Because we encountered a high failure rate of the acetabular component of the uncemented, hydroxy-apatite coated, Omnifit total hip prosthesis (Osteonics corporation, Allendale, NJ, USA), we conducted a retrospective study of 418 consecutive total hip arthroplasties with a mean follow up of 60 months. The results of 418 hydroxy-apatite coated, uncemented Omnifit total hip arthroplasties, conducted between 1989 and 1996 were evaluated. Two different acetabulum cups were used: 145 screwcups with one central screwhole, and 273 press fit (PF) cups with several screwholes. The internal geometry of these cups and the fixation of the polyethylene insert in the metal cups were identical. In 339 arthroplasties a 32-mm femur-head was used, in 79 a 28-mm head. Patients’ records and x-rays were evaluated for clinical findings, polyethylene (PE) wear, acetabular and femoral osteolysis and findings during revision surgery. Revision surgery was performed in 73 patients, mainly because of symptomatic acetabular osteolysis (79%). Mean PE wear was 0.16 mm/year (0.19 mm in PF cups, 0.11 mm in screwcups). Acetabular osteolysis was found to be present in178 hips (70 screwcups and 108 PF cups). In both cupdesigns the osteolysis was mainly found around the screwholes of the metal cups. During revision surgery these osteolytic defects were a lot larger than suggested by x-ray imaging. In 22.6% of the hips osteolysis was also present in the proximal femur. Kaplan-Meier survival analysis showed, after 6 year follow up, a better survival for of the screwcup (96%, confidence interval 93–99%) than the PF cup (66%, 95%CI 56–77%). We hypothesized that this specific combination of metal cup and polyethylene insert -possibly due to an insufficient fitting- is responsible for the migration of polythylene wear particles through the screwholes in the metal cup, causing acetabular osteolysis and neces-satating revision surgery. For this reason we abandonned the use of this type of uncemented acetabular component.
