Polydactyly literally means “many digits.” The condition can occur on its own or from a genetic or familial inheritance pattern. The supernumerary digit may be a fully functional digit or a skin tag-type of digit that is non-functional. Polydactyly occurs in approximately two out of every 1,000 live births and about 30 percent of patients have a positive family history.1-3
Polydactyly occurs when the blueprint of the hand or foot is altered and further development includes an extra digit.3 In an isolated form, polydactyly has a dominant inheritance pattern and when it is associated with a syndrome, it has a recessive inheritance pattern.4
Causes of polydactyly include:
• Carpenter syndrome
• Ellis-van Creveld syndrome
• familial polydactyly
• trisomy 13
Temtamy and McKusick classified polydactyly into two main types: preaxial and postaxial.5 A central type of polydactyly can also occur but it is not as common.
Clinicians define preaxial polydactyly as an extra digit to the medial ray or first digit. Physicians see these cases in about 8 to 15 percent of patients.4 There are four classified subtypes:
• Type 1 – mere duplication of the first digit
• Type 2 – polydactyly of a triphalangeal first digit
• Type 3 – polydactyly of the second digit
• Type 4 - polysyndactyly
Postaxial polydactyly is an extra digit on the lateral ray or fifth digit. This is the most common form of polydactyly, accounting for about 79 to 86 percent of patients.6 Venn-Watson describes the most common classification system for postaxial polydactyly.7
• Type 1 – wide metatarsal head
• Type 2 – T-shaped
• Type 3 – Y-shaped
• Type 4 – partial polydactyly
• Type 5 – complete duplication
Most treatment revolves around the difficulty with shoe gear and the emotional stress that an extra digit may cause as the child grows up. For an extra digit that is purely a skin tag, the surgeon often ties a ligature around the toe at birth and allows the tissue to die and fall off. If the digit is functional, surgical excision occurs.
Physicians widely debate the proper timing of surgical excision. The average age of surgical intervention is about 1 year. Trying to operate sooner runs the risk of not removing the correct digit due to incomplete ossification of the bones involved. The general principle is to keep the digit that is most developed, has the most normal joint articulation and gives the best contour to the foot.1,2
Editor’s note: One may contact Dr. Bowman via www.houstonfootspecialists.com  .
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2. Coughlin MS (ed.). Surgery of the Foot and Ankle, eighth edition. Elsevier, Philadelphia, 2006.
3. National Human Genome Research Institute. Polydactyly research study: General information about polydactyly. National Institutes of Health. Available at http://www.genome.gov/27529688  . Accessed Nov. 26, 2013.
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