C sign (talocalcaneal coalition)
The C sign is an important radiological sign which may be seen on a lateral radiograph of ankle in those with a tarsal coalition (talocalcaneal coalition).
A continuous C-shaped arc is seen on a lateral ankle radiograph which is formed by the medial outline of the talar dome and posteroinferior aspect of the sustentaculum tali.
Possible differential considerations include:
- subtalar syndesmosis or synchondrosis: CT is helpful in differentiating
- positional artefact
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