There are three bones in the knee, the femur, tibia and patella. The ends of those bones are covered with cartilage (a smooth material that cushions the bone and allows the joint to move easily without pain). The cartilage acts as a shock absorber. Between the bones of the knees are two crescent-shaped discs of connective tissue, called menisci, which also act as shock absorbers to cushion the lower part of the leg from the weight of the rest of the body.
Meniscus tears can occur during a rotating movement while bearing weight, such as when twisting the upper leg while the foot stays in one place during sports and other activities. Tears can be minor, with the meniscus staying connected to the knee, or major, with the meniscus barely attached to the knee by a cartilage thread.
Some meniscal tears can be repaired by suturing (stitching) the torn pieces together. Whether a tear can be successfully treated with repair depends upon the type of tear, as well as the overall condition of the injured meniscus. Because the meniscus must heal back together, recovery time for a repair is much longer than from a meniscectomy.