Lateral radiograph of the foot revealing a classic C sign, which is a C-shaped line formed by the medial outline of the talar dome and the inferior outline of the sustentaculum tali. This is a sign of subtalar coalition. It is a reliable indicator of subtalar coalition on the lateral radiograph and represents the bony bridge between the talar dome and the sustentaculum tali.
Reference
Lateur LM, Van Hoe LR, Van Ghillewe KV, Gryspeerdt SS, Baert AL, Dereymaeker GE: Subtalar coalition: diagnosis with the C sign on lateral radiographs of the ankle. Radiology 1994 Dec;193(3):847-51.
