Septic Arthritis

(Bacterial Arthritis; Infectious Arthritis; Pyogenic Arthritis)

by Sid Kirchheimer

Definition

Septic arthritis is a serious infection of the joints caused by bacteria. This infection causes the 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.

This condition is considered 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. It can result from:

• Infection due to an injection
• Penetration wound
• Surgery
• Injury that affects the joint

Septic arthritis can strike at any age. But, it occurs most often in children aged three and younger. In infants, the hip is a frequent site of infection. In toddlers, it is the shoulders, knees, and hips. In these young patients, the most common bacterial causes are:

• Staphylococcus aureus (staph infection)
• Streptococcus species (can also trigger strep throat)
• Streptococcus pneumoniae (causes most cases of pneumonia)

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

Joint Damage in Knee

© 2009 Nucleus Medical Media, Inc.

Risk Factors

The following factors increase your chance of developing septic arthritis. If you have any of these risk factors, tell your doctor:

• Diseases that weaken the immune system, such as HIV, or taking drugs that suppress immunity
• A history of joint problems or having other types of arthritis, gout, or lupus
• A history of IV drug use
• Chronic illnesses (eg, anemia, diabetes, sickle cell, kidney failure)
• Joint replacement or organ transplant surgery
• Skin conditions (eg, psoriasis, eczema)

Symptoms

If you experience any of these symptoms do not assume it is because of septic arthritis. These symptoms may be caused by other, less serious conditions. If you experience any one of them, see the doctor:

• Newborn or infants
  • Crying when the infected joint is moved (eg, during a diaper change)
  • Immobility of the limb of the infected joint
  • Irritability
  • Fever
  • Persistent crying for any reason
• Children and adults
  • Intense joint pain
  • Joint swelling and redness
  • Fever
  • Chills
  • Immobility of the infected joint or its limb

Diagnosis

Your doctor will ask about your or your child’s symptoms and medical history, and do a physical exam. Your doctor may refer you to a rheumatologist or orthopedics specialist. Tests may include:

• Taking a sample of synovial fluid (fluid that lubricates the joint) from the affected joint to test it for white blood cells and bacteria
• Doing blood and urine tests to rule out other causes (eg, gout)
• Ordering x-rays to assess joint damage
• Possibly draining fluid from the infected joint—In severe cases, surgery is needed.

Treatment

Antibiotic therapy is started as soon as a diagnosis is made. Sometimes, antibiotics are given via an IV (a needle that goes into your arm). This is to ensure that the infected joint receives medicine to kill the bacteria. The specific medicines used depend on the type of bacteria that is causing 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.

If you are diagnosed with septic arthritis, follow your doctor's instructions.

Prevention

To help reduce your chance of getting septic arthritis, take the following steps:

• Get prompt treatment of bacteria infections that could lead to septic arthritis.
• Persons in a high risk group may be given antibiotics as a preventative measure.

The Arthritis Foundation
http://www.arthritis.org/

National Arthritis and Musculoskeletal and Skin Diseases Information Clearinghouse
http://www.niams.nih.gov/

Arthritis Society of Canada
http://www.arthritis.ca/

Health Canada
http://www.hc-sc.gc.ca/index_e.html/

REFERENCES:

Arthritis. The US Library of Medicine website. Available at: http://www.nlm.nih.gov/medlineplus/arthritis.html. Accessed October 29, 2006.

Septic arthritis. The Milton S. Hershey Medical Center College of Medicine website. Available at: http://www.hmc.psu.edu/healthinfo/s/septicarthritis.htm. Accessed October 29, 2006.

Last reviewed November 2009 by David L. Horn, MD, FACP
Last Updated: 12/2/2009