Gouge features on metal-on-metal hip bearings can result from high stresses during rim contact

Surface gouges were observed on the femoral heads of eight different retrieved metal-on-metal (MoM hip) designs, and 87% of 76 hips studied. The gouges appear to be plastically deformed indentations from edge contact; their occurrence is inconsistent with retrieval artefact. Gouge geometry is consistent with the indentations predicted by computer modeling of head-to-rim contact resulting from subluxation of the head out of the acetabular cup. The surface gouging observed in this study suggests that bearing damage due to micro-separation and subsequent edge loading is common among all designs of MoM hips and can be an important factor in clinical performance.