High Yield Overview

RADIAL TUNNEL SYNDROME

Posterior Interosseous Nerve Compression | Pain Without Weakness | Controversial Diagnosis

4-5 cmRadial tunnel length (radial head to supinator)

5Potential entrapment sites in tunnel

0%Motor weakness (differentiates from PIN syndrome)

60-80%Success with conservative management

FIVE POTENTIAL COMPRESSION SITES

1. Fibrous Bands

PatternAnterior to radial head (Henry et al)

TreatmentMost proximal site

2. ECRB Edge

PatternTendinous margin of ECRB

TreatmentCommon compression site

3. Arcade of Frohse

PatternProximal edge of supinator

TreatmentMost common site (70%)

4. Distal Supinator

PatternDistal edge of supinator muscle

TreatmentCompression during pronation

5. Leash of Henry

PatternRecurrent radial vessels

TreatmentVascular compression

Critical Must-Knows

Pain without weakness - distinguishes from PIN syndrome (motor palsy)
Arcade of Frohse - fibrous arch at proximal supinator edge (70% of cases)
Rule of 9s test - pain with resisted long finger extension at 9cm distal to lateral epicondyle
Conservative management first - 3-6 months trial before considering surgery
Electrodiagnostics usually normal - clinical diagnosis, not confirmed by EMG/NCS

Examiner's Pearls

"
Radial tunnel syndrome = pain only; PIN syndrome = motor palsy
"
Differential diagnosis includes lateral epicondylitis (tennis elbow)
"
Arcade of Frohse is present in 30% of population (fibrous in 50% of those)
"
Surgical decompression has variable outcomes (50-90% success)

Clinical Imaging

Imaging Gallery

The drawing provides an anterior view of the course of the radial nerve at the elbow. Posterior interosseous nerve (PIN) entrapment may occur due to prominent radial recurrent artery (RRA), medial edg — The drawing provides an anterior view of the course of the radial nerve at the elbow. Posterior interosseous nerve (PIN) entrapment may occur due to pCredit: Dong Q et al. via Radiol Res Pract via Open-i (NIH) (Open Access (CC BY))

Illustration of the radial tunnel content through a dorsal approach demonstrating the bifurcation of the radial nerve into superficial and deep branches. The deep branch becomes the posterior inteross — Illustration of the radial tunnel content through a dorsal approach demonstrating the bifurcation of the radial nerve into superficial and deep branchCredit: Hazani R et al. via Eplasty via Open-i (NIH) (Open Access (CC BY))

T2 turbo spin-echo weighted magnetic resonance imaging demonstrating a space-occupying lesion in the radial tunnel. L indicates lesion; R, proximal radius. — T2 turbo spin-echo weighted magnetic resonance imaging demonstrating a space-occupying lesion in the radial tunnel. L indicates lesion; R, proximal raCredit: Cha J et al. via Eplasty via Open-i (NIH) (Open Access (CC BY))

Anterior approach to posterior interosseous nerve decompression. Superficial dissection. BR indicates brachioradialis; RA, radial artery; SRN, superficial radial nerve. — Anterior approach to posterior interosseous nerve decompression. Superficial dissection. BR indicates brachioradialis; RA, radial artery; SRN, superfiCredit: Cha J et al. via Eplasty via Open-i (NIH) (Open Access (CC BY))

Critical Radial Tunnel Syndrome Exam Points

No Motor Weakness

RTS is a pain syndrome WITHOUT motor weakness. If extensor weakness is present, this is Posterior Interosseous Nerve (PIN) syndrome, not radial tunnel syndrome. Pure sensory pain in the proximal forearm is the hallmark.

Five Compression Sites

FACES mnemonic: Fibrous bands, Arcade of Frohse (most common 70%), ECRB edge, Supinator distal edge, Leash of Henry. The arcade is a fibrous arch at the proximal supinator in 30% of population.

Rule of 9s Test

Pain with resisted long finger MCP extension at 9cm distal to lateral epicondyle is the specific test. This localizes the PIN at the radial tunnel and differentiates from lateral epicondylitis (pain at epicondyle).

Controversial Diagnosis

RTS is controversial - some surgeons question its existence. Electrodiagnostics are usually normal. Diagnosis is clinical. Conservative management for 3-6 months is mandatory before considering surgery.

Differential Diagnosis - RTS vs Lateral Epicondylitis vs PIN Syndrome

Feature	Radial Tunnel Syndrome	Lateral Epicondylitis	PIN Syndrome
Pain location	Mobile mass 4-5cm distal to lateral epicondyle	Lateral epicondyle (fixed)	Proximal forearm (with weakness)
Motor weakness	None (key feature)	None	Extensor weakness (thumb, fingers)
Resisted wrist extension	Pain distal to epicondyle	Pain at epicondyle	Weakness with pain
Rule of 9s test	Positive (pain at 9cm)	Negative	May be positive with weakness
Electrodiagnostics	Normal	Normal	Abnormal (denervation of PIN-innervated muscles)

At a Glance

Radial tunnel syndrome is a controversial pain syndrome without motor weakness, distinguishing it from PIN syndrome which causes extensor paralysis. The posterior interosseous nerve is compressed at one of five sites (FACES mnemonic), with the Arcade of Frohse (fibrous proximal supinator edge) being most common (70%). Diagnosis is clinical using the Rule of 9s test - pain with resisted long finger MCP extension at 9cm distal to the lateral epicondyle - as electrodiagnostics are typically normal. Conservative management (activity modification, NSAIDs, splinting) should be trialled for 3-6 months before considering surgical decompression, which has variable outcomes (50-90% success).

Mnemonic

FACESFACES - The Five Compression Sites

Fibrous bands

Anterior to radial head (proximal-most site)

Arcade of Frohse

Proximal supinator edge (most common - 70%)

ECRB edge

Tendinous margin of extensor carpi radialis brevis

Exit from supinator

Distal edge of supinator muscle

Leash (vessels)

Recurrent radial vessels (leash of Henry)

Memory Hook:The PIN FACES five obstacles as it passes through the radial tunnel

Mnemonic

NINENINE - Rule of 9s Test Components

Nine centimeters

Distance distal to lateral epicondyle

Index or long finger

Resist MCP extension (long finger most specific)

No motor weakness

Pain only, no extensor palsy

Elbow extension

Test with elbow extended, forearm pronated

Memory Hook:NINE helps remember the rule of 9s test - 9cm distal, long finger resistance, no weakness

Mnemonic

SPRINTSPRINT - Conservative Management Protocol

Splint

Forearm supination splint to reduce compression

Physical therapy

Stretching and strengthening exercises

Rest from aggravating activities

Activity modification

Injection

Steroid injection into radial tunnel (diagnostic and therapeutic)

NSAIDs

Anti-inflammatory medication

Time

3-6 months trial before surgery

Memory Hook:SPRINT through conservative treatment before considering surgical decompression

Overview and Epidemiology

Radial Tunnel Syndrome (RTS) is a controversial clinical entity characterized by pain in the proximal lateral forearm attributed to compression of the posterior interosseous nerve (PIN) within the radial tunnel, without motor weakness.

The radial tunnel:

Extends from the radial head to the distal edge of the supinator muscle
Approximately 4-5cm in length
Contains the posterior interosseous nerve (deep branch of radial nerve)
Has five potential compression sites along its course

Why Controversial?

RTS is controversial because: (1) electrodiagnostic studies are usually normal, (2) there is significant overlap with lateral epicondylitis, (3) surgical outcomes are variable (50-90% success), and (4) some authors question whether it is a distinct entity. Conservative management is always tried first.

Key distinguishing feature:

RTS = pain WITHOUT motor weakness
PIN syndrome = motor weakness (extensor palsy)

Clinical presentation:

Aching pain in the proximal dorsal forearm
Pain described as a mobile tender mass 4-5cm distal to lateral epicondyle
Exacerbated by repetitive pronation-supination and gripping
No weakness of thumb or finger extension (if weakness present = PIN syndrome)

Anatomy and Pathophysiology

Radial Nerve Anatomy

The radial nerve divides into superficial radial nerve (sensory) and posterior interosseous nerve (motor) at the level of the radiocapitellar joint. The PIN enters the radial tunnel and passes through the supinator muscle to innervate all finger and thumb extensors (except ECRL, which is innervated before the split).

Radial nerve course:

Proximal forearm: Radial nerve lies between brachialis and brachioradialis
Radiocapitellar joint level: Divides into superficial branch (sensory) and deep branch (PIN - motor)
Radial tunnel entry: PIN enters tunnel anterior to radial head
Supinator passage: PIN passes through supinator muscle via arcade of Frohse
Tunnel exit: Emerges at distal supinator edge to innervate extensors

The five potential compression sites (FACES):

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.

Pathophysiology:

Repetitive Compression

Repetitive pronation-supination activities cause mechanical compression of PIN at one or more sites in the radial tunnel. Most commonly at the arcade of Frohse during pronation.

Nerve Irritation

Chronic compression leads to perineural inflammation and nerve irritation. The nerve does not develop significant demyelination or axonal injury (hence normal electrodiagnostics).

Pain Syndrome

Patients develop chronic pain in the proximal forearm without motor dysfunction. The pain is thought to be from nociceptive C-fibers in the nerve sheath, not from nerve dysfunction.

Clinical Presentation and Diagnosis

Classic History

Patient presents with aching pain in the proximal dorsal forearm, 4-5cm distal to the lateral epicondyle. Pain is worse with repetitive pronation-supination (turning a screwdriver, doorknob) and gripping. No motor weakness. Often misdiagnosed as lateral epicondylitis (tennis elbow).

History:

Symptoms

Pain location: Proximal dorsal forearm
Quality: Deep, aching, burning
Radiation: May extend to dorsal forearm
Aggravating factors: Pronation, supination, gripping
Relieving factors: Rest, forearm supination
Duration: Usually insidious onset over weeks to months
No paresthesias or numbness (purely motor nerve)

Risk Factors

Occupational: Repetitive pronation-supination activities
Sports: Racquet sports, golf, weightlifting
Previous trauma: Radial head fracture, elbow dislocation
Anatomic: Fibrous arcade of Frohse
Coexisting conditions: Lateral epicondylitis (5% overlap)
Space-occupying lesions: Lipoma, ganglion (rare)

Physical Examination:

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.

Investigations

Electrodiagnostics in RTS

EMG and nerve conduction studies are USUALLY NORMAL in radial tunnel syndrome. This is because the compression causes pain but not significant demyelination or axonal injury. Normal electrodiagnostics do NOT rule out RTS. Diagnosis is clinical.

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).

Management

Treatment Hierarchy

Conservative management for 3-6 months is MANDATORY before considering surgical decompression. Surgery has variable outcomes (50-90% success) and should be reserved for patients who fail comprehensive non-operative treatment. Diagnostic injection can help select surgical candidates.

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.

Complications

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.

Evidence Base

Natural History and Conservative Management

Naam NH, Nemani S • J Hand Surg Am (2012)

Finding: Conservative management successful in 60-80% of patients with radial tunnel syndrome treated with activity modification, splinting, and NSAIDs for minimum 3 months.

Clinical Implication: This evidence guides current practice.

Surgical Decompression Outcomes

Konjengbam M, Elangbam J • Indian J Orthop (2010)

Finding: Surgical decompression provided good to excellent results in 67% of patients at mean 4-year follow-up. Positive diagnostic injection correlated with better surgical outcomes.

Clinical Implication: This evidence guides current practice.

Electrodiagnostic Findings

Rosenbaum R • Muscle Nerve (1999)

Finding: Electrodiagnostic studies (EMG/NCS) are typically normal in radial tunnel syndrome, distinguishing it from posterior interosseous nerve syndrome which shows denervation changes.

Clinical Implication: This evidence guides current practice.

Anatomical Studies - Arcade of Frohse

Spinner M • J Bone Joint Surg Am (1968)

Finding: Arcade of Frohse is present in 30% of population and is fibrous (non-yielding) in 50% of those cases. Most common site of PIN compression in radial tunnel syndrome.

Clinical Implication: This evidence guides current practice.

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOModerate

Scenario 1: Differentiating RTS from Lateral Epicondylitis

EXAMINER

"A 42-year-old office worker presents with 4 months of lateral elbow pain. She describes the pain as being 'a few centimeters below the bony point' on the outside of the elbow. Pain is worse with typing and turning doorknobs. No history of trauma. She has tried rest and ibuprofen with minimal improvement. How would you assess and manage this patient?"

EXCEPTIONAL ANSWER

This patient has lateral elbow pain that may represent radial tunnel syndrome, lateral epicondylitis, or both. I would take a systematic approach. **History**: I would clarify the exact pain location, aggravating activities (pronation-supination versus wrist extension), and any radiation. I would ask about paresthesias or weakness. The description of pain distal to the epicondyle suggests RTS rather than classic lateral epicondylitis. **Examination**: I would palpate the lateral epicondyle (lateral epicondylitis) and then 4-5cm distally (radial tunnel). I would perform resisted wrist extension (lateral epicondylitis), the rule of 9s test (RTS), and resisted long finger extension. I would assess motor strength of all finger and thumb extensors to rule out PIN syndrome. The mobile mass sign (tenderness moving with pronation/supination) would support RTS. **Investigations**: I would obtain plain radiographs to rule out bone pathology. Electrodiagnostics (EMG/NCS) would be normal in RTS but would help rule out PIN syndrome or C7 radiculopathy. **Management**: Initial conservative management for 3-6 months: activity modification, forearm supination splint, NSAIDs, and physical therapy. If symptoms persist at 6 weeks, I would consider diagnostic injection (2-3mL triamcinolone + lidocaine) into the radial tunnel. Significant pain relief would confirm the diagnosis and predict surgical success. If conservative measures fail after 6 months and diagnostic injection is positive, I would discuss surgical decompression of the radial tunnel via Thompson approach, releasing all five potential compression sites. I would counsel about variable outcomes (50-90% success) and 3-6 month recovery.

KEY POINTS TO SCORE

**Differentiate RTS from lateral epicondylitis**: Pain location (distal to epicondyle versus at epicondyle), mobile versus fixed tenderness

**Rule of 9s test**: Specific for RTS - pain with resisted long finger extension at 9cm distal to lateral epicondyle

**Conservative first**: Minimum 3-6 months trial before surgery

**Diagnostic injection**: Confirms diagnosis and predicts surgical outcome

COMMON TRAPS

✗Assuming all lateral elbow pain is tennis elbow - RTS is an important differential

✗Operating too early - conservative management mandatory for 3-6 months

✗Not checking motor strength - missing PIN syndrome

✗Not counseling about variable surgical outcomes

LIKELY FOLLOW-UPS

"What is the arcade of Frohse? - Fibrous arch at proximal supinator edge, present in 30%, fibrous in 50% of those, most common compression site"

"How do you differentiate RTS from PIN syndrome? - RTS has pain without weakness; PIN syndrome has motor weakness (finger/thumb extension) with abnormal EMG"

"What is your surgical approach? - Thompson approach (between ECRL and EDC), release all five compression sites (FACES)"

"What if the patient has both lateral epicondylitis and RTS? - Treat both simultaneously if surgical - lateral epicondylitis release and radial tunnel decompression"

VIVA SCENARIOStandard

Scenario 2: PIN Syndrome versus RTS

EXAMINER

"A 35-year-old carpenter presents with 6 weeks of progressive difficulty extending his fingers. He reports no pain, but noticed his wrist deviates to the radial side when he extends it. No history of trauma. On examination, he has weak finger and thumb extension but normal wrist extension strength. What is your diagnosis and management?"

EXCEPTIONAL ANSWER

This patient presents with progressive extensor weakness without pain, which is concerning for **posterior interosseous nerve syndrome** (PIN palsy), not radial tunnel syndrome. **Key distinguishing features**: The presence of **motor weakness** (finger and thumb extension) with **no pain** indicates nerve palsy, not RTS. The radial deviation of the wrist during extension occurs because ECRL/ECRB (radial nerve proper) are intact but ECU (PIN) is weak, causing unopposed radial wrist extensors. **Differential diagnosis**: PIN syndrome versus radial nerve palsy versus C7 radiculopathy. The intact wrist extension rules out radial nerve palsy (proximal to PIN bifurcation). The absence of neck pain and isolated PIN distribution suggests PIN syndrome. **Examination**: I would assess all PIN-innervated muscles: supinator, ECU, EDC, EPL, EPB, APL, EIP. I would expect weakness (MRC 3-4/5) in all. ECRL, ECRB, and brachioradialis should be normal (radial nerve proper). Wrist extension is preserved but deviates radially. I would examine the neck to rule out radiculopathy. **Investigations**: **EMG/NCS is critical** - would show denervation (fibrillations, positive sharp waves) in PIN-innervated muscles. This confirms PIN syndrome and differentiates from RTS (normal EMG). MRI of the forearm to look for space-occupying lesion (lipoma, ganglion) compressing the PIN. **Management**: If space-occupying lesion identified on MRI, I would recommend urgent surgical decompression and excision of the mass. If no mass and symptoms are progressive or severe, I would recommend surgical decompression of the radial tunnel via Thompson approach. If symptoms are mild and non-progressive, I could observe for 3 months as spontaneous recovery can occur in some cases. Post-operatively, early active ROM and nerve glides, followed by progressive strengthening. Recovery may take 3-6 months, and full motor recovery is not guaranteed if axonal loss is significant.

KEY POINTS TO SCORE

**PIN syndrome has motor weakness; RTS has pain only** - this is the critical distinction

**Radial wrist deviation**: ECRL/ECRB intact but ECU weak (unopposed radial deviation)

**EMG is abnormal in PIN syndrome**: Denervation in PIN-innervated muscles

**Look for compressive mass**: MRI to identify lipoma, ganglion, or tumor

COMMON TRAPS

✗Confusing PIN syndrome with radial nerve palsy - check wrist extension (preserved in PIN syndrome)

✗Waiting too long to decompress - progressive motor weakness needs urgent treatment

✗Not ordering MRI - may miss space-occupying lesion

✗Assuming all PIN compression is idiopathic - always look for structural cause

LIKELY FOLLOW-UPS

"What muscles are weak in PIN syndrome? - All PIN-innervated: supinator, ECU, EDC, EPL, EPB, APL, EIP. ECRL/ECRB normal"

"Why does the wrist deviate radially? - ECU (PIN) weak, ECRL/ECRB (radial nerve) intact, unopposed radial deviation"

"What is the most common cause of PIN syndrome? - Space-occupying lesions (lipoma, ganglion) or trauma (Monteggia fracture-dislocation)"

"What is your surgical approach? - Thompson approach, decompress all five sites, excise any compressive mass"

VIVA SCENARIOStandard

Scenario 3: Failed Surgical Decompression

EXAMINER

"A 48-year-old patient underwent radial tunnel decompression 4 months ago for chronic lateral forearm pain. Post-operatively, he had mild improvement for 6 weeks but now reports pain has returned to pre-operative levels. He is frustrated and asks what went wrong. How would you manage this patient?"

EXCEPTIONAL ANSWER

This patient has failed radial tunnel decompression, which occurs in 10-30% of cases. I would approach this systematically to identify the cause. **Causes of failure**: Wrong diagnosis (was not RTS), incomplete decompression (missed compression site), coexisting pathology (lateral epicondylitis not addressed), nerve injury during surgery, or scar/adhesion formation. **History**: I would review the original presentation and compare to current symptoms. Are symptoms identical or different? Any new features such as weakness (nerve injury) or sensory changes? Review surgical details: what approach was used, were all five sites released, were any masses found? **Examination**: Complete examination of elbow and forearm. Assess motor strength of all PIN-innervated muscles to rule out nerve injury. Palpate for tenderness at lateral epicondyle (coexisting lateral epicondylitis) and radial tunnel. Check for mobile mass sign. Perform rule of 9s test and resisted wrist extension. **Investigations**: **Repeat EMG/NCS** to assess for nerve injury (denervation would indicate PIN injury during surgery). **MRI** to look for: incomplete release (residual compression), space-occupying lesion that was missed, scar tissue causing re-compression. **Diagnostic injection** into the radial tunnel - significant relief would suggest incomplete decompression; no relief suggests wrong diagnosis. **Management**: If diagnostic injection is positive and MRI shows incomplete decompression, I would discuss **revision decompression**. I would counsel that revision surgery has lower success rates than primary surgery. If injection is negative, I would focus on conservative management: activity modification, PT, NSAIDs. If nerve injury is identified on EMG, I would observe for 6 months for recovery. If coexisting lateral epicondylitis is identified, I would treat with injection or surgery. **Counseling**: Honest discussion about variable outcomes of radial tunnel surgery, possibility of alternative diagnosis, and realistic expectations for revision surgery. Some patients may not benefit from further intervention.

KEY POINTS TO SCORE

**Failed decompression occurs in 10-30%** - important to counsel pre-operatively

**Systematic work-up**: History, exam, EMG, MRI, diagnostic injection

**Identify cause**: Wrong diagnosis, incomplete release, coexisting pathology, nerve injury, scar

**Revision surgery** only if clear cause identified (incomplete release, mass)

COMMON TRAPS

✗Rushing to revision surgery without identifying cause of failure

✗Not considering alternative diagnosis (lateral epicondylitis, C7 radiculopathy)

✗Not checking for nerve injury with EMG

✗Overpromising on revision surgery outcomes

LIKELY FOLLOW-UPS

"What are the five compression sites? - FACES: Fibrous bands, Arcade of Frohse, ECRB edge, Exit from supinator, Leash of Henry"

"What imaging would you obtain? - MRI to assess for incomplete release, mass, scar tissue"

"When would you consider revision surgery? - Only if diagnostic injection positive and MRI shows clear cause (incomplete release or mass)"

"What if EMG shows denervation? - Nerve injury during primary surgery, observe 6 months for recovery, consider neurolysis if no improvement"

MCQ Practice Points

Exam Pearl

Q: What is the key clinical difference between radial tunnel syndrome and posterior interosseous nerve (PIN) syndrome?

A: Radial tunnel syndrome: Pain only, NO motor weakness. PIN syndrome: Motor weakness (finger/thumb extension), NO pain or sensory loss. Both involve PIN compression in the radial tunnel, but radial tunnel syndrome affects sensory afferents in nerve sheath while PIN syndrome causes axonal damage to motor fibers. Treatment also differs: RTS often conservative, PIN syndrome often requires surgery.

Exam Pearl

Q: What are the five sites of compression in the radial tunnel (FACES mnemonic)?

A: Fibrous bands anterior to radiocapitellar joint, Arcade of Frohse (most common, 70%), C (ECRB medial edge), Exit of PIN from supinator, S (leash of Henry - recurrent radial vessels). The Arcade of Frohse is a fibrous arch at the proximal edge of supinator, present in 30% of people, fibrous in 50% of those. Most surgical releases focus on this structure.

Exam Pearl

Q: What examination findings help differentiate radial tunnel syndrome from lateral epicondylitis?

A: Both cause lateral forearm pain. Radial tunnel syndrome: Tender 4-5 cm distal to lateral epicondyle (over radial tunnel), pain with resisted middle finger extension (ECRB edge stretches over PIN), pain with resisted supination. Lateral epicondylitis: Tender at lateral epicondyle itself, pain with resisted wrist extension. Can coexist in up to 5% of cases.

Exam Pearl

Q: What muscles does the posterior interosseous nerve supply?

A: Supinator (first branch), then ECU, EDC, EDM, APL, EPL, EPB, EIP. Notably does NOT supply ECRL or ECRB (these are supplied by radial nerve proper before division). This explains why PIN palsy causes finger and thumb drop but preserved wrist extension (radially deviated due to intact ECRL/ECRB without ECU balance).

Exam Pearl

Q: What is the role of EMG/NCS in radial tunnel syndrome diagnosis?

A: EMG/NCS are typically NORMAL in radial tunnel syndrome (this is a pain syndrome without denervation). This differentiates from PIN syndrome where EMG shows denervation of PIN-innervated muscles. Diagnosis of radial tunnel syndrome is clinical. Diagnostic injection of local anesthetic into the radial tunnel with pain relief supports diagnosis. MRI may show muscle edema but is often normal.

Australian Context

Conservative Care: Radial tunnel syndrome is primarily managed conservatively in Australia. PBS-subsidised NSAIDs and physiotherapy through Enhanced Primary Care (EPC) plans are first-line treatments.

Specialist Referral: Patients failing 3-6 months of conservative management are referred to hand surgeons. Electrodiagnostic studies (NCS/EMG) are often performed to rule out other conditions but are typically normal in RTS.

Surgical Management: Radial tunnel decompression is performed as day surgery under regional or general anaesthesia. Post-operative hand therapy is important for optimizing outcomes.

Workers Compensation: RTS is recognized as an occupational condition particularly in workers with repetitive forearm pronation-supination. Documentation of work-related activity modification is important for compensation claims.