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Posterior Cruciate Ligament (PCL) Injury

The PCL is one of the two major ligaments crossing (hence the term cruciate) in the center of the knee. It connects on the thigh bone (femur) at the front of the knee and attaches to the lower leg bone (tibia) at the back of the knee. The “posterior” in PCL refers to it’s insertion on the back of the tibia. Although it appears as a single large ligament, on close inspection, there are normally 2 described bundles that the ligament is comprised of.

These 2 bundles seem to have differing points of maximum tension during knee range of motion. This has implications on the technique of reconstructing the PCL. There are also 2 smaller ligaments associated with the PCL known as the meniscofemoral ligaments because they attach between the thigh bone (femur) where the PCL does and the menisci (shock absorbing tough cartilage located within the knee joint). These somewhat variable structures provide significant additional strength to the function of the PCL.

The PCL is an extremely strong ligament and is in fact 1.5 times the size of the more commonly discussed ACL. The main role of the PCL is to keep the ends of the 2 bones of the knee (tibia and femur) centered on each other during normal knee activities. Specifically, the PCL resists backwards motion of the lower leg. Unlike the ACL, which is mainly functional during certain high risk athletic activities, the PCL is important and is functioning almost all the time even during simple walking.

It extends from the top-rear surface of the tibia (bone between the knee and ankle) to the bottom-front surface of the femur (bone that extends from the pelvis to the knee).
The ligament prevents the knee joint from posterior instability. That means it prevents the tibia from moving too much and going behind the femur.

The PCL is usually injured by overextending the knee (hyperextension). This can happen if you land awkwardly after jumping. The PCL can also become injured from a direct blow to the flexed knee, such as smashing your knee in a car accident (called "dashboard knee") or falling hard on a bent knee.

Most PCL injuries occur with other ligament injuries and severe knee trauma.

Symptoms of Posterior Cruciate Ligament Injuries

Unlike those with ACL injuries, patients who have PCL injuries do not usually experience much knee pain or swelling. They usually report vague symptoms such as unsteadiness or insecurity of the knee. Patients who have longstanding PCL injuries that have never been diagnosed may report pain around the kneecap.

There are a number of physical tests that can be used to detect a PCL injury. One of the most widely recognised is the posterior drawer test. The test is done with the patient lying on their back, the knee bent to a right-angle, and the foot flat on the table. In this position, the Tibial Plateau should lie 1 cm in front of the Femoral Condyles. The degree of PCL injury is determined by the extent that the tibia can be pushed backwards by the examiner X-rays are useful to rule out avulsion fractures (where the PCL has been pulled away from one of its bony attachments). An MRI Scan is useful in confirming the diagnosis. However, when the injury is longstanding, an MRI may show an apparently normal PCL even though laxity may be present.

In most cases of a complete PCL injury surgical treatment is performed. Most commonly this requires removal of the torn ligament and a new ligament to be reconstructed in the old ligament’s place. The new ligament graft can be from many sources, however most commonly it is an allograft (tissue graft from a cadaveric donor). Which specific allograft tissue is up to the discretion of the operating surgeon and may be taken from one of various tendons of the ankle or from the quadriceps tendon at the knee. Then the injured PCL is removed with the help of the arthroscope (small camera) using a few very small incisions. Any other associated cartilage and meniscus injury can be treated at the same time. Then a tunnel is created in the end of the thigh bone (femur) where the PCL attaches. The bone where the PCL attaches to the back of the lower leg (tibia) is also prepared to receive the graft. The new PCL graft is then connected the bone at each end with one of various fixation devices (screws or staples) and therefore recreates the PCL. Because much of the surgery for a PCL reconstruction is performed in the back of the knee, there is a greater risk of a nerve or blood vessel injury than in most knee surgeries. It is important that an athlete is checked both during and after surgery that damage to one of these important structures did not occur.

There are some hotly debated controversies in PCL reconstruction. These involve whether a single large graft or a double-bundle graft with 2 smaller limbs should be used. There is some evidence the double-bundle graft may be mechanically stronger. However, there has been no clinical evidence that patients do better with one versus the other.

Another, controversy involves how the graft is attached to the back of the tibia. One technique involves performing the surgery almost entirely through the small incisions with the help of the arthroscope. The other technique (tibial inlay) involves making a larger incision at the back of the knee and directly attaching the new PCL graft at that point. There is some evidence that performing the surgery in this manner is more mechanically advantageous to the graft. The graft might not be stretched as much and may have a lower rate of failing. The ideal technique of PCL reconstruction may vary somewhat on a case by case basis and therefore would normally be discussed with the treating sports medicine surgeon.

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