Varied Anatomy of the Thumb Pulley System: Implications for Successful Trigger Thumb Release

Abstract

The anatomical arrangement of the thumb pulley system continues to be revised through ongoing investigative research, changing our previous assumptions. This study demonstrates the components and anatomical features of this pulley system in an effort to improve surgical outcomes and to clarify current misconceptions. Researchers procured 75 hand specimens from 41 adult cadavers through our institution's anatomical donations program. Dissections of the thumb and thenar compartment identified the various pulleys. A detailed analysis of the thumb pulleys was performed through various measurements. Four different pulley categories were identified: type I (n = 5), type II (n = 29), type III (n = 29), and type IV (n = 12). The variable annular pulley was present in 70 of 75 hands (93%) in 1 of 3 arrangements: transverse, oblique, or fused with the A1 pulley. The pulley system of the thumb is composed of 4 components, as opposed to the traditional view of only 3. Along with the A1 pulley, the additional variable annular pulley might contribute to stenosis in trigger thumb. This might necessitate a more extensive surgical incision and its partial release to relieve triggering. Understanding the anatomical configuration of the thumb pulley system will aid in the surgical attempt to resolve triggering while avoiding complications such as bowstringing of the flexor pollicis longus tendon and iatrogenic nerve injury.