Objective To explore the mechanical properties of modified cortical bone trajectory(MCBT)and cortical bone trajectory(CBT)in lumbar revision surgery using finite element analysis and to analyze the advantages of MCBT over CBT in lumbar revision.Methods A three-dimensional(3D)model of the L1-5 vertebral body,endplate,annulus fibrosus,and nucleus pulposus was established based on CT tomography data.The traditional trajectory(TT)was used for pedicle screw placement in the vertebral body model;then,the TT screws were removed,retaining the TT screw path,and revision screws were placed on the vertebral body with MCBT and CBT screws.The mechanical properties of the MCBT and CBT during revision surgery were analyzed using finite element analysis.Results Under flexion,extension,lateral bending,and axial rotation,the range of motion(ROM)in the CBT revision group decreased by 12.07％,19.60％,8.72％,and 7.66％,respectively;the annulus stress of L3-4 segment increased by 11.27％,30.43％,35.52％,and 25.36％,respectively;and the annulus stress of L4-5 segment decreased by 39.84％,52.64％,23.91％,and 15.77％,respectively,compared with the control group.The ROM in the MCBT revision group decreased by 13.18％,20.27％,25.63％,and 8.59％,respectively;the annulus stress of the L3-4 segment increased by 10.41％,21.60％,15.83％,and 18.41％,respectively;and the annulus stress of the L4-5 segment decreased by 37.14％,61.94％,39.46％,and 35.23％,respectively,compared with the control group.The ROM of the MCBT revision group decreased by 1.26％,0.83％,18.53％,and 1.00％,respectively.The annulus stress of the L3-4 segment decreased by 0.77％,6.77％,14.53％,and 5.54％,respectively,whereas that of the L4-5 segment decreased by 2.82％,15.91％,19.79％,and 8.75％,respectively,compared to the CBT revision group.Compared with the CBT revision group,the annulus stress of the L4-5 segment in the MCBT revision group increased by 4.49％under flexion and decreased by 19.65％,20.44％,and 23.11％under extension,lateral bending,and axial rotation,respectively.Conclusions Both MCBT and CBT can provide mechanical properties that meet the requirements of vertebral fixation,and the fixation performance and safety of MCBT are comparable to those of CBT.This study provides a reference for using the MCBT and CBT techniques in revision surgery in clinical practice.

Objective To study mechanical properties of traditional trajectory (TT) and modified cortical bone trajectory (MCBT) on osteoporotic vertebrae through finite element analysis. Methods The three-dimensional model of L4 segment was established, and pedicle screw (PS) (diameter 6.0 mm, length 45 mm) and MCBT screw (diameter 4.5 mm, length 40 mm) were placed on both sides of the lumbar spine. The pull-out strength and the load-displacement ratio of screws in two different screw trajectories under up, down, left, right working conditions were analyzed, and the stability between the screw and vertebral body under osteoporotic conditions was evaluated. Results Compared with TT, the pull-out strength of MCBT screw was increased by 13.1%. Compared with PS, the load-displacement ratio of MCBT screw under up, down and left working conditions was increased by 57.2%, 32.4%, and 31.6%. Under right working condition, although the load-displacement ratio of MCBT screw was higher than that of PS, no statistical difference was found. The load-displacement ratio of vertebral body in MCBT group under lateral bending and axial rotation was significantly higher than that in TT group. The load-displacement ratio of vertebral body in MCBT group under flexion was lower than that in TT group. Although the load-displacement ratio of vertebral body in MCBT group under extension was higher that that in TT group, no statistical difference was found. Conclusions MCBT is superior to TT in pull-out strength, screw stability and vertebral body stability under lateral bending and axial rotation, but its vertebral body stability under flexion and extension was weaker than that of TT. The research findings demonstrate the superiority of MCBT under osteoporotic conditions and lay the foundation for clinical application of MCBT.