| Modified Blauth classification of hypoplastic thumb | ||
| I | Minimal shortening and narrowing | |
| II | Thumb-Index web space narrowing Hypoplastic intrinsic thenar muscles Metacarpophalangeal joint instability |
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| III | A | Type II features, plus extrinsic tendon abnormalities and Hypoplastic metacarpal, stable carpometacarpal |
| B | Type II features, plus extrinsic tendon abnormalities and Partial metacarpal aplasia, unstable carpometacarpal |
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| IV | Floating thumb | |
| V | Absent thumb | |