THOR Injury Criteria

Overview

The Thor Injury Criteria metric was created for the THOR-50M ATD to estimate injury risk based on 11 different injury metrics [1]. Each injury metric is evaluated by comparing the ATD's measured force or deflection values to real-world and experimental data [1]. The Abbreviated Injury Scale (AIS) represents a scale of injury severity ranging from 1 (minor injury) to 6 (unsurvivable injury) [2]. In Thor Injury Criteria, AIS levels of 2 (moderate injury), 3 (serious injury), and 4 (severe injury) are referenced [2].

Required Signals

• Angular Velocity at Head CG ($w_{x}$, $w_{y}$ and $w_{z}$)
• Flexion/Extension Moment of the Upper or Lower Neck (Y)
• Tension/Compression Force of the Upper or Lower Neck (Z)
• Displacement at the Chest (X)
• Acceleration at the Chest (X, Y, and Z)
• Force at the Pelvis Acetabulum (X, Y, and Z)
• A-P Moment at the Tibia (Y)
• L-M Moment at the Tibia (X)
• Axial Force at the Tibia (Z)

Calculation

1. Calculates HIC15 with required signals
2. Calculates the probability of an AIS score of 2 or above with the calculated HIC15 value (Equation 1a)
3. Calculates the probability of an AIS score of 3 or above with the calculated HIC15 value (Equation 1b)

$$p(\text{AIS 2+}) = \Phi (\frac{ln(HIC_{15}) - 6.96362}{0.84687}) \quad (\text{Equation 1a})$$ $$p(\text{AIS 3+}) = \Phi (\frac{ln(HIC_{15}) - 7.45231}{0.73998}) \quad (\text{Equation 1b})$$

4. Calculates BrIC with required signals
5. Calculates the probability of an AIS score of 3 or above with the calculated BrIC value (Equation 2a)
6. Calculates the probability of an AIS score of 4 or above with the calculated BrIC value (Equation 2b)

$$p(\text{AIS 3+}) = 1 - e^{-(\frac{BrIC - 0.523}{0.532})^{1.8}} \quad (\text{Equation 2a})$$ $$p(\text{AIS 4+}) = 1 - e^{-(\frac{BrIC - 0.523}{0.647})^{1.8}} \quad (\text{Equation 2b})$$

7. Calculates Nij with required signals
8. Calculates the probability of an AIS score of 2 or above with the calculated Nij value (Equation 3a)
9. Calculates the probability of an AIS score of 3 or above with the calculated Nij value (Equation 3b)

$$p(\text{AIS 2+}) = (\frac{1}{1 + e^{(5.819 - 5.681*Nij)}}) \quad (\text{Equation 3a})$$ $$p(\text{AIS 3+}) = (\frac{1}{1 + e^{(6.047 - 5.44*Nij)}}) \quad (\text{Equation 3b})$$

10. Calculates the peak resultant chest deflection with required signals
11. Calculates the probability of an AIS score of 3 or above with the calculated peak resultant chest deflection (Equation 4)

$$p(\text{AIS 3+}) = 1 - e^{-(\frac{R_{max}}{58.183})^{2.977}} \quad (\text{Equation 4})$$

Where $R_{max}$ represents the peak resultant chest deflection

12. Calculates the peak abdomen compression with required signals
13. Calculates the probability of an AIS score of 3 or above with the calculated peak abdomen compression (Equation 5)

$$p(\text{AIS 3+}) = 1 - e^{-(\frac{\Delta_{max}}{106.222})^{4.3127}} \quad (\text{Equation 5})$$

Where $\Delta_{max}$ represents the peak abdomen compression

14. Calculates the peak resultant acetabulum force with required signals
15. Calculates the probability of a hip fracture with the calculated peak resultant acetabulum force (Equation 6)

$$p(\text{Hip fracture}) = \Phi (\frac{ \ln(1.429) \cdot (F_{AR}) - 1.6058}{0.2339}) \quad (\text{Equation 6})$$

Where $F_{AR}$ represents the peak resultant acetabulum force

16. Calculates the peak compressive z-axis force measured at the femur with required signals
17. Calculates the probability of an AIS score of 2 or above with the calculated peak femur compressive force (Equation 7)

$$p(\text{AIS 2+}) = \Phi (\frac{\ln(1.299) \cdot (F_{LC}) - 2.62}{0.3014}) \quad (\text{Equation 7})$$

Where $F_{LC}$ represents the peak femur compressive force

18. Calculates the peak compressive z-axis force measured at the upper tibia with required signals
19. Calculates the probability of an AIS score of 2 or above with the calculated peak upper tibia compressive force (Equation 8)

$$p(\text{AIS 2+}) = (\frac{1}{1 + e^{(5.7415 - 0.8189*F_{\text{upper tibia}})}}) \quad (\text{Equation 8})$$

Where $F_{\text{upper tibia}}$ represents the peak upper tibia compressive force

20. Calculates the peak compressive z-axis force measured at the lower tibia with required signals
21. Calculates the probability of an AIS score of 2 or above with the calculated peak lower tibia compressive force (Equation 9)

$$p(\text{AIS 2+}) = (\frac{1}{1 + e^{(3.7544 - 0.4683*F_{\text{lower tibia}})}}) \quad (\text{Equation 9})$$

Where $F_{\text{lower tibia}}$ represents the peak lower tibia compressive force

22. Calculates the peak resultant moment measured at the tibia with required signals
23. Calculates the probability of an AIS score of 2 or above with the calculated peak tibia resultant moment (Equation 10)

$$p(\text{AIS 2+}) = 1 - e^{-e^{-(\frac{ln(M_res) - 5.8704}{0.2947})}} \quad (\text{Equation 10})$$

Where $M_{res}$ represents the peak tibia resultant moment

24. Calculates the revised tibia index with required signals
25. Calculates the probability of an AIS score of 2 or above with the calculated revised tibia index (Equation 11)

$$p(\text{AIS 2+}) = 1 - e^{-e^{-(\frac{ln(RTI) - 0.3376}{0.3213})}} \quad (\text{Equation 11})$$

Where $RTI$ represents the revised tibia index

References

[1] Craig M, Parent D, Lee E, Rudd R, Takhounts E. "Injury Criteria for the THOR 50th Male ATD." Human Injury Research Division, National Highway Traffic Safety Administration.

[2] Rapsang A, Shyam D. "Scoring Systems of Severity in Patients with Multiple Trauma." Cirugía Española, Volume 93, Issue 4, 2015.