A 16 year-old boy fell from a motorcycle, and his radial nerve was severely damaged because of a fracture of the midshaft of the humerus. Which of the following conditions would most likely result from this accident?
A. Loss of wrist extension leading to wrist drop
B. Weakness in pronating the forearm
C. Sensory loss over the ventral aspect of the base of the thumb
D. Inability to oppose the thumb
E. Inability to abduct the fingers

A. Loss of wrist extension leading to wrist drop.

Explanation:

An injury to the radial nerve always results in loss of wrist extension, that usually leads to to wrist drop. This is because the median nerve innervates the pronator teres, pronator quadratus, and opponens pollicis muscles and also the skin over the ventral aspect of the thumb.

The ulnar nerve innervates the

dorsal interosseous muscles, which act to abduct the fingers.

So any injury at the radial nerves will make the it hard or impossible for the wrist to extend and it will make the wrist to drop.