Postaxial polydactyly

Last revised by Rohit Sharma on 23 Apr 2024

Postaxial polydactyly refers to polydactyly where the additional digit is on the ulnar margin of the hand, or lateral to the 5th (little) toe.


Postaxial polydactyly is more common than preaxial polydactyly, with an estimated incidence of 1 in 3000 5.



The majority of cases are idiopathic. Associations with mutations to the GLI3 gene on chromosome 7 as well as a second locus mapped to chromosome 13 have been implicated in postaxial polydactyly 5.


Several different classification systems exist for postaxial polydactyly of the hands, including the Pritsch, Rayan and Al-Qattan, and Duran classification systems.

Duran et al. introduced their classification system for post-axial polydactyly in 2015 6. This classification was created as it was felt that the previous systems in use were not comprehensive for coverage of the different post-axial forms.

  • type I: skin nub without nail or bone elements

  • type II: hypoplastic proximal phalanx

  • type III: proximal phalangeal malformations

    • IIIa: bifid proximal phalanx

    • IIIb: duplicated proximal phalanx

  • type IV: metacarpal malformations

    • IVa: fusion of the metacarpal

    • IVb: bifid metacarpal

    • IVc: duplication of the metacarpal

  • type V: (complicated type) with triplication of the small finger, polysyndactyly, or both

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