Congenital thumb hypoplasia presents as a wide range of first ray deficiencies and frequently occur as part of a larger systemic syndrome such as Holt-Oram, Fanconi’s, or Apert’s syndrome. To function correctly, the thumb must be positioned so that it can oppose the adjacent medial fingers and grasp objects securely from an antiposed (abducted, slightly extended, and pronated) position. Although normal motion is usually not required at the MP or interphalangeal joints, thumb function is greatly dependent on preserving a full arc of circumduction at the carpometacarpal (CMC) joint. The CMC joint must be sufficiently stable to provide resistance during grasp and pinch. The Blauth's classification ranges from type I to V and Types IIIB to V are treated with pollicization. The key difference between a Blauth IIIA and IIIB is the presence of carpometacarpal joint stability in Blauth IIIA.
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PMID:4874597 (Link to Abstract)