In a mid-shaft humerus fracture, which nerve is most commonly injured and what deficits would you expect?

• A. Median nerve with ape hand.
• B. Ulnar nerve with claw hand.
• C. Radial nerve with wrist drop and sensory loss on the dorsum of the hand.
• D. Axillary nerve with deltoid weakness and loss of arm abduction.

Answer: (C)

In a mid-shaft humerus fracture, the radial nerve is the nerve most likely to be injured because it runs in the radial groove along the posterior aspect of the humerus, making it vulnerable to trauma at that level.

The typical deficits are wrist drop from paralysis of the extensor muscles of the wrist and fingers (extensor carpi radialis longus/brevis and finger extensors), and sensory loss over the dorsum of the hand supplied by the superficial branch of the radial nerve. Elbow extension is often preserved because the triceps receives innervation before this point in the nerve’s course. This pattern differentiates it from injuries to other nerves in different fracture locations, where you’d see ape hand (median nerve), claw hand (ulnar nerve), or deltoid weakness with loss of arm abduction (axillary nerve).