9 Simulation by Finite Elements of Bone Remodelling After Implantation of Femoral Stems Luis Gracia et al. * Engineering and Architecture Faculty, University of Zaragoza, Spain 1. Introduction Degenerative osteoarthritis and rheumatoid diseases lead to a severe destruction of the hip joint and to an important functional disability of the patient. Several attempts by many surgeons were documented, in the history of Orthopedic Surgery, to restore an adequate function of the pathologic joint. All these attempts failed due to the use of inadequate materials or due to technical problems. In the past 20th century, during the sixties, a successful replacement of a pathologic hip joint was finally achieved. It was the first arthroplasty of the hip providing a good functional outcome. This new technique was described by Charnley in 1961 (Charnley, 1961). Two materials were then introduced in the orthopedic surgery, the polyethylene and the polymethyl methacrylate. This later is known as bone cement, and allowed a good fixation of the prosthetic implants into the femoral canal and the pelvic acetabulum. This technique represented one of the most important advances in the Orthopedic Surgery during the 20th century. Based on the original model developed by Charnley, total cemented hip implants have been improved with new materials and prosthetic designs. The most important advances have been described in the cements and cementation techniques (Mulroy & Harris, 1990; Noble et al., 1998; Reading et al., 2000), and in the sterilization and manufacture of the prosthetic polyethylene (Medel et al., 2004; Urries et al., 2004; D’Antonio et al, 2005; Oral et al., 2006; Faris et al., 2006; Gordon et al., 2006; Wolf et al., 2006). Nevertheless, the original stem design of Charnley remains unaltered and fully operational. First generation cemented prosthesis, inserted by manual techniques (first generation cement fixation), were associated with high rates of aseptic loosening and mechanical failures (Olsson et al., 1981; Stauffer, 1982; Harris et al., 1982; Halley & Wroblewski, 1986; * Elena Ibarz 1 , José Cegoñino 1 , Antonio Lobo-Escolar 2,3 , Sergio Gabarre 1 , Sergio Puértolas 1 , Enrique López 1 , Jesús Mateo 2,3 , Antonio Herrera 2,3 1 Engineering and Architecture Faculty, University of Zaragoza, Spain 2 Medicine School, University of Zaragoza, Spain 3 Miguel Servet University Hospital, Zaragoza, Spain