Medicine – Radial Nerve Palsy

Radial nerve palsy causes weakness of muscles supplied by the radial nerve, especially the extensor muscles of the wrist and fingers. The most characteristic clinical sign is wrist drop.

The exact pattern depends on the level of the lesion, because the radial nerve gives off branches at different points along the arm and forearm.

1. Main Function of the Radial Nerve

The radial nerve mainly supplies the extensor compartments of the upper limb.

Its motor functions include extension at the:

Elbow.

Wrist.

Metacarpophalangeal joints.

It also contributes to forearm supination through the supinator muscle.

2. Wrist Drop

The classic sign of radial nerve palsy is:

Wrist drop.

This occurs because the wrist extensors are weak or paralysed, while the flexor muscles remain relatively unopposed.

As a result, the hand falls into flexion at the wrist.

3. Finger Extension Weakness

Patients may also have difficulty extending the fingers at the metacarpophalangeal joints.

This can interfere with:

Opening the hand.

Releasing objects.

Positioning the fingers for grip.

Grip strength may also appear reduced because effective gripping requires the wrist to be stabilised in extension.

4. Sensory Loss

The radial nerve supplies sensation to part of the posterior arm and forearm and the dorsolateral hand.

A commonly tested area is the skin over the:

First dorsal web space between the thumb and index finger.

This area is particularly useful for testing the superficial radial nerve.

5. Correction of “First Dorsal Interosseus”

The original note says sensory loss occurs over the first dorsal interosseus.

More precisely, sensory testing is performed over the:

First dorsal web space.

The first dorsal interosseous muscle itself is supplied by the ulnar nerve, not the radial nerve.

Therefore:

Radial sensory testing → first dorsal web space.

6. No Intrinsic Hand Muscles Supplied

The original note correctly emphasizes that the radial nerve supplies no intrinsic muscles of the hand.

Intrinsic hand muscles are mainly supplied by:

Ulnar nerve.

and

Median nerve.

The radial nerve acts mainly through extrinsic extensor muscles located in the forearm.

7. Why Hand Function Is Still Affected

Even though the radial nerve does not supply intrinsic hand muscles, radial palsy can significantly impair hand function.

This is because wrist and finger extension are essential for normal:

Grip strength.

Release of objects.

Fine positioning of the hand.

Therefore, radial nerve palsy can produce major functional disability despite sparing the intrinsic hand muscles.

8. Humeral Shaft Fracture

A classic cause of radial nerve palsy is:

Fracture of the shaft of the humerus.

The radial nerve travels in the radial groove along the posterior aspect of the humerus.

It is therefore vulnerable to injury in mid-shaft fractures.

9. Features of a Radial Groove Lesion

A lesion at the radial groove commonly causes:

Wrist drop.

Finger extension weakness.

Sensory loss over the dorsolateral hand, especially the first dorsal web space.

Triceps function is often relatively preserved because most branches to the triceps arise proximal to the radial groove.

10. Saturday Night Palsy

Saturday night palsy is a compression neuropathy of the radial nerve.

It classically occurs after prolonged pressure on the upper arm, often when a person falls asleep with the arm compressed over a chair or firm surface.

The name historically reflects association with intoxication and prolonged unconscious positioning.

11. Mechanism of Saturday Night Palsy

Compression usually affects the radial nerve around the:

Radial groove of the humerus.

This produces:

Wrist drop.

Finger extension weakness.

Variable sensory loss.

The lesion is often neuropraxic and may recover over time if axonal injury is limited.

12. Mononeuritis Multiplex

Mononeuritis multiplex can also affect the radial nerve.

This refers to an asymmetric disorder involving multiple individual peripheral nerves, often due to:

Vasculitis.

Diabetes.

Inflammatory disease.

If the radial nerve is affected, wrist drop may occur.

13. Higher Radial Nerve Lesions

A very proximal radial nerve lesion, such as in the axilla, can affect more functions.

Possible findings include:

Weak elbow extension due to triceps involvement.

Wrist drop.

Finger extension weakness.

More extensive sensory loss.

This may occur with prolonged axillary compression, such as improper crutch use.

14. Posterior Interosseous Nerve Palsy

The posterior interosseous nerve is a deep motor branch of the radial nerve.

A lesion here causes mainly:

Finger extension weakness.

Thumb extension weakness.

Importantly:

There is no sensory loss, because the posterior interosseous nerve is motor.

Wrist extension may be preserved, although it may be weak and radially deviated.

15. Superficial Radial Nerve Lesion

The superficial radial nerve is predominantly sensory.

A lesion may cause:

Numbness or paraesthesia over the dorsolateral hand.

There is:

No motor weakness.

This helps distinguish it from a more proximal radial nerve palsy.

16. Examination

Important aspects of examination include testing:

Wrist extension.

Finger extension.

Thumb extension.

Elbow extension if a proximal lesion is suspected.

Sensation over the first dorsal web space.

The pattern helps localise the lesion.

17. Wrist Extension

The patient is asked to extend the wrist against resistance.

Weakness suggests radial nerve dysfunction.

In a major lesion, the wrist cannot be actively extended and falls into flexion.

18. Finger Extension

The patient is asked to extend the fingers at the metacarpophalangeal joints.

Weakness is typical of radial nerve or posterior interosseous nerve dysfunction.

This should be distinguished from interphalangeal extension, which also involves intrinsic hand muscles supplied by median and ulnar nerves.

19. Sensory Examination

The most useful autonomous sensory zone for the radial nerve is:

The first dorsal web space.

Reduced sensation here supports involvement of the superficial sensory fibres of the radial nerve.

20. Investigations

Many cases can be diagnosed clinically.

Further tests may include:

X-ray if fracture is suspected.

Nerve conduction studies.

Electromyography.

These are particularly useful when the lesion is severe, persistent, or when localisation is uncertain.

21. Treatment

Treatment depends on the cause.

Management may include:

Treating the underlying fracture or compression.

Avoiding further pressure.

Wrist splinting.

Physiotherapy and occupational therapy.

Monitoring recovery.

Surgical exploration may be required in selected traumatic or persistent lesions.

22. Radial Nerve Palsy – Note Form

Main motor deficit: weakness of wrist and finger extensors.

Classic sign: wrist drop.

Sensory loss: first dorsal web space.

Intrinsic hand muscles: not supplied by radial nerve.

Common cause: humeral shaft fracture.

Compression cause: Saturday night palsy.

Systemic cause: mononeuritis multiplex.

Proximal lesion: may also weaken triceps.

Posterior interosseous lesion: motor weakness without sensory loss.

Key Clinical Pattern

Think of radial nerve palsy as:

WRIST DROP + FINGER EXTENSION WEAKNESS + FIRST DORSAL WEB SPACE SENSORY LOSS.

Important causes are:

Humeral shaft fracture + prolonged radial-groove compression (Saturday night palsy) + mononeuritis multiplex.

And remember the anatomical distinction:

Radial nerve supplies forearm extensors, but NO intrinsic hand muscles.