Avascular necrosis of the talus: a pictorial essay.

The talus is predisposed to avascular necrosis (AVN), or bone death due to ischemia, owing to its unique structure, characteristic extraosseous arterial sources, and variable intraosseous blood supply. Both traumatic and atraumatic causes have been implicated in talar AVN. The risk of posttraumatic AVN can be predicted using the Hawkins classification system. In addition, the "Hawkins sign" can be used as a radiographic marker that excludes the development of AVN. At radiography, talar AVN typically manifests as an increase in talar dome opacity (sclerosis), followed by deformity and, in severe cases, articular collapse and bone fragmentation. At any stage of this sequence, the radiographic findings can vary depending on differences in the vascular status of the talus and the degree of bone repair. Magnetic resonance imaging is the most sensitive technique for detecting talar AVN and can be used when AVN is strongly suspected clinically despite normal radiographic findings. Computed tomography (CT) also demonstrates typical patterns and can be used to confirm radiographic findings. Coronal CT is required for viewing the articular surface of the talar dome to rule out subtle depression, collapse, and fragmentation. Nevertheless, radiography remains the mainstay of the diagnosis and temporal observation of talar AVN.