Documentation:FIB book/problems/Restraints and Spinal Injury

A 40-year-old woman is the driver of a car involved in a frontal car crash and is taken to a hospital with a hangman's fracture. She is 154 cm tall and weighs 54 kg.

Question 1

What two injury modes could cause a hangman's freacture and how could this have been caused by a restraint in the car?

[show]SOLUTION (expand to show)

Injury Mode: - Tension-extension - Compression-extension. The woman could have obtained a hangman's fracture from an airbag as she is shorter than average so would, therefore, be sitting closer to the steering wheel and out of position. This may have caused the airbag to catch under her chin before fully inflated and then inflate further pushing her chin up causing her neck to experience tension-extension. This is known as membrane loading.

Question 2

Describe the restraint maxims that an airbag fulfils and how it fulfills them.

[show]SOLUTION (expand to show)

Maximise the time over which the restraint forces are applied. The airbag deploys very quickly so applies restraint force over the maximum time. Maximise the distance over which the restraint forces act. The airbag deploys very quickly so applies restraint force over the maximum distance. Minimise the rotation or translation at occupant's joints, deformation of anatomic structures, and rate of deformation of structures. The airbag helps hold the occupant upright reducing rotation in their neck and spine. Distribute restraint forces over the greatest possible area. The airbag is large so spans across a large area of the body. Apply restraint forces to bony anatomies such as the femur, pelvis, upper thorax, shoulder, and head. The airbag is intended to be impacted by the upper thorax and head. Apply restraint forces as soon as possible. The airbag system is designed to deploy very quickly after detecting an impact.

Question 3

What is the other injury mechanism and the associated injuries that airbags could cause if someone is sitting out of position?

[show]SOLUTION (expand to show)
Injury Mechanism: Punch out Associated Injuries: this could cause brain trauma and abdominal and thoracic organ injury.

Question 4

Crash Injury Research Engineering Network (CIREN) are investigating this crash and are looking to undertake some research into membrane loading using either cadavers or anthropomorphic test devices (ATDs). If they were to decide to use cadavers for this test, what challenges would they encounter in maintaining head and neck alignment in cadavers and how are these challenges currently overcome?

[show]SOLUTION (expand to show)

Cadavers have no muscle tension in their neck resulting in difficulty maintaining head and neck alignment during testing. Three ways they currently used to replicate this muscle tension are: - Restraints and straps attached to the rest of the body. - Masses and springs attached to the head with the bottom of the neck fixed. - Advanced muscle force replication using springs, hooks and string attached to different locations on the neck to replicate muscle forces and stiffness.

Question 5

What type of ATD would be best suited for this test and what instramentation is present in this type of ATD that would be usefull for this test?

[show]SOLUTION (expand to show)
Hybrid III 5th percentile female as this injury can be caused by sitting closer to the steering wheel which this dummy would simulate due to its shorter size. The instrumentation most relevant to this test is the upper and lower neck load cells.

Question 6

Its decided to use the best suited ATD for this test instead of a cadaver. The results from one test are shown below. Calculate Nij for this test. (Fz positive = tension and My positive = extension). Explain what implication that this has in terms of likelihood of injury.

Test Results

Time (ms)	Fz (N)	My (Nm)
20	-1579	-52
25	2791	27
30	4391	63
35	3941	41

[show]SOLUTION (expand to show)
As discussed in Question 5, Hybrid III 5th percentile female ATD was used. $N_{TE}=\left({\frac {F_{Z}}{F_{ZC}}}\right)+\left({\frac {M_{Y}}{M_{YC}}}\right)$ $N_{TE}=\left({\frac {4391}{4287}}\right)+\left({\frac {63}{67}}\right)$ $N_{TE}=1.96$ Serious neck injury is expected as Nij is greater than 1.