Nygren(1) showed that whiplash injuries in rear-end collisions often lead to permanent disability. Ten percent of those initially complaining about neck pain after a rear—end collision had remaining problems 5 years after the accident and were judged as permanently, medically disabled.

It was also shown that fitted headrests had little effect in preventing whiplash injuries. Fixed headrests reduced the incidence of whiplash injuries by 24 percent, while adjustable headrests reduced the risk by only 14 percent. The results of whiplash injuries in terms of permanent disability were not affected by headrest fitting and type.

The present study is based on 339,675 accidents and determines if the variations of the effects of headrests in different car models could be explained by their type and position.