Classifications in Brief: The Wassel Classification for Radial Polydactyly

Excerpt

Radial (preaxial) polydactyly is among the most common congenital anomalies of the hand, with an incidence of 0.08 to 1.4 per 1000 live births [1, 11, 17, 21]. Although radial polydactyly is commonly described as “thumb duplication,” it is uncommon that the two thumbs are truly duplicated with equal size and function. More commonly, one “dominant” thumb is more developed anatomically and functionally than the other, leading some surgeons to prefer the term “split thumb” to communicate the concept that neither thumb is fully formed nor complete. Radial polydactyly originally was classified as a “duplication” by the International Federation of Societies for the Surgery of the Hand rather than as a “failure of formation” or “failure of differentiation” [19]. It since has been reclassified as a “malformation,” a failure of axis formation, and/or differentiation of the radioulnar hand plate in the Oberg, Manske, and Tonkin classification, which classifies anomalies based on developmental biology and pathogenesis rather than on morphologic features, and recognizes that processes such as formation and differentiation occur together and not independently [15]. From the genetic perspective, most radial polydactyly occur owing to a sporadic genetic mutation, but triphalangeal thumbs are inherited in an autosomal dominant manner [26]. …