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Updated: Sep 20, 2026
Novel Diagnostics in Revision Arthroplasty: Implant Sonication and Multiplex Polymerase Chain Reaction
Published on: December 3, 2017
Synovial absolute polymorphonuclear neutrophil cell count: A simple and inexpensive marker for diagnosing
Sujeesh Sebastian1, Jennyfer A Mitterer1, Youssef Ahmed1
1Michael Ogon Laboratory for Orthopedic Research, Orthopedic Hospital Vienna Speising, Vienna, Austria.
Purpose:
This study aimed to establish the optimal cutoff value for synovial absolute polymorphonuclear neutrophil (APMN) count in distinguishing between septic and aseptic hip and knee revision arthroplasties. We also investigated its effectiveness as an indicator in revision arthroplasties with challenging microbiological findings, including (i) aseptic cases with a single unexpected positive intraoperative culture (UPICs), (ii) septic cases with unexpected negative ICs (UNICs) and (iii) infections caused by high- and low-virulent pathogens.
Methods:
A total of 616 revision arthroplasties (177:hip, 439:knee) included. Using European Bone and Joint Infection Society (EBJIS) criteria, 325 (52.8%) were classified as infection confirmed, 271 (44%) infection unlikely and 20 (3.2%) as infection likely. International Consensus Meeting (ICM) 2018 criteria classified 308 (50%) as infected, 269 (43.7%) not infected, and 39 (6.3%) as inconclusive. Diagnostic accuracy was assessed through receiver operating characteristic curves and area under the curve (AUC).
Results:
Optimal APMN count thresholds using EBJIS criteria in hip and knee joints were 783.6 cells/µL (AUC: 0.92) and 549 cells/µL (AUC: 0.91), respectively. With the ICM criteria, its optimal cutoff values remained unchanged, except for the knee, which shifted to 594.2 cells/µL. Comparing UPICs to other aseptic cases showed no significant median APMN count differences when both criteria's applied, potentially ruling out infection suspicion. In septic cases, APMN counts differed between UNICs and culture positives but were statistically significant with EBJIS criteria (Hip:p = 0.01, Knee:p = 0.03) but not with ICM (p = 0.08). Median APMN counts were significantly elevated in high-virulent compared to low-virulent organisms, with similar trends in most of the other markers. Compared to alpha-defensin, APMN count exhibited better AUC, sensitivity and negative predictive value.
Conclusions:
The APMN count represents a simple and inexpensive method that may serve as a complementary diagnostic marker in hip and knee revision arthroplasties with challenging microbiological findings.
Level Of Evidence:
Level III, retrospective study.
Insights
The synovial absolute polymorphonuclear neutrophil (APMN) count effectively distinguishes septic from aseptic hip and knee revision arthroplasties. This simple marker aids diagnosis in complex cases with uncertain microbiological results.
Area of Science:
- Orthopedic Surgery
- Infectious Disease Diagnostics
- Biomarker Analysis
Background:
- Distinguishing septic from aseptic hip and knee revision arthroplasties is critical for patient outcomes.
- Challenging microbiological findings can complicate diagnosis in revision arthroplasties.
- Reliable diagnostic markers are needed to guide treatment decisions.
Purpose of the Study:
- To determine the optimal cutoff value for synovial absolute polymorphonuclear neutrophil (APMN) count in differentiating septic and aseptic hip and knee revision arthroplasties.
- To evaluate the APMN count's diagnostic utility in complex cases with unusual microbiological results, including unexpected positive or negative cultures and varying pathogen virulence.
- To compare the diagnostic performance of APMN count with other markers, such as alpha-defensin.
Main Methods:
- Retrospective analysis of 616 revision arthroplasties (177 hip, 439 knee).
- Classification of cases using European Bone and Joint Infection Society (EBJIS) and International Consensus Meeting (ICM) 2018 criteria.
- Diagnostic accuracy assessed using receiver operating characteristic curves and area under the curve (AUC).
Main Results:
- Optimal APMN count thresholds were established for hip and knee joints using EBJIS criteria (e.g., 783.6 cells/µL for hip, AUC: 0.92).
- APMN count showed diagnostic utility in cases with unexpected positive intraoperative cultures and unexpected negative cultures, differentiating between septic and aseptic conditions.
- APMN count demonstrated superior performance (AUC, sensitivity, negative predictive value) compared to alpha-defensin.
Conclusions:
- The synovial absolute polymorphonuclear neutrophil (APMN) count is a valuable, simple, and cost-effective diagnostic marker for revision arthroplasties.
- APMN count aids in diagnosing challenging cases with ambiguous microbiological findings.
- This marker can complement existing diagnostic methods for infection in revision joint surgery.
