1014 - A Beer Run Gone Wrong: Posterior Interosseous Nerve Palsy after a Biceps Tendon Rupture and Repair

Case Diagnosis: Posterior Interosseous Nerve Syndrome

Case Description: A 51 year old male with past medical history of left shoulder pain presented for weakness of the left finger extensors. Patient underwent biceps repair for distal rupture of biceps tendon while carrying a case of beer. Post-surgery, patient reports weakness in finger extension and decreased sensation on dorsum of forearm to all fingers. Reported limited ROM of left elbow flexion with improvement.

On exam, reduced strength left wrist extension compared to right, decreased sensation on left posterior forearm. Positive Hawkin’s on left. Electrodiagnostic studies revealed active denervation in extensor indicis pollicis (EIP), extensor digitorum communis (EDC), and extensor carpi ulnaris (ECU). Voluntary motor units recruited in EDC and EDU, and none in EIP. Leading diagnosis was posterior interosseous mononeuropathy of left forearm with moderate severity in branches to the EDC and ECU showing signs of reinnervation and severe in branches to the EIP without signs of reinnervation.

Discussions: Patient instructed to repeat EMG in 4-6 weeks, begin physical therapy, and e-stimulation. Surgical repairs to reattach the biceps tendon and can restore full/near-full strength following tendon rupture. Injury to the posterior interosseous nerve (PIN), lateral antebrachial cutaneous nerve, and superficial radial nerve are common risks. The PIN can be injured due to proximity to the bicipital tuberosity, and complication rates have been reported at 5%.

The PIN is a deep motor branch of the radial nerve at the radiocapitellar joint level. It courses through the radial tunnel, between the heads of the supinator muscle to innervate the forearm extensors. Injury results in weakness of lateral fingers and wrist drop.

Conclusions: PIN Syndrome is a serious complication of distal biceps repair surgery that must be identified quickly after the procedure. Utilizing rehabilitative services early, along with serial EMGs provides the best prognosis for recovery in patients with PIN syndrome.