Question

Later when you see the patient it is clear that he has pronounced neurological deficits. There is lack of cutaneous sensation between his thumb and index finger on the dorsal side, diminished sensation on the dorsal surface of the forearm, arm, and lateral side of the shoulder. He has "wrist drop" (inability to extend the wrist), lack of extension at the elbow, and although abduction can be initiated, it cannot be completed. Flexion, extension, medial and lateral rotation of the arm are not significantly affected. There is no "winging of the scapula." Later exploration by a neurosurgeon reveals that a single large nerve bundle posterior to the artery was also severed, accounting for the neurological findings

The large nerve bundle lying posterior to the artery which was also severed was the:
A. C 7 root
B. middle trunk
C. posterior cord
D. posterior division
E. radial nerve

Answer 1

The most likely severed nerve accounting for the described neurological deficits, including 'wrist drop' and lack of sensation in specific hand and arm regions, is the radial nerve.

Step-by-step explanation:

The patient presents with neurological deficits, including lack of cutaneous sensation between the thumb and index finger on the dorsal side, diminished sensation on the dorsal surface of the forearm, arm, and lateral side of the shoulder, as well as "wrist drop" which is an inability to extend the wrist, and lack of extension at the elbow. These symptoms are typically associated with damage to a nerve that innervates these regions. Given the information provided, the nerve that was severed is most likely the radial nerve. The radial nerve is responsible for extending the wrist and fingers, and for providing sensation to the posterior aspect of the forearm and the dorsolateral aspect of the hand. As there is no "winging of the scapula," this suggests that the serratus anterior, which is innervated by the long thoracic nerve, is intact. Consequently, the neurological findings do not correspond with a lesion in the brachial plexus components such as the C7 root, middle trunk, posterior cord, or posterior division.