Infection of one or more joints by microorganisms. Septic arthritis can be caused by bacteria, viruses, and fungi of these most common causes of septic arthritis is bacteria.

Causes for septic arthritis are post surgery (iatrogenic), joint injury and any septic focus in the body. Risks factors are taking medications that suppress the immune system i.e., steroids, intravenous drug abuse, past joint disease and underlying medical illnesses such as diabetes, alcoholism, sickle cell disease and rheumatic diseases.