High Ankle Sprain (Syndesmosis Injury)

A high ankle sprain is an injury to the distal tibiofibular syndesmosis, the ligament complex that binds the distal tibia and fibula together.

It is less common than a lateral ankle sprain but is seen more often in contact and collision sports. Recovery usually takes longer, and a missed or undertreated injury can leave persistent pain, chronic syndesmotic instability and post-traumatic osteoarthritis. Under-recognition is the main clinical hazard.

The syndesmosis has 4 ligaments:

• •Anterior inferior tibiofibular ligament (AITFL): the most commonly injured
• •Posterior inferior tibiofibular ligament (PITFL)
• •Interosseous ligament, continuous with the interosseous membrane
• •Inferior transverse ligament, the deep part of the PITFL

Mortise stability also depends on the deep deltoid ligament medially.

The classic mechanism is external rotation or hyperdorsiflexion of the foot on a relatively fixed leg, common in rugby, football and skiing. The anterior talar dome is wider than the posterior, so in these positions the talus acts as a wedge, forcing the tibia and fibula apart from anterior to posterior.

West Point grading:

• •Grade I: stable, no diastasis on stress
• •Grade II: stable on static imaging but unstable on dynamic or stress assessment
• •Grade III: frank diastasis, unstable, and typically needs surgical stabilisation

Associated injuries to exclude: Maisonneuve fracture, medial or posterior malleolar fracture, deep deltoid rupture and osteochondral lesion of the talus.