**Question:** A patient came with history of fall and on examination there was tenderness between the extensor pollicis longus and brevis. The likely lesion is

A. Radial nerve injury
B. Ulnar nerve injury
C. Extensor digitorum tendon injury
D. Displaced fracture of the radius

**Correct Answer:**.

**Core Concept:**
The extensor pollicis longus (EPL) and brevis (EPLB) are two muscles in the forearm that extend the thumb. They are innervated by the radial nerve, which is a branch of the brachial plexus. The radial nerve emerges from the brachial plexus and travels through the lateral intermuscular septum to supply motor innervation to the muscles of the forearm, including EPL and EPLB.

**Why the Correct Answer is Right:**
In this case, the patient presents with tenderness between the EPL and EPLB, indicating possible damage to the radial nerve. This nerve is responsible for the innervation of these muscles, leading to the characteristic symptoms and signs of radial nerve injury.

**Why Each Wrong Option is Incorrect:**
A. Radial nerve injury (option A) is possible, but the correct answer focuses on the location of the lesion in relation to the EPL and EPLB.
B. Ulnar nerve injury (option B) would result in sensory changes, not motor deficits and tenderness in the radial nerve territory.
C. Extensor digitorum tendon injury (option C) is incorrect as the radial nerve supplies both EPL and EPLB, not the extensor digitorum tendon.
D. Displaced fracture of the radius (option D) is a possible consequence of radial nerve injury, but the correct answer focuses on the location of the lesion and its effects on the EPL and EPLB.

**Clinical Pearl:**
In cases where patients present with tenderness between EPL and EPLB, a radial nerve lesion should be considered. This can result from trauma, inflammation, or compression mechanisms, such as in tennis elbow or Guyon's canal syndrome. Clinical examination, including the presence of muscle weakness or atrophy in the radial nerve territory, is crucial in differentiating between radial and ulnar nerve injuries.