We retrospectively reviewed 137 consecutive total hip arthroplasties performed with AML-A stems and Tri-Lock cups to see whether design modifications made to these components would achieve durable biological fixation in the Japanese population in whom developmental dysplasia of the hip (DDH) is relatively common. Patients from our initial clinical series using these components are available for more than 10 years' follow-up.
Between April 1988 and June 1994, we performed 137 total hip arthroplasties using the AML-A prosthesis for the patients with osteoarthritis of the hip joint. We excluded 26 hips with less than 10 years' follow-up and five hips from patients who died before the 10-year follow-up. The mean follow-up for the 105 remaining THAs is 155.2 months (range 120-237 months). The average age of these patients at the time of surgery was 53.1 years (range 22-81 years).
In total, 17 THAs required component revisions. In seven cases, the first revision was limited to a liner exchange for polyethylene wear or osteolysis. Another seven hips underwent revision surgery for recurrent dislocation. Three cups have been revised owing to aseptic loosening. Because of the high incidence of wear-related revisions, Kaplan-Meier survivorship at the 15-year follow-up, using acetabular component revision for any reason as an endpoint, was 75.0% (95% CI 69.4%-83.8%). In contrast, no revision of the femoral stem was performed. Severe stress shielding occurred in 12 hips. Thigh pain was mild, however, and all of the femoral stems remained stable.
Despite revisions for wear-related complications, the fixation achieved with these porous-coated components remained durable throughout the 15-year follow-up. Acetabular osteolysis has been associated with cup reoperation, but femoral stress shielding has never resulted in stem loosening.