Almost everyone has heard of a famous footballer, soccer player or skier having a knee reconstruction. This almost always refers to an ACL or Anterior Cruciate Ligament Reconstruction. PCL or Posterior Cruciate Ligament injuries are uncommon compared to ACL injuries and require surgery far less often.
The posterior cruciate ligament (PCL) gets its name from where it attaches to the tibia or shin bone (posterior to or behind the ACL – posterior means behind and anterior mean in front). The PCL is larger than the ACL and also acts as a knee stabilizer working in almost the completely opposite way than the ACL does. The function of the PCL is to provide stability during twisting or turning movements of the knee and when walking up slopes. It is a large ligament in a reasonably well protected area of the knee and is therefore no often injured. The PCL is technically found outside the knee (extrasynovial) and can heal to some extent (the ACL which sits in synovial fluid rarely heals).
How is the PCL injured?
The PCL is usually injured by the tibia being forced backwards too far (this is one of the motions the PCL is supposed to stop) such as hitting your knee on the dashboard in a car accident or falling heavily straight onto the knee. It can also be injured if the knee is hyperextended (the tibia moves too far forward and the toes move towards the face in a direction they should not be able to move) which stretches and then tears the ligament.
The knee is usually very sore and swollen after the injury but most people are able to walk sooner than they would for an ACL injury. Many people are not aware of exactly what has been injured as the pain is not always felt at the back of the knee. Many doctors are not used to thinking about PCL injuries so the diagnosis may be missed initially. If the PCL injury is combined with another injury, like a posterolateral corner tear, there may be significant bruising and swelling.
Ongoing symptoms vary widely from nothing to pain to the sensation that the knee might give way or buckle (or just not be trusted). They can be minor and only present playing sport, or major, with severe kneecap pain and giving way of the knee when on uneven ground.
Many people are able to return to high level sport after a PCL injury but do have some problems from time to time.
Classification of PCL Injuries
PCL injuries are graded based on (1) Severity, (2) Time since injury, and (3) Presence of associated injuries.
PCL tears are graded I to III based on the degree of backwards shift of the shin bone (tibial translation) compared with that of the other leg. On average, the front of the shin sits 1 mm in front of the inner thigh bone with the knee bent to 90degrees. Grade I tears have 0 to 5 mm of extra backward movement; but the ‘step-off’ described above is maintained. Grade II tears have 5 to 10 mm of excess translation, which allows the shin to become flush with the thigh bone. Grade III injures have more than 10 mm of extra backward movement.
Grade I and II injuries represent partial tears of the PCL, whereas grade III tears represent complete tears and there are often associated injuries found to the knee.
Classification of acute versus chronic PCL injuries is important when discussing outcomes of treatment. Acute injury is defined as within 3 weeks of injury. Chronic PCL injures can allow stretching of the joint capsule which makes the knee less stable.
Classification into single versus multiple ligament injuries is important for treatment decisions. Isolated injuries to the PCL may have good results without surgery but multi-ligament injured knees tend to have better outcomes with surgery.
Patients with PCL injuries may present with minimal symptoms with a history of a simple fall months ago or may present after a severe motor vehicle accident with acute bleeding in the knee.
MRI scanning is the best test for a recent PCL injury but is less good for chronic PCL tears. Unfortunately the PCL can look normal on MRI as early as 6 months after injury but this does not correlate with an improvement in how the knee functions.
The true natural history of untreated PCL tears remains a controversial topic. The general consensus has been that isolated PCL tears do well without surgery and multiple ligament injured knees involving the PCL should be operated on.
Can PCL tears be treated without surgery?
Patients with a ruptured PCL who are content with activities that require little in the way of side stepping (running in straight lines, cycling and swimming) may opt for conservative treatment.
PCL reconstruction is far more reliable and safe as an operation than it was 10 years ago. It still requires about 6 weeks in a brace, time on crutches and about 12 months of physiotherapy before you can return to sport. For the right patient this can be a very good operation.