Evaluating the Diagnostic Utility of Serum Laboratory Studies and Synovial Fluid Analysis in Identifying Periprosthetic Joint Infection in Metal Hip Revisions

Background Metal-on-metal (MoM) bearing surfaces have been implicated as a cause of increased complication rates in total hip arthroplasty (THA), with local and systemic reactions identified. These reactions may cause abnormal laboratory results in common tests that are used to diagnose periprosthetic joint infection (PJI). The purpose of this study was to evaluate the utility of common laboratory studies in the diagnosis of PJI in patients undergoing revision THA with MoM bearings. Methods A retrospective case series of 81 patients undergoing THA revision of MoM bearings from January 2010 to May 2023 at a single institution was performed. Patient data was extracted from the electronic medical record. All patients were evaluated using the 2018 International Consensus Meeting (ICM) definition of PJI. Descriptive statistics were calculated for the clinical characteristics of all patients. Univariate analyses were performed to compare patients who met the ICM criteria for infection with those deemed indeterminate. Results Fifty-one (63.0%) patients were deemed not infected according to ICM criteria, 19 (23.5%) were deemed indeterminate, and 11 (13.6%) were deemed infected. Clinically, four patients had two or more positive cultures and were formally treated for PJI; all patients were deemed inconclusive, and the remaining seven patients deemed infected were clinically treated as not infected, and all remained infection-free. There were significant differences between patients deemed inconclusive and those deemed infected in synovial WBC count (17,539 vs. 90,196 cells/μL, p = 0.049) and synovial polymorphonuclear (PMN) neutrophils (38 vs. 79%, p = 0.002). No other significant differences in laboratory values or outcomes were noted between groups. Conclusions Patients undergoing revision THA with MoM bearings may be more likely to present with a clinical picture that is concerning for infection and may benefit from a more aggressive preoperative workup. The synovial PMN neutrophil percentage may help differentiate between hips that are infected and those that are not.