Posterior Cruciate Ligament (PCL) Injury

PCL injuries produce less dramatic swelling and instability than ACL tears, so they are often diagnosed late — sometimes years later when the patient presents with kneecap pain or early arthritis in the inner compartment 1.

The mechanism is the clue: a knee that hit a dashboard, a fall onto a bent knee, or a hyperextension injury. Where the mechanism fits, the ligament is tested specifically rather than assumed intact.

The PCL resists the shin sliding backwards. Hamstring contraction pulls it in exactly that direction, so early open-chain hamstring work loads the healing ligament and is avoided 1. Quadriceps work does the opposite and protects it.

This is the reverse of ACL rehabilitation, and applying an ACL protocol to a PCL injury slows recovery. Bracing in extension during early healing is used, and prone positioning avoids the shin sagging under gravity.

Combined injuries — PCL with posterolateral corner, ACL or collateral ligament damage — behave differently and are usually reconstructed. Isolated high-grade laxity with persistent instability after a full rehabilitation programme is the other situation where surgery is discussed.

The posterior cruciate is usually injured by a blow to the front of the bent knee — a dashboard, a fall onto the kneecap — and the initial swelling and pain are often modest compared with an anterior cruciate injury.

People frequently walk away and present months later with vague instability going downstairs. The examination sign is subtle and it is missed unless specifically looked for.

Most athletes with an isolated tear do. In a prospective series of 46 athletes with grade II or III isolated tears who started treatment within four weeks of injury, initial bracing followed by individually progressed rehabilitation returned them to full competition after an average of 16.4 weeks, and 91.3% were playing at the same or a higher level two years later 2. An earlier cohort of 133 active patients showed a wider spread: about half returned to the same sport at the same or higher level, a third at a lower level, and one in six did not return to that sport, whatever the degree of laxity 3. Interval running may begin at around 12 weeks, followed by agility and sport-specific training 1.

It can, and the degree of looseness does not predict who is affected. When 44 patients were re-examined a mean of 14.3 years after an isolated PCL injury treated without surgery, 11% had moderate to severe osteoarthritis and quadriceps strength averaged 97% of the other leg; neither the arthritis grade nor the patients' own knee scores differed with the degree of laxity 4. Reviews of long-term series nonetheless describe a high rate of wear in the inner compartment and behind the kneecap, driven by the altered mechanics of a PCL-deficient knee 1.