Grade Clinical manifestations
I
Narrow, small (near normal) Minimal underdevelopment Stable Mild intrinsic hypoplasia
IIA
Narrow, small Adduction contracture Uniaxial Ulnar Collateral ligament (UCL) Metacarpophalangeal (MP) joint instability Poorly developed thenar muscles
IIB 2A plus bi-axial/global MP joint instability and/or extrinsic anomalies
IIC 2B plus inadequate Carpometacarpal (CMC) joint
IIIA
Aplasia proximal 1/3 thumb MC (absent CMC joint) Severe underdevelopment Unstable Extensive intrinsic and extrinsic musculotendinous deficiencies
IIIB
3A with aplasia proximal 2/3 thumb Metacarpal (absent CMC joint)
IV Absent Metacarpal (Pouce flottant)
V Absent thumb