Twenty-three neutrophil granulocytes in 10 high-power fields is the best histopathological threshold to differentiate between aseptic and septic endoprosthesis loosening

The histopathological diagnosis of infection in periprosthetic tissue from loose total joint endoprosthesis has been the subject of controversy. The aim was to define a histological criterion that would best differentiate between aseptic and septic endoprosthesis loosening. Neutrophilic granulocytes (NG) were enumerated histopathologically in 147 periprosthetic membranes obtained from aseptic and septic revision surgery, using periodic acid-Schiff (PAS) stains and CD15 immunohistochemistry. Cell numbers were correlated with the results of microbiological culture and the clinical diagnoses. Using receiver-operating characteristics, an optimized threshold was found at 23 NG in 10 high-power fields (HPF). Using this threshold, histopathological examination had a sensitivity of 73% and specificity of 95% when compared with microbiological diagnosis (area under the curve 0.881), and a sensitivity of 77% and specificity of 97% when compared with clinical diagnosis (area under the curve 0.891). We therefore recommend a counting algorithm with a threshold of >= 23 NG in 10 HPF (visual field diameter 0.625 mm) for the histopathological diagnosis of septic endoprosthesis loosening. If the enumeration of NG is difficult in conventional haematoxylin and eosin-stained slides, CD15 immunohistochemistry should be performed, whereas the PAS stain has not proven to be helpful .