A 35-year-old carpenter presents with inability to abduct the thumb and weakness of pinch grip. Nerve conduction studies confirm a thenar branch lesion of the median nerve at the wrist. The motor branch supplying the thenar muscles arises from the median nerve in its most common anatomical variant at:

• A Proximal to the wrist crease in the distal forearm
• B Transligamentous, piercing the flexor retinaculum
• C Subligamentous, looping beneath the distal edge of the retinaculum
• D Within the carpal tunnel, arising from the radial side of the median nerve in an extraligamentous position (most common variant — 46%) ✓

Explanation

The recurrent (thenar) motor branch of the median nerve most commonly arises extraligamentously just distal to the flexor retinaculum on its radial side (approximately 46% of cadaveric studies), then loops back (recurs) to supply the thenar muscles (abductor pollicis brevis, opponens pollicis, superficial head flexor pollicis brevis). Other variants include subligamentous (31%) and transligamentous (23%) origins; these variants are critical during carpal tunnel release to avoid inadvertent division of the motor branch. Surgeons always extend the skin incision radially and avoid lateral dissection at the distal tunnel to protect this branch.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.