The Knee Meniscus: A Complex Tissue of Diverse Cells

This review describes the knee meniscus and its diverse cell populations. Situated between the femur and tibia, the meniscus acts to transmit loads within the knee while maintaining joint stability. Not only does this tissue display complex geometry and anatomy, its cellular profile ranges from fibroblast-like to chondrocyte-like. When the tissue first begins to develop in the body, its cells are similar in shape and morphology, but as it matures, these cells take on distinct characteristics. The spindle-shaped cells of the outer meniscus are well-suited to maintaining a fibrous extracellular matrix rich in collagen type I. The round, inner meniscus cells produce both collagen types I and II, and glycosaminoglycans, giving rise to a hyaline-like inner portion of the tissue. Cells intermediately located display characteristics of both cell types. Fibrochondrocytes are also known to be highly dependent on mechanical stimulation to maintain healthy tissue, and display regional variation in response to different biomolecular cues. Investigating this cell population under a variety of conditions can lead to a better understanding of the pathophysiology and regenerative processes of the meniscus.