What is the meniscus?

The meniscus which is part of the knee joint, is a half moon shaped piece of cartilage that lies between the weight bearing joint surfaces of the femur and the tibia. It is triangular in cross section and is attached to the lining of the knee joint along its periphery. There are two menisci in a normal knee; the outside one is called the lateral meniscus, the inner one the medial meniscus.

The menisci play an important role in absorbing about a third of the impact load that the joint cartilage surface experiences. It has been shown that complete removal of a meniscus can result in progressive arthritis in the joint within a decade or so in a younger patient, sooner in patients who are older with pre-existing "wear-and-tear" osteoarthritis. The menisci also cup the joint surfaces of the femur and therefore provide some degree of stabilization to the knee.

The meniscus itself is for the most part avascular, that is it doesn't bleed if cut and doesn't have blood vessels inside. The exception to this is at the periphery where it joins to the vascular knee lining providing the outermost 20% of the meniscus with a blood supply. As a result of this avascularity a torn meniscus doesn't have the ability to heal itself unless there is just a small tear confined to the peripheral vascular zone. Similarly the nerve supply providing pain and sensation to the meniscus is for the most part limited to the zone where the blood vessels are located.

In terms of descriptive terminology orthopaedic surgeons divide the meniscus into thirds with three geographical zones; the front third is referred to as the anterior horn, the back third the posterior horn, and the middle third the body.