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C sign - talocalcaneal coalition

Last revised by Dr Daniel J Bell on 22 Jun 2021

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 non-osseous coalition.

Radiographic appearance

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.

Differential diagnosis

Considerations include:

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Cases and figures

  • Case 1: annotated image
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  • Case 5
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