Transcript Low Speed Rear-End Collisions

Low Speed Rear-End
Collisions
Mechanism of Injury
www.InjuryResources.com
© Copyright 2002, BodyMind Publications.
Proper Head
Restraint Positioning
Improper Head
Restraint Positioning
Viano and Gargan documented the head restraint position of 1,915
vehicles at an intersection. They found that only 10% of the occupants
had the head restraint in the proper position to avoid hyperextension.
Only ¼ of the adjustable head restraints were in the “up” position.
•
Viano DC, Gargan MF. Headrest position during normal driving: implication to neck injury risk in rear crashes. Accident Analysis
and Prevention 1996;28(6):665-674.
The Phases of a Rear-End Collision
1. Normal Position
3. Head Extension
2. Spine Straightens
4. Rebound
0 milliseconds
• Car seat begins to
move forward
• Occupant remains
stationary, due to inertia
• No occupant forces
100 milliseconds
• Car seat pushes into
occupants torso
• Torso is accelerated
forward with the seat
• Head is still stationary,
due to inertia
150 milliseconds
• Torso fully accelerated
by the car seat
• Lower neck is pulled
forward by the rapidly
moving torso
• Causing the head to
rotate backward over
the head restraint
175 milliseconds
• Head is still moving
backwards
• Car seat begins to
spring forward
• Torso is again
accelerated forward
300 milliseconds
• Head and torso are
accelerated forward
ahead of the car seat,
resulting in flexion of
the spine
Normal Cervical Spine
Normal Cervical Spine Extension
• Normal, smooth
curvature of the spine
• Each intervertebral joint
contributes evenly to
the motion
Normal Flexion and Extension
Normal spinal motion
results from small
motions in each
individual vertebral joint.
The normal motion of
each joint is limited to
just a few degrees of
movement.
Click on image to start or pause video
Motion During a Collision
0 milliseconds
At the moment of impact, the
car seat just begins to move
and the occupant has not yet
been accelerated forward.
Motion During a Collision
Head remains stationary
50 milliseconds
As the car seatback pushes
the torso forward, the spine
moves forward, resulting in a
straightening of the thoracic
and cervical spine.
Spine
straightens
Seatback pushes torso forward
Motion During a Collision
75 milliseconds
At this point in the collision, the car seat is rapidly
pushing the occupant's torso forward, while the
head remains stationary due to inertia.
This difference in motion
between the neck and torso
results in an S-shaped
curve, where nearly all of
the bending in the cervical
spine takes place in the
lower cervical spine.
This rapid bending in just a
few joints can result in
ligament damage in the
lower spine.
Seatback pushes
torso forward
Head remains
stationary
Spine forms
an abnormal
S-shape
formation
Injury Causing Motion
50 milliseconds
Spine Straightens
75 milliseconds
S-Shaped Curve
Motion During a Collision
Head rotates back
150 milliseconds
At about 150 milliseconds, the
torso has pulled so far forward on
the lower neck that the head is
forced backwards over the head
restraint.
Depending on the severity of the
collision, the ligaments in the front
portion of the spine can be injured
during this phase of the collision.
Seatback
pushes torso
forward
Motion During a Collision
Head thrown forward
200 milliseconds
Finally, the head and torso
are thrown forward by the
force of the car seat.
Force from car seat
Ligaments of the Cervical Spine
Facet
capsular
ligaments
The Cervical Facet Joints
Vertebral Body
Normal Gliding Motion
Facet Joints
Facets
Intervertebral Disc
Spinous Process
The Facet Joint
X-ray of facet joint.
The arrows show the
normal gliding motion of
these joints.
Facet joint
Normal Facet Motion
The cervical vertebrae
are designed for smooth,
even motion.
The facet joints stabilize
the spine and allow this
forward and backward
movement.
Click on image to start or pause video
Animation of Abnormal Spinal Motion
During a low speed,
rear-end collision, the
movement of the
head and neck is
focused on just a few
spinal segments.
This results in the sshaped curve motion
that can cause injury.
Click on image to start or pause video
Normal vs. Abnormal Motion
Normal Flexion/Extension:
Abnormal S-Shaped Curve:
Smooth, even motion of all
spinal segments
Dramatic movement in just a
few spinal segments
Click on image to start or pause video
Abnormal Facet Motion
Facet Joint
Pinching of facet
Reflectors
Tearing of
ligaments
and disc
Torso movement forward
Stretch
of facet
capsule
Torso moving forward
Vertebral Motion During Impact
Instead of a smooth
motion, the cervical
spine experiences
simultaneous
compression and shear.
This can cause tearing
in the front portion of the
spine and pinching in
the facet joints.
Click on image to start or pause video
Areas of Injury
The rapid motion of the neck
during a crash can result in a
number of injuries - many of
which are impossible to see on
x-rays or MRI. Here are some of
the injuries that have been
shown after whiplash crashes.
1.
Rim Lesions
2.
Endplate avulsions
3.
Tears of the anterior
longitudinal ligament
4.
Uncinate process
5.
Articular subchondral
fractures
6.
Articular pillar
7.
Articular process
8.
Ligament Tear
Nerves of the Facet Joint
The pain from inflamed facet
joints is transmitted by the
medial branch of the dorsal
ramus. Stimulation of the
facet nerves often results in
referred pain.
Spinal Cord
Facet Joints
Medial Branch
Dorsal Ramus
Spinous Process
Referred Pain Patterns
"... the prevalence of
cervical zygapophysial
joint pain was 60%."
C2/3, C3
The most common
facets to be injured were
C3/4, C4/5, C4
at C2/C3 and C5/C6.
Wallis BJ, Lord SM, Bogduk N.
Resolution of psychological distress
of whiplash patients following
treatment by radiofrequency
neurotomy: a randomised, doubleblind, placebo-controlled trial. Pain
1997;73:15-22.
C6/7, C6, C7
C2/3, C3/4, C3
C4/5, C5/6, C4, C5
C4/5, C5/6, C4
C7/T1, C7
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Live Occupant Footage Credit
The crash test footage is copyrighted by
Biomechanics Research and Testing.
Permission to use this footage was
generously provided by:
Biomechanics Research and Testing, LLC
1827 Ximeno Ave Ste 2
Long Beach, CA 90815
Phone: (562) 494-8310
Fax: (562) 494-4412
The video they produce contains crash test
footage of five collisions between 1-6 miles per
hour, and includes all of the data gathered
during the crash tests.