Atypical Wassel type VI thumb duplication treated with on-top plasty.

Congenital thumb duplication is estimated to occur between 0.08 and 7.6 times per 1,000 live births; however its cause is still undetermined. In this report, we present a case of Wassel type VI thumb polydactyly. clinical examination revealed an optimal functional position and an aesthetically pleasing shape of the ulnar thumb as well as a superior nail and pulp. However, preoperative X-ray indicated a well formed carpometacarpal joint of the radial thumb compared to an underdeveloped CMC joint of the ulnar thumb. Through surgical procedure we combined the best parts of both thumbs with on-top plasty to achieve the most optimal outcome. In conclusion, it is important to determine an adequate treatment strategy for a patient based on both clinical and radiological assessments.