The meniscus is cartilage inside the knee joint. Tearing can occur on either side, the medial (inside) or lateral (outside). Meniscus is the name for either of two pieces of tough cartilage inside the knee joint. They are shaped like half moons and are sometimes called semilunar cartilage. One is on the medial side and one is on the lateral side. They act as cushions between the femur, or the thigh bone, and the tibia, which is the major bone of the lower leg, to which they are connected.
Besides acting as shock absorbers, the menisci help to keep the knee joint stable. They also help maintain the shiny, white joint surface on the ends of the bones (the hyaline cartilage).
Tears in the meniscus can vary quite a bit in size and amount of displacement. The pattern of the tear may be lengthwise or radial, or form a flap, or a horizontal split. Another kind is called a bucket-handle tear. In this case, a lengthwise tear flips completely into the joint, instead of staying in its normal place around the edge of the joint. These tears happen suddenly, and are usually caused by a twisting injury. In contrast, degenerative tears are a result of the aging process.
Some small meniscus tears cause no symptoms. Usually, though, after a twisting injury to the knee, the person feels pain on the side of the knee. Later the knee swells and stiffens, gives way, and may lock up. The initial symptoms may subside, only to return with activity. If the knee is injured repeatedly, the tear may become larger.
Examination of the knee shows tenderness at the joint line of the knee next to the meniscus tear. There may be swelling, called water on the knee. A locked knee will not fully straighten, although bending is nearly normal. Usually a person can walk on a knee with a torn meniscus, sometimes with a limp. Rarely, the person cannot bear weight because it hurts too much. A doctor can do special twisting maneuvers, such as the McMurray test, to help detect a meniscus tear.
X-rays do not show a meniscus tear, unless dye is injected into the knee in an arthrogram. X-rays are best able to show bone, not soft tissues like meniscus or ligament. However, x-rays are usually done to find other problems that might mimic a meniscus tear. These problems include arthritis and a moving bone chip in the knee, also called a loose body or a joint mouse. Although the diagnosis of a meniscus tear can made on the basis of symptoms and signs, an MRI, or special three-dimensional image using magnets, may be done to confirm it. An MRI shows not only the bone, but also the meniscus, ligament and muscle, and is much more expensive than an x-ray. The person does not feel anything while the MRI is being done, but closed MRI machines can make some people feel claustrophobic. They may need medications, such as
Once in a while a meniscus will heal on its own and cause no more trouble. A small tear in the edge of the meniscus, near the capsule around the joint, can sometimes heal because it has a blood supply. Most tears do not heal, and become larger, because the inner two-thirds of the meniscus has no blood supply for healing. If the usual meniscus tear is not treated, problems in the knee will increase with time. The ultimate trouble can be the development of arthritis.
After an acute injury, RICE (rest, ice, compression, and elevation) will make the person more comfortable. Nonsteroidal anti-inflammatory drugs (NSAIDs), such as
Sometimes the tear can be repaired, if it is simple and at the edge of the meniscus. Repair works best with a person under the age of 50 who is willing to accept a more complicated treatment. The operation takes longer and usually involves another longer incision. It takes about six weeks on crutches after the surgery, and several months before the person can return to sports.
In contrast, a simple arthroscopy to remove the torn portion uses two or more small incisions. Only about five days are spent on crutches after the surgery. The operation is done most often on an outpatient basis at a surgical center or hospital, and the individual is admitted and discharged on the same day. Anesthesia can be general, or local with sedation, or spinal. Pain after the operation varies from almost none to quite a bit. The amount of pain depends mostly on the amount of swelling which, in turn, relates to the difficulty of the surgery. Usually the person needs to take pain medication, such as
The knee is wrapped in a bulky bandage after surgery. If the meniscus has been repaired, a knee immobilizer or splint is used.
Often the person can exercise the knee after the operation with instructions from the surgeon. Physical therapy helps to speed the return of motion, strength and function of the knee. A knee brace is not needed unless the knee ligaments are also damaged. After completing rehabilitation, the person can usually return to full activity including sports, unless arthritis or an unstable ligament prevent it.
The knee can become stiff if it is immobilized for too long. If strengthening exercises are not started, the knee will weaken. This is because the quadriceps, the muscle on the front of the thigh that is the main support of the knee, atrophies, or becomes smaller, due to the injury and lack of use.
Usually arthroscopy to remove the torn part of the meniscus results in an almost normal knee. However, some people continue to have pain, stiffness, and weakness in the knee. The remaining part of the meniscus could tear with the right kind of twisting injury. When there is a lot of scarring in the knee after surgery, it is called arthrofibrosis. This may require physical therapy, knee manipulation, or forceful bending under anesthesia, or another arthroscopy to break up the scar tissue.
During arthroscopy, it is possible for a ligament to be injured, which may cause the knee to be unstable. Infection is very uncommon. Rarely, blood clots develop in the veins of the leg, which is known as phlebitis, or travel from the leg to the lungs, a condition called pulmonary embolism. The knee is checked over time for recurring pain on the side, swelling, locking, or giving way. If any of these occur, the doctor should be consulted.
Author:John A.K. Davies, MD
Reviewer:William M. Boggs, MD