Bacterial (Septic) Arthritis: An Overview

Bacterial arthritis—also called septic arthritis and infectious arthritis—is a rare and sometimes serious infection of one or more joints. It occurs when an infection spreads to a joint and causes inflammation of the joint and surrounding tissues.

The terms "septic arthritis" and "infectious arthritis" refer to infections from all sources, such as bacteria, viruses, and fungi. In contrast, "bacterial arthritis" refers to bacteria as the source of infectious or septic arthritis.

With bacterial arthritis, the inflammation occurs at the surface of the cartilage lining the joints and the synovial fluid responsible for lubricating the joints. Bacteria can cause an infection elsewhere in the body that spreads through the bloodstream and infects a joint.

The article will cover the symptoms and causes of bacterial arthritis and how it is diagnosed and treated.

Bacterial Arthritis Symptoms

The primary symptoms of bacterial arthritis are swelling, pain, and stiffness. It tends to be monoarticular, meaning it affects only one joint. It might also cause other symptoms of arthritis and infections, such as warmth in the affected joint and fever.

Additional symptoms of bacterial arthritis include:

• Chills
• Fatigue
• General weakness
• Inability to move the affected joint
• Severe, intense pain in the affected joints, especially with movement, that is generally not seen in nonbacterial arthritis
• Skin rash

The joints most commonly affected by bacterial arthritis are the knees, hips, shoulders, elbows, wrists, and fingers, but septic arthritis can occur in any joint.

Bacteria can also trigger reactive arthritis. The joint symptoms in reactive arthritis are not due to bacteria infecting the joint, but instead are due to the body's reaction to an infection elsewhere. It is often triggered by either a gastrointestinal (digestive tract) infection or a sexually transmitted infection (STI).

Causes

Bacterial arthritis is caused by bacteria that spread from the bloodstream to a joint. It can also occur from a bacterial infection at an open wound or a surgical opening after surgery, as might be the case if a knee is affected by bacterial arthritis following a knee replacement.

Both children and adults can develop bacterial arthritis if they are infected with Staphylococcus (the bacterium responsible for staph infections) or Streptococcus (the bacterim responsible for strep throat).

In people who are sexually active, the bacterium Neisseria gonorrhoeae (responsible for the STI gonorrhea) is a common cause of bacterial arthritis.

Once bacteria from any of these sources enter the bloodstream and infect a joint, inflammation, pain and other arthritis symptoms will occur. 

Who Is at Risk?

Young children, older adults, and people who are immunocompromised (have weak immune systems) have the highest risk for septic arthritis. However, anyone at risk for contracting bacteria in a joint has an increased risk for septic arthritis.

This might include anyone who has:

• An existing joint condition like rheumatoid arthritis or osteoarthritis
• Joint damage
• Had joint surgery recently
• A skin infection
• A history of intravenous drug use
• Been on long-term antibiotic therapy

Studies have found that bacterial arthritis affects 4 to 60 people per every 100,000 every year. There are higher incidences among immunocompromised people and those with prosthetic joints (devices that replace missing body parts). This group has 70 cases of septic arthritis per 100,000 people each year.

Diagnosis

Bacterial arthritis must be diagnosed and treated quickly because it can spread to other joints and cause joint damage if left untreated. It can lead to the rapid destruction of joints if not swiftly and adequately treated.

Signs of bacterial arthritis tend to be subtle, sometimes increasing the time for appropriate diagnosis and treatment. It can also mimic other types of arthritis, especially inflammatory types, like gout and psoriatic arthritis.

A diagnosis of bacterial arthritis typically begins with a physical examination of the affected joint. Your healthcare provider will also ask about what symptoms you have experienced and other conditions you might have.

A physical exam and a medical history generally aren't enough to make a diagnosis of bacterial arthritis. Therefore, your healthcare provider will request additional testing.

Additional tests might include:

• Joint fluid analysis: This test takes fluid from an affected joint. The lab will look for a high white blood cell count, indicating infection, inflammation, or both. The lab will look for bacteria and other organisms to determine the cause so it can be treated appropriately. Joint fluid analysis is the gold standard for confirming septic arthritis.
• X-rays or magnetic resonance imaging (MRI): Your healthcare provider might request an X-ray of the affected joint to look for joint damage. An MRI scan can detect early joint destruction and more clearly show inflammation in joints and tissues.
• Blood work: Blood work can detect and monitor inflammation. If inflammation is chronic, this can lead to joint damage.
  

Treatment

Bacterial arthritis is considered a medical emergency and requires hospitalization to treat. If your healthcare provider diagnoses you with septic arthritis, they will likely have you admitted to the hospital for treatment.

Bacterial arthritis is treated with antibiotics and draining synovial fluid in an infected joint. If the cause of infectious arthritis is a virus or fungus, the condition might be treated with antivirals or antifungal medicines. The joint fluid analysis helps determine the source of infection.

Because bacterial arthritis can progress quickly, your healthcare provider will start you on antibiotics immediately. In most cases, antibiotic treatment starts with administering treatment via intravenous (IV) infusion directly into the bloodstream.

Most people will see improvement in symptoms within a day or two on IV antibiotics. Some may need to continue IV antibiotic treatment for longer. Oral antibiotics will follow for up to six weeks, depending on the type of bacteria.

Your healthcare provider might drain the fluid from the affected joint to remove harmful bacteria. They will do this with a syringe or using a procedure called an arthroscopy, in which a small incision is made and a drainage tube is inserted in the affected joint.

Most people who develop bacterial arthritis will have a complete recovery after treatment. But untreated bacterial arthritis can lead to permanent joint and tissue damage. The effects of that damage will depend on the affected joints. For example, if your knee is affected by septic arthritis, you may have damage that affects your ability to walk or stand.

Bacterial arthritis can also lead to osteomyelitis, an infection of one or more bones. Severe osteomyelitis can cause osteonecrosis (bone death).

Untreated bacterial arthritis can become life-threatening. According to one 2021 report, the rate of lifelong disability and mortality for septic arthritis is around 11%. Researchers believe antibiotic failure might be to blame in these cases, along with the immune system's inability to eradicate the bacteria.

Summary

Bacterial arthritis is a rare, severe infection of a joint. It can lead to permanent joint, bone, and tissue damage. The cause of bacterial arthritis is a bacterial infection.

Symptoms of bacterial arthritis include joint and swelling, fever, chills, and fatigue. The condition needs early and aggressive treatment to avoid complications. Once treatment begins, most people recover with little or no lasting damage.

A Word From Verywell

Seek emergency care for symptoms of bacterial arthritis. Treatment needs to be started as soon as possible.

To improve your outlook, keep moving during your recovery. Your healthcare provider or physical therapist will recommend you start slowly. The gentle movement might help you to recover quicker and reduce joint stiffness. It also might help to prevent long-term damage to your joints.