Radial nerve - posterior interosseous nerve lesions

Causes

• Entrapment at the radiohumeral joint capsule.
• Entrapment at the sharp edge of the extensor carpi radialis muscle.
• Entrapment at the arcade of Frohse (fibrotendineous arch where the nerve enters supinator muscle).
• Entrapment within supinator muscle (supinator channel syndrome).
• Compression by brachiocephalic arteriovenous fistula.
• Compression by tumor, ganglia or cysts.
• Direct acute or chronic injury.
• Amyloid neuropathy in multiple myeloma.

Symptoms & signs

• Supinator muscle is spared.
• Weakness and atrophy of extensor carpi ulnaris, extensor digitorum, extensor indicis, extensor digiti minimi and abductor pollicis longus and brevis.
• Difficulty in extending the wrist in ulnar direction.
• Radial deviation of wrist during extension.
• Drop-thumb deformity.
• No sensory deficits.
• Pain in the dorsal wrist and lateral elbow might exist.