What are the signs and symptoms of the injury?

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 alprazolam or diazepam, to sedate them before the test, or to use the less common open MRI machines.

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.