Septic Arthritis (Infectious Arthritis)

Bacterial, fungal, and viral infections may cause septic arthritis.

Septic, or infectious, arthritis is infection of one or more joints by microorganisms. Normally, the joint is lubricated with a small amount of fluid that is referred to as synovial fluid or joint fluid. The normal joint fluid is sterile and, if removed and cultured in the laboratory, no microbes will be detected. With this form of arthritis, microbes are identifiable in an affected joint's fluid.

Most commonly, infectious arthritis affects a single joint, but occasionally more joints are involved. The joints affected vary somewhat depending on the microbe causing the infection and the predisposing risk factors of the patient affected. Septic arthritis is also called infectious arthritis.

Septic arthritis can be caused by bacteria, viruses, and fungi. The most common causes of septic arthritis are bacterial, including Staphylococcus aureus (staph) and Haemophilus influenzae. In certain "high-risk" individuals, other bacteria may cause septic arthritis, such as E. coli and Pseudomonas spp. in intravenous drug abusers and the elderly, Neisseria gonorrhoeae in sexually active young adults, and Salmonella spp. in young children or in people with sickle cell disease. Other bacteria that can cause septic arthritis include Mycobacterium tuberculosis and the spirochete bacterium that causes Lyme disease.

Viruses that can cause septic arthritis include hepatitis A, B, and C, parvovirus B19, herpes viruses, HIV (AIDS virus), HTLV-1, adenovirus, Coxsackieviruses, mumps, and Ebola. Fungi that can cause septic arthritis include Histoplasma, Coccidioides, and Blastomyces.

Septic arthritis is not contagious. However, many of the microbes that cause infectious arthritis can be transmitted from an infected patient to another, including Neisseria gonorrhoeae, Staphylococcus aureus, Mycobacterium tuberculosis, and HIV.

While joint infection occasionally affects people with no known predisposing risk factors, it more commonly occurs when certain risk situations are present. Risks for the development of septic arthritis include taking medications that suppress the immune system, intravenous drug abuse, past joint disease, injury, or surgery, and underlying medical conditions and diseases including diabetes, alcoholism, sickle cell disease, rheumatic diseases (for example, rheumatoid arthritis), and immune deficiency disorders. People with any of these conditions who develop symptoms of septic arthritis should promptly seek medical attention.

Clinical symptoms of septic arthritis include fever, chills, as well as joint pain, swelling, redness, stiffness, and warmth. Joint pain most commonly affects large joints, such as the knees, ankles, hips, and elbows. In patients with risk factors for joint infection, unusual joints can be infected, including the joint where the collarbone (clavicle) meets the breastbone (sternum). With uncommon microbes, such as Brucella spp., atypical joints can be infected, such as the sacroiliac joints.

Health care professionals make a diagnosis of septic arthritis by identifying infected joint fluid. During an arthrocentesis (joint aspiration), synovial fluid can easily be removed from the joint space of a patient in an office, hospital, or clinical setting with a needle and syringe. The synovial fluid is analyzed in a laboratory to determine if there is an elevated number of white blood cells to suggest inflammation. A culture of the synovial fluid can identify the particular microbe and determine its susceptibility to a variety of antibiotics.

X-ray studies of the joint can be helpful to detect injury of bone adjacent to the joint. MRI scanning is very sensitive in evaluating joint destruction. Blood tests are frequently used to detect and monitor inflammation. These tests include the white blood cell count, sedimentation rate, and C-reactive protein.

Septic arthritis is a medical emergency. Doctors who treat septic arthritis include emergency physicians, internists, rheumatologists, orthopedists, infectious disease physicians, and rehabilitation-medicine providers.

Treatment of septic arthritis includes antibiotic therapy and drainage of the infected joint (synovial) fluid from the joint (arthrocentesis).

Optimally, antibiotics are given immediately. Often, health care professionals administer intravenous antibiotics in a hospital setting. The choice of antibiotics can be guided by the results of the culture of joint fluid. Until those results are known, empiric antibiotics are chosen to cover a wider range of possible infectious agents. Sometimes, combinations of antibiotics are given. Antibiotics may be required for four to six weeks.

Drainage is essential for rapid clearing of the infection. Drainage of a joint effusion can be done by regular aspirations with a needle and syringe, often daily early on, or via surgical procedures. Arthroscopy can be used to irrigate the joint and remove infected joint lining tissue. If adequate drainage cannot be accomplished with joint aspirations or arthroscopy, open joint surgery is used to drain the joint. After arthroscopy or open joint surgery, drains are sometimes left in place to drain excess fluid that can accumulate after the procedure.

No. Septic arthritis is a medical emergency and requires acute treatment by an appropriate medical team.

The outlook for septic arthritis depends on the precise microbe causing the infection, the duration of the infection, and the underlying overall health of the individual infected. Some types of microorganisms are more aggressive and difficult to treat than others. The longer the infection is present, the more opportunity for damage to affect the joint. People whose immune systems are not functioning optimally are also at risk for more joint damage. Moreover, if septic arthritis leads to infection in other parts of the body, other organs can be affected.

Rapid clearing of the infection is critical to preserve the joint. If appropriate antibiotics are begun immediately, joint integrity can be maintained, and return to function is expected. If the infection has been longstanding, the possibility of joint destruction exists. The keys to successful outcome are rapid medical attention and drainage and the accurate administration of antibiotics to which the offending microbes are susceptible.

It is possible to prevent septic arthritis by avoiding infections, puncture wounds, and damage to the skin.