Review Question - QID 4634

Based on the choices above, fibrillations will be seen in the extensor pollicis longus, supinator and abductor pollicis longus muscles.

The radial nerve splits into the superficial radial branch and the posterior interosseous nerve (PIN) at the anterior aspect of the radiocapitellar joint, just proximal to the supinator muscle. The PIN innervates the EDC, EDM, ECU, EPB, EPL, EIP, APL and sometimes the ECRB. Compressive neuropathy of the PIN leads to motor dysfunction, namely weakness with wrist and finger extension.

Lubhan et al. review uncommon compression neuropathies affecting the upper extremity. They indicate that PIN syndrome may be caused by rheumatoid arthritis and compressive ganglion cysts. Depending on which nerve branch is affected, partial lesions may develop. They recommend use of conservative measures (rest, activity modification and splinting) first. Decompressive procedures may be indicated in symptoms lasting greater than 3 months.

Illustration A shows the course of posterior interosseous nerve from proximal to distal along the course of the supinator. This proximal edge of the supinator (Arcade of Froshe), the fibrous edge of the ECRB and the leash of Henry are three main points of compression of the PIN.

Incorrect Answers
Answer 1, 2, 4: The radial nerve proper innervates the ECRL, ECRB and Brachoradialis
Answer 5: The recurrent motor branch of the median nerve innervates the APB