Makindo Medical Notes

💤 Saturday night palsy: weakness of wrist & finger extensors on waking after alcohol-induced sleep due to prolonged radial nerve compression.

🧩 Origin and Course

• Origin:
  • Posterior cord of brachial plexus (C5–T1).
  • Carries all posterior division fibres → major motor to extensors.
• Course:
  • Descends posterior to axillary artery → radial groove of humerus.
  • Winds laterally → anterior to lateral epicondyle.
  • Divides in proximal forearm into:
    • Deep branch (posterior interosseous nerve).
    • Superficial sensory branch.

🌿 Branches of the Radial Nerve

• Muscular branches: triceps, anconeus, brachioradialis, extensor carpi radialis longus.
• Cutaneous branches:
  • Posterior cutaneous of arm.
  • Inferior lateral cutaneous of arm.
  • Posterior cutaneous of forearm.
• Deep branch (Posterior interosseous nerve) → all forearm extensors.
• Superficial branch → sensory to dorsum of hand (thumb, index, middle, radial half of ring finger; NOT fingertips).

⚙️ Functions

• Motor: elbow extension (triceps), wrist/finger extension, supination (supinator).
• Sensory: posterior arm & forearm, dorsum of hand (radial side).

🚨 Clinical

• Radial nerve palsy ("Saturday night palsy", "honeymoon palsy"):
  • Wrist drop ✋ (cannot extend wrist/fingers).
  • Sensory loss over dorsal hand.
  • Usually temporary (resolves over weeks).
• Humeral shaft fracture:
  • High risk of nerve injury in radial groove.
  • Motor/sensory loss pattern as above.
• Compression injuries:
  • Axilla: “crutch palsy”.
  • Forearm: posterior interosseous entrapment (pure motor weakness).

🧪 Investigations

• Clinical exam: test wrist/finger extension, check sensory dorsum of hand.
• Electrophysiology: EMG, nerve conduction studies → localise lesion.
• Imaging: X-ray for humeral fracture; MRI/US for entrapment or soft tissue mass.

📋 Causes

• Pressure palsy (sleep, crutches, prolonged positioning).
• Mononeuropathy: diabetes, alcohol, B12 deficiency.
• Trauma: humeral fracture, dislocation.

💊 Management

• Remove/avoid cause (e.g. avoid alcohol sleep posture, replace B12).
• Splint wrist to prevent contractures + OT/PT for recovery.
• Neuropathic pain management if present.
• Most palsies recover in weeks–months; poor prognosis if severe axonal loss on EMG.

🔑 Exam tip: Wrist drop + humeral fracture = radial nerve injury. Posterior interosseous branch → pure motor deficit without sensory loss.