A patient has difficulty pinching a sheet of paper between the thumb and index finger, using a hyperextended thumb IP joint and flexed index MCP joint to compensate. There is complete absence of sensation over the palmar aspect of the affected digits, and the thenar muscles are not wasted. Which nerve is involved?

• A Anterior interosseous nerve ✓
• B Recurrent branch of the median nerve at the carpal tunnel
• C Ulnar nerve at Guyon's canal
• D Deep branch of the ulnar nerve

Explanation

The pinch posture described is Froment-like but the giveaway combination here is pure motor weakness of FPL, FDP to index and middle, and pronator quadratus with total sparing of sensation. The anterior interosseous nerve is a purely motor branch of the median nerve arising just below the elbow, so an AIN syndrome has no sensory loss, unlike any median lesion at or distal to the forearm. Recurrent median branch lesions spare the long flexors and produce thenar wasting.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.