膝下義肢的功用為輔助膝下截肢患者獨立進行日常生活所需行動。其中膝下義肢承套是與人體殘肢接觸的部分，兩者間之介面滑動與應力分布情形，一直以來是探討膝下義肢穿戴合適與否的重要焦點。影響介面應力的原因很多，如：承套的修型、殘肢形狀及其長度、軟組織的量及其勁度、義肢校正等等。其中內襯材料更是重要因素之一，內襯材料的表現包括內襯勁度及內襯與殘肢間介面摩擦係數大小。本研究以有限元素分析的方式，透過六位膝下截肢患者殘肢及內襯模型的建立，並施以單腳站立負荷，探討四種內襯勁度(Soft Pelite, Regular Plastazote, Poron, Silicone)在不同摩擦係數下，對全接觸式膝下義肢承套(total surface bearing socket)與殘肢間介面應力的影響。
　　研究結果顯示，隨著楊氏係數的減少，內襯將藉由變形來重新分布介面上的應力，如此可導致介面應力極值的減低，但會伴隨滑動量的增加。然而從滑動量的範圍來看，四種內襯的滑動量數值都很小(2mm以內)，因此，由楊氏係數改變而造成的滑動量影響，在臨床的考慮是可以忽略的。此結果顯示，直接更換較軟(勁度較小的)的內襯或許是改善介面情形的一個有效選擇。而摩擦係數增加，介面壓應力及滑動量極值漸減，但伴隨介面剪應力極大值上升。值得注意的是，當摩擦係數大於0.6，再提高摩擦係數，介面壓應力極值及滑動量減少的量有限，而介面剪應力極值卻仍顯著增加。以一般的介面情形為基準(μ=0.6)，較低摩擦係數對壓應力與滑動量極值的影響較大，改變幅度大約在30%左右；而剪應力極值的表現在較高摩擦係數時較顯著，依患者而異，剪應力極值改變量由10%~100%不等。根據本研究結果顯示，在考慮靜態負荷下，較佳的摩擦係數範圍約在0.4至0.6之間。

　　Many researches indicated that the prosthetics performance could be reflected by the interface stresses distribution between the stump and prosthetic socket. Improper stresses distribution or excessive peak stresses might cause discomfort even necrosis on the stump. Placed between the stump and prosthetic socket, the liner plays a role to distribute the stresses under loading. The properties of the liner, such as the Young’s modulus, coefficient of friction would influence the interface stress, thus the prosthetics performance and the amputee’s wearing comfort. In this study, three-dimensional nonlinear finite element models transtibial prostheses were developed for six subjects respectively to investigate the interface stress variations with different liner material properties for total surface bearing (TSB) socket.
　　Four materials (Soft Pelite, Regular Plastazote, Poron, Silicone) were simulated in this study. The Young’s modulus allocated to these liners was assumed to be linear except for the Silicone material. All the materials were simplified as isotropic and homogeneous except for the soft tissue, which was assumed to be regional homogeneous. The outer surface of liner was fixed to simulate a hard socket boundary condition. Downward displacements at the superior surface of the bone were applied as the loading condition. The downward displacement terminated when the reaction force reached patients’ body weight.
　　The outcome indicated that, with the decreasing of Young’s modulus, the liner would redistribute the stress by deformation, which induced a decreasing in peak interface stresses. However, this would also company with larger sliding distance. But the range of sliding was minimal (less than 2mm in all models); therefore the effect of sliding distance increasing could be neglected. To conclude more compliant liners would benefit interface stress distribution for TSB socket, because they effectively reducing the peak interface stresses. Under the static simulation of this study, the softest liner (0.3MPa) has almost the same advantage with nonlinear liner (0.3 to 1.5MPa).
　　As the coefficient of friction increased (0.2 to 1.0), the magnitude of maximum pressure and sliding distance decreased, as the shear stresses increased. However when the coefficient of friction was larger than 0.6, the decreasing of peak interface pressure and sliding distance were insignificant. Nevertheless, the increasing of shear stress was noticeable in all coefficient of friction range. The dominant effect of coefficient of friction is on shear stress, however, its influence varied on individual subject. To conclude, reducing the coefficient of friction would increase the pressure and sliding, but the increasing is within an acceptable range comparing with the advantages in decreasing the shear stress. Based on the static loading, the suggested coefficient of friction range is between 0.4~0.6.

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