The association between occupant restraint systems and risk of injury in frontal motor vehicle collisions

Background: An evaluation of seat belt use and airbag deployment, either alone or in combination, on risk of injury to specific body regions has yet to be completed. Methods: A retrospective cohort study of front seat occupants involved in police-reported, tow-away, frontal motor vehicle collisions using data from the 1995 through 2000 National Automotive Sampling System was conducted. Only vehicles with a change in velocity (delta-V) of greater than or equal to 15 km/h were included. Risk of injury (Abbreviated Injury Scale score 2: 2) to specific body regions was compared according to seat belt use and airbag deployment. Results: Compared with completely unrestrained occupants, those using a seat belt alone or in combination with an airbag had a reduced overall risk of injury (relative risk, 0.42 and 0.71, respectively); no association was observed for those restrained with an airbag only (relative risk, 0.98). This pattern of results was similar for,specific body regions with the exception of the lower extremity, wherein a significantly increased risk was observed for airbag deployment alone. Conclusion: Airbag deployment does not appear to significantly reduce the risk of injury either alone or in combination with seat belts. Airbag deployment without associated seat belt use may increase the risk of lower extremity injury.