Radial nerve

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RADIAL NERVE

Anatomy
Lesions
Axillary
Spiral groove
Radial tunnel
Posterior interosseus
Superficial radial
DDx
Finger extensor weak
Triceps weak

External link

Sensory

Gowers

Motor

Anatomy

Formed by: Axons from
- Roots: C5 to T1
- Brachial plexus
  - Trunks: Superior, Medial & Inferior
  - Cord: Posterior
Axons pass through
- Spiral groove of humerus
- Fibrous arch attachment of triceps to humerus
- Lateral intermuscular septum below deltoid insertion
- Arcade of Frohse: Above supinator & Below elbow
Branches
- Above elbow
  - Above spiral groove (Humerus)
    - Cutaneous nerves to arm: Posterior; Lower lateral
    - Cutaneous nerve to forearm: Posterior
      - Nosology: Posterior cutaneous nerve of forearm; Posterior antebrachial cutaneous
    - Triceps brachii: 3 to 5 branches
    - Anconeus
  - Below spiral groove
    - Brachioradialis: Distal to lateral intermuscular septum
    - Extensor carpi radialis longus & brevis
- At or below elbow
  - Above arcade of Frohse (Supinator): Final bifurcation
    - Superficial radial nerve
      - Sensory: Dorsolateral hand & 1st 3 digits
      - May overlap with: Dorsal ulnar cutaneous nerve
    - Posterior interosseus nerve (Deep branch): Extensor carpi radialis brevis & Supinator
  - Passes through arcade of Frohse
    - Arcade of Frohse location: Between 2 heads of supinator muscle
    - Posterior interosseus nerve: Anatomy
      - Passes through the supinator muscle
      - Innervates: All extrinsic wrist extensors except ECRL
        
        Finger & thumb extensors
        
        Most distal radial innervated muscle: Extensor indicis proprius
        
        Extensor carpi ulnaris
        Abductor pollicis longus
        Sensory: Articular branches to wrist joint
      - External link: Anatomy

Lesions ³

General
- Common causes: Nerve trauma
  - Nerve compression
  - Humoral fractures
- Common location: Arm > Forearm
- Branches involved: Common
  - Extensor indicis proprius
  - Extensor digitorum communis
  - Brachioradialis
- Neuropathy associations
  - Multifocal motor
  - Brachial plexopathy
- Electrodiagnostic
  - Non-traumatic disorders: Conduction block more common; SNAPs preserved
  - Localization: Spiral groove > Distal
  - Triceps: May be involved with spiral groove compressive lesions
Axilla
- Clinical
  - Weakness: Triceps; Wrist drop
  - DDx from posterior cord of brachial plexus: No deltoid weakness
  - DDx from C7 root: Brachioradialis weakness
- Pressure palsy (Triad neuropathy)
  - With median & ulnar nerves
  - Usually occurs in sedated or inebriated patients
- Missile injuries
Upper arm (Spiral groove)
- Clinical
  - Weakness
    - Brachioradialis; Wrist & Finger extensors; Supinator
    - Spared: Triceps; Anconeus
  - Sensory loss
    - Superficial radial sensory nerve
    - Hand: Lateral dorsum
    - Fingers: Thumb dorsum; Dorsal proximal phalanges 2, 3, 4
- NCV
  - Superficial radial SNAPs: Low amplitude
  - Distal radial CMAP: Low amplitude
- Causes
  - Pressure on medial arm: Compression against humerus
    - Sleep paralysis (Saturday night palsy)
    - Anesthesia
    - Tourniquet
  - Fractures: Humerus
    - Management
      - Closed fractures: Recover spontaneously
      - Complex fractures or after closed reduction: Surgical exploration
  - Triceps contraction: Sudden; Severe
  - Injections
  - Neonatal
Radial tunnel ¹
- Anatomy
  - Location: Humeroradial joint to Supinator muscle
  - Nerve segment: Posterior (PIN) interosseous
  - Compression sites: Similar to PIN syndrome
    - Radiocapitellar joint
    - Radial recurrent branches
    - Extensor carpi radialis brevis
    - Arcade of Frohse
    - Distal edge of supinator
- Clinical
  - Pain
    - Location: Radial proximal forearm; Lateral elbow
    - Tenderness: Over radial tunnel
    - Provocation: Resisted middle finger extension
    - Worse with repetitive activity
    - Differential diagnosis: Tennis elbow (Lateral epicondylitis); Lateral antebrachial cutaneous nerve compression
  - Weakness: Little or None
  - Possible treatments: Decompression, Physiotherapy, Steroid injection, Immobilization
Posterior interosseus ¹
- Anatomy
  - Origin: Deep motor branch that pierces supinator muscle at elbow level
  - Supplies: Extensor carpi radialis brevis & supinator before entering arcade of Froshe
  - Supplies all extrinsic wrist extensors except Extensor carpi radialis longus
- Clinical
  - Epidemiology
    - Males > Females
    - Right > Left
  - Weakness
    - Abductor pollicis longus
    - Finger drop: Finger & Thumb extensors; Especially medial 3 fingers; May be patchy
    - Wrist
      - Involved: Extensor carpi radialis brevis; Supinator; Extensor carpi ulnaris
      - Spared: Extensor carpi radialis, Long head; Extensor carpi radialis brevis (Proximal branch)
    - Spared proximal: Triceps, Anconeus, Brachioradialis, Extensor carpi radialis longus
  - Sensation: Normal
  - Pain
    - Forearm, dorsal (From deep sensory axons)
    - See: Radial tunnel syndrome (Forearm pain without weakness)
  - Hand position: Radial deviation with wrist extension
  - Differential diagnosis
    - Extensor tendon rupture
    - Radial lesion at spiral groove: Abnormal superficial radial (First dorsal web space) sensation
- NCV
  - Superficial radial SNAPs: Normal amplitude
  - Distal radial CMAP: Low amplitude
- Lesions
  - Fractures: Radius
  - Elbow deformity
    - Late paralysis after fracture or osteomyelitis
    - Rheumatoid arthritis
  - Soft tissue masses
  - Compression
    - Extensor carpi radialis brevis muscle
    - Arcade of Frohse
  - Laceration: Rare because nerve is deep to extensor muscles
  - Idiopathic
    - Supinator syndrome
      - ? Related to repetitive pronation-supination movements
      - Sports: Tennis, Throwers, Bodybuilders, Swimmers, Gymnasts
    - "Resistant tennis elbow": Inflammation of attachment of forearm extensors to lateral epicondyle
      - Weakness: Absent or minimal
      - Pain: Extensor forearm; Worse at night
      - Tenderness: 5 cm distal to lateral epicondyle
      - True tennis elbow has tenderness at lateral epicondyle
  - PIN Mimics ²
    - Radial neuropathy, Fascicular
      - Lesions
        
        Location: Proximal radial nerve lesion at upper arm levels
        
        Focus: 8.3 cm proximal to humeroradial joint
        
        Some in: Posterior cord of brachial plexus
        Diagnosis: MR neurography
        
        Fascicular: Partial lesion; Often (75%) follow somatotopic pattern
        Involve fascicles forming posterior interosseous nerve
      - Clinical features
        
        Similar to PIN syndrome
        
        Early: Pain in some patients
        
        Course: May progress to involve more proximal muscles
      - Frequency in PIN clinical syndromes: Up to 80%
    - Brachial neuritis
    - Mononeuritis multiplex
    - Multifocal motor neuropathy
Superficial Radial nerve
- Nosology
  - Cheiralgia paresthetica
  - Wartenberg syndrome
- Clinical
  - Pain
  - Sensory loss
    - Common: Dorsolateral hand, Thumb & 1st 2 or 3 digits
    - Anomalous innervation: Dorsomedial hand (9% of hands; 16% of patients)
  - Itch
  - Strength: Normal
  - May be associated with: De Quervain tenosynovitis
- NCV
  - Superficial radial SNAPs: Low amplitude
  - Distal radial CMAP: Normal
- Causes
  - Elbow: Ruptured synovial effusion
  - Forearm: Aberrant couse through muscles
  - Wrist
    - Compression: Handcuffs, Casts, Wristbands
    - Trauma
    - Surgery: de Quervain's release
    - Injections & Arterial puncture
    - Nerve tumors
- Entrapment sites
  - Extensor carpi radialis brevis
  - Radiocapitellar joint
  - Leash of Henry,
  - Arcade of Frohse
  - Supinator border
  - Proximal: Triangular space; Spiral groove

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References
1. J Hand Surg 2008;33:72-78, J Bone Joint Surg Am 2008;90:420-428
2. Neurology 2016;87:1884–1891
3. Muscle Nerve 2025 Dec 14

12/16/2025