From Jonathan Cluett, M.D.,
Your Guide to Orthopedics.
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About.com Health's Disease and Condition content is reviewed by Kate Grossman, MD

What is the PCL?
The posterior cruciate ligament, or PCL, is one of four ligaments important to the stability of the knee joint. The anterior cruciate ligament, or ACL, sits just in front of the PCL. The ACL is much better known, in part because injuries to the ACL are much more common than injuries to the PCL.

The PCL is the ligament that prevents the tibia (shinbone) from sliding too far backwards. Along with the ACL which keeps the tibia from sliding too far forwards, the PCL helps to maintain the tibia in position below the femur (thigh bone).

How is the PCL injured?
The most common mechanism of injury of the PCL is the so-called "dashboard injury." When the knee is bent, and an object forcefully hits the tibia backwards, this can push the tibia back, and cause a PCL tear. The other mechanism of injury is hyperflexion of the knee, with the foot held pointing downwards. These movements stress the PCL, and if the force is high enough, a PCL tear will result.

What are the symptoms of a PCL injury?
The most common symptoms of a PCL tear are quite similar to the symptoms of an ACL tear. Knee pain, swelling, and decreased motion are common with both injuries. Patients may have a sensation that their knee "popped" or gave out. Problems with instability in the weeks and months following PCL injury are not as common as instability following an ACL tear. When patients have instability after a PCL injury they usually state that they can't "trust" their knee, or that it feels as though the knee may give away. If this complaint of instability is a problem after a PCL injury, it may be an indicator that surgery is recommended.

How is a PCL injury diagnosed?
Part of the diagnosis of a PCL tear is made by knowing how the injury happened. Knowing the story of the injury (for example, the position of the leg and the action taking place) will help in making the diagnosis. Specific maneuvers can test the function of the PCL. The most reliable is the posterior drawer test. With the knee bent, your doctor will push the tibia backwards; this stresses the PCL. If the PCL is deficient or torn, the tibia will slide too far backwards, and indicate an injury to the PCL. X-rays and MRIs are also helpful in clarifying the diagnosis and detecting any other structures of the knee that may be injured. It is common to find other ligament injuries or cartilage damage when a PCL tear is found.

What is the treatment for a PCL tear?
Treatment of PCL tears is controversial, and, unlike treatment of an ACL tear, there is little agreement as how best to proceed. Treatment of the pain and swelling with crutches, ice, and elevation is done early after the injury. Once these symptoms have settled, physical therapy is beneficial to improve overall knee function and to maximize the other stabilizing structures of the knee.

Surgical reconstruction of the PCL is controversial. Because of the technical difficulty of the surgery, some orthopedic surgeons do not see the benefit of PCL reconstruction. Others, however, believe PCL reconstruction can lead to improved knee stability and lower the likelihood of problems down the road.

Surgical PCL reconstruction is difficult in part because of the position of the PCL in the knee. Trying to place a new PCL graft in this position is difficult, and over the years these grafts are notorious for stretching out and becoming less functional. Generally, surgical PCL reconstruction is reserved for patients who have injured several major knee ligaments, or for those who cannot do their activities because of persistent knee instability.