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

Slide3

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

-1

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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

-1

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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

0

2

4

6

8

10

12

14

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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