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http://upload.orthobullets.com/topic/6024/images/radial tunnel syndrome.jpg
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  • A compressive neuropathy of the posterior interosseous nerve (PIN) with pain only 
    • no motor or sensory dysfunction, and EMG/NCS is not useful
  • Pathophysiology
    • involves same sites of compression as PIN syndrome, which 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 
  • Radial Tunnel
    • 5cm 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
  • Symptoms
    • deep aching pain in dorsoradial proximal forearm q
      • 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
      • may have paresthesias in the first dorsal web space
    • motor
      • no motor manifestations
  • 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
  • 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 Diagnosis
  • 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 
  • 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%)
  • 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 (1)

(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? Review Topic


Radiocapitellar Arthritis




Radial tunnel syndrome




Carpal tunnel syndrome




Lateral epicondylitis




Intersection Syndrome



Select Answer to see Preferred Response


The patient has radial tunnel syndrome, which often presents with insidious onset of pain and tenderness several centimeters distal to the lateral epicondyle, and pain elicited with active extension of the long finger against resistance can help differentiate the condition from lateral epicondylitis.

Radial tunnel syndrome is a compressive neuropathy that can occur between the mobile wad laterally and the biceps aponeurosis and brachialis insertion medially as the nerve courses over the radiocapitellar joint into the forearm. Patients usually have diffuse pain over the site of the radial tunnel, sometimes have radiating pain in the distribution of the superficial radial nerve, and occasionally have subtle weakness or fatigue of the wrist and extrinsic finger extensors. Initial treatment should include conservative measures such as stretching, activity modification, and NSAIDS; Injections can be performed for both diagnostic and therapeutic reasons. Surgical intervention is indicated if pain persists despite exhausting conservative measures. The most common anatomic causes of radial tunnel syndrome are fibrous adhesions between the brachialis and brachioradialis, the Leash of Henry (radial recurrent vessels), the fibrous edge of the ECRB, the arcade of Fröhse (supinator arch), and fibrous bands of the leading edge of the supinator muscle.

Dang et al. discuss compression neuropathies of the upper extremity in their 2009 review article. They highlight the importance of the clinical exam in diagnosing radial tunnel syndrome, especially the location of pain, which is distal to that of lateral epicondylitis. Additionally ruling out other less common diagnoses on the differential can be assisted by EMG (radiculopathy or plexopathies), MRI (tumor or other causes of mass effect), and diagnostic injections.

Illustration A shows the anatomy of the five common sites of compressing in the radial tunnel.

Incorrect Answers:

1. Radiocapitellar arthritis would not be antagonized by stretch of the common extensors of the wrist
3. Carpal tunnel syndrome is diagnosed by evidence of nerve compression of the median nerve at the wrist and should not be associated with pain near the origin of the wrist extensors
4. Lateral epicondylitis can very much mimic radial tunnel syndrome; however, the location of the pain and tenderness on exam can be a very helpful
5. Intersection syndrome is a chronic tenosynovitis of the ECRL and ECRB characterized by pain at the intersection of the 1st and 2nd dorsal compartments of the wrist


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