Investigation of the Safety Effects of Knee Bolster Air Bag Deployment in Similar Real-World Crash Comparisons

Abstract

Objective: The lower extremity is the most frequently injured body region and knee–thigh–hip (KTH) injuries account for half of these injuries. Knee bolster air bags (KBABs) have been incorporated in some vehicles to serve as an additional restraint for the occupant's knees and reduce KTH injuries. To investigate the safety benefits of KBABs, similar frontal crashes with opposing KBAB deployment were selected from the Crash Injury Research and Engineering Network (CIREN) database.

Methods: An 8-point similarity scoring algorithm was used to quantify crash and occupant similarity and select case comparisons. A total of 183 cases without a KBAB were scored for similarity to 9 KBAB cases. These similarity scores were used to select 31 final case comparisons. The effect of KBAB deployment on occupant injury patterns was investigated with a particular focus on KTH injuries.

Results: Over half of the occupants exposed to a KBAB sustained no KTH injuries and a reduction in femur fractures was observed in KBAB occupants (P = .036). However, increases in proximal tibia/fibula and foot/ankle fractures were observed in KBAB occupants (P = .022 and .002, respectively). Mildly significant decreases in pelvic fractures and Abbreviated Injury Scale (AIS) 2+ head injuries were observed in the KBAB occupants, supporting the notion that KBABs reduce forward occupant excursion (P = .094 and .055, respectively). Investigation of each case comparison yielded further insight into the reasons for injury pattern differences between cases with opposing KBAB deployment. In addition to KBAB deployment status, differences in occupant factors (age, height, and weight) and crash factors (delta V and belt use) between the cases for a particular comparison could explain variation in injury patterns.

Conclusions: The current study presents a preliminary in-depth qualitative and quantitative assessment of KBAB safety benefits. However, further investigation is recommended to provide conclusive evidence of KBAB effectiveness.

Keywords:

• comparison
• fracture
• knee–thigh–hip
• knee bolster
• motor vehicle crash
• similarity

Acknowledgments

The authors acknowledge Mao Yu and the Toyota–Wake Forest University School of Medicine CIREN team for their assistance with the data collection. Philip Brown assisted with figure creation. Work was performed for the Crash Injury Research and Engineering Network (CIREN) Project at Wake Forest University School of Medicine in cooperation with the United States Department of Transportation/National Highway Traffic Safety Administration (USDOT/NHTSA). Funding has been provided by Toyota Motor North America Inc. under Cooperative Agreement Number DTNH22-05-H-61001 and the NHTSA under Cooperative Agreement Number DTNH22–10-H-00294. Views expressed are those of the authors and do not represent the views of any of the sponsors or the NHTSA.