The dorsal cutaneous branch of the ulnar nerve divides from the main ulnar nerve proximal to the wrist and passes subcutaneously around the ulnar aspect of the wrist to supply the dorsal hand and fingers. Because it divides proximal to Guyon canal, its sensation is preserved in wrist-level ulnar nerve compression. The presence of dorsal ulnar sensory loss indicates an ulnar nerve lesion proximal to the wrist (cubital tunnel level).
| Origin | Ulnar nerve 5 to 6 cm proximal to the wrist, posterior to the FCU |
|---|---|
| Course | Passes dorsally deep to flexor carpi ulnaris, pierces the deep fascia and winds around the ulnar border of the wrist over the ulnar head to supply the dorsal ulnar hand and the dorsal ring and little fingers to the PIP joint |
| Sensory |
|
Testing dorsal ulnar hand sensation helps localise ulnar nerve lesions: intact dorsal sensation with palmar numbness of the ring and little fingers points to Guyon canal, while numbness on both surfaces points to the elbow or higher. The branch crosses the ulnar side of the wrist close to the ulnar head and styloid, so it is at risk in ulnar styloid fractures, distal ulna resection, TFCC repair and other ulnar-sided wrist incisions. Injury causes dorsal ulnar hand numbness and can leave a painful neuroma.
Preserved dorsal ulnar sensation with palmar numbness localises ulnar neuropathy to Guyon canal rather than the cubital tunnel at the elbow.
Incisions for TFCC repair or distal radioulnar joint procedures can cut the branch as it crosses over the ulnar head, causing dorsal ulnar hand numbness and a painful neuroma.
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