1639 - Posterior Interosseous Nerve Lesion: A Sequela of Sequential Distal Radial Fractures

Posterior Interosseous Nerve Lesion 

Case Description:

 A 71-year-old female presents with a left wrist drop after a fall on an outstretched hand in 2024 which necessitated an ORIF procedure. She also has a prior history of left wrist fracture causing upper extremity numbness and tingling requiring plate fixation in 2013. Evaluation included a detailed neurological examination, a nerve conduction study (NCS) and electromyography (EMG).. Physical exam revealed left wrist drop and weakness in finger extensors, with 3+/5 strength in the extensor indicis proprius and 4+/5 in wrist extensors. A NCS confirmed a normal left radial sensory response and a left radial motor neuropathy with a conduction velocity drop in the forearm. An EMG showed polyphasic potentials suggestive of active denervation in the extensor indicis proprius and extensor carpi radialis brevis. 

Discussions:

 Posterior interosseous nerve (PIN) syndrome is a rare compressive neuropathy causing motor impairments without sensory deficits in the hand. The electrodiagnostic studies suggest a true PIN lesion, a proximal radial nerve lesion, or a cervical radiculopathy (C7). Due to localization of radial nerve motor deficits in the forearm with sparing of the radial sensory nerve, a PIN lesion is most likely. The mechanism is likely multifactorial, involving post-traumatic fibrosis from the initial surgeries, direct entrapment from the recent fracture, or nerve stretching from her most recent fall in 2024.

Conclusions:

This case highlights PIN syndrome as a critical, though often overlooked, complication of distal radial fractures, surgical intervention or trauma. Electrodiagnostic studies are crucial for accurate diagnosis and localization, guiding appropriate management to prevent permanent functional deficit. Future research should focus on identifying predictive factors for PIN injury after distal radius fractures, optimizing surgical approaches to minimize risk, and evaluating long-term functional outcomes.