What is Guyon's canal syndrome?
Guyon's canal syndrome refers to a collection of symptoms and signs due to compression of the ulnar nerve in the Guyon's canal, which is also known as the ulnar tunnel. When it is encountered in cyclists due to repetitive trauma, it is referred to as the handlebar palsy.
What causes it?
There are a number of potential causes of compression:
- Hook of hamate fracture or nonunion
- Ulnar artery thrombosis or aneurysm
- Repetitive trauma
- Ulnar sided wrist instability
Symptoms & Signs
- The ulnar nerve bifurcates into the superficial and deep branches. Depending on the location of compression within Guyon's canal, the presentation may be
- Mixed motor and sensory
- Pure motor
- Pure sensory
- Paraesthesia and tingling affecting the little and ulnar half of ring finger (dorsum of hand is spared in Guyon's canal syndrome in contradistinction to cubital tunnel syndrome where the ulnar dorsum of the hand is also affected).
- Clawing of ring and little fingers (tend to be worse than cubital tunnel syndrome, the so-called "ulnar paradox").
- Weakened grasp, pinch
- Abducted posture of the little finger (Wartenberg sign)
- Wasting of hypothenar muscles and guttering of the hand (wasting of interosseous muscles)
- Radiographs in the case of wrist trauma
- CT scan may be necessary to delineate hook of hamate fracture
- MRI scan is useful to exclude any space-occupying lesion e.g. ganglion
- Doppler ultrasound is useful to evaluate the flow in the ulnar artery
- Neurophysiology is employed to confirm the diagnosis
- Activity modification (such as in cyclists in terms of posture, adjustment of bike and protective equipment)
- Surgical decompression of the ulnar nerve by removing any potential offending structures in Guyon's canal
- Carpal tunnel release may indirectly decompress Guyon's canal
- In late cases, tendon transfers can be considered to correct fingers clawing, to restore pinch or to correct abducted little finger.
What should I expect when undergoing a Guyon's canal release?
- It is performed as a day-case procedure, under general or regional anaesthesia.
- At the end of the procedure, a bulky dressing is applied over the wrist and palm but the fingers and thumb are left free.
- Sometimes, a volar slab is applied to support the wrist for 5-7 days.
- The dressing is reduced within a week and sutures are removed at 2 weeks.
- The recovery can be prolonged but the sensory symptoms tend to improve over the initial days to weeks. If there was pre-existing muscle weakness/wasting, the recovery might take many months and might not be complete. Thus it would be preferable to intervene earlier rather than when the muscles are already wasted.
What are the risks?
Surgical decompression is safe and effective in specialist's hands. There are however potential risks of wound infection, nerve injury, pain syndrome, incomplete recovery and recurrence. Some may experience scar tenderness but this tends to improve with time and therapy.