Radial Tunnel Syndrome

Introduction

An uncommon syndrome that entails entrapment of the radial nerve somewhere along the course between the elbow joint and distal border of the supinator muscle resulting in forearm pain. RTS is considered a “pain syndrome” without objective documentable findings.

Anatomy

From the distal lateral edge of the biceps tendon, the dorsal branch of the radial nerve (DBRN) courses obliquely and enters the proximal supinator edge approximately 3.5 cm from the radiohumeral (RH) joint. The DBRN exits the supinator muscle as the PIN approximately 7.5 cm distal to the RH joint

Pathogenesis

Use the mnemonic “FREAS” to remember the sites of compression (similar sites seen PIN syndrome):

• ibrous bands at the elbow
• adial recurrent vessels (Leash of Henry)
• xtensor carpi radialis brevis (fibrous border of ECRB)
• rcade of Frohse – the fibrous, proximal border of the superficial portion of supinator. This is the most common site of entrapment and lies 3-5 cm distal to Heuter’s line (epicondylar axis).
• upinator (distal border)

Natural History

Describe the natural history,epidemiology and prognosis

Patient History and Physical Findings

History:

• Forearm pain. There is no motor deficit as in posterior interosseous syndrome.

Physical Findings:

• TTP overlying the radial neck, mobile wad, supinator
• Radial nerve impingement is exacerbated with elbow extension, forearm pronation, and wrist flexion.
• Provocative maneuvers:
  • Active wrist extension and forearm supination against resistance, however this will also aggravate lateral epicondylitis symptoms.
  • resisted supination with the elbow extended
  • resisted extension of the long finger MCP joint with the elbow extended and forearm supinated

Imaging and Diagnostic Studies

Radiography:

• MRI may reveal muscle denervation along PIN distribution; Possibly signs of mechanical compression.

Electrophysiology:

• Studies are negative in most cases of radial tunnel syndrome, as opposed to posterior interosseous nerve syndrome which often has positive EMG findings
• Positive test: motor latency between nerve to brachioradialis and nerve to extensor carpi ulnaris of greater than 1.8ms.

Differential Diagnosis

• Posterior Interosseous Syndrome : Whereas radial tunnel syndrome is characterized by forearm pain without motor deficit, posterior interosseous syndrome is characterized by a motor deficit.
• Lateral epicondylitis symptoms are similar to radial tunnel syndrome and the two commonly coexist. Diagnostic/therapeutic injections can be used to differentiate them. Also, lateral epicondylitis will have pain with resisted wrist extension.
• Osteoarthritis

Treatment

Nonoperative treatment:

• Activity modification
• rest, stretching, splinting
• Consider corticosteroid injection near the nerve after 6-12 months of failed conservative treatment

Operative treatment:

• Surgical release of PIN and potentially treatment of coexistent lateral epicondylitis
• Technique:
  • Approach: Thomson (dorsal approach)
    • Landmarks: lateral epicondyle and Lister’s tubercle distally. Incision is in line with these two points
  • Identify ECRB -EDC interval
  • Dissect EDC from fibrous border of ECRB
  • Dissect fascia overlying the supinator
  • Palpate the PIN underlying the supinator
  • Sharply dissect through the supinator in line with the course of the PIN
  • Release the “FREAS” structures
  • Treat potential coexisting lateral epicondylitis

Pearls and Pitfalls

Postoperative Care

Outcome

Complications

References