PERFORMANCE EVALUATION OF AUTOMOBILE HEAD RESTRAINTS 720034

Accident cases involving cars without head restraints are compared with cars having this device to evaluate the effectiveness of head restraints, their position when impact occurred and to provide some details concerning the relationship between occupant position, seat back damage and cervical injury. A reduction in non-dangerous cervical injury was associated with the head restraint group. However, due to small numbers this could not be confirmed, statistically.

Approximately 73 percent of the adjustable head rests were in their lowest position. The position of the occupant on the seat strongly influenced injury. Larger amounts of rearward rotation of the seat back were associated with lower injury severity than limited rotation.

Injuries to the cervical region resulting from automobile accidents have been the subject of a number of research reports. Concern over these injuries culminated in Federal Motor Vehicle Safety Standard Number 202 which requires that a head restraint be provided for front seat occupants of cars manufactured since 1 January 1969.

The term most commonly associated with neck injuries observed in rear impact accidents is “whiplash.” Although the term has been derided by many authors as describing an injury mechanism and not a diagnosis, it continues to have widespread usage. The injury it is intended to describe results from hyperextension or hyperflexion of the neck as the head rotates to the rear in a rear end collision. The resulting injury may range from pain or simple muscular sprains to torn ligaments, cervical fractures or dislocations, or combinations of these injuries.

A report by Kihlberg¹ indicated that neck injury was more frequent among front seat passengers than among rear seat passengers in the same car, and that the frequency of driver's injuries did not differ substantially from that of their rear passengers. Seat back damage, i. e., rearward bending of the seat, was associated with a lower frequency of neck injury to the occupant although this damage usually occurred in the more severe accidents. Kihlberg also found that the frequency of neck injury did not appear to be related to the height of the occupants, possibly because the top of the seat back is lower than the neck and shoulder area for most adults. Interestingly enough, neck injury was up to twice as frequent among women as among men. No explanation was found for this difference but it was hypothesized that the neck structure of women might not be as strong as that of men.

In the present report, head restraint position and neck injuries among occupants of cars with head restraints are compared with those among occupants of cars without such devices.