Finite element analysis of biomechanical effect of annulus fibrosus suture on the lumbar spine after microendoscopic discectomy

English Keywords:Annulus fibrosus suture  Finite element analysis  Biomechanics

English Abstract:

  【Abstract】 Objective: To investigate the effects of annulus fibrosus(AF) suture or not on the lumbar biomechanics following microendoscopic discectomy(MED) through establishing finite element models(FEMs) of unsutured AF incision and sutured AF incision. Methods: A 27-year-old healthy young adult male volunteer was recruited and underwent lumbar CT to exclude spinal deformities, tumors, and other osseous pathologies. CT images of the L4/L5 segment were imported into the software Mimics for three-dimensional reconstruction and contour extraction. The resulting model was further processed using Geomagic, SolidWorks, and Workbench for solid modeling. An intact L4/5 segment model, an L4/5 model with an unsutured AF incision following MED(unsutured AF model), and an L4/5 model with a sutured AF incision following MED(sutured AF model) were established. Intervertebral range of motion(ROM), Von-Mises stress on the facet joints, and Von-Mises stress on the AF of the models were measured, and model validity was verified by comparison with previously published studies. After validation, the inferior end of the L5 vertebral body in all the three models was fixed. An axial load of 500N was applied to the superior end of the L4 vertebral body, and a bending moment of 7.5N·m was separately applied under six physiological loading conditions(flexion, extension, left/right lateral bending, and left/right axial rotation). The biomechanical properties of the three models at the L4/5 level, including intervertebral ROM and Von-Mises stress in facet joints, and Von-Mises stress on the AF were compared under different loading conditions. Results: No significant discrepancies were noted when data obtained under these six motion conditions were compared with the findings from prior literature, thus validating the models. Stress nephogram results revealed that under each motion condition, high-stress areas were located at the unsutured defect of the intervertebral disc AF and the surrounding facet joint processes. Compared with the intact model, the intervertebral ROM of the sutured AF model was 8.6802°, 8.596°, 4.8514°, 5.0249°, 2.2474°, and 1.9092°, respectively, under the six motions, while that of the unsutured AF model was 8.7475°, 8.9453°, 5.6441°, 5.2546°, 2.5886°, and 1.9487°, respectively. The ROM of the sutured AF model was 9%, 19%, 44%, 38%, 50%, and 40% higher than that of the intact model; Compared with the unsutured AF model, it was reduced by 1%, 4%, 14%, 4%, 13%, and 2% respectively. For Von Mises stress on the AF under the six motion conditions, the stress of the sutured AF model was 2%, 65%, 21%, 32%, 51%, and 38% higher than that of the intact model, but 8%, 48%, 52%, 10%, 37%, and 48% lower than that of the unsutured AF model respectively. For Von-Mises stress in facet joints, the stress values of the sutured AF model were 12.109MPa, 8.3601MPa, 13.998MPa, 12.969MPa, 10.219MPa, and 10.074MPa respectively, while those of the unsutured AF model were 13.399MPa, 9.6094MPa, 18.175MPa, 17.967MPa, 12.409MPa, and 11.6384MPa respectively. The stress values of Von-Mises stress in facet joints of the sutured AF model was 5%, 10%, 32%, 17%, 31%, and 34% higher than that of the intact model; Compared with the unsutured AF model, it was decreased by 9%, 13%, 22%, 27%, 17%, and 13% respectively. Conclusions: Among the three constructed L4/5 FEMs, the sutured AF model exhibits more favorable intervertebral ROM, and Von-Mises stress of facet joints and AF compared with the unsutured AF model. This indicates that AF suture contributes to enhancing intervertebral stability.