**Question:** Pen test is done for which nerve injury?

A. Radial nerve injury
B. Ulnar nerve injury
C. Median nerve injury
D. Scapular nerve injury

**Core Concept:** The pen test is a clinical test used to assess the integrity of the median nerve, specifically its sensory function. It is named after the pen, which is commonly used as a probe to palpate the sensory response.

**Why the Correct Answer is Right:** The correct answer is option C (median nerve injury) because the pen test involves testing the sensation to touch and pressure on the thenar eminence, which is supplied by the sensory branch of the median nerve. This test helps to differentiate between a true sensory deficit and a motor deficit in the setting of a suspected median nerve injury.

**Why Each Wrong Option is Incorrect:**

A. Radial nerve injury: The pen test is not relevant for radial nerve injury because the radial nerve has separate sensory distribution in the forearm and hand.
B. Ulnar nerve injury: The pen test is not relevant for ulnar nerve injury as the ulnar nerve has separate sensory distribution in the hand.
D. Scapular nerve injury: The pen test is not relevant for scapular nerve injury as the scapular nerve is a sensory branch of the brachial plexus and is not directly related to the pen test.

**Clinical Pearl:** The pen test is a useful and simple clinical test to assess median nerve injury, particularly in cases where the patient presents with a suspected median nerve injury and preserved motor function. A negative result (no sensation to light touch) indicates a possible median nerve injury, while a positive result (sensation to light touch) suggests a normal median nerve function. This test should be combined with other neurological examinations and clinical findings to formulate a comprehensive evaluation of a suspected nerve injury.