The normal knee joint has 2 peripheral rings of soft cartilage around each side of the joint. These cartilage rings are called meniscus cartilage. There is a medial meniscus (on the inside part of the knee) and a lateral meniscus (on the outside part of the knee).

When injured, the meniscus cartilage can tear, resulting in a flap of meniscus that catches inside the knee joint (not unlike a hangnail catches on objects). When this occurs, the problem can be easily treated by a relatively small, outpatient surgery called a knee arthroscopy. Knee arthroscopy involves 2 or 3 small (1/4 inch) incisions used to insert a small video camera into the knee joint to visualize the torn meniscus, and other instruments to trim off or repair the torn part of the meniscus (often like clipping off the hangnail). This type of surgery is extremely successful and allows patients to return to very active lifestyles without further problems in most cases. Recovery is usually quick, returning patients back to normal activities within a few days to a few weeks.