Septic arthritis, also known as infectious arthritis or joint infection, is the purulent invasion of a joint by an infectious agent which produces arthritis. People with artificial joints are more at risk than the general population but have slightly different symptoms, are infected with different organisms and require different treatment. Septic arthritis is considered a medical emergency. If untreated, it may destroy the joint in a period of days. The infection may also spread to other parts of the body.