Radial polydactyly: proposal for a new classification system based on the 159 duplicated thumbs.

Background: Polydactyly is one of the most common congenital differences that affect the hand. It has various anatomic and morphologic features. Although the Wassel classification has been used widely for radial polydactyly, it is based on the anatomic level of duplication and has some limitations in describing the concrete morphology of the duplication. The authors devised a new classification system based on the anatomic pattern of duplication to facilitate surgical correction of the deformity and evaluated surgical outcomes. Methods: A total of 159 duplicated thumbs in 142 patients who were treated surgically from 1990 to 2007 and followed for >12 months were included in this series. The authors categorized all cases of radial polydactyly into the following: type I (joint type), where the extra digit has its own joint at its origin; type II (single epiphyseal type), where the origin of the extra digit is derived directly from the common epiphysis; type III (osteochondroma-like type), where the origin of the extra digit resembles an osteochondroma; and type IV (hypoplastic type), where the extra digit is connected to the main digit by soft tissue alone. All patients underwent surgical treatment based on this classification. The surgical outcomes were assessed using the Tada score. Results: Of the 159 radial polydactyly cases, 84 (50%) were classified as the joint type-37 (22%) as the osteochondroma-like type, 33 (19%) as the single epiphyseal type, and 15 (9%) as the hypoplastic type. All the cases were classified with the proposed classification system. In the evaluation of the surgical outcomes, 134 (84%), 17 (11%), and 8 (5%) were rated as good, fair, and poor, respectively. Conclusions: This new classification system for radial polydactyly is practical and closely related to the surgical strategies.