Type III-A hypoplastic thumb.

Thirteen type III-A hypoplastic thumbs were reviewed. The abnormalities included those found in type II hypoplasia (narrow thumb-index web space, hypoplastic thenar muscles, unstable metacarpophalangeal joint, as well as extrinsic tendon abnormalities); all had stable carpometacarpal joints. They are differentiated from type III-B hypoplastic thumbs, which have an unstable carpometacarpal joint due to a deficient base of the metacarpal. The extrinsic tendon abnormalities included absent extensor pollicis longus tendon, absent or aberrant flexor pollicis longus tendon, and a tendon interconnection between the flexor pollicis longus and extensor aponeurosis. Twelve of the thumbs had surgical reconstruction. None was treated with ablation and index pollicization.