septic arthritis

What is 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 found. With septic arthritis, microbes are identifiable in an affected joint fluid.

Most commonly, septic 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 person affected. Septic arthritis is also called infectious arthritis.

What microbes cause septic arthritis?

Septic arthritis can be caused by bacteria, viruses, and fungi. The most common causes of septic arthritis are bacteria, including Staphylococcus aureus 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, coxsackie viruses, mumps, and ebola. Fungi that can cause septic arthritis include histoplasma, coccidiomyces, and blastomyces.

Who's at Risk for Septic Arthritis?

Young children and elderly adults are most likely to develop septic arthritis. People with open wounds are also at a higher risk for septic arthritis. In addition, people with a weakened immune system and those with pre-existing conditions such as cancer, diabetes, intravenous drug abuse, and rheumatic and immune deficiency disorders have a higher risk of septic arthritis.

What Are the Symptoms of Septic Arthritis?

Symptoms of septic arthritis usually come on rapidly with intense pain, joint swelling, and fever. Septic arthritis symptoms may include:

• chills
• fatigue and generalized weakness
• fever
• inability to move the limb with the infected joint
• severe pain in the affected joint, especially with movement
• swelling (increased fluid within the joint)
• warmth (the joint is red and warm to touch because of increased blood flow)

How Is Septic Arthritis Diagnosed?

A procedure called arthrocentesis is commonly used to make an accurate diagnosis of septic arthritis. This procedure involves a surgical puncture of the joint to draw a sample of the joint fluid, known as synovial fluid. Normally, this fluid is sterile and acts as a lubricant.

In arthrocentesis, a needle is inserted into the affected joint. Fluid from the joint is collected in the needle and sent to a lab for evaluation. The lab compares the white blood cell count with normal synovial fluid, and watches the fluid for any bacterial growth. This will help the doctor determine if an infection is present, and which organism is causing it.

X-rays, MRIs, and blood tests can also be used to monitor inflammation. MRI scanning is sensitive in evaluating joint destruction. Blood tests can also be taken to detect and monitor inflammation.

What's the Treatment for Septic Arthritis?

Septic arthritis treatments include using a combination of powerful antibiotics as well as draining the infected synovial fluid from the joint. It's likely that antibiotics will be administered immediately to avoid the spread of the infection. Intravenous (IV) antibiotics may be given, which requires admission to the hospital.

Initially, empiric antibiotics are chosen to cover a wide range of infections. If the bacteria can be identified, antibiotics specific to that organism are used. It may take four to six weeks of treatment with antibiotics to ensure complete eradication of the infectious agents.

Is the Infected Fluid Drained?

Yes. Drainage of the infected area is critical for rapid clearing of the infection. Drainage is performed by removing the fluid with a needle and syringe. Often the draining occurs daily or with multiple surgical procedures. The exact method depends on the location of the joint. Warm compresses on the joint, elevation of the limb, and bed rest may be necessary.

Using arthroscopy, your doctor can irrigate the joint and remove the infected tissue. If drainage cannot be accomplished with joint aspirations or arthroscopy, open joint surgery is often necessary to drain the joint. If the fluid buildup is significant, the drains are left in place to remove excess fluid that may build up after the surgery.

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