The Posterior Cruciate Ligament

In the last decade, orthopaedic surgeons have done much research to find out about anterior cruciate ligament (ACL) injuries of the knee so they can treat the problems better. Much less research has been done on the posterior cruciate ligament (PCL) because it is injured far less often than the ACL. In fact, orthopaedic knowledge and research of the PCL lags behind that of the ACL by about 10 years.

Your thigh bone (femur) and lower leg bones (tibia and fibula) meet in the knee joint and are held together by tissue called ligaments. In the middle of the knee are two ligaments called the anterior (front) cruciate ligament and the posterior (back) cruciate ligament. The ACL prevents the femur from moving too far backward over the tibia. The PCL prevents the femur from moving too far forward over the tibia. The PCL is the knee’s basic stabilizer and is almost twice as strong as the ACL. It provides a central axis about which the knee rotates.

Posterior cruciate ligament injuries comprise between 3% and 20% of all knee ligament injuries. However, the true incidence of PCL injuries remains unknown. The most common cause of PCL injuries is athletic, motor vehicle, or industrial accidents. Most athletic PCL injuries occur during a fall on the flexed (bent) knee with the foot plantar flexed (the toes pointing down with the top of the foot in line with the front of the leg). The shin (tibia) strikes the ground first and is pushed backward (Fig. 2). In motor vehicle accidents, the dashboard can drive the shin backward on the flexed knee. Hyperflexion (bending too far) of the knee without a direct blow to the tibia can also cause an isolated PCL injury, which means no other ligaments are damaged. The PCL can be injured by other ways, but these injuries usually involve more ligaments, such as the ACL, medial and lateral collateral ligaments (located on either side of the knee), and the posterolateral corner (back outer side) of the knee.

Examination
The doctor examines your injured knee to find out if only the PCL is injured or if other ligaments are torn too. The type of injury dictates the type of treatment you need. Your doctor will move your knee in different directions to see how lax, or loose, it is.

The doctor can also do tests, such as magnetic resonance imaging (MRI), to help see what tissues are damaged in the knee, especially if you have injured more than one ligament and have much soft tissue damage.

Treatment
The treatment options are somewhat controversial among orthopaedists, but following are some general guidelines. If you have an acute (recent) PCL tear that does not cause much laxity, you will probably be treated with physical therapy that stresses aggressive rehabilitation of the quadriceps muscles, which are in the front of the thigh. Strong quadriceps muscles can take the place of the PCL to a certain extent, helping to prevent the femur from moving too far forward over the tibia.

If you have an acute PCL tear that causes significant laxity or if you have injured more than one ligament, you may need surgery to repair or reconstruct your PCL.
Repairing a ligament means the torn fibers are reattached to each other (Fig. 3). The rich blood supply in the tissues around the ligament helps the PCL heal well if it is repaired soon after the injury.

If not enough fibers remain to repair the PCL or if the surgeon sees that the tissue has degenerated beyond repair, the PCL can be reconstructed. Reconstructing a ligament means the ligament is replaced with tissue from another part of your body or from a donor. Part of your patellar tendon (tissue that connects muscle to the patella) or hamstrings (muscles in the back of the thigh) can be used in the reconstruction. Or, donor tissue may be used instead.

Sometimes, a portion of bone is pulled off with the torn ligament. If the fragment is large enough, the bone is usually reattached. If the fragment is too small, it is discarded and the PCL is repaired or reconstructed.

All long-term PCL injuries are initially treated with an aggressive quadriceps rehabilitation program. Your doctor may consider reconstructing the PCL if the aggressive rehabilitation program fails, if there is significant laxity in your knee, or if degenerative changes in the knee joint can be seen on x-rays. Having an operation to treat a long-term PCL injury does not make your knee normal, but it may decrease your laxity somewhat.

Overall, the state of the art in treatment of PCL injuries is evolving, and the specific treatment varies from person to person. Proper diagnosis, aggressive rehabilitation, and knowledge of the operative and nonoperative options are the keys to appropriate treatment of PCL injuries at this time.

Timothy R. Stapleton, M.D.
Evans, Georgia