THE BIOMECHANICS OFTHORACIC TRAUMA IN FRONTAL

IMPACT

JM CavanaughBME, ECE, ME 7160

Introduction• The U.S. Centers for Disease Control (CDC) reported that

injuries to the torso are the second major cause of death byspecific body region next to the head and neck.

• During a motor vehicle impact, the thorax can contact variouscomponents of the automobile interior, including restraintsystems. Contacts include unrestrained driver or passenger withsteering wheel or instrument panel, and contact with active orpassive restraints, including three point lap/shoulder belts,two-point shoulder belts, knee bolsters, and air bags.

• Injury to the thorax commonly occurs in frontal and side impactsand in oblique directions intermediate to these two.

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Epidemiology• Nirula and Pintar analyzed the National Automotive Sampling

System (NASS) databases from 1993 to 2001 and the CrashInjury Research and Engineering Network (CIREN) databasesfrom 1996 to 2004.

• The incidence of severe chest injury (AIS 3 and greater) inNASS and CIREN were 5.5% and 33%, respectively.

• The steering wheel, door panel, armrest and seat were identifiedas contact points associated with an increased risk of severechest injury. The door panel and arm rest were consistently afrequent cause of severe injury.

Nirula R, Pintar FA (2008) Identification of vehicle components associated with severe thoracic injury in motor vehicle crashes: aCIREN and NASS analysis. Accident; analysis and prevention 40 (1):137-141. doi:10.1016/j.aap.2007.04.013

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Epidemiology• In a study of motor vehicle crashes in the UK, Morris et al. examined

vehicle crash injury data to determine to determine the relative injuryrisk of occupants of different age groups.

• For all occupants, the body region most prone to injury in frontalimpact crashes was the chest.

• Older and middle-aged occupants were at greater risk of sustainingMAIS3+ chest injuries.

• In frontal impacts, the majority of chest injuries were caused by therestraint system, whereas other interior vehicle componentsaccounted for only 4% of the injuries.

• A significant portion of middle-aged and older passengers werefemale. A seat-belt pre-tensioner was found to have a general effect ofreducing the risk of MAIS 3+ chest injury to all age groups.

Morris A, Welsh R (2003) Requirements for the crash protection of older vehicle passengers. Annu Proc Assoc Adv Automot Med47:165-180

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Outline of talk

• Epidemiology• Introduction to FMVSS 208• Chest anatomy• Chest injury mechanisms• Chest injury tolerance• Chest injury criteria adapted by NHTSA

and IIHS5

The following 5 slidesfrom Jeff Pike’s lecture

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New FMVSS 208 Injury Criteria

• I

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yCriteria

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208 Phase In

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ANATOMY OF THE THORAX

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AIS INJURY SCALING

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AIS: RIB FRACTURES

• AIS 1: 1 RIB FRACTURE• AIS 2: 2-3 RIB FRACTURES• AIS 3: > 3 ON ONE SIDE, =< 3 ON OTHER

SIDE• AIS 4: > 3 RIB FRACTURES ON BOTH SIDES;

ALSO FLAIL CHEST• AIS 5: BILATERAL FLAIL CHEST

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AIS: OTHER CHEST INJURY• AIS 1: skin abrasion, contusion or minor

laceration• AIS 2: major skin laceration, partial

thickness tear of bronchus• AIS 3: minor heart contusion, unilateral

lung contusion• AIS 4: severe heart contusion, intimal

tear of aorta• AIS 5: major aortic laceration, heart

perforation, ventricular heart rupture 20

Aortic Trauma

• In studies from the 1980s it was estimated that7500-8000 cases of blunt aortic injury occurredeach year (Jackson, 1984; Mattox, 1989).

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Prospective study at 50 trauma centers(Fabian et al, 1997)

• 274 cases over 2.5 years• 81% caused by MVAs

Of these, 72% head on, 24% side impact• Overall mortality was 31%• This does not include the 80-85% who are dead

at the scene.

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Various Aortic Injury MechanismsProposed

• Traction or shear forces between mobile pointsof the vessel and points of fixation.

• Direct compression over the vertebral column.• Sudden increases in intraluminal pressure.

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Prof. King-Hay YangHuman Thorax vs. FE Thorax

AortaPulmonary Trunk Heart Lung DiaphragmSVC25

Parametric Study

0 (6.5)30 (6.5)

60 (6.5)

90 (6.5 and 6.9)

120 (6.5)

150 (6.5)180 (6.5)

L

R

AP

Mass: 23 kg

Diameter: 150 mm

Edge Radius: 12 mm

Impactor

Impact angle (Velocity in m/s)

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FE Aorta

Isthmus

Root

Valve

Mid Descending

Level of Hiatus

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Hardy WN, Shah CS, Kopacz JM, Yang KH, Van Ee CA, Morgan R, Digges K(2006) Study of potential mechanisms of traumatic rupture of the aorta using

insitu experiments. Stapp Car Crash J 50:247-266

Hardy et al. investigated TRA mechanisms in PMHS in four quasi-static and onedynamic tests . The quasi-static tests included anterior, superior, and lateraldisplacement of the heart and aortic arch in the mediastinum, resulting in partial tears tocomplete transection. All injuries occurred within the peri-isthmic region.

The average failure load and stretch were 148 N and 30 % for the quasi-static tests.The results indicated that intraluminal pressure and whole-body acceleration are notrequired for TRA to occur and that the role of the ligamentum-arteriosum is likelylimited.

The studies indicated that tethering of the descending thoracic aorta by the parietalpleura was a principal aspect of this injury.

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Hardy WN, Shah CS, Mason MJ, Kopacz JM, Yang KH, King AI, Van Ee CA,Bishop JL, Banglmaier RF, Bey MJ, Morgan RM, Digges KH (2008) Mechanisms

of traumatic rupture of the aorta and associated peri-isthmic motion anddeformation. Stapp Car Crash J 52:233-265

Hardy et al. investigated the mechanisms of traumatic rupture of the aorta (TRA) ineight unembalmed PMHS which were inverted and tested in various dynamic bluntloading modes . Impacts were conducted using a 32-kg impactor with a 152-mm face.High-speed biplane x-rays of radiopaque markers on the aorta were used to visualizeaortic motion.

Clinically relevant TRA was observed in seven of the tests. Peak average longitudinalLagrangian strain was 0.644 and the average peak strain for all tests was 0.208 +/-0.216. Peak intraluminal pressure was 165 kPa.

Longitudinal stretch of the aorta was found to be a principal component of injurycausation. Stretch of the aorta was generated by thoracic deformation, which wasrequired for injury to occur. Atherosclerosis further promoted injury.

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INJURY CRITERIA

IN FRONTAL IMPACT

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Acceleration Criterion

• 60 g limit in FMVSS 208 for adults.

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Colonel John Stapp, MD

• Rocket sled acceleration studies in 1950s.• Human tolerance when belt restraints worn.• 40-45 g’s for 100 ms or less was tolerated.• 30 g’s reached at 1000 g/s were not tolerated.

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Eiband analyzed Stapp data

• Acceleration tolerance decreased asduration of exposure increased

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Mertz and Gadd (1971)

• Studied 16 free falls in a 40 year oldstunt man.

• 27-57 foot fall onto a thick mattress• Chest decel measured in 10 tests• Authors concluded that 50 g chest

acceleration for pulses < 100 ms waswithin tolerance for healthy adult males.

• 60 g with pulse < 100 ms wasrecommended as a tolerance limit untilfurther data became available. 36

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Indy car study (Melvin et al,1998)

• Showed that with tight wide double shoulderbelts, uniform body support and lack of intrusionthere was no serious torso injury in 202 Indyrace car crashes. The mean peak chassis decelwas 53 g with 7 cases above 100 g.

• The Melvin study throws into question the useof peak acceleration as a sole injury criterion.

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Critique

• Spinal acceleration is an indicator of overallseverity of impact but does not necessarilyreflect local impact conditions.

• Compression, rate of compression, and forcecan account for these.

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Force Criterion

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Unrestrained cadaver -sled tests

• Patrick (1965)• Gadd and Patrick (1968)• Patrick et al (1969)

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Data used in the developmentof the energy absorbing

steering column

• 3.3 kN hub load to the sternum• 8.8 kN distributed load to the

shoulder and chest• Resulted in only minor trauma

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Force Criterion - Belt Loading

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Bendjellal et al (1997) field study,belt loads

• Evaluated the 6 kN programmed restraintsystem (PRS)

• Only two cases of AIS 3• Recommended further reduction to 4 kN belt

loading

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Foret-Bruno (1998), belt loads

• 50% probability of AIS 3+ injury at 6.9 kN beltload

• 4 kN limit with a specially designed airbag couldprotect 95% of those in frontal impact from AIS+ chest injuries.

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Bag-belt loading (NHTSAstudies)

• Yoganandon et al (1993)• Morgan et al (1994)• Kallieris (1995)• Kuppa et al (1998)

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Compression Criterion

• 3 inch (76 mm) limit in old FMVSS 208based on work of Kroell, Nahum andViano.

• 2.5 inch (63 mm) limit in new FMVSS208 to limit probability of chest AIS to 4or less.

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Loading to mid-sternum(1970s)

• Kroell et al (1971,74)• Nahum et al (1970, 1971, 1975)• Stalnaker (1973)• Lobdell (1973)• Neathery (1974)

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Kroell corridors, 23.4 kgimpactor, mid sternum impact

• 4.02-5.23 m/s impacts• 6.71-7.38 m/s impacts

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Compression Criterion -Kroell et al

• AIS = -3.78 + 19.56 C• 30% Cmax (AIS 2): 69 mm• 40 % Cmax (AIS 4): 92 mm

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Compression Criterion

• 40% Cmax - 92 mm in 50th percentile• 40% Cmax - flail chest - Nahum et al (1975)• 40% Cmax - severe internal injury Viano (1978)

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Compression Criterion

• 32% Cmax - maintain rib cage integrity - 74 mm- Viano (1978)

• Old FMVSS 208 - 76 mm limit

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Development of new FMVSS 208

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Combined Thoracic Index(CTI)

• Reported by Kuppa et al (1998)• 71 human surrogate (cadaver) tests• Multi-center study

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Combined Thoracic Index(CTI)

• 3 point belt• 2 point belt/ knee bolster• 3 point belt/ air bag• air bag/ knee bolster• air bag/ lap belt

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Data used

• Chest bands at the 4th and 8th ribs• T1 triaxial accelerations

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Chest loading - bag-like andbelt-like

• Bag like: more uniform deformation ofthe chest.

• Belt like: more concentrateddeformation at the belt line.

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Univariate and mutlivariateanalyses

• 3 ms clip T1 resultant accel• Dmax• Vmax• Vcmax• Combinations of these responses

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Insurance Institute forHighway Safety

www.iihs.orgThe Insurance Institute for Highway Safety (IIHS) is an independent,nonprofit scientific and educational organization dedicated to reducing thelosses — deaths, injuries and property damage — from crashes on thenation's roads.

The Highway Loss Data Institute (HLDI) shares and supports this missionthrough scientific studies of insurance data representing the human andeconomic losses resulting from the ownership and operation of differenttypes of vehicles and by publishing insurance loss results by vehicle makeand model.

Both organizations are wholly supported by these auto insurers andinsurance associations.

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Viscous Criterion

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Viscous Criterion (VCmax)

• Lau and Viano (1981a, 1981b)• Viano and Lau (1983, 1985)• Lau and Viano (1986)

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Viscous Criterion (VCmax)

• Kroell et al (1981, 1986)• Rouhana (1986, 1987)

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Viscous Criterion (VCmax)

• Soft tissue injury is compression dependent andrate dependent

• VCmax is a measure of the energy dissipated bythe viscous elements of the chest (Viano andLau, 1985)

• Derivation (attached)

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Viano and Lau (1985)

• Analyzed 39 cadaver test performed by Kroelland others

• VCmax of 1.3 m/s, 50% prob of AIS 3+• VCmax of 1.0 m/s, 25% prob of AIS 3+

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Lau and Viano (SAE # 861882)

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Summary

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Peak chest or spineacceleration reflects the

overall severity of torso impactto the occupant

• Peak acceleration upper limit of 60 g tospine in frontal impact in old and newFMVSS 208

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Chest compression reflects localskeletal injury and underlying soft

tissue injury due to crush.• Cmax of 32-33% between chest wall and

spine was old FMVSS 208 criteria to avoidflail chest and severe chest injuries in sternalimpacts. (3 inch limit for 50th percentile male)

• Cmax of 27% to limit probability of AIS 4 to5% or less in new FMVSS 208. (2.5 inch limitfor 50th percentile male).

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The Viscous Responsereflects rate dependent softtissue injury and to some

extent, skeletal injury.• VCmax of 1.0 m/s to limit internal organ

injury to the chest and rate-dependentrib cage injury.

• Adapted by the IIHS but not in NHTSArulemaking

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Compression/ accelerationcombinations were proposedby the NHTSA but have not

been adopted

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THANK YOU

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