Proteoglycans are extracellular matrix molecules that have a central protein core or backbone structure with covalently attached glycosaminoglycans. Proteoglycans, cartilage, and water are the main constituents of human cartilage.

In osteoarthritis, the breakdown of articular cartilage caused by chronic repetitive use and inflammation results in the decreased synthesis of proteoglycans by the chondrocytes. The loss of this component of cartilage is reflected at the macroscopic level by cartilage degradation and bone-bone contact osteoarthritic degenerative joint disease. Decreased proteoglycan secretion is expected on arthrocentesis, synovial fluid may show few leukocytes, but otherwise will be without evidence of acute inflammation or infection.