ABSTRACT: The bone strength depends on its mineralization and its geometry, which depend themselves on the supported solicitations. The bone optimizes its mass and geometry in order to improve its strength. The optimization process is called bone remodeling. This phenomenon can be deteriorated by metabolic diseases like osteoporosis. This disease weakens the bone structure and causes bone fractures. Among those fractures, femoral neck fractures (hip articulation) are the most recurrent and involve the replacement of the entire hip articulation by a mechanic articulation (Total Hip Arthroplasty). In this paper, finite element models were developed to evaluate, firstly, the stress distribution within osteoporotic human femur bone tissue and secondly, the influence of the perturbation of the stress distribution by Total Hip Arthroplasty on its first stability. The geometry of the femur and the prosthesis was obtained by helicoid scanner acquisition. The bone was considered as two separate types of tissue: cortical bone and cancellous bone. The cortical bone was separated from the trabecular bone by apparent density threshold. In the case of osteoporotic femur the results obtained from the simulations suggest that the mechanism of load transmission is pertubated by the bone remodelling. The degradation of trabecular architecture causes high stresses in the antero-inferior zone of the cortical bone. For the femur with hip prosthesis, the results showed that the implant has significant effects on the stress distribution within bone tissue. High stresses, due to the implant, weak the bone tissue in the lateral zone of the proximal dyaphisis and in the medial zone of the distal part at the end of the stem.