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Understanding Septic Arthritis: Causes, Symptoms, and Treatment Options

Jerome Albert Ecker | MD

Medically reviewed by Jerome Albert Ecker | MD, Assistant Professor of Medicine, Duke University - Durham, NC on September 5th, 2023.

Key Takeaways

  • Bacteria enter joints through bloodstream spread, direct trauma, or nearby infections, with Staphylococcus aureus causing 60% of cases in adults and group B strep dominating in newborns.

  • Classic presentation involves the "4 cardinal signs"—severe joint pain, swelling, warmth, and redness—plus fever above 101°F and complete inability to bear weight or move the affected joint.

  • Highest risk occurs in infants under 3 months (immature immune systems), adults over 65, and patients with prosthetic joints, diabetes, or immunosuppression from cancer treatments.

  • Emergency joint aspiration (arthrocentesis) within 6-8 hours is critical—synovial fluid typically shows white blood cell counts exceeding 50,000-100,000 cells/μL with positive bacterial cultures.

  • IV antibiotic therapy lasts 2-6 weeks depending on organism and response, starting with empirical coverage like vancomycin plus ceftriaxone before culture results guide specific treatment.

Septic arthritis, also known as infectious arthritis, is a painful and potentially serious condition that occurs when a joint becomes infected. The infection is usually caused by bacteria, but it can also be caused by viruses or fungi. Septic arthritis typically affects a single large joint, such as the knee or hip, but it can sometimes involve multiple joints.

Causes of Septic Arthritis

Septic arthritis is usually caused by bacteria that spread through the bloodstream from another part of the body. It can also result from a bacterial infection that enters the body through an open wound or during a surgical procedure, such as knee surgery. The most common bacteria that cause septic arthritis in adults and children are staphylococcus and streptococcus, while neisseria gonorrhoeae is the most common cause in young, sexually active adults.

In some cases, septic arthritis can be caused by viral infections, such as hepatitis A, B, and C, parvovirus B19, HIV, and others. Fungal infections, such as those caused by histoplasma, coccidioides, and blastomyces, can also lead to septic arthritis, although these infections typically develop more slowly than bacterial infections.

Risk Factors for Septic Arthritis

Certain groups of people are at a higher risk of developing septic arthritis, including:

  • Young children and elderly adults

  • People with open wounds

  • Individuals with weakened immune systems

  • Those with pre-existing conditions such as cancer, diabetes, and immune deficiency disorders

  • Intravenous drug users

  • People with previously damaged joints

Symptoms of Septic Arthritis

Symptoms of septic arthritis usually come on quickly and may include:

  • Intense pain in the affected joint, especially with movement

  • Swelling and warmth in the joint

  • Redness of the skin around the joint

  • Fever and chills

  • Fatigue and generalized weakness

  • Inability to move the affected joint by yourself or allow others to move it with the infected joint

Understanding Septic Arthritis: Causes, Symptoms, and Treatment Options

Diagnosing Septic Arthritis

To diagnose septic arthritis, doctors often perform a procedure called arthrocentesis. During this procedure, a needle is used to remove a sample of synovial fluid (the fluid that lubricates the joint) from the affected joint. The fluid is then sent to a lab for analysis, where a white cell count and bacterial culture are performed to determine if an infection is present and to identify the specific organism causing the infection.

X-rays may also be taken to look for joint damage, and blood tests can be used to monitor inflammation. In some cases, an MRI scan may be ordered to evaluate joint destruction, although this is less useful in the early stages of the infection.

Treating Septic Arthritis

Treatment for septic arthritis typically involves a combination of antibiotics and drainage of the infected synovial fluid from the joint. Antibiotics are usually administered intravenously (IV) to prevent the spread of the infection, and patients may need to be hospitalized for initial treatment. The specific antibiotics used will depend on the type of organism causing the infection, and treatment may continue for four to six weeks to ensure complete eradication of the infectious agents.

Drainage of the infected joint is crucial for rapid clearing of the infection. This can be done using a needle and syringe, arthroscopy (a minimally invasive surgical procedure), or open joint surgery, depending on the location of the joint and the severity of the infection. In some cases, drains may be left in place to remove excess fluid that builds up after the surgery.

If you suspect that you or a loved one may have septic arthritis, it is important to seek medical attention promptly. Early diagnosis and treatment can help prevent serious complications and long-term joint damage.

For more information on septic arthritis, visit:

The Bottom Line

This medical emergency requires immediate hospital treatment within hours to prevent irreversible cartilage destruction and potential sepsis. Any combination of severe joint pain, fever, and inability to move a joint warrants emergency evaluation, as delays beyond 24 hours significantly worsen outcomes. If you're experiencing these concerning symptoms, Doctronic can help connect you with urgent care guidance.

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