The medial and lateral menisci are shock absorbers and force distributors located between the femur and the tibia.View image Consequently, menisci can tear due to traumatic injury or degenerative wear (e.g., in knee joint arthritis), and can compromise force distribution across the knee joint, increasing force concentration on the cartilage and other joint structures. 
Damage to the meniscus due to rotational forces directed to a flexed knee (as may occur with twisting sports) is the usual underlying mechanism of injury. A valgus force applied to a flexed knee with the foot planted and the femur rotated externally can result in a lateral meniscus tear. A varus force applied to the flexed knee when the foot is planted and the femur rotated internally can result in a tear of the medial meniscus.
Tears produce rough surfaces inside the knee, which cause catching, locking, buckling, pain, or a combination of these symptoms. Abnormal loading patterns and rough surfaces inside the knee, especially when coupled with return to sports, significantly increase the risk of developing arthritis if not already present.