Preaxial and Postaxial Polydactyly



Preaxial and Postaxial Polydactyly


Robert Carrigan





ANATOMY



  • In cases of digit duplication, one may observe duplication in some or all of the elements of the finger (bone, nail, joints, and tendon). The duplicate finger may be well formed and near normal in appearance or underdeveloped and rudimentary in appearance.


  • Wassel published a classification of thumb duplication based on the work of Adrian Flatt, MD (Table 1).


  • Postaxial polydactyly classification



    • Type A: well-formed duplicate small finger with bone or tendon attachments (FIG 1)


    • Type B: small pediculated nubbin


PATHOGENESIS



  • Duplication of the digits occurs early in embryogenesis.


  • Patterning of the limb is demonstrated in three axis: proximodistal axis (modulated by the apical ectodermal ridge [AER]), anteroposterior axis (modulated by the zone of polarizing activity [ZPA]), and the dorsoventral axis regulated by the Engrailed 1 protein (EN1).


  • Abnormal or ectopic presence of sonic hedgehog protein is implicated in preaxial polydactyly.


  • Familial cases of postaxial polydactyly demonstrate a defect in the GLI3 gene.








Table 1 Wassel Classification of Thumb Duplication





























Type


Description


I


Bifid distal phalanx


II


Duplicate distal phalanx


III


Bifid proximal phalanx


IV


Duplicate proximal phalanx


V


Bifid metacarpal


VI


Duplicate metacarpal


VII


Triphalangeal thumb


From Wassel HD. The results of surgery for polydactyly of the thumb. Clin Orthop Relat Res 1969;64:175-193.



PATIENT HISTORY AND PHYSICAL FINDINGS



  • The diagnosis of polydactyly is straightforward, clinical examination and radiographs are sufficient to make the diagnosis.


IMAGING AND OTHER DIAGNOSTIC STUDIES



  • Standard radiographs (three views—anteroposterior, lateral, and oblique) of the hand and affected digit are sufficient to determine the area of involvement (FIG 2).


  • Advanced imaging such as magnetic resonance imaging (MRI) and computed tomography (CT) is rarely needed.




NONOPERATIVE MANAGEMENT



  • Observation may be considered for duplicated digits that do not impair function of the hand.


SURGICAL MANAGEMENT


Preoperative Planning



  • Timing of surgery is variable.


  • Type B postaxial polydactyly may be removed in the office under local anesthesia, when the child is just a few weeks old.


  • Preaxial polydactyly reconstruction and type A postaxial reconstructions are elective procedures and are generally performed after 1 year of age and before the start of school.






FIG 1 • Type A postaxial polydactyly.







FIG 2 • Preoperative radiograph of the patient in FIG 1 with type A postaxial polydactyly, depicting the bifacet metacarpal head.


Positioning



  • The patient is positioned supine on the table and the body is pulled over to the affected side.


  • The arm is placed on a radiolucent hand table and an arm tourniquet is applied.


Approach

Jul 22, 2016 | Posted by in ORTHOPEDIC | Comments Off on Preaxial and Postaxial Polydactyly
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