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AnalysisofAsepticLooseningoftheAcetabularCupinCementedTotalHip
Replacement
TadhgAdderley,Dr.F.McEvoy,Dr.Y.Blake,Mr.R.Flavin.
1. MechanicalEngineeringDepartment,InstituteofTechnologyTallaght,Dublin.
2. OrthopaedicSurgeon,GalwayUniversityHospital.
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Analysis of Aseptic Loosening of the Acetabular Cup
Overview
1.
Introduction
2.
Project Objectives
3.
Pelvis Model Design & Validation
4.
Foam Compression Tests & Results
5.
Hip Simulator Design & Calibration
6.
Future Work
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Analysis of Aseptic Loosening of the Acetabular Cup
1. Introduction
Over1millionTotalHipReplacements(THR)performedworldwideeachyear. 300,000inAmerica 50,000inEngland&Wales 3,389inIreland(2004)
Vhipaidout18milliononTHRin04/05. 11,500peroperation
Between710%ofTHRwillrequirearevision.
75%ofrevisionscausedbyasepticloosening.TA4
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TA4 AsepticlooseningofTHRisthemajorreasonforrevisionsurgery.
Thispaperaimstovalidateapelvismodel,socementedcupscanbetestedandexaminedforcausesofasepticloosening.
Thepelvismodelwillbeusedonapurposebuilthipsimulatortotestcementedacetabularcups.TadhgAdderley,29/01/2009
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Analysis of Aseptic Loosening of the Acetabular Cup
2. Project Objectives
Design&build: HipSimulatortoBS&ISOstandards. PelvisModel.
Findsuitablereplacementmaterialforbone.
Determine: Theinitiatingfactorsthatcauseasepticloosening. Inwhichzoneorareafailureoccurs.
Investigatethemigrationofthecupoveritslifespan.
Identifytheoptimumdesigncriteriafortheacetabularcup.
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Analysis of Aseptic Loosening of the Acetabular Cup
Total Hip Replacement
3.Pelvis Model Design
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Analysis of Aseptic Loosening of the Acetabular Cup
3. PelvisModel
0.3 1.7
15 25
Majumderetal.(2004)
2.21
17.68
Cilingiretal.(2007)
Lamvoheeetal.(2006)
ObtainedResults
1.2 3.53 Trabecular Bone
15 16.48 Cortical Bone
7.27 8.84 7.06 Cement
{9 12}
15.3
{10.34}
Cup
VonMisesStress(MPa)
Cu p
Cortical Bone
Cemen t
Loading Conditions on Pelvis Model
Von Mises Stress Results
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Analysis of Aseptic Loosening of the Acetabular Cup
0.12g/cc Cellular Rigid Polyurethane Foam
0.32g/cc Cellular Rigid Polyurethane Foam
Crack
4. CompressionTests
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Analysis of Aseptic Loosening of the Acetabular Cup
4. Compression Test Results
0
1
2
3
4
5
6
7
8
9
0% 1% 2% 3% 4% 5% 6%
TrueStrain
Tru
eStres
s(M
Pa)
0.2%ProofStress=6.25MPa
Young'sModulus=298.76MPa
UltimateStress=7.63MPa
0.3g/cc Trabecular Bone Youngs Modulus 200 MPa
Yield Point 8 MPa
Ultimate Stress 8-10 MPa
[Bartel et al. (2006) & Nordin et al. (2001)]
0.32g/cc Cellular Rigid Polyurethane Foam
Strain Rate = 0.0208s
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Analysis of Aseptic Loosening of the Acetabular Cup
4. Compression Test Results
0
1
2
3
4
5
6
7
8
9
0% 1% 2% 3% 4% 5% 6%
TrueStrain
Tru
eStres
s(M
Pa)
0.2%ProofStress=7.7MPa
Young'sModulus=345.76MPa
UltimateStress=8.30MPa
0.32g/cc Cellular Rigid Polyurethane Foam & Epoxy Sheets
Strain Rate = 0.0208s
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Analysis of Aseptic Loosening of the Acetabular Cup
4. Compression Test Results
Strain Rate Sensitivity
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Analysis of Aseptic Loosening of the Acetabular Cup
CompressionTests
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2
4
6
8
10
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0 0.5 1 1.5 2 2.5
Displacement(mm)
Load
(kN
)
0.01/sCellularFoam 0.001/sCellularFoam 0.01/sSolidFoam 0.001/sSolidFoam
4. Instron Testing
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Analysis of Aseptic Loosening of the Acetabular Cup
5. Hip Simulator
Stem Path
Pneumatic Cylinder
Gimbal Section
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Analysis of Aseptic Loosening of the Acetabular Cup
5. Calibration of Hip SimulatorRegulatorPressureversusInputVoltage
[Alldatapoints]
RegulatorPressure=1.499321178280810*InputVoltage+1.508361740837780
R2 =0.999992111474258
0
1
2
3
4
5
6
7
8
9
1 0 1 2 3 4 5
InputVoltage(V)
Reg
ulatotPress
ure(bar)
LoadCellCalibrationInputVoltage10V
Load=484.136144693950000*Voltage+1.182978741572300
R2 =0.999998465370372
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
0 1 2 3 4 5 6 7 8 9 10
OutputVoltage(mV)
Load
(N)
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Analysis of Aseptic Loosening of the Acetabular Cup
FatiguetestsonInstron. PEcupsamplescementedintofoamblocks.
ExperimentsoncementedacetabularcupsusingPelvisModelinHipSimulator.
Investigatemigrationofcups. UsingCMM,measurepositionofcupsbefore&aftertesting.
UsingCTscans,examinespecimensforfailure.
6. Future Work
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Analysis of Aseptic Loosening of the Acetabular Cup
ThankyouforListeningAnyquestions?
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