**Holstein Lewis Sign:** This sign is associated with the ulnar nerve, particularly when it is compressed or irritated in the cubital tunnel.

**Core Concept:** Holstein-Lewis sign is a clinical test used to assess the integrity of the ulnar nerve. It is named after its discoverers, Sir William Holstein and Sir Reginald Lewis.

**Why the Correct Answer is Right:** The correct answer, C, represents the ulnar nerve, which is responsible for various functions, including sensation and motor control in the medial aspect of the hand, pinky finger, and part of the ring finger. The cubital tunnel is a bony tunnel formed by the medial epicondyle of the humerus and the coronoid process of the ulna. When the ulnar nerve becomes compressed or irritated in this tunnel, it can lead to symptoms such as pain, numbness, and weakness in the hand.

**Why Each Wrong Option is Incorrect:** A. The radial nerve is responsible for motor control of the thumb and forearm, not the ulnar nerve. B. The median nerve is responsible for motor control of the thumb and index finger, not the ulnar nerve. D. The posterior tibial nerve is responsible for motor control of the ankle and foot, not the ulnar nerve.

**Clinical Pearl:** To properly perform the Holstein-Lewis sign, the examiner gently applies pressure to the wrist over the cubital fossa while the patient holds their elbow flexed at a 90-degree angle and the hand in a neutral position. A positive sign would indicate compression or irritation of the ulnar nerve at the cubital tunnel, necessitating further evaluation and management.

**Correct Answer:** C. ulnar nerve