Biomechanical Comparison of Lateral Interbody Fusion with and without Fixation

Objective: To compare biomechanical behaviors of lumbar lateral interbody fusion with and without posterior fixation. Methods: Three kinds of three-dimensional nonlinear finite element models of lumbar vertebrae (L3-S1) were developed: traditional lateral interbody fusion with bilateral pedicle 4 screws and 2 rods internal fixation; only lateral interbody fusion; intact model. The models were supported to a 500N follower load with a 7.5-N.m moment of flexion, extension,lateral bending,and rotation. The change of the range of motion (ROM) and intervertebral disc pressure (IDP) of the surgical segment and adjacent segments are compared. Results: Compared with the intact model, both surgical methods reduce the range of motion at the surgical segment in all motion modes, but have almost no effect on adjacent segments. The addition of fixation induce the further reduction of ROM in the surgical segment, and the ROM is almost 0° in all motion modes except for rotation. While for the model of only lateral interbody fusion, the ROM range from 0.4° to 2.2°. Moreover, the variation of the intervertebral disc pressure in surgery groups are extremely subtle in all the segments and all the postures. Conclusion: Compared to the only lateral interbody fusion,the traditional internal fixation with bilateral pedicle 4 screws and 2 rods for lateral interbody fusion showed more bimechanical stability of the surgical segment. The extra fixation for lumbar lateral interbody fusion is indispensable for surgeon.