Friction in Femoral Prosthesis and Photoelastic Model Cone Taper Joints

Abstract

Static axial push-on and lift-off, and push-on and twist-off experiments were designed and performed to measure the effective, room-temperature coefficient of friction μ for different design femoral prosthesis cone taper joints comprising a universal head on a stem spigot. Alumina and metal heads were tested on metal spigots using either distilled water, Ringer's solution, blood or no lubricant. Complementary push-on and lift-off friction tests of Araldite model joints for subsequent frozen-stress, photoelastic stress analysis were performed at 130°C. It was found that lubricant caused little decrease in the values of the coeficient of friction in prosthesis tapers. The values measured were typically μ =0.2 for an alumina head on a Co-Cr-Mo or Ti-6Al-4V spigot, μ = 0.15 for a Co-Cr-Mo head on a Co-Cr-Mo or Ti-6Al-4V spigot and μ =0.13 for a stainless steel head on a stainless steel spigot. For Araldite photoelastic models of an alumina head on a Vitallium spigot, as-cast taper surfaces lubricated with silicone grease gave consistent friction of typically μ = 0.14. The axial displacements of model heads on their spigots were compared with predicted values and previously measured values for prosthesis heads.