2 - The Chemistry of the Ground Substance of Joint Cartilage

Abstract

This chapter discusses the general composition of cartilage, glycosaminoglycans, keratan sulfate, hyaluronic acid, and proteoglycans. Several types of connective tissue represented by ligaments, tendons, synovial membrane, and cartilage are found in diarthrodial joints. However, with the exception of cartilage, little is known about the ground substance of these tissues. Cartilage is an avascular tissue in which the cells are sparsely distributed in a stiff matrix. It is mechanically perhaps the most important tissue of diarthrodial joints and is well adapted to perform an exacting mechanical function, in having to withstand very high repetitive compressive loads that generate localized stresses. The water content of articular cartilage is about 65–75% and is highest near the joint surface of normal femoral condyles. The water content of patellar cartilage is similar. Although the content of water is high, it is precisely the presence of water in conjunction with proteoglycans and collagen that makes cartilage tough and resilient. Collagen accounts for about half the dry weight of human adult articular cartilage.