ulnar polydactyly

Last reviewed 01/2018

Ulnar or post-axial polydactyly is the most common form of polydactyly. It has a racial predilection for African and African Americans boys with an approximate incidence of 1 in 300; this group tends to have a small, poorly formed digit with an autosomal dominant inheritance. The Stelling Classification describes a categorisation for the extra digit or parts of digit in the upper limb:

• Type 1: incomplete digit comprising soft tissue alone:
  • attached to the neighbouring digit by a soft tissue pedicle
  • most frequent form
  • more common in black population
  • tends to occur in association with conditions like Ellis-van Creveld syndrome and chondroectodermal dysplasia in white children
  • treated by clip or suture ligation, or more favourably by formal excision with an ellipse of skin and burying of the neurovascular bundle
  • usually have full longterm hand function
  • complications include neuroma formation and a residual nubbins of soft tissue, particularly with clip or suture ligation
• Type 2: complete or incomplete extra digit:
  • articulates with a metacarpal or phalanx
  • excised with use of a flap of skin from the digit to cover point of articulation
• Type 3: complete extra digit and metacarpal:
  • extra digit and metacarpal are excised
  • a corrective osteotomy may occasionally be necessary
  • may require reinsertion of muscles from the excised digit onto the residual ulnar sided digit eg abductor digiti minimi
  • ulnar collateral ligament may need reconstruction
  • tend to have good longterm hand function but little finger may exhibit a reduced range of motion

Alternatively, another classification scheme divides ulnar polydactyly into:

• type A: a well-developed supernumerary digit
• type B: a small nubbins connected by a soft tissue bridge

Ref: Temtamy SA, McKusick VA. Birth Defects Orig Art Ser (1978); 14: 1-619.