A female presented with loss of extension of little and ring finger, hypothenar atrophy and metacarpophalangeal joint hyperextension. The nerve injured is?
**Core Concept**
The question tests the knowledge of the anatomy and function of the ulnar nerve, which is a branch of the brachial plexus. The ulnar nerve is responsible for innervating muscles in the forearm and hand, particularly those involved in finger extension and intrinsic hand muscle function.
**Why the Correct Answer is Right**
The symptoms described are characteristic of ulnar nerve damage, specifically at the level of the elbow. The loss of extension of the little and ring fingers is due to the ulnar nerve's innervation of the extensor digitorum minimi and the extensor digitorum muscle, which are responsible for finger extension. Hypothenar atrophy is a result of the ulnar nerve's innervation of the interosseous and lumbrical muscles of the hand. Metacarpophalangeal joint hyperextension is also consistent with ulnar nerve damage, as the ulnar nerve innervates the flexor digitorum profundus muscle, which helps in flexion of the fingers.
**Why Each Wrong Option is Incorrect**
**Option A:** The median nerve is primarily responsible for innervating the muscles of the anterior forearm and the thenar muscles of the thumb. It does not innervate the muscles responsible for finger extension or the intrinsic muscles of the hand.
**Option B:** The radial nerve is responsible for innervating the extensor muscles of the arm and forearm, but it does not innervate the intrinsic muscles of the hand or the flexor digitorum profundus muscle.
**Option C:** The musculocutaneous nerve primarily innervates the biceps brachii and brachialis muscles, which are responsible for elbow flexion, and does not innervate the muscles of the hand or forearm.
**Option D:** The axillary nerve primarily innervates the deltoid muscle and the teres minor muscle, which are involved in shoulder function, and does not innervate the muscles of the hand or forearm.
**Clinical Pearl / High-Yield Fact**
The ulnar nerve is commonly injured at the elbow, particularly at the cubital tunnel, where it passes through a narrow space in the medial epicondyle of the humerus. This area is prone to compression due to repetitive flexion and extension of the elbow, leading to ulnar nerve damage.
**Correct Answer:** C. The ulnar nerve is injured.