In anterior interosseous nerve (AIN) syndrome, the patient is unable to make the 'OK sign'. Which specific muscles are paralysed?

• A Flexor pollicis longus and flexor digitorum profundus to the index finger (and pronator quadratus) ✓
• B Flexor digitorum superficialis and flexor pollicis longus
• C Abductor pollicis brevis and flexor pollicis longus
• D Pronator teres and flexor carpi radialis

Explanation

The AIN is a pure motor branch of the median nerve that arises just distal to the medial epicondyle. It supplies flexor pollicis longus (FPL), the radial half of flexor digitorum profundus (FDP) — to the index and middle fingers — and pronator quadratus. Paralysis of FPL and FDP to the index finger prevents terminal phalanx flexion at the thumb and index finger; patients cannot form a pinch/OK sign and instead form a 'pinch with extended distal phalanges'. Flexor digitorum superficialis, pronator teres, and flexor carpi radialis are all supplied by the main median nerve trunk above the AIN takeoff.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.