**Core Concept**
The deep radial nerve, a branch of the radial nerve, is susceptible to compression at the level of the supinator muscle, leading to radial tunnel syndrome or radial neuropathy. This condition is characterized by pain and weakness in the forearm, particularly on the posterior aspect, due to impaired nerve function.

**Why the Correct Answer is Right**
The deep radial nerve, also known as the posterior interosseous nerve (PIN), is compressed by the supinator muscle as it passes through the radial tunnel. This compression leads to radial neuropathy, which presents with pain, weakness, and paresthesias in the forearm. The location of the pain, 2 cm distal to and posteromedial to the lateral epicondyle, is consistent with radial tunnel syndrome. The supinator muscle is a common site for nerve compression, and steroid injections and rest are often recommended to alleviate symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** Compression of the median nerve by the pronator teres typically presents with symptoms in the palmar aspect of the hand, such as thenar weakness and numbness, rather than pain in the posterior forearm.

**Option B:** Compression of the median nerve by the flexor digitorum superficialis would also present with palmar hand symptoms, such as thumb weakness and numbness.

**Option C:** Compression of the superficial radial nerve by the brachioradialis would typically cause symptoms on the radial aspect of the forearm and hand, rather than the posterior aspect.

**Clinical Pearl / High-Yield Fact**
Radial tunnel syndrome or radial neuropathy can be challenging to diagnose, as the symptoms may be subtle and similar to those of lateral epicondylitis (tennis elbow). A thorough history and physical examination, including palpation of the radial tunnel, are essential for accurate diagnosis.

**✓ Correct Answer: D. Compression of the deep radial nerve by the supinator**