Hedia H S, Abdl-Shafi A A, Fouda N
Product and M/C Design Engineering Department, Mansoura University, Egypt.
Biomed Mater Eng. 2000;10(3-4):141-56.
In cemented acetabular cup design it is acknowledged that bone resorption and fatigue fracture of cement may cause the most common problems after total hip replacement. Previous studies have optimized the shape of metal backing (MB) shell used in cemented acetabular components in order to minimize the fatigue notch factor (Kf) in cement, whilst at the same time maximizing Kf in bone at the central part of acetabulum to prevent stress shielding and subsequent bone resorption [1]. The optimal shape was found to be thin at the edges and thick at the dome. The present study describes the effect of changing the elastic modulus of the backing material on Kf and stresses as predicted by the initial shape of the backing shell of (3 mm) thick, and the optimized backing shape of non-uniform thickness in order to find the optimal material for the backing shell. It is recommended to use a backing shell material with elastic modulus equals 70 GPa (which can be readily attained using a fiber reinforced polymer composite). It is shown that such a material will decrease the fatigue notch factor and the stresses in cement at cup edges, at the same time it will increase the stresses and the fatigue notch factor in bone at the central part of acetabulum. Thereby, reducing the possibility of fatigue fracture of cement, whilst at the same time decreasing the stress shielding effect and the resulting bone resorption. The effect of lower bone resorption and lower probability of fatigue fracture of the cement will also reduce the incidence of loosening and premature revision operations.
在骨水泥型髋臼杯设计中，人们公认骨水泥的骨吸收和疲劳骨折可能是全髋关节置换术后最常见的问题。先前的研究已经优化了骨水泥型髋臼组件中使用的金属背衬（MB）壳的形状，以尽量减少骨水泥中的疲劳缺口因子（Kf），同时在髋臼中心部分的骨中最大化Kf，以防止应力屏蔽和随后的骨吸收[1]。发现最佳形状是边缘薄而穹顶厚。本研究描述了改变背衬材料的弹性模量对Kf和应力的影响，这些影响是根据初始厚度为3mm的背衬壳的形状以及厚度不均匀的优化背衬形状预测得出的，以便找到背衬壳的最佳材料。建议使用弹性模量等于70GPa的背衬壳材料（使用纤维增强聚合物复合材料可以很容易地达到这一要求）。结果表明，这种材料将降低髋臼杯边缘处骨水泥中的疲劳缺口因子和应力，同时会增加髋臼中心部分骨中的应力和疲劳缺口因子。从而降低骨水泥疲劳骨折的可能性，同时减少应力屏蔽效应和由此导致的骨吸收。较低的骨吸收和较低的骨水泥疲劳骨折概率的影响也将降低松动和过早翻修手术的发生率。
