Synpolydactyly of the hand: a radiographic classification.

UNLABELLED: Synpolydactyly is an uncommon congenital anomaly characterized by polydactyly with syndactyly in the central hand. The purpose of this investigation was to develop and assess the reliability of a radiographic classification system for synpolydactyly. We identified 56 hands with central synpolydactyly and developed a radiographic classification system that categorizes by the location within the hand, the bony level of polydactyly, and the presence of a delta phalanx. Four paediatric hand surgeons independently reviewed each radiograph to establish reliability. There was exact agreement among raters in 40 cases (71%). The inter-rater reliability was 0.97 and intra-rater reliability was at least 0.87. Seven of 16 bilateral cases had symmetric deformity classification. The most common presentations were types 1A and 2A. We present a new, reliable radiographic classification system for synpolydactyly that will allow improved communication between clinicians and serve as a foundation for future investigations. LEVEL OF EVIDENCE: 2.