Abstract

A high incidence of acetabular osteolysis (43%), associated with osteolytic lesions in the proximal femur (22.6%) and leading to a high revision rate, was experienced with the Omnifit total hip prosthesis. We reviewed the clinical and radiological results with 429 Omnifit total hips in 356 patients after a mean follow-up of 60 months. Time to revision and wear of the polyethylene liner with different acetabular shell types were specifically analysed. Pelvic osteolysis first became manifest in the acetabular bone opposite to the holes in the metal shell. Osteolysis occurred predominantly adjacent to the central hole in the metal shell of threaded cups ; widespread and larger defects were found in press fit cups with peripheral screw holes. Kaplan Meier survival analysis demonstrated a higher probability for retaining the threaded cup at 6 years (96% ; 95%-confidence interval : 93-99%) compared to the survival of the press fit cup (66% ; 95%-CI : 56-77%). The results suggest a negative relationship between backside wear, the larger number of holes in the cup, the extent of osteolysis and survival rate of the press fit cups. Based on these findings and supported by similar reports about osteolysis related to the same cup design, it was hypothesised that backside wear due to the insufficient locking mechanism of the Omnifit acetabular cup was the major cause of the unsatisfactory results in our patients. For this reason we discontinued using this type of uncemented socket.