November 22, 2005

Brachial Plexus Injuries

Brachial Plexus
image from site thefullwiki.org
UPPER EXTREMITY
NERVES OF THE ARM, FOREARM AND HAND
MUSCULOCUTANEOUS NERVE (C5,6,7)
The musculocutaneous nerve originates from the lateral cord of the brachial plexus. It pierces the coracobrachialis and crosses to the lateral side of the arm. A short distance above the elbow it pierces the deep fascia lateral to the tendon of the biceps and continues into the forearm as the lateral cutaneous nerve of the forearm.
Branches:
Muscular: to the coracobrachialis, biceps brachii and the brachialis

Cutaneous: lateral cutaneous nerve of the forearm
except the flexor carpi ulnaris.
Opponens pollicis
Flexor pollicis brevis
common palmar digital nerves (3) which divide into proper palmar digital nerves to supply cutaneous innervation to the lateral 3 1/2 digits. Motor innervation to the first two lumbrical muscles (i.e., to index and middle fingers) also comes from these nerves.
3rd and 4th lumbrical muscles (i.e. to ring and little fingers)
adductor pollicis


THE MEDIAN NERVE (C6,7,8,T1)
The median nerve originates from both the medial and lateral cords of the brachial plexus. It accompanies the brachial artery, lying lateral to the artery proximally, but gradually crossing anterior to the artery in the middle of the arm to lie medial to it at the elbow. In the forearm, it passes between the two heads of the pronator teres, between the flexors digito-rum superficialis and profundus, and then deep to the flexor retinaculum (carpal tunnel). In the hand, it is covered only by skin and the palmar aponeurosis.
Branches:
Muscular: to all the superficial flexor muscles of the forearm
a) anterior interosseous nerve (deep branch of median nerve) accompanies the anterior interosseous artery. It supplies all the deep flexor muscles of the forearm except the ulnar half of the flexor digitorum profundus. (The deep flexors are flexor pollicis longus, pronator quadratus, and flexor digitorum profundus)
b) recurrent median nerve arises from the median nerve to innervate the three thenar muscles:
Abductor pollicis brevis
(Since this nerve is quite superficial, it is vulnerable to injury and loss of thumb muscle function is very disabling.)
Cutaneous:
palmar cutaneous branch - to proximal palm
Lesions affecting the median nerve include lacerations of the medial aspect of the cubital fossa, by slashing the wrists, or fractures of the distal forearm. These lesions might result in:
  1. Paralysis of most of the wrist flexors, pronators and thenar muscles.
  2. Weak flexion and abduction at the wrist, with the hand inclin-ing to the ulnar side.
  3. "Ape hand" deformity (thumb in plane of hand and thenar atrophy).
  4. Inability to oppose or flex the thumb. Difficulty in abducting the thumb.
  5. Weakened grip, expecially in the thumb, index and middle fingers.
  6. Inability to flex the distal phalanx of the thumb, index, and middle fingers.

Carpal Tunnel Syndrome: Inflammation of the synovial sheaths of flexor tendons in the carpal tunnel causes the median nerve to be compressed against the un-yielding flexor retinaculum, thereby compressing the nerve gradually. This syndrome is characterized by partial paralysis and atrophy of the thenar muscles and burning sensations in the radial half of the palm and the palmar aspects of the first 3 1/2 digits. Decompression of the nerve by section of the flexor retinaculum may be required for relief.
THE ULNAR NERVE (C8,T1)
The ulnar nerve comes from the medial cord and lies medial to the brachial artery. At the middle of the arm, it pierces the medial inter-muscular septum with the superior ulnar collateral artery. It passes posterior to the medial epicondyle at the elbow and continues into the forearm by passing through the flexor carpi ulnaris. Proximal to the wrist it gives off a dorsal cutaneous branch to the posteromedial hand and medial 1 1/2 digits. Passing superficial to the flexor retinaculum at the wrist, it gives off a palmar cutaneous branch and then continues into the hand. The ulnar nerve is most vulnerable to injury at the elbow.
Branches:
Muscular: to flexor carpi ulnaris and ulnar half of the flexor digitorum profundus in the forearm.
The deep branch of the ulnar nerve supplies:
3 hypothenar muscles
all interossei

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