Subungual exostosis of the foot.

Eleven subungual exostoses of the foot (10 on the hallux, 1 on the third toe) were studied. The initial symptom was subungual pain. When a subungual mass of fibrous tissue appeared, the nail was pushed up and in one case the mass became infected. X-rays exhibited a bone mass protruding from the terminal phalanx on the dorsomedial aspect of the toe in all cases. All patients underwent surgical excision of the lesions with partial onychectomy. Three layers were identified in five cases: a cap of fibrous tissue, a middle zone of hyaline cartilage with enchondral ossification, and a deep zone of cancellous bone. In three other cases, the histological pattern was pleomorphic and poorly characterized. The study shows that most subungual bone masses exhibited the pathological features of conventional osteochondromas. Nonetheless, a small number of lesions were pleomorphic and differed from osteochondromas, with abundant fibrous tissue merging irregularly into scattered islets of cartilage that was not organized in columns. Radical excision of the mass achieved complete relief of symptoms and recovery without recurrences in all cases.