Carpal tunnel syndrome (CTS) is a condition that results from compression of the median nerve within the carpal tunnel of the wrist. It is the most commonly diagnosed neuropathy of the upper limb, accounting for up to 90% of such cases. [1] Symptoms are progressive and manifestations such as pain, numbness and weakened grip can substantially reduce quality of life. The condition also generates considerable socio-economic costs and is a leading cause of work absence. For example, in the United States annual expenditures for CTS exceed USD 2 billion, and the average affected worker loses some 27 days of work per year. [2]
Anatomy of the problem: the carpal tunnel and the median nerve
To understand the disorder, it is helpful to review wrist anatomy. The carpal tunnel is a narrow canal on the palmar side of the wrist. Its floor and sides are formed by eight carpal bones, while its roof is formed by a strong transverse fibrous band known as the flexor retinaculum (transverse carpal ligament). [3] This osteofibrous structure is rigid and of fixed volume, so any increase in volume within the tunnel can result in compressive pathology. Ten structures traverse the carpal tunnel: the median nerve and nine flexor tendons for the fingers. [3] The median nerve lies relatively superficially within the tunnel, which renders it particularly susceptible to compression. It supplies sensation to the thumb, index, middle and radial half of the ring finger. [4] In addition, it innervates the thenar muscles responsible for precise pinch and opposition movements that are essential for many activities of daily living. [4]
Pathophysiology of carpal tunnel syndrome
The primary pathogenic factor is increased pressure within the carpal tunnel. Under normal conditions, tunnel pressure ranges from 2 to 10 mmHg. [1] In patients with CTS this pressure frequently exceeds 30 mmHg, impairing perfusion of the small vessels that supply the nerve. [5] Pressure can rise up to eightfold with maximal wrist flexion. [1] This explains why symptoms commonly worsen at night, when wrists are often kept flexed unconsciously. [5] Elevated tunnel pressure initiates a cascade of deleterious events: [1]
- Ischaemia - compression of microvasculature reduces oxygen delivery to the nerve.
- Edema - disruption of the blood-nerve barrier allows fluid to extravasate into the nerve, causing swelling.
- Vicious cycle - a swollen nerve occupies more space in the tunnel, further elevating pressure and exacerbating ischaemia.
- Structural damage - chronic compression first injures the nerve’s myelin sheath and, over time, the axons themselves; the connective tissue lining the tunnel also thickens and fibroses. [5]
Clinical presentation by stage
CTS symptoms are progressive and may be classified into stages:
- Early (mild) stage - symptoms are predominantly nocturnal. Patients awaken with numbness, paraesthesia or burning pain affecting the thumb, index, middle and radial half of the ring finger.Vigorous shaking of the hand often brings temporary relief - the so-called "shake sign".
- Moderate stage - symptoms increasingly occur during daytime activities such as driving, holding a phone or typing. Grip strength declines, objects may be dropped, and fine motor tasks (e.g. buttoning) become difficult.
- Advanced (severe, grade 3) stage - irreversible nerve injury may have occurred.
- Numbness becomes constant and tactile and thermal sensation are markedly reduced. The most serious sign is atrophy of the thenar muscles, leading to flattening of the palm and loss of precision pinch.
Major causes and risk factors
CTS is seldom attributable to a single cause; it usually results from a combination of factors. The most important include:
- Occupational factors - risk increases with repetitive wrist movements, high force gripping, or use of vibrating tools (e.g. on assembly lines, in meat processing, or with pneumatic hammers).
- Systemic diseases and conditions - obesity is one of the strongest risk factors; each one-unit increase in BMI raises risk by approximately 8%. Other predisposing conditions include diabetes mellitus, rheumatoid arthritis, hypothyroidism and hormonal changes (CTS may develop during pregnancy and the menopausal transition).
- Anatomical factors and trauma - a congenitally narrow carpal tunnel, previous wrist fractures or dislocations, or space-occupying lesions (e.g. ganglia) can physically reduce available space for the nerve.
- Genetic predisposition - familial occurrence has been reported, indicating a hereditary component. Women are affected two to five times more frequently than men, and incidence peaks between ages 40 and 60.
Diagnosis - from clinical tests to imaging
Diagnosis is based on history, physical examination and supplementary investigations. The clinician assesses sensation, muscle strength and looks for atrophy. [1] Provocative tests that transiently increase tunnel pressure and reproduce symptoms are commonly used: the Phalen manoeuvre (maximal wrist flexion) and Tinel’s sign (percussing the nerve). The Durkan compression test - direct pressure over the carpal tunnel - is considered highly sensitive. [1]
Nerve conduction studies (NCS/ENG), EMG and ultrasound
Electrophysiological testing remains the diagnostic “gold standard” for CTS. [1] Nerve conduction studies (electroneurography, ENG) measure the conduction velocity of impulses along the nerve; CTS is characterised by a delay across the wrist segment. Electromyography (EMG) assesses muscle activity and can detect denervation changes in advanced disease. [1]
Ultrasonography (US) is increasingly valuable because it visualises the nerve directly. In CTS the median nerve is visibly swollen and its cross-sectional area is enlarged; values of 9–10 mm² or greater strongly suggest the diagnosis. US also detects other abnormalities such as ganglia or tenosynovitis. Magnetic resonance imaging (MRI) is used less frequently and is reserved for atypical or complex cases. [1]
Conservative treatment - what helps?
Non-surgical therapy is the first-line approach for mild to moderate CTS. The aim is to reduce pressure within the carpal tunnel. Conservative measures are most effective when implemented early. Key elements include activity modification and ergonomics.
Splints, medications and physiotherapy
Effective conservative strategies include:
- Wrist splinting - nocturnal splints maintain the wrist in a neutral position and are particularly important overnight. For patients wondering how to sleep with CTS, a wrist brace is the most effective measure to prevent inadvertent flexion and nocturnal symptoms. [6]
- Pharmacotherapy - oral non-steroidal anti-inflammatory drugs (NSAIDs) may provide short-term symptomatic relief but do not address the underlying cause. [1] Local corticosteroid injections (so-called steroid blocks) are considerably more effective: their potent anti-inflammatory action rapidly reduces oedema and symptoms, although the benefit may be temporary. [9]
- Physiotherapy - targeted exercises such as neural gliding (nerve "sliders") and stretching can provide significant symptom relief. [6] Manual therapy and physical modalities (e.g. therapeutic laser, shockwave therapy) may also be beneficial.
Surgical treatment - when and what does it involve?
Surgical intervention is the most effective method of treating CTS. It is considered when conservative treatment does not bring improvement, EMG examination confirms the advanced stage of the disease or when muscle atrophy is visible.[1] The operation involves cutting the transverse carpal ligament, which permanently increases the volume of the canal and relieves the nerve from compression.[6]
Open versus endoscopic release
The procedure may be performed by two principal techniques:
- Open carpal tunnel release - the traditional approach involves a 3–5 cm incision in the palm. This allows direct visualisation of the ligament and controlled division but is associated with a larger scar and a longer return to full function. [10]
- Endoscopic carpal tunnel release - a minimally invasive technique using one or two small incisions (≈1 cm) through which a camera and microsurgical instruments are introduced to divide the ligament from the inside. Advantages include less postoperative pain, improved cosmetic outcome and faster recovery. [6]
Regardless of the technique chosen, structured rehabilitation is essential. Early finger mobilisation, scar management to prevent adhesions and progressive strengthening of the grip are important components of postoperative care.
Minimally invasive and regenerative options
There are also emerging alternatives that aim to promote nerve regeneration with minimal invasiveness.
Hydrodissection and regenerative therapies (PRP)
Ultrasound-guided hydrodissection is a minimally invasive procedure in which fluid (e.g. normal saline) is precisely injected around the compressed nerve. The injected fluid acts as a “hydraulic scalpel,” mechanically freeing the nerve from adhesions. The procedure is performed with a fine needle, leaves no scar and allows rapid recovery. [11]
Regenerative therapies (platelet-rich plasma - PRP) - PRP injections derived from the patient’s own blood aim not only to reduce inflammation but principally to stimulate intrinsic tissue repair mechanisms. Studies indicate that PRP may produce more durable effects than corticosteroids. [12]
Prognosis and prevention
Treatment success depends on early intervention. Conservative measures are highly effective in the early stages. [6] Surgical decompression relieves pain and paraesthesia in over 90% of cases, but restoration of full function depends on the degree of preoperative nerve damage. [1] Where muscle atrophy is already present, recovery may be incomplete. [6]
Prevention is centred on ergonomics: maintaining a neutral wrist posture, using ergonomic keyboards and mice (e.g. vertical mice), taking regular breaks for exercises, and controlling body weight and chronic diseases. Early diagnosis is crucial to prevent permanent nerve injury and preserve long-term hand function.
Bibliography
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- Median nerve: Anatomy, origin, branches, course - Kenhub, https://www.kenhub.com/en/library/anatomy/the-median-nerve
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