Comparison of in vivo wear between polyethylene liners articulating with ceramic and cobalt-chrome femoral heads

At yearly intervals we compared the radiological wear characteristics of 81 alumina ceramic femoral heads with a well-matched group of 43 cobalt-chrom e femoral heads. Using a computer-assisted measurement system we assessed t wo-dimensional penetration of the head into the polyethylene liner. We used linear regression analysis of temporal data of the penetration of the head to calculate the true rates of polyethylene wear for both groups. At a mea n of seven years the true rate of wear of the ceramic group was slightly gr eater (0.09 mm/year, so 0.07) than that of the cobalt-chrome group (0.07 mm /year, so 0,04), Despite the numerous theoretical advantages of ceramic ove r cobalt-chrome femoral heads, the wear performance in vivo of these compon ents was similar.