Injury to the posterior interosseous nerve (deep branch of radial nerve) at the radial neck causes which specific pattern?

• A Complete wrist drop with loss of all wrist and finger extension and sensory loss over dorsum of hand
• B Weakness of triceps and wrist drop with sensory loss
• C Wrist drop with finger/thumb extension weakness, but wrist extension and triceps are spared and sensation is preserved ✓
• D Loss of finger extension only, with preserved wrist extension and sensory loss on thumb web space

Explanation

The posterior interosseous nerve (PIN) is a purely motor branch of the radial nerve arising at the radial neck after passing through the supinator. PIN injury spares: (1) triceps (supplied above, from main radial nerve in arm), (2) brachioradialis and extensor carpi radialis longus (supplied before PIN origin). The wrist may drift radially on extension (ECRL intact, ECU paralyzed). Finger and thumb extension (common and extensor digitorum, EDQ, EIP, APL, EPB, EPL) are lost. No sensory loss occurs because PIN is purely motor; cutaneous sensation from dorsum of hand is via superficial radial nerve.

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

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Written and medically reviewed by the StethoPrep medical team.