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Radial Tunnel Syndrome

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Topic updated on 06/07/14 2:55pm
Introduction
  • A compressive neuropathy of the posterior interosseous nerve (PIN) with pain only 
    • no motor or sensory dysfunction
  • 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 edge of the supinator (arcade of Frohse
        • most frequent site of entrapment of the PIN
      • distal edge of the superfcial layer of the supinator
  • Associated conditions
    • lateral epicondylitis 
      • RTS is difficult to distinguish from lateral epicondylitis and coexists in 5% of patients 
Anatomy
  • 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 membrance
      • 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 capusle
          • 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 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
      • resisted supination test (with elbow and wrist in extension)
        • reproduces pain at radial tunnel 
      • passive pronation with wrist flexion
        • reproduces pain at radial tunnel
        • passive stretch of supinator muscle increases pressure inside radial tunnel
      • 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
Imaging
  • MRI
    • usually negative
    • indications
      • to identify muscle changes in muscles innervated by PIN
        • denervation edema/atrophy within the supinator/extensor  
      • to evalute 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 synvitis, 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 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 
Treatment
  • Nonoperative
    • activity modification, temporary splinting, NSAIDS
      • indications
        • first line of treatment for at least one year
      • technique
        • 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 disapointing 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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(OBQ08.21) A 35-year-old female office worker reports 6 months of deep aching on her lateral dominant elbow which worsens with repetitive movements. On physical exam, the patient has tenderness located 4cm distal to the lateral epicondyle. She also complains of night pain. What is the most likely diagnosis? Topic Review Topic

1. Lateral epicondylitis
2. Radial tunnel syndrome
3. Carpal tunnel syndrome
4. Erb's palsy
5. Multiple sclerosis

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This video demonstrates a radial tunnel release.
2/23/2013
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