Abstract
Surgeons' ability to interpret electrodiagnostic (EDX) studies has greatly enhanced patient selection and outcome for nerve surgeries as it has informed our understanding of the classification of nerve injury. EDX measures axons present, lost, or demyelinated. It does not measure an area where axons experience chronic ischemia, making a Sunderland Zero nerve injury a clinical diagnosis that should be suspected when patients have normal EDX, decreased recruitment on electromyography (EMG), and no atrophy. Only observation of recovery in the earliest postoperative period would confirm a Sunderland Zero. In this article, we present an expanded classification of nerve injury, highlighting Sunderland Zero or ischemic neurapraxia, and provide a historical and pathophysiological overview of how it came to be recognized. We also offer a user-friendly classification and an equation we call the Nerve Injury Calculator (NIC) that calculates the percent axonal loss, demyelinating loss, and ischemic axons to predict timing and quality of recovery. The clinical utility of the NIC is exemplified with three cases. With the development and introduction of the NIC, there is a paradigm shift amongst surgeons, physiatrists, and neurologists that allows us all to speak the same language of EDX and nerve surgery, enabling improved patient education, prediction of prognosis and timing of recovery, and efficient follow up with respect to patients' postoperative period.