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Landmarks and Measurements in the Treatment of Trigger Thumb
Ronak Patel, MD; Brian Chilelli, MD; Andre Ivy, MD; David Kalainov, MD; Northwestern University
Northwestern University - Feinberg School of Medicine, Chicago, IL, USA

Landmarks and Measurements in the Treatment of Trigger Thumb

Purpose:

The purpose of this study is to define hand surface landmarks and anatomic measurements that may be used to locate the thumb A1 pulley and the volar digital neurovascular structures in the treatment of trigger thumb.

Methods:

Twenty fresh frozen adult hands were studied. Four surface landmarks were highlighted: 1) the radial border of the index finger, 2) the ulnar border of the thumb, 3) the thumb interphalangeal joint flexion creases, and 4) the thumb metacarpophalangeal joint creases. The radial artery of each specimen was injected with red latex and the thumbs were dissected. A digital caliper was used to measure the relevant portions of the thumb flexor tendon sheath, and the positions of the volar digital neurovascular structures in relationship to the surface landmarks and the A1 pulley.

Results:

The longitudinal width of the A1 pulley measured 6 +- mm. The proximal margin of the A1 pulley was located within 3.2 mm of the most proximal metacarpophalangeal joint crease. The radial digital nerve was positioned immediately adjacent to the A1 pulley, whereas the ulnar digital nerve and both digital arteries were usually positioned at greater distances from this portion of the sheath. The ulnar digital nerve was located within 3.9 mm of intersecting lines drawn along the radial border of the index finger and the ulnar border of the thumb. Both digital nerves were situated a minimum of 1.5 mm from the skin surface at the level of the A1 pulley and the radial digital nerve coursed over the FPL tendon at an oblique angle 6.4 mm or less from the A1 pulley.

Conclusions:

Skin surface landmarks may be useful in mapping the locations of the thumb A1 pulley and the volar digital neurovascular structures. Awareness of the variable width of the A1 pulley, and the relationships between the volar neurovascular structures and the A1 pulley, may improve the safety and efficacy of trigger thumb treatment.


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