A patient with an ulnar nerve lesion at the wrist within Guyon's canal has complete intrinsic motor loss and sensory loss on the palmar surfaces of the little and medial half of the ring finger. Sensation over the dorsum of the hand and the dorsal surfaces of these fingers is normal. Why is dorsal sensation preserved?

• A The dorsal cutaneous branch regenerates faster than motor fibres
• B The dorsal skin is supplied by the median nerve
• C The palmar cutaneous branch carries all dorsal fibres
• D The dorsal cutaneous branch arises proximal to the wrist and does not pass through Guyon's canal ✓

Explanation

The dorsal cutaneous branch of the ulnar nerve arises about 5 to 8 cm proximal to the wrist, passes superficial to the flexor carpi ulnaris and supplies the dorsum of the hand without entering Guyon's canal. D lesion confined to the canal therefore spares dorsal sensation while affecting the superficial sensory and deep motor branches within it. This finding clinically distinguishes an ulnar lesion at the wrist from one at the elbow, where dorsal sensation would be lost.

Reference: Gray's Anatomy for Students, 4th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.