Which nerve is most commonly injured with a midshaft humeral fracture?

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

Answer: (B)

The key idea is that the radial nerve is most at risk when the humerus is fractured in the midshaft because it runs in the radial groove along the posterior aspect of the shaft there. When the fracture disrupts the nerve, the patient often cannot extend the wrist or fingers, producing a wrist drop, and may have sensory loss on the dorsoradial hand and the proximal dorsal forearm. The nerve’s intimate course at the midshaft explains why it’s the most commonly injured in this location. In contrast, different fracture sites are more likely to injure other nerves: the axillary nerve with injuries near the shoulder, the median nerve with injuries closer to the elbow or distal humerus, and the ulnar nerve with medial elbow injuries.