An evaluation of the tribological performance of zirconia and CoCrMo femoral heads

Five new zirconia, five new CoCrMo and three explanted CoCrMo femoral heads were wear-tested in bovine serum for five million cycles using the Durham Hip Joint Wear Simulator. Wear was measured gravimetrically and surface top ography with a 3D non-contacting profilometer. This allowed an evaluation o f the different head types on UHMWPE acetabular cup wear rates and the effe ct of roughening of the femoral head on acetabular cup wear. The mean aceta bular cup wear rate against the five CoCrMo femoral heads was 40.8 mm(3)/10 (6) cycles which was significantly higher (p = 0.03) than against zirconia (33.3 mm(3)/10(6) cycles). The initial surface roughness of the CoCrMo femo ral heads (R-a = 4.6 nm) was statistically significantly higher than for th e zirconia heads (R-a = 3.1 nm). Over the wear test the CoCrMo heads got st atistically significantly rougher (R-a = 10.5 nm) whilst the zirconia heads showed no statistically significant change. The three explanted CoCrMo fem oral heads had initial mean surface roughness, Ra, values of 19, 24 and 55 nm with corresponding cup wear rates of 97.6, 131.2 and 148.4 mm(3)/10(6) c ycles respectively. The very high wear rates against the explanted heads hi ghlight the need for scratch resistant femoral head surfaces. (C) 1999 Kluw er Academic Publishers.