Phalangeal osteochondroma: an unusual cause of swan-neck deformity.

A 4-year-old child with a proximal phalangeal osteochondroma of the index finger presented with a rigid swan-neck deformity. The dorsal apparatus overlying the tumor was stretched, causing increased tension on the central slip and thus hypertension of the proximal interphalangeal joint. Excision of the tumor resulted in complete restoration of digital motion.