A patient presents with hypothenar muscle wasting and loss of sensation of medial one and a half digits. Which nerve is involved?
## **Core Concept**
The question tests knowledge of peripheral nerve anatomy and its correlation with clinical presentation. Specifically, it involves identifying a nerve responsible for motor supply to the hypothenar muscles and sensory innervation to the medial one and a half digits of the hand. The **ulnar nerve** is primarily responsible for these functions.
## **Why the Correct Answer is Right**
The correct answer, **Ulnar Nerve (C)**, is right because it supplies the hypothenar muscles (opponens digiti minimi, abductor digiti minimi, and flexor digiti minimi brevis) and provides sensory innervation to the little finger and the medial half of the ring finger. This matches the clinical presentation given: hypothenar muscle wasting and loss of sensation over the medial one and a half digits.
## **Why Each Wrong Option is Incorrect**
- **Option A:** The **Median Nerve** primarily supplies the thenar muscles and provides sensory innervation to the lateral three and a half digits (thumb, index, middle finger, and the lateral half of the ring finger). This does not match the clinical presentation.
- **Option B:** The **Radial Nerve** mainly supplies the muscles of the posterior arm, forearm, and hand (extensor muscles) and provides sensory innervation to the back of the arm, forearm, and the dorsum of the hand (except the medial one and a half fingers). This also does not match.
- **Option D:** The **Anterior Interosseous Nerve**, a branch of the median nerve, primarily provides motor innervation to some deep muscles of the forearm (flexor pollicis longus, pronator quadratus, and the radial half of flexor digitorum profundus) without any sensory function. This does not correlate with the symptoms described.
## **Clinical Pearl / High-Yield Fact**
A key clinical correlation to remember is that the **ulnar nerve** runs through Guyon's canal at the wrist. Compression here can lead to symptoms similar to those described, known as ulnar neuropathy or "funny bone" neuropathy. A classic presentation includes wasting of the hypothenar eminence and sensory loss over the little finger and the medial half of the ring finger.
## **Correct Answer: C. Ulnar Nerve**