Biomechanics of Bone.ppt

voodoo stuff

1. Biomechanics of Bone

2. Characteristics
•Purposeoftheskeletalsystem:toprotectinternalorgans,
providerigidkinematiclinksandmuscleattachmentsites,and
facilitatemuscleactionandbodymovement
•Bone:
•hasuniquestructureandmechanicalpropertiesthatallowittocarry
outtheseroles.
•amongthebody'shardeststructures;onlydentinandenamelinthe
teethareharder.
•Ahighlyvasculartissue,anexcellentcapacityforself-repairandcan
alteritspropertiesandconfigurationinresponsetochangesin
mechanicaldemand.
–changesinbonedensityafterperiodsofdisuseandofgreatly
increaseduse
–changesinboneshapeduringfracturehealingandaftercertain
operations
–adaptstothemechanicaldemandsplacedonit.

3. Bone Composition and Structure
•Normalhumanboneiscomposedof:
•Mineralorinorganicportion:
•consistsprimarilyofcalciumandphosphate,
mainlyintheformofsmallcrystalsresembling
synthetichydroxyapatitecrystalswiththe
compositionCa
10(PO
4)
6(OH)
2.
•accountsfor60to70%ofitsdryweight
•Water:5-8%
•Organicmatrix:remainderofthetissue

4. Organic Components
(e.g. collagen)
Inorganic Components
(e.g., calcium and phosphate)
65-70%
(dry wt) H
2O
(25-30%)
one of the
body’s hardest
structures
viscoelastic
ductile
brittle
Biomechanical Characteristics of Bone -Bone Tissue
25-30%
(dry wt)

5. Composition
Inorganicphase:
•Ceramiccrystalline–impureformofcalcium
phosphatereferredadhydroxyapatite
•Phosphatesareimpure-containsK,Mg,strontium,
Na,carbonate(inplaceofCa+ions)andchlorideor
fluoride(inplaceofhydroxyions)
OrganicPhase:
•TypeICollagen(90%bywtg)
•Minorcollagens(typeIIIandVI)
•Non-collagenproteins-Osteocalcin,Osteonectin,
Osteoppontinandbonesialoproteins.

6. Structure
•Collagen molecules arrange in parallel with
each other with gap or hole zone (40nm)
•Mineralization begins in the gap zone resulting
mineralized fibril
•Collagen fibrils –20 to 40 nm in diameter
•There are about 200 to 800 collagen
molecules in a cross section

7. Bone structure
•Composition:acellularcomponent+anextracellularmatrix.
•Thecellularcomponentismadeof
•Osteoblasts:bone-formingcells,
•Osteoclasts:bone-destroyingcells,and
•Osteocytes:bone-maintainingcellswhichareinactive
osteoblaststrappedintheextracellularmatrix.
•Extracellularmatrix:
•responsibleforthemechanicalstrengthofthebonetissue
•formedbyanorganicandamineralphase.
•organicphase:mainlycomposedofcollagenfibres
•mineralphase:composedofhydroxyapatitecrystals.
•aliquidcomponentisalsopresent.

8. Five types of bones in the human body
•Longbones:
–characterizedbyashaft,thediaphysis,thatismuchgreater
inlengththanwidth.
–comprisedmostlyofcompactboneandlesseramountsof
marrow,whichislocatedwithinthemedullarycavity,and
spongybone.
–Examples:mostbonesofthelimbs,includingthoseofthe
fingersandtoes.Exceptionsarebonesofthewrist,ankle
andkneecap
•Shortbones
–roughlycube-shaped,andhaveonlyathinlayerofcompact
bonesurroundingaspongyinterior.
–Examples:bonesofthewristand,asarethesesamoid
bones.

9. Five types of bones in the human body
•Flatbones
–thinandgenerallycurved,withtwoparallellayersofcompactbones
sandwichingalayerofspongybone.
–Examples:Mostofthebonesoftheskull,asisthesternum.
•Irregularbones
–donotfitintotheabovecategories.
–consistofthinlayersofcompactbonesurroundingaspongyinterior.
–theirshapesareirregularandcomplicated.
–Examples:bonesofthespineandhipsareirregularbones.
•Sesamoidbones:
–bonesembeddedintendons.
–Sincetheyacttoholdthetendonfurtherawayfromthejoint,theangle
ofthetendonisincreasedandthustheforceofthemuscleisincreased.
–Examples:thepatellaandthepisiform

10. Long Bones

11. Two main types of bone
Longitudinal section of human femur. The direction of principal stresses are shown in
the scheme on the right

12. Characteristics
•Osseoustissue:
•primarytissueofbone
•relativelyhardandlightweightcompositematerial,formed
mostlyofcalciumphosphateinthechemicalarrangement
termedcalciumhydroxylapatite
•givesbonestheirrigidity.
•Bone:
•relativelyhighcompressivestrengthbutpoortensile
strength(resistspushingforceswell,butnotpulling
forces).
•essentiallybrittle,buthasasignificantdegreeofelasticity,
contributedchieflybycollagen.
•consistoflivingcellsembeddedinthemineralizedorganic
matrixthatmakesuptheosseoustissue.

13. Compact bone or (Cortical bone)
•Thehardouterlayerofbonesiscomposedof
compactbonetissue,so-calledduetoits
minimalgapsandspaces.
•Thistissuegivesbonestheirsmooth,white,
andsolidappearance,andaccountsfor80%
ofthetotalbonemassofanadultskeleton.
•Compactbonemayalsobereferredtoas
densebone.

14. Trabecular bone
•Itisanopencellporousnetworkalsocalled
cancellousorspongybonefillingtheinteriorof
theorgan
•Itiscomposedofanetworkofrod-andplate-
likeelementsthatmaketheoverallorgan
lighterandallowingroomforbloodvesselsand
marrow.
•Itaccountsfortheremaining20%oftotalbone
mass,buthasnearlytentimesthesurfacearea
ofcompactbone.

15. Cortical and Trabecular Bone

16. Sectional View of the Femur Head
Sectionthroughtheheadofthe
femur,showingtheouterlayer
ofcompactboneandthesoft
centeroftrabecularbone,filled
withredbonemarrowanda
spotofyellowbonemarrow
(whitebar=1centimeter)

17. Cancellous bone
Illustrationofasection
throughlongbone,with
spongyboneinitscenter.
Lightmicrographof
cancellousbone,stained
withhematoxylinand
eosin,showingbone
trabeculae(stainedpink)
andmarrowtissue(stained
blue).

18. Lamellar structure of osteons in
cortical bone
Cortical bone is the more dense tissue usually found on the surface of bones. It is
organised in cylindrical shaped elements called osteons composed of concentric
lamellae
Lamellar structure of osteons in cortical bone

19. Trabecular bone
Trabecular structures in the L1 vertebra
of a 24 year old
Trabecular structures in the calcaneus
of a 24 year old
Trabecularboneisquiteporousanditisorganizedintrabeculesoriented
accordingtothedirectionofthephysiologicalload.Theconfigurationofthe
trabecularstructuresishighlyvariableanditdependsontheanatomicalsite.

20. Cross-section through a region of
compact bone
This image scanned from a textbook, Basic Medical Anatomy, by Alexander Spence
A cross-section through a region of compact bone, you will see rings of Haversian
systems, each with a hole, the canal, in the center

24. Distinguish between Cortical &
Trabecular bone
Porosity
•C.B –less than 30%
–Volume fraction Vf> 0.70 (Vf= 1-P)
–Vfis defined as the volume of actual bone tissue to bulk
volume of the specimen
–Porosity of adult C.B can vary
»5% at age 20
»30% at age above 80
•T.B –porosity of adult is 70% in femoral neck
upto95% in elderly spine.

26. Cont..
Other common measures of bone density
–Tissuedensity(ρ
tissisdefinedasratioofmassto
volumeofactualbonetissue)-varieslittleinadult
about2.0g/cm3
–Apparentdensity(ρ
appisdefinedasratioofthe
massofbonetissuetothebulkvolumeof
specimen,includingthevolumeassociatedwith
vascularchannelsandhighlevelporosity)
Volume fraction, tissue density and apparent
density are related by
ρ
app = ρ
tiss. Vf

28. Cont..
•ρ
app of hydrated C.B is 1.85 g/cm3 –does not
vary across anatomical sites or specimen
•ρ
app of T.B depends much on anatomical sites
–Low as 0.10 g/cm3 for spine
–0.3 g/cm3 for human tibia
–0.60 g/cm3 for load bearing portions of proximal
femur
After skeletal maturity (age 25 to 30)
–T.B density decreases with age at 6% /decade.

29. The effect of aging
Trabecular structures of vertebrae in
a 36 year old woman
Trabecular structures of vertebrae
in a 74 year old woman

30. Cont..
Spatially-T.B has high porosity. It forms network
of interconnected pores filled with bone marrow
–It form irregular lattice of small rods and plates-
trabeculae
–Thickness –100-300 micrometer
–Spatial arrangement varies across anatomic site
and with age
–As age increases Volume fraction decreases
–Architecture becomes increasingly rod like-
becomes thin and perforated

32. Bone Compressive Strength
Material Compressive
Strength (MPa)
Femur (cortical)131-224
Tibia (cortical)106-200
Wood (oak) 40-80
Steel 370
From: Biomechanics of the Musculo-skeletal System, Nigg and Herzog

34. Relative Strength of Bone

35. Bone Elastic Modulus. E

36. Effect of Strain Rate

38. Mechanical Properties of Bone
Thedifferentstructuresofcorticalboneandtrabecularbone
resultindifferentmechanicalproperties.
Bonemechanicalpropertiesarehighlyvariableaccordingto
species,age,anatomicalsite,liquidcontent,etc.
Ultimate strength (MPa) and ultimate strain (%) of cortical bone
from the human femur as a function of age

39. Anisotropic Property of Cortical Bone
Corticalboneisananisotropicmaterial,meaningthatitsmechanical
propertiesvaryaccordingtothedirectionofload.
Corticalboneisoftenconsideredanorthotropicmaterial.Orthotropic
materialsareaclassofanisotropicmaterialscharacterizedbythreedifferent
Young'smoduliE
1,E
2,E
3accordingtothedirectionofload,threeshearmoduli
G
12,G
13,G
23andsixPoisson'sratiosν
12,ν
13,ν
23,ν
21,ν
31,ν
32.
Comparisonbetweenthe
mechanicalbehaviourof
isotropicandanisotropic
materials

43. Elastic constants of cortical bone from
different anatomical sites
Average elastic constants of mandible
bone in corpus and ramus
Average elastic constants of corpus cortical
bone in inferior, lingual and buccal zones

44. Average elastic constants of human
mandibular bone by tooth location

46. Young'smodulusoftrabecularboneasafunctionofdensityofbone.
Bonedensityρisexpresseding/cm
3
andYoung'smodulusEinMPa
Themechanicalcharacterizationoftrabecularboneisevenmoredifficult.The
mechanicalpropertiesoftrabecularboneasawholeareduetothemechanical
characteristicsofsingletrabeculesandtoitshighlyporousstructure

48. Heterogeneity
Variation in microstructural parameter
•porosity
•percentage of mineralization
Modulus and Ultimate strength decreases by half when porosity
increases from 5 to 30%
Small increase in percentage mineralization, large increases in both
modulus and strength
Aging
•TensileU.stressdecreasesatarateofapp.2%perdecade
•T.U.Straindecreasesbyabout10%ofitsyoung-value/decadefrom5%
•Energytofracture,lessforoldbonethanforyoungerbone
•Fracturetoughnessdecreaseswithaging,OldC.Baremorebrittlethanyoung
•Mineralizationdoesnotchangemuchwithaging.Itisduetocollagenchanges
•Agerelatedchanges–Porosityincreaseswithage
•Strength&ductilitydecreaseswithage–ElasticModuluschangeswithage
•Fracturemechanicsstudies-showsdecreaseinfraturetoughnesswithage

59. Bone remodelling
•Boneadaptsandremodelsinresponsetothestress
applied.
•Wolff'slaw:bonesdevelopastructuremostsuitedto
resisttheforcesactinguponthem,adaptingboththe
internalarchitectureandtheexternalconformation
tothechangeinexternalloadingconditions.This
changefollowsprecisemathematicallaws.
•Whenachangeinloadingpatternoccursstressand
strainfieldsinthebonechangeaccordingly.
•Bonetissueseemstobeabletodetectthechangein
strainonalocalbasesandthenadaptsaccordingly.

60. Bone Remodelling
•Theinternalarchitectureisadaptedintermsof
changeindensityandindispositionoftrabecules
andosteonsandtheexternalconformationinterms
ofshapeanddimensions.
•Whenstrainisintensifiednewboneisformed.
–microscopicscale:bonedensityisraised
–macroscopicscale:theboneexternaldimensionsare
incremented.
•Whenstrainisloweredboneresorptiontakesplace.
–microscopicscale:bonedensityislowered
–macroscopicscale:theboneexternaldimensionsare
reduced

61. Effect of reduction (from A to B) and of intensification of
strain (from B to A) on bone trabecules

62. Remodelling
•Whenthechangeinstrainisduetoachangeindirectionof
load
•microscopicscale:thestructureoftrabeculesandosteons
isrearranged
•macroscopicscale:achangeinboneshapemayoccur.
•Remodellingiscarriedoutbythecellularcomponentofbone.
•Resorption:osteoclastsreabsorbcollagenandmineralphase
whicharethentakenintothecirculatorysystem.
•Deposition:osteoblastsgrouponthedepositionsurfaceand
buildthecollagennetworkofbone.Mineralizationtakesplace
afterwards.

63. Bone resorption and deposition
Bone deposition
Bone resorption
Bone resorption is the process by which osteoclasts break down bone and
release the minerals, resulting in a transfer of calcium from bone fluid to the blood

64. Equilibrium strain state
•Boneresorptionandbonedepositionprocessesarealways
activeinbone.
•Anequilibriumstrainstateexistsincorrespondencetowhich
thetwoactivitiesareperfectlybalanced.
•Strainintensity>theequilibriumstrain:
•depositionactivityismoreintensethanresorptionactivity
andnetdepositionoccurs.
•Strainintensity<theequilibriumstrain:
•depositionactivityislessintensethanresorptionactivity
andnetresorptionoccurs.
•Dynamicalequilibriumbetweenresorptionanddepositionis
againachievedwhentheequilibriumstrainstateisnewly
established.

65. Schematic diagram of the Davy and
Hart model for bone remodelling

66. Bone Fracture
Typesofbonefractures:Complete,
Incomplete,CompoundandSimple.
completefracture:thebonesnaps
intotwoormoreparts
incompletefracture:thebone
cracksbutdoesnotbreakalltheway
through.
compoundoropenfracture:the
bonebreaksthroughtheskin;itmay
thenrecedebackintothewoundand
notbevisiblethroughtheskin.
simpleorclosedfracture:thebone
breaksbutnoopenwoundintheskin.

67. Simple Fractures
•Greenstickfracture:anincompletefractureinwhichthebone
isbent.Thistypeoccursmostofteninchildren.
•Transversefracture:afractureatarightangletothebone's
axis.
•Obliquefracture:afractureinwhichthebreakslopes.
•Comminutedfracture:afractureinwhichthebonefragments
intoseveralpieces.
•Animpactedfractureisonewhoseendsaredrivenintoeach
other.Thisiscommonlyseeninarmfracturesinchildrenand
issometimesknownasabucklefracture.
•Othertypesoffracturearepathologicfracture,causedbya
diseasethatweakensthebones,andstressfracture,a
hairlinecrack.

68. Bone Repair
Whilethepatientispain-free(generalor
localanesthesia),anincisionismadeover
thefracturedbone.Theboneisplacedin
properpositionandscrews,pins,orplates
areattachedtoorinthebonetemporarily
orpermanently.Anydisruptedblood
vesselsaretiedofforburned(cauterized).
Ifexaminationofthefractureshowsthata
quantityofbonehasbeenlostasaresult
ofthefracture,especiallyifthereisagap
betweenthebrokenboneends,the
surgeonmaydecidethatabonegraftis
essentialtoavoiddelayedhealing.
Ifbonegraftingisnotnecessary,thefracturecanberepairedbythefollowing
methods:
oneormorescrewsinsertedacrossthebreaktoholdit.
asteelplateheldbyscrewsdrilledintothebone.
alongflutedmetalpinwithholesinit,isdrivendowntheshaftofthebonefrom
oneend,withscrewsthenpassedthroughtheboneandthroughaholeinthepin.

69. Repair of a fractured bone
Anillustrationoftherepairofa
fracturedbone(a)isshowninthis
diagram.Bloodinfiltratesthe
damagedsite,formingahematoma
(b),asoftcallusoffibrocartilageforms
aroundthehematomatoprovide
support(c),osteoblastsproducea
hardcallustostrengthenthesoft
callus(d),andfinally,osteoclasts
removeexcessboneandcallus(e).

70. What is Osteoporosis?
Asystematicskeletaldiseasecharacterizedbylowbonemass,increaseof
bonefragilityandsusceptibilitytofracture.Osteoporosiscanleadto
irreversibledeteriorationofbonestructure
Symptoms
Aches and pains
Loss of height
Fractures of the
Hip, Spine, Wrist
Disability
Risk Factors
Age : > 45 yrs in Female and > 60 yrs in Male
Lifestyle -lack of exercise
Low Vitamin D in take
Low calcium intake
Smoking
Life style & osteoporosis prevention
Be ON YOUR FEET
Exercise at least 3 hours per week
Take a meal rich in Calcium and Vitamin D
Consume adequate calories
Avoid Smoking
AVOID TOBACCO & ALCOHOL

71. Rheumatoid arthritis
Rheumatoidarthritis(RA)isachronic,systemic
autoimmunedisorderthatcausestheimmunesystem
toattackthejoints,whereitcausesinflammation
(arthritis)anddestruction.Itcanalsodamagesome
organs,suchasthelungsandskin.Itcanbea
disablingandpainfulcondition,whichcanleadto
substantiallossoffunctioningandmobility.Itis
diagnosedwithbloodtests(especiallyatestcalled
rheumatoidfactor)andX-rays.Diagnosisandlong-
termmanagementaretypicallyperformedbya
rheumatologist,anexpertinthediseasesofjointsand
connectivetissues.
Varioustreatments
physicaltherapyandoccupationaltherapy
Analgesia(painkillers)andanti-inflammatorydrugs,
steroids,areusedtosuppressthesymptoms
disease-modifyingantirheumaticdrugs(DMARDs)
areoftenrequiredtoreversethediseaseprocessand
preventlong-termdamage.

72. Osteoarthritis
Osteoarthritis(OA,alsoknownas
degenerative arthritis,
degenerativejointdisease),isa
clinicalsyndromeinwhichlow-grade
inflammationresultsinpaininthe
joints,causedbyabnormalwearing
ofthecartilagethatcoversandacts
asacushioninsidejointsand
destructionordecreaseofsynovial
fluidthatlubricatesthosejoints.
Causes
Aging
Anotherdiseaseorconditionlikeobesity,repeatedtraumaorsurgerytothejoint
structures,abnormaljointsatbirth(congenitalabnormalities),gout,diabetes,and
otherhormonedisorders.
Crystaldepositsinthecartilagecancausecartilagedegenerationand
osteoarthritis.Uricacidcrystalscausearthritisingout,whilecalcium
pyrophosphatecrystalscausearthritisinpseudogout.
Hormonedisturbances,suchasdiabetesandgrowthhormonedisorders,are
alsoassociatedwithearlycartilagewearandsecondaryosteoarthritis.

73. Juvenile Arthritis
Juvenileidiopathicarthritis(JIA),formerlyknownasjuvenilerheumatoid
arthritis(JRA)isnotadegenerativediseasesuchasosteoarthritis.Itcanbe
classifiedasanauto-immunediseaseandisthereforecausedbytheimmune
systemattackingthebody.Thenormalfunctionoftheimmunesystemisto
wardoffoutsideenemiessuchasviruses,butinauto-immunediseases,the
bodyturnsonitself.JuvenilearthritisisalsoknownasJuvenilechronicarthritis
(JCA)Itaffectschildrensixteenyearsoldorunder.JRAcanbedivideintothree
distincttypes:Pauciarticular,PolyarticularandSystemic.

74. Juvenile Arthritis
•Pauciarticularonsetjuvenileidiopathicarthritis(JIA)or
pauciarthritis
–subsetofJIAthatincludespatientswithinvolvementoffewerthan
fivejoints.
–mostcommonsubgroup,constitutingabout50percentofcasesofJIA
•Polyarticularonsetjuvenileidiopathicarthritis
–subsetofjuvenileidiopathicarthritis(JIA)thatisdefinedbythe
presenceofmorethanfouraffectedjointsduringthefirstsixmonths
ofillness.
–comprises20to30percentofpatientswithJIA.
•SystemiconsetJRA
–referredtopatientswithrashandintermittentfever,inadditionto
arthritisofanynumberofjoints.
–Itisresponsibleforabout10to15percentofJRAcases.

75. Autoimmune Diseases
•Occurswhenthebody’simmunesystemattacksanddestroys
healthybodytissuebymistake.Therearemorethan80typesof
autoimmunedisorders.
•Theimmunesystemdoesnotdistinguishbetweenhealthytissue
andantigens.Asaresult,thebodysetsoffareactionthat
destroysnormaltissues.
•Exactcauseofautoimmunedisordersisunknown.
–somemicroorganisms(suchasbacteriaorviruses)ordrugsmaytrigger
changesthatconfusetheimmunesystem.
–mayhappenmoreofteninpeoplewhohavegenesthatmakethemmore
pronetoautoimmunedisorders
•Result:Thedestructionofbodytissue,Abnormalgrowthofan
organ,Changesinorganfunction
•Areasaffected:Bloodvessels,connectivetissues,endocrine
glandssuchasthethyroidorpancreas,joints,muscles,redblood
cells,skin

76. Biomechanical Properties of Bone
•Biomechanically,bonetissuemayberegardedasatwo-
phase(biphasic)compositematerial;withthemineralas
onephaseandthecollagenandgroundsubstanceasthe
other.
•Insuchmaterials(anon-biologicalexampleisfiberglass)
inwhichastrong,brittlematerialisembeddedina
weaker,moreflexibleone,thecombinedsubstancesare
strongerfortheirweightthaniseithersubstancealone.
•Functionally,themostimportantmechanicalproperties
ofboneareitsstrengthandstiffness.

77. Typical Load-Deformation Curve
Load-deformationcurveforastructurecomposedofasomewhatpliable
material.Ifaloadisappliedwithintheelasticrangeofthestructure(AtoBon
thecurve)andisthenreleased,nopermanentdeformationoccurs.Ifloadingis
continuedpasttheyieldpoint(B)andintothestructure'splasticrange(BtoC
onthecurve)andtheloadisthenreleased,permanentdeformationresults.The
amountofpermanentdeformationthatoccursifthestructureisloadedtopoint
Dintheplasticregionandthenunloadedisrepresentedbythedistance
betweenAandD.Ifloadingcontinueswithintheplasticrange,anultimate
failurepoint(C)isreached.

78. Testing of Bone
Stress-strain curve for a cortical bone
sample tested in tension (pulled), Yield
point (B)
Standardizedbonespecimenina
testingmachineThestraininthe
segmentofbonebetweenthetwo
gaugearmsismeasuredwitha
straingauge.Thestressis
calculatedfromthetotalload
measured.

79. Stress-Stress Curves in
Compression
Exampleofstress-straincurvesofcorticalandtrabecularbonewith
differentapparentdensities,Testingwasperformedincompression.The
figuredepictsthedifferenceinmechanicalbehaviorforthetwobone
structures.

80. Mechanical Properties of Bone
•Mechanicalpropertiesdifferinthetwobonetypes.
Corticalboneisstifferthancancellousbone,
withstandinggreaterstressbutlessstrainbefore
failure.
•Cancellousboneinvitromaysustainupto50%of
strainbeforeyielding,whilecorticalboneyieldsand
fractureswhenthestrainexceeds1.5-2%.Cancellous
bonehasalargecapacityforenergystorage
•Thephysicaldifferencebetweenthetwobone
tissuesisquantifiedintermsoftheapparentdensity
ofbone,whichisdefinedasthemassofbonetissue
presentinaunitofbonevolume(g/cc)

81. Schematic stress-strain curves for
three materials
Metalhasthesteepestslopeintheelasticregion
andisthusthestiffestmaterial.Theelastic
portionofthecurveformetalisastraightline,
indicatinglinearlyelasticbehavior.
Thefactthatmetalhasalongplasticregion
indicatesthatthistypicalductilematerialdeforms
extensivelybeforefailure.
Glass,abrittlematerial,exhibitslinearlyelastic
behaviorbutfailsabruptlywithlittledeformation,
asindicatedbythelackofaplasticregiononthe
stress-straincurve.
Bonepossessesbothductileandbrittlequalities
demonstratedbyaslightcurveintheelastic
region,whichindicatessomeyieldingduring
loadingwithinthisregion.

82. Mechanical Properties of Selected
Biomaterials
Ultimate
Strength (MPa)
Modulus
(GPa)
Elongation(%)
Metals -Co-Cr alloy
Cast 600 220 8
Forged 950 220 15
Stainless steel850 210 10
Titanium 900 110 15
Polymers -Bone cement20 2.0 2-4
Ceramic -Alumina 300 350 <2
Biological
Cortical bone 100-150 10-15 1-3
Trabecular bone8-50 2-4
Tendon, ligament 20-35 2.0-4.0 10-25

83. Fracture of Ductile and Brittle
Materils
Fracturesurfaceofsample,ofaductile
andabrittlematerial.Thebrokenlineson
theductilematerialindicatetheoriginal
lengthofthesample.beforeitdeformed.
Thebrittlematerialdeformedverylittle
beforefracture.
When piecedtogetherafter
fracture,theductilematerialwill
notconformtoitsoriginalshape
whereasthebrittlematerialwill.
Boneexhibitsmorebrittleormore
ductilebehaviordependingonits
age(youngerbonebeingmore
ductile)andtherateatwhichitis
loaded(bonebeingmorebrittleat
higherloadingspeeds)

84. Anisotropic behavior of cortical
bone
Anisotropic behavior of cortical bone specimens from a human femoral
shaft tested in tension (pulled) in four directions: longitudinal (L), tilted 30°
with respect to the neutral axis of the bone, tilted 60°, and transverse (T).

85. Stress-Strain Behaviour of Trabecular Bone
Exampleoftensilestress-strain
behavioroftrabecularbonetested
inthelongitudinalaxialdirectionof
thebone.
Trabecularorcancellousboneis
approximately25%asdense,5to
10%,asstiff,andfivetimesas
ductileasconicalbone.

86. Schematic representation of
various loading modes
Themechanicalbehaviororbone-its
behaviorundertheinfluenceofforces
andmoments-isaffectedbyits
mechanicalproperties,itsgeometric
characteristics,theloadingmodeapplied,
directionofloading,rateofloading,and
frequencyofloading
Forcesandmomentscanbeappliedtoa
structureinvariousdirections,producing
tension,compression,bending,shear,
torsion,andcombinedloading.Bonein
vivoissubjectedtoalloftheseloading
modes.

87. Rate dependency of cortical bone
Thebiomechanicalofbonebehavior
varieswiththerateatwhichthebone
isloaded.Ratedependencyof
corticalboneisdemonstratedatfive
strainrates.Bothstiffness(modulus)
andstrengthincreaseconsiderably
atincreasedstrainrates.
Thefigureshowscorticalbone
behaviorintensiletestingatdifferent
physiologicalstrainrates.Ascanbe
seenfromthefigure,thesame
changeinstrainrateproducesa
largerchangeinultimatestress
(strength)thaninelasticity(Young's
modulus).Thedataindicatesthatthe
boneisapproximately30%stronger
forbriskwalkingthanforslow
walking.

88. Influence of Muscle Activity on Stress
Distribution in Bone
Calculated stresses on the
anterolateral cortex of a human
tibia during walking
Calculated stresses on the
anterolateral cortex of a human
tibia during jogging

89. Summary
•Boneisacomplextwo-phasecompositematerial.Onephase
iscomposedofinorganicmineralsaltsandtheotherisan
organicmatrixofcollagenandgroundsubstance.The
inorganiccomponentmakesbonehardandrigid,whereasthe
organiccomponentgivesboneitsflexibilityandresilience.
•Microscopically,thefundamentalstructuralunitofboneisthe
osteon,orhaversiansystem,composedofconcentriclayersof
amineralizedmatrixsurroundingacentralcanalcontaining
bloodvesselsandnervefibers.
•Macroscopically,theskeletoniscomposedofcorticaland
cancellous(trabecular)bone.Corticalbonehashighdensity
whiletrabecularbonevariesindensityoverawiderange.

90. Summary…
•Boneisananisotropicmaterial,exhibitingdifferent
mechanicalpropertieswhenloadedindifferent
directions.Matureboneisstrongestandstiffestin
compression.
•Boneissubjectedtocomplexloadingpatternsduring
commonphysiologicalactivitiessuchaswalkingand
jogging.Mostbonefracturesareproducedbya
combinationofseveralloadingmodes.
•Musclecontractionaffectsstresspatternsinboneby
producingcompressivestressthatpartially