骨水泥假体柄与股骨界面应力传递简化模型

Simple modeling of stress transfer at interface of cemented prosthesis and femur

将股骨、骨水泥和假体柄看成为线弹性和各项同性材料结合的同心圆锥体,建立包含热效应时的轴对称界面应力传递简化模型.在骨水泥、假体柄承受压缩应力的状态下,应用弹性力学的基本方程,获得了假体柄、骨水泥、股骨轴向应力以及界面剪切应力随轴向位置的分布.界面失效是假体柄、骨水泥、骨结构承载的主要失效形式.热残余温差的存在,加速了假体柄、骨水泥和股骨界面的失效和假体柄的松动,加剧了股骨应力遮盖效应,这主要是骨水泥具有较高的热膨胀系数所致.由于Ti-6Al-4V(钛合金)材料的弹性模量和热膨胀系数比钴铬合金小,在一定程度上缓和了界面和股骨的失效,这和临床所见一致.

Assuming that the prosthesis, the cement and the femur are concentric cylinders made of linear elastic and isotropic materials, the axisymmetric interfacial simple stress transfer model considering thermal effect was established. When the prosthesis bears the compress stress, the distribution of axial stress of the prosthesis, the cement and the femur was analyzed by using the basic equations of axisymmetric elastic mechanics, and the interfacial shear stress at the prosthesis-cement interface and at the cementfemur interface in axial direction was obtained. Interfacial failure was the main failure form of prosthesiscement-femur structure under the external load. The existence of thermal residual temperature difference accelerated the failure and destroy of the prosthesis-cement interface and the cement-femur interface, accelerated the relaxation of the prosthesis, and aggravated stress shielding effect of the femur. The main reason is that the cement has a relatively high thermal expansion coefficient. The elastic modulus and the thermal expansion coefficient of Ti-6Al-4V material were smaller than that of cobalt-chromium alloy material. The existence of thermal effect alleviated the failure of the interface and the femur to a certain degree, which is unanimous with the clinical finding.