Biomechanics Section, TUHH Hamburg University of Technology, Denickestrasse 15, 21073 Hamburg, Germany.
J Biomech. 2010 Feb 10;43(3):521-6. doi: 10.1016/j.jbiomech.2009.09.052. Epub 2009 Nov 12.
Primary stability of uncemented resurfacing prosthesis is provided by an interference fit between the undersized implant and the reamed bone. Dependent on the magnitude of interference, the implantation process causes high shear forces and large strains which can exceed the elastic limit of cancellous bone. Plastification of the bone causes reduced stiffness and could lead to bone damage and implant loosening. The purpose in this study was to determine press-fit conditions which allow implantation without excessive plastic bone deformation and sufficient primary stability to achieve bone ingrowth. In particular, the influence of interference, bone quality and friction on the micromotion during walking and stair-climbing was investigated. Therefore elastic and plastic finite element (FE) models of the proximal femur were developed. Implantation was realized by displacing the prosthesis onto the femur while monitoring the contact pressure, plastic bone deformation as well as implantation forces. Subsequently a physiologic gait and stair-climbing cycle was simulated calculating the micromotion at the bone-implant interface. Results indicate that plastic deformation starts at an interference of 30microm and the amount of plastified bone at the interface increases up to 90% at 150microm interference. This effect did not reduce the contact pressure if interference was below 80microm. The micromotion during walking was similar for the elastic and plastic FE models. A stable situation allowing bony ingrowth was achieved for both constitutive laws (elastic, plastic) for walking and stair climbing with at least 60microm press-fit, which is feasible with clinically used implantation forces of 4kN.
非骨水泥表面置换假体的初始稳定性是通过减小尺寸的假体与扩髓后的骨之间的过盈配合来提供的。根据过盈量的大小，植入过程会产生高剪切力和大应变，这些应变可能超过松质骨的弹性极限。骨的塑性化会导致刚度降低，并可能导致骨损伤和植入物松动。本研究的目的是确定压配合条件，使植入物在不产生过度塑性骨变形的情况下能够植入，并具有足够的初始稳定性以实现骨长入。特别是，研究了过盈量、骨质量和摩擦对行走和爬楼梯时微动的影响。因此，开发了股骨近端的弹性和塑性有限元（FE）模型。通过将假体推向股骨来实现植入，同时监测接触压力、骨的塑性变形以及植入力。随后，模拟生理步态和爬楼梯周期，计算骨-植入物界面的微动。结果表明，在 30μm 的过盈量下开始发生塑性变形，在 150μm 的过盈量下，界面上的塑性骨量增加到 90%。如果过盈量低于 80μm，这种效应不会降低接触压力。弹性和塑性 FE 模型在行走时的微动相似。对于行走和爬楼梯两种运动状态，在具有 60μm 压配合的情况下，两种本构定律（弹性、塑性）都达到了稳定的允许骨长入的状态，这在临床使用的 4kN 的植入力下是可行的。
