CHARACTERIZING WEAR PROCESSES ON ORTHOPEDIC MATERIALS USING SCANNING PROBE MICROSCOPY

The operational lifetime of hip replacement prostheses can be severely limited due to the occurrence of excessive wear at the load-bearing i nterfaces. The aim of this study was to investigate how the surface to pography of articulating counterfaces evolves over the duration of a l aboratory wear run. It was observed that modular stainless steel femor al heads wearing against ultrahigh molecular weight polyethylene (UHMW PE) can themselves be subject to wearing. A comparison with retrieved in vivo-aged femoral heads shows many topographical similarities: in a qualitative sense, scratching and pitting are evident on laboratory a nd in vivo-worn femoral heads; quantitatively, roughness comparisons b etween the new and worn devices are seen to increase typically by a fa ctor of 4 after laboratory wearing. The observations suggest that a pa rticular wear mode, namely third-body wear, is responsible for the inc reased roughness. It is conjectured that third bodies might arise thro ugh surface fatigue wear on the metal counterface, Wear debris is also observed to have been generated from the polymer surface, creating ro unded debris with sizes predominantly in the range 0.4-0.8 microns: di mensions that are comparable to values previously reported for in vivo generated debris.