Posterior Cruciate Ligament
The Posterior Cruciate Ligament (PLC) originates from the posterior part of the lateral surface of the medial femoral condyle in the intercondylar notch. The PCL has an average length of 38mm and an average width of 13mm. It is narrowest in its mid portion and fans out to a greater extent superiorly and inferiorly. The fibres are attached to the tibial insertion which occurs in a depression posterior to the intra-articular upper surface of the tibia. This is therefore outside the knee joint per se. The attachment extends for up to 1cm distally onto the adjoining posterior surface of the tibia. Immediately proximal to the tibial attachment the PCL has slips that blend with the posterior horn of the lateral meniscus. These slips variably pass anterior to the PCL (ligament of Humphrey) and/or posterior to the PCL (ligament of Riesburg).
The normal PCL has a uniformly low signal intensity on MRI studies with a hockey stick shape (MRI image of PCL). Tears of the ligament appear as bright signal intensity within the ligament substance or with discontinuity of the fibres.
The PCL is considered to be the primary stabiliser of the knee because it is located close to the central axis rotation of the joint is almost twice as strong as the ACL. The PCL has been shown to provide approximately 95% of the total restraint to posterior translation of the tibia on the femur. The PCL is maximally taught at full flexion and also becomes tighter with internal rotation. Two inseparable components of the PCL have been identified. The anterior fibres form the bulk of the ligament and are believed to be taut in flexion and lax in extension. The opposite applies to the thinner posterior portion which is taut in extension and lax in flexion. The PCL appears to function in concert with the LCL and popliteus tendons to stabilise the knee
Injuries to the PCL are less common than the ACL and usually result from hyperextension or anterior blows to the flexed knee. Rarely do these injuries result in symptomatic instability but they may be associated with chronic pain. Significant degenerative changes that involve the medial compartment in 90% of cases have been associated with chronic PCL injuries.