大腿残肢步态过程的非线性有限元分析

目的利用三维有限元分析方法研究大腿截肢患者在行走过程中3个不同时相下残肢的生物力学特性,为建立完整的大腿接受腔测量、设计与评估系统提供研究基础。方法首先根据CT图像三维重建大腿截肢患者的骨骼、肌肉软组织和接受腔的三维几何模型;定义软组织为超弹性和线弹性材料属性,并相应建立两个有限元仿真模型;定义残端与接受腔之间的接触关系,约束残肢近端,对模型的远端施加膝关节载荷,模拟步态周期中足跟着地时期、站立相中期、脚尖离地3个时相下大腿残肢-接受腔系统所受载荷;计算分析接触界面上的应力,并对比分析超弹性和线弹性软组织力学特性对接触界面力学行为特性的影响。结果无论线弹性还是超弹性模型,3个时相下大腿残肢-接受腔界面的最大接触压力均在残肢末端达到最大值。超弹性模型3个时相下接触压力峰值分别为55.80、47.63和50.44 kPa;而线弹性模型接触压力的最大值都增加2倍以上,其值分别为149.86、118.55和139.68 kPa。同时通过分析接触面间的径向剪切应力和轴向剪切应力发现,3个时相下接触界面间的应力在残肢末端较集中,在足跟着地到脚尖离地过程中,有部分力通过接受腔后侧缘传递转向接受腔前缘传递。结论不同时相下残肢与接受腔接触界面的压力和剪切应力分布情况不同,在设计接受腔时需要充分考虑其受力特点。

Non-linear finite element analysis on trans-femoral residual limb during gait phase

Objective To investigate biomechanical properties of the contact interface between residual limb and prosthetic socket of the transfemoral amputee during walking by using threedimensional (3D) finite element analysis method, so as to provide references for establishing the complete system of measurement, design and evaluation on prosthetic socket. Methods Based on CT images, two 3D geometric models of a trans-femoral amputee including the femur, soft tissues and transfemoral socket was established, with soft tissues defined as non-linear hyper-elastic and linear elastic material, respectively. The behaviors of the interface between trans-femoral residual limb and prosthetic socket were defined as nonlinear contact. Dynamic loads on the knee joint were applied on distal ends of both the hyper-elastic model and linear elastic model to simulate loading on residual limb-prosthetic socket system during heel strike, mid-stance and toe off phase in a gait cycle, respectively. The stress distributions on interface between trans-femoral residual limb and prosthetic socket were calculated to compare and analyze the effects of different mechanical properties (i.e. hyper-elasticity and linear elasticity) of the femur soft tissue on biomechanical behaviors of the interface. Results For both the hyper-elastic model and linear elastic model, the peak contact pressures were all located on the distal end of the residual femur during different gait phases. The peak contact pressure on the interface of the hyper-elastic model during heel strike, mid-stance and toe off phase was 55.80, 47.63 and 50.44 kPa, respectively, while that on linear elastic model was increased by two times, being 149.86, 118.55 and 139.68 kPa, respectively. Simulation on longitudinal and circumferential shear stress distributions at the limb-socket interface showed that stress on the interface was higher at the distal end of soft tissue during different gait phases. From heel strike to toe off phase, some pressures were transferred from the rear edge to the front edge of the socket. Conclusions The pressure and shear stress distributions on the contact interface between transfemoral residual limb and prosthetic socket were different during different gait phases, thus the relative mechanical properties should be considered in the socket design.