Polyethylene wear with an entirely HA-coated total hip replacement: 79 hips followed for 5 years.

We measured the eccentricity of the femoral head in the metal backing annually during 5 years in 79 consecutive total hip replacements (73 patients). The mean age of the patients was 57 (32-73) years and the female/male ratio 63/22. The prostheses were entirely coated with hydroxyapatite. Modular 32 mm stainless steel heads and hemispherical, self-tapping screw cups with polyethylene liners were used. We found accelerating eccentricity throughout the observation period. The mean eccentricity at 5 years was 0.71 mm (95% CI 0.53-0.90), resulting in a mean eccentricity rate of 0.14 mm (0.11-0.18) per year. The 5-year eccentricity was 0.5 mm or less in 45 hips and more than 1.5 mm in 13 hips, 2 in the latter group apparently having worn through the polyethylene liner. The true wear may be twice as great. The use of 32 mm stainless steel heads and thin polyethylene inlays may have aggravated the wear problems. These HA-coated prostheses must all be checked regularly, so that cases with excessive polyethylene wear can be reoperated on before wear-through of the liner.