Different cup migration in rheumatoid arthritis and arthrosis - A radiographic analysis of 127 uncemented acetabular cups

We compared retrospectively the radiographic migration profiles of 82 acetabular components in 61 patients having rheumatoid arthritis with those of 45 hips having arthrosis who underwent a standardized technique of cementless arthroplasty with the Zweymuller prosthesis (Alloclassic(R)). We used a modification of Dickob's technique of digital migration analysis that corrects for magnification errors and horizontal pelvic tilt. The rheumatoid patients were stratified as having oligoarticular, polyarticular, or mutilating arthritis. The overall rate of acetabular loosening in rheumatoid hips after mean 88 (26-117) months was 4%. Loosening was seen only in cases with mutilating arthritis and acetabular protrusion, where the direction of cup migration was also clearly different from that detected in the other types of rheumatoid arthritis and in arthrosis. The different patterns of cup migration in cementless hip replacement for rheumatoid arthritis, depending on disease severity, is of importance when comparing outcome of total hip arthroplasty in rheumatoid patients.