Friction couples in total hip replacement

SummaryThe problem of friction couples remains unresolved to this day. Improvements in femoral and acetabulum implant anchorage over the last 20 years have significantly extended total hip replacement (THR) implant lifespan; the formation of wear debris, however, leads to resorption and osteolysis, considerably shortening implant lifespan in active patients. Alumina–alumina friction couples provide an excellent friction coefficient, with wear particles that do not cause any osteolysis. There is, however, a problem of acetabulum anchorage of solid alumina, and the risk of fracture persists with ceramic implants despite improvements in their mechanical properties. Metal–metal couples also display very good tribological behavior, but at the cost of the formation of Co and Cr ions impacting surrounding bone tissue and accumulating in remote organs. The behavior of such “hard–hard” couples greatly depends on implant component positioning and on the consequences of repeated neck-insert contact. Very highly crosslinked polyethylene (PE) shows very significant improvement in terms of wear at five years’ follow-up compared to conventional PE, but the behavior of this new concept will need to be monitored in the clinical situation if the disappointments experienced with previous hylamer-type improved PE are to be avoided. All these friction couples need to be validated by prospective clinical studies conducted over more than five years, to provide orthopedic surgeons with an eclectic choice of friction couples adapted to the patient's activity.