Home / Conditions / Carpal tunnel syndrome
The median nerve runs through a narrow tunnel at the wrist. When the pressure inside that tunnel rises, the thumb, index and middle fingers go numb — and it usually happens at night.
Numbness in the hand has three common sources, and they are told apart mostly by which fingers are affected and what makes it worse. This is worth working through before any test, because the tests are different too.
| Carpal tunnel at the wrist | Cubital tunnel at the elbow | Nerve root at the neck | |
|---|---|---|---|
| Fingers affected | Thumb, index, middle, half the ring | Little finger and the other half of the ring | Varies with the level — thumb and index, or the middle finger |
| The little finger | Normal | Numb | Sometimes |
| At night | Wakes you; shaking the hand helps | Worse when you sleep with the elbow bent | Depends more on how the neck is propped |
| What provokes it | Holding a phone, driving, gripping a book | Leaning on the elbow, long phone calls | Neck movement, coughing, straining |
| Pain above the wrist | Can ache up the forearm | Along the inner forearm | Usually travels down from the neck, past the elbow |
| Weakness shows as | A flattened thumb pad, weak pinch | Trouble spreading the fingers, weak grip | A whole muscle group for that level |
Two can be true at once. A nerve that is already irritated at the neck tolerates pressure at the wrist less well, so the two sometimes coexist. That is the usual explanation when a carpal tunnel release helps but does not finish the job, and it is a reason the neck is examined at the same visit rather than afterwards.
The tunnel is a fixed space. Its floor and sides are the wrist bones; its roof is a tough band of ligament across the front of the wrist. Nine tendons that bend the fingers pass through it, and so does the median nerve — which has the least room and the least tolerance.
What a picture cannot show is that the pressure inside is not constant. It rises when the wrist is held bent or extended, which is why symptoms arrive during sleep, at the wheel, or holding a phone to your ear. It also rises when the tissue inside swells, which is why pregnancy, thyroid problems, diabetes and rheumatoid arthritis all make it more likely.
The same nerve does two jobs: sensation to those fingers, and power to the small muscles at the base of the thumb. That is why long-standing pressure shows up as a flattened thumb pad and a weak pinch, not only as numbness.
A normal nerve study does not close the question. Early cases can test normally while the symptoms are real, and the examination and the history still carry weight. Equally, a study can look abnormal in someone whose symptoms are mild. The test informs the decision; it does not make it.
Most people start — and many finish — without an operation. What decides the step is how long the numbness lasts each day and whether the thumb muscles have begun to weaken.
A splint holds the wrist straight during sleep, which is when the pressure peaks. Worn nightly it settles symptoms for a good number of people, and it is the first thing to try where the numbness comes and goes. Adjusting how the hand is used at work does the rest.
An injection into the tunnel reduces the swelling around the nerve. Relief is often good but may be temporary. It is also informative: a hand that responds well to an injection is a hand likely to do well after surgery, which makes it useful when the diagnosis is in doubt.
Carpal tunnel release divides the ligament forming the roof of the tunnel, which lets the space open and takes the pressure off the nerve. It can be done through a small open incision or endoscopically. It is a day procedure under local or regional anaesthetic; the hand is used for light activity almost immediately, and the scar can stay tender for a few months.
Release stops the pressure. It does not repair a nerve already damaged by years of it. Night symptoms usually go quickly; constant numbness and a wasted thumb pad recover slowly, and sometimes not fully. That is the argument against waiting once the numbness has stopped coming and going.
The wrist drifts into a bent position during sleep, and the pressure inside the tunnel is highest when the wrist is bent. Fluid also redistributes when you lie flat. That combination is why the classic story is waking at two in the morning and shaking the hand out.
It can settle symptoms, particularly where numbness comes and goes and is mostly nocturnal. It works by keeping the wrist straight, so it has to be worn to work. It does not make the tunnel bigger, which is why symptoms often return if the underlying cause remains.
Less than its reputation suggests. Forceful, repetitive gripping and vibrating tools carry a clearer association than keyboard work. Many people develop it with no occupational cause at all, and pregnancy, thyroid problems and diabetes are more useful things to ask about.
The hand is used for light activity within days. Night symptoms often settle in the first week or two. Grip strength and scar tenderness take longer, usually a few months, and heavy or forceful work is the last thing to come back.
Recurrence is uncommon. Where symptoms persist, the more usual explanations are that the nerve was already damaged before the release, or that some of the problem was never at the wrist — the elbow or the neck contributing as well.
No. Bring any nerve conduction study or scan reports, and a note of which fingers are affected and whether the numbness is now constant.
Wrist pain · Cubital tunnel syndrome · Radial tunnel syndrome · Cervical radiculopathy · Neuropathic pain · Trigger finger
Be ready to say which fingers go numb, and whether it still comes and goes. Those two answers decide most of what follows.
