A meniscus tear is a common knee injury. The meniscus is a rubbery, C-shaped disc that cushions your knee. Each knee has two menisci (plural of meniscus)-one at the outer edge of the knee and one at the inner edge. The menisci keep your knee steady by balancing your weight across the knee. A torn meniscus can prevent your knee from working right.

A meniscus tear is usually caused by twisting or turning quickly, often with the foot planted while the knee is bent. These tears can occur when you lift something heavy or play sports. Other knee injuries, such as a torn ligament, can happen at the same time. As you get older, your meniscus gets worn. This can make it tear more easily.

There are three types of meniscus tears. Each has its own set of symptoms.

With a minor tear, you may have slight pain and swelling. This usually goes away in 2 to 3 weeks.

With a moderate tear, you may feel pain at the side or center of your knee. Swelling slowly gets worse over 2 or 3 days. This may make your knee feel stiff and limit how well you can bend your knee. Usually you are still able to walk. You might feel a sharp pain when you twist your knee or squat. These symptoms go away but can come back if you twist or overuse your knee.

In severe tears, pieces of the torn meniscus can move into the joint space. This can make your knee catch, pop, or lock. You may not be able to straighten it. Your knee may feel "wobbly" or buckle without warning. It may swell and become stiff right after the injury or within 2 or 3 days.

If you are older and your meniscus is worn, you may not know what you did to cause the tear. Or you may only remember feeling pain after you got up from a squatting position, for example. Pain and slight swelling are often the only symptoms.

Your doctor will ask how the injury happened and if you have ever had any other knee injuries. Your doctor may also ask you about pain, swelling, locking, or buckling of the knee. You will have a physical exam to find out if you have a torn meniscus and to rule out other knee injuries.

Your doctor will check both knees for tenderness, range of motion, and knee stability. X-rays are usually done. Based on your symptoms and the physical exam, your doctor may diagnose a meniscus tear. He or she may suggest that you follow up with an orthopedic surgeon , although it is not always needed. Your doctor or the orthopedic surgeon may suggest other tests such as an MRI or arthroscopy.

If your pain is very bad at first, you might go to the emergency room. If your pain is not so bad, you may wait to see if it goes away. Most people go to the doctor when pain and swelling comes back after they use their knee.

Magnetic resonance imaging (MRI) is a test that provides pictures of organs, bones, and joints. It makes these images by using a magnetic field and pulses of radio wave energy. MRI gives a good picture of the size of a meniscus tear and where it is. It also shows ligaments, cartilage, and tendons.

MRIs of the knee are helpful to identify a meniscus tear and to find any related injuries to the ligament, cartilage, and tendons.

Arthroscopy is a way to find problems and do surgery inside a joint without making a large cut (incision). Your doctor puts a lighted tube with a tiny camera-called an arthroscope, or scope-and surgical tools through small incisions.

Your doctor may advise you to have arthroscopy instead of MRI if he or she thinks that you need surgery, based on your symptoms and the physical exam. For example, severe tears usually cause more pain, swelling, stiffness, and problems walking. Arthroscopy may be done in these cases, because surgical repair of the meniscus or other parts of the knee may be needed.

You will not have any side effects from the MRI test. But you may have some discomfort. For example:

• The table you lie on may be hard, and the room may be chilly.
• You may have discomfort from lying in one position for a long time.
• Some people feel worried or anxious inside a standard, closed-type MRI machine. If this keeps you from lying still, you can be given medicine to help you relax. Or you can talk with your doctor about using an open MRI machine, which is less confining than a standard MRI.

Risks of arthroscopy include:

• Bleeding within the joint.
• Infection.
• Blood clotting in your leg.
• Nerve or joint damage.
• A rare risk of compartment syndrome if pressure builds within the leg. When this occurs, you need treatment right away to release the pressure.

After arthroscopy, you may have swelling around the incision. This should go away within 2 weeks. It's normal for the site to feel tender for about a week. A small amount of bleeding from the incision is normal. Ask your doctor how much drainage to expect.

It may take several weeks to recover from arthroscopy. Your doctor will give you pain medicine and recommend rehabilitation exercises for you to do while you recover. You may have some soreness and pain after the procedure. You may need to apply ice to the joint and prop up the leg to reduce swelling and pain. Keep the bandages that cover your incision clean and dry.

How your doctor treats your meniscus tear depends upon the size and location of the tear; when the injury happened; your pain, age, health status, and activity level; and your surgeon's preference. Your treatment choices are:

• Nonsurgical treatment with rest, ice, compression, elevation, and physical therapy. You may wear a temporary knee brace.
• Surgical repair to sew the tear together.
• Partial meniscectomy, which is surgery to remove the torn section of the meniscus.
• Total meniscectomy, which is surgery to remove the entire meniscus. This is generally avoided, because this option increases the risk for osteoarthritis in the knee.

Other knee injuries, such as to the anterior cruciate ligament (ACL) or the medial collateral ligament , may happen at the same time as a meniscus tear. Your doctor may be able to find this out during a physical exam. In these cases, the meniscus tear will be treated as part of the treatment for the other injury.

Your doctor may advise you to have an MRI test or arthroscopy because:

• Your symptoms suggest that your tear is severe or that you have other injuries.
• You have trouble walking.
• These tests can see other injuries to knees, ligaments, and tendons.
• Surgical repair of your meniscus may reduce the risk of long-term problems with your joints.