Can an untreated posterolateral corner injury make ACL surgery fail?

Why the graft is put at risk

The ACL controls forward movement and rotation of the shin, while the posterolateral corner controls outward opening and outward rotation. When the corner is deficient, every step and pivot loads the new ACL graft with forces it was not designed to resist alone. Over months the graft can stretch, and the knee becomes unstable again, sometimes without a new injury.

The same applies to PCL reconstruction, where an untreated corner injury is closely linked to persistent laxity.

Other risks of leaving it untreated

• A wobbling, bow-legged gait on walking, sometimes with the knee snapping back into hyperextension
• Instability on stairs, slopes and uneven ground
• Extra load on the inner compartment of the knee, which may speed up cartilage wear and arthritis
• Pain at the back and outer side of the knee with activity

Signs this may apply to you

If your knee still feels unstable after an ACL reconstruction, especially when standing straight, walking or turning outward, or if your original injury was high-energy, it is worth having the outer side assessed. Not every failed ACL is due to the posterolateral corner; tunnel position, graft healing, alignment and new injuries are other common reasons.

How it is managed

Assessment includes examination for rotation and outer-side opening, stress X-rays, standing alignment X-rays and MRI or CT to look at previous tunnels. Revision surgery then addresses every contributing factor, which may mean reconstructing the posterolateral corner at the same time as a revision ACL, and sometimes correcting alignment first. At Aman Hospital in Doha, Dr. Gelber offers second opinions for patients whose knee remains unstable after previous surgery.