MRIs Show Knee Damage

Report #6396

When an athlete injures his knee, doctors usually order a special test called an MRI, to determine if the cartilage is broken. A study in the American Journal of Sports Medicine showed that an MRI often demonstrates broken cartilage even when the knee is normal.

The ends of bones are protected by a thick, tough white gristle called cartilage. Once an athlete breaks the cartilage in his knee, it will never heal and often will continue to break with heavy physical exercise. Doctors can remove lose pieces of cartilage, but they cannot operate to replace the lost cartilage.

The cartilages in the knee fit together like gears in your car. When cartilage of the lower leg extends upward, cartilage in the upper leg extends downward. When you break cartilage, the fit is less perfect and a hard force on the joint can cause further breakage of cartilage. Therefore, people who break cartilage in their knees are usually cautioned to avoid hard exercises that may continue to break cartilage in the knee and eventually require a knee replacement.

Doctors usually check for cartilage damage with a test called an MRI. However, recent studies show that up to 24 percent of MRI's will show signs of cartilage damage in normal knees. Therefore, if your knee is swollen from an injury, you probably have cartilaginous damage and should avoid hard trauma to your knee for the rest of your life. If your knee hurts, but is not swollen, your doctor may order an MRI, but an abnormal MRI does not necessarily mean that you have broken the cartilage in your knee. More on knee injuries

By Gabe Mirkin, M.D., for CBS Radio News