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The Effect of Body Size on Adult Human Rib Structural Properties

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Abstract

Rib fractures sustained during motor vehicle crashes are a common cause of increased mortality, and their causes within and between individuals is not fully understood. This study aimed to identify the effect of body height, body weight, and body mass index (BMI) on measured structural properties of human ribs. Two‐ hundred sixty one ribs from one‐hundred forty seven individuals were impacted in a dynamic (2.0 m/s) bending scenario representing a frontal thoracic impact. Linear regression revealed body height and weight each had a significant positive relationship with peak force and stiffness (p<0.001 for all), and weaker relationships with total energy (p=0.003 and 0.015, respectively), although explanatory power remained low for all relationships (R 2 =10‐12%). The introduction of age as an additional variable in multiple regressions increased the ability to predict structural properties: R 2 =33%, 17%, and 41% for peak force, stiffness and total energy, respectively. Body size parameters have a measurable effect on rib properties, but should be used with caution to understand variance in dynamic whole rib response because the source of the majority of variation remains unaccounted for in all models explored here. Future work will incorporate rib‐specific variables and explore the utility of these relationships on scaling and normalization techniques.
Abstract
Ribfracturessustainedduringmotorvehiclecrashesareacommoncauseofincreasedmortality,andtheir
causeswithinandbetweenindividualsisnotfullyunderstood.Thisstudyaimedtoidentifytheeffectofbody
height,bodyweight,andbodymassindex(BMI)onmeasuredstructuralpropertiesofhumanribs.Two
hundredsixtyoneribsfromonehundredfortysevenindividualswereimpactedinadynamic(2.0m/s)bending
scenariorepresentingafrontalthoracicimpact.Linearregressionrevealedbodyheightandweighteachhada
significantpositiverelationshipwithpeakforceandstiffness(p<0.001forall),andweakerrelationshipswith
totalenergy(p=0.003and0.015,respectively),althoughexplanatorypowerremainedlowforallrelationships
(R2=1012%).Theintroductionofageasanadditionalvariableinmultipleregressionsincreasedtheabilityto
predictstructuralproperties:R2=33%,17%,and41%forpeakforce,stiffnessandtotalenergy,respectively.
Bodysizeparametershaveameasurableeffectonribproperties,butshouldbeusedwithcautionto
understandvarianceindynamicwholeribresponsebecausethesourceofthemajorityofvariationremains
unaccountedforinallmodelsexploredhere.Futureworkwillincorporateribspecificvariablesandexplorethe
utilityoftheserelationshipsonscalingandnormalizationtechniques.
KeywordsEnergy,Force,Fracture,Stiffness,Thoraxinjury
I. INTRODUCTION
Thethorax,andespeciallyribs,arecommonlyinjuredinmotorvehiclecrashes(MVC)andthistrauma
representsasignificantthreattolife[1].Understandingribresponseiscrucialtoelucidatespecificmechanisms
offractureanddevelopaccuratetools(e.g.,anthropomorphictestdevicesandcomputationalmodels)designed
toassistinmeasuringthoracicresponseinanMVCandultimatelytomitigatefracturerisk.
Humanribstructuralpropertieshavepreviouslybeenreportedastohowtheyrelatetoindividual
characteristicssuchaschronologicalageandsexwithlimitedsuccess[2].However,theinfluenceofbodysize
onstructuralpropertiesisrelativelyunexplored,andtheseparametershavepotentialtoexplainadditional
variationinpropertiesthatageandsexalonedonot.Therehavebeenonlyafewstudiesexploringhumanbody
sizeanditseffectsondynamicribpropertiesrepresentativeofloadinginacarcrashscenario[2,3].
Furthermore, many researchers rely on scaling techniques which utilize height and weight to normalize
impactresponsedataobtainedfromexperimentaltesting[46]. Severalnormalizationtechniquesutilizeother
morecomplexanthropometricvariablesbeyondheightandweightbutstilloperateundertheassumptionthat
the human body behaves as a simple mechanical system and therefore the relationship between impact
responseandbodysizeparameterscanbeobtainedthroughlinearscalefactorratios[710].However,whereas
thesenormalizationtechniquesareeffectivewhenappliedtoresponsedatafromtestsubjectsthathavesmall
variationsinsize/weightaboutacentralpopulation(i.e.,approximate50thmaletestsubjectsnormalizedtoa
precise50thmaleanthropometry),thetechniquestendtoperformworsewhenadjustingonepopulationtoa
vastly different one (e.g., 50th male to child), likely due to anatomical variation and differences in skeletal
geometricormaterialproperties(tissuequality)thataretoocomplextobeaccountedforusinglinearscaling
ratios.Forexample,[11]exploredvariationinbothribcrosssectionalgeometryandthecombinationofcross
sectional and gross geometry and found these parameters could successfully predict impact response.
Furthermore,theauthorsnotedtheserelationshipswereindependentofbodysize(definedsimplyasweight
multiplied by bone length), indicating there is potential for using specific bone geometry to improve existing
scalingtechniques.
Nonetheless,itisimportanttofirstunderstandtheeffectsofsubjectlevelvariables,suchasbodyheightand
TheEffectofBodySizeonAdultHumanRibStructuralProperties
A.M.Agnew,M.M.Murach,E.Misicka,K.Moorhouse,J.H.BolteIV,Y.S.Kang
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weight,ontheresponseandfractureriskofcomponentsofthehumanbodywhichareatahighriskofinjury
duringmotorvehicleaccidentssuchasthehumanthorax.Forexample,[12]conductedafiniteelement(FE)
studyinwhichbodyweightandheightaswellasareamomentsofinertiaoftheribcageandribsalonewere
variedtoinvestigatetheireffectsontheresponseofthethorax.Althoughtheauthorsconcludedthatthearea
momentsofinertiawerethemostimportantparameters,theyalsofoundthatweightandheightwere
significantpredictorsofthemaximumforceandmaximumchestdeflection,respectively.
AstheseFEmodelsbecomeincreasinglyutilizedinthefieldofinjurybiomechanics,itisimportantthatthe
loadbearingcomponentofthehumanthorax,theribs,bescaledandmodeledappropriately.Severalstudies
havefocusedontherelationshipbetweenbodysizeandgrossribgeometryandfoundingeneralthatincreases
inbodysizeresultedinincreasesinribgeometry[1,3,13].However,theinfluenceofbodysizeonthestructural
responseofindividualribstodynamicloadingthatisrepresentativeofacarcrashscenariohasyettobe
investigated.Identifyingparametersthatcanbereadilyquantifiedsuchasbodysizethatareimportantfor
understandingfractureriskwillallowforimprovementstoscalingtechniquesandinjurycountermeasures.
Therefore,theobjectiveofthisstudyistoidentifytheeffectoftotalbodyheight,bodyweight,andbodymass
index(BMI)onribstructuralstiffness,peakforce,andtotalenergy.
II. METHODS
Sample
Twohundredsixtyonemidlevelribs(47)from147adultpostmortemhumansubjects(PMHS)were
analyzedinthissample,including67femalesand194males.RibswereacquiredethicallyviatheOhioState
University’sBodyDonationProgramandLifelineofOhio.Totalbodyheightandbodyweightwererecordedat
thetimeofdeath,andbodymassindex(BMI)wascalculatedas:[weight(kg)/height(m)2].BMIwasfurther
categorizedaccordingtotheWorldHealthOrganization(WHO)standards:<18.5=underweight,18.5
24.9=normalweight,25.029.9=overweight,and30.0+=obese[14].Heightwasnotrecordedforoneindividual
forwhichoneribwastested,sothetotalsamplesizeisreducedbyoneforheightandBMI.Table1includes
descriptivestatisticsforthesample.
TABLEI
SAMPLE
HeightWeightBMIAge
(cm)(kg)(kg/cm2)UnderweightNormalOverweightObese(yrs)
n(ribs)260261260231137945261
Mean174.776.625.116.621.827.034.556.6
SD9.518.65.81.61.731.44.6423.3
Min142.232.212.5‐
*18.5*25.0*>30.0*15
Max199.4136.048.4<18.5*24.9*29.9*‐
*108
*
WHOdefinedcorridors
ExperimentalTesting
Completeribsfromcostovertebraltocostochondraljunctionwereexcisedfromindividualsimmediatelynear
thetimeofdeath,wrappedinnormalsalinesoakedgauze,andstoredat‐20°C.Topreparefortesting,ribs
werethawedandcleanedofallexternalsofttissue,andtheendswerepottedin4x4x3cm3blocksofBondo®
BodyFiller(BondoCorporation,Atlanta,GA)insingleplaneorientation.Twostraingauges(CEA06062UW350,
VishayMicroMeasurement,Shelton,CT,)eachwereappliedtothepleuralandcutaneoussurfacesat30%and
60%ofthetotalcurvelength(Cv.Le)oftheribfromvertebraltosternalend.Spanlength(Sp.Le),alinear
measurementbetweenribends,wasalsodocumented.Ribswerekeptwellhydratedwithnormalsaline
throughoutpreparationandtesting.
Allribswereimpactedinadynamic(average2.0m/sand0.5strain/s)bendingscenariorepresentingafrontal
thoracicimpactwiththesternalribendtranslatedtowardsthevertebralend.Thiswasaccomplishedina
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custompendulum(54kg)fixture.Theexperimentalcoordinatesystemwasconstructedsuchthattheprimary
loadingaxiswasdefinedastheXaxis,withtheYaxisextendingverticallyaccordingtotheSAEJ211standard
(Fig.1).Inthisconfiguration,bendingwasrestrictedtotheXYplanealmostentirely.Displacementofthe
sternalribendwasmeasuredbyalinearstringpotentiometer(RayelcoP20A,AMETEK,Inc.Berwyn,PA)fixed
tothemovingplateofthefixture.Forcesandmomentswererecordedbya6axisloadcell(CRABIneckload
cell,IF954,Humanetics,Plymouth,MI)behindthefixedplate.
Fig.1.Bending
experimentshowinga
ribinthetestfixture
DataAnalysis
ForceanddisplacementdatawerefilteredusingaCFC180filter[15].Utilizingtheforcedisplacement(FD)
curvefromeachimpact,structuralstiffnesswascalculatedastheslopeof2080%ofthelinearelasticportion
[16],peakforcewasdefinedasthemaximumforceintheX(primary)loadingdirectionpriortofracture,and
totalenergywascalculatedastheareabeneaththeFDcurvefromtimezerototimeoffailure.Thestructural
propertiesoflinearstructuralstiffness(K),peakforce(Fpeak),andtotalenergy(Utot)aretreatedasdependent
variablesinthisstudy.Height,weight,andBMIweretreatedasindependentvariablesandwereallassessedas
continuousdatapointstoinvestigatepredictiverelationshipswithstructuralproperties.Thiswasaccomplished
usingbothunivariateandmultipleregressionmodels.Additionally,differencesinmeansofBMIclassifications
werecomparedusinganalysisofvariance(ANOVA)forallstructuralproperties.Anα
valueof<0.05was
consideredsignificantforallstatisticaltests.
III. RESULTS
DescriptivestatisticsforeachstructuralpropertyfortheentiresampleandwhendividedbyBMIcategory
canbefoundinTableII.UnivariateregressionresultsarepresentedinTableIIIandFigure2.Bodyheighthada
significantpositiverelationshipwithpeakforce(p<0.001),stiffness(p<0.001),andtotalenergy(p=0.003).Body
weighthadasignificantpositiverelationshipwithpeakforce(p<0.0001)andstiffness(p<0.0001),andaslightly
weakerrelationshipwithtotalenergy(p=0.015).Bodymassindex(BMI)assessedasdiscretevalueshada
significantpositiverelationshipwithpeakforce(p=0.005)andstiffness(p=0.003),butnottotalenergy
(p=0.200).Heightandweightpredictedpeakforceandstiffnessbest,explainingapproximately1012%of
varianceinthedata.
Sincepreviousanalysisonasubsamplehasshownagetohaveastatisticallysignificantinfluenceonthe
structuralpropertiespresentedhere[2],agewasincludedalongwithheightandweightasapredictorvariable
inmultipleregressionanalysis.Thesedatawerestandardizedandcenteredpriortoapplicationinthemodels,
andtheresultscanbefoundinTableIV.Inshort,age,heightandweighttogetherexplainedaround33%of
varianceinpeakforce,17%instiffness,and41%intotalenergy(p<0.0001forallthreemodels),butage
contributestoexplainingthemajorityofvarianceineachcase.
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TableII
DESCRIPTIVESTATISTICS
TotalSampleBMIClassification
UnderweightNormalOverweightObese
PeakForce(N)110.7
(±49.3)
86.2
(±35.6)
100.4
(±46.2)
130.5
(±53.0)
114.3
(±44.1)
Stiffness(N/mm)3.33
(±1.69)
2.48
(±1.25)
3.01
(±1.58)
3.85
(±1.60)
3.66
(±1.95)
TotalEnergy(N*mm)3714
(±2934)
2710
(±2551)
3535
(±2989)
4329
(±3169)
3598
(±2360)
TableIII
UNIVARIATEREGRESSIONRESULTS
PeakForceStiffnessTotalEnergy
R2(%)PvalueR2(%)PvalueR2(%)Pvalue
Age19.3<0.00017.4<0.000136.9<0.0001
Height12.9<0.00019.8<0.00013.40.003
Weight10.3<0.000110.5<0.00012.30.015
BMI3.00.0053.50.0030.60.200
Note:boldedvaluesarestatisticallysignificant
TableIV
MULTIPLEREGRESSIONRESULTS
PeakForceStiffnessTotalEnergy
Contribution
(%)pvalueContribution
(%)pvalueContribution
(%)pvalue
Age18.4<0.00016.49<0.000137.19<0.0001
Height7.55<0.00013.900.0242.140.002
Weight6.070.0045.200.0020.230.972
Age*Height0.060.5400.190.2990.650.099
Age*Weight1.230.0441.070.1840.100.092
Height*Weight0.060.6540.040.8540.370.153
Age*Height*Weight0.000.9920.440.2560.550.133
Total R2=33.36<0.0001R2=17.33<0.0001R2=41.22<0.0001
Note:boldedvaluesarestatisticallysignificant
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PeakForceStiffnessTotalEnergy
200190180170160150140
300
250
200
150
100
50
0
Heigh t (cm)
Peak Force (N)
200190180170160150140
9
8
7
6
5
4
3
2
1
0
Heigh t (c m)
Stiffness (N/mm)
200190180170160150140
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
Heigh t (c m)
Ene rgy (N*mm)
1501251007550
300
250
200
150
100
50
0
Weight (kg)
Peak Force ( N)
1501251007550
9
8
7
6
5
4
3
2
1
0
Weight (kg)
St iff nes s ( N/mm)
1501251007550
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
Weight (kg)
Ene rg y (N* mm)
5040302010
300
250
200
150
100
50
0
Body Mass Index (BMI)
Peak Force (N)
5040302010
9
8
7
6
5
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3
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1
0
Body Mass Index (BMI)
Stiffness (N/mm)
5040302010
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
Body Mass Index (BMI)
Ene rgy ( N*mm)
Fig.2.Scatterplotsshowingindependentrelationshipsofpeakforce(left),stiffness(center),andtotalenergy(right)withheight
(top),weight(middle),andBMI(bottom)
WhenBMIwasassessedcategorically,acleartrendforallstructuralpropertiesemergedofincreasingwith
meanBMIfromtheunderweighttonormaltooverweightcategoriesandthendecreasingfromtheoverweight
toobesecategories(Fig.3).ANOVAresultsrevealsignificantdifferencesinBMIgroups(p<0.0001)forpeak
forceandstiffness,whilenostatisticallysignificantdifferenceswerefoundbetweengroupsfortotalenergy
(p=0.083)despitethesamedistincttrend.Toidentifywherethedifferencesliebetweengroups,posthocTukey
testswereperformed.Nosignificantdifferenceswerefoundbetweenunderweightandnormalgroupsor
betweenoverweightandobesegroups,butadifferencewasfoundbetweennormalandoverweightgroupsfor
peakforceandstiffness.
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ObeseOverweightNormalUnderweight
150
140
130
120
110
100
90
80
70
Body Mass Index Classification
Peak Force (N)
95% CI for the Mean
ObeseOverweightNormalUnderweight
5000
4500
4000
3500
3000
2500
2000
1500
Body Mass Index Classification
Total Energy (N*mm)
95% CI for the Mean
Fig.3.Intervalplotsshowingmeanand95%confidenceintervalsofeachBMIclassificationforPeakForce(left)
andTotalEnergy(right).Stiffnessresultsarenotshown,butthetrendappearssimilarwithanincreasein
structuralpropertiesaccompanyinganincreaseinBMI,exceptforintheobesecategory.
IV. DISCUSSION
Thisresearchfoundthatbodysizeparametersplayaroleinthedeterminationofindividualdynamicrib
responseinafrontalloadingscenario.Fewotherstudieshaveexploredtheeffectsofbodysizeonribor
thoracicproperties,althoughtherehasbeenresearchconductedtoexploretherangesofvariationseeninrib
orthoraxgeometryrelatedtosizeparameters.Forexample,[13]usedComputedTomography(CT)datato
developastatisticalribcagegeometrymodelandfoundasignificantinfluenceofheight,BMI,andsex,in
additiontoaweakereffectofage.Similarly,[1]foundalargereffectofBMIthanageonribangle.Despite
thesefindings,therehavebeenfewattemptstolinkthoracicgeometrychangeswithskeletalmechanical
properties.
Kalraetal[17]performed3pointbendingonadultribsegmentsataquasistaticrateandfoundnoheightor
weighteffectonequivalentmeasuresofmomentandstiffness.Sincethisexperimentwaspointloadingona
smallsectionofribanddidnottaketheoverallsizeoftheboneintoaccount,itisreasonabletoconcludethat
theribcrosssection(presumablyprovidingthemostresistancetobendinginthistest)wouldbelessinfluenced
bytotalbodysize.Althoughinasimilarquasistatic3pointbendingribtestas[17],asignificantrelationship
betweenmomentandheightinchildrenwasfound[18].Tofurtherexploretheeffectoftotalribsizeon
properties,aposthocanalysisonthesampleinthecurrentstudywasconductedutilizingthefollowing
measuresofribsize:totallengthalongthecurvatureoftherib(Cv.Le)andminimumlinearlengthbetweenthe
vertebralandsternalribends(Sp.Le).Asignificant(p<0.0001)correlationwasfoundbetweentotalribsize,
curvelength(Cv.Le)andspanlength(Sp.Le),withbodyheight(Pearson’sr=0.447and0.319,respectively),but
notwithbodyweight(p=0.624and0.185,respectively).Thisisconsistentwithpreviousstudieswhichfoundrib
curvelengthtobeassociatedwithtotalbodyheight[3,19].However,inourstudyanadditionalposthoc
analysisutilizingalinearregressionrevealsnorelationshipbetweenCv.LeorSp.Leandanyofthestructural
properties,suggestingmoreworkneedstobedoneinthisarea.Itisanticipatedthatribcrosssectional
geometryormicrostructuralvariableswillhelpprovideadditionalunderstanding.Forinstance,inasimulation
study,[12]foundbodyheightandweighttoinfluencethoracicinjuries,butthatribspecificmeasurements(e.g.,
areamomentofinertia)couldbetteraccountforoverallthoracicresponsesandinjuries.
Interestingly,[11]foundthatribcrosssectionalgeometry(totalcrosssectionalarea,corticalbonearea,and
sectionmodulus)aswellthecombinationofcrosssectionalandgrossgeometry(robusticityandwholebone
strengthindex)wereallsignificantpredictorsofmeasuredpeakforceandstiffnessandcanaccountforasmuch
as75%ofthevariationseeninthesestructuralproperties.Althoughskeletalmorphology(i.e.grossgeometry)
isrelatedtobodysize,thecrosssectionalgeometryisdependentonavarietyoffactorssuchasspecificloading
environmentandgenetics[20],andthereforemayprovideawaytoaccountforthesedifferencesbetween
individuals.Thisworkprovidespreliminaryevidencethatinclusionofskeletalgeometrymayimproveexisting
scalingtechniquesandallowforpredictableadjustmentstovariouspopulations(pediatricorelderly),however
moreresearchneedstobedoneinthisarea.
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ThetrendinstructuralpropertiesacrossdiscreteBMIclassificationswhereeachpropertyincreasesfrom
underweighttonormalweight,continuestoincreaseandpeaksintheoverweightcategory,butthenisreduced
inobesity,presentsaninterestingdiscussiontopic.Thedescribedpattern,whichisobservableforallthree
structuralproperties,suggestsafunctionaladvantageintheformofhigherresistancetobendingasmorebody
sizeisgained(tallerandheavier),untilathresholdwherethesebenefitsarethenoutweighedbythedeleterious
effectsofobesity.Theeffectofobesity(i.e.,excessiveadiposetissue)onfractureriskiswidelydebatedinthe
literature[21].However,thereisevidencethatthetrendobservedinthecurrentstudyisrepresentativeof
fractureriskvariationsacrossBMIclassificationsseenintheclinicalenvironment[22]suggestingthatadvanced
obesityhasnegativeimpactsonbonequality[23].Theseresultsshouldbeapproachedwithcautionasthereis
greatvariationintheBMIdataasseeninFigure2,andthereareunequalnumbersofsubjectsineachBMI
category.
Displacementwasnotincludedasadependentvariableinthisstudy,becausepotentialrelationshipswith
bodysizemaybeconfoundedbyitstypicalpresentationasavariablenormalizedbyribspanlength[2,16].This
complicatedinteractionwillbeexploredinfutureworkinconjunctionwiththoracicanthropometry(e.g.,chest
depth)tobetterunderstandhowthesizeandshapeofthethorax,isinfluencedbyindividualribresponse.
Additionally,itwillbecrucialtolearnthespecificrolethatindividualribresponseplaysinoverallthoracic
response.Thisaddedlayerofcomplexitywillaidourunderstandingofthoracicinjuryrisk,asthisisbasedmostly
onchestcompression.
Sexwasnotincludedinthemodelspresentedhere.Pastworkonasubsetofthissamplefoundsexto
influencepeakforce,stiffness,andtotalenergy[2].However,thesedifferencesmayhavebeenduetosexual
dimorphism,inwhichcaseincludingsexhereinwouldconfoundthemodelusingbodysizeparameters.Infact,a
posthocanalysisrevealedsignificantdifferencesinheightandweightbetweenmalesandfemales(studentt
test,p<0.0001forboth),supportingtheuseofapooledsampleforthispreliminarywork.Futureresearchaims
toutilizeamorecomplexstatisticalmodelabletoteaseoutsexdifferentiatedstructuralpropertieswhile
controllingforbodysize.Furthermore,apossiblesamplingbiascouldbeinfluencingresultsasnotallagesor
bodysizesareequallyrepresentedinthesample.
Itwasassumedherethatlinearregressionmodelswereappropriateforanalysisofthisdataset.While
previousribdataanalysishasutilizeddifferentandmorecomplexmodelingtechniques[2,16],thoseresultsare
veryconsistentwithsimpleregressionmodelsasprovidedhere,andthereforetheanalysiswassimplifiedfor
thispreliminarywork.Futurestudiescanfurtherexploremorecomplicatedmodelsandpossiblynonlinearfits.
V. CONCLUSIONS
Bodysizeparametershaveaneffectonstructuralpropertiesofhumanribs,butevenwhenincludedwithage,
predictivemodelsstilldonotexplainthemajorityofvariationinpeakforce,stiffness,ortotalenergy.Future
workwillinvestigatetherelationshipbetweenthoracicanthropometryandribsizeandproperties.Additionally,
morebiologicallyrelevantvariablesrelatedtothespecificgeometry,crosssectionalgeometry,and
microstructureofribswillbeexploredaspredictorsofribstructuralresponsetoloading.Thesedatacan
ultimatelybeadvantageoustoaidinimprovingsizebasedscalingtechniques.
VI. ACKNOWLEDGEMENT
ThankyoutotheNationalHighwayTrafficSafetyAdministration(NHTSA)forfundingthiswork.Allopinions
expressedwithinthismanuscriptaresolelythoseoftheauthorsanddonotrepresenttheviewsofthesponsor.
WeareindebtedtotheanatomicaldonorswhomadethisresearchpossibleviaTheOhioStateUniversity’sBody
DonorProgramandLifelineofOhio.ThankyoualsotostudentsandstaffoftheInjuryBiomechanicsResearch
CenterincludingArriannaWillis,JulieBing,RakshitRamachandra,DavidStark,JonBlank,RandeeHunter,and
AksharaSreedhar.
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... Computational FE thorax models have been developed and extensively utilized in the last two decades. 1,10,24,35 Based on field data analysis, age is a crucial factor related to thorax injury risk. 5,30 Consequently, age-dependent FE thorax models are commonly utilized, 35 but their accuracy is dependent on proper thoracic geometry, as well as rib material and structural properties with respect to age. ...
... 21,35 However, rib mechanical properties (material and structural) considered in conjunction with body sizes as inputs for model validation, especially for small females and large males, are rarely explored. 1 Biomechanical targets used to validate FE thorax models in frontal impact scenarios were developed using rib coupon and 3-point bending data, 15,16 whole rib structural data, 7 isolated thorax impact data, 39 hub impact data, 22 bench top impact data, 18 and full sled test data. 36 Although biomechanical data from whole body PMHS tests are critical to improve overall thoracic responses and injury prediction (e.g., rib fractures) of FE thorax models, biomechanical targets constructed from components, such as rib material and structural tests, should also be accounted for in the model validation processes to ensure accuracy across the anatomical hierarchy. ...
... A few studies have explored body size and its relationship with individual rib responses. 1,2 Agnew et al. 1,2 found only very weak positive trends between body size parameters and rib properties, suggesting a reduced effect of bone-specific changes on whole body injury results. Similarly, when different body sizes for the male ribs (mid-size vs. large male) from middle to older age groups were considered in this study, no differences in force and % displacement were found. ...
Article
Thorax injuries mainly due to rib fractures have been associated with high rates of morbidity and mortality in motor vehicle crashes. Thoracic biomechanics has been studied extensively, but there are no robust biomechanical response targets for ribs that consider age, sex, body size, and vulnerability factors. The objective of this study was to generate biomechanical targets for human rib response with respect to age, sex, and body size. Two-hundred sixty-one ribs from 171 individuals were dynamically loaded to failure in anterior–posterior bending. Force and displacement at the time of fracture in young adults were greater than in older adults (p < 0.0001). Sex differences were found in those over 40 years old (p < 0.0001). Fracture force from 5th percentile female ribs was lower than 50th and 95th male (p < 0.005). Vulnerable ribs were successfully identified by examining the percentile of both force and displacement at the time of fracture in the proposed samples. The biomechanical targets generated in this study will have useful applications to computational thorax and rib models to aid in injury prevention measures.
... Although extensive whole thoracic experiments have been conducted, individual rib tests have been conducted at both quasistatic and dynamic rates on considerably larger samples [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. ...
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The objective of this study was to develop an analytical model using strain-force relationships from individual rib and eviscerated thorax impacts to predict bony thoracic response. Experimental eviscerated thorax forces were assumed to have two distinct responses: an initial inertial response and subsequently, the main response. A second order mass-spring-damper model was used to characterize the initial inertial response of eviscerated thorax force using impactor kinematics. For the main response, equivalent strains in rib levels 4-7 were mapped at each time point and a strain-based summed force model was constructed using individual rib tests and the same ribs in the eviscerated thorax test. A piecewise approach was developed to join the two components of the curve and solve for mass, damping, stiffness parameters in the initial response, transition point, and scale factor of the strain-based summed force model. The final piecewise model was compared to the overall experimental eviscerated thorax forces for each PMHS (n=5) and resulted in R2 values of 0.87-0.96. A bootstrapping approach was utilized to validate the model. Final model predictions for the validation subjects were compared with the corridors constructed for the eviscerated thorax tests. BRSS values were approximately 0.71 indicating that this approach can predict eviscerated responses within one standard deviation from the mean response. This model can be expanded to other tissue states by quantifying soft tissue and visceral contributions, therefore successfully establishing a link between individual rib tests and whole thoracic response.
... Comparing rib levels across tissue states, the peak strain magnitudes were highly variable indicating that all subjects even in the same demographic may not have the same thorax behavior. Previous component level testing of individual ribs demonstrated that age, sex, and body size did not accurately predict rib response and that other factors need to be explored to explain the variation in structural properties [10,27]. Similarly, the variation in strain magnitudes seen across rib levels of thoraces in the five 50 th percentile male subjects likely follow the same complexity. ...
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Due to high-rate loads placed on the torso during motor vehicle crashes, the human thorax is commonly injured, and resulting rib fractures are linked to fatalities. The goal of this study was to explore the variation in strain modes, magnitudes, and rates of rib levels 3-8 in a dynamic, distributed loading scenario in a series of hierarchical tissue states of 50 th percentile males. Strain modes varied by rib level where superior level ribs demonstrated tension on the cutaneous surface, and inferior ribs, rib 8 specifically, experienced compression. Peak strain and peak strain rates varied between rib levels at the anterior and posterior locations (p<0.0001). Intact thoraces generally demonstrated higher peak strain values across rib levels and eviscerated thoraces exhibited higher peak strain rates across rib levels. Rib levels 4-6 experienced higher peak strain than other levels at the anterior location while level 8 experienced higher peak strains at the posterior location. After whole thorax testing, ribs 4-7 were removed and tested to failure in anterior-posterior bending. Peak strains from individual rib testing did not vary between rib levels 4-7 at anterior or posterior locations (p=0.17 and p=0.79, respectively). This study revealed local deformation patterns across ribs while maintaining the structural integrity of the thorax in distributed loading as well as component testing to failure across rib levels. The results from this study can be used to further understand rib connections during loading events and help to define accurate rib-specific properties to improve the biofidelity of computational human body models.
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The objective of this study is to evaluate different rib bone surrogates by comparing them to specific, male PMHS data from Charpail et al. (2005), Kindig (2009), Agnew et al. (2018) and Kang et al. (2020). The Fraunhofer EMI 5 th male rib surrogates were fabricated from Scalmalloy® (AlMg4.5Sc0.7Zr0.3) using additive manufacturing. The CTS PRIMUS breakable dummy from Crashtest-Service-Dummy-Solution GmbH is already being used as an anthropomorphic test device (ATD) in various areas. Its cast 5 th left rib, constructed from a mixture of epoxy resin and aluminium powder, was also included in this study. A test setting based on the setup of Charpail et al. (2005) was developed. The specimens were dynamically (500 mm/s) loaded to failure in a bending scenario imitating a frontal thoracic impact. During the tests, not only force and displacement were measured, but also the strain distribution using 3D digital image correlation (3D-DIC) and compared to PMHS data of the previously mentioned studies. Both rib surrogates show strong deviations from the PMHS characteristic values. Nevertheless, there are also common characteristics in key variables to certain age groups of the PMHS data. The differences shown are an important contribution to the further development and improvement of both surrogates.
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Thoracic injuries are frequently observed in motor vehicle crashes, and rib fractures are the most common of those injuries. Thoracic response targets have previously been developed from data obtained from post-mortem human subject (PMHS) tests in frontal loading conditions, most commonly of mid-size males. Traditional scaling methods are employed to identify differences in thoracic response for various demographic groups, but it is often unknown if these applications are appropriate, especially considering the limited number of tested PMHS from which those scaling factors originate. Therefore, the objective of this study was to establish a new scaling approach for generating age-, sex-, and body size-dependent thoracic responses utilizing structural properties of human ribs from direct testing of various demographics. One-hundred forty-seven human ribs (140 adult; 7 pediatric) from 132 individuals (76 male; 52 female; 4 pediatric) ranging in age from 6 to 99 years were included in this study. Ribs were tested at 2 m/s to failure in a frontal impact scenario. Force and displacement for individual ribs were used to develop new scaling factors, with a traditional mid-size biomechanical target as a baseline response. This novel use of a large, varied dataset of dynamic whole rib responses offers vast possibilities to utilize existing biomechanical data in creative ways to reduce thoracic injuries in diverse vehicle occupants.
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The human thorax is commonly injured in motor vehicle crashes, and despite advancements in occupant safety rib fractures are highly prevalent. The objective of this study was to quantify the ability of gross and cross-sectional geometry, separately and in combination, to explain variation of human rib structural properties. One hundred and twenty-two whole mid-level ribs from 76 fresh post-mortem human subjects were tested in a dynamic frontal impact scenario. Structural properties (peak force and stiffness) were successfully predicted (p < 0.001) by rib cross-sectional geometry obtained via direct histological imaging (total area, cortical area, and section modulus) and were improved further when utilizing a combination of cross-sectional and gross geometry (robusticity, whole bone strength index). Additionally, preliminary application of a novel, adaptive thresholding technique, allowed for total area and robusticity to be measured on a subsample of standard clinical CT scans with varied success. These results can be used to understand variation in individual rib response to frontal loading as well as identify important geometric parameters, which could ultimately improve injury criteria as well as the biofidelity of anthropomorphic test devices (ATDs) and finite element (FE) models of the human thorax.
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Thoracic injuries from motor vehicle crashes (MVCs) are common in children and the elderly and are associated with a high rate of mortality for both groups. Rib fractures, in particular, are linked to high mortality rates which increase with the number of fractures sustained. Anthropomorphic test devices (ATDs) and computational models have been developed to improve vehicle safety, however these tools are constructed based on limited physical datasets. To-date, no study has explored variation of rib structural properties across the entire age spectrum with data obtained using the same experimental methodology to allow for comparison. One-hundred eighty-four ribs from 93 post mortem human subjects (PMHS) (70 male, 23 female; ages 4 to 99) were subjected to dynamic bending tests simulating a frontal impact to the thorax. Structural mechanical properties were calculated and a multi-level statistical model quantified the sample variance as explained by age and sex. Displacement (δX), peak force (Fpeak), linear structural stiffness (K), energy absorption to fracture (Utot), and plastic properties including post-yield energy absorption (UPl), plastic displacement (δPl), and the ratio of elastic to secant stiffness (K-ratio) all showed negative relationships with age, while only Fpeak, K, and Utot were dependent on sex. Despite these relationships being statistically significant, only 7 – 39% of variance is explained by age and only 3 – 17% of variance is explained by sex. This demonstrates that variability in bone properties is more complex than simply chronological age- and sex-dependence and should be explored in the context of biological mechanisms instead.
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In the elderly population, rib fracture is one of the most common injuries sustained in motor vehicle crashes. The current study was conducted to predict the biomechanical fracture responses of ribs with respect to age, gender, height, weight and percentage of ash content. Three-point bending experiments were conducted on 278 isolated rib samples extracted from 82 cadaver specimens (53 males and 29 females between the ages of 21 and 87 years) for 6th and 7th levels of ribs. Statistical analyses were carried out to identify differences based on age and gender. It was found that, in comparison to males, females had significantly lower values for maximum bending moments, slopes of bending moment-angle curves, and average cortical-bone thickness (p < 0.05). Samples of ribs taken from elderly specimens failed at lower values of fracture moments than those from younger specimens, and had lower slopes of bending moment-angle curves, both in males and females (p < 0.05). The generalized estimated equations were developed to predict the values of biomechanical response and average cortical thickness based on age, gender, height and weight of individual specimens. Results from the current study illustrate that biomechanical responses and rib cortical thicknesses are functions of age, gender, height and weight. However, the current study is limited to a quasi-static loading scheme, which is different from real crash conditions. Hence, rib-material properties, which are dependent on strain rate, and are needed for wholebody finite element models representing different populations, still require more research.
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In this study, we developed a statistical rib cage geometry model accounting for variations by age, sex, stature and body mass index (BMI). Thorax CT scans were obtained from 89 subjects approximately evenly distributed among 8 age groups and both sexes. Threshold-based CT image segmentation was performed to extract the rib geometries, and a total of 464 landmarks on the left side of each subject׳s ribcage were collected to describe the size and shape of the rib cage as well as the cross-sectional geometry of each rib. Principal component analysis and multivariate regression analysis were conducted to predict rib cage geometry as a function of age, sex, stature, and BMI, all of which showed strong effects on rib cage geometry. Except for BMI, all parameters also showed significant effects on rib cross-sectional area using a linear mixed model. This statistical rib cage geometry model can serve as a geometric basis for developing a parametric human thorax finite element model for quantifying effects from different human attributes on thoracic injury risks.
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