How does one tear the posterior cruciate ligament (PCL)?

PCL tears occur much less frequently than those of the ACL. In general, the disability of a PCL tear is less than with an ACL tear.

Situations in which the PCL can tear include -

• excessive hyperflexion (forced bending), eg falling onto the shin with a bent knee and foot pointed
• dashboard injury in a car - where the knee is bent to a right angle and a sudden force drives the tibia backwards

Both cruciates are necessary for full stability of the knee. Take a look at this illustration. Just look at the brown bone bits and the mauve cruciates in the middle of the illustration. You can see how the ACL and the PCL cross over one another.

If the tibia is pulled forwards the ACL takes the strain.

If the tibia is pulled backwards the PCL takes the strain.