Documentation:FIB book/problems/Thoracic Injury

Imagine a side-impact crash test to a 4-door passenger car. For this test, two Hybrid III 50^th percentile male ATDs were buckled into the front and rear seats of the impacted side (see Figure 1).

Figure 1. Side impact to a 4-door passenger car with two ATDs on impacted side.

Question 1

What injury criteria specific to thoracic injury could be used to assess this side impact scenario? Explain your reasoning, keeping in mind the type of dummy utilized in this test.

[show]SOLUTION (expand to show)

At a minimum, your answer should include the bolded content (the wording may vary): One cannot evaluate any thoracic injury criteria for this crash scenario when using a Hybrid III ATD because this dummy is not appropriate for side impacts. The Hybrid III ATD was built for frontal crashes and, among other things, it lacks instrumentation able to capture chest deflection during side impacts. Moreover, the TTI (Thoracic Trauma Index) cannot be calculated since the Hybrid III ATD does not have accelerometers in its spine.

Question 2

a) Which ATD would you suggest to use for this particular test, rather than the Hybrid III?

b) Name and describe two injury criteria specific to thoracic injury that you could assess for this particular test, assuming that the test was performed with an ATD appropriate for side impacts.

[show]SOLUTION (expand to show)

Solution to part a: Your answer should include one of the following, which are dummies appropriate for side impacts: BioSID SID SID IIs SID-H III (SID with a Hybrid III head & neck) WorldSID-50M WorldSID-5F EuroSID-1 ES-2 ES 2re ___________________________________ Solution to part b (the wording may vary, and different descriptions can be accepted as accurate, as long as they cover the main points of each criterion): Thoracic Trauma Index (TTI) and Viscous Criterion (VC). The TTI consists of an empirical formula that accounts for the age and mass of the test subject, and statistically relates rib and spine acceleration to trauma, but not to particular injuries. It can only be calculated for side impacts and has been adopted by the Federal Motor Vehicle Safety Standards (FMVSS) No. 214, "Side impact protection" to measure trauma for side impact protection. It considers the upper abdominal organs (liver, kidneys, spleen), but not the middle or lower ones. The VC can be evaluated for frontal and side impacts (each with the appropriate crash test dummy). It predicts the "probability and severity of impact injuries in the body's soft tissues, including the heart, liver, and central nervous system." The VC is calculated by multiplying the velocity of the deformation by the ratio of deformation and the initial torso thickness.

Question 3

Assume that the same test was performed using a 4-door passenger car, but this time with SID dummies.

The following data was recorded during the test:

• The maximum of the absolute value of the lateral acceleration of the 4th and 8th rib on the struck side: 90 g
• The maximum of the absolute value of the lateral acceleration of the 12th thoracic vertebra: 81 g

a) Would the 4-door vehicle described have passed the FMVSS 214 criteria for TTI(d)?

b) What about a 2-door passenger car (for these same values)?

[show]SOLUTION (expand to show)

Pertinent information: TTI(d) = 0.5*(RIBy + T12y), where RIBy stands for the maximum of the absolute value of the lateral acceleration of the 4th and 8th rib on the struck side and T12y is the maximum of the absolute value of the lateral acceleration of the 12th thoracic vertebra. According to the FMVSS 214, the maximum value of TTI(d) for a SID dummy is 85 g for a side impact involving a 4-door passenger car and 90 g for a 2-door passenger car. _________________________ Solution to part a: TTI(d) = 0.5*(90 g + 81 g) = 0.5 * 171 g TTI(d) = 85.5 g (> 85 g) Thus, the 4-door passenger car would not have passed the FMVSS 214 criteria. _________________________ Solution to part b: For these same values, a 2-door passenger car would have passed the FMVSS criteria because TTI(d) = 85.5 g < 90 g.

Question 4

A 25-year-old, 97.4 kg male driver was involved in a side crash while driving his 4-door passenger car. His body underwent the same acceleration values as the SID dummy mentioned above.

a) Calculate the TTI for this situation.

b) Name two types of thoracic injury that this driver has a fair probability (~25%) of suffering according to the TTI results.

c) If this individual had lost 30 kg before being involved in this crash, what would the new TTI value be, and how would this affect his probability of suffering an AIS 4+ injury?

[show]SOLUTION (expand to show)

Pertinent information: TTI = 1.4*AGE + 0.5*(RIBy + T12y)(M/Mstd), where AGE stands for the age of the subject [years], M is the mass of the subject [kg], and Mstd refers to a standard mass of 75 kg (RIBy and T12y were defined in the solution to question 3). ___________________________________ Solution to part a: TTI = 1.4*AGE + 0.5*(RIBy + T12y)(M/Mstd) TTI = 1.4*25 + 0.5(90 + 81)(97.4/75) TTI ~ 146 ___________________________________ Solution to part b: Considering that a TTI = 145 indicates a ~25% probability of an AIS 4+ injury occurring, several examples of AIS 4+ thoracic injury could be included in your answer, including (among others): Flail chest - a condition where multiple (3+) ribs on either side are each fractured in several places, allowing a segment of the chest wall to displace and move independently ("free-floating") from the rest of the chest wall 4 or more rib fractures on each of two sides 4 or more rib fractures with hemo- or pneumothorax Bilateral flail chest Bilateral lung laceration Minor aortic laceration Major heart contusion Major aortic laceration Lung laceration with tension pneumothorax Aortic laceration with hemorrhage not confined to the mediastinum ___________________________________ Solution to part c: The new TTI after the driver lost 30 kg: TTI = 1.4*AGE + 0.5*(RIBy + T12y)(M/Mstd) TTI = 1.4*25 + 0.5(90 + 81)(67.4/75) TTI ~ 111.8 (< 146), therefore, the driver has a lower likelihood of experiencing an AIS4+ injury after losing 30 kg because the new TTI value is sufficiently below the threshold value of 145.