Pediatric Septic (Infectious) Arthritis

Septic arthritis is an infection in the joint fluid (synovial fluid) and joint tissues. It occurs more often in children than in adults. The infection usually reaches the joints through the bloodstream. In some cases, joints may become infected because of an injection, surgery or injury.

Different types of bacteria, viruses and fungi can infect a joint. The common types that can cause septic arthritis include:

• Staphylococcus aureus. These are common bacteria that often cause skin infections.
• Haemophilus influenzae. These are bacteria that can infect the larynx, trachea and bronchi.
• Gram-negative bacilli. This is a group of bacteria that includes Escherichia coli (E. coli).
• Streptococci. This is a group of strep bacteria that can lead to many different diseases.

The most common type of bacteria that cause septic arthritis is Staphylococcus aureus, or staph. It is also known as S. aureus. These bacteria can enter the body in many ways, such as:

• An infection that spreads from another place on the body, such as the skin or genitals
• An infected wound
• A broken bone that goes through the skin (open fracture)
• Foreign object that goes through the skin
• Injury that breaks the skin

Septic arthritis may occur without any known risk factors. But children who have an open skin wound and a weakened immune system may be at greater risk. A weakened immune system can be caused by diabetes, kidney disease, HIV infection or cancer.

The most common joints affected by septic arthritis are the knee, hip, shoulder, elbow and wrist. Most often, only one joint is affected. Symptoms may vary in each child. Common symptoms include:

• Fever
• Joint pain, often severe
• Joint swelling
• Redness in the affected area
• Warmth around the affected area
• Limited use of the affected limb, such as not wanting to walk
• Guarding or protecting the affected area to keep it from being touched or seen
• Other symptoms of illness, such as vomiting, sore throat or headache
• Being grouchy (irritable)
• Loss of appetite

These symptoms can seem like other health conditions. Make sure your child sees a healthcare provider for a diagnosis.

Early diagnosis of septic arthritis is important. It can prevent long-term (permanent) damage to the joint. Your child’s healthcare provider will ask about your child’s health history and give your child a physical exam. Tests may also be done, such as:

• Removal of joint fluid. This is done to check for white blood cells and bacteria in the fluid.
• Blood tests. These are done to look for bacteria.
• Phlegm, spinal fluid, and urine tests. These are done to look for bacteria and find the source of infection.
• X-ray. This test uses a small amount of radiation to make images of internal tissues, bones and organs.
• Bone scan. This imaging test uses a tiny amount of a radioactive substance to look for arthritis changes in the joints.
• MRI. This test uses large magnets and a computer to make detailed images of organs and other tissues without using X-rays.
• Radionuclide scans. These scans use a tiny amount of a radioactive substance to look at organs and the blood flow to them.

Treatment will depend on your child’s symptoms, age and general health. It will also depend on how severe the condition is.

Septic arthritis often needs treatment right away with antibiotics if bacteria are the source of infection. This can improve symptoms within 48 hours. Some infections caused by fungi need treatment with antifungal medicine. Viral infections are not treated with medicine.

Pus may be drained from the joint. Pus buildup can damage the joint. The pus is drained with a needle, tube or surgery. Other treatment may include:

• Medicines for pain and fever
• Physical therapy to keep muscle strength
• A splint on the joint to ease pain

Septic arthritis can cause joint damage. If your child’s growth plate was affected, this may cause an arm or leg to not grow to the full adult length. The growth plate is the part of the bone where new bone is created. This area of the bone helps determine its final adult length. Make sure to follow up with your child's healthcare provider to prevent long-term problems.

Tell the healthcare provider if your child’s symptoms get worse or about any new symptoms.