Definition of Posterior Cruciate Ligament (PCL) Injury
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 commonly diagnosed than injuries to the PCL. Interestingly, it is thought that PCL injuries account for about 20 of knee ligament injuries, however, the PCL is seldom talked about because these injuries are often left undiagnosed.
The PCL is the ligament that prevents the tibia (shin bone) from sliding too far backwards. Along with the ACL which keeps the tibia from sliding too far forward, 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.” This occurs when the knee is bent, and an object forcefully strikes the shin backwards. It is called a ‘dashboard injury’ because this can be seen in car collisions when the shin forcefully strikes the dashboard. The other common mechanism of injury is a sports injury when an athlete falls on the front of their knee. In this injury, the knee is hyperflexed (bent all the way back), with the foot held pointing downwards. These types of injuries 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 knee 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 out. 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.
PCL tears are graded by the severity of injury, grade I through grade III. The grade is determined by the extent of laxity measured during your examination. In general, grading of the injury corresponds to the following:
- Grade I: Partial tears of the PCL.
- Grade II: Isolated, complete tear to the PCL.
- Grade III: Tear of the PCL with other associated ligament injury.
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. Initial treatment of the pain and swelling consists of the use of crutches, ice, and elevation. Once these symptoms have settled, physical therapy is beneficial to improve knee motion and strength. Non-operative treatment is recommended for most grade I and grade II PCL tears.
Surgical reconstruction of the PCL is controversial, and usually only recommended for grade III PCL tears. 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 time 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 usual activities because of persistent knee instability.