Pediatric trigger thumb is caused by a mismatch between the flexor pollicis longus tendon and its sheath. Patients present with a hard, palpable nodule (Notta's node) at the base of the metacarpal and an inability to extend the thumb beyond 30 degrees, which can rarely be accompanied by triggering, snapping, or a digit locked in extension (summary by Wang et al., 2012). [from
OMIM]