Congenital stenosing tenosynovitis of the thumb is a result of a discrepancy between the size of the flexor pollicis longus tendon and the A1 pulley of the thumb's flexor tendon sheath. It may not be appreciated at birth due to the tendency to flex all digits. Both sides are involved in approximately 30% of children. There is an inability to extend the thumb interphalangeal joint fully and a nodule may be felt at the level of the metacarpophalangeal joint - Notta's node. The interphalangeal joint may be fixed in flexion or may still be mobile. Passive manipulation of the thumb into extension may be associated with a sudden release as the site of tendon thickening instantaneously escapes from the edge of the pulley.