The relationship of seat backrest angle and neck injury in low-velocity rear impacts

Abstract

Car-rear-impact-induced cervical spine injuries present a serious burden on society and, in response, seats offering enhanced protection have been introduced. Seats are evaluated for neck protection performance but only at one specific backrest angle, whereas in the real world this varies greatly owing to the variation in occupant physique. Changing the backrest angle modifies the seat geometry and thereby the nature of its interaction with the occupant.Low-velocity rear-impact tests on a BioRID II anthropomorphic test dummy (ATD) have shown that changes in backrest angle have a significant proportionate effect on dummy kinematics. A close correlation was found between changes in backrest angle and the responses of neck injury predictors such as lower neck loading and lower neck shear but not for the neck injury criterion NIC max . Torso ramping was evident, however, with negligible effect in low-velocity impacts.The backrest angle ranged from 20°to 30°whereas the BioRID II spine was adapted to a range from 20°to 26.5°. Nevertheless, in general, instrumentation outputs correlated well, indicating that this ATD could be used for evaluating seats over a 20-30°range rather than solely at 25°as required by current approval test specifications.shown and the hypothesis that there is relationship between backrest angle and neck injury is tested.bolton.ac.uk D22404

Incorporation of Lower Neck Shear Forces to Predict Facet Joint Injury Risk in Low-Speed Automotive Rear Impacts

“…However, a controlled biomechanical investigation of these factors is required to delineate their effects. Although lower neck shear force proved to be sensitive to changes in seatback orientation (Latchford et al 2005) and occupant orientation relative to the seatback (Benson et al 1996;Sundararajan et al 2004) in the present and previous investigations, trends were somewhat contradictory. Present results are supported by Benson et al (1996) in that higher shear forces resulted when occupants were seated more vertically relative to the seat, whereas Latchford et al (2005) reported decreased shear forces for more vertically oriented seatbacks.…”

“…Although lower neck shear force proved to be sensitive to changes in seatback orientation (Latchford et al 2005) and occupant orientation relative to the seatback (Benson et al 1996;Sundararajan et al 2004) in the present and previous investigations, trends were somewhat contradictory. Present results are supported by Benson et al (1996) in that higher shear forces resulted when occupants were seated more vertically relative to the seat, whereas Latchford et al (2005) reported decreased shear forces for more vertically oriented seatbacks. Increased facet joint ligament strains for more vertical seating positions obtained during the computational part of the present study are supported by facet joint stretch magnitudes in PMHS reported by Sundararajan et al (2004) and indicate increased injury risk for more vertical seating positions.…”

“…A possible explanation for differences in shear force trends with regard to occupant orientation lies in the ATD models incorporated during testing. The former study incorporated the Hybrid III ATD (Benson et al 1996) and the latter incorporated the BioRID II (Latchford et al 2005). Differences with regard to ATD models were also identified by Cappon et al (2005), wherein correlations to actual injury data were very high for the RID3D and lower for the BioRID II.…”

“…These two protocols resulted in opposite trends with regard to lower neck shear forces. Benson et al (1996) reported up to a 196 percent increase in lower neck shear forces with occupants pitched forward, whereas Latchford et al (2005) reported decreases in lower neck shear forces and all injury criteria with more vertically oriented seats. Though both studies demonstrated lower neck shear force sensitivity to changes in occupant position during rear impacts, results with regard to the ability of the metric to predict neck injuries were not conclusive.…”

“…The first study employed the Hybrid III anthropomorphic test device (ATD) and stock automobile seats tested with the ATD in normal and pitched forward positions (Benson et al 1996). The second study tested the BioRID ATD in a single stock automobile seat with seatback angles between 20 and 30 degrees from vertical (Latchford et al 2005). These two protocols resulted in opposite trends with regard to lower neck shear forces.…”