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Carpal Tunnel Syndrome
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In one pass Carpal tunnel syndrome is a nerve being squeezed inside the wrist, not an inflamed tendon.
Educational content, not medical advice — consult a clinician.
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Chapter 1
A narrow tunnel in the wrist
Carpal tunnel syndrome is a nerve being squeezed inside the wrist, not an inflamed tendon. Turn your palm up and look at the base of the wrist. Under the skin, the wrist bones form a trough, and a band of ligament runs across the top of it. Together they make a narrow tunnel, the carpal tunnel. Through it run the tendons that bend the fingers, and one nerve: the median nerve.
The median nerve carries feeling from the thumb, index finger, and middle finger, so the typical picture is numbness, tingling, and pain in those three fingers. It is the most common peripheral nerve entrapment in the world (a nerve pinched where its path is narrow). Once you know it is a nerve, the rest makes sense: why those three fingers, why it is worst at night, and why treatment aims to take pressure off the nerve.
If the numbness becomes constant, the muscle at the base of the thumb gets thinner, or your hand keeps getting clumsier, the nerve is already losing function, and you should see a doctor in person soon.
The median nerve carries feeling from the thumb, index finger, and middle finger, so the typical picture is numbness, tingling, and pain in those three fingers. It is the most common peripheral nerve entrapment in the world (a nerve pinched where its path is narrow). Once you know it is a nerve, the rest makes sense: why those three fingers, why it is worst at night, and why treatment aims to take pressure off the nerve.
If the numbness becomes constant, the muscle at the base of the thumb gets thinner, or your hand keeps getting clumsier, the nerve is already losing function, and you should see a doctor in person soon.
Chapter 2
Bend the wrist, and the pressure climbs
The tunnel's volume is fixed, but the angle of the wrist changes its shape. One study threaded a pressure catheter straight into the carpal tunnel. In people with carpal tunnel syndrome, the pressure with the wrist level averaged 32 mmHg. Bending the wrist 90 degrees toward the palm raised it to 94, and bending it 90 degrees back raised it to 110. In people without the condition, it was only 2.5 with the wrist level.
Those numbers answer the question people ask most: why is it worst at night? If the wrist stays bent during sleep, the pressure stays high and the nerve is squeezed all night. Once the wrist is straight again, the pressure drops. That is why a night splint holds the wrist straight.
In the same study, surgery that cut the band of ligament brought the pressure down immediately and for good, the most direct evidence for the idea of taking pressure off the nerve.
Those numbers answer the question people ask most: why is it worst at night? If the wrist stays bent during sleep, the pressure stays high and the nerve is squeezed all night. Once the wrist is straight again, the pressure drops. That is why a night splint holds the wrist straight.
In the same study, surgery that cut the band of ligament brought the pressure down immediately and for good, the most direct evidence for the idea of taking pressure off the nerve.
Chapter 3
Mouse hand: can a computer cause it
In Chinese, carpal tunnel syndrome is often called mouse hand, as if daily computer use causes it. The evidence is far more cautious than the name.
A systematic review found 8 epidemiological studies of computer work and carpal tunnel syndrome, and every one had clear limitations: how much people used a computer, and whether they really had the condition, were measured imprecisely; the studies were too small; and bias was possible. Three of them found that more use went with higher risk, while three others found a lower risk in computer users. The authors concluded that there is not enough evidence that computer work causes carpal tunnel syndrome.
The mechanism fits. Pressures measured in the tunnel under typical computer-use wrist postures were below the levels considered harmful. Only one study measured pressure rising to a possibly harmful level during actual mouse use, and what years of that repeated pressure would do is unknown. So there is no need to blame the computer; but keeping your wrist as level as possible on the keyboard and mouse fits the finding that bending the wrist drives the pressure up.
A systematic review found 8 epidemiological studies of computer work and carpal tunnel syndrome, and every one had clear limitations: how much people used a computer, and whether they really had the condition, were measured imprecisely; the studies were too small; and bias was possible. Three of them found that more use went with higher risk, while three others found a lower risk in computer users. The authors concluded that there is not enough evidence that computer work causes carpal tunnel syndrome.
The mechanism fits. Pressures measured in the tunnel under typical computer-use wrist postures were below the levels considered harmful. Only one study measured pressure rising to a possibly harmful level during actual mouse use, and what years of that repeated pressure would do is unknown. So there is no need to blame the computer; but keeping your wrist as level as possible on the keyboard and mouse fits the finding that bending the wrist drives the pressure up.
Chapter 4
What splints, injections and surgery are worth
All three common treatments follow the same line of taking pressure off the nerve, but the strength of evidence differs a lot.
Night splint: it holds the wrist straight during sleep, aimed right at the night-time pressure rise. A systematic review pooling the available trials is restrained: overall, it is still uncertain whether splints help; only one small trial suggests that wearing a splint at night makes improvement more likely than no treatment. Splints are cheap, the side effects reported in trials were short-lived, and people who do not want an injection or surgery can try one first.
Steroid injection: at one month after the injection, symptoms improved more than with a placebo injection; whether it still works after one month has not been shown. Two injections are no better than one.
Surgery (cutting the band of ligament): in one randomized trial, 80% improved with surgery vs 54% with a splint at 3 months, and 90% vs 75% at 18 months, by which time 41% of the splint group had also had surgery. Surgery worked better, but most people in the splint group improved too.
Night splint: it holds the wrist straight during sleep, aimed right at the night-time pressure rise. A systematic review pooling the available trials is restrained: overall, it is still uncertain whether splints help; only one small trial suggests that wearing a splint at night makes improvement more likely than no treatment. Splints are cheap, the side effects reported in trials were short-lived, and people who do not want an injection or surgery can try one first.
Steroid injection: at one month after the injection, symptoms improved more than with a placebo injection; whether it still works after one month has not been shown. Two injections are no better than one.
Surgery (cutting the band of ligament): in one randomized trial, 80% improved with surgery vs 54% with a splint at 3 months, and 90% vs 75% at 18 months, by which time 41% of the splint group had also had surgery. Surgery worked better, but most people in the splint group improved too.
Evidence · how firm is the night-splint number
The splint evidence comes from the 2023 Cochrane systematic review, which included 29 trials. Its most striking number: for a night splint vs no treatment, the of short-term overall improvement was 3.86 (people wearing a splint were about 3.86 times as likely to improve; 95% 2.29 to 6.51, meaning the true value probably lies in that range). That works out to one extra person improving for every 2 treated.Read it with its conditions attached: the number comes from one study of 80 people, and the certainty of the evidence is low. The same review reports short-lived side effects in 7/40 people with splints vs 0/40 without, with a confidence interval that includes no difference. Whether splints reduce how many people end up having surgery is very uncertain.
So the accurate statement is: a night splint is a low-cost option worth trying first, not a proven therapy. In the authors' own words, small benefits might be enough to justify using it, especially for people who do not want an injection or surgery.
Chapter 5
When to see a doctor
When a nerve has been squeezed for long enough, the damage goes beyond numbness: carpal tunnel syndrome sometimes leads to muscle wasting, reduced sensation, and a clumsy hand. These mean the nerve is losing function. See a doctor in person soon, rather than waiting it out at home with a splint, if:
The muscle at the base of the thumb looks flatter or thinnerNumbness goes from coming and going to always thereButtons and small objects get harder to handle, and things often slip from your hand
One more point: numb fingers do not always come from the carpal tunnel, because nerve problems elsewhere can cause similar numbness. This list is for knowing when to go, not for diagnosing yourself. The good news is that the condition can usually be diagnosed quickly and responds well to treatment.
This site provides general education and advice. It does not replace a physician's diagnosis and treatment.
The muscle at the base of the thumb looks flatter or thinnerNumbness goes from coming and going to always thereButtons and small objects get harder to handle, and things often slip from your hand
One more point: numb fingers do not always come from the carpal tunnel, because nerve problems elsewhere can cause similar numbness. This list is for knowing when to go, not for diagnosing yourself. The good news is that the condition can usually be diagnosed quickly and responds well to treatment.
This site provides general education and advice. It does not replace a physician's diagnosis and treatment.
References · 6
- Padua, L., Coraci, D., Erra, C., Pazzaglia, C., Paolasso, I., Loreti, C., Caliandro, P., & Hobson-Webb, L. D. (2016). Carpal tunnel syndrome: clinical features, diagnosis, and management. The Lancet Neurology, 15(12), 1273-1284. Narrative review: CTS is the most common peripheral nerve entrapment syndrome worldwide; evidence on the best assessment and treatment selection is limited, but patients can be diagnosed quickly and respond well to treatment. 10.1016/S1474-4422(16)30231-9
- Karjalainen, T. V., Lusa, V., Page, M. J., O'Connor, D., Massy-Westropp, N., & Peters, S. E. (2023). Splinting for carpal tunnel syndrome. Cochrane Database of Systematic Reviews, 2023(2), CD010003. 29 trials, 1937 adults. Insufficient evidence to conclude whether splinting benefits CTS; small improvements not excluded. Night-time splint vs no treatment: short-term overall improvement RR 3.86 (95% CI 2.29-6.51; 1 study, 80 participants; NNTB 2; low certainty). Effect on referral to surgery very uncertain (RR 0.47, 0.14-1.58). Transient adverse events 7/40 vs 0/40 (CI includes no effect). Background: CTS is a compression neuropathy of the median nerve causing pain, numbness and tingling typically in the thumb, index and middle finger, sometimes muscle wasting, diminished sensitivity and loss of dexterity. 10.1002/14651858.CD010003.pub2
- Gelberman, R. H., Hergenroeder, P. T., Hargens, A. R., Lundborg, G. N., & Akeson, W. H. (1981). The carpal tunnel syndrome. A study of carpal canal pressures. Journal of Bone and Joint Surgery (American Volume), 63(3), 380-383. Wick-catheter pressures in 15 patients with CTS and 12 controls. Patients: mean 32 mmHg with the wrist neutral, 94 mmHg at 90 degrees flexion, 110 mmHg at 90 degrees extension. Controls: 2.5 mmHg neutral, 31 flexion, 30 extension. Carpal tunnel release produced an immediate and sustained fall in pressure. pubmed.ncbi.nlm.nih.gov/7204435
- Thomsen, J. F., Gerr, F., & Atroshi, I. (2008). Carpal tunnel syndrome and the use of computer mouse and keyboard: a systematic review. BMC Musculoskeletal Disorders, 9, 134. Eight epidemiological studies, all with limitations (imprecise exposure/outcome, low power, possible bias); three showed exposure-response, three found risks below 1. Carpal tunnel pressures under typical computer-use postures were below harmful levels; one study found potentially harmful pressure during actual mouse use, long-term effects unknown. Conclusion: insufficient epidemiological evidence that computer work causes CTS. 10.1186/1471-2474-9-134
- Marshall, S., Tardif, G., & Ashworth, N. (2007). Local corticosteroid injection for carpal tunnel syndrome. Cochrane Database of Systematic Reviews, 2007(2), CD001554. Local corticosteroid injection gives greater symptom improvement than placebo at one month; relief beyond one month not demonstrated. Better than oral corticosteroid up to three months; no better than anti-inflammatory plus splinting at eight weeks; two injections add no benefit over one. (audit:citation-doi reports volume 2009: Crossref carries the reissue date; PubMed PMID 17443508 has 2007(2):CD001554.) 10.1002/14651858.CD001554.pub2
- Gerritsen, A. A., de Vet, H. C., Scholten, R. J., Bertelsmann, F. W., de Krom, M. C., & Bouter, L. M. (2002). Splinting vs surgery in the treatment of carpal tunnel syndrome: a randomized controlled trial. JAMA, 288(10), 1245-1251. Intention-to-treat success at 3 months 80% surgery (62/78) vs 54% splinting (46/86); at 18 months 90% (61/68) vs 75% (59/79), by which time 41% (32/79) of the splint group had also had surgery. Open carpal tunnel release gave better outcomes than wrist splinting. 10.1001/jama.288.10.1245