Short- and medium-term results of the thrust plate prosthesis in patients with polyarthritis

The thrust plate prosthesis is an implant with metaphyseal fixation to the proximal femur, which leaves the diaphyseal bone untouched. Therefore, this implant is preferred in younger patients. It is dependent on good bone quality in the proximal femur. Because the bone quality is reduced in patients with polyarthritis, this kind of endoprosthesis may have a higher failure rate than conventional stemmed endoprostheses in these patients. Therefore, in patients with polyarthritis, even short- and medium-term results of the thrust plate prosthesis should be analyzed. In all, 47 thrust plate prostheses were implanted in 42 patients with polyarthritis (29 with rheumatoid arthritis, 6 with juvenile chronic arthritis, and 7 with spondylarthritis) and followed prospectively. The average age at operation was 40.8 ± 10.7 years. Each patient was clinically and radiologically examined preoperatively, 3 and 6 months after the operation, and at the end of each postoperative year. The mean follow-up was 26.1 ± 10.7 months. The clinical findings were evaluated using the Harris hip score. Radiologically, 8 different zones of the thrust plate prosthesis were analyzed for radiolucencies. During the 1st year, the Harris hip score rose continuously from the preoperative average of 42.4 ± 6.5 points to 78.8 ± 10.3 points 3 months postoperatively, 82.3 ± 9.8 points 6 months postoperatively, and 86.8 ± 10.1 points 1 year after the operation. The subsequent examinations showed Harris hip score remained at the same level. Five patients (5 joints, 10.6%) had to undergo a revision of the thrust plate prosthesis due to aseptic loosening in 3 and septic loosening in 2. Six prostheses (12.6%) showed radiolucencies, mostly below the thrust plate in zones 1 and 2. Two of them were certainly radiologically loose, which raised the failure rate to 7 of 47 (14.8%). The thrust plate prosthesis improves function and alleviates pain in patients with polyarthritis to a satisfactory degree. Concerning the failure rate, this type seems to yield slightly worse results than cementless stemmed endoprostheses in the same patient group. Due to the preservation of the diaphyseal bone of the femur and the possibility of an unproblematic change to a stemmed endoprosthesis, the thrust plate prosthesis can be recommended for younger patients with polyarthritis. Received: 29 April 1999