Epidemiology^[2]

• The elbow is the most common site of compression of the ulnar nerve.
• Cubital tunnel syndrome is the second most common compressive neuropathy.
• Cubital tunnel syndrome affects men more often than women.

Aetiology

• Constricting fascial bands.
• Compromise under general anaesthetic.
• Subluxation of the ulnar nerve over the medial epicondyle.
• Cubitus valgus.
• Bony spurs.
• Joint deformity in osteoarthritis or rheumatoid arthritis: osteoarthritic or rheumatoid narrowing of the ulnar groove and constriction of the ulnar nerve as it passes behind the medial epicondyle.
• Associated with medial epicondylitis ('golfer's elbow').
• Tumours.
• Ganglia.
• Direct compression, eg habitual leaning on elbows.
• Repetitive elbow flexion and extension, heavy manual work, frequently playing guitar.

Other causes of ulnar nerve lesions at the elbow include:

• Fractures: friction of the ulnar nerve due to cubitus valgus (a possible sequel to childhood supracondylar fractures - 'tardy ulnar palsy') can cause fibrosis of the ulnar nerve and ulnar neuropathy.
• Elbow dislocation.
• Venepuncture.
• Severe haematoma.

Presentation

• Ulnar nerve palsy causes wasting and weakness of the small muscles of the hand and partial clawing of the ring and little finger.
• The extent of the deformity and disability depends on the site of the lesion.
• Patients often have numbness and tingling along the little finger and ulnar half of the ring finger, often associated with a weakness of grip, and particularly when the patient rests on, or flexes, the elbow.
• Patients may experience pain and tenderness at the level of the cubital tunnel. The severity of pain is very variable and the distribution of pain may spread proximally and/or distally.
• Symptoms may be intermittent at first and then become more constant.
• Patients with chronic ulnar neuropathy may complain of loss of grip and pinch strength and loss of fine dexterity.
• Severe prolonged compression may present with intrinsic muscle wasting and clawing or abduction of the little finger.

Signs

• Examination may be normal in recent-onset mild ulnar nerve palsy or show marked neurological abnormalities in prolonged severe ulnar nerve compression.
• Inspection for claw hand (hyperextension at the metacarpophalangeal joints and flexion of the interphalangeal joints; mainly little finger and ring finger) and wasting of the small muscles of the hand.
• Loss of sensation over the palmar and dorsal aspect of the little finger and the medial half of the ring finger.
• Palpate the cubital tunnel region to exclude mass lesions.
• Tinel's sign:
  • Tapping over the cubital tunnel causes pain, tingling or shock-like sensation down the arm into the fingers.
  • A positive Tinel's sign finding is typically present in cubital tunnel syndrome. However, Tinel's sign may be positive in asymptomatic people.
• The elbow flexion test:
  • Is the most diagnostic test for cubital tunnel syndrome.
  • The patient flexes the elbow past 90°, supinating the forearm, and extending the wrist.
  • Result is if discomfort is reproduced or paraesthesia occurs within 60 seconds.
  • The addition of shoulder abduction may enhance the sensitivity of the test.
• Froment's sign:
  • The patient holds a piece of paper between the thumb and the side of the adjacent index finger as the paper is pulled away.
  • A patient with an ulnar nerve palsy will flex the thumb at the interphalangeal joint to try to keep hold of the paper.

Differential diagnosis

• Other sites of ulnar nerve lesion, eg Guyon's canal at the wrist. Causes of ulnar nerve lesions at the wrist include compression by tumour or ganglion, blunt trauma, fractures.
• Other causes of neurological dysfunction along the C8-T1 distribution, eg cervical spondylosis with cervical radiculopathy, brachial plexus damage, thoracic outlet syndrome, syringomyelia, Pancoast's tumour (apical lung cancer).
• Carpal tunnel syndrome.
• Polyneuropathy, eg diabetes, renal disease, multiple myeloma, amyloidosis, chronic alcoholism, malnutrition, leprosy.

Investigations

• Ultrasound of cubital tunnel: there is a correlation between the stage of ulnar nerve palsy and the diameter of the major axis.^[3]
• MRI scan is sensitive and specific for diagnosis of ulnar nerve lesions at the elbow.^[4]

Management

Management includes physiotherapy, splinting, non-steroidal anti-inflammatory drugs, surgical transposition of the nerve and surgical decompression for cubital tunnel syndrome. The treatment depends on the site and severity of the lesion:

• Avoidance of aggravating factors such as full elbow flexion and pressure on the elbow may be sufficient in mild cases.
• Simple decompression of the nerve and decompression with transposition to the front of the medial epicondyle are equally effective.^[5]
• There is currently insufficient evidence to recommend a 'best treatment'.
• Recovery may be slow and incomplete; often the symptoms are temporarily exacerbated.

Prognosis

• Prolonged compromise to the nerve can lead to complete loss of function.
• More pronounced ulnar nerve thickening at the time of the diagnosis is associated with poor outcome at follow-up, especially in conservatively treated cases.^[6]
• Conduction study signs of demyelination on testing usually indicate a favourable outcome.^[6]