Postaxial polydactyly

Last revised by Daniel J Bell on 30 May 2023

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

Epidemiology

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

Associations

Postaxial polydactyly can be associated with:

Pathology

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.

Classification

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

Duran et al. introduced their new classification system for post-axial polydactyly in 2015 6. This new classification was created as it was felt that the current 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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