Concentration and localization of YKL-40 in hip joint diseases

YKL-40 is a major secretory protein from human chondrocytes and synovial fibroblasts. We evaluated the concentrations and localization of YKL-40 in hip joint diseases, and analyzed the possibility of YKL-40 as a new inflammatory joint marker.

The concentration of YKL-40 in synovial fluid (SF) was measured by a sandwich-type ELISA. SF samples were collected from 19 hips with osteoarthritis (OA) of the hip joint, 21 hips with osteonecrosis of the femoral head (ONFH), and 5 hips with failed total hip arthroplasty (failed THA). In all cases of failed THA, cartilage tissue in hip joints was removed completely during the previous THA. The localization of YKL-40 was determined through immunohistochemical analysis using a specific antibody.

The mean SF concentration of YKL-40 was significantly higher in ONFH and failed THA than in OA. Comparison by OA grade was not significantly different. In staging of ONFH, Ficat stage III with collapsed femoral head showed significantly higher YKL-40 concentrations than the other stages. Immunohistochemical studies showed that YKL-40 was localized in chondrocytes in the superficial and middle layers of the cartilage. In the synovium, YKL-40 was localized in fibroblasts and macrophages.

YKL-40 reflects the degree of inflammation rather than cartilage metabolism. YKL-40 may be a useful inflammatory marker of hip joint diseases.