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2. The effect of changing the shape and material of
tibial component on the performance of
total knee replacement
دراسة تأثير التغير فى شكل ومادة مكون الساق على أداء مفصل الركبة الصناعى
Supervisor’s Committee
Prof. Dr. Tawfik Tawfik El-Midany
Prof. of Production Engineering
Faculty of Engineering, Mansoura University
Associate Prof. Dr. Noha Fouda Salama
Associate Prof. of Mechanical Design Engineering
By:
Eng. Basma Muhammad Eltlhawy Elsayed
March 2016

3. Presentation Structure
Introduction
Knee Joint
Knee Replacement Surgery
Problems Appeared after Knee Replacement
Aim of the Work
Natural & Artificial Tibia Models
Shape Optimization
Material Selection
Metallic Stem Material
HA Coating
Attached Plastic Tip
Optimized Model
Case Study
Conclusions

4. Introduction
Knee Joint

5. Introduction Knee Replacement Surgery Total Knee Replacement TKR PKR
RKR

6. Problems Appeared after Knee Replacement
Tibial femoral instability
Patellar instability
Wear of the UHMWPE
Fatigue (weakness) failure
Tibia stress shielding
Tibial tip stress concentration
Tibia aseptic loosening

7. Aim of the Work
So a finite element analysis with optimized shape and material is carried out through this study in order to solve these conflicting problems.

8. Natural & Artificial Tibia Models
Materials & Method
Geometry: CATIA V5R18
FEM: ANSYS 14.5
Static structural application
Tetrahedral elements
Natural Model
Material
Elastic Modulus (GPa)
Poisson's Ratio
Diaphyseal Cortical Bone 17
0.3
Metaphyseal Cortical Bone 5
Cancellous Eiphyseal Bone
0.4
Cancellous Diaphyseal Bone
0.1
UHMWPE Insert 1
Ti6Al4V Tibia
110
0.33
Initial Model

9. Natural & Artificial Tibia Models

10. Natural & Artificial Tibia Models
Results

11. Shape Optimization Materials & Method Objective: Design Variables:
Maximize the von-mises stress under the metal tibial tray on cancellous bone.
Design Variables:
12mm ≤ D proximal stem dia. ≤ 16mm
40mm ≤ L length of the stem ≤ 120mm
3mm ≤ H tibial tray height ≤ 6mm
Constraints:
σ tip-natural ≤ σ tip-optimal ≤ σ tip-initial
τ natural ≤ τ optimal ≤ τ initial

12. Shape Optimization Materials & Method Geometry: CATIA V5R18
Parameters: SolidWorks 2012
FEM: ANSYS 14.5
Static structural application
Tetrahedral elements
90hrs DOE run time

13. Shape Optimization
Results

14. Metallic Stem Material
Material Selection
Metallic Stem Material
A comparison among three different metallic stem material; Ti6Al4V, Ti13Nb13Zr and CrNiMo stainless steel to get the ideal model.
Material
Elastic Modulus (GPa)
Poisson's Ratio
Ti6Al4V
110
0.33
Ti13Nb13Zr 79
0.3
CrNiMo Stainless Steel
200

15. Metallic Stem Material
Material Selection
Metallic Stem Material

16. Material Selection HA Coating
Coating the ideal tibial stem with PLA-HA polylactic acid hydroxyapatite coating.
A comparison between 0.5mm and 1mm coating thickness.
Material
Elastic Modulus (GPa)
Poisson's Ratio
PLA-HA Coating 5
0.3

17. Material Selection
HA Coating

18. Material Selection Attached Plastic Tip
Attaching a plastic tip at the end of the ideal metallic tibial tray.
A comparison between 5mm and 10mm plastic tip length.
Material
Elastic Modulus (GPa)
Poisson's Ratio
Plastic Tip 1
0.3

19. Material Selection
Attached Plastic Tip

20. Optimized Model

21. Case Study
CP Model

22. Case Study
CP Model

23. Conclusions
The optimal shape of uncemented tibial tray for TKR is to be a short cylindrical stem with a small diameter at the distal stem tip and a long metal height to house the polymer insert. This improves the stress shielding.
The suitable metallic stem material is Ti6Al4V alloy.
Using a thin layer of HA bioactive coating around the stem is to improve the implant fixation method (thicker coating).
Using a polymer tip attached the stem end improves the stress concentration at the stem tip as well as the aseptic loosening (longer tip).
Comparing among the optimal Ti6Al4V shape, HA coated and attached plastic tip models proves that the attached plastic tip is the optimized model.
New model (case study) provides the most optimum case for optimizing the model shape and its material.

24. Publications
N. Fouda, B. Eltlhawy, T. El-Midany, "The effect of using PLA-HA coating on uncemented tibia prosthesis to decrease aseptic loosening and stress shielding", International Journal of Mechanical & Mechatronics Engineering, IJMME-IJENS, Vol 15(6), pp , (Dec. 2015).
B. Eltlhawy, N. Fouda, T. El-Midany, "The influence of tibial prosthesis shape optimization on reducing stress shielding and aseptic loosening", Trends in Biomaterials and Artificial Organs Journal, Vol 29(3), (2015).
N. Fouda, B. Eltlhawy, T. El-Midany, "A three dimensional finite element comparative study for three new different tibia knee designs", under-publication.