Development and Validation of a Biofidelic Pediatric ATD Lower Extremity

Principal Investigator: Amanda Agnew, PhD, The Ohio State University

Below is an executive summary of this project. Please note that this summary describes results and interpretation that may not be final. Final interpretation of results will be in the peer-reviewed literature.

As vehicle safety continues to improve, life-threatening injuries from motor vehicle crashes are declining. This progress increases the need for injury research to expand beyond the brain and other vital organs to include injuries that can lead to long-term disabilities such as those to the lower extremity. Limited research has been conducted into the biomechanics of pediatric lower extremity injury. Recent testing conducted by The Ohio State University (OSU) of child interactions with knee-bolster air bags raised questions regarding the extent to which the lower extremities of pediatric anthropomorphic test devices (ATDs) are “human-like” (i.e., biofidelic). This identified a specific need for a tibia load cell to accurately measure forces and an ATD ankle with accurate range of motion and stiffness.

The current version of the Hybrid III 6-year-old ATD has a simple clevis joint at the ankle, which severely compromises the accuracy of the joint’s response and may create unrealistic responses at other points in the limb. Using previously collected child volunteer data from OSU’s lab, a new 6-year-old ATD lower extremity (ATD-LE) was designed, which included a tibia load cell and a more biofidelic ankle joint with range of motion stops and stiffness bumpers.

The aim of this study was to validate the new ATD-LE, and the process included two phases: a biofidelity assessment and knee bolster air bag tests. The biofidelity assessment compared leg and foot anthropometry (measurements of the human body), ankle range of motion, and ankle stiffness between the ATD-LE and previously collected volunteer data.

The second phase of validation evaluated the response of the ATD-LE by recreating the knee-bolster air bag tests previously conducted by OSU researchers in 2011. Four configurations were used for the knee-bolster air bag tests:


Results demonstrated that the anthropometry of the new ATD-LE was representative of the 6-year-old child. However, range of motion measurements revealed differences between the ATD-LE and volunteers. The knee bolster air bag tests demonstrated that the ATD-LE functioned well in all scenarios and indicated that the condition most likely to be injurious was the third configuration, which caused the air bag to hit the bottom of the foot, resulting in both axial loading and forced dorsiflexion of the ankle. When evaluated separately, peak tibia forces and moments did not exceed injury threshold, but when evaluated together (tibia index), the relative risk of producing a fracture was above the injury threshold.

The results of this study demonstrated that ankle biofidelity in the 6-year-old ATD is improving but still requires some modification to more closely represent the 6-year-old ankle. Improving the accuracy of ankle range of motion will help to ensure proper force transmission through the ankle. A properly instrumented pediatric ATD will not only allow for advances in automotive safety and the manufacturing of safer child restraint systems, but also give researchers the opportunity to directly measure the effects of optimal and suboptimal positioning of the child with a more accurate picture of the forces experienced by the lower extremity.

Project Team Member

Yun Seok Kang, PhD, The Ohio State University


Laura Boucher, PhD, The Ohio State University

IAB Mentors

Doug Longhitano, American Honda Motor Co., Inc.; Rodney Rudd, National Highway Traffic Safety Administration