The PCL is the other very important ligament that exists inside the knee joint. Like the ACL, it occurs in the part of the knee known as the intercondylar notch. It serves to guide and maintain the tibia (leg bone) in the correct relationship to the femur (thigh bone) – preventing a backward movement of the tibia on the femur as opposed to the ACL’s prevention of forward movement. The PCL sustains injury from forced and excessive hyperextension or hyperflexion of the knee, which can occur from a hard fall on the flexed knee, or an external twist of the leg when the knee is struck from the outside as in contact sports. It can also occur from a backward force exerted on the upper tibia as occurs when the upper tibia hits the dashboard in an auto accident. PCL injuries are not common – there is one for every 10 ACL injuries. And because many of these injuries are not terribly symptomatic, as with ACL injuries, they are not often brought to urgent medical attention. Most PCL injuries can be treated with a short period of immobilization (for comfort) followed by a modified rehabilitation program, which is similar to the rehabilitation of the graft leg following ACL surgery. Most patients with an isolated PCL injury can return to their previous sports within three to six weeks.

Fortunately, symptomatic posterior PCL instability is rare, because the PCL can heal on its own. For this reason, surgery is rarely needed and done only on highly unstable knees, or those with severe combined instabilities. Over time, X-ray changes indicating the presence of arthritis may occur – though few PCL deficient patients will actually become symptomatic.