Hip Force

Overview

The hip injury metric refers to the force transmitted through the femur into the hip [1]. This metric is crucial in assessing the potential for hip injuries during car crashes, as the hip is one of the primary load-bearing joints in the body [1]. Additionally, if an Injury Assessment Reference Value (IARV) is associated with the ATD used in the selected load test, the calculated peak force will be reported as a percentage of the IARV [2]. The IARV is a threshold value used to assess injury risk during an impact. Each ATD has its own IARV, which varies depending on the type, sex, and size of the dummy [2].

Required Signals

• Force at the Left Femur (Z)
• Force at the Right Femur (Z)

Calculation

1. Convert femur force to newtons (N) (if applicable)
2. Filter femur force signal (CFC = 600)
3. Checks the force values are properly oriented
   • If the magnitude of the minimum force value (compression peak) is smaller than the magnitude of the maximum force value (tension peak), the signal is inverted (multiplied by -1)
4. Calculates the peak force value and the time at which the peak occurs
5. Calculates the percent of the femur force IARV the peak femur force reaches
6. Calculates impulse
   • Finds the start and end points for calculating the impulse by locating where the signal crosses a specified force threshold
   • The signal is truncated to focus on the time period where the force is above the threshold
   • Calculated impulse by integrating the force signal during the truncated period

$$\text{Impulse} = \int_{\text{start}}^{\text{end}} \text{Femur Force}(t) \, dt$$

8. Calculate the percent of the impulse IARV that the calculated impulse value reaches

References

[1] Rupp JD, Schneider LW. Injuries to the hip joint in frontal motor-vehicle crashes: biomechanical and real-world perspectives. Orthop Clin North Am. 2004 Oct;35(4):493-504, vii.

[2] "Frontal Offset Crashworthiness Evaluation". Guidelines for Rating Injury Measures, Insurance Institute for Highway Safety, June 2009.