Finding the PIN in the Haystack: Case report on the localization of a Posterior Interosseous Nerve lesion




Colucci, Patricia
Mirochnitchenko, Alissa
Ooi, Preston


0000-0001-8341-3588 (Colucci, Patricia)

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Background: Posterior interosseous nerve (PIN) lesions are uncommon, with an incidence of 0.003%. This case report investigates a PIN lesion distal to the Arcade of Frohse with an unknown etiology. Case Information: A 45 year old male with a history of multilevel anterior cervical spine discectomy and fusion (ACDF) and right cubital tunnel release presented to clinic with persistent right hand weakness. Although his numbness had improved in the fourth and fifth digits, he still experienced dorsal forearm fatigue and thumb extension weakness on the right side. He denied recent trauma or any other comorbid chronic conditions. Physical exam revealed 5/5 strength in bilateral upper extremities, 1/5 strength in first digit extension and abduction, 2/5 strength in second digit extension, and 4/5 strength in third through fifth digits. A nerve conduction study (NCS) was conducted and revealed appropriate amplitudes, latencies and conduction velocities in the median and ulnar sensory and motor nerves, and radial sensory nerves bilaterally. Electromyography (EMG) revealed residual abnormalities attributed to recent ulnar nerve impingement and chronic findings due to C5-6 ACDF. EMG was further suggestive of a radial neuropathy between the takeoff of the nerve to abductor pollicis longus (APL) and extensor pollicis brevis (EPB). The patient was referred to surgery for further management. Conclusions: This case demonstrates the importance of the investigation of new pathology when multiple, chronic pathologies exist. Furthermore, this case highlights that EMG, NCS, and anatomical knowledge play crucial roles in uncovering complex pathology.