Ligaments are tissues made up of fibrous bands of collagen, that join a bone to another bone. Stability and limited excess motion are what ligaments provide joints. The knee contains four main ligaments: the medial collateral (MCL), lateral collateral (LCL), anterior cruciate (ACL) and posterior cruciate (PCL) ligaments. Each of these ligaments performs a specific role in creating stability in the knee. If a ligament is injured, both the function and stability of the knee can be drastically reduced. There are three grades of ligament damage:Grade I is considered a sprain of the ligament. The actual ligament experiences no tear. Individuals with a grade I injury experience minimal symptoms, but may report feeling pain near the ligament and a tenderness to the touch. The knee may feel stiff. Activities that stress the joint may cause some discomfort. Grade II injuries are partial tears of the ligament. Individuals may experience pain, tenderness, swelling and have difficulty flexing or extending the knee. There can be a feeling of the knee “giving out” and instability when performing twisting motions. There may also be some laxity or looseness of the joint when tested. Grade III ligament injuries are full tears. Individuals can experience pain, swelling and loss of range of motion in the knee. There is a prominent feeling of instability and “giving out” of the knee when weight is placed on the joint. The use of a knee brace may be required to help stabilize, rest and heal the ligament and joint. There is significant laxity when the joint is tested. Grade IV is called a “medial column injury” due to the injury affecting more than just the medial collateral ligament (for example: the meniscus or ACL). These injuries can require surgery. Grade IV injuries must be diagnosed by a specialist to identify the severity of the injury.