(Kiosk 2) PIN Neuropathy Following ORIF: A Case Report

Case Diagnosis: Left Posterior Interosseous Nerve (PIN) Neuropathy

Case Description or Program Description: A 56-year-old male patient with no pertinent past medical history was referred for a left upper extremity electrodiagnostic evaluation.

Setting: The patient suffered massive trauma to the left forearm resulting in an open wound treated with ORIF.

Assessment/Results: The patient then noticed weakness with left finger extension, and his physical exam supported his complaint with the left extensor indicis proprius (EIP) demonstrating 0/5 strength. His physical exam was also notable for 4/5 strength of the left finger extensors and diminished sensation along the left anterior forearm and wrist. NCS findings were consistent with left-sided motor radial neuropathy between the wrist and elbow. With a normal left superficial radial nerve response on NCS and no activity found in the left EIP muscle on EMG, the lesion was isolated between the extensor carpi radialis brevis (ECRB) and the EIP muscles, which would locate the lesion to the left PIN.

Discussion (relevance): Radial tunnel syndrome, or entrapment of the PIN, is an uncommon cause of forearm pain. It may be clinically difficult to distinguish from radial nerve impingement at the spiral groove. Both posterior interosseous neuropathy and spiral groove radial nerve entrapment may demonstrate wrist-drop or finger-drop with sparing of elbow extension; however, patients with PIN neuropathy may have radial deviation on wrist extension due to the involvement of the extensor carpi ulnaris. PIN compression is common in the fibrous bands of the brachialis and brachioradialis muscles, or the arcade of Frohse, fibrous bands associated with the supinator, and the tendinous margin of ECRB.

Conclusions: In patients with wrist numbness, tingling, or extensor weakness following surgery, it may be warranted to perform a subsequent EMG/NCS study to distinguish a possible PIN neuropathy due to trauma or surgery.