重度骨质疏松条件下后路枢椎三种内固定方式的有限元分析

Finite element analysis of three kinds of internal fixation method of posterior axis in the condition of severe osteoporosis

目的通过有限元分析重度骨质疏松(Severe osteoporosis,SOP)条件下后路枢椎不同植钉方式在上颈椎中的生物力学特性。方法对1例健康成年男性进行上颈椎CT扫描,获得图像。结合有限元前处理软件,设置材料属性模拟出SOP的寰枢椎(C_(1)-C_(2))失稳模型,依据手术方案建立后路寰椎双侧椎弓根螺钉(B-C_(1)PS)+枢椎3种不同植钉方式固定:枢椎双侧椎弓根螺钉(B-C_(2)PS,模型A);枢椎双侧椎板螺钉(B-C_(2)TL,模型B);B-C_(2)PS联合B-C_(2)TL(模型C)。分析3种模型屈伸、侧弯和轴向旋转工况下的C_(1)-C_(2)关节活动度、C_(1)位移以及C_(2)螺钉应力分布情况。结果在SOP的C_(1)-C_(2)失稳有限元模型上,模型C在不同工况下C_(1)-C_(2)关节活动度和C_(1)位移最小。C_(2)联合固定时螺钉受到的最大应力较单一固定小:模型C枢椎椎板钉在各个工况下最大应力值小于模型B,模型C枢椎椎弓根螺钉在各个工况下最大应力值小于模型A。模型C应力主要集中于C_(2)PS根部及寰枢椎椎弓根螺钉与钉棒连接处。结论在SOP条件下采取模型C内固定方式较模型A、B稳定性更好。枢椎螺钉受到的应力产生分散,枢椎螺钉更加不容易产生术后疲劳性松动脱出。

Objective To analyze the biomechanical characteristics of posterior axis different planting methods in upper cervical vertebra under severe osteoporosis(SOP).Methods A CT scanning on cervical vertebra was performed on a healthy adult man.Combined with the finite element pre-processing software,the atlantoaxial instability model(C_(1)~C_(2))of SOP was stimulated by setting material properties.According to the surgical plan,posterior bilateral atlas pedicle screw(B-C_(1)PS)+Axis of three different ways of planting nail fixation was established:axis bilateral pedicle screw(B-C_(2)PS,model A)fixation,axis bilateral laminar screw(B-C_(2)TL,model B)fixation,B-C_(1)PS combined with B-C_(2)TL fixation(model C).The range of motion of C_(1)-C_(2)joint,C_(1)displacement and C_(2)screw stress distribution of the three internal fixation methods were analyzed under the bending extension,lateral bending and axial rotation conditions of the finite element model.Results The finite element model of C_(1)-C_(2)instability in the SOP,Model C had the lowest range of motion of C_(1)-C_(2)joint,C_(1)displacement in different conditions.Fixed screw under the maximum stress of C_(2)joint combined fixation was smaller than that of single fixation.The maximum stress of pedicle screw of the axis in the Model C was less than that of Model B under various working conditions,that of pedicle screw in the Model C was less than that of Model A.In Model C,the stress was mainly concentrated at C_(2)PS roots and the joint between atlanto-axial vertebral pedicle screw and screw rod.Conclusions The inner fixation stability of Model C is better than that of Model A and Model B under SOP condition.The stress of axis is dispersed,and the axis screw is less prone to postoperative fatigue loosening and prolapse.