Male with unilateral preaxial<unk>  affecting the left thumb. The supernumerary digit had normal sensation but no joint and hence could not move independently. In humans/animals this condition can present itself on one or both hands. The extra digit is usually a small piece of soft tissue that can be removed. Occasionally it contains bone without joints; rarely it may be a complete functioning digit. The extra digit is most common on the ulnar (little finger) side of the hand, less common on the radial (thumb) side, and very rarely within the middle three digits. These are respectively known as postaxial (little finger), preaxial (thumb), and central (ring, middle, index fingers)<unk> . The extra digit is most commonly an abnormal fork in an existing digit, or it may rarely originate at the wrist as a normal digit does. The incidence of congenital deformities in newborns is approximately 2%, and 10% of these deformities involve the upper extremity. Congenital anomalies of the limb can be classified in seven categories, proposed by Frantz and O’Rahilly and modified by Swanson, based on the embryonic failure causing the clinical presentation. These categories are failure of formation of parts, failure of differentiation, duplication, overgrowth, undergrowth, congenital constriction band syndrome, and generalized skeletal abnormalities.<unk>  belongs to the category of duplication. Because there is an association between<unk>  and several syndromes, children with a congenital upper extremity deformity should be examined by a geneticist for other congenital anomalies. This should also be done if a syndrome is suspected, or if more than two or three generations of the family are affected. Research has shown that the majority of congenital anomalies occur during the 4-week embryologic period of rapid limb development.<unk>  has been associated with 39 genetic mutations. More specific loci and genetic mechanisms responsible for disorders of duplications will be defined with time, as molecular research continues.<unk>  can be divided into three major types, which are discussed below. Ulnar or postaxial<unk>  Postaxial<unk>  This is the most common situation, in which the extra digit is on the ulnar side of the hand, thus the side of the little finger. This can also be called postaxial<unk> . It can manifest itself very subtly, for instance only as a nubbin on the ulnar side of the little finger, or very distinctly, as a fully developed finger. Most commonly, the extra finger is rudimentary, consisting of an end phalanx with a nail, and connected to the hand with a small skin pedicle. Mostly one neurovascular bundle can be identified, with no tendons present in the extra digit. In case of a fully developed extra finger, the duplication usually presents itself at the level of the metacarpophalangeal joint. A triplication of the little finger is very rare. Ulnar<unk>  occurs ten times more often in African populations. The incidence in Caucasians is reported as 1 in 1,339 live births, compared with 1 in 143 live births in Africans and African Americans. Ulnar<unk>  is also often part of a syndrome. In patients with African ancestry ulnar<unk>  mostly occurs isolated, whereas the presentation in Caucasians is often associated with a syndrome, though in a retrospective review, only 4 of 37 cases of ulnar<unk>  in Caucasians were syndromic. Radial or preaxial<unk>  Preaxial<unk>  This is a less common situation, in which the affectation is on the side of the hand towards the thumb. Radial<unk>  refers to the presence of an extra digit (or extra digits) on the radial side of the hand. It is most frequent in Indian populations and it is the second most common congenital hand disorder. The incidence of radial<unk>  is reported as 1 in every 3,000 live births. The clinical features of radial<unk>  will depend upon the extent of duplication. Radial<unk>  varies from a barely visible radial skin tag to complete duplication. Thumb<unk>  varies from barely visible broadening of the distal phalanx to full duplication of the thumb including the first metacarpal. Radial<unk>  is frequently associated with several syndromes. Central<unk>  This is a very rare situation, in which the extra digit is on the ring, middle or index finger. Of these fingers, the index finger is most often affected, whereas the ring finger is rarely affected. This type of<unk>  can be associated with syndactyly, cleft hand and several syndromes. Polysyndactyly presents various degrees of syndactyly affecting fingers three and four.
Polydactyly
Clinodactyly
Oligodactyly
Syndactyly
Brachydactyly
Sclerodactyly
Pachydermodactyly
Arachnodactyly