- complete when the fingers are fused all the way to the tip, including the nail folds
- incomplete when the nail folds are not involved
- simple when the fingers are fused by a skin bridge
- complex when the bones are fused together
- Mild constriction ring is often asymptomatic.
- Moderate constriction ring causes lymphedema distal to the ring.
- Severe constriction ring blocks circulation of the arterial and venous system and causes nerve palsy resulting from nerve compression.
I : bifid distal phalanx (DP)(bone under the finger nail)
II: duplicated DP
III: bifid proximal phalanx (PP) (digit bone nearest the palm)
IV: most common type with duplication of proximal phalanx which rest on broad metacarpal
V: bifid metacarpal (MC) (bone in palm)
VI: duplicated MC
A prospective investigation of 1166 neonates showed no trigger thumb at birth, but two cases were observed at a 1-year follow-up. Several other studies have also supported the opinion that childhood trigger thumb is an acquired rather than congenital condition. However, cases of trigger thumb associated with trisomy 13 (Patau syndrome), fraternal twins, and families with generational occurrence indicate that there may be a heritable component in certain patient populations.
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