FINITE ELEMENT ANALYSIS OF KNEE IMPLANT AND …FINITE ELEMENT ANALYSIS OF KNEE IMPLANT AND PROTOTYPE FABRICATION USING RPT PROCESS B.Rajesh, L.Radhakrishna and K.Venkata Reddy Assistant

http://www.iaeme.com/IJMET/index.asp 197 [email protected]

International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 12, December 2017, pp. 197–205, Article ID: IJMET_08_12_020 Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=12 ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Scopus Indexed

FINITE ELEMENT ANALYSIS OF KNEE

IMPLANT AND PROTOTYPE FABRICATION

USING RPT PROCESS

B.Rajesh, L.Radhakrishna and K.Venkata Reddy

Assistant Professor, Department of Mechanical Engineering, S R Engineering College, Warangal, Telangana, India

ABSTRACT

The aim of this research work is to do finite element analysis of patient specific

knee implant and compare the stress analysis results with commercially available

knee implant and Fabrication of prototypes of Patient Specific knee implant and

commercially available knee implant are done using FDM additive manufacturing

process.

In this research, it is proposed to develop a three-dimensional model of knee

implant from .stl file of knee joint using software’s like meshlab, NetFabb and CATIA

software’s. The data is obtained from Sunshine Hospital, Secunderabad. Based on the

dimensions of knee joint, it is proposed to Design a Knee implant in Catia software.

Once the 3D CAD model is designed in Catia software, it is meshed in ANSYS and

finite element analysis is performed for varying loads (500N-5000N). The obtained

results are compared with the commercially available knee implant. According to

walking condition the patient specific knee implant is analyzed for different flexion

angles (15, 45, 60 degrees). Fabrication of prototypes of patient Specific knee implant

and commercial available knee implants are done using FDM additive manufacturing

process.

Keywords: finite element, knee implant, RPT

Cite this Article: B.Rajesh, L.Radhakrishna and K.Venkata Reddy, Finite Element Analysis of Knee Implant and Prototype Fabrication using Rpt Process, International Journal of Mechanical Engineering and Technology 8(12), 2017, pp. 197–205. http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=12

1. INTRODUCTION

1.1 KNEE JOINT

The knee is one of the largest and most complex joint in the human body. The knee joins the thigh bone (femur) to the shin bone (tibia). The smaller bone runs alongside the tibia (fibula) and the knee-cap (patella) and the other bones that make the knee joint. Tendons connect the knee bones to the leg muscles that move the knee joint. Ligaments join the knee bones and provide stability to the knee joint:

Finite Element Analysis of Knee Implant and Prototype Fabrication using Rpt Process


• The anterior cruciate ligament prevents the femur from sliding backward on the tibia (or the tibia sliding forward on the femur).

• The posterior cruciate ligament prevents the femur from sliding forward on the tibia (or the tibia from sliding backward on the femur).

• The medial and lateral collateral ligaments prevent the femur from sliding side to side.

Two C-shaped pieces of cartilage called the medial and lateral menisci act as shock absorbers between the femur and tibia. Numerous bursae, or fluid-filled sacs, help the knee move smoothly.

Figure 1 Knee Implant

Reasons for damage of Knee Implant: the main reasons for the damage of the knee joint are as follows:

• Wear and loosening: Friction caused by joint surfaces rubbing against each other wears away the surface of the implant causing bone loss and loosening of the implants.

• Infection: Large metal and plastic implants can serve as a surface onto which bacteria can latch.

• Fracture: Fractures around the knee implant that disrupt its stability may require revision surgery.

• Instability: A sensation of the knee "giving away" may mean that the soft-tissue surrounding the knee is too weak to support standing and walking. Improperly placed implants may also cause instability.

• Stiffness: Loss of range of motion which causes pain and a functional deficit.[12]

Implant material

Generally Implants are manufactured with materials like metals, and ceramics. The metals used like Titanium, cobalt, chromium and stainless steel as shown in Table 1

Table 1 Common metals and properties used for implants

Material Density (g/cc) Compresive

strength (Mpa)

Elastic modulas

(Gpa)

Toughness

(Mpa)

Titanium 4.4-4.5 590-1117 55-117 55-115

Stainless steel 7.9-8.1 170-310 189-205 50-200

Co-cr-mo alloy 8.3-9.2 450-1896 200-253 100



2. PROBLEM STATEMENT

Knee arthritis has been a serious problem facing around 70 million patients worldwide. Total knee replacement has become an acceptable method of treating severe arthritis of the knee. The operative procedure must be performed with precise skill and accuracy. Great care and importance is given while selecting a proper and suitable biocompatible material for fabricating an implant. To make a bio-compatible implant it is important to know where it is located in the body. For the structural mechanics of human body involving bones, tissues and organs, it is almost impossible to conduct mechanical experiments. The finite element model to simulate such mechanical experiments has thus become an effective tool.

In this research, analysis of knee Implant is done which is designed according to the dimensions obtained from the STL file of knee joint and compared with the commercially available knee implant for three different bio-materials based on patient body weight acting on human body under different walking conditions. The patient specific knee implant is also analyzed for different flexion angles. Fabrication of designed and commercial knee implants is done using Fused Deposition Modeling RPT Process.

3. RESULTS AND DISCUSSIONS

This chapter presents the results obtained after adopting the research methodolgy discussed in earlier chapter. The finite element analysis of the patient specific Knee implant is done under static condition for different Flexion angles viz 0,15,45,60 degrees. The zero degres of Flexion angle represents the normal standing condition of the human being.

Analysis of patient specific Knee implant at zero degrees of three different bio-

compatible materials

Table 2 Comparison of Von-mises stress for different bio-compatible materials

Load (N) Von-mises stress (mpa)

Ti-6Al-4V Co-Cr-Mo SS 316L

500 2.65 3.08 3.07

1000 5.30 6.16 6.14

1500 7.95 9.24 9.21

2000 10.60 12.32 12.29

2500 13.25 15.41 15.36

3000 15.90 18.49 18.43

3500 18.55 21.57 21.51

4000 21.20 24.65 24.58

4500 23.85 27.74 27.65

5000 26.50 30.82 30.73

Table 3 Comparison of Total deformation for different bio-compatible materials

Load (N) Total deformation (mm)

Ti-6Al-4V Co-Cr-Mo SS 316L

500 0.0027 0.0020 0.0021

1000 0.0055 0.0040 0.0042

1500 0.0083 0.0060 0.0064

2000 0.0111 0.0080 0.0085



2500 0.0139 0.010 0.0106

3000 0.0165 0.012 0.0128

3500 0.0194 0.014 0.0149

4000 0.0222 0.016 0.0170

4500 0.0250 0.018 0.0192

Analysis of patient specific Knee implant of various flexion angles

The 3D cad model of Knee implant assembly is rotated to 15,45,60 degrees in catia software, according to walking condition and are imported in ANSYS IGES format and analysis was carried out for three different materials with combination of ultra-high-molecular-weight-polyethylene (UHMWPE). The results were found out in the form of von-mises stress, total deformation and contact pressure at each degree of flexion

Table 4 Comparison of Von-mises stress and Total deformation at Titanium alloy and different flexion angles

Flexion angles (deg) Von-mises stress (Mpa) Total deformation (mm)

500N 2500N 500N 2500N

15˚ 8.97 44.876 0.005 0.02

45˚ 8.84 44.23 0.015 0.07

60˚ 7.13 35.696 0.03 0.15

Figure 2 Graph plotted between Von-mises stress and Total deformation at Ti-4Al-6V

Table 5 Comparison of Von-mises stress and Total deformation at SS 316 alloy and different flexion

angles

Flexion angles (deg) Von-mises stress(Mpa) Total deformation (mm)

500N 2500N 500N 2500N

15˚ 9.18 45.94 0.004 0.02

45˚ 9.20 46.02 0.014 0.07

60˚ 7.64 38.2 0.02 0.14



Table 6 Comparison of Von-mises stress and Total deformation at Co-Cr-Mo alloy and different flexion angles

Flexion angles (deg) Von-mises stress (Mpa) Total deformation (mm)

500N 2500N 500N 2500N

15˚ 9.21 46.05 0.004 0.02

45˚ 9.18 45.9 0.014 0.07

60˚ 7.72 38.64 0.02 0.13

Figure 3 graph plotted between Von-mises stress and Total deformation at SS 316L

Figure 4 graph plotted between Von-mises stress and Total deformation at Co-Cr-Mo

Comparison of Analysis Results for patient specific and Commercial Knee

Implants

The von-mises stress and total deformation values obtained for the designed and commercially available Knee implants for three different bio-compatible materials are compared as shown in tables 6.8, 6.9,6.10 and correspondingly graphs are drawn as shown in figures.

6.4.1. For Titanium alloy

The von-mises stress and total deformation values obtained for the patient specific and commercially available Knee implants for three different bio-compatible materials are compared as shown in tables 6.8 and graphs is plotted as shown in fig 6.20 and 6.21



Table 7 Comparison of Equivalent Stress and Total Deformation for patient specific and Commercial knee Implants made of Titanium alloy.

LoadApplied (N) Equivalent Stress (MPa) Total Deformation (mm)

Patient specific Commercial Patient Specific Commercial

500 2.65 3.15 0.0027 0.0066

1000 5.30 6.31 0.0055 0.013

1500 7.95 9.46 0.0083 0.019

2000 10.60 12.62 0.0111 0.026

2500 13.25 15.77 0.0139 0.033

3000 15.90 18.93 0.0165 0.039

3500 18.55 22.09 0.0194 0.046

4000 21.20 25.24 0.0222 0.053

4500 23.85 28.40 0.0250 0.059

5000 26.50 31.55 0.0278 0.066

Figure 5 Comparison of Equivalent Stress for Designed(patient specific) and Commercial Knee

implants made of Titanium alloy.

Figure 6 Comparison of Total Deformation for Designed (patient specific) and Commercial Knee

Implants made of Titanium alloy.



6.4.2. For SS 316L alloy

hevon-mises stress and total deformation values obtained for the patient specific and

commercially available Knee implants for three different bio-compatible materials are compared as shown in tables 6.10 and graphs is plotted as shown in fig 6.24 and 6.25.

Table 6.10 Comparison of Equivalent Stress and Total Deformation for patient specific and

Commercial knee Implants made of SS 316L alloy.

Load Applied (N) Equivalent Stress (MPa) Total Deformation (mm)

patient specific Commercial patient specific Commercial

500 3.07 4.20 0.0021 0.005

1000 6.14 8.41 0.0042 0.01

1500 9.21 12.62 0.0064 0.016

2000 12.29 16.83 0.0085 0.021

2500 15.36 21.04 0.01 0.026

3000 18.43 25.25 0.012 0.032

3500 21.51 29.46 0.014 0.037

4000 24.58 33.66 0.017 0.043

4500 27.65 37.87 0.019 0.048

5000 30.73 42.08 0.02 0.053

Figure 7 Comparison of Von-Mises stress for Designed(patient specific) and Commercial Knee

implants made of SS 316L alloy.



Figure 8 Comparison of Total Deformation for Designed (patient specific) and Commercial Knee

implants made of SS 316L alloy.

7. CONCLUSIONS

The aim of this research work is to do finite element analysis of patient specific knee implant and compare the stress analysis results with results of commercially available knee implant. Manufacturing of patient specfic knee implant and Commercial Knee implants Prototypes are done using FDM additive manufacturing process. Knee implant is designed by taking the dimensions from .STL file in CATIA software and analysis is performed in ansys software to determine the von-mises stress under various walking conditions. The values obtained are tabulated accordingly as mentioned in research and methodology.

Following are the conclusions made from the Research Methodology adopted.

� For Proposed patient specific Knee implant, the von-misses stresses and deformation values obtained for different bio-materials under walking condition are as follows:

• For Ti-4A-l4V alloy, the maximum von-misses stress and total deformation values obtained are 26.50 MPa and 0.0278 mm respectively.

• For SS-316L material, the maximum von-misses stress and total deformation values obtained are 30.73 MPa and 0.02 mm respectively.

� For Commercially available Knee implant, the von-misses stresses and deformation values obtained for different bio-materials under walking condition are as follows:

• For Ti-4Al46V alloy, the maximum von-misses stress and total deformation values obtained are 31.55MPa and 0.066 mm respectively.

• For SS-316L material, the maximum von-misses stress and total deformation values obtained are 42.08 MPa and 0.053 mm respectively.

• For Cr-Co-Mo alloy, the maximum von-misses stress and total deformation values obtained are 43.28MPa and 0.041mm respectively.

� From the first study (FEM analysis when knee is in normal position) it is clear that even under extreme loading conditions, the prosthesis is safe (values obtained are below allowable stress) and gives good results for all selected biomaterials - Ti-6Al-4V, Co-Cr, SS-316L, UHMWPE



� At applied 5000 N load, least and maximum deformation values found for Cobalt alloy is 0.020 mm and for Titanium alloy is 0.027 respectively, similarly least and maximum equivalent stresses develop were Titanium alloy is 26.50 MPa, whose allowable stress is 880 MPa and Cobalt alloy is 30.82 MPa whose allowable stress is 612 MPa respectively.

� From the finite element analysis results obtained by rotating the designed knee implant at different flexion angles (15, 45, 60 degrees), it is observed that even if maximum load is applied i.e. 2500N the von misses stress values are obtained are 44.876 MPa for Titanium Alloy and 45.94 MPa for SS 316L Alloy and 46.05 MPa for Co-Cr-Mo alloy which are less compared to maximum allowable stress of three bio-compatible materials.

� For the two designs which are analysed in the thesis work, von-mises stress values obtained indicate that , titanium alloy material is best sutible compared to Co-Cr-Mo alloy and SS 316L.

� From this study it is found that stress induced for all selected biomaterials Ti-6Al-4v,and Co-Cr-Mo alloy and SS 316 L are with in allowable limit for maximum force and least deformation among all cases was found to be for Cobalt alloy.

Fabrication of patient specific and Commercial Knee implants are done using fused deposition Modeling machine. The printing time and material consumed for patient specific and Commercial Knee implants are 25 min, 9.24 gms and 50 min, 18 gms.

REFERENCE

[1] A. Sreenivasa Rao and K Venkata Rao. A Study on Machining Characteristics in Milling of Ti-6Al-4V using Experimental and Finite Element Analysis. International Journal of Civil Engineering and Technology, 8(7), 2017, pp. 457–469.

[2] R. Deendayal, Behaviour of a Single Pile Located on Sloping Ground of a Soil Under Cyclic Loading: A Finite Element Analysis. International Journal of Civil Engineering and Technology, 8(10), 2017, pp. 925–932

[3] S. P. Chaphalkar and V. S. Byakod, Design and Analysis of Bridge with Two Ends Fixed on Vertical Wall Using Finite Element Analysis, International Journal of Civil Engineering and Technology, 7(2), 2016, pp. 34- 44.

[4] S. Jayavelu, C. Rajkumar, R. Rameshkumar and D. Surryaprakash, Design and Analysis of Vibration and Harshness Control For Automotive Structures Using Finite Element Analysis, International Journal of Civil Engineering and Technology, 8(10), 2017, pp. 1364–1370.

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FINITE ELEMENT ANALYSIS OF KNEE IMPLANT AND …FINITE ELEMENT ANALYSIS OF KNEE IMPLANT AND PROTOTYPE FABRICATION USING RPT PROCESS B.Rajesh, L.Radhakrishna and K.Venkata Reddy Assistant