Documentation:FIB book/problems/Neck Injury Criteria

The neck is an incredibly important part of the human body and is instrumental for supporting the weight of the head and torso, range of motion, and protecting the spinal cord. Cervical spinal cord damage is especially of interest in the field of injury biomechanics because of the potential for severe neurological consequences such as paralysis. The following problem concerns the criteria most often used to quantify and understand neck injury.

Question 1

N_ij is a commonly used criterion to understand neck injury resulting from excessive tension-compression and flexion-extension. N_ij is designed to be used for frontal impacts and is calculated from the axial neck loads and moments about the occipital condyle; this value must remain below 1.0 to avoid severe injury.

What are the other major two neck injury criteria covered in this course called? Please provide a brief explanation of the other two criteria and define:

a) the type of impact they are intended to be used for,

b) parameters their equations are calculated from,

c) maximum threshold values, and

d) what reaching these values represents.

There is no need to go into detail on any of the sub-criteria or "flavours" of these, a general explanation will suffice.

[show]SOLUTION (expand to show)

The other two neck injury criteria I'm looking for are NIC and Nkm. Students do not necessarily need to write the formulas out or have specified all of the information written below, but should have included the bolded content at a minimum. NIC NIC stands for neck injury criterion, and this was developed to quantify soft tissue neck injuries in minor rear-end impacts. Calculation of NIC is based on the relative acceleration and velocity between the centre of gravity of the head and the bottom of the neck (T1). NIC is further derived from fluid flow and pressure gradients in the spinal column. NIC has a threshold of $15{\frac {m^{2}}{s^{2}}}$ for achieving at least 50% probability of short-term neck injury. Long-term symptoms occur at $24{\frac {m^{2}}{s^{2}}}$. Students should not go into differentiating between NICgeneric, NICmax, or NICprotraction in this portion. $NIC(t)=0.2a_{rel}\left(t\right)+v_{rel}\left(t\right)^{2}$ Nkm Nkm stands for neck protection criterion and was developed for quantifying sagittal shear forces and moments in low-energy rear-end collisions. It is comparable to Nij. Alternatively, students may write that the criterion is based off of anterior and posterior flexion and extension. Similarly to Nij, Nkm has a maximum threshold of 1.0 to reach severe neck injury. It may be further written that an Nkm score of 1.0 is associated with a 22% risk of AIS3 neck injury. $N_{km}(t)={\frac {F_{x}(t)}{F_{int}}}+{\frac {M_{y}(t)}{M_{int}}}$

Question 2

How do NIC_max and NIC_protraction differ from NIC_generic?

[show]SOLUTION (expand to show)

NICgeneric only provides reasonable values while velocity and acceleration are both rearward. The equation for NICgeneric is the same as the standard NIC equation, but calculations are confined to the window of time when velocity and acceleration are BOTH negative (rearward). NICmax represents the maximum value of NIC(t) between the start of the collision and the point in time in which the head reverses its direction of motion relative to the neck. NICprotraction was introduced for low speed frontal impacts. It can be understood to be the absolute value of the minimum value of NICgeneric(t), or $\left\vert min(NIC_{generic}(t))\right\vert$.

Question 3

Based on the information provided in the below formula and table, please calculate NIC_max and comment on the likelihood of injury.

$NIC(t)=0.2a_{rel}(t)+v_{rel}(t)^{2}$

Time (ms)	ahead CoG (m/s2)	aT1 (m/s2)	vhead CoG (m/s)	vT1 (m/s)
5	1.5	0.2	5.0	1.5
10	1.9	0.5	7.0	3.0

[show]SOLUTION (expand to show)

Students should calculate the relative values for acceleration and velocity as follows: ahead - aT1 = 0.3 m/s2 at 5 ms, and 0.4 m/s2 at 10 ms vhead - vT1 = 3.5 m/s at 5 ms, and 4.0 m/s at 10 ms Plugging the values at 5 ms and 10 ms into the above formula at each timepoint would give NICmax values of approximately 12.3 m/s2 and 16.1 m/s2, respectively. Students should indicate that the 10 ms value indicates a likelihood of achieving over a 50% probability of short-term neck injury as it is higher than the threshold of $15{\frac {m^{2}}{s^{2}}}$ . Long-term symptoms are not expected, as they occur at $24{\frac {m^{2}}{s^{2}}}$.

Question 4

Auto manufacturers would like to design a sled test to model the injury response of a person sitting in a car during heavy traffic who is hit from behind at low speeds in a fender bender. Which ATD would you recommend them to use for the purpose of modelling injury likelihood of the neck? Describe the included instrumentation that makes this ATD appropriate for such a scenario.

Which neck injury criterion would you recommend be used in conjunction with this ATD? (Hint: there may be more than one right answer.) Why are other criteria mentioned earlier in this problem inadequate for assessing this specific impact scenario?

[show]SOLUTION (expand to show)

Students should identify the BioRID as the optimal ATD for modelling a rear-end impact - it was designed for such scenarios, especially for low-speed. BioRID has suitable neck biofidelity with 24 individual vertebrae and muscle-simulating springs, which is especially important for modeling the increased musculature at the neck. In terms of instrumentation, the BioRID includes upper and lower neck load cells as well as accelerometers at the C4 and T1 spine (extra points if they mention T1 as the location for measuring NIC values.) Students should not recommend the Hybrid III, as this ATD was designed for frontal impacts and is not particularly sensitive to or biofidelic in rear impact scenarios. Students should indicate Nkm or NICgeneric/max as the best injury criteria for this type of crash scenario. NICprotraction is designed for low speed frontal impacts and Nij for frontal impacts, making them unsuitable for use in this type of impact scenario.