The posterior cruciate ligament (PCL) courses from the posterior intercondylar area of the tibia to the medial condyle of the femur. It gives dynamic stability to the knee by preventing posterior displacement of the tibia on the femur. The PCL is an extrasynovial structure composed of a large anterolateral portion and a small posteromedial portion.
The PCL resists 85-100% of posteriorly directed forces at 30º and 90º of knee flexion. The 2 bands of the PCL, the anterolateral band and the posteromedial band, have different tension patterns. The anterolateral band is under great tension during knee flexion, whereas the posteromedial band is under more tension during knee extension.
Related Medscape Reference topics:
Posterior Cruciate Ligament Injury [Sports Medicine]
Related Medscape resource:
Resource Center Joint Disorders
Posterior cruciate ligament (PCL) injuries are usually the result of a direct blow to the anterior part of the tibia, with a hyperextension moment at the knee. Biomechanical studies have shown an increase in PCL force with knee flexion and the application of internal tibial torque, while other studies have shown that PCL-deficient knees have greater external tibial rotation. Several mechanisms have been implicated in PCL injury, including the following  :
Posterior translation of the proximal tibia
Dashboard injuries in motor vehicle accidents (the most common mechanisms)
Falling on a flexed knee (the most common injury in sports, particularly in wrestling and football)
Forced hyperflexion of the knee joint
A posterior force applied against a hyperextended knee with the foot fixed
Forced hyperextension of the knee
There is a variable incidence of posterior cruciate ligament (PCL) injuries in the US population. In a retrospective study by Schulz and colleagues, 33% of the injuries were sports related.  As many as 20% of all knee ligament injuries consisted of PCL trauma.
International data about posterior cruciate ligament (PCL) injuries are limited. In Germany, approximately 8-10% of all severe ligament injuries involve the PCL, which means that annually, 4000-5000 members of the German population suffer a PCL rupture.
Chronic posterior cruciate ligament (PCL) deficiency can cause or predispose individuals to these pathologies: (1) medial compartment osteoarthritis of the knee, (2) increased risk for meniscal injury, and (3) patellofemoral osteoarthritis. 
In Schulz's study, the mean age at which posterior cruciate ligament (PCL) injury occurred was 27.5 years ± 9.9 years. 
What would you like to print?