A constant radiological sign in Bosworth's fractures: "the Axilla sign".

We describe a rare ankle fracture pattern called "the Bosworth fracture," originally described in 1947. A Bosworth fracture has been defined as a fixed posterior fracture-dislocation of the distal part of the fibula in which the proximal fibular shaft fragment locks behind posterior tibial tubercle. This fracture is frequently irreducible by closed means. Severe early and late morbidity, resulting from failure to identify and promptly treat this fracture pattern, have been reported. We describe a new radiographic sign seen on anterior-posterior mortise radiographic view showing cortical density in the axilla of the medial tibial plafond: "the Axilla sign." This feature was also noted on the radiographs of other case reports with this unique injury. The presence of this sign should alert the treating surgeon to a possible Bosworth fracture.