Polydactyly of the thumb is the most common congenital malformation of the hand, manifesting as two thumbs, either separate or combined, with an incidence of approximately 1 in 1,000. In polydactyly, the thumb is often smaller than the normal thumb, and the two thumbs often share a set of neurovascular tendons and muscles. Diagnosis Diagnosis is relatively straightforward and relies on physical examination, although x-rays are often required to identify skeletal abnormalities and development. Treatment The main treatment relies on surgery. Surgical treatment is not simply the removal of the redundant thumb, but the reconstruction of a new thumb with normal appearance and function. Surgery is considered to preserve the main one thumb, correct the bones, and reconstruct the tendons, joints and ligaments. The design of the incision is also considered in order to reconstruct a thumb with a better appearance. Usually, the poorly developed thumb is removed, and as mentioned above, both thumbs share a set of neurovascular and tendon muscles, so it is important to preserve the appropriate skin, tendons, blood vessels, nerves, nails, and muscles from the excess thumb removed to form a new normal thumb. The surgery is often performed around one year of age.