Postaxial polydactyly

Polydactyly or polydactylism (from Greek πολύς (polys), meaning 'many', and δάκτυλος (daktylos), meaning 'finger'), also known as hyperdactyly, is a congenital physical anomaly in humans and animals resulting in supernumerary fingers and/or toes. Polydactyly is the opposite of oligodactyly (fewer fingers or toes).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) polydactyly. 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.Polydactyly is associated with different mutations, either mutations in a gene itself or in a cis-regulatory element responsible for the expression of a specific gene. Mutations in Hoxa- or Hoxd clusters are reported leading to polydactyly. Interactions of Hoxd13 and GLI3 induce synpolydactyly, a combination of extra and consolidated digits. Other signal transduction pathways in this context are the Wnt signaling pathway or Notch.Classification is performed by using x-ray imaging to see the bone structures.Ulnar polydactyly usually does not interfere with hand function, but for social reasons it can be treated operatively.There are no substantive outcome studies regarding the function of these hands following surgical intervention. This is mainly caused by the fact that there is a generally normal function of these patients’ hands following ablation with collateral ligament reconstruction. In a study on 27 patients undergoing surgical excision for Type A ulnar polydactyly, only one complication was noted in the form of an infectionHowever, no investigators have objectively reviewed functional range of motion or articular stability.The condition has an incidence of 1 in every 500 live births. Postaxial hand polydactyly is a common isolated disorder in African black children, and autosomal dominant transmission is suspected. Postaxial polydactyly is more frequent in native Africans living in the Eastern and Central than the Caucasians and Mongoloids and is more frequent in male children. In contrast, postaxial polydactyly seen in white children is usually syndromic and associated with an autosomal recessive transmission. One study by Finley et al. combined data from Jefferson County, Alabama, United States and Uppsala County, Sweden. This study 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.Polydactyly occurs in numerous types of animals. The defect is sporadically seen in livestock, where it affects cattle, sheep, pigs, and occasionally horses. Conversely, it is a common trait in several heritage chicken breeds. Chickens normally have 4 toes on each foot. The chicken breeds known for being polydactyl are the Dorking, Faverolle, Houdan, Lincolnshire Buff, Meusienne, Sultan, and non-bearded Silkie Bantams. The breed standard of these varieties of chickens calls for 5 toes on each foot, although sometimes more than 5 toes will occur. The extra digit in these breeds presents as an extra 'thumb' that does not touch the ground. Mixed-breed chickens may also have extra digits if the aforementioned breeds are part of their genetic makeup.Rooster with feathered legs (Aldrovandi himself did not notice the five toes)Kitten with 23 toesMuscovy duck, both feet have 5 toesMuscovy duck, both feet have 5 toes