Effects of Head Restraint Position on Neck Injury in Rear Impact

Although whiplash is typically classified as a minor injury, the economic cost ofwhiplash has been estimated at roughly $4.5 billion per year in the United States. International research efforts have included computational modeling, crash reconstructions, biomechanical testing of animals and human cadavers, and experimental rear impact tests using both anthropomorphic dummies and human subjects. Despite these efforts, the mechanisms and tolerances of whiplash injuries are still largely unknown. This paper uses a computational modeling approach to better understand the effects of head restraint position on the risk of cervical injury under rear impact conditions. Both height and backset are varied over a wide range, while various engineering parameters believed to be related to cervical injury risk are examined. Simulation results for this model of a 50’ percentile male indicate that for a head restraint height of 3 1.5 inches, the relative rotations, relative displacements, tensile loads, shear loads, bending moments, NE values and NIC values are relatively low for backsets of about 2 inches or less. Similarly, the results indicate that for a head restraint height of 29.5 inches, the value of these parameters are relatively low for backsets of 1 inch or less. These lower values suggest that a head restraint position that is higher and closer to the head may lead to a reduced risk of cervical spine injury. Introduction Whiplash injuries of the neck are one of the most common injuries reported from automotive rear impacts. Although these injuries are classified as minor (AIS I), their high incidence rate and often longterm consequences lead to significant societal costs. Based on data collected in the National Automotive Sampling System Crashworthiness Data System (NASS CDS), it has been estimated that more than 740,000 whiplash injuries occur annually[ I]. Assuming an average cost of more th& $6,000 per injury (including medical, legal, insurance, loss of productivity, and loss of work), the total annual monetary cost of whiplash in the United States is roughly $4.5 billion. Since January 1, 1969, passenger cars have been required by Federal Motor Vehicle Safety Standard (FMVSS) No. 202 to provide head restraints that meet specified requirements for each designated