NEET PG Medical 2014

Question 6

A 27-year-old woman is involved in a motorcycle collision. She landed on her right shoulder, causing a forceful lateral extension of her head and neck. At this point, she is unable to abduct, laterally rotate, and flex the shoulder. Which injury is the most likely cause of these deficits?

• Avulsion-separation of the roots of spinal nerves C5 to C6
• Avulsion-separation of the roots of spinal nerves C8 to T1
• Injury to the medial cord of the brachial plexus
• Injury to the posterior cord of the brachial plexus
• Interruption of the C7 spinal nerve

The physical problems observed in this patient suggest an injury to more than a single nerve because no single muscle or group of muscles could cause the described deficits. In addition, the type of injury, the head and neck being forcefully pulled away from the shoulder, puts significant strain on the upper portion of the brachial plexus. Furthermore, spinal cord segments C5 and C6 innervate muscles that act on the shoulder joint. Thus, the classic result of the mechanism of injury described in this case and the resulting deficits is an avulsion-separation of the roots of spinal nerves C5 to C6.

Question 7

A 72-year-old man comes to his physician's office for his regular yearly examination. He has difficulty abducting his arm and extending his elbow and wrist. Which nervous structure is most likely injured?

• Axillary
• Lateral cord of the brachial plexus
• Posterior cord of the brachial plexus
• Radial
• Suprascapular

Loss of extension at the elbow and wrist indicates an injury to the radial nerve. However, the radial nerve is not involved in abduction of the arm. The axillary nerve is primarily responsible for abduction of the arm. Thus, the injury has to be to the part of the brachial plexus that gives rise to the axillary and radial nerves, which is the posterior cord of the brachial plexus, answer 3.

Question 8

A 32-year-old woman suffers a deep knife wound to her palm. Assuming a nerve has been severed, which of the following movements will be lost?

• Abduction of the first digit
• Adduction of the fourth digit
• Extension of the first digit
• Flexion of the distal interphalangeal joint
• Flexion of the wrist

The injury is to a nerve in the hand, and the actions described in answers 3, 4, and 5 are all accomplished by muscles coming into the hand from the forearm. Similarly, two muscles, one in the posterior compartment of the forearm and one in the thenar eminence accomplish abduction of the first digit. Although the muscle in the thenar eminence could have lost its nerve supply by this injury, the ability to abduct the first digit would not have been lost because the muscle in the forearm was not injured. The only action completely lost because of this injury would be adduction of the fourth digit, resulting from the deep branch of the ulnar nerve being cut.

Question 9

A 64-year-old man has clawing of the left hand that involves the second through fifth digits. He is also unable to actively abduct or adduct these digits. Which nervous structure is most likely injured?

• Median nerve
• Posterior trunk of the brachial plexus
• Radial nerve
• Ulnar nerve
• Upper trunk of the brachial plexus

Clawing of the hand can be related to an injury to either the ulnar or median nerves. However, an inability to abduct and adduct the second through fifth digits can only be due to an injury to the ulnar nerve, answer 4.

Question 10

While trimming a tree, a 32-year-old woman falls and hyperabducts her arm when she grabs a tree limb to stop her fall. Which area is most likely to have lost sensation because of the violent abduction of her arm?

• Thenar eminence
• Posterior brachium
• Medial antebrachium
• Lateral antebrachium
• Anterior brachium

Violent abduction of the arm, as described in this injury, results in a stretching of the lower components of the brachial plexus. This can result in an avulsion injury of the lower roots, C8 and T1, of the plexus. Cutaneous innervation to the medial brachium (arm) and medial antebrachium (forearm) passes through nerves derived from this portion of the brachial plexus and a loss of sensation could occur in these two areas as a result of this injury.