The lateral and medial meniscus, together, are a crescent-shaped structure made up of fibrocartilage.  They act like a shock absorber between the upper and lower leg at the knee.  When abnormal shear forces act on the knee, a meniscus may be torn.  A surgical consultation may be needed with a severe tear.  Proper balancing of the knee musculature through rehabilitation can both assist in recovery and prevent reoccurrence of this injury.