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Thumb hypoplasia
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Thumb hypoplasia

Contributors: Michael Catanzaro MD, Danielle Wilbur MD
Other Resources UpToDate PubMed


Causes / typical injury mechanism: Thumb hypoplasia is a congenital defect with a spectrum of presentations ranging from a slight decrease in thumb size to complete thumb absence. Thumb hypoplasia belongs to the radial longitudinal deficiency spectrum of diseases.

  • Age – Present from birth.
  • Sex / gender – There is no difference in prevalence due to sex.
Risk factors: Approximately 80% of cases of hypoplastic thumb have an associated condition.

Syndromes associated with hypoplastic thumb include:
Pathophysiology: Embryologic origin remains unclear.

Grade / classification system:
Blauth Classification
  • Type I: Minor generalized hypoplasia.
  • Type II: Absence of the intrinsic thenar muscles. First web space narrowing. Ulnar collateral ligament (UCL) insufficiency.
  • Type III: Musculotendinous and osseous deficiencies.
    • A – stable carpometacarpal (CMC) joint
    • B – unstable CMC joint
    • C – remnant head of metacarpal only
  • Type IV: Pouce flottant, or floating thumb.
  • Type V: Aplasia.


Q71.30 – Congenital absence of unspecified hand and finger

253936008 – Hypoplasia of thumb

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Last Reviewed:12/25/2022
Last Updated:01/03/2023
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Thumb hypoplasia
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