Septic arthritis may develop when an infection elsewhere in your body spreads through your bloodstream to a joint. Although they do not cause septic arthritis, several risk factors-including a suppressed immune system, drug abuse, and other diseases, such as rheumatoid arthritis, diabetes, cancer, anemia, lupus, and liver disease-make it more likely to develop. Artificial joints and recent joint surgery or arthrocentesis (inserting needles into the joint) are also risk factors for septic arthritis. However, the risk from these sources is small. The biggest risk factor for septic arthritis is advanced age. Roughly half the cases of septic arthritis occur in people over age 60. In these patients, 75 percent of the infections occur in joints that have already been affected by arthritis, especially the hips, knees, and shoulders.