The distribution of the types of thumb polydactyly in a Middle Eastern population: a study of 228 hands.

Several series have reported the distribution of the types of thumb polydactyly in the Caucasian and Far Eastern populations. No data are available for the Middle East. A total of 196 Saudi patients (228 hands) with thumb polydactyly were reviewed. The most common type was Wassel type IV (33.8%) and the least common was Wassel type I (0.4%). A total of 26 hands (11.4%) did not fit into the classic Wassel types including 18 cases of rudimentary duplications, two cases of thumb triplication, and five cases of thumb duplication with symphalangism. Concurrent ipsilateral little finger triplication (one case) and contralateral thumb aplasia/hypoplasia (two cases) were seen and the developmental biology of these cases are discussed. After reviewing our results and other series in the literature, we concluded that Wassel types IV and I remain to be the most and least common types respectively in almost all races. However, the genetic pools of various races greatly affect the distribution of other non-classic duplications (unclassifiable by Wassel classification) such as rudimentary duplication in the Far East, triplication in the Southwestern region of the Netherlands, and symphalangism in Asia.