A patient with a posterior interosseous nerve (PIN) palsy will have which clinical pattern?

• A Wrist drop with inability to extend wrist, fingers, and thumb
• B Finger drop (MCP extension loss) with preserved wrist extension (radial deviation on extension) ✓
• C Loss of thumb opposition and abduction with sensory loss over thenar eminence
• D Clawing of ring and little fingers with sensory loss over ulnar 1.5 digits

Explanation

The posterior interosseous nerve (deep branch of radial nerve) is a pure motor nerve supplying the extensor compartment muscles distal to the extensor carpi radialis longus (ECRL). PIN palsy causes: inability to extend fingers and thumb at MCP joints (extensor digitorum, EIP, EPL, APL involvement), but WRIST EXTENSION IS PRESERVED (ECRL is innervated proximal to PIN entry). Wrist extension is radially deviated because ECRL acts without its ulnar counterpart extensor carpi ulnaris. Sensory loss is absent (PIN = deep/motor branch only). Classic radial nerve palsy (above PIN) causes wrist drop.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.