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Biomechanics

Biomechanics - Poster Session C

Poster D10 - Human Body Model Lumbar Loading Metrics in Stock Car Motorsport Crash Loading Conditions

Friday, October 25, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Motor vehicle crashes (MVCs) are common contributors to thoracolumbar injury, and the incidence of MVC-related thoracolumbar injuries has been increasing [1-3]. However, the biomechanics of lumbar spine fracture during MVCs has not been well characterized [4]. Finite element human body models (HBMs) have emerged as an alternative to anthropomorphic test devices and postmortem human subjects for investigating the biomechanics of MVCs at a higher level of detail [5,6]. Recently, Tushak et al. developed two HBM-specific lumbar spine fracture risk functions using the Global Human Body Models Consortium (GHBMC) 50th percentile male occupant model (M50-O). One injury risk metric (Lfx) was developed based on the structural response during pure compression/flexion loading, while the other (95th percentile von Mises stress; VM95) is material-based and less likely to be tied to a specific loading condition [7]. The variation in risk between these two metrics in real-world scenarios is unknown. Stock car motorsports represent a unique real-world environment where drivers experience MVCs with high velocities and omnidirectional loading with potential for lumbar spine injury [8]. The objective of this study was to investigate differences between structural based (Lfx) and material-based (VM95) lumbar spine fracture risk metrics across frontal, side, and vertical collisions in a motorsport environment in a limited sample from the 2023 racing season.

Materials and

Methods:  A modular HBM (simplified HBM with detailed head, neck, and spine) [9] was positioned in a stock car environment via a morphing procedure. Homologous landmarks were developed between a previously positioned GHBMC M50-OS model and the modular model, and a thin plate spline radial basis function morphing algorithm was applied. The stock car environment included a helmet, head and neck restraint, seat, foam insert, head surround, and 7-point restraint. In each simulation, the modular model was gravity settled into the seat for 40 ms while belt tightening was applied (approximately 91 N and 110 N for shoulder and lap belts, respectively).

Vehicle kinematics were obtained from a stock car racing series. Vehicles were instrumented with incident data recorders (IDRs) mounted to the left frame rail. IDRs recorded approximately 10 seconds of linear acceleration for each crash. Vehicle acceleration pulses (approximately 250 ms in duration) were extracted and filtered at CFC60. Crashes were categorized into frontal, side, and vertical loading groups based on the component axis experiencing the greatest acceleration magnitude. Nine crashes (3 from each group) were selected from the top third of acceleration magnitudes within each loading group and simulated with the modular HBM in LS-Dyna R.12.1.0. Flexion/extension moments, compression/tension forces, and fracture risks were extracted for each lumbar level (L1-L5). Kinetics and injury risks were compared across loading conditions.

Results, Conclusions, and Discussions: The average peak resultant linear acceleration of crash pulses was 21 g with a range of 5 g to 44 g (vertical: 5-18 g, frontal: 16-44 g, side: 23-36 g). Average flexion (extension) across lumbar levels was 12.4 (-0.4) N*m, 49.6 (-0.3) N*m, and 6.8 (-0.9) N*m for vertical, frontal, and side loading scenarios, respectively. Average compression (tension) across lumbar levels was -0.848 (0.058) kN, -2.484 (0.067) kN, and -0.499 (0.103) kN for vertical, frontal, and side loading scenarios, respectively. No crashes resulted in injuries.

Average lumbar AIS 3+ fracture risks based on Lfx and VM95 are reported in Table 1. Fracture risks were low for vertical (max risk 1.9%) and side (max risk 5.1%) loading cases across lumbar levels, but VM95-based risk tended to be greater compared to Lfx-based risk (0.6 and 1.4 percentage points [pp] greater, on average, in vertical and side cases). Similar trends were observed for two frontal crashes (max risk 6.1% and VM95 2.2 pp greater, on average). One frontal scenario (peak acceleration 44 g, average flexion 94.8 N*m, average compression 4.2 kN) produced a maximum Lfx risk of 63.3% and VM95 risk of 76.5%, with greater Lfx-based risk observed at L1 (+51.3 pp), L2 (+26.1 pp), L4 (+7.5 pp), and L5 (+16.8 pp) and greater VM95 risk at L3 (+43.3 pp).

This study utilized a modular HBM to compare lumbar spine fracture risk metrics in stock car motorsport crashes. Across loading conditions, the lumbar spine experienced compression/flexion and minimal tension/extension. In most cases, fracture risk was low, and VM95 tended to estimate slightly greater risk compared to Lfx. Increased VM95 risk may be explained by stress-based response experienced in non-compression/flexion loading, to which Lfx is not sensitive [7]. In one case of high flexion/compression frontal loading, Lfx predicted higher risk than VM95 in 4 of 5 lumbar regions. High predicted risk without observed injury may indicate overestimation of risk. This could be related to factors such as crash pulse quality, restraint systems, driver age, or simplifying modeling assumptions. The metrics are potentially a useful tool for investigating design change effects on occupant safety.

Acknowledgements (Optional):  This project was supported in part by the Rowan University/Kern Family Foundations (Prime Award No. 2022-02044; Subaward No. 57283-1) eREU KEEN grant in the Department of Biomedical Engineering at Wake Forest University School of Medicine

Biomechanics of Injury/Rehabilitation Sub-track