Biomechanical Evaluation of Posterior Dynamic Stabilization Systems in Lumbar Spine
Biomechanical Evaluation of Posterior Dynamic Stabilization Systems in Lumbar Spine

Author: Bharath K. Parepalli

Publisher:

Published: 2009

Total Pages: 204

ISBN-13:

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Fusion has been the gold standard treatment for treating the disc degeneration. Fusion surgeries restrict the motion at the implanted level there by imposing additional load at the adjacent levels. Many clinical studies have showed that adjacent segment degeneration was observed in patients over time. In order to overcome problems with fusion devices, dynamic stabilization systems are being used to treat disc degeneration related problems. These implants restore intersegmental motion across the implanted level with minimal effects on the adjacent levels. In vitro cadaveric testing was conducted on seven harvested sheep spines using established protocols. Axient was implanted in the spines 3 months prior to sacrificing. Main aim of this testing is to see if the performance is altered by the presence of surrounding muscle tissue. The specimens were prepared and tested under load control protocol. All six loading modes were tested by applying a pure moment of 10Nm (in steps of 2.5Nm) and angular displacement was calculated for the following cases: 1) Intact spine + Axient with surrounding muscle tissue, 2) Intact spine + Axient with muscle tissue removed, 3) Intact spine (with implant removed). Relative motion of L4 vertebra with respect to L5 was calculated. Statistical analysis was performed (on the implanted level data) to see if there is a statistical significance between cases 1 and 2. Biomechanical testing was also performed on 4 human cadavers to observe the trend with Axient compared to FE results. A validated 3-D non linear finite element model of the L3-S1 lumbar spine was used to evaluate biomechanics of various dynamic stabilization systems in comparison with traditional rigid rod system. The model was modified at L4-L5 level to simulate three different dynamic stabilization systems (DSFM-1, DSFM-2 and Axient, Innovative Spinal Technologies Inc., Mansfield, MA). Grade I was simulated at L4-L5 level. Follower preload of 400N and a 10Nm bending moment was applied to simulate physiological flexion, extension, lateral bending and axial rotation. Range of motion (ROM), intra discal pressure (IDP) and facet loads were calculated for all the models. Implant with better performance was then compared with fusion system in both grade I and grade II degenerated spines. In vitro results showed that there is no significant difference in the performance of the Axient with and without surrounding muscle tissue in terms of range of motion. Coming to FE results, Axient performed better over the other two implants (DSFM-1 and DSFM-2). Axient device was able to restore the motion at the implanted level compared to fusion device. Higher motions were observed at the adjacent level (L5-S1) with fusion device compared to intact and injured models. Both devices were able to stabilize the diseased spine and unload the treated disc.

A Biomechanical Evaluation of Dynamic Stabilization Systems
A Biomechanical Evaluation of Dynamic Stabilization Systems

Author: Sri Lakshmi Vishnubhotla

Publisher:

Published: 2005

Total Pages: 422

ISBN-13:

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Dynamic stabilization may provide a more physiologic alternative to fusion for patients suffering from low back pain. A validated 3-D nonlinear finite element model of the intact L3-S1 lumbar spine was used to evaluate the biomechanics of various dynamic stabilization systems in comparison with rigid screw rod system that is used in conventional fusion. The intact model was modified at L4-L5 to simulate stabilization with, rigid screw-rod system, rigid screw flexible rod system, Dynesys system, Cosmic system, and Wallis system. These devices were also simulated in decompression surgery to evaluate the stability. The load control and hybrid protocols were used to evaluate these devices. Various biomechanically relevant parameters like range of motion, facet loading, disc stresses, implant stresses, instantaneous axis of rotation and load sharing were evaluated. Results show that the flexible rod system does not vary much in terms of stiffness and load sharing capabilities from the rigid screw rod system. Dynesys, Cosmic and Wallis systems are more flexible than rigid systems but not flexible enough to say that they preserve motion. However, they have the ability to allow for loading through the intervertebral disc. All the flexible stabilization systems were capable of stabilizing the decompression surgery in flexion and extension and lateral bending. Dynesys and Cosmic systems do not restore stability in axial rotation.

Biomechanical Comparison of Various Posterior Dynamic Stabilization Systems for Different Grades of Facetectomy and Decompression Surgery
Biomechanical Comparison of Various Posterior Dynamic Stabilization Systems for Different Grades of Facetectomy and Decompression Surgery

Author: Rachit Parikh

Publisher:

Published: 2010

Total Pages: 119

ISBN-13:

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Spinal stenosis is a degenerative process, caused by progressive narrowing of the lumbar spinal canal and neural foramen, leading to a constriction of the nerve roots of the cauda equina. Currently, facetectomy and laminectomy combined with fusion are the standard methods of decompression for the degenerative lumbar spinal stenosis with resultant alteration in established inter-relationships between various vertebral column components. However due to myriad of degenerative complications at the fused level and adjacent level degeneration, numerous new posterior dynamic stabilization systems have been developed. The objective of this biomechanical study was to investigate the influence of different grades of factectomy, spinal decompression and laminectomy procedures in conjunction with various dynamic stabilization implants viz. Dynesys, In-Space spacer and Stabilimax. A validated, 3-D, nonlinear finite element model of the intact L3-S1 lumbar spine was used to evaluate the biomechanics of these devices. The load control protocol was used to evaluate these devices. Various biomechanically relevant parameters like range of motion, facet loading, disc stresses were evaluated. An in vitro study was also performed comparing Dynesys with novel PEEK Rod dynamic stabilization system for decompression surgery with discectomy. The finite element results showed that the Dynesys and Stabilimax systems were capable of stabilizing the decompression surgery in flexion, extension and lateral bending. The In-Space spacer effectively reduced motion in extension and did not interfere with motion in other loading modes at the implanted level. All the systems were capable of loading through the intervertebral disc. Results also showed that after complete facetectomy the systems did not restore stability in axial rotation. Further a cadaveric study was to done to compare the Dynesys stabilization system with that of a novel PEEK rod pedicle screw stabilization system after simulating decompression surgery. The biomechanical comparison of monosegmental fixation on L4-L5 and bi-segmental fixation of L3-L5 as topping off procedure with fusion were done for this study. The predicted range of motion for the PEEK rod stabilization system was consistent with the Dynesys for monosegmental fixation.

Effect of Design Variables on Biomechanics of Lumbar Spine Implanted with Single, Multilevel and Hybrid Posterior Dynamic Stabilization Systems
Effect of Design Variables on Biomechanics of Lumbar Spine Implanted with Single, Multilevel and Hybrid Posterior Dynamic Stabilization Systems

Author: Divya V. Ambati

Publisher:

Published: 2010

Total Pages: 192

ISBN-13:

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Dynamic stabilization devices such as the Stabilimax (Applied Spine Technologies Inc.) are being considered as a viable alternative to fusion for patients suffering from low back pain. As opposed to fusion, the Stabilimax provides controlled range of motion in patients undergoing decompression procedures for central or lateral lumbar spinal stenosis at one or two adjacent levels. This pedicle screw based system features an internal dual spring mechanism which combined with a ball and socket joint provides stability by allowing controlled motion to the treated level(s) of the lumbar region. In the recent times, efforts are being made to have the motion preserving devices stabilize the segments, like the rigid instrumentation, if needed. The Stabilimax could be made to achieve this goal by limiting the range of motion of the treated segment with different spring travel lengths (interpedicular travel). More recently, hybrid stabilization has been proposed with an intention to treat patients with segmental lumbar degenerative pathologies. If needed, Stabilimax could also be modified to achieve this goal by using it in conjunction with rigid rod instrumentation. The aim of this study was to evaluate the biomechanics of the decompressed segment (s) implanted with single, multilevel, and hybrid Stabilimax devices with three different spring travel distances. The hypotheses here are 1) the overall stabilization of the decompressed segment implanted with Stabilimax devices does not change with variations in interpedicular travel. 2) A dynamic system in conjunction to a fusion system reduces the risk of adjacent level degeneration as seen in lumbar arthrodesis. A validated 3-D nonlinear finite element model of the intact L3-S1 lumbar spine was used to evaluate the biomechanics of the following devices: a) L4-L5 Single level Stabilimax b) L3-L4-L5 Multilevel Stabilimax c) L4-L5-S1 Multilevel Stabilimax d) L4-L5 Stabilimax + L5-S1 Fusion. The intact model was modified to simulate the decompression at the corresponding level(s) followed by the implantation of the devices. The load control and hybrid protocols were used to evaluate these devices. Various biomechanically relevant parameters like Range of motion, Intradiscal pressure, Facet loads, Implant stresses, Instantaneous axis of rotation (COR), Maximum spring forces and displacements were calculated. Results show that different Stabilimax devices are capable of stabilizing the decompressed segment (s) in flexion, extension and lateral bending but not in axial rotation. The overall stabilization of the decompressed segment (s) with Stabilimax devices did not alter with variations in interpedicular device travel in most of the cases. The hybrid stabilization system also produced favorable results ascertaining with our hypothesis that a dynamic system in conjunction to a rigid rod system reduces the risk of adjacent level degeneration as seen in lumbar arthrodesis.

Handbook of Spine Technology
Handbook of Spine Technology

Author: Boyle C. Cheng

Publisher: Springer

Published: 2021-04-01

Total Pages: 0

ISBN-13: 9783319444239

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This handbook is the most authoritative and up-to-date reference on spine technology written for practitioners, researchers, and students in bioengineering and clinical medicine. It is the first resource to provide a road map of both the history of the field and its future by documenting the poor clinical outcomes and failed spinal implants that contributed to problematic patient outcomes, as well as the technologies that are currently leading the way towards positive clinical outcomes. The contributors are leading authorities in the fields of engineering and clinical medicine and represent academia, industry, and international government and regulatory agencies. The chapters are split into five sections, with the first addressing clinical issues such as anatomy, pathology, oncology, trauma, diagnosis, and imaging studies. The second section, on biomechanics, delves into fixation devices, the bone implant interface, total disc replacements, injury mechanics, and more. The last three sections, on technology, are divided into materials, commercialized products, and surgery. All appropriate chapters will be continually updated and available on the publisher’s website, in order to keep this important reference as up-to-date as possible in a fast-moving field.

Biomechanics of Spine Stabilization
Biomechanics of Spine Stabilization

Author: Edward C. Benzel

Publisher: Thieme

Published: 2011-01-01

Total Pages: 552

ISBN-13: 1604067373

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Over the past two decades there have been major advances in the treatment of spinal disorders including anterior decompression of the neural structures as well as various forms of spinal stabilization by utilization of implants. These changes primarily reflect the development of better techniques of diagnosis and anesthesia, as well as new fusion procedures that are often supplemented with instrumentation. Biomechanics of Spine Stabilization bridges the gap that has existed between the physics of biomechanical research and the clinical arena. The book helps surgeons to plan treatments for the injured spine based on sound biomechanical principles - principles that will influence the surgeon's choice for the surgical approach, type of fusion and type of instrumentation. Biomechanics of Spine Stabilization begins with the essentials, proceeds gradually toward the development of an understanding of biomechanical principles, and, finally, provides a basis for clinical decision-making. These features make it a cover-to-cover must-read for anyone who is involved with the care of a patient with an unstable spine. Chocked full of illustrations, Biomechanics of Spine Stabilization includes: -Physical principles and kinematics -Segmental motion, stability and instability -Spine and neural element pathology -Surgical approaches and spinal fusion -Spinal instrumentation: General principles -Spinal instrumentation constructs: biomechanical attributes and clinical applications -Non-operative spinal stabilization -Special concepts and concerns -CD-ROM containing illustrations from book to create mental images of critical anatomical, biomechanical and clinical points

Stability Imparted by a Posterior Lumbar Interbody Fusion Cage Following Surgery
Stability Imparted by a Posterior Lumbar Interbody Fusion Cage Following Surgery

Author: Vadapalli Sasidhar

Publisher:

Published: 2004

Total Pages: 264

ISBN-13:

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In order to promote solid fusion across a decompressed spinal segment, inter-body spacers/cages are used with and without posterior instrumentation to provide an initial "rigid" fixation of the segment. Inter-body spacers (cages) of various shapes (e.g., rectangular, cylindrical) and materials are currently available on the market. Important factors affecting the biomechanics of the fused segment are (i) cage shape and placement, (ii) cage material property (iii) surgical approach used-posterior vs. antero lateral (iv) cage with additional instrumentation. The objective of this study is to address change in the stability and stress patterns associated with the various factors described above. A cadaveric study using established protocols and a finite element (FE) study were conducted. For the cadaveric study, nine fresh ligamentous lumbar spine specimens (L1-S2) were radiographed out of which six specimens were prepared for testing by fixing a base to the sacrum and a loading frame to the top-most vertebra. Each specimen was subjected to pure moment (6 Nm in steps of 1.5 Nm) in six loading modes: flexion, extension, right and left lateral bending, and right and left axial rotation. The load-displacement data was collected in a sequential manner for the following cases: 1) intact spine, 2) insertion of rectangular cages (Vertebral spacer PR, Synthes, Inc.), 3) fixation with posterior instrumentation, 4) fatiguing the instrumented spine. The relative motion of L4 with respect to L5 was calculated for all these cases. A validated three-dimensional, nonlinear FE model of lumbar spine from L3-L5 was used. The model was modified to simulate the bilateral placement of cages alone. Contact surfaces were defined between the cages and the endplates to simulate the bone-implant interface. The cages were placed using posterior approach and left antero lateral approach to see the effect of the surgical approach on the stability of the segment. In the FE model with cage placed using posterior approach, posterior instrumentation was added. For this model the material property of the cage was changed form PEEK to titanium to study the change in load sharing and stresses on the endplates. For all the models a 6Nm moment was applied and all the six loading cases were simulated. The relative motion of L4 with respect to L5 was calculated, stresses in the implants and endplates were studied. Results from the in vitro study indicate that the stability of the spine decreased after the stand alone placement of bilateral cage when compared to the intact for all the loading cases except in flexion. However, no statistically significant difference was seen in the stability between intact and stand alone cage placement. After stabilization with posterior fixation using the pedicle screw rod system, the stability increased in all loading cases. There was no significant change in stability after fatiguing. The FE model predictions for the bilateral cage alone and with additional instrumentation placed at L4-L5 disc space were within 1 SD of the cadaveric data in all loading modes. There was no change in stability offered by stand alone cage placement using antero lateral approach and posterior approach. For the cage made of titanium peak Von mises stress in the endplates were twice of that for cage made of PEEK. Cages placed laterally from the mid-sagittal plane provide better stability in bending when compared to medially placed cages.

Investigation Into Lumbar Spine Biomechanics of 360 Motion Preservation Systems
Investigation Into Lumbar Spine Biomechanics of 360 Motion Preservation Systems

Author: Ali Kiapour

Publisher:

Published: 2010

Total Pages: 200

ISBN-13:

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Lumbar disc arthroplasty is a novel technology which may provide a more physiologic alternative to fusion for patients suffering from a variety of conditions related to lumbar intervertebral disc. There are various designs proposed for discs. Most of these designs require an anterior surgical procedure for placement of the implant at designated level. There are numerous clinical, experimental and computational biomechanical studies available on present disc arthroplasty systems. Some of these studies have shown satisfactory clinical and biomechanical outcomes following replacement of such devices. However, facet pain and degeneration, improper load balance and spinal alignment have surfaced the main deficiencies of such devices. The difficulties in surgical approach and revision surgery are other disadvantageous of current anterior disc arthroplasty procedures. In this thesis in vitro testing and finite element modeling are used to design and biomechanically evaluate a new 360 motion preservation construct which included a matched pair posterior disc and dynamic stabilization system. Biomechanical studies were done to optimize the design of this construct through measuring parameters such as range of motion, stresses in implants, center of rotation and intradiscal pressure (IDP). Based on the parameters evaluated in the study, the new 360 motion preservation system was found to be able to preserve the normal kinematics at index and adjacent segments of spine. The 360 arthroplasty construct preserved the normal quality of motion by having extension-to-flexion center of rotation close to that of intact. Having relatively low stresses at implant components at full motion was a good indicator of satisfactory long term performance of the system in vivo. The intact like load sharing at the intervertebral disc adjacent to 360 system would lessen the risk of disc and facet degeneration as well. The developed 360 system has the advantage of relatively easier surgical procedure compared to the available anterior disc designs. Also the revision surgery becomes easier compared to anterior approach. The proposed design has the potential to address posterior joint degeneration which is the main contradiction of available anterior disc arthroplasties. Moreover this new design broadens the indications for disc replacement to low back pain patients due posterior joint degeneration, like spinal stenosis. Further biomechanical studies were done on components of the poster dynamic stabilization system (PDS) to find a proper configuration for standalone PDS for application in treatment of lumbar spine stenosis. The proposed PDS configurations were able to provide the spinal segment with a constrained range of motion and stability while maintaining lower stresses at pedicle screws compared to traditional rigid fixation systems. Unlike some available semi-rigid stabilization constructs, the PDS was shown to have more restricted flexibility in transverse plane while maintaining a favorable kinematics in other planes of motions.

Rehabilitation in the dynamic stabilization of the lumbosacral spine
Rehabilitation in the dynamic stabilization of the lumbosacral spine

Author: G. Calvosa

Publisher: Springer Science & Business Media

Published: 2008-09-28

Total Pages: 41

ISBN-13: 3540738029

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This publication describes the indications and the various phases of technical rehabilitation to be used after surgical treatment of lumbar degenerative spine. A work of fundamental importance, it will benefit those interested in this area of orthopaedics.