Carpal Tunnel Syndrome (CTS)

What Is It?

Anatomy of the Carpal Tunnel

• Floor/sides: Arching carpal bones (hamate, pisiform medially; scaphoid tubercle, trapezial ridge laterally)
• Roof: Flexor retinaculum (transverse carpal ligament, TCL)

• The median nerve - the most palmar (superficial) structure in the tunnel
• Nine flexor tendons lying dorsal to the nerve: 4x flexor digitorum superficialis, 4x flexor digitorum profundus, 1x flexor pollicis longus

Key anatomical point: The palmar cutaneous branch of the median nerve exits proximal to the flexor retinaculum, so CTS causes numbness in the distal thumb, index, and middle fingers but NOT over the thenar eminence itself - a useful diagnostic clue.

• Goldman-Cecil Medicine, p. 4088
• Gray's Anatomy for Students, p. 920

Pathophysiology

1. Venous congestion
2. Nerve edema
3. Anoxic damage to capillary endothelium of the median nerve
4. Progressive demyelination and, in severe cases, axonal loss

• Gray's Anatomy for Students, p. 920
• Campbell's Operative Orthopaedics 15e, p. 4502

Causes and Risk Factors

The cause is idiopathic in most cases. Work association is difficult to substantiate, and non-dominant hand involvement is frequent.

• Campbell's Operative Orthopaedics 15e, p. 4503
• Firestein & Kelley's Textbook of Rheumatology, p. XXX

Clinical Features

Symptoms

• Paresthesia (tingling/numbness) in the thumb, index, and middle fingers (+/- radial half of ring finger) - classic median nerve distribution
• Nocturnal symptoms are hallmark - waking the patient at night
• Relief by shaking or elevating the hand ("flick sign")
• Diffuse aching or throbbing pain radiating up the forearm
• Occasionally proximal symptoms including shoulder pain
• In severe/late cases: thenar muscle atrophy and weakness (abductor pollicis brevis, opponens pollicis)
• Subjective numbness can spread to the whole hand (even ulnar distribution) - this does not exclude CTS

Signs

• Bradley and Daroff's Neurology in Clinical Practice, p. 549
• Firestein & Kelley's Rheumatology, p. XXX

Provocative Tests

The CTS-6 is as sensitive and specific as EMG/nerve conduction studies (NCS) and is free, non-invasive, and immediate.

• Campbell's Operative Orthopaedics 15e, p. 4502

Investigations

Nerve Conduction Studies (NCS) + EMG

• Gold standard for confirmation
• Abnormal values: distal motor latency >4.5 ms, sensory latency >3.5 ms
• EMG may show: increased insertional activity, positive sharp waves, fibrillations at rest, decreased motor recruitment
• NCS: 90% sensitive, 60% specific
• Important caveat: Studies can be normal in symptomatic patients and abnormal in asymptomatic patients. They are not predictors of functional recovery post-surgery.
• Useful for ruling out cervical radiculopathy, thoracic outlet syndrome, and proximal nerve compression

Ultrasound

• Increasingly used; can show median nerve enlargement (cross-sectional area) at the wrist
• High sensitivity/specificity comparable to NCS in many studies

Blood tests to screen for secondary causes

• Campbell's Operative Orthopaedics 15e, p. 4503
• Bradley and Daroff's Neurology, p. 549

Differential Diagnosis

• Cervical disc disease / radiculopathy (C6/C7)
• Thoracic outlet syndrome
• Diabetic or other peripheral neuropathy
• Pronator teres syndrome (median nerve compression at elbow)
• Autoimmune/inflammatory conditions

Treatment

Conservative (First-line)

• Best used at night to prevent provocative wrist positioning
• Should hold wrist at neutral to 10 degrees extension - NOT hyperextension
• Use sparingly during the day to avoid secondary muscle weakness
• Effective for mild cases; long-term benefit is limited

• Methylprednisolone injection into the carpal tunnel
• Highly effective short-term; long-term efficacy is mixed
• Risk of median nerve injury if performed incorrectly
• Best reserved for: pregnancy-related CTS, or when surgery must be temporarily deferred

Surgical (Definitive)

• Failed conservative treatment
• Objective sensory loss (late finding) - prompt early referral
• Thenar atrophy (late finding) - prompt early referral
• Severe electrodiagnostic abnormalities

• Surgery is highly effective, with most patients obtaining relief
• Endoscopic approach is generally preferred over open
• Revision surgery is occasionally needed for recurrent symptoms
• Firestein & Kelley's Rheumatology, p. XXX
• Goldman-Cecil Medicine, p. 4088
• Campbell's Operative Orthopaedics 15e, p. 4502

Special Populations

Pregnancy

• CTS is common in pregnancy (fluid retention increases tunnel pressure)
• Usually resolves spontaneously after delivery
• Corticosteroid injection is reasonable if symptoms are severe
• Goldman-Cecil Medicine, p. 4088

Children

• CTS is unusual in children
• Associated with: congenital bone abnormalities, hypothyroidism, lysosomal storage disease, myopathic contractures, or strong family history
• Symptoms differ: decreased dexterity, diffuse pain, absent Phalen/Tinel in late stages

Summary: Clinical Approach

SUSPECT CTS:
Nocturnal hand tingling + median nerve distribution + flick sign
          ↓
EXAMINE:
Phalen / Tinel / Durkan test + thenar atrophy + CTS-6 score
          ↓
SCREEN BLOODS:
TFTs, fasting glucose, FBC, CRP, RF (exclude secondary causes)
          ↓
CONFIRM (if needed):
NCS/EMG or wrist ultrasound
          ↓
TREAT:
Mild-Moderate: Night splint ± NSAIDs → corticosteroid injection if inadequate
Severe/refractory/atrophy: Surgical release (endoscopic preferred)

Recent Evidence (2025)

• Conservative treatments comparison (splints, injections, physiotherapy, hydrodissection): PMID 40315975
• Ultrasound-guided nerve hydrodissection outperforms some conservative options: PMID 39894044
• Neurodynamic tests (Phalen, Tinel) have moderate diagnostic accuracy: PMID 40156954