The neck injury index, NII, was developed in ISO 13232-5 (2005) as a testing and evaluation procedure for assessing the risk of injury to the AO/C1/C2 region of the cervical spine in motorcycle riders. A recent series of 36 head/neck component tests was used to examine the risk of neck injury in frontal impacts and to assess the predictive capability of NII for impacts of various orientations. Neck injuries produced in the testing ranged from AIS 1 to AIS 5. Using force and moment load cell cadaver experimental data, injury risk was assessed using NII evaluated with the ISO 13232-5 algorithms. The injury risk predictions are compared with the injury outcomes from the head/neck cadaver. The average predicted risk of injuries for the experimental injury tests based on NII at the corresponding MAIS level observed in testing was 0.7% though there were 11 AIS 3+ injuries in the testing. Using the experimental injury outcomes and the experimental force and moment time histories, the normalizing coefficients from NII are reevaluated to minimize the difference between NII risk assessment and the experimental injury outcome in the L2 basis. This reanalysis is compared with existing human and cadaver neck injury criteria.
Limitations of this study are primarily the limitations of the source data including lack of dynamic muscle response, anthropometric and age differences between experimental and epidemiological populations, and limitations on the principal direction of impact, generally flexion/compression and flexion/tension. Further, the injuries seen in the source data include both upper neck (OC-C2) and lower neck (C3-T1) injuries; the NII injury criterion is intended to assess the potential for upper neck injuries.