Histological examination of surface repair tissue after successful osteotomy for osteoarthritis of the hip joint.

In this study biopsy specimens of the surface repair tissue from the weightbearing area of the hip joint were collected from 15 patients who had undergone successful valgus osteotomy, and these were examined histologically. In 6 of the 15 patients the specimens stained strongly with safranin-O in all three layers of the matrix. However, the repair tissue from another 6 patients showed strong staining only in the intermediate and deep layers, while that from 2 patients stained only in the deep layer. Specimens from 5 patients were stained for S-100 protein and positive cells were detected in all cases, demonstrating that the cells in the repair tissue were chondrocytes. However, there was no tide mark in the repair tissue and the arrangement of the cells differed from that in normal cartilage. Discontinuity of the subchondral bone was also noted. These findings make it likely that the repair tissue was of bone marrow origin.