抄録
We evaluated the clinical results and radiographical acetabular cup setting angles after Harris-type total hip replacement (THR) for rheumatoid arthritis (RA), to determine the most suitable angle of acetabular cup setting with Harris-type THR system. Between 1986 and 1991, we performed THR in 48 RA patients, and 42 hips (34 patients) were evaluated.
There were 8 males and 26 females, whose average age at the time of surgery was 55.4 years. The prosthesis that we used in all cases was the Harris precoat THR system with cement. Anteroposterior radiographs were made postoperatively to evaluate the acetabular cup setting angles (cup angle), anterior tilting angles (tilt angle), bulging out angles (bulge angle) and radiolucent lines around the prosthesis. The averages of the cup angle, tilt angle and bulge angle were 43.4°, 19.7° and -4.8°, respectively. In our test group, the cup angles were less than 40°, there was no more improvement in range of motion, especially with abduction, than in the other group, with cup angles over 40°. Radiolucent lines were most frequently observed in the former group. Cup angles were 50° or more and cup angles were less than 40°. Bulge angles were less than -20°, much lower than the other group, but there was no correlation between tilt angle and the radiolucent lines. Also, there was no correlation between these angles and functional improvement. In the test group, the cup angles were between 40° and 50°, and were lower than the other two groups in the frequency of radiolucencies. We therefore concluded that the most suitable angle for acetabular cup setting was 40°- 50°, and we recommend a cup setting angle of 45° for actual practical operations.
