C sign - talocalcaneal coalition
The C sign is an important radiological sign which may be seen on a lateral radiograph of the ankle in those with the talocalcaneal subtype of tarsal coalition. It can be seen in both osseous and nonosseous coalition.
A continuous C-shaped arc on a lateral ankle radiograph is formed by the medial outline of the talar dome and posteroinferior aspect of the sustentaculum tali due to their bridging.
- subtalar syndesmosis or synchondrosis: CT is helpful in differentiating
- positional artifact