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Peripheral Nerve

Median Neuropathy (Carpal Tunnel Syndrome)

The most common pinched nerve — highly treatable, and often cured with a small operation.

In brief

Compression of the median nerve at the wrist
Causes numbness, tingling and pain in the hand, often worst upon waking first thing in the morning
The most common nerve entrapment
Diagnosed clinically, confirmed with nerve conduction studies
Treated with splinting, injections, or a quick carpal tunnel release

Introduction

Carpal tunnel syndrome is compression of the median nerve where it passes through a tight tunnel at the front of the wrist. It is the most common nerve entrapment syndrome in the body, affecting between three and four in every hundred adults.¹ It is about twice as common in women as in men and is most often diagnosed in middle age. Many people improve with simple measures; when they do not, carpal tunnel release is among the most reliable and durable operations in surgery.²

What is the carpal tunnel?

The carpal tunnel is a narrow passage on the palm side of the wrist, its floor and sides formed by the small carpal bones and its roof by a strong band of fibrous tissue, the transverse carpal ligament. Nine tendons that bend the fingers and thumb pass through it, and alongside them runs the median nerve — which carries sensation from the thumb, index and middle fingers and the thumb side of the ring finger, and supplies the small muscles at the base of the thumb. Because the tunnel is enclosed by bone and unyielding ligament it cannot expand, so anything that increases the volume of its contents, or narrows the tunnel itself, raises the pressure on the nerve. Sustained pressure first interferes with the nerve’s blood supply and its insulating myelin sheath, producing intermittent tingling. If it continues, nerve fibres themselves are lost — which is why longstanding compression causes constant numbness and wasting of the thumb muscles.

The median nerve and its branches in the hand (left); the area of numbness and pain (centre); and the carpal tunnel in cross-section, normal above and compressed below (right).

What causes carpal tunnel syndrome?

In most people no single cause is found; the usual finding at operation is thickening of the lining of the tendons, which crowds the nerve. Recognised risk factors include:

Excess body weight — obesity roughly doubles the risk.³
Diabetes, an underactive thyroid, rheumatoid arthritis and other inflammatory joint disease.
Previous wrist fracture or injury.
Pregnancy — about a third of women report carpal tunnel symptoms, largely from fluid retention.⁴
Occupational hand-transmitted vibration and forceful, highly repetitive hand work.5
A family history — carpal tunnel syndrome has a substantial inherited component.

Two points are worth making plainly. Ordinary keyboard and computer mouse use has repeatedly failed to be established as a cause of carpal tunnel syndrome, despite being widely blamed for it.⁵ And a great many patients have none of the risk factors above — developing carpal tunnel syndrome does not mean anything has been done wrong.

What are the symptoms?

Numbness and tingling in the hand — classically the thumb, index and middle fingers and the thumb side of the ring finger, although in practice symptoms are often felt more diffusely across the whole hand.
Waking at night — the single most characteristic feature. Patients typically wake in the early hours with a numb, painful hand and gain relief by shaking it or hanging it out of bed.
Aching or burning pain in the wrist and hand, sometimes extending up the forearm.
Clumsiness and dropping things — difficulty with buttons, keys and fine tasks.
Later features — numbness that is constant rather than intermittent, visible wasting of the muscle bulge at the base of the thumb, and weakness lifting the thumb away from the palm.

Symptoms are frequently present in both hands, and when nerve testing is performed many of the apparently unaffected hands prove to be abnormal already.

Features that should prompt earlier review

Constant (rather than intermittent) numbness, visible wasting at the base of the thumb, or weakness lifting the thumb from the palm all indicate that nerve fibres are being lost rather than merely irritated. These findings argue for earlier surgery rather than a further trial of non-operative treatment. Recovery remains possible once wasting has appeared, but it is slower and less complete. Separately, severe numbness and pain coming on rapidly over hours to days — most often after a wrist fracture or other injury — suggests acute carpal tunnel syndrome. This is a different problem from the gradual condition described here and needs urgent assessment, as prompt release protects the nerve.

A note on carpal tunnel syndrome in both hands

In older patients, particularly men, carpal tunnel syndrome affecting both hands can precede transthyretin amyloidosis — a condition in which an abnormal protein is deposited in tissues including the heart — typically by several years. Among patients screened five to fifteen years after surgery for carpal tunnel syndrome on both sides, 4.8% were found to have cardiac amyloidosis.⁶ Bilateral carpal tunnel syndrome is now listed as a recognised warning sign in European cardiology guidelines.⁷ This does not mean everyone with symptoms in both hands needs heart investigations — most will not — but where other features are present it is worth considering, and Mr Russell will raise it if relevant.

Conditions that can be mistaken for it

Cervical radiculopathy — a pinched nerve in the neck, particularly at C6 or C7, causing numbness in the same fingers. See the separate Victoria Neurosurgery information sheet on cervical radiculopathy.
Ulnar neuropathy at the elbow (cubital tunnel syndrome) — numbness of the little and ring fingers with weakness of grip.
Generalised peripheral neuropathy, for example from diabetes — glove-like numbness in both hands and often the feet.
Arthritis at the base of the thumb or tendon problems around the wrist — pain, but not true numbness.

These can also coexist. It is not unusual to have both a compressed nerve root in the neck and carpal tunnel syndrome in the same arm — sometimes called a “double crush” — and part of the assessment is deciding which is producing the symptoms that trouble you most.

How is carpal tunnel syndrome diagnosed?

The diagnosis is primarily clinical, made from the history and examination. This is not a fallback in the absence of a better test: structured clinical criteria — most widely the CTS-6 — perform as well as any investigation, and current guidelines state they can be used to make the diagnosis in place of the routine use of ultrasound or nerve conduction studies.⁸ Nerve conduction studies measure how quickly and strongly signals travel along the median nerve across the wrist. Current guidelines do not require them before every operation,⁸ but Mr Russell arranges them routinely: they confirm the diagnosis, document the severity of nerve involvement, provide a baseline against which later recovery can be judged, and help exclude other causes such as a compressed nerve in the neck. A normal study does not, however, exclude carpal tunnel syndrome — about one in four patients with clinically definite disease have normal nerve conduction studies,⁹ and where the clinical picture is convincing Mr Russell will still recommend decompression. Ultrasound measures the swelling of the median nerve as it enters the tunnel. Its accuracy is comparable to nerve conduction studies, and its particular value is in identifying a structural cause such as a ganglion cyst or an unusual nerve or artery, which occasionally changes the operative plan. MRI is not used to diagnose carpal tunnel syndrome.⁸

What happens if it is not treated?

Carpal tunnel syndrome does not inevitably progress, but neither does it reliably settle. Among patients followed for two years without treatment, 47.6% improved, 28.8% were unchanged and 23.4% deteriorated.¹⁰ The common assumption that mild symptoms can safely be left alone is not well founded: spontaneous improvement is, if anything, more likely in those with more severe nerve involvement at the outset. Carpal tunnel syndrome arising in pregnancy behaves more favourably, though not as quickly as is often said — around half of women are still symptomatic a year after delivery, but very few ever require surgery.¹¹ Night splinting alone is usually sufficient during and after pregnancy. There is no evidence for a point in time beyond which nerve damage becomes irreversible; even patients with established wasting regain measurable strength after surgery. What is clear is that severe, longstanding compression is associated with slower and less complete recovery, which is the practical argument against waiting indefinitely.

Non-surgical treatment

Night splints — a splint worn overnight holds the wrist straight, the position in which pressure inside the tunnel is lowest. It is a reasonable, low-risk first step, particularly for mild or intermittent symptoms and in pregnancy. The evidence is weaker than its popularity implies: a review of 29 trials concluded there is insufficient evidence to establish how much splinting helps,¹² and in a randomised trial comparing splinting with surgery, 41% of splinted patients had come to surgery within 18 months.¹³
Corticosteroid injection — an injection into the carpal tunnel gives genuine relief for up to about six months and modestly reduces the chance of needing surgery in the first year. It is not a long-term solution: in a placebo-controlled trial, 73% of patients given the higher steroid dose still came to surgery within a year, compared with 92% given placebo,¹⁴ and current guidelines state on strong evidence that injection does not produce long-term improvement.⁸ It is most useful for short-term relief, in pregnancy, or where surgery must be deferred.
Treating contributing conditions — optimising diabetic control, treating an underactive thyroid, weight reduction and modifying heavy vibrating tool use are all sensible, though none has been shown on its own to reverse established compression.

A number of widely offered treatments have been tested and do not produce lasting benefit: oral corticosteroids (which help only briefly), anti-inflammatory tablets, diuretics, vitamin B6, therapeutic ultrasound, low-level laser, kinesiotaping, shockwave therapy, platelet-rich plasma, hydrodissection, nerve and tendon gliding exercises, and manual therapy.⁸ It is reasonable to try simple conservative measures; it is not reasonable to spend many months and considerable expense on treatments the evidence does not support while a nerve is being progressively compressed.

When is surgery considered?

Symptoms persist despite an adequate trial of non-operative treatment — usually 6 to 12 weeks of night splinting, with or without an injection.
Sleep is regularly disturbed, or hand function is meaningfully limited.
Numbness has become constant, there is wasting at the base of the thumb, or thumb abduction is weak — in which case surgery should not be delayed.
Nerve conduction studies show severe involvement.

Surgery is more effective than continued splinting: in the principal randomised trial the success rate at three months was 80% after surgery compared with 54% with splinting, and 90% compared with 75% at eighteen months.¹³ The decision is made individually, on the severity of your symptoms, the state of the nerve, and how much the condition is affecting your life.

What does carpal tunnel release involve?

Carpal tunnel release divides the transverse carpal ligament, the roof of the tunnel, immediately enlarging the tunnel and taking the pressure off the nerve. The ligament is not repaired; the two ends separate slightly and heal in a lengthened position. It is a day procedure and you go home the same day. The operation can be performed under local anaesthetic alone — for which there is strong evidence⁸ — under local anaesthetic with sedation, or under a general anaesthetic; which approach is used is decided with you beforehand.

Open carpal tunnel release

This is Mr Russell’s standard technique. A short incision, generally 2–3 cm, is made in the palm in line with the ring finger; it does not cross the wrist crease. The transverse carpal ligament is divided from end to end under direct vision and the median nerve inspected along its length, confirming that the release is complete and that there is no unexpected additional cause of compression. The skin is closed and a soft dressing applied, and the hand can be used for light activities straight away. Seeing the ligament and the nerve directly throughout is the principal argument for the open technique.

Endoscopic carpal tunnel release

In endoscopic release the ligament is divided from within the tunnel using a small camera. Mr Russell does not perform it, and it is worth explaining why. Symptom relief and hand function beyond three months are equivalent to open release, and return to work is on average about eight days earlier — though the trials supporting this are of low quality, and endoscopic release more often causes temporary irritation of the nerve.¹⁵ Revision surgery is also more likely, by a small margin over ten years,¹⁶ and by a wider margin in the first year after surgery,¹⁷ and the current guideline notes that complication rates for endoscopic release may be higher than previously described.⁸ Because the ligament is divided without the nerve being seen along its whole length, Mr Russell prefers the open technique, where every structure is under direct vision throughout. Patients who would like to consider endoscopic release can be referred to a surgeon who offers it.

Expected recovery

Elevation — keep the hand elevated for the first 48 hours, while the bulky dressing is still on, to reduce swelling and the pain that goes with it.
Dressing — reduced to a simple adhesive dressing after two to three days.
Using the hand — light activities from the first day, within the limits of comfort.
Driving — usually around 1 to 2 weeks, once you can grip the wheel and brake safely.
Office or non-manual work — around 3 weeks, though many return sooner on modified duties.
Manual work — around 5 to 6 weeks, depending on the demands of the job.
Grip strength — dips in the first weeks, returns to baseline by around 3 months and is typically better than before surgery by 6 months.
Night symptoms — usually the first thing to settle, often within days.
Numbness — recovers over weeks to months. Where compression has been severe and longstanding, some numbness may be permanent.

Routine supervised hand therapy and routine post-operative splinting are not required and current guidelines recommend against prescribing them as a matter of course.⁸ Please contact the rooms if the wound becomes increasingly red, hot or swollen, if it discharges, if you develop a fever, or if pain increases rather than settles after the first few days.

What are the risks of surgery?

Carpal tunnel release is among the safest operations performed on the upper limb and serious complications are rare. Risks include:

Scar tenderness and “pillar pain” — aching either side of the scar, noticed when taking weight through the palm; common in the early months and the great majority settle by six months.
Wound infection — well under 1%.
Altered sensation around the scar — usually temporary.
Incomplete relief or persistent symptoms — more likely where compression has been severe and
longstanding, and in patients with diabetes.
Recurrence requiring further surgery — approximately 1% at five years and 1.6% at ten years.¹⁶
Injury to the median nerve or one of its branches, including the small motor branch to the thumb muscles — rare.
Complex regional pain syndrome — an uncommon disorder of persistent pain, swelling and stiffness.
Anaesthetic and general surgical risks — very low for a short day procedure, and lower again under local anaesthetic alone.

What is the outlook?

For most people it is excellent. At a minimum of ten years after open carpal tunnel release, 88% of patients were completely or very satisfied and 74% reported that their symptoms had resolved entirely.² Night symptoms improve first, often within days; tingling settles over weeks; numbness and strength recover more slowly. Outcomes are less predictable where compression has been severe and prolonged, particularly once there is wasting of the thumb muscles, and in patients with diabetes. Surgery undertaken in the context of a workers’ compensation claim also tends to do less well — on average about five weeks longer to return to work, a lower rate of return to the pre-injury occupation, and higher rates of complications and persistent pain.¹⁸ None of these is a reason not to operate — all of these groups improve — but they are reasons to be realistic about how much and how quickly. Mr Russell will discuss what your particular findings mean for you at your consultation.

References

Helpful links

Carpal tunnel release — procedure animation A short medical animation of how the procedure works

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Median Neuropathy (Carpal Tunnel Syndrome) — patient information sheet PDF · prepared by Mr Jeremy Russell

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Content on this page is for education and information only and is not a substitute for advice from your doctor. Medically reviewed by Mr Jeremy Russell.