Distribution of immunoreactive fibronectin and collagen (type I, III, IV) in mouse joints. Fibronectin, an essential component of the synovial cavity border.

Hyaluronic acid traditionally has been held to play a major role in the control of transsynovial exchanges and in the biomechanical properties of synovial fluid and cartilage surfaces. As with previous ultrastructural observations, immunohistochemical data show that a more complex differentiation must be envisaged for interstitial tissues bordering the synovial cavity. In particular, the elective concentration of fibronectin in the lining layer of the synovial membrane and its presence as a fine layer at the articular cartilage surfaces indicate that this glycoprotein, along with hyaluronic acid, may play an important role in joint physiology. Only immunoreactivity for type III procollagen is diffusely distributed in the entire synovial membrane and, in addition, is found associated with fibronectin immunoreactivity at the articular cartilage surfaces.