Radial Nerve Injury

• Originates from the posterior cord (C5–T1)

• Travels through the axilla, along the spiral (radial) groove of the humerus

• Divides near the elbow into:

  • Posterior interosseous nerve (PIN) – motor

  • Superficial radial nerve – sensory

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1. Very High Radial Nerve Palsy (Axilla)

Cause

• Compression or injury at the axillary level

Motor Deficits

• Involvement of all radial nerve branches distal to the axilla

• Loss of function of:

  • Triceps (long and medial heads) ? weak elbow extension

  • Wrist extensors (ECRL, ECRB) ? wrist drop

  • Finger extensors ? inability to extend fingers

Clinical Test

• Even when the wrist is passively extended, the patient cannot actively extend the fingers

Sensory Deficits

• Loss of sensation over:

  • Dorsum of the lateral 3½ digits (excluding nail beds)

  • Distribution of the superficial radial nerve

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Common Clinical Scenarios

Saturday Night Palsy

• Prolonged compression of the nerve in the axilla

• Often associated with alcohol intoxication

• Arm compressed against chair back, bar edge, or hard surface

Honeymoon Palsy

• Compression caused by another person sleeping on the arm overnight

Crutch Palsy

• Prolonged axillary pressure from improper use of crutches

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2. High Radial Nerve Palsy (Upper Arm to Elbow)

Cause

• Compression or injury within the spiral groove of the humerus

• Commonly due to fracture of the distal third of the humerus

Motor Deficits

• Loss of wrist and finger extension

• Wrist drop is a prominent feature

• Triceps function may be preserved (depending on injury level)

Sensory Deficits

• Sensory loss in the distribution of the superficial radial nerve

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Holstein–Lewis Fracture

• Spiral fracture of the distal third of the humerus

• High risk of associated radial nerve injury

• Presents with:

  • Wrist drop

  • Weak finger extension

  • Sensory loss over dorsum of hand

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3. Low Radial Nerve Palsy (Below the Elbow)

Causes

1. Entrapment of the posterior interosseous nerve (PIN) at the Arcade of Frohse

2. Fracture–dislocations around the elbow

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Posterior Interosseous Nerve (PIN) Injury

• PIN is a purely motor nerve

• No sensory loss

Clinical Features

• Weakness or paralysis of finger extension

• Wrist extension may be preserved

• Patient unable to extend fingers at MCP joints

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Arcade of Frohse

• Fibrous arch of the supinator muscle

• Most common site of PIN entrapment

• Leads to posterior interosseous nerve syndrome

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Monteggia Fracture

• Fracture of the proximal third of the ulna with dislocation of the radial head

• Radial nerve injury occurs due to secondary compression

• Key findings:

  • Difficulty with finger extension

  • Careful neurovascular examination is essential

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4. Wartenberg’s Syndrome (Wrist Level)

Cause

• Compression of the superficial branch of the radial nerve

Clinical Features

• Pain and paresthesia over:

  • Dorsum of the hand

• Pain typically localized ~8 cm proximal to the radial styloid

Examination

• Positive Tinel’s sign over the superficial radial nerve

• No motor weakness (pure sensory neuropathy)

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Key Summary Table