Additional Erythrocyte Curve Improves the Diagnostic Value of Graphic Type Differentiation of Synovial Cell Count Analytics for Diagnosis of Late Periprosthetic Joint Infection

Author(s): Marius Hoyka, Florian Hubert Sax, Benedikt Blersch, Elke Weissbarth, Philipp Schuster, Irina Berger, Hannsjörg Baum, Bernd Fink

Aim: The determination of the synovial aspirate cell count is one of the central parameters for diagnosing late periprosthetic joint infection (PJI). A number of different threshold values between 1,100 cells/μL and 5,000 cells/μL have been described, which can be caused by counting of additional abrasion or wear particles using automated cell counters. A new graphic cell distribution charts defined six so-called LMNE matrices (leukocyte-monocyte-neutrophil-eosinophil matrices): abrasion type (type I), infection type (type II), mixed type (type III), indifference type (type IV), haematoma type (type V) and mixed type II (haematoma and infection) (type VI), whereby types I - IV correspond to the histological classification of Morawietz and Krenn. The aim of the study was to evaluate the diagnostic value of the graphical cell type differentiation and the correlation between the LMNE types and the histological types using the new automated cell counter Yumizen H500 and to verify if the new additional erythrocyte curve of this device gives additional helpful information.

Methods: Synovial aspirates of 585 knee and 196 hip arthroplasties (410 women, 371 men) were examined by cultivation, alpha-defensin and cell count analysis (using the Yumizen H500 haematology analyser with cell distribution plots (LMNE matrices)) according to the ICM criteria 2018. Periprosthetic tissue obtained from 288 knee prostheses and 116 hip prostheses during revision surgery was analysed microbiologically and histologically using the Morawietz and Krenn classification.

Results: The LMNE matrices significantly increased the diagnostic value of the cell count, especially for cell count values < 1500 cells/ μL (sensitivity: 96.4-97.3%, specificity: 99.0%). There was a highly significant correlation between the LMNE types I - IV and the histological classification according to Morawietz (p < 0.001 and Cramer's V value of 0.96). The erythrocyte field is helpful to identify leucocytes related to hematoma in the aspirate.

Conclusion: The graphical representation of the synovial cell count analysis is a reproducible and helpful method for differentiating between real periprosthetic infections with an increased leukocyte count and falsepositive values due to the presence of wear particles with advantages of the new Yumizen H500.