Etiology

The most common cause of ankle fractures is a low-energy fall, and studies suggest that the proportion of fractures resulting from this mechanism can range from 38% to 80%.[4][13] The next most common causes are an inversion injury to the ankle (31.5%), sporting injury (10.2%), fall down stairs (around 8%), fall from a height (4.5%), and motor vehicle accident (4.2%).[4]

Pathophysiology

Malleolar fractures typically result from a rotatory force as opposed to an axial force. Lauge-Hansen described the pathomechanics behind malleolar fractures derived from experiments on cadaveric feet.[3] In general, it was found that when the foot was in a supinated position and a force in adduction was applied, either the lateral ligaments avulse from the fibula or a transverse infrasyndesmotic fracture of the fibula is created. If the force continues, a shearing fracture of the medial malleolus may occur. If the foot is in a supinated position and is externally rotated (it has been argued that a slight valgus force also needs to be applied), then injury occurs in stages: the first is disruption of the anterior tibiofibular ligaments; the second is a transsyndesmotic fracture of the fibula; the third is either disruption of the posterior tibiofibular ligaments or a posterior malleolus fracture; and the fourth is either a deltoid ligament rupture or a medial malleolar fracture.[15]

If the foot is pronated at the time of injury and an abduction force is applied, the first stage of damage is either a deltoid ligament rupture or a transverse fracture of the medial malleolus, the next stage is anterior tibiofibular ligament damage, and the last stage is either a transsyndesmotic or suprasyndesmotic fracture of the fibula, potentially with a degree of comminution. Similar stages are seen if the force is instead in external rotation. The first injury is a deltoid ligament rupture or fracture of the medial malleolus, the second stage is rupture of the anterior tibiofibular ligament, and the third stage is a suprasyndesmotic fracture of the fibula.

It may be the case that a patient's mechanism of injury may not occur exactly in these ways and may in fact be a combination of forces. Results from one study suggest that the above scheme does not necessarily predict the ligament damage associated with ankle fractures.[15]

Classification

Orthopaedic Trauma Association (OTA) comprehensive fracture classification (modified AO-Weber classification)[2]

There are 3 types based on fracture morphology of the lateral malleolus. Subgroups incorporate fractures of the medial malleolus and posterior malleolus:

  • Type A: infrasyndesmotic

  • Type B: transsyndesmotic

  • Type C: suprasyndesmotic.

Lauge-Hansen classification[3]

There are 4 categories of injury based on mechanism:

  • Supination: adduction injuries

  • Supination: external rotation injuries

  • Pronation: abduction injuries

  • Pronation: external rotation injuries.

Displaced versus nondisplaced

Nondisplaced ankle fractures show no displacement in the fractures and a congruent ankle joint (mortise).

Talar shift versus no talar shift

Talar shift implies that the talus is not anatomically placed underneath the tibia. This occurs if either the medial malleolus is fractured or the deltoid ligament is ruptured. Most commonly talar shift refers to lateralization of the talus under the tibia.

Reducible versus nonreducible

A fracture is reducible if it is able to be put back in either an anatomic or near anatomic position. This also applies to the ability to reduce or "put" the talus back in its anatomic position under the tibia.

Open versus closed

An open fracture is one that communicates through the skin, and is synonymous with the term compound.

Bimalleolar, trimalleolar

A bimalleolar fracture is one with any 2 malleoli fractured, usually the lateral and medial. A trimalleolar fracture is one that has all 3 malleoli fractured: the medial, lateral, and posterior malleolus.

Syndesmotic injury

Refers to a disruption of the distal tibia-fibular relationship.

Comminuted versus noncomminuted

A comminuted fracture is a fracture that has more than 2 fracture fragments.

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