Effect of Femoral Head Size to Contact Stress at Pure Titanium Femoral Ball Head Outer Surface of Hip Joint Implant Agung Setyo Darmawan, Waluyo Adi Siswanto, Haryanti Samekto Faculty of Mechanical and Manufacturing Engineering Universiti Tun Hussein Onn Malaysia, 86400 Parit Raja - Batu Pahat E-mai :agungsetyod@yahoo.com ABSTRACT Titanium alloys are commonly used in the application of biomechanics parts. One of the applications for hip joint prostheses. When wearing is one parameter that mostly considered, the Titanium alloy is much more superior compared to that from polyethylene derivatives. Although the wear of existing Ti- 6Al-4V Titanium Alloy on Ti-6Al-4V Titanium Alloy hip joint prostheses is much lower than the more widely used polyethylene on metal bearings, there are some concerns about the toxicity of Al and V wear debris in the human body that might negative side effects to the human body. For this reason, the use of pure Titanium is a potential metal and safer to replace Ti-6Al-4V Titanium Alloy bearings. An investigation has been conducted to see the effect of femoral head size to Contact Stress at Pure Titanium Femoral Ball Head Outer Surface of Hip Joint Implant. The radius of femoral heads are 27 mm, 28 mm, and 30 mm. Numerical analysis based on Finite Element Method is used to simulate and calculate the contact stresses of the bearings. A commercial package CATIA V5 R14 is employed to analyse the contact stresses. For the radius of 27mm, 28mm, and 30 mm the largest contact pressures of each radius are 6.33 x 10 11 N/m 2, 4.92 x 10 11 N/m 2, and 2.9 x 10 11 N/m 2, respectively. These values illustrates that the larger the radius, the smaller the contact stress. Keywords: Hip Joint, Pure Titanium, Contact Stress. 1. Introduction Hip joint is an important component of the human skeletal system. It is located at the junctions between the pelvis and the upper leg bone (femur). The primary disease of the hip is osteoarthritis, and is usually described as the degeneration and progressive loss of normal structure and function of articular cartilage. Osteoarthritis affects 90 % of the human population by the age of 70 years. thus increasing joint friction [1]. Hence, hip joint needs to be replaced. A schematic diagram of the artificial hip joint is presented in Fig. 1a; Fig. 1b shows an X- ray of a total hip replacement. Hip joint replacement is described as the greatest achievement in orthopedic surgery in the twentieth century. The field has been dominated for some forty years by implants based upon metallic femoral heads and stems and polymeric acetabular cups [2]. Other hip disease is rheumatoid arthritis. Osteoarthritis and rheumatoid arthritis result in physical wear of the articular surface, leading to joint paint, restriction of motion and deformity. Under these conditions, damage to the synovial fluid is inevitable, which causes a decrease in viscosity under all possible shear rates,
plasma treatment or by appropriate coating films [10-11]. Metal on metal bearings have been shown to result in much lower wear volume [12]. Their higher stiffness allows metal on metal components to be manufactured with larger diameters. The purpose of this study was therefore to investigate effect of femoral head size to contact stresses at outer surface of femoral ball head. 2. Methods Figure 1 (a) Schematic diagram and (b) x-ray of an artificial total hip replacement [3]. The use of polymer for total hip replacement has increase significantly in recent years, mainly as a consequence of their good combination of mechanical and surface properties together with recent improvements in biocompatibility and bioactivity [4]. The wear of polymer cup in hip implants lead to loosening of the implant and osteolysis. Mass loss as a result of wear leading to osteolysis may cause dislocation and subsequently revision and/or replacement of the implant [5]. A significant number of total joint replacements fail long before their expected life causing severe traumas to the patients. Hence, ceramic on ceramic, and metal on metal bearing pairs are an interesting alternative [6-9]. One of the high potential metals on metal is made from Pure Titanium, which is appreciated for its light weight, good biocompatibility, and elastic properties similar to natural bone. Several attempts have been undertaken to improve the surface properties of titanium alloys either by The material used for this work is pure titanium. The properties of the material are young modulus of 1.14 x 10 11 N/m 2, Poisson ratio of 0.34, density of 4460 kg/m 3, and yield strength of 8.25 x 10 8 N/m 2. Three different diameters of femoral ball head are considered: 54 mm, 56 mm, and 60 mm, respectively. The femoral ball head, stem, and acetabular cup are shown in Figure 2. To determine the stress distribution in the titanium femoral ball head for the 5 kn, the load of 5 kn is applied as a pressure of 1.5 x 10 7 N/m 2 as shown in Figure 3. Figure 2 The components of an artificial total hip replacement.
Figure 3. A pressure of 1.5 x 10 7 N/m 2 is applied at black colour part. 3. RESULT AND ANALYSIS Numerical simulation results for various radius obtained by CATIA are shown from Figure 3 to Figure 5. Figure 3. A numerical simulation result of 27 mm radius femoral ball head
Figure 4. A numerical simulation result of 28 mm radius femoral ball head Figure 5. A numerical simulation result of 30 mm diameter femoral ball head The largest contact stresses on each radius of the femoral head outer surfaces are listed in table 1. This table demonstrates that the larger femoral ball head may induce larger contact stress. For the radius of 27mm, 28mm, and 30 mm the largest contact pressures of each radius are 6.33 x 10 11 N/m 2, 4.92 x 10 11 N/m 2, and 2.9 x 10 11 N/m 2, respectively. Curve for contact pressure versus radius is shown in Fig. 6. The largest contact stress of the femoral head outer surface is reduced because of the increased area.
Table 1. The largest contact stresses on outer surface of femoral ball head No Radius (mm) Largest Contact Stress (N/m 2 ) 1 27 6.33 x 10 11 2 28 4.92 x 10 11 3 30 2.90 x 10 11 7 6 5 4 3 2 1 0 26 27 28 29 30 31 Radius (mm) Figure 6. Contact stress versus Diameter curve CONCLUSION From this study, it can be concluded that the larger the radius, the smaller the contact stress ACKNOWLEDGEMENT This work was supported by MOSTI under research grant Science fund Vot S015. Thanks to Agus Dwi Anggono, Bana Handaga, and Bambang Waluyo Febriyantoko for the CATIA discussion. REFERENCES [1] Bowsher, J.G., 2001, Accelerated Wear Testing Methodologies for Total Hip Replacements, Ph.D Thesis, Queen Mary University of London [2] Dowson, D., 2001, New Joints for the Millennium: Wear Control in Total Replacement Hip Joints, Proc Institute of Mechanical Engineers Vol. 215 Part II, page 335-358 [3] Callister, W.D., 2007, Materials Science and Engineering: An Introduction 7ed, John Wiley and Son, New York. [4] Wilches, L.V., Uribe, J.A., Toro, A., 2008, Wear of Materials Used for Artificial Joints in Total Hip replacement, Wear 265, page 143-149 [5] Alhassan, S., Goswami, T., 2008, Wear Rate Model for UHMWPE in Total Joint Application, Wear 265, page 8-13 [6] Mak, M.M., Jin, Z.M., 2002, Analysis of Contact Mechanics in Ceramic on Ceramic Hip Joint Replacement, Proc Institute of Mechanical Engineers Vol. 216 Part H, page 231-236 [7] Nevelos, J.E., Ingham, E., Doyle, C., Nevelos, A.B., Fisher, J., 2001, Wear of HIPed and non HIPed Alumina- Alumina Hip Joint Under Standard and Severe Simulator Testing Condition, Biomaterials Vol.22, page 2191-2197 [8] Zhou, Y.S., Ikeuchi, K., Ohashi, M., 1997, Comparison of The Friction Properties of Four Ceramic Materials for Joint Replacements, Wear Vol.210, page 171-177 [9] Jagatia, M. Jin, Z.M., 2001, Elastohydrodynamic Lubrication Analysis of Metal on Metal Hip Prostheses Under Steady State Entraining Motion, Proc Institute of Mechanical Engineers Vol. 215 Part H, page 531-541 [10] Osterle, W., Klaffke, D., Griepentrog, M., Gross, U., Kranz, I., Knabe, Ch., 2008, Potential of Wear Resistant Coatings on Ti-6Al-4V for Artificial Hip Joint Bearing Surface, Wear Vol.264, page 505-517 [11] Fisher, J., Hu, X.Q., Tipper, J.L., Steward, T.D., Williams, S., Stone, M.H., Davies, C., Hatto, P., Bolton, J.,
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