Performance of established test methods in diagnosing persistent infection at the second stage of a two-stage procedure for periprosthetic hip and knee infections

Listen to Simon and Amy discuss the paper 'Performance of established test methods in diagnosing persistent infection at the second stage of a two-stage procedure for periprosthetic hip and knee infections' published in the October 2025 issue of Bone & Joint Open.

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 Open. Today we are discussing the paper 'Performance of established test methods in diagnosing persistent infection at the second stage of a two-stage procedure for periprosthetic hip and knee infections', published in October 2025 by M Luger and colleagues. I am Simon and I am joined by my co-host, Amy.

Hello Simon and greetings to all our listeners. The topic this week is highly relevant, given the challenges in diagnosing and managing periprosthetic joint infections, also known as PJIs. These infections are a significant complication following hip and knee replacements.

Indeed, this paper evaluates the performance of various diagnostic tests in identifying persistent infections during the second stage of a two-stage revision procedure. This is crucial because the timing of reimplantation is key to reducing reinfection rates and enhancing patient outcomes.

The researchers explored a range of tests including serum parameters, like C-reactive [00:01:00] protein and white blood cell count, synovial fluid analysis, tissue and sonication fluid cultures and histology. They also employed Kaplan-Meier curves to analyse infection-free prosthesis survival rates.

Let's discuss the methods first. They conducted a retrospective study from January 2015 to January 2023 involving 133 patients who underwent two-stage exchange arthroplasty due to PJIs. Notably, they excluded patients who did not proceed to reimplantation, such as those who had an amputation or a spacer as the definitive treatment.

Exactly, they meticulously documented various diagnostic results prior to or during the second stage of the procedure. Interestingly, they found that serum C-reactive protein had the highest diagnostic value among all tests, albeit with moderate accuracy. The sensitivity was 51.7% and specificity was 73.1%. To give you an idea, [00:02:00] the area under the curve for C-reactive protein was 0.624.

That's quite interesting, Amy. However, even though C-reactive protein showed the best performance, it was still not reliable enough to predict persistent infection or reinfection on its own. This highlights the ongoing challenge in accurately diagnosing PJIs. They observed that a high C-reactive protein level before reimplantation was associated with higher reinfection rates.

Yes. Patients with elevated C-reactive protein levels greater than or equal to 10 milligrams per litre had a reinfection rate of 35% compared to just 16% for those with normal C-reactive protein levels. This underscores the complexity of using serum markers alone to make clinical decisions.

Interestingly, none of the other tests provided sufficient accuracy either. For instance, synovial fluid, white blood cell counts, and culture tests also showed limited sensitivity. Synovial fluid culture had a sensitivity of just [00:03:00] 16.7%, but a high specificity of 96.6%, meaning it is good at confirming an infection if the result is positive, but it fails to identify many cases where an infection is present.

And regarding culture tests, it's worth noting that positive cultures did not necessarily lead to higher reinfection rates. This suggests that even if cultures are positive, it may not justify additional surgeries or prolonged antibiotic treatments. Instead, a thorough debridement during the second stage might be more beneficial.

Exactly. One key takeaway from this study is the importance of a well-rounded approach in diagnosing and managing PJIs. Relying on a single diagnostic test is inadequate. Instead, integrating multiple diagnostic tools and clinical evaluations seems crucial.

Absolutely. Another interesting point is that the paper highlighted the issue of persistent versus new infections. In their cohort only 17% of reinfections were caused by the same [00:04:00] microorganisms identified initially, which means most reinfections were due to different organisms. This raises questions about the challenges in preventing cross-contamination and managing bacterial resistance.

Definitely Amy, this emphasizes the need for continuous monitoring and perhaps more innovative diagnostic approaches in the future. Another point worth noting is that percentage of polymorphonuclear cells, although not widely used, showed potential in predicting outcomes. Patients with elevated serum percentage polymorphonuclear cells had a significantly shorter infection-free survival, suggesting it could be a useful marker in predicting reinfections.

That's an excellent point, Simon. Clearly there's much more work to be done in this area. To summarize our discussion, while C-reactive protein showed the best individual performance, no single test could reliably predict persistent infections on its own. Thus, a multifaceted approach and in-depth clinical evaluations remain essential.

Despite its limitations, this study offers important insights that could [00:05:00] influence future guidelines and help refine our diagnostic strategies.

Absolutely, Simon. For all our listeners, we hope you found today's episode on this pivotal research enlightening. Remember to stay updated with Bone & Joint Open for more studies like this one.

Thank you, Amy, and thank you to our listeners for tuning in.