Ulnar nerve - lesions above elbow level

Causes

• Lesion of medial cord of brachial plexus.
• Compression injury during sleep.
• Arteriovenous fistula in dialysis patients.
• Compression by hematoma, nerve sheath tumor or other masses.
• Direct injury in supracondylar humerus fractures.
• Entrapment by medial intermuscular septum.

Symptoms & signs

• Sensory deficit in dorsal and palmar surfaces of 4th, 5th and ulnar half of 3th fingers as well as the ulnar part of the hand.
• Atrophy of hypothenar eminence and interosseous muscles.
• Paresis of interosseous and ulnar lumbrical muscles leaves the action of long finger extensors and flexors unopposed, resulting in the characteristic claw-hand deformity where the 4th and 5th fingers are hyperextended at the metacarpophalangeal and flexed at the interphalangeal joints.
• Weakness of ulnar flexion of the wrist.
• Weakness of flexion at the terminal phalanges of 4th and 5th fingers and metacarpophalangeal joints of 2nd to 5th fingers.
• Weakness of extension at interphalangeal joints of 2nd to 5th fingers.
• Weakness of abduction and adduction of 2nd to 5th fingers.
• Weakness of adductor pollicis results in Froment’s sign.
• In 15-31% of people the intrinsic muscles of the hand are innervated by median nerve or anterior interosseous nerve fibers that anastomose with ulnar nerve usually 3-10 cm distal to the medial humeral epicondyle (Martin-Gruber anastomosis). In these patients an ulnar neuropathy above the elbow may leave these muscles unaffected.

Examination

• Froment’s sign is tested by asking the patient to grasp a sheet of paper between index and thumb as you try to pull it from their grasp. Patients with ulnar nerve palsy will have difficulty maintaining hold and will compensate by activating the flexor pollicis longus muscle. This results in flexion of the interphalangeal joint of the thumb instead of adduction of the thumb.