The joints that septic arthritis affects may be swollen, inflamed, and feel warm to the touch. A person can also experience nonvisual symptoms, including fatigue, a fast heart rate, and a lack of appetite.

Septic arthritis, also known as infectious arthritis, is a painful infection in a joint. It may affect any joint but is most common in the knee.

Bacteria, viruses, or fungi can cause this condition. Without treatment, septic arthritis may cause severe damage to the affected joint and surrounding tissues, so people with symptoms should seek prompt medical help.

This article explains the visual and nonvisual signs of septic arthritis, including pictures, the most commonly affected joints, and when to contact a doctor.

Septic arthritis symptoms typically develop quickly. In most cases, localized symptoms will only affect one joint.

Joints affected with septic arthritis may appear swollen or inflamed and have a decreased range of motion. However, deeper joints, such as the hips, may not present with swelling.

People may also have a generally ill appearance. If septic arthritis affects the knee, a person may develop a limp when walking.

Septic arthritis is a medical emergency requiring prompt diagnosis and treatment to prevent joint damage and other complications.

Other symptoms of septic arthritis can include:

These nonvisual symptoms will also typically have a quick onset.

Septic arthritis can affect any joint but most often affects the knee. Other commonly affected joints include:

The type of bacteria or virus causing septic arthritis may determine which joints it affects:

  • Staphylococcal infections: Septic arthritis due to a staph infection typically affects only one joint.
  • Neisseria infection: This infection typically involves multiple joints.
  • Streptococcal bacteria (group B strep): A group B strep infection typically affects the sternoclavicular, which is between the collarbone and breastbone, and sacroiliac joints in the lower back.

A prompt diagnosis is vital to prevent complications due to septic arthritis.

To diagnose this condition, a healthcare professional will initially complete a thorough medical history and physical examination. The doctor will look for signs of infection and inflammation, both local to the joint and more generally.

They may also conduct various tests to support their diagnosis, including:

Other conditions, such as gout, cellulitis, and rheumatoid arthritis, can mimic septic arthritis. The above diagnostic chests can help to rule out other conditions.

According to the Arthritis Foundation, treatment typically involves antibiotics and joint drainage.

Doctors may give a person oral antibiotics or administer them intravenously — through a vein. Antibiotic treatment may last from a few days to several months.

For fungal infections, doctors may prescribe antifungal medications. Viral infections may go away without specific treatment.

To remove joint fluid, doctors may use the following procedures:

  • Needle aspiration: This involves repeatedly drawing fluid out of the joint with a needle.
  • Arthroscopic drainage: A minimally invasive surgical procedure in which a doctor inserts a small camera and instruments into the joint to remove fluid and infected tissue.
  • Open surgery (arthrotomy): This may be necessary in severe cases or when the infection is difficult to clear.

People may also need physical therapy to prevent muscle atrophy and restore joint mobility. If septic arthritis affects someone with a prosthetic joint, they may need to remove or replace the prosthesis.

People should speak with a doctor if they experience any symptoms of septic arthritis. Additionally, the following factors increase the risk of developing septic arthritis and warrant prompt medical attention if symptoms develop:

  • recent joint surgery or injection into a joint
  • open wounds near a joint, which may allow bacteria to enter the joint space
  • having diabetes
  • older age
  • factors or conditions that compromise the immune system, such as:
  • joint prosthesis

Septic arthritis is more common in children. A parent or caregiver should take a child to see a doctor if they display symptoms of septic arthritis.

Septic arthritis typically presents with notable swelling, warmth, and pain around the affected joint. Other symptoms can include general illness, lack of mobility, and a lack of appetite.

This type of arthritis most often affects one joint but may affect multiple joints, depending on the type of infection.

Other conditions, including different types of arthritis, can mimic septic arthritis. It is vital to seek a prompt diagnosis and treatment if a person has signs of septic arthritis to avoid complications, including severe joint damage.