FCPS part 1 Medicine solved mcqs with explanation Q22

A patient has fracture of surgical neck of humerus. Now he cannot raise his arm above his shoulder and also has sensory loss on lateral surface of arm. Which of the following nerves is damaged?

a) Musculocutaneous nerve

b) Axillary nerve

c) Radial nerve

d) Ulnar nerve

Correct Answer: b

Explanation:

The Axillary Nerve comes off the posterior cord of brachial plexus and has a root value of C5 & C6. During its course it is accompanied by the posterior circumflex humeral artery and vein.

Motor Supply: Deltoid muscle (abductor at the shoulder joint), Teres Minor muscle

Sensory Supply: Skin over the lower half of deltoid muscle, shoulder joint

The nerve most commonly damaged due to fracture of surgical neck of humerus is the Axillary nerve. It is a very commonly tested nerve. Commit it to memory. It supplies the major abductor (unable to raise the arm above the head) of the arm – Deltoid muscle. Also there is loss of sensation from the lower half of skin covering the deltoid (lateral aspect of arm).