The Relationship of Proximal Locking Screws to the Axillary Nerve During Antegrade Humeral Nail Insertion of Four Commercially Available Implants

Abstract

The purpose of this study was to determine the proximity of proximal interlocking mechanisms in 4 current antegrade humeral nails to the axillary nerve and its branches. Cadaveric study. Anatomy laboratory. Anatomic relationships. Four humeral nail designs (labeled SS, SL, SZ, and SN) were each inserted in successive antegrade fashion in 10 cadaveric upper extremity specimens. Three variables were measured: from acromion to the axillary nerve, from acromion to entry sites of proximal locking devices, and from locking devices to axillary nerves and their branches. In nail SS, the proximally directed oblique locking screw came into contact with the ascending branch of the axillary nerve in 6 of 10 specimens. Mean distance from spiral blades in nails SS and SL were 26 mm to the axillary nerve and 16 mm to its ascending branch. Interlocking screws for nails SZ, SN, and SL did not violate the axillary nerve or its branches in any specimen. Mean distance from lateral acromion to the axillary nerve measured 58.7 mm. Nail SS's oblique locking screw may injure the ascending branch of the axillary nerve. Three of the 4 nails tested did not endanger the axillary nerve. However, when transverse proximal locking screws are inserted from a lateral-to-medial direction, they may endanger an arborized axillary nerve. Blunt dissection should be performed with a visible path to bone before instrumentation to reduce the risk of axillary nerve injury.