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.
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
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 bacteria
X-ray—to identify swelling within a joint and throughout the surrounding soft tissues
Arthrocentesis—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.
Definitive diagnosis of an infectious process relies on the identification of
the pathogen (disease-causing organism) in stained smears from synovial
fluid and isolation of the pathogen from cultures of synovial fluid. Prompt treatment includes antibiotics (usually for 4 to 6 weeks taken orally or by vein). Often, the infected joint space must be drained to eradicate the infection, hasten recovery, and reduce pain. This can be done by repeated arthrocentesis, by surgical irrigation (washing the joint out with sterile solutions), or by debridement (removal of decaying tissue). Septic arthritis can lead to joint damage and destruction, eventually requiring joint replacement surgery.
American Academy of Orthopedic Surgeons (AAOS)http://www.aaos.com
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Sources: Arthritis Foundation, American Academy of Family Physicians, American Academy of Orthopedic Surgeons
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TOPIC: BONE AND JOINT DISEASE
Zeller JL, Lynm C, Glass RM. Septic Arthritis. JAMA. 2007;297(13):1510. doi:10.1001/jama.297.13.1510