With total hip replacement (THR) patients now being younger, more active younger, and anticipating much greater longevity, reduced bearing wear becomes increasingly important. Compared to the wear and osteolysis incidence with metal-polyethylene bearings, the historical results of alternate bearings such as metal-on-metal (MOM) and ceramic-on-ceramic (COC) generally showed much lower wear rates and osteolysis was seemingly quite rare. The laboratory wear-rates for metal-metal bearings have generally fallen into the range 1-7 mm3/million cycles (Mc) and 0.1-1 mm3/Mc for run-in and steady-state phases, respectively.