A ligament is a tissue anywhere in the body that connects one bone to another. Within the knee, four ligaments stabilize the joint: the Anterior Cruciate Ligament, the Medial and Lateral Collateral Ligaments, and the Posterior Cruciate Ligament, or PCL. This report details what occurs when your PCL tears, either completely or partially. An injury to the PCL or any other ligament is known as a "sprain," or, more commonly, a "tear" when it is most severe, and is the rarest of the four types of major ligament tears within the knee.

The PCL runs from the front of the femur, or thighbone, to the back of the tibia, or shinbone, and prevents the tibia from moving too far backward relative to the femur. The PCL is injured or torn when the tibia is forced backward relative to the femur, stretching or tearing the ligament. The injury can happen in one of three "grades":

• Grade 1, in which the ligament is stretched, but not torn.
  
• Grade 2, where the PCL is partially torn.
  
• Grade 3, in which the PCL is completely torn and instability, or looseness of the joint, occurs.

Depending upon the level of activity of the individual, an orthopedic surgeon may decide to operate or pursue conservative methods to manage the PCL tear. A PCL tear often accompanies dislocation or an ACL tear.