Radial nerve entrapment at the radial tunnel (radial tunnel syndrome / posterior interosseous nerve syndrome) causes weakness of which specific muscles without sensory loss?

• A Triceps and brachioradialis
• B Extensor carpi ulnaris, extensor digitorum, and supinator; sparing brachioradialis and extensor carpi radialis longus ✓
• C Extensor carpi radialis longus and brachioradialis
• D All wrist and finger extensors including extensor carpi radialis longus

Explanation

The posterior interosseous nerve (PIN) is the purely motor deep branch of the radial nerve that passes through the supinator via the arcade of Frohse. Entrapment here spares brachioradialis and extensor carpi radialis longus (which branch from the radial nerve proximal to the arcade), but weakens supinator, extensor carpi ulnaris, extensor digitorum, extensor digiti minimi, extensor pollicis longus/brevis, abductor pollicis longus, and extensor indicis. Wrist extension is asymmetric (radially deviated due to intact ECRL). There is no sensory deficit because the PIN is purely motor; this distinguishes it from a high radial nerve lesion.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.