Supination trauma occurs when the foot is twisted on the outside of the ankle.
The three outer ligaments of the ankle joint are located here (anterior talofibular ligament, posterior talofibular ligament, and calcaneofibular ligament). Supination trauma can result in overstretching, tearing or bony avulsion of these ligaments.
The anterior ligament (anterior talofibular ligament) is most commonly affected; this ligament is injured in almost all supination traumas. The middle ligament (calcaneofibular ligament) is still involved in two thirds of all cases, although injuries to the posterior ligament (posterior talofibular ligament) occur only very rarely.