Biofidelity of THOR 5th percentile female ATD in ankle eversion and inversion 2020-01-0528
Females have higher frequency and risk of foot and ankle injuries in motor vehicle collisions than similar-sized males. Therefore, lower extremity biofidelity and accurate injury prediction of female ATDs is critical. This paper aims to compare the THOR 5th percentile female (THOR-F05) anthropomorphic test device (ATD) response with male and female PMHS data of various sizes, and further examines the effectiveness of equal-stress equal-velocity scaling of PMHS data for ATD design.
In this study, the THOR-F05 lower extremity was subjected to dynamic inversion and eversion ankle loading with a constant 2000N axial force applied through the tibia. Twelve THOR-F05 tests were performed with boundary conditions consistent with previous post-mortem human subject (PMHS) lower extremity tests. The biofidelity of THOR-F05 ankle stiffness was evaluated via comparison of measured and equal-stress equal-velocity scaled data (using mass-based scale factors) from previous PMHS datasets with mid-size males, small females and larger females.
THOR-F05 ankle moment-angle response falls within previously developed corridors for inversion and eversion, which were created using scaled mid-size male and larger female PMHS data. However, when ankle stiffness was compared to measured small female PMHS response, THOR-F05 response was less stiff. THOR-F05 response was 45% and 50% less stiff in eversion and inversion respectively, when compared to the average of the measured small female PMHS dataset (stiffness calculated as the slope of ankle moment-angle curve).
The THOR-F05 ankle response in inversion and eversion matches scaled response but is not representative of measured ankle stiffnesses of small female PMHS. Because ATD stiffness differs from measured PMHS ankle stiffness, injury risk functions (IRF) developed from PMHS cannot directly be implemented with the THOR-F05. Adjustments to IRF (transfer functions applied to capture stiffness response) are needed prior to use of THOR-F05 ATD for ankle injury prediction.
Shubham Kulkarni, Carolyn Roberts, Patrick Foltz, Jason Forman