PCL Avulsion Injuries

The PCL is one of two cruciate ligaments in the knee joint that cross to form an X. It is a vital structure that helps stabilize the knee and control its movement. The PCL is the largest and strongest ligament in the knee. It has two very distinct portions: one that goes from the back of the tibia to the roof of the femoral notch (in the thigh bone) called the anterolateral bundle, and a second smaller portion that goes to the side of the notch called the posteromedial bundle. Both bundles work together to prevent the knee from slipping backward, especially when it is bent.

Recall that the PCL has two bundles: the anterolateral bundle and the posteromedial bundle. The anterolateral bundle prevents excessive front-to-back motion of the tibia while the posteromedial bundle prevents excessive rotation of the tibia.

Two important structures associated with the PCL are the meniscofemoral ligaments. These are small ligaments that can sometimes be found in the knee joint. These structures attach to the lateral meniscus and follow a similar course alongside the PCL in order to attach to the femur. One of meniscofemoral ligaments attaches in the front of the posterior cruciate ligament (Ligament of Humphrey’s) and the other attaches in the back (Ligament of Wrisberg). The anterior one is present in 30% of patients and the posterior one is found in 60% of knees. Both ligaments help the PCL and prevent the knee from slipping backwards.

Given the PCL’s size and strength, it takes a significantly traumatic injury to tear it. Consequently, a PCL tear by itself, called an isolated PCL tear, is not that common. Instead, PCL injuries are usually associated with other ligamentous injuries (MCL, LCL or ACL) or meniscal injuries. Most isolated PCL tears occur as a result of an injury to the front of the knee when it is bent. Falling on a bent knee while playing sports, slipping on ice, or hitting a dashboard during a traffic accident are some common ways that the PCL is injured.

While the majority of PCL injuries are intrasubstance tears, a small subset of injuries involves avulsion fractures off the femoral or tibial attachment of the PCL. PCL avulsion fractures at the femoral attachment are much less common than tibial-sided avulsion fractures.

Patients can present with swelling, discomfort, and pain, typically when the knee is bent. When combined injuries are diagnosed, severe instability can be present. In these cases, arteries or nerves can be compromised, and therefore, it is important to rule these injuries out.