Finite element analysis of a stemmed hip prosthesis to reduce stress shielding in the proximal femur

Abstract

A finite element analysis (FEA) was performed on four prosthesis designs with different internal structures within identical prosthetic stem geometry. A novel hexagonal structure akin to one of the strongest structures in nature is used internally in the stem. The hip implant designs were then analyzed for an applied force of 3227 N. This force was selected because a typical gait cycle generates forces up to 3.87 times the body weight in the hip joint. The FEA results were compared for various stem designs with rectangular cross-sections. The design objective for a hip stem is to have a low stiffness and stress shielding together with a very high fatigue life. The stress shielding reduction of the prothesis was measured by observing the change in stress distribution in a FE femur model before and after implant. Stress shielding was quantified volumetrically, and the surface stresses of the femur were considered to appraise any increased risk of periprosthetic fracture due to increased bone stress. Subsequently, the stems that had the lowest stress shielding models were then optimized. Results showed a reduction of stiffness of 18%, and a reduction in stress shielding of 30% compared to a solid stem.