Carpal Tunnel Syndrome
Carpal tunnel syndrome is the most common peripheral entrapment neuropathy, caused by compression of the median nerve within the carpal tunnel at the wrist. It affects up to 5% of the population and is characterized by pain, numbness, and tingling in the median nerve distribution.
Anatomical Basis
The carpal tunnel is an osseofibrous canal at the wrist bounded by carpal bones posteriorly and the flexor retinaculum anteriorly. It contains 9 flexor tendons and the median nerve. The median nerve is most superficial and vulnerable to compression. Any condition that increases tunnel pressure or decreases tunnel volume can cause CTS.
Relevant Structures
Mechanism
Increased pressure within the carpal tunnel causes median nerve ischemia and demyelination. Risk factors include repetitive wrist flexion/extension, pregnancy, hypothyroidism, diabetes, rheumatoid arthritis, obesity, and wrist fractures. Tenosynovitis of the flexor tendons is a common cause.
Clinical Presentation
- âĒNumbness and tingling in thumb, index, middle, and radial half of ring finger
- âĒPain radiating to forearm and shoulder
- âĒSymptoms worse at night (waking from sleep)
- âĒWeakness of thumb opposition and abduction
- âĒDropping objects
- âĒThenar atrophy in advanced cases
Physical Examination
- âPhalen's test: Wrist flexion for 60 seconds reproduces symptoms
- âTinel's sign: Tapping over carpal tunnel causes tingling
- âSensory testing: Decreased sensation in median nerve distribution
- âThenar muscle examination: Weakness of abductor pollicis brevis and opponens pollicis
- âTwo-point discrimination: Increased threshold in affected fingers
- âDurkan's test: Direct pressure over carpal tunnel reproduces symptoms
Treatment
- âConservative: Wrist splinting in neutral position (especially at night), activity modification, NSAIDs
- âCorticosteroid injection: Provides temporary relief, may delay surgery
- âSurgical: Carpal tunnel release - division of the flexor retinaculum (open or endoscopic)
- âTreatment of underlying cause: Thyroid hormone replacement, diabetic control, etc.
Prognosis
Excellent with timely treatment. Conservative management effective in mild-moderate cases. Surgical release has >90% success rate. Delayed treatment may result in irreversible nerve damage and persistent symptoms.
Study Tips
- ðĄMedian nerve supplies LOAF muscles in hand: Lumbricals 1-2, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis
- ðĄThenar eminence sensation is SPARED (palmar cutaneous branch passes superficial to retinaculum)
- ðĄNight symptoms are classic - distinguish from cervical radiculopathy which is position-related
- ðĄNerve conduction studies are the gold standard for diagnosis
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Common questions about this condition
During sleep, wrist flexion increases carpal tunnel pressure. Additionally, fluid redistribution when lying down and lack of the "muscle pump" effect of hand movement allows edema to accumulate in the tunnel.
The palmar cutaneous branch of the median nerve branches off proximal to the carpal tunnel and passes superficial to the flexor retinaculum. Therefore, it is not compressed in carpal tunnel syndrome.