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Updated: May 5, 2026
Novel Diagnostics in Revision Arthroplasty: Implant Sonication and Multiplex Polymerase Chain Reaction
Published on: December 3, 2017
Lower synovial leucocyte count and polymorphonuclear percentage reliably differentiate periprosthetic joint infection
Stefanie Donner1, Georg Matziolis2, Yves Gramlich3,4
1Center for Musculoskeletal Surgery, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Purpose:
This study aimed to determine diagnostic thresholds for synovial fluid leucocyte count and polymorphonuclear (PMN) percentage to identify the diagnosis periprosthetic joint infection (PJI) in patients with failed unicompartmental knee arthroplasties (UKAs).
Methods:
This multicentre retrospective cohort study included 239 patients who underwent revision of an UKA for either septic or aseptic indications at five university-affiliated medical centres. Among these, 30 patients (13%) underwent revision for PJI and 209 (87%) for noninfectious causes. PJI was diagnosed according to the European Bone and Joint Infection Society (EBJIS) criteria. Preoperative synovial fluid leucocyte count, synovial PMN percentage, serum C-reactive protein (CRP) and white blood cell (WBC) count were evaluated. Diagnostic performance and optimal thresholds for each parameter were assessed using receiver operating characteristic curves and Youden's index.
Results:
The PJI group demonstrated significantly higher median synovial leucocyte counts (11,399/μL vs. 429/μL, p < 0.001), and significantly higher synovial PMN percentage (82% vs. 28%, p < 0.001) compared to the non-PJI group. The optimal diagnostic cut-off for synovial fluid leucocyte count was 2318/μL (area under curve [AUC] 0.93; sensitivity 83%, specificity 95%) and for PMN percentage, 64% (AUC 0.90; sensitivity 76%, specificity 95%). Serum CRP (cut-off 9 mg/L; AUC 0.85) and WBC count (cut-off 8 G/L; AUC 0.71), showed lower diagnostic accuracy.
Conclusions:
This study establishes UKA-specific diagnostic thresholds for PJI, which are consistent with the EBJIS PJI criteria established for TKA. Synovial biomarkers, particularly synovial fluid leucocyte count and PMN percentage, demonstrated superior diagnostic performance compared to serum CRP and WBC count. These findings underscore the need for tailored diagnostic criteria to improve the accuracy of PJI diagnosis and guide clinical decision-making in UKA revision.
Level Of Evidence:
Level III.
Insights
This study establishes specific diagnostic thresholds for periprosthetic joint infection (PJI) in unicompartmental knee arthroplasty (UKA) revisions. Synovial fluid biomarkers offer superior accuracy for diagnosing PJI compared to blood tests.
Area of Science:
- Orthopedic Surgery
- Infectious Diseases
- Diagnostic Biomarkers
Background:
- Periprosthetic joint infection (PJI) is a significant complication following knee arthroplasty.
- Accurate diagnosis of PJI in revision unicompartmental knee arthroplasty (UKA) is challenging.
- Existing diagnostic criteria may not be optimal for UKA revisions.
Purpose of the Study:
- To determine optimal diagnostic thresholds for synovial fluid leucocyte count and polymorphonuclear (PMN) percentage in failed UKAs.
- To evaluate the diagnostic performance of these biomarkers for identifying periprosthetic joint infection (PJI).
- To compare the efficacy of synovial fluid analysis versus serum markers (CRP, WBC) for PJI diagnosis in UKA revisions.
Main Methods:
- A multicentre retrospective cohort study of 239 patients undergoing UKA revision.
- Patients were classified into periprosthetic joint infection (PJI) (n=30) or non-infectious (n=209) groups.
- Diagnostic performance of synovial fluid leucocyte count, PMN percentage, serum CRP, and WBC count was assessed using ROC curves and Youden's index.
Main Results:
- Significantly higher synovial leucocyte counts and PMN percentages were observed in the PJI group compared to the non-PJI group (p < 0.001).
- Optimal diagnostic cut-offs were identified: synovial fluid leucocyte count ≥ 2318/μL (AUC 0.93) and PMN percentage ≥ 64% (AUC 0.90).
- Synovial biomarkers demonstrated superior diagnostic accuracy (sensitivity 83%, specificity 95% for leucocyte count; sensitivity 76%, specificity 95% for PMN percentage) compared to serum CRP and WBC count.
Conclusions:
- This study provides UKA-specific diagnostic thresholds for periprosthetic joint infection (PJI), aligning with European Bone and Joint Infection Society (EBJIS) criteria.
- Synovial fluid leucocyte count and PMN percentage are highly accurate biomarkers for diagnosing PJI in UKA revisions.
- Tailored diagnostic criteria using synovial biomarkers are crucial for improving PJI diagnosis accuracy and guiding clinical decisions in UKA revision surgery.
