Anterior cervical fusion: a biomechanical comparison of 4 techniques

Object Cervical instrumented fusion is currently performed using several fixation methods. In the present paper, the authors compare the following 4 implantation methods: a stand-alone cage, a cage supplemented by an anterior locking plate, a cage supplemented by an anterior dynamic plate, and a dynamic combined plate–cage device. Methods Four finite element models of the C4–7 segments were built, each including a different instrumented fixation type at the C5–6 level. A compressive preload of 100 N combined with a pure moment of 2.5 Nm in flexion, extension, right lateral bending, and right axial rotation was applied to the 4 models. The segmental principal ranges of motion and the load shared by the interbody cage were obtained for each simulation. Results The stand-alone cage showed the lowest stabilization capability among the 4 configurations investigated, but it was still significant. The cage supplemented by the locking plate was very stiff in all directions. The 2 dynamic plate configurations reduced flexibility in all directions compared with the intact case, but they left significant mobility in the implanted segment. These configurations were able to share a significant part of the load (up to 40% for the combined plate–cage) through the posterior cage. The highest risk of subsidence was obtained with the model of the stand-alone cage. Conclusions Noticeable differences in the results were detected for the 4 configurations. The actual clinical relevance of these differences, currently considered not of critical importance, should be investigated by randomized clinical trials.

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Biomechanical Comparison of Posterior Fixation Combinations with an Allograft Spacer between the Lateral Mass and Pedicle Screws

Applied Sciences ◽

10.3390/app10207291 ◽

2020 ◽

Vol 10 (20) ◽

pp. 7291

Author(s):

Soo-Bin Lee ◽

Hwan-Mo Lee ◽

Tae-Hyun Park ◽

Sung Lee ◽

Young-Woo Kwon ◽

...

Keyword(s):

Pedicle Screws ◽

Element Model ◽

Axial Rotation ◽

Posterior Fixation ◽

Hybrid Technique ◽

Lateral Mass ◽

Lateral Bending ◽

Flexion Extension ◽

Hybrid Motion ◽

Biomechanical Comparison

Background: There are a few biomechanical studies that describe posterior fixation methods with pedicle screws (PS) and lateral mass screws (LMS); the combination of both screw types and their effect on an allograft spacer in a surgically treated cervical segment is unknown. Methods: Finite element model (FEM) analyses were used to investigate the effects of a hybrid technique using posterior PS and LMS. Stress distribution and subsidence risk from a combination of screws under hybrid motion control conditions, including flexion, extension, axial rotation, and lateral bending, were investigated to evaluate the biomechanical characteristics of different six-screw combinations. Findings: The load sharing on the allograft spacer in flexion mode was highest in the LMS model (74.6%) and lowest in the PS model (35.1%). The likelihood of subsidence of allograft spacer on C6 was highest in the screws from the distal LMS (type 5) model during flexion and extension (4.902 MPa, 30.1% and 2.189 MPa, 13.4%). In lateral bending, the left unilateral LMS (type 4) model screws on C5 (3.726 MPa, 22.9%) and C6 (2.994 MPa, 18.4%) yielded the greatest subsidence risks, because the lateral bending forces were supported by the LMS. In counterclockwise axial rotation, the left unilateral LMS (type 4) model screws on C5 (3.092 MPa, 19.0%) and C6 (3.076 MPa, 18.9%) demonstrated the highest subsidence risks. Conclusion: The asymmetrical ipsilateral use of LMS and posterior PS in lateral bending and axial rotation demonstrated the lowest stability and greatest subsidence risk. We recommend bilateral symmetrical insertion of LMS or posterior PS and posterior PS on distal vertebrae for increased stability and reduced risk of allograft spacer subsidence.

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Biomechanical analysis of stand-alone lumbar interbody cages versus 360° constructs: an in vitro and finite element investigation

Journal of Neurosurgery Spine ◽

10.3171/2021.9.spine21558 ◽

2021 ◽

pp. 1-9

Keyword(s):

Interbody Fusion ◽

Posterior Instrumentation ◽

Axial Rotation ◽

Posterior Fixation ◽

Interbody Cage ◽

Lateral Bending ◽

Flexion Extension ◽

Lateral Interbody ◽

Flexion And Extension

OBJECTIVE Low fusion rates and cage subsidence are limitations of lumbar fixation with stand-alone interbody cages. Various approaches to interbody cage placement exist, yet the need for supplemental posterior fixation is not clear from clinical studies. Therefore, as prospective clinical studies are lacking, a comparison of segmental kinematics, cage properties, and load sharing on vertebral endplates is needed. This laboratory investigation evaluates the mechanical stability and biomechanical properties of various interbody fixation techniques by performing cadaveric and finite element (FE) modeling studies. METHODS An in vitro experiment using 7 fresh-frozen human cadavers was designed to test intact spines with 1) stand-alone lateral interbody cage constructs (lateral interbody fusion, LIF) and 2) LIF supplemented with posterior pedicle screw-rod fixation (360° constructs). FE and kinematic data were used to validate a ligamentous FE model of the lumbopelvic spine. The validated model was then used to evaluate the stability of stand-alone LIF, transforaminal lumbar interbody fusion (TLIF), and anterior lumbar interbody fusion (ALIF) cages with and without supplemental posterior fixation at the L4–5 level. The FE models of intact and instrumented cases were subjected to a 400-N compressive preload followed by an 8-Nm bending moment to simulate physiological flexion, extension, bending, and axial rotation. Segmental kinematics and load sharing at the inferior endplate were compared. RESULTS The FE kinematic predictions were consistent with cadaveric data. The range of motion (ROM) in LIF was significantly lower than intact spines for both stand-alone and 360° constructs. The calculated reduction in motion with respect to intact spines for stand-alone constructs ranged from 43% to 66% for TLIF, 67%–82% for LIF, and 69%–86% for ALIF in flexion, extension, lateral bending, and axial rotation. In flexion and extension, the maximum reduction in motion was 70% for ALIF versus 81% in LIF for stand-alone cases. When supplemented with posterior fixation, the corresponding reduction in ROM was 76%–87% for TLIF, 86%–91% for LIF, and 90%–92% for ALIF. The addition of posterior instrumentation resulted in a significant reduction in peak stress at the superior endplate of the inferior segment in all scenarios. CONCLUSIONS Stand-alone ALIF and LIF cages are most effective in providing stability in lateral bending and axial rotation and less so in flexion and extension. Supplemental posterior instrumentation improves stability for all interbody techniques. Comparative clinical data are needed to further define the indications for stand-alone cages in lumbar fusion surgery.

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Biomechanics of lateral lumbar interbody fusion constructs with lateral and posterior plate fixation

Journal of Neurosurgery Spine ◽

10.3171/2013.11.spine13617 ◽

2014 ◽

Vol 20 (3) ◽

pp. 291-297 ◽

Cited By ~ 31

Author(s):

Guy R. Fogel ◽

Rachit D. Parikh ◽

Stephen I. Ryu ◽

Alexander W. L. Turner

Keyword(s):

Interbody Fusion ◽

Plate Fixation ◽

Spinous Process ◽

Pedicle Screws ◽

Axial Rotation ◽

Interbody Cage ◽

Lateral Bending ◽

Lateral Plate ◽

Flexion Extension ◽

Supplemental Fixation

Object Lumbar interbody fusion is indicated in the treatment of degenerative conditions. Laterally inserted interbody cages significantly decrease range of motion (ROM) compared with other cages. Supplemental fixation options such as lateral plates or spinous process plates have been shown to provide stability and to reduce morbidity. The authors of the current study investigate the in vitro stability of the interbody cage with a combination of lateral and spinous process plate fixation and compare this method to the established bilateral pedicle screw fixation technique. Methods Ten L1–5 specimens were evaluated using multidirectional nondestructive moments (± 7.5 N·m), with a custom 6 degrees-of-freedom spine simulator. Intervertebral motions (ROM) were measured optoelectronically. Each spine was evaluated under the following conditions at the L3–4 level: intact; interbody cage alone (stand-alone); cage supplemented with lateral plate; cage supplemented with ipsilateral pedicle screws; cage supplemented with bilateral pedicle screws; cage supplemented with spinous process plate; and cage supplemented with a combination of lateral plate and spinous process plate. Intervertebral rotations were calculated, and ROM data were normalized to the intact ROM data. Results The stand-alone laterally inserted interbody cage significantly reduced ROM with respect to the intact state in flexion-extension (31.6% intact ROM, p < 0.001), lateral bending (32.5%, p < 0.001), and axial rotation (69.4%, p = 0.002). Compared with the stand-alone condition, addition of a lateral plate to the interbody cage did not significantly alter the ROM in flexion-extension (p = 0.904); however, it was significantly decreased in lateral bending and axial rotation (p < 0.001). The cage supplemented with a lateral plate was not statistically different from bilateral pedicle screws in lateral bending (p = 0.579). Supplemental fixation using a spinous process plate was not significantly different from bilateral pedicle screws in flexion-extension (p = 0.476). The combination of lateral plate and spinous process plate was not statistically different from the cage supplemented with bilateral pedicle screws in all the loading modes (p ≥ 0.365). Conclusions A combination of lateral and spinous process plate fixation to supplement a laterally inserted interbody cage helps achieve rigidity in all motion planes similar to that achieved with bilateral pedicle screws.

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Restabilization of the Occipitocervical Junction After a Complete Unilateral Condylectomy: A Biomechanical Comparison of Unilateral and Bilateral Fixation Techniques

Operative Neurosurgery ◽

10.1093/ons/opz341 ◽

2019 ◽

Vol 19 (2) ◽

pp. 157-164 ◽

Cited By ~ 1

Author(s):

Ilyas M Eli ◽

Michael Karsy ◽

Darrel S Brodke ◽

Kent N Bachus ◽

William T Couldwell ◽

...

Keyword(s):

Biomechanical Testing ◽

Axial Rotation ◽

Neurological Injury ◽

Occipital Condyle ◽

Posterior Fixation ◽

Lateral Bending ◽

Flexion Extension ◽

Fixation Techniques ◽

The Difference ◽

Biomechanical Comparison

Abstract BACKGROUND Occipitocervical instability may result from transcondylar resection of the occipital condyle. Initially, patients may be able to maintain a neutral alignment but severe occipitoatlantal subluxation may subsequently occur, with cranial settling, spinal cord kinking, and neurological injury. OBJECTIVE To evaluate the ability of posterior fixation constructs to prevent progression to severe deformity after radical unilateral condylectomy. METHODS Eight human cadaveric specimens (Oc-C2) underwent biomechanical testing to compare stiffness under physiological loads (1.5 N m). A complete unilateral condylectomy was performed to destabilize one Oc-C1 joint, and the contralateral joint was left intact. Unilateral Oc-C1 or Oc-C2 constructs on the resected side and bilateral Oc-C1 or Oc-C2 constructs were tested. RESULTS The bilateral Oc-C2 construct provided the greatest stiffness, but the difference was only statistically significant in certain planes of motion. The unilateral constructs had similar stiffness in lateral bending, but the unilateral Oc-C1 construct was less stiff in axial rotation and flexion-extension than the unilateral Oc-C2 construct. The bilateral Oc-C2 construct was stiffer than the unilateral Oc-C2 construct in axial rotation and lateral bending, but there was no difference between these constructs in flexion-extension. CONCLUSION Patients who undergo a complete unilateral condylectomy require close surveillance for occipitocervical instability. A bilateral Oc-C2 construct provides suitable biomechanical strength, which is superior to other constructs. A unilateral construct decreases abnormal motion but lacks the stiffness of a bilateral construct. However, given that most patients undergo a partial condylectomy and only a small proportion of patients develop instability, there may be scenarios in which a unilateral construct may be appropriate, such as for temporary internal stabilization.

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Biomechanical Comparison of Four C1 to C2 Rigid Fixative Techniques: Anterior Transarticular, Posterior Transarticular, C1 to C2 Pedicle, and C1 to C2 Intralaminar Screws

Neurosurgery ◽

10.1227/01.neu.0000197222.05299.31 ◽

2006 ◽

Vol 58 (3) ◽

pp. 516-521 ◽

Cited By ~ 131

Author(s):

Samir B. Lapsiwala ◽

Paul A. Anderson ◽

Ashish Oza ◽

Daniel K. Resnick

Keyword(s):

Pedicle Screw ◽

Screw Fixation ◽

Axial Rotation ◽

Lateral Bending ◽

Transarticular Screw ◽

Transarticular Screw Fixation ◽

Flexion Extension ◽

Fixation Techniques ◽

Biomechanical Comparison ◽

Cable Fixation

Abstract OBJECTIVE: We performed a biomechanical comparison of several C1 to C2 fixation techniques including crossed laminar (intralaminar) screw fixation, anterior C1 to C2 transarticular screw fixation, C1 to 2 pedicle screw fixation, and posterior C1 to C2 transarticular screw fixation. METHODS: Eight cadaveric cervical spines were tested intact and after dens fracture. Four different C1 to C2 screw fixation techniques were tested. Posterior transarticular and pedicle screw constructs were tested twice, once with supplemental sublaminar cables and once without cables. The specimens were tested in three modes of loading: flexion-extension, lateral bending, and axial rotation. All tests were performed in load and torque control. Pure bending moments of 2 nm were applied in flexion-extension and lateral bending, whereas a 1 nm moment was applied in axial rotation. Linear displacements were recorded from extensometers rigidly affixed to the C1 and C2 vertebrae. Linear displacements were reduced to angular displacements using trigonometry. RESULTS: Adding cable fixation results in a stiffer construct for posterior transarticular screws. The addition of cables did not affect the stiffness of C1 to C2 pedicle screw constructs. There were no significant differences in stiffness between anterior and posterior transarticular screw techniques, unless cable fixation was added to the posterior construct. All three posterior screw constructs with supplemental cable fixation provide equal stiffness with regard to flexion-extension and axial rotation. C1 lateral mass-C2 intralaminar screw fixation restored resistance to lateral bending but not to the same degree as the other screw fixation techniques. CONCLUSION: All four screw fixation techniques limit motion at the C1 to 2 articulation. The addition of cable fixation improves resistance to flexion and extension for posterior transarticular screw fixation.

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Motion preservation surgery for scoliosis with a vertebral body tethering system: a biomechanical study

European Spine Journal ◽

10.1007/s00586-021-07035-4 ◽

2021 ◽

Author(s):

Luis Fernando Nicolini ◽

Philipp Kobbe ◽

Jana Seggewiß ◽

Johannes Greven ◽

Marx Ribeiro ◽

...

Keyword(s):

Vertebral Body ◽

Tracking System ◽

Axial Rotation ◽

Biomechanical Study ◽

Lateral Side ◽

Lateral Bending ◽

Flexion Extension ◽

Pure Moment ◽

L1 And L2 ◽

Hybrid Construction

Abstract Purpose There is a paucity of studies on new vertebral body tethering (VBT) surgical constructs especially regarding their potentially motion-preserving ability. This study analyses their effects on the ROM of the spine. Methods Human spines (T10-L3) were tested under pure moment in four different conditions: (1) native, (2) instrumented with one tether continuously connected in all vertebrae from T10 to L3, (3) additional instrumented with a second tether continuously connected in all vertebrae from T11 to L3, and (4) instrumented with one tether and one titanium rod (hybrid) attached to T12, L1 and L2. The instrumentation was inserted in the left lateral side. The intersegmental ROM was evaluated using a magnetic tracking system, and the medians were analysed. Please check and confirm the author names and initials are correct. Also, kindly confirm the details in the metadata are correct. The mentioned information is correct Results Compared to the native spine, the instrumented spine presented a reduction of less than 13% in global ROM considering flexion–extension and axial rotation. For left lateral bending, the median global ROM of the native spine (100%) significantly reduced to 74.6%, 66.4%, and 68.1% after testing one tether, two tethers and the hybrid construction, respectively. In these cases, the L1-L2 ROM was reduced to 68.3%, 58.5%, and 38.3%, respectively. In right lateral bending, the normalized global ROM of the spine with one tether, two tethers and the hybrid construction was 58.9%, 54.0%, and 56.6%, respectively. Considering the same order, the normalized L1-L2 ROM was 64.3%, 49.9%, and 35.3%, respectively. Conclusion The investigated VBT techniques preserved global ROM of the spine in flexion–extension and axial rotation while reduced the ROM in lateral bending.

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Biomechanical analysis of a newly developed interspinous process device conjunction with interbody cage based on a finite element model

PLoS ONE ◽

10.1371/journal.pone.0243771 ◽

2020 ◽

Vol 15 (12) ◽

pp. e0243771

Author(s):

In-Suk Bae ◽

Koang-Hum Bak ◽

Hyoung-Joon Chun ◽

Je Il Ryu ◽

Sung-Jae Park ◽

...

Keyword(s):

Finite Element ◽

Lumbar Spine ◽

Finite Element Model ◽

Element Model ◽

Axial Rotation ◽

Biomechanical Analysis ◽

Interbody Cage ◽

Lateral Bending ◽

Flexion Extension ◽

Interspinous Process Device

Purpose This study aimed to investigate the biomechanical effects of a newly developed interspinous process device (IPD), called TAU. This device was compared with another IPD (SPIRE) and the pedicle screw fixation (PSF) technique at the surgical and adjacent levels of the lumbar spine. Materials and methods A three-dimensional finite element model analysis of the L1-S1 segments was performed to assess the biomechanical effects of the proposed IPD combined with an interbody cage. Three surgical models—two IPD models (TAU and SPIRE) and one PSF model—were developed. The biomechanical effects, such as range of motion (ROM), intradiscal pressure (IDP), disc stress, and facet loads during extension were analyzed at surgical (L3-L4) and adjacent levels (L2-L3 and L4-L5). The study analyzed biomechanical parameters assuming that the implants were perfectly fused with the lumbar spine. Results The TAU model resulted in a 45%, 49%, 65%, and 51% decrease in the ROM at the surgical level in flexion, extension, lateral bending, and axial rotation, respectively, when compared to the intact model. Compared to the SPIRE model, TAU demonstrated advantages in stabilizing the surgical level, in all directions. In addition, the TAU model increased IDP at the L2-L3 and L4-L5 levels by 118.0% and 78.5% in flexion, 92.6% and 65.5% in extension, 84.4% and 82.3% in lateral bending, and 125.8% and 218.8% in axial rotation, respectively. Further, the TAU model exhibited less compensation at adjacent levels than the PSF model in terms of ROM, IDP, disc stress, and facet loads, which may lower the incidence of the adjacent segment disease (ASD). Conclusion The TAU model demonstrated more stabilization at the surgical level than SPIRE but less stabilization than the PSF model. Further, the TAU model demonstrated less compensation at adjacent levels than the PSF model, which may lower the incidence of ASD in the long term. The TAU device can be used as an alternative system for treating degenerative lumbar disease while maintaining the physiological properties of the lumbar spine and minimizing the degeneration of adjacent segments.

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Biomechanical Evaluation of Lumbar Decompression Adjacent to Instrumented Segments

Neurosurgery ◽

10.1227/neu.0000000000001419 ◽

2016 ◽

Vol 79 (6) ◽

pp. 895-904 ◽

Cited By ~ 7

Author(s):

Peter Grunert ◽

Phillip M. Reyes ◽

Anna G.U.S. Newcomb ◽

Sara B. Towne ◽

Brian P. Kelly ◽

...

Keyword(s):

Minimally Invasive ◽

Axial Rotation ◽

Mechanical Effect ◽

Distribution Analysis ◽

Lumbar Stenosis ◽

Lateral Bending ◽

Flexion Extension ◽

Pure Moment ◽

Biomechanical Evaluation ◽

Laminectomy And Fusion

Abstract BACKGROUND: Multilevel lumbar stenosis, in which 1 level requires stabilization due to spondylolisthesis, is routinely treated with multilevel open laminectomy and fusion. We hypothesized that a minimally invasive (MI) decompression is biomechanically superior to open laminectomy and may allow decompression of the level adjacent the spondylolisthesis without additional fusion. OBJECTIVE: To study the mechanical effect of various decompression procedures adjacent to instrumented segments in cadaver lumbar spines. METHODS: Conditions tested were (1) L4-L5 instrumentation, (2) L3-L4 MI decompression, (3) addition of partial facetectomy at L3-L4, and (4) addition of laminectomy at L3-L4. Flexibility tests were performed for range of motion (ROM) analysis by applying nonconstraining, pure moment loading during flexion-extension, lateral bending, and axial rotation. Compression flexion tests were performed for motion distribution analysis. RESULTS: After instrumentation, MI decompression increased flexion-extension ROM at L3-L4 by 13% (P = .03) and axial rotation by 23% (P = .003). Partial facetectomy further increased axial rotation by 15% (P = .03). After laminectomy, flexion-extension ROM further increased by 12% (P = .05), a 38% increase from baseline, and axial rotation by 17% (P = .02), a 58% increase from baseline. MI decompression yielded no significant increase in segmental contribution of motion at L3-L4, in contrast to partial facetectomy and laminectomy (<.05). CONCLUSION: MI tubular decompression is biomechanically superior to open laminectomy adjacent to instrumented segments. These results lend support to the concept that in patients in whom a multilevel MI decompression is performed, the fusion might be limited to the segments with actual instability.

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Zero-profile hybrid fusion construct versus 2-level plate fixation to treat adjacent-level disease in the cervical spine

Journal of Neurosurgery Spine ◽

10.3171/2014.7.spine131059 ◽

2014 ◽

Vol 21 (5) ◽

pp. 753-760 ◽

Cited By ~ 7

Author(s):

Andrew T. Healy ◽

Swetha J. Sundar ◽

Raul J. Cardenas ◽

Prasath Mageswaran ◽

Edward C. Benzel ◽

...

Keyword(s):

Repeated Measures ◽

Axial Rotation ◽

Lateral Bending ◽

Adjacent Level ◽

Test Protocol ◽

Single Level ◽

Test Conditions ◽

Flexion Extension ◽

Intact Condition ◽

Pure Moment

Object Single-level anterior cervical discectomy and fusion (ACDF) is an established surgical treatment for cervical myelopathy. Within 10 years of undergoing ACDF, 19.2% of patients develop symptomatic adjacent-level degeneration. Performing ACDF adjacent to prior fusion requires exposure and removal of previously placed hardware, which may increase the risk of adverse outcomes. Zero-profile cervical implants combine an interbody spacer with an anterior plate into a single device that does not extend beyond the intervertebral disc space, potentially obviating the need to remove prior hardware. This study compared the biomechanical stability and adjacent-level range of motion (ROM) following placement of a zero-profile device (ZPD) adjacent to a single-level ACDF against a standard 2-level ACDF. Methods In this in vitro biomechanical cadaveric study, multidirectional flexibility testing was performed by a robotic spine system that simulates flexion-extension, lateral bending, and axial rotation by applying a continuous pure moment load. Testing conditions were as follows: 1) intact, 2) C5–6 ACDF, 3) C4–5 ZPD supraadjacent to simulated fusion at C5–6, and 4) 2-level ACDF (C4–6). The sequence of the latter 2 test conditions was randomized. An unconstrained pure moment of 1.5 Nm with a 40-N simulated head weight load was applied to the intact condition first in all 3 planes of motion and then using the hybrid test protocol, overall intact kinematics were replicated subsequently for each surgical test condition. Intersegmental rotations were measured optoelectronically. Mean segmental ROM for operated levels and adjacent levels was recorded and normalized to the intact condition and expressed as a percent change from intact. A repeated-measures ANOVA was used to analyze the ROM between test conditions with a 95% level of significance. Results No statistically significant differences in immediate construct stability were found between construct Patterns 3 and 4, in all planes of motion (p > 0.05). At the operated level, C4–5, the zero-profile construct showed greater decreases in axial rotation (–45% vs –36%) and lateral bending (–55% vs –38%), whereas the 2-level ACDF showed greater decreases in flexion-extension (–40% vs –34%). These differences were marginal and not statistically significant. Adjacent-level motion was nearly equivalent, with minor differences in flexion-extension. Conclusions When treating degeneration adjacent to a single-level ACDF, a zero-profile implant showed stabilizing potential at the operated level statistically similar to that of the standard revision with a 2-level plate. Revision for adjacent-level disease is common, and using a ZPD in this setting should be investigated clinically because it may be a faster, safer alternative.

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VALIDATION OF FINITE ELEMENT MODELS OF THORACOLUMBAR T11-T12 AND T12-L1 AND COMPARISON OF THEIR BIOMECHANICAL RESPONSES

Journal of Musculoskeletal Research ◽

10.1142/s0218957705001576 ◽

2005 ◽

Vol 09 (03) ◽

pp. 133-143 ◽

Cited By ~ 1

Author(s):

Tian-Xia Qiu ◽

Ee-Chon Teo ◽

Qing-Hang Zhang

Keyword(s):

Finite Element ◽

Axial Rotation ◽

Finite Element Models ◽

Lateral Bending ◽

Physiological Loading ◽

Flexion Extension ◽

Biomechanical Responses ◽

Left And Right ◽

Loading Modes ◽

Flexion And Extension

The objective of this study was to build and validate the FE models of thoracolumbar junctional T11-T12 and T12-L1 functional spinal units (FSUs) and compare the biomechanical responses of the two FSUs under physiological loading modes: flexion, extension, lateral bending and axial rotation. Anatomically accurate FE models of thoracolumbar T11-T12 and T12-L1 FSUs were developed and validated against published experimental results in terms of load displacement responses and range of motion (ROM) under flexion and extension pure moments of 7.5 Nm, left and right lateral bending pure moments of 7.5 Nm and left and right axial torque of 7.5 Nm. The overall responses predicted by the T11-T12 and T12-L1 FE models showed differences in stiffness under different load configurations. Amongst all loading configurations, the motions at T11-T12 and T12-L1 were the stiffest under axial torque. The lateral bending motions of T11-T12 and T12-L1 were relatively flexible. Under sagittal moments, the motion in extension was greater than in flexion at level T11-T12, while the rotation in flexion was greater than in extension at level T12-L1.

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