Numerical-experimental method for the validation of a controlled stiffness femoral prosthesis

The influence on strain shielding of material stiffness of press-fit femoral components

The investigation and development of hip prostheses that can provoke identical strain patterns with those of the intact femur (physiological strains) are challenging design problems that have been addressed by several researchers. The modification of the physiological femoral strain pattern provokes adverse tissue biological reactions such as bone hypertrophy, as well as possible mechanical failure of the bone-implant construction. Investigators have used numerical and experimental methods to study the influence of the prosthesis material and geometry on physiological strain deviation. Within the present study, same geometry femoral components composed of different materials have been analysed using strain gauges. The effect of stem stiffness on the strain deviation relatively to those obtained with the intact femur was assessed. Five similar Freeman's prostheses made of different materials (steel, aluminium, composite and polyurethane) at the proximal and middle distal regions were manufactured and tested. The results revealed that only at the proximal lateral and proximal medial aspects of the femur were some differences observed between the strain patterns of the prostheses studied.