Finite element analysis of lumbar biomechanical effects of cage subsidence in oblique lateral interbody fusion

English Keywords:Oblique lateral interbody fusion  Complications  Cage subsidence  Finite element  Biomechanics

English Abstract:

  【Abstract】 Objectives: To analyze the effect of cage subsidence on the biomechanics of the lumbar spine after oblique lateral interbody fusion(OLIF) using three-dimensional finite element method. Methods: To construct a three-dimensional finite element model of the L3-L5 segments of the normal lumbar spine according to the CT scan data of a case of a healthy adult, to simulate the L4/5 segment OLIF surgery, and to construct Grade0, Grade1, Grade2, Grade3 and Grade4 according to the degree of cage subsidence into the vertebral body 0, 1%-25%, 26%-50%, 51%-75% and 76%-100% of the vertebral body. Constructed a total of 10 groups of models(5 groups of stand-alone subsidence and 5 groups of additional posterior bilateral pedicle screws). The lower surface of the L5 vertebral body was fixed, a preloaded load of 400N was set on the upper surface of the L3 vertebral body, and a torque of 10N·m was applied to simulate the anterior flexion, posterior extension, lateral flexion, and rotational motion of the spine. The L4/5 range of motion(ROM), peak cage stresses and peak stresses of the pedicle screw fixation system were analysed for different physiological movements of the lumbar spine. Results： The ROM of the model for L3/4 and L4/5 vertebrae under different physiological motions was similar to published cadaver studies, demonstrated the validity of the model. Of the six states of motion to which the model was loaded, the ROM of Grade3 in the sedimentation group was the largest, and the maximum stress of cage occurred in the forward flexion movement of Grade2, which reached 82.7MPa, an increase of 241% compared with Grade0. After the addition of pedicle screw fixation system, the peak stress of ROM and cage in the spine decreased, especially the change of Grade2 was the most significant. Compared with stand-alone cage subsidence, the average ROM of Grade2 decreased by 63%, and the peak stress of cage decreased by 51% under the extension exercise. Conclusions: Cage subsidence has a great influence on the biomechanics of the lumbar spine, in which the stability of the spine is the worst when the cage subsidence is 51%-75%, and the risk of further collapse of the cage is the highest when the cage subsidence is 26%-50%. The addition of pedicle screw fixation system can increase the stability of the spine and reduce the risk of subsidence.