Guyon Canal Syndrome
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Direct answer
Guyon canal syndrome is compression of the ulnar nerve at the wrist, within the canal bounded by the pisiform and the hook of the hamate. Its features depend on the zone of compression, and the Gross and Gelberman zones separate mixed motor and sensory lesions, motor-only lesions and sensory-only lesions. Ganglia and hook of hamate fractures are among its common causes.
What you must remember
- Canal boundaries: the pisiform and hook of hamate form the sides, with the palmar carpal ligament forming the roof and the pisohamate ligament and transverse carpal ligament forming the floor.
- Zone 1: proximal to the bifurcation of the ulnar nerve, compression causes both motor and sensory deficits, often from a hamate fracture, malunion or ganglion.
- Zone 2: the deep motor branch alone is involved, giving intrinsic weakness with no sensory loss, and the classic clinical picture includes a claw and a positive Froment sign.
- Zone 3: the superficial sensory branch alone is involved, giving numbness of the palmar little finger and ulnar half of the ring finger with normal intrinsic power.
- Sensory pattern: the palmar surface of the little finger and ulnar half of the ring finger lose sensation, while the palm, the hypothenar eminence and the dorsum of the hand are spared.
- Causes: ganglion, hook of hamate fracture, cyclist's palsy from handlebar pressure, and repetitive pressure from hand tools.
- Investigation: nerve conduction studies localise the zone, while ultrasound or MRI shows a ganglion or a fracture of the hook.
A stepwise approach to localising the lesion
Guyon canal syndrome is localised by matching the motor pattern with the sensory pattern, since the zone of compression decides which deficits appear. The steps below follow the reasoning used in examinations and clinics.
- Check the motor pattern: intrinsic weakness and a claw of the ring and little fingers suggests the deep motor branch is involved.
- Check the sensory pattern: palmar numbness of the little finger and ulnar half of the ring finger points to the superficial sensory branch.
- Combine the two: when both motor and sensory deficits are present, the compression lies in zone 1, proximal to the bifurcation.
- Test the hypothenar eminence: sensation there is normal, because the palmar cutaneous branch leaves the ulnar nerve before the wrist.
- Confirm and image: nerve conduction across the wrist confirms the lesion, and ultrasound or MRI looks for a ganglion or hook fracture.
- Decompress: the cause is removed, with ganglion excision or hook of hamate excision, and the canal is released.
Where the exam tries to catch you
Guyon canal questions are usually decided by knowing which branch is spared and which zone produces which deficit.
- Trap: expecting hypothenar numbness in a Guyon canal lesion. Correct: the palmar cutaneous branch leaves proximal to the wrist, so the hypothenar eminence is spared.
- Trap: assuming every Guyon canal lesion causes both motor and sensory loss. Correct: zone 2 is motor-only and zone 3 is sensory-only, so the zone must be identified.
- Trap: treating a symptomatic compressive ganglion conservatively. Correct: a ganglion causing a nerve deficit is decompressed, since delay risks permanent intrinsic weakness.
Frequently asked questions
What are the Gross and Gelberman zones of Guyon canal?
The Gross and Gelberman zones divide the ulnar nerve in Guyon canal by where the compression lies. Zone 1 is proximal to the bifurcation and causes mixed motor and sensory loss. Zone 2 involves the deep motor branch alone, and zone 3 involves the superficial sensory branch alone.
Why is the hypothenar eminence spared in Guyon canal syndrome?
The hypothenar eminence is spared in Guyon canal syndrome because the palmar cutaneous branch of the ulnar nerve leaves the nerve proximal to the wrist. Sensory loss in a Guyon canal lesion therefore affects only the palmar little finger and ulnar half of the ring finger instead. This distinguishes the lesion from a more proximal ulnar lesion.
What are common causes of Guyon canal syndrome?
Ganglia and fractures of the hook of the hamate are among the common causes of Guyon canal syndrome. Cyclist's palsy from handlebar pressure and repetitive pressure from hand tools are other recognised causes. Treatment begins with removing the underlying cause and decompressing the canal.
How does Guyon canal syndrome differ from cubital tunnel syndrome?
Guyon canal syndrome affects the ulnar nerve at the wrist, while cubital tunnel syndrome affects it at the elbow. The dorsal and palmar cutaneous branches leave the nerve between the elbow and the wrist, so a distal Guyon lesion spares the dorsum and hypothenar eminence, whereas an elbow lesion can involve them. Sensory mapping together with nerve conduction studies separates the two sites.