A patient has weakness of the intrinsic hand muscles on both the ulnar and median nerve distributions, with sparing of the thenar muscles. The injury is most likely at which level?

• A Median nerve at the wrist (carpal tunnel syndrome)
• B Posterior cord of the brachial plexus
• C Ulnar nerve at the cubital tunnel
• D Lower trunk or medial cord of the brachial plexus (C8-T1) ✓

Explanation

Intrinsic hand muscles (lumbricals 3-4, interossei, hypothenar muscles) are supplied by the ulnar nerve (C8-T1). The thenar muscles (opponens, abductor pollicis brevis, flexor pollicis brevis-superficial head) receive median nerve supply (C8-T1 via recurrent branch), and the first two lumbricals receive median nerve supply. If all intrinsic muscles including median-supplied lumbricals 1-2 but excluding thenar muscles are weak, the lesion must be proximal — at the C8-T1 level (lower trunk or medial cord) — where the fibres that will eventually form both the ulnar nerve and the median nerve's contribution to hand intrinsics travel together, while the thenar recurrent branch territory may be variably spared by the level of lesion.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.