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).
- 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