. Cramer GD, Cantu JA, Dorsett RD, Greenstein JS, McGregor M, Howe JE, et  al. Dimensions of the lumbar intervertebral foramina as determined from the sagittal plane magnetic resonance imaging scans of 95 normal subjects. J Manip Physiol Ther. 2003;26(3):160–70.

Setting of Operation Room and Patient Position and Equipment Shih Min Lee

1 General Operating Room Layout

routinely established. Generally, the operating room setups are (Figs. 1 and 2):

The basic design of a typical operating room starts with a rectangular space of ∼20 × 20 feet, although a larger size of around 30  ×  30  feet would be preferable to take a wider variety of transforaminal endoscopic procedures. The room should have adequate temperature-controlled ventilation channels and adequate storage space for surgical instruments. A laminar airflow system is required to prevent the growth of unwanted infectious organisms [1, 2]. Specific equipment and staff locations for transforaminal endoscopic surgery are usually

1. Surgeon faces the side of the patient to be operated on. 2. Nurse to surgeon’s right. 3. Table with surgical instrumentals in the nurse’s direct room. 4. Anesthesiologist and patient’s monitor is located to the left side of the surgery. 5. C-arm, video equipment and its monitor, and x-ray technician are positioned in front of the surgeon. An assistant/circulating nurse stands next door in the operating room.

S. M. Lee (*) Department of Neurosurgery, Chungdam Wooridul Spine Hospital, Seoul, Republic of Korea e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 S.-H. Lee et al. (eds.), Transforaminal Endoscopy for Lumbar Spine, https://doi.org/10.1007/978-981-19-8971-1_3

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S. M. Lee

22 C-ARC X-Ray

Video Equipment X—ray Technician Image Processing

Anesthetist

Technician

Patient monitor

Laser machine Surgeon

Nurse

Instrument Table

Fig. 1  Schematic illustration of the optimal operating room layout

Fig. 2  The optimal operating room layout

Setting of Operation Room and Patient Position and Equipment

2 Positioning This is the most important step in preoperative posture setting that requires special attention when determining the patient’s surgical posture. In particular, it is necessary to clearly distinguish where to approach the procedure on the left or

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right. If the patient’s lesion is on the right, the patient’s head is on the surgeon’s right side, and if the lesion is on the left side, the patient’s head should be on the surgeon’s left side (Figs. 3 and 4). Sufficient padding at the pressure points in each joint is essential to reduce skin damage associated with the surgical site.

Fig. 3  The patient’s head is positioned to the surgeon’s left side because the ruptured disc is to the left side

d

hea

Fig. 4  The patient’s head is positioned to the surgeon’s left side because the ruptured disc is to the left side

S. M. Lee

24

Prone position is probably the most commonly used position in spinal surgery. Since it allows the direct approach to the posterior midline and lateral pathology, it is also used at the transforaminal endoscopic approach. Although most procedures do not waste a lot of time, nonetheless all pressure points must be carefully padded with special attention paid to the eyes.

3 Equipment

Endoscope machine

Equipment placement in the operating room is a very important step in numerous surgical procedures, especially in endoscopic procedures, because there are more instruments and machines to prepare the procedure. Several instruments which are required for transforaminal endoscopic surgery are as follows (Figs. 5, 6 and 7): • Operating table: A radiolucent table is essential for successful spinal surgery even if laser surgery. • Fluoroscope: C-arm.

C-arm monitor

monitor

Irrigation pump

Computer

Fig. 6  Endoscope tower and laser machine

C-arm

ble

Scope

esia ta

Aneth

Surgeon

r

onito Pt’s m

Nurse

tower

Lase

r

Instrument table

Fig. 5  The actual scene during surgery

Setting of Operation Room and Patient Position and Equipment

Laser machine

Fig. 7  Endoscope tower and laser machine

• Endoscopy cart: Contains a video monitor, light source, recording device, and irrigation pump. • Laser machine and radiofrequency generator. • Motorized high-speed drill console. • Anesthesia table: This equipped with infusion pump, emergency medications and pulse monitor, oxygen saturation, blood pressure and electrocardiographic monitoring. • Irrigation fluid stand for endoscopic procedures. • Computer console for easy access of the patient’s information such as radiographic images.

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Most equipment must be positioned to bespoke for optimal flow work of the entire surgical team. The operative table is located in the center of the operating room and is able to verify the radiographic images during surgery by enabling radiolucent transmission. The operative table should be tailored to the convenience of the surgeon by allowing sufficient bending and up-­and-­down motion. Then, the patient’s vital sign monitor and anesthesia machines are placed on the surgeon’s left side. The endoscopic cart is positioned at the foot end alongside an irrigation fluid stand and laser machine. The laser machine should be located on the head or leg of the patient according to the surgical posture and can be connected to the endoscope by sterile manner to be used during surgery. An important point is that the left and right sides change according to the patient’s disease lesion, mainly by reversing the direction of the patient’s head and legs. Most machines and physicians don’t change their initial positions.

4 Summary In summary, as shown in this chapter, the operating room layout and positioning with appropriate equipment settings will be required for efficient endoscopic procedure, which will result in satisfactory surgical results for patients.

References 1. Kim DH, Choi G, Lee S-H, Fessler RG. Endoscopic spine surgery. 2nd ed. New York: Thieme; 2018. 2. Kim J-S, Lee JH, Ahn Y.  Endoscopic procedures on the spine. New York: Springer; 2013.

Instruments for Transforaminal Endoscopy and Its Handling Shin-Jae Kim

1 Introduction Currently, many techniques of spine surgeries involve minimally invasive spine (MIS) procedures. Endoscope is a new MIS device replacing the conventional microscope system. The concept of MIS procedure includes preserving normal tissue and minimizing the length of the incision, which lead to rapid recovery of the patient. Although there are many kinds of endoscopic system, uniportal transforaminal endoscopy is a very unique system as an aspect of MIS approach [1, 2]. Unlike other endoscopic methods which usually involve the posterior spine structure and destruct the normal bone structures such as lamina and facet joints, TELD approaches through normal anatomical corridor that we call “Kambin triangle” [3] and preserves the posterior spine structure. By preserving the normal structures of the spine, it is of great significance in that it minimizes the effect on degeneration of the spine and prevents the progression of iatrogenic instability. Numerous TELD system devices are on the market. Although there are differences in the devices of each company, the basic configuration is as follows in common [4] (Fig. 1).

Fig. 1  An endoscopic system is composed of an imaging system (endoscope, endoscopic camera, monitor) and a light transmitting system (light source, light cable, endoscope)

S.-J. Kim (*) Department of Neurosurgery, Chungdam Wooridul Spine Hospital, Seoul, Republic of Korea e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 S.-H. Lee et al. (eds.), Transforaminal Endoscopy for Lumbar Spine, https://doi.org/10.1007/978-981-19-8971-1_4

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S.-J. Kim

28

2 Endoscopic Visualization

4 Working Cannula

Endoscopic visualization system shows the endoscopic surgical field on the screen through the endoscopic camera. It is composed of an imaging system (endoscope, endoscopic camera, monitor) and a light transmitting system (light source, light cable, endoscope). After inserting the endoscope to the target, LED light that is generated from the light projector is input through a flexible fiber glass light cable into an endoscope. Video images taken from the endoscopic camera are reversely output through the endoscope to the monitor.

A cannula is inserted along the dilator. If the sharp end of the cannula enters the cranial direction, injury to the exiting root may occur [5]. Therefore, rotating the cannula and placing the sharp end on the caudal part is very important. Rotate the cannula clockwise on the right side of the patient and counterclockwise on the left side. “Rotate-to retract technique” is useful for decreasing the injury of the exiting root during TELD in cases of foraminal disc herniation. The minimum skin incision required to insert a working cannula is about 8 mm (Fig. 3).

3 Dilator After the guide needle and wire are inserted to the target under C-arm guide, a dilator is used to make the tunnel through the muscles. Sequential type of dilator (1 mm, 2 mm, 4 mm, 5 mm diameter) has a benefit of reducing the muscle pain during the procedure. One-step dilator has a benefit of saving the procedure time (Fig. 2).

Fig. 3  Various types of working cannula. Sharp end has a benefit of root retraction

Fig. 2  One-step dilator and sequential type of dilator (1 mm, 2 mm, 4 mm, 5 mm diameter). (Permitted by Dirk Goethel 2020)

Instruments for Transforaminal Endoscopy and Its Handling

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5 Endoscopes

6 Fluid

The basic structure of endoscopes is given in Fig. 4. The outer diameter (OD) for TELD endoscope is about 6 to 7 mm. The working channel diameter (WChD) is about 3 to 5 mm. The irrigation channel diameter (IC) is almost 1.5 mm. The optical angle (OA) is about 15 to 30 degrees. The working channel length (WL) is 170 to 210 mm. The total length (TL) is about 250 to 290  mm. Depending on the size of the working channel diameter and optical angle, there are many kinds of different endoscopes. Surgeons choose the appropriate type of endoscopes according to the location and type of disc herniation, index level, and anatomical feature of the patient (Fig. 4).

Continuous fluid circulation is important for securing a space for the endoscope. Cold saline irrigation helps the coagulation. By reducing intraoperative bleeding, a clear surgical field vision is ensured. Continuous antibiotic mixed irrigation also decreases the infection rate compared to open microscopic surgery. The pressure of the fluid causes neural compression, and symptoms such as headache, nausea, vomiting, and dizziness may occur. Control of fluid pressure might be important. The recommended pressure during TELD is 20–40 mmHg at 100% flow rate.

7 Reamer/Drill WChD IC

WL IC

OD

OA

TL

Fig. 4  Basic structure of endoscope. WChD working channel diameter, IC irrigation channel diameter, OD outer diameter, WD working channel length, OA optical angle, TL total length

In case of high-grade migrated disc or axillary location disc, superior articular process and cranial part of the lower pedicle might interfere with the approach or limit the movement of the endoscope. A reamer and drill can be used for widening and securing the working space. A reamer can be used prior to the insertion of the cannula. As soon as the reamer meets a bone, clockwise rotation is applied to drill the bone. The serrated tip of the reamer should not cross the medial line of the superior articular process to avoid nerve damage. The surgeon should pay attention to the neurologic change of the patient. The drilling device can be inserted through the working cannula. The drill uses a diamond bur with a diameter of 3.0 mm or 3.5 mm, which is capable of delicate work. Also, because drilling is performed while looking directly at the endoscope, the possibility of damaging the nerve structure is relatively less than that of a reamer. Several papers have demonstrated the efficacy of the two devices [6] (Fig. 5).

S.-J. Kim

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Fig. 5  Reamer and drill expand the working space of TELD. (Permitted by Dirk Goethel 2020) Fig. 6 Radiofrequency device performs the role of soft tissue ablation and coagulation. (Permitted by Dirk Goethel 2020)

8 Radiofrequency Device

9 Laser

An radiofrequency device performs the role of soft tissue ablation and coagulation. It is useful for clearing the operation field. It is safer than laser to remove the annulus and PLL adjacent to the traversing root. Radiofrequency systems in the bipolar application form are generally linked to actively articulatable electrodes for this purpose in order to achieve the full field of view generated by the 25° articulated telescope subject to the straight working channel of the endoscope (Fig. 6).

During TELD, a laser device can decompress the annulus tissue and reduce the procedure time efficiently. Holmium:yttrium-aluminum-garnet (Ho:YAG) laser is the most frequently used laser that is combined with TELD endoscope [7]. It is a side-firing laser that is used in a pulsed mode. The Ho:YAG laser has the benefit of less thermal conduction to the surrounding tissues and for this reason is called a cold laser. This is the most frequently used laser in endoscopic procedures. The side-firing laser beam can treat any remote or

Instruments for Transforaminal Endoscopy and Its Handling

corner site, which can be difficult to approach, and can ablate or coagulate a specific lesion while protecting normal tissues. The Ho:Yag laser can directly remove any offending ligamentum flavum, can safely dissect fibrotic scar tissue, and can evaporate shoulder osteophytes. The power setting of the laser is usually 40 to 60 W for soft tissue ablation and can be increased to 80 watts for bone ablation. In order to prevent nerve damage, the laser should be used only within the area where the field of view of the endoscope is secured. Direct laser to the endplate should be avoided to avoid thermal necrosis. In order to prevent damage to the endoscope lens, the endoscope lens and the

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laser tip must be kept at an appropriate distance (Fig. 7).

10 Hand Instruments Various kinds of hand instruments can be used during an endoscope procedure. The features of devices are similar to microscopic instruments but much small that they should go through the working cannula. Special hand instruments are necessary in order to be able to carry out all necessary functions full-endoscopically for tissue preparation such as dissection, grasping, cutting, and punching (Fig. 8a–d).

Fig. 7  Holmium:yttrium-aluminum-garnet (Ho:YAG) laser is the most frequently used laser that is combined with TELD endoscope (side-firing laser tip)

S.-J. Kim

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a

b

d c

Fig. 8 (a) Straight and articulatable dissectors for palpation, dissection, and mobilization. (b) Straight and articulated punches for resection of ligament structures. (c)

11 Summary Even though there are many types of endoscopes to treat disc disease, TELD is a more minimally invasive spine technique that preserves the posterior spinal structure. Although various products have been released, the basic principle and configuration of the device are similar. It is composed of an imaging system (endoscope, endoscopic camera, monitor) and a light transmitting system (light source, light cable, endoscope). Depending on the location and type of the disc, new devices and various technical skills are still being developed, and the indications for TELD are gradually expanding.

References 1. Butler AJ, Alam M, Wiley K, Ghasem A, Rush AJ III, Wang JC. Endoscopic lumbar surgery: the state of the art in 2019. Neurospine. 2019;16(1):15. 2. Khandge AV, Sharma SB, Kim J-S.  The evolution of transforaminal endoscopic spine surgery. World Neurosurg. 2021;145:643–56.

Punches for resection of bones and ligaments. (d) Rongeurs and grasping forceps for gripping and removing tissue. (Permitted by Dirk Goethel 2020) 3. Fanous AA, Tumialán LM, Wang MY. Kambin’s triangle: definition and new classification schema. J Neurosurg Spine. 2019;32(3):390–8. 4. Kim J-S, Lee JH, Ahn Y.  Endoscopic procedures on the spine. New York: Springer; 2019. 5. Gu S, Hou K, Jian W, Du J, Xiao S, Zhang X. Working cannula-based endoscopic foraminoplasty: a technical note. Biomed Res Int. 2018;2018:4749560. 6. Wu B, Xiong C, Huang B, Zhao D, Yao Z, Yao Y, et al. Clinical outcomes of transforaminal endoscopic lateral recess decompression by using the visualized drilled foraminoplasty and visualized reamed foraminoplasty: a comparison study. BMC Musculoskelet Disord. 2020;21(1):1–11. 7. Kim S-J, Bae J. Physics and general principle of spinal laser. In: Laser spine surgery. New York: Springer; 2021. p. 9–15.

Historical Review and Pros and Cons of Different Surgical Approaches: Outside-In Vs. Inside-Out Ki-Hyoung Moon

1 Introduction In the 1970s, Kambin [1] and Hijikata [2] reported the first intradiscal debulking procedure through percutaneous posterolateral lumbar approach to treat degenerative lumbar disc disease. Ever since, endoscopic spine surgery has been evolved. The improvement of spinal endoscopes and endoscopic instruments has contributed to the development of full endoscopic discectomy techniques. Initially, transforaminal endoscopic spine surgery was known as an intradiscal procedure

achieved by indirect decompression, used to treat contained disc herniation. Since then, the working space of transforaminal endoscopic spine surgery limited to intradiscal space switched to the epidural space, allowing treatment of various types of extruded disc herniations. At the same time, endoscopic foraminal decompression techniques to treat lumbar foraminal stenosis were also developed, expanding the clinical indications of transforaminal endoscopic spine surgery. The inside-out and outside-in techniques are known as the two main categories of transforaminal approaches to treat degenerative lumbar disc disease (Fig. 1).

K.-H. Moon (*) Department of Neurosurgery, Seoul Gimpo Airport Wooridul Spine Hospital, Seoul, Republic of Korea

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 S.-H. Lee et al. (eds.), Transforaminal Endoscopy for Lumbar Spine, https://doi.org/10.1007/978-981-19-8971-1_5

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K.-H. Moon

34 Pre-endoscope

By endoscope 1990

2005

Report on Kambin’s Triangle

1973 Posterolateval decompression By Craig cannula, Kambin

Extreme lateral approach Ruetten

Percutaneous nucleotomy, Hijikata

2007

1999

1991

1975

1970

inside-out technique

Posterolateral decompression By Craig cannula, Kambin

Half & Half technique, Lee

YESS system, Yeung

1990

2000

1996 Foraminal fiberoptic endoscope, Mathews

2001

2018

Laser-assisted Foraminoplasty knight

Introduction of PELD term, Mayer & Brock

THESSYS, Hoogland

Ventral facectectomy, Sairyo

2008

Foraminoplasty By endoscopic burr, Choi

2000 1992

2020

2010

2005 Outside-in technique, Hoogland

2014

Mobile outside-in technique, Kim

Foraminotamy By endoscopic burr, Ahn

Outside-in technique

Fig. 1  The evolution and inventors of percutaneous endoscopic transforaminal approach from 1970 to 2020. PELD, percutaneous endoscopic lumbar discectomy.

YESS Yeung Endoscopic Spine System, THESSYS Thomas Hoogland Endoscopic Spine System

2 Inside-Out Technique

original “inside-out technique” in 1999. After placing the cannula in the intradiscal space through Kambin’s triangle, the intradiscal pain generator was removed. This technique was primarily applied to treat contained disc herniations. However, it was not advanced enough to treat sequestrated disc herniation or foraminal stenosis [3, 7]. The ­technique was based on the principle of identification of in  vivo visualization of pain generators in the foramen and replaced previous indirect percutaneous discectomy technique. In 2002, Yeung and Tsou published the results of 307 patients treated with the inside-out technique. Central or paramedian disc herniation as well as foraminal or extraforaminal disc herniation was included and had a follow-up period of 19 months. Satisfactory results were obtained in 89.3% and reoperation was performed in 4.2%. Remarkably, low incidence of dysesthesia was noted with 1.9% (6/307) [8]. If necessary, foraminal decompression was performed using holmium yttrium-aluminum-garnet laser. Tzaan also treated 134 patients with contained disc or non-contained disc with contiguous disc

In the mid-1980s, Kambien et al. reported a percutaneous disc decompression by nucleotomy using Craig Cannula through the posterolateral approach. They reported an 88% of success rate in a study of 50 patients [1]. Hijukata et al. also reported a 72% of success rate treating 136 patients by percutaneous posterolateral approach [2]. The concept of nonvisualized percutaneous transforaminal disc decompression was introduced. The transforaminal approach began to make great strides in 1990 when Kambin announced the Kambin triangle, a safe working zone that allows access to disc space through the foramen [3]. In addition, the optics of spinal endoscopes began to be developed. In 1991, Lue devised a foraminoscope to treat foraminal and extraforaminal disc herniation and [4] Mathews also reported foraminal epidural endoscopic surgery using a fiber-optic endoscope for the first time [5]. In 1997, Yeung designed the Yeung Endoscopic Spine System (YESS, continuous saline irrigation, multichannel, angled endoscope) [6] by applying joint arthroscopy and published the

Historical Review and Pros and Cons of Different Surgical Approaches: Outside-In Vs. Inside-Out

herniation using the inside-out technique and obtained satisfactory results in 89% during the 8 months follow-up period. Reoperation was performed in 4.5% (6/134) and the incidence of dysesthesia was 6% (8/134) [9]. A lot of experience was accumulated through these two endoscopic techniques in the 2000s. An inside-out modified technique called “the half-­ and-­half technique” was published by Lee et al. [10] using the YESS system. The window of the beveled working sheath is approached across the disc space so that the epidural space and the annulus and PLL are visible together in the endoscopic view. In the mid-2000s, Ruetten et  al. published another inside-out technique, “the extreme lateral access technique.” This technique reaches at an angle of 10° with the cannula landing on the dorsal annulus and the posterior longitudinal ligament then performed intradiscal and extradiscal decompression. However, this technique has difficulty accessing L5-S1 or the upper lumbar spine. When removing a contained central disc herniation, another inside-out technique, “the intraannular approach,” may be used to preserve the intact disc as much as possible and to remove only the herniated disc [11]. This method reported by Shin is an application of the approach used in percutaneous endoscopic annuloplasty [12]. It is important to place the working channel directly on the annular defect site, and then perform a herniotomy removing the herniated disc preserving the posterior longitudinal ligament (PLL). The approach angle is lower than the conventional transforaminal approach (intraannular subligamentous herniotomy). This approach is not recommended in case that extruded disc penetrated the PLL highly migrated from the disc space, and if the foraminal or disc space narrowing is severe. The inside-out technique is performed on the ipsilateral side of disc herniation. However, If the cannula is positioned further to the opposite side, it is possible to access the contralateral side including lateral recess, allowing the removal of the contralateral disc herniation. In other words, both sides of the poster annulus can be checked. In the early 2000s, Yeom

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and Kim et al. treated highly migrated herniated disc using a contralateral approach [13, 14]. When treating huge central disc herniation or highly migrated disc, the conventional inside-out technique may be associated with a high failure rate of 4.3 to 10% if foraminoplasty is not performed [15, 16]. Therefore, when implementing the insideout technique, foraminoplasty may be performed after intradiscal work or levering the cannula against the ventral facet to direct the cannula trajectory to the dorsal or ventral disc cavity [17].

3 Outside-In Technique In 1996, Mathews reported on the treatment of patients with paramedian or foraminal, or extraforaminal HNP that contained disc herniation using a foraminal epidural endoscope that he developed in the early 1990s [5]. However, Hoogland experienced the limitations of treating diseases such as sequestrated disc herniation and foraminal disc herniation with the foraminal epidural endoscope made by Mathews. So, he had thought that foraminoplasty was necessary to treat various types of herniated disc and developed the “Tom-Shidi reamer system” for foraminoplasty in 1994. He built the Thomas Hoogland Endoscopic Spine System (THESSYS) with Joimax, introducing the “outside-in technique” using THESSYS. It is a technique based on serial dilation of the intervertebral foramen with dilators, cannulated reamers or trephines, etc. Unlike the inside-out technique developed by Yeung, the procedure begun from the foraminal epidural space. Laser is not only used to realize annulotomy in the disc herniation, but also to perform foraminoplasty. In 2001, Knight reported 716 cases of patients with back pain and sciatica treated with endoscopic foraminoplasty using laser, a technique published back in 1991. He reported that the complications were much lower (1.6%) than those presented during open surgery [18]. However, it has been reported that postoperative transient dysesthesia increases by up to 19% when excessive side-firing lasers are used during foraminoplasty [19].

K.-H. Moon

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With the evolution of endoscopic drills in the mid-2000s, Choi [20] et al. announced a foraminoplastic technique including partial pediculectomy using endoscopic drill in 2008. This technique allowed safer removal of highly migrated discs without transient dysesthesia. Since then, the use of endoscopic drill in foraminoplasty became increasingly popular [21]. With the evolution of foraminoplasty technique in the 2010s, it allowed the treatment of foraminal stenosis caused by severe bony stenosis. Ahn et al. reported the results of 33 patients with foraminal stenosis who underwent foraminotomy using an endoscopic drill in 2014. Based on the modified MacNab criteria, excellent or good results were obtained in 81.8% of the patients, and dysesthesia was observed in 2 patients and 1 patient required fusion surgery due to incomplete decompression with 2 years follow-up. The difference in incidence rate of transient dysesthesia caused by exiting nerve root irritation depending on whether the SAP tip is removed or the base of the SAP is removed during foraminoplasty was also reported [22]. Yang et al. reported transient dysesthesia in 6.4% (5/78) of patients with disc herniation accompanying lateral recess stenosis after foraminoplasty with removing tip of the SAP. However, there was no dysesthesia when the base of the SAP was removed. Other researchers also reported that the incidence rate of dysesthesia was as low as 3.5% (3/85) ~ 3.7% (5/134) when performing foraminoplasty with removing the base of the SAP instead of ­removing the tip of the SAP [23, 24]. This is much lower than the incidence of dysesthesia (10.5%) reported by Yeung using the inside-out technique. At the end of 2010, Sairyo et al. further developed endoscopic foraminotomy and performed ventral facetectomy through a transforaminal approach. In order to more extensively remove the lateral recess stenosis as well as the foraminal stenosis, the tip of SAP, a portion of the inferior articular process (IAP), and part of the pedicle were removed. This technique was named “percutaneous endoscopic ventral facetectomy” [25]. However, it has been reported that the case of patients with foraminal stenosis accompanying

lateral recess stenosis (entry zone foraminal stenosis) has poorer outcomes compared to patients with extraforaminal or midforaminal stenosis [26]. As the foraminoplasty technique became common, Madhavan et al. performed endoscopic foraminotomy for patients with foraminal stenosis and disc herniation (16 patients, coronal deformity 10–41 degree) accompanying scoliosis and reported good short-term results [27]. Recently, Kim et al. [28] presented “a mobile outside-in technique.” Is a modified technique that takes advantages of both inside-out and outside-­ in techniques? Intradiscal pathology removal and free movement of cannula in the epidural space are the main advantages of this technique. The working cannula is landed on Kambin’s triangle like the outside-in technique and intradiscal decompression is sufficiently performed under half-and-half view. Working channel levered downwards to achieve a “halfand-half” view in which the dorsal half shows PLL, epidural space, dura, and traversing nerve root while the ventral half shows annulus and disc fragment ventral to the PLL. And then targeted fragmentectomy is performed. A total of 184 patients with up-migration or down-migration disc herniation were treated. The results showed satisfactory results according to the MacNab criteria in 97.3% (179/184) of the patients. Recurrence was seen in 15 patients (7.89%), and all of them underwent repeated PELD or open discectomy.

4 Results 4.1 Disc Herniation Treatment by Inside-Out Technique 4.1.1 Evidence Level 2 Data Ruetten et al. treated 463 patients with disc herniation using the inside-out technique with extreme lateral access. Satisfactory results were obtained in 95% and the recurrence rate was 6.9% (32/463), of which 90% (29/32) had recurrence within 5  months after surgery in 1-year follow-­up [29].

Historical Review and Pros and Cons of Different Surgical Approaches: Outside-In Vs. Inside-Out

4.1.2 Evidence Level 3 Data As previously mentioned, Yeung and Tsou reported in 2002 the treatment of disc herniation using the inside-out technique in 307 patients. The subjects were patients with central or foraminal or extraforaminal HNP, and foraminal decompression using laser was also implemented. Mean follow-up was 19 months; 89.3% of the patients showed excellent or good outcome and 4.2% (13/307) underwent surgery. Transient dysesthesia was rare, reported at 1.9% (6/307) [8]. Tzaan reported on the treatment of patients using the inside-out technique, in which excellent or good outcome was achieved in 89% in the 8-month follow-up; 4% (6/134) received an additional surgery and 6% (8/134) developed dysesthesia [9]. In the 2014 review article of the inside-out technique on HNP by Yeung and Gore, postoperative dysesthesia was reported as high as 14.6% (20/137).

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4.2.2 Evidence Level 3 Data Krzok et al. reported a 1-year follow-up of 137 lumbar disc herniation patients after outside-in technique (transforaminal approach for 124 and transpedicular approach for 13), and 92% of the patients displayed good or excellent outcome and 5.12% reported overall disc recurrence [31]. Choi et  al. treated 59 patients with highly migrated disc herniation using partial pediculectomy or half-and-half technique. In the 25.4-month follow-­ up, 91.4% displayed satisfactory outcome and 10% (6/59) received reoperation [20].

4.3 Foraminal Stenosis Treatment by Inside-Out Technique

4.3.1 Evidence Level 3 Data The meta-analysis of studies implementing endoscopic transforaminal foraminotomy on foraminal stenosis (14 total studies; 600 total patients) shows excellent or good postoperative outcome 4.2 Disc Herniation Treatment by in 85% (78–90%); same level recurrent foraminal Outside-In Technique stenosis rate and revision surgery rate were low at 1.4% (0–4.3%) and 1.2% (0–3.7%), respectively 4.2.1 Evidence Level 2 Data [32]. However, the authors conducted an analysis Lee treated 116 patients with migrated disc her- without differentiating inside-out and outside-in niation using foraminoplasty. From the 14.5-­ techniques in the included studies. month follow-up, 91.3% (106/116) displayed In 2019, Yeung et  al. [33] reported a 5-year good or excellent outcome, and no recurrence or follow-up study of foraminal stenosis with disc complication was reported [10]. herniation after inside-out technique in 86 Hoogland reported on the treatment of post- patients. After the operation, 83% of the patients operative recurrent disc herniation using the displayed good or excellent outcome and nine outside-­ ­ in technique in 262 patients. In the patients (10.5%) had disc recurrence. Among 2-year follow-up, 85.7% showed good or excel- them, six patients (6.9%) received additional lent outcome and 7.1% underwent reoperation surgery. Dysesthesia was reported in nine [30]. Li et al. reported treatment of uncontained patients (10.5%). disc herniation in 148 patients with 92% (124/134) having excellent or good outcome and 3.7% (5/134) with dysesthesia and recurrence, 4.4 Foraminal Stenosis Treatment individually [23]. The authors removed the base by Outside-In Technique of SAP when performing foraminoplasty. Kim et al. treated 184 patients using mobile outside- 4.4.1 Evidence Level 2 Data in technique and reported successful outcome in Ahn et  al. reported a 2-year follow-up of 33 97.3% (179/184) from the 19 months follow-up. patients with foraminal stenosis after treatment, Recurrence was found in 7.9% of the patients and 81.1% showed excellent or good outcome. (15/190) and they received repeated PELD or Foraminotomy was performed by removing the open discectomy. base of SAP. Dysesthesia was found in 6% (2/33)

K.-H. Moon

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and fusion was performed in one patient (3%) due to incomplete decompression. No other complications were reported [34]. Knight et al. reported a 34-month follow-up of 24 patients with isthmic spondylolisthesis after performing foraminal decompression using laser; 79% (19/24) displayed excellent or good outcome, and two patients (8.3%) later received fusion after their symptoms worsened. No dysesthesia was reported [35].

4.4.2 Evidence Level 3 Data Lewandrowski reported that patients with foraminal stenosis accompanying lateral recess stenosis (entry zone foraminal stenosis) did not have as good outcomes as patients with extraforaminal or midforaminal stenosis [26]. However, Li reported good outcomes using the outside-in technique even in lateral recess stenosis [24]. The 2-year follow-up of 96 patients showed 90.5% excellent or good outcome (dysesthesia 3.5% [3/85], recurrence 2.3% [2/85]). In 2020, Lewandrowski [36] reported a 5-year follow-up of 90 patients with foraminal stenosis after treatment using the outside-in technique. After surgery, 93% of the patients displayed good or excellent outcome, but 17 patients (18.8%) had disc recurrence and received additional surgery (the recurrence occurred in the ipsilateral side in nine patients and on the opposite side of the same level in eight patients). Dysesthesia was found in eight patients (8.9%). Compared to Yeung’s study using the inside-out technique (dysesthesia 10.5%, recurrence 10.5%), [33] there was no significant difference in dysesthesia and the recurrence rate was higher when the outside-­in technique was used. In 2020, Yeung and Lewandrowski reported a 5-year follow-up of patients with back pain and radiating pain caused by foraminal stenosis after treatment using inside-out and outside-in techniques, [37] comparing data from two studies [33, 36]. The reoperation rate was significantly higher in the outside-in group (35.6%) than the insideout group (8.1%) when the surgery of the adjacent level was also included. The secondary fusion rate was also higher in the outside-in group (8.9%) than in the inside-out group (2.3%). The authors speculated that the inside-out technique has a low

reoperation rate in long-term follow-up because it allows direct visualization of the patho-anatomy by placing a working cannula inside the intervertebral disc and sufficiently removing the source of pain, compared to the outside-in technique which does not employ intradiscal visualization.

5 Summary Inside-out and outside-in technique. Which technique is superior? Pathologies in the posterior annulus at the ventral side of the dura can be examined using the inside-out technique. Although the surgery begins from the inside of the disc, epidural space can be visualized via discectomy at the area of the annular tear [33]. Also, contralateral lateral recess can be approached by further insertion of the cannula [13, 14]. Therefore, it has the advantage that allows examination of both sides of the posterior annulus and ventral dura. In case of foraminal narrowing or highly migrated or severe central herniation, foraminal widening using outside-­in technique is required. Outside-in technique will be useful in painful conditions associated with the foramen caused by inflamed disc, inflamed nerve, hypertrophied superior articular process, and superior foraminal facet osteophyte [18]. Furthermore, if annular pathology accompanying disc herniation needs to be examined, additional inside-out technique might be necessary. Rather than determining which method is superior, a proper identification of pain generator in symptomatic motion segment of the patient will be more important to determine the adequate technique.

References 1. Kambin P, Sampson S.  Posterolateral percutaneous suction-excision of herniated lumbar intervertebral discs. Report of interim results. Clin Orthop Relat Res. 1986;207:37–43. 2. Hijikata S. Percutaneous nucleotomy. A new concept technique and 12 years’ experience. Clin Orthop Relat Res. 1989;238:9–23. 3. Kambin P. Arthroscopic microdiskectomy. Mt Sinai J Med. 1991;58(2):159–64.

Historical Review and Pros and Cons of Different Surgical Approaches: Outside-In Vs. Inside-Out 4. Tieber F, Lewandrowski K-U.  Technology advancements in spinal endoscopy for staged management of painful spine conditions. J Spine Surg. 2020;6(Suppl 1):S19–28. 5. Mathews HH.  Transforaminal endoscopic microdiscectomy. Neurosurg Clin N Am. 1996;7(1):59–63. 6. Yeung AT.  Minimally Invasive Disc Surgery with the Yeung Endoscopic Spine System (YESS). Surg Technol Int. 1999;8:267–77. 7. Kambin P.  Arthroscopic microdiscectomy. Spine J. 2003;3(3 Suppl):60S–4S. 8. Yeung AT, Tsou PM. Posterolateral endoscopic excision for lumbar disc herniation: surgical technique, outcome, and complications in 307 consecutive cases. Spine (Phila Pa 1976). 2002;27(7):722–31. 9. Tzaan W-C.  Transforaminal percutaneous endoscopic lumbar discectomy. Chang Gung Med J. 2007;30(3):226–34. 10. Lee S, Kim S-K, Lee S-H, Kim WJ, Choi W-C, Choi G, Shin S-W.  Percutaneous endoscopic lumbar discectomy for migrated disc herniation: classification of disc migration and surgical approaches. Eur Spine J. 2007;16(3):431–7. 11. Sang-Ha Shin, Sang-Ho Lee Minimally invasive spinal surgery 2018, Kai-Uwe Lewandrowski, Michael D Schubert, Jorge F Ramirez Leon, Richard G Fessler. Percutaneous endoscopic intra-annular subligamentous herniotomy, p 123–129 JP Medical Ltd London. 12. Choi K-C, Kim J-S, Kang B-U, Lee CD, Lee S-H. Changes in back pain after percutaneous endoscopic lumbar discectomy and annuloplasty for lumbar disc herniation: a prospective study. Pain Med. 2011;12(11):1615–21. 13. Yeom K-S, Choi Y-S.  Full Endoscopic contralateral transforaminal discectomy for distally migrated lumbar disc herniation. J Orthop Sci. 2011;16(3):263–9. 14. Kim J-S, Choi G, Lee S-H.  Percutaneous endoscopic lumbar discectomy via contralateral approach: a technical case report. Spine (Phila Pa 1976). 2011;36(17):E1173–8. 15. Choi K-C, Lee J-H, Kim J-S, Sabal LA, Lee S, Kim H, Lee S-H.  Unsuccessful percutaneous endoscopic lumbar discectomy: a single-center experience of 10,228 cases. Neurosurgery. 2015;76(4):372–80; discussion 380–1; quiz 381. 16. Zhou Y, Li C, Liu J, Xiang L.  Risk factors for failure of single-level percutaneous endoscopic lumbar discectomy Hongwei Wang. J Neurosurg Spine. 2015;23(3):320–5. 17. Gore S, Yeung A.  The “inside out” transforaminal technique to treat lumbar spinal pain in an awake and aware patient under local anesthesia: results and a review of the literature. Int J Spine Surg. 2014;8:28. 18. Knight MT, Ellison DR, Goswami A, Hillier VF.  Review of safety in endoscopic laser foraminoplasty for the management of back pain. J Clin Laser Med Surg. 2001;19(3):147–57. 19. Knight MTN, Jago I, Norris C, Midwinter L, Boynes C. Transforaminal endoscopic lumbar decompression & foraminoplasty: a 10 year prospective survivability

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outcome study of the treatment of foraminal stenosis and failed back surgery. Int J Spine Surg. 2014;8:21. 20. Choi G, Lee S-H, Lokhande P, Kong BJ, Shim CS, Jung B, Kim J-S.  Percutaneous endoscopic approach for highly migrated intracanal disc herniations by foraminoplastic technique using rigid working channel endoscope. Spine (Phila Pa 1976). 2008;33(15):E508–15. 21. Ahn Y, Oh H-K, Kim H, Lee S-H, Lee H-N.  Percutaneous endoscopic lumbar foraminotomy: an advanced surgical technique and clinical outcomes. Neurosurgery. 2014;75(2):124–33; discussion 132–3. 22. Yang J-S, Chu L, Chen C-M, Wang X-F, Xie P-G, Deng R, Yu K-X, Shi L, Zhang Z-X, Rong L-M, Hao D-J, Deng Z-L.  Foraminoplasty at the Tip or base of the superior articular process for lateral recess stenosis in percutaneous endoscopic lumbar discectomy: a multicenter, retrospective, controlled study with 2-year follow-up. Biomed Res Int. 2018;2018:7692794. 23. Li Z-Z, Hou S-X, Shang W-L, Song K-R, Zhao H-L.  Modified percutaneous lumbar Foraminoplasty and percutaneous endoscopic lumbar discectomy: instrument design, technique notes, and 5 years follow-­up. Pain Physician. 2017;20(1):E85–98. 24. Li Z-Z, Hou S-X, Shang W-L, Cao Z, Zhao H-L.  Percutaneous lumbar foraminoplasty and percutaneous endoscopic lumbar decompression for lateral recess stenosis through transforaminal approach: Technique notes and 2 years follow-up. Clin Neurol Neurosurg. 2016;143:90–4. 25. Sairyo K, Chikawa T, Nagamachi A.  State-of-the-­ art transforaminal percutaneous endoscopic lumbar surgery under local anesthesia: discectomy, foraminoplasty, and ventral facetectomy. J Orthop Sci. 2018;23(2):229–36. 26. Lewandrowski K-U. “Outside-in” technique, clinical results, and indications with transforaminal lumbar endoscopic surgery: a retrospective study on 220 patients on applied radiographic classification of foraminal spinal stenosis. Int J Spine Surg. 2014;8:26. 27. Madhavan K, Chieng LO, McGrath L, Hofstetter CP, Wang MY. Early experience with endoscopic foraminotomy in patients with moderate degenerative deformity. Neurosurg Focus. 2016;40(2):E6. 28. Kim HS, Raorane HD, Wu PH, Yi YJ, Jang IT.  Evolution of endoscopic transforaminal lumbar approach for degenerative lumbar disease. J Spine Surg. 2020;6(2):424–37. 29. Komp M, Godolias G. An extreme lateral access for the surgery of lumbar disc herniations inside the spinal canal using the full-endoscopic uniportal transforaminal approach-technique and prospective results of 463 patients Sebastian Ruetten. Spine (Phila Pa 1976). 2005;30(22):2570–8. 30. Hoogland T, van den Brekel-Dijkstra K, Schubert M, Miklitz B. Endoscopic transforaminal discectomy for recurrent lumbar disc herniation: a prospective, cohort evaluation of 262 consecutive cases. Spine (Phila Pa 1976). 2008;33(9):973–8.

40 31. Krzok G. Transforaminal endoscopic surgery: outside­in technique. Neurospine. 2020;17(Suppl 1):S44–57. 32. Giordan E, Billeci D, Del Verme J, Varrassi G, Coluzzi F. Endoscopic transforaminal lumbar foraminotomy: a systematic review and meta-analysis. Pain Ther. 2021;10(2):1481–95. 33. Yeung A, Roberts A, Zhu L, Qi L, Zhang J, Lewandrowski K-U. Treatment of soft tissue and bony spinal stenosis by a visualized endoscopic transforaminal technique under local anesthesia. Neurospine. 2019;16(1):52–62. 34. Goswami A.  Management of isthmic spondylolisthesis with posterolateral endoscopic foraminal decompression Martin knight. Spine (Phila Pa 1976). 2003;28(6):573–81.

K.-H. Moon 35. Lewandrowski K-U, Ransom NA.  Five-year clinical outcomes with endoscopic transforaminal outside-in foraminoplasty techniques for symptomatic degenerative conditions of the lumbar spine. J Spine Surg. 2020;6(Suppl 1):S54–65. 36. Yeung A, Lewandrowski K-U.  Five-year clinical outcomes with endoscopic transforaminal foraminoplasty for symptomatic degenerative conditions of the lumbar spine: a comparative study of inside-out versus outside-in techniques. J Spine Surg. 2020;6(Suppl 1):S66–83. 37. Lewandrowski K-U.  The strategies behind “inside-­ out” and “outside-in” endoscopy of the lumbar spine: treating the pain generator. J Spine Surg. 2020;6(Suppl 1):S35–9.

Principles of Transforaminal Endoscopic Approach Technique Sang-Joon Park

1 Introduction There are many treatment options for degenerative lumbar disc disease, such as medication, physical therapy, epidural injection, percutaneous or endoscopic procedures under local anesthesia, minimally open microscopic surgery under general anesthesia, dynamic stabilization surgery, and instrumented fusion surgery. Various treatment methods for degenerative spine disease could be selected in a stepwise manner (Fig. 1). Among the Fig. 1  Modern concept of treatment for degenerative disc disease. The modern concept of minimally invasive treatment is considered to apply the lowest level of treatment methods that can ensure successful results

treatment methods that can ensure successful results, applying the treatment corresponding to lowest step of the stairs is considered a modern concept of minimally invasive treatment. Lumbar microdiscectomy is still at the forefront of minimally invasive spine surgery (MISS) in the sense that it has the advantages of both minimal invasiveness and a wide range of indications [1, 2]. However, open microdiscectomy usually requires general anesthesia and removal of the posterior element of the spine, and can lead

Modern Concept of Treatment

Fusion Surgeries Dynamic Stabilization

Artifical Disc Replacement Open Minimal Surgeries Percutaneous or Endoscopic Treatments

Conservative Treatment

S.-J. Park (*) Department of Neurosurgery, Dongrea Wooridul Spine Hospital, Busan, Korea (Republic of) © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 S.-H. Lee et al. (eds.), Transforaminal Endoscopy for Lumbar Spine, https://doi.org/10.1007/978-981-19-8971-1_6

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S.-J. Park

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to several complications associated with open surgery [3–9]. As a result of efforts to avoid general anesthesia and develop more minimally invasive methods, transforaminal approaches of treatment had been introduced [10–17]. These treatments have been progressively evolved through anatomical studies and advances in equipment and access techniques [18–23]. Subsequently, transforaminal endoscopic lumbar discectomy (TELD) has gradually garnered many clinical reports of favorable outcomes [24–34]. The TELD is one of the most advanced minimally invasive spine surgeries. There are many advantages of TELD [3–5, 10, 21, 24, 25, 31, 33, 34, 47–52, 54]. In summary, TELD can solve only the problem (disc herniation) without any sacrifice (laminectomy, ligament and soft tissue injury, facetectomy, general anesthesia, indwelling catheters, postoperative pain, long duration of hospitalization, and other complications related open surgery) (Fig.  2). In addition to avoiding unnecessary sacrifice, one of the most important concepts and advantages of TELD is that it enables ventral decompression of nerves without retraction through a posterolateral approach. In the past, the TELD was regarded as minimally invasive but only useful procedures in highly selective cases. However, the evolution of

equipment and the development of surgical techniques have allowed the treatment area of TELD to be extended. The development of TELD has progressively advanced the treatment fields from contained disc herniation to uncontained disc herniation, and from indirect decompression to direct decompression with targeted fragmentectomy, from lateral zone disc herniation to the central zone of intracanal disc herniation, and from disc level to beyond the disc level [10–17, 21–28, 35–45]. Improved success rates in these areas have led to the expansion of indications of TELD. Although randomized control trials (RCTs) are lacking and most studies have not had high level of evidence, many studies including RCTs and meta-analyses have reported that TELD showed similar or more favorable clinical outcomes compared to open lumbar microdiscectomy [5, 24, 25, 31, 33, 46–54]. What is more, most of those studies have highlighted the ­advantages of TELD in terms of minimal invasiveness, which is an innate characteristic of TELD [5, 24, 25, 31, 33, 47–52, 54]. The rates of recurrence in the case of TELD were reported to be similar to those of open microdiscectomy in most comparative studies, and there was a meta-analysis that reported a lower rate in TELD [31, 46, 47, 50, 55]. However,

Advantages and Concept of TELD a

Fig. 2 The concept and advantages of TELD. Preoperative (a) and postoperative (b) MRI demonstrates that all spinal structures were normalized after TELD.  Postoperative MRI showed that there were no

b

unnecessary sacrifices other than removal of the herniated disc. It can be seen that the epidural fats were also well preserved

Principles of Transforaminal Endoscopic Approach Technique

although the statistical significance was not clear, there were quite a few articles that reported a higher reoperation rate than open lumbar microdiscectomy in patients who underwent TELD [33, 46, 49, 51, 55, 56]. The reason that the reoperation rate was higher for TELD than for open lumbar microdiscectomy was associated with insufficient decompression due to residual herniated discs or early recurrence [46, 56]. The failure rate and reoperation rate of TELD may be related to technical aspects, including surgeon’s proficiency [57–60]. On the other hand, it may be related to indications. There are probably very few spine surgeons who deny that lumbar microdiscectomy is still the gold standard of MISS.  The reason may be that lumbar microdiscectomy has a wide range of indications and provides the means for a consistent successful surgical resolution rather than its higher success rate. When it comes to treatment for soft disc herniation, it is expected that TELD will suffice to qualify for a forefront position in the field of MISS.  To achieve that, high-quality clinical studies to prove that TELD is a treatment based on evidence-based medicine, expansion and establishment of indications, and efforts to achieve a constant and high success rate are required. The establishment and expansion of indications is related to the identification of prognostic factors and technical capability. Practically, it would be closely related to the accessible range and limitations of the surgeon’s endoscopic forceps. The improvement and consistency of the success rate of TELD depends on the appropriate patient selection and the technical aspects to approach the target closely. In this chapter, the author describes indications and prognostic factors, methods to increase the accessible range of endoscopic forceps, appropriate utilization of equipment characteristics, and approach techniques to reach the target as closely as possible. For standardization of terms, this chapter mainly used the nomenclature and classification of lumbar disc pathology recommended by the North American Spine Society, American Society of Spine Radiology, and American Society of Neuroradiology [61, 62]. Endoscopic treatments for foraminal stenosis and

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foraminal disc herniation are partially transforaminal procedures. In this chapter, effective treatment methods of transforaminal endoscopic lumbar discectomy for intracanal lumbar disc herniations, which are the main areas of transforaminal endoscopic treatment, are described with an emphasis on approach techniques.

2 Indications Increasing the success rate of TELD requires knowledge of the indications as well as the implementation of advanced and skilled techniques. Briefly, all symptomatic soft disc herniations within the accessible range of the surgeon’s endoscopic forceps are indications of TELD. However, in order to increase patient satisfaction and success rate by selecting appropriate patients, it is necessary to know in detail the clinical, radiological, and technical aspects included in this indication. Knowledge of clinical and radiological factors related to prognosis and understanding of the reachable range and limitations of endoscopic approaches are very helpful in achieving successful outcomes and improving the capacity of surgeons.

2.1 Clinical Considerations In general, the clinical indications for TELD are intractable back pain and persistent radiating lower extremity pain despite conservative treatment such as medication, physical therapy, and epidural injection. Published articles related to clinical prognostic factors of TELD suggested that duration of symptoms [32, 63–65], positive Straight Leg Raising (SLR) test [63], age [32, 34, 58, 59, 64, 66, 67], and body mass index (BMI) [59, 66] were statistically related to success rate and recurrence rate. There were also reports that patients with diabetes, smoking, and intense physical labor were associated with surgical outcomes and relapses [58, 68]. Regarding age, many studies have reported that the younger the patient, the more favorable

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the outcomes [32, 34, 58, 59, 64, 66, 67]. In one nationwide cohort study involving many cases (n  =  15,817), percutaneous endoscopic lumbar discectomy for older patients (≥57 years) had a higher reoperation risk during the postoperative 3.4 years than open discectomy [67]. However, it should not be overlooked that many patients at an old age were able to avoid incisional surgery under general anesthesia through endoscopic procedures. TELD can be regarded as belonging to the category of surgery in a broad sense, but it would be a small procedure with a minimal wound less than 1  cm performed under local anesthesia. Some articles reported no significant association between age and clinical outcomes or relapses after TELD [68–70]. Although it is necessary to be careful about postoperative management in older age groups, age and gender do not seem to be factors to be seriously considered in selecting an appropriate patient. One consideration in the different application of treatment between men and women in the field of TELD is that women may be better indications than men at the L5-S1 level, since men tend to have more limitations in the transforaminal endoscopic approach due to their different pelvic structures. Studies of prognostic factors related to symptom duration reported that patients with shorter duration of symptoms before TELD had better outcomes [32, 63–65]. In selecting a patient, it is worth considering the severity of the symptoms before the TELD. Usually, patient satisfaction is related to differences in visual analogue scale (VAS) pain scores before and after treatment. Therefore, the milder the symptoms before surgery, the less likely the patient’s satisfaction after treatment would be. Even though the surgeon stands on early stage of learning curve, it is recommended to select patients with severe herniated disc with a high VAS pain score rather than a low VAS score with mild symptoms. The positive SLR test is helpful in predicting the severity of disc herniation and can also serve as a predictor of favorable outcome of TELD treatment [63, 71]. Muscle weakness or sensory deficits are not considered contraindications as long as these neu-

S.-J. Park

rological deficits result from a soft disc herniation. And if sufficient decompression is expected to be achieved with TELD, applying TELD would be a better treatment option than choosing other surgeries that involve nerve retraction that could aggravate the neurological deficit. It is necessary to carefully examine the possibility that the main cause of the symptoms and signs was not caused by a disc herniation, but by other accompanying spinal diseases. The cause of sudden severe symptoms with straight leg raising (SLR) test positive at 0

Fig. 3  TELD for up-migrated disc herniation with grade 1 Spondylolisthesis. A 54-year-old female patient presented with right leg radiating pain. Preoperative radiologic study showed highly down-migrated disc herniation and grade I spondylolisthesis without significant instability (a, b). She had never had intermit-

tent claudication before. Complete removal of the herniated disc fragments was achieved by TELD without sacrificing any posterior spinal structures (c, d). Her follow-up duration was about 5  years. The final VAS score for leg pain was 0. GI Spondylolisthesis patients without NIC

thesis with significant instability and bilateral foraminal stenosis with severe central stenosis might be contraindications of TELD. In patients with conjoined root, which makes it difficult to access through the foramen, there may be access through the contralateral foramen or decompression through the secondary axilla of the conjoined root (Fig.  4). However, most of the anomalies of nerves passing through the caudal area of the intervertebral foramen belong to the contraindications of TELD.  If the amount of foraminoplasty required for access to the herniated disc fragments is too destructive, it would be a relative contraindication of TELD. Any soft disc herniations can be indications of TELD as long as the primary cause of symptoms is the herniated disc and the locations are not inaccessible. But, the characteristics of disc herniation at the index level and several accompanying radiologic findings may affect treatment outcomes. According to published articles related to radiological prognostic factors, several preoperative findings, such as protrusion type, smaller-­ sized herniated discs, central location of herniation, central located high-canal compro-

mised herniation, migrated herniation, axillary type herniation, high-grade migration, concurrent lateral recess stenosis, Pfirrmann grade III, higher disc height index, larger sagittal range of motion, segmental kyphosis of index level, high grade of disc degeneration of adjacent level, and presence of Modic change were associated with unfavorable outcomes of TELD [38, 41, 57, 59, 64–66, 68, 70, 73–76]. Among these factors, central zone disc herniation, migrated disc herniation, and axillary type herniation were mainly related to surgical failure [38, 57, 59]. These surgical failures can be said to have a lot to do with the technical aspects related to the accessible range of the endoscope. In addition, factors related to surgical failure can be evaluated as technically demanding or prone to mistakes. For the development of TELD, a challenging attitude will be required rather than giving up by excluding these factors from indications. Many of the factors described above were findings from studies related to recurrence, and the factors related to recurrence were not significantly different from those of open microdiscectomy [77, 78].

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Conjoined Nerve Root a

b

e

d

g

f c

Extraforaminal procedure through the secondary axilla

Fig. 4  A case of conjoined nerve root. A 26-year-old male patient presented with severe radiating pain in the right lower extremity. Preoperative radiologic studies showed disc herniation located in the subarticular zone at L5-S1 level (b, d), conjoined root at L4–5 level (a, c), and suspicious conjoined root at L5-S1 level with relatively lower lying L5 exiting root at L5-S1 level (a, b). A conjoined root was identified in the endoscopic field of view at L5-S1 level (e), and the working cannula could not

enter the intervertebral foramen during TELD (e, f). Successful removal of the herniated disc was performed with an extraforaminal procedure through the secondary axilla without any specific sequelae (g). However, it was a very demanding procedure. When planning a TELD, it is always necessary to check the shape of the left and right intervertebral foramen on the MRI to check for anomalies of the exiting nerve root

Protruded disc herniations were reported to be worse prognostic factors for both recurrence and clinical outcome than extruded disc herniations, and smaller-sized herniated discs were reported to be more associated with early recurrence than larger-sized herniated discs [66, 70, 73, 74]. In the classification according to the shape of disc herniation, the degree of disc herniation and nerve compression are usually more severe in the case of extrusion than in protrusion. Therefore, these findings suggest that the more severe disc herniation is selected for treatment by the surgeon, the better the clinical outcome is likely to be obtained. It is considered to be a matter to pay

particular attention to at the beginning of the learning curve. Extruded disc herniations would be better indications than protruded disc herniations, and transannular herniations might be better indications than contained disc herniations. The studies published in relation to the radiological prognostic factors described above included only recurrent cases or cases that underwent early reoperation, or included only the last clinical results without knowing whether reoperation was performed. It has been difficult to find studies that identify prognostic factors, including both cases of surgical failure and the final clinical outcomes of patients.

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Principles of Transforaminal Endoscopic Approach Technique

In author’s prospective study of case series analysis for prognostic radiological factors of TELD for intracanal extruded disc herniation (81 consecutive patients, mean age 35.8  years with range 16–82, 51 males, mean follow-up 24 months, including 24 cases of migrated disc herniation, 19 cases of severe volume of herniation more than 66% canal compromising, 10 cases of concurrent stenosis), there were three major factors predicting an unfavorable outcome: (1) calcifications around the base of herniation (calcifications of annulus or posterior longitudinal ligament, endplate osteosclerosis) (P  =  0.009), (2) prominent Modic change (P  =  0.002), and (3) incomplete removal of extruded herniation as seen on the immediate postoperative MRI (P = 0.004) (Fig. 5). In this study, patients were selected based on the clinical and radiological indications described above, and unsuccessful outcomes (6.2%, 5 cases) defined as: (1) Failure of procedure leading to open surgery due to remaining disc fragments (2 cases), (2) No significant improvement of VAS or ODI ( 2.9mm

10mm –> 5.8mm 15mm –> 8.6mm

5.8mm

2.9mm

5.8mm

2.9mm

10mm

5mm

30 degrees

10mm

5mm

Fig. 8  Schematic drawings of the tangential value according to the approach angle and the progression of entry

Principles of Transforaminal Endoscopic Approach Technique

51

The range of reachable space for endoscopy according to the angle of access a

Steep Approach

b

Flat Approach

L4-5 Level

Fig. 9 The range of reachable space for endoscopy according to the angle of access. If the approach angle is too steep, only indirect decompression can be achieved (a). When approaching too horizontally, there is a possi-

Annuls Entry point of mid-pedicular line

L4-L5 Level

bility of injury to the exiting root and the traversing root due to the effect of narrowing the dorsoventral width of the triangular safe zone (b)

Annuls Entry point of medial pedicular line

Annulus

Annulus

30º

10mm

5mm

30º

10mm

5mm

Fig. 10  Schematic drawings of difference in the accessible range of endoscopic forceps depending on whether the annulus entry point is the mid-pedicular line or the medial pedicular line

the endoscope, appropriate selection of endoscopic tools, and performing foraminoplasty. Among them, the use of appropriate access trajectory including the entry point and approach angle, the effective utilization of the obturator, and the proper positioning of the working cannula are crucial processes as methods to approach the target closely. Effective use of obturator plays an important role in determining the annulus entry point. As methods for expanding the treatment area and increasing the accessible range of the endoscopic forceps, adequate annular releas-

ing and levering of the endoscope also contribute, but foraminoplasty plays the biggest role. Given the limitations of the accessible range mentioned above, it would be very difficult to completely capture the herniated disc fragments if the center of the extruded fragments was migrated more than 7  mm away from the endplate level. However, even these cases are not included in the contraindications of TELD.  In these cases, it is necessary to advance the endoscope to the epidural space outside the annulus, and cases with a very large foramen may be

S.-J. Park

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Accessible range of endoscopic forceps according to the annulus entry point Mid-Pedicular Line

Medial Pedicular Line

Fig. 11  Accessible range of endoscopic forceps depending on whether the annulus entry point is the mid-­pedicular line or the medial pedicular line. The reachable range of

the endoscopic forceps may vary depending on the annulus entry point as well as the approach angle

selected, but in most cases, access is possible if foraminoplasty is performed. Foraminoplasty is an important process that allows the TELD procedure to be performed completely through the intervertebral foramen, facilitates access to the displaced herniated disc and epidural space, overcomes obstacles, and increases the access range of endoscopic forceps. Besides the approach techniques, the accessible range of endoscopic forceps depends on ­differences in anatomical structures according to the index level and the selected access route (foraminal or interlaminar window). Compared to the lower lumbar vertebrae, the upper lumbar vertebrae have characteristics such as narrower lamina width, lamina overhanging the disc space, wider space between ventral surface of superior facet and the dorsal surface of vertebral body,

more sagittal orientation of facet, and deeper superior vertebral notch above the pedicle (Fig. 12). The upper lumbar disc and upper lumbar vertebrae are characterized by a concave dorsal surface (Fig.  12d). As it goes down to the lower lumbar region, the opposite characteristics proceed, and the concavity of the dorsal surface of the vertebral body and disc disappears, and the facets become larger and thicker than those of the upper lumbar region. In the upper and lower lumbar regions, the triangular safe zone has a slightly different triangular shape depending on the travel angle of the exiting nerve root corresponding to the hypotenuse, and the width of the dura is also slightly different. The distance from the exiting nerve root to the superior articular process usually gradually decreases from the lower lumbar level to the upper lumbar level [20].

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Principles of Transforaminal Endoscopic Approach Technique

a

c

b

L2-3

L4-5

d

L2

L3

L5

Fig. 12  Characteristics of upper and lower lumbar spine. The upper and lower lumbar levels show differences in lamina width (a), facet joint size and orientation (a), superior vertebral notch depth (b, c), and concavity of the dorsal surface of the disc and vertebral body (d). It is necessary

to understand the difference between the upper and lower lumbar spine because the approach route, the approach trajectory including the initial target point and the approach angle, and the required approach techniques are different according to the characteristics of each index level

Depending on these characteristics of each index level, the approach route, the approach trajectory including the initial target point and the approach angle, and the required approach techniques may and should be different. Even if the approach is at the same angle, the range of the reachable space of the endoscopic forceps varies according to the index level (Fig. 13). In order to enter the epidural space in the endoscopic procedure for lower lumbar disc herniation, it is ­necessary to approach at a flatter angle or to lever the working cannula more horizontally than in the case of upper lumbar disc herniation (Fig. 13). In TELD for upper lumbar disc herniation, the accessible range of endoscopic forceps is relatively wide because it is easy to enter the epidural space outside the annulus and to access the space beyond the disc level (Figs. 13 and 14). The reason may be simply due to the wide foraminal dimension, but also due to the sagittal orientation of the facet, the small pedicle diameter, the concavity of the disc dorsal surface, and the deep superior vertebral notch (Fig. 12b, d). This can be a clue to the area where foraminoplasty is required. At the upper lumbar level, the exiting

nerve root has a lot of vertical travel, and the dural sac is relatively wide laterally and has compact neural elements inside. Therefore, caution should always be taken to avoid injury to the dura and nerves when approaching and levering the working cannula. Unlike the other levels, the L5-S1 level is usually located ventral and below the iliac crest. The facets are large and have a horizontal orientation in the coronal plane. In addition, the L5-S1 level has a wide interlaminar space, and the lamina has a horizontal orientation in the sagittal plane (Fig. 12a). Due to these characteristics, transforaminal approaches to the L5-S1 level have more limitations compared to other levels. If TELD is performed on patients with a narrow width between the bilateral iliac crest, the approach will be too steep. In order to approach at a relatively low angle, the start of the entry must be quite cranial, and this approach makes it difficult to access the intracanal area completely through the intervertebral foramen. That is, a partially transforaminal procedure is performed rather than a complete transforaminal in the true sense. Although the topic of this chapter is the transforaminal approach, it should be borne

S.-J. Park

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Accessible range of endoscopic forceps according to index level and entry angle L2-3 level

L4-5 level

Same approach angle L2-3 level

L4-5 level

Approach epidural space

Fig. 13  Accessible range of endoscopic forceps according to the index level and approach angle

‘Theoretical’ maximal accessible range of endoscopic forceps without foraminoplasty

a

b

L3 (L2-3 level)

Fig. 14  The theoretical maximum accessible range of endoscopic forceps at L2-3 level (a) and L4-5 level (b) without foraminoplasty. The maximal accessible range of endoscopic forceps without foraminoplasty varies according to the index level. In actual treatment, since the exiting

L5 (L4-5 level)

nerve root often runs vertically close to the superior articular process at the upper lumbar level, extreme care must be taken to lever the working cannula as shown in figure (a) above. Therefore, the expression “theoretical” is used

Principles of Transforaminal Endoscopic Approach Technique

in mind that spinal endoscopy uses two windows: transforaminal and interlaminar. In fact, in L5-S1 level endoscopic treatment, it is often useful to use the interlaminar approach using the characteristics of the wide interlaminar space and the horizontal orientation of L5 lamina [31, 79–81]. However, when comparing the transforaminal and interlaminar approaches, the transforaminal approach has many advantages. There is no nerve r­ etraction process in the transforaminal approach, and the possibility of dura and nerve injury, the degree of damage to the yellow ligament and annulus, and the possibility of epidural scarring are lower than that of the interlaminar approach. In addition, the working time in the epidural space, which is the most painful section during the endoscopic procedure under local anesthesia, is shorter during the transforaminal approach. Therefore, if a successful approach is feasible, it is considered to be good to use the transforaminal approach. If the approach trajectory is well established and the foraminoplasty technique is used, successful TELD can be achieved even at the L5-S1 level in many cases [36, 81–83]. In the case of women, the height of the iliac crest is relatively low, the lumbosacral lordotic angle is often large, and the distance between the iliac crests on both sides is relatively far, so transforaminal approaches are relatively easy for many female patients (Fig. 15). In TELD for L5-S1, the foraminal zone and subarticular zone are relatively less difficult to

a

Fig. 15  Characteristics of female (a) and male (b) pelvic structures related to the iliac bone. In general, women are more easily treated with transforaminal approaches than

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access than the central zone due to the lateral location of the lesions (Figs.  16 and 17). Successful TELD for L5-S1 level central zone disc herniations is feasible in selected cases and usually requires foraminoplasty (Fig. 18). In the case of central zone L5-S1 disc herniation, where the amount of foraminoplasty required for TELD is too destructive to the facet joint with a narrow gap between the bilateral iliac bones, it may be a relative contraindication. Highly up-migrated disc herniations at L5-S1 level are also considered relative contraindications. In the TELD procedure for L5-S1 level, most of the access trajectory is directed from the cranial to the caudal because of the obstacles of overlying iliac bone. Accordingly, in the case of up-migrated disc herniation at L5-S1 level, there is a high possibility that the herniated disc fragment is out of reach of the endoscopic forceps through the transforaminal approach. It is recommended to use an interlaminar approach for highly up-­ migrated disc herniation at L5-S1 level (Fig. 19). Equipment upgrade is important to increase the reach of endoscopic forceps, and further efforts are needed for equipment development in the future. Given the above-mentioned limitations of the endoscope and the problems such as forceps out of sight, it is worth considering the development of a flexible endoscope and upgrading to an endoscope capable of adjusting the optic angle of the endoscope.

b

men. Even with similar iliac crest heights, the distance between the bilateral iliac crests facilitates TELD procedures for women (a)

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TELD for L5-S1 level (Foraminal zone)

Fig. 16  A case of successful TELD for foraminal disc herniation with foraminal stenosis at L5-S1 level. A 44-year-old male presented with severe radiating pain in

the lower extremities. TELD achieved complete decompression with foraminoplasty using an endoscopic drill and electric shaver

TELD for L5-S1 level (Subarticular zone)

Fig. 17  A case of successful TELD for lumbar disc herniation of subarticular zone at L5-S1 level. A 21-year-old female patient presented with right leg radiating pain. Complete herniated disc removal was performed by TELD

The accessible range of the endoscopic forceps can also be determined by the surgeon’s technical capabilities on the learning curve. The treatment results of TELD are related to the surgeon’s experience and skill [57–60]. Indications would also be expanded depending on the surgeon’s technical competence and proficiency. Since the indications for treatment would be altered according to the accessible range and limitations of each surgeon’s

endoscopic forceps, it is necessary to know how far they can reach and also to make efforts to gradually expand the range. The success of TELD in the treatment of lumbar herniated disc depends on whether the endoscopic forceps reach a location where the herniated disc fragments can be retrieved. If the location is accessible, it would be an indication; if not, it would be a contraindication (Fig. 20).

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Principles of Transforaminal Endoscopic Approach Technique

TELD for L5-S1 level (Central zone) a

b

Fig. 18  A case of successful TELD for lumbar disc herniation of central zone at L5-S1 level (a). A 21-year-old female patient presented with right leg radiating pain.

Complete herniated disc removal was performed by TELD (b). During the TELD procedure, foraminoplasty (round dotted line) was required to access the target area

Interlaminar: Sublaminar Cephalad Approach

a

c

e

f b

d

Fig. 19  A successful case treated with an interlaminar approach of endoscopic procedure for highly up-migrated disc herniation at L5-S1 level. A 47-year-old male patient presented with severe lower extremity radiating pain. Preoperative MRI showed severe migrated disc herniation (a, b). It was difficult to distinguish whether it was down-­

migrated disc herniation of L4–5 level or up-migrated disc herniation of L5-S1 level (a). Successful removal of the herniated disc was achieved by endoscopic procedure using the L5-S1 interlaminar window (e, c, d). Postoperative MRI showed detached ligamentum flavum according to the access route (f)

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Fig. 20  Accessible range of endoscopic forceps. The indications for treatment would be different depending on the accessible range and limitations of endoscopic forceps

for each surgeon. It is necessary to know how far endoscopic forceps can reach and also to make efforts to gradually expand the range

3 Surgical Technique

teristics of equipment and tools, (2) accurate targeting process to access through appropriate trajectory, effective use of obturator insertion technique, and positioning of the working cannula as close to the target as possible, (3) efforts to secure clear vision and work within the endoscopic field of view, (4) utilization of additional techniques such as foraminoplasty, levering, and annular releasing, which are tips to approach the target point more closely, (5) effective method of working around the base of the herniated disc at the target point and how to remove the herniated

In order to achieve successful TELD, it is necessary to safely reach the target area and secure the endoscopic field of view. In addition to that, the endoscope must be approached close enough to remove the herniated disc fragments. Success or failure is highly dependent on whether the endoscopic forceps can reach a position where it can capture herniated disc fragments (HDF). Therefore, the important points for a successful procedure are: (1) appropriate use of the charac-

Principles of Transforaminal Endoscopic Approach Technique

disc without remaining herniated discs. In addition, it is necessary to properly utilize access techniques according to the disc herniation pattern of each patient and the characteristics of the spine structures at the index level. The surgical steps of the usual TELD are performed in the following order: (1) Operative room and instruments setting, (2) Anesthesia and position of the patient, (3) Initial target point and skin entry point determination, (4) Needle and obturator insertion, (5) Placement of working cannula, (6) Subannular space decompression and annular releasing, (7) Foraminoplasty (Work of widening the foraminal window), (8) Fragmentectomy, (9) Conform the decompression, (10) Closure. The order of No. 7, No. 8, and No. 9 above may be changed case by case. Foraminoplasty may be performed before subannular decompression. Foraminoplasty may be omitted. The order of subannular decompression and fragmentectomy can also be changed, and sometimes they are performed simultaneously. Fragmentectomy is usually performed after subannular decompression (inside to out tactics), but in some cases, subannular decompression may be performed after fragmentectomy (outside to in tactics).

3.1 Preoperative Setting, Positioning of the Patient, and Anesthesia The proper preparation for effective and smooth TELD should include setting the operating room and instruments, sufficient anesthesia to provide a comfortable environment for the patient and operator, and safe and stable positioning of the patient. In addition, cooperation between the operating surgeon, anesthesiologist, nurse, and radiologic technician is required. A comfortable procedure can lead to perfect treatment results. In the TELD, which is usually performed under local anesthesia, the patient is placed in the prone position. The prone position is more stable for the patient than the lateral decubitus position and provides the surgeon with easier handling of instruments. It is convenient to identify the midline and the zone of coronal plane through antero-

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posterior (AP) view monitoring using C-arm fluoroscopy whenever necessary during the procedure. If the lateral view is frequently monitored during the TELD, the procedure can be performed in the lateral decubitus position. The lateral decubitus position can be frequently used in endoscopic procedures with an interlaminar approach because it provides the surgeon with comfortable handling of the instrument. The patient should be comfortable during the procedure. Although monitoring the patient’s muscle strength and sensation can be important, it is not recommended to force the patient to tolerate the severe pain caused during the procedure due to shallow anesthesia. Pain in the course of TELD procedure under local anesthesia ­frequently occurs during the entry of the dilator and the working cannula into the annulus, during the procedure at the junction of the annular surface and the endplate near the midline, and during the procedure in the epidural space close to the nerves and around blood vessels. Pain control during the procedure is a very important part for a successful procedure. The degree of pain that occurs during TELD can affect not only patient satisfaction but also successful procedure. In the author’s prospective randomized control study in which 51 patients (32 males and 19 females, mean age 37.3  years) were included, there were differences in the visual analogue scale (VAS) score during the endoscopic discectomy procedure, the satisfaction rate after the procedure, and the rate of complete herniated disc removal according to the anesthesia method. In this study, a comparative analysis was conducted between the group A patients who received local anesthetic just before the procedure by the surgeon through the access route and the group B patients who received interlaminar epidural block 30 min before the procedure by the anesthesiologist. Group A patients were given opioid ­analgesics whenever necessary during the procedure, and group B patients were administered appropriate sedatives and opioids as needed with the help of an anesthesiologist. The procedure was effective to relieve their radiating leg pain in all patients. The overall mean VAS score for leg

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pain decreased from 7.77 to 1.98 immediately after procedure, and to 0.55 finally (mean final follow-­up: 12 months, P  2.9mm

10mm –> 5.8mm 15mm –> 8.6mm

Annulus

5.8mm

2.9mm

30º

10mm

5mm

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cessful procedures and expand indications. Foraminoplasty contributes the most to the expansion of indications and plays the most important role in increasing the accessible range in TELD.

2.2.1 Indications of Foraminoplasty The indications for foraminoplasty in TELD are summarized as follows: 1. Central disc herniations in which the initial primary target point cannot be set close to the medial pedicular line. These are cases where it is not easy to access close to the MPL for intracanal access due to hypertrophied facet, narrow foramen due to disc height loss, horizontal oriented wide facet, and central zone disc herniation at L5-S1. 2. Sequestrated disc herniations migrated beyond the disc level. Foraminoplasty is usually required if the dislocated herniated disc is not located at the disc level and there is no continuity with the parent disc. 3. Highly migrated disc herniations in which the center of the herniated disc fragment is more than 7  mm away from the endplate level. Considering the anatomical structure and dimensions of the intervertebral foramen and the characteristics of endoscopic instruments, further migration is very difficult to resolve without foraminoplasty. In addition, foraminoplasty can be used as a treatment for foraminal stenosis. Not all migrated disc herniations require foraminoplasty. If the center of extruded fragment migrated less than 7 mm and it does not belong to the first and second indications of foraminoplasty mentioned above, it would be possible to grab the fragment completely and to retrieve the herniated disc using these methods other than foraminoplasty. However, in the case of migrated disc herniation, in which the center of the prolapsed disc mass is more than about 7 mm away from the endplate level, it is difficult to ensure the complete removal of the

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herniated disc fragments when other methods are used without using foraminoplasty. Therefore, it is an indication for foraminoplasty of TELD. In previously published papers, the classification of the migration degree of herniated disc is based on the disc height at index level or the location of the herniated disc fragment in relation to the pedicle. And the degree of migration for each study was classified according to different criteria [3, 49, 50, 72]. Also, it was not clear whether the degree of migration was determined based on the center of the herniated disc fragment or the distal end. In the TELD field, it is considered reasonable to classify migrated disc herniation according to the degree of migration by determining whether the center of the migrated disc fragment is more than 7 mm away from the endplate as the criterion for “highly” of migrated disc herniation. The reason is that it is useful as a practical guideline to determine whether foraminoplasty is necessary. In the downward migrated disc herniation, it is considered that TELD at the index level is feasible until the center of the HDF moves away from the endplate by about 12  mm downward. In cases of further migration beyond that, microdiscectomy may be recommended as the foraminoplasty requirement may be too destructive. If it is necessary to treat further migration with an endoscopic procedure, it may be performed using a transpedicular approach or by adding a transforaminal or interlaminar approach at a lower level [73–75]. When applying the TELD to treatment, knowing the reachable range and limitations of each surgeon’s endoscopic forceps is important for selecting an appropriate patient. In order to overcome the limitations and expand the indications by increasing the accessible range of the endoscopic forceps, it is necessary to utilize the advanced equipment and access techniques and select an appropriate access route according to the index level. The accessible range of the endoscopic forceps is directly related to the indications of TELD (Fig. 6).

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Fig. 6  Accessible range of endoscopic forceps. The accessible range of endoscopic forceps is closely related to the indications of TELD

2.3 Surgical Technique 2.3.1 Positioning of the Patient and Anesthesia The prone position is more stable for the patient than the lateral decubitus position, and since this position provides the surgeon with easier handling of instruments, TELD procedures are usually performed in the prone position. Pain control during the procedure is a very important part for a successful procedure. The degree of pain that occurs during TELD can affect

not only satisfaction but also treatment outcomes. In particular, during TELD for migrated disc herniation, extended foraminoplasty may be required and the procedure in the epidural space may be prolonged, so sufficient anesthesia is very important. In addition to sufficient preoperative epidural anesthesia, appropriate use of IV sedatives is recommended. Midazolam or Fentanyl can be used as intermittent sedatives as needed, but intravenous sedatives such as Dexmedetomidine administered as continuous infusion with the help of an anesthesiologist have more advantages and are more effective.

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2.3.2 Planning for Initial Access and Needle Insertion Although a three-dimensional sense of space is required for needle insertion, the optimal trajectory in TELD is not complicated because it is a straight trajectory connecting the starting point and the ending point. It is recommended to first select the initial primary target point corresponding to the destination point and then determine the skin entry point, which is the starting point. The ideal primary (initial) target point is a point close to the herniated disc fragments (HDF) and medial pedicular line (MPL) located on the annular surface of the triangular safe zone. When it is difficult to select the initial target area as this ideal point and it is necessary to perform foraminoplasty first, the ventrolateral surface of the superior articular process can be selected as the initial primary target point. In TELD for migrated disc herniation, it is better to decide more precisely in the selection of the skin entry point. The following four procedures are recommended for determining the skin entry point: (1) On the preoperative MRI axial image, draw a line from the initial target point (a point close to the HDF and MPL located above the annular surface of the triangular safe zone) through the ventral or ventrolateral surface of the superior articular process to the skin. At this time, this line should be drawn so that it does not pass through the nerve and peritoneum. A line passing through the ventral bony portion rather than the ventral surface of the superior articular process may be drawn when planning the foraminoplasty. Measure the distance from the point where this line meets the skin to the midline. (2) On the patient’s skin, draw a craniocaudal line connecting points separated from the midline by the distance measured on the MRI.  In the C-arm fluoroscopic true AP view, draw a horizontal line parallel to the index disc and select the point where the two lines cross as the primary candidate point for the skin entry point. (3) According to the direction of the herniated disc, it is necessary to select the skin entry point along the craniocaudal line from the primary candidate point to the cranial side in the case of the caudal direction and vice versa in the cranial direction. It is helpful to determine how

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much up or down the skin entry point is by drawing a line toward the center of the migrated disc fragment in the C-arm fluoroscopic true AP view. (4) Press the patient’s skin while predicting the levering effect after entering the working cannula and the endoscope. The final skin entry point is determined by examining the accessibility of both the herniated disc fragment and the subannular space around the base of the herniated disc. Specifically, the final skin entry point is determined as a point that is expected to be accessible to the subannular space among the points where the herniated disc fragment can be removed using foraminoplasty and levering effect later. The skin entry point should be determined as a point that can minimize foraminoplasty. When approaching highly down-migrated disc herniation, the entry angle needs to be well determined not only from the axial plane, but also from the coronal plane through the process No. 3 above. Setting the approach angle in the coronal plane excessively large makes it difficult to enter the subannular space and may also cause damage to the endplate upon entry. Therefore, it is good to anticipate the levering effect and set the angle not too much. Using c-arm fluoroscopy to draw many landmark lines, such as midline, medial pedicular line, measured skin entry line, and posterior vertebral line, is helpful for accurate targeting. Since the success or failure of TELD can be determined even with a difference of only 2–3 mm, it is critical to check whether it is a true anteroposterior (AP) view and a true lateral view in this process. When planning the procedure steps for a TELD, it is necessary to decide whether to proceed as an inside-out tactic or an outside-in tactic. Inside-out and outside-in may proceed simultaneously and may be used interchangeably. In general, it is more stable and advantageous to proceed with the inside-out tactic. Outside-in tactics are often used for foraminoplasty first in TELD for migrated disc herniations. In the case of TELD for migrated and sequestrated disc herniation that causes severe intractable pain, outside-in tactic can be used if performing fragmentectomy first is advantageous for the progress of the procedure. However, if access to MPL is possible at the time of initial

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entry during TELD for migrated disc herniation, it may be better to proceed inside to out tactic in most cases.

2.3.3 Obturator Insertion Technique and Annulus Entry Point After replacing the initially inserted needle with an obturator, proper handling of obturator helps to reach a deeper area and closer to the target by readjusting the entry trajectory. Since the obturator has a blunt tapered end and it is easier to control the distal end than a needle, it can complete the trajectory by safely and closely approaching the desired target area. An important role of the obturator is to determine the annulus entry point as well as the establishment and correction of the trajectory. The effective use of the obturator is also critical to a successful procedure because it determines the position of the working cannula at an early stage. 2.3.4 Proper Working Cannula Placement In TELD for highly down-migrated disc herniation, a long beveled cannula is useful because it facilitates foraminoplasty and secures a wide working space. The position at which the working cannula is initially anchored can be set differently depending on whether subannular space decompression or foraminoplasty is first performed. In the case of highly down-migrated disc herniation, it is often necessary to override the working cannula on the ventromedial surface of the superior vertebral notch to finally perform fragmentectomy. 2.3.5 Full Visualized Endoscopic Procedure There may be cases where it can be seen in the endoscopic field of view but is difficult to capture. This is probably because it is out of reach of the endoscopic forceps by not getting close to the target point. However, if you cannot see or have a clear vision, a successful and safe procedure is almost impossible. Securing a clear view of the target area along with a close approach to the target is essential for success. In the past, fluoroscopic guided tools such as reamers and manual

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drills were actually used a lot, and a high-speed drill for open surgery driven by compressed air was also used with a modified drill bit. However, the performance of electric drills developed in recent years has been greatly improved in terms of stability and high power. The development of instruments passing through the endoscope enables safe and effective procedures and greatly contributes to the expansion of indications. Blurred vision may be a problem with the lens or optical cable, but bleeding is the most common cause. In the case of bleeding, it is recommended not to proceed with the procedure in a bad field of vision, but to proceed with the procedure after securing a clear field of view through faithful hemostasis. During TELD for highly migrated disc herniation, bleeding that obstructs the field of view is relatively frequent, so it is essential to the success of the procedure to perform hemostasis faithfully.

2.3.6 Foraminoplasty Foraminoplasty corresponds to the step of completing the access route in the case of TELD for highly migrated disc herniation. Foraminoplasty is an important process that enables a procedure that completely passes through the intervertebral foramen, facilitates access to the displaced herniated disc and epidural space, overcomes obstacles, and increases the access range of endoscopic forceps. Foraminoplasty has contributed greatly to the expansion of indications. TELD for sequestrated disc herniations that migrated beyond the disc level in the sagittal plane usually requires foraminoplasty. Considering the length of the actuating jaw corresponding to the finite reach of the endoscopic forceps, if the center of the extruded fragment has migrated more than 7  mm downward from the endplate level, the position of the working cannula should be located outside the annulus, and foraminoplasty is required in most cases. At the upper lumbar level, it is relatively easy to access the epidural space outside the annulus, and there are many cases where TELD for migrated disc herniation can be performed using a light foraminoplasty or without the need for foraminoplasty (Fig. 7). The reason may be sim-

Paramedian Migrated Disc Herniation

a

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b

L2-3 level

L4-5 level

Fig. 7  Characteristics of upper and lower lumbar spine. At upper lumbar levels (a), access to the epidural space outside the annulus is relatively easier than at lower lumbar levels (b)

ply due to the wide foraminal dimension, but also due to the sagittal orientation of the facet, the small pedicle diameter, the concavity of the disc dorsal surface, and the deep superior vertebral notch (Fig. 8). Considering the ease of access to the epidural space and migrated disc fragments during TELD for upper lumbar disc herniation, the area of foraminoplasty can be designed with the concept of creating a foraminal window similar to the upper lumbar region in the lower lumbar region (Fig. 9). Foraminoplasty is a procedure to cut the ventrolateral area of ​​the superior articular process to be similar to the sagittal orientation of facet in the upper lumbar region. For caudally migrated disc herniation, the process of widening the medial portion of the superior vertebral notch as deep and wide as the structure of the upper lumbar vertebrae is additionally performed. The superior vertebral notch consists of the ventrocaudal area of ​​the superior articular process, the superior surface of the pedicle, and the dorsal

surface of the vertebral body around the superior endplate. These areas are the sites where foraminoplasty is performed. In the case of cranially migrated disc herniation, along with the ventral surface of the superior articular process, the lamina lateral part below the pars can be additionally shaved if necessary. Tools for performing foraminoplasty include endoscopic forceps, endoscopic punches, flexible radiofrequency cautery, side-firing holmium:yttrium-aluminum-garnet (Ho:YAG) laser, endoscopic chisel, endoscopic shaver, endoscopic drill, and endoscopic shaft (endo-­ kerrison) punch. In the case of highly down-­ migrated disc herniation, extended foraminoplasty with bone work is required rather than light foraminoplasty that removes only soft tissue (Fig. 10).

2.3.7 Levering The working cannula approached through a long track has difficulty in translational movement but

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a

c

b

d

Fig. 8  Characteristics of upper and lower lumbar spine. Compared to the lower lumbar levels, the upper lumbar levels are characterized by a relatively wider foraminal dimension, narrower lamina width with more sagittal ori-

a

entation of facet (a), smaller pedicle diameter, concavity of the dorsal surface of the vertebral body and disc (d), and a deeper and wider superior vertebral notch (b, c)

b

c

d

e

Fig. 9  Characteristics of upper and lower lumbar spine (a) and usual target areas of foraminoplasty (b–e)

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a

b

c

d

Fig. 10  Process of foraminoplasty with endoscopic high-­ speed drill. The performance of electric drills developed in recent years has greatly improved in terms of stability and high power. Note that down-migrated disc fragments

(*) were exposed (d) after foraminoplasty in the ventrolateral area of the superior articular process and medial portion of the superior vertebral notch (a–c)

relatively easy movement by levering. The levering of the endoscope allows the instruments that have passed through the working channel of the endoscope to be closer to the target point. The effective utilization of levering can be a method to increase the reach of the endoscopic forceps and to facilitate access to the epidural space with foraminoplasty. During levering, caution should be exercised against bending or damage of the endoscope and injury to the exiting nerve root. If it is difficult to position the herniated disc fragment

within the accessible range of the endoscopic forceps, it is better to additionally perform foraminoplasty rather than excessive levering. Since the exiting nerve root at the upper lumbar level has a lot of vertical travel and the gap between the superior articular process and the exiting root is relatively narrow, the levering of the endoscope should be performed very carefully. The closer the annular puncture point to MPL, the higher the effect of levering movement and the lower the possibility that the exiting nerve is compressed.

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2.3.8 Procedure of Discectomy (Subannular Space Decompression and Fragmentectomy) It is recommended to perform subannular space decompression for the purpose of preparing the surrounding free space for removal of herniated disc fragments and to prevent recurrence and residual symptoms. It is usually performed at an early stage of the procedure, but it can also be performed as a final stage after fragmentectomy. In particular, in the case of highly down-migrated disc herniation, a relatively large annular defect may have occurred during the development of herniated disc and during the procedure. Therefore, subannular space decompression is important to prevent recurrence along with annular shrinkage using a radiofrequency coagulator in the finishing process. Annular releasing for retrieval of herniated disc fragments may be recommended using the existing annulus fibrous defect on the medial side rather than lateral to medial direction. When performing TELD for highly migrated disc herniations, there is a high possibility that disc fragments cannot be removed using only releasing of the existing annular defect site. In these cases, it may be necessary to retreat back the working cannula to perform an additional annular cut from the side. In TELD for highly down-­ migrated disc herniations, annular releasing is not critical, but slight annular releasing from the lateral side facilitates entry of the endoscopic forceps toward the migrated disc fragments. Annular releasing should be performed as small as possible for annular competence. For complete removal of the herniated disc fragments, it is necessary to allow the endoscopic forceps to reach the center rather than the tip of the prolapsed disc fragment through sufficient foraminoplasty and decompression of the area surrounding the prolapsed disc. Once the grab of the prolapsed disc fragment has been secured, gently rocking it and rolling it like a spaghetti roll with endoscopic forceps rather than simply pulling it quickly can be a fragmentectomy tip that facilitates removal of the caudally migrated disc. The “Rolling Method” is an effective retrieving

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method of a herniated disc that allows the herniated disc fragment to come out of the prolapsed location gradually by rolling it with the rotational motion of the endoscopic forceps (Fig. 11). It is very helpful to completely remove the herniated disc by performing a grasping motion several times so that the cracked pieces do not remain and confirming through C-arm fluoroscopy whether the position of the endoscopic forceps corresponds to the position of the prolapsed disc in MRI.

2.3.9 Confirmation of Decompression The most effective method for adequate removal of the herniated disc and nerve decompression during the procedure is to use a flexible bipolar probe and actuating jaw of endoscopic forceps. Gentle insertion of these tools into the ventral space of the nerves and dissection of the peridural layer allows to check decompression and residual disc fragments in the endoscopic field of view. In addition, at this time, it is absolutely necessary to check whether they have entered the position necessary for confirmation of decompression through fluoroscopy. Since the final confirmation is postprocedure MRI, it is recommended to conduct the examination as soon as possible after the procedure. 2.3.10 Hemostasis 및 Closing Bleeding in TELD is usually very mild, and hemostasis can be easily accomplished using a radio frequency coagulator. However, in TELD for migrated disc herniation, as in open microdiscectomy, epidural space bleeding after HDF removal may be quite large in some cases. Although not detected by irrigation fluid, there may be cases in which bone bleeding due to foraminoplasty is not small. In TELD for highly migrated disc herniation, hemostasis should be performed more faithfully, and if necessary, it may be better to consider inserting a drain tube. It is recommended to consider inserting a drain tube for TELD when there is uncontrolled bleeding in the epidural space after removal of the disc fragment of migrated disc herniation or extensive foraminoplasty with bone work is performed in elderly patients.

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Fig. 11  Process of fragmentectomy (“Rolling method”). Gently rocking and rolling with endoscopic forceps rather than simply pulling can be a fragmentectomy tip that

facilitates complete removal without missing a migrated disc fragment

In the process of removing the working cannula, it is also necessary to check for bleeding in the arterial vessels around the intervertebral foramen. After the hemostasis procedure and removal of the working cannula, the skin is usually closed with subcutaneous sutures and sterile adhesive tapes.

dure and there is no recovery or worsening of muscle strength, an additional endoscopic procedure or open surgery is recommended immediately rather than follow-up. If the drain tube has been inserted, it can be removed after maintaining it for about 3–4 h. Usually, patients are discharged from the hospital after checking the progress of symptoms for 6–12  h. Upon discharge, it re-educates that disc herniation is a disease that can recur, and emphasizes the importance of maintaining the lumbar lordotic curvature during the healing period of about 2–3 weeks. Follow-up visits after the procedure are usually performed 3–4 weeks, 3 months, 6 months, and 1 year after the procedure. It is recommended to check the T2-weighted MRI at 1 year after the procedure to evaluate whether the management was successful without recurrence and to evaluate the procedure. For long-term follow-up, a visit may be recommended for 2 or 3 years or more after the procedure.

2.4 Postoperative Consideration Evaluation of the patient’s postprocedure symptoms and neurological and physical examination can be performed immediately after the procedure. It is recommended to avoid epidural anesthesia using long-acting local anesthetics because it may be difficult to determine whether the decrease in sensation and muscle strength is due to complications of the procedure or the effect of anesthesia after the procedure. Postoperative MRI is also recommended immediately. If there are residual disc findings on MRI after the proce-

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2.5 Clinical Outcomes and Case Illustration 2.5.1 Clinical Outcomes With the activation of foraminoplasty and the development of its techniques and equipment, the feasibility and success rate of TELD for the treatment of migrated disc herniation seem to be gradually increasing. According to a review of case series studies that performed endoscopic discectomy for migrated lumbar disc herniation, the overall favorable outcome in each paper was reported to be about 84.6% to 94.3% based on the Macnab criteria [3, 49, 50, 72–76]. These success rates might be comparable with open microdiscectomy. Among the reviewed case series studies, one article published in 2007 reported that it was unfavorable in far-migrated disc herniations. Each surgeon may have different indications depending on the degree of migration. In a­ ddition, the four papers that provided the definition of high grade all presented different criteria. The evaluation of the success rate according to the

degree of migration may not be very meaningful. However, studies on migrated disc herniation are all worthwhile in the sense of trying to broaden the indications of TELD. Author’s case series study conducted involving 123 consecutive patients (a total of 116 patients enrolled excluding 7 patients who underwent spinal surgery for problems other than the index level or had not been followed for more than a year) who underwent endoscopic surgery as a treatment for migrated lumbar intracanal disc herniation showed a significant improvement in pain (7.7 to 1.1 for mean visual analogue scale (VAS) score of leg pain and 6.3 to 1.2 for mean VAS score of back pain, p