Anatomy
- Terminal branch of the medial cord of the brachial plexus (C8, T1), often with a C7 contribution
- Pierces the medial intermuscular septum near the arcade of Struthers, about 8 cm above the medial epicondyle
- Passes behind the medial epicondyle in the cubital tunnel beneath Osborne ligament, then between the two heads of FCU
- Supplies FCU and FDP to the ring and little fingers in the forearm
- Dorsal cutaneous branch arises 5 to 8 cm above the wrist and supplies the dorsoulnar hand
- Enters the hand through Guyon canal, between the pisiform and the hook of hamate, and divides into superficial sensory and deep motor branches
- Deep branch supplies the hypothenar muscles, interossei, ulnar two lumbricals, adductor pollicis and deep head of FPB
Clinical Features
Low lesion
- Claw hand with MCP hyperextension and IP flexion of the ring and little fingers
- Intrinsic wasting, most visible in the first web space
- Froment sign, thumb IP flexion by FPL substituting for weak adductor pollicis
- Wartenberg sign, little finger abducted by EDM
- Sensory loss over the little finger and ulnar half of the ring finger
High lesion
- Adds weakness of FCU and FDP to the ring and little fingers
- Clawing is less marked than in a low lesion (ulnar paradox) because FDP is weak
- Sensory loss over the dorsoulnar hand from the dorsal cutaneous branch
- Paraesthesia worse with elbow flexion, with positive elbow flexion and Tinel tests
- See Cubital Tunnel Syndrome
Guyon canal syndrome
- Causes include ganglion, hook of hamate fracture, ulnar artery thrombosis (hypothenar hammer syndrome) and cycling
- Dorsal sensation is spared, which separates it from cubital tunnel syndrome
Investigations
- Nerve conduction studies localise the lesion and grade severity, with imaging for masses or a hook of hamate fracture
Management
- Night splinting with the elbow extended for mild cubital tunnel syndrome
- In situ decompression or anterior transposition for persistent or severe symptoms. See Ulnar Nerve Decompression and Transposition
- Excision of a ganglion or hamate hook fragment for Guyon canal compression
- Tendon transfers for established palsy to restore pinch and correct clawing
Prognosis
- Intrinsic recovery is poor once wasting is established
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.