Septic arthritis is an infection that affects one or more joints. Bacteria most often cause it, although fungi and viruses may cause it in rare situations. Certain factors can increase your risk.

Septic arthritis is joint inflammation that’s caused by an infection. Most of the time, septic arthritis only affects a single joint. However, it can affect multiple joints 5–10% of the time.

Overall, septic arthritis is a rare condition. Researchers estimate that 4–60 out of 100,000 people develop septic arthritis each year.

Septic arthritis is considered an orthopedic emergency. This is because it can lead to severe joint damage and potentially sepsis if left untreated for too long.

Keep reading to learn more about what causes septic arthritis, who’s at risk, and how septic arthritis is diagnosed and treated.

There are many potential causes of septic arthritis.

Septic arthritis happens when an infection reaches your joints. This can occur when:

  • an infection elsewhere in your body reaches one of your joints via your bloodstream
  • you sustain an injury that introduces germs into the area around your joint
  • you develop an infection as a complication of surgery, including joint surgery, or joint injection

Bacteria are the most common cause of septic arthritis. Staphylococcus aureus is the most common. S. aureus can be either methicillin-sensitive (MSSA) or methicillin-resistant (MRSA).

Other types of bacteria that can potentially cause septic arthritis include:

In rare situations, fungi or viruses may cause septic arthritis. A couple of examples of fungal causes are Candida species and Coccidioides species.

Examples of viral causes include:

Several things can increase your risk of developing septic arthritis. These include:

It’s important to remember that having risk factors doesn’t mean you will absolutely get septic arthritis. It simply means your risk is higher than those without risk factors.

Is septic arthritis a lifelong condition?

Septic arthritis is typically an acute condition. This means it comes on suddenly and lasts for a short time.

However, the effects of septic arthritis can be lifelong. If treatment is delayed, the effects of septic arthritis can lead to serious joint damage and potential disability.

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The symptoms of septic arthritis typically appear quickly and develop over a period of a few days. They include:

While septic arthritis can affect any joint, the most commonly affected joint is the knee. Other joints most often affected include the hip, shoulder, and elbow.

The joints at risk for people who inject drugs are fairly unique and include the sacroiliac joint and acromioclavicular joint.

It’s important to visit a doctor promptly if you develop symptoms of septic arthritis. If left untreated, it can cause joint damage and disability and may lead to bone infections, sepsis, or even death.

Having an artificial joint, such as a knee or hip replacement, is one of the risk factors for septic arthritis. In some situations, the infection of an artificial joint can lead to revision surgery being necessary.

Doctors have divided artificial joint infections into three stages based on how long after the surgery they occur. The bacteria that typically cause the infection can also vary by stage.

The three stages are:

  • Early: Early stage infections happen within 3 months of surgery.
  • Delayed: Delayed-stage infections occur between 3 months and 2 years after surgery.
  • Late: Late-stage infections develop at or over 2 years after surgery.

To diagnose septic arthritis, a doctor first gets your medical history and performs a physical exam. During the exam, they’ll evaluate your affected joint.

The doctor then orders tests to determine what’s causing your symptoms. Diagnostic tests include:

Treating septic arthritis

After a doctor diagnoses septic arthritis, they will prescribe intravenous antimicrobial medications. Since most diagnoses of septic arthritis are due to bacteria, this typically involves antibiotics. Antifungals are given in the case of a fungal cause.

Infected joint fluid is also often drained, and the joint is immobilized as a part of treatment. The initial drainage procedure typically occurs in the hospital. The joint is then monitored to determine whether additional drainage is needed. Sometimes, a doctor places a stent.

In severe situations, surgery may be needed to help clear the infection from the joint.

Bacteria typically cause septic arthritis. The most common type of bacteria that causes septic arthritis is S. aureus, which can be antibiotic-sensitive or antibiotic-resistant. In rare cases, fungi and viruses cause septic arthritis.

A recent joint surgery, injection, or injury increases the risk of septic arthritis. People with an artificial joint also have a higher risk, as are people with weakened immune systems and individuals with health conditions like rheumatoid arthritis and diabetes.

Septic arthritis is an emergency. It can lead to complications like lasting joint damage, bone infections, and sepsis. Because of this, seek immediate medical care if you develop symptoms of septic arthritis.