Synovial Fluid Biomarkers for the Diagnosis of Periprosthetic Joint Infection-A Systematic Review and Meta-Analysis of Their Diagnostic Accuracy According to Different Definitions.

BACKGROUND: Different synovial fluid biomarkers have emerged to improve periprosthetic joint infection (PJI) diagnosis. The goals of this paper were (i) to assess their diagnostic accuracy and (ii) to evaluate their performance according to different PJI definitions. METHODS: A systematic review and meta-analysis was performed using studies that reported diagnostic accuracy of synovial fluid biomarkers using validated PJI definitions published from 2010 to March 2022. A database search was performed through PubMed, Ovid MEDLINE, Central, and Embase. The search identified 43 different biomarkers with four being the more commonly studied, with 75 papers overall: alpha-defensin; leukocyte esterase; synovial fluid C-reactive protein; and calprotectin. RESULTS: Overall accuracy was higher for calprotectin, followed by alpha-defensin, leukocyte esterase, and synovial fluid C-reactive protein with sensitivities of 78 to 92% and specificities of 90 to 95%. Their diagnostic performance was different according to which definition was adopted as the reference. Specificity was consistently high across definitions for all four biomarkers. Sensitivity varied the most with lower values for the more sensitive European Bone and Joint Infection Society or Infectious Diseases Society of America definitions with higher values for the Musculoskeletal Infection Society definition. The International Consensus Meeting 2018 definition showed intermediate values. CONCLUSION: All evaluated biomarkers had good specificity and sensitivity, making their use acceptable in the diagnosis of PJI. Biomarkers perform differently according to the selected PJI definitions.

The optimal diagnostic cut-off of WBC and PMN counts for joint aspiration in periprosthetic joint infection is 2479/µL and 67%, respectively: ICM criteria thresholds are too high.

BACKGROUND: Various organizations have published definitions for periprosthetic joint infection (PJI) with significant differences in the cut-offs of white blood cell (WBC) count and polymorphonuclear (PMN) leukocyte cells. Herein, we aim to analyze optimal cut-offs in patients which are planned to undergo a prosthesis revision and compare them with the actual published thresholds of the International Consensus Meeting (ICM) and European Bone and Joint Infection Society (EBJIS). METHODS: A test kit was compiled in a monocentric prospective study, according to the ICM criteria (2018) and 2021 EBJIS criteria. The kit was implemented using: blood samples (including leukocyte count and C-reactive protein); samples for examining the synovial fluid (WBC count, PMN cell differentiation, microbiological culture for incubation over 14 days, alpha-defensin ELISA laboratory test, and leukocyte-esterase test). The cut-offs for WBC and PMN counts were investigated using ROC analyses and Youden index. The ICM 2018 criteria were applied, using alpha-defensin in all cases. Patients which have to undergo a prosthesis revision were included, a pre-operative joint aspiration had been performed, and the patients had been followed up prospectively. RESULTS: 405 patients were examined with the compiled test kit; 100% had a complete dataset with respect to alpha-defensin; 383 patients, according to WBC count; and 256, according to PMN cell differentiation The cut-off of 2478.89 cells/µl in the WBC count (sensitivity: 87.70%; specificity: 88.10%) and the cut-off of 66.99% in PMN differentiation showed the best accuracy (sensitivity: 86.00%; specificity: 88.80%). Other published cut-offs for WBC were tested in this cohort and showed the following accuracy: 3000/µl (EBJIS/ICM; sensitivity: 82.10%; specificity: 91.00%), 2000/µl (sensitivity: 89.60%; specificity: 83.40%), and 1500/µl (sensitivity: 91.50%; specificity: 75.00%). The published cut-offs for PMN had the following accuracy in this cohort: 80% (ICM; sensitivity: 66.3%; specificity: 96.50%), 70% (sensitivity: 82.6%; specificity: 90%), and 65% (EBJIS, sensitivity: 86%; specificity: 88.8%). CONCLUSIONS: This study aims to improve current cut-offs for PMN- and WB-Count, even though PJI diagnosis is based on the combination of all defined tests. The optimal diagnostic cut-off of WBC and PMN counts was found to be 2479/µL and 67%, respectively, whereas ICM cut-offs in this cohort seem too high, as they provide high specificity but very low sensitivity. On the other hand, a cut-off for WBC count of 1500/µl alone would be very low, leading to low specificity and very high suspicion of PJI. The current consensus guidelines could be actualized considering these results to significantly improve the diagnostic quality. LEVEL OF EVIDENCE: II.

Gut permeability may be associated with periprosthetic joint infection after total hip and knee arthroplasty.

A growing number of recent investigations on the human genome, gut microbiome, and proteomics suggests that the loss of mucosal barrier function, particularly in the gastrointestinal tract, may substantially affect antigen trafficking, ultimately influencing the close bidirectional interaction between the gut microbiome and the immune system. This cross-talk is highly influential in shaping the host immune system function and ultimately affecting the outcome of interventions. We hypothesized that the loss of mucosal barrier in the gut may be associatedto acute and chronic periprosthetic joint infections (PJI). Zonulin, soluble CD14 (sCD14), and lipopolysaccharide (LPS) were tested in plasma as part of a prospective cohort study of patients undergoing primary arthroplasty or revision arthroplasty because of an aseptic failure or PJI (as defined by the 2018 criteria). All blood samples were collected before antibiotic administration. Samples were tested using commercially available enzyme-linked immunosorbent assays as markers for gut permeability. A total of 134 patients were included in the study of which 44 patients had PJI (30 chronic and 14 acute), and the remaining 90 patients were categorized as non-infected that included 64 patients revised for aseptic failure, and 26 patients undergoing primary total joint arthroplasty. Both Zonulin (7.642 ± 6.077 ng/mL vs 4.560 ± 3.833 ng/mL; p < 0.001) and sCD14 levels (555.721 ± 216.659 ng/mL vs 396.872 ± 247.920 ng/mL; p = 0.003) were significantly elevated in the PJI group compared to non-infected cases. Higher levels of Zonulin were found in acute infections compared to chronic PJI (11.595 ± 6.722 ng/mL vs. 5.798 ± 4.841 ng/mL; p = 0.005). This prospective study reveals a possible link between gut permeability and the 'gut-immune-joint axis' in PJI. If this association continues to be borne out with a larger cohort and more in-depth analysis, it will have a clinically significant implication in managing patients with PJI. It may be that in addition to the administration of antimicrobials, patients with PJI and other orthopaedic infections may benefit from administration of gastrointestinal modulators such as pro and prebiotics.

Activated polymorphonuclear derived extracellular vesicles are potential biomarkers of periprosthetic joint infection.

BACKGROUND: Extracellular vesicles (EVs) are considered as crucial players in a wide variety of biological processes. Although their importance in joint diseases or infections has been shown by numerous studies, much less is known about their function in periprosthetic joint infection (PJI). Our aim was to investigate activated polymorphonuclear (PMN)-derived synovial EVs in patients with PJI. QUESTIONS/PURPOSES: (1) Is there a difference in the number and size of extracellular vesicles between periprosthetic joint aspirates of patients with PJI and aseptic loosening? (2) Are these vesicles morphologically different in the two groups? (3) Are there activated PMN-derived EVs in septic samples evaluated by flow cytometry after CD177 labelling? (4) Is there a difference in the protein composition carried by septic and aseptic vesicles? METHODS: Thirty-four patients (n = 34) were enrolled into our investigation, 17 with PJI and 17 with aseptic prosthesis loosening. Periprosthetic joint fluid was aspirated and EVs were separated. Samples were analysed by nanoparticle tracking analysis (NTA) and transmission electron microscopy (TEM) and flow cytometry (after Annexin V and CD177 labelling). The protein content of the EVs was studied by mass spectrometry (MS). RESULTS: NTA showed particle size distribution in both groups between 150 nm and 450 nm. The concentration of EVs was significantly higher in the septic samples (p = 0.0105) and showed a different size pattern as compared to the aseptic ones. The vesicular nature of the particles was confirmed by TEM and differential detergent lysis. In the septic group, FC analysis showed a significantly increased event number both after single and double labelling with fluorochrome conjugated Annexin V (p = 0.046) and Annexin V and anti-CD177 (p = 0.0105), respectively. MS detected a significant difference in the abundance of lactotransferrin (p = 0.00646), myeloperoxidase (p = 0.01061), lysozyme C (p = 0.04687), annexin A6 (p = 0.03921) and alpha-2-HS-glycoprotein (p = 0.03146) between the studied groups. CONCLUSIONS: An increased number of activated PMN derived EVs were detected in the synovial fluid of PJI patients with a characteristic size distribution and a specific protein composition. The activated PMNs-derived extracellular vesicles can be potential biomarkers of PJI.

Which Minor Criteria is the Most Accurate Predictor for the Diagnosis of Hip and Knee Periprosthetic Joint Infection in the Asian Population?

BACKGROUND: The aim of this study was to evaluate the diagnostic performance of minor criteria from the 2018 International Consensus Meeting (ICM) for the diagnosis of chronic periprosthetic joint infection (PJI) in an Asian population. METHODS: We retrospectively reviewed 76 patients who underwent a revision knee or hip arthroplasty at an academic institution between September 2018 and December 2019. All major and minor 2018 ICM criteria were available for all patients included. Cases with at least 1 major criterion or score ≥6 in minor criteria were considered as infected. The diagnostic performance was evaluated by a receiver operative characteristic curve analysis and area under the curve (AUC) for each minor criterion. An AUC value of more than 0.9 was considered outstanding and 0.8-0.9 as excellent. RESULTS: When using 2018 ICM threshold, the diagnostic performance ranked based on AUC was the following: alpha defensin (0.92), positive histology (0.83), leukocyte esterase (0.82), synovial white blood cell (0.81), serum erythrocyte sedimentation rate (0.78), synovial polymorphonuclear neutrophils (0.77), serum C-reactive protein (0.74), D-dimer (0.59), single positive culture (0.53), and positive intraoperative purulence (0.51). Alpha defensin was considered as an outstanding test among the 2018 ICM minor criteria. Positive histology, leukocyte esterase, and synovial white blood cell were considered as excellent tests. CONCLUSION: Based on our findings, alpha-defensin has the best diagnostic performance in Asian population among the minor criteria of 2018 ICM.

GMI, an Immunomodulatory Peptide from Ganoderma microsporum, Restrains Periprosthetic Joint Infections via Modulating the Functions of Myeloid-Derived Suppressor Cells and Effector T Cells.

Periprosthetic joint infections (PJIs) caused by Staphylococcus aureus infection are difficult to treat due to antibiotic resistance. It is known that the biofilms from methicillin-resistant S. aureus (MRSA) promote expansion of myeloid-derived suppressor cells (MDSCs) to suppress T-cell proliferation and benefit bacterial infections. This study finds that GMI, a fungal immunomodulatory peptide isolated from Ganoderma microsporum, suppresses MDSC expansion to promote the proliferation of cytotoxic T cells. The enhancement is likely attributed to increased expression of IL-6 and TNF-α and reduction in ROS expression. Similar beneficial effects of GMI on the suppression of MDSC expansion and IL-6 expression are also observed in the whole blood and reduces the accumulation of MDSCs in the infected bone region in a mouse PJI infection model. This study shows that GMI is potentially useful for treating S. aureus-induced PJIs.

Detecting Periprosthetic Joint Infection by Using Mass Spectrometry.

BACKGROUND: Novel methods for diagnosing periprosthetic joint infection (PJI) are currently being explored. Mass spectrometry (MS) is an approach that can detect whole-protein changes in synovial fluid and may represent a promising method. METHODS: Between March 2017 and July 2018, we successively collected synovial fluid samples from patients who were undergoing diagnostic hip or knee aspiration because PJI was suspected. A PJI diagnosis was based on the modified Musculoskeletal Infection Society (MSIS) criteria. Cluster analysis and receiver operating characteristic (ROC) curves were used to evaluate the results, which were quantitatively confirmed with parallel reaction monitoring in another patient group who underwent aspiration between August 2018 and January 2019. RESULTS: A total of 117 synovial samples, including 51 PJI and 66 non-PJI samples, were analyzed with liquid chromatography-tandem MS (LC-MS/MS). The cluster analysis sensitivity and specificity based on differentially expressed proteins were 0.961 (95% confidence interval [CI], 0.854 to 0.993) and 0.924 (95% CI, 0.825 to 0.972), respectively. Myeloid nuclear differentiation antigen (MNDA) and polymorphonuclear leukocyte serine protease 3 (PRTN3) were the 2 most important markers for detecting PJI. The areas under the curves (AUCs) of MNDA and PRTN3 were 0.969 (95% CI, 0.936 to 1.000) and 0.900 (95% CI, 0.844 to 0.956), respectively. When MNDA and PRTN3 were combined as variables of a predictive model to diagnose PJI, the AUC reached 0.975 (95% CI, 0.943 to 1.000). Our parallel reaction monitoring-based quantitative analysis of another 40 synovial samples confirmed this result. CONCLUSIONS: MS could be a powerful tool for diagnosing PJI using proteome information or 2 specific markers, MNDA and PRTN3. The parallel reaction monitoring strategy simplified the PJI detection process and provided quantitative results with similar conclusions. CLINICAL RELEVANCE: The clinical application of MS adds a new powerful tool for the diagnosis of PJI, and the parallel reaction monitoring strategy lays a foundation for the clinical application of MS. LEVEL OF EVIDENCE: Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Diagnostic Utility of a Novel Point-of-Care Test of Calprotectin for Periprosthetic Joint Infection After Total Knee Arthroplasty: A Prospective Cohort Study.

BACKGROUND: Despite several synovial fluid biomarkers for the diagnosis of periprosthetic joint infection (PJI) having been investigated, point-of-care (POC) tests using these biomarkers are not widely available. Synovial calprotectin has recently been reported to effectively exclude the diagnosis of PJI. Thus, the objective of this study was to test the value of a calprotectin POC test for PJI diagnosis in patients undergoing total knee arthroplasty (TKA) using the 2013 Musculoskeletal Infection Society (MSIS) PJI diagnosis criteria as the gold standard. METHODS: Synovial fluid samples were prospectively collected from 123 patients who underwent revision TKA at 2 institutions within the same health-care system from October 2018 to January 2020. The study was conducted under institutional review board approval. Data collection comprised demographic, clinical, and laboratory data in compliance with the MSIS criteria. Synovial fluid samples were analyzed by calprotectin POC tests in accordance with the manufacturer's instructions. Revisions were categorized as septic or aseptic using MSIS criteria by 2 independent reviewers blinded to the calprotectin results. Calprotectin test performance characteristics with sensitivities, specificities, positive predictive values, negative predictive values, and areas under the receiver operating characteristic curve (AUC) were calculated for 2 different PJI diagnosis scenarios: (1) a threshold of ≥50 mg/L, and (2) a threshold of ≥14 mg/L. RESULTS: According to the MSIS criteria, 53 revision TKAs were septic and 70 revision TKAs were aseptic. In the ≥50-mg/mL threshold scenario, the calprotectin POC performance showed a sensitivity of 98.1%, a specificity of 95.7%, a positive predictive value of 94.5%, a negative predictive value of 98.5%, and an AUC of 0.969. In the ≥14-mg/mL threshold scenario, the sensitivity was 98.1%, the specificity was 87.1%, the positive predictive value was 85.2%, the negative predictive value was 98.4%, and the AUC was 0.926. CONCLUSIONS: The calprotectin POC test has excellent PJI diagnostic characteristics, including high sensitivity and specificity in patients undergoing revision TKA. This test could be effectively implemented as a rule-out test. However, further investigations with larger cohorts are necessary to validate these results. LEVEL OF EVIDENCE: Diagnostic Level I. See Instructions for Authors for a complete description of levels of evidence.

What is the performance of novel synovial biomarkers for detecting periprosthetic joint infection in the presence of inflammatory joint disease?

AIMS: The aim of this study was to further evaluate the accuracy of ten promising synovial biomarkers (bactericidal/permeability-increasing protein (BPI), lactoferrin (LTF), neutrophil gelatinase-associated lipocalin (NGAL), neutrophil elastase 2 (ELA-2), α-defensin, cathelicidin LL-37 (LL-37), human ß-defensin (HBD-2), human ß-defensin 3 (HBD-3), D-dimer, and procalcitonin (PCT)) for the diagnosis of periprosthetic joint infection (PJI), and to investigate whether inflammatory joint disease (IJD) activity affects their concentration in synovial fluid. METHODS: We included 50 synovial fluid samples from patients with (n = 25) and without (n = 25) confirmed PJI from an institutional tissue bank collected between May 2015 and December 2016. We also included 22 synovial fluid samples aspirated from patients with active IJD presenting to Department of Rheumatology, the first Medical Centre, Chinese PLA General Hospital. Concentrations of the ten candidate biomarkers were measured in the synovial fluid samples using standard enzyme-linked immunosorbent assays (ELISA). The diagnostic accuracy was evaluated by receiver operating characteristic (ROC) curves. RESULTS: BPI, LTF, NGAL, ELA-2, and α-defensin were well-performing biomarkers for detecting PJI, with areas under the curve (AUCs) of 1.000 (95% confidence interval, 1.000 to 1.000), 1.000 (1.000 to 1.000), 1.000 (1.000 to 1.000), 1.000 (1.000 to 1.000), and 0.998 (0.994 to 1.000), respectively. The other markers (LL-37, HBD-2, D-dimer, PCT, and HBD-3) had limited diagnostic value. For the five well-performing biomarkers, elevated concentrations were observed in patients with active IJD. The original best thresholds determined by the Youden index, which discriminated PJI cases from non-PJI cases could not discriminate PJI cases from active IJD cases, while elevated thresholds resulted in good performance. CONCLUSION: BPI, LTF, NGAL, ELA-2, and α-defensin demonstrated excellent performance for diagnosing PJI. However, all five markers showed elevated concentrations in patients with IJD activity. For patients with IJD, elevated thresholds should be considered to accurately diagnose PJI. Cite this article: Bone Joint J 2021;103-B(1):32-38.

Blood and synovial fluid calprotectin as biomarkers to diagnose chronic hip and knee periprosthetic joint infections.

AIMS: Calprotectin (CLP) is produced in neutrophils and monocytes and released into body fluids as a result of inflammation or infection. The aim of this study was to evaluate the utility of blood and synovial CLP in the diagnosis of chronic periprosthetic joint infection (PJI). METHODS: Blood and synovial fluid samples were collected prospectively from 195 patients undergoing primary or revision hip and knee arthroplasty. Patients were divided into five groups: 1) primary total hip and knee arthroplasty performed due to idiopathic osteoarthritis (OA; n = 60); 2) revision hip and knee arthroplasty performed due to aseptic failure of the implant (AR-TJR; n = 40); 3) patients with a confirmed diagnosis of chronic PJI awaiting surgery (n = 45); 4) patients who have finished the first stage of the PJI treatment with the use of cemented spacer and were qualified for replantation procedure (SR-TJR; n = 25), and 5) patients with rheumatoid arthritis undergoing primary total hip and knee arthroplasty (RA; n = 25). CLP concentrations were measured quantitatively in the blood and synovial fluid using an immunoturbidimetric assay. Additionally, blood and synovial CRP, blood interleukin-6 (IL-6), and ESR were measured, and a leucocyte esterase (LE) strip test was performed. RESULTS: Patients with PJI had higher CLP concentrations than those undergoing aseptic revision in blood (median PJI 2.14 mg/l (interquartile range (IQR) 1.37 to 3.56) vs AR-TJR 0.66 mg/l (IQR 0.3 to 0.83); p < 0.001) and synovial fluid samples (median PJI 20.46 mg/l (IQR 14.3 to 22.36) vs AR-TJR 0.7 mg/l (IQR 0.41 to 0.95); p < 0.001). With a cut-off value of 1.0 mg/l, blood CLP showed a sensitivity, specificity, positive predictive value, and negative predictive value of 93.3%, 87.5%, 89.4%, and 92.1%, respectively. For synovial fluid with a cut-off value of 1.5 mg/l, these were 95.6%, 95%, 95.5%, and 95%, respectively. CONCLUSION: This small study suggests that synovial and blood CLP are useful markers in chronic PJI diagnosis with similar or higher sensitivity and specificity than routinely used markers such as CRP, ESR, IL-6, and LE. CLP was not useful to differentiate patients with PJI from those with rheumatoid arthritis. Cite this article: Bone Joint J 2021;103-B(1):46-55.

Antimicrobial peptides in human synovial membrane as (low-grade) periprosthetic joint infection biomarkers.

BACKGROUND: Safe diagnosis of periprosthetic joint infection (PJI) is of utmost importance for successful exchange arthroplasty. However, current diagnostic tools show insufficient accuracy in the clinically common and challenging chronic low-grade infections. To close this diagnostic gap, reliable (bio)markers display the most promising candidates. Antimicrobial peptides (AMPs) are part of the innate immune response towards microbial growth. Recently we could show significant intraarticular levels of human cathelicidin LL-37 and ß-defensin-3 (HBD-3) with high diagnostic accuracy in PJI synovial fluid. Consequently, these promising biomarkers were evaluated in PJI synovial membrane and synoviocytes, which may significantly facilitate histological diagnosis of PJI to improve outcome of septic joint replacement. METHODS: In this prospective single-center controlled clinical study (diagnostic level II), consecutive patients with total hip (THR) and knee (TKR) replacements were included undergoing primary arthroplasty (n = 8), surgical revision due to aseptic loosening (n = 9) and septic arthroplasty with coagulase-negative staphylococci (n = 8) according to the criteria of the Musculoskeletal Infection Society (MSIS). Semiquantitative immunohistochemical (IHC) analysis of LL-37, HBD-3 and HBD-2 in synovial membrane and isolated synoviocytes based on Total Allred Score (TS) and Immunoreactive Remmele and Stegner score (IRS) was performed. For statistical analysis, SPSS 26.0/R3.6.3 (p < 0.05) was used. RESULTS: The AMPs LL-37 and HBD-3 were significantly elevated (up to 20×) in synovial membranes from PJI compared to aseptic loosening or primary arthroplasty. The area under the curve (AUC) in a receiver operating characteristic curve analysis was equal to 1.0 for both scores revealing excellent diagnostic accuracy. Isolated synoviocytes as cellular AMP source showed comparable results with a significant LL-37/HBD-3-increase up to 3 × in PJI. In contrast, local HBD-2 levels were negligible (p > 0.23) upon PJI with a lower diagnostic accuracy (AUC = 0.65) in analogy to our previous findings with synovial fluid. CONCLUSIONS: Our results implicate AMPs as promising and specific biomarkers for the histological diagnosis of PJI.

The stability of carbapenems before and after admixture to PMMA-cement used for replacement surgery caused by Gram-negative bacteria.

BACKGROUND: Prosthetic joint infection (PJI) is a serious complication of orthopedic implant surgery. Treatment often includes the use of an antibiotic-loaded Polymethyl methacrylate (PMMA) bone cement spacer. Several antibiotics are commonly used for the preparation of these spacers, but due to the increasing number of infections with resistant Gram-negative bacteria, there is a need for the use of carbapenem antibiotics such as meropenem and imipenem as drugs of last resort. Unfortunately, the reaction heat generated during the preparation of the bone cement can be a major problem for the stability of these antibiotics. In the present study, the stability of meropenem and imipenem was tested before and after the admixture to PMMA bone cements. METHODS: High-performance liquid chromatography with ion-pairing reversed-phase separation and spectrophotometric detection was used for analysis. Stability tests with meropenem and imipenem were performed with antibiotics in solution and solid form at different temperatures (37 °C, 45 °C, 60 °C, 90 °C) and times (30 min, 60 min, 120 min). To test the stability of both antibiotics in PMMA after exposure to the reaction heat during polymerization, three different bone cements were used to generate specimens that contained defined amounts of antibiotics. Reaction heat was measured. The form bodies were mechanically crushed and aliquots were dissolved in ethyl acetate. Samples were prepared for HPLC DAD analysis. RESULTS: Meropenem and imipenem showed the highest degradation levels after heat stressed in solution, with maximum levels of 75% and 95%, respectively. In solid form, degradation levels decreased dramatically for meropenem (5%) and imipenem (13%). Stability tests of both carbapenems in bone cement showed that they remained largely stable during PMMA polymerization, with retrieved amounts of about 70% in Palacos® R and Copal® G+V, and between 80 and 90% in Copal® spacem. CONCLUSIONS: In contrast to the results of meropenem and imipenem in solution, both antibiotics remain stable in solid form and mostly stable in the cement after PMMA polymerization. The low degradation levels of both antibiotics after exposure to temperatures > 100 °C allow the conclusion that they can potentially be used for an application in PMMA cements.

Diagnostic accuracy of D-dimer in periprosthetic joint infection: a diagnostic meta-analysis.

BACKGROUND: Periprosthetic joint infection (PJI) is one of the most devastating complications after total joint replacement (TJA). Up to now, the diagnosis of PJI is still in a dilemma. As a novel biomarker, whether D-dimer is valuable in the diagnosis of PJI remains controversial. This meta-analysis attempts to determine the diagnostic accuracy of D-dimer in PJI. METHODS: Relevant literature was retrieved from PubMed, Embase, Web of Science, and Cochrane Library (from database establishment to April 2020). Literature quality was evaluated using Revman (version 5.3). The random effect model was used in the Stata version 14.0 software to combine sensitivity, specificity, likelihood ratio (LR), diagnostic odds ratio (DOR), summary receiver operating characteristic (SROC) curve, and area under SROC (AUC) to evaluate the diagnostic value of overall D-dimer for PJI. Meta regression and subgroup analysis were performed according to the threshold, the study design, the sample size, the diagnostic gold standard, the country of study, and the type of sample. RESULTS: A total of 9 studies were included in this study, including 1592 patients. The pooled sensitivity and specificity of D-dimer for PJI diagnosis are 0.82 (95% CI, 0.72~0.89) and 0.73 (95% CI, 0.58~0.83), respectively. The pooled positive likelihood ratio (PLR) and negative likelihood ratio (NLR) were 2.99 (95% CI, 1.84~4.88) and 0.25 (95% CI, 0.15~0.41), respectively. The pooled AUC and diagnostic odds ratios were 0.85 (95% CI, 0.82~0.88) and 12.20 (95% CI, 4.98~29.86), respectively. CONCLUSION: D-dimer is a promising biomarker for the diagnosis of PJI, which should be used in conjunction with other biomarkers or as an adjunct to other diagnostic methods to enhance diagnostic performance.

A profile on the Synovasure alpha defensin test for the detection of periprosthetic infections.

INTRODUCTION: Clinicians have waited a long time for a 'universal' marker that may help them distinguish infected from non-infected total joint arthroplasties when doubts persist after using classical clinical and biological signs of infection. In recent years, synovial fluid biomarkers including leukocyte esterase, alpha-defensins, and CRP have shown promising results for the diagnosis of periprosthetic joint infections (PJIs). AREAS COVERED: This review provides an overview of the rational and the use of the Synovasure® alpha-defensin tests in patients with a suspicion of PJI. Using a systematic investigation by keywords, we looked for all citations (and the citations to these citations) of the selected papers. EXPERT OPINION: The Synovasure® alpha-defensin tests demonstrate high potential for the diagnosis of PJIs. However, the data currently available also show that the universal marker of infection in the settings of PJIs is still to be discovered.

Comparative analysis of 23 synovial fluid biomarkers for hip and knee periprosthetic joint infection detection.

There is interest in novel synovial fluid biomarkers for the detection of periprosthetic joint infection (PJI). Here, we assessed the diagnostic accuracy of 23 simple or sophisticated synovial fluid biomarkers for periprosthetic hip or knee infection detection. One hundred seven subjects were studied, 57 of whom had aseptic failure (AF) and 50 PJI. The following synovial fluid biomarkers were tested using spectrophotometric assays, immunoassays, lateral flow tests, or test strips: leukocyte count, monocyte percentage, lymphocyte percentage, neutrophil percentage, C-reactive protein (CRP), glucose, lactate, granulocyte-macrophage colony-stimulating factor, interferon-γ, interleukin-1ß (IL-1ß), IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12p70, IL-13, IL-17A, IL-23, tumor necrosis factor-α, α-defensin, and leukocyte esterase. The best-performing synovial fluid biomarkers to differentiate PJI from AF-that is, those with highest area under the curve compared to all other biomarkers-were leukocyte count, percent neutrophils and percent monocytes, CRP, and α-defensin (P < .0001).

Synovial Fluid Interleukin-16 Contributes to Osteoclast Activation and Bone Loss through the JNK/NFATc1 Signaling Cascade in Patients with Periprosthetic Joint Infection.

Because of lipopolysaccharide (LPS)-mediated effects on osteoclast differentiation and bone loss, periprosthetic joint infection (PJI) caused by Gram-negative bacteria increases the risk of aseptic loosening after reimplantation. Synovial fluid interleukin-16 (IL-16) expression was higher in patients with PJI than in patients without joint infection. Thus, we explored the effects of IL-16 on bone. We investigated whether IL-16 modulates osteoclast or osteoblast differentiation in vitro. An LPS-induced bone loss mice model was used to explore the possible advantages of IL-16 inhibition for the prevention of bone loss. IL-16 directly activated p38 and c-Jun N-terminal kinase (JNK)/mitogen-activated protein kinase (MAPK) signaling and increased osteoclast activation markers, including tartrate-resistant acid phosphatase (TRAP), cathepsin K, and nuclear factor of activated T cells 1 (NFATc1). IL-16 directly caused monocytes to differentiate into TRAP-positive osteoclast-like cells through NFATc1 activation dependent on JNK/MAPK signaling. Moreover, IL-16 did not alter alkaline phosphatase activity or calcium deposition during osteoblastic differentiation. Finally, IL-16 inhibition prevented LPS-induced trabecular bone loss and osteoclast activation in vivo. IL-16 directly increased osteoclast activation through the JNK/NFATc1 pathway. IL-16 inhibition could represent a new strategy for treating infection-associated bone loss.

Laser-structured spike surface shows great bone integrative properties despite infection in vivo.

Implant associated infections can result in devastating consequences for patients. One major cause is the formation of bacterial biofilms, which result in increased resistance against antimicrobial therapeutics. A reduction of implant associated infections can be achieved by functionalization of implant surfaces. The generation of three dimensional surface structures by femtosecond laser ablation is one method to fabricate bacterial repellent large scaled surfaces without altering the material chemical composition. The challenge is to reduce bacterial growth while improving cellular ongrowth. For this purpose, spike structures were created as small as possible by used fabrication method on cubic Ti90/Al6/V4-rods and their effectiveness against bacterial colonization was compared to unstructured Ti90/Al6/V4-rods. Rods were implanted in the rat tibia and infected intraoperatively with 103 CFU of Staphylococcus aureus. Besides clinical behaviour and lameness, the vital bacterial biomass, morphological appearance and the volume of eukaryotic cells were determined on the implant surface after 21 days. Bone alterations were examined by radiological and histological techniques. Unexpectedly, the laser-structured implants did not show a lower bacterial load on the implant surface and less severe infection related bone and tissue alterations compared to the group without structuring. Simultaneously, a better bony integration and a higher cellular colonization with eukaryotic cells was detected on the laser-structured implants. These findings don't support the previous in vitro results. Nevertheless, the strong integration into the bone is a powerful argument for further surface modifications focussing on the improvement of the antibacterial effect. Additionally, our results underline the need for in vivo testing of new materials prior to clinical use.

Synovial Fluid Aspirates Diluted with Saline or Blood Reduce the Sensitivity of Traditional and Contemporary Synovial Fluid Biomarkers.

BACKGROUND: Recent criteria-based diagnostic tools to diagnose periprosthetic infection (PJI), such as the International Consensus Meeting (ICM) definition of PJI, are heavily reliant on synovial fluid laboratory results. Despite the importance of synovial fluid in PJI diagnosis, the effect of the quality of synovial fluid aspirate on testing results has not been studied. Our laboratory has established quality control parameters to identify synovial fluid aspirates that are highly diluted by saline or blood, which appear to degrade the diagnostic performance of synovial fluid laboratory tests. QUESTIONS/PURPOSES: (1) What proportion of synovial fluid aspirates analyzed at one laboratory are of poor quality (defined as having a red blood count > 1M cells/uL or an optical density at 280 nm < 0.324 or > 1.19)? (2) Does a poor-quality aspirate decrease the sensitivities of International Consensus Meeting-based scores and other synovial fluid biomarker tests in terms of their ability to anticipate a positive culture? METHODS: From January 2016 to July 2019, a total of 123,549 synovial fluid samples were submitted to one laboratory for the purpose of diagnostic testing. Of these, 14% (16,773 of 123,549) samples were excluded because they were from a site other than a hip, knee, or shoulder arthroplasty, and an additional 33% (35,660 of 106,776) were excluded due to insufficient requested tests, resulting in 58% (71,116 of 123,549) samples included in this study. Specimens diluted with extreme levels of saline or blood were identified (defined as having a red blood count >1 M cells/uL or an optical density at 280 nm < 0.324 or > 1.19) as poor-quality aspirates. The sensitivities of synovial fluid C-reactive protein, alpha defensin, neutrophil elastase, white blood cell count, polymorphonuclear cell percentage, and the 2018 ICM-based tool were assessed in good-quality versus poor-quality synovial fluid samples. To avoid bias from using these evaluated tests within the reference definition of PJI in this study, a positive culture resulting from the synovial fluid served as the reference diagnosis defining a control cohort of PJI-positive samples. Although the low false-positive rate of synovial fluid culture allows for the valid estimation of synovial fluid test sensitivity, the high false-negative rate of synovial fluid culture prevents the valid estimation of test specificity, which was not evaluated in this study. RESULTS: Of the samples analyzed, 8% (6025 of 71,116) were found to have poor quality, in that they were substantially compromised by saline and/or blood. The sensitivity of all tests to detect culture-positive synovial fluid was lower in poor-quality than in good-quality samples: 2018 International Consensus Meeting-based tool (83% [95% CI 80 to 86] versus 97% [95% CI 96 to 97]), synovial fluid C-reactive protein (65% [95% CI 61 to 69] versus 88% [95% CI 87 to 89]), alpha defensin (70% [95% CI 66 to 73] versus 93% [95% CI 93 to 94]), neutrophil elastase (80% [95% CI 77 to 83] versus 96% [95% CI 96 to 97]), synovial fluid white blood cell count (69% [95% CI 65 to 73] versus 93% [95% CI 93 to 94]), and the polymorphonuclear cell percentage (88% [95% CI 85 to 91] versus 95% [95% CI 94 to 95]), with all p < 0.001. CONCLUSIONS: When synovial fluid is substantially diluted with saline or blood, the biomarkers and cells being measured are also diluted, decreasing the sensitivity of laboratory testing. We recommend that future diagnostic studies exclude these samples because an artificial reduction in test sensitivity will be observed. CLINICAL RELEVANCE: Clinicians should avoid relying on negative synovial fluid testing to rule out PJI when the fluid submitted is substantially constituted of saline or blood. Further studies are necessary to understand the diagnostic utility, if any, of these diluted aspirate samples.

Analysis of synovial biomarkers with a multiplex protein microarray in patients with PJI undergoing revision arthroplasty of the hip or knee joint.

INTRODUCTION: Diagnosing a (low-grade) periprosthetic joint infection (PJI) after hip or knee arthroplasty remains a diagnostic challenge. The aim of this study was to evaluate the utility of using a novel multiplex protein microarray system for synovial biomarkers in determining PJI in patients undergoing revision knee or hip arthroplasty. MATERIALS AND METHODS: The individual synovial fluid levels of 12 cytokines (IL-1b, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12, IL-17, GM-CSF, TNF-α, and INF-γ) were analysed with a novel multiplex protein microarray system in 32 patients undergoing revision hip (n = 22) or knee (n = 10) arthroplasty. Cases were classified into septic and aseptic groups on basis of pre- and interoperative findings: [PJI (n = 14) vs. non-PJI (n = 18)]. Receiver operator characteristic (ROC) curves were calculated to assess the discriminatory strength of the individual parameters. A multiple regression model was used to determine the utility of using a combination of the tested cytokines to determine the infection status. RESULTS: The levels of all of the evaluated cytokines were significantly elevated in the PJI-group. Best sensitivity and specificity were found for IL-6, followed by IL-1b, IL-10, and IL-17. The multiple regression models revealed a combination of IL-2, IL-4, IL-5, IL6, lL-12, and GM-CSF to be associated with the best sensitivity (100%) and specificity (88.9%) for a cut-off value of 0.41, with a likelihood ratio of 9.0. CONCLUSION: Analysis of individual synovial fluid cytokine levels showed both high sensitivity and high specificity in diagnosing PJI. A combined model using several cytokines showed even higher sensitivity and specificity in diagnosing PJI and could thus be a useful predictive tool to determine the probability of PJI in patients with a painful prosthesis. LEVEL OF EVIDENCE: Diagnostic IV.

Interleukin-1ß and tumor necrosis factor are essential in controlling an experimental orthopedic implant-associated infection.

Orthopedic implant-associated infection (OIAI) is a major complication that leads to implant failure. In preclinical models of Staphylococcus aureus OIAI, osteomyelitis and septic arthritis, interleukin-1α (IL-1α), IL-1ß, and tumor necrosis factor (TNF) are induced, but whether they have interactive or distinctive roles in host defense are unclear. Herein, a S. aureus OIAI model was performed in mice deficient in IL-1α, IL-1ß, or TNF. Mice deficient in IL-1ß or TNF (to a lesser extent) but not IL-1α had increased bacterial burden at the site of the OIAI throughout the 28-day experiment. IL-1ß and TNF had a combined and critical role in host defense as mice deficient in both IL-1R and TNF (IL-1R/TNF-deficient mice) had a 40% mortality rate, which was associated with markedly increased bacterial burden at the site of the OIAI infection. Finally, IL-1α- and IL-1ß-deficient mice had impaired neutrophil recruitment whereas IL-1ß-, TNF-, and IL-1R/TNF-deficient mice all had impaired recruitment of both neutrophils and monocytes. Therefore, IL-1ß and TNF contributed to host defense against S. aureus OIAI and neutrophil recruitment was primarily mediated by IL-1ß and monocyte recruitment was mediated by both IL-1ß and TNF.