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Classification

Authoring team

The established scheme for categorising thumb hypoplasia was first described by Blauth in 1967(1). Manske(2) subsequently went on to subdivide the third category into IIIa and IIIb:

  • type I:
    • all structures present
    • generalised hypoplasia - clinically minimally shortened and narrowed
    • mild hypoplasia of:
      • bones
      • muscles: opponens pollicis, abductor pollicis brevis
  • type II:
    • more hypoplasia
    • bones smaller:
      • phalanges
      • trapezium
      • scaphoid
      • metacarpal
    • intrinsic thenar muscles of thumb hypoplastic or absent
    • narrowing of first web space
    • may be only one neurovascular bundle
    • possible extrinsic muscle absence or hypoplasia eg FPL, EPL
  • type III:
    • all the features of a class II anomaly but with a more severe phenotype eg severe first web space contracture, severe hypoplasia of intrinsic and extrinsic muscles, significant reduction in thumb size
    • subclassified by Manske into IIIa and IIIb with important implications for treatment:
      • IIIa: carpometacarpal joint present and stable; usually hypoplastic extrinsic muscles
      • IIIb: carpometacarpal joint absent and instability at this level; absent extrinsic muscles
  • type IV:
    • also known as pouce flottant or floating thumb
    • rudimentary phalanges, no metacarpal
    • small soft tissue bridge between thumb and side of hand
    • often single residual neurovascular bundle
  • type V:
    • complete absence of thumb

Ref: (1) Blauth W(1967) Arch Orthop Unfall Chir 62: 225-246. (2) Manske PR, McCarroll HR Jr, James M. (1995). J Hand Surg 20: 246-253.


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