Exostosis presenting as solitary loose body in the ankle of two children.

Two children, aged 5 and 11 years, presented clinically with ankle pain and a mobile bony hard lump in the ankle. Radiological examination revealed a large radio-opaque shadow in relation to the talus. Intraoperatively, a loose body was found. It resembled a detached exostosis with cartilaginous cap and was confirmed histologically as an osteochondroma. In the older child, there was a remnant stalk attached to the lateral surface of the talus. In the younger child, the exostosis probably came from the talus as the osteochondroma could not originate from the epiphyses that form the ankle mortise.