The presence of a sixth finger, referred to as polydactyly, occurs in one in 3,000 births. It is one of the most common malformations of the hand and can result in either a fully formed sixth digit or a small skin tag on the side of the hand.
There are two classifications of polydactyly, depending on the side of the hand the extra digit is located. Postaxial polydactyly identifies an extra digit located alongside the little finger, while preaxial polydactyly refers to the thumb side of the hand. The occurrence of polydactyly is second only to syndactyly, a fusion of the skin or fingers.