Carpal Tunnel Syndrome: Diagnosis and Management

Overview

• Carpal tunnel syndrome (CTS) is the most common peripheral compressive neuropathy.
• It results from compression of the median nerve within the carpal tunnel, producing sensory and motor symptoms in the median nerve distribution.
• The severity spectrum ranges from mild intermittent nocturnal paraesthesiae to severe thenar wasting with permanent sensory loss.

Anatomy and Biomechanics

• The carpal tunnel is a rigid osseofibrous canal bounded by the carpal bones posteriorly and the transverse carpal ligament (TCL, flexor retinaculum) anteriorly.
• It transmits the four tendons of flexor digitorum superficialis, four of flexor digitorum profundus, flexor pollicis longus, and the median nerve.
• It does not transmit the flexor carpi radialis (separate tunnel) or the ulnar nerve (Guyon's canal).
• The carpal tunnel is not classified as a compartment for the purposes of compartment syndrome.

Carpal tunnel pressures (Gellman):

$$P_{\text{neutral (CTS)}} \approx 32\ \text{mmHg} \quad P_{\text{flexion 90°}} \approx 99\ \text{mmHg} \quad P_{\text{extension 90°}} \approx 110\ \text{mmHg}$$

$$P_{\text{neutral (control)}} \approx 25\ \text{mmHg} \quad P_{\text{flexion (control)}} \approx 31\ \text{mmHg}$$

This pressure elevation underlies Phalen's test physiology and the rationale for neutral-position splinting.

Surgical Anatomy

Clinical Assessment

History

CTS is primarily a clinical diagnosis. Characteristic features:

• Paraesthesiae (numbness, tingling, burning) in the thumb, index, middle, and radial half of ring finger
• Nocturnal symptoms: awakening with burning/numbness relieved by shaking the hand (flick sign)
• Symptom provocation by sustained wrist flexion (driving, reading, phone use)
• Forearm aching common; proximal radiation raises suspicion of cervical radiculopathy or double-crush phenomenon
• Functional decline: difficulty with fine tasks, dropping objects

80% pre-test probability of CTS when all six features are present: symptoms in median-innervated digits, nocturnal symptoms, thenar atrophy or weakness, positive Tinel test, positive Phalen test, and loss of two-point discrimination.

Provocative and Sensibility Tests

High diagnostic probability when all four of the following are abnormal: hand diagram (patient self-marks symptom distribution), positive Durkan test, abnormal Semmes-Weinstein testing, and night pain.

Differentials

Investigations

Electrodiagnostic Studies

NCS are the gold-standard confirmatory investigation but are not mandatory before surgery for clinically typical CTS. Indications for NCS:

• Atypical or uncertain diagnosis
• Bilateral symptoms with systemic disease
• Medico-legal or occupational compensation context
• Severity stratification and prognostication

Electrodiagnostic Criteria for CTS

Electrodiagnostic Severity Grading

Prognostic note: Absent sensory potentials or severe denervation on EMG preoperatively correlates with incomplete postoperative neurological recovery, particularly in patients >70 years or with thenar atrophy.

Ultrasound

• High-resolution ultrasound is useful when NCS findings are equivocal or when clinical CTS is present with normal nerve conduction (~10% of cases).
• A median nerve cross-sectional area (CSA) ≥10-11 mm² at the pisiform level is diagnostic in most validated studies.
• Ultrasound can identify space-occupying lesions (ganglion, lipoma, anomalous muscle) causing secondary CTS.

Plain Radiography

Routine radiographs have limited diagnostic value in CTS but should be obtained if:

• Trauma history (distal radius fracture, acute CTS)
• Suspected bony impingement or supracondylar process
• Suspected calcium pyrophosphate or other crystal arthropathy

Non-operative Management

Indications

• Mild to moderate CTS without denervation
• Pregnancy-related CTS (frequently resolves postpartum)
• Reversible precipitating causes (hypothyroidism, pregnancy, dialysis-related)
• Medical comorbidities precluding surgery or patient preference

Modalities

Corticosteroid Injection

Injection of corticosteroid (e.g. methylprednisolone 20-40 mg or triamcinolone 20-40 mg ± 1 mL local anaesthetic) into the carpal canal provides meaningful but time-limited benefit.

• Technique: Needle inserted at the wrist crease ulnar to palmaris longus (or between PL and FCR) at 30-45°, directed toward the ring finger, to deposit steroid within the canal ulnar to the median nerve.
• Ultrasound guidance reduces intraneural injection risk.

More effective for:

• Shorter symptom duration
• Mild-moderate severity
• Pregnancy-associated CTS
• Diagnostic confirmation (relief supports the diagnosis)

Predictors of poor response:

• Severe electrodiagnostic findings
• Thenar wasting
• Prolonged symptom duration (>12 months)
• Diabetes mellitus

Effect on subsequent surgery: Prior corticosteroid injection does not significantly prejudice the outcome of subsequent surgical decompression.

Operative Management

Indications for Surgery

Open Carpal Tunnel Release (OCTR)

Complete division of the TCL under direct vision via a palmar incision is the standard operation.

Key principles:

• Incision placed ulnar to the thenar crease (in line with ring finger axis) to protect the palmar cutaneous branch (radial) and recurrent motor branch
• Extends from ~1 cm proximal to the wrist flexion crease to Kaplan's cardinal line, terminating at the level of the superficial palmar arch
• TCL divided under direct vision
• Internal neurolysis and epineurotomy are not recommended: no additional benefit demonstrated and associated with worse outcomes in meta-analyses
• Flexor tenosynovectomy indicated only for florid inflammatory tenosynovitis (e.g. rheumatoid arthritis)
• Camitz opponensplasty (palmaris longus transfer to APB) may be added for elderly patients with severe thenar atrophy and poor opposition

Endoscopic Carpal Tunnel Release (ECTR)

• Two principal techniques: single-portal (Agee) and dual-portal (Chow).
• A slotted cannula is introduced proximal to the wrist; a blade divides the TCL from its deep surface under endoscopic visualisation.

Open vs Endoscopic CTR Comparison

• Both techniques achieve equivalent symptom relief, patient-reported outcomes, and neurophysiological recovery at 12 months.
• Choice should be individualised based on patient occupation, surgeon experience, and anatomy.

Complications

Outcomes and Prognosis

• Corticosteroid injection: ~80% symptom relief at 6 weeks; ~20% sustained benefit at 12 months. Useful as a bridge or for pregnancy-related CTS.
• Surgical release: Highly effective; maximal improvement within the first 6 months postoperatively. Beyond 6 months, no significant further improvement in Phalen/Tinel tests, pinch strength, motor latency, or functional scores.
• Predictors of better surgical outcome: Shorter symptom duration, younger age, mild-moderate NCS changes, no thenar atrophy, absence of diabetes.
• Predictors of incomplete recovery: Age >70, severe EMG denervation, absent sensory potentials, thenar atrophy (resolves slowly if at all), diabetes mellitus (long-term outcomes inferior at 10 years using Boston Carpal Tunnel Questionnaire).
• Metabolic syndrome (≥3 of: diabetes/hypertension, elevated triglycerides ≥150 mg/dL, low HDL <50 mg/dL women, central obesity, elevated fasting glucose) delays but does not preclude recovery.

Validated outcome measures: Boston Carpal Tunnel Questionnaire (BCTQ, symptom severity scale + functional status scale), QuickDASH, PRWHE.

Paediatric Considerations

• Idiopathic CTS in children is uncommon.
• Presentation is atypical, rarely sensory complaints; more often nocturnal pain, hand clumsiness, and thenar atrophy.

Underlying causes:

• Mucopolysaccharidoses / lysosomal storage diseases (most common metabolic causes in children)
• Hypothyroidism
• Congenital bony abnormalities
• Myopathic contractures
• Electrodiagnostic confirmation is appropriate given atypical presentation.
• Surgical release is indicated when symptoms are persistent and progressive, especially with thenar atrophy; results are generally excellent.

Decision Algorithm Summary

Suspected CTS (clinical features)
 ↓
Clinical diagnosis confirmed?
(Durkan +, hand diagram, night symptoms, Phalen/Tinel)
 ↓
Mild-moderate, no thenar atrophy → Non-operative management
 • Neutral splinting (nocturnal)
 • Corticosteroid injection (diagnostic + therapeutic)
 • Treat reversible causes (hypothyroidism, pregnancy, etc.)
 ↓
Persistent or severe symptoms / progressive deficit / thenar wasting
 ↓
Confirm with NCS (severity grading, prognosis)
 ↓
Surgical release:
 OCTR (standard, lower complication rate)
 OR
 ECTR (earlier return to work, equivalent long-term outcomes,
 slightly higher early complication rate, requires expertise)

Clinical Scenario Summary