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A 44-year-old woman who worked as an emergency medical technician (EMT) presented to the ED with ankle pain after she twisted her ankle stepping out of the back of an ambulance.


Her ankle radiographs are shown in Figure 1.


  • Is this a single malleolar fracture, a bimalleolar fracture, or a trimalleolar fracture?
  • In which way did the patient twist her ankle to cause this injury?

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There are many types of fracture classification systems. The simplest schemes describe the injury anatomically. Other classification systems elucidate the mechanism of injury or are based on treatment and prognosis.


Even though the ankle is a relatively simple hinge joint, there are a number of different classification systems for ankle injuries. The most basic classification scheme simply describes the number of fractures about the ankle—either one, two, or three malleoli. (The third malleolus is the posterior margin of the distal tibia.) Although this classification system is straightforward, it oversimplifies ankle injuries and has little relevance to mechanism of injury or treatment. In addition, the term “bimalleolar fracture” is ambiguous because it can be used for fractures of any two of the three malleoli.


By contrast, the Lauge-Hansen classification system includes 13 separate injuries divided into four groups (Table 1). This classification system is based on the mechanical forces responsible for various ankle injuries. Each injury is classified by two terms: the position of the foot at the time of injury (either supinated or pronated), and the direction of the force applied to the ankle (Figure 2).

Table Graphic Jump Location
Table 1 Lauge-Hansen Classification—Based on Mechanism of Injury

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