Updated: 7/31/2022

Radial Tunnel Syndrome

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  • Summary
    • Radial Tunnel Syndrome is a compressive neuropathy of the posterior interosseous nerve (PIN) at the level of proximal forearm (radial tunnel).
    • Diagnosis is made clinically with pain only (maximal tenderness 3-5 cm distal to lateral epicondyle) without any motor or sensory dysfunction.
    • Treatment is a prolonged course of conservative management with NSAIDs, temporary splinting and CSIs with radial tunnel decompression reserved for refractory cases.
  • Epidemeology
    • Incidence
      • rare
        • ~3 per 100,000 annually
    • Demographics
      • male > females
  • Etiology
    • Pathophysiology
      • involves same sites of compression as PIN syndrome
      • include (from proximal to distal)
        • fibrous bands anterior to radiocapitellar joint
        • radial recurrent vessels (leash of Henry)
        • medial edge of ECRB
        • proximal aponeurotic/tendinous edge of the supinator (arcade of Frohse)
          • most frequent site of entrapment of the PIN
          • normal radial tunnel pressure 50mmHg
          • with supinator stretch (forced wrist flexion) pressure increases to 250mmHg
        • distal edge of the superficial layer of the supinator
      • risks
        • constant prono-supination with 1kg force and elbow in 0°-45° flexion
    • Associated conditions
      • lateral epicondylitis
        • RTS is difficult to distinguish from lateral epicondylitis and coexists in 5% of patients
  • Anatomy
    • Radial Tunnel
      • 5 cm in length
      • from the level of the radiocapitellar joint, extending distally past the proximal edge of the supinator
      • boundaries
        • lateral
          • brachioradialis
          • ECRL
          • ECRB
        • medial
          • biceps tendon
          • brachialis
        • floor
          • capsule of the radiocapitellar joint
    • PIN
      • origin
        • PIN is a branch of the radial nerve that provides motor innervation to the extensor compartment
      • course
        • passes between the two heads of origin of the supinator muscle
        • direct contact with the radial neck osteology
        • passes over abductor pollicis longus muscle origin to reach interosseous membrane
        • transverses along the posterior interosseous membrane
      • innervation
        • motor
          • common extensors
            • ECRB (often from radial nerve proper, but can be from PIN)
            • Extensor digitorum communis (EDC)
            • Extensor digiti minimi (EDM)
            • Extensor carpi ulnaris (ECU)
          • deep extensors
            • Supinator
            • Abductor pollicis longus (APL)
            • Extensor pollicus brevis (EPB)
            • Extensor pollicus longus (EPL)
            • Extensor indicis proprius (EIP)
        • sensory
          • sensory fibers to dorsal wrist capsule
            • provided by terminal branch which is located on the floor of the 4th extensor compartment
          • no cutaneous innervation
  • Presentation
    • Symptoms
      • deep aching pain in dorsoradial proximal forearm
        • from lateral elbow to wrist
        • increases during forearm rotation and lifting activities
      • muscle weakness
        • because of pain and not muscle denervation
    • Physical exam
      • tenderness
        • over mobile wad over the supinator arch
        • maximal tenderness is 3-5cm distal to lateral epicondyle
          • more distal than lateral epicondylitis
      • provocative tests
        • resisted long finger extension test
          • reproduces pain at radial tunnel (weakness because of pain)
        • resisted supination test (with elbow and wrist in extension)
          • reproduces pain at radial tunnel (weakness because of pain)
        • passive pronation with wrist flexion
          • reproduces pain at radial tunnel
          • passive stretch of supinator muscle increases pressure inside radial tunnel to 250mmHg (normal 50mmHg)
        • radial tunnel injection test
          • diagnostic if injection leads to a PIN palsy and relieves pain
      • sensory
        • no cutaneous sensory manifestations 
        • if changes present in the first dorsal web space consider more proximal pathology
      • motor
        • no motor manifestations
  • Imaging
    • MRI
      • usually negative
      • indications
        • to identify muscle changes in muscles innervated by PIN
          • denervation edema/atrophy within the supinator/extensor
        • to evaluate compression sites
          • may show thickened edge of ECRB, prominent radial recurrent vessels (leash of Henry), swelling of PIN
        • to identify other causes of entrapment (rare)
          • tumors, ganglia, radiocapitellar synovitis, bicipital bursitis, radial head fractures and dislocations
  • Studies
    • Electrodiagnostic studies
      • EMG/NCV are inconclusive because
        • PIN carries unmyelinated Group IV fibers (C-fibers, nociception) and small myelinated Group IIA afferent fibers (temperature)
        • pressure on these fibers produces pain
        • these fibers cannot be evaluated by EMG/NCV
        • the large myelinated fibers of PIN remain normal, producing normal EMG/NCV
    • Diagnostic injection
      • injection of local anesthetic (LA) into the area of localized tenderness
      • ensure that LA does not spread to lateral epicondyle
  • Differential
    • Key differential
      • Lateral epicondylitis 
        • both conditions coexist in 5% of patients
        • in lateral epicondylitis, tenderness is directly over the lateral epicondyle
        • in RTS, tenderness is 3-5cm distal to the lateral epicondyle
      • Cervical radiculopathy at C6-7 
        • electrodiagnostic studies may show denervation
  • Diagnosis
    • Clinical
      • diagnosis is made with careful history and physical examination
  • Treatment
    • Nonoperative
      • activity modification, temporary splinting, NSAIDS
        • indications
          • first line of treatment for at least one year
        • technique of activity modification
          • avoid prolonged elbow extension with forearm pronation and wrist flexion
      • corticosteroid injection
        • indications
          • both diagnostic and therapeutic
        • outcomes
          • 70% improvement at 6 weeks
          • 60% pain free at 2 years
    • Operative
      • radial tunnel release
        • indications
          • extensive nonoperative treatment fails
        • outcomes
          • surgical release has disappointing results
            • only 50-90% good to excellent results
            • delayed maximal recovery of up to 9-18 months
          • lower success rate in the following groups
            • concomitant multiple entrapment neuropathies (60%)
            • concomitant lateral epicondylitis (40%)
            • workers compensation patients (30%)
  • Techniques
    • Radial tunnel release
      • approach
        • dorsal approaches to the PIN
          • 3 planes have been described
            • between ECRB and EDC
            • between brachioradialis and ECRL
            • transmuscular brachioradialis-splitting
        • anterior approach to the PIN
          • between brachioradialis and biceps
      • technique
        • release arcade of Frohse
        • release distal edge of supinator
        • release fibrous bands superficial to the radiocapitellar joint
      • outcomes
        • success rate of surgical decompression is 70-90%
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Questions (4)
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(OBQ18.125) A 52-year-old construction worker presents with pain in the right proximal dorsoradial forearm over the last 8 months. He reports that his pain is worsened when using a screwdriver and lifting heavy objects. On exam, there is tenderness over the radial head and mobile wad, and pain with resisted supination and resisted third finger extension. There is no tenderness over the lateral epicondyle. There is no appreciable motor weakness or sensory deficits. Electromyography reveals no abnormalities. His radiographs are shown in Figures A and B. The patient has not sought any treatment up until this point. What is the likely diagnosis and first line treatment?

QID: 213021

Radial tunnel syndrome; physical therapy and activity modification



Lateral epicondylitis; debridement of the extensor carpi radialis brevis



PIN Syndrome; surgical release of the leash of Henry and arcade of Froshe



Radial tunnel syndrome; steroid injection into the radial tunnel



Lateral epicondylitis; steroid injection into the lateral epicondyle



L 2 A

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(OBQ08.21) A 35-year-old female office worker reports 6 months of deep aching pain that is worse at night on her lateral dominant elbow. The pain also worsens with repetitive movements. On physical exam, the patient has tenderness located 4cm distal to the lateral epicondyle over the mobile wad, and she has subtle weakness of the wrist extensors. Extending her long finger against resistance with a flexed wrist is very painful for her. She also complains of her pain worsening at night. What is the most likely diagnosis?

QID: 407

Radiocapitellar Arthritis



Radial tunnel syndrome



Carpal tunnel syndrome



Lateral epicondylitis



Intersection Syndrome



L 2 C

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