腰椎单双侧椎弓根螺钉固定后的有限元分析比较

摘要

目的 建立两节段L3-L5三维有限元模型,并分别行L3-L5两节段单双侧椎弓根螺钉固定,用三维有限元法分析固定后螺钉的应力分布特点.方法 收集人正常L3-L5节段的CT扫描数据,利用Scan IP等软件建立人正常L3-L5三维有限元模型(INT),并在此基础上分别建立L3-L5单侧椎弓根螺钉内固定模型(unilateral pedicle screws,UPS)及双侧椎弓根螺钉内固定模型(bilateral pedicle screws,BPS).并于L3上表面施加500 N预载荷,再施加8N·m的力矩模拟腰椎前屈、后伸、侧屈及旋转等生理活动,观察不同工况下两种模型中椎弓根螺钉应力分布情况.结果 由应力分布图可知,两种模型椎弓根螺钉所受应力主要集中在椎弓根螺钉根部、钉棒连接处；相比于上下螺钉,中间椎弓根螺钉基本不受应力；下位椎弓根螺钉承受较高应力.在各个工况下,单侧椎弓根螺钉内固定组最大应力值都高于双侧椎弓根螺钉内固定组.结论 模拟邻近两节段内固定后正常生理活动时,下位椎弓根螺钉钉棒连接处承受较大应力,易发生断裂,且单侧置椎弓根钉相比于双侧置椎弓根钉,在各个状态下内固定承受更大应力,发生内固定断裂失败等风险较大.%Objective To construct an intact L3-L5 finite element model, then to evaluate the stress characteristics following unilateral and bilateral pedicle screw fixation based on the intact model. Methods A intact L3-L5 three-dimensional finite element model was developed by using the computed tomography scans of a healthy male. Based on the intact one, two new models were created by simulating the unilateral pedicle screws (UPS) fixation and the bilateral pedicle screws (BPS) fixation. Meanwhile,500 N preload was loaded on the upper surface of L3 ,then 8 N ? m moments was added to simulate lumbar axial compression, flexion, extension, lateral bending, and axial rotation. The pedicle screw characteristics was recorded under all the different motions. Results Most of the stress concentrated on the tail part of the pedicle screws and the junction of the screw-rod. The middle pedicle screw was almost endured no stress compared with the upper and the lower one, while the lower one got the highest stress. The maximum stress in UPS was higher than that in BPS under all the motions. Conclusions In simulating the normal lumbar movements after the fixation for two levels,the tail part of lower pedicle screw and the junction of screw - rod got higher stress and had a high risk forrnfracture,as a higher risk does in the UPS model in contrast to in the BPS model.