Abstract— The primary cause of Total Hip Replacement (THR) failure for younger patients is aseptic loosening. This complication is twice more likely to happen in acetabular cup than in femoral stem. Excessive micromotion between bone and implant will cause loosening and it depends in patient activities, age and bone. In this project, the effects of different metal back design of press fit on osseointegration of the acetabular cup are carried out. Commercial acetabular cup designs, namely Spiked, Superfix and Quadrafix are modelled and analyzed using commercial finite element software. The diameter of acetabular cup is based on the diameter of acetabular rim to make sure the component fit to the acetabular cavity. A new design of acetabular cup are proposed and analyzed to get better osseointegration between the bones and implant interface. Results shows that the proposed acetabular cup designs are more stable compared to other designs with respect to stress and displacement aspects. I. INTRODUCTION improving the quality of life for millions of patients worldwide especially who experienced osteoarthritis. Ironically, it has become the victim of its own success. Originally intended for old people with age 50 years old and above, THR is increasingly used on younger person, nowadays. The younger and active person requires a prosthesis that can last longer and endure an active lifestyle without the need of revision. According to Wroblewski (2002), design goal have advanced from simply lighting pain and uncomforted for the elderly patients, to returning young active patients to more physically demanding lifestyle as well as sport activities [1]. The primary cause of THR failure for younger patients is aseptic loosening especially at the acetabular cup. The cause of aseptic loosening is still clearly debated, but the final explanation might be sought in the combination of multiple etiologic factors including, prosthesis stiffness, particulate reaction and stress shielding. In this study, four different model of acetabular cup are used to analyze the micromotion and stress of press fit hip replacement surgery on acetabular cavity. The models namely, Nor Azali Azmir is with the Faculty of Mechanical and Manufacturing, Universiti Tun Hussien Onn Malaysia, 86400 Batu Pahat, Johor, Malaysia (e- mail: azali@uthm.edu.my). Iskhrizat Taib was with Faculty of Mechanical and Manufacturing, Universiti Tun Hussien Onn Malaysia, 86400 Batu Pahat, Johor, Malaysia (e- mail: iszat@uthm.edu.my). Mohammed Rafiq Abdul Kadir is with the Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia (e-mail: rafiq@fkbsk.utm.my). quadrafix, spiked, superfix and proposed model are analyzed using a commercial finite element simulation together with an in-house experimentally validated micromotion algorithm. The purpose of this study is to investigate the effect of different metal back design of press fit on osseointegration of the acetabular cup. II. FINITE ELEMENT MODEL Finite Element model of the pelvis bone was reconstructed from a normal healthy bone data set. The geometry of pelvis bone is based on computed tomography (CT) scan data. A good visualization of the details on the CT scan data could only be achieved by defining the appropriate threshold for the cortical bone and cancellous bone. Finite element model of human pelvis which consist of three part namely, ilium, ischium and pubic, is illustrated in Fig. 1 while different type of acetabular cup in Fig. 2. The diameter of acetabular cup is depending on diameter of patient acetabulum cavity. Due to the reason, selection of suitable acetabular cup design and diameter must be selected before a surgery can be proceed. The prosthesis, comprising a titanium hemispherical metal shell inserted with 450 inclinations and 250 anteversion. Size of triangular mesh element of bone must be almost the same as the implant as well to make sure nodes between two models were connected each others. The surface mesh of both the implant and the bone were used for creating bone-implant contact. Fig. 1 3-D model of human pelvis bone Nor Azali Azmir, Iskhrizat Taib, and Mohammed Rafiq Abdul Kadir The Effect of Press Fit on Osseointegration of Acetabular Cup T OTAL Hip Replacement (THR) is an effective procedure in acetabular cup, loosening. Keywords—Finite element analysis, total hip replacement, World Academy of Science, Engineering and Technology International Journal of Biomedical and Biological Engineering Vol:6, No:10, 2012 480 International Scholarly and Scientific Research & Innovation 6(10) 2012 scholar.waset.org/1307-6892/783 International Science Index, Biomedical and Biological Engineering Vol:6, No:10, 2012 waset.org/Publication/783