[Articular cartilage: structure and histochemical composition]

Articular cartilage is a main component of the synovial joints that provides a low friction surface in joint motion and, during locomotion and standing distributes the load applied to the joint, therefore minimizing the stresses on the subchondral bone. One of the initial sign of Osteoarthritis (OA) consists in the degeneration of the extracellular matrix of articular cartilage leading to a progressive failure in the biomechanical properties of cartilage, compromising its full functionality. Because osteoarthritis is one of the most common diseases in humans, is highly prevalent in clinical rheumatology and its pathophysiology based on changes of cartilage, it is important for rheumatologists and physicians interested in this area are updated with regard to its structure, composition and key regulatory mechanisms. Thus, this article intends to make an updated review of the structure and histochemical composition of normal cartilage, from which depends the viscoelasticity and dynamic stiffness to compression properties. Furthermore, the nonhomogeneous stratified architecture in the typical four layers, as well as the main macromolecules of the solid matrix, collagen and proteoglicans are described. Finally, a description of the chondrocytes at their ultrastructural level, variations with depth of cartilage and metabolism is done.