Abstract
This paper describes a method of parametric optimisation to determine the optimal stiffness characteristics of cement, metal backing and UHMWPE (Ultra High Molecular Weight Polyethylene) materials, which minimises the probability of fatigue fracture of cement at all interfaces with the metal backing and the bone, while limiting the amount of bone resorbed. The parameters describing the elastic moduli of cement, metal backing and UHMWPE were considered as design variables. The method was applied to an axisymmetric finite element model of acetabular cup in combination with an optimisation procedure using the ANSYS program.
Young's moduli of about 0.63, 207 and 0.72 GPa are optimal materials for cement, metal backing (MB) and UHMWPE, respectively. These characteristics decreased fatigue notch factor Kf in cement by 8.2 and 10.6% and also decreased the maximum von Mises stress in cement by 21 and 27% at cement/bone and cement/metal backing interfaces, respectively. The optimal design reduces the probability of fatigue fracture of cement at all interfaces with the bone and the metal backing while limiting the amount of bone resorbed as a result of increasing von Mises stress and Kf in the central bone of the acetabulum by 34 and 30.6%, respectively.
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