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Child crash test dummies not crashworthy?
For
background information, view here
For images,
view here.
3 July 2008
We’re not protecting young car passengers as well as we
could, according to researchers at Sydney’s Prince of Wales Medical Research
Institute.
They’ve shown that the spine of a young child is
significantly different from that of an adult in ways which could influence the
risk of spinal cord injury and the results of crash testing. And they’ve called
for new crash dummy designs that better mimic what happens to a real child in a
crash.
“Our studies have found huge differences in flexibility
and stiffness between young and mature spines. And in a collision, a younger,
more flexible, spine is likely to place greater strain on the spinal cord
inside,” says Elizabeth (Liz) Clarke, a researcher at the Institute.
Car crashes are the most
common cause of spinal cord injuries in Australia. Such injuries can lead to
permanent paralysis. Fortunately only about two percent of these injuries are in
young children. The wide use of child restraints is probably reducing the risk.
Young children, however,
may be more susceptible to spinal cord damage than these statistics would lead
us to believe, says Liz. “We’ve found that the young spine is softer and about
three times more flexible than that of an adult. Because the young spine allows
more overall movement, the spinal cord inside may be stretched to a higher
degree. So, it is possible that a much smaller impact would be required to cause
spinal cord damage in a poorly or unprotected child than an adult.
“Also, while it is
extremely rare in adults for the spinal cord to be damaged without fracturing
the vertebrae, it is not uncommon in spinal cord injuries in young children,
possibly due to this increased flexibility.”
Liz and her colleagues
believe that the higher risk for younger children is hidden as they are less
likely to be exposed to dangerous driving, and are better protected in the car
by using child restraints. Other work at the Institute has shown the importance
of an appropriate, approved child restraint in providing maximum protection to
children. However, with better testing it may be possible to identify and/or
design restraints which further reduce the risk of paralysing injuries,
particularly in children too big for current child restraint designs.
The researchers have also
discovered that flexibility along the length of a young spine varies markedly
from flexibility along the adult spine. The young spine is very flexible in all
directions and at all levels—the neck, and upper and lower back—whereas the
adult spine is far less flexible in the middle of the back, and when twisting to
the left or right.
“Child crash test dummies
have been modelled as scaled-down versions of adult crash test dummies,” Liz
says, “but these research findings suggest that there is significant scope for
improvement. Current child crash test dummies can tell us if a restraint will
contain a child during an accident, but they don’t adequately model the spine.”
“We hope that our results
will be used to improve crash test dummy design and eventually lead to a new
generation of dummies. Better child crash test dummies will give us the tools we
need to make travelling in cars safer for children of all ages.”
Elizabeth Clarke is one of
16 early-career scientists chosen for Fresh Science, a national program
sponsored by the Federal and Victorian governments.
Media contacts: Elizabeth
Clarke on 02 93991041, 0413 683 151, e.clarke@powmri.edu.au; Sarah Brooker on
0413 332 489; and Niall Byrne on 0417 131 977 or
niall@freshscience.org
Background
Abstract
Immature sheep
spines are more flexible than mature spines: an in vitro biomechanical study.
Clarke EC, Appleyard RC, Bilston LE.,Spine,. 2007 Dec 15;32(26):2970-9
STUDY DESIGN: Dynamic
triaxial biomechanical testing of immature and mature ovine spine motion
segments. OBJECTIVE: To compare torque-deflection parameters of mature and
immature spine motion segments and to investigate whether scaling
relationships apply between mature and immature motion segment
torque-deflection responses. SUMMARY OF BACKGROUND DATA: While previous
studies have examined the cervical region in a limited number of loading
directions, a comprehensive multiaxial study of the response of the
pediatric spine at all 3 spinal levels (cervical, thoracic, and lumbar) has
not been performed. METHODS: Motion segments from cervical, thoracic, and
lumbar levels were tested under moment application about 3 axes for newborn
and 2-year-old sheep. Range of motion, neutral zone, and stiffness were
calculated for each motion segment and compared for immature and mature
spine. RESULTS: Immature spine motion segments exhibited a significantly
larger range of motion (P < 0.001) and neutral zone (P < 0.001) and
significantly lower stiffness (P < 0.001) in comparison to mature spine
segments about the 3 moment axes, at the 3 spinal levels tested. There were
statistically significant interactions between specimen age and the moment
axis and/or spinal level for some torque-deflection parameters. CONCLUSION:
The significantly greater neutral zone of immature spine suggests greater
ligament laxity. Significantly higher range of motion and lower stiffness of
the immature spine may be implicated in spinal cord injury mechanisms and
implies a change in relative tolerance of the spine to damage with spinal
maturity. Significant statistical interactions between spinal maturity and
moment axis or motion segment level suggest that scaling torque-deflection
parameters from mature to immature spine may not be appropriate.
Abstract
Contrasting Biomechanics and
Neuropathology of Spinal Cord Injury in Neonatal and Adult Rats Following
Vertebral Dislocation
Clarke EC, Bilston LE., Journal of
Neurotrauma, In Press (accepted April 1st, 2008)
Clinically, spinal cord
injuries (SCI) in infants are different from SCIs in adults. SCI is rarer in
infants, and the most common types of associated spinal column injury are
different for adults and infants. Initially, infants tend to have higher
injury severities and mortality, however young survivors of SCI typically
have greater and more rapid functional recovery. The objective of this study
was to contrast the biomechanics and neuropathology of SCI in adult and
neonatal rats to investigate these differences. Thoracolumbar vertebrae of
anaesthetized rats were dislocated laterally (T12 held stationary and L1
displaced laterally, with T13 between these levels) by 10mm at 250mm/s in
adults and by 4mm at 100mm/s in neonates (13-15 days), and rats were
euthanized 6 hours later. Spinal cord sections were stained to detect
hemorrhage (H&E), axonal injury (ßAPP), and neuronal nuclei (NeuN). Maximum
load was significantly higher in adults (25.7 ± 2.4N) than neonates (11.0 ±
2.4N) (p<0.001). Adult and neonatal hemorrhage volumes were not
significantly different for either the raw or normalized data-sets (p=0.064
for normalized dataset). Un-normalized axonal injury densities were similar
for adults and neonates but normalized axonal injury density was
significantly higher in neonates (p<0.001). Reduction of NeuN
immunoreactivity was significantly lower in neonates, for both un-normalized
(p<0.004) and normalized (p<0.001) data-sets. The findings of this study may
explain the different common types of spinal column injury associated with
SCI, and the greater initial severity of SCI in infants.
Images
Click on image for high resolution image for download
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Crash reconstruction using 6 year old crash test
dummy - pre-impact.
L Bilston and J Brown, Impact Injuries Laboratory,
Prince of Wales Medical Research Institute |
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Crash
reconstruction using 6 year old crash test dummy - following impact.
L
Bilston and J Brown, Impact Injuries Laboratory, Prince of Wales Medical
Research Institute |
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