Comparison of conventional and hybrid modulus press-fit proximal femoral prostheses

The aim of the this study was to compare the load transfer mechanisms of a standard press-fit proximal femoral prosthesis fabricated from three conventional implant materials, cobalt-chrome, titanium and an 'isoelastic' material with that produced by a hybrid modulus prosthesis using the finite element method. In particular, both the periosteal and the endosteal bone stresses were examined. Comparison of the results from the three conventional implant materials were similar to those reported in the literature, with the isoelastic prosthesis producing the least stress shielding of the proximal medial femur and the stiffer implant materials producing low proximal medial interface pressures and cancellous bone stress distributions. The hybrid prosthesis combined these features to produce, overall, the most favourable periosteal and endosteal stress distributions. However, all of the prostheses produced stresses which approach or exceeded the fatigue strength of the supporting cancellous bone suggesting that all would have high migration rates and correspondingly high rates of late aseptic loosening.