The meniscus is a C-shaped cartilaginous structure that serves to distribute weight evenly between the thighbone (femur) and the shinbone (tibia). It is comprised of two specific ligaments: the lateral menisci and the medial menisci. A meniscus tear occurs when there is injury to menisci. Many people refer to a meniscus tear as simply "torn cartilage".

Injury most often occurs to the meniscus from a rotating, weight-bearing movement where the foot remains planted. Activities most commonly associated with this type of injury are football, soccer, and snow skiing. Age may also be a factor.

Orthopedic surgical procedures can be used to either repair a menisci that has undergone traumatic injury or a degenerative menisci due to aging. ACL injury often accompanies the condition.

Further Reading:

American Academy of Orthopaedic Surgeons: Meniscal Tears

BioMet: Sports Knee Injuries: Meniscus Tear