Synovial Neutrophils Research Articles

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.

Synovial fluid leukocytes as diagnostic marker in periprosthetic shoulder infection

BackgroundLimited data exist regarding the diagnostic accuracy of synovial fluid leukocyte count (SFLC) in diagnosing periprosthetic shoulder infection (PSI). The main objective of this study was to determine the diagnostic value of leukocyte count at a common threshold of 3 cells/nL and the optimal cut-off value. MethodsPatients, who underwent shoulder arthroplasty revision surgery and aspiration with SFLC between 2012 and 2023 were retrospectively included. The International Consensus Meeting (ICM) 2018 definition was used to characterize infection status for SFLC threshold and synovial fluid neutrophil percentage (SFNP). Sensitivity and specificity were presented using cross tabulation. The area under the curve was calculated, and the optimal cut-off was determined using maximized Youden Index. Results35 cases with an average age of 71 years (43% male) were included in our study. At a threshold of 3 cells/nL, SFLC showed a sensitivity of 70% and specificity of 83%. The corresponding positive and negative predictive values (PPV, NPV) were 89% and 59%. We found the optimal cut-off for our cohort at 4.7 cells/nL, increasing specificity to 92% while maintaining sensitivity at 70% (PPV = 94%, NPV = 61%). SFNP at a cut-off of 80% demonstrated 50% sensitivity and 91% specificity, with corresponding PPV and NPV of 92% and 48%. The optimum threshold for SFNP was 54%, which had a sensitivity of 77% and a specificity of 64%, as well as a PPV of 81%, and NPV of 58%. The area under the curve was 0.72 for SFLC and 0.74 for SFNP. Sonication detected pathogens in 63% of cases, while 57% of all cases showed positive tissue cultures and 43% positive aspirate cultures. Especially the most frequently found microorganism, Cutibacterium acnes, was detected less often in aspirate culture. ConclusionsSFLC shows good specificity but moderate sensitivity for diagnosing PSI when using a threshold of 4.7 cells/nL. Therefore, it can serve as a confirmatory test for diagnosing PSI but not for ruling out infection.

Tryptophanyl tRNA synthetase is an alternative synovial biomarker for diagnosis of septic arthritis in knee joint

BackgroundTo evaluate the diagnostic characteristics of tryptophanyl tRNA synthetase (WRS) for the diagnosis of septic arthritis of the knee joint and to determine whether it is a reliable and sensitive synovial biomarker for discriminating septic arthritis from other types of arthritis.MethodsPatients joint effusions for which septic arthritis was suspected were prospectively recruited between January 2019 and September 2020. A total of 9 patients had septic arthritis, 6 had acute gout attack, 1 had an acute flare of chronic rheumatic arthritis, and 46 had pseudogout or reactive arthropathy. Traditional inflammatory markers were measured, and their diagnostic abilities were compared. Neutrophil count, C-reactive protein (CRP) level, WRS, and human neutrophil α-defensin levels were assessed in the synovial fluids. Demographic parameters and biomarkers with a P < 0.05 in differentiating septic from nonseptic arthritis were included in a multivariable model. A multivariable logistic regression with a stepwise selection was performed to build the final combined model. Receiver operating characteristic curves were used to establish optimal thresholds for the diagnosis of septic arthritis of the knee joint, and the area under the curve was calculated to determine the overall accuracy of these tests compared with patients with nonseptic inflammatory arthritis.ResultsPatients with septic arthritis were more likely to display higher serum WBC and CRP levels, synovial neutrophil counts, and levels of two synovial biomarkers, including WRS and α-defensin. WRS showed the highest specificity (87.5%) and sensitivity (83.3%) with α-defensin among the three synovial biomarkers.ConclusionsSynovial fluid WRS is a relevant biomarker in discriminating septic arthritis from other inflammatory arthritis and should be tested in an independent cohort.Level of evidence: prospective observational study, III.

Periprosthetic joint infection in patients with rheumatoid arthritis: case series

Introduction The differential diagnosis of periprosthetic joint infection (PJI) is challenging in patients with systemic diseases due to identical clinical and laboratory patterns and activity of the inflammatory process.The objective was to evaluate the diagnostic data and results of debridement of PJI in patients with rheumatoid arthritis using a case series.Material and methods A retrospective analysis of surgical treatment of PJI was produced in patients with rheumatoid arthritis between 2014 and 2022. PJI was verified based on ICM criteria. A poor outcome included the presence of clinical and laboratory signs of infection on admission to the second stage of treatment and recurrence after successful debridement.Results Among the 524 cases of PJI, 35 (6.7 %) were patients with rheumatoid arthritis with 48.6 % receiving antibiotics prior to admission. Culture-negative infection was recorded in 38.4 %. PJI was not confirmed in five cases (14.3 %). High average values of inflammatory markers were registered in the blood (ESR, CRP and D-dimer) before and after debridement; decreased ESR and leukocyte count in the synovial fluid was statistically significant. Favorable outcomes were obtained in 82.9 % of cases at mid term with every fifth patient treated with a spacer or arthrodesis.Discussion The incidence of culture-negative infection in patients with systemic diseases was reported as much as 27–37 %. A systematic review of the literature showed that the percentage of band neutrophils in synovial fluid has a sensitivity of 95.2 % and a specificity of 85.0 %, with an optimal threshold of 78 % sufficient to verify infection. The poor outcomes we identified resulted from two- or three-stage surgical treatment. Other authors reported better outcomes with two-stage debridement.Conclusion Culture-negative infection was common in cases of PJI observed in patients with rheumatoid arthritis. Favorable outcomes were seen mostly with two-stage surgical treatment. Inflammatory markers ESR, CRP and D-dimer did not reach normal values during diagnosis and treatment of infection indicating the inapplicability of standard diagnostic criteria for PJI in patients with rheumatoid arthritis.

Deletion of RANKL in regulatory T cells ameliorates bone erosion in arthritis

Abstract Rheumatoid arthritis (RA) is an autoimmune disease that leads to bone erosion mediated through osteoclasts.Osteoclast differentiation is promoted through engagement of RANK by its ligand (RANKL) expressed by multiple lineages. Whereas regulatory T cells (Tregs) typically suppress osteoclastogenesis, Tregs developing in a pro-inflammatory environment can express RANKL and promote osteoclast function (Levescot et al.2021).To test the importance of osteoclastogenic Tregs in vivo, we developed a mouse selectively lacking RANKL expression in Tregs (FoxP3YFP/creRANKLflox/flox, hereafter RANKLΔTreg). Arthritis was induced by administration of K/BxN serum containing arthritogenic IgG antibodies. Joint inflammation and synovial neutrophil infiltration in RANKLΔTreg mice were similar to WT animals. Compared with Tregs from lymph nodes, Tregs from inflamed joints exhibited increased expression of activation markers including CD25,Foxp3,CD44, and CTLA4, without a difference between RANKLΔTreg and WT animals; RANKLΔTreg mice exhibited a trend for higher Treg PD-1 expression. In WT mice, the percentage of Tregs expressing RANKL was elevated in synovial fluid compared to lymph nodes. Correspondingly, microCT showed a significant reduction in bone erosion in RANKLΔTreg compared to WT mice (p=0.003). These findings are consistent with a pathogenic role of RANKL-expressing Treg for RA bone erosion in arthritis; whether RANKL impacts other Treg functions remains to be established.

Ideal Timing of Reimplantation in Patients with Periprosthetic Knee Infection Undergoing 2-Stage Exchange: A Diagnostic Scoring System.

This study evaluated appropriate thresholds for serum biomarkers, synovial fluid white blood cell (SF-WBC) count, and synovial fluid neutrophil (polymorphonuclear leukocyte [PMN]) percentage to predict infection in a patient group who underwent definitive reimplantation after receiving a continuous course of antibiotic therapy for chronic knee periprosthetic joint infection (PJI). These thresholds were then used to generate a scoring system to predict recurrence (or persistence) of infection. The study included 153 patients with a median age of 73 years (range, 46 to 91 years) who underwent 2-stage revision for chronic knee PJI. Staphylococci were identified at baseline in 107 (70%) of the patients. After the 96-week follow-up period, 12% (19) of the 153 patients had recurrence of the PJI. A receiver operating characteristic (ROC) curve analysis was used to assess the predictive value of common serum biomarkers and SF aspiration before reimplantation, and the area under the curve (AUC) was evaluated. Variables that were significantly different between patients with and without infection recurrence were evaluated using a multivariable logistic regression model. A half-integer-point scoring system was created based on the final beta coefficients. Regarding the prediction of recurrent infection, a D-dimer level of >1110 ng/mL yielded a sensitivity of 74%, specificity of 61%, and AUC of 0.69; an SF-WBC count of >934 cells/µL showed a sensitivity of 68%, specificity of 90%, and AUC of 0.79; and an SF-PMN percentage of >52% showed a sensitivity of 73%, specificity of 90%, and AUC of 0.82. The beta coefficients were approximated to 1.5 for the D-dimer level and to 2 for the SF-WBC count and SF-PMN percentage. A total score of >2 was used to classify patients with a high risk of infection recurrence. The ability to discriminate infection recurrence was demonstrated by an AUC of 0.90 (95% confidence interval: 0.82 to 0.99). Patients with a score of >2 on our proposed scoring system based on serum biomarkers, SF-WBC count, and SF-PMN percentage should not undergo reimplantation, as they are at a high risk for recurrent PJI. Patients with a score of ≤2 can undergo definitive reimplantation with the lowest risk of recurrence. Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.

Treating Periprosthetic Joint Infection With Silver-Impregnated Carbon-Coated Spacers: Mid-Term Outcomes

Background. Periprosthetic joint infection (PJI) is a severe complication of arthroplasty. The widely accepted treatment standard for PJI is a two-stage revision arthroplasty involving the articulating spacers. The implant surface provides an ideal environment for bacterial adhesion, facilitating mature biofilm formation. To prevent bacterial adhesion effectively, the surface of the implanted device must be modified with an efficient coating. The ability of a modified coating based on two-dimensional linear carbon chains (2D LCC) with silver (Ag) impregnation to inhibit biofilm formation and provide efficient bacterial eradication has been investigated in several experimental studies. However, there is a lack of publications on clinical studies evaluating the effectiveness of such coatings.&#x0D; The aim of the study — to assess mid-term outcomes of knee and hip PJI treatment using spacers coated with two-dimensional linear carbon chains impregnated with silver.&#x0D; Methods. This study is based on the results of the examination and two-stage revision arthroplasty of 144 patients with newly diagnosed knee and hip PJI. Patients were divided into two groups: the first (main) group received articulating spacers coated with 2D LCC+Ag, while the second (control) group received articulating spacers with antibiotics. Anamnestic, clinical, laboratory, microbiological, and statistical methods were used in this study. The evaluation of short-term results was performed using the KSS, Harris, VAS, and EQ-5D-5L scales at 3 months after surgery, and mid-term results were assessed at 2 years.&#x0D; Results. The study confirmed the high antibiofilm activity and safety of spacers coated with 2D LCC+Ag. Both groups showed a reduction in inflammation markers during treatment. Before the second stage of treatment, both groups experienced a statistically significant decrease in CRP, procalcitonin, and presepsin levels, as well as synovial cytosis and neutrophil content. The frequency of recurrences after two-stage treatment was significantly lower in the first group compared to the second group. In the mid-term period, the first group had higher scores on the KSS and Harris scales by 20.5 and 7.0 points, respectively. Results on the EQ-5D-5L were 10/0.08 points higher, and the intensity of pain according to VAS was three times lower in the first group.&#x0D; Conclusion. The use of spacers coated with 2D LCC+Ag allows for a faster resolution of the inflammatory process, reduces the incidence of PJI recurrences, and predicts active protection of the implant surface from microbial colonization and biofilm formation. This, combined with antibiotic prophylaxis, provides a favorable therapeutic and preventive effect against PJI recurrence.

How Reliable Is the Absolute Synovial Polymorphonuclear Neutrophil Cell Count in Diagnosing Periprosthetic Joint Infection?

BackgroundDiagnosing periprosthetic joint infection (PJI) is a daunting task for even the most experienced orthopedic surgeons, as there is currently no test available that can provide absolute accuracy. Utilizing an established synovial indicator for detecting PJI without incurring additional costs or resources would be the optimal solution for predicting the presence of infection. Therefore, we hypothesized that synovial absolute neutrophil count (ANC) would improve the diagnostic accuracy of chronic knee and hip PJI. MethodsThe study included 260 patients (134 men and 126 women, mean age of 70 years [range, 26 to 89]) who underwent aspiration during preoperative workup. Of these, 109 patients (41.9%) were diagnosed with chronic PJI (50 knees, 59 hips), and 151 patients (58.1%) were diagnosed as aseptic (94 knees, 57 hips). Data obtained from all patients included age, sex, procedure type (total hip or total knee arthroplasty), operation side, synovial white blood cell count (cells/μL), synovial polymorphonuclear cells percentage, and synovial α-defensin immunoassay value at the admission were retrieved from the electronic medical record. ResultsThe calculated optimal threshold for synovial ANC of 1,415.5 cells/μL was associated with an area under the receiver operating characteristic curve (AUC) of 0.930 for chronic knee PJI diagnosis. The calculated optimal threshold for synovial ANC of 2,247 cells/μL was associated with an AUC of 0.905 for chronic hip PJI diagnosis. ConclusionsThis study has conclusively shown that the synovial ANC serves as a valuable marker in the complicated diagnosis of PJI. This highly effective and efficient approach should be utilized for obtaining further information through standard tests, thereby ruling out the possibility of PJI. Level of evidenceIII.

The effects of Phycocyanobilin on experimental arthritis involve the reduction in nociception and synovial neutrophil infiltration, inhibition of cytokine production, and modulation of the neuronal proteome.

The antinociceptive and pharmacological activities of C-Phycocyanin (C-PC) and Phycocyanobilin (PCB) in the context of inflammatory arthritis remain unexplored so far. In the present study, we aimed to assess the protective actions of these compounds in an experimental mice model that replicates key aspects of human rheumatoid arthritis. Antigen-induced arthritis (AIA) was established by intradermal injection of methylated bovine serum albumin in C57BL/6 mice, and one hour before the antigen challenge, either C-PC (2, 4, or 8 mg/kg) or PCB (0.1 or 1 mg/kg) were administered intraperitoneally. Proteome profiling was also conducted on glutamate-exposed SH-SY5Y neuronal cells to evaluate the PCB impact on this key signaling pathway associated with nociceptive neuronal sensitization. C-PC and PCB notably ameliorated hypernociception, synovial neutrophil infiltration, myeloperoxidase activity, and the periarticular cytokine concentration of IFN-γ, TNF-α, IL-17A, and IL-4 dose-dependently in AIA mice. In addition, 1 mg/kg PCB downregulated the gene expression for T-bet, RORγ, and IFN-γ in the popliteal lymph nodes, accompanied by a significant reduction in the pathological arthritic index of AIA mice. Noteworthy, neuronal proteome analysis revealed that PCB modulated biological processes such as pain, inflammation, and glutamatergic transmission, all of which are involved in arthritic pathology. These findings demonstrate the remarkable efficacy of PCB in alleviating the nociception and inflammation in the AIA mice model and shed new light on mechanisms underlying the PCB modulation of the neuronal proteome. This research work opens a new avenue to explore the translational potential of PCB in developing a therapeutic strategy for inflammation and pain in rheumatoid arthritis.

Can the Current Thresholds for Synovial Cell Count and Neutrophil Percentage to Diagnose Prosthetic Joint Infection be Applied to Metal-on-Metal Rotating Hinge Total Knee Arthroplasty?

BackgroundSynovial leukocyte count analysis is an important tool in the diagnosis of PJI. However, results can be poor if metallosis is present. The issue of metallosis was established for some rotating hinge knee arthroplasty designs. MethodsThis was a retrospective single-center analysis that included 108 patients who had a single-design metal-on-metal rotating hinge knee arthroplasty who underwent revision surgery and had prior synovial fluid analysis performed. The diagnostic accuracy of leukocyte count and the percentage of polymorphonuclear neutrophiles (% PMN) were investigated. ResultsPatients who had a PJI had a higher median leukocyte count and % PMN compared to aseptic revisions (7,905/μL (interquartile range (IQR) 2,419 to 37,400) and 85% (IQR 70.3 to 93.8) versus 450 (IQR 167 to 1,215) and 46% (IQR 28.5 to 67.4%), P < .001). The respective areas under the curves were 0.916 (95% confidence interval 0.862 to 0.970) for leukocyte count and 0.821 (95% confidence interval 0.739 to 0.902) for % PMN. We calculated an optimal cut-off value of 1,200 leukocytes/μL (Sensitivity 94.5%/specificity 75.5%) and 63% PMN (Sensitivity 85.5%/specificity 73.6%) to define PJI. Established thresholds were less sensitive, but more specific. The “infection likely” scenario of the European Bone and Joint Infection Society (EBJIS) definition was closest to the calculated thresholds. ConclusionCurrently used thresholds for leukocyte cell count and %PMN to define PJI were less sensitive and specific in the diagnosis of PJI in metal-on-metal RHK knees. Surgeons must consider lower cut-off values when evaluating such implants for PJI.

The role of interleukin-18 and interleukin-18 binding protein in K/BxN serum transfer-induced arthritis.

Interleukin-18 is a proinflammatory cytokine, the activity of which is regulated by its natural inhibitor, IL-18 binding protein (IL-18BP). Elevated circulating levels of IL-18 have been observed in patients with systemic juvenile idiopathic arthritis (sJIA) and adult-onset Still's disease (AOSD), two conditions associated with dysregulated innate immune responses. This study examines the expression and function of IL-18 and IL-18BP in K/BxN serum transfer arthritis (STA), a model that is uniquely dependent on innate immune responses. Naïve and serum transfer-induced arthritis (STA) wild-type (WT) mice were used to examine the articular levels of IL-18 and IL-18BP mRNA by RT-qPCR. The cellular sources of IL-18BP in the joints were determined by using Il18bp-tdTomato reporter knock-in mice. The incidence and severity of arthritis, including mRNA levels of different cytokines, were compared in IL-18BP or IL-18 knock-out (KO) mice and their WT littermates. IL-18 and IL-18BP mRNA levels were significantly increased in arthritic as compared to normal joints. Synovial neutrophils, macrophages, and endothelial cells represented the cellular sources of IL-18BP in arthritic joints, whereas IL-18BP production was limited to endothelial cells in non-inflamed joints. The incidence and severity of arthritis were similar in IL-18BP KO and IL-18 KO compared to their WT littermates. Transcript levels of different inflammatory cytokines were not different in the two KO mouse lines compared to WT mice. Although IL-18 and IL-18BP levels were increased in arthritic joints, our results show that the IL-18/IL-18BP balance is not involved in the regulation of STA.

What's New in Musculoskeletal Infection.

What's New in Musculoskeletal Infection.

Absolute synovial polymorphonuclear neutrophil cell count as a biomarker of periprosthetic joint infection.

The aim of this study was to evaluate the diagnostic accuracy of the absolute synovial polymorphonuclear neutrophil cell (PMN) count for the diagnosis or exclusion of periprosthetic joint infection (PJI) after total hip (THA) or knee arthroplasty (TKA). In this retrospective cohort study, 147 consecutive patients with acute or chronic complaints following THA and TKA were included. Diagnosis of PJI was established based on the 2018 International Consensus Meeting criteria. A total of 39 patients diagnosed with PJI (32 chronic and seven acute) and 108 patients with aseptic complications were surgically revised. Using receiver operating characteristic curves and calculating the area under the curve (AUC), an optimal synovial cut-off value of 2,000 PMN/µl was determined (AUC 0.978 (95% confidence interval (CI) 0.946 to 1)). Using this cut-off, sensitivity and specificity of absolute synovial PMN count for PJI were 97.4% (95% CI 91.2 to 100) and 93.5% (95% CI 88.9 to 98.1), respectively. Positive and negative predictive value were 84.4% (95% CI 72.7 to 93.9) and 99.0% (95% CI 96.7 to 100), respectively. Exclusion of 20 patients with acute complications improved specificity to 97.9% (95% CI 94.6 to 100). Different cut-off values for THA (< 3,600 PMN/µl) and TKA (< 2,000 PMN/µl) were identified. Absolute synovial PMN count correlated strongly with synovial alpha-defensin (AD) (r = 0.759; p < 0.001). With a positive AD result, no additional PJI could be identified in any case. Absolute synovial PMN count is a widely available, rapid, cost-effective, and accurate marker in PJI diagnostics, whereas synovial AD appears to be a surrogate parameter of absolute synovial PMN count. Despite limitations in the early postoperative phase, wear, and rheumatic diseases in confirming PJI, an absolute synovial PMN count below 2,000/µl is highly suitable for ruling out PJI, with specific cut-off values for THA and TKA.

Evaluation of Synovial Calprotectin by Using a Lateral Flow Test for the Diagnosis of Prosthetic Joint Infections

The analysis of synovial fluid is a crucial step in the diagnosis of prosthetic joint infections (PJIs). Recently several studies illustrated the efficacy of synovial calprotectin in supporting the diagnosis of PJI. In this study, synovial calprotectin was analyzed by a commercial stool test to explore whether it might accurately predict PJIs. The synovial fluids of 55 patients were analyzed and calprotectin levels were compared to other synovial biomarkers of PJI. Of the 55 synovial flu-ids, 12 patients were diagnosed with PJI and 43 with an aseptic failure of the implant. Specificity, sensitivity, and AUC of calprotectin resulted in 0.944, 0.80, and 0.852 (95%CI: 0.971-1.00), respectively, with a set threshold of 529.5 µg/g. Calprotectin had a statistically relevant correlation with the synovial leucocyte counts (rs = 0.69, p < 0.001) and the percentage of synovial neutrophils (rs = 0.61, p < 0.001). From this analysis, it can be concluded that synovial calprotectin is a valuable biomarker that correlates with other established indicators of local infection, and the use of a commercial lateral flow stool test could be a cost-effective strategy delivering rapid and reliable results and supporting the diagnostic process of PJI.

Hyaluronic Acid in Synovial Fluid Prevents Neutrophil Activation in Spondyloarthritis

Spondyloarthritis (SpA) patients suffer from joint inflammation resulting in tissue damage, characterized by the presence of numerous neutrophils in the synovium and synovial fluid (SF). As it is yet unclear to what extent neutrophils contribute to the pathogenesis of SpA, we set out to study SF neutrophils in more detail. We analyzed the functionality of SF neutrophils of 20 SpA patients and 7 disease controls, determining ROS production and degranulation in response to various stimuli. In addition, the effect of SF on neutrophil function was determined. Surprisingly, our data show that SF neutrophils in SpA patients have an inactive phenotype, despite the presence of many neutrophil-activating stimuli such as GM-CSF and TNF in SF. This was not due to exhaustion as SF neutrophils readily responded to stimulation. Therefore, this finding suggests that one or more inhibitors of neutrophil activation may be present in SF. Indeed, when blood neutrophils from healthy donors were activated in the presence of increasing concentrations of SF from SpA patients, degranulation and ROS production were dose-dependently inhibited. This effect was independent of diagnosis, gender, age, and medication in the patients from which the SF was isolated. Treatment of SF with the enzyme hyaluronidase strongly reduced the inhibitory effect of SF on neutrophil activation, indicating that hyaluronic acid that is present in SF may be an important factor in preventing SF neutrophil activation. This finding provides novel insights into the role of soluble factors in SF regulating neutrophil function and may lead to the development of novel therapeutics targeting neutrophil activation via hyaluronic acid or associated pathways.

Synovial fluid neutrophil extracellular traps could improve the diagnosis of periprosthetic joint infection.

This study aimed to explore the diagnostic value of synovial fluid neutrophil extracellular traps (SF-NETs) in periprosthetic joint infection (PJI) diagnosis, and compare it with that of microbial culture, serum ESR and CRP, synovial white blood cell (WBC) count, and polymorphonuclear neutrophil percentage (PMN%). In a single health centre, patients with suspected PJI were enrolled from January 2013 to December 2021. The inclusion criteria were: 1) patients who were suspected to have PJI; 2) patients with complete medical records; and 3) patients from whom sufficient synovial fluid was obtained for microbial culture and NET test. Patients who received revision surgeries due to aseptic failure (AF) were selected as controls. Synovial fluid was collected for microbial culture and SF-WBC, SF-PNM%, and SF-NET detection. The receiver operating characteristic curve (ROC) of synovial NET, WBC, PMN%, and area under the curve (AUC) were obtained; the diagnostic efficacies of these diagnostic indexes were calculated and compared. The levels of SF-NETs in the PJI group were significantly higher than those of the AF group. The AUC of SF-NET was 0.971 (95% confidence interval (CI) 0.903 to 0.996), the sensitivity was 93.48% (95% CI 82.10% to 98.63%), the specificity was 96.43% (95% CI 81.65% to 99.91%), the accuracy was 94.60% (95% CI 86.73% to 98.50%), the positive predictive value was 97.73%, and the negative predictive value was 90%. Further analysis showed that SF-NET could improve the diagnosis of culture-negative PJI, patients with PJI who received antibiotic treatment preoperatively, and fungal PJI. SF-NET is a novel and ideal synovial fluid biomarker for PJI diagnosis, which could improve PJI diagnosis greatly.Cite this article: Bone Joint Res2023;12(2):113-120.

Tanshinone IIA Improves Acute Gouty Arthritis in Rats through Regulating Neutrophil Activation and the NLRP3 Inflammasome.

To investigate the prevention and treatment effect of tanshinone IIA (TIIA) on acute gouty arthritis (AGA) and its mechanism. The anti-AGA effect of TIIA was observed in vivo and in vitro. Neutrophils were isolated from the abdominal cavity of mice, and the anti-AGA effect of TIIA was investigated in a rat model of MSU-induced AGA. The pathological changes of the ankle joint tissues were assessed by H&E. Cytokine and chemokine expression were determined by ELISA and RT-qPCR. The NLRP3 inflammasome pathway protein levels in the ankle joint tissues were evaluated via western blotting. Neutrophil migration was evaluated in air pouch and transwell assays. Immunohistochemistry and immunofluorescence analysis evaluate the release of myeloperoxidase (MPO), neutrophil elastase (NE), and citrullination of histone H3 (CitH3). Beclin-1 and LC3B expressions were determined using western blotting and immunofluorescence. Key Findings. Treatment with TIIA alleviated synovial hyperplasia and neutrophil infiltration, regulated cytokine and chemokine expressions, and inhibited NLRP3 activation in AGA rats, neutrophil migration, MPO, NE, and CitH3 expression, and LC3B and Beclin-1 protein expression. These results demonstrate that TIIA can effectively enhance AGA by focusing on the neutrophils and NLRP3 inflammasome, demonstrating that TIIA may act as a potential helpful agent for AGA.

Phenotypic and functional characterisation of synovial fluid-derived neutrophils in knee osteoarthritis and knee infection

An increase in the number of neutrophils (NEUs) has long been associated with infections in the knee joints; however, their impact on knee osteoarthritis (KOA) pathophysiology remains largely unexplored. This study compared the phenotypic and functional characteristics of synovial fluid (SF)-derived NEUs in KOA and knee infection (INF). KOA NEUs were characterised by a lower expression of CD11b, CD54, and CD64 and higher expression of CD62L, TLR2, and TLR4 compared with INF NEUs. Except for CCL2, lower levels of inflammatory mediators and proteases were detected in KOA SF than in INF SF. Functionally, KOA NEUs displayed increased reactive oxygen species production and phagocytic activity compared with INF NEUs. Moreover, KOA and INF NEUs differed in cell sizes, histological characteristics of the surrounding synovial tissues, and their effects on the endothelial cells assessed by human umbilical vein endothelial cells. When KOA patients were subdivided based on the SF NEU abundance, patients with high NEUs (10%-60%) were characterised by i) elevated SF protein levels of TNF-α, IL-1RA, MMP-9, sTREM-1, VILIP-1 and ii) lower CD54, CD64, TLR2 and TLR4 expression compared to patients with low NEUs (<10%). Analysis of paired SF samples suggests that low or high NEU percentages, respectively, persist throughout the course of disease. Our findings suggest that NEU may play a significant role in KOA pathophysiology. Further studies should explore the mechanisms that contribute to the increased number of NEUs in SF and the clinical consequences of neutrophilic phenotype in KOA.

Reliable Diagnostic Tests and Thresholds for Preoperative Diagnosis of Non-Inflammatory Arthritis Periprosthetic Joint Infection: A Meta-analysis and Systematic Review.

The current diagnostic criteria for periprosthetic joint infection (PJI) are diverse and controversial, leading to delayed diagnosis. This study aimed to evaluate and unify their diagnostic accuracy and the threshold selection of serum and synovial routine tests for PJI at an early stage. We searched the MEDLINE and Embase databases for retrospective or prospective studies which reported preoperative-available assays (serum, synovial, or culture tests) for the diagnosis of chronic PJI among inflammatory arthritis (IA) or non-IA populations from January 1, 2000 to June 30, 2022. Threshold effective analysis was performed on synovial polymorphonuclear neutrophils (PMN%), synovial white blood cell (WBC), serum C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR) to find the relevant cut-offs. Two hundred and sixteen studies and information from 45,316 individuals were included in the final analysis. Synovial laboratory-based α-defensin and calprotectin had the best comprehensive sensitivity (0.91 [0.86-0.94], 0.95 [0.88-0.98]) and specificity (0.96 [0.94-0.97], 0.95 [0.89-0.98]) values. According to the threshold effect analysis, the recommended cut-offs are 70% (sensitivity 0.89 [0.85-0.92], specificity 0.90 [0.87-0.93]), 4100/μL (sensitivity 0.90 [0.87-0.93], specificity 0.97 [0.93-0.98]), 13.5 mg/L (sensitivity 0.84 [0.78-0.89], specificity 0.83 [0.73-0.89]), and 30 mm/h (sensitivity 0.79 [0.74-0.83], specificity 0.78 [0.72-0.83]) for synovial PMN%, synovial WBC, serum CRP, and ESR, respectively, and tests seem to be more reliable among non-IA patients. The laboratory-based synovial α-defensin and synovial calprotectin are the two best independent preoperative diagnostic tests for PJI. A cut off of 70% for synovial PMN% and tighter cut-offs for synovial WBC and serum CRP could have a better diagnostic accuracy for non-IA patients with chronic PJI.

Synovial fluid neutrophil gelatinase-associated lipocalin can be used to accurately diagnose prosthetic joint infection

ObjectivesNeutrophil gelatinase-associated lipocalin (NGAL) in synovial fluid (SF) may have potential diagnostic value for prosthetic joint infection (PJI). This study aimed to study (i) the diagnostic performance of SF-NGAL levels for diagnosing PJI and (ii) the impact of previous antibiotic use on the SF-NGAL levels. MethodsConsecutive patients who needed hip or knee revision surgery were included prospectively from January 2017 to September 2018. The patients were divided into the PJI group and the aseptic failure group. An enzyme-linked immunosorbent assay was used to determine the SF-NGAL level. ResultsA total of 50 of 78 included patients were diagnosed with PJI. The median SF-NGAL level was 3633 ng/ml (interquartile range [IQR], 1332-10,737) in the PJI group and 26.8 ng/ml (IQR, 12.4-52.5) in the aseptic failure group (P <0.0001). When the SF-NGAL threshold was 263 ng/ml, the area under the curve was 0.98, the sensitivity was 92.9%, and the specificity was 98%. The median level was 5779 ng/ml (IQR, 1425-13,072) in the antibiotic group and 2590 ng/ml (IQR, 932-8970) in the nonantibiotic group (P = 0.1). ConclusionSF-NGAL level can be used as a diagnostic indicator of PJI. The use of antibiotics before sampling does not affect the SF-NGAL level.