Midshaft humerus fracture injures which nerve?

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

Answer: (C)

Midshaft humerus fractures commonly injure the radial nerve because this nerve travels in the radial groove along the posterior aspect of the humerus at the midshaft, running closely with the bone. When the humerus is fractured here, the radial nerve can be damaged directly, leading to loss of extension in the wrist and fingers (a wrist drop) due to impaired motor innervation to the extensor muscles. Sensation is also affected on the posterior forearm and the dorsum of the hand (and dorsal aspect of the lateral three-and-a-half digits) because the radial nerve provides cutaneous branches there. The other nerves are less likely at this level: the axillary nerve is around the surgical neck, the median nerve travels anteriorly in the arm and is more at risk with different fracture patterns, and the ulnar nerve runs medially near the elbow. Thus, the radial nerve is the one most at risk with a midshaft humeral fracture.