A 45-year-old man presents with inability to flex the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger, with a positive pinch attitude when attempting to make an OK sign. Sensory testing over the hand is completely normal. The lesion is in the:

• A Median nerve at the carpal tunnel
• B Median nerve in the forearm between the two heads of pronator teres
• C Ulnar nerve at Guyon canal
• D Anterior interosseous nerve ✓

Explanation

The anterior interosseous nerve is a purely motor branch of the median nerve supplying FPL, FDP to index and middle fingers, and pronator quadratus. Its compression produces the characteristic pinch attitude with normal sensation, because the cutaneous branches leave proximal to its origin. Carpal tunnel and pronator teres syndromes both cause thenar wasting and sensory loss in the lateral three and a half digits, which are absent here.

Reference: Campbell's Operative Orthopaedics, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.