Modeling of damage to articulating surfaces by third body particles in total joint replacements

Numerous small scratches and some larger scratches have been observed on me tallic femoral heads of explanted hip prostheses, with the larger scratches believed to be a major contributor to increased wear of the polyethylene a cetabular cups. Previous work in our group has shown that smaller scratches , with a mean lip height up to 0.35 mu m, can be caused by bone cement and bone particles up to 500 mu m in size [1]. However, the larger scratches we re not readily replicated with these particles. Therefore in this study exp erimental and theoretical models have been developed to investigate the dam age caused by harder metallic and ceramic particles. Small 10 mu m diameter spherical metallic particles were also found to produce small fine scratch es on the metallic counterface. However larger diameter spherical metal par ticles greater than 100 mu m in diameter, which were embedded in polyethyle ne pins, caused severe sharp scratching of the metallic counterface with sc ratch lips greater than 0.5 mu m. This level of damage, which was comparabl e to the severe damage found in vivo, was also simulated by a three body fi nite element model. Thus the larger metal particles led to the type of dama ge which was predicted to increase wear dramatically. This technique for si mulating severe in vivo third body damage using spherical metal particles w as found to be reproducible and reliable and will be used in the future in hip simulator testing to replicate third body damage and wear. (C) 2000 Klu wer Academic Publishers.