Migration of 65 Charnley stems implanted with modern cementing techniques was studied by roentgen stereophotogrammetry. There were 25 patients with rheumatoid arthritis (RA) and 40 with osteoarthritis (OA) followed up for two years. In 43 cases a bone sample for histomorphometric analysis was obtained from the femur during the operation. In 22 cases the mean subsidence of the prosthetic head was 0.40 mm and in 20 the mean posterior migration was 1.25 mm. There was no difference in migration between the two diagnostic groups (p = 0.8) after adjusting for variations in gender, age and weight. Male gender was associated with increased subsidence (p = 0.006). Histological examination showed that the RA series had more osteoid surface (p = 0.04), but neither this, nor any of the other histomorphometric variables, influenced migration. These results suggest that, unlike the acetabular socket, the cemented Charnley femoral component is equally secure in osteoarthritis and in rheumatoid arthritis, and that its initial fixation is not influenced by the quality of the local cancellous bone. Our results provide data with which the early performance of new prosthetic designs and fixation methods can be compared.

Socket migration and rotation in the Charnley total hip replacement were evaluated by roentgen stereophotogrammetric analysis in 23 patients with rheumatoid arthritis and 23 patients with osteoarthritis. The two groups were matched with regard to age and sex. The follow-up time was two years. In the rheumatoid patients socket migration was most prominent in the proximal direction and averaged 0.6 mm at 24 months as compared with 0.1 mm in the osteoarthritic group (p = 0.0003). Within the rheumatoid group a preoperative acetabular protrusion in five patients was associated with increased migration and rotation in all directions. The increased proximal migration in rheumatoid arthritis was consistent (p = 0.0009) even after the exclusion of the five protrusion cases. In the rheumatoid patients there was a correlation between low body-weight and proximal migration, but there was no such correlation in the osteoarthritic group. Our results suggest that socket fixation is less secure in patients with advanced inflammatory arthritis.