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)
- F – Fibrous bands between Brachioradialis (BR) & capsule at radial head
- R – Recurrent vessels from Radial artery (Leash of Henry) crossing PIN
- E – ECRB tendinous edge
- A – Arcade of Frosche (most common, vessels proximal to supinator)
- S – Supinator belly or distal edge
Radial Tunnel – Region extending up to the supinator
Non-Anatomic Causes
- Lipomas
- Ganglions
- Synovitis in RA
- Monteggia fracture
- Chronic radial head dislocation
- 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)