__II. Thumb-Index web space narrowing
__Hypoplastic intrinsic thenar muscles
__Metacarpophalangeal joint instability
__III. Type II features, plus extrinsic tendon abnormalities and:
__IIIA. Hypoplastic metacarpal, stable carpometacarpal
__IIIB. Partial metacarpal aplasia, unstable carpometacarpal
__IV. Floating thumb
__V. Absent thumb