Lateral radiograph of the ankle shows the continuous C sign | Figure 1

CincyKidsRad

Cincinnati Children's Radiology

Lateral radiograph of the ankle shows the continuous C sign (image 2) of a talocalcaneal coalition (arrow on image 3). Coalitions of the foot most commonly occur between the talus and calcaneus or the calcaneus and the navicular. While most patients with a talocalcaneal coalition are asymptomatic, some patients can present with repeated ankle sprains and pain present with pain at the site of coalition distal to the medial malleolus. The pain is aggravated by running, jumping, or prolonged standing. #MSKMonday #MusculoskeletalMonday

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AP x-ray of the foot and lateral x-ray of the ankle shows coalition (arrow) of the medial cuneiform and the navicular bone. A coalition is an abnormal bridging of the bones. It is usually congenital. The most common site of a coalition in the feet is either between the calcaneus and the navicular or between the calcaneus and the talus. #MSKMonday](https://app.figure1.com/case-detail/06302466-7586-4613-91f9-de6a2ade0099)



Image description
Lateral ankle radiograph shows a continuous C-sign (arrow), reflecting osseous bridging between the talus and calcaneus. The normal subtalar joint is not visualized.

Teaching point
Talocalcaneal coalition results from abnormal fusion between the talus and calcaneus. The continuous C-sign represents continuity between the medial talar dome and sustentaculum tali and is a classic radiographic feature. Coalitions may restrict subtalar motion and present with hindfoot pain or stiffness.](https://app.figure1.com/case-detail/174cd951-ed2a-403c-a51a-f988b61bd553)



Oblique radiographs of the left foot (image 1 and zoomed-in focusing on the area of abnormality on image 2) show a calcaneonavicular coalition (arrow). Calcaneonavicular coalition is often best seen on the oblique image. An ossific bar connects the anterior process of the calcaneus to the lateral navicular. The coalition can be fibrous or bony. If symptomatic, the coalition can be resected (image 3).](https://app.figure1.com/case-detail/23f2c0d1-e913-4d57-8103-c452ea83e382)



Sagittal T1 MR in a pre-teen with ankle pain shows elongation, irregularity, and low signal intensity of the anterior process of the calcaneus and the adjacent navicular. However, no osseous continuity is seen. These findings are typical of a fibrocartilaginous calcaneonavicular coalition. This tarsal coalition can be suggested on lateral foot radiographs by an elongated calcaneal anterior process but is best visualized with an oblique foot radiograph. Conservative therapy may be tried initially, but resection of the coalition is often performed for definitive treatment. #MSKMonday](https://app.figure1.com/case-detail/299abf7d-4d10-4f9d-b1ee-47141f50edbf)