Mak M M, Besong A A, Jin Z M, Fisher J
Department of Mechanical and Medical Engineering, University of Bradford, Bradford, UK.
Proc Inst Mech Eng H. 2002;216(6):403-8. doi: 10.1243/095441102321032193.
The contact mechanics in ceramic-on-ceramic hip implants are investigated in this study under the microseparation condition where the edge contact occurs between the superolateral rim of the acetabular cup and the femoral head. A three-dimensional finite element model is developed to examine the effect of the microseparation distance between the femoral head and the acetabular cup on the contact area and contact stresses between the bearing surfaces. It is shown that microseparation leads to edge contact and elevated contact stresses, and these are mainly dependent on the magnitude of separation, the radial clearance between the femoral head and the acetabular cup, and the cup inclination angle. For a small microseparation distance (less than the diametrical clearance), the contact occurs within the acetabular cup, and consequently an excellent agreement of the predicted contact pressure distribution is obtained between the present three-dimensional anatomical model and a simple two-dimensional axisymmetric model adopted in a previous study [5]. However, as microsegregation is increased further, edge contact between the superolateral rim and the femoral head occurs. Consequently, the predicted contact pressure is significantly increased. The corresponding contact area resembles closely the stripe wear pattern observed on both clinically retrieved and simulator-tested ceramic femoral heads [8, 9, 11]. Furthermore, introducing a fillet radius of 2.5 mm at the mouth of the acetabular cup is shown to reduce the contact stress due to edge contact, but only under relatively large microseparation distances.
本研究在微观分离条件下对陶瓷对陶瓷髋关节植入物的接触力学进行了研究,微观分离条件下髋臼杯的上外侧边缘与股骨头之间会发生边缘接触。建立了一个三维有限元模型,以研究股骨头与髋臼杯之间的微观分离距离对承载面之间接触面积和接触应力的影响。结果表明,微观分离会导致边缘接触和接触应力升高,而这些主要取决于分离的大小、股骨头与髋臼杯之间的径向间隙以及髋臼杯倾斜角度。对于较小的微观分离距离(小于直径间隙),接触发生在髋臼杯内,因此,在本三维解剖模型与先前研究[5]中采用的简单二维轴对称模型之间,预测的接触压力分布取得了极好的一致性。然而,随着微观分离进一步增加,上外侧边缘与股骨头之间会发生边缘接触。因此,预测的接触压力会显著增加。相应的接触面积与在临床回收和模拟器测试的陶瓷股骨头上观察到的条纹磨损模式非常相似[8, 9, 11]。此外,研究表明,在髋臼杯口处引入2.5 mm的圆角半径可降低边缘接触引起的接触应力,但仅在相对较大的微观分离距离下有效。