Injuries to the meniscus are common, particularly in athletes. A torn meniscus is also seen in older patients as the result of a degenerative process.
There are two menisci in the knee, the medial (inner) and lateral (outer) meniscus. These c-shaped "cushions" of cartilage help protect the articular cartilage, the lining of the bones that allows them to glide smoothly against one another during motion. These structures also act as shock absorbers, distributing load across the knee.
Some meniscus injuries can be treated non-surgically with rest, physical therapy, and activity modification. However, in a young and active person, choosing to forgo surgical repair of a torn meniscus is likely to result in persistent instability, swelling, and pain in the knee, as well as setting the stage for progressive wear of the lining articular cartilage. This results in degenerative arthritis which may require corrective surgery, including knee replacement surgery.