(BQ) Part 1 book “Dynamic reconstruction of the spine” has contents: Dynamic stabilization of the lumbar spine, cervical and lumbar disc replacement, center of rotation, biomechanical testing of the lumbar spine, kinematics of the cervical spine motion, finite element analysis,… and other contents.
Dynamic Reconstruction of the Spine 2nd Edition Daniel H Kim, MD, FAANS, FACS Professor Director of Spinal Neurosurgery Reconstructive Peripheral Nerve Surgery Department of Neurosurgery Memorial Hermann The University of Texas Health Science Center at Houston Houston, Texas Dilip K Sengupta, MD, DrMed Director, Clinical Research Attending Spine Surgeon Texas Back Institute Plano, Texas Frank P Cammisa Jr., MD, FACS Chief Spinal Surgical Service Attending Surgeon Spine Care Institute Hospital for Special Surgery Professor of Orthopedic Surgery Weill Medical College of Cornell University New York, New York Do Heum Yoon, MD, PhD Professor Department of Neurosurgery Yonsei University College of Medicine Seoul, Republic of Korea Richard G Fessler, MD, PhD Professor Department of Neurological Surgery Rush University College of Medicine Chicago, Illinois 701 illustrations Thieme New York • Stuttgart • Delhi • Rio de Janeiro Thieme Medical Publishers, Inc 333 Seventh Ave New York, NY 10001 Executive Editor: Timothy Y Hiscock Managing Editor: Sarah Landis Editorial Assistant: Genevieve Kim Production Editor: Mason Brown International Production Director: Andreas Schabert Senior Vice President, Editorial and Electronic Product Development: Cornelia Schulze International Marketing Director: Fiona Henderson Director of Sales, North America: Mike Roseman International Sales Director: Louisa Turrell Vice President, Finance and Accounts: Sarah Vanderbilt President: Brian D Scanlan Printer: Replika Press Pvt Ltd Library of Congress Cataloging-in-Publication Data Dynamic reconstruction of the spine / [edited by] Daniel H Kim, Dilip K Sengupta, Frank P Cammisa Jr., Do Heum Yoon, Richard G Fessler 2nd edition p ; cm Includes bibliographical references and index ISBN 978-1-60406-873-3 (hardback) ISBN 978-1-60406-874-0 (eISBN) I Kim, Daniel H., editor II Sengupta, Dilip K., editor III Cammisa, Frank P., Jr., editor IV Yoon, Do Heum, editor V Fessler, Richard G., editor [DNLM: Spine surgery Arthroplasty, Replacement-methods Prostheses and Implants WE 725] RD768 617.5'6059 dc23 2014021235 Important note: Medical knowledge is ever-changing As new research and clinical experience broaden our knowledge, changes in treatment and drug therapy may be required The authors and editors of the material herein have consulted sources believed to be reliable in their efforts to provide information that is complete and in accord with the standards accepted at the time of publication However, in view of the possibility of human error by the authors, editors, or publisher of the work herein or changes in medical knowledge, neither the authors, editors, nor publisher, nor any other party who has been involved in the preparation of this work, warrants that the information contained herein is in every respect accurate or complete, and they are not responsible for any errors or omissions or for the results obtained from use of such information Readers are encouraged to confirm the information contained herein with other sources For example, readers are advised to check the product information sheet included in the package of each drug they plan to administer to be certain that the information contained in this publication is accurate and that changes have not been made in the recommended dose or in the contraindications for administration This recommendation is of particular importance in connection with new or infrequently used drugs Some of the product names, patents, and registered designs referred to in this book are in fact registered trademarks or proprietary names even though specific reference to this fact is not always made in the text Therefore, the appearance of a name without designation as proprietary is not to be construed as a representation by the publisher that it is in the public domain Copyright © 2015 by Thieme Medical Publishers, Inc Thieme Publishers New York 333 Seventh Avenue, New York, NY 10001 USA 1-800-782-3488, customerservice@thieme.com Thieme Publishers Stuttgart Rüdigerstrasse 14, 70469 Stuttgart, Germany +49 [0]711 8931 421, customerservice@thieme.de Thieme Publishers Delhi A-12, Second Floor, Sector -2, NOIDA -201301 Uttar Pradesh, India +91 120 45 566 00, customerservice@thieme.in Thieme Publishers Rio de Janeiro, Thieme Publicaỗừes Ltda Argentina Building 16th oor, Ala A, 228 Praia Botafogo Rio de Janeiro 22250-040 Brazil +55 21 3736-3631 Printed in India ISBN 978-1-60406-873-3 Also available as an ebook: eISBN 978-1-60406-874-0 54321 This book, including all parts thereof, is legally protected by copyright Any use, exploitation, or commercialization outside the narrow limits set by copyright legislation without the publisher's consent is illegal and liable to prosecution This applies in particular to photostat reproduction, copying, mimeographing or duplication of any kind, translating, preparation of microfilms, and electronic data processing and storage To my family, wife Anslie, daughters Elise, Rebecca, and Sarah, for their loving support Daniel H Kim To my father, the late Naresh Chandra Sengupta, for giving me the inspiration to make this endeavor Dilip K Sengupta I dedicate this volume to my wife Gail and our children Annie, Trey, and Jack I will always appreciate their support throughout this endeavor Frank P Cammisa Jr To my wife, Young-ran, and my sons, Dong-whan and Dong-min, for their encouragement, tolerance, and unending love I will always appreciate their support throughout this endeavor Do-Heum Yoon To my teachers and mentors, Sean Mullan, Al Rhoton, Fred Brown, and Javad Hekmatpanah, for giving me the opportunity to utilize the knowledge, skills, and advice that they so generously gave to me for the benefit of the many patients for whom I have had the privilege to care Richard G Fessler | 27.02.15 - 10:53 Contents Preface xi Acknowledgments xiii Contributors xv Part Motion Preservation of the Spine in Context Dynamic Stabilization of the Lumbar Spine Dilip K Sengupta Cervical and Lumbar Disc Replacement Do Heum Yoon, Karen M Shibata, Daniel H Kim, and Dilip K Sengupta The Rationale behind Dynamic Posterior Spinal Instrumentation 20 Paul C McAfee, Bryan W Cunningham, and Dilip K Sengupta Part Clinical Biomechanics of the Spine Basic Principles in Biomechanics: Force and Effects 32 Paul C Ivancic Basic Principles in Biomechanics: Loads and Motion (Kinematics) 38 Vikas Kaul, Ata M Kiapour, Constantine K Demetropoulos, Anand K Agarwal, and Vijay K Goel Center of Rotation 46 Dilip K Sengupta Biomechanical Testing of the Lumbar Spine 54 Avinash G Patwardhan, Robert M Havey, and Leonard I Voronov Kinematics of the Cervical Spine Motion 61 Ata M Kiapour and Constantine K Demetropoulos Biomechanical Testing Protocol for Evaluating Cervical Disc Arthroplasty 70 Dilip K Sengupta 10 Finite Element Analysis 75 Ali Kiapour, Vivek Palepu, Ata M Kiapour, Constantine K Demetropoulos, and Vijay K Goel 11 Biomaterials and Design Engineering 85 Michael B Mayor Part Restoration of the Cervical Movement Segment 12 Biomechanical Aspects Associated with Cervical Disc Arthroplasty 90 Dilip K Sengupta 13 Rationale and Indications for Cervical Disc Arthroplasty 98 Jesse L Even, Joon Y Lee, Moe R Lim, and Alexander R Vaccaro vii | 27.02.15 - 10:53 Contents 14 Metal-on-Metal Cervical Disc Prostheses 104 Darren R Lebl, Federico P Girardi, and Frank P Cammisa Jr 15 Design Rationale and Surgical Technique of Metal-on-Poly Cervical Disc Prostheses 112 Darren R Lebl, Federico P Girardi, and Frank P Cammisa Jr 16 Bryan Cervical Disc Device 118 Dilip K Sengupta 17 M6-C Artificial Cervical Disc 125 Carl Lauryssen and Domagoj Coric 18 PEEK and Ceramic Cervical Disc Prostheses 135 Matthew N Songer 19 Complexities of Single- versus Multilevel Cervical Disc Arthroplasty 145 William E Neway III, Lisa Ferreara, and James Joseph Yue 20 Update on FDA IDE Trials on Cervical Disc Arthroplasty 152 Uday Pawar, Abhay Nene, and Dilip K Sengupta 21 Complications of Cervical Disc Replacement 157 Troy Morrison, Richard D Guyer, and Donna D Ohnmeiss 22 Retrieval Analysis of Cervical Total Disc Replacement 162 JayDeep Ghosh, Peng Huang, and Dilip K Sengupta Part Restoration of the Lumbar Motion Segment 23 Kinematics of the Lumbar Spine 172 Haibo Fan 24 Kinetics of the Lumbar Spine 177 Ata M Kiapour, Haibo Fan, and Constantine K Demetropoulos 25 Rationale and Principles of Dynamic Stabilization in the Lumbar Spine 184 Dilip K Sengupta 26 Design Rationale, Indications, and Classification for Pedicle Screw–Based Posterior Dynamic Stabilization Devices 189 Dilip K Sengupta 27 Dynamic Stabilization with Graf Ligamentoplasty 196 Young-Soo Kim, Dong-Kyu Chin, and Dilip K Sengupta 28 Clinical Application of Dynesys Dynamic Stabilization 202 Gilles G DuBois and Dilip K Sengupta 29 Dynamic Stabilization for Revision of Lumbar Spinal Pseudarthrosis with Transition 207 Paul C McAfee, Liana Chotikul, Erin M Shucosky, and Jordan McAfee 30 Nonfusion Stabilization of the Degenerated Lumbar Spine with Cosmic Archibald von Strempel viii 213 | 20.02.15 - 13:27 Restoration of the Lumbar Motion Segment The primary goal of dynamic stabilization is treatment of mechanical back pain due to spinal instability Radicular pain or claudication pain can be adequately treated by decompression alone; the role of additional dynamic stabilization here is only to prevent instability and back pain The evidence of clinical efficacy of a dynamic stabilization device can be established only by application of the device to treat mechanical back pain in the absence of decompression Once that is established, application in conjunction with decompression procedures could be considered 26.6.2 Interspinous Process Distraction Devices Primary indication: Central spinal canal stenosis—with neurogenic claudication Secondary indication: Foraminal stenosis—with radicular symptoms Interspinous process distraction (IPD) devices are ideally suited for indirect, less invasive decompression of the spinal canal or the foramen Conventionally, laminectomy and undercutting facetectomy can achieve a better and direct decompression and ensure more definitive relief of symptoms without an implant To justify routine use of IPDs, decreased morbidity compared with conventional decompression must be established Some IPD proponents recommend them in the treatment of axial back pain Currently, a sound rationale, justification, or evidence in favor of this indication is lacking 26.6.3 Dynamic Stabilization Devices A true dynamic stabilization device should have the capability to control the motion of the instrumented segment and also should be capable of unloading the disc and/or facet joints Therefore, the device needs to be rigidly fixed to the vertebral body This is done by way of pedicle screws, which offer the strongest fixation mechanism to the vertebral body, so that the device is capable of bearing load, sharing load with the disc and facet joint, and thereby unloading these structures By this definition, the pedicle screw–based posterior dynamic stabilization (PDS) devices represent true dynamic stabilization devices IPD devices, on the other hand, floating devices They offer mainly restriction of extension, but they are minimally effective to control other motion These devices are floating between the spinous processes and not anchored to the vertebral bodies These devices can be load bearing except during extension The IPD devices are therefore not a true representative of dynamic stabilization devices, but these are still often classified together with the dynamic stabilization devices because of their nature of nonfusion as well as partial control of motion and loadbearing during extension Some of the PDS devices are too rigid to allow motion preservation These are essentially designed for semirigid fixation to achieve solid fusion, as opposed to rigid fusion using titanium rods, which may have a stress-shielding effect that affects formation of a solid fusion mass Typical devices in this category are the Isobar TTL (Scient’x, Inc., West Chester, PA) and Accuflex (Globus Medical, Inc., Audubon, PA), CD Horizon Legacy Percutaneous PEEK Rod System (Medtronic Sofamor Danek, Memphis, TN), among others The Isobar TTL is a semirigid metal rod 192 with disc springs in the midsection acting as a dampener The CD Horizon Legacy Percutaneous PEEK Rod System is a semirigid alternative to titanium fusion rods These devices are not typical motion preservation devices, and their classification as true PDS devices is inappropriate Facet replacement devices such as the ACADIA Facet Replacement System (Globus Medical, Inc., Audubon, PA) and TOPS System (Premia Spine, Ltd., Herzeila, Israel) are prosthetic devices because they replace the anatomical structure and function in the lumbar motion segment In contrast, dynamic stabilization devices work in conjunction with the motion segment, without replacing any anatomical part of it Their role may be to supplement total disc replacement in the presence of posterior joint disease, converting it to a total motion segment replacement The true pedicle screw–based posterior dynamic stabilization devices like the Dynesys Dynamic Stabilization System (Zimmer Spine, Minneapolis, MN) and Transition Stabilization System (Globus Medical, Inc., Audubon, PA), are introduced in the U.S market as a fusion device under 510(k) approval from the Food and Drug Administration (FDA) This has led to frequent use of these devices as fusion devices The argument in favor of using dynamic stabilization devices for semirigid fixation over rigid fixation to achieve fusion is that the fusion mass may be more robust, being free from stress shielding Their use as dynamic stabilization devices without fusion in the United States represents off-label use only 26.6.4 Classification of the Pedicle Screw–Based Posterior Dynamic Stabilization Devices9 (a) Nonmetallic devices Graf Ligament System (SEM Co., Montrouge, France) Dynesys Transition (b) Metallic devices Bioflex Spring Rod System (Bio-Spine Corp., Seoul, Korea) Stabilimax NZ (Applied Spine Technologies, Inc., Rocky Hill, CT) Cosmic Posterior Dynamic System (Ulrich Medical, Ulm, Germany) (c) Hybrid devices Hybrid devices (metallic component with plastic bumper) a) CD Horizon Agile (Medtronic Sofamor Danek, Memphis, TN) b) NFlex (Synthes, Inc., West Chester, PA) Nonmetallic Devices Graf Ligament: Henry Graf introduced the earliest PDS device for the treatment of low back pain in 1992.1 This may be considered the first-generation PDS device This is a very simple device, consisting of braided polypropylene circular bands, which is looped around the pedicle screw heads under tension Essentially, the device locks the facet joints under compression, presumably preventing any abnormal and pain movement, the so-called instability | 20.02.15 - 13:27 Design for Pedicle Screw-Based Posterior Dynamic Stabilization Devices Henry Graf never presented any peer-reviewed article on the design rationale or mechanism of action of the Graf Ligament The exact mechanism of action of the Graf Ligament therefore remains an educated guess rather than being established on a sound biomechanical basis The apparent clinical success may project the Graf Ligament as an attractive surgical option, particularly in young subjects with intractable back pain secondary to multilevel disc degeneration where fusion is a difficult choice Unfortunately, as a result of the compression applied to the screws, there is a high incidence of radicular symptoms secondary to either disc herniation or foraminal narrowing.12,13 The compressive force may also have a deleterious effect on the facet joint and may lead to back pain Dynesys: The most extensively used PDS device around the world is the Dynesys.10,14 The design rationale is based on improvement over the Graf Ligament, preventing compression between the screws by introduction of a polythene spacer This device may therefore be called a second-generation PDS device The plastic cylinder (sulene-polycarbonate urethane [PCU]) is placed around the cord to apply a distraction force between the pedicle screws, thereby unloading the facet joints, which addresses a disadvantage of the Graf Ligament The biomechanical effect of the Dynesys on the ROM as seen in cadaveric experiments in vitro is diametrically opposite to its in vivo effect after implantation in patients In the cadaver spine, Dynesys holds the motion segment in near full flexion and permits minimal further flexion.15 It can still allow significant extension by an abnormal distraction of the disc space, with the plastic cylinder acting like a fulcrum This is shown by an abnormal negative disc pressure during extension.16 Conversely, the in vivo Dynesys limits extension more than flexion,17 The device acts like an extension stop and becomes a totally load-bearing structure in extension This may explain why screw loosening or breakage had been so rare with the Graf Ligament but is fairly common with the Dynesys, as high as 17% in some clinical series.14,18 Transition Stabilization System: The Transition evolved from the Dynesys, addressing its several design limitations It may therefore be considered a third-generation PDS device It consists of a cylindrical PCU spacer around a polyethylene tetraphthalate (PET) cord similar to the Dynesys There are three major design improvements in the Transition system compared with the Dynesys: (1) use of a regular top-loading pedicle screw, (2) active restoration of lordosis with instrumentation, and (3) increased pedicle-to-pedicle distance excursion by use of an additional bumper The other major design improvement over the Dynesys is that the system comes preassembled, avoiding the need for assembly from components and tensioning of the cord directly onto the spine at surgery The use of regular, toploading pedicle screws simplifies implantation of the system and conversion to fusion as a salvage procedure when needed Whereas the Dynesys may potentially cause loss of lordosis, this system creates an active lordosis of the instrumented segment Finally, the Transition system is adapted for application adjacent to a rigid instrumented fusion segment because it uses regular pedicle screws for the rigid rod as well as the flexible component (▶ Fig 26.4) The Transition device has only been recently approved by the FDA under 510(k) as a fusion device, but no clinical outcome has been reported in the peer-reviewed literature.19 Fig 26.4 The Dynesys (Zimmer Spine) requires three different screw designs to accommodate dynamic stabilization adjacent to a fusion segment (b) It can be inserted preassembled, over a conventional top-loading pedicle screw, and (c) the same screw design may be used for rigid fixation or dynamic stabilization to the adjacent segment Bioflex20: The Bioflex consists of a nitinol coil spring made of mm diameter wires, which is applied between the pedicle screws Nitinol provides increased flexibility The device was developed in Seoul, Korea This device has been used most commonly in conjunction with interbody cages to achieve fusion, although it has also been used as a stand-alone nonfusion device.21 Recently, a titanium version of the device has been approved by the FDA under 510(k) as a fusion device, but no clinical use in the United States has been reported yet Stabilimax NZ22: The Stabilimax NZ was developed by Panjabi This system consists of a dual core spring device, designed to apply soft resistance against both compression and distraction The design rationale is to limit the NZ motion but leave the elastic zone unaffected as much as possible This device started an FDA-controlled investigational device exemption (IDE) clinical trial to assess whether the Stabilimax NZ has equivalent safety and efficacy compared with fusion in patients receiving decompression surgery for the treatment of clinically symptomatic spinal stenosis at one or two contiguous vertebral levels from L1 to S1.23 Due to initial screw failure the manufacturer (Applied Spine Technologies) voluntarily suspended enrollment in August 2008 Following appropriate device modification the trial resumed enrollment in 2009 Cosmic Posterior Dynamic System24: The Cosmic system has a unique design; in contrast to conventional PDS devices, the rods connecting the pedicle screws are rigid, but the pedicle screws have hinged heads that permit motion This is described as a combination of rigid rod and dynamic pedicle screws, which produces posterior dynamic transpedicular stabilization (PDTS) No biomechanical data are available in the peerreviewed literature In a prospective clinical study with a minimum 2-year follow-up, Kaner et al25 reported an equivalent clinical outcome with the Cosmic stabilization system (n = 26) versus rigid fusion (n = 20) in degenerative spondylolisthesis In another clinical outcome study the same group of authors reported that Cosmic stabilization was found safe and effective 193 | 20.02.15 - 13:27 Restoration of the Lumbar Motion Segment in 40 patients with recurrent disc herniation treated with microdiscectomy and PDTS at a minimum 2-year follow-up.26 Hybrid Devices Hybrid devices: The hybrid devices incorporate a combination of a metallic rod connected to a flexible segment, which consists of a nonmetallic bumper The design rationale is to allow shock absorption as well as some degree of pedicle-to-pedicle excursion These devices can be used with a regular top-loading pedicle screw like a regular rigid fusion rod and therefore can be used for “topping off” an adjacent segment to rigid fusion CD Horizon Agile: The CD Horizon Agile system incorporates a plastic cylindrical bumper at the end of a fusion rod, held by a metallic cable in its center This system was launched in 2007 for single-level dynamic stabilization or as a so-called toppingoff hybrid construct adjacent and superior to fusion A study was terminated in December 2007 because of the recall of the implant due to high failure rates One of the study sites recently reported the outcome of 40 patients (18 single-level stabilizations and 22 “topping off” adjacent to fusion) enrolled at that center, and explored which radiographic parameters are linked to failure of this device Thirty-seven of forty patients completed the 2-year follow-up, of which 10 (27%) had implant failure The authors found that two important factors predictive of implant failures are greater disc height and “implant translation.” The authors concluded that implant translation was associated with a high failure rate, which is due to insufficient resistance to shear forces by the implant.27 NFlex: The NFlex was designed to accommodate physiologic motion via a bumper element that permits elongation and angulation during flexion and allows compression during extension The system is semirigid and composed of a titanium rod with one end containing a composite titanium-polycarbonate urethane sleeve positioned over the titanium core Although the device may permit compression and elongation, its ability to permit anteroposterior translation remains a concern The device has been used clinically since fall 2006.28 In a biomechanical study in cadaver spines (n = 7), Mageswaran et al reported that the system displayed stability characteristics similar to a solid, all-metal construct The system essentially transformed a one-level lumbar fusion into a two-level lumbar fusion, with exponential transfer of motion to the fewer remaining discs.29 26.7 Summary Dynamic stabilization was introduced to address mechanical low back pain without fusion, after the limitations of fusion were appreciated The primary goal of pedicle screw-based PDS is to relieve activity-related mechanical back pain The secondary indication is to prevent spinal instability after decompression Unfortunately, most of the dynamic stabilization devices have been introduced in the United States during the last decade without proper understanding of their mechanism of action These devices have been used primarily to prevent spinal instability following decompression or applied to segments adjacent to fusion, without prior evidence of their efficacy to treat spinal instability or back pain It is essential that the efficacy of a dynamic stabilization device be established before it is recommended for use 194 in conjunction with decompression or fusion The spinous process distraction devices have been primarily introduced to treat spinal stenosis with claudication, or radicular pain by indirect decompression, as a less invasive surgical alternative to conventional decompressive laminectomy Product development and marketing are expensive; therefore most clinical trials are aimed at proven success rather than a proper scientific evaluation of clinical efficacy The alternate route for quick introduction of a new device in the U.S market is FDA approval under 510(k) as a fusion device Their use in the United States for dynamic stabilization without an attempt of fusion represents an off-label use Dynamic stabilization has raised a great deal of enthusiasm, theoretical promises, and many expectations As with any new technology, these procedures are apt to breed clinical failures The need for detailed consideration toward design rationale and proper clinical evaluation without confounding factors to prove safety and efficacy is of the utmost importance In the short term all the devices may relieve pain by stiffening the diseased segment, but the biggest challenge with any dynamic stabilization device would be to maintain its structural integrity without fatigue failure despite allowing motion In the spectrum of surgical treatment of degenerative low back pain, the expected role of dynamic stabilization may be treatment of a moderate degree of disc or facet degeneration Fusion still remains the method of choice for advanced disc/facet degeneration and gross instability However, disc degeneration in multiple segments, particularly in young patients with concerns about adjacent segment disease following fusion, will likely constitute the main indication for posterior dynamic stabilization Future applications of dynamic stabilization may include salvage of failed total disc replacement or nuclear replacement and to provide temporary mechanical support for pharmacological treatment aiming for repair or regeneration of the disc Facet replacement devices may be more appropriate for use in conjunction with a disc replacement to achieve total joint replacement of a lumbar spinal unit for combined disc and facet joint degeneration 26.8 References [1] Graf H Lumbar instability: surgical treatment without fusion Rachis 1992; 412: 123–137 [2] Pope MH, Panjabi M Biomechanical definitions of spinal instability Spine 1985; 10: 255–256 [3] Mulholland RC, Sengupta DK Rationale, principles and experimental evaluation of the concept of soft stabilization Eur Spine J 2002; 11 Suppl 2: S198– S205 [4] Frymoyer JW, Krag MH Spinal stability and instability: definitions, classification, and general principles of management In: Dunsker SB, Schmidek HH, Frymoyer JW, Kahn A, eds The Unstable Spine New York: Grune & Stratton; 1986 [5] McNally DS, Shackleford IM, Goodship AE, Mulholland RC In vivo stress measurement can predict pain on discography Spine 1996; 21: 2580–2587 [6] Panjabi MM Clinical spinal instability and low back pain J Electromyogr Kinesiol 2003; 13: 371–379 [7] Fujiwara A, Tamai K, An HS et al The relationship between disc degeneration, facet joint osteoarthritis, and stability of the degenerative lumbar spine J Spinal Disord 2000; 13: 444–450 [8] Nockels RP Dynamic stabilization in the surgical management of painful lumbar spinal disorders Spine 2005; 30 Suppl: S68–S72 [9] Sengupta DK, Herkowitz HN Pedicle screw-based posterior dynamic stabilization: literature review Adv Orthop 2012; 2012: 424268 [10] Stoll TM, Dubois G, Schwarzenbach O The dynamic neutralization system for the spine: a multi-center study of a novel non-fusion system Eur Spine J 2002; 11 Suppl 2: S170–S178 | 20.02.15 - 13:27 Design for Pedicle Screw-Based Posterior Dynamic Stabilization Devices [11] Schnake KJ, Schaeren S, Jeanneret B Dynamic stabilization in addition to decompression for lumbar spinal stenosis with degenerative spondylolisthesis Spine 2006; 31: 442–449 [12] Hadlow SV, Fagan AB, Hillier TM, Fraser RD The Graf ligamentoplasty procedure Comparison with posterolateral fusion in the management of low back pain Spine 1998; 23: 1172–1179 [13] Grevitt MP, Gardner AD, Spilsbury J et al The Graf stabilisation system: early results in 50 patients Eur Spine J 1995; 4: 169–175, discussion 135 [14] Grob D, Benini A, Junge A, Mannion AF Clinical experience with the Dynesys semirigid fixation system for the lumbar spine: surgical and patient-oriented outcome in 50 cases after an average of years Spine 2005; 30: 324–331 [15] Schmoelz W, Huber JF, Nydegger T, Dipl-Ing , Claes L, Wilke HJ Dynamic stabilization of the lumbar spine and its effects on adjacent segments: an in vitro experiment J Spinal Disord Tech 2003; 16: 418–423 [16] Schmoelz W, Huber JF, Nydegger T, Claes L, Wilke HJ Influence of a dynamic stabilisation system on load bearing of a bridged disc: an in vitro study of intradiscal pressure Eur Spine J 2006; 15: 1276–1285 [17] Beastall J, Karadimas E, Siddiqui M et al The Dynesys lumbar spinal stabilization system: a preliminary report on positional magnetic resonance imaging findings Spine 2007; 32: 685–690 [18] Sapkas GS, Themistocleous GS, Mavrogenis AF, Benetos IS, Metaxas N, Papagelopoulos PJ Stabilization of the lumbar spine using the dynamic neutralization system Orthopedics 2007; 30: 859–865 [19] Segupta DK Posterior dynamic stabilization In: Herkowitz HN, Garfin SR, Eismont FJ, Bell GR, Balderston RA, eds Rothman Simeone The Spine 6th ed New York: Elsevier; 2011 [20] Kim YSMB Bioflex spring rod pedicle screw system In: Kim DH CFJ, Fessler RG, eds Dynamic Reconstruction of the Spine New York: Thieme; 2006:340– 346 [21] Kim YS, Zhang HY, Moon BJ et al Nitinol spring rod dynamic stabilization system and Nitinol memory loops in surgical treatment for lumbar disc disorders: short-term follow up Neurosurg Focus 2007; 22: E10 [22] Yue JJ, Timm JP, Panjabi MM, Jaramillo-de la Torre J Clinical application of the Panjabi neutral zone hypothesis: the Stabilimax NZ posterior lumbar dynamic stabilization system Neurosurg Focus 2007; 22: E12 [23] Yue JJ, Malcolmon G, Timm JP The Stabilimax NZ Posterior Lumbar Dynamic Stabilization System In: Yue JJ, Bertagnoli R, McAfee PC, An HS, eds Motion Preservation Surgery of the Spine—Advanced Techniques and Controversies Philadelphia, PA: Saunders Elsevier; 2008:476–482 [24] Karabekir HS, Sedat C, Mehmet Z Clinical outcomes of Cosmic Dynamic Neutralization System: preliminary results of 1-year The Internet Journal of Minimally Invasive Spinal Technology 2008; [25] Kaner T, Dalbayrak S, Oktenoglu T, Sasani M, Aydin AL, Ozer AF Comparison of posterior dynamic and posterior rigid transpedicular stabilization with fusion to treat degenerative spondylolisthesis Orthopedics 2010; 33 [26] Kaner T, Sasani M, Oktenoglu T, Aydin AL, Ozer AF Minimum two-year follow-up of cases with recurrent disc herniation treated with microdiscectomy and posterior dynamic transpedicular stabilisation Open Orthop J 2010; 4: 120–125 [27] Hoff E, Strube P, Rohlmann A, Gross C, Putzier M Which radiographic parameters are linked to failure of a dynamic spinal implant? Clin Orthop Relat Res 2012; 470: 1834–1846 [28] Wallach CJ, Teng AL, Wang JC NFlex In: Yue JJ Bertagnoli R, McAfee PC, An HS, eds Motion Preservation Surgery of the Spine—Advanced Techniques and Controversies Philadelphia, PA: Saunders Elsevier; 2008:505–510 [29] Mageswaran P, Techy F, Colbrunn RW, Bonner TF, McLain RF Hybrid dynamic stabilization: a biomechanical assessment of adjacent and supraadjacent levels of the lumbar spine J Neurosurg Spine 2012; 17: 232–242 195 | 20.02.15 - 13:27 Restoration of the Lumbar Motion Segment 27 Dynamic Stabilization with Graf Ligamentoplasty Young-Soo Kim, Dong-Kyu Chin, and Dilip K Sengupta Degenerative involution of the spine causes destruction of the spinal stabilizer, which consists of bone, ligament, joint capsule, and disc, which substantially leads to hypermobility and instability of the spine.1,2 As the degenerative changes in the lumbar spine progress, the spinal canal is also compressed by a protruded disc, hypertrophied facet, and ligaments.3,4 In the surgical treatment of such patients, decompression of the spinal canal is mandatory But the structures that are removed during decompressive laminectomy are elements of a stable spine, and postlaminectomy iatrogenic spinal instability may become complicated.5 In patients with preexisting instability or a high risk of postlaminectomy iatrogenic spinal instability, surgical insertion of an internal fixation device, as well as spinal arthrodesis, have been the usual solutions.6–9 The recent development of internal fixation devices such as the pedicle screw fixation system and interbody fusion cages has allowed rigid spinal stability and outstanding surgical outcomes.6,9 However, acquiring stiffness and spinal stability has required the sacrifice of the unique physiologic function (i.e., motion) of the spinal segment, which is, without doubt, a disadvantage Generally, the rigid fixation system has been used to treat lumbar instability However, it can result in complications such as nonunion, screw loosening, screw fracture, and flat back syndrome.10,11 Rigid fixation also increases the biomechanical stresses on the adjacent segments to the fusion level.12,13 Clinically, the results of several long-term follow-up studies have suggested that spinal fusion might cause deterioration of the adjacent segment.14,15,16 The complications of rigid fixation have led to the invention of a nonfusion technology that is more physiological than any other fixation devices.17,18,19 The concept of “dynamic stabilization” is to restrict the hypermobility of an unstable spinal segment rather than eliminating it Among the types of soft stabilization systems, the Graf soft stabilization system (SEM Co., Montrouge, France) was one of the first relatively widely practiced methods.19 27.1 Concept and Rationale The Graf soft stabilization system was invented by Henry Graf.19 It consists of the surgical implantation of a titanium pedicle screw linked with polyester threaded bands as a ligament to connect the pedicle screws across the unstable segment (▶ Fig 27.1) Graf believed that instability was related to the development of an abnormal rotatory movement This abnormal rotatory movement and distraction at the facet joints might be a cause of low back pain The basic concept is to dynamically stabilize abnormal rotatory movements in physiological lordosis using the Graf band, which results in the alteration of annular and end plate load bearing This posterior immobilization in lordosis closes degenerative annular tears and degenerative gaps in the facet joint, allowing the healing of damaged tissues.19,20 Some biomechanical studies using cadavers show that Graf ligamentoplasty reduces the range of motion and provides flexibility under some loading conditions.21,22,23 Strauss et al21 196 Fig 27.1 Graf pedicle screws and polyester tension bands The Graf soft stabilization system consists of the surgical implantation of titanium pedicle screws linked with polyester threaded bands as a ligament to connect the pedicle screws across the unstable segment (Used with permission from SEM Co., Montrouge, France.) found that Graf ligamentoplasty significantly reduced range of motion for flexion-extension but had little effect on the translation motion This finding suggests that Graf ligamentoplasty had the potential to treat “flexion instability.” The advantages of Graf ligamentoplasty are as follows: (1) a less invasive procedure, (2) more physiological mechanics, (3) reduced biomechanical stress on adjacent segments, (4) no risk of pseudarthrosis, and (5) no donor-site pain.24 The authors think the Graf soft stabilization system gave birth to the concept of dynamic stabilization, making surgeons realize the significance of the ideal stiffness Undoubtedly, this progress is considered a big leap in the field of degenerative lumbar spine surgery 27.2 Indications and Contraindications Our surgical indication for Graf ligamentoplasty is chronic degenerative lumbar disc disorders with or without segmental instability Each patient has complained about chronic low back pain that has been resistant to conservative treatment over a 6month or longer period Initially, degenerative black disc and facet syndrome were included after a specific diagnostic protocol such as discography and facetogram However, the clinical outcomes in those entities were not as good Now that a certain amount of experience in Graf ligamentoplasty has been gained, degenerative black disc and facet syndrome, which Graf initially listed as indications, have been excluded from the indications In chronic degenerative disc disorders with canal stenosis, Graf ligamentoplasty can be used after decompressive laminectomy or discectomy, which can prevent postoperative iatrogenic instability, and this turns out to be our major indication | 20.02.15 - 13:27 Dynamic Stabilization with Graf Ligamentoplasty Grade I spondylolisthesis and degenerative slipping ( < 25%) of the vertebral body might be indications too However, we have to be aware that Graf ligamentoplasty is not a procedure that can completely replace spinal fusion and arthrodesis fixed retractors are replaced by blunt retractors, held by an assistant After the articular area is uncovered without opening the capsule, the transverse process is exposed This allows the surgeon to identify the entry for implant insertion 27.2.1 Indications for Graf Ligamentoplasty 27.3.3 Implant Placement Chronic degenerative disc disease with or without canal stenosis a) When postoperative iatrogenic instability is anticipated, Graf ligamentoplasty may be indicated Multiple spondylotic lumbar spinal stenosis a) After wide decompressive laminectomy, Graf ligamentoplasty may prevent postoperative iatrogenic instability Lumbar instability syndrome a) Flexion instability is a good indication Stabilization of the adjacent segment above or below the main pathology a) Graf ligamentoplasty may reduce the mechanical stress imposed on the adjacent segment Degenerative spondylolisthesis ( < 25%) of the vertebral body Interbody fusion should be added in the following conditions: a) Postdiscectomy b) Modic degeneration c) Translational instability d) Narrowed disc height or neural foramen e) When anterior column support is indicated 27.2.2 Contraindications for Graf Ligamentoplasty Isthmic spondylolisthesis Retrolisthesis Degenerative spondylolisthesis greater than grade I Tumors, infection, or trauma Scoliosis deformity Rigid kyphotic deformity The pedicular implant entry point is located approximately halfway between the superior and inferior edges of the transverse process at the junction of the articular processes It is sometimes necessary to remove some of the external superior articular facet to free space between the implant and the vertebra At the insertion point, the remaining bony crest should be removed using a gouge The sacral implant entry point is located ~5 mm from the articular facet L5–S1 and halfway from the foramen S1 Great care should be exercised for sacral implant placement It should follow a path parallel to the L5 implant in the direction of the sacral promontory To reinforce insertion quality, it is recommended to secure the attachment by slightly perforating the anterior cortical promontory without penetrating the cortex wall completely The awl is used to perforate a mm hole in the cortical bone With gentle, twisting motions, the pedicular path is determined by using a graduated blunt curette The appropriate screw length is determined by reading the graduation on the blunt curette The implant placement follows the anatomical pedicular axis, which varies from one vertebra to another Selection of screw size is based on the length measured in the preceding step, and the diameter is determined on preoperative imaging studies Implant insertion is made with the male hexagonal screwdriver or the implant holder The length of these instruments allows the surgeon to insert screws through a skin counterincision To unscrew the implant holder, one of the two implant holders is needed (▶ Fig 27.2) 27.3.4 Band Placement Band size varies by 2.5 mm increments The bands are measured with the band size measurer, which is used to grasp the head of the implanted pedicular screws The measurer is used 27.3 Operative Techniques 27.3.1 Patient Operative Position The patient operative position is derived from one described by McNab However, the trunk is placed in a horizontal position with pressure on the upper limbs to obtain an “on-all-fours” position The cushion is mounted to the table to provide mild support of the rib cage so that it allows the abdomen to be dependent In this position, the lumbar spine is left in a mean supple lordosis Care is taken to avoid undue pressure on bony prominences, genitalia, and neurovascular structures A radiological control allows detection of the involved vertebrae corresponding with the cutaneous guide 27.3.2 Surgical Approach A midline linear incision and exposure are made above the involved segments The surgical approach is made in an asymetrical manner: Fig 27.2 Implant placement (a) Implant insertion is made with the male hexagonal screwdriver or the implant holder (b,c) To unscrew the implant holder, one of the two implant holders is needed (Used with permission from SEM Co., Montrouge, France.) 197 | 20.02.15 - 13:27 Restoration of the Lumbar Motion Segment to calculate the desired tension and size of the band to be used The tension chosen must be sufficient to eliminate local instability For bands smaller than 25 mm, tension with graduation is sufficient (read band size measurer) Over 25 mm, graduation 10 is suitable The band is placed on the implant head using the band tension forceps by making small rotational horizontal movements Prior to band placement, the implants must be arranged so that their upper collar is face to face The band pusher may help to slip the band over the implant head and to control band tension To secure band placement a half rotation is applied to position the screw top hemispherical flange in the opposite direction to the other screw Such rotation retains the bands securely in position For a two-level construction, a titanium screw cap is placed on the top of the middle implant to secure the band’s positioning (▶ Fig 27.3) 27.3.5 Operative Precautions It is important to protect the bands from abrasion by the facet joints Therefore the following are recommended: ● Check that sufficient space is left between the metallic implant and the external face of the articular facet ● Check that the band does not rub against the facet ● Prepare and correct the path of the band with a gouge forceps or a chisel ● Do not screw the metallic implant tight; this will cause band– bone contact 27.3.6 Clinical Outcome with Graf Ligament Stabilization Clinical outcome in the short-term follow-up (up to years) is reported to be as good as that with conventional fusion Grevitt et al presented their early clinical results in 50 cases (mean age 41, 32 F, 18 M) with low back pain.25 All had chronic back pain, but the mean period of severe disability was 24 months The mean preoperative Oswestry Disability Index (ODI) score was 59% The average period of follow-up was 24 months (range 19–36 months) At the latest review, the mean ODI score was 31% The clinical results were classified as “excellent” or “good” in 72% of patients, “fair” in 10%, “the same” in 16%, and “worse” in 2% All but three patients felt that surgery was worthwhile The results have not deteriorated over the period of follow-up However, the recognized incidence of new-onset radicular pain after Graf ligamentoplasty is secondary to foraminal stenosis in nearly 25% of cases The long-term outcome with Graf ligament stabilization has conflicting reports in the literature Gardner and Pande followed up the foregoing series of cases and presented a 7-year outcome (range 5.6–8.5 years) in 40 of the 50 patients, of whom 31 still had Graf instrumentation in situ.26 The authors reported excellent and good subjective results in 62% of patients; 61% reported significant or total relief of low-back pain, and 77% never or occasionally used analgesics The mean ODI score was 59 ±10% preoperatively and 37.7 ±14% after years (p < 0.05) The results of this study suggest that the beneficial effects of Fig 27.3 Band placement (a) The band size measurer is used to grasp the head of the implanted pedicular screws (b,c) The band is placed on the implant head using the band tension forceps by making small rotational horizontal movements (d) The band pusher may help to slip the band over the implant head and to control band tension (e) One-half rotation is applied to position the screw top hemispherical flange in the opposite direction of the other screw (f) For a two-level construction, a titanium screw cap is placed on the top of the middle implant to secure the band’s positioning (Used with permission from SEM Co., Montrouge, France.) 198 | 20.02.15 - 13:27 Dynamic Stabilization with Graf Ligamentoplasty Graf ligamentoplasty are sustained in the longer term in spite of the presence of an established degenerative process In another long-term study, Markwalder and Wenger27 presented results with an average follow-up of 7.4 years in 39 highly selected, consecutive patients Their patient population included young patients with lumbar mechanical disorders resistant to conservative treatment with (1) no or mild facet joint degeneration, (2) minor disc degeneration, (3) welltrained low back muscles, (4) pain relief after trial anesthesia, and (5) a probative rigid plastic jacket After 7.4 years the clinical results in 39 patients were excellent, good, fair, unchanged, and worse in 43.6, 20.5, 10.2, 23.1, and 2.6%, respectively Seven unchanged patients were converted to arthrodesis In the questionnaire 66.6% reported total disappearance of back pain, in 25.7% it was significantly less, and in 7.7% back pain was a bit less The visual analog scale for low back pain was in 69.2%, 2.5 in 15.4%, and in 15.4% of patients For leg pain it was nil in 92.3% and 2.5 in 7.7% The authors concluded that soft system stabilization of lumbar motion segments in young patients with painful mechanical disease resistant to conservative treatment yields favorable long-term results only in a highly select patient population On the other hand, Hadlow et al28 performed a retrospective matched case-control comparison between Graf ligamentoplasty and instrumented posterolateral fusion in a consecutive series of 83 patients suffering from low back pain, operated by a single surgeon Patients underwent either soft tissue stabilization or posterolateral fusion with pedicle screw instrumentation, according to their preference after informed consent that the soft tissue stabilization system, although experimental, was a reversible procedure There was no significant difference between these two patient groups in their preoperative demographics, number of segments instrumented, or back pain scores The authors found a significantly better outcome, when measured by the Low-Back Outcome Score in the group of patients managed by posterolateral fusion at year (p = 0.02), although at years the difference was less (p < 0.34) Patients with facet joint–related pain did no better after soft tissue stabilization than did patients of other diagnostic groups The patients receiving compensation did better at year after fusion (p < 0.003), although again the difference was less marked at years (p = 0.09) There was a trend toward a higher revision rate in the soft tissue stabilization system group (p = 0.11) at year with a statistically significant (p = 0.01) difference apparent at years The authors concluded that soft stabilization using the Graf ligament produces a worse outcome at year and a significantly higher revision rate at years Kanayama et al29 reported a minimum 10-year follow-up of posterior dynamic stabilization using the Graf artificial ligament in a total of 43 consecutive patients with degenerative spondylolisthesis in 23 patients, disc herniation with flexion instability in 13 patients, spinal stenosis with flexion instability in patients, and degenerative scoliosis in patients Singlelevel procedures were performed in 36 patients; multilevel procedures were performed in patients The authors reported that the disability due to low back pain and/or sciatic symptoms was significantly improved in the patients with degenerative spondylolisthesis or flexion instability However, degenerative scoliosis and/or laterolisthesis were associated with poor clinical improvement In radiographic assessment, segmental lordosis was maintained in 10.9 degrees, and flexion-extension motion was averaged to 3.6 degrees at the final follow-up Facet arthrodesis eventually occurred in 14 patients (32.6%) at an average of 82 months postsurgery Additional surgeries were required in patients (7.0%) for adjacent segment pathologies The authors concluded that the long-term results with Graf ligamentoplasty showed that Graf ligamentoplasty was an effective treatment option for low-grade degenerative spondylolisthesis and flexion instability However, this procedure had limitations in regard to correcting spinal deformity, and the authors did not advocate its use for the treatment of degenerative scoliosis and lateral listhesis In 2006, in the previous edition of this book, Kim et al presented a series of 106 patients with lumbar spinal degenerative disc disease with canal stenosis who were treated with the Graf soft stabilization system following decompressive laminectomies.30 Sixty patients had angular instability, and 21 translational instability Graf ligamentoplasty was found particularly effective in patients with flexion instability due to degenerative facet loosening These corrections of instability were due to its role as an artificial ligament of the Graf soft stabilization system (▶ Fig 27.4) The authors concluded that the radiological outcome was good, but the clinical outcome was not satisfactory, and they felt that the main limitations of Graf ligamentoplasty were the lack of anterior column support and the production of joint overlocking In our series of Graf ligamentoplasty, 27.4 Graf Ligamentoplasty with Anterior Column Support–Hybrid Stabilization The posterior buckling of the ligamentum flavum and the joint capsule after Graf ligament stabilization may compress the nerve root at the neural foramen Graf ligamentoplasty after discectomy may also result in nerve root compression at the Fig 27.4 Radiographs showing Graf ligaments and pedicle screws (a) Anteroposterior and (b) lateral radiographs were obtained after decompression at L4–L5 was performed and the Graf implant was inserted bilaterally 199 | 20.02.15 - 13:27 Restoration of the Lumbar Motion Segment Fig 27.5 Radiographs showing Graf ligamentoplasty and anterior column support with interbody fusion (a) Preoperative magnetic resonance imaging (b) Lateral radiograph showing degenerative slipping at the L4–L5 level There may be an advanced loss of disc height and a loss of anterior column support after decompressive laminectomy and Graf ligamentoplasty (c) Postoperative lateral radiograph showing Graf ligamentoplasty and anterior column support with interbody fusion cages neural foramen The intervertebral disc is a key structure that supports the anterior column when applying compressive force to the pedicle screws, and the disc space should be preserved to avoid joint overlocking and iatrogenic neuroforaminal stenosis There may be an advanced loss of disc height and a loss of anterior column support with Graf ligamentoplasty in the following conditions: (1) postdiscectomy, (2) Modic degeneration, (3) translational instability, and (4) narrowed disc height or neural foramen Kim and Chin30 recommended that anterior column support with interbody fusion should be used in such conditions (▶ Fig 27.5) They modified the concept of Graf ligamentoplasty: the main pathological segment is stabilized with posterior lumbar interbody fusion (PLIF) The main pathological segment and the adjacent segment are stabilized with the Graf soft stabilization system to prevent adjacent segment degeneration This posterior instrumentation with the Graf band can also help the fusion process in PLIF Kim et al31 reported a total of 120 patients with lumbar spinal degenerative disc disease with canal stenosis who were treated with PLIF and Graf ligamentoplasty They reported a satisfactory clinical outcome and 110 patients (88.7%) showed an excellent or good outcome.31 27.5 Summary Traditionally, spinal fusion has been the mainstay of surgical procedures for the treatment of degenerative lumbar instability However, rigid fixation increases the biomechanical stresses on the segments adjacent to the fusion level,12,13 leading to transitional disease This complication of rigid fixation has led to the invention of a more physiologic fixation device with dynamic stabilization Even in dynamic stabilization, anterior column support is crucial Because the intervertebral disc is a key structure to support the anterior column, dynamic stabilization without anterior column support is likely to fail The long-term outcome of Graf ligament stabilization is not favorable A hybrid stabilization with fusion of the main pathological segment, and soft stabilization of the adjacent segment using the Graf ligament, may 200 be expected to produce a better long-term clinical outcome Although one can expect a better outcome with modified Graf ligamentoplasty with anterior column support, this procedure cannot completely replace spinal arthrodesis 27.6 References [1] Panjabi MM, White AA III Basic biomechanics of the spine Neurosurgery 1980; 7: 76–93 [2] Schneck CD The anatomy of lumbar spondylosis Clin Orthop Relat Res 1985; 193: 20–37 [3] Kirkaldy-Willis WH, Farfan HF Instability of the lumbar spine Clin Orthop Relat Res 1982; 165: 110–123 [4] Kirkaldy-Willis WH, Wedge JH, Yong-Hing K, Reilly J Pathology and pathogenesis of lumbar spondylosis and stenosis Spine 1978; 3: 319–328 [5] Posner I, White AA III Edwards WT, Hayes WC A biomechanical analysis of the clinical stability of the lumbar and lumbosacral spine Spine 1982; 7: 374–389 [6] Roy-Camille R, Saillant G, Mazel C Internal fixation of the lumbar spine with pedicle screw plating Clin Orthop Relat Res 1986; 203: 7–17 [7] Luque ER The anatomic basis and development of segmental spinal instrumentation Spine 1982; 7: 256–259 [8] McGuire RA, Amundson GM The use of primary internal fixation in spondylolisthesis Spine 1993; 18: 1662–1672 [9] Steffee AD, Biscup RS, Sitkowski DJ Segmental spine plates with pedicle screw fixation A new internal fixation device for disorders of the lumbar and thoracolumbar spine Clin Orthop Relat Res 1986; 203: 45–53 [10] Deburge A Modern trends in spinal surgery J Bone Joint Surg Br 1992; 74: 6–8 [11] Frymoyer JW, Hanley EN Jr Howe J, Kuhlmann D, Matteri RE A comparison of radiographic findings in fusion and nonfusion patients ten or more years following lumbar disc surgery Spine 1979; 4: 435–440 [12] Schlegel JD, Smith JA, Schleusener RL Lumbar motion segment pathology adjacent to thoracolumbar, lumbar, and lumbosacral fusions Spine 1996; 21: 970–981 [13] Hilibrand AS, Robbins M Post-arthrodesis adjacent segment degeneration In: Vaccaro A, Anderson DG, Crawford A, et al, eds Complications of Pediatric and Adult Spinal Surgery New York: Marcel Dekker; 2003 [14] Lee CK Accelerated degeneration of the segment adjacent to a lumbar fusion Spine 1988; 13: 375–377 [15] Lehmann TR, Spratt KF, Tozzi JE et al Long-term follow-up of lower lumbar fusion patients Spine 1987; 12: 97–104 [16] Leong JC, Chun SY, Grange WJ, Fang D Long-term results of lumbar intervertebral disc prolapse Spine 1983; 8: 793–799 [17] Ray CD The PDN prosthetic disc-nucleus device Eur Spine J 2002; 11 Suppl 2: S137–S142 | 20.02.15 - 13:27 Dynamic Stabilization with Graf Ligamentoplasty [18] Cinotti G, David T, Postacchini F Results of disc prosthesis after a minimum follow-up period of years Spine 1996; 21: 995–1000 [19] Graf H Lumbar instability: surgical treatment without fusion Rachis 1992; 412: 123–137 [20] Kanayama M, Hashimoto T, Shigenobu K Rationale, biomechanics, and surgical indications for Graf ligamentoplasty Orthop Clin North Am 2005; 36: 373–377 [21] Strauss PJ, Novotny JE, Wilder DG, Grobler LJ, Pope MH Multidirectional stability of the Graf system Spine 1994; 19: 965–972 [22] Wild A, Jaeger M, Bushe C, Raab P, Krauspe R Biomechanical analysis of Graf’s dynamic spine stabilisation system ex vivo Biomed Tech (Berl) 2001; 46: 290–294 [23] Hasegawa K, Takano K, Endo N et al A biomechanical study on the stabilizing effect of Graf ligamentoplasty in a graded destabilization model of porcine lumbar spine [in Japanese] Rinsho Seikei Geka 2004; 39: 133–140 [24] Gardner ADH An alternative concept in the surgical management of lumbar degenerative disc disease flexible stabilization In: Margulies JY, ed Lumbosacral and Spinopelvic Fixation Philadelphia: Lippincott-Raven;1992:889–905 [25] Grevitt MP, Gardner AD, Spilsbury J et al The Graf stabilisation system: early results in 50 patients Eur Spine J 1995; 4: 169–175, discussion 135 [26] Gardner A, Pande KC Graf ligamentoplasty: a 7-year follow-up Eur Spine J 2002; 11 Suppl 2: S157–S163 [27] Markwalder TM, Wenger M Dynamic stabilization of lumbar motion segments by use of Graf’s ligaments: results with an average follow-up of 7.4 years in 39 highly selected, consecutive patients Acta Neurochir (Wien) 2003; 145: 209–214, discussion 214 [28] Hadlow SV, Fagan AB, Hillier TM, Fraser RD The Graf ligamentoplasty procedure Comparison with posterolateral fusion in the management of low back pain Spine 1998; 23: 1172–1179 [29] Kanayama M, Hashimoto T, Shigenobu K, Togawa D, Oha F A minimum 10-year follow-up of posterior dynamic stabilization using Graf artificial ligament Spine 2007; 32: 1992–1996, discussion 1997 [30] Kim YS, Chin DK Graf soft stabilization: Graf ligamentoplasty In Kim DH, Cammisa FP, Fessler RG, eds Dynamic Reconstruction of the Spine New York, NY: Thieme; 2006 [31] Kim YS, Cho YE, Jin BH, Chin DK, Yoon DH Soft Graf fixation and posterior lumbar interbody fusion in multiple degenerative lumbar diseases J Korean Neurosurg Soc 1998; 27: 229–236 201 | 20.02.15 - 13:27 Restoration of the Lumbar Motion Segment 28 Clinical Application of Dynesys Dynamic Stabilization Gilles G DuBois and Dilip K Sengupta During the course of the natural evolution of vertebral disc degeneration, from incipient discopathy to stenosis with fixed terminal deformation, the functional tripod (disc and facets) will experience a long period of destabilization with abnormal movements Dynamic stabilization with the Dynesys Dynamic Stabilization System (Zimmer Spine, Inc., Warsaw, IN) provides distinct benefits (▶ Fig 28.1) in the phase of degeneration where symptoms are caused by discovertebral dyskinesis; that is, between early stages of symptomatic degenerative changes of the spinal segment and structural deformities associated with spontaneous ossification The goal of dynamic stabilization with Dynesys is to realign and stabilize one or more intervertebral lumbar or lumbosacral segments in a position close to the normal anatomic position, with the intent of encouraging a return to improved intervertebral physiology while enabling a certain degree of range of motion 28.1 Technical Aspects Dynesys (Dynamic Neutralization System for the Spine) was developed by DuBois in 1994 This may be considered to be the second-generation dynamic stabilization It improves over the first-generation posterior dynamic stabilization (PDS) system, the Graf ligament, by incorporating a plastic cylinder between the pedicle screws, which prevents narrowing of the neural foramen The Dynesys system consists of titanium alloy (Protasul 100) pedicle screws, polyester (Sulene-polyethylene tetraphthalate [PET]) cords, and polycarbonate urethane (Sulene-PCU) spacers The cord controls the range of motion in flexion, whereas the spacer limits extension movements, enabling the posterior elements to be repositioned in accordance with a near normal anatomical situation Several biomechanical in vitro experiments were conducted to study the efficacy of the system These were discussed in greater detail in Chapter 25 Fatigue testing of the complete assembly was performed to 10 million cycles, which is believed to represent a time in vivo of approximately years In an initial Fig 28.1 (a) Functional model of Dynesys, and (b) an example on a sawbone model phase (1–2 million cycles), the system showed stress relaxation and remained stable at a substantial load level afterward This internal bracing device enables the posterior elements, annulus, and posterior longitudinal ligament to be retensioned It repositions the articulating surfaces to the areas in which they function normally, suppresses dyskinetic movements caused by loss of viscoelasticity of the disc, and restores the posterior pretensioning It thus brings about anatomic conditions of the intervertebral joint that enable restoration of a better discovertebral physiology, allowing a certain degree of freedom to be preserved due to the elasticity of the spacer It limits the impact of the biomechanical stresses on the adjacent levels 28.2 Indications The main goal of Dynesys is to address dynamic instability with autoreducible lesions in the early stages of degeneration as defined by Kirkaldy-Willis.1 These include dynamic stenosis or stenosis with degenerative olisthy as evidenced by either or both neurogenic pain and low back pain (▶ Fig 28.2) Other indications for Dynesys are mono- or multisegmental degenerative disc disease (DDD) causing low back pain as well as iatrogenic instability following decompression Fig 28.2 A 40-year-old woman presented with degenerative disc disease in combination with spondylolisthesis Dynesys (Zimmer Spine) was implanted without any additional surgical procedure X-rays show (a) preoperative and (b) immediate postoperative functional X-rays and (c) anteroposterior and lateral X-rays years postoperatively 202 | 20.02.15 - 13:27 Clinical Application of Dynesys Dynamic Stabilization In multilevel DDD, Dynesys may also be combined with a fusion procedure such as posterior lumbar interbody fusion (PLIF), depending on the severity of segmental disc disruption Dynesys is not indicated as a primary stabilization method in lytic (isthmic) spondylolisthesis and severe degenerative scoliotic or kyphotic deformation 28.3 Surgical Technique The surgical approach is along the median line, opening the lumbar aponeurosis, rasping the paravertebral muscles if the surgeon wishes to carry out intracanal activities aimed at associated decompression at the same time as the dynamic stabilization procedure If no intracanal procedure is needed and if the lesion is of the dynamic stenosis type due to a soft lesion, then an intermuscular bilateral approach according to Wiltse or an intermuscular paraspinal approach can be performed This approach does not interfere with the posterior muscles or the lumbar aponeurosis and provides direct access to the articular–transverse junction without interfering with the articulating surface and its capsule It also enables the screw to be implanted at an angle that is almost always perfect Whatever approach is used, it is important not to interfere with the articular processes and their capsule The point of intrapedicular penetration must be located at the external junction of the articular and transverse surfaces The steps for posterior compression or distraction of the screw heads enable determination of the exact length (6– 45 mm) of the required spacer This choice depends on the pathology being treated and on the degree of stabilization to be achieved With interpedicular distraction, the length of the spacer must ensure that the end plates of the level where Dynesys is implanted are perfectly parallel to avoid causing kyphosis of the segments Restoration of lordosis of the segments may be left to the surgeon’s discretion; however, hypercompression of the facet joints must be avoided under all circumstances because this may be detrimental to the appropriate functioning of the device as well as contrary to the underlying concept The assembly is completed with insertion of the cord and tensioning of the system 28.4 Disc Regeneration with Dynamic Stabilization Various “regeneration” phenomena have been described anecdotally by Dynesys users One prospective cohort study specifically addresses this Some authors reported a partial restoration of the T2-weighted magnetic resonance imaging (MRI) signal of the nucleus (▶ Fig 28.3) The latter is a strong indicator for disc rehydration This finding is in accordance with the results of an experimental study in New Zealand in white rabbits, where it was found that degenerated dehydrated discs may regenerate after undergoing dynamic distraction.2 Because the intradiscal liquid can be mobilized by the effect of pressure, and these pressures are redistributed and returned to a situation that resembles normalcy more closely, the alternating movements may be restored between the subchondral bone and the intradiscal environment Given that this move- Fig 28.3 (a) A 43-year-old woman presented with multilevel pathology necessitating discectomy, foraminotomy, and posterolateral fusion in L5–S1 and Dynesys implantation in L3–L4 (b) Magnetic resonance imaging 18 months postoperatively shows rehydration of the disc at the Dynesys level ment of liquid governs the balance between cell anabolism and catabolism, it will allow restoration of the fundamental substance, consisting of a highly hydrated proteoglycan gel inside the network of collagen (mainly type II) This interpretation was prompted by the clinical improvement of those patients who had benefited from dynamic stabilization and by the findings of the radiological follow-up It currently remains, however, a purely intellectual construction to the extent that it is not supported by any histologic or biochemical studies Vaga et al3 investigated the long-term effect of dynamic stabilization in vivo, through the quantification of glycosaminoglycan (GAG) concentration within instrumented and adjacent levels by means of the delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) protocol The authors evaluated 10 patients with chronic low back pain with a dGEMRIC protocol to quantify GAG concentration before and months after Dynesys stabilization (▶ Fig 28.4) The authors found that the Pfirrmann scale could not detect any change, whereas dGEMRIC data already showed a general improvement in the instrumented levels: GAG was increased in 61% of the instrumented levels, whereas 68% of the noninstrumented levels showed a decrease in GAG, mainly in the posterior disc portion The authors concluded that the dynamic stabilization of the lumbar spine is able to stop and partially reverse the disc degeneration, especially in seriously degenerated discs, while incrementing the stress on the adjacent levels, where it induces a matrix suffering and an early degeneration 28.5 Clinical Outcome The initial clinical results were reported by Stoll et al in 2002.1 Their prospective, multicenter study evaluated the outcome of a consecutive series of 83 patients treated with Dynesys for lumbar instability conditions, the pathology mainly involving lumbar stenosis (60% of patients) and degenerative discopathy (24%) Thirty patients had had previous lumbar surgery The mean age at operation was 58.2 (range, 26.8–85.3) years; the 203 | 20.02.15 - 13:27 Restoration of the Lumbar Motion Segment Fig 28.4 Example of ΔT1 maps obtained in three implanted (IMP) and two adjacent (ADJ) disc levels, presurgery, at months (FU1), and after years (FU2) from surgery Lower ΔT1 values, associated with high concentrations of glycosaminoglycans (GAG), are expressed in blue tones, whereas high values, associated with low concentrations of GAG, are in red tones In the colorbar, the value of 70 ms, used as normal threshold for the classification of presurgical disc segments, is indicated with an arrow (Reproduced with permission from Ciavarro C, Caiani EG, Brayda-Bruno M, et al Mid-term evaluation of the effects of dynamic neutralization system on lumbar intervertebral discs using quantitative molecular MR imaging J Magn Reson Imaging 2012;35 (5):1145–1151.) mean follow-up time was 38.1 months (range, 11.2–79.1) In 56 patients the Dynesys instrumentation was combined with a direct decompression procedure Pain, function as measured by the Oswestry Disability Index (ODI), and radiological data were evaluated pre- and postoperatively and improved significantly from baseline to follow-up as follows: back pain scale from 7.4 to 3.1, leg pain scale 6.9 to 2.4, ODI 55.4 to 22.9% Most of the complications were unrelated to the implant Additional lumbar surgery in the follow-up period included implant removal and conversion into spinal fusion with rigid instrumentation for persisting pain in three cases, laminectomy of an index segment in one case, and screw removal due to loosening in one case In seven patients, adjacent segment degeneration necessitated further surgery The authors concluded that the study results compare favorably with those obtained by conventional procedures; however, mobile stabilization is less invasive than fusion The natural course of polysegmental disease in some cases necessitates further surgery as the disease progresses Dynamic stabilization with Dynesys proved to be a safe and effective alternative in the treatment of unstable lumbar conditions 204 Cakir et al4 published a retrospective comparative study in 2003 where they analyzed the functional outcome (ODI) and the quality of life (Short Form [SF]-36 Health Survey) of patients with degenerative lumbar instability with spinal stenosis who underwent decompression surgery with dorsoventral fusion or decompression surgery with posterior dynamic stabilization In a small group of patients (n = 20), they showed a slightly better outcome for the Dynesys group Furthermore, hospital stay and operation time were much shorter in the nonfusion group They conclude that dynamic stabilization seems to be a promising alternative to fusion in patients with degenerative instability with spinal stenosis but point out the need for bigger studies Putzier et al5 compared the outcome of discectomy alone (49 cases) with discectomy followed by stabilization with Dynesys (35 cases) for the treatment of symptomatic disc prolapse The mean duration of follow-up was 34 months Clinical symptoms, ODI score, and visual analog scale (VAS) score improved significantly in both groups after months At follow-up, a significant increase in the ODI score and in the VAS score was seen only in the nonstabilized group In the Dynesys group, no progression of disc degeneration was noted at follow-up, whereas radiological signs of accelerated segmental degeneration existed in the solely nucleotomized group There were no implant-associated complications The authors concluded that the Dynesys system is useful to prevent progression of initial degenerative disc disease of lumbar spinal segments after discectomy Grob et al6 published a retrospective study where 50 patients were implanted with the Dynesys and the results of 31 patients (20 F, 11 M) with a follow-up time of at least years were presented Mean age was 50 ± 13 standard deviation (SD) The primary indication for surgery was degenerative disease (disc/ stenosis) with associated “instability.” Thirteen of 31 (42%) patients underwent additional decompression Eleven of 31 (35%) patients had had prior spinal surgery In 32% cases, one level was instrumented, in 52% two levels, in 13% three levels, and in 3% four levels Within the 2-year follow-up period, of 31 (19%) patients had required or were scheduled for a further surgical intervention The authors concluded that both back and leg pain were, on average, still moderately high years after instrumentation with the Dynesys system Only half of the patients declared that the operation had helped and had improved their overall quality of life; less than half reported improvements in functional capacity The reoperation rate after Dynesys was relatively high The results provide no support for the notion that semirigid fixation of the lumbar spine results in better patient-oriented outcomes than those typical of fusion Schaeren et al7 reported a prospective clinical study with a minimum 4-year follow-up of spinal stenosis with degenerative spondylolisthesis treated with decompression and dynamic stabilization with Dynesys Twenty-six consecutive patients (mean age, 71 years) with symptomatic lumbar spinal stenosis and degenerative spondylolisthesis underwent interlaminar decompression and stabilization with Dynesys Only 19 of 26 patients could be evaluated with a mean follow-up of 52 months (range, 48–57 months) Pain scores on the VAS and walking distance improved significantly (P < 0.001) at years and remained unchanged at years follow-up Radiographically, spondylolisthesis did not progress, and the motion segments remained stable, even in the three patients who showed slight screw loosening at and years follow-up One patient showed screw breakage with low back pain | 20.02.15 - 13:27 Clinical Application of Dynesys Dynamic Stabilization and motion at the instrumented level in flexion-extension views At years follow-up, 47% of the patients showed some degeneration at adjacent levels Overall, patient satisfaction remained high, and 95% would undergo the same procedure again The authors concluded that in elderly patients with spinal stenosis and degenerative spondylolisthesis, decompression and dynamic stabilization leads to excellent clinical and radiological results Enough stability is maintained to prevent progression of spondylolisthesis Because no bone grafting is necessary, donor site morbidity, which is one of the main drawbacks of fusion, is eliminated However, the degenerative disease is still progressive, and degeneration at adjacent motion segments remains a problem Hoppe et al8 presented the long-term outcome in a retrospective analysis of 39 consecutive patients with symptomatic degenerative lumbar spondylolisthesis at the L4–L5 level, treated with bilateral decompression and Dynesys instrumentation At a mean follow-up of 7.2 years (range 5.0–11.2 y) back pain improved in 89% and leg pain improved in 86% of patients compared with preoperative status Eighty-three percent of patients reported global subjective improvement, 92% would undergo the surgery again, and eight patients (21%) required further surgery due to symptomatic adjacent segment disease (six cases), late-onset infection (one case), and screw breakage (one case) In nine cases radiological progression of spondylolisthesis at the operated segment was found Seventy-four percent of operated segments showed a limited flexion-extension range of less than degrees Adjacent segment pathology, though without clinical correlation, was diagnosed at the L5–S1 (17.9%) and L3–L4 (28.2%) segments In four cases asymptomatic screw loosening was observed The authors concluded that monosegmental Dynesys instrumentation of degenerative spondylolisthesis at L4–L5 shows good long-term results Yu et al9 presented a comparison of fusion (PLIF = 26 patients) versus Dynesys stabilization (27 patients) with spinal stenosis at L4–L5 with or without spondylolisthesis Dynesys stabilization resulted in significantly higher preservation of motion at the index level (p < 0.001), and significantly less (p < 0.05) hypermobility at the adjacent segments ODI and VAS scores for back and leg pain improved significantly with both methods, but there was no significant difference between groups Operation time, blood loss, and length of hospital stay were all significantly (p < 0.001) less in the Dynesys group The author remarked that less postoperative morbidity may particularly benefit elderly patients and those with significant comorbidities Putzier et al10 reported their experience with dynamic stabilization, similar to that with Dynesys, adjacent to single-level fusion for asymptomatic, initially degenerated adjacent segments (iASD) after 6-year follow-up They compared dynamic fixation of a clinically asymptomatic iASD, with circumferential lumbar fusion alone Sixty patients with symptomatic degeneration of L5–S1 or L4–L5 (Modic ≥ degrees) and asymptomatic iASD (Modic = degree, confirmed by discography) were divided into two groups Thirty patients were treated with circumferential single-level fusion (SLF) In dynamic fixation transition (DFT) patients, additional posterior dynamic fixation of iASD was performed using the Allospine Dynesys Transition System (Zimmer, Winterthur, Switzerland) (▶ Fig 28.5) At final follow-up, two nonfusions were observed in both groups Six SLF patients and one DFT patient presented a progression of adjacent segment degeneration (PASD) In two DFT patients, a PASD occurred in the segment superior to the dynamic fixation, and in one DFT patient, a fusion of the dynamically fixated segment was observed Four DFT patients presented radiological implant failure Although no differences in clinical scores were observed between groups, improvement from the preoperative conditions was significant (all p < 0.001) Clinical scores were equal in patients with PASD and/or radiologically adverse events The authors did not recommend dynamically fixating the adjacent segment in patients with clinically asymptomatic iASD The lower number of PASD with dynamic fixation was accompanied by a high number of implant failures and a shift of PASD to the superior segment 28.5.1 Hybrid Stabilization with Dynesys As discussed earlier in this chapter, Dynesys is contraindicated in the presence of advanced disc degeneration with collapse of the disc height An interbody fusion with PLIF/TLIF may be recommended for the segment with advanced degeneration, and soft stabilization with Dynesys may be applied to the adjacent segment showing a moderate degree of degeneration This can be achieved by using a rigid rod or Dynesys in combination with an interbody cage for achieving solid fusion of the primary segment with advanced degeneration, and Dynesys alone may be used for the soft stabilization of the adjacent segment There are some clinical reports of such hybrid stabilization with Dynesys Fig 28.5 The Allospine Dynesys Transition device (Zimmer) implanted to a spine model A connector links the rigid to the dynamic fixation 205 | 20.02.15 - 13:27 Restoration of the Lumbar Motion Segment Schwarzenbach et al11 reported their experience, which they described as “segment-by-segment stabilization for degenerative disc disease: a hybrid technique” for multilevel degenerated disc disease The authors used Dynesys in some levels as a nonfusion device and in other segments in combination with a PLIF as a fusion device They reported a consecutive case series of 16 females and 15 males with a mean age of 53.6 years (range 26.3–76.4 years) At mean follow-up of 39 months (range 24–90 months), the back pain improved from 7.3 ± 1.7 to 3.4 ± 2.7, leg pain from 6.0 ± 2.9 to 2.3 ± 2.9, and ODI score from 51.6 ± 13.2% to 28.7 ± 18.0% Screw loosening occurred in of a total of 222 implanted screws (0.45%) The authors concluded that segment-by-segment treatment with Dynesys in combination with interbody fusion is technically feasible, safe, and effective for the surgical treatment of multilevel DDD Maserati et al12 reported a retrospective study of 22 of their 24 patients with 1- to 22-month follow-up using posterior lumbar instrumentation with the Dynesys-to-Optima (DTO) hybrid dynamic stabilization and fusion system The VAS score improved from 8.8 pre- to 5.3 postoperative In three patients treatment failed, defined as persistent preoperative symptoms requiring reoperation 28.6 Summary Dynamic stabilization with Dynesys is indicated for mobile and self-reducible lesions when they occur during discovertebral degeneration The suppression of abnormal movements enables improvement of the pain symptoms and the appearance of healing at both the posterior and nuclear annular-ligamentary level and the level of the end plates and articular processes Due to the preservation of a certain degree of freedom in an area that functions normally from the anatomic point of view, this facilitates a return to local conditions that foster healing of the cartilaginous structures The most important technical problem is fixation of the pedicle screws, which must be absolutely perfect, with no technical error whatsoever and, in particular, no screw back-out during implantation Dynesys has been the most widely used dynamic stabilization system in clinical practice worldwide The short- and long-term 206 clinical outcome in general is promising, particularly among surgeons in Europe But there are some mixed reviews among surgeons regarding the efficacy of Dynesys when used without concomitant decompression of the segment 28.7 References [1] Stoll TM, DuBois G, Schwarzenbach O The dynamic neutralization system for the spine: a multi-center study of a novel non-fusion system Eur Spine J 2002; 11 Suppl 2: S170–S178 [2] Kroeber M, Unglaub F, Guehring T et al Effects of controlled dynamic disc distraction on degenerated intervertebral discs: an in vivo study on the rabbit lumbar spine model Spine 2005; 30: 181–187 [3] Vaga S, Brayda-Bruno M, Perona F et al Molecular MR imaging for the evaluation of the effect of dynamic stabilization on lumbar intervertebral discs Eur Spine J 2009; 18 Suppl 1: 40–48 [4] Cakir B, Ulmar B, Koepp H, Huch K, Puhl W, Richter M Posterior dynamic stabilization as an alternative for dorso-ventral fusion in spinal stenosis with degenerative instability [in German] Z Orthop Ihre Grenzgeb 2003; 141: 418–424 [5] Putzier M, Schneider SV, Funk JF, Tohtz SW, Perka C The surgical treatment of the lumbar disc prolapse: nucleotomy with additional transpedicular dynamic stabilization versus nucleotomy alone Spine 2005; 30: E109–E114 [6] Grob D, Benini A, Junge A, Mannion AF Clinical experience with the Dynesys semirigid fixation system for the lumbar spine: surgical and patientoriented outcome in 50 cases after an average of years Spine 2005; 30: 324–331 [7] Schaeren S, Broger I, Jeanneret B Minimum four-year follow-up of spinal stenosis with degenerative spondylolisthesis treated with decompression and dynamic stabilization Spine 2008; 33: E636–E642 [8] Hoppe S, Schwarzenbach O, Aghayev E, Bonel H, Berlemann U Long-term outcome after monosegmental l4/5 stabilization for degenerative spondylolisthesis with the Dynesys device J Spinal Disord Tech 2012 [9] Yu SW, Yang SC, Ma CH, Wu CH, Yen CY, Tu YK Comparison of Dynesys posterior stabilization and posterior lumbar interbody fusion for spinal stenosis L4L5 Acta Orthop Belg 2012; 78: 230–239 [10] Putzier M, Hoff E, Tohtz S, Gross C, Perka C, Strube P Dynamic stabilization adjacent to single-level fusion: part II No clinical benefit for asymptomatic, initially degenerated adjacent segments after years follow-up Eur Spine J 2010; 19: 2181–2189 [11] Schwarzenbach O, Rohrbach N, Berlemann U Segment-by-segment stabilization for degenerative disc disease: a hybrid technique Eur Spine J 2010; 19: 1010–1020 [12] Maserati MB, Tormenti MJ, Panczykowski DM, Bonfield CM, Gerszten PC The use of a hybrid dynamic stabilization and fusion system in the lumbar spine: preliminary experience Neurosurg Focus 2010; 28: E2 ... of Dr Henry Graf.) | 20.02 .15 - 13 :22 Dynamic Stabilization of the Lumbar Spine Fig 1. 3 The concept of the fulcrum-assisted soft stabilization (FASS) system (a) Application of a ligament to the. .. Instrumentation 20 | 20.02 .15 - 13 :22 Motion Preservation of the Spine in Context Dynamic Stabilization of the Lumbar Spine Dilip K Sengupta 1. 1 Introduction Stabilization of the spine by way of spontaneous... across the motion segment increases the load at the posterior aspect of the disc (b) Introduction of a fulcrum in front of the ligaments in the FASS system may unload the disc Fig 1. 4 (a) The Dynesys