BACKGROUND: The main reason for reducing the life of joint prosthesis is prosthetic loosening. In addition to prosthesis design, surgical technique, prosthetic material and the resulting wear particles, bone quality also plays a very important role in prosthetic loosening. Bone tissue microstructure has an important impact on bone quality. Recently, the quantification of bone architecture based on micro-CT has been widely used in the research of various bone diseases. OBJECTIVE: To observe the osteoarthritis- and rheumatoid arthritis-related changes in the properties of the proximal femur based on micro-CT, thus to compare the bone microstructure in osteoarthritis and rheumatoid arthritis patients. METHODS: Femoral heads were collected from primary osteoarthritis (n=10) and rheumatoid arthritis (n=7) patients undergoing total hip replacement. A 10-mm segment of the femoral neck was cut from each individual femur, perpendicular to the main trabecular direction on X-ray films. The specimens were analyzed by using micro-CT system. After scanning, the data were transferred to three-dimensional images, and then detailed structural parameters of the cortical bone, cancellous bone and femoral neck were statistically analyzed based on novel unbiased, model-free three-dimensional methods. RESULTS AND CONCLUSION: There was no significant difference in the microstructure of the femoral head (cortical bone, cancellous bone and the entire) between the primary osteoarthritis and rheumatoid arthritis groups. The overall microstructure properties of the femoral neck were similar to those of the cancellous bone. Primary osteoarthritis patients were characterized by a more loss of the connectivity to the trabecular bone, an increase in degree of anisotropy for the cortical bone, but a decrease in degree of anisotropy for the cancellous bone and the entire trabecular bone, when compared to the rheumatoid arthritis group. These findings show that there is no difference in the microstructure of the cortical bone, the cancellous bone and the entire femoral neck between patients with primary osteoarthritis and rheumatoid arthritis, suggesting that primary osteoarthritis and rheumatoid arthritis have a similar trend of global microarchitectural degeneration in the femoral neck.