Polydactyly

Polydactyly

Polydactyly is the radial, ulnar or central duplication of digits. This article details the classification, treatment and aetiology of this congenital condition.

Summary Card

Definition
Congenital duplication of digits that can be radial, ulnar or central.

Radial Polydactyly
A pre-axial duplication of the thumb classified by Wassell.

Ulnar Polydactyly
Post-axial duplication of little finger classified by Stelling.


Definition of Polydactyly

Polydactyly is a congenital duplication of a finger. It can be pre-axial (radial), central and post-axial (ulnar) and is caused by disruption at the ZPE and AER embryological signalling zones.

Definition of Polydactyly

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Tip: Polydactyly is classified by Swanson's congenital hand anomalies as "duplication".


Radial Polydactyly


Key Point

A pre-axial duplication of the thumb classified by Wassell.


Radial (pre-axial) polydactyly is an isolated thumb duplication that is generally unilateral and non-syndromic.

Radial Polydactyly

Classification of Radial Polydactyly

Radial polydactyly is a duplication of the thumb. It is classified using by Wassell into 7 groups based on the degree of bony duplication.

  • Type I: Bifid Distal Phalanx
  • Type II: Duplicate Distal Phalanx
  • Type III: Bifid Proximal Phalanx + Duplicate Distal Phalanx
  • Type IV: Duplicate Distal Phalanx + Duplicate Distal Phalanx
  • Type V: Bifid 1st metacarpal + Duplicate Distal and Proximal Phalanx
  • Type VI: Duplicate 1st metacarpal + Distal Phalanx + Proximal Phalanx
  • Type VII: Triphalangeal thumb + normal thumb

This Wassell classification of radial polydactyly is illustrated below.

Wassell Classification for Radial Polydactyly

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Fun Fact: Type IV is the most common radial polydactyly

Management of Radial Polydactyly

Surgery aims to create an anatomically aligned thumb with joint stability that enables the function. Ideally, it is performed prior to the development of the thumb-pinch index at age 1.

The Wassell classification can guide management:

  • Types I + II can be treated with the Bilhaut-Cloquet technique, which removes adjacent inners halves of each duplicate, and out segments are fused.
  • Type III + IV require reconstruction of radial collateral ligaments, intrinsic muscles, and joint osteotomies.
  • Types V + VI also requires web space reconstruction, basal joints and metacarpals with osteotomy.

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Tip: Ideally, the ulnar thumb should be preserved as the ulnar collateral ligament is required for pinch stability. 

The surgical correction of radial polydactyly is shown in the video below.

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Fun Fact: The radial duplicate is usually more hypoplastic and smaller than the ulnar. 


Ulnar Polydactyly


Key Point

Post-axial duplication of little finger classified by Stelling.


Ulnar post-axial polydactyly is a congenital duplication of the little finger digits. Unlike radial polydactyly, it is commoner in African Americans males and is more often bilateral.

Classification of Ulnar Polydactyly

Ulnar polydactyly can be described using Stelling's classification. It also guides management.

  • I: "Nubbin" - soft tissue without bone excised or ligated as a neonate.  
  • II: extra digit is structurally complete and articulates with normal or bifid metacarpal or phalanx.
  • III: extra digit is structurally complete and has its own metacarpal.

Types II and III patients require resection and reconstruction of abductor digiti minimi and ulnar collateral ligament in the adjacent finger.

An alternative classification can be Type A (well developer supernumerary digit) or Type B (digit is rudimentary and pedunculated).

Ulnar Poydactyly X-Ray

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Fun Fact: Polydactyly is linked to a HOX gene mutation resulting in the disruption of the AER and APZ signalling pathways. This is discussed in more detail in the upper limb embryology topic.

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