A medial meniscus is a C-shaped wedge of cartilage inside the knee joint. It is often damaged when someone has all her weight on that leg, with the knee slightly bent, and then suddenly twists the knee joint. A torn medial meniscus cannot always be related to a specific event, but it typically gives rise to knee pain and sometimes swelling, and the knee joint may occasionally "lock." Mild tears may heal without treatment, but a more serious cartilage injury is usually managed using knee surgery to repair, remove or replace the meniscus.
The knee joint is the body's largest joint and also the most complicated. Where the femur, or thigh bone, meets the tibia, or shin bone, the medial meniscus and lateral meniscus are found, resting on the top surface of the tibia. Each meniscus is a shock-absorbing cushion of cartilage, which is semicircular in shape with a thick outer border and a thin inner edge. Situated on the inner side of the knee, the medial meniscus has its mobility limited by a strong ligament, called the medial collateral ligament. This attaches to the outer edge of the meniscus, restricting its movement and making it more likely to tear when the knee joint is subjected to sudden force.
A torn medial meniscus is a common injury, especially when playing sports where sudden rotation of the knee joint occurs. Alternatively, a cartilage tear can develop over time where there are numerous episodes of minor damage. Signs of a torn cartilage include: intermittent pain, difficulty straightening the knee, "locking" of the joint and sometimes swelling. Although the outer part of the meniscus has a reasonable blood supply, the central part does not, so larger tears which extend into the middle of the cartilage are less likely to heal by themselves.
Initially, a torn medial meniscus may be treated by resting the affected leg, elevating it and applying ice. Painkillers may be required and the patient should avoid putting weight on the knee, perhaps by using crutches. While a small tear may heal in a few weeks, larger or more central tears might require surgery. Keyhole surgery may be used to repair the torn medial meniscus and sew it into place or, if this is impossible, a torn section might be trimmed away. Relatively recent treatment options involve using implants that grow to fill the areas where cartilage is absent or transplants, using donor tissue, where the whole meniscus has to be removed.