A METHOD FOR SHAPE OPTIMIZATION OF A HIP-PROSTHESIS TO MAXIMIZE THE FATIGUE LIFE OF THE CEMENT

The long term success of total joint replacement can be limited by fat igue failure of the acrylic cement and the resulting disruption of the bone-cement interface. The incidence of such problems may be diminish ed by reduction of the fatigue notch factor in the cement, so that str ess concentrations are avoided and the fatigue crack initiation time m aximized. This study describes a method for numerical shape optimizati on whereby the finite element method is used to determine an optimal s hape for the femoral stem of a hip prosthesis in order to minimize the fatigue notch factor in the cement layer and at interfaces with the b one and stem. A two-dimensional model of the proximal end of a femur f itted with a total hip prosthesis was used which was equivalent to a s implified three-dimensional axisymmetric model. Software was developed to calculate the fatigue notch factor in the cement along the cement/ stem and cement/bone interfaces and in the proximal bone. The fatigue notch factor in the cement at the cement/stem interface was then minim ized using the ANSYS finite element program whit constraining the fati gue notch factor at the cement/bone interface al or below its initial level and maintaining levels of stress in the proximal bone to prevent stress shielding. The results were compared with those from other opt imization studies. Copyright (C) 1996 Elsevier Science for IPEMB.