What Is Carpal Tunnel Syndrome?

Carpal tunnel syndrome is a compression neuropathy of the median nerve at the wrist, caused by raised pressure inside the carpal tunnel, the rigid passage formed by the carpal bones and the overlying transverse carpal ligament. Nine flexor tendons and the median nerve share that space, so any swelling of the tendon sheaths, thickening of the ligament, or sustained increase in tunnel pressure loads the nerve. It is the most common entrapment neuropathy in humans and one of the most frequently compensated occupational disorders.

Symptoms follow the sensory distribution of the median nerve: numbness and tingling in the thumb, index, middle, and radial half of the ring finger, characteristically worse at night, along with weakness and eventual wasting of the thenar muscles. The National Institute of Neurological Disorders and Stroke notes that the little finger is spared, a detail that helps distinguish median nerve compression from a cervical radiculopathy or an ulnar neuropathy. Contributing factors include pregnancy, diabetes, hypothyroidism, rheumatoid arthritis, wrist fracture, and anatomically small tunnel dimensions.

Biomechanics and Occupational Exposure

Pressure inside the carpal tunnel is roughly 2 to 3 millimeters of mercury in a neutral wrist and rises steeply with flexion or extension, with pinch grip, and with external pressure on the palm. Sustained elevation impairs epineurial blood flow and eventually produces demyelination and fibrosis. This mechanism links the condition to work exposure. A prospective study of workplace and individual risk factors conducted by NIOSH investigators combined direct job observation and videotaping with physical examination and nerve conduction testing, and found force and repetition measures to be associated with incident cases alongside personal factors such as body mass index. Ergonomic engineering responds with tool redesign, keyboard and mouse geometry that keeps the wrist near neutral, vibration damping in powered hand tools, and job rotation schedules that limit continuous exposure.

Electrodiagnosis and Imaging

Nerve conduction studies remain the clinical reference standard. Surface or needle electrodes record the sensory and motor responses of the median nerve across the wrist, and the diagnosis rests on prolonged distal sensory and motor latencies relative to an unaffected nerve in the same limb, most often the ulnar. Comparison techniques, which subtract the latency of a neighboring nerve rather than relying on an absolute cutoff, improve sensitivity in mild cases. High-resolution ultrasound has become a common adjunct, measuring the cross-sectional area of the median nerve at the tunnel inlet, where enlargement above roughly 10 square millimeters supports the diagnosis. Work correlating ultrasound findings with nerve conduction results shows the two modalities are complementary: imaging identifies structural causes such as ganglia or tenosynovitis that electrophysiology cannot localize.

Treatment

Conservative management uses neutral-position night splinting, activity modification, and corticosteroid injection into the tunnel. When symptoms persist or when electrodiagnosis shows axonal loss, surgical release of the transverse carpal ligament is offered, either through an open palmar incision or endoscopically through one or two small portals. Both decompress the tunnel; endoscopic release generally returns patients to work sooner while carrying a slightly different profile of nerve injury risk. Instrumented outcome measurement, including grip and pinch dynamometry and patient-reported symptom severity scales, is used to track recovery.

Applications

Carpal tunnel syndrome is studied and addressed across several fields, including:

• Occupational health surveillance and workers' compensation epidemiology
• Ergonomic design of keyboards, hand tools, and assembly workstations
• Clinical neurophysiology and electrodiagnostic instrumentation
• Musculoskeletal ultrasound and magnetic resonance neurography
• Orthotic and splint design
• Minimally invasive surgical instrument development