Finite Element Analysis of Composite Hip Prosthesis

M. Sivasankar, D.Chakraborty, S.K.Dwivedy M. Sivasankar, D.Chakraborty, S.K.Dwivedy

Department of Mechanical EngineeringDepartment of Mechanical Engineering

Indian Institute of Technology, GuwahatiIndian Institute of Technology, Guwahati

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Scope of the Present Work

An overview of hip replacementReferences on total hip replacement (THR)ObjectiveMaterial selection Finite element modelComparison of results

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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

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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

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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.

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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.

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

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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

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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

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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

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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) A.Philips (2001)  

8 G.Dillon (1995) S.Srinivasan (2000) C.Li (2002)  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 H.Katoozian (2001)    14 M.T.Raimondi (1999)      15 C.M.Styles (1998)      16 I.Hilal (1999)      17 Darryl.D      18 S.Srinivasan (2000)      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)      

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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.

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Biomaterials

Stainless Steel Alloys

Cobalt-Chrome alloys (Vitallium)

Titanium alloys

Composites

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Comparison of Characteristics

Characteristic S-Steel Co-Cr alloy Titanium Alloy

Stiffness High Medium Low

Strength Medium Medium High

Corrosion -resistance Low Medium High

Biocompatibility Low Medium High

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Need of Composites

The isotropic alloys used for stem have much higher stiffness than that of the boneAlmost all monoclinic implants have 5 to 20 times more stiffness than the boneA 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 weakThe total hip joint has weak anchorage in a weak skeleton and may failThe remedy is a prosthetic shaft manufactured from metal alloys with stiffness similar to bone

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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

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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.

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SOLID 92 Element

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Composite Model

Basic Composite Model With Elements

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Conical Stem

Cemented prosthesis model contains three main parts:

Conical Stem with head

Cement layer

Cortical bone

Basic Model

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Chopped Fiber Core

Model With Chopped Fiber Core

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Material Properties

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 25Stem radius 10Stem outer radius 10Stem inner radius 7.5 

Cement Layer

UHMWPE-AL2O3

1x103 0.39 Inner radius 10.5Outer radius 12.2182Length 100 

Cortical Bone

AS4/PEEK 3x103 0.30 Inner radius 20.5Outer radius 30

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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)

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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 Inclination (in degree)

Maximum Shear Stress(in MPa)

 45 17.314

47.5 20.383

50 22.964

Neck Length (in mm)

Maximum Shear Stress(in MPa)

 45 13.337

47.5 17.376

50 17.314

52.5 25.363

Stem Inner Radius (in mm)

Maximum Shear Stress(in MPa)

 

7.5 17.314

8 20.655

8.5 19.443

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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

Continued...

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Hip Prosthesis 

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

Dimensions of Hip Prosthesis Before Optimization

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Femoral Components

Design Variables of Femoral ComponentsAfter Optimisation

Design Variables Dimension (mm)

Stem outer radius 9.9301

Stem inner radius 8.0405

Stem length 153.22

Neck length 50.975

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Shear Stresses

SXY

x-y component

SYZ

y-z component

SXZ

z-x component

Shear Stresses in the Interface of Stem and Cortical Bone

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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

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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.

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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

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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, 343-366.[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, 697-703.[4] M.Baleani, M.Viceconti, R. Muccini, M. Ansaloni, 2000, Endurance verification of custom-made hip prostheses, International journal of fatigue 22, 865-871. [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, 239-246.[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, 503-509.[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, 499-510.[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.

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Questions?

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Thank You for Attending…

A copy of my slides will be available on my website www.biosankar.4t.com

My email address is: sivasankar@iitg.ernet.in

IITG Biomechanics center: www.iitg.ernet.in

Work supported by Department of Mechanical Engineering,

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