If the lateral malleolus is intact, and the lateral injury involves a rupture of the lateral collateral ligaments (the calcaneo-fibular ligament and the anterior and posterior talo-fibular ligaments), with a medial malleolar fracture (oblique or vertical), this is classified as an AO/OTA 44A2.1 fracture.
Infrasyndesmotic fractures (AO/OTA Type 44A) occur with the foot supinated and an adduction force applied to the talus, causing the lateral structures to fail in tension. If the talus continues to tilt, it causes a shearing compression fracture of the medial malleolus. These are classified as AO/OTA 44A2 fractures, and correspond to the supination-adduction fractures stage II in the Lauge-Hansen classification.
Complete radiological evaluation (AP, lateral and AP with internal rotation) is crucial for correct classification and decision making.