Thorax

This section of the documentation is under development

This section is being updated

Thoracic Components Identifier Overview

Component Group	Identifier Range (Start)
Thoracic Vetebra and Ligaments	401000
Thoracic Intervertebral Discs/Joints	402000
Ribcage	403000
Thoracic Internal Organs	405000

Bones

Ribcage

The ribcage is modelled based on the generic rib model by Iraeus et al.¹ that has been validated for kinematics, kinetics and strain in Iraeus et al.² and validated with regards to injury risk in Pipkorn et al.³. The original model represented an average male. It has been updated to represent an average female using a similar workflow as for the original generic ribcage, which can be seen in teh figure below. Rib cross section geometry and cortical bone thickness (steps 1 through 3) were based on a male dataset presented in ⁴. As it has been shown that cortical thickness is not significantly different between sexes⁵, the thickness was not updated for the average female model. The next step (4) was to create the curved ribs representative of the average female using a statistical shape model for the ribcage⁶. The average shaped female sternum, modelled in step 5, was based on another statistical shape model⁷. Intercostal muscles were modelled with a thickness according to the same regression model as was used for the male ribcage². Finally, the costal cartilage geometry was based on a geometry of a 50th percentile female, the same as was used for other body parts where statistical shape models were not available.

For the cortical bone the LS-DYNA material model *MAT_PIECEWISE_LINEAR_PLASTICITY was used with the same material parameters as used for the male ribcage¹. Young's modulus was set to 14.7GPa, the yield stress 100.7MPa, and a hardening modulus of 1.94GPa. The trabecular bone was modelled using the same material model, but with material parameters, Young's modulus 0.04GPa, a yield stress of 1.8MPa and hardening modulus of 0.032GPa. All solid elements were modelled using LS-DYNA element formulation 1, with hourglass type 2 (default hourglass parameters). The shells were modelled using LS-DYNA shell element formulation 16, with hourglass type 8. The material model for the intercostal muscles was LS-DYNA material model *MAT_SIMPLIFIED_RUBBER, with material parameters tuned to material data measured on intercostal muscles⁸. The material model for the costal cartilage was LS-DYNA material model *MAT_PIECEWISE_LINEAR_PLASTICITY with material parameters, Young's modulus 0.049GPa, yiled stress 0.00485 GPa with a non-linear hardening.

Thoracic Spine

Model Components

Thoracic Spine Identifier Numbering

PID	Component
401XX1	TX-Spine-TXX-Cortical-M
401XX2	TX-Spine-TXX-Trabecular-M
- - - XX -	Represents the Thoracic Spine Level, ranges from 01 to 12, M indicates mid-sagittal (common identifier for left and right halves)

Vertebrae

The thoracic vertebrae are modelled similar to the original VIVA model⁹, and are defined as rigid elements. The elements of the cortical and trabecular bone are constrained together with *CONSTRAINED_RIGID_BODY.

Intervertebral Joints

The intervertebral joints in the thoracic spine are modeled as zero-length discrete beam elements (*MAT_GENERAL_NONLINEAR_6DOF_DISCRETE_BEAM), with stiffness properties from an in-vitro study¹⁰.

Soft tissues

Skin

The skin was modelled as 1mm thick membranes using LS-DYNA material model *MAT_FABRIC, with non-linear material properties based on ¹¹. The "along langer lines" (the stiffer skin direction) definitions was used in both skin directions.

Muscles and adipose tissue

The outer soft tissue in the thorax (PIDs 406002 and 456002), pelvis (PIDs 606002 and 656002), upper arms (PIDs 305122 and 355122) and upper legs (PIDs 705112 and 755112) is modelled using the adipose tissue model from Naseri et al. ¹², ¹³. The model, which represents the average range of compressive stiffness from experiments, is implemented as *MAT_OGDEN_RUBBER with material parameters given by RO = 9.0e-7, PR = 0.49998, MU1 = 3.5E-8, ALPHA1 = 20.0, G1 = 1.3E-6, BETA1 = 3.0E-4, G2 = 1.8E-6, BETA2 = 0.05, G3 = 2.2E-6, BETA3 = 0.6. The solid elements are modelled using LS-DYNA element formulation 1 with hourglass type 5 (Hourglas stiffness 0.1)

Thoracic Cavity

The lungs are modeled using *MAT_LOW_DENSITY_FOAM with material parameters from Rater¹⁴. Solid elements with LS-DYNA element formulation 1 was used together with hourglass formulation 5 (with default hourglass parameters)

Contacts in the Thorax

The main contact for the thorax and pelvis interior is a *CONTACT_AUTOMATIC_SINGLE_SURFACE (CID 400001) with parameter SOFT=2. The interaction between the thoracic cavity soft tissue and the rib cage is also handled by this contact.

To connect the outer soft tissue in the thorax to the ribcage and abdomen, a *CONTACT_AUTOMATIC_SURFACE_TO_SURFACE_TIEBREAK with OPTION=4 is used (CID 403710). This contact takes load in tension and compression, but allows tangential sliding in order to mimic the vacuum in the body that prevents the internal organs from separating.

A *CONTACT_TIED_NODES_TO_SURFACE (CID 403505) between the thorax outer soft tissue and the sternum is used to model the muscle attachment to the sternum.

References

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1. Johan Iraeus, Karin Brolin, and Bengt Pipkorn. Generic finite element models of human ribs, developed and validated for stiffness and strain prediction – to be used in rib fracture risk evaluation for the human population in vehicle crashes. Journal of the Mechanical Behavior of Biomedical Materials, 106:103742, jun 2020. doi:10.1016/j.jmbbm.2020.103742. ↩↩

2. Johan Iraeus and Bengt Pipkorn. Development and validation of a generic finite element ribcage to be used for strain-based fracture prediction. In International Research Council on the Biomechanics of Injury $IRCOBI$. 2019. ↩↩

3. Bengt Pipkorn, Johan Iraeus, Magnus Björklund, Olle Bunketorp, and Lotta Jakobsson. Multi-scale validation of a rib fracture prediction method for human body models. In IRCOBI Conference Proceedings, 175–192. 2019. ↩

4. Choi Hyung and Kwak Dai-Soon. Morphologic characteristics of korean elderly rib. Journal of Automotive Safety and Energy, 2$2$:122, 2011. ↩

5. Amanda M. Agnew, Michelle M. Murach, Victoria M. Dominguez, Akshara Sreedhar, Elina Misicka, Angela Harden, John H. Bolte, Jason Stammen, and Kevin Moorhouse. Sources of variability in structural bending response of pediatric and adult human ribs in dynamic frontal impacts. In SAE Technical Paper Series. SAE International, nov 2018. doi:10.4271/2018-22-0004. ↩

6. Xiangnan Shi, Libo Cao, Matthew P. Reed, Jonathan D. Rupp, Carrie N. Hoff, and Jingwen Hu. A statistical human rib cage geometry model accounting for variations by age, sex, stature and body mass index. Journal of Biomechanics, 47$10$:2277–2285, jul 2014. doi:10.1016/j.jbiomech.2014.04.045. ↩

7. Ashley A. Weaver, Samantha L. Schoell, Callistus M. Nguyen, Sarah K. Lynch, and Joel D. Stitzel. Morphometric analysis of variation in the sternum with sex and age. Journal of Morphology, 275$11$:1284–1299, jun 2014. doi:10.1002/jmor.20302. ↩

8. David Poulard and Damien Subit. Unveiling the structural response of the ribcage: contribution of the intercostal muscles to the thoracic mechanical response. In 24th International Technical Conference on the Enhanced Safety of Vehicles $ESV$ National Highway Traffic Safety Administration, number 15-0387. 2015. ↩

9. Jonas Östh, Manuel Mendoza-Vazquez, Fusako Sato, Mats Y. Svensson, Astrid Linder, and Karin Brolin. A female head–neck model for rear impact simulations. Journal of Biomechanics, 51:49–56, jan 2017. doi:10.1016/j.jbiomech.2016.11.066. ↩

10. Manohar M Panjabi, RA Brand Jr, and AA White 3rd. Mechanical properties of the human thoracic spine as shown by three-dimensional load-displacement curves. The Journal of bone and joint surgery. American volume, 58$5$:642–652, 1976. ↩

11. J.F.M. Manschot and A.J.M. Brakkee. The measurement and modelling of the mechanical properties of human skin in vivo—II. the model. Journal of Biomechanics, 19$7$:517–521, jan 1986. doi:10.1016/0021-9290$86$90125-9. ↩

12. OSCCAR. Populations of validated and robust passive hbms. Technical Report, OSCCAR, 2021. ↩

13. Hosein Naseri, Håkan Johansson, and Karin Brolin. A nonlinear viscoelastic model for adipose tissue representing tissue response at a wide range of strain rates and high strain levels. Journal of Biomechanical Engineering, feb 2018. doi:10.1115/1.4038200. ↩

14. Jan-Frederik Rater. Thorax soft tissue response for validation of human body models and injury prediction. Master's thesis, Chalmers University of Technology / Department of Applied Mechanics, 2013. ↩

15. F. Scott Gayzik, J. Jason Hoth, and Joel D. Stitzel. Finite element–based injury metrics for pulmonary contusion via concurrent model optimization. Biomechanics and Modeling in Mechanobiology, 10$4$:505–520, aug 2010. doi:10.1007/s10237-010-0251-5. ↩

16. D. L. Vawter. A finite element model for macroscopic deformation of the lung. Journal of Biomechanical Engineering, 102$1$:1–7, feb 1980. doi:10.1115/1.3138193. ↩

17. Samuel R. Polio, Aritra Nath Kundu, Carey E. Dougan, Nathan P. Birch, D. Ezra Aurian-Blajeni, Jessica D. Schiffman, Alfred J. Crosby, and Shelly R. Peyton. Cross-platform mechanical characterization of lung tissue. PLOS ONE, 13$10$:e0204765, oct 2018. doi:10.1371/journal.pone.0204765. ↩