A 45-year-old male arrived at the emergency depament with injuries to his left elbow after he fell in a bicycle race. Radiographic and MRI examinations show a fracture of the medial epicondyle and a torn ulnar nerve. Which of the following muscles would be most likely to be paralyzed?

**Core Concept**
The ulnar nerve is responsible for innervating several muscles in the forearm and hand, particularly those involved in wrist and finger flexion, as well as thumb opposition.

**Why the Correct Answer is Right**
The ulnar nerve innervates the flexor carpi ulnaris (FCU) and the flexor digitorum profundus (FDP) to the little and ring fingers. The FCU is responsible for wrist flexion and ulnar deviation, while the FDP is involved in finger flexion. The ulnar nerve also innervates the adductor pollicis, which contributes to thumb opposition. In the case of a torn ulnar nerve, these muscles would likely be paralyzed, resulting in weakness or inability to perform these functions.

**Why Each Wrong Option is Incorrect**
**Option A:** Brachialis - This muscle is primarily innervated by the musculocutaneous nerve, not the ulnar nerve.
**Option B:** Extensor carpi radialis brevis - This muscle is primarily innervated by the radial nerve, not the ulnar nerve.
**Option C:** Pronator teres - This muscle is primarily innervated by the median nerve, not the ulnar nerve.
**Option D:** Flexor pollicis longus - This muscle is primarily innervated by the anterior interosseous branch of the median nerve, not the ulnar nerve.

**Clinical Pearl / High-Yield Fact**
The ulnar nerve is commonly injured at the elbow, particularly at the cubital tunnel, where it can be compressed or stretched, leading to symptoms such as numbness, tingling, and weakness in the hand.

**Correct Answer:** D. Flexor pollicis longus

✓ Correct Answer: D. Flexor carpi ulnaris