Performance of established test methods for diagnosing chronic periprosthetic joint infections caused by low-virulence pathogens

Listen to Simon and Amy discuss the paper 'Performance of established test methods for diagnosing chronic periprosthetic joint infections caused by low-virulence pathogens' published in the December 2025 issue of Bone & Joint Research.

Click here to read the paper.

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Transcript

[00:00:00] Welcome back to another episode of AI Talks with Bone & Joint from the publishers of Bone & Joint Research. Today we're discussing the paper 'Performance of established test methods for diagnosing chronic periprosthetic joint infections caused by low-virulence pathogens', published in December 2025 by M Luger and colleagues. I'm Simon, and I'm joined by my co-host, Amy.

Hello Simon! I'm really looking forward to today's discussion. Chronic periprosthetic joint infections caused by low-virulence pathogens are fascinating and pose significant challenges for clinicians.

Indeed. These low-virulence pathogens like coagulase-negative staphylococci and cutibacterium species don't exhibit the typical symptoms we see with more aggressive infections.

This makes them difficult to diagnose, which is why this paper is so crucial. This team examined the accuracy of various diagnostic tests. The study involved a cohort of 420 patients undergoing revision, total hip or knee arthroplasty with 60 chronic [00:01:00] PJIs caused by low-virulence pathogens and 213 as septic cases.

They used the European Bone and Joint Infection Society criteria for diagnosis. The primary aim was to evaluate the diagnostic accuracy of common tests like serum CRP, synovial fluid white blood cell count, and the percentage of polymorphonuclear neutrophils among others.

One of the most intriguing findings pertained to the cine fluids percentage of polymorphonuclear neutrophils. The study discovered that a cutoff of greater than 67% provided the best preoperative diagnostic performance. This threshold demonstrated a sensitivity and specificity of around 97%, which is rather impressive. Those are remarkable numbers. It's crucial since the traditional cutoff used to be 80%, which as the study indicated was less accurate, this is significant given that low-virulence pathogens often elicit lower inflammatory responses.

Exactly. They also emphasize the importance of the synovial fluid white blood cell count. A count above [00:02:00] 2,403 cells per microliter proved to be a strong indicator with a sensitivity of 85% and a specificity of 100%. This differs slightly from the established 3000 cells per microliter threshold, but the study suggests that the lower cutoff could be more diagnostically specific for low-virulence infections.

Another notable point was the use of intraoperative and postoperative histological analysis. Permanent paraffin fixed sections of deep tissue samples had the best performance values showing a sensitivity of about 89% and specificity of 100%. This was slightly better than frozen sections, but both proved highly effective.

Yes, they found that frozen sections were particularly useful intraoperatively. In cases where the preoperative diagnosis was unclear, frozen sections helped confirm the diagnosis in nearly 89% of the cases. The study also highlighted the role of sonication fluid culture, especially in detecting biofilm, forming low-virulence pathogens.

[00:03:00] This method showed high sensitivity and specificity even when considering low colony-forming unit thresholds. Yes, the researchers suggested lowering the cutoff to more than four colony-forming units from the previously used 50 colony-forming units to improve diagnostic accuracy. This adjustment significantly increased sensitivity without compromising specificity.

It's fascinating how all these diagnostic methods combine to provide a more accurate diagnosis of chronic PJIs caused by low-virulence pathogens. They also discussed combining different methods like two concordant samples, which improved diagnostic accuracy compared to single methods. Indeed, the combined evaluation showed a sensitivity of 78% and a specificity of 100%. This underscores the importance of a multifaceted diagnostic approach, especially for these elusive pathogens. So Amy, what are the main takeaways from today's discussion?

I would say the key insight is the importance of adjusting our diagnostic thresholds and adopting a combination of methods. [00:04:00] The lower percentage of polymorphonuclear neutrophils cutoff of more than 67% and synovial fluid white blood cell count cutoff of more than 2,403 cells per microliter have shown high diagnostic value. Additionally, the use of both permanent and frozen histological sections, along with improved sonication protocols offers a robust framework for addressing these infections.

Well, summarized Amy, this study indeed opens up new avenues for diagnosing these difficult infections more effectively. That concludes today's episode of AI Talks with Bone & Joint. Thanks for joining us, and we look forward to exploring more intriguing research in our next episode. Take care everyone.