A PCL injury refers to damage to the posterior cruciate ligament. The PCL is one of two important ligaments inside the knee. The other is the anterior cruciate ligament (ACL). These two main ligaments criss-cross each other between the femur (thigh bone) and the tibia (shin bone). Together, they hold the joint stable during motion.
The PLC stands for posterolateral corner. It designates a group of ligaments and muscles along the back and outside edge of the knee joint. These include the lateral head of the gastrocnemius (calf) muscle, the popliteus (muscle), and three specific ligaments.
Damage to this corner of the joint is rare but can occur with traumatic injury from a sports-related accident, car accident, or fall. An isolated injury to the PLC can occur. But usually it's linked with trauma to some other part of the knee (including a PCL injury).
In some cases, the PLC injury was present along with the PCL injury. But symptoms of the PCL injury were most predominant. It wasn't until much later that the presence of a PLC injury became obvious. It can take quite a bit of examination and testing to sort out the specifics of such an injury.
And often, it's not until the surgeon performs an arthroscopic exam (or even the surgical procedure itself) before the PLC injury is noticed.