Design process of a novel cemented hip femoral stem concept

The development of a new cemented hip prosthesis is certainly a complex task to improve actual performance and success rates. This study presents a methodology applied to design and develop a novel hip stem concept. It was based on the comparison of performance of best cemented stems on the market. A simplified numerical model of the hip replacement was used to generate the final geometry of the femoral stem. Realistic numerical models also allowed us to determine cement mantle stresses of commercial stems that were compared with those obtained for the new concept stem. Fatigue tests performed allowed us to determine the density of cracks in the cement mantles and debonding at the interfaces. Detail design geometry of the new stem concept were analyzed, namely the collar position and orientation, medial radius of the stem geometry and geometry tip to minimize the magnitude of the cement stresses. The new model was prototyped and tested through in vitro fatigue tests. The novel hip prosthesis presents an innovative collar, “organic” geometry sections and a geometry tip that minimizes the magnitude of stresses. The new stem reduces the cement stresses in an average of 25% relatively to the commercial stems used in the study.