The cruciate ligaments are two ligaments that cross inside the knee joint. ("Cruciate" means cross). By connecting the thighbone (femur) with the shinbone (tibia), they help stabilize the knee. The ACL is in front. It protects the tibia from going too far forward in relation to the femur. The PCL crosses behind the ACL. It's made up of two bands that work together to stabilize the knee when the lower leg is moving backward or rotating outward.
You hear more about the ACL because ACL injuries are more common. They also tend to result in more pain and symptoms than PCL injuries. However, recent studies suggest that PCL injuries may be more common than previously thought, accounting for roughly 20 percent of all knee injuries. Researchers have recently turned more of their attention to PCL injuries, to develop more effective treatments.