Central polydactyly

Central polydactyly describes an extra digit or part of a digit affecting the central digits of the hand. It is not as common as polydactyly affecting the border digits. Usually, it is sporadic but it can be associated with autosomal dominant inheritance. However, a specific form of ring finger duplication and syndactyly has been associated with a mutation in the chromosome 2 gene HOXD13.

Clinical features may be as minor as a fused nail bed but can be as severe as extra digits within a mass of fused digits. Concomitant syndactyly is relatively common (synpolydactyly) and indeed may mask the polydactyly within a mass of fused central digits.

Treatment is problematic and dependent upon the extent of polydactyly:

• a normal extra central digit does not require removal if full function
• a single extra digit with limited motion is treated with ray resection; neighbouring digits are transposed into the space and the intermetacarpal ligament is reconstructed
• synpolydactyly:
  • separation of syndactyly
  • attempted removal of extra digit; often unsuccessful as limited by factors such as local blood supply to the remaining digits
  • often appearance is improved but with little improvement in function
• partial central polydactyly with duplication of distal elements of a digit:
  • components of both digit may be combined
  • often results in a poorer functional digit despite the improved cosmesis