Comparison of femoral head penetration rates between cementless acetabular components with 22-mm and 28-mm heads.

Between April 1993 and July 1994, the senior author (R.C.J.) performed 151 consecutive primary total hip arthroplasties using a Harris-Galante II acetabular component and a polished Iowa femoral component. In 105 hips, 22-mm head components were used, and in 46 hips, 28-mm head components were used. Femoral head penetration into the acetabular shell was measured using digital edge detection techniques. The group average penetration for the initial 2-year bedding-in period was 0.35 mm/y for the 22-mm and 0.31 mm/y for the 28-mm head components. The long-term rate of penetration into the shell was 0.11 mm/y for the 22-mm heads and 0.17 mm/y for the 28-mm heads, a significant difference (P=.029). The dislocation rate was significantly higher, however, with the 22-mm heads (P=.001). The 22-mm components showed significantly less wear but at the expense of an increase in the prevalence of dislocation.