Changes in the flexor pollicis longus tendon during spontaneous resolution of pediatric trigger thumb

Area of Science:

• Orthopedics
• Pediatric Surgery
• Musculoskeletal Imaging

Background:

• Pediatric trigger thumb (PTT) is a common condition affecting thumb function.
• Spontaneous resolution of PTT is observed, but the underlying biomechanical changes are not fully understood.
• Understanding these changes can inform non-surgical management strategies.

Purpose of the Study:

• To evaluate conformational changes in the flexor pollicis longus (FPL) tendon and A1 pulley during PTT resolution.
• To compare these changes with the contralateral normal thumb.
• To investigate the relationship between these changes and improvement in thumb interphalangeal (IP) joint extension lag.

Main Methods:

• Ultrasonography was performed on 36 patients with unilateral PTT before and after spontaneous resolution (>10° improvement in IP joint extension lag).
• Measurements included anteroposterior (AP) and radioulnar (RU) diameters of the FPL tendon proximal to the A1 pulley and the inner space of the A1 pulley.
• Comparison was made between the affected and contralateral normal thumbs.

Main Results:

• Significant improvement in thumb IP joint extension lag was observed (35.6° to 14.2°).
• On the PTT side, the FPL tendon showed minimal diameter increase (AP 0.3%, RU 1.9%), while the A1 pulley inner space enlarged significantly (AP 15.3%, RU 5.0%).
• The contralateral normal thumb showed greater FPL tendon diameter increases (AP 12%, RU 9.3%) and moderate A1 pulley space enlargement (AP 9.9%, RU 4.6%).

Conclusions:

• Spontaneous resolution of PTT is associated with reduced mismatch between the FPL tendon and A1 pulley space due to asymmetric growth.
• The A1 pulley space demonstrates greater relative expansion compared to the FPL tendon during PTT resolution.
• These findings highlight the dynamic biomechanical adaptations occurring during PTT recovery.