Which of the following is a radiographic sign of talocalcaneal coalition?

• A. Fractures of the lateral malleolus
• B. C sign or halo sign
• C. Osteophyte formation
• D. Joint effusion

Answer: (B)

The C sign or halo sign is a radiographic indicator specifically associated with talocalcaneal coalition, which is a condition characterized by an abnormal connection between the talus and calcaneus bones in the foot. This coalition can lead to limited motion in the subtalar joint, and the C sign is formed by the outline of the coalition on imaging, visually resembling the letter "C" or a halo around the joint.

This sign is particularly significant in diagnosing talocalcaneal coalition as it provides visual evidence of the coalitional connection and its impact on the anatomy of the foot. Radiographs showing this sign help clinicians to confirm the presence of the coalition and to differentiate it from other pathologies.

In contrast, other choices such as fractures of the lateral malleolus, osteophyte formation, and joint effusion are not specific indicators of talocalcaneal coalition. While they may occur in various conditions affecting the foot and ankle, they do not provide the targeted information needed to identify the coalition itself. Thus, the C sign or halo sign stands out as the crucial radiographic finding for this particular diagnostic purpose.