Validation of a parametric finite element human femur model

ABSTRACT

Objective: Finite element (FE) models with geometry and material properties that are parametric with subject descriptors, such as age and body shape/size, are being developed to incorporate population variability into crash simulations. However, the validation methods currently being used with these parametric models do not assess whether model predictions are reasonable in the space over which the model is intended to be used. This study presents a parametric model of the femur and applies a unique validation paradigm to this parametric femur model that characterizes whether model predictions reproduce experimentally observed trends.

Methods: FE models of male and female femurs with geometries that are parametric with age, femur length, and body mass index (BMI) were developed based on existing statistical models that predict femur geometry. These parametric FE femur models were validated by comparing responses from combined loading tests of femoral shafts to simulation results from FE models of the corresponding femoral shafts whose geometry was predicted using the associated age, femur length, and BMI. The effects of subject variables on model responses were also compared with trends in the experimental data set by fitting similarly parameterized statistical models to both the results of the experimental data and the corresponding FE model results and then comparing fitted model coefficients for the experimental and predicted data sets.

Results: The average error in impact force at experimental failure for the parametric models was 5%. The coefficients of a statistical model fit to simulation data were within one standard error of the coefficients of a similarly parameterized model of the experimental data except for the age parameter, likely because material properties used in simulations were not varied with specimen age. In simulations to explore the effects of femur length, BMI, and age on impact response, only BMI significantly affected response for both men and women, with increasing BMI producing higher impact forces.

Conclusions: Impactor forces from simulations, on average, matched experimental values at the time of failure. In addition, the simulations were able to match the trends in the experimental data set.

KEYWORDS:

• Lower extremity injury
• motor vehicle crashes
• Total Human Model for Safety (THUMS)

Acknowledgments

The authors thank Prabha Narayanaswamy for her support with the statistical analyses, the University of Virginia Center for Applied Biomechanics and Dr. Johan Ivarsson for providing information about their study and the CT scan data, and University of Michigan students Kyle Apsey, Kyle Boyle, Christian Calyore, Alex Copenhaver, Lauren Cromer, Stacie DeSousa, Paige Hammerl, Brandon Harrison, Tim Huebner, Kyle Liepelt, Andrew Nikolai, Sadiq Omar, Samuel Steinberg, Trevor Sultana, Brian Tew, Simon Tong, and Katherine Uvick, who extracted femur geometry.

Funding

This project was funded by the National Highway Traffic Safety Administration under contract number DTNH22-10-H-00288 and the National Science Foundation under award number 1300815.