Previous research has detailed contributing factors to thoracolumbar compression fracture injury risk during frontal impacts in motorsport drivers utilizing a nearly recumbent driving position (Katsuhara, Takahira, Hayashi, Kitagawa, & Yasuki, 2017; Trammell, Weaver, & Bock, 2006; Troxel, Melvin, Begeman, & Grimm, 2006). This type of injury is very rare for upright seated motorsport drivers. While numerous improvements have been made to the driver restraint system used in the National Association for Stock Car Auto Racing, Incorporated (NASCAR®) since 2000, two instances of lumbar compression fractures have occurred during frontal impacts. Through the use of computation modeling, this study explores the influence of initial driver position and seat ramp design on thoracolumbar loading during frontal impacts.
Quasi-static component testing, dynamic component testing, an instrumented driver fit check, a seat ramp angle survey, and sled testing were conducted to provide computational finite element (FE) model inputs and serve as validation tests. Upright magnetic resonance imaging (MRI) was conducted with a driver to visualize vertebral body locations with respect to the driver seat. FE modeling was conducted with the 50th percentile male Hybrid III FE model (Humanetics, Plymouth, MI) to validate a motorsport restraint system model. Sprague and Geers analysis was used to quantify and identify the optimally tuned FE model parameters. A 3-factor latin hypercube (LHD) sample space was created for acceleration magnitude and the principal direction of force (PDOF) about the Z-axis and about the Y-axis across 20 simulations. The Toyota Total Human Model for Safety (THUMS) was then used in four unique seat ramp angles in both slouched and upright postures, for a total of eight THUMS seated configurations. All eight configurations were subjected to the 20 variable values of the LHD sample space for a total of 160 simulations.
A FE motorsport restraint system model was developed and validated against empirical component and sled test data. The THUMS was used in the validated motorsport restraint system. As seat ramp angles (SRA) increased, peak axial compressive force of T12, L1 and L2 decreased. For each SRA, the slouched THUMS initial position (TIP), which positioned the ischial tuberosities closer to the seat ramp, produced lower peak axial compressive forces. The peak XY resultant bending moment of T12 and L1 also decreased as SRA increased.