Medicine – Ulnar Nerve Palsy

Ulnar nerve palsy causes weakness and wasting of muscles supplied by the ulnar nerve, together with sensory loss over the medial part of the hand. The exact pattern depends on whether the lesion occurs at the elbow or more distally at the wrist.

A key clinical feature is clawing of the ring and little fingers, especially in distal lesions.

1. Main Functions of the Ulnar Nerve

The ulnar nerve supplies many of the intrinsic muscles of the hand.

Important motor functions include:

Finger abduction.

Finger adduction.

Hypothenar movements.

Flexion at the metacarpophalangeal joints of the ring and little fingers through the medial two lumbricals.

Thumb adduction through adductor pollicis.

It also supplies some forearm muscles, especially:

Flexor carpi ulnaris.

Medial half of flexor digitorum profundus.

2. Lesion at the Elbow

A lesion at the elbow affects both the forearm and hand branches of the ulnar nerve.

This can produce:

Weakness of ulnar-innervated forearm muscles.

Weakness and wasting of intrinsic hand muscles.

Sensory loss over the medial one and a half fingers.

The classic site is around the medial epicondyle and cubital tunnel.

3. Forearm Wasting

The original note describes wasting of the medial side of the forearm.

This may occur because proximal ulnar nerve lesions weaken:

Flexor carpi ulnaris.

and

The ulnar half of flexor digitorum profundus.

However, the most striking wasting is often in the hand rather than the forearm.

4. Hypothenar Wasting

The hypothenar eminence contains muscles controlling the little finger.

Ulnar nerve palsy may cause wasting and weakness of:

Abductor digiti minimi.

Flexor digiti minimi.

Opponens digiti minimi.

This produces flattening of the hypothenar eminence.

5. Interosseous Muscle Weakness

All the interossei are supplied by the ulnar nerve.

Therefore, ulnar palsy causes weakness of:

Finger abduction.

Finger adduction.

A useful mnemonic is:

DAB = Dorsal interossei ABduct.

PAD = Palmar interossei ADduct.

6. Testing Finger Abduction

The patient is asked to spread the fingers apart against resistance.

Weakness suggests dysfunction of the:

Dorsal interossei.

This is a classic test of ulnar nerve function.

7. Testing Finger Adduction

The patient is asked to bring the fingers together against resistance.

Weakness reflects impairment of the:

Palmar interossei.

A simple bedside test is to ask the patient to hold a piece of paper between adjacent fingers.

8. Medial Two Lumbricals

The third and fourth lumbricals, corresponding mainly to the ring and little fingers, are supplied by the ulnar nerve.

These muscles normally:

Flex the metacarpophalangeal joints.

and

Extend the interphalangeal joints.

Therefore, ulnar palsy causes impaired coordinated finger movement.

The original note says “weak finger flexion,” but more precisely the lumbricals help flex the MCP joints while extending the IP joints.

9. Claw Hand Deformity

The classic deformity is an ulnar claw.

This especially affects the:

Ring finger.

Little finger.

The deformity consists of:

Hyperextension at the MCP joints.

with

Flexion at the interphalangeal joints.

This results from loss of the medial lumbricals and interossei.

10. Why the Fingers Claw

Normally, the lumbricals and interossei flex the MCP joints and extend the IP joints.

When these muscles are paralysed:

Extensor digitorum hyperextends the MCP joints.

while

Long finger flexors flex the IP joints.

The result is:

Clawing.

11. Ulnar Paradox

An important clinical principle is the ulnar paradox.

A distal lesion at the wrist may produce more obvious clawing than a proximal lesion at the elbow.

Why?

In a proximal lesion, the ulnar half of flexor digitorum profundus is also weakened, reducing flexion at the distal interphalangeal joints of the ring and little fingers.

Therefore:

More proximal lesion → more weakness, but sometimes less obvious clawing.

This is called the ulnar paradox.

12. Sensory Loss

The ulnar nerve supplies sensation to approximately the:

Little finger.

and

Ulnar half of the ring finger.

This corresponds to the medial one and a half fingers.

Sensory loss may affect both the palmar and dorsal surfaces depending on the level of the lesion.

13. Sensory Distribution at the Elbow

A lesion at or above the elbow usually affects both:

Palmar ulnar sensation.

and

Dorsal ulnar sensation.

This is because the dorsal cutaneous branch arises in the distal forearm, proximal to the wrist.

14. Causes of Ulnar Nerve Lesions at the Elbow

Common causes include:

Compression around the cubital tunnel.

Fracture or dislocation around the elbow.

Prolonged leaning on the elbows.

Degenerative changes such as osteoarthritis.

Mononeuritis multiplex.

15. Fracture or Dislocation at the Elbow

The ulnar nerve passes behind the medial epicondyle and is therefore vulnerable to trauma.

Fracture or dislocation around the elbow may cause:

Motor weakness.

Hand wasting.

Clawing.

Sensory loss.

16. Occupational Compression

Repeated or prolonged pressure on the elbow can compress the ulnar nerve within the cubital tunnel.

Examples include:

Leaning on elbows for long periods.

Frequent elbow flexion.

Certain occupational postures.

Patients may initially complain of tingling in the ring and little fingers.

17. Osteoarthritis

Degenerative changes around the elbow may narrow the cubital tunnel or produce local compression.

This can lead to chronic ulnar neuropathy.

Symptoms may progress slowly.

18. Mononeuritis Multiplex

Ulnar nerve palsy may occur as part of mononeuritis multiplex, where several individual peripheral nerves are affected asymmetrically.

This pattern is particularly associated with:

Vasculitis.

Diabetes.

Systemic inflammatory disease.

19. Wrist Lesions

A lesion at the wrist affects the ulnar nerve after the forearm branches have already been given off.

Therefore, ulnar-innervated forearm muscles are spared.

The main deficits involve the intrinsic hand muscles.

20. Motor Findings in Wrist Lesions

A wrist-level ulnar lesion may cause weakness of:

Hypothenar muscles.

Interossei.

Medial two lumbricals.

Adductor pollicis.

This produces:

Finger abduction and adduction weakness.

Clawing of ring and little fingers.

Weak thumb adduction.

21. Dorsal Sensation Is Spared in Wrist Lesions

This is an important localisation clue.

The dorsal cutaneous branch of the ulnar nerve usually leaves the main nerve in the distal forearm before the nerve reaches the wrist.

Therefore, a lesion at the wrist may spare:

Sensation over the dorsum of the ulnar side of the hand.

This matches the original note.

22. Palmar Sensory Loss at the Wrist

Although dorsal sensation may be spared, a wrist lesion can still cause sensory loss over the:

Palmar little finger.

Palmar ulnar half of the ring finger.

The exact pattern depends on whether the superficial sensory branch is involved.

23. Guyon Canal Syndrome

A common site for distal ulnar nerve compression is Guyon canal at the wrist.

Compression here may occur with:

Cycling or prolonged handlebar pressure.

Ganglion cysts.

Trauma.

Occupational repetitive pressure.

The motor and sensory pattern depends on which branch is compressed.

24. Froment Sign

Froment sign tests ulnar nerve function through adductor pollicis.

The patient holds a piece of paper between the thumb and index finger.

If adductor pollicis is weak, the patient compensates by flexing the thumb interphalangeal joint using flexor pollicis longus, which is supplied by the median nerve.

Therefore:

Positive Froment sign → ulnar nerve weakness.

25. Wartenberg Sign

Another possible finding is Wartenberg sign.

The little finger remains abducted because of weakness of the palmar interossei and imbalance of muscle forces.

This may be seen in ulnar neuropathy.

26. Examination

Important tests include:

Finger abduction.

Finger adduction.

Thumb adduction.

Hypothenar strength.

Sensation over the little finger and ulnar half of the ring finger.

Inspection for interosseous wasting and clawing.

27. Interosseous Wasting

Ulnar neuropathy can produce visible wasting between the metacarpals.

This may be especially noticeable in the:

First dorsal interosseous space.

The hand may appear hollowed between the metacarpal bones.

28. Investigations

Diagnosis is often clinical, but further tests may include:

Nerve conduction studies.

Electromyography.

X-ray of the elbow if trauma or arthritis is suspected.

Ultrasound or MRI in selected compressive lesions.

These can help identify the lesion level and severity.

29. Treatment

Treatment depends on the cause.

Management may include:

Avoiding prolonged elbow pressure.

Reducing excessive elbow flexion.

Splinting.

Physiotherapy and occupational therapy.

Treating underlying inflammatory or metabolic disease.

Surgical decompression or transposition in selected severe or persistent cases.

30. Ulnar Nerve Palsy – Lesion at the Elbow

Forearm muscles: may be weak.

Hand muscles: interossei, hypothenar muscles, medial two lumbricals and adductor pollicis affected.

Clawing: ring and little fingers.

Finger abduction: weak.

Finger adduction: weak.

Thumb adduction: weak.

Sensation: medial one and a half fingers, palmar and dorsal surfaces may be affected.

Causes: elbow fracture/dislocation, cubital tunnel compression, leaning on elbows, osteoarthritis, mononeuritis multiplex.

31. Ulnar Nerve Palsy – Lesion at the Wrist

Forearm muscles: spared.

Intrinsic hand muscles: weak.

Clawing: often more obvious than in a proximal lesion.

Finger abduction/adduction: weak.

Thumb adduction: weak.

Dorsal hand sensation: usually spared.

Palmar ulnar sensation: may be impaired.

Typical site: Guyon canal.

32. Elbow versus Wrist Localisation

Elbow lesion:

Forearm + hand weakness.

Dorsal and palmar sensory loss may occur.

Clawing may be less pronounced because flexor digitorum profundus is also weak.

Wrist lesion:

Intrinsic hand weakness only.

Dorsal sensation usually spared.

Clawing may be more pronounced.

This is the basis of the ulnar paradox.

Key Clinical Pattern

Think of ulnar nerve palsy as:

CLAWING OF RING + LITTLE FINGERS + INTEROSSEOUS WASTING + WEAK FINGER ABDUCTION/ADDUCTION + SENSORY LOSS OF MEDIAL 1½ FINGERS.

For localisation:

Elbow lesion → forearm + hand weakness + dorsal sensory loss may occur.

Wrist lesion → intrinsic hand weakness + dorsal sensation spared.

And remember:

DAB = dorsal interossei abduct.

PAD = palmar interossei adduct.

Positive Froment sign = weak adductor pollicis from ulnar nerve palsy.