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
| Structure | Relevance |
|---|---|
| Palmar cutaneous branch of median nerve | Arises ~5 cm proximal to wrist crease; passes radial to TCL - at risk with radially deviated incisions |
| Recurrent (thenar) motor branch | Exits median nerve distal to TCL; most commonly extraligamentous (~46%) but may be subligamentous or transligamentous - at risk with lateral incisions |
| Ulnar neurovascular bundle | Lies in Guyon's canal immediately ulnar to hook of hamate - at risk with excessive ulnar dissection |
| Superficial palmar arch | Distal boundary of TCL; at risk with aggressive distal cut |
| Hook of hamate | Radial wall of Guyon's canal; key endoscopic landmark for ulnar boundary |
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
| Test | Technique | Sensitivity | Specificity | Notes |
|---|---|---|---|---|
| Phalen's test | Maximum passive wrist flexion ×60 s; positive if paraesthesiae reproduced | ~75% | ~47% | Most sensitive provocative test |
| Tinel's sign | Percussion over median nerve at wrist | ~50% | ~77% | Most specific provocative test; least sensitive |
| Durkan's (carpal compression) test | Direct sustained thumb pressure over carpal tunnel ×30 s | ~87% | ~90% | Superior to both Phalen and Tinel; preferred screening test |
| Two-point discrimination | Static or moving; >6 mm abnormal | Low (late finding) | High | Indicates advanced sensory axonal loss |
| Semmes-Weinstein monofilaments | Threshold testing | Correlates with electrodiagnostic severity | - | More sensitive than 2PD for early compression |
| Thenar wasting / APB weakness | Observation and resisted palmar abduction | Late finding | High | Indicates severe or chronic disease; present in ~50% requiring surgery |
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
| Condition | Distinguishing Features |
|---|---|
| Cervical radiculopathy (C6/C7) | Neck pain, positive Spurling's, proximal symptoms; Phalen's negative |
| Pronator syndrome | Forearm pain, palmar cutaneous branch territory involved, provoked by resisted pronation or resisted middle finger PIP flexion; Phalen's negative; Tinel's proximal (not at wrist) |
| Thoracic outlet syndrome | Positional, bilateral, often ulnar-predominant |
| Diabetic peripheral neuropathy | Stocking-glove pattern, bilateral |
| De Quervain's / trapeziometacarpal OA | Radial-sided pain rather than paraesthesiae |
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
| Parameter | Abnormal Threshold | Notes |
|---|---|---|
| Median distal sensory latency (DSL) | >3.5 ms (14 cm antidromic) | Most sensitive single parameter |
| Median distal motor latency (DML) | >4.5 ms | To APB at 8 cm |
| Median sensory nerve conduction velocity | <50 m/s across wrist | - |
| Median-ulnar sensory latency difference (ring finger) | >0.5 ms | High sensitivity for mild CTS |
| Median-radial sensory latency difference (thumb) | >0.5 ms | Useful in early CTS |
| EMG of APB | Fibrillation potentials, reduced recruitment | Indicates axonal loss; poorer prognosis |
Electrodiagnostic Severity Grading
| Grade | NCS Findings |
|---|---|
| Mild | Prolonged sensory latency only; normal motor latency |
| Moderate | Prolonged sensory and motor latency |
| Severe | Absent sensory response; prolonged or absent motor response |
| Very severe | Absent sensory and motor potentials; EMG shows APB denervation |
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
| Intervention | Evidence / Effect | Duration of Benefit |
|---|---|---|
| Neutral wrist splinting (nocturnal) | Good evidence; particularly effective for night symptoms and pregnancy-related CTS | Requires ongoing use; symptoms may recur |
| Activity modification | Reduces provocative postures and vibration exposure | Adjunctive |
| NSAIDs / oral corticosteroids | Short-term symptom relief | Limited duration; systemic side effects |
| Corticosteroid injection (carpal canal) | ~80% symptom relief at 6 weeks; ~20% sustained at 1 year | Temporary |
| Therapeutic ultrasound / physiotherapy | Limited evidence | Adjunctive |
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
| Indication | Urgency |
|---|---|
| Failed non-operative management (≥3-6 months) | Elective |
| Moderate-severe electrodiagnostic changes | Elective |
| Thenar wasting or APB weakness | Semi-urgent |
| Severe or progressive neurological deficit | Semi-urgent |
| Acute CTS (post-fracture, haematoma) | Urgent |
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
| Feature | Open CTR | Endoscopic CTR |
|---|---|---|
| TCL visualisation | Direct | Endoscopic from deep surface |
| Return to work | Longer (4-6 weeks heavy work) | Earlier by ~1-2 weeks |
| Scar tenderness | More common short-term | Less common |
| Complication rate | Lower overall | Slightly higher (nerve/vessel injury), especially early in learning curve |
| Incomplete TCL division | Less common | More common early in learning curve |
| Long-term outcome | Equivalent | Equivalent |
| Learning curve | Shorter | Longer |
| Cost | Lower | Higher (disposable equipment) |
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
| Complication | Notes |
|---|---|
| Incomplete TCL division | Most common cause of persistent symptoms; more common in ECTR early in learning curve |
| Recurrent (thenar) motor branch injury | Risk with radially deviated incision (OCTR) or improper portal (ECTR) |
| Palmar cutaneous branch injury | Risk with radially placed incision |
| Ulnar nerve / vessel injury | Higher risk with ECTR; improper portal placement |
| Superficial palmar arch injury | Described with ECTR; aggressive distal dissection |
| Pillar pain | 10-30%; tenderness at thenar/hypothenar bases; usually resolves by 3-6 months; less frequent with ECTR |
| Scar hypertrophy / dysaesthesia | More common OCTR; 5-10% |
| Infection | <1% both techniques |
| CRPS | Rare; more common with psychological distress |
| Incomplete neurological recovery | More common with severe or chronic CTS, age >70, diabetes |
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
| Clinical Scenario | Preferred Management |
|---|---|
| Mild CTS, short duration, no denervation | Splinting ± corticosteroid injection |
| Pregnancy-related CTS | Splinting; injection if needed; usually resolves postpartum |
| Moderate CTS, failed non-operative ≥3-6 months | CTR (open or endoscopic per surgeon/patient preference) |
| Severe CTS with thenar atrophy | Prompt CTR; consider Camitz opponensplasty if severe opposition loss in elderly |
| Acute CTS post-distal radial fracture | Remove constricting dressings, extend wrist to neutral; persistent symptoms → urgent CTR |
| Diabetic patient with typical CTS | CTR effective short-term; counsel regarding potentially slower/incomplete long-term recovery |
| Inflammatory tenosynovitis (e.g., RA) | CTR + flexor tenosynovectomy |