A 12-year-old boy has bilateral rigid flatfoot with restriction of subtalar motion and tightness of the peroneal muscles. Lateral ankle radiograph shows a continuous sclerotic line extending from the dome of the talus to the sustentaculum tali. This radiographic finding indicates coalition between which two bones?
- A Talus and calcaneus ✓
- B Calcaneus and navicular
- C Talus and navicular
- D Calcaneus and cuboid
Correct answer: A. Talus and calcaneus
Explanation
The C sign on the lateral radiograph, a continuous sclerotic arc from the talar dome to the sustentaculum tali, indicates talocalcaneal (subtalar) coalition, usually at the middle facet. Calcaneonavicular coalition, the other common type, is best seen on a 45 degree oblique radiograph as an anterolateral bony bridge, and produces a different appearance. Talonavicular and calcaneocuboid coalitions are rare. CT is the investigation of choice to define the extent once the coalition is suspected.
Reference: Campbell's Operative Orthopaedics, 14th ed.
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