Pathological findings from synovium of early osteoarthritic knee joints with persistent hydrarthrosis

Aim Nonspecific chronic synovitis of the knee joint was reported by P ollard in 1962 and its pathogenesis is considered to be a physiological reaction to intra‐articular disease. In this study, we evaluated the pathological findings of the synovium of early osteoarthritis ( OA )‐affected knee joints with hydrarthrosis in comparison to typical OA . Methods Synovial tissues were harvested from early OA knee joints with hydrarthrosis graded 0–2 according to the K ellgren and L awrence classification and examined by histopathology. Results The synovial tissues showed proliferation of fibroblast‐like synoviocytes ( FLS ) as if in rheumatoid arthritis ( RA ), and were immunohistochemically positive for matrix metalloproteinase 3, tumor necrosis factor α and interleukin 6. Conclusions The histology of RA is characterized by marked proliferation of FLS . In this study, the synovial tissues of early OA with hydrarthrosis showed moderate FLS proliferation. They also expressed the cytokines that are detected in the synovial tissues of RA . We suggest long‐term follow‐up is needed because early OA with hydrarthrosis might progress to overt RA .