Posterior Interosseous Nerve Compression Syndrome

As eluded to last week Posterior Interosseous Nerve (PIN) Compression Syndrome, a deep branch of the radial nerve, is felt to be radial tunnel syndrome with paralysis.

• Symptoms depend on whether the PIN is compressed before or after it divides into medial and lateral branches.
  • Before: Results in complete paralysis of the digital extensors, and extensor Capri ulnaris. Wrist will become dorsoradial deviated.
  • After-Medial Branch: Paralysis of extensor carpi ulnaris, extensor digiti quinti, and extensor digitorum communis
  • After-Lateral Branch: Paralysis of abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis proprius
• Common causes:
  • Synovitis and Joint Ganglions
  • Nerve compression following fracture repair
  • Idiopathic Compression can occur at these sites
    • Fibrous bands anterior to the radial head
    • Tendinous origin of Extensor Carpri Radialis Brevis
    • Arcade of Froshe –Most common, it is the tendinous proximal border of supinator
    • Distal Edge of Supinator –Least Common
• Exam:
  • Increased pain with resisted supination of the forearm
  • Supination with Wrist Flexion symptoms will likely be reproduced.
  • Pain with resisted extension of the middle finger
  • Unable to extend thumbs or fingers at MCP joints, but can extend at PIP and DIP joints