Dugdale EM, Uvodich ME, Osmon DR, Pagnano MW, Berry DJ, Abdel MP
J Arthroplasty. 2021 Nov 10:S0883-5403(21)00842-1.
Summary by Mohammad S Abdelaal MD, MSc
Assessing a patient for periprosthetic joint infection (PJI) can be challenging in the early postoperative period as it can be difficult to distinguish abnormally elevated laboratory values from those expected with typical perioperative inflammation[1,2]. ESR, CRP, synovial fluid WBC count, and synovial neutrophil percentage are normally elevated immediately following total joint arthroplasty with values gradually declining over time[1,3]. The purpose of this study was to determine optimal cutoff values of these laboratory tests in order to accurately diagnose PJI in the early postoperative period (≤12 weeks).
In the current study, Dugdale et al. retrospectively identified 43 hips that underwent arthrocentesis within 12 weeks of their index total hip replacement (THA) at 3 institutional locations from 2000-2019. The cohort was divided into 2 groups: those who underwent laboratory workup ≤ 6 weeks from the primary THA and those with laboratory workup performed between 6-12 weeks postoperatively. Presence of infection in each group was defined according to the 2011 Musculoskeletal Infection Society major diagnostic criteria. The median values of ESR, CRP, synovial WBC count, synovial neutrophil percentage, and synovial absolute neutrophil count (ANC) were compared between infected and non-infected patients within both the 6 weeks and 6-12 weeks groups. The authors found that both within 6 weeks and between 6-12 weeks postoperatively, median laboratory values were significantly higher in infected THAs. For the 6 weeks group, optimal laboratory cutoff values were: CRP >100 mg/L, synovial WBCs >4390 cells/mL, neutrophil percentage >74%, and ANC >3249 cells/mL. Between 6 and 12 weeks, optimal cutoffs were: CRP >33 mg/L, synovial WBCs >26,995 cells/mL, neutrophil percentage >93%, and ANC >25,645 cells/mL. They concluded that the optimal laboratory cutoff values and their effectiveness in diagnosing PJI of the hip vary within different time periods of the early postoperative period. Generally, both serum and synovial laboratory tests became more effective at diagnosing PJI of the hip between 6 and 12 weeks compared to 6 weeks postoperatively.
Study limitation included its retrospective design with risk of confounding factors, small sample size (n=43), selection bias due to exclusion of ambiguous cases and finally not accounting for medical conditions that can affect inflammatory markers.
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