大腿假肢支撑期有限元分析

目的分析大腿截肢患者的硅胶套材料属性,对支撑期残肢与接受腔之间接触面的力学分布的影响,为大腿假肢适配方案中硅胶套的选取提供参考。方法利用计算机断层扫描技术获取大腿截肢患者残端与接受腔的断层图像,通过影像学信息和工程学方法,分别获取接受腔、硅胶套、残肢、骨骼等结构的三维模型;根据角度变化调整模型,获得初始接触期、负荷反应期、站立中期、站立末期、摆动前期5个时相的组装模型;根据三维动作捕捉系统Motion和Kistler三维测力平台测得的地面反作用力及髋关节角度变化的结果,对5个时相下大腿假肢模型分别进行有限元非线性接触分析;在此基础上,模拟分析了硅胶套不同弹性模量的变化对残肢表面等效应力以及剪切应力分布的影响。结果穿戴不同弹性模量的硅胶套时,残肢所受最大等效应力以及最大剪切应力在初始接触期、负荷反应期、站立中期、站立末期时相时出现在残肢内侧和接受腔口型边缘对应的残肢位置,在摆动前期时相时则出现在残肢内侧、接受腔口型边缘对应的残肢位置和坐骨周围等位置。当硅胶套弹性模量在0.98~2.70 MPa范围内变化时,在摆动前期残肢所受等效应力变化范围为13.85~23.55 k Pa,最大剪切应力变化范围为7.82~13.46 k Pa,而其他时相基本一致。结论硅胶套的力学特性影响大腿假肢残肢与接受腔之间接触面的受力分布,摆动前期残肢所受最大等效应力与最大剪切应力随硅胶套弹性模量变化大,在实际适配过程中需注意。

Finite element analysis of trans-femoral prosthesis with liner in stance phase

Objective To analyze the influence of material properties of liners on pressure distribution between residual limb and socket during the stance phase, which provides reference for the fitting scheme of liners for trans-femoral prosthesis. Methods CT images of stump and socket were obtained with computer tomography technology,and 3D models were obtained with information science and engineering methods,such as socket, liner, amputation, bones. Then we adjusted the models according to the changes of hip joint in stance phase, obtained the assemble model of phases of initial contact, loading response, mid-stance, terminal stance,pre-swing. We analyzed the assemble models with nonlinear finite element methods according to the measured results of ground reaction force and the changes of hip joint through Motion and Kistler. On this basis,we simulated the influence of material properties of the liners on the equivalent stress and the maximum shear stress distribution between stump and socket. Results With different liner elastic modulus,the maximum equivalent stress and shear stress of stump appeared in the medial residual limb and in the position of the residual limb corresponding to the edge of socket in phases of initial contact,loading response,mid-stance, and terminal stance. The maximum equivalent stress and shear stress of stump appeared in the medial residual limb,in the position of the residual limb corresponding to the edge of socket and around the ischium in phase of pre-swing. When the elastic modulus of the silicone liner changed at the range of 0.98 MPa to 2.70 MPa, the equivalent stress was in the range of 13.85 kPa to 23.55 kPa,and the shear stress was in the range of 7.82 kPa to 13.46 kPa in phase of pre-swing, while the other phases were basically the same. Conclusions The mechanical properties of silicon liners affect the pressure distribution of the interface between residual limb and socket,the maximum equivalent stress and shear stress of stump vary greatly during the pre-swing period. We should pay more attention to the process of prosthesis fitting.