Biomechanics of Cervical Spine Injuries in Rear End Car Impacts: Influence of Car Seats and Possible Evaluation Criteria

Soft tissue neck injuries or cervical spine distortion injuries (CSD) are dominant injuries in all claimed car collisions. The injury mechanisms are currently not fully understood because some symptoms are rated subjectively and even modern radiological imaging techniques (CT, MRI, PET, etc.) cannot detect structures damaged. One attempt was made using the new internationally accepted QTF (Quebec Task Force) classification on CSD injuries to differentiate between three grades (1 = microlesion, 2 = muskulosceletal, 3 = neurological) of this minor (AIS 1) injury within a large amount of retrospective insurance data material, which covers 15,000 car to car collisions with injured occupants in Germany. From this sample, 517 rear-end collisions have been analyzed medically and technically in order to get an overview about the real accident scenario. The task of the accident investigation is to identify risk factors and population at risk, and to define countermeasures. Summarizing the conclusions, it can be said that females showed a generally higher risk and older people showed a higher risk for high graded CSD injuries. The QTF injury degree positively correlates with time of work absence and full recovery but not with j v, which could be biased through a high aggravation rate in the lower j v ranges. First results indicate that high-positioned head restraints have a significant protection effect, whereas no headrests and low-positioned head restraints lead to a higher injury incidence. A human volunteer sled test series based on different anthropometric measurements will be discussed. Forty-three rear end sled tests performed at the same car seat and two j v ranges have been performed. Because females show in most real world accident analysis a higher injury incidence, 6 tests with females have been performed with the aim to detect possible differences. Possible correlation between different parameters was tested statistically. It was shown that neck circumference correlates well with peak head x -acceleration. Moreover, muscular electrode measurements for the deep and superficial cervical musculature during a rear end impact sled test series with volunteers ( j v 6.5 and 9.5 km/h) are presented. This test series also integrates the deep Musculus semispinalis capitis, which could be associated with common muscular pain after CSD. The current injury hypothesis describes now 3 phases (extension, head-impact, rebound), because muscular measurement shows also at the rebound phase a maximum contraction of the deep cervical spine muscles. Seat comparison tests had been performed with two different dummies (HIII TRID, BIORID 2); the realism and possible biomechanical evaluation criteria will be discussed.