Theulnar nerve is anerve that runs near theulna, one of the two long bones in theforearm. Theulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest in the human body unprotected by muscle or bone, so injury is common.[1] This nerve is directly connected to thelittle finger, and the adjacent half of thering finger, innervating thepalmar aspect of these fingers, including both front and back of thetips, perhaps as far back as thefingernail beds.
This nerve can cause an electric shock-like sensation by striking themedial epicondyle of the humerus posteriorly, or inferiorly with the elbow flexed. The ulnar nerve is trapped between the bone and the overlying skin at this point. This is commonly referred to as bumping one's "funny bone".[2] This name is thought to be apun, based on thesound resemblance between the name of the bone of the upper arm, thehumerus, and the word "humorous".[3] Alternatively, according to theOxford English Dictionary, it may refer to "the peculiar sensation experienced when it is struck".[4]
The ulnar nerve originates from theC8-T1 nerve roots (and occasionally carriesC7 fibers which arise from thelateral cord),[5][6] which then form part of the medial cord of thebrachial plexus, and descends medial to thebrachial artery, up until the insertion point ofcoracobrachialis muscle (middle 5 cm over the medial border of the humerus). Then, it pierces the medial intermuscular septum and enters the posterior compartment of the arm, accompanied by superior ulnar collateral vessels. It runs at the posteromedial aspects of the humerus, passing behind the medial epicondyle (in thecubital tunnel) at the elbow, where it can be palpated by hand.[7]
Palmar branch of ulnar nerve - arises from the middle part of the forearm and supplies the skin over the hypothenar eminence.[7]
Dorsal branch of ulnar nerve - arises from 7.5 cm above the wrist, winds backwards to supply the skin of the proximal part of the ulnar one and half fingers and the adjoining area between the fingers.[6][7]
Articular branches are given off to the elbow joint.[7]
The ulnar nerve can suffer injury anywhere between its proximal origin of the brachial plexus all the way to its distal branches in the hand. It is the most commonly injured nerve around the elbow.[9][10] Although it can be damaged under various circumstances, it is commonly injured by local trauma orphysical impingement ("pinched nerve"). Injury of the ulnar nerve at different levels causes specific motor and sensory deficits.
Common mechanisms of injury:Cubital tunnel syndrome, fracture of the medial epicondyle of the humerus (causing direct ulnar nerve injury), fracture of the lateral epicondyle of the humerus (causingcubitus valgus with tardy ulnar nerve palsy), Driver's Elbow[11]
Motor deficit:
Weakness in flexion of the hand at the wrist, loss of flexion of ulnar half of digits, or the 4th and 5th digits, loss of ability to cross the digits of the hand. (Note: Motor deficit is absent or very minor incubital tunnel syndrome as the ulnar nerve iscompressed in the cubital tunnel, rather than transected.)
Weakness of adduction of the thumb, which may be assessed by the presence ofFroment's sign.
Sensory deficit: Loss of sensation orparesthesiae in ulnar half of the palm and dorsum of hand, and the medial 1½ digits on both palmar and dorsal aspects of the hand
Theclaw hand deformity is more prominent with injury at the wrist as opposed to a lesion higher up in the arm, for instance, at the elbow, as the ulnar half of theflexor digitorum profundus is not affected. This pulls the distal interphalangeal joints of the 4th and 5th digit into a more flexed position, producing a more deformed 'claw'. This is known as theulnar paradox.
Weakness of adduction of the thumb, which may be assessed by the presence ofFroment's sign.
Sensory deficit: Loss of sensation orparesthesiae in ulnar half of the palm, and the medial 1½ digits on the palmar aspect of the hand, with dorsal sparing. The dorsal aspect of the hand is unaffected as the posterior cutaneous branch of the ulnar nerve is given off higher up in the forearm and does not reach the wrist.
In severe cases, surgery may be performed to relocate or "release" the nerve to prevent further injury.
^Hendrickson, Robert A. (2004).The Facts on File Encyclopedia of Word and Phrase Origins (Facts on File Writer's Library). New York: Checkmark Books. p. 281.ISBN0-8160-5992-6.
^abcdefghijkKrishna, Garg (2010). "8 - Arm".BD Chaurasia's Human Anatomy (Regional and Applied Dissection and Clinical) Volume 1 - Upper limb and thorax (Fifth ed.). India: CBS Publishers and Distributors Pvt Ltd. p. 91,110,111.ISBN978-81-239-1863-1.
Anatomy figure: 07:04-04 at Human Anatomy Online, SUNY Downstate Medical Center - "Anterior view of the nerves, vessels, and superficial tendons that cross the leftwrist."
