The effect of reclined seats on mortality in motor vehicle collisions.

Background: Motor vehicle collisions are the leading cause of trauma-related death in the United States. Reclined seatbacks may alter crash kinetics and affect occupant outcome. We examined the effect of reclined seatbacks on occupant mortality.
Methods: Our study population consisted of United States traffic crashes from 1995 to 2005, using data from the Crash Injury Research and Engineering Network and the National Automotive Sampling System Crashworthiness Data System. Phase 1, we performed a detailed review of crash kinetics and biomechanical factors resulting in injury patterns in fully reclined occupants. Phase 2, we performed a population-based retrospective cohort study comparing outcome in upright, partial, and full recline positions. Primary outcome measure was 30-day mortality.
Results: Phase 1, flexion and compression injuries over pretensioned lap and shoulder belts resulted in severe thoracoabdominal and spine injuries in restrained occupants, with a high associated mortality. Increased lower extremity injuries from additional force loads into bolsters and panels were also noted. Phase 2, the majority (>50%) of front-seat occupants was partially reclined. Fully reclined occupants were younger (30 vs. 39 years, p < 0.0001), more likely to be male (70% vs. 49%, p < 0.0001) and less likely to wear a seat belt (58% vs. 78%, p < 0.0001) than upright or partially reclined occupants. Mortality was increased in both partially (adjusted odds ratio 1.15, 95% confidence interval 1.05-1.26) and fully reclined occupants (adjusted odds ratio 1.77, 95% confidence interval 1.09-2.88).
Conclusion: The reclined position is associated with increased occupant mortality in motor vehicle collisions.