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.

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.

Biomechanical Analysis of Dynamic Stabilization Under the Effects of Patient Conditions
Biomechanical Analysis of Dynamic Stabilization Under the Effects of Patient Conditions

Author: KwonSoo Chun

Publisher:

Published: 2010

Total Pages:

ISBN-13:

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While coronary heart diseases are considered the most deadly medical conditions in terms of overall deaths per year, orthopedic maladies are the costliest. One of the most prevalent orthopedic conditions is low back pain, which stems from degenerative tissue changes within the spinal column and associated spinal cord and peripheral nerve injuries. Treatment successes in conservative and surgical treatment are mixed, although the rates of spine surgery have dramatically increased over the past decade. Surgical treatment is considered a last resort, and of all the surgical approaches, spinal fusion is the most common for the treatment of low back pain. Since spinal fusion has been in use in the clinic for several decades now, results of long-term retrospective clinical reviews are now becoming available. Some of these studies have shown that spinal fusion may induce secondary injuries such as adjacent tissue regeneration, which may require additional surgical treatment. To overcome some of these complications, posterior dynamic stabilization has been introduced as an alternative to fusion surgery. Posterior dynamic stabilization is still considered mostly experimental and the majority of spine companies with ambitions in this field have not yet settled on particular design goals and implant concepts. A significant hurdle for entry to the market for such devices is the lack of understanding of what the ideal function of the device is, and how the implants should interact with the spinal column. The objective of this thesis was to evaluate the functionality of posterior dynamic stabilization depending on patient conditions such as mobility and body mass and to suggest efficient rigidities of the dynamic device when considering patients' characteristics. This study is divided into three specific aims. The purpose of the first aim was to investigate the significant influence of a patient's spinal kinematics on dynamic stabilization. The patients were divided by segmental range of motion (L3-L4) into two groups (hyper-mobility and hypo-mobility) and finite element (FE) models were generated for these respective groups. This study showed that patient characteristics such as mobility produced different spinal kinematics after dynamic stabilization and demonstrated that the effectiveness of dynamic stabilization was increased when the mechanical properties of the device were changed in response to patient characteristics. The purpose of the second aim was to evaluate the stabilization devices in relation to patients' body mass and spinal mobility, testing the effects of dynamic stabilization devices of varying levels of rigidity. Based on analyzed results of the spinal mobility at the diseased level (L4-L5), the hyper-mobility patients were divided into three groups, based on severity. Depending on the body mass in the hyper-mobility patients, the patients were divided into three groups. The findings of the study demonstrated the significant influence of patients' body mass and mobility on spinal kinematics after dynamic stabilization. The purpose of the third aim was to investigate the effect of implant rigidity on spinal kinematics utilizing a cadaveric tissue model. This in-vitro study was designed to validate the biomechanical influence of physiological loading after dynamic stabilization. The results of this in-vitro study showed that patients' characteristics change spinal segmental motion and different implant rigidities of the dynamic stabilization device also produce varying spinal kinematics depending on patients' conditions. Through these in-vitro tests, this thesis readdresses the importance of considering patient characteristics in the design of appropriate devices for spinal stabilization, and to select the right implants for the right patient population.

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.

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.

In Vitro Biomechanical Testing and Computational
In Vitro Biomechanical Testing and Computational

Author: Mageswaran Prasath

Publisher:

Published: 2012

Total Pages: 127

ISBN-13:

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Abstract: Two separate in vitro biomechanical studies were conducted on human cadaveric spines (Lumbar) to evaluate the stability following the implantation of two different spinal fixation devices; interspinous fixation device (ISD) and Hybrid dynamic stabilizers. ISD was evaluated as a stand-alone and in combination with unilateral pedicle rod system. The results were compared against the gold standard, spinal fusion (bilateral pedicle rod system). The second study involving the hybrid dynamic system, evaluated the effect on adjacent levels using a hybrid testing protocol. A robotic spine testing system was used to conduct the biomechanical tests. This system has the ability to apply continuous unconstrained pure moments while dynamically optimizing the motion path to minimize off-axis loads during testing. Thus enabling precise control over the loading and boundary conditions of the test. This ensures test reliability and reproducibility. We found that in flexion-extension, the ISD can provide lumbar stability comparable to spinal fusion. However, it provides minimal rigidity in lateral bending and axial rotation when used as a stand-alone. The ISD with a unilateral pedicle rod system when compared to the spinal fusion construct were shown to provide similar levels of stability in all directions, though the spinal fusion construct showed a trend toward improved stiffness overall. The results for the dynamic stabilization system showed stability characteristics similar to a solid all metal construct. Its addition to the supra adjacent level (L3- L4) to the fusion (L4- L5) indeed protected the adjacent level from excessive motion. However, it essentially transformed a 1 level into a 2 level lumbar fusion with exponential transfer of motion to the fewer remaining discs (excessive adjacent level motion). The computational aspect of the study involved the development of a spine model (single segment). The kinematic data from these biomechanical studies (ISD study) was then used to validate a finite element model of the spine.

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.

OPLL
OPLL

Author: Atsushi Okawa

Publisher: Springer Nature

Published: 2020-05-14

Total Pages: 278

ISBN-13: 9811538557

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This publication brings together information on all aspects of OPLL - epidemiology, etiology, diagnosis, and treatment. It contains contributions by Japanese researchers and surgeons, including members of the Ministry of Health and Welfare Investigation Committee, and by American surgeons with expertise in the field. Until now, little has been published on the subject in English. This collection of reports is amply augmented with illustrations.

Surgery of the Spine and Spinal Cord
Surgery of the Spine and Spinal Cord

Author: Erik van de Kelft

Publisher: Springer

Published: 2016-07-04

Total Pages: 746

ISBN-13: 3319276131

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This book offers essential guidance on selecting the most appropriate surgical management option for a variety of spinal conditions, including idiopathic problems, and degenerative disease. While the first part of the book discusses the neuroanatomy and biomechanics of the spine, pain mechanisms, and imaging techniques, the second guides the reader through the diagnostic process and treatment selection for disorders of the different regions of the spine, based on the principles of evidence-based medicine. I.e., it clearly explains why a particular technique should be selected for a specific patient on the basis of the available evidence, which is carefully reviewed. The book identifies potential complications and highlights technical pearls, describing newer surgical techniques and illustrating them with the help of images and accompanying videos. Though primarily intended for neurosurgeons, the book will also be of interest to orthopaedic surgeons, specialists in physical medicine, and pain specialists. ​