1. INTRODUCTION & PROBLEM STATEMENT
T01_013: Performance Study of Polyethylene Tibial Insert in Total Knee
Replacement During Deep Knee Flexion
INTRODUCTION
INTRODUCTION & PROBLEM STATEMENT
RESULTS AND DSCUSSION
Knee is defined as a joint where having three components. The thigh bone (the femur) joins the large shin bone (the tibia) to combine the main knee joint [1]. From the aspect of anatomy human body, the knee is the complicated joint in the human body. Knee have two structurally and functionally different, yet interrelated joint, which are tibiofemoral and patella femoral joint [2]. Commonly, there are two ways of knee injury; natural injury due to the sport activities and aging as well as accident event such as road accident, work site accident etc. In year 2006 NexGen Legacy® LPS-Flex Mobile Bearing had produce by Zimmer Incorporated has improved the design knee implant for deep knee flexion (155o), however in this study will extend the knee implant up to 165˚.
Figure 1: Total deformation (mm) versus angle of flexion (degree)
Figure 2: Equivalent stress (MPa) versus angle of flexion (degree)
Figure 4: Contact pressure (MPa) versus angle of flexion (degree)
Figure 3: Shear stress (MPa) versus angle of flexion (degree)
OBJECTIVE
[1] Redesign the metallic tibia tray component in total knee replacement of deep knee flexion. [2] Analyse the metallic tibia tray component in total knee replacement of deep knee flexion. [3] Access the performance tibia tray component of high flexion.
Figure 1.1: Contact pressure zero degree (standing position)
Figure 2.1: Contact pressure 90 degree (kneeling position)
Figure 3.1: Contact pressure 135 degree (squat position)
Figure 4.1: Contact pressure (deep flexion position)
Based on the FEA simulation, the highest stress value is lower than Young Modulus elasticity value, so that every deformation still in elastic modulus. Elastic modulus is defined as deformation on implant and the slope of its stress–strain curve in the elastic deformation region. Yield strength is the critical boundary between elasticity and plastic region. Every stress value must be lowered than yield strength to avoid plastic region.
METHODOLOGY
Start
Benchmarking
Reverse engineering benchmarking model
Identify where the critical part to modify the existing design
Modelling different improvement design
Model design 1
Model design 2
Model design3
Table 1: Material improvement from base material
Table 2: Comparison criteria existing and new design
Part
Selected material
Young Modulus elasticity (MPa)
Femoral
Cobalt Chrome Alloy
220,000
Tibial insert
Ultra High Molecular Weight Polyethylene (UHMWPE)
,500
Tibia
Titanium
110,320
Angle of flexion (degree)
Deformation (mm)
Von Mises stress (MPa)
Shear stress (MPa)
Contact pressure scale (MPa)
Existing design
New design
0.469
0.0076
29.703
4.216
16.506
2.162
14.767
1.675 90
0.0199
0.0305
38.761
29.441
19.965
15.713
7.642
12.86
135
0.93
0.3
244.47
48.522
132.35
27.549
60.078
55.181
165
0.535
0.447
253.55
144.31
128.43
79.059
553.98
188.47
(A)
Selection of the best design
Choice the best design
Selected improvement design
CONCLUSION
(B)
FEA for design improvement
The present work which aims to redesign a knee implant that can extend the flexion angle up to 165° compared to the existing design in which the maximum flexion angle is 155° [8]. From the FEA analysis using Ansys 15.0 software, the new design has produced criteria of von Mises stress, shear stress and contact pressure which are about 43%, 38% and 66% respectively. This study proves that the deep flexion up to 165° for knee implant is still feasible with the finding values of von Mises stress, shear stress and contact pressure.
Improvement design success?
Figure 1:
Picture of existing design.
(B) Picture of new
design. NO
YES
New design
End