What Is the Impact of Automated Synovial Cell Counting on Different Aseptic Causes and Periprosthetic Conditions Associated With Revision THA?

Abstract

Background Studies have suggested that automated synovial cell counting may overestimate the white blood cell (WBC) count, resulting in false positive tests when evaluating patients for the possibility of periprosthetic joint infection (PJI) after THA. However, associations between WBC counts high enough to mimic PJI in patients whose arthroplasties are not infected but rather are experiencing a variety of aseptic problems-including but not limited to metallosis, polyethylene wear, and recurrent dislocation-have not, to our knowledge, been adequately addressed. In addition, there is a lack of analyses about the polymorphonuclear percentage (PMN%) when assessed by automated analyzers in this context. Questions/purposes In the context of different indications for aseptic revision and different periprosthetic hip pathologic findings, we asked: (1) What were the synovial WBC count levels, and what proportion of values were above the 2018 International Consensus Meeting (ICM) cutoff (3000 cells/ mL)? (2) What were the synovial PMN% levels, and what proportion of values were above the 2018 ICM (70%)? Methods We retrospectively studied the preoperative cell count analyses of synovial fluid in patients who underwent revision THA for aseptic reasons at our tertiary referral arthroplasty center between January 2015 and December 2017. We considered all revisions performed on patients during that time potentially eligible, and after prespecified exclusions were applied (exclusions mainly included 15% [197 of 1306] sporadic missing data and 12% [155 of 1306] insufficient synovial fluid obtained in the aspirate), a total of 702 patients undergoing revision THA for aseptic reasons remained for the final analysis. As far as we know, no patients underwent re-revision for PJI at a mean follow-up of 46 6 11 months, which tends to confirm our impression that indeed these hips did not have PJI. Cell count analyses were conducted using an automated analyzer. Clinical findings, preoperative radiographs, and surgical reports-confirmed by available histologic results--were used to establish diagnoses. We evaluated these hips considering the recommendations of the 2018 ICM (WBC count of One of the authors (MC) certifies receipt of personal payments or benefits, during the study period, in an amount of less than USD 10,000 from W. Link & Co KG, outside the submitted manuscript. One of the authors (TG) certifies receipt of personal payments or benefits, during the study period, in an amount of USD 10,000 to USD 100,000 from W. Link & Co KG, in an amount of USD 10,000 to USD 100,000 from Zimmer Biomet Inc, and in an amount of USD 10,000 to USD 100,000 from CeramTec Co, all outside the submitted manuscript. All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research® editors and board members are on file with the publication and can be viewed on request. Ethical approval for this study was obtained from the Ethik-Komission der Arztekammer Hamburg, Hamburg, Germany (WF-115120).

CORR Insights®: What Is the Impact of Automated Synovial Cell Counting on Different Aseptic Causes and Periprosthetic Conditions Associated With Revision THA?

“…The current study by Abdelaziz and colleagues [1] confirms what Thomas Bayes explained over 200 years ago, and what we need to constantly be reminded of: A cell count without a history, physical exam, or radiographs is relatively meaningless.…”

“…For example, patients with an acute gout flare can have dramatically elevated cell counts in the absence of PJI, and patients with unicompartmental knee arthroplasty have a higher threshold for the diagnosis of infection [3, 11]. The current study by Abdelaziz and colleagues [1] is yet another reminder that no single WBC count threshold should be applied to every patient’s circumstance without careful consideration of all clinical data points.…”

Synovial fluid pH is as specific as synovial leukocyte count but less sensitive for the diagnosis of chronic prosthetic joint infection

“…Furthermore, most recently Abdelaziz et al [ 23 ] investigated differences in synovial cell count for different aseptic reasons for revision arthroplasty in 702 cases of revision THA. They found that for some indication such as polyethylen wear or osteolysis, common diagnostic threshholds in cell count for PJI can’t be applied and that im some instances cell count might be greater than 7000 leuocytes per μl.…”

Is a preoperative pathogen detection a prerequisite before undergoing one-stage exchange for prosthetic joint infection of the hip?

“…In addition, the inclusion of culture-negative cases was-together with increased CRP and anamnesisbased on the 2021 EBJIS joint aspiration criteria of more than 3000 cells [12]. While this cut-off has been shown specify and sensitivity values of 90% according to a 2018 meta-analysis [1], these results could not be confirmed by all studies [35]. PJI definition in these culture-negative cases are thus not necessarily fulfilled according to other definitions such as the Musculoskeletal Infection Society criteria, in which aspiration is considered a minor criterion only [36].…”