Makindo Medical Notes.com

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

Weakness of the wrist and finger extensors on waking after alcohol-induced sleep

Origin and Course

• Origin:
  • The radial nerve originates from the brachial plexus, specifically from the posterior cord, which is formed by the union of the posterior divisions of the upper, middle, and lower trunks. Arises from the posterior cord of the brachial plexus, carrying fibers from the C5 to T1 spinal nerves.
• Course:
  • Descends posterior to the axillary artery and travels along the posterior aspect of the humerus in the radial groove.
  • Wraps around the humerus laterally and passes anterior to the lateral epicondyle at the elbow.
  • Divides into a deep branch (posterior interosseous nerve) and a superficial branch in the proximal forearm.

Branches of the Radial Nerve

• Muscular Branches:
  • Innervate the triceps brachii, anconeus, brachioradialis, and extensor carpi radialis longus muscles.
• Cutaneous Branches:
  • Posterior cutaneous nerve of the arm: Provides sensation to the posterior surface of the arm.
  • Inferior lateral cutaneous nerve of the arm: Provides sensation to the lower lateral aspect of the arm.
  • Posterior cutaneous nerve of the forearm: Provides sensation to the posterior surface of the forearm.
• Deep Branch (Posterior Interosseous Nerve):
  • Passes through the supinator muscle and continues along the posterior aspect of the forearm.
  • Innervates the extensor muscles of the forearm, including the extensor digitorum, extensor carpi ulnaris, and extensor pollicis longus.
• Superficial Branch:
  • Travels along the lateral side of the forearm under the brachioradialis muscle.
  • Provides sensory innervation to the dorsal surface of the hand, including the thumb, index, and middle fingers (excluding the fingertips).

Functions of the Radial Nerve

• Motor Functions:
  • Extension of the elbow via the triceps brachii.
  • Extension of the wrist and fingers via the extensor muscles of the forearm.
  • Supination of the forearm via the supinator muscle.
• Sensory Functions:
  • Sensation to the posterior arm and forearm.
  • Sensation to the dorsal aspect of the hand, including the thumb, index, and middle fingers (excluding the fingertips).

Clinical

• Radial Nerve Palsy:
  • Also known as "Saturday night palsy" or "honeymoon palsy," it occurs due to prolonged compression of the nerve.
  • Symptoms include wrist drop (inability to extend the wrist and fingers) and loss of sensation in the dorsal hand.
• Fracture of the Humerus:
  • Can lead to radial nerve injury due to its close proximity to the humerus in the radial groove.
  • May result in loss of motor and sensory function as described above.
• Compression Injuries:
  • Compression at various points along the nerve's course, such as in the axilla (e.g., crutch palsy) or at the elbow, can cause radial nerve dysfunction.

Investigations

• Clinical Examination:
  • Assessment of motor function by testing the ability to extend the wrist and fingers.
  • Evaluation of sensory function by testing sensation in the areas innervated by the radial nerve.
• Electrophysiological Tests:
  • Electromyography (EMG) and nerve conduction studies to assess the function of the radial nerve and identify the site of injury.
• Imaging:
  • MRI or ultrasound to visualize the nerve and surrounding structures.
  • X-rays to check for fractures or other bony abnormalities.

Causes

• Pressure palsy
• Mononeuropathy - Diabetes, B12 deficiency, Alcohol

Management

• Avoid causes e.g. alcohol, replace B12 if low
• Physiotherapy and OT and splinting can help
• Manage neuropathic pain
• Improves over weeks and months