Optimal design of a hip joint implant with hallow stem using finite element method

Complication of artificial joint replacement is often attributed to the distribution of mechanical stresses over the bone-cement, and cement-implant interfaces. This study represents the analysis and optimization of a hollow-stem hip prosthesis to reduce the micro-motion and maintain uniformity of stress distribution over the interface regions. A three-dimensional finite element model of the proximal femur was constructed in ANSYS, including the cortical bone, the cancellous bone, the bone cement and the femoral component of hip joint implant. Three design parameters were considered for the implant stem, including the length of the stem and the length and radius of the distal cylindrical cavity. The optimization criterion was defined as a linear combination of the standard deviations of the equivalent Von-Mises stresses and the total displacements at the cement-implant interface nodes. The Response Surface Method and sensitivity analysis indicated that the length of the stem has a major impact on the optimization criterion and the length and the radius of the cavity stand as the minor factors. The optimal design was obtained to have a 10.5 cm length stem with a cylindrical cavity of 23.4 mm length and 1.3 nun radius. The assumed optimization criterion reduced substantially from 3.1 in the initial design to 2.52 in the optimal deign.