If there is a simple, oblique fibular fracture at the level of the syndesmotic ligaments, associated with a posterior malleolar fracture, and the injury on the medial side is a rupture of the deltoid ligament, this is classified as an AO/OTA 44B3.1 fracture.
The fracture of the posterior tibia may be a small cortical avulsion. Much more common is a larger compression fracture, the fragment bearing a variable area of the posterior articular surface.
The anterior syndesmotic ligament is ruptured, or it may be avulsed, either at its fibular (Le Fort / Wagstaff), or tibial (Tillaux-Chaput) insertion).
The most common injury pattern occurs with axial loading of a supinated foot as described for 44B1 and 44B2 fractures. Progressive talar external rotation results in further opening of the fibular fracture, with posterior displacement of the lateral malleolus. Finally the talus exits the ankle mortise posteriorly and disrupts the medial collateral structures. In some cases, as the talus dislocates posteriorly out of the mortise, it fractures the posterior tibial rim (Volkmann's fracture).
Complete radiological evaluation (AP, lateral and AP with internal rotation) is crucial for correct classification and decision making.