ULNAR NERVE
- ULNAR NERVE
- ORIGIN AND ROOT VALUE
- mainly arises from medial cord
- C8-T1 ( mostly z , sometimes yz)
- COURSE
- ARM
- arises from Medial cord
- descends medial to brachial artery
-
- middle 5cm over the medial border of humerus
- pierces medial intermuscular septum
- enters posterior compartment of arm
- accompanied by superior ulnar collateral vessels
- runs at posteromedial aspect of humerus
- passing behind medial epicondyle
- in cubital tunnel at elbow palpated by hand
- FOREARM
- Not a content of cubital fossa
- It enters the anterior (flexor) compartment of the forearm
- between the two heads of flexor carpi ulnaris
- lies along the lateral border of the flexor carpi ulnaris.
- runs between the
- flexor digitorum superficialis (laterally)
- flexor digitorum profundus medially.
- near the wrist it courses superficial to
- flexor retinaculum of hand
- but covered by volar carpal ligament
- branches
- HAND
- Enters palm of hand via guyons canal
- superficial to the flexor retinaculum
- lateral to the pisiform bone.
- branches
- 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. Although it can be damaged under various circumstances, it is commonly injured by local trauma or physical impingement (“pinched nerve”). Injury of the ulnar nerve at different levels causes specific motor and sensory deficits.
- At the elbow
- 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 in cubital tunnel syndrome as the ulnar nerve is compressed in the cubital tunnel, rather than transected.)
- Weakness of adduction of the thumb, which may be assessed by the presence of Froment's sign.
- At the wrist
- Common mechanism: penetrating wounds, Guyon canal cyst (and other lesions)
- Motor deficit:
- Loss of flexion of ulnar half of digits, or the 4th and 5th digits, loss of ability to cross the digits of the hand.
- The claw 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 the flexor 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 the ulnar paradox.
- Weakness of adduction of the thumb, which may be assessed by the presence of Froment's sign.
- Sensory deficit: Loss of sensation or paresthesiae 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.
