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BACKGROUND: Pedicle screw fixation is the preferred surgical treatment for clinical treatment of lumbar degenerative disease currently. The stability of pedicle screw fixation system can be evaluated from the perspective of biomechanics and finite element method is more and more popular in analyzing stress of pedicle screw fixation of vertebral body for researchers. OBJECTIVE: To analyze the stress and displacement changes of human lumbar spine in bending movement from the biomechanical point of view when unilateral and bilateral pedicle screws are fixed, providing theoretical reference for practical clinical application. METHODS: Three-dimensional models were established based on CT data of the volunteers. The volunteers signed the informed consent. This study was approved by the Hospital Ethics Committee. Abaqus software was used to simulate the actual stress conditions. Finite element analysis of lumbar spine flexion was performed during unilateral and bilateral pedicle screw fixation. The stress and displacement of lumbar vertebra, disc and pedicle screw were observed under two fixation methods. RESULTS AND CONCLUSION: (1) Under bilateral fixation, the stress on the left screw was 22.2 MPa, and the stress on the right screw was 21.14 MPa, which was far less than the stress of the screw under unilateral fixation (79.19 MPa). The stress of intervertebral disc in unilateral fixation was 87% larger than that in bilateral fixation; the stress of vertebral body in bilateral fixation was 72% smaller than that in unilateral fixation. (2) From the perspective of displacement, the displacement of screw, lumbar disc and centrum under bilateral fixation were 53%, 55% and 62% smaller than that under unilateral fixation, respectively. (3) Therefore, from the mechanical point of view, bilateral pedicle screw fixation has less stress level, which is friendlier to the human body than unilateral fixation and thus more conducive to the recovery of patients. [ABSTRACT FROM AUTHOR]