Injury Biomechanics Workshop at IRCOBI Asia 2018

Transcription

1 Injury Biomechanics Workshop at IRCOBI Asia 018 Kai-Uwe Schmitt and Ciaran Simms Agenda Introduction Methods/ History/ Basic calculations Example: head injury Group work Summary

2 0 Accidentology Accident data Accident reconstruction Accident severity Injury data Medical records Injury classification Injury severity (AIS) Injury biomechanics Injury mechanisms Injury modelling Injury risk assessment Injury prevention / safety engineering

3 Injury biomechanics direct trauma <> fatigue/ overuse Injury biomechanics

4 Injury Biomechanics in History Hippocrates [ca 400 BC] he who falls from a very high place is in most danger of sustaining a fracture... whereas, he that falls upon a softer object is likely to suffer less injury. Military protection: Animal Biomechanics: De Motu Animalium Aristotle (384 BC 3 BC) Giovanni Alfonso Borelli ( ) No systematic evaluation of injuries Trinity Centre for Bioengineering 7 Reverend Samuel Haughton ( ) On hanging from a Mechanical & Physiological point of view. London, Edinburgh and Dublin Philosophical Magazine and Journal of Science, Vol. 3 No. 13 (July 1866) Transport revolution: large scale non military injuries 1869 first recorded road fatality: Mary Ward: artist & scientist, crushed by steam carriage wheels Ireland Trinity Centre for Bioengineering 8

5 Impact Tolerance Late C19 th, Otto Messerer (German medical doctor) Strength of human bones Publications: Experimental examinations of skull fracture On the elasticity and strength of human bones Today: Trinity Centre for Bioengineering 9 Safety as a concept Hugh de Haven (engineer): importance of restraint system following plane crash Epidemiology of accidents: Crash Injury Research project in 194 (aeroplanes) Automotive Crash Injury Research project in 1953 When I showed [my commanding officer] the causes of extreme injuries in crashes, I encountered a dedicated inertia. he believed that the resulting pathology represented solely the luck of the game. When I suggested that the luck could be changed by better engineering and design, he felt that the hand had been dealt as it was and that change would amount to stacking the deck. Trinity Centre for Bioengineering 10

6 Injury Biomechanics: Organized Science Stapp Car Crash Conference (1955 ) IRCOBI Conference on Biomechanics of Injuries (1973 ) Murray Mackay, OBE, FREng., DSc Trinity Centre for Bioengineering s Bertil Aldman (Swedish medical doctor): Co founder of IRCOBI 196 PhD Biodynamic Studies on Impact Protection Full scale car to barrier crash tests with different belts New crash test dummy with instrumentation Superiority of lap and shoulder belt system Rear facing child seat Trinity Centre for Bioengineering 1

7 The last twenty years Airbag technology advances Collision avoidance & detection technology integrated safety Numerical models: occupant sizes, active and passive, Stochastic modelling Human tissue behaviour: Barclay Morrison (IRCOBI VP): cell death and changes in electrophysiological function are more meaningful than mechanical failure criteria Injuries in sport and blast Consumer testing Trinity Centre for Bioengineering 13 Cannot Crash Test Humans need Modelling Methods Volunteers: Animals: Cadavers: Dummies: Computer models: Real accident studies: Trinity Centre for Bioengineering 14

8 HUMAN VARIABILITY Age, gender, build 50% Male 95% Male 5% Female wikipedia Trinity Centre for Bioengineering 15 Crash Safety Standards U.S: 1966: National Traffic and Motor Vehicle Safety Acts Empowered Federal Government to set vehicle safety standards FMVSS standards (National Highway Safety Bureau) Many initial standards reflected best practice limited biomechanical input Federal standards mandated in the United States around 1970 Europe lagged behind the US at this time [Mackay IRCOBI ] Trinity Centre for Bioengineering 16

9 Some Basic Impact Equations NEWTON II: F m. a Force Rate of change Mass d F m. v dt Mass acceleration Velocity t 1 I F. dt m. v F. t t 0 Time interval 1 t Impulse Momentum change Average force 0 Get velocity change when mass, average force and duration are known 17 SINGLE CAR CRASH Vehicle mass m striking a rigid barrier at a velocity v. No rebound. Contact force F between the vehicle and barrier decelerates the vehicle. Differential equation of motion for the centre of gravity of the vehicle: M x F Manipulate and integrate t t1 x x x x dt F m F x m let crush d F v d m t t1 CRUSH CRUSH t t1 x x dt t t1 x F M dt Assuming barrier force is constant t xt and xt vt 1 0 M x, x, x Average force is proportional to the square of impact speed and inversely proportional to the crush depth 18

10 ENERGY IN A SINGLE CAR COLLISION EKINETIC 1 mv IF ALL KINETIC ENERGY IS ABSORBED AND NO REBOUND: E KINETIC E ABSORBED 1 Mv F d CRUSH 1 Mv M ad CRUSH a 1 v d CRUSH Average acceleration is proportional to square of speed and inversely proportional to crush 19 Two Vehicle Collision: Momentum equation shows mass ratio for colliding cars is dominant. Assuming no rebound and defining Collision Closing Speed (V CCS ) as difference between two vehicle velocities (v 1 & v ), and defining the final speed as v f then: m1v1 mv m1 m v f ( v1 vf v 1 ) and ( v vf v ) Can manipulate to get: m v1 m m 1 V CCS and m1 v V m m 1 CCS Using velocity change (Δv) as measure of severity, then relative risk is higher for the occupants of the lighter car than the heavier car. 0

11 Head Impact Model: spring mass system: 0 conditions at instant of contact: for 0 0 and : Acceleration depends on impact speed () and natural frequency ( ) 1 Summary: Injury Biomechanics is about transient injurious loading mechanical: bone fractures, tissue tears functional: eg. diffuse axonal injuries Equipment Design Pedestrians Sports impacts Animal tests Models Anthropometrics IRCOBI: International Research Council on Biomechanics of Injury Trinity Centre for Bioengineering Volunteer tests

12 Agenda Introduction Methods/ History/ Basic calculations Example: head injury Group work Summary Head injury- overview

13 Head injury AIS classification AIS: Abbreviated Injury Scale AIS code examples 1 nose fracture mild concussion without loss of consciousness 3 single contusion cerebellum basilar fracture maxilla fracture LeFort III 4 small epidural or subdural hematoma 5 large epidural or subdural hematoma, brain stem compression, DAI, rupture of bridging veins 6 Massive destruction of both cranium and brain Injury tolerance skull fracture force [kn] frontal lateral Nahum et al Hodgson et al Schneider et Nahum 197 Advani et al Allsop et al Nahum et al Schneider et Nahum 197 Advani et al. 197 Allsop et al occipital 1.5 Advani et al. 197

14 Injury mechanism TBI centripetal theory of concussion (CTC) OMMAYA AK, GENNARELLI TA: CEREBRAL CONCUSSION AND TRAUMATIC UNCONSCIOUSNESS. Brain (1974) 97,

15 Injury tolerance Wayne State-University: Cerebral Concussion Tolerance Curve translational, resultant acceleration impact on flat, rigid plane skull fracture as measure for brain injury correlation of acceleration and impact duration Injury tolerance Wayne State Tolerance Curve (WSTC)

16 Injury tolerance Wayne State Tolerance Curve (WSTC) irreversible reversible Injury tolerance rotational acceleration depends on brain mass

17 Injury tolerance rotational acceleration e.g. experiments with boxers: 3500 rad/s without injury; impact on ATD head: maximum 700 rad/s threshold dw/dt [rad/s] injury 1700 AIS 3000 AIS AIS AIS5, rupture of bridging veins Rotational head loading [Davidsson et al, 009]

18 Football 335 football players >> subconcussive and 57 concussive head impacts. [Rowson et al. 01] protection criterion Injury criteria Link between physical measure and injury probability injury criterion injury probability threshold value acceptable not acceptable injury criterion (physical measure) injury probability

19 Head injury criteria 1966: SI 1985: GAMBIT 000: HIP 197: HIC 1980: max. angular vel./ acc. 007: NSI 013 BrIC Criteria A3ms 3ms Criterion (a 3ms ) based on WSTC resultant head acceleration for a 3ms duration threshold: 80 g application: e.g. frontal impact (ECE-R 94) modified version (a5ms): 5ms duration, <= 150g, helmets (ECE-R )

20 Criteria - HIC HIC (Head Injury Criterion): based on WSTC threshold 1000 (FMVSS 08) (often lower values used in (automotive) industry),5 t 1 HIC max a( t) dt ( t t1) t t1 t1 a: acceleration [g], t: time [s] Criteria - HIC mild neurol. inj. severe neurol. inj. skull fracture subdural haemat. [Marjoux et al. 008]

21 Further criteria GAMBIT (Generalized Acceleration Model for Brain Injury Threshold, Newman 1980) threshold for 50% risk (0.5) or irreversible head injury: 1.0 a: transl. acc. [g] : rot. acc. [krad/s ] GAMBIT Further criteria BrIC (Brain Injury Criterion, Takhounts et al. 013) based on mathematical brain models,, :rotational velocities x-,y- and z-axis,, :critical values of angular velocity

22 Agenda Introduction Methods in Injury Biomechanics Example: head injury Group work Summary Head Impact Model: spring mass system: 0 conditions at instant of contact: for 0 0 and : Acceleration depends on impact speed () and natural frequency ( ) 44

23 Group exercise: get into groups of approximately 5 people Aim: Simple calculation for general insight into head impact. Case: helmeted vs un helmeted head impact on flat surface (eg motorcyclist on ground or occupant striking windscreen). Assume head impact speed is 5 m/s,.;.. Task: First guess and then use the spring mass model to estimate: 1. The peak & average head acceleration for no helmet.. The magnitude of peak force & time to reach to peak force 3. The benefit of a helmet for reducing head acceleration. 4. The angular acceleration of the head. Think about the assumptions made Trinity Centre for Bioengineering 45 Group exercise Aim: Discuss helmet design and how to assess its protective potential

24 Test A Group exercise Task: Discuss the following questions: What is the design concept of a helmet? Which injuries should a helmet address? Which biomechanical loading and which injury criteria are relevant in this context? Test B What is the effect of the two drop-test procedures shown here? [Halldin, 015] Contact Prof. Dr. Ciaran Simms, csimms@tcd.ie Prof. Dr. Kai-Uwe Schmitt, schmitt@ethz.ch