Ulnar Nerve Disorders

See the separate Cubital Tunnel Syndrome article.

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 innervations^[2]

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 disorders^[3]

• 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 or following a previous poorly healed supracondylar fracture of the humerus or due to osteophytic encroachment in osteoarthritis.
• 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 at work.

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^[1].
• The frequency 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 elbow^[7]

• The term cubital tunnel syndrome is often used for ulnar nerve compression at the elbow.
• Total paralysis of the nerve, including those branches of the nerve serving the flexor digitorum profundus and flexor carpi ulnaris muscles, causes wasting along the medial side of the forearm.
• Paralysis of the nerve also leads to weakness of flexion of the fourth and fifth fingers; if proximal portions of these fingers are held steady, the patient is unable to flex terminal phalanges.
• With paralysis of the hypothenar muscles, abduction of the fifth finger is impossible.
• Paralysis of interossei and the medial two lumbricals causes 'claw hand' deformity, mainly seen in the ulnar fingers.
• There may be wasting of the hypothenar muscles, interossei and the medial part of the thenar eminence. Also, there may be weakness in movement of fingers and abduction to the extended thumb against the palm.
• There is sensory loss of the dorsal and palmar aspects of the medial side of the hand together with the medial one and a half fingers.
• With compression of the ulnar nerve, the ulnar nerve is often palpably enlarged in the ulnar groove and for a short distance proximal to the elbow.

Lesions at the wrist^[1]

• Cutaneous sensation of the hand and fingers is often spared.
• If the lesion is just proximal to the wrist, it causes impaired sensation on the palmar aspects of the hand and the fourth and fifth fingers and muscle weakness, especially in the hypothenar eminence.
• 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, ie 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.

Investigations

• Blood tests may be appropriate to rule out various disorders causing neuropathy - eg, 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^[10]

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 (eg, 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.
• A Cochrane review found that simple decompression and decompression with transposition were equally effective in idiopathic ulnar neuropathy at the elbow, including when the nerve impairment was severe^[11]. 
• A comparison of subcutaneous anterior transposition versus decompression and medial epicondylectomy found no statistically significant difference but commented that medial epicondylectomy may be preferred over ulnar transposition as it was less technically demanding, with less soft tissue dissection of the nerve^[12].
• One study reported the successful use of an endoscope to assist in cubital tunnel surgery^[13]
• Use of a vascularised adipose sling to secure the ulnar nerve during anterior subcutaneous transposition is also being explored^[14].
• Autologous vein graft wrapping has been used successfully in patients with cubital tunnel syndrome resistant to conventional surgery^[15].
• The surgical treatment for wrist lesions includes exploration of ganglia.

Prognosis^[10]

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.