Knee > Meniscus Tear

What is the Meniscus?

The menisci - the medial meniscus and lateral meniscus - are crescent-shaped bands of thick, rubbery cartilage that are attached to the shinbone (tibia) and, by dispersing the weight of the body over a large surface area, act as shock absorbers and stabilizers in the knee. The medial meniscus, which is on the inner side of the knee joint, is longer from front to back than the lateral meniscus, which is on the outside of the knee.

A meniscus tear can occur from a sudden twisting of the knee with the foot planted on the ground, or it can develop over time because the meniscus gradually loses resiliency and a portion may break off, leaving frayed edges. 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. Or, the tear can be barely noticeable only to resurface years later, triggered by something as innocuous as tripping over a sidewalk curb.

Athletes who play sports that require running and pivoting, such as basketball, football, and soccer, are particularly susceptible to meniscus tears. Still, most meniscal injuries occur in everyday situations, usually resulting from sudden twisting motions in which the knee joint's normal motion is disrupted. Repeated kneeling or squatting, particularly among older people, also can cause meniscus tears, creating uneven surfaces that irritate the knee joint.

If your knee has a stable ACL and PCL (anterior and posterior cruciate ligaments), the success rate for repairing the torn meniscus through surgery is approximately 80 percent. Possible long-term complications include chronic pain and an increased risk of re-injury. A meniscus repair will take longer to rehabilitate - at least eight to 12 weeks before you can return to strenuous activity - but will have a better long-term prognosis than a meniscus removal. A tear on the outer portion of the meniscus, where the blood supply is better, can be repaired more effectively than a tear on the inner portion. Similarly, a younger patient will more likely be a successful candidate for meniscus repair than an older person whose menisci may have begun to degenerate. Arthroscopic partial meniscectomy, or removal of the torn piece of the meniscus, is not as effective in patients with arthritis, and can take up to six months to rehabilitate, compared to 3-4 weeks if no arthritis is present. Patients without arthritis who have undergone total meniscectomy, or removal of the entire meniscus, may be candidates for meniscal transplantation, which involves transplanting a meniscus from a cadaver knee. Since the menisci have been found to degenerate with age, an older person with a meniscus tear is a less likely candidate for repair. Patients over the age of forty tend to have tears with frayed surfaces that cannot be sewn back together satisfactorily.

There are usually three parts to an orthopedic evaluation: medical history, physical examination, and tests your physician may order.

Your doctor will likely ask you how you injured your knee, how it has been feeling since the injury, and if your knee has been previously injured. Physicians also typically ask about other conditions, such as diabetes and allergies, and medications currently being taken. If you know or suspect you have a torn meniscus, it is important to describe your symptoms accurately. For example, the degree of pain and when the swelling occurred can provide your physician with important clues about the location and severity of the injury. Inform you physician of any recurrent swelling or of your knee repeatedly "giving way." The doctor may also ask about your physical and athletic goals - information that will help him decide what treatment might be best for you in achieving those goals.

To determine the extent of your injury, your physician will manipulate your knee manually, and will also check for range of motion. This may involve some pain, as the physician will hold your heel while you lie on your back and, with your leg bent, straighten your leg with his other hand on the outside of your knee as he rotates your foot inward. He also may place both hands on your foot while you are lying on your back with your leg bent at a 90-degree angle, and rotate your foot outward and downward.

MRI (magnetic resonance imaging) is commonly used to diagnose meniscal injuries. The meniscus should appear in black on the MRI, and any tears will show up as white lines. Your MRI should be interpreted by an experienced knee surgeon or musculoskeletal radiologist. Meniscus tears, indicated by MRI, are classified in three grades. Grades one and two are not considered serious and may not even be apparent through an arthroscopic examination. Grade three is a true meniscus tear. MRI is 70 to 90 percent accurate for diagnosing meniscus tears, so these findings along with your symptoms will help the physician make a diagnosis. However, meniscus tears do not always appear on MRIs. If your MRI indicates a grade one or two tear, but your symptoms and physical exam are inconsistent with a tear, your physician may elect to forgo surgery. Grade 3 tears usually will require an arthroscopic examination to determine whether surgical repair is needed. An arthroscope is close to 100 percent accurate in diagnosing a grade III meniscal tear. X-rays will not show meniscal damage, though they can reveal calcification of the cartilage (chondrocalcinosis), a condition that can make the meniscus more prone to tears. X-rays also show bone spurs and joint narrowing, conditions that can reduce the success rate of treatments such as arthroscopy.

RELATED TOPICS

   Imaging techniques