[Patellar changes during long-term observations on the Blauth knee joint endoprosthesis].

Changes in the position and structure of the patella and their importance with regard to pain patterns are described on the basis of long-term observation of the Blauth prosthesis. Examinations were performed on 206 knee prostheses on average 37.6 months (min. 12, max. 120 months) after implantation. Axial roentgenograms showed the patella to be laterally subluxated in 12% of the cases, and luxated in one. Also in 12% of the cases, osteolytic destruction of the posterior surface of the patella was found; there was a statistically significant correlation between the two groups, but they were not identical. In cases with changes in the patellar structure, initial pain on walking was significantly more frequent, though this was not so in cases where the kneecap had shifted from its normal position. The authors discuss possible connections with curvature radii and with the distances between the center of rotation and the sliding support on the femoral part of the prosthesis as causes of increased complaints in low kneecaps and for the increased incidence of structural changes in high kneecaps. The term "retropatellar pain syndrome" is applied to patients who experience pain when climbing stairs, rising from chairs and when starting to walk, in whom at least 2 of these complaints are positive: A total of 10.2% of the patients complained of considerable retropatellar pain. A patellectomy was performed in 8 of these patients. The radiological and histological analyses of 3 of the patellae removed showed evidence of arthrosis deformans at different stages, with concomitant synovitis.