Biomechanical Analysis Of Unilateral Biportal Endoscopic Lumbar Interbody Fusion

Objective:Unilateral biportal endoscopic lumbar interbody fusion(UBE-LIF)as a novel minimally invasive technique has been widely used in the treatment of lumbar degenerative diseases.By establishing a finite element model of UBE-LIF,the biomechanical characteristics of UBE-LIF technology were analysed and evaluated.The risk of cage subsidence was also evaluated.Methods:Based on the CT data of healthy adult male volunteers,the finite element models of L4-L5 vertebral body were constructed.According to the UBE-LIF operation method,the model with different cage heights of 8 mm,10 mm and 12 mm were successively constructed(normal bone and osteoporosis).The flexion,extension,right lateral bend,left lateral bend,right axial rotation,and left axial rotation motions were simulated in 6models with different bone conditions on the upper surface of L4 with 500 N followed load and 10 Nm torsional torque.The range of motion(ROM),Pedicle screw-rod system stress and endplate stress of each model under different working conditions were observed and analysed.Results:The ROM of the 12 mm model was the lowest,simultaneously,the maximum stress of the pedicle screw-rod system of the 12 mm model was the lowest.However,the 12 mm model has the largest endplate stress.The maximum stress of the L4 inferior endplate was greater than that of the L5 superior endplate in the UBE-LIF surgical models(24.1%).Compared with the normal model,the ROM of the osteoporosis model increased by5.4%,the maximum stress of the pedicle screw-rod system increased by 14%,and the maximum stress of the endplate increased by 7.5%.Conclusion:The results show that the appropriate height of the cage should be selected during the operation to ensure the stability of the segment and avoid the risk of the subsidence caused by the high cage.This is especially important for patients with osteoporosis.