Changes in flexor pollicis longus tendon cross-sectional dimensions after A1 pulley release for paediatric trigger thumb

In this study, 30 patients with unilateral paediatric trigger thumb were examined with measurements taken within 1 month before surgery, and at 3 months after surgery. We measured the dorsal-palmar (DP) diameter, radioulnar (RU) diameter and cross-sectional area (CSA) of the flexor pollicis longus (FPL) tendon at two sites: just proximal to the A1 pulley and underneath the A1 pulley using ultrasonography. Following surgical A1 pulley release, the DP diameter, RU diameter and CSA of the FPL tendon just proximal to the A1 pulley significantly decreased from 2.6 mm to 2.2 mm, from 5.1 mm to 4.2 mm and from 11 mm2 to 7.8 mm2, respectively. Additionally, the RU diameter and CSA of the FPL tendon at the area beneath the A1 pulley significantly increased from 2.2 mm to 3.2 mm and from 4.3 mm2 to 5.8 mm2, respectively. This finding suggests that the conformation of the FPL tendon of the affected thumb tends to return to that of the contralateral uninvolved thumb after A1 pulley release. Underdevelopment of the inner space around the A1 pulley may contribute to the development of paediatric trigger thumb.Level of evidence: III.