Septic Arthritis in Children

by Brian Alverson, MD

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    00:00 So, in general, let’s focus first on septic arthritis. About half of cases of septic arthritis are in infants and children under 3 years of age and it’s usually just 1 joint and usually a lower extremity, most commonly a knee, after that a hip. Patients will generally present with red, swollen, hot, painful joints. There will be a decreased range of motion due to pain and this pain is severe. In septic arthritis, it’s unlikely that a child will even be willing to bear weight if it’s their knee or their hip. They almost always have a fever and they will generally be very irritable in neonates. Neonates are so nonspecific in how they present because they can’t complain of a particular pain. So, if you see a patient with septic arthritis, you have to think about other problems and I’ll just list a few. Let’s say we have a patient with a septic arthritis in their knee. That knee will be red, hot, swollen, they will not want to move it. This is a little bit different than a transient synovitis. Transient synovitis is from a concurrent viral infection or a very recent viral URI infection. These children will have a lot of swelling but will be able to limp along and tolerate the pain reasonably well. Reactive arthritis is usually gastroenteritis previously, maybe a week or 2 earlier, these children will also be able to bear weight reasonably well. JIA or juvenile idiopathic arthritis is more indolent. It slowly comes on and involves multiple joints. It’s unlikely to be an acute presentation of a very painful joint. Viral arthritis very rare but could look similar to septic arthritis. Lyme arthritis looks very severe and has a lot of swelling but usually isn’t that painful and not that hot to the touch and tuberculosis is also a bit more indolent, they might have a previous respiratory infection and they’re generally febrile. Okay. If we suspect a septic arthritis, the first thing we want to do is generally tap the joint. Tapping the joint is going to help us understand whether or not a patient has a septic arthritis. We’re going to see the bacteria, we’re going to see the white cells, we’re going to make that diagnosis. The challenges while a knee is so easy to tap, a hip is harder to tap. So, in our decision to use a hip, and this is specific to children, we will use the Kocher criteria. So, the Kocher criteria help us know whether or not we should tap a hip. Here’s the Kocher criteria.

    02:38 So, what are these 4 criteria? Well, one is non-weightbearing. These children don’t want to bear weight. They should be febrile to a temperature higher than 38.5 degrees Celsius. They should have a blood erythrocyte sedimentation rate or ESR of more than 40. They’ll generally have a white count of more than 12. So, if they have 1 criteria, we’re unlikely to tap the hip unless we’re really concerned about something. If they have 2 criteria, we’ll consider it but if they have 3 or 4 criteria, we almost always will tap that hip. When I say we, I’ll usually call an orthopedist because tapping a hip carries a risk of invading that neurovascular bundle that runs past the hip. So, let’s talk about the CRP and the sed rate. I promised I would and I want to go through it because it’s important to understand something. There was actually a study they did once where they took adult volunteers and injected them with bacterial endotoxin and then measured CRP and sed rate. We’ve learned that the CRP is very quick onset and very quick offset, generally within a day. Whereas the sed rate takes a slower time to ramp up and a lot longer to go away. Thus, with both, we can generally make something intelligent in terms of when was this inflammation likely to have happened? If a patient very recently got sick, the sed rate might be low and the CRP might be high. If they’ve been effectively treated, the CRP might have come down but the sed rate continues on. So, we will get both of these tests in all patients with both joint and bone infections. This is because we’re going to follow the CRP to make sure they’re getting better and the sed rate is more likely to yield a positive result. It really triggers to say "Yes, this might be a septic arthritis." Additionally, we’re going to draw blood cultures on all these patients because the yield is as high as 50% and knowing the bacteria is critical especially in this day of MRSA. We need to know whether to treat MRSA or not to treat MRSA. So, we’re going to get the CRP, the sed rate, the blood culture and a CBC.

    04:51 That CBC will generally show an elevated white count and it’s especially helpful for the Kocher criteria. Now, let’s say we’ve decided we’re going to tap that joint because we suspect a septic arthritis. What are we going to look for? Well, we need to culture that fluid. We’d love to culture it because we’re, again, really dedicated to finding the organism that’s causing this so we know especially whether to treat MRSA or not. A gram stain is useful because an early gram stain that’s positive really closes in, this is definitely a septic arthritis. A negative gram stain doesn’t really tell you one way or the other and we will get a cell count. The cell count tends to be very high, more than 50,000 in septic arthritis, could be more than 30,000 but generally more than 50,000. In slightly reactive infections like Lyme or tuberculosis, there might be a lower level of white cells but in transient synovitis or reactive synovitis, we generally see a very much lower number of white cells as is shown on this graph. Other labs we consider getting are a Lyme PCR which is about 75% sensitive in patients with Lyme disease or in the event we’re worried about tuberculosis, we would certainly send an acid fast stain in addition to the regular gram stain. So, we can also do imaging studies to prove whether a patient has septic arthritis or not. The x-ray may show increased joint space especially in the hips and the knees but it is not helpful or diagnostic in a patient with septic arthritis. You might get it though if there is that history of trauma and you’re worried there might be some indolent fracture or something but generally the x-ray isn’t helpful in making a diagnosis specifically of septic arthritis. An ultrasound of the hips is sometimes useful because it’ll tell us whether it's in fact fluid in there to go tap but the ultrasound again is unlikely to yield a definitive result in terms of septic arthritis. The MRI is really the gold standard. This is going to light up really well when there’s an infection because of the amount of fluid that collects around that infection lighting up on the MRI. So, how do we manage septic arthritis? In general, we really need to drain these joints and wash them out to prevent further complications such as, down the road, development of osteoarthritis. A delay in surgery can result in worse outcomes. Now, it’s not an emergency.

    07:24 They don’t need to come in right away but generally it seems that in patients who have more than 4 days of delay between when symptoms start and when they get their joint wash out, those children are probably at increased risk for development of osteoarthritis or reduced mobility of that joint down the road. We will provide IV antibiotics but quickly transition to oral antibiotics when we’re confident that we’re killing the bacteria and that the patient is improving. They generally improve pretty quickly. We usually see these patients in the hospital for maybe 2 or 3 days, maybe 4. But our total duration of antibiotics is typically on the range of 2 to 3 weeks, the first several days IV and then home on oral antibiotics once we’re comfortable that the antibiotic we’ve chosen is working. Antibiotic selection. This can be tricky especially in those cases when you don’t have a bacteria to grow in the lab and see what it’s sensitive to. In general, we’ll start with IV cefazolin or first generation cephalosporin. This is because for reasons that we aren’t sure, MRSA infections of septic arthritis are less common than MSSA infections. So, we’ll start with IV cefazolin and then transition to oral cephalexin as an outpatient for group A <i>Strep</i> or MSSA and what’s cool is that those antibiotics also are very effective against <i>Kingella</i>, that unusual pathogen in children under 6. In patients where we suspect MRSA or where MRSA is growing, we usually start with IV clindamycin with a plan to transition to oral clindamycin for MRSA. In areas where there is clindamycin resistance, we may not have another option. We may have to do vancomycin. The problem with vancomycin, which we will use for very severe children or where we strongly suspect a resistant organism, is that there’s no really good oral alternative. A drug such as linezolid is effective but that is incredibly expensive, almost $1,000 a day and can cause significant side effects such as bone marrow suppression as it continues along. Some practitioners like to add steroids to their treatment of septic arthritis. This is because in 3 studies now, all of them randomized controlled trials, we have seen improved outcomes and prevention of long-term complications. In one study, the steroids significantly reduced the duration of stay in the hospital. Most studies have a 5-day course of Orapred as their steroid of choice.

    About the Lecture

    The lecture Septic Arthritis in Children by Brian Alverson, MD is from the course Pediatric Infectious Diseases. It contains the following chapters:

    • Clinical Presentation and Diagnosis of Septic Arthritis
    • Management of Septic Arthritis

    Included Quiz Questions

    1. Corticosteroids
    2. Daily joint aspiration
    3. Place a PICC line for prolonged IV antibiotics.
    4. Draw daily CBCs to track improvement.
    1. Hematoma
    2. Painful joint
    3. Decreased range of movement due to pain
    4. Fever
    5. Irritability
    1. Elevated CRP
    2. Refusal to bear weight
    3. Temperature higher than 38.5°C
    4. ESR >40
    5. WBC > 12
    1. Septic arthritis
    2. Lyme arthritis
    3. TB arthritis
    4. Transient synovitis
    5. Reactive arthritis
    1. MRI
    2. X-ray
    3. CT scan
    4. Ultrasound
    5. Synovoscopy

    Author of lecture Septic Arthritis in Children

     Brian Alverson, MD

    Brian Alverson, MD

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    Excellent lecture
    By Jalil Z. on 05. August 2020 for Septic Arthritis in Children

    I particularly liked the remarks concerning the antibiotic selection and the differential diagnosis.