A finite element analysis of the effect on the biomechanics at the surgical segment of transforaminal endoscopic lumbar discectomy combined with non-fused elastic rod pedicle screw internal fixation

English Keywords:Transforaminal endoscopic lumbar discectom  Elastic rod fixation  Surgical segment  Finite element analysis

English Abstract:

  【Abstract】 Objectives: To evaluate the biomechanical effects of transforaminal endoscopic lumbar discectomy(TELD) combined with a spinal dynamic stabilization system(SDSS) on the surgical segment using three-dimensional finite element (FE) analysis. Methods: The CT scan data from the lumbar spine of a healthy volunteer was selected. FE methods were employed to construct normal L3-S1 model(FE), as well as L3-S1 TELD and TELD+SDSS surgical models, with the surgical segment simulated at L4/5. After validating the models′ effectiveness through computational accuracy(ACC), a hybrid loading method was applied. An axial load of 150N was applied to the top of the L1 vertebral body, along with gradually increasing constraint torque. Range of motion(ROM) values were extracted to ensure the three models achieved the following ROM: flexion (15°), extension (10°), lateral bending (5°), and rotation (3°). The ROM, peak stress at the intervertebral disc and posterior annulus fibrosus, and shear stress in the annulus fibrosus at the L4/5 segment under these six directional conditions were compared across the three models. Results: The ROM values of L3-S1 segments under different loading conditions in flexion, extension, and rotation were compared with previous in vitro tests, with ACC exceeding 90%, validating the model′s effectiveness. For L4/5 ROM: in TELD model, it was 4.47°(flexion), 3.3°(extension), 1.72°(left bending), 1.73°(right bending), 0.94°(left rotation), and 0.92°(right rotation); In TELD+SDSS model, it was 2.15°, 1.21°, 1.38°, 1.43°, 0.67°, 0.67° respectively. The ROM in TELD model increased by 5% in flexion and 7% in extension, which in TELD+SDSS model reduced by 19-61% in all directions. For L4/5 disc stress: in TELD model, the peak stress was 14.58MPa, 15.08MPa, 7.92MPa, 5.32MPa, 0.9MPa, and 0.65MPa respectively under flexion, extension, left bending, right bending, left rotation, right rotation conditions; In TELD+SDSS model, it was 5.35MPa, 1.77MPa, 3.45MPa, 3.42MPa, 0.55MPa, and 0.48MPa. The peak stress of L4/5 disc in TELD model increased by 36% and 45% in extension and bending, which in TELD+SDSS model reduced by 27-84% in all directions. For posterior annulus stress: the peak stress in TELD model was 2.04MPa, 2.08MPa, 1.44MPa, 0.99MPa, 0.41MPa, and 0.29MPa respectively under flexion, extension, left bending, right bending, left rotation, right rotation conditions; In TELD+SDSS model, it was 0.54MPa, 0.23MPa, 0.72MPa, 0.7MPa, 0.21MPa, and 0.18MPa. The peak stress at posterior annulus in TELD increased by 10-99% in flexion, extension, and lateral bending, while in TELD+SDSS model it reduced by 20-63% in all directions. For annulus shear stress: in TELD model, it was 0.4MPa, 0.32MPa, and 0.2MPa in extension and left and right bending, which increased by 17%, 76%, and 85%, while in TELD+SDSS model, it reduced by 12-98% in all directions. Conclusions: TELD+SDSS retains certain lumbar motion, affecting lumbar stability less compared to TELD, and provides a low-pressure stress environment.