Which nerve injury is associated with a midshaft humerus fracture?

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

Answer: (D)

The main idea is that the radial nerve runs along the posterior humerus in the spiral (radial) groove, which makes midshaft fractures particularly likely to injure it. When the radial nerve is damaged at this level, the extensor muscles of the forearm lose their innervation, so you get weakness or loss of wrist and finger extension, commonly presenting as a wrist drop. Sensory loss is usually on the dorsal aspect of the hand and posterior forearm where the radial nerve provides sensation. Elbow extension is often preserved because the nerve branches to the triceps are given proximally, before this injury site, so the midshaft fracture typically spares triceps function. This pattern distinguishes midshaft injuries from nerve injuries tied to other fracture locations, such as the axillary nerve with proximal humeral or shoulder injuries, or median and ulnar nerve injuries associated with injuries toward the elbow or forearm.