Carpal Tunnel and Guyon's Canal: Two Trapped Nerves at the Wrist
Median nerve (carpal tunnel)
Ulnar nerve (Guyon's canal)
Both squeeze a nerve inside a narrow tunnel at the wrist, but they affect opposite sides of the hand. Carpal tunnel syndrome is the common one and involves the median nerve on the thumb side. Guyon's canal syndrome is much rarer and involves the ulnar nerve on the little-finger side.
Carpal Tunnel Syndrome
Median nerve, squeezed under the flexor retinaculum in the carpal tunnel
Where it is felt. Thumb, index and middle fingers, and the thumb-side half of the ring finger, on the palm side. It is often worse at night, and many people shake the hand to settle it. The skin over the base of the thumb is usually spared, because the small nerve branch that supplies it passes over the tunnel rather than through it.[1,8]
Pins, needles and numbness. Felt in that same thumb-side territory, and it can travel up into the forearm.
Weakness and loss. As it advances, the muscles of the thumb pad weaken and can waste, so pinch and grip feel clumsy and objects are dropped.[1]
Guyon's Canal (Ulnar Tunnel) Syndrome
Ulnar nerve, passing through Guyon's canal on the little-finger side of the wrist
Where it is felt. Little finger and the little-finger-side half of the ring finger, on the palm side only. The back of the hand is spared, which helps separate a wrist-level problem from one starting at the elbow.[5]
Pins, needles and numbness. Confined to that little-finger-side territory.
Weakness and loss. Weak grip and pinch, difficulty spreading the fingers, sometimes clawing of the ring and little fingers, with wasting of the small hand muscles in longer-standing cases. It is often a purely motor problem, with no numbness at all, particularly when the cause is a ganglion cyst.[5]
Two ways the nerve gets loaded
Compression
Anything that reduces the space in the tunnel raises the pressure on the nerve: swelling, fluid retention, a cyst, or arthritic change.
Overuse
Repeated or forceful gripping, sustained wrist bending, and hand-held vibrating tools load the nerve over time. Most cases are a blend of the two.
What makes it more likely
Pregnancy is a well-recognised trigger, particularly in the third trimester, driven by fluid retention and hormonal change. It usually settles once the baby has arrived.[1,7]
Health-related. Being overweight, diabetes, an underactive thyroid, rheumatoid arthritis, and a previous wrist fracture or wrist osteoarthritis.[1]
Occupational. Work that involves repeated or forceful gripping, sustained or awkward wrist positions, and hand-held vibrating tools is associated with carpal tunnel syndrome. For Guyon's canal in particular, long-distance cycling and ganglion cysts stand out.[1,5]
How it is diagnosed
Diagnosis starts with the history and a hands-on examination. Provocative tests at the wrist, such as tapping over the nerve (Tinel's), holding the wrist bent (Phalen's), or pressing on the tunnel (Durkan's), can reproduce the symptoms. On their own these tests are only moderately reliable, so the overall clinical picture matters more than any single test.[6]
Where the diagnosis is unclear, or surgery is being considered, nerve conduction studies confirm it and grade how far the nerve is affected.[6] For Guyon's canal, an ultrasound or MRI scan is often used to look for a cause such as a ganglion cyst.[5] A careful assessment also helps work out whether the problem is coming from the wrist, the elbow, or the neck, which changes what should happen next.
The treatment options that exist
These are the recognised options in general. What suits any one person depends on the cause, the severity, and how far the nerve is affected.
1. Conservative and manual therapy
A neutral wrist splint, especially at night, changing the activities and postures that provoke it, nerve-gliding exercises, and hands-on soft-tissue and mobilisation work. In one randomised trial in women with carpal tunnel syndrome, a manual therapy programme matched surgery for pain and function over the medium and longer term, and did better in the short term. It was a single trial in women only, using one specific protocol, so it should be read with that in mind.[3]
2. Corticosteroid injection
A steroid injection into the wrist can relieve mild to moderate carpal tunnel symptoms for up to around six months, and may reduce the need for surgery over the following year. Serious side effects are uncommon.[2]
3. Surgery
Releasing the tunnel, whether a carpal tunnel release or decompression of Guyon's canal along with dealing with any cause such as a cyst, is usually kept for severe cases, cases where the nerve is being damaged, or where other measures have not helped.[4]
How long it may last
It varies with the cause and the severity. Up to a third of milder cases settle without specific treatment.[2]
Pregnancy-related carpal tunnel generally has a good outlook and eases in the weeks after the birth as fluid retention resolves, although in a minority the symptoms carry on into the postpartum months and occasionally longer.[7]
More established cases tend to persist or slowly progress rather than clear on their own, which is why numbness that has become constant, or weakness that is getting worse, is worth acting on rather than waiting.[1]
Get it checked promptly if the numbness has become constant, the muscle at the base of the thumb is wasting, or the weakness is getting worse. These point to the nerve being under real pressure, and nerve conduction studies may be advised.
