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. 2022 May;104(5):334-339.
doi: 10.1308/rcsann.2021.0186. Epub 2021 Dec 23.

The combined measurement of synovial markers in the diagnosis of periprosthetic joint infection

A Felstead  1 , P Kundasamy  1 , G Penfold  1 , K Whiting  1 , J Buck  1 , S Sturridge  1 , M Meda  1
Affiliations

The combined measurement of synovial markers in the diagnosis of periprosthetic joint infection

A Felstead et al. Ann R Coll Surg Engl. 2022 May.

Abstract

Introduction: Currently there is no single test for periprosthetic joint infection (PJI) that demonstrates an acceptable level of sensitivity. The aim of this pilot study was to identify a combination of biomarkers that could exclude periprosthetic infection prior to revision surgery in hip and knee arthroplasty. This would help in equivocal cases of PJI, such as those with low-virulence organisms, chronic low-grade infection or 'aseptic' loosening. Current research has focused on measuring the levels of biomarkers in the patient's synovial fluid, and these can be combined to improve accuracy.

Methods: We selected synovial white cell count (SF-WCC) and C-reactive protein (SF-CRP), as they demonstrated an acceptable level of sensitivity and specificity which could be measured using existing equipment. One hundred and sixty-one synovial fluid samples from 134 patients were collected and analysed prospectively using calculated cut-off values of 10mg/l for SF-CRP and 3,000×106/l for SF-WCC. Samples were deemed positive for infection when either of the SF-CRP or SF-WCC values were above the cut-off.

Results: The combined test demonstrated a sensitivity greater than 98.5% and specificity above 80% in all samples analysed or looked at separately for total hip replacement and total knee replacement infections. All ten aspirates taken from chronically infected joints tested positive.

Conclusions: The combination of SF-CRP and SF-WCC measurement has been shown to have high sensitivity of over 99% in detecting both acute and chronic PJI in both hip and knee arthroplasty. This ability of the test to exclude infection with a high degree of certainty will help in preoperative planning of PJIs.

Keywords: CRP; Infection; Joint; Periprosthetic; Synovial.

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Figures

Figure 1
Figure 1
Classification of infection type and joint type of synovial fluid aspirates at the time of sample collection
Figure 2
Figure 2
ROC curves for (a) synovial fluid and (b) WBC. Red markers indicate a threshold of 10mg/l value for CRP and of 3,000×106/l for WBC count.
See this image and copyright information in PMC

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