The Knee Joint

The knee joint is the largest and most heavily loaded joint in the body. It connects the upper leg with the lower leg and transfers the entire weight of the body to the lower leg. Especially during sports activities involving rotational and transverse movements, strong forces act on the knee joint. This often leads to excessive strain and painful injury to the knee structures,in particular the cruciate ligaments, cartilage surfaces, and menisci. Very often there is combined ligament and meniscus damage. Given that this type of injury leads to an unstable knee and excessive wear and tear of the joint, the earliest possible surgical stabilization is essential.

What is the Function of the Meniscus?

The menisci are comprised of tough, rubbery, fibrous tissue and are located in the knee joint between the femur and the tibia. The menisci conform to the surfaces of the bones upon which they rest, with the medial meniscus on the inside of the knee, and the lateral meniscus resting on the outside of the knee. The "C" shape and wedged profile of each meniscus help maintain stability in the joint.

The medial meniscus and lateral meniscus have multiple functions. First, they act as shock absorbers for the knee, lowering the stress to the articular cartilage in the joint and helping to prevent or delay degenerative arthritis. Another function of these structures is to help distribute weight and improve knee joint stability. Finally, by acting as spacers between two main bones in the knee (the femur and the tibia) the menisci prevent friction between the bones and help distribute normal joint fluid into the articular cartilage. If there is no meniscus in the knee, body weight is unevenly applied to the leg bones, causing excessive forces in specific areas and leading to arthritis.

Nourishment is provided to each meniscus by small blood vessels, although there is a large area in the center of the structure which has no direct blood supply. The absence of blood supply to this region means it is difficult to heal following a meniscus injury.

The meniscus is often described by three zones: the front third is known as the anterior horn, the back third is the posterior horn, and the middle section is the body of the meniscus.

There are several differences between the medial and lateral meniscus, both anatomically (how they look) and functionally (how they work). Since the medial meniscus is attached to the joint capsule all around its outer edge, it does not slide much in any direction and is therefore more likely to tear. The lateral meniscus is more rounded, and there is a section where it is not attached to the joint capsule wall. Therefore it is more likely to move rather than tear.

An undamaged meniscus is key to a fully functioning knee.  However, this fact has only been really understood in the last 20 years.  Prior to this realization a damaged meniscus was often simply removed.  Although patients initially did quite well after this procedure, they later often developed osteoarthritis or other knee problems.

Today treatment varies depending on the extent and location of the meniscus tear.  For a minor tear, when pain and other symptoms go away on their own, muscle strengthening exercises may be all that is recommended. The doctor may advise working with a physical therapist to make sure exercises are done properly.