Makindo Medical Notes.com

Related Subjects: |Radial Nerve |Median Nerve |Ulnar Nerve |Musculocutaneous nerve |Axillary nerve |Brachial plexus |Dermatomes

About

• The median nerve is formed by the union of branches from the lateral and medial cords of the brachial plexus, which contain fibers from the C5 to T1 spinal nerves.

Anatomy

• Origin:
  • Arises from the lateral and medial cords of the brachial plexus, carrying fibers from C5, C6, C7, C8, and T1 spinal nerves.
• Course:
  • Descends the arm within the anterior compartment, initially lateral to the brachial artery and then crossing anteriorly to lie medial to it at the elbow.
  • Passes through the cubital fossa, deep to the bicipital aponeurosis.
  • Enters the forearm between the two heads of the pronator teres muscle.
  • Travels down the forearm between the flexor digitorum superficialis and flexor digitorum profundus muscles.
  • Enters the hand through the carpal tunnel.
• Muscular Branches:
  • Innervate most of the anterior forearm muscles, including the pronator teres, flexor carpi radialis, palmaris longus, and flexor digitorum superficialis.
  • The anterior interosseous nerve, a branch of the median nerve, innervates the flexor pollicis longus, pronator quadratus, and the lateral half of the flexor digitorum profundus.
• Palmar Cutaneous Branch:
  • Arises in the distal forearm and provides sensation to the skin of the lateral palm.
• Branches in the Hand:
  • Recurrent branch: Innervates the thenar muscles (abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis).
  • Digital cutaneous branches: Provide sensory innervation to the palmar aspect of the lateral three and a half fingers (thumb, index, middle, and lateral half of the ring finger) and the dorsal fingertips of these fingers.

Function

• Motor Functions:
  • Flexion of the wrist and fingers through the innervation of the flexor muscles in the forearm.
  • Pronation of the forearm via the pronator teres and pronator quadratus muscles.
  • Thumb opposition and abduction through the thenar muscles.
• Sensory Functions:
  • Sensation to the lateral palm and the palmar surface of the thumb, index, middle, and lateral half of the ring fingers.
  • Sensation to the dorsal fingertips of these fingers.

Clinical

• Carpal Tunnel Syndrome:
  • Caused by compression of the median nerve within the carpal tunnel.
  • Symptoms include numbness, tingling, and pain in the thumb, index, middle, and lateral half of the ring fingers, along with weakness in the thenar muscles.
• Pronator Teres Syndrome:
  • Compression of the median nerve at the elbow as it passes between the heads of the pronator teres muscle.
  • Symptoms include pain and tenderness in the proximal forearm and similar sensory disturbances to carpal tunnel syndrome.
• Anterior Interosseous Syndrome:
  • Injury or compression of the anterior interosseous nerve branch.
  • Results in weakness of the flexor pollicis longus, pronator quadratus, and the lateral half of the flexor digitorum profundus muscles, causing difficulty with pinch grip and forearm pronation.
• Hand of Benediction:
  • Occurs due to a high lesion of the median nerve, resulting in the inability to flex the index and middle fingers at the metacarpophalangeal joints when attempting to make a fist.

Investigations

• Clinical Examination:
  • Assessment of hand and finger movements, including thumb opposition and flexion of the fingers.
  • Evaluation of sensation in the median nerve distribution area.
• Electrophysiological Tests:
  • Electromyography (EMG) and nerve conduction studies to assess the function of the median nerve and identify the site of injury or compression.
• Imaging:
  • Ultrasound or MRI to visualize the nerve and surrounding structures, especially in cases of suspected compression.

Management

• See Carpal tunnel syndrome
• Splinting, steroid injection, surgical decompression
• The median nerve supplies the following structures in the hand: The lateral two lumbricals. The skin of the lateral three and half fingers. The flexor pollicis longus is also supplied by the median nerve but is not one of the intrinsic hand muscles, being located in the forearm with its main action being thumb flexion.