Biomechanical Finite Element Analysis Of Lateral Displacement Of The Cage After Oblique Lumbar Interbody Fusion

Objective:To evaluate the effect of lateral displacement of cage on the lumbar biomechanics after oblique lateral interbody fusion（OLIF）with finite element analysis,and to provide biomechanical basis for the treatment of this condition.Methods:A healthy male was selected to undergo lumbar CT scanning,and the scanning data were obtained.The three-dimensional finite element model of L3-L5 was established by Mimics,Geomagic,Solid Works and ANSYS Workbench software,which was set as normal control group（M₀）.Then,OLIF Stand alone fixation group（SA）and OLIF with bilateral pedicle screws fixation group（BPS）were established.According to the degree of Cage displacement,the SA group was divided into five groups:the cage non-displaced model（SA₀）,the midpoint of the right edge of the cage shifted to the right 1/8 point（SA₁）,2/8 point（SA₂）,3/8 point（SA₃）,and 4/8 point（SA₄）of the transverse diameter of the upper endplate of L5.On the basis of SA grouping,the models with bilateral pedicle screws were BPS₀,BPS₁,BPS₂,BPS₃and BPS₄respectively.The same loading conditions were applied to different models to simulate the flexion,extension,lateral flexion and rotation of the spine.The range of motion（ROM）of the lumbar spine and the stress peak of the cage and screw-rod system were observed under different working conditions.Results:The ROM of SA₀,SA₁and SA₂was lower than that of M₀in different motion states,while the ROM of SA₃and SA₄was greater than that of M₀in extension and right flexion states.Under different conditions,the ROM and the peak stress of the cage in the SA group and the BPS group were increased with the increase of the lateral distance of the cage.When the cage was in the same position,the activity and the peak stress of the cage in all states in the BPS group were lower than that in the SA group.In each state,the peak stress of the screw and rod system in the BPS group was BPS₀<BPS₁<BPS₂<BPS₃<BPS₄.Conclusion:When the left side of the cage was displaced after OLIF Stand alone,the range of motion of the lumbar spine and the stress peak of the cage in various states were gradually increased with the increase of the displacement distance,showing a tendency of spinal instability.On this basis,combined with bilateral pedicle screw fixation,better biomechanical stability of lumbar spine can be obtained.