"He's not sure how he did this," my colleague said. "He said he accidentally stepped on a toy in the living room, twisted his ankle, and fell to the ground. What would you call this?"
I love emergency orthopedic radiography, and there was more than one answer. I would give three, but one was better than the rest:
- Weber C distal fibular fracture
- Trimalleolar fracture equivalent
- An exorotation fracture, likely supination
The Weber classification describes distal fibular fractures based only on whether the fracture is above, below, or at the syndesmosis. Weber Type A fractures are below the level of the tibial plafond and stable. Type C fractures are above the level of the tibial plafond and unstable. The rule of the ring mandates looking for a second fracture. Type B fractures at the level of the syndesmosis could be stable or unstable.
Bimalleolar and trimalleolar fractures are common terms related to ankle fractures. In this case, the oblique fibular fracture above the syndesmosis and the tertius fracture (posterior malleolus) are clearly seen. One might think that this would be a funky bimalleolar fracture involving the lateral and posterior malleoli, but that would be wrong. The medial aspect of the ankle has an obvious injury. The AP ankle view displays a tilted talus. The mortis view is much more gapped on the tibial side than the fibula side. One must suspect deltoid ligament damage. Because there is no bony injury on the medial side, this is considered a trimalleolar equivalent.
The Lauge-Hansen classification of ankle fractures is more complex. It explains the fracture mechanics to a greater extent, however. There are two movements to consider: supination or pronation and side-to-side or rotary movement of the talus. The combinations yield four potential outcomes. The side-to-side movement of the talus directly knocks the fibula. These fractures tend to be transverse and less likely to involve the posterior malleolus. On the other hand, rotary movement of the talus tends to cause increasing grades of injury, resulting in the tertius fractures at the posterior malleolus.
The four stages of a supination-external rotation injury are:
Stage 1: Anterior tibiofibular ligament rupture
Stage 2: Spiral or oblique fracture of the fibula
Stage 3: Posterior tibiofibular ligament with or without a tertius fracture
Stage 4: Deltoid ligament rupture with or without a medial malleolus fracture
Describing a fracture in an orthopedist's language can create confidence in your knowledge. The best answer would be the last one—an exorotation injury.
Tip to Remember: Rotational injuries of the ankle have oblique rather than transverse fibular fractures, and often involve the posterior malleolus.
"Ankle Fractures-Everything You Want to Know-Dr. Nabil Ebraheim," YouTube. August 26, 2016; https://bit.ly/3bcsVJJ.