A meniscus is a piece of fibrocartilage found between the ends of two bones. It serves to cushion and protect the bones and can be found in several joints in the human body. There are two wedge-shaped menisci in the knee, the medial meniscus and the lateral meniscus. They cushion the space between the femur (thigh bone) and the tibia (shin bone). The outside 1/3 of each meniscus has a rich blood supply and is sometimes referred to as the ‘red zone.’ A tear in this red zone can often heal on its own or be repaired surgically. The remaining 2/3 of each meniscus lacks blood supply. Tears in this ‘white zone’ are not candidates for surgical repair because the tissue cannot heal without good blood supply.
A meniscus tear can be caused suddenly by injury (a traumatic tear) or by a gradual wearing down over time (a degenerative tear). Athletes and people who work in an occupation that requires spending an extended amount of time in a squat position, such as miners and carpet layers, are at higher risk of developing a meniscus tear. Common symptoms of a meniscus tear include pain, catching/locking, and giving way. Diagnosis is made by a combination of physical examination and MRI.
Common causes of a traumatic meniscus tear include injuries that involve twisting the leg with the foot planted, hyperextension of the knee, and hyperflexion of the knee. The medial meniscus is more likely to be involved than the lateral, and these traumatic tears tend to affect athletes and people under the age of 40.
Over time, the menisci become weakened, less flexible, and more brittle. Development of osteoarthritis in the knee also contributes to degeneration and makes the menisci more susceptible to tear. A degenerative meniscus tear is very common and occurs in approximately 60% of people over the age of 65. Because the blood supply to the menisci decreases with age, these degenerative tears are more difficult to heal than the traumatic kind.
Most meniscus tears do not require surgery. In the case of degenerative tears, where the material is only frayed, or traumatic tears which are small and stable, symptoms often improve with use of anti-inflammatory medication and physical therapy.
If the tear is large or unstable, surgical intervention may be required. The most common type of surgery for this issue is an arthroscopic partial meniscectomy in which the torn piece of meniscus is removed. Rehab after partial meniscectomy is provided by a physical therapist who will use exercises to improve range of motion, strength, balance, and mobility, along with modalities such as electrical stimulation and ice to control pain and swelling.
In the case of a traumatic tear affecting the red zone of the meniscus in an athletic person under the age of 30, surgical repair of the meniscus may be an option. After this type of surgery, a brace is worn on the affected knee for the first 4-6 weeks, locked to allow no more than 90° of bend and no hyperextension of the knee. The patient initially uses crutches, but is allowed to gradually increase weight-bearing through the affected leg with the brace on until he or she is able to walk comfortably without the crutches. Rehab involves the same treatments described above, but is progressed more slowly after this type of surgery in order to allow the repaired meniscus to heal.