Along with the Anterior Cruciate Ligament (ACL), the Posterior Cruciate Ligament (PCL), Medial Collateral Ligament (MCL) and Lateral Collateral Ligament (LCL) make up the four main ligaments in the knee that attach the tibia (shin bone) to the femur (thigh bone).  Each ligament serves a crucial role in stabilizing the knee joint.  Injuries to the PCL, MCL and LCL are less common than ACL injuries.  Many contact sports injuries can result in damage to more than one ligament, and a full physical examination is necessary to determine the complete diagnosis.

The posterior cruciate ligament (PCL) is located inside the knee joint and runs just behind the ACL.  The PCL prevents backward (posterior) translation of the tibia (shin bone) with respect to the femur (thigh bone). PCL injuries are often seen in contact sport athletes and result from direct trauma to the knee and the front of the tibia (shin bone).  PCL tears can also result from forced hyperflexion of the knee.  Damage to the PCL often occurs in multi-ligament knee injuries.  Nonoperative treatment options are often used for PCL injuries, but surgical repair can be considered if instability of the joint is severe.

The medial collateral ligament (MCL) is located on the medial side (inside) of the knee and provides stability to the inner knee.  MCL injuries commonly result from direct trauma to the lateral side (outside) of the knee. MCL injuries can also result from abrupt pivoting and twisting of the knee.  Damage to the MCL can be graded on a I-III scale depending on the severity of the tear in the ligament.  The majority of MCL injuries can be treated nonoperatively, however with severe MCL injuries, especially those associated with other ligament injuries, an MCL repair may be indicated.

The lateral collateral ligament (LCL) is located on the lateral border (outside) of the knee and prevents the knee from bending outward.  LCL injuries commonly result after direct trauma to the medial side (inside) of the knee.  Similar to MCL injuries but in the opposite direction, LCL injuries can also result from abrupt pivoting and twisting of the knee.  MCL and LCL injures are often seen in contact sports (football) and skiing accidents because of direct impact of a planted or fixed leg or with a sudden change in direction, respectively.  Similar to the MCL, damage to the LCL can be graded on a I-III scale depending on the severity of the tear in the ligament.  The LCL is also frequently torn with other structures in the back outside part of the knee.  This injury in known as a posterolateral corner (PLC) injury.  Surgical fixation is highly recommended for PLC injuries, especially in the setting of another ligament injury (ACL or PCL), as non-surgical treatment results in persistent knee instability.

In isolation PCL, MCL, and LCL injuries have several nonoperative treatment options including physical therapy, bracing, activity modification, oral anti-inflammatory medications (NSAIDs), ice and occasionally steroid injections.  Surgical repair is considered on a case by case basis depending on the severity of the injury and extent of the instability.  When multiple ligaments are injured at the same time, it is a sign of a much more severe injury, and the knee joint itself likely shifted partially out of place (subluxated) or completely out of place (dislocated).  In both cases, strict attention must be paid the integrity and condition of the nerves and blood vessels behind the knee, as these can also be injured during a multi-ligamentous knee injury.  In rare cases surgery is required to fix a torn blood vessel.  In most cases where the nerves and blood vessels are uninjured, surgical fixation of the damaged ligaments is highly recommended to stabilize the knee.  The specific type of surgery is dictated by the number and nature of ligaments that are injured.