Hyaline cartilage of joints

(hematoxylin and eosin)

The structure of articular cartilage #1, #2 is distinct in that its articulating surfaces #1, #2 have no perichondrium. There is subchondral osseous tissue with osteons beneath the articular cartilage.

This kind of cartilage consists of 3 zones with no abrupt boundary in between:

• superficial (tangential) zone contains collagen fibers (which are parallel to the articulating surface), an outer acellular cartilage sheet, and a layer of flattened chondroblasts;
• transitional zone contains rounded chondrocytes that are larger; they are found in lacunae as solitary cells #1, #2 or in small isogenous groups;
• deep (radial) zone where collagen fibers are oriented radially to the articulating surface. The zone is divided by a basophilic tidemark #1, #2 into noncalcified (outer) and calcified (inner) layers. The zone contains chondrocyte columns where some part has become dystrophic.

The subchondral bone contains small blood vessels, which may permeate the calcified cartilaginous zone; a boundary between cartilaginous and osseous tissue has a complicated relief #1, #2, #3.

The articular cartilage nutrition is provided mainly by diffusion from the synovial fluid of joint cavity, and to lesser extent from the subchondral bone vessels.