Localizing Nerve Injury, Defining Injury Severity, and Estimating Prognosis (Nerve SPACE 2025).

Background: Localizing nerve injury, defining injury severity, and estimating prognosis are critical factors in surgical decision-making when indicating patients for operative intervention following traumatic nerve injury. Where are we now?: Current methods for localizing nerve injury and determining severity of injury include physical examination, electrodiagnostic studies, imaging including ultrasound and magnetic resonance imaging, and surgical exploration. However, these methods remain suboptimal, especially in cases of segmental or multilevel injury as is often seen in blunt force trauma as well as in cases of partial (axonotmetic) injury. A period of observation is often required to determine if spontaneous recovery will occur. In neurotmetic injuries, it is challenging to accurately determine the zone of injury intraoperatively to ensure that reconstruction is performed using healthy, viable nerve. As a result of these shortcomings, it has been difficult to accurately and consistently classify nerve injury according to location and severity which has resulted in difficulty estimating the prognosis for many injuries. Where do we need to go?: Better diagnostic methods are needed to be able to accurately determine the location of nerve injury to direct surgical intervention and determine prognosis, especially in blunt, ballistic, multilevel, or segmental injuries. Additionally, improved methods are needed to evaluate partial axonotmetic injuries in which the epineurium remains grossly intact on inspection intraoperatively, but with varying degrees of axonotmetic injury within the nerve. This includes a need for both noninvasive preoperative imaging and biomarkers as well as intraoperative modalities to more accurately determine the degree of intraneural damage and assist in preoperative indications and intraoperative decision-making. Improving these diagnostic modalities will allow classification of injuries by location and severity on a more consistent and accurate basis, leading to improved ability to estimate prognosis, surgical indications, and intraoperative decision-making. How do we get there?: Emerging diagnostic modalities, including simultaneous positron emission tomography and magnetic resonance imaging, nerve-specific fluorescence imaging, quantitative ultrasound and magnetic resonance imaging, peripheral nerve diffusion tensor imaging, magnetic resonance neurography, polarization-sensitive optical coherence tomography, and serum biomarkers for peripheral nerve injury, offer promising advances that may help better localize and define injury severity in peripheral nerve injury. More research and funding are needed to better understand how best to apply each of these modalities for traumatic nerve injury, leading to broader adoption, more accurate classification and consistent reporting of data that can be linked to patient outcomes and ultimately help improve our ability to estimate prognosis after nerve injury.