Duplication of proximal phalanx

Partial or complete duplication of the proximal phalanx of the thumb may be treated in several ways:

• if the ulnar digit is small or there is near equality of size:
  • the radial bones are excised but the soft tissue from the radial thumb is used to create soft tissue flaps to augment the ulnar digit
  • an abnormal axis to the proximal phalanx and its joint surfaces may necessitate an osteotomy
  • tendons are typically inserted anomalously and require re-routing
  • alternatively, a Bilhaut-Cloquet procedure can be employed again but results in a relatively stiff digit
• if the ulnar digit is dominant:
  • it is conserved
  • if completely duplicated, the flared end of the metacarpophalangeal joint will need to be reduced in size
  • the abductor pollicis brevis typically inserts into the radial side of the base of the proximal phalanx of the radial digit; it must be detached and reinserted into the base of the proximal phalanx of the ulnar digit
  • the radial collateral ligament must be reconstructed with fascia or periosteum from the removed digit
  • again, osteotomy may be required to correctly align the joints
  • if the MCPJ is not stabilised in the reconstructed thumb, a zigzag deformity may result with time