1. Finite Element Analysis of Composite Hip Prosthesis
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Finite Element Analysis of Composite Hip Prosthesis
M. Sivasankar, D.Chakraborty, S.K.Dwivedy
Department of Mechanical Engineering
Indian Institute of Technology, Guwahati

2. Scope of the Present Work
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Scope of the Present Work
An overview of hip replacement
References on total hip replacement (THR)
Objective
Material selection
Finite element model
Comparison of results

3. An Overview of Hip Replacement
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An Overview of Hip Replacement
Anatomy of hip joint
Hip prosthesis
Types of prosthesis fixation
Reasons for hip failure
A Typical Hip
Prosthesis
A Typical Hip Prosthesis

4. Anatomy of Hip Joint Largest weight bearing joint
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Anatomy of Hip Joint
Largest weight bearing joint
Composed of rounded head of the femur joining the acetabulum of pelvis in a ball and socket arrangement

5. Reasons for Hip Failure
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Reasons for Hip Failure
Long-term aseptic loosening.
Primary hip arthoplasties are subjected to failure due to bone resorption i.e. bone loss.
Failure due to fatigue loading of hip joint.
Relative micro motions resulting from improper implant fitting in the bone cavity.

6. Reasons for Hip Failure Cont..
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Reasons for Hip Failure Cont..
In cementless implants load transfer between a stiff implant and relatively flexible bone results in extremely unnatural stress distribution in bone, i.e. excessive stress concentrations near to the implant ends.
Stress shielding followed by bone resorption in the other areas of bone-implant interface.

7. Reasons for Hip Failure Cont..
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Reasons for Hip Failure Cont..
Hip failure due to bone loss is caused by the production of wear particles associated with the deterioration of the prosthesis
For an average hip patient, the prosthesis have to resist thirty-four million blows

8. Damaged Femoral Head Femoral head cartilage
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Damaged Femoral Head
Femoral head cartilage
The neck is cut-off as in figure
Marrow cavity is made inside the femur
Hip prosthesis is fitted either by PMMA cement or press fitted

9. References on Total Hip Replacement
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References on Total Hip Replacement
Many researchers carried out advanced researches in the field of THR using Finite Element Method and other methods

10. Literature Review Researches in this area has been carried out in:
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Literature Review
Researches in this area has been carried out in:
Cemented Joint
Cement less Joint
Finite Element Analysis
Experimental with design models

11. Researches Carried Out
S.No.
Experiment Based
FEM based
Cemented Joint
Cementless Joint 1
G.Bergmann(2001)
C.F.Scifert (1999)
S.K.Senapathi (2002)
P.Kowalczyk (2001) 2
G.Selvaduray(2002)
A.Philips (2001)
P.Colombi (2002) 3
H.Katoozian (2001)
P.Kovalczyk(2001)
A.B.Lennon (2003) 4
J.A.Simoes (2000)
P.B.Chang (2001)
Sheryl Zimmarman (2002) 5
M.Baleani(2000)
R.Huiskes (1992)
V.Waide (2004) 6
C.Kaddick (1997)
C.Li (2002)
P.J.Prendergast (1997) 7
N.H.Tai (1995)
W.Van Papegem (2001) 8
G.Dillon (1995)
S.Srinivasan (2000) 9
X.Diao (1997)
H.F.El.Sheikh (2003) 10
B.W.Stansfield (2003)
S.Gross (2001) 11
M.Pawlikowwski
S.H.Teoh (2002) 12
S.L.Evans (1998)
Bernard Weisse (2003) 13
R.P.Morris 14
M.T.Raimondi (1999) 15
C.M.Styles (1998) 16
I.Hilal (1999) 17
Darryl.D 18 19
L.J.Lee (1996) 20
W.Vanpaepegem (2002) 21
S.Ramakrishna (2001) 22
K.L.Reifs nider (1991) 23
S.K.Roy Choudhury (2004) 24
A.Rajadurai (2002) 25
R.De.Santis (2004) 26
Vesa Saikko (2002) 27
Debera.E Hurwitz (2003) 28
B.Mavcic (2002)

12. Recent Work
Few researchers like A.Phillips[1], P.J.Prendergast [2] ,H.Katoozian [6], C.Li [9] etc., work in the area of cemented prosthesis.

13. Biomaterials Stainless Steel Alloys Cobalt-Chrome alloys (Vitallium)
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Biomaterials
Stainless Steel Alloys
Cobalt-Chrome alloys (Vitallium)
Titanium alloys
Composites

14. Comparison of Characteristics
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Comparison of Characteristics
Characteristic
S-Steel
Co-Cr alloy
Titanium Alloy
Stiffness
High
Medium
Low
Strength
Corrosion -resistance
Biocompatibility

15. SIVA FROM IITG
Need of Composites
The isotropic alloys used for stem have much higher stiffness than that of the bone
Almost all monoclinic implants have 5 to 20 times more stiffness than the bone
A stiff shaft of a total hip prosthesis stress shields the upper part of the thigh bone
The shielded bone does not thrive, loses its substance and becomes weak
The total hip joint has weak anchorage in a weak skeleton and may fail
The remedy is a prosthetic shaft manufactured from metal alloys with stiffness similar to bone

16. Advantages of Composites
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Advantages of Composites
Low stiffness of composite stems can enhance proximal bone ingrowths
Tailorability property in strength and stiffness.
Excellent biocompatibility
A controlled stiffness prosthesis can reduce stress shielding and bone resorption
Less weight of the prosthesis

17. SIVA FROM IITG
Composite Prosthesis
Clinical studies reported early fatigue fracture of a femoral component made from laminated fiber reinforced composites.
The new designs are Constructed of short glass fibers/epoxy resin and CF/PEEK composites.

18. SOLID 92 Element

19. SIVA FROM IITG
Composite Model
Basic Composite Model With Elements

20. Conical Stem Cemented prosthesis model contains three main parts:
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Conical Stem
Cemented prosthesis model contains three main parts:
Conical Stem with head
Cement layer
Cortical bone
Basic Model

21. Model With Chopped Fiber Core
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Chopped Fiber Core
Model With Chopped Fiber Core

22. Material Properties Used for Analysis of Total Hip Prosthesis
Parts
Material
Young’s Modulus (MPa)
Poisson's Ratio
Geometrical Parameter (All dimensions are in mm)
Head and Stem
 Ti6Al4V
110x103
0.33
Sphere radius 25
Stem radius 10
Stem outer radius 10
Stem inner radius 7.5
Cement Layer
UHMWPE-AL2O3
1x103
0.39
Inner radius 10.5
Outer radius
Length 100
Cortical Bone
AS4/PEEK
3x103
0.30
Inner radius 20.5
Outer radius 30

23. Maximum Shear Stress Region
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Maximum Shear Stress Region
Enlarged View of the Deformed Stem and Cortical Bone Showing the Maximum Shear Stress Region (Path Aa)

24. Variation of Shear Stresses
Variation of Maximum Shear Stress
With System Parameters
Stem Length
(in mm)
Maximum Shear Stress
(in MPa)
145
17.314
145.5
15.522
147.5
21.033
150
20.919
152.5
17.144
155
20.262
Neck Length
(in mm)
Maximum Shear Stress
(in MPa) 45
13.337
47.5
17.376 50
17.314
52.5
25.363
Neck Inclination
(in degree)
Maximum Shear Stress
(in MPa) 45
17.314
47.5
20.383 50
22.964
Stem Inner Radius
(in mm)
Maximum Shear Stress
(in MPa)
7.5
17.314 8
20.655
8.5
19.443

25. Continued...
The variation in the above parameters do not show a particular trend
Hence the design optimization has been carried out to minimize the magnitude of maximum shear stress

26. Dimensions of Hip Prosthesis Before Optimization
Dimensions of Hip Prosthesis Before Optimization
Parts
State Variables
Design Variables
Femur
Sphere Radius
25 mm
Stem Outer Radius
10 mm
Stem Inner Radius
7.5 mm
Neck Inclination
450
Stem Length
145.5 mm
Neck length
50 mm

27. Design Variables of Femoral Components
After Optimisation
Design Variables
Dimension (mm)
Stem outer radius
9.9301
Stem inner radius
8.0405
Stem length
153.22
Neck length
50.975

28. SIVA FROM IITG
Shear Stresses
SXY
x-y component
SYZ
y-z component
SXZ
z-x component
Shear Stresses in the Interface of Stem and Cortical Bone

29. Shear Stresses - Continued…
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Shear Stresses - Continued…
SXY
x-y component
SYZ
y-z component
SXZ
z-x component
Shear Stresses in the Interface of Stem and Cortical Bone

30. Conclusion
A 3D finite element analysis has been done for analysis of composite hip prosthesis which consists of a conical stem with a cement layer.
Location and magnitude of shear stresses show the region of failure which is in agreement with the earlier published results.

31. Continued…
As the variation of the parameters do not show a particular trend, design optimization has been carried out to minimize the magnitude of maximum shear stress
The optimum dimensions obtained from the present analysis show considerable reduction in shear stress

32. References
[1] A. Phillips, 2001, Finite element analysis of the acetabulum after impaction grafting, The University of Edinburgh.
[2] P.J.Prendergast, 1997, Review paper – Finite element models in tissue mechanics and orthopaedic implant design, Clinical Biomechanics, Vol. 12, No. 6,
[3] C. F. Scifert, T. D.Brown, J. D.Lipman, 1999, Finite element analysis of a novel design approach to resisting total hip dislocation, Clinical Biomechanics, 14,
[4] M.Baleani, M.Viceconti, R. Muccini, M. Ansaloni, 2000, Endurance verification of custom-made hip prostheses, International journal of fatigue 22,
[5] P. B. Chang, B. J. Williams, K.S. B.Bhalla, T. W. Belknap, T. J. Santner, W. I. Notz, D. L. Bartel, 2001, Design and analysis of robust total joints replacements: Finite element model experiments with environmental variables, ASME, Journal of Biomechanical .Engineering, 123,
[6] H. Katoozian, D. T. Davy, A. Arshi, U. Saadati, 2001, Material Optimization of femoral component of total hip prosthesis using fiber reinforced polymeric composites, Medical Engineering and Physics, 23,
[7] S. K. Senapati, S. Pal, 2002, UHMWPE-ALUMINA ceramic composite, an improved prosthesis material for an artificial cemented hip joint, Trends in Biomaterials Artificial. Organs, 16(1), 5-7.
[8] J.Stolk, N. Verdonschot, L. Cristofolini, A. Toni, R. Huiskes, 2002, Finite element and experimental models of cemented hip joint reconstructions can produce similar bone and cement strains in pre-clinical tests, ASME, Journal of Biomechanics 35,
[9] C. Li, C. Granger, H. D. Schutte Jr, S. B. Biggers Jr, J. M. Kennedy, R. A. Latour Jr, 2003, Failure analysis of composite femoral components for hip arthroplasty, Journal of Rehabilitation Research and Development, 40(2), 131–146.

33. Questions?

34. Thank You for Attending…
A copy of my slides will be available on my website
My address is:
IITG Biomechanics center:
Work supported by Department of Mechanical Engineering,
contact +91 (361)