A meniscus is a type of cartilage that exists in your knee joint. There are two menisci in your knee; each rests between the thigh bone (femur) and shin bone (tibia). The meniscus is made of tough cartilage and conforms to the surfaces of the bones upon which they rest. One meniscus is on the inner side of your knee--the medial meniscus. The other meniscus is on the outer side of your knee--the lateral meniscus.
The knee joint is very important in allowing people to go about performing almost any activity. The joint is made up of three bones: the femur (thigh bone), the tibia (shin bone), and the patella (knee cap). The surfaces of these bones within the joint are covered with a layer of cartilage. This important surface allows the bones to smoothly glide against each other without causing damage to the bone. The meniscus sits between the cartilage surfaces of the bone to distribute weight and to improve the stability of the joint.
Function of the Meniscus CartilageThe meniscus functions to distribute your body weight across the knee joint. Without the meniscus present, the weight of your body would be unevenly applied to the bones in your legs (the femur and tibia). This uneven weight distribution would cause excessive forces in specific areas of bone leading to early arthritis of knee joint. Therefore, the function of the meniscus is critical to the health of your knee.
The meniscus is C-shaped and has a wedged profile. The wedged profile helps maintain the stability of the joint by keeping the rounded femur surface from sliding on the flat tibial surface. The meniscus is nourished by small blood vessels, but the meniscus also has a large area in the center that has no direct blood supply (avascular). This presents a problem when there is an injury to the meniscus as the avascular areas tend not to heal. Without the essential nutrients supplied by blood vessels, healing of the meniscus cannot take place.
A Meniscus TearThe two most common causes of a meniscus tear are due to traumatic injury (often seen in athletes) and degenerative processes (seen in older patients who have more brittle cartilage).
It is not uncommon for the meniscus tear to occur along with other damage inside the knee. Injuries commonly occur to structures including the anterior cruciate ligament (ACL) and the medial collateral ligament (MCL). When all three of these injuries occur together, they are known as the "unhappy triad," an injury pattern seen in sports such as football when the player is hit on the outside of the knee.
Meniscus Tear or Cartilage Tear?
Both the covering of the bone within the joint and the meniscus are made of cartilage--however, they are different types of cartilage. People often say 'cartilage' to mean the meniscus (the wedges of cartilage between the bone) or to mean the joint surface (so-called articular cartilage which caps the ends of the bone).
When people talk about a cartilage tear, they are generally talking about a meniscus tear. When people talk about arthritis and worn cartilage, they are talking most often about the articular cartilage on the ends of the bone.
Symptoms of a Meniscus Tear?Individuals who experience a meniscus tear usually experience pain and swelling as their primary symptoms. Another common complaint is joint locking, or the inability to completely straighten the joint. This is due to the torn cartilage physically preventing the normal motion of the knee.
The most common symptoms of a meniscus tear are:
- Knee pain
- Swelling of the knee
- Tenderness when pressing on the meniscus
- Popping or clicking within the knee
- Limited motion of the knee joint
Diagnosis of a Meniscus TearAny patient who has knee pain will be evaluated for a possible meniscus tear. A careful history and physical examination can help differentiate patients who have a meniscus tear from patients with knee pain from other conditions. Specific tests can be performed by your doctor to detect meniscus tears.
X-rays and MRIs are the two tests commonly used in patients who have meniscus tears. An x-ray can be used to determine if there is evidence of arthritis in the knee joint. The MRI is helpful to actually see the torn meniscus. However, simply 'seeing' a torn meniscus on MRI does not necessarily mean a specific treatment is needed. Treatment of meniscus tears depends on several factors, as not all meniscus tears require surgery.trim the torn portion of meniscus, a procedure called a meniscectomy. Meniscus repair and meniscal transplantation are also surgical treatment options. Determining the most appropriate meniscus tear treatment is something you can discuss with your doctor.
Greis PE, et al. "Meniscal Injury: II. Management" J. Am. Acad. Ortho. Surg., May/June 2002; 10: 177 - 187.