Many of you have friends or have heard it said that they have “torn cartilage” in their knees. They are probably not talking about the cartilage that covers the end of the bone – the articular cartilage – but rather a tear of one of the two bushings in the knee, a meniscal tear. These are rather common injuries in athletes and in the general population and tend to increase in frequency with increasing age of the individual.
Each knee has two of these fibrocartilaginous bushings, the medial meniscus (inside) and the lateral meniscus (outside). These menisci act as shock absorbers in the knee and help to conform the shape of the two bones of the knee, femur (thigh bone) and tibia (shin bone) to one another. The menisci also act in concert with the ligaments and muscles to provide stability to the knee. The medial meniscus is attached securely to the ligaments on the back and on the inner side of the knee and because of this attachment is the more frequently torn of the two.
The menisci can be torn when there is a sudden, unexpected twisting motion to the knee. This motion traps the meniscus between the ends of the two bones and causes a shearing action on the tissue. This frequently happens in conjunction with ligament injuries, especially ACL tears. As you get older your menisci becomes softer and the blood supple decreases. This can lead to tears with little or no trauma; sometimes just a misstep will cause a tear.
When your meniscus tears you will usually feel a sharp pain on that side of the knee at the joint line. Generally, the knee will then start to swell within a few hours. You may find your knee locks up on you and you are unable to straighten it all the way. This occurs because the meniscus flips into the joint and forms a mechanical block to motion. The swelling will eventually decrease and the pain will subside with time and you may feel your knee is back to “normal”. It might not even bother you too much when walking straight ahead; however, when trying a sharp cut or turn you may experience a return of the sharp pain.
To determine whether you have a meniscal tear, your doctor will ask you questions about how the injury occurred and then will examine your knee. This usually involves moving the knee around if it is not too inflamed and pressing over your joint line on either side. Sometimes as your knee is moved from bent to straight a pop can be felt as the torn meniscus moves out of the way. X-rays are usually taken just to assure there are no broken bones or loose bodies floating around the knee. The X-ray will not show the torn meniscus as X-rays only show bone detail and not soft tissue. Sometimes, if there is question remaining after examination, your doctor may order an MRI to confirm the diagnosis or determine if the meniscal tear may be repaired.
In Part II we will discuss treatment options for this common knee condition….