Triplicated thumbs: a rarity?

Abstract

Triplication of the thumb is supposed to be a rare condition and a complex form of radial polydactyly. However, we encountered an unusually high number of triplicated thumbs at our unit. Is triplication of the thumb indeed a rare condition? In our study, 121 patients with radial polydactyly were recorded between 1933 and 2005. In nine patients of this group, triplicated thumbs, either unilateral or bilateral, were identified. This complex type of radial polydactyly occurs in various forms. A total of 11 triplicated thumbs were found, and all cases were combined with triphalangeal components. Only one of these 11 triplicated thumbs could be classified according to currently used classifications. In all cases, aberrant rays were excised, thumb length and alignment restored by osteotomies, joints were stabilised, tendons reinserted and nails and nail walls corrected if necessary. Also, in all cases, a correction of triphalangeal components was carried out. Triplications are a rarity, and have only been presented in single case reports. We found that triplicated thumbs are not so rare. The likely explanation for this is the identification of a genetic isolate (a deformity located at chromosome 7q36) with radial polydactyly and triphalangeal thumbs in the southwest region of the Netherlands. Treatment for the presented triplicated thumbs was based on the same general principles as for less complex forms of radial polydactyly (i.e. to assemble useful elements of the separate [partial] thumbs to reconstruct one functioning, stable thumb).