Finite Element Analysis Of The Effect Of Cage Subsidence On The Biomechanics Of The Lumbar Spine With Oblique Lateral Interbody Fusion

Objective:A three-dimensional finite element method was used to analyse the effect of cage subsidence on the biomechanics of the lumbar spine after oblique lateral interbody fusion.Methods:A 3D finite element model of the normal lumbar L3～L5 segment was constructed from CT scan data of a healthy adult and simulated to perform OLIF surgery on L4～5 segment.Grade0,Grade1,Grade2,Grade2,Grade4 were constructed according to the degree of cage subsidence into the vertebral body 0,1%～25%,26%～50%,51%～75%,76%～100%.Grade3 and Grade4 models were constructed in a total of 10 groups(5 groups with cage subsidence alone and 5 groups with additional posterior pedicle screw fixation).The lower surface of the L5 vertebra was fixed and a preload of 400 N was applied to the upper surface of the L3 vertebra,followed by a torque of 10N-M to simulate forward flexion,extension,lateral flexion and rotation 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 L3/4 and L4/5 vertebrae under different physiological movements of the model was similar to that of published cadaveric studies,demonstrating the validity of the model.Of the six states of motion to which the model was loaded,the maximum ROM in the subsidence group was Grade3,and the maximum stress peak in cage was 82.7 MPa in Grade2 in forward flexion,241% increase compared to Grade 0.The peak ROM and cage stresses were reduced after the attachment of the pedicle screw fixation system,with the most significant change in Grade2 in particular.Compared to unattached internal fixation,the average ROM of Grade2 decreased by 63% and the peak cage stress decreased by 51% with posterior extension.Conclusion:Cage subsidence has a significant impact on lumbar stability,with the worst spinal stability at 51%-75% cage settlement;peak cage stress is highest at 26%-50% cage subsidence,with the potential for further collapse,and this risk can be reduced with the addition of an internal pedicle screw fixation.