Andreaus U, Colloca M
Department of Structural and Geotechnical Engineering, Sapienza University of Rome, Rome, Italy.
Proc Inst Mech Eng H. 2009 Jul;223(5):589-605. doi: 10.1243/09544119JEIM559.
In cementless total hip replacement surgery the conditions for micromotion initiation at the bone-stem interface and the role of stair climbing versus gait in promoting incipient slipping deserve attention. The goal of the present paper was to propose a finite element approach for analysing the structural behaviour of hip joint prostheses under physiological loadings and boundary conditions, which allows the prediction of micromotion initiation with low computational effort. In this paper, three-dimensional (3D) finite element analyses were performed of intact and implanted human femurs in order to address the above-mentioned problems. Accurate finite element models based on computed tomography images of a human femur were employed; tetrahedral elements were used to construct the models and the contact options of a full bond between the femoral bone and stem were also used. The shear strains at the contact between femoral bone and stem were evaluated. Two loading cases, namely walking and stair climbing, were applied to investigate the effect of different loading conditions on the shear strain patterns. Shear strains in the z direction can be reasonably considered a significant stimulus of slip initiation or fibrous tissue formation or both at the bone-stem interface, whereas shear strains in the x-y plane can be assumed to be a sensible measurement of the tendency to implant-bone micromotion under torsional loads. Comparisons with other studies are complicated by the difference in the methods and testing conditions used. If mobilization is to be initiated, rotational displacements at the interface should be sensible and significant parameters, i.e. the material, should be distorted to some extent. Thus, for a particular point on the bone-metal interface, the maximum shear strain in any direction within the interface plane will indicate the likelihood of slippage initiation at that point. The different femur states (intact and implanted) and loading conditions (walking and stair climbing) are compared. The stair-climbing loads resulted in the highest strains observed under any conditions, either intact or implanted.
在非骨水泥型全髋关节置换手术中，骨 - 柄界面处微动起始的条件以及爬楼梯与步态在促进初始滑动方面的作用值得关注。本文的目的是提出一种有限元方法，用于分析髋关节假体在生理载荷和边界条件下的结构行为，该方法能够以较低的计算量预测微动起始。本文对完整和植入假体的人体股骨进行了三维有限元分析，以解决上述问题。采用基于人体股骨计算机断层扫描图像的精确有限元模型；使用四面体单元构建模型，并采用股骨与柄之间完全粘结的接触选项。评估了股骨与柄之间接触处的剪切应变。应用两种加载情况，即行走和爬楼梯，以研究不同加载条件对剪切应变模式的影响。z 方向的剪切应变可合理地被视为骨 - 柄界面处滑动起始或纤维组织形成或两者的重要刺激因素，而 x - y 平面内的剪切应变可被认为是在扭转载荷下植入物 - 骨微动趋势的合理测量指标。由于所使用的方法和测试条件不同，与其他研究的比较变得复杂。如果要启动松动，界面处的旋转位移应该是明显且重要的参数，即材料应该在一定程度上发生变形。因此，对于骨 - 金属界面上的特定点，界面平面内任何方向的最大剪切应变将表明该点处滑动起始的可能性。比较了不同的股骨状态（完整和植入）和加载条件（行走和爬楼梯）。在任何条件下，无论是完整的还是植入假体的，爬楼梯载荷都导致观察到的应变最高。
