What is septic arthritis?

Definition

Septic arthritis is a serious infection of the joints caused by
bacteria. This infection causes a joint to be filled with pus cells, which in turn
release substances directed against the bacteria. However, this action can damage
the bone and surrounding cartilage.

Septic arthritis is a medical emergency. If left untreated, it causes loss of
function in the affected joint and can lead to septic shock,
a potentially fatal condition. With early treatment, however, recovery is usually
good.

Causes

Septic arthritis develops when bacteria spreads from the source of infection through the bloodstream to a joint. This condition can result from direct infection through an injection or a penetration wound, during surgical procedures, or from an injury that directly contaminates the joint.

Septic arthritis can strike at any age but occurs most often in children
younger than age three years. In infants, the hip is a frequent site of infection;
in toddlers, common sites of infection are the shoulders, knees, and hips. In
these young persons, the most common bacterial causes are staphylococci (which
cause staph infections), streptococci (which triggers strep
throat), and Streptococcus pneumoniae, the
bacterium responsible for most identified cases of pneumonia.

Septic arthritis rarely occurs from early childhood through adolescence. After
this time, its incidence increases. In adults, it most commonly affects
weight-bearing joints such as the knees. Mycobacterium, which
causes tuberculosis, and Borrelia, the bacterium
that causes Lyme
disease, can also lead to septic arthritis.

Risk Factors

The following increase one’s chances of developing septic arthritis: diseases
that weaken the immune system, such as human immunodeficiency
virus infection, or taking drugs that suppress immunity; a
history of joint problems or having other types of arthritis,
gout, or lupus; a history of intravenous drug use; chronic
illnesses such as anemia, diabetes, sickle cell
disease, or kidney failure; joint replacement or organ
transplant surgery; and skin conditions such as psoriasis or
eczema that could allow for infections to penetrate through
the skin.

Symptoms

Symptoms of septic arthritis, in newborns or infants, include crying when the infected joint is moved (such as during a diaper change), immobility of the limb of the infected joint, irritability, fever, and persistent crying for any reason. In children and adults, the symptoms include intense joint pain, joint swelling and redness, fever, chills, and immobility of the infected joint or its limb.

Screening and Diagnosis

A doctor, who will ask about symptoms and medical history and will perform a physical exam, may refer the patient to a rheumatologist or an orthopedics specialist. Tests may include withdrawing a sample of synovial fluid (fluid that lubricates the joint) from the affected joint to test it for white blood cells and bacteria, performing a culture of blood and urine to rule out other causes (such as gout), X rays to assess joint damage, and draining fluid from the infected joint. Severe cases may require surgery.

Treatment and Therapy

Antibiotic therapy, which is started as soon as a diagnosis is made, is
sometimes initially given intravenously to ensure the infected joint receives
medication to kill the bacteria. The specific medications used depend on the type
of bacteria determined to cause the infection. The remaining course of
antibiotics may be given orally. Rest, immobilizing the
joint, and warm compresses may be used to manage pain. Physical therapy or
exercises may also speed recovery.

Prevention and Outcomes

To help reduce the chance of getting septic arthritis, one should get prompt
treatment for bacterial infections that could lead to septic arthritis.
Persons in a high-risk group may be given antibiotics as a preventive measure.

Bibliography

Forbes, Betty A., Daniel F. Sahm, and Alice S. Weissfeld. Bailey and Scott’s Diagnostic Microbiology. 12th ed. St. Louis, Mo.: Mosby/Elsevier, 2007.

Górski, Andrzej, Hubert Krotkiewski, and Michał Zimecki, eds. Inflammation. Boston: Kluwer, 2001.

Klein, Deborah G. “Shock and Sepsis.” In Introduction to Critical Care Nursing, edited by Mary Lou Sole, Deborah G. Klein, and Marthe J. Moseley. 5th ed. St. Louis, Mo.: Saunders/Elsevier, 2009.

Melvin, Jeanne L., and Virginia Wright, eds. Pediatric Rheumatic Diseases. Vol. 3. Bethesda, Md.: American Occupational Therapy Association, 2000.

Seibel, M. J., P. Robin Simon, and John P. Bilezikian, eds. Dynamics of Bone and Cartilage Metabolism. 2d ed. San Diego, Calif.: Academic Press, 2006.