Posterior Cruciate Ligament (PCL) Injury
Posterior Cruciate Ligament (PCL) Injury
What is the Posterior Cruciate Ligament (PCL)?
  • The Posterior Cruciate Ligament (PCL) is the strongest ligament in the knee
  • The PCL extends from the posterior (backend) part of the central upper tibia to the medial (inner) femoral condyle

What is the function of the PCL?
  • The main function of the PCL is to prevent the tibia moving backwards (posterior) in relation to the femur
  • The PCL is a secondary stabiliser to internal and external rotation of the tibia in relation to the femur

How common is a PCL injury?
  • The PCL is not commonly injured
  • PCL injuries make up less than 20% of all knee injuries
  • PCL injury is thought to affect 2 per 100,000 people every year
  • In comparison an ACL injury affects 1 in 3,500 people every year

What is the size of the PCL?
  • The PCL is 11-13 mm in diameter
  • The PCL is 35-38 mm in length

Why is the PCL injured far less commonly than the ACL?
  • The PCL is much stronger than the ACL 
  • The reason for this is due to:
    • The diameter of the PCL is 1.5 times bigger than the ACL meaning that the ligament itself is much harder to break
    • The area of bone that the PCL attaches is three times larger than that of the ACL:
      • This means that the PCL attaches much stronger to the tibia and femur than the ACL so it is harder to tear off from these points of attachment 

How is the PCL commonly injured?
  • PCL injury is most commonly caused by a direct blow on the tibia pushing it in a backwards direction in relation to the femur whilst the knee is flexed (bent): 
    • Dashboard injury: 
      • This occurs when the tibia hits the dashboard during a road traffic collision
    • Fall: 
      • Landing hard directly onto the tibia with the knee bent
    • These mechanisms of injury essentially overstretch and break the PCL by driving the tibia excessively posterior (backward) in relation to the femur
  • PCL injuries can also happen with hyperextension or hyperflexion injury but these are less common
  • Therefore unlike the ACL where the principle mechanism of injury is non-contact, the PCL is more commonly injured by a large direct blow to the knee (that pushes the tibia backwards)

Are PCL injuries associated with other injuries?
  • Isolated PCL injuries are rare
  • >90% of all PCL injuries are associated with other ligament injuries in the knee:
    • Posterolateral corner injury
    • Multiligament injury
    • Knee dislocation
Classification of PCL injury
  • This is based on the amount of posterior translation of the tibia relative to the femoral condyles with the knee bent at 90 degrees:
    • Grade I: 1-5mm (mild sprain)
    • Grade II: 6-10mm (moderate sprain; usually more than 50% torn):
    • Grade III: >10mm (complete tear and highest risk of other ligamentous injury)
Symptoms of acute PCL injury
  • The symptoms are less marked than with an ACL injury
  • This means that patients often present many months later
  • Pain and tenderness often quite vague and deep within the knee, but sometimes felt towards the back
  • Pain is less marked than an ACL and patient can often walk off the field of play unlike ACL injuries when normally they require assistance
  • Tearing can be felt but there is no pop like an ACL tear
  • Swelling: 
    • Knee swelling following a PCL rear is much less than an ACL tear
  • Stiffness
  • Symptoms will depend on severity of PCL injury:
    • Grade I: 
      • knee will feel stable
      • Some pain and discomfort towards the back of the knee
    • Grade II: 
      • PCL will be loose but not commonly associated with instability
      • If knee does feel unstable often associated with another ligament injury
    • Grade III: 
      • Commonly associated with other ligament injuries such as lateral collateral ligament (LCL) and posterolateral corner (PLC)
      • Knee feels unstable
      • Difficulty going downstairs and downhills

Why do PCL injuries tend to present late (i.e a long time after the initial injury)?
  • PCL injuries often present late because: 
    • They are overall not as symptomatic as other ligamentous injuries 
    • They cause less acute pain, less knee swelling and less rotational instability than an ACL tear
  • As a result of PCL injuries being less symptomatic in the acute phase they tend to be found coincidentally when the patient presents with symptoms consequent to a chronic PCL tears 

What are the consequences of chronic PCL injuries?
  • The consequences of chronic PCL injuries are:
    • Increased back and forth sliding of the tibia in relation to the femur
    • Increased risk of medial (inner) meniscal tears
    • Increased risk of arthritis in the medial (inner) part of the knee:
      • At 5 years following a PCL tear 80% of patients will have medial knee arthritis 
    • Increased risk of arthritis behind the patella (kneecap):
      • At 5 years following a PCL tear 50% of patients will have arthritis behind their patella

How do chronic PCL injuries present?
  • Chronic PCL injuries present with:
    • Pain at the medial (inner) part of their knee due to medial meniscal tear and medial arthritis
    • Pain at the front of the knee due to arthritis behind the patella 
    • Pain going down stairs and down slopes due to arthritis behind the patella 
    • Pain and instability on turning, twisting and pivoting
    • Pain and instability with decelerating movements
How is a PCL injury diagnosed? 
  • PCL injury is suggestive from the history of the injury and the examination findings
  • X-rays: 
    • Required to exclude fractures
    • Stress radiographs are very helpful:
      • These are X-rays taken with pressure on the tibia to push it backward which can then be detected on X-rays and therefore demonstrate the clinical insufficiency of the PCL to prevent this movement
  • MRI scan: 
    • Helps to diagnose PCL injury
    • Helps exclude other knee pathology which most often exist such as other ligament, meniscal and cartilage injuries
What is the treatment of a PCL Injury?
  • Most isolated Grade I PCL sprains do well with appropriate conservative management:
    • Special knee brace must be applied promptly that helps bring the tibia forwards to the neutral position in relation to the femur
    • This helps position the tibia in the optimal position for the PCL to heal
    • Without the brace the tibia sits too far backwards and the knee will remain slack and unstable
    • Extensive physiotherapy rehabilitation focusing mainly on quadriceps strength
  • Most Grade III (complete) tears require prompt PCL reconstruction
  • There is increasing evidence that Grade II PCL injuries especially those that have symptomatic instability should be surgically treated in order to avoid early knee degeneration 
  • Bracing of knees with chronic PCL injuries will not aid or improve PCL healing but can provide symptomatic relief
  • The presence of other ligament injuries in addition to the PCL tear then surgery tends to be the recommended option
  • If at the time of PCL reconstruction other ligament injuries are not addressed then there is high risk of failure
What is the prognosis following a PCL tear?
  • Most people do well following a PCL injury if managed correctly
  • Chronic PCL deficient knee poses increased risk for:
    • 75% chance of developing cartilage degeneration within 5 years to medial femoral condyle
    • 50% chance of developing cartilage degeneration within 5 years to patella

How does a PCL tear differ to an ACL tear?
  • The PCL is injured typically when there is a strong impact on the tibia pushing it backwards such as falling directly onto the knee or hitting the tibia on the dashboard whereas the ACL is torn by a non-contact twisting knee injury
  • PCL tears are most commonly partial tears whereas ACL tears tend to be complete tears
  • When the PCL is injured the pain and swelling is not as severe as when the ACL is injured 
  • That is why many PCL injuries present late once secondary damage have occurred and become symptomatic such as meniscal and cartilage degenerative changes
  • On the other hand since ACL tears tend to be complete and present straight away with instability patients seek early medical consultation
  • The PCL is much thicker and therefore much stronger than the ACL  requiring a lot more force to injure it
  • A far greater proportion of PCL injuries can be managed non-surgically in a suitable knee brace and intensive physiotherapy whereas most ACL tears will need reconstruction
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