OVERVIEW OF IMPLANT MATERIALS IN ORTHOPAEDICS.pdf

OVERVIEW OF IMPLANT MATERIALS IN ORTHOPAEDICS-MUKESH SUNDARARAJAN

1. OVERVIEW OF IMPLANTMATERIALS
IN ORTHOPAEDICS
MUKESH SUNDARARAJAN

2. OUTLINE
•INTRODUCTION
•BASICCONCEPTS/DEFINITIONS
•COMMON ORTHOPAEDIC IMPLANT MATERIALS
&CLINICALAPPLICATIONS
•GENERALTISSUE-IMPLANTRESPONSES
•COMPLICATIONSASSOCIATEDWITHIMPLANTS
•RECENTADVANCES
•CONCLUSION

3. INTRODUCTION
•Implants are biomaterial devices
•Essentialinthe practiceoforthopaedics
•Abiomaterialisanysubstanceorcombination
ofsubstances (otherthan adrug),syntheticor
natural in origin, that can be used for any period
oftimeas awholeor partofa systemthat
treats,augmentsor replacesanytissue, organor
function ofthe body

4. BASICCONCEPTS&
DEFINITIONS
•STRESS:Theforceappliedperunitcross-
sectionalareaofthebodyoratestpiece
(N/mm²)
•STRAIN: The change in length (mm) as a fraction
ofthe originallength(mm)
-relativemeasure of deformationofthebodyor
atestpieceasaresultofloading

5. STRESS-STRAINCURVE

6. DEFINITIONS
•YOUNG’SMODULUSOFELASTICITY:Thestress
per unit strain in the linear elastic portion of the
curve(1N/m² =1Pascal)
•DUCTILITY: The abilityof the materialto
undergo a large amount of plastic deformation
beforefailure e.gmetals
•BRITTLENESS:Thematerialdisplayselastic
behaviourrightup to failuree.gceramics

7. DEFINITIONS
•STRENGTH: The degree of resistance to
deformationofamaterial
-Strong ifithas ahightensile strength
•FATIGUEFAILURE:Thefailureof a materialwith
repetitiveloadingat stresslevelsbelowthe
ultimate tensilestrength
•NOTCHSENSITIVITY:Theextenttowhich
sensitivity of a material to fracture is increased
bycracksor scratches

8. DEFINITIONS
•ULTIMATETENSILESTRESS:Themaximum
amountof stressthematerialcanwithstand
beforewhichfracture isimminent
•TOUGHNESS: Amount of energy per unit volume
thata materialcanabsorbbeforefailure
•ROUGHNESS:Measurement ofa surfacefinishof
amaterial
•HOOKE’SLAW→Stressα Strainproduced
-Thematerial behaveslikeaspring

9. BONEBIOMECHANICS
•Boneisanisotropic:
-it’selasticmodulusdependsondirectionof
loading
-weakestinshear,thentension,then
compression
•Bone is also viscoelastic → the stress-strain
characteristicsdependon therateofloading
•Bonedensitychangeswithage, disease,use and
disuse
•WOLF’S LAW → Bone remodelling occurs along
the lineof stress

10. IDEALIMPLANTMATERIAL
•Chemicallyinert
•Non-toxictothebody
•Greatstrength
•Highfatigueresistance
•LowElasticModulus
•Absolutelycorrosion-proof
•Goodwearresistance
•Inexpensive

11. CLINICALAPPLICATIONSOF
ORTHOPAEDICIMPLANTS
•Osteosynthesis
•Jointreplacements
•Nonconventionalmodular tumorimplants
•Spineimplants

12. COMMONIMPLANTMATERIALSIN
ORTHOPAEDICS
•MetalAlloys:
-stainlesssteel
-Titaniumalloys
-Cobaltchromealloys
•Nonmetals:
-Ceramics&Bioactiveglasses
-Polymers(Bonecement,polyethylene)

13. STAINLESSSTEEL
•Contains:
-Iron(62.97%)
-Chromium(18%)
-Nickel(16%)
-Molybdenum(3%)
-Carbon(0.03%)
•Theformusedcommonlyis316L(3%
molybd,16%nickel&L=Lowcarbon
content)

14. STAINLESSSTEEL
•Advantages:
1.Strong
2.Relativelyductile
3.Biocompatible
4.Relativelycheap
5.Reasonable coorsion
resistance
•Used inplates,screws,
IMnails,extfixators
•Disadvantages:
-Susceptibilityto
creviceandstress
corrosion

15. TITANIUMALLOYS
•Contains:
-Titanium(89%)
-Aluminium(6%)
-Vanadium(4%)
-Others(1%)
•Most commonly orthopaedic titanium alloy
isTITANIUM64 (Ti-6Al-4v)

16. TITANIUMALLOYS
•Advantages:
1.Corrosionresistant
2.Excellent
biocompatibility
3.Ductile
4.Fatigueresistant
5LowYoung’smodulus
6.MRscancompatible
•Usefulinhalos,plates,
IMnailsetc.
•Disadvantages:
1.Notchsensitivity
2.poor wear
characteristics
3.Systemictoxicity–
vanadium
4.Relativelyexpensive

17. COBALTCHROMEALLOYS
•Contains primarilycobalt(30-60%)
•Chromium (20-30%) added to improve
corrosionresistance
•Minor amounts of carbon, nickel and
molybdenumadded

18. COBALTCHROMEALLOYS
•Advantages:
1.Excellent resistance
to corrosion
2.Excellent long-term
biocompatibility
3.Strength(very
strong)
•Disadvantages:
1.Very high Young’s
modulus
-Riskofstress
shielding
2.Expensive

19. YOUNG’SMODULUSANDDENSITYOF
COMMONBIOMATERIALS
MATERIAL YOUNG’SMODULUS(GPa)DENSITY(g/cm³)
Cancellousbone 0.5-1.5 -
UHMWPE 1.2 -
PMMAbonecement 2.2 -
Corticalbone 7-30 2.0
Titaniumalloy 110 4.4
Stainlesssteel 190 8.0
Cobaltchrome 210 8.5

20. COMPARISON OFMETALALLOYS
ALLOY Young’smodulus
(GPa)
Yieldstrength
(MPa)
Ultimatetensile
strength(MPa)
StainlessSteel316L190 500 750
Titanium64 110 800 900
Cobaltchrome
F562
230 1000 1200

22. CERAMICS
•Compounds of metallic elements e.g
Aluminiumboundionicallyor covalentlywith
nonmetallicelements
•Commonceramicsinclude:
-Alumina(aluminiumoxide)
-Silica(siliconoxide)
-Zirconia(Zirconiumoxide)
-Hydroxyapatite(HA)

23. CERAMICS
•Advantages:
1.Chemicallyinert&
insoluble
2.Best
biocompatibility
3.Verystrong
4.Osteoconductive
•Disadvantages:
1.Brittleness
2.Verydifficultto
process –high
meltingpoint
3.Very expensive

24. CERAMICS
•UsedforfemoralheadcomponentofTHR
-Not suitable for stem because of its
brittleness
•Used as coating for metal implants to
increasebiocompatibilitye.gHA

25. POLYMERS
•Consists of many repeating units of a basic
sequence(monomer)
•Usedextensivelyinorthopaedics
•Mostcommonlyusedare:
-Polymethylmethacrylate(PMMA,Bone
cement)
-UltrahighMolecularWeightPolyethylene
(UHMWPE)

26. PMMA(BONECEMENT)
•Mainlyusedtofixprosthesisinplace
-canalsobeusedas voidfillers
•Availableasliquidandpowder
•Theliquidcontains:
→ThemonomerN,N-dimethyltoluidine(the
accelerator)
→Hydroquinone(theinhibitor)

27. PMMA
•Thepowder contains:
-PMMAcopolymer
-Bariumor Zirconiumoxide(radio-opacifier)
-Benzoylperoxide(catalyst)
•Clinicallyrelevantstagesofcement reaction:
1.Sandystage
2.Mixtureappearsstringy
3.Cementisdoughy
4.Cementishard

28. UHMWPE
•Apolymerofethylenewith MWof2-6million
•Usedfor acetabularcupsinTHRprostheses
•Metal on polyethylene is gold standard
bearingsurfaceinTHR(highsuccessrate)
•Osteolysis produced due to polyethylene
wear debris causesasepticloosening

30. THR-IMPLANTBEARINGSURFACES
•Metal-on-polyethylene•Metal-on-metal

31. BEARINGSURFACES
•Ceramic-on- •Ceramic-on-ceramic
polyethylene

32. BIODEGRADABLEPOLYMERS
•Ex; Polyglycolic acid, Polylactic acid,
copolymers
•As stiffness of polymer decreases, stiffness of
callusincreases
•Hardware removalnotnecessary(reduces
morbidityandcost)
•Used in phalangeal fractures with good
results

33. GENERAL TISSUE-IMPLANT
RESPONSES
•Allimplantmaterials elicitsomeresponsefrom
the host
•The responseoccursat tissue-implantinterface
•Responsedependonmanyfactors;
-Typeoftissue/organ;
-Mechanicalload
-Amountofmotion
-Compositionoftheimplant
-Ageofpatient

34. TISSUE-IMPLANTRESPONSES
•Thereare4typesof responses(Hench& Wilson,
1993)
1.Toxicresponse:
-Implantmaterial releases chemicalsthat
kill cells andcausesystemicdamage
2.Biologicallynearlyinert:
-Most commontissueresponse
-Involvesformationofnonadherentfibrous
capsuleinanattempt toisolatetheimplant
-Implant maybesurroundedbybone

35. TISSUE-IMPLANTRESPONSES
-Can lead tofibrousencapsulation
-Depend on whether implant has smooth
surfaceorporous/threadedsurface
-Ex;metalalloys,polymers,ceramics
3.Dissolutionofimplant:
-Resorbableimplantaredegraded
graduallyovertimeandarereplacedby
hosttissues
-Implantresorptionrate need to matchtissue-
repairratesofthebody

36. TISSUE-IMPLANTRESPONSES
-Ex; Polylactic and polyglycolic acid polymers
whicharemetabolizedtoCO2&water
4.Bioactiveresponse:
-Implantformsabondwithboneviachemical
reactionsattheirinterface
-Bondinvolvesformationofhydroxyl-
carbonate apatite (HCA) on implant surface
creatingwhatissimilartonaturalinterfaces
between bonesandtendonsandligaments
-Ex;hydroxyapatite-coating onimplants

37. COMPLICATIONS
•AsepticLoosening:
-Causedbyosteolysisfrom body’sreactionto
wear debris
•StressShielding:
-Implant prevents bone from being properly
loaded
•Corrosion:
-Reaction of the implant with its environment
resultinginitsdegradationtooxides/hydroxides

38. COMPLICATIONS
•Infection:
-colonization of implant by bacteria and
subsequentsystemic inflammatoryresponse
•Metalhypersensitivity
•Manufacturingerrors
•VARIOUSFACTORSCONTRIBUTETOIMPLANT
FAILURE

39. RECENTADVANCES
•Aim is to use materials with mechanical
propertiesthatmatchthoseofthe bone
•Modifications to existing materials to
minimizeharmfuleffects
-Ex; nickel-freemetalalloys
•Possibility of use of anti-cytokine in the
preventionofosteolysis aroundimplants
•Antibacterialimplant

40. CONCLUSION
•Adequateknowledgeofimplantmaterialsis
anessentialplatformtomakingbestchoices
forthepatient
•Nocompletelysatisfyingresultsfromuseof
existingimplantmaterials
•Advancesinbiomedicalengineeringwillgoa
longwayinhelpingtheorthopedicsurgeon
•Thesearchison…

41. THANKYOU