Hourglass Constriction of a Single Fascicle of the Anterior Interosseous Nerve

Hourglass fascicular constrictions have been reported in fewer than 100 cases globally and only in the upper limb. The etiology remains unknown. Patients often present with self-limiting pain in the affected limb followed by flaccid paralysis. As the external architecture of the nerve remains normal on traditional radiological studies, the diagnosis can be missed. The purpose of this case report is to describe this rare clinical entity and a successful treatment approach including ultrasound localization and targeted intraneural microsurgical neurolysis followed by excellent functional recovery.