Three-dimensional shape optimization of hip prostheses using a multicriteria formulation

A multicriteria optimization model is developed to obtain the optimal geometry of the femoral component of a hip prosthesis. The objective function minimizes both the relative tangential displacement and the contact normal stress. For cementless stems, these two factors are relevant for the prosthesis stability and therefore for the implant success. The three-dimensional optimization procedure developed allows us to characterize the stem shape that minimizes displacement and stress individually, or simultaneously using a multicriteria approach. Design variables characterize successive stem sections, and are subjected to linear geometric constraints to obtain clinically admissible geometries. Multiple loads are considered to incorporate several daily life activities. The system bone-stem is considered a structure in equilibrium with contact condition on the interface. Results show that thin stem tips minimize the interface stress while collared stems minimize displacement. The multicriteria formulation leads to balanced solutions.