What is affected in carpal tunnel syndrome?

Carpal Tunnel Syndrome: Affected Structures and Pathophysiology

Carpal tunnel syndrome is caused by compression of the median nerve as it travels through the carpal tunnel, resulting in pain, paresthesia, and sometimes weakness in the distribution of the median nerve. 1

Anatomy and Pathophysiology

The carpal tunnel is a narrow passageway in the wrist through which the median nerve and several tendons pass. Key structures involved include:

• Median nerve: The primary affected structure in carpal tunnel syndrome
• Carpal bones: Form the floor and sides of the tunnel
• Transverse carpal ligament (flexor retinaculum): Forms the roof of the tunnel
• Flexor tendons: Nine tendons that share the tunnel with the median nerve

When inflammation occurs within this confined space, it causes compression of the median nerve, leading to the characteristic symptoms of carpal tunnel syndrome.

Clinical Manifestations

Compression of the median nerve results in:

• Pain and paresthesia in the distribution of the median nerve (thumb, index, middle finger, and radial half of the ring finger)
• Numbness and tingling in affected fingers
• Weakness of thumb abduction (in advanced cases)
• Thenar muscle atrophy (a late finding that is highly specific for CTS) 1

Diagnostic Evaluation

Clinical Assessment

• Provocative maneuvers:
  • Phalen test (wrist flexion)
  • Tinel sign (tapping over the median nerve)
  • These tests have varying sensitivity and specificity 1
• Physical examination findings:
  • Hypalgesia in median nerve distribution
  • Weak thumb abduction
  • Thenar atrophy (in advanced cases)

Diagnostic Testing

• Ultrasound: Recommended as an initial diagnostic test due to its high sensitivity and specificity 2

  • Key measurement: Cross-sectional area of the median nerve (>15 mm² is diagnostic)
  • Can identify median nerve enlargement and anatomic variants

• Electrodiagnostic studies: Gold standard when combined with clinical examination 2

  • Nerve conduction studies show:
    • Reduced conduction velocities
    • Reduced sensory and motor amplitudes
    • Abnormal temporal dispersion
    • Partial motor conduction blocks
  • A "sural-sparing" pattern is characteristic 2

Treatment Approach

Treatment is based on disease severity:

Mild to Moderate CTS

• Conservative management (for 6-12 weeks):
  • Wrist splinting in neutral position (night-only splinting is as effective as continuous wear) 2, 1
  • Local corticosteroid injections (provide greater symptom improvement than splinting at 6 weeks) 2

Severe CTS

• Surgical decompression is indicated for:
  • Objective weakness
  • Sensory deficits
  • Thenar atrophy 2, 1
  • Both endoscopic and open carpal tunnel release techniques are equally effective 1

Important Considerations

• Normal electrodiagnostic findings do not rule out carpal tunnel syndrome, especially in early stages 2
• Over-the-counter analgesics like NSAIDs and acetaminophen have not shown benefit for CTS 1
• CTS frequently occurs during pregnancy due to fluid retention, with conservative management preferred 2
• Ergonomic assessment and modifications are important, including avoiding vibratory tools and repetitive wrist movements 2

Understanding the anatomy and pathophysiology of carpal tunnel syndrome is essential for accurate diagnosis and appropriate treatment selection to improve patient outcomes and quality of life.