Posterior cruciate ligament injury

The posterior cruciate ligament (PCL) runs inside the knee joint, linking the femur and tibia to keep them stable during movement. It starts at the lateral edge of the medial femoral condyle and the roof of the intercondyle notch, then angles backward and outward to attach to the back of the tibia just below its joint surface. Its job is to prevent the tibia from shifting backward behind the femur—the primary function of the PCL is resisting posterior tibial displacement. PCL injuries are rarer than other knee ligament problems, but they happen from direct hits to a bent knee—like smashing it into a dashboard during a car crash or landing hard on it—as well as from sudden hyperflexion, hyperextension, or the so-called dashboard mechanism.

Because of its tricky location and the technical difficulty of operating, surgical repair for the PCL is a debated option. Doctors and physiotherapists often use the posterior drawer test to check for injury. Another method is the posterior sag test, where no active force is applied: the patient lies on their back with someone holding their leg so the hip and knee are both bent to 90 degrees. The key measure here is the step-off—the shortest gap from the femur to an imaginary line that runs tangent to the tibial surface from the tibial tuberosity upward. Normally, this step-off is about 1 cm, but in a PCL injury it shrinks (Grade I), disappears (Grade II), or even reverses (Grade III). Anyone suspected of a PCL injury should also be checked for other knee damage that often occurs alongside it, such as cartilage or meniscus tears, bone bruises, ACL tears, fractures, posterolateral injuries, and collateral ligament issues.

The PCL is a single structure but is described as having two sections—anterolateral and posteromedial—based on where they attach and how they work. As the knee moves, the PCL rotates: the anterolateral part tightens during knee flexion but loosens in extension, while the posteromedial bundle tightens in extension and loosens in flexion. The ligament’s laxity in these sections makes it vulnerable to injury during hyperflexion, hyperextension, and dashboard injuries. Ligaments are viscoelastic, meaning they can handle more stress only if the load builds slowly.