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The menisci - the medial meniscus and lateral meniscus - are crescent-shaped bands of thick, rubbery cartilage attached to the shinbone (tibia). They act as shock absorbers and stabilize the knee. The medial meniscus is on the inner side of the knee joint. The lateral meniscus is on the outside of the knee.
Meniscus tears can vary widely in size and severity. A meniscus can be split in half, ripped around its circumference in the shape of a C or left hanging by a thread to the knee joint. A barely noticeable tear may resurface years later, triggered by something as simple as tripping over a sidewalk curb.
A meniscus tear can occur when the knee is suddenly twisted while the foot is planted on the ground. A tear can also develop slowly as the meniscus loses resiliency. In this case, a portion may break off, leaving frayed edges.
Symptoms of a Torn Meniscus
If you have a torn meniscus you may:
- Be unable to extend your leg comfortably and may feel better when your knee is bent (flexed)
- Develop pain gradually along the meniscus and joint line when you put stress on your knees (usually during a repeated activity). This most often happens when the tear develops over a period of time.
- Have swelling, stiffness or tightness in your knee
In sports, a meniscus tear usually happens suddenly. Severe pain and swelling may occur up to 24 hours afterward. Walking can become difficult. Additional pain may be felt when flexing or twisting the knee. A loose piece of cartilage can get stuck in the joint, causing the knee to temporarily lock, preventing you from fully extending your leg.
Diagnosing a Torn Meniscus
Typically, your doctor will ask you how the injury occurred, how your knee has been feeling since the injury and whether you have had other knee injuries. You may be asked about your physical and athletic goals to help your doctor decide on the best treatment for you.
Your doctor will hold your heel while you lie on your back and, with your leg bent, straighten your leg with his or her other hand on the outside of your knee as he or she rotates your foot inward. There may be some pain. It is important to describe your symptoms accurately. The amount of pain and first appearance of swelling can give important clues about where and how bad the injury is. Tell your doctor of any recurrent swelling or of your knee repeatedly giving way.
A magnetic resonance imaging (MRI) scan is often used to diagnose meniscal injuries. The meniscus shows up as black on the MRI. Any tears appear as white lines. An MRI is 70 to 90% accurate in identifying whether the meniscus has been torn and how badly. However, meniscus tears do not always appear on MRIs.
Meniscus tears, indicated by MRI, are classified in three grades. Grades 1 and 2 are not considered serious. They may not even be apparent with an arthroscopic examination. Grade 3 is a true meniscus tear and an arthroscope is close to 100% accurate in diagnosing this tear.
Treating a Torn Meniscus
If your MRI indicates a Grade 1 or 2 tear, but your symptoms and physical exam are inconsistent with a tear, surgery may not be needed.
Grade 3 meniscus tears usually require surgery, which may include:
- Arthroscopic repair. An arthroscope is inserted into the knee to see the tear. One or two other small incisions are made for inserting instruments. Many tears are repaired with dart-like devices that are inserted and placed across the tear to hold it together. The body usually absorbs these over time.
Arthroscopic meniscus repairs typically takes about 40 minutes to do. Usually you will be able to leave the hospital the same day.
- Arthroscopic partial meniscectomy. The goal of this surgery is to remove a small piece of the torn meniscus in order to get the knee functioning normally.
- Arthroscopic total meniscectomy. Occasionally, a large tear of the outer meniscus can best be treated by arthroscopic total meniscectomy, a procedure in which the entire meniscus is removed.