The thrust plate prosthesis is an implantat with metaphyseal fixation at the proximal femur, which leaves the diaphyseal bone untouched. Therefore this implant preferably is employed in younger patients. It is dependent on a good bone quality in the proximal femur. Because bone quality is reduced in patients with polyarthritis, this kind of endoprosthesis may have a higher failer rate than conventional stemmed endoprostheses in these patients. Therefore in patients with polyarthritis even short- end midterm results of the thrust plate prosthesis should be analyzed.
47 thrust plate prostheses were implanted in 42 patients with polyarthritis (29 with rheumatoid arthritis, 6 with juvenile chronic arthritis and 7 patients with spondarthritis) and followed prospectively. The average age at the operation was 40. 8 ± 10. 7 years. Each patient was clinically and radiologically examined preoperative, 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 at the thrust plate prosthesis were analyzed for radiolucencies.
During the first 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 following examinations showed Harris-Hip-Scores at the same level. 5 patients (5 joints, 10. 6%) had to undergo a revision of the thrust plate prosthesis due to aseptic loosening in 3 cases and septic loosening in 2 cases. 6 prostheses (12. 6 %) showed radiolucencies, mostly below the thrust plate in zone 1 and 2. 2 of these prostheses were certainly radiologically loose which raised the failure rate to 7 of 47 (14. 8 %).
The thrust plate prosthesis improves function and 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 diaphysial bone of the femur and the possibility of an unproblematic change to a stemmed endoprosthesis the thrust plate prosthesis keeps its indication in younger patients with polyarthritis.
We evaluated histologically samples of synovial tissue from the knees of 50 patients with rheumatoid arthritis (RA). The samples were taken during revision for aseptic loosening. The findings were compared with those in 64 knees with osteoarthritis (OA) and aseptic loosening and in 18 knees with RA without loosening. The last group had been revised because of failure of the inlay or the coupling system of a constrained prosthesis. All the patients had had a total ventral synovectomy before implantation of the primary prosthesis. In all three groups a foreign-body reaction and lymphocellular infiltration were seen in more than 80% of the tissue samples. Deposits of fibrin were observed in about one-third to one-half of the knees in all groups. Typical signs of the reactivation of RA such as rheumatoid necrosis and/or proliferation of synovial stromal cells were found in 26% of knees with RA and loosening, but not in those with OA and loosening and in those with RA without loosening. Our findings show that reactivation of rheumatoid synovitis occurs after total knee replacement and may be a cofactor in aseptic loosening in patients with RA.
