The posterior cruciate ligament (PCL) is one of the less commonly injured ligaments of the knee. Understanding this injury and developing new treatments for it have lagged behind the other cruciate ligament in the knee, the anterior cruciate ligament (ACL), probably because there are far fewer PCL injuries than ACL injuries.
This guide will help you understand
Where is the PCL, and what does it do?
Ligaments are tough bands of tissue that connect the ends of bones together. The PCL is located near the back of the knee joint. It attaches to the back of the femur (thighbone) and the back of the tibia (shinbone) behind the ACL.
The PCL is the primary stabilizer of the knee and the main controller of how far backward the tibia moves under the femur. This motion is called posterior translation of the tibia. If the tibia moves too far back, the PCL can rupture.
More recent research has shown us that the PCL also prevents medial-lateral (side-to-side) and rotatory movements. This confirms the suspicion that the PCL’s effect on knee joint function is more complex than previously thought.
The PCL is made of two thick bands of tissue bundled together. One part of the ligament tightens when the knee is bent; the other part tightens as the knee straightens. This is why the PCL is sometimes injured along with the ACL when the knee is forced to straighten too far, or hyperextend.
Both bundles of the PCL not only change length with knee flexion and extension, but they also change their orientation (direction of the fibers) from front-to-back and side-to-side. This function allows the ligament to keep the tibia from sliding too far back or slipping from side-to-side.
How do PCL injuries occur?
PCL injuries can occur with low-energy and high-energy injuries. The most common way for the PCL alone to be injured is from a direct blow to the front of the knee while the knee is bent. Since the PCL controls how far backward the tibia moves in relation to the femur, if the tibia moves too far, the PCL can rupture.
Sometimes the PCL is injured during an automobile accident. This can happen if a person slides forward during a sudden stop or impact and the knee hits the dashboard just below the kneecap. In this situation, the tibia is forced backward under the femur, injuring the PCL. The same problem can happen if a person falls on a bent knee. Again, the tibia may be forced backward, stressing and possibly tearing the PCL.
Other parts of the knee may be injured when the knee is violently hyperextended, but other ligaments are usually injured or torn before the PCL. This type of injury can happen when the knee is struck from the front when the foot is planted on the ground.
What does an injured PCL feel like?
The symptoms following a tear of the PCL can vary. The PCL is not actually enclosed inside the knee joint like the ACL. So unlike an ACL tear, which swells the joint with blood, PCL injuries don’t make the knee swell as much. Most patients with a PCL injury sense a feeling of stiffness and some swelling. Some patients may also have a feeling of insecurity and giving way of the knee, especially when trying to change direction on the knee. The knee may feel like it wants to slip.
The pain and moderate swelling from the initial injury will usually be gone after two to four weeks, but the knee may still feel unstable. The symptom of instability and the inability to trust the knee for support are what requires treatment. Also important in the decision about treatment is the growing realization by orthopedic surgeons that long-term instability leads to early arthritis of the knee.
How do doctors identify the problem?
The history and physical examination is probably the most important tool in diagnosing a ruptured or deficient PCL. During the physical examination, special stress tests are performed on the knee. Three of the most commonly used tests are the posterior Lachman test, the posterior sag test, and the posterior drawer test. The posterior drawer test is a very sensitive and specific test for PCL injuries. The doctor will place your knee and leg in various positions and then apply a load or force to the joint. Any excess motion or unexpected movement of the tibia relative to the femur may be a sign of ligament damage and insufficiency.
Tests are also done to see if other knee ligaments or joint cartilage have been injured. Damage to the PCL along with damage to the posterolateral corner (PLC) of the joint cartilage often leads to rotatory instability. This means the tibia slides back on the femur and twists or rotates at the same time. Rotatory instability can affect walking ability. Failure to diagnose a PCL injury can be a major cause of failure of surgery to repair a ruptured anterior cruciate ligament (ACL). The doctor may order X-rays of the knee to rule out a fracture. Ligaments and tendons do not show up on X-rays.
The magnetic resonance imaging (MRI) scan is probably the most accurate test without actually looking into the knee. The MRI machine uses magnetic waves rather than X-rays to show the soft tissues of the body. This machine creates pictures that look like slices of the knee. The pictures show the anatomy, and any injuries, very clearly. This test does not require any needles or special dye and is painless.
In some cases, arthroscopy may be used to make the definitive diagnosis if there is a question about what is causing your knee problem. Arthroscopy is a type of operation where a small fiber-optic TV camera is placed into the knee joint, allowing the surgeon to look at the structures inside the joint directly. The vast majority of PCL tears are diagnosed without resorting to this type of surgery, although arthroscopy is sometimes used to repair a torn PCL.