Re-evaluating the neck injury index (NII) using experimental PMHS tests

Area of Science:

• Biomechanics
• Injury Biomechanics
• Road Safety Research

Background:

• The Neck Injury Index (NII) is a standard for evaluating cervical spine injury risk in motorcycle riders.
• Existing NII criteria, developed for motorcyclist anthropomorphic test devices (MATD), require reevaluation for postmortem human subject (PMHS) data.

Purpose of the Study:

• To reevaluate the ISO 13232 NII using a PMHS dataset.
• To reformulate the NII criterion for applicability to PMHS tests and improve injury prediction accuracy.

Main Methods:

• Utilized 36 PMHS head/neck component tests with frontal impacts.
• Assessed injury risk using NII algorithms with force and moment load cell data from PMHS experiments.
• Reanalyzed NII normalizing coefficients based on experimental injury outcomes and force/moment data.

Main Results:

• The original NII criterion significantly underestimated injury incidence in PMHS tests (0.7% predicted vs. 30.6% observed AIS 3+ injuries).
• A reformulated NII(PMHS) criterion was developed using PMHS loads and injury outcomes.
• The new criterion removes dependency on MATD simulations and aligns better with PMHS experimental data.

Conclusions:

• The reformulated NII(PMHS) provides a more accurate prediction of neck injury risk in PMHS tests.
• This advancement enhances the evaluation of cervical spine injury criteria using direct human subject data.
• The NII(PMHS) retains the multi-axial nature of the original NII while improving applicability to PMHS testing.