Relationship of the axillary nerve to the proximal screws of a flexible humeral nail system: An anatomic study

Objective: To investigate the risk of axillary nerve injury during placement of the proximal interlock and tension screws of the Synthes Titanium Flexible Humeral Nail System (Synthes, Paoli, PA). Design: Cadaver study. Main Outcome Measure: Anatomic relationships. Methods: A titanium flexible humeral nail was inserted in an antegrade manner in 10 fresh-frozen cadaver shoulders. Proximal interlock and tension screws were inserted. The axillary nerve was carefully exposed, and the distance from the center of the nerve to each screw was measured. Results: In 8 of 10 specimens, the nerve traversed the interval between the proximal interlock screw and the tension screw. The average distance from the axillary nerve to the closer of the two proximal screws was 2.6 mm. The proximal interlock screw transected the axillary nerve in one specimen. Conclusions: There is significant risk to the axillary nerve when inserting the proximal interlock screw and the tension screw of this flexible humeral nail system. We recommend blunt dissection through the deltoid, direct visualization of the lateral humeral cortex, and use of a soft tissue protection sleeve when predrilling and placing these screws.