Posterior Cruciate Ligament (PCL) Injury
The Posterior Cruciate Ligament (PCL) is located within the knee and is responsible for resisting excessive posterior rotational instability of the tibia (shin bone) in relation to the femur (thigh bone). The PCL is larger and stronger than the ACL and requires a more unlikely position in order for it to become compromised, making PCL injuries less common than ACL injuries. Injury is usually caused by anterior trauma to the knee where the knee is forced into sudden hyperflexion (bending beyond normal limits).
Damage to the PCL is usually accompanied by damage to surrounding structures and as such may present with sudden pain but only a small amount of swelling (due to joint capsule rupture) followed by discolouration of the back of the calf a few days following the incident.