The meniscus is a very important shock absorber of the knee made of a very strong substance called fibrocartilage. It protects the cartilage of the joint, keeping it from wearing out and causing early arthritis. A large percentage of our body weight is distributed through the meniscus as we walk, run, and jump. The meniscus adds to the stability of the knee joint by helping the shape of the femur or thigh bone conform to the tibia or leg bone. The meniscus also plays a role in the nourishment of the joint cartilage that covers the bones in the joint.
An acute meniscal tear may be heard as a "pop" and felt as a tear or rip in the knee. Many are followed within a few minutes to hours by swelling of the knee as a result of blood accumulation. Some do not result in much swelling and some present themselves in a less acute fashion. Patients with meniscal tears often describe a popping or catching in their knee. Some actually can feel something out of place. In the most dramatic situations the knee will actually lock, preventing the patient from fully extending or straightening the knee -- or occasionally from flexing or bending it. The pain or discomfort is usually along the joint line or where the femur and tibia bone come together. It often starts out relatively painful; then with time, much (if not all) of the pain disappears except with certain activities. Some patients will have the tear become asymptomatic (no symptoms) for a time, especially if their activity level decreases significantly.
Tenderness is elicited by deep palpation (examination using the hands) along the joint line. Twisting the knee while flexing it will occasionally cause or reproduce the patient's symptoms.
Meniscal tears do not show up on plain X-rays because the meniscus does not contain calcium the way bones do. There are some specialized tests such as the MRI scan which are helpful in further evaluating the meniscus.
Several events can cause the meniscus to become damaged. It can tear or rip from force, pinching it between the femur and the tibia. Most frequently this is a twisting-type force and is relatively common in sports-related knee injuries. Occasionally it is associated with a ligament rupture. It does not always require a major fall or twist to cause a meniscal tear. Some occur with nothing more than getting up from a squatting position. Certain meniscal tears occur gradually over a long period of time. In older patients these may represent so-called degenerative meniscal tears and may not be symptomatic. The location of the tear within the meniscus may determine the type of treatment which is most appropriate.