Total Hip Arthroplasty Using AML® Prosthesis: Minimum 20-Year Follow-Up of the Patients

Abstract

Purpose:We reviewed the radiological outcomes and survival rate of the total hip arthroplasty (THA) with AML ® (Anatomic Medullary Locking, DePuy, Warsaw, IN, USA) hip prosthesis on long-term follow-up. Materials and Methods: From May 1988 to December 1990, 93 hip arthroplasties were performed on 77 patients in our hospital. In this study, 30 patients, of whom 41 hips underwent the procedure, were alive and able to be included. Follow-up was average of 21.4 years. The mean patient age was 45 years (35-60 years) at the time of operation. Of the hip procedures included in our study, the reasons for THA were osteonecrosis of the femoral head in 25 hips, rheumatoid arthritis in 3 and acetabular dysplasia in 2. We analyzed the wear rate of the polyethylene, osteolysis of the femur and acetabulum and stress shielding of the femur on the followup radiographs. In addition, we investigated the survival rate of the prosthesis and causes of revision in the last follow-up. Results:The polyethylene wear rate of the surviving acetabular cup was 0.15 mm/yr. Acetabular osteolysis was detected in 33 hips and was mostly in zone 2 and 3. Femoral osteolysis was showed in 32 hips in zone 1 and 7. Stress shielding over grade 3 was found in 5 of 21 femoral stems in over 13.5 mm in diameter. The grade of stress shielding did not progress with follow-up. Of the 33 hips, 26 (63.4%) cups were revised for polyethylene wear and osteolysis. There were 6 (21%) femoral stems revised for osteolysis. Conclusion:The cause of a high revision rate of the prosthesis was polyethylene wear and osteolysis. We predict that THA using AML ® prosthesis with wear-resistant bearing surfaces could increase the survival rate on long-term follow-up over 20 years.