Polydactyly or polydactylism also known as hyperdactyly, is a congenital physical anomaly in humans resulting in supernumerary fingers and/or toes.
This condition can present itself on one or both hands.
The extra digit is usually a small piece of soft tissue that is removable.
Occasionally , the extra digit contains bone without joints, and rarely it may be a complete functioning digit.
The extra digit is most common on the ulnar side of the hand.
Less commonly the extra digit is on the radial side, and very rarely within the middle three digits: respectively known as postaxial (little finger), preaxial (thumb), and central (ring, middle, index fingers) polydactyly.
The incidence of congenital deformities in newborns is approximately 2%, and 10% of these deformities involve the upper extremity.
There is an association between polydactyly and several syndromes.
The majority of congenital anomalies occur during the 4-week embryologic period of rapid limb development.
It is associated with 39 genetic mutations.
Postaxial polydactyly is the most common type, in which the extra digit is on the ulnar side of the hand, thus the side of the little finger.
Postaxial polydactyly can manifest very subtly, only as a nubbin on the ulnar side of the little finger, or very distinctly, as a fully developed finger.
The extra finger is usually rudimentary, consisting of an end phalanx with a nail, and connected to the hand with a small skin pedicle.
There are no tendons present in the extra digit, but 1neurovadvular bundle
If a fully developed extra finger exists, the duplication is at the level of the metacarpophalangeal joint.
A triplication of the little finger is very rare.
Ulnar polydactyly is often bilateral and associated with syndactyly and polydactyly of the feet.
Ulnar polydactyly occurs ten times more often in African populations.
The incidence in Caucasians is reported as 1 in 1,339 live births.
It occurs 1 in 143 live births in Africans and African Americans.
With African ancestry ulnar polydactyly mostly occurs as an isolated event.
In Caucasians polydactyly is more often associated with a syndrome, which is inherited.
Syndromic polydactyly is passed on in an autosomal dominant manner with variable expression and incomplete penetrance.
Radial or preaxial polydactyly occurs on the side of the hand towards the thumb,and is less common than ulnar polydactyly.
Radial polydactyly refers to the presence of an extra digit on the radial side of the hand.
Radial polydactyly varies from a barely visible radial skin tag to complete duplication.
Radial polydactyly is most frequent in Indian populations and it is the second most common congenital hand disorder.
The incidence of radial polydactyly is reported as 1 in every 3,000 live births.
Central polydactyly is very rare with an extra digit is on the ring, middle or index finger.
Central polydactyly has an incidence of 1 in every 500 live births.
Central polydactyly can be associated with syndactyly, cleft hand and several other syndromes.
Central polydactyly is most often associated with the index finger, whereas the ring finger is rarely affected.
Central polydactyly can be associated with syndactyly, cleft hand and several syndromes.
While polydactyly can occur by itself, it is more commonly, a feature of a syndrome of congenital anomalies.
When it occurs in isolation, it is associated with autosomal dominant mutations in single genes.
Mutations in a variety of genes can give rise to polydactyly.
97 genetic syndromes have been associated with different kinds of polydactyly.
Ulnar polydactyly usually does not interfere with hand function.
Satisfactory surgical correction of central polydactyly is difficult to achieve and that outcomes are generally poor.
Postaxial hand polydactyly is a common isolated disorder in African black children, and autosomal dominant transmission is suspected.
In a study combining data from United States and Sweden showed incidence of all types of polydactyly to be 2.3 per 1000 in Caucasian males, 0.6 per 1000 in Caucasian females, 13.5 per 1000 in African males, and 11.1 per 1000 in African females.