Ulnar Nerve Disorders

The course of the ulnar nerve is as follows:

• 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.
• The ulnar nerve then enters the anterior compartment of the forearm through the two heads of flexor carpi ulnaris and runs alongside the ulna bone.
• The ulnar nerve continues distally alongside the ulnar artery deep to the flexor carpi ulnaris muscle.
• The ulnar nerve enters the palm of the hand, passing with the ulnar artery superficial to the flexor retinaculum of the hand via the ulnar canal (Guyon canal).

• 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)

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

• Ulnar nerve entrapment is the second most frequent entrapment neuropathy in the upper extremity.¹ The elbow is the most common area for entrapment.²
• The wrist is the second most common area of entrapment.
• Entrapment of the ulnar nerve may occur simultaneously at more than one level.²

See separate article Neurological Examination of the Upper Limbs.

Lesions at the elbow

• 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 medial side of forearm.
• Paralysis of the nerve also leads to weakness of flexion of fourth and fifth fingers; if proximal portions of these fingers are held steady, patient is unable to flex terminal phalanges.
• With paralysis of hypothenar muscles, abduction of fifth finger is impossible.
• Paralysis of interossei and medial two lumbricals causes 'claw hand' deformity, mainly seen in the ulnar fingers.
• There may be wasting of hypothenar muscles, interossei and medial part of thenar eminence. Also 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 wrist

• Cutaneous sensation of hand and fingers is often spared.
• If lesion is just proximal to the wrist, it causes impaired sensation on the palmar aspects of hand and the fourth and fifth fingers and muscle weakness, especially in the hypothenar eminence.
• Positive Tinel's sign on percussion over ulnar nerve at wrist (light percussion over the nerve causes a sensation of "pins and needles" in the distribution of the nerve, i.e. ulnar side of hand and fourth and fifth fingers).²
• Positive Phalen's test with paraesthesias in fourth and fifth fingers (patient holds their wrist in maximum flexion for 30–60 seconds).²

• Cervical disc disease
• Brachial plexus abnormalities, cervical ribs, thoracic outlet syndrome, Pancoast tumour
• Elbow abnormalities, epicondylitis
• Neuropathy associated with e.g. diabetes mellitus, hypothyroidism, rheumatoid arthritis and alcoholism
• Wrist fractures
• Ulnar artery aneurysms or thrombosis at the wrist

• Blood tests may be appropriate to rule out various disorders causing neuropathy, e.g. 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 chest if a Pancoast tumour is suspected.
  • X-rays of elbow and wrist are essential to rule out possible associated bone or joint abnormalities, or alternate diagnoses.
• Ultrasound of cubital tunnel.⁴
• Electromyography tests and nerve conduction studies to confirm the area of entrapment.

Conservative treatment

• Is most successful when paraesthesias are transient and caused by malposition of the elbow or blunt trauma.
• Resting on elbows at work, using elbows to lift the body from bed, and resting elbows on car windows while driving all are causes of paraesthesia that can be corrected without surgical treatment.
• Anterior elbow extension splinting.
• Correction of ergonomics at work or with home computer may be all that is required.
• Non-steroidal anti-inflammatory medications also are useful adjuncts to relieve nerve irritation.

Surgery

• Indications for surgery include:
  • If there has been no improvement in presenting symptoms after 6-12 weeks of conservative treatment.
  • When there is progressive palsy or paralysis.
  • When there is clinical evidence of a long-standing lesion (e.g. muscle wasting, clawing of the fourth and fifth digits).
• The surgical treatment for elbow lesions due to repeated compression involves surgical transposition of nerve, and decompression in cubital tunnel syndrome.⁵
• The surgical treatment for wrist lesions includes exploration of ganglia.

Duration of entrapment and severity of numbness and muscle weakness are important factors in prognosis.

• With early appropriate decompression the result should be a return to normal function. Return to normal function is almost immediate.
• With transposition of the nerve following decompression, post-operative immobilisation, and rehabilitation, return to normal function may take 3-6 months.
• In chronic palsy (greater than 3-4 months duration) associated with pain, muscle weakness, and/or atrophy, surgical outcome is less certain. Improvement may be limited or may not occur following decompression and transposition but further progression can be halted with repeated decompression.