Up-regulation of CD44-positive cells in medial meniscus of medial compartmental osteoarthritis of the knee

The degeneration of medial meniscus in the medial compartmental osteoarthritic knee (OA knee) was investigated by the histological and immunohistochemical analysis. The series included 16 OA knees in 11 patients with mean age of 78.8±4.4 years (range, 73–86). The medial menisci were divided into the anterior, the middle and the posterior portion. They were subsequently stained with hematoxylin and eosin (H.E.) to evaluate the histological findings, and after that, immunohistochemical staining was performed and CD44-positive cells were counted. Tears of collagen fibers and degenerative changes of the medial meniscul structure were observed in all portions. The advancement of these degenerative changes was severer in the posterior portion than in the other and more remarkable as the osteoarthritis advanced. Immunohistochemical staining of the specimens revealed that CD44-positive cells concentrated around vessels and along tears adjacent to these vessels. In each grade (a radiographical grading system for OA knees — Koshino T, Machida J. Grading system of articular cartilage degeneration in osteoarthritis of the knee. Bull Hosp Jt Dis 1993;53:41–46), the mean number of CD44-positive cells in the middle and the posterior part was more than that in the anterior, especially in Grade 2 and 3 (P<0.05). In the medial compartmental OA knee, the advancement of degeneration in the meniscus was positively correlated with the advancement of the radiological grade, and the mechanical stress on the middle and the posterior part may up-regulate CD44 expression.