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The operational lifetime of hip replacement prostheses can be severely limited due to the occurrence of excessive wear at the load-bearing interfaces. The aim of this study was to investigate how the surface topography of articulating counterfaces evolves over the duration of a laboratory wear run. It was observed that modular stainless steel femoral heads wearing against ultrahigh molecular weight polyethylene (UHMWPE) 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 and in vivoworn femoral heads; quantitatively, roughness comparisons between the new and worn devices are seen to increase typically by a factor of 4 after laboratory wearing. The observations suggest that a particular wear mode, namely third-body wear, is responsible for the increased roughness. It is conjectured that third bodies might arise through surface fatigue wear on the metal counterface. Wear debris is also observed to have been generated from the polymer surface, creating rounded debris with sizes predominantly in the range 0.4-0.8 microns: dimensions that are comparable to values previously reported for in vivo generated debris.Materials that are in intimate mechanical contact, particularly in some dynamic sense, can be subject to forms of surface deterioration that severely limit their usefulness in the application for which they are intended. Chief among the phenomena responsible for such deterioration is the process of wear: the removal of material from one contacting body as a result of its interaction with another. Wear processes are clearly recognizable throughout the engineering and manufacturing industries and represent a problem of substantial economic importance on a global scale [1].Wear also represents a considerable problem in loadbearing biomechanical systems such as joints, and particularly in hip and knee replacement prostheses. For the former

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