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.