The menisci are two crescent shaped structures of fibrocartilage. There’s the medial and the lateral meniscus. Both menisci serve to bridge the incongruities of the two bone surfaces that make up the knee joint. Their elasticity allows them to act as a kind of shock absorber, reducing part of the load on the joint.
Damage to a meniscus can occur due to either acute trauma or repetitive stress. How it tears would depend on the area of the injury, as well as the type and depth of the tear. Possible affected areas are the anterior horn, the posterior horn, and the middle body. The most common injury types are vertical, radial, horizontal, bucket handle, parrot beak, and flap tears. There are also complex tears, where there is often a combination of patterns.