Biomechanics I (Head / Neck)

Transcription

1 Biomechanics I (Head / Neck)

2 Head Anatomy

3

4

5

6 Physical Parameters Contact Area Stiffness Impact Direction 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 Ono, 1999

7 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)

8

9 Comparison of Head Impacts with Hard wide and Hard Focal Surfaces Skull Fracture Fracture tolerance and type of fracture dependent on hardness and geometry of impacting structure

10 Mechanical Response of the skull peak force and peak acceleration as a function of free-fall drop height, for impacts against a rigid Head impact response peak force/drop Head impact response peak acceleration / drop height

11 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

12 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 N/mm (9900 lb/in) for the zygomatic arch 4939 N/mm (28,200 lb/in) for the zygoma

13 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

14 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

15 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

16 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

17 Coup contrecoup injury

18 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

19 Gadd s Severity Index (GSI) 2.5 Gadd s Line: TA 1000 SI = 2.5 a t dt Injury: SI > 1000 Gadd s Line: Risk of Injury 5% for AIS 4 and above.

20 Head Injury Criteria (HIC) t t 2 1 HIC t 2 t1 a dt t 2 t1 t1 2 t ms or 36 ms to maximize HIC HIC > 1000 serious brain injury NHTSA Signal Processing Software:

21

22 HIC Revision HIC time interval (1972) was 36ms Dummy Type Existing/Proposed HIC Limit Mid-Sized Male Small Female 6 Year Old Child 3 Year Old Child 12 Month Old Infant In 2000 revision, maximum critical time reduced from 36 to 15 ms Dummy Type Large Sized Male Mid- Sized Male Small Sized Female 6-Year Old Child 3-Year Old Child 1-Year Old Child HIC 15 Limit

23 Head Injury Criterion (HIC 15 )

24 Rotational Acceleration and Brain Trauma

25 Measuring Head Acceleration

26 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)

27 Proposed Rotational Brain Injury Tolerances: Human

28 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)/a c ) m +(α(t)/α c ) n ] 1/s

29 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 m / c n G t a t a t c GAMBIT with m 2, n 2, s 2, a 250 g, rad / s 50% risk of AIS 3at 1 G a x x Newman 3 5 m 4 m 10 m 10 1 G a x x Lee et al m 1 4 m 10 8 m 10, c Gm 4amx10 4 mx10 Kramer & Appel c 2

30 GAMBIT Criteria Does not account for time dependence Inadequate validation

31 HIP criterion Baseline mass and inertial characteristics for a 50 th percentile male head HIP ma a dt ma a dt ma a dt x x y y z z I dt I dt I dt xx x x yy y y zz z z HIP 4.50a a dt 4.50a a dt 4.50a a dt x x y y z z dt dt dt x x y y z z = linear acceleration at the head s centre of gravity about anatomical coordinate axis i (i=x,y,z) = rotational acceleration about axix i, a y 2 m/ s 2 y rad / s Newman et al. (2000)

32 Evaluation of Head Evaluation of Head Injury Assessment Functions Proposed local injury measures for brain tissue 1 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 vonmises 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

33 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

34

35 Vertebrae Body Pedicle Laminae Spinous Process Transverse Process

36 Cervical Vertebrae 7 bones Atlas/Axis Characteristics Small bodies Oval transverse foramen Verterbral Arteries pass here Short spinous processes 6 th and 7 th much longer Vertebra prominens 3 rd -6 th bifid

37 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

38 Facet Joints Facet Joints in Motion

39 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

40 Anterior Neck Muscles Platysma Sternocleidomastoid Omohyoid Sternothyroid Sternohyoid

41 Splenius Capitis/Cervicis Scalene Levator Scapulae Semispinalis Capitis (med/lat) Cervicis Longissimus Capitis/Cervicis Illiocostalis cervicis Posterior Neck Muscles

42 Nerve roots exit between vertebrae through the intervertebral foramen Vertebral fracture, disk rupture or impingement can affect neural performance Pain Paralysis Neural Tissue Spinal cord runs down the foramen between the vertebral centrum and posterior elements Bony cage protects the cord

43 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).

44 SPINAL MOTIONS Lateral Bending Rotation Extension Lateral Bending Rotation Flexion

45 Range of motion

46

47

48 Neck Injury Mechanisms Vertical Compression No major ligament Trauma Bony fracture Vertical Compression Burst fracture Canal encroachment AIS > 3 Stable injury AIS < 3 Compression - flexion Ligament trauma C2-C3 Bony fracture C4-C5 Unstable injury AIS > 3 Fracture Mechanisms of a Cervical Spine Segment IM107a Flexion/Compression Fracture

49 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

50 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 TENSION-FLEXION INJURIES IM116 Hangman s Fracture of C2

51 Mechanical Response of the Neck Neck response in flexion Neck response in extension

52

53 Mechanical Response of the Neck The overall averages for sagittal and lateral motion were and 71.0 degrees (deg) Rotation of the head about a superiorinferior axis had an overall range of deg Voluntary Range of Static Neck Bending 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 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 highspeed collision Neck response in lateral flexion

54 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 highspeed 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 KJD SAT Lateral Flexion Left (deg) Right (deg) LMP SAT Oblique Flexion 45 Deg Mode Toward (deg) Away (deg) LMP Oblique Flexion 135 Deg Mode Toward (deg) Away (deg) LMP

55 Injury Criterion Peak force alone is NOT to be a useful predictor of cervical spine damage.

56 Injury Criterion N ij and NIC

57 Dummy and Computational models

58 H-III and Thor necks

59 BioRID neck

60 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.

61 Thanks More on dummies and models later