Ulnar nerve disorders

The course of the ulnar nerve is as follows:¹

• The ulnar nerve originates from the medial cord of the brachial plexus and runs inferior to the posteromedial aspects of the humerus, passing behind the medial epicondyle (in the cubital tunnel) at the elbow where it is exposed for several centimetres.

• It then enters the anterior compartment of the forearm through the two heads of flexor carpi ulnaris and runs alongside the ulna bone.

• It continues distally alongside the ulnar artery, deep to the flexor carpi ulnaris muscle.

• It enters the palm of the hand, passing with the ulnar artery superficial to the flexor retinaculum of the hand via the ulnar canal (Guyon's canal).

Muscle and skin innervations²

Muscles

• In the forearm, via the muscular branches of ulnar nerve:

  • Flexor carpi ulnaris.

  • Flexor digitorum profundus (medial half).

• In the hand, via the deep branch of ulnar nerve:

  • Hypothenar muscles.

  • Adductor pollicis.

  • The third and fourth lumbrical muscles.

  • Dorsal interossei.

  • Palmar interossei.

• In the hand, via the superficial branch of ulnar nerve:

  • Palmaris brevis.

Skin

The ulnar nerve also provides sensory innervation to the part of the hand corresponding to the fourth and fifth fingers:

• Palmar branch of ulnar nerve (anterior).

• Dorsal branch of ulnar nerve (posterior).

Causes of ulnar nerve disorders³

• The ulnar nerve can be damaged by dislocation, or fracture dislocation of the elbow, and can be compressed by those who habitually lean on their elbows.

• It may be associated with medial epicondylitis (golfer's elbow).

• The nerve can become entrapped in the cubital tunnel of the elbow during heavy manual work, following a previous poorly healed supracondylar fracture of the humerus, or due to osteophytic encroachment in osteoarthritis. See the separate Cubital tunnel syndrome article.

• One study found that over half of a group of 91 patients labelled 'idiopathic' were found to have a specific cause after careful ultrasound evaluation.⁴

• Causes of compression of the ulnar nerve at the wrist include aneurysm of the ulnar artery, thrombosis, synovial inflammation and ganglia, or by repeated trauma, for example, work related.

How common are ulnar nerve disorders? (Epidemiology)

• Ulnar nerve entrapment is the second most frequent entrapment neuropathy in the upper extremity (the first being the median nerve and its branches).⁵ The elbow is the most common area for entrapment.

• The incidence of ulnar nerve compression is increasing, partly due to the use of mobile phones, as the elbow is held flexed for long periods of time.⁶

• The wrist is the second most common area of entrapment.

• Entrapment of the ulnar nerve may occur simultaneously at more than one level.¹

History and examination

See the separate article dealing with upper limb neurological examination: Neurological examination of the upper limbs.

Lesions at the elbow⁷

The term cubital tunnel syndrome is often used for ulnar nerve compression at the elbow - see separate leaflet for more information.

Lesions at the wrist¹

• Compression of the ulnar nerve at the wrist is known as ulnar tunnel syndrome, handlebar palsy, or Guyon's canal syndrome. It is less common than cubital tunnel syndrome.

• If the lesion is just proximal to the wrist, it causes impaired sensation of the ulnar side of the hand and the fourth and fifth fingers, and muscle weakness, especially in the hypothenar eminence. Sensory loss affecting the hand is not present if the compression is at the wrist,

• Loss of thumb adduction can occur.

• There may be clawing of the 4th and 5th fingers, and Wartenber sign (abduction of the 5th finger).

• Positive Tinel's sign on percussion over the ulnar nerve at the wrist (light percussion over the nerve causes a sensation of 'pins and needles' in the distribution of the nerve, that is, the ulnar side of the hand and the fourth and fifth fingers).

• Positive Phalen's test with paraesthesiae in the fourth and fifth fingers (the patient holds their wrist in maximum flexion for 30-60 seconds).

Differential diagnosis

• Cervical disc disease.

• Brachial plexus abnormalities, cervical ribs and thoracic outlet syndrome, Pancoast's tumour.

• Elbow abnormalities, epicondylitis.

• Neuropathy associated with, for example, diabetes mellitus, hypothyroidism, rheumatoid arthritis and alcoholism.

• Wrist fractures.

• Ulnar artery aneurysms or thrombosis at the wrist.

Diagnosing ulnar nerve disorders (investigations)

• Blood tests may be appropriate to rule out various disorders causing neuropathy - for example, anaemia, diabetes mellitus, hypothyroidism and rheumatoid arthritis.

• X-rays:

  • Neck X-rays if cervical disc disease is suspected and to rule out cervical ribs.

  • X-rays of the chest if a Pancoast's tumour is suspected.

  • X-rays of the elbow and wrist are essential to rule out possible associated bone or joint abnormalities, or alternative diagnoses.

• Ultrasound of the cubital tunnel.⁸ High-resolution ultrasonic assessment of the ulnar nerve for swelling and textural abnormalities can be a powerful diagnostic method.⁹

• MRI scanning may also be useful.⁸

• Electromyography (EMG) tests and nerve conduction studies to confirm the area of entrapment.¹

Management of ulnar nerve disorders¹⁰

Ulnar entrapment neuropathies can improve with conservative treatment including splinting, physical therapy, bracing, or corticosteroid injection, while others may require surgical intervention.

Conservative treatment

• Is most successful when paraesthesiae are transient and caused by malposition of the elbow or by blunt trauma.

• Resting on the elbows at work, using the elbows to lift the body from bed and resting the elbows on car windows while driving are all causes of paraesthesia that can be corrected without surgical treatment.

• Anterior elbow extension splinting.

• Correction of ergonomics at work or with a home computer may be all that is required.

• Non-steroidal anti-inflammatory medications also are useful adjuncts to relieve nerve irritation.

Surgery

• The time to abandon conservative treatment and opt for surgery is not always clear.¹¹ However, common practice is to perform surgery when:⁸

  • There is no improvement in presenting symptoms.

  • There is progressive palsy or paralysis.

  • There is clinical evidence of a long-standing lesion (for example, muscle wasting, clawing of the fourth and fifth digits).

• The surgical treatment for elbow lesions due to repeated compression includes surgical transposition of the nerve, medial epicondylectomy and decompression in cubital tunnel syndrome.

• The surgical treatment for wrist lesions includes local decompression and carpal tunnel release.

Prognosis¹⁰

Duration of entrapment and severity of numbness and muscle weakness are important factors in prognosis. Mild cases may resolve without treatment. Having late presentation and diagnosis decreases the likelihood of full recovery and good clinical outcome.