Osteoarthritis may be associated with different risk factors. Age, gender, ethnicity, bone density, estrogen, nutrition, and genetics can each play a role in making us susceptible. Biomechanical factors such as obesity, joint injury, sports participation, and muscle weakness can then determine the location and severity. Rheumatoid arthritis is not yet fully understood, but the immune system plays a role in causing inflammation and joint damage. Genes, hormones, and environmental factors are involved.