12 Biomech I Head Neck v2

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Biomechanics I (Head / Neck)

Head Anatomy

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

Anatomical

Features

Skull Injury Focal Injury Diffuse Injury

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)

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

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

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

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

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

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

Proposed In Vivo Injury

Mechanisms

Pressure causes a changein tissue volume, therebycausing damage

Deformation causesextension, shear and/orcompression of tissue,causing primary damage

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

Coup – contrecoup injury

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

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

a t dt

HIC Revision

• HIC time interval (1972) was 36ms

• In 2000 revision, maximum critical time reduced from 36

to 15 ms

Dummy Type Mid-Sized

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

Female

6-Year

3-Year

1-Year

HIC15 Limit 700 700 700 700 570 390

Head Injury Criterion (HIC15)

Rotational Acceleration and Brain

Trauma

Measuring Head Acceleration

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)

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)

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

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

a 2/m s

/rad s

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

vonMises

Vertebrae

• Body

Pedicle• Laminae

• Spinous Process

•Transverse Process

Cervical Vertebrae

• 7 bones

• Atlas/Axis

• Characteristics

– Small bodies

– Oval transverse foramen

• Verterbral Arteries pass

– Short spinous processes• 6th and 7th much longer

• Vertebra prominens

– 3rd-6th bifid

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

Facet Joints

Facet Joints in Motion

Posterior Neck Muscles

• Splenius

– Capitis/Cervicis

• Scalene

• Levator Scapulae

• Semispinalis

– Capitis (med/lat)

– Cervicis

• Longissimus

– Capitis/Cervicis

• Illiocostalis

– cervicis

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).

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

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

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

Injury Criterion

• Peak force alone is NOT to be a useful

predictor of cervical spine damage.

H-III and Thor necks

BioRID neck

Thanks

12 Biomech I Head Neck v2

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