Septic Arthritis

Septic arthritis is an infection in a joint. The infection can be caused by bacteria, viruses, fungi, or parasites. Joint infection caused by fungi or parasites is much less common than that caused by bacteria or viruses. Typically, septic arthritis affects a single large joint, such as the knee or hip, but it is possible for several joints to be infected.

Septic arthritis is also referred to as infectious arthritis. Septic arthritis is considered a medical emergency because of the serious damage that can occur to bone and cartilage. Septic arthritis can cause septic shock, which can be fatal.

Causes

A septic arthritis infection can originate anywhere in the body. The infection may also begin as the result of an open wound, surgery, or unsterile injections. Whatever the initial source of infection, septic arthritis occurs when the infective organism gets into the joint.

Symptoms

Signs and symptoms associated with septic arthritis include:

• Fever
• Chills
• Severe pain in the affected joint
• Swelling of the affected joint (joint effusion)
• Warmth near the affected joint
• Nausea

Diagnosis

After considering your medical history and physical examination, your healthcare provider will order certain tests. The tests used to diagnose septic arthritis include:

• Blood tests to identify elevated white cell count and bacteria
• X-rays or other imaging studies to assess joint damage
• Arthrocentesis, or joint aspiration, using a needle to remove and then analyze synovial (joint) fluid for several parameters that could indicate infection

Treatment

For bacterial septic arthritis, it is necessary to identify the specific bacteria causing the infection. Once the bacterium is identified, you can begin taking the appropriate antibiotics. Antibiotics that kill the bacteria are usually taken either orally or intravenously (IV, through a vein) for four to six weeks—however, new research suggests a shorter duration of antibiotics of two weeks may be just as effective.

You may also need the infected joint space drained, either by arthrocentesis, surgical irrigation (washing out the joint with sterile solutions), or debridement (removal of decaying tissue). Significant joint damage may result from septic arthritis and could eventually lead to joint replacement surgery.

Risk Factors

Certain factors increase your risk of developing septic arthritis. Those include:

• Previous joint problems from other types of arthritis, joint surgery, or joint injury
• A weakened immune system from diseases or from taking immunosuppressant medications
• Skin wounds or open wounds allowing bacteria access to the body
• Injectable drug use and alcoholism associated with high infection risk

Prevalence

Septic arthritis can affect anyone at any age—including infants and children, although it is most common in infants and older adults. In adults, weight-bearing joints (hips, knees, ankles) are most affected. In children, hips are commonly affected. As the population ages, healthcare providers are seeing more patients with septic arthritis.

Points of Interest

• The most common type of bacteria causing septic arthritis is Staphylococcus aureus, usually referred to as "staph."
• When viruses attack joints, it is called viral arthritis, and the condition usually resolves on its own. However, sometimes antiviral therapy is required. 
• Joint infection caused by a fungus, known as fungal arthritis, is considered very rare.

Remember, seek immediate medical attention if you have signs or symptoms that point to septic arthritis.