How is a PCL injury different from an ACL injury?

What do the ACL and PCL do?

The anterior cruciate ligament (ACL) prevents the shin bone from sliding forwards and controls rotation of the knee. The posterior cruciate ligament (PCL) prevents the shin bone from sliding backwards. Together they cross inside the knee joint and provide stability during movement.

The PCL is thicker and stronger than the ACL, which is one reason why PCL injuries are less common.

How do the injuries happen?

ACL injuries usually occur without contact, during sudden stopping, changing direction or landing from a jump, often with a pop and rapid swelling. They are common in football, basketball, skiing and netball.

PCL injuries often result from a direct blow to the front of the shin with the knee bent, such as hitting the dashboard in a car accident or falling onto a bent knee. Symptoms can be milder, with pain at the back of the knee and less swelling, so they are sometimes missed.

How are they treated?

A clinical practice guideline on knee ligament sprains covers rehabilitation for both ACL and PCL injuries, including range-of-motion exercises, quadriceps strengthening, neuromuscular training and progression to sport-specific activities 1.

For PCL injuries, rehabilitation emphasises quadriceps strength, which helps compensate for the loss of the ligament, and may include a brace that supports the back of the shin in the early weeks. For ACL injuries, the choice between rehabilitation alone and reconstruction depends on activity demands, instability and associated injuries.

What is the long-term outlook after an isolated PCL injury?

In a study of 68 people with acute isolated PCL injuries treated without surgery and followed prospectively, 44 were examined at a mean of 14.3 years after injury 2. Mean quadriceps strength was 97 per cent of the uninjured leg, all had normal knee range of motion, and the prevalence of moderate to severe osteoarthritis was 11 per cent 2.

Results did not differ according to the degree of PCL laxity, and patients reported remaining active with good subjective scores 2.

When does a PCL injury need surgery?

Surgery is more often considered when the PCL injury occurs together with other ligament injuries, such as combined injuries of the posterolateral corner, when the ligament has been pulled off with a piece of bone, or when there is persistent instability despite rehabilitation.

Multi-ligament knee injuries are serious and can involve damage to nerves and blood vessels, so they need urgent specialist assessment.

How long does recovery take?

Isolated PCL injuries treated with rehabilitation often allow return to sport within a few months, depending on severity. After ACL reconstruction, return to pivoting sports usually takes many months.

In both cases, return to sport is based on strength, movement quality, confidence and sport-specific testing rather than time alone.

Why is quadriceps strength so important after a PCL injury?

The quadriceps muscles at the front of the thigh pull the shin bone forwards, which counteracts the backward sagging that occurs when the PCL is injured. Strong quadriceps therefore help stabilise the knee and reduce symptoms during daily activities and sport.

Rehabilitation often avoids heavy hamstring exercises in the early stages, as these pull the shin bone backwards. Programmes progress to squats, leg press, step exercises and sport-specific drills as the knee becomes more stable.

When should a knee injury be seen urgently?

Seek urgent assessment for a knee that is visibly deformed, a cold or pale foot, numbness or weakness in the foot, or severe swelling after a high-energy injury. These features may indicate a knee dislocation with damage to blood vessels or nerves.

Rapid swelling, a pop, inability to bear weight or a knee that gives way should also be assessed promptly.

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