The pathways of dynamic recrystallization in all-metal hip joints

In the present study metal-on-metal (MoM) McKee-Farrar prostheses of the first generation were investigated by means of transmission electron microscopy (TEM). It was possible to observe the worn regions using a novel taper section preparation technique without producing any artefacts. Thereby, it could be shown that the wear in vivo leads to a reduction in grain size by a factor of up to 20,000. This is achieved by recrystallization via two pathways which act simultaneously within the subsurface regions. One is dominated by the metallurgical characteristics of the material and follows the gradient of the friction induced shear strains from the bulk towards the surface. The other one is merely acting within the tribological contact volume directly at the surface. Both mechanisms lead to a significant increase in strength.