Septic arthritis is an infection in a joint. The infection can be caused by bacteria, viruses, or, less frequently, by fungi or parasites. Usually the infection involves a single large joint, such as the knee, but many joints may be involved. The initial infectious process can begin elsewhere in the body and travel through the bloodstream to the joint. Other sources include open wounds, surgery, and unsterile injections. Young children and elderly individuals are most likely to develop joint infections. The April 4, 2007, issue of JAMA includes an article that categorizes clinical findings that help identify patients who may have septic arthritis.
Fever
Chills
Severe pain in the affected joint, especially with movement
Swelling (increased fluid within the joint)
Warmth (the joint is red and warm to touch due to increased blood flow)
Fatigue and generalized weakness
Weak immune system—people with diabetes, kidney and liver problems, and HIV infection, and those taking drugs that suppress their immune system have an impaired ability to fight against infections.
Alcohol or other drug abuse
Cancer
Previous joint problems—conditions that affect joints, including other types of arthritis, may increase risk of septic arthritis. Previous joint surgery, joint replacements, and joint injuries also increase risk.
Skin wounds—open skin wounds give bacteria easy access to the body.
Blood tests—to identify an increase in white blood cells (WBCs) and bacteriaX-ray—to identify swelling within a joint and throughout the surrounding soft tissuesArthrocentesis—a needle can be inserted into the joint and a sample of synovial (joint) fluid obtained for evaluation. Synovial fluid normally appears clear. Bacterial infections can alter the color, consistency, volume, and makeup of normal joint fluid. Analysis of the sample can determine the number of WBCs along with the type of bacteria.Diagnostic tests—a variety of tests can be used to identify the presence and extent of an infectious process. Nuclear scans (using dyes and x-ray), magnetic resonance imaging, and computed tomography are commonly used