Transverse Anatomic Landmarks for the A1 Pulley of the Thumb

Abstract

Triggering of the thumb is a common entity resulting in pain and disability. Operative management requires accurate knowledge of the pulley system for proper release of the A1 pulley. The purpose of this study was to predict the location of the A1 pulley with surface anatomic landmarks while avoiding injury to the neurovascular bundles and the critical oblique pulley. Thirteen fresh cadaveric thumbs were dissected while the volar digital creases of the thumb served as our potential anatomic landmarks for the A1 pulley. These included the distal crease and the two identifiable proximal creases. Measurements from the proximal edge of the A1 pulley to the surface landmarks were obtained. The pulley system was also inspected for variability, and the length of the A1 pulley was measured. Of the three volar creases in the thumb, the proximal-proximal crease (PPC) corresponded anatomically to the A1 pulley and demonstrated minimal variability compared to the other landmarks. It measured 0.10 ± 0.15cm distal to the proximal edge of the A1 pulley. The average length of the thumb A1 pulley measured 0.61 ± 0.17cm. Therefore, the distal edge of the A1 pulley is predicted to be located 0.51cm distal to the PPC. Hand surface landmarks can be used reliably to predict the location of the thumb A1 pulley, thus avoiding injury to adjacent structures such as the critical oblique pulley.