Causes / typical injury mechanism: Pediatric trigger thumb is a developmental deformity resulting from thickening and proliferation of the thumb flexor pollicis longus (FPL) tendon. This is in contrast to adult trigger finger, in which pathologic changes are found within the tendon pulley.

Classic history and presentation: Patients typically present to a pediatrician's office with a thumb that is held in flexion at the thumb interphalangeal (IP) joint. Triggering can occur early in the presentation before a flexion contracture develops. There is often a palpable nodule (Notta node) over the thumb A1 pulley, which lies at the level of the thumb metacarpophalangeal (MP) joint on the volar surface of the hand.

Prevalence: Thought to affect less than 0.05% of children, with one study reporting an incidence of 3.3 in 1000 children aged younger than 1 year.

• Age – Typically presents in children aged 1-4 years.
• Sex / gender – No sex predilection.

Pathophysiology: Thickening and synovial proliferation of the FPL tendon and size mismatch within the thumb A1 pulley lying over the thumb MP joint. A nodule may be observed in the flexor tendon sheath of the FPL at the A1 pulley.