The posterior cruciate ligament is located in the back of the knee. It is one of several ligaments that connect the femur (thighbone) to the tibia (shinbone). The posterior cruciate ligament keeps the tibia from moving backwards too far. An injury to the posterior cruciate ligament requires a powerful force.
https://orthoinfo.aaos.org/en/diseases–conditions/posterior-cruciate-ligament-injuries/