OVERVIEW
Pediatric septic arthritis is an infection involving a joint. This can occur in any joint but is most common in the hip. The knee is another common location and septic arthritis needs to be considered whenever there is redness, pain, and swelling of a major body joint. The bacteria can enter the joint and spread through the bloodstream (called hematogenous spread) or from an adjacent infection in the bone or muscles around a joint or from direct injury. This is an urgent issue and it is very important to have prompt evaluation and treatment. If not treated quickly, an infected joint can cause severe damage to the cartilage in the joint and cause growth and arthritis problems in the future. Septic arthritis is most commonly caused by Staphylococcus aureus and Streptococcus species, but the potential causes vary based on the child’s age. In newborns, Neisseria honorrhoeae can cause septic arthritis. In young infants, E. coli and group B strep need to be considered. In babies and preschool-age children, Kingella Kinage, streptococcus pneumoniae should be considered. In unimmunized children, Haemophilus influenzae type b can be a cause.
SYMPTOMS
Joint pain, swelling, redness, tenderness, and limping are common symptoms of septic arthritis. Typically, the child will not want to walk and will commonly be ill with fevers. The child may also have other systemic symptoms like chills, poor energy level, poor appetite, irritability. With septic arthritis of the hip, a child will often posture the hip flexed (bent) and abducted/externally rotated (held out from body). A child will not typically tolerate much movement of a septic joint. The pain associated with septic arthritis is usually constant and does not respond well to medications like acetaminophen and ibuprofen. The pain is usually localized to a specific area of the body, rather than coming and going from a variety of locations.
Several conditions can mimic septic arthritis. Transient synovitis is common several weeks following a minor illness. This typically responds well to an anti-inflammatory medicine. Juvenile idiopathic arthritis and inflammatory diseases can cause joint pain and swelling. Trauma can also cause joint pain and swelling. It is important to realize that septic arthritis can result from trauma (though it is much more commonly just spread through the blood). Pain associated with an injury is expected to improve over several days, whereas pain from septic arthritis will continue to build and worsen. Your doctor will run tests to help determine if your child has septic arthritis or a different condition.
EVALUATION
The first step in evaluation is a careful examination to determine where your child hurts, how well he/she tolerates motion of the joints, and whether there is redness or swelling. Radiographs are often used to help look for infection in the bone or fractures that could explain the pain and swelling. Ultrasound is often used to evaluate for joint swelling, which typically can’t be seen well on a radiograph. Sometimes, MRI will be used to better look at the bones, joints, and muscles.
Blood work will also be done to look for signs of infection, such as a high white blood cell count and high inflammatory markers. Inflammatory markers, like C reactive protein (CRP) and erythrocyte sedimentation rate (ESR), are signs of inflammation or infection in your child’s blood. Your child’s blood will also be sent for culture, to see if bacteria can be identified in the blood. This test, however, takes several days to determine.
If there is a concern for septic arthritis after the imaging and blood tests, a sample of joint fluid will be needed. This is obtained by pulling fluid from the joint with a needle in a procedure called aspiration, or arthrocentesis. Depending on the age of the child, sedation may be necessary to obtain this fluid. This fluid is sent to the lab and can quickly be evaluated for signs of infection like a high white blood cell count, the presence of bacteria, and other factors.
TREATMENT
Without treatment, a septic joint can cause severe damage. Treatment needs to occur within a certain timeframe to prevent this from happening. To clean the infection from the joint, a surgery called irrigation and debridement is needed. In this surgery, your surgeon will open the joint and wash out the infection. A small drain is often used, to help prevent infection from building back up. Sometimes, more than one trip to the operating room to wash out the infection may be necessary.
Antibiotics are a very important part of treatment for septic arthritis. Your child will typically be started on antibiotics that cover many bacteria (called broad spectrum coverage) until cultures identify what specific bacteria is causing your child’s infection. Once identified, the antibiotics are changed to focus on those bacteria. Your child will receive antibiotics through an IV at the start. Labs are typically drawn every few days to monitor how your child responds. Once a good response is seen, the antibiotics will change from IV to ones taken by mouth. Infectious disease doctors may be consulted to help monitor your child’s infection. The amount of time on the antibiotic can vary, but most children are typically on antibiotics between 2 to 6 weeks.
Monitoring is needed after the infection to make sure that your child recovers properly. If treated quickly, most children make a full recovery. However, there can be issues with growth and arthritis that may require longer monitoring for your child.
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