(C-120) Parameter Sensitivity of a Finite Element Ovine Rib Model

Introduction:: The use of ovine models to study injury biomechanics is increasing due to their favorable size and physiological characteristics [1]. However, the physiological characteristics become less favorable when previous models of the ovine thorax ignore the effects of specific anatomies, such as trabecular bone within the ribs. This is particularly a hindrance when studying high-rate non-penetrating blunt impact (high rate NPBI). The Gibbons et al., model utilizes an ovine thorax model to study similar injuries [2]. This model represents ribs as shell elements with only cortical bone representation from quasi-static tests, leaving a gap in trabecular bone material properties and its interaction with cortical bone. To fill this gap, the objective of this study is to deepen the knowledge of trabecular bone behavior under quasi-static forces.

Materials and Methods:: A finite element (FE) model of a three-point bend test was constructed to match the experimental procedure outlined in Thomas et al. [3]. This included a three-point bend setup with a span length of 8 cm. The leftmost support was placed at ¼ distance of the length of the rib to match experiments. Rib 6 was taken from the ovine thorax model developed by Caffrey [4]. Material properties for cortical bone were derived from Thomas et al. and trabecular bone properties were derived from Gibbons et al. [2-3]. LS-Dyna was utilized for running a parameter sensitivity study. This was a set of three-point bend tests that doubled and halved values for various rib bone properties to determine what would have a significant effect on the rib behavior. Table 1 shows the simulations that tested these values. Simulation 1 represents the values currently in the ovine model by Caffrey [4]. Each subsequent simulation was compared with this control data to determine the percent difference and thus significance of the changes in each variable.

Results, Conclusions, and Discussions:: The force vs. displacement data is shown in Figure 2. Force data was filtered using the 180 Hz SAE filter in LS-Dyna. The trabecular bone elastic modulus does not have a significant effect on stiffness (Figure 2) but does determine peak force and number of peaks post-failure. Stiffness and peak forces can be numerically seen in Table 1. The percent differences shown in Table 1 from the control simulation shows that there is a significant change in both peak force and changes in post-yield behavior when studying trabecular bone elastic modulus.

The changes in value of peak force based on trabecular bone elastic modulus (Simulation 2 and 3) are significant enough to justify further study to optimize the trabecular bone material properties, particularly the failure characteristics. Future work will involve taking the trabecular bone elastic modulus and optimizing that value against experimental results found in Thomas et al. for the three-point bending conditions. These results also call for future work to optimize cortical bone thickness over the surface of the bone.



Acknowledgements (Optional): :

US Army Research Lab, Grant W911NF2120034.
This project was supported in part by the NSF REU Site (Award #1950281) in the Department of Biomedical Engineering at Wake Forest University School of Medicine

References (Optional): :

[1] Foley, S. R., Thrombosis Research, (2014). 134(2), 468-473.
[2] Gibbons M. J. Biomech. Eng. (2015) 137:1-9.
[3] Thomas, P. K., Biomed Eng. (2023) 51:1513-1522
[4] Caffrey, J. M., (2022). Master’s thesis. Wake Forest University.