Lumbar vertebrae fracture injury risk in finite element reconstruction of CIREN and NASS frontal motor vehicle crashes

ABSTRACT

Introduction: The objective of this study was to reconstruct 4 real-world motor vehicle crashes (MVCs), 2 with lumbar vertebral fractures and 2 without vertebral fractures in order to elucidate the MVC and/or restraint variables that increase this injury risk.

Methods: A finite element (FE) simplified vehicle model (SVM) was used in conjunction with a previously developed semi-automated tuning method to arrive at 4 SVMs that were tuned to mimic frontal crash responses of a 2006 Chevrolet Cobalt, 2012 Ford Escape, 2007 Hummer H3, and 2002 Chevrolet Cavalier. Real-world crashes in the first 2 vehicles resulted in lumbar vertebrae fractures, whereas the latter 2 did not. Once each SVM was tuned to its corresponding vehicle, the Total HUman Model for Safety (THUMS) v4.01 was positioned in 120 precrash configurations in each SVM by varying 5 parameters using a Latin hypercube design (LHD) of experiments: seat track position, seatback angle, steering column angle, steering column telescoping position, and d-ring height. For each case, the event data recorder (EDR) crash pulse was used to apply kinematic boundary conditions to the model. By analyzing cross-sectional vertebral loads, vertebral bending moments, and maximum principal strain and stress in both cortical and trabecular bone, injury metric response as a function of posture and restraint parameters was computed.

Results: Tuning the SVM to specific vehicle models produced close matches between the simulated and experimental crash test responses for head, T6, and pelvis resultant acceleration; left and right femur loads; and shoulder and lap belt loads. Though vertebral load in the THUMS simulations was highly similar between injury cases and noninjury cases, the amount of bending moment was much higher for the injury cases. Seatback angle had a large effect on the maximum compressive load and bending moment in the lumbar spine, indicating the upward tilt of the seat pan in conjunction with precrash positioning may increase the likelihood of suffering lumbar injury even in frontal, planar MVCs.

Conclusion: In conclusion, precrash positioning has a large effect on lumbar injury metrics. The lack of lumbar injury criteria in regulatory crash tests may have led to inadvertent design of seat pans that work to apply axial force to the spinal column during frontal crashes.

KEYWORDS:

• Lumbar
• vertebra
• finite element
• injury
• THUMS

Acknowledgments

The authors thank Johan Iraeus and Mats Lindkvist for providing the SVM geometry used in the case reconstructions. Computations were performed on the Wake Forest University DEAC Cluster, a centrally managed resource with support provided in part by the university, and the Blacklight system at the Pittsburgh Supercomputing Center (PSC). The authors acknowledge Bharath Koya, Xin Ye, and Jeff Suhey for supporting data processing and Logan Miller and Nick White for the implementation of injury metrics in THUMS. The authors acknowledge Ryan Barnard for his programming contributions.

Funding

Funding for this project was provided by Toyota's Collaborative Safety Research Center. We gratefully acknowledge the National Highway Traffic Safety Administration's support of the CIREN program and WFU-VT CIREN Center (Cooperative Agreement DTN22-10-H-00294). Views expressed are those of the authors and do not represent the views of any sponsors.