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Biomechanics

Biomechanics - Poster Session C

Poster E1 - Human Body Model Lumbar Metrics in Stock Car Motorsports Crashes with Predominantly Frontal Components

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

Introduction:  In recent decades, safety in motorsport has been revolutionized. Some impactful changes include widespread use of head and neck restraints (HNR) [1], addition of the Halo in the Formula series of the Fรฉdรฉration Internationale de l'Automobile (FIA) [2], and inclusion of steel and foam energy reduction (SAFER) barriers in the National Association for Stock Car Auto Racing (NASCAR) [3]. As a result, severe injuries and mortality rates in motorsport are falling; however, spinal loads contributing to injuries remain a challenge particularly in frontal impacts [4, 5]. This is of concern to the racing industry as spinal injuries may have negative consequences requiring rehabilitation [6]. Recent literature investigating motor vehicle crashes (MVC) has integrated the use of finite element analysis of simplified vehicle models (SVM) to understand how frontal impacts influence spinal injuries [7]; however, most of this research is dedicated to commercial MVC. The objective of this study was to evaluate lumbar spine loads and estimated injury risk relative to chassis accelerations with predominantly frontal components.

Materials and

Methods:  Accelerations from crash events that occurred during the 2023 racing season were collected from the NASCAR incident data recorder (IDR) rigidly mounted to the driver side of the vehicle chassis and filtered with a CFC60 filter following SAE J211 standards. Crash events were selected according to whether the resultant peak linear acceleration (PLA) was greater than 10g and contained a predominantly anterior-posterior (A-P) component (lateral and vertical peak accelerations less than 50% of the frontal component). The selected crash events were applied to a NASCAR stock car virtual vehicle environment (including a helmet, head and neck restraint, seat, foam insert, head surround, and 7-point restraint). Seated in this model was the Global Human Body Models Consortium (GHBMC) 50th percentile male simplified seated occupant model, with a detailed head, neck, and spine integrated within the model. All simulations were conducted in LS-Dyna (ver. 12.1.0). Lumbar spine compression (kN) and flexion moment (N-m) across accelerations from frontal impacts were used to calculate injury risk metrics ๐ฟ๐‘“๐‘ฅ (a parameter which combines compression force, flexion moment, the cross-sectional area (CSA) of the middle vertebral body, and an optimized tuning factor (ฮฑ = 0.4), as represented in equation 1) and von Mises stress which were used to estimate an abbreviated injury scale (AIS) 3+ risk [8,9].

Results, Conclusions, and Discussions: Nine impacts (-10.03 g < PLA (A-P) < -26.27 g) from the 2023 season were categorized as predominantly frontal impacts. The largest compression experienced by a single vertebra in the lumbar spine was 2.43 kN (L3) and the largest flexion moment was 48.70 N-m (L1). These metrics were then used to calculate ๐ฟ๐‘“๐‘ฅ (1.62 MPa, L1) and von Mises stress (92.49 MPa, L3) as well as their respective AIS 3+ injury risk (11.40%, L1 and 27.80%, L3). As expected, an increase in acceleration of the chassis resulted in a greater compression force (Figure 1). Across the levels of vertebrae, there was little difference between compression forces, which produced an average coefficient of variation (COV) of 1.24%. On the other hand, there was more variability among flexion moments (Figure 2). For frontal impacts, the L1 vertebra experienced the greatest flexion moment, averaging 17.59 N-m across all 9 impacts; whereas the L5 vertebra experienced the smallest flexion moment, only averaging 2.86 N-m. ๐ฟ๐‘“๐‘ฅ value and its corresponding risk was greatest for the L1 vertebrae across the nine impacts, resulting in an average a risk percentage for an AIS 3+ injury of 1.72%; however the von Mises stress was greatest in the L3 vertebra, averaging a risk percentage of 9.01%. Additionally, flexion moment loads were evenly distributed throughout the lumbar spine for impacts that had a less dominant anterior to posterior components. None of the crashes examined in this study resulted in any spinal fractures.

This study provides context to some of the risks predicted by a human body model due to these pulses. While the metrics are a useful tool for design and may provide some directional guidance for the improvement of countermeasures from seating, to restraints, to vehicle, to environment, the risks seem overestimated for these crashes for which no injuries occurred and should be interpreted with caution.

Acknowledgements (Optional):  This project was supported in part by the Wake Forest Summer Research Internship Program in the Department of Biomedical Engineering at Wake Forest University School of Medicine as well as the National Association for Stock Car Auto Racing (NASCAR).