Congenital absence or hypoplasia of the thumb is often associated with congenital longitudinal deficiency of the radius. The spectrum of the defect varies from simple hypoplasia and miniature thumb to total absence of the thumb.
Hypoplastic Thumb
In the normal hand, the tip of the thumb reaches to the middle of the proximal phalanx of the index finger. When the thumb is shorter than this it can be classified as hypoplastic.
It is crucial to rule out associated abnormalities because often this malformation is a manifestation of a syndrome.
There could be associated abnormalities of the heart, spine, and gastrointestinal tract.
A short slender first metacarpal may be a feature of the Fanconi or Holt-Oram syndrome, whereas a short broad first metacarpal may be associated with such disorders as Cornelia de Lange syndrome or diastrophic dwarfism.
If the small thumb is associated with a short great toe, one should be beware of myositis ossificans progressiva.
Brachydactyly of the proximal or the distal phalanx of the thumb may be an isolated finding or a manifestation of such syndromes as Rubinstein-Taybi, Apert’s, or Carpenter’s.
Grasp and prehension are hampered when the thumb is short. Recessing the web thumb is short. Recessing the web proximally will effectively lengthen the thumb, but stability of the carpometacarpal joint is a pre-requisite.
Two or four flap Z-plasties are the best techniques to deepen the web space between the thumb and index finger.
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