Radial Tunnel Syndrome

Arcade of Frohse (Most Common - 70%)

Anatomy:

• Fibrous arch at the proximal edge of the supinator muscle
• Present in approximately 30% of the population
• When present, it is fibrous (non-yielding) in 50% of cases
• Formed by the tendinous margin of the superficial head of supinator

Mechanism of compression:

• PIN passes beneath the arcade as it enters the supinator
• Pronation increases tension on the arcade
• Repetitive pronation-supination causes chronic irritation
• Fibrous arcade does not yield during forearm rotation

Clinical significance:

• Most common site of compression in radial tunnel syndrome
• Target of surgical decompression (release the arcade)
• Variable anatomy explains inconsistent surgical outcomes

This is the most important compression site to know for exams.

2. Fibrous Bands (Anterior to Radial Head)

• Described by Henry et al as fibrovascular bands
• Most proximal potential site of compression
• Anterior to the radial head and radiocapitellar joint
• Variable presence

3. ECRB Tendinous Edge

• Extensor carpi radialis brevis (ECRB) tendinous margin
• PIN passes deep to the ECRB muscle belly
• Tight ECRB edge can compress the nerve
• May coexist with lateral epicondylitis

4. Distal Supinator Edge

• Compression at the distal (exit) edge of supinator
• PIN emerges from supinator to innervate extensors
• Compression during pronation activities
• Less common site

5. Leash of Henry (Recurrent Radial Vessels)

• Recurrent radial artery and veins crossing the PIN
• Named after A. K. Henry
• Vascular leash can compress the nerve
• Released during surgical decompression

All five sites must be addressed during surgical decompression.

Posterior Interosseous Nerve Motor Distribution

PIN innervates:

• Supinator (first muscle)
• Extensor carpi ulnaris (ECU)
• Extensor digitorum communis (EDC)
• Extensor digiti minimi (EDM)
• Abductor pollicis longus (APL)
• Extensor pollicis longus (EPL)
• Extensor pollicis brevis (EPB)
• Extensor indicis proprius (EIP)

NOT innervated by PIN:

• ECRL - innervated by radial nerve proper before bifurcation
• ECRB - innervated by radial nerve proper before bifurcation
• Brachioradialis - innervated by radial nerve proper

Clinical implication:

• In PIN palsy (not RTS), wrist extension is preserved (ECRL/ECRB intact)
• But wrist deviates radially because ECU is paralyzed
• Finger and thumb extension is lost

RTS has NO weakness of any of these muscles - pain only!

Inspection

• No visible deformity in most cases
• No muscle wasting (differentiates from PIN syndrome)
• Compare both forearms for symmetry

Palpation

• Tenderness at 4-5cm distal to lateral epicondyle (over radial tunnel)
• Patient describes tender area as a mobile mass
• Tenderness moves with pronation and supination
• No tenderness directly at lateral epicondyle (if present, consider lateral epicondylitis)

Mobile mass sign:

• PIN and radial tunnel move during forearm rotation
• Tender point moves distally with pronation, proximally with supination
• Differentiates RTS from lateral epicondylitis (fixed tenderness at epicondyle)

Palpation is the most important examination finding.

Rule of 9s Test (Most Specific)

Technique:

1. Elbow extended, forearm pronated
2. Palpate 9cm distal to lateral epicondyle
3. Resist long (middle) finger MCP extension
4. Positive: Pain at the point of palpation

Sensitivity: Approximately 90% for RTS Specificity: Higher than other tests

Resisted Supination Test

Technique:

1. Elbow flexed to 90 degrees
2. Forearm pronated
3. Resist active supination
4. Positive: Pain in proximal forearm

Rationale: Supinator muscle contraction tightens arcade of Frohse

Resisted Long Finger Extension

Technique:

1. Resist long finger MCP extension with forearm pronated
2. Positive: Pain in radial tunnel (not at epicondyle)

Rationale: EDC activity increases compression in the tunnel

Injection Test (Diagnostic)

Technique:

1. Inject 2-3mL of local anesthetic + steroid into radial tunnel
2. Retest special tests after 10-15 minutes
3. Positive: Significant pain relief (temporary)

Value: Confirms diagnosis and predicts surgical success

All special tests aim to compress or irritate the PIN in the radial tunnel.

Motor Examination (Key - Must Be Normal)

Wrist extension:

• ECRL and ECRB: Normal strength (MRC 5/5)
• Wrist extends but may deviate radially if patient splints

Finger extension:

• EDC, EIP: Normal strength (MRC 5/5)
• Test each finger individually

Thumb extension:

• EPL, EPB: Normal strength (MRC 5/5)
• Thumb-up sign should be strong

If ANY weakness present: This is PIN syndrome, not RTS

Sensory Examination

Superficial radial nerve distribution:

• Dorsal first web space (radial nerve sensory branch)
• Normal sensation (superficial branch not affected in RTS)

No paresthesias or numbness in RTS because PIN is purely motor

Normal motor and sensory exam is required for RTS diagnosis!

Electromyography (EMG) and Nerve Conduction Studies (NCS)

Typical findings in RTS:

• Normal motor latencies (radial nerve and PIN)
• Normal sensory latencies (superficial radial nerve)
• No denervation on needle EMG
• Normal recruitment in PIN-innervated muscles

Role:

• Rule out PIN syndrome (which shows denervation)
• Rule out radial nerve palsy (proximal lesion)
• Rule out C7 radiculopathy (cervical spine)
• Confirm clinical diagnosis is not due to nerve pathology

If EMG shows denervation of PIN muscles: This is PIN syndrome, not RTS

Findings in PIN Syndrome (for comparison)

• Denervation in PIN-innervated muscles (supinator, ECU, EDC, EPL, APL)
• Fibrillation potentials and positive sharp waves on needle EMG
• Reduced recruitment in affected muscles
• Indicates axonal injury requiring surgical decompression

Electrodiagnostics differentiate RTS (normal) from PIN syndrome (abnormal).

Plain Radiographs

Indications:

• All patients with elbow/forearm pain
• Rule out bone pathology

Views:

• AP and lateral elbow
• AP and lateral forearm

Look for:

• Radial head fracture (previous trauma)
• Elbow arthritis (alternative diagnosis)
• Heterotopic ossification (post-traumatic)
• Bone tumors (osteochondroma, etc.)

Expected: Normal in isolated RTS

Ultrasound

Utility:

• Visualize space-occupying lesions (lipoma, ganglion)
• Dynamic assessment of PIN during pronation-supination
• Operator-dependent

Findings:

• Usually normal
• May show swelling of PIN at compression site
• Can guide injection

MRI

Indications:

• Atypical presentation
• Rule out mass lesion
• Pre-operative planning

Findings:

• Usually normal
• May show signal changes in PIN (rare)
• Can identify lipoma, ganglion, or tumor
• Evaluate for lateral epicondylitis (coexisting)

Role: Rule out alternative diagnoses, not routinely needed

Diagnostic Injection

Technique:

• Inject 2-3mL of 1% lidocaine + corticosteroid into radial tunnel
• Injection point: 4-5cm distal to lateral epicondyle, deep to mobile point of tenderness
• Retest after 10-15 minutes

Positive test:

• Significant pain relief (more than 50% improvement)
• Predicts good surgical outcome

Value:

• Diagnostic: Confirms RTS
• Therapeutic: May provide lasting relief in some patients
• Prognostic: Positive response predicts surgical success

Diagnostic injection is the most valuable test for RTS.

Must Rule Out:

Always consider coexisting lateral epicondylitis (5% of cases).

Conservative Management (First-Line - 60-80% Success)

Duration: Minimum 3-6 months trial before surgery

1. Activity Modification

• Avoid repetitive pronation-supination activities
• Avoid forceful gripping with forearm pronated
• Ergonomic workplace modifications
• Limit aggravating sports activities

2. Splinting

• Forearm supination splint to reduce compression
• Wear during activities and at night
• 6-8 weeks trial
• Keeps forearm in neutral to supination (opens arcade of Frohse)

3. NSAIDs

• Ibuprofen 400-600mg three times daily with food
• Naproxen 500mg twice daily
• Duration: 2-4 weeks
• Watch for GI side effects

4. Physical Therapy

• Stretching: Forearm flexor and extensor stretches
• Strengthening: Progressive resistance exercises
• Nerve gliding: Radial nerve glides to reduce adhesions
• Modalities: Ice, ultrasound (limited evidence)

5. Corticosteroid Injection

• Indication: Failure of conservative measures at 6 weeks
• Technique: 2-3mL of triamcinolone 40mg/mL + 1% lidocaine
• Injection site: 4-5cm distal to lateral epicondyle, deep to brachioradialis
• Expected: Immediate relief if diagnosis correct
• Repeat: Can repeat once if partial response at 6 weeks
• Value: Diagnostic AND therapeutic

6. Observation

• Regular follow-up every 4-6 weeks
• Reassess symptoms and examination
• Reassess differential diagnosis if not improving

Most patients (60-80%) improve with conservative management.

Indications for Surgical Decompression

Absolute indications:

• None (RTS is not a surgical emergency)

Relative indications:

• Failure of 3-6 months conservative management
• Positive diagnostic injection (predicts surgical success)
• Significant functional impairment
• Normal electrodiagnostics (rules out PIN syndrome)
• Exclusion of alternative diagnoses

Contraindications:

• Less than 3 months of conservative treatment
• Negative diagnostic injection
• Abnormal EMG suggesting PIN syndrome
• Active infection
• Patient unable to comply with post-operative rehab

Pre-operative counseling:

• Success rate: 50-90% (variable in literature)
• Complete relief: Approximately 70%
• Partial relief: 20%
• No relief: 10-30%
• Recovery time: 3-6 months for full benefit
• Alternative: Continue conservative management

Careful patient selection is critical for surgical success.

Surgical Decompression of the Radial Tunnel

Positioning:

• Supine with arm on arm board
• No tourniquet (preserve vascular landmarks - leash of Henry)
• Arm in neutral rotation

Approach: Thompson (Posterior Interosseous) Approach (Preferred)

Incision:

• Longitudinal incision centered over mobile point of maximum tenderness
• Approximately 6-8cm long
• From lateral epicondyle extending distally over proximal forearm

Superficial dissection:

1. Incise skin and subcutaneous tissue
2. Identify interval between ECRL and EDC
3. Develop this internervous plane (both radial nerve innervated)
4. Protect lateral cutaneous nerve of forearm (crosses superficially)

Deep dissection:

1. Retract ECRL anteriorly and EDC posteriorly
2. Identify supinator muscle
3. Identify arcade of Frohse at proximal supinator edge
4. Carefully incise arcade longitudinally (avoid injury to PIN)
5. Trace PIN proximally and distally through entire tunnel

Decompression of five sites (FACES):

1. Fibrous bands anterior to radial head: Release
2. Arcade of Frohse: Release completely (critical step)
3. ECRB edge: Release tendinous margin if tight
4. Distal supinator: Continue release to distal edge
5. Leash of Henry: Identify and carefully mobilize (do not injure vessels)

Inspection:

• Inspect PIN throughout tunnel
• Ensure no kinking or compression
• Check for space-occupying lesions (lipoma, ganglion)

Closure:

• No drain typically required
• Close deep fascia loosely (avoid re-compression)
• Subcutaneous and skin closure

Alternative: Kocher Approach

• Between EDC and anconeus
• Risk of PIN injury higher (PIN crosses field)
• Less commonly used for radial tunnel release

Thompson approach is safer for PIN visualization and decompression.

Post-operative Protocol

Immediate (0-2 weeks):

• Soft dressing (no rigid splint)
• Early active ROM encouraged from day 1
• Avoid forceful pronation-supination for 2 weeks
• Wound care: Keep clean and dry
• Pain control: Oral analgesics as needed

Early rehabilitation (2-6 weeks):

• Progressive ROM: Full active and passive motion
• Gentle strengthening: Forearm supination/pronation against light resistance
• Nerve glides: Radial nerve gliding exercises
• Scar management: Massage and desensitization

Intermediate (6-12 weeks):

• Progressive strengthening: Wrist and finger extensors
• Functional activities: Gradual return to work tasks
• Sport-specific training if applicable

Return to activities:

• Light activities: 2-4 weeks
• Full activities: 3-6 months
• Full benefit: May take 3-6 months to assess outcome

Follow-up schedule:

• 2 weeks: Wound check, remove sutures
• 6 weeks: Assess ROM and strength
• 3 months: Assess functional outcome
• 6 months: Final outcome assessment

Early motion is critical to prevent adhesions and stiffness.

Intra-operative Complications

Posterior interosseous nerve injury (Most serious - 1-5%):

• Mechanism: Direct injury during dissection, stretch injury, thermal injury
• Presentation: Post-operative finger and thumb extensor weakness
• Prevention: Careful identification and protection of PIN throughout decompression
• Management: Observation for 3-6 months (most recover), nerve exploration/repair if no recovery

Vascular injury:

• Leash of Henry (recurrent radial vessels) can be injured
• Prevention: Careful dissection, no tourniquet (see vessels)
• Management: Direct pressure, ligation if necessary

Early Post-operative Complications (less than 6 weeks)

Wound complications:

• Infection: Less than 1%, treat with antibiotics +/- washout
• Hematoma: Rare without tourniquet, may require evacuation
• Dehiscence: Rare, secondary closure

Persistent pain:

• Incomplete decompression: May need revision
• Wrong diagnosis: Consider alternative diagnosis
• Nerve injury: Neuropathic pain

Late Complications (more than 6 weeks)

Recurrent symptoms (10-30%):

• Incomplete decompression: Most common cause
• Scar formation: Nerve re-compression
• Adhesions: Nerve tethering
• Management: Revision decompression in selected cases

Loss of supination strength (10-20%):

• Supinator muscle partially released
• Usually minimal functional impact
• Improves with strengthening exercises

Lateral antebrachial cutaneous nerve injury:

• Numbness/dysesthesia in lateral forearm
• Prevention: Identify and protect during superficial dissection
• Usually resolves over 6-12 months

Chronic regional pain syndrome (CRPS):

• Rare (less than 1%)
• Disproportionate pain, autonomic changes
• Management: Early PT, desensitization, pain clinic

PIN injury is the most serious complication - prevention is key.

Approach to Failed Decompression

Causes of failure:

1. Wrong diagnosis (was not RTS)
2. Incomplete decompression (missed site)
3. Coexisting pathology (lateral epicondylitis)
4. Nerve injury during surgery
5. Scar/adhesion formation

Work-up:

• Detailed history: Compare pre-op and post-op symptoms
• Re-examination: Look for objective findings
• Repeat injection: Assess response
• EMG/NCS: Rule out nerve injury
• MRI: Look for mass, scar tissue

Management options:

• Conservative: PT, NSAIDs, activity modification
• Injection: Steroid injection may provide relief
• Revision surgery: Only if clear cause identified (incomplete release, mass)
• Alternative diagnosis: Re-evaluate for lateral epicondylitis, C7 radiculopathy

Prognosis:

• Revision surgery has lower success rate than primary surgery
• Careful patient selection critical

Failed surgery emphasizes importance of correct diagnosis initially.