Design and test of hip stem for medullary revascularization.

This study aims at developing a femoral stem which maintains appropriate mechanical properties for clinical use and provides enough medullary space for revascularization. Hollow and drilled stems were designed to gain sufficient medullary space. Three-dimensional finite element models of the hollow stems were built including the hollow parameters of different wall thicknesses, bore depths and transverse hole patterns. The effects of these parameters on stress under load bearing were investigated. The results indicated that the effects of thickness on the stem depended on their location along the stem. The hollow depth should be designed as deep as possible to ensure a smooth change of cross-sectional area and avoid unexpected stress concentrations. The transverse hole pattern must be arranged very carefully to avoid high stress concentrations. Then the proper parameters of hollow stem were determined. Through the above processes, the appropriate shape of femoral stem for medullary revascularization was determined as a hollow structure with gradually changing thickness and a distinct hole pattern. Fatigue tests were conducted on three prototypes, which all three prototypes passed. The finite element models and design processes were therefore proved useful for our purpose.