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7/30/2019 12 Biomech I Head Neck v2
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Biomechanics I (Head / Neck)
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Head Anatomy
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Physical Parameters Impact Direction
Ono, 1999
• Contact Area
• Stiffness
• Frontal Lateral
• Occiputal Pariental
• Skull/Outer Inner Shape
• Performance of Skull Strength
• Characteristics of Brain Itself
Head
Anatomical
Features
Skull Injury Focal Injury Diffuse Injury
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Brain Injury Mechanisms
Force and Acceleration
• Force can also cause anacceleration of the skull/brain
structure
•
Accelerator is either rotational or translational
• Acceleration creates
intracranial pressures and
movement and distortion of brain tissue (strain)
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Skull Fracture
Comparison of Head Impacts with
Hard wide and Hard Focal Surfaces
Fracture tolerance
and type of fracture
dependent onhardness and
geometry of
impacting structure
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Mechanical Response of the skull
Head impact response – peak force/drop Head impact response – peak
acceleration / drop height
peak force and peak acceleration as a function of free-fall drop height, for
impacts against a rigid
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Mechanical Response of the skull
• Fresh cadavers
• scalp thickness is greater
in embalmed heads than
in unembalmed onesbecause some of the
embalming fluid
• Design of dummy heads,
which are usually metalhead forms covered by a
soft vinyl coverHead impact response – peak force/
pendulum impact velocity
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Mechanical Response of the Face
• Injury to the face, while presenting the
problem of possible disfigurement, not
considered as brain injury
• Static loads to zygoma [890 N (200 lb)] or the
zygomatic arch [445N(100lb)].
• Stiffness -
– 1734 N/mm (9900 lb/in) for the zygomatic arch
– 4939 N/mm (28,200 lb/in) for the zygoma
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Impact Response of the Brain
• quantitative data by the useof a high-speed biaxial x-raymachine which produced x-ray pictures of an
instrumented cadavericbrain at 500 frames persecond (fps)
• Two neutral densityaccelerometers (NDA’s)
(small squares), the twopressure transducers (ovals)and low density targets(small dots) X-ray of cadaveric brain
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Impact Response of the Brain
• For low-level occipitalimpacts of 60 to 100 g,the displacement curvescomputed from the two
different methods wereidentical
• The strain along aposterior-anterior axis
due to a 100-g occipitalimpact was approximately8 percent Comparison: absolute
displacement of the brain
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Proposed In Vivo Injury
Mechanisms
Pressure causes a changein tissue volume, therebycausing damage
Deformation causesextension, shear and/orcompression of tissue,causing primary damage
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Brain Injury: Major Mechanisms
• Direct contusion from skull deformation
and/or fracture
• Contusion from internal movements
• Indirect contusion or contrecoup
• Reduced blood flow
•
Tissue stress and strain• Edema and Interstitial Pressure
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Coup – contrecoup injury
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BRAIN INJURY IS NOT
UNIDIMENSIONAL!!• DIFFERENT CAUSES
• DIFFERENT MECHANISMS
•
DIFFERENT TYPES• DIFFERENT AMOUNTS
• DIFFERENT LOCATIONS
• DIFFERENT PATHOPHYSIOLOGY• DIFFERENT TREATMENT
Is one Injury Predictor Appropriate?
T. Gennarelli
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Gadd’s Severity Index (GSI)
• Gadd’s Line:
• SI =
• Injury: SI > 1000
• Gadd’s Line: Risk of Injury 5% for AIS 4
and above.
2.51000TA
2.5
a t dt
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HIC Revision
• HIC time interval (1972) was 36ms
• In 2000 revision, maximum critical time reduced from 36
to 15 ms
Dummy Type Mid-Sized
Male
Small
Female
6 Year
Old Child
3 Year
Old Child
12 Month
Old Infant
Existing/Proposed
HIC Limit
1000 1000 1000 900 600
Dummy Type Large
Sized
Male
Mid-
Sized
Male
Small
Sized
Female
6-Year
Old
Child
3-Year
Old
Child
1-Year
Old
Child
HIC15 Limit 700 700 700 700 570 390
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Head Injury Criterion (HIC15)
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Rotational Acceleration and Brain
Trauma
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Measuring Head Acceleration
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Angular Acceleration
• Researchers have shown a positive correlationbetween magnitude of angular acceleration andseverity of injury (Abel et al., 1978; Higgens andSchmall, 1967; Ono et al., 1980; Hodgson et al.,
1983; Margulies and Thibault, 1992)• However, others have shown that duration of
angular acceleration is also a determinant of injury type wherein short duration impacts result
in focal injury while long duration result in DBI(Margulies and Thibault, 1992; Ono et al., 1980;Shatsky et al., 1974; Stalnaker et al., 1973)
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GAMBIT CriteriaGeneralized Acceleration Model for Brain Injury Tolerance
Based on instantaneous values of resultant
translational and rotational accelerations
Weights effects of the two forms of motion
similar to principal shear stress theory
General form of GAMBIT equation:
• G(t)=[(a(t)/ac)m+(α(t)/αc)
n]1/s
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HIP criterion
• Baseline mass and inertial characteristics for a50th percentile male head
= linear acceleration at the head’s centre of gravity about anatomical coordinate axis i (i=x,y,z)
= rotational acceleration about axix i,
Newman et al. (2000)
4.50 4.50 4.50
0.016 0.024 0.022
x x y y z z
xx x x yy y y zz z z
x x y y z z
x x y y z z
HIP ma a dt ma a dt ma a dt
I dt I dt I dt
HIP a a dt a a dt a a dt
dt dt dt
y
a 2/m s
y 2
/rad s
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Evaluation of Head Evaluation of
Head Injury Assessment FunctionsProposed local injury measures for brain tissue
Gennarelli et al., 1989;Thibault, 1990; Galbraith et al., 1993;
Bain et al., 1997; Bain and Meaney, 2000; Morrison et al., 2003
Goldstein et al., 1997; Viano and Lovsund, 1999; King et al., 2003
Shreiber et al., 1997; Miller et al., 1998; Anderson et al., 1999
CSDM (Cumulative Strain Damage Measure)
Bandak and Eppinger, 1994; DiMasi et al., 1995; Takhountset al., 2003
Strain Energy
Shreiber et al., 1997
1
vonMises
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Vertebrae
• Body
•
Pedicle• Laminae
• Spinous Process
•Transverse Process
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Cervical Vertebrae
• 7 bones
• Atlas/Axis
• Characteristics
– Small bodies
– Oval transverse foramen
• Verterbral Arteries pass
here
– Short spinous processes• 6th and 7th much longer
• Vertebra prominens
– 3rd-6th bifid
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Intervertebral Disks
Intervertebral disk
• Flexible proteoglycan filled structure –
Nucleus pulposis (NP)
•
Fibrous outer capsule – AnnulusFibrosis (AF)
— Alternating layers of collagenous lamallae
(fibrocartilage)
Acts as a thick walled cylinder to
distribute/cushion load
• Pressure increases in NP
• Hoop stress increase in AF
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Facet Joints
Facet Joints in Motion
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Posterior Neck Muscles
• Splenius
– Capitis/Cervicis
• Scalene
• Levator Scapulae
• Semispinalis
– Capitis (med/lat)
– Cervicis
• Longissimus
– Capitis/Cervicis
• Illiocostalis
– cervicis
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Spinal Nerves
• 31 pairs of spinal nerves: 8cervical, 12 thoracic, 5 lumbar5 sacral, 1 coccygeal
• Spinal nerves exit throughintervertebral foramen.
• C1 through C7 spinal nervesemerge above their vertebralsegments
• C8 spinal nerve exits below C7vertebra
• All remaining spinal nervesexit below their associatedvertebral segment (e.g. T1exits through intervertebral
foramen below T1 vertebrae).
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Neck Injury MechanismsCOMPRESSION-EXTENSION C5 Fracture
Dislocation
Compression -
extension
Ligament trauma
Unstable injury
AIS > 3
FLEXION INJURIES
• Anterior compression
• Posterior tension• Vertebral body fracture
• Posterior disk rupture
• Interspinous ligament
• Posterior logitudinal ligament
• Subluxation of C5 on C6
• Fracture of spinous process
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Mechanical Response of the Neck
• The overall averages for sagittal and lateral
motion were 103.7 and 71.0 degrees (deg)
• Rotation of the head about a superior-
inferior axis had an overall range of 136.5
deg
•
Stretch reflex times varied from about 30 to70 ms
• Average isometric lateral pull forces ranged
from 52.5 N (11.8 lb) for elderly females to
142.8 N (32.1 lb) for middle-age males
• Total time to reach maximal muscle force is
on the order of 130 to 170 ms and is
probably too long to prevent injury in a high-
speed collision
Neck response in lateral flexion
Voluntary Range of Static Neck Bending
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Injury Criterion
• Peak force alone is NOT to be a useful
predictor of cervical spine damage.
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H-III and Thor necks
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BioRID neck
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