Radial Nerve Lesion - Wrist Drop

Mnemonic

BEST muscles are supplied by the radial nerve:

• B - Brachioradialis
• E - Extensors, of the wrist and fingers
• S - Supinator
• T - Triceps

The level of the lesion determines what survives:

• Axilla (crutch palsy): triceps lost as well, so extension of the elbow fails
• Spiral groove (Saturday night palsy, humeral shaft fracture): triceps spared, wrist drop with sensory loss over the anatomical snuffbox
• Posterior interosseous (below the elbow): no sensory loss, finger drop with the wrist deviating radially, since extensor carpi radialis longus is spared

Expansion

• Wrist drop - inability to extend the wrist and fingers against gravity
• Level matters - a lesion in the axilla also weakens triceps, while a spiral groove lesion spares triceps but still causes wrist drop
• Sensory loss - a small patch over the first dorsal web space (the anatomical snuffbox area)
• Test extension of the wrist and metacarpophalangeal joints to confirm