Congenital triangular bones in the hand.

From the literature we found reports of 105 patients whom we judged had a triangular deformity of one of the bones of the hand or foot. We found 49 patients of our own with 84 delta-shaped phalanges limited strictly to the hand. This represents an incidence of 3.5% of our congenital abnormalities of the upper extremity. The deformity is associated with many abnormalities: syndactyly, polydactyly, symphalangism, triphalangeal thumb, cleft hand, and hypoplastic hand are the most frequent Triangular deformity of the bone of the index finger usually is associated with Apert's syndrome. Triangular deformity of the proximal phalanx of the ring finger often is found with central polydactyly. Our average follow-up time on these 49 patients was 14 years, giving us a chance to establish some guidelines and general rules about the natural history and treatment of the delta bone.