The ultrastructure and biochemistry of meniscal cartilage.

The meniscus is characterized at the light microscopic and ultrastructural levels by thick collagen fibers that are predominantly circumferential in orientation. The extracellular matrix of the meniscus is composed mainly of collagen, with smaller quantities of proteoglycans, matrix glycoproteins, and elastin. The collagen is predominantly Type I, with smaller quantities of Types II, III, and V. The proteoglycans are mainly large, aggregating proteoglycans with chondroitin sulfate as their dominant glycosaminoglycan. A small proportion of small dermatan sulfate proteoglycans is probably present. The matrix glycoproteins include the link proteins, the 116-k protein, and a group of adhesive or potentially adhesive proteins that includes Type VI collagen (here classified as a glycoprotein with a collagenous domain), fibronectin, and thrombospondin. The fibrochondrocytes of the meniscus appear to have considerable potential to respond to growth and other modulating factors in the repair or regeneration of the tissue.