Posterior cruciate ligament tears occur when the knee is forcefully twisted or stressed often during impact. The posterior cruciate ligament prevents posterior translation of the tibia on the femur and external rotation. This means it prevents the lower leg moving backwards relative to the upper thigh. When torn sometimes a pop is heard and there is significant swelling. PCL injuries can most often be maged conservatively however sometimes require require surgical intevention and repair particularly in the sporting population where rotatory stability is important.