Total Knee Replacement

Femoral Component

Ujwal A. Parikh

Why TKR

• Osteoarthritis (wear and tear)

• Rheumatoid arthritis

• Post-traumatic arthritis caused by: – Fractures– Ligament injuries– Meniscus tears

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

Design Input

Distal Portion of FemurBUECHEL-PAPPAS™ KNEE REPLACEMENT SYSTEM by Endotech

Design Input

Features

• Internal Support

• Pegs

• Patellar flange

• Polycentric

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

MethodBox cut

Sketch Rectangle (Right Plane) Side 1 (Lateral Side) : Blind @ 1.88”

Side 2 (Medial Side): Blind @ 1.62”

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

MethodSweep

Trajectory

Section

Design Feature

Polycentric Trajectory

MethodPatellar flange

• Curved base having radius of curvature same as that femoral notch of human knee

MethodIntercondular notch

1. Sketch Top Plane

2. Extrude, Remove material symmetric

Notch @ 0.64”

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”

Component operationFamily Table

Component operationTool Cut/ Bone Cuts

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

FEA Test

• Test I : Yield tensile strength test

• Test II: Fatigue strength test

( Both tests force applied on lateral condyle)

FEAConstraints

• One end is fixed- Displacement constraint

• Other end force given on lateral condyle- Force constraint

• New material Ti6Al4V added to the implant

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

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

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

Conclusion

• On rounding the internal edges there is a reduction in stress and it is uniformly distributed

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

Final Assembly

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

Thank You