Facet Joint Stress Research Articles

Does the novel artificial cervical joint complex resolve the conflict between stability and mobility after anterior cervical surgery? a finite element study.

Our group has developed a novel artificial cervical joint complex (ACJC) as a motion preservation instrument for cervical corpectomy procedures. Through finite element analysis (FEA), this study aims to assess this prosthesis's mobility and stability in the context of physiological reconstruction of the cervical spine. A finite element (FE)model of the subaxial cervical spine (C3-C7) was established and validated. ACJC arthroplasty, anterior cervical corpectomy and fusion (ACCF), and two-level cervical disc arthroplasty (CDA) were performed at C4-C6. Range of motion (ROM), intervertebral disc pressure (IDP), facet joint stress (FJS), and maximum von Mises stress on the prosthesis and vertebrae during loading were compared. Compared to the intact model, the ROM in all three surgical groups demonstrated a decline, with the ACCF group exhibiting the most significant mobility loss, and the highest compensatory motion in adjacent segments. ACJC and artificial cervical disc prosthesis (ACDP) well-preserved cervical mobility. In the ACCF model, IDP and FJS in adjacent segments increased notably, whereas the index segments experienced the most significant FJS elevation in the CDA model. The ROM, IDP, and FJS in both index and adjacent segments of the ACJC model were intermediate between the other two. Stress distribution of ACCF instruments and ACJC prosthesis during the loading process was more dispersed, resulting in less impact on the adjacent vertebrae than in the CDA model. The biomechanical properties of the novel ACJC were comparable to the ACCF in constructing postoperative stability and equally preserved physiological mobility of the cervical spine as CDA without much impact on adjacent segments and facet joints. Thus, the novel ACJC effectively balanced postoperative stability with cervical motion preservation.

Biomechanical evaluation on a new type of vertebral titanium porous mini-plate and mechanical comparison between cervical open-door laminoplasty and laminectomy: a finite element analysis.

Objective: Compare the spine's stability after laminectomy (LN) and laminoplasty (LP) for two posterior surgeries. Simultaneously, design a new vertebral titanium porous mini plate (TPMP) to achieve firm fixation of the open-door vertebral LP fully. The objective is to enhance the fixation stability, effectively prevent the possibility of "re-closure," and may facilitate bone healing. Methods: TPMP was designed by incorporating a fusion body and porous structures, and a three-dimensional finite element cervical model of C2-T1 was constructed and validated. Load LN and LP finite element models, respectively, and analyze and simulate the detailed processes of the two surgeries. It was simultaneously implanting the TPMP into LP to evaluate its biomechanical properties. Results: We find that the range of motion (ROM) of C4-C5 after LN surgery was greater than that of LP implanted with different plates alone. Furthermore, flexion-extension, lateral bending, and axial rotation reflect this change. More noteworthy is that LN has a much larger ROM on C2-C3 in axial rotation. The ROM of LP implanted with two different plates is similar. There is almost no difference in facet joint stress in lateral bending. The facet joint stress of LN is smaller on C2-C3 and C4-C5, and larger more prominent on C5-C6 in the flexion-extension. Regarding intervertebral disc pressure (IDP), there is little difference between different surgeries except for the LN on C2-C3 in axial rotation. The plate displacement specificity does not significantly differ from LP with vertebral titanium mini-plate (TMP) and LP with TPMP after surgery. The stress of LP with TPMP is larger in C4-C5, C5-C6. Moreover, LP with TMP shows greater stress in the C3-C4 during flexion-extension and lateral bending. Conclusion: LP may have better postoperative stability when posterior approach surgery is used to treat CSM; at the same time, the new type of vertebral titanium mini-plate can achieve almost the same effect as the traditional titanium mini-plate after surgery for LP. In addition, it has specific potential due to the porous structure promoting bone fusion.

Biomechanical Finite Element Analysis of Percutaneous Endoscopic Lumbar Discectomy via a Transforaminal Approach

Based on the previously established 3-dimensional model, this study uses the finite element analytical method to observe the effects of superior articular process resection and intervertebral discectomy on the stress of the surgical segment under different motion states. A validated L3-S1 finite element model was modified for simulation. And on the basis of the normal lumbar spine model, the superior articular process and discs of different parts of L4-L5 were simulated for resection. The resection models were divided into 6 groups, and the stress characteristics of articular process and discs of the lumbar spine under different postoperative motion conditions were examined under the same loading conditions. Simultaneous resection of the tip and base of the superior articular process increased the stress on the facet joint under various motion states compared with separate resections. In addition, the fewer herniated discs that are removed, the smaller the increase in facet joint stress. excision of the tip of the superior articular process caused a smaller stress increase in the facet joint than excision of the base under the forward bending and right-lateral flexion, and the opposite results were found under left-lateral flexion, posterior extension, and rotation. Resection of the tip of the superior articular process increases disc stress more than resection of the base of the superior articular process. Select resection of the superior articular process base as much as possible to expose the target of the disc. And minimize annulus damage and disc removal.

Finite element analysis of optimized novel additively manufactured non-articulating prostheses for cervical total disc replacement.

Ball-and-socket designs of cervical total disc replacement (TDR) have been popular in recent years despite the disadvantages of polyethylene wear, heterotrophic ossification, increased facet contact force, and implant subsidence. In this study, a non-articulating, additively manufactured hybrid TDR with an ultra-high molecular weight polyethylene core and polycarbonate urethane (PCU) fiber jacket, was designed to mimic the motion of normal discs. A finite element (FE) study was conducted to optimize the lattice structure and assess the biomechanical performance of this new generation TDR with an intact disc and a commercial ball-and-socket Baguera®C TDR (Spineart SA, Geneva, Switzerland) on an intact C5-6 cervical spinal model. The lattice structure of the PCU fiber was constructed using the Tesseract or the Cross structures from the IntraLattice model in the Rhino software (McNeel North America, Seattle, WA) to create the hybrid I and hybrid II groups, respectively. The circumferential area of the PCU fiber was divided into three regions (anterior, lateral and posterior), and the cellular structures were adjusted. Optimal cellular distributions and structures were A2L5P2 in the hybrid I and A2L7P3 in the hybrid II groups. All but one of the maximum von Mises stresses were within the yield strength of the PCU material. The range of motions, facet joint stress, C6 vertebral superior endplate stress and path of instantaneous center of rotation of the hybrid I and II groups were closer to those of the intact group than those of the Baguera®C group under 100N follower load and pure moment of 1.5 Nm in four different planar motions. Restoration of normal cervical spinal kinematics and prevention of implant subsidence could be observed from the FE analysis results. Superior stress distribution in the PCU fiber and core in the hybrid II group revealed that the Cross lattice structure of a PCU fiber jacket could be a choice for a next-generation TDR. This promising outcome suggests the feasibility of implanting an additively manufactured multi-material artificial disc that allows for better physiological motion than the current ball-and-socket design.

Does Lumbar Interbody Fusion Modality Affect the Occurrence of Complications in an Osteoporotic Spine Under Whole-Body Vibration? A Finite Element Study

To evaluate the effects of 3 lumbar interbody fusion techniques on the occurrence of complications in an osteoporotic spine under whole-body vibration. A previously developed and validated nonlinear finite element model of L1-S1was modified to develop anterior lumbar interbody fusion (ALIF), posterior lumbar interbody fusion (PLIF), and transforaminal lumbar interbody fusion (TLIF) models with osteoporosis. In each model, the lower surface of the sacrum was absolutely fixed, a follower load of 400N was applied through the axis of the lumbar spine, and an axial sinusoidal vertical load of ±40N (5 Hz) was imposed on the superior surface of L1, to perform a transient dynamic analysis. The maximal values of intradiscal pressure, shear stress on annulus substance, disc bulge, facet joint stress, and screw and rod stress, along with their dynamic response curves, were collected. Among these 3 models, the TLIF model generated the greatest screw and rod stress, and the PLIF model generated the greatest cage-bone interface stress. At the L3-L4 level, compared with the other 2 models, the maximal values and dynamic response curves of intradiscal pressure, shear stress of annulus ground substance, and disc bulge were all lower in the ALIF model. However, the facet contact stress at the adjacent segment in the ALIF model was higher than that in the other 2 models. In an osteoporotic spine under whole-body vibration, TLIF has the highest risk of screw and rod breakage, PLIF has the highest risk of cage subsidence, and ALIF has the lowest risk of upper adjacent disc degeneration, but the highest risk of adjacent facet joint degeneration.

Biomechanical Effect of Osteoporosis on Adjacent Segments After Anterior Cervical Corpectomy and Fusion

Adjacent segmental degeneration (ASD) is one common long-term complication of anterior cervical corpectomy and fusion (ACCF), and osteoporosis is one basic disease in the elderly. After ACCF, patients may experience osteoporosis with age. However, the influence of osteoporosis on ASD remains unclear. The purpose of this study was to determine whether osteoporosis could affect the development of ASD following ACCF. Three finite element models of the cervical spine, including 1 normal model, 1 ACCF model, and 1 ACCF with osteoporosis model, were constructed. ACCF was simulated at the C4-C6 level. A 73.6N follower load and a 1 Nm moment were imposed on the normal model, and the same follower load together with an adjusted moment was applied to the ACCF model and the ACCF with osteoporosis model, to simulate movement in each direction. The range of motion, intradiscal pressure, shear stress on anulus fibrosus, and facet joint stress at C3-C4 and C6-C7 levels of the models were calculated. In this study, the normal model was well validated. In flexion, extension, right lateral bending, and right axial rotation, the overall range of motion was 8.92°, 19.7°, 15.37°, and 45.27° in the normal model, and the adjusted moment was 1.4 Nm, 2.7 Nm, 1.1 Nm, and 2.6 Nm in the ACCF model, and 1.3 Nm, 2.5 Nm, 1.1 Nm, and 2.4 Nm in the ACCF with osteoporosis model. Despite of a few exceptions, the maximum values of the outcome measurements were mostly found in the ACCF model, and the minimum values in the normal model. Compared with the ACCF model, most of the outcome measurements were decreased in the ACCF with osteoporosis model. Osteoporosis can retard the adverse influence of ACCF on adjacent segments.

Incorporating strategy in hybrid surgery for continuous two-level cervical spondylosis from a biomechanical perspective

Background and objectiveHybrid surgery, incorporating cervical disc replacement and anterior cervical discectomy and fusion, has shown good clinical results in the treatment of multilevel cervical spondylosis according to early follow-ups. This study investigated the surgical strategy of hybrid surgery for two-level cervical spondylosis by distinguishing the biomechanical characteristics with different incorporating modes. MethodA finite element model of a healthy cervical spine including C2-T1 was developed, and hybrid surgery was simulated by replacing at one level with Prestige-LP and fusion at another level with the anterior plate in C3–C5 (Hybrid-S1: replaced at C3–C4, Hybrid-S2: replaced at C4–C5), and in C4–C6 (Hybrid-M1: replaced at C4–C5, Hybrid-M2: replaced at C5–C6) and in C5–C7 (Hybrid-U1: replaced at C5–C6, Hybrid-U2: replaced at C6–C7). The motion of C2 vertebrae in flexion, extension, axial rotation, and lateral bending was imposed on all hybrid models following the displacement control testing protocol. ResultsThe largest range of motion (ROM) in a healthy spine was observed at C5-C6, followed by C3-C4, C4-C5 and C6-C7. On average, the ROM at the replaced segment increased by 175.7%, 202.7%, 176.3%, 117.1%, 139.4%, and 236.0% in Hybrid-S1, Hybrid-S2, Hybrid-M1, Hybrid-M2, Hybrid-U1, and Hybrid-U2, respectively. The facet joint stress at the replaced segment increased by 186.9%, 124.4%, 111.1%, 60.3%, 62.7%, and 144.7%, and the adjacent intradiscal pressure (IDP) increased by 45.2%, 38.7%, 2.7%, 2.1%, 13.9%, and 20.1%. ConclusionsIncorporating mode in hybrid surgery affects cervical biomechanics. Hybrid surgery with replacement at a segment with a greater ROM and fusion at a segment with a lower ROM can results in fewer changes in terms of overall cervical stiffness, ROM at the operative level, facet joint stress, and adjacent IDP. In hybrid surgery, it is better to implement disc replacement at a level with a greater ROM and fusion of another segment.

Impact of cage position on biomechanical performance of stand-alone lateral lumbar interbody fusion: a finite element analysis

BackgroundThis study aimed to compare the biomechanical performance of various cage positions in stand-alone lateral lumbar interbody fusion(SA LLIF).MethodsAn intact finite element model of the L3-L5 was reconstructed. The model was verified and analyzed. Through changing the position of the cage, SA LLIF was established in four directions: anterior placement(AP), middle placement(MP), posterior placement(PP), oblique placement(OP). A 400 N vertical axial pre-load was imposed on the superior surface of L3 and a 10 N/m moment was applied on the L3 superior surface along the radial direction to simulate movements of flexion, extension, lateral bending, and axial rotation. Various biomechanical parameters were evaluated for intact and implanted models in all loading conditions, including the range of motion (ROM) and maximum stress.ResultsIn the SA LLIF models, the ROM of L4-5 was reduced by 84.21–89.03% in flexion, 72.64–82.26% in extension, 92.5-95.85% in right and left lateral bending, and 87.22–92.77% in right and left axial rotation, respectively. Meanwhile, ROM of L3-4 was mildly increased by an average of 9.6% in all motion directions. Almost all stress peaks were increased after SA LLIF, including adjacent disc, facet joints, and endplates. MP had lower stress peaks of cage and endplates in most motion modes. In terms of the stress on facet joints and disc of the cephalad segment, MP had the smallest increment.ConclusionIn our study, SA LLIF risked accelerating the adjacent segment degeneration. The cage position had an influence on the distribution of endplate stress and the magnitude of facet joint stress. Compared with other positions, MP had the slightest effect on the stress in the adjacent facet joints. Meanwhile, MP seems to play an important role in reducing the risk of cage subsidence.

Comparison of the Biomechanical Effect of the FFX Device Compared With Other Lumbar Fusion Devices: A Finite Element Study.

Lumbar decompression can result in postsurgical instability and spondylolisthesis in patients with lumbar spinal stenosis (LSS). While pedicle screw (PS) constructs improve stability and support fusion, their use can lead to adjacent level degeneration due to rigidity and resultant overload of anatomical structures. The FFX device is a facet spacer designed to be a less invasive alternative for obtaining fusion compared with PS. The present study aimed to compare biomechanical performance of the FFX device to different lumbar spine procedures using the finite element (FE) method. Comparative biomechanical study by FE method. An FE model for the lumbar spine was developed and validated to assess vertebral displacement and stress variations in the facet joints and discs following surgery. Modeled scenarios included a healthy spine as a reference model, laminectomy (LAM), and prior to/following L4-L5 fusion for LAM + FFX and LAM + PS. LAM increased displacement compared with the healthy spine and both instrumented spine procedures. Facet joint stress at adjacent levels for LAM + PS was significantly higher than with LAM + FFX prior to fusion (+13.5% for L3-L4; +15.7% for L5-S1). Adjacent level disc stress at L5-S1 was 7.7% higher for LAM + PS vs LAM + FFX. Adjacent level facet joint and disc stresses for LAM + FFX were equivalent to LAM + PS once fusion occurred. Instrumented spine fixation prevents the risk of lumbar instability associated with LAM alone. Compared with PS, the FFX device is a less invasive alternative for the treatment of LSS, which potentially lowers the risk of adjacent segment degeneration prior to fusion that provides equivalent stability once fusion is achieved.

Single-level cervical disc arthroplasty in the spine with reversible kyphosis: A finite element study.

BackgroundOur previous studies found the single‐level cervical disc arthroplasty (CDA) might be a feasible treatment for the patients with reversible kyphosis (RK). Theoretically, the change of cervical alignment from lordosis to RK comes with the biomechanical alteration of prostheses and cervical spine. However, the biomechanical data of CDA in the spine with RK have not been reported. This study aimed at establishing finite element (FE) models to (1) explore the effects of RK on the biomechanics of artificial cervical disc; (2) investigate the biomechanical differences of single‐level anterior cervical discectomy and fusion (ACDF) and CDA in the cervical spine with RK.MethodsThe FE models of the cervical spine with lordosis and RK were constructed, then three single‐level surgical models were developed: (1) RK + ACDF; (2) RK + CDA; (3) lordosis + CDA. A 73.6‐N follower load combined with 1 N·m moment was applied at the C2 vertebra to produce cervical motion.ResultsAt the surgical level, “lordosis + CDA” had the greatest ROM (except for flexion) while “RK + ACDF” had the minimum ROM. However, at adjacent levels, the ROM of “RK + ACDF” increased by 4.05% to 38.04% in comparison to “RK + CDA.” “RK + ACDF” had the greatest prosthesis interface stress, while the maximum prosthesis interface stress of “RK + CDA” was at least 2.15 times higher than “lordosis + CDA.” Similarly, “RK + ACDF” had the greatest intradiscal pressure (IDP) at adjacent levels, while the IDP of “RK + CDA” was 1.6 to 6.7 times higher than “lordosis + CDA.” At the surgical level, “RK + CDA” had the greatest facet joint stress (except for extension), which was 1.9 to 11.2 times higher than “lordosis + CDA.” At the adjacent levels, “RK + CDA” had the greatest facet joint stress (except for extension), followed by “RK + ACDF” and “lordosis + CDA” in descending order.ConclusionsRK significantly changed the biomechanics of CDA, which is demonstrated by the decreased ROM and the significantly increased prosthesis interface stress, IDP, and facet joint stress in the “RK + CDA” model. Compared with ACDF, CDA overall exhibited a better biomechanical performance in the cervical spine with RK, with the increased ROM of surgical level and facet joint stress and the decreased ROM of adjacent levels, prosthesis interface stress, and IDP.

Biomechanical Changes of Adjacent and Fixed Segments Through Cortical Bone Trajectory Screw Fixation versus Traditional Trajectory Screw Fixation in the Lumbar Spine: A Finite Element Analysis

The finite element method was used to investigate the biomechanical adjustments of adjacent and fixed segments after lumbar fusion and fixation with traditional trajectory (TT) and cortical bone trajectory (CBT) screws. The model used was a validated nonlinearly L3-S1 finite element model. Interbody fusion cages and 2 types of screws were used to work on the L4-L5. To simulate flexion, extension, lateral bending, and axial rotation, all models were loaded in 3 planes with a compressive pre-load of 400 N and a bending moment of 7.5 N/m. Under various loading conditions, the range of motion (ROM), peak Von Mises stress of the vertebral body, stress of the intervertebral disc, stress of the facet joints, stress of the endplate, and stress of internal fixation were compared. In all instrumentation models, the ROM at fixed segments decreased. At adjacent segments, the ROM of the CBT model was greater than that of the TT model. The CBT model had a greater peak Von Mises stress of the L4 and L5 vertebral bodies, as well as greater stress of internal fixation, than the TT model. Furthermore, as compared with the TT model, the CBT model's facet joint and endplate stress were lower at fixed segments but higher at adjacent segments. The stress on the L3-L4 and L5-S1 intervertebral discs in the CBT and TT models, on the other hand, was nearly equivalent. At the fixed section, CBT may provide slightly better stability, endplate tension, and facet joint stress than TT. The greater ROM, endplate stress, and facet joint stress of CBT in adjacent segments, on the other hand, should be taken into account in the future.

Finite element analysis of wedge and biconcave deformity in four different height restoration after augmentation of osteoporotic vertebral compression fractures

PurposeBiomechanical comparison of wedge and biconcave deformity of different height restoration after augmentation of osteoporotic vertebral compression fractures was analyzed by three-dimensional finite element analysis (FEA).MethodsThree-dimensional finite element model (FEM) of T11-L2 segment was constructed from CT scan of elderly osteoporosis patient. The von Mises stresses of vertebrae, intervertebral disc, facet joints, displacement, and range of motion (ROM) of wedge and biconcave deformity were compared at four different heights (Genant 0–3 grade) after T12 vertebral augmentation.ResultsIn wedge deformity, the stress of T12 decreased as the vertebral height in neutral position, flexion, extension, and left axial rotation, whereas increased sharply in bending at Genant 0; L1 and L2 decreased in all positions excluding flexion of L2, and T11 increased in neutral position, flexion, extension, and right axial rotation at Genant 0. No significant changes in biconcave deformity. The stress of T11-T12, T12-L1, and L1-L2 intervertebral disc gradually increased or decreased under other positions in wedge fracture, whereas L1-L2 no significant change in biconcave fracture. The utmost overall facet joint stress is at Genant 3, whereas there is no significant change under the same position in biconcave fracture. The displacement and ROM of the wedge fracture had ups and downs, while a decline in all positions excluding extension in biconcave fracture.ConclusionsThe vertebral restoration height after augmentation to Genant 0 affects the von Mises stress, displacement, and ROM in wedge deformity, which may increase the risk of fracture, whereas restored or not in biconcave deformity.

Biomechanical evaluation of a novel decompression surgery: Transforaminal full-endoscopic lateral recess decompression (TE-LRD)

BackgroundTransforaminal full endoscopic lateral recess decompression (TE-LRD) can decompress lateral recess stenosis transforaminally under the endoscopy procedure. However, the biomechanical effects of the TE-LRD compared to the conventional decompression techniques are not reported. The purpose of this study is to compare the biomechanical effects of TE-LRD with conventional decompression techniques using finite element method. MethodsThree finite element models of lumbar functional spinal unit (FSU) of the L4-L5 levels were created: 1) normal disc 2) moderate grade disc degeneration 3) severe grade disc degeneration. For each of these three models, the following decompression techniques were simulated, 1) 50% TE-LRD, 2) 100% TE-LRD, 3) Unilateral laminectomy, 4) Bilateral laminectomy. The lower endplate of the fifth lumbar vertebra was fixed and 10Nm of moment in flexion/extension, left/right bending and axial rotation was applied to the upper endplate of the fourth lumbar vertebra, under a follower load of 400N. The range of motion, intervertebral disc stress, and facet joint stress were compared. Results50% TE-LRD was found to be the most stable decompression technique in all intervertebral disc models. Though the increase in the range of motion of 100% TE-LRD was higher than other decompression techniques in the normal disc model, it was not significantly different from 50% TE-LRD or unilateral laminectomy techniques in the degenerated disc models. The increase in the intervertebral disc stress was lowest for the 50% TE-LRD surgery in all intervertebral disc models. The increase in the facet stresses for 50% TE-LRD was lower than in the conventional decompression techniques for all intervertebral disc models. Conclusions50% TE-LRD was the decompression surgical technique with the least effect on spinal instability. 100% TE-LRD showed to be effective for cases with degenerative discs. 50% TE-LRD may decrease the risk of postoperative intervertebral disc and facet joint degeneration.

Friday, September 28, 2018 8:00 AM–9:00 AM interdisciplinary spine forum: abstract presentations: 144. Biomechanical effects of lateral bending position on performing cervical spinal manipulation for cervical disc herniation: a three-dimensional finite element analysis

BACKGROUND CONTEXT Most studies report that the common position of cervical spinal manipulation (CSM) for treating symptomatic cervical disc herniation (CDH) is lateral bending to the herniated side. However, the rationality of lateral bending position on performing CSM for CDH is still unclear. PURPOSE The purpose of this study is to investigate the biomechanical effects of lateral bending position on performing CSM for CDH. STUDY DESIGN/SETTING A finite element analysis study. OUTCOME MEASURES Cervical disc displacement, annulus fiber stress (von Mises stress) and facet joint stress (von Mises stress) were observed during the simulation of CSM. METHODS Afinite element (FE) model of CDH (herniated on the left side) was generated in C5–C6 segment based on the normal FE model. The FE model was performed CSM in left lateral bending position, neutral position and right lateral bending position, respectively. Cervical disc displacement, annulus fiber stress and facet joint stress were observed during the simulation of CSM. RESULTS The cervical disc displacement on herniated side moved forward during CSM, and the maximum forward displacements were 0.23, 0.36 and 0.45mm in left lateral bending position, neutral position and right lateral bending position, respectively. As the same trend of cervical disc displacement, the annulus fiber stress on herniated side from small to large were 7.40, 16.39 and 22.75MPa in left lateral bending position, neutral position and right lateral bending position, respectively. However, the maximum facet stresses at left superior cartilage of C6 in left lateral bending position, neutral position and right lateral bending position were 6.88, 3.60 and 0.12MPa, respectively. CONCLUSIONS Compared with neutral position and right lateral bending position, though the forward displacement of cervical disc on herniated side was smaller in left lateral bending position, the annulus fiber stresson herniated sidewas declined by sharing load on the left facet joint. The results suggested that lateral bending to the herniated side on performing CSM tend to protect the cervical disc on herniated side. Future clinical studies are in need to verify that.

Biomechanical Analysis of Lateral Lumbar Interbody Fusion Constructs with Various Fixation Options: Based on a Validated Finite Element Model.

Lateral lumbar interbody fusion using cage supplemented with fixation has been used widely in the treatment of lumbar disease. A combined fixation (CF) of lateral plate and spinous process plate may provide multiplanar stability similar to that of bilateral pedicle screws (BPS) and may reduce morbidity. The biomechanical influence of the CF on cage subsidence and facet joint stress has not been well described. The aim of this study was to compare biomechanics of various fixation options and to verify biomechanical effects of the CF. The surgical finite element models with various fixation options were constructed based on computed tomography images. The lateral plate and posterior spinous process plate were applied (CF). The 6 motion modes were simulated. Range of motion (ROM), cage stress, endplate stress, and facet joint stress were compared. For the CF model, ROM, cage stress, and endplate stress were the minimum in almost all motion modes. Compared with BPS, the CF reduced ROM, cage stress, and endplate stress in all motion modes. The ROM was reduced by more than 10% in all motion modes except for flexion; cage stress and endplate stress were reduced more than 10% in all motion modes except for rotation-left. After interbody fusion, facet joint stress was reduced substantially compared with the intact conditions in all motion modes except for flexion. The combined plate fixation may offer an alternative to BPS fixation in lateral lumbar interbody fusion.

Biomechanical Effects of Lateral Bending Position on Performing Cervical Spinal Manipulation for Cervical Disc Herniation: A Three‐Dimensional Finite Element Analysis

Background Most studies report that the common position of cervical spinal manipulation (CSM) for treating symptomatic cervical disc herniation (CDH) is lateral bending to the herniated side. However, the rationality of lateral bending position on performing CSM for CDH is still unclear. Objective The purpose of this study is to investigate the biomechanical effects of lateral bending position on performing CSM for CDH. Methods A finite element (FE) model of CDH (herniated on the left side) was generated in C5-6 segment based on the normal FE model. The FE model performed CSM in left lateral bending position, neutral position, and right lateral bending position, respectively. Cervical disc displacement, annulus fiber stress, and facet joint stress were observed during the simulation of CSM. Results The cervical disc displacement on herniated side moved forward during CSM, and the maximum forward displacements were 0.23, 0.36, and 0.45 mm in left lateral bending position, neutral position, and right lateral bending position, respectively. As the same trend of cervical disc displacement, the annulus fiber stresses on herniated side from small to large were 7.40, 16.39, and 22.75 MPa in left lateral bending position, neutral position, and right lateral bending position, respectively. However, the maximum facet stresses at left superior cartilage of C6 in left lateral bending position, neutral position, and right lateral bending position were 6.88, 3.60, and 0.12 MPa, respectively. Conclusion Compared with neutral position and right lateral bending position, though the forward displacement of cervical disc on herniated side was smaller in left lateral bending position, the annulus fiber stress on herniated side was declined by sharing load on the left facet joint. The results suggested that lateral bending to the herniated side on performing CSM tends to protect the cervical disc on herniated side. Future clinical studies are needed to verify that.

Finite Element Analysis of Influence of Axial Position of Center of Rotation of a Cervical Total Disc Replacement on Biomechanical Parameters: Simulated 2-Level Replacement Based on a Validated Model

Finite element models have been widely used to predict biomechanical parameters of the cervical spine. Previous studies investigated the influence of position of rotational centers of prostheses on cervical biomechanical parameters after 1-level total disc replacement. The purpose of this study was to explore the effects of axial position of rotational centers of prostheses on cervical biomechanics after 2-level total disc replacement. A validated finite element model of C3-C7 segments and 2 prostheses, including the rotational center located at the superior endplate (SE) and inferior endplate (IE), was developed. Four total disc replacement models were used: 1) IE inserted at C4-C5 disc space and IE inserted at C5-C6 disc space (IE-IE), 2) IE-SE, 3) SE-IE, and 4) SE-SE. All models were subjected to displacement control combined with a 50 N follower load to simulate flexion and extension motions in the sagittal plane. For each case, biomechanical parameters, including predicted moments, range of rotation at each level, facet joint stress, and von Mises stress on the ultra-high-molecular-weight polyethylene core of the prostheses, were calculated. The SE-IE model resulted in significantly lower stress at the cartilage level during extension and at the ultra-high-molecular-weight polyethylene cores when compared with the SE-SE construct and did not generate hypermotion at the C4-C5 level compared with the IE-SE and IE-IE constructs. Based on the present analysis, the SE-IE construct is recommended for treating cervical disease at the C4-C6 level. This study may provide a useful model to inform clinical operations.

A Validated Finite Element Analysis of Facet Joint Stress in Degenerative Lumbar Scoliosis

To develop modified finite element models to simulate degenerative lumbar scoliosis (DLS) based on the normal lumbar spine model and to investigate the facet joint force of the DLS. A 3-dimensional finite element model of a normal lumbar spine was modified to simulate 3 different Cobb angles conditions (12.3°, 22.2°, and 31.8°). The stresses on the facet joint were calculated on both sides (right and left) of the each vertebra. Changes of stress and asymmetry in contact forces between facet joints in the development of DLS were quantitatively analyzed to better understand the development of DLS and the biomechanical forming mechanism. The results show that asymmetric responses of the facet joint forces exist in various postures and that such effect is amplified with larger curve. When the Cobb angle was smaller, the convex side of the facet joints suffered larger force. When the Cobb angle was larger than 20°, the concave side of the facet joints suffered larger force. In the axial-rotation cases, the facet joint compression is less often located on the ipsilateral side than the contralateral side at the same level. With the asymmetric loading, facet joints compressive deformation appears on the concave side, and it decreases in the effect of the facet joints to limit the vertebral rotation and listhesis. Asymmetric loading on facet joint contact forces accelerates asymmetry in the lumbar spine.

Sacrum Injury

HISTORY: A 44-year-old secretary fell down from 4 meter above from the ground. After detailed physical and neurologic examination she had fixation operation due to fracture of left sacrum and pubic bones. While staying at the hospital, she had an decubitus ulceration on left sacroiliac joint and posterior inferior iliac spine. In spite of decubitus ulceration needed flapping, she rejected operatively treatment. After decubitus ulceration healed itself, she had pain on right side of sacrum and she had an corticostreoid injection on right sacroiliac joint. After injection, pain decreased but still exists. PHYSICAL EXAMINATION: Examination of paravertebral muscles and T12- L5 spinos processes pain and moderate tenderness detected. There was no numbness, allodynia and reflex deficits. Both flexion and extension movements of back were painful. active lomber flexion, her hands reached knee level. She could not sit symetrically. When she sits longer than ten minutes, she felt severe pain on sacrum. DIFFERENTIAL DIAGNOSIS: – Strain of paravertebral, piriformis and Quadratus Lumborum muscles. – Sacroiliac dysfunction – Facet Joint Syndrome TEST AND RESULTS: – Special provocation tests for sacroiliac joint – Lomber facet Joint stress tests – Pressure Pain Thresholds – Back Performance Scale TREATMENT AND OUTCOMES: – Myofascial releasing technics applied to muscles and thoracolomber fascia. – Post-isometric relaxation technics for Piriformis and Quadratus Lumborum muscles on right side. – Physiotherapist guided lomber stabilization exercise – Kinesiotaping application for scar tissue on decubitus ulceration area. – After 4 months later she had painless sitting, standing and walking abilities.

BIOMECHANICAL ANALYSIS OF DIFFERENT PRODISC-C ARTHROPLASTY DESIGNS AFTER IMPLANTATION: A NUMERICAL SENSITIVITY STUDY

Ball-and-socket disc prostheses are the leading type of artificial disc replacement (ADR) and are typically used to treat degenerative cervical spine instability. Previous publications focused on the influence of different ProDisc-C design parameters in view of biomechanics. However, more beneficial data could be gathered if the implant was implanted prior to testing. Therefore, this study aimed to estimate the effect of different ProDisc-C arthroplasty designs and alignments when implanted at the C5-6 segment. This research can provide advice on the design of artificial discs as well as optimal placement. The geometry of the vertebrae was developed based on computed tomography (CT) images of a 32-year-old healthy male (170 cm height and 68 kg weight) with a slice thickness of 0.625 mm. A finite element (FE) model of intact C5–C6 segments including vertebrae and disc was developed and validated. A ball-and-socket artificial disc prosthesis model (ProDisc-C, Synthes) was implanted into the validated FE model. The curvature of the ProDisc-C prosthesis as well as the implanted position was varied. All models were loaded with a 74 N compressive force and pure moments of 1.8 Nm in flexion-extension, bilateral bending and axial torsion. The radius of the artificial disc influenced the ROM, facet joint force and capsule ligament tension only in flexion, while the position influenced these aspects in all loading conditions. The disc with a 6 mm radius had a greater ROM in flexion, and lower stress on the polyethylene (PE) insert without apparent stress concentrations, but it had a greater facet joint force and ligament tension compared to other radii. For all the designs, the implant position in the anterior–posterior direction had a significant influence on the disc biomechanics. Disc design and surgical procedure, such as implantation position, are important factors in postoperative rehabilitation, especially regarding the ROM in flexion/extension and implant stress. Thus, a suitable disc design should consider preserving an adequate range of motion (ROM) as well as a moderate facet joint force or stress, and proper implant positioning along the anterior–posterior direction should be monitored.