Early failure of smooth hydroxyapatite-coated press-fit acetabular cup--7 years of follow-up.

The early results of smooth hydroxyapatite-coated press-fit acetabular cup are comparable to porous-coated press-fit cup, but these results deteriorate dramatically after 5 years. In this study, 66 primary total hip arthroplasties performed between 1994 and 1998 were reviewed. The average follow-up was 6.5 years. Of the 66 arthroplasties, 8 acetabular cups were revised for aseptic loosening presenting as rapid change of cup position. The average duration of symptoms before revision was 3 months. The survival of the cups at 5 and 9 years were 95.4% and 83%, respectively. The rapid clinical deterioration after 5 years may be due to lack of bone ingrowth into the cup making it unable to resist the shearing stress in the acetabulum. Radiolucent line was not an accurate sign for the detection of mechanical failure.