4. | Information/Discussion on Whiplash Injury Criteria for Regulation

4.b. Status of JARI Research: Reviews on Injury Parameters and Injury Criteria for Minor Neck Injuries during Rear-end Impacts

JARI/Koshiro Ono (KO) presented a review on injury parameters and injury criteria for minor neck injuries during rear-end impacts (WCWID-01-05).

Objectives of this study: review the published papers and current knowledge for reducing minor neck injuries; review of injury evaluation parameters from human volunteer tests and accident reconstruction simulations.

A chain of evidence from different sources (PMHS tests, volunteer tests, animal tests etc.) was presented:

• Excessive deflection leads to soft tissue injury
• Facet joint is most common injury site
• Strain rate affects rupture strength of soft
• Stretch of facet capsule is related with pain

Symptoms from six volunteer tests were presented. It was noted that each subject received multiple tests, from 4 to 9.4 km/h delta-v. The strains in the facet joints were estimated from the high-speed x-ray data and safe and failure zones defined. The correlations of the strains and strain rates (principal and shear) with candidate injury criteria were presented. The injury criteria were calculated for each volunteer (not for the BioRID II). Head and neck loads were calculated using inverse dynamics and external forces from strain gauges on the head restraint supports.

Accident reconstructions (20 occupants in 15 cars) were then presented. The THUMS FE model was scaled based on the height and weight of the occupant (with the mass scaled by adjusting the density). The head restraint backset was not known, so a standard backset of 50 mm was used.

Injury classified as WAD 2+, so WAD 1 (pain only with no identifiable physical change) was classified as non-injury.

The correlation between the candidate criteria and the strain / strain rate in the simulations was presented. KM noted that the correlations are for a lower level of injury than we are
targeting with the regulation.

A comparison between the Japan and US approaches and suggested criteria was presented, followed by a comparison of facet joint strains for tensed and relaxed muscle conditions.

Upper facet joint strain was higher in the relaxed state; lower facet joint strains were higher in the tensed stated.

It seems not to be possible to evaluate neck injury risk from OC-T1 kinematics alone; NIC, and neck forces/moments are also required. This is because the head-neck motion is not achieved by a simple rotation of a straight line neck, but includes an s-shaped neck.

Concluding, various injury risk curves (IRC) were presented for human subjects, with 95% confidence intervals. Good correlations with WAD2+ were found for NIC, upper neck Fx & My, lower neck Fx & My.

For IV-NIC of 1.1, an 82.9% risk of WAD2+ was derived. As such, when the neck is flexed or extended 10% above the physiological range, an 82.9% risk of WAD2+ exists.