Abstract： Objective:To investigate the biomechanical effects of osteoporosis on adjacent vertebral bodies after lateral lumbar interbody fusion (LLIF) .Methods:In this study, L 3-S 1 was used to simulate the normal bone mineral density (BMD) and the state of osteoporosis of lumbar spine before and after LLIF, and to establish the finite element model (FEM) . By endowing FEM with different material properties, the normal finite element model (NFEM) and the osteoporosis finite element model (OFEM) after surgery were simulated. The surgical segment is simulated at L 4-L 5. A follower force of 500 N and a moment load of 7.5 N·m were applied to the model to simulate the different postures of flexion and extension, lateral bending and axial rotation of the lumbar spine. The peak Von Mises force of the vertebral cancellous bone and endplates of the adjacent segments (L 3 and S 1) of NFEM and OFEM were calculated under different postures. Results:Compared with the NFEM group, the peak Von Mises force of L 3 cancellous bone in the OFEM group was significantly decreased in all six postures of anterior-posterior flexion and extension, left and right lateral bending, and left and right axial rotation (8%, 12%, 21%, 16%, 20%, 29%) . Observing the S 1 cancellous bone, and peak Von Mises force of the OFEM group increased in the left-bending, right-bending, left-axial rotation, and right-axial rotation postures (49%, 17%, 25%, 14%) , and decreased in the flexion and left-axial rotation postures (31%, 12%) . Compared with the L 3 cancellous bone, the direction of stress change of the S 1 cancellous bone was different in each posture. Compared with the NFEM group, the peak Von Mises force of the L 3 lower endplate was significantly increased in all six postures in the OFEM group (42.10%, 34.13%, 30.05%, 17.88%, 26.50%, 24.15%) . Compared with the NFEM group, the OFEM group had an increase in the peak Von Mises force of the S 1 upper endplate in the flexion, lateral bending, and axial rotation postures (23.25%, 0.07%, 29.94%, 22.69%, 32.43%) , and decreased stress in the extension posture (5.36%) . Compared with the NFEM group, the peak Von Mises force of the adjacent endplates of the L 4~L 5 segment increased significantly in the OFEM group. Conclusions:In the osteoporosis model, the biomechanics of the adjacent vertebral body obviously changed after LLIF, the stress of the adjacent vertebral endplate obviously increased, and the stress of the cancellous bone in the cephalic side obviously decreased, the stress of caudal cancellous bone showed an increasing trend.