The articular surface of the distal femur, the articular surface on the posterior aspect of the patella and the articular surfaces on the tibial plateau are covered by a variety of hyaline cartilage termed articular hyaline cartilage. Articular hyaline cartilage offers a firm, smooth and relatively friction-free surface facilitating joint movements. The thickness of articular hyaline cartilage in the knee is not uniform and varies from 3mm to 7mm. Articular hyaline cartilage possesses a degree of compressibility and elasticity. These features enable the articular surfaces to dissipate laterally the vertical compressive forces to which the knee joint is subjected during weight transmission. Articular hyaline cartilage does not usually ossify.

The surface of articular hyaline cartilage is lubricated by synovial fluid secreted by the synovial membrane lining the inner surface of the joint capsule. However, the articular cartilage itself is not covered by synovial membrane. As with hyaline cartilage in extraarticular sites, the substance of articular hyaline cartilage is made up of cells termed chondroblasts and chondrocytes, and an intercellular matrix elaborated by the chondrocytes. The intercellular matrix is biochemically complex, and is composed of various proteins including different types of collagen, a variety of cell adhesion molecules and glycosaminoglycans, and lipids. The glycosaminoglycans are arranged systematically about a core protein to form complex hydrophilic molecules termed proteoglycans. The proteoglycans are chiefly responsible for the impressive viscoelastic biomechanical properties of articular cartilage.

Healthy articular hyaline cartilage in the young individual has a pale and glistening appearance, and a firm and smooth texture. With age degenerative changes begin to appear, and cartilage loses its smooth and glistening character.

At the histological level, articular hyaline cartilage is seen to be made up of four layers or zones on the basis of differences in cellular morphology, cellular density as well as differences in the composition of extracellular matrix.

Of the four layers, the most superficial layer faces the joint cavity, and the deepest layer is apposed to, and fused with, the subchondral bone.

From superficial to deep, these layers are named as follows:

i) Tangential stratum (Zone 1)
ii) Transitional stratum (Zone 2)
iii) Radiate stratum (Zone 3)
iv) Calcified stratum (Zone 4)

The region between Zone 3 and Zone 4 is called the tidemark and is readily discernible in young cartilage. The progressive ossification of Zone 4, which accompanies aging, results in the blurring of the tidemark.

Articular hyaline cartilage is devoid of innervation and lymphatic vessels. Except for the presence of a few blood vessels in Zone 4, articular hyaline cartilage is also normally devoid of vascularity, and is believed to derive its nutrition mainly by diffusion from synovial fluid and from the vascular plexus in synovial membrane.