The stress begins at the anterior syndesmotic ligament and results in a ligamentous rupture or in an avulsion fracture of the anterior syndesmotic ligament's fibular or tibial insertion (Lauge-Hansen, SE stage I). Further stress due to continued external rotation of the talus leads to the fibular fracture (Lauge-Hansen, SE stage II).
Often, a third fragment represents the detachment of the tip of the main proximal fibular fragment. This third fragment usually bears some intact portion of the anterior syndesmotic ligament. It may become entrapped between the main proximal fibular fragment and the lateral malleolar fragment, impeding reduction. The interosseous ligament is not ruptured.
These are classified as AO/OTA 44B1.3 fractures, and are truly multifragmentary.
The most common injury pattern occurs with axial loading of a maximally supinated (adducted) foot. Subtalar inversion results in external rotation of the talus in the mortise. This causes an oblique fracture of the fibula, starting at the level of the ankle joint and extending proximally from anterior to posterior. This may be a non-displaced crack fracture, if the deforming force ceases at this point. Progressive talar rotation causes posterior displacement of the lateral malleolus, opening the oblique fibular fracture. These fractures correspond to the supination-eversion fractures, stages I-II, in the Lauge-Hansen classification.
Complete radiological evaluation (AP, lateral and AP with internal rotation) is crucial for correct classification and decision making.