The Knee Cartilages

The knee cartilage (minisci) are a crucial part of the knee joint and easy to injure. 

General structure

The word cartilage is misleading as this normally refers to the smooth friction-free surfaces of our joints.

The knee cartilages are properly called menisci (singular meniscus, a lens), and are C-shaped structures shaped rather like banked tracks. They are made of gristle (fibrocartilage), have flat lower surfaces and lie in a crescent shape in the knee joint.

There are two menisci in each knee, one in the inner compartment of the knee and one in the outer. They fill in some of the gap between the rounded thigh bone knuckle (femoral condyle) and the flat surface of the shin bone (tibial condyle).

The outer meniscus is more mobile as the inner meniscus is attached to the medial ligament. The blood supply penetrates 10-30% into the meniscus, and the nerves supply the outer part of each meniscus. The inner two-thirds of the menisci have no nerves.

Chemical structure

Fibrochondrocytes (fibro=fibrous tissues, chondro=cartilage, cytes=cells) form the meniscus mainly from water, collagen and proteoglycan chemicals (which hold 50 times their weight in water).

As the knee bends and straightens, the cartilages glide very slightly forwards and backwards.

What are the cartilages for?

The function of the menisci is not entirely clear, but it is possible they could contribute to the knee in various ways:

1. The cartilages carry load across the joint from the thigh bone to the shin bone and may also act as shock absorbers during dynamic movements.
2. Menisci work with the ligaments to stabilize the knee, as the rounded knuckle of the thigh bone fits into the shape of the meniscus and is prevented from moving too far off centre.
3. The menisci prevent friction between the two bones by acting as spacers, and with their movement they promote the circulation of the lubricating synovial fluid throughout the joint. Loss of the menisci can lead to arthritic changes in the joint surfaces.
4. The menisci may reduce the stresses through the joint surfaces by distributing it and protect them from arthritic change.

Read further for how knee cartilages get injured.