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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

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

Introduction Knee Joint

Introduction Knee Replacement Surgery Total Knee Replacement TKR PKR RKR

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

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.

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

Natural & Artificial Tibia Models

Natural & Artificial Tibia Models Results

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

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

Shape Optimization Results

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

Metallic Stem Material Material Selection Metallic Stem Material

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

Material Selection HA Coating

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

Material Selection Attached Plastic Tip

Optimized Model

Case Study CP Model

Case Study CP Model

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.

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, 153906-8787-IJMME-IJENS, Vol 15(6), pp. 76-83, (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.