Gene expression of type II collagens in chondro-osteophytes in experimental osteoarthritis.

The formation of chondro-osteophytes in osteoarthritic joints is a unique example of adult neochondrogenesis that bears some similarities to growth plate elongation and fracture callus formation. This study uses in situ hybridization histochemistry to define the molecular phenotype of cells in active chondro-osteophytes. Chondro-osteophytes are composed of fibrocytes and osteoblasts that express type I procollagen mRNA, mesenchymal prechondrochytes that express type IIA procollagen mRNA, and maturing chondrocytes that express type IIB procollagen mRNA. Based on the spatial pattern of gene expression and cytomorphology, the neochondrogenesis associated with chondro-osteophyte formation closely resembles that of healing fracture callus.