What Is Postaxial Polydactyly?

Postaxial polydactyly is the formation of an extra fifth digit on the hand or foot. It can occur independently as a random genetic error or problem with fetal development, and may also be associated with a larger genetic syndrome that may include other manifestations. Many cases of postaxial polydactyly are treated shortly after birth with removal of the extra digit. Some parents may opt to leave the additional finger in place until later in life, allowing the child to make a decision about treatment as an adult.

There are two distinct forms of this condition. In type A postaxial polydactyly, the extra digit is fully formed and functional. It has bones and articulates with the bones of the hand or foot, allowing the patient to move it and use it in grasping and manipulating tasks. Sometimes this finger articulates with the existing fifth metacarpal, and in other cases the metacarpal bone is also duplicated, creating a new point of articulation for the extra digit.

Patients with the type B form of this condition have a more crude extra finger or toe. It may not have bones, consisting of a small lump of extra tissue, and may lack nerves and the ability to articulate. These cases sometimes require treatment because the extra finger gets in the way, since the patient cannot move it while using the hands or feet. The digit may protrude from the side of the hand or foot, or from the fifth finger or toe itself.

This condition is not uncommon, although the incidence of adults with postaxial polydactyly is rare because treatment is often treated in childhood. Patients considering surgical treatment can meet with a hand or foot specialist to discuss the nature of the case and to learn about treatment options. It is usually possible to take the growth off with minimal scarring. Levels of pain and discomfort during healing depend on the location and whether it is a type A or B polydactyly.

Historically, some superstition surrounded people with supernumerary digits as seen in postaxial polydactyly. Extra fingers and toes were sometimes used as evidence of witchcraft or other suspicious activities, and extra digits were sometimes added after the fact to make people appear more villainous. Anne Boleyn, for example, was reported to have an extra pinkie finger in smear campaigns initiated after her fall from royal favor, although there is no evidence that she actually had postaxial polydactyly.