[Thumb duplication].
Thumb duplication is one of the most frequent congenital abnormality. Treatment is rarely limited to surgical amputation of one of the thumb duplicate. Wassel proposed a classification of seven categories based on the level of skeletal division, the most frequent being the type IV. Factors influencing the surgical result are numerous, including the importance of angular deviation of both duplicates, the joint stability and the duplicate size. In the distal categories (type I and II), when both duplicates are symmetrical, thumb reconstruction should be achieved by fusion of both duplicates on the midline after partial resection of the central portion (Bilhaut-Cloquet procedure). In more proximal types, one of the thumb duplicates will usually be retained whereas the other smaller one will be removed. Additional surgical steps are also required including ligament reconstruction at the MCP level to improve stability, osteotomy to correct angular deviation in the frontal plane, and soft tissue augmentation with a local flap harvested from the resected duplicate. If acceptable thumbs can usually be obtained both on a cosmetic and functional standpoint, these thumbs are never perfect with at least a reduced ROM at the IP and/or MP level.