Radial Nerve Compression Syndromes

Sites of Compression

  • Upper Arm – Humeral fracture, Saturday night palsy
  • Around Elbow – Posterior Interosseous Nerve (PIN) palsy, Radial Tunnel Syndrome (RTS)
  • Forearm – Wartenberg’s Syndrome (Cheiralgia Parasthetica)

PIN Compression

Anatomic Causes (FREAS Mnemonic)

  1. F – Fibrous bands between Brachioradialis (BR) & capsule at radial head
  2. R – Recurrent vessels from Radial artery (Leash of Henry) crossing PIN
  3. E – ECRB tendinous edge
  4. A – Arcade of Frosche (most common, vessels proximal to supinator)
  5. S – Supinator belly or distal edge

Radial Tunnel – Region extending up to the supinator

Non-Anatomic Causes

  1. Lipomas
  2. Ganglions
  3. Synovitis in RA
  4. Monteggia fracture
  5. Chronic radial head dislocation
  6. Parsonage Turner Syndrome (more common in AIN)

Clinical Features

Presentation

  • Rapid-onset weakness
  • Occasional lateral forearm ache
  • Wrist radially deviates on extension (ECRL function intact)
  • ECRL & Brachioradialis preserved (suggests Radial nerve involvement)

History

  • Recent viral infection, shoulder pain? → Consider Parsonage Turner Syndrome

Investigations

  • EMG/NCS
    • EMG is very accurate for PIN compression
  • MRI
    • To rule out space-occupying lesions

Management

  • Usually requires decompression due to motor deficit
  • Decompress distal to proximal by identifying supinator distally
  • Surgical Approaches:
    • Anterior approach – Good access to all structures up to supinator
    • Posterior (Thompson) approach – Better visualization of the whole nerve

Radial Tunnel Syndrome (RTS)

  • Rare condition
  • Compression of sensory part of Radial Nerve

Radial Tunnel Anatomy

  • Located between:
    • Fibrous bands of Brachioradialis
    • Proximal edge of Supinator
  • PIN dives into Supinator
  • Superficial Radial Nerve (SRN) runs on top of Supinator
  • Causes are the same as for PIN Palsy (except for Supinator compression)

Clinical Presentation

  • Pain, but no weakness
  • Pain over mobile wad, radiating distally

Diagnosis

  • Difficult to diagnose clinically
  • EMG is normal
  • Maximal pain is 1.5 cm anterior & distal to lateral epicondyle
  • Middle Finger Extension Test
    • Resisted extension = mobile wad pain
    • Pathognomonic but can mimic Tennis Elbow

Differential Diagnosis

  • Tennis Elbow
  • Compression of Lateral Cutaneous Nerve of the Forearm

Key Statistics

  • >50% of RTS cases have concurrent Tennis Elbow
  • Only 1% of Tennis Elbow cases have RTS
  • Best differentiator: Targeted local anesthetic (LA) injection

Management

  • Rule out Tennis Elbow
  • Decompress as for PIN, but results are often unpredictable

Wartenberg’s Syndrome (Cheiralgia Parasthetica)

Definition

  • Compression of the Superficial Radial Nerve (SRN) in the forearm beyond the Radial Tunnel
  • Caused by scissoring between ECRL & Brachioradialis during pronation

Etiology

  • Extrinsic Compression (watches, bracelets, tight bands)
  • Spontaneous

Clinical Features

  • Pain & numbness (No weakness)

Diagnosis

  • NCS – Delayed conduction
  • Examination:
    • Forced pronation provokes symptoms
    • Tinel’s sign over nerve

Management

  • Non-operative first
  • If fails & other causes ruled out → Surgical decompression
  • Ensure decompression beneath Brachioradialis (usual site of compression)
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