Fracture of the surgical neck of the humerus commonly injures which nerve?

• A. Radial nerve
• B. Axillary nerve
• C. Median nerve
• D. Ulnar nerve

Answer: (B)

Fracture at the surgical neck of the humerus commonly injures the axillary nerve because this nerve courses closely around the surgical neck in the deltoid region, passing through the quadrangular space to reach the shoulder. It supplies the deltoid and teres minor and provides sensation over the lateral aspect of the shoulder (the regimental badge area). When injured, the deltoid muscle weakens or is paralyzed, leading to diminished ability to abduct the arm beyond the initial few degrees (initial abduction is mainly by supraspinatus). Sensory loss over the lateral shoulder may also be present.

The radial nerve is more at risk with fractures of the midshaft of the humerus, where it runs in the radial groove. Median and ulnar nerves are located more medially and are not typically affected by a fracture at the surgical neck unless there is a broader plexus injury or dislocation.