Tian X, et al. - Via a total of 122 children with 157 congenital ulnarly deviated thumbs at the distal phalanges, including those with isolated deformity or polydactyly were assessed by the researchers to investigate anatomic abnormalities causing a congenital ulnarly deviated thumb at the distal phalanx. In 2 thumbs with Wassell IV polydactyly, a previously undescribed cause was found. Furthermore, abnormal hypertrophic epiphysis in 96 thumbs and a distance of more than 2 mm between the abnormal bone and the distal phalanx suggesting a triphalangeal thumb were concluded as the 2 main causes of a congenital ulnarly deviated thumb.