Back to the Anatomy Lab to Redefine the Pulley System of the Thumb: Is There an A0 Pulley?

Background: There are various anatomical descriptions of the pulley system of the fingers and thumb. The A0 pulley, often referred to as palmar aponeurosis of the fingers, is of keen interest, especially regarding surgical release of the A1 pulley for trigger finger; however, there has been no anatomical description of the A0 pulley in the thumb.

Methods: Twenty-four cadaveric thumbs were dissected to expose the entire pulley system. Each structure, including the A2, Aob, Av, A1 pulleys, and any proximal transverse elements, were cataloged.

Results: Three distinct transverse elements were identified proximal to the A1 pulley including: (1) the named ligament of Grapow; (2) the proximal commissural ligament and associated transverse fascial tissues; and (3) a definable A0, identified in 10/12 (83.3%) cadavers and 15/24 (62.5%) thumbs. Ten A0 pulleys occurred bilaterally, while 5 occurred unilaterally.

Conclusions: The presence of an A0 pulley in greater than 80% of the studied thumbs serves as an important anatomic finding that should be considered in surgical treatment. An additional finding of importance is that the pulley system anatomy demonstrated variability in laterality. Based on these anatomic findings, not only can the A0 pulley be defined as a unique anatomic structure of the thumb, but its repair also has implications for successful surgical treatment of thumb pulley system pathologies.