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Updated: May 7 2023

Radial Tunnel Syndrome

Images leash.jpg compression.jpg tunnel syndrome.jpg tunnel lateral.jpg leash.jpg
  • 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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