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

Head Anatomical Features

Skull Injury Focal Injury Diffuse Injury

Brain Injury Mechanisms

Force and Acceleration

• Force can also cause an

acceleration 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 on

hardness 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 ones because some of the embalming fluid

• Design of dummy heads, which are usually metal head forms covered by a soft vinyl cover

Head 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 use of a high-speed biaxial x-ray machine which produced x-ray pictures of an instrumented cadaveric brain at 500 frames per second (fps)

• Two neutral density accelerometers (NDA’s) (small squares), the two pressure transducers (ovals) and low density targets (small dots)

X-ray of cadaveric brain

Impact Response of the Brain

• For low-level occipital impacts of 60 to 100 g, the displacement curves computed from the two different methods were identical

• The strain along a posterior-anterior axis due to a 100-g occipital impact was approximately 8 percent Comparison: absolute

displacement of the brain

Proposed In Vivo Injury

Mechanisms

Pressure causes a change in tissue volume, thereby causing damage

Deformation causes extension, shear and/or compression 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.

2.5 1000TA

2.5

a t dt

Head Injury Criteria (HIC)

ms or 36 ms to “maximize” HIC HIC > 1000 serious brain injury NHTSA Signal Processing Software: http://www-nrd.nhtsa.dot.gov/software/signal-analysis/downloads.html

2

1

2.5

2 1

2 1

1t

t

HIC t t a dtt t

2 1 15t t

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

Head Injury Criterion (HIC15)

Rotational Acceleration and Brain

Trauma

Measuring Head Acceleration

Angular Acceleration

• Researchers have shown a positive correlation between magnitude of angular acceleration and severity of injury (Abel et al., 1978; Higgens and Schmall, 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)

Proposed Rotational Brain Injury Tolerances: Human

GAMBIT Criteria Generalized 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

Generalized Acceleration Model for Brain

Injury Tolerance – GAMBIT

A number of different researchers have determined coefficients for

the GAMBIT function. None of them include directional

dependence

1 3

2

3 5

4 3

1 2.52.5 2.5

3 5

/

2, 2, 2, 250 , 25000 /

50% 3 1

4 10 10 1

1 4 10 8 10 ,

4 10 4 10 &

m n

c c

c c

m m m

m m m

m m m

G t a t a t GAMBIT

with m n s a g rad s

risk of AIS at

G a x x Newman

G a x x Lee et al

G a x x Kramer Appel

GAMBIT Criteria • Does not account for time dependence

• Inadequate validation

HIP criterion

• Baseline mass and inertial characteristics for a 50th 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

ya 2/m s

y 2/rad s

Evaluation of Head Evaluation of Head Injury Assessment Functions

Proposed 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; Takhounts et al., 2003

Strain Energy Shreiber et al., 1997

1

vonMises

Neck Injury

Neck Injuries – U. S. Stats Rear Impact => 85% of all neck injuries

AIS=1 neck injury => $ 10 billion U. S. (1996)

=> £ 2.5 billion U. K. (1996)

=> $ 0.5 billion Canada (1997)

=> 1 in 1000 incidence

=> Major problem in Western Countries

Vertebrae

• Body

• Pedicle

• Laminae

• Spinous Process

• Transverse Process

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

Intervertebral Disks

Intervertebral disk

• Flexible proteoglycan filled structure – Nucleus pulposis (NP)

• Fibrous outer capsule – Annulus Fibrosis (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

Ligaments

Connected between adjacent vertebrae along length of spine

Act to limit excessive motion

Regular

• Anterior and posterior longitudinal ligaments (ALL, PLL)

• Ligamentum flavum (LF)

• Inter and superspinous ligaments (ISP, SSP)

• Intertransverse ligaments (IT)

• Facet joint capsules

Ligament Nuchae

Anterior Neck Muscles

• Platysma

• Sternocleidomastoid

• Omohyoid

• Sternothyroid

• Sternohyoid

Posterior Neck Muscles

• Splenius

– Capitis/Cervicis

• Scalene

• Levator Scapulae

• Semispinalis

– Capitis (med/lat)

– Cervicis

• Longissimus

– Capitis/Cervicis

• Illiocostalis

– cervicis

Neural Tissue

Nerve roots exit between vertebrae through the intervertebral foramen

Vertebral fracture, disk rupture or impingement can affect neural performance

• Pain

• Paralysis

Spinal cord runs down the foramen between the vertebral centrum and posterior elements

• Bony ‘cage’ protects the cord

Spinal Nerves • 31 pairs of spinal nerves: 8

cervical, 12 thoracic, 5 lumbar 5 sacral, 1 coccygeal

• Spinal nerves exit through intervertebral foramen.

• C1 through C7 spinal nerves emerge above their vertebral segments

• C8 spinal nerve exits below C7 vertebra

• All remaining spinal nerves exit below their associated vertebral segment (e.g. T1 exits through intervertebral foramen below T1 vertebrae).

SPINAL MOTIONS

Lateral Bending

Lateral Bending

Rotation Extension

Rotation Flexion

Range of motion

Neck Injury Mechanisms

Vertical Compression No major ligament Trauma Bony fracture Stable injury AIS < 3

Vertical Compression Burst fracture Canal encroachment AIS > 3

Fracture Mechanisms of a Cervical Spine Segment IM107a Flexion/Compression Fracture

Compression - flexion Ligament trauma C2-C3 Bony fracture C4-C5 Unstable injury AIS > 3

Neck Injury Mechanisms COMPRESSION-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

Neck Injury Mechanisms (contd) EXTENSION INJURIES

• Anterior tension • Posterior compression • Marginal fracture of vertebral

body • Anterior disk rupture • Sternomastoid tear • Lesion anterior longitudinal

ligament • Fracture of spinous process • Posterior subluxation

IM116 Hangman’s Fracture of C2

TENSION-FLEXION INJURIES

Mechanical Response of the Neck

Neck response in flexion Neck response in extension

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 to

70 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

Mechanical Response of the Neck

• voluminous data acquired at the Naval Biodynamics Laboratory, New Orleans – constitutes a valuable source of

neck response data for volunteers

• More recent unpublished results obtained from cadavers and through the use of a biaxial high-speed x-ray/camera device at frame rates in excess of 250 per second demonstrated that – Compression began early in the impact

event

– There was both relative translation and rotation between adjacent lower cervical vertebrae

Volunteer Flexion (deg) Extension (deg) Total Range

(deg)

LMP 51 82 133

KJD 65 73 138

SAT 63 69 132

Lateral Flexion

Left (deg) Right (deg)

LMP 42 43 85

SAT 35 39 74

Oblique Flexion 45 Deg Mode

Toward (deg) Away (deg)

LMP 35 56 91

Oblique Flexion 135 Deg Mode

Toward (deg) Away (deg)

LMP 53 38 91

Injury Criterion

• Peak force alone is NOT to be a useful predictor of cervical spine damage.

Injury Criterion Nij and NIC

Dummy and Computational models

H-III and Thor necks

BioRID neck

ACKNOWLEDGEMENTS

• Material in the presentations is adapted from different sources including presentations made in the annual TRIPP safety course, material available on the www, LS Dyna manual as well as other published material.

• We also acknowledge the support from Ratnakar Marathe in preparing some of the contents.

Thanks

More on dummies and models later