The knee joint includes the tibiofemoral, patellofemoral and superior tibiofibular joints. There are two menisci which are semilunar-shaped discs of fibrocartilage between the femoral condyles and tibial plateaus. Their main functions are shock absorption and stability enhancement. There are many ligaments to provide stability and prevent excessive motion. The anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL) are the key ligaments for stabilization of the knee joint.