矢向轴动态椎弓根钉棒系统固定腰椎失稳有限元分析

目的]利用有限元方法对矢向轴动态椎弓根钉棒内固定系统固定腰椎失稳模型的生物力学特性进行评价,为此动态内固定系统临床应用提供生物力学基础和理论依据.方法]采用预先获取的健康成年中国男性志愿者的腰椎CT数据建立腰椎正常模型及L4,5失稳模型.根据矢向轴动态椎弓根钉棒系统和坚强椎弓根钉棒系统的材料参数计算和构建有限元模型,并将其导入已通过验证的腰椎失稳模型,分别构建L4,5单节段动态固定模型和坚强固定模型.约束L5椎体下终板,在轴向500N载荷和10N·m力矩下分别模拟人体腰椎正常生理轴向载荷、前屈、后伸、侧弯和旋转五种工况,分别记录4种模型轴向载荷工况下L4,5轴向位移及后四种工况下L4,5固定节段及L3,4邻近节段活动度、椎间盘应力、邻近节段小关节的应力和器械应力,并进行分析比较.结果]矢向轴动态椎弓根钉棒系统固定失稳腰椎可让固定节段椎间关节留有大于坚强固定组、小于完整脊柱组运动范围的适当活动度,对邻近节段腰椎活动度的影响也小于坚强固定组,同时固定节段椎间盘应力较坚强固定组大,器械应力却小于坚强椎弓根钉棒系统,邻近节段腰椎间盘及椎间小关节应力也小于坚强固定组.结论]应用矢向轴动态椎弓根钉棒系统固定失稳腰椎,既保留了腰椎固定节段适当活动性,又能提供即刻的稳定性;同时该系统与脊柱合力承担载荷,能有效避免因术后应力遮挡及器械应力集中引起的内固定失效等并发症;它也能降低邻近节段椎间盘及椎间关节的应力,对邻近节段腰椎活动度影响也较坚强固定小,理论上有利于减少和预防邻近节段退变.

Finite Element Analysis of the Sagittal Axial Dynamic Pedicle Screw and Rod System for Unstable Lumbar

Objective] To analyse the biomechanical characteristics of the lumbar instability model with the sagittal axial dynamic pedicle screw and rod system by the finite element method,providing the biomechanical ba-sis and theoretical for the clinical application of the dynamic internal fixation system.Methods]The normal lum-bar model and L4/L5instability model was established on the base of by lumbar CT data of a healthy Chinese male adult volunteer,which was previously acquired.The finite element models were calculated and established on the basis of the material parameters of the sagittal axial dynamic pedicle screw and rod system and the strong pedicle screw and rod system,and were introduced into the verified L4and L5instability model to establish the single-seg-ment dynamic fixation model and the single-segment strong fixation model.Under the constraints of L5 vertebral endplate and under axial 500N load and 10 N · m torque,five working conditions of normal physiological axial load,flexion,extension,lateral bending and rotation of the human lumbar were simulated respectively.Under the axial load conditions of the 4 models,the axial displacement of L4,5 and the fixed segments of L4,5in the latter four conditions are recorded respectively;at the same time,the L3,4adjacent segment activity,the intervertebral disc stress,the stress of the adjacent facet joints and the stress of the instrument were analyzed and compared.Results] The axial dynamic pedicle screw rod system fixation of unstable lumbar vertebrae can make the motion range of the fixed segment of intervertebral joint have a proper range of motion,which was larger than that of the strong fixation group,less than the complete spinal group.The effect of the model on the lumbar motion of the ad-jacent segments was also less than that of the rigid fixation group.At the same time,the stress of the fixed seg-ment intervertebral disc was greater than that of the rigid fixation group,but the stress of the instrument was less than that of the strong pedicle screw rod system,while the stress of the adjacent segment of lumbar intervertebral disc and facet joint was smaller than that of the rigid fixation group.Conclusion]The application of dynamic pedi-cle screw rod system in fixation of unstable lumbar spine not only retains the lumbar fixation segments appropriate activity,and but also provides immediate stability.At the same time,the system bears the load with the spinal column,which can effectively avoid the complications of internal fixation failure,caused by stress shielding and stress concentration of the instrument.It can also reduce the stress of intervertebral disc and intervertebral joint in the adjacent segment.Compared with the rigid fixation,its influence on adjacent segment lumbar activity is rather small,which theoretically,is beneficial to reduce and prevent adjacent segment degeneration.