total knee replacement
DESCRIPTION
Total Knee ReplacementTRANSCRIPT
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Total Knee Replacement
Femoral Component
Ujwal A. Parikh
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Why TKR
• Osteoarthritis (wear and tear)
• Rheumatoid arthritis
• Post-traumatic arthritis caused by: – Fractures– Ligament injuries– Meniscus tears
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What is TKR?
• Femoral- replaces arthritic portion of thigh bone
• Tibial- replaces arthritic portion of shin bone
• Tibial insert- replaces cartilage and acts as shock absorber
• Patella- replaces knee cap
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Design Input
Distal Portion of FemurBUECHEL-PAPPAS™ KNEE REPLACEMENT SYSTEM by Endotech
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Design Input
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Features
• Internal Support
• Pegs
• Patellar flange
• Polycentric
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Material
• Ti6Al4V
• Biocompatible• Less Corrosive• Tensile strength close to bone
Tensile Strength, Yield 128000 psi
Modulus of Elasticity 16500 ksi
Fatigue Strength 34800 psi at 1E+7 cycles
CTE, linear 500°C 5.39 µin/in -F (Average over the range 20-650ºC)
Poisson's Ratio 0.342
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MethodBox cut
Sketch Rectangle (Right Plane) Side 1 (Lateral Side) : Blind @ 1.88”
Side 2 (Medial Side): Blind @ 1.62”
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MethodBox Cut (Chamfer Cut)
1. Chamfer Cut (Right Plane)
2. Symmetric Extrusion, Remove Material.
3. Chamfer cut tangential to bone
4. Decides cut of bone.
Measured value Accepted range
TKA Slope
8.75o 6o-9o
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MethodSweep
Trajectory
Section
Design Feature
Polycentric Trajectory
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MethodPatellar flange
• Curved base having radius of curvature same as that femoral notch of human knee
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MethodIntercondular notch
1. Sketch Top Plane
2. Extrude, Remove material symmetric
Notch @ 0.64”
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Method Rounds Features
1. Variable radii
2. Stress prone edges moved before Sweep cut
Radii
Outer edges 0.1”-0.05”
Inner edges 0.03”-0.02”
Pegs & Support 0.02”
Stress Edges 0.10”
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Component operationFamily Table
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Component operationTool Cut/ Bone Cuts
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Finite Element Analysis (FEA)Load
• Average weight of men in USA : 190 lbs
• To test the implant for different stress conditions
• Test I: When a person jumps body weight aprrox. 4-times i.e. 800 lbs
• Test II: When a person walks body weight aprrox 2-3 times i.e. 450 lbs
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FEA Test
• Test I : Yield tensile strength test
• Test II: Fatigue strength test
( Both tests force applied on lateral condyle)
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FEAConstraints
• One end is fixed- Displacement constraint
• Other end force given on lateral condyle- Force constraint
• New material Ti6Al4V added to the implant
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Preliminary Results
Load (lbs) Max. Stress (kpsi)
Max. allow value
(kpsi)
Yield tensile strength
800 187-163.6 128
Fatigue strength
450 92.0-78.87 34.8
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ResultsLoad (lbs)
Max. Stress (kpsi)
Max. allow value (kpsi)
Yield tensile strength
800 121.1-81.1
128
Fatigue strength
450 68.4-45.64
34.8
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Max Stress Reduction
• The max stress reduces from– 187 to 121.1 kpsi in yield strength test– 92 to 68.4 kpsi in fatigue test
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Conclusion
• On rounding the internal edges there is a reduction in stress and it is uniformly distributed
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Design OutputImplant (mm) Reference (mm)
INT 16.51(0.65”) 22
M/L 77.47 (3.05”) 80.6
A/P 65.79 (2.59”) 76.6
PEG 12.95 (0.51) 13.7
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Final Assembly
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References
• http://www.endotec.com/• http://www.eorif.com/• http://www.freepatentsonline.com/4353135.pdf• http://asm.matweb.com/search/SpecificMaterial.asp?
bassnum=MTP641• Components for Knee Replacement Surgery”. DePuy
Orthopaedics, Inc. 2 April, 2003. http://www.jointreplacement.com
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Thank You