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
    - up until insertion point of coracobrachialis muscle
      - 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
      - muscular branches
        
        flexor carpi ulnaris and medial half of flexor digitorum profundus
      - palmar branch of ulnar nerve
        
        supplies skin over hypothenar eminence
      - dorsal branch of ulnar nerve
        
        arises 7.5 cm above wrist
  - HAND
    - Enters palm of hand via guyons canal
      - superficial to the flexor retinaculum
      - lateral to the pisiform bone.
    - branches
      - superficial branch
      - deep branch
        
        accompanies deep branch of ulnar artery
        
        In the hand, via the deep branch of ulnar nerve:
        
        Hypothenar muscles
        
        Opponens digiti minimi
        
        Abductor digiti minimi
        
        Flexor digiti minimi brevis
        
        The third and fourth lumbrical muscles
        
        Dorsal interossei
        
        Palmar interossei
        
        Adductor Pollicis
        
        Flexor pollicis brevis (deep head)

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
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 (causing cubitus valgus with tardy ulnar nerve palsy), Driver's Elbow[10]
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.)
- Presence of a claw hand deformity when the hand is at rest, due to hyperextension of the 4th and 5th digits at the metacarpophalangeal joints, and flexion at the interphalangeal joints.
- 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 dorsum of hand, and the medial 1½ digits on both palmar and dorsal aspects of the hand

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.
- Presence of a claw hand deformity when the hand is at rest, due to hyperextension of the 4th and 5th digits at the metacarpophalangeal joints, and flexion at the interphalangeal joints.
- 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.
In severe cases, surgery may be performed to relocate or “release” the nerve to prevent further injury.