Hand surface landmarks and measurements in the treatment of trigger thumb

To determine hand surface landmarks and measurements that may be useful in localizing the A1 pulley and digital neurovascular structures in the treatment of trigger thumb.

We highlighted 4 surface landmarks in 20 adult cadaveric hands: the radial border of the index finger, the ulnar border of the thumb, the thumb interphalangeal joint flexion creases, and the thumb metacarpophalangeal joint creases. We injected the radial arteries with red latex and dissected the thumbs.

The proximal margin of the A1 pulley was located an average of 0.3 mm proximal (range, 3.2 mm proximal to 2.3 mm distal) to the most proximal metacarpophalangeal joint flexion crease. The ratio of measurements from the thumb tip to the midpoint of the interphalangeal joint flexion creases and from this point to the proximal margin of the A1 pulley averaged 1.1:1. The radial digital nerve crossed obliquely over the flexor pollicis longus tendon and approached the proximal margin of the A1 pulley at a mean distance of 2.7 mm (range, 0-12.9 mm). The ulnar digital nerve was located deep to intersecting lines drawn along the radial border of the index finger and the ulnar border of the thumb and coursed parallel to the A1 pulley at a mean distance of 5.4 mm (range, 0-11.1 mm). At the level of the A1 pulley, the digital arteries were positioned dorsal to the digital nerves, and both nerves were located 1.0 to 4.2 mm from the skin surface.

The findings from our study clarify hand surface landmarks in localizing the thumb A1 pulley and digital neurovascular structures.

Awareness of topographical landmarks in localizing the A1 pulley and digital neurovascular structures and the relationships between the digital neurovascular structures and the A1 pulley may improve the safety and efficacy of trigger thumb treatment.