Total interruption of the radial nerve at midarm produces specific findings on physical examination. The most complete description of the neurologic deficit includes:

C. Paralysis of the brachioradialis, extensor carpi radialis longus and brevis, extensor carpi ulnaris, thumb extensors, and metacarpophalangeal (MCP) joint extensors, and loss of cutaneous sensibility at the dorsal aspect of the thumb and index fingers.

DISCUSSION: The extensor carpi radialis, extensor carpi ulnaris, and thumb extensors are innervated by the radial nerve. Although finger MCP joint extension is performed by the extensor digitorum communis muscle, which is innervated by the radial nerve, the interphalangeal joints of the fingers are extended by the intrinsic muscles in the hand, which are innervated by the ulnar and median nerves. The extensor carpi radialis longus and brevis, the abductor pollicis longus, and the extensor pollicis longus and brevis are all innervated by the radial nerve. However, answer B is not complete because MCP joint extension of the fingers and radial sensory deficit are not included. The brachioradialis, extensor carpi radialis longus and brevis, extensor carpi ulnaris, thumb extensors, and finger MCP joint extensors are all innervated by the radial nerve. The superficial radial nerve provides sensibility to the dorsal aspect of thumb and index finger in the dorsal radial aspect of the hand. The extensor carpi radialis longus and brevis and thumb extensors are innervated by the radial nerve. The superficial radial nerve provides sensibility at the dorsal aspect of thumb and index. Not included in answer D is the extensor carpi ulnaris. It should be remembered that although the extensor ulnaris is on the ulnar aspect of the wrist and uses the term ulnaris, it is innervated not by the ulnar nerve but by the radial nerve and would not function with complete interruption of the radial nerve at midarm. In addition, despite the fact that the wrist flexor on the radial aspect of the wrist is termed the flexor carpi radialis, it is not innervated by the radial nerve. It is innervated by the median nerve. Therefore, it should not be included in this list.