1. What Is a Meniscus?
The meniscus is a C-shaped piece of fibrocartilage that acts like a cushion between the femur (thigh bone) and tibia (shin bone). It is wedge-shaped, such that it is larger on the outer rim of the meniscus and tapers towards the inner rim. There is one on the lateral side and one on the medial side of the knee. The medial one is torn approximately three times more often than the lateral meniscus.
2. What Is Its Function?
The meniscus serves to distribute the forces more evenly across the joint. The end of the femur is curved, whereas the tibia is relatively flat. A curved object meeting a flat surface only has a small contact area, and therefore higher peak contact pressures. The meniscus "cups" the end of the femur and spreads out the pressure. It also functions as a shock-absorber. Its collagen fibers are oriented both radially and circumferentially to accomplish these tasks.
3. How Is It Torn?
The meniscus can be torn with an injury (traumatic) or with wear-and-tear over time (degenerative). Traumatic tears usually happen in younger patients, with twisting motions or sudden changes in direction or speed. They also happen in conjunction with other injuries, especially anterior cruciate ligament (ACL) tears, up to 70% of the time in some studies. Degenerative tears occur because the meniscus thins out and becomes more easily torn. Over time, the meniscus has less collagen and more water content. It is less able to resist the forces put upon it. There are numerous configurations of meniscus tears--horizontal, vertical, radial, longitudinal, complex, bird beak, flap and bucket-handle tears.
4. How Do I Know If I Tore My Meniscus?
People with traumatic tears can sometimes pinpoint it to a specific activity, oftentimes associated with a popping or tearing sensation. In other cases, there is no inciting event and no limitations to activity, except for occasional pain. Common symptoms include pain and swelling, tenderness on the joint line, effusion (water on the knee), catching or locking, and a sensation of your knee giving out. Sometimes, the tear is large and unstable. It can flip inside-out upon itself, like the handle of a pail (bucket-handle tears). When that happens, the knee can lock up and get stuck at a certain angle or it is unable to be fully straightened. A radiograph (x-ray) may be useful in ruling out other causes of these symptoms, but it largely only shows bones. Remember, the meniscus is made up of cartilage. Magnetic resonance imaging (MRI) is useful in diagnosis, because it shows not only bones, but muscles, tendons, ligaments, articular cartilage and, of course, the meniscus.
5. I Don't Want Surgery--What Are My Options?
Non-surgical treatments include rest, anti-inflammatory medications and physical therapy. Meniscus tears tend not to heal by themselves due to a poor blood supply. However, it may get to the point where it doesn't bother you, especially with smaller tears. There are plenty of people out there walking around with meniscus tears. By calming down the inflammation and strengthening the muscles around the knee, the tear may only cause an occasional twinge or flare-up. If you know certain activities aggravate the meniscus tear, but if you can live within those limitations, then you may want to just observe tear to see what happens. On the other hand, if the symptoms are affecting the activities you want to do, then it's probably time to talk about surgery.
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