May 23, 2010

C Sign of Talocalcaneal Coalition

Fig. 1: Lateral radiograph of the right ankle shows a C sign (yellow dotted line) that extends from the talar dome through the coalition component of the posterior talocalcaneal joint to the sustentaculum tali.
Fig. 2: Coronal reformatted CT image confirms the presence of talocalcaneal coalition (arrows) between the talus (T) and calcaneus (C).

Facts: Tarsal Coalition
  • Abnormal bony, cartilaginous or fibrous articulation between two tarsal bones
  • Congenital, caused by lack of bony segmentation
  • Most common between calcaneus-talus and calcaneus-navicular
  • Bilateral in 20% of cases

  • C sign seen on lateral view when middle facet talocalcaneal coalition is present (as in our case)
  • Talar beak is an indirect sign of abnormal talonavicular motion, it is a bony spur from anterior superior aspect of talus
  • CT is an excellent method to identify and characterize tarsal coalition

Chew FS, Bui-Mansfield LT, Kline MJ. Musculoskeletal Imaging, 2003.

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