During a Kocher's approach to the elbow for lateral condyle fracture repair in a child, the surgeon inadvertently injures the posterior interosseous nerve (PIN). Which movements would be specifically lost?

• A Wrist extension at the radiocarpal joint and finger extension at MCP joints
• B Elbow flexion and forearm supination
• C Extension of thumb IP joint, finger MCP extension, radial deviation of wrist during extension ✓
• D Wrist flexion and pronation of forearm

Explanation

The PIN (deep branch of radial nerve) enters the radial tunnel and passes through the arcade of Frohse (supinator arch). It supplies all muscles in the posterior compartment of the forearm EXCEPT extensor carpi radialis longus (which is innervated proximal to PIN origin). PIN injury causes loss of finger MCP extension, thumb extension and abduction, and ulnar deviation of wrist during extension (because ECRL pulling the wrist radially is preserved but ECU is lost). Pure PIN injury spares wrist extension (via ECRL) so there is no complete wrist drop, which distinguishes PIN from complete radial nerve palsy.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.