The menisci form during the first 8 weeks of gestation as condensations and differentiation of mesenchymal cells.
As the fetus develops, collagenous fibers appear and are oriented in a circumferential pattern, with the meniscus morphology and relationship to the rest of the knee being established by the 14th week of development. The organization and concentration of collagen fibers increase into early adulthood, then remains constant for the next 50 years before decreasing.
During the initial formation of the menisci, there is an abundance of cells and vas- cularity. With neonatal development, both the number of cells and extent of vascularity decrease. At birth, the vascular network ex- tends from the peripheral perimeniscal cap- illary plexus to the free central margin of the meniscus. Over the first few months of life, the vascularity decreases such that by the ninth month the inner third of the meniscus is avascular. This process continues so that by adulthood only the peripheral 10% to 30% has a vascular supply. A similar phenome- non occurs with the cells of the meniscus. Replete with cells at birth, the meniscus be- comes progressively less cellular with age. These changes are believed to be induced by the increased joint motion and weight bear- ing seen in early child development.
The proteoglycan content also shifts with age, with an increase in chondroitin sulfate and a decrease in chondroitin sulfate. The water content does not change. The percentage of noncollagenous proteins also declines from 20% at birth to 10% in individuals older than 50 years. A gradual discoloration is seen in the menisci with the normal aging process.