[Text on screen: Ohio State Health & Discovery
How we can tell it's a PJI]

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[Text on screen: Douglas Chonko, DO
Orthopedic Surgeon
Ohio State Wexner Medical Center]

Douglas Chonko, DO:
The diagnosis of periprosthetic joint infections, or PJIs, can be very complex, and we have a number of scales that we use. Clinical exams are a big, important part of that, but we use a couple different scales, and one of those is the Musculoskeletal Infection Society Scale, and there's two others that are commonly used. 

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We have the Infectious Disease Society of America, or the IDSA, and we also have the International Consensus, or the ICM scale. They're all very similar to each other, and they use a number of different things when we're looking at the patient.

One of the things that we get with all patients that we are considering for a PJI is blood work. There are three things that we primarily look at in that blood work, and that's going to be the white blood cell count, the C-reactive protein, or what we call a CRP, and the third thing is the erythrocyte sedimentation rate, or an ESR.

We're going to include an aspiration oftentimes with the diagnosis. Actually, in the majority of cases, we included an aspiration, which is the collection of fluid from the knee or the hip. We are then going to analyze that fluid, and we send it off to the laboratory. The fluid will be looked at very carefully for a number of different things that are going to be contained in that.

We get a cell count and differential, and that's going to look at the number of white blood cells primarily. Early on, the number of white blood cells can be a little bit higher than a thousand. However, we like that number overall to be less than a thousand. There's a type of white blood cell that we call PMNs, and PMNs are one of the types of white blood cells that fight infection, and we're going to see the percentage of those go up when we have a periprosthetic joint infection. That number typically is going to be less than 65% in the majority of patients that don't have an infection. If it goes over 65% of all white blood cells, then we start to consider that maybe we have an infection. When that number gets over 90 to 92%, oftentimes that's very indicative of an infection.

We look at cultures, and we're going to take that fluid and we're going to put it in a Petri dish, which they introduce then into an incubator, and let that fluid see if it's going to grow bacteria or a fungus. And that will indicate that we've got growth of one of those microorganisms, and that's another part of that scale that we're going to look at.

So these scales run with the number scale, and we utilize a low, medium, or a high likelihood of infection. And surgeons don't like, or doctors don't like, anything that says likelihood. We like a yes or a no, but unfortunately, because of the complexity of the diagnosis of this, we have to use all these different numbers, and we put it in a scale, and oftentimes that's what we're presenting to patients, is a low, medium, or high likelihood.

One of the ways to really easily make the diagnosis is if you have an opening or a sinus that goes inside the human body near the incision or right along the incision. If you have a sinus tract that's leaking out what we call purulent material, or purulent fluid, which is another name for pus, that's an indicator of infection, and we don't need any of those other markers, and that puts you right into the high likelihood of infection. If we see the implant, and on occasion we actually do, especially on the knee, the opening can get large enough and you're looking at the implant from the outside world. That is also in the high likelihood of an infection. So there's a number of different things, and it can be very complex. 

We try to be very efficient in the time that it requires to diagnose a periprosthetic joint infection, but it can take a little bit of time. The majority of information that we receive back in the first two to three days gives us a very good indication of whether an infection is present. We will get the majority of the lab work back, and we will get the cell count and differential back.

The thing that won't come back immediately will be the cultures, and we're going to hold onto your cultures for up to 42 days to see if anything's going to grow in that Petri dish in the incubator. And there are some very slow-growing organisms out there, and that's why we hold onto some of the cultures for that length of time, which is six weeks.

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And occasionally we see something, and the diagnosis comes as late as six weeks later. But in the vast majority of patients, and that's about 98%, we're going to be able to diagnose your infection in the first three days.

[Text on screen: Ohio State Health & Discovery
For more information, visit:
wexnermedical.osu.edu/orthopedics]

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