Aims. The diagnosis of periprosthetic joint infection (PJI) continues to present a significant clinical challenge. New biomarkers have been proposed to support clinical decision-making; among them, synovial fluid alpha-defensin has gained interest. Current research methodology suggests reference methods are needed to establish solid evidence for use of the test. This prospective study aims to evaluate the diagnostic accuracy of high-performance liquid chromatography coupled with the mass spectrometry (LC-MS) method to detect alpha-defensin in synovial fluid. Methods. Between October 2017 and September 2019, we collected synovial fluid samples from patients scheduled to undergo revision surgery for painful total knee arthroplasty (TKA). The International Consensus Meeting criteria were used to classify 33 PJIs and 92 aseptic joints. LC-MS assay was performed to measure alpha-defensin in synovial fluid of all included patients. Sensitivity, specificity, positive predictive value, negative predictive value, and the area under the receiver operating characteristic curve (AUC) were calculated to define the test diagnostic accuracy. Results. The AUC was 0.99 (95% confidence interval (CI) 0.98 to 1.00). Receiver operating characteristic (ROC) analysis showed that the optimal cut-off value of synovial fluid alpha-defensin was 1.0 μg/l. The sensitivity of alpha-defensin was 100% (95% CI 96 to 100), the specificity was 97% (95% CI 90 to 98), the positive predictive value was 89.2% (95% CI 82 to 94), and negative predictive value was 100% (95% CI 96 to 100). ROC analysis demonstrated an AUC of 0.99 (95% CI 0.98 to 1.0). Conclusion. The present study confirms the utility of alpha-defensin in the synovial fluid in patients with painful TKA to select cases of PJI. Since LC-MS is still a time-consuming technology and is available in highly specialized laboratories, further translational research studies are needed to take this evidence into routine procedures and promote a new diagnostic approach. Cite this article: Bone Joint J 2022;104-B(9):1047–1051

Aims. To establish the utility of adding the laboratory-based synovial alpha-defensin immunoassay to the traditional diagnostic work-up of a prosthetic joint infection (PJI). Methods. A group of four physicians evaluated 158 consecutive patients who were worked up for PJI, of which 94 underwent revision arthroplasty. Each physician reviewed the diagnostic data and decided on the presence of PJI according to the 2014 Musculoskeletal Infection Society (MSIS) criteria (yes, no, or undetermined). Their initial randomized review of the available data before or after surgery was blinded to each alpha-defensin result and a subsequent randomized review was conducted with each result. Multilevel logistic regression analysis assessed the effect of having the alpha-defensin result on the ability to diagnose PJI. Alpha-defensin was correlated to the number of synovial white blood cells (WBCs) and percentage of polymorphonuclear cells (%PMN). Results. Intraobserver reliability and interobserver agreement did not change when the alpha-defensin result was available. Positive alpha-defensin results had greater synovial WBCs (mean 31,854 cells/μL, SD 32,594) and %PMN (mean 93.0%, SD 5.5%) than negative alpha-defensin results (mean 974 cells/μL, SD 3,988; p < 0.001 and mean 39.4% SD 28.6%; p < 0.001). Adding the alpha-defensin result did not alter the diagnosis of a PJI using preoperative (odds ratio (OR) 0.52, 95% confidence interval (CI) 0.14 to 1.88; p = 0.315) or operative (OR 0.52, CI 0.18 to 1.55; p = 0.242) data when clinicians already decided that PJI was present or absent with traditionally available testing. However, when undetermined with traditional preoperative testing, alpha-defensin helped diagnose (OR 0.44, CI 0.30 to 0.64; p < 0.001) or rule out (OR 0.41, CI 0.17 to 0.98; p = 0.044) PJI. Of the 27 undecided cases with traditional testing, 24 (89%) benefited from the addition of alpha-defensin testing. Conclusion. The laboratory-based synovial alpha-defensin immunoassay did not help diagnose or rule out a PJI when added to routine serologies and synovial fluid analyses except in cases where the diagnosis of PJI was unclear. We recommend against the routine use of alpha-defensin and suggest using it only when traditional testing is indeterminate. Cite this article: Bone Joint J 2020;102-B(5):593–599

Aims. The aim of this study was to evaluate the diagnostic accuracy of the synovial alpha-defensin enzyme-linked immunosorbent assay (ELISA) for the diagnosis of prosthetic joint infection (PJI) in the work-up prior to revision of total hip (THA) and knee arthroplasty (TKA). Patients and Methods. Inclusion criteria for this prospective cohort study were acute or chronic symptoms of the index joint without specific exclusion criteria. Synovial fluid aspirates of 202 patients were analyzed and semiquantitative laboratory alpha-defensin ELISA was performed. Final diagnosis of PJI was established by examination of samples obtained during revision surgery. Results. Sensitivity and specificity of the alpha-defensin ELISA for PJI were 78.2% (95% confidence interval (CI) 66.7 to 88.5) and 96.6% (95% CI 93.0 to 99.3). Positive and negative predictive values were 89.6% (95% CI 80.6 to 97.8) and 92.2% (95% CI 87.5 to 96.1). The test remained false-negative in 22% of septic revisions, most of which were due to coagulase-negative staphylococci all occurring in either late-chronic or early-postoperative PJI. Conclusion. The routine use of synovial fluid alpha-defensin laboratory ELISA in the preoperative evaluation of symptomatic THAs and TKAs is insufficient to accurately diagnose PJI. Particularly in cases involving low-virulence organisms, such as coagulase-negative staphylococci, there remains a need for tests with a higher sensitivity. Cite this article: Bone Joint J 2019;101-B:970–977

Aims. The purpose of this current multicentre study is to analyse the presence of alpha-defensin proteins in synovial fluid using the Synovasure lateral flow device and to determine its diagnostic reliability and accuracy compared with the prosthetic joint infection (PJI) criteria produced by the Musculoskeletal Infection Society (MSIS). Patients and Methods. A cohort of 121 patients comprising 85 total knee arthroplasties and 36 total hip arthroplasties was prospectively evaluated between May 2015 and June 2016 in three different orthopaedic centres. The tests were performed on patients with a chronically painful prosthesis undergoing a joint aspiration in a diagnostic pathway or during revision surgery. Results. Based on the MSIS criteria, 34 patients (28%) would have had a PJI, and 87 patients had no PJI. Testing with the lateral flow device had a sensitivity of 97.1% (95% confidence intervals (CI) 84.5 to 99.9) and a specificity of 96.6% (95% CI 90.3 to 99.2). The positive predictive value was 91.7% (95% CI 77.7% to 98.3), and the negative predictive value was 98.8% (95% CI 93.6 to 99.9). Receiver operator characteristics analysis demonstrated an area under the curve for the Synovasure test of 0.97 (95% CI 0.93 to 1.00). Conclusion. Our findings suggest that the Synovasure test has an excellent diagnostic performance to confirm or reject the diagnosis of a PJI. The results are promising for the care of the painful or problematic knee and hip joint arthroplasty and the test should be considered as part of the diagnostic toolbox for PJIs. Cite this article: Bone Joint J 2017;99-B:1176–82

Aims. The aim of this review was to evaluate the available literature and to calculate the pooled sensitivity and specificity for the different alpha-defensin test systems that may be used to diagnose prosthetic joint infection (PJI). Materials and Methods. Studies using alpha-defensin or Synovasure (Zimmer Biomet, Warsaw, Indiana) to diagnose PJI were identified from systematic searches of electronic databases. The quality of the studies was evaluated using the Quality Assessment of Studies of Diagnostic Accuracy (QUADAS) tool. Meta-analysis was completed using a bivariate model. Results. A total of 11 eligible studies were included. The median QUADAS score was 13 (interquartile range 13 to 13) out of 14. Significant conflicts of interest were identified in five studies. The pooled sensitivity for the laboratory alpha-defensin test was 0.95 (95% confidence interval (CI) 0.91 to 0.98) and the pooled specificity was 0.97 (95% CI 0.95 to 0.98) for four studies with a threshold level of 5.2 mgl. -1. The pooled sensitivity for the lateral flow cassette test was 0.85 (95% CI 0.74 to 0.92) and the pooled specificity was 0.90 (95% CI 0.91 to 0.98). There was a statistically significant difference in sensitivity (p = 0.019), but not specificity (p = 0.47). Conclusion. Laboratory-based alpha-defensin testing remains a promising tool for diagnosing PJI. The lateral flow cassette has a significantly lower performance and pooled results are comparable to the leucocyte esterase test. Further studies are required before the widespread adoption of the lateral flow cassette alpha-defensin test. Cite this article: Bone Joint J 2018;100-B:703–11

Background. Two-stage revision arthroplasty is the standard treatment for chronic hip and knee periprosthetic joint infections (PJI). Accurate diagnosis of persistent infections at 2nd stage using established biomarkers and diagnostic criteria is of paramount importance. This study aimed to evaluate the diagnostic value of synovial calprotectin and alpha-defensin, and compare established diagnostic criteria from the International Consensus Meeting (ICM 2018) and the European Bone and Joint Infection Society (EBJIS 2021) to determine persistent PJI at the 2nd stage of a two-stage revision arthroplasty. Methods. We retrospectively analyzed 97 patients who underwent 100 two-stage revisions (hip: 39, knee: 61). Synovial fluid samples were assessed for calprotectin and alpha-defensin levels. ICM 2018 and EBJIS 2021 were applied to all patients undergoing 2nd stage revision. Receiver operating characteristic (ROC) curves and Youden Index were utilized to determine optimal cut-off values, and correlations between biomarkers were evaluated. The microbiological spectrum was analyzed at 2nd stage and re-revision surgery. Results. Calprotectin levels showed a sensitivity of 66.7%, specificity of 32.9%, and accuracy of 38.0% in predicting septic failure. Alpha-defensin showed sensitivity of 28.6%, specificity of 87.8%, and accuracy of 79.2%. Significant correlations included: calprotectin with PMN% (r = 0.471, p = 0.05) and alpha-defensin with WBC (r = 0.830, p < 0.01) in the successful cohort. For septic re-revisions, calprotectin and alpha-defensin were highly correlated (r = 0.969, p < 0.01). ICM correctly diagnosed persistent PJI in 26.7%, while EBJIS diagnosed 24.2%. The microbial spectrum shifted from gram-positive to gram-negative bacteria between reimplantation and re-revision surgeries. Conclusion. Synovial calprotectin and alpha-defensin demonstrated limited accuracy in ruling out persistent PJI at reimplantation. The low sensitivity of current diagnostic criteria, combined with the observed shift in microbial spectrum, underscores the challenges in diagnosing persistent PJI during 2nd stage of a two-stage revisions arthroplasty

Aim. Quantitative assessment of alpha-Defensin offers a promising approach for diagnosing a periprosthetic joint infection (PJI) with sensitivities and specificities ranging from 97% to 100% and 95% to 100%, respectively. However, to the best of our knowledge and after due inquiry little information exists concerning qualitative measurements of alpha-Defensin. The aim of this study was to assess the diagnostic accuracy of the alpha-Defensin test, a lateral flow test for the qualitative detection of alpha-Defensin. Method. In this study, 50 patient with indicated revision surgery met the inclusion criteria due to septic or aseptic loosening. In addition to clinical standard diagnostics of PJI, the alpha-Defensin test. *. for the assessment of the qualitative alpha-Defensin in the synovial fluid was performed. The results were compared with the sensitivity and specificity of currently available clinical tests, specifically C-reactive protein (CRP), frozen section, definitive histology, bacteriology and sonication. Results. Based on the Musculoskeletal Infection Society's (MSIS) definition of PJI, 36 cases were categorized as aseptic and 13 as septic revisions. Due to the lack of an indicated control line (“C”), one alpha-Defensin test. *. was inconclusive. Qualitative alpha-Defensin had an area under the curve, sensitivity, specificity, and positive and negative likelihood ratios of 0.82, 69%, 94%, 12.46, and 0.33, respectively. Adjusted p-values using the method of Hochberg showed that the alpha-Defensin test. *. is significantly at least as good when diagnosing PJI as histology (p=0,0042) and bacteriology with at least one positive culture (p=0,0327). Conclusions. Qualitative alpha-Defensin tests could be an effective supplement in diagnosing PJI with a diagnostic accuracy comparable to histology and bacteriology (≥ 1 positive culture)

Aim. Alpha-defensin is a new synovial fluid biomarker for the diagnosis of periprosthetic joint infections (PJI). We compared the performance of two different alpha-defensin assays: quantitative ELISA test and qualitative lateral flow test. Method. In this prospective cohort study, consecutive patients with a painful prosthesis of the lower limb were eligible for inclusion. In addition to standard diagnostics of PJI, alpha-defensin was determined in the aspirated synovial fluid between October 2016 and April 2017. PJI was defined according to the modified Zimmerli criteria, the Musculoskeletal Infection Society (MSIS) criteria and the Infectious Disease Society of America (IDSA) criteria. A positive quantitative alpha-defensin test was defined at a cut-off value of 5.2 mg/L. The sensitivity, specificity, accuracy and area under the curve of each test were determined and the AUCs were compared among each other. Results. We included 72 patients (55 knee, 27 hip prosthesis) with a median age of 70 years (range: 41 – 85 years). Based on the modified Zimmerli criteria, 23 cases (32%) were categorized as septic and 49 (68%) as aseptic prosthesis failure. The sensitivity, specificity, accuracy, and AUC of quantitative alpha-Defensin were 48%, 98%, 82%, and 0.73, respectively; for qualitative alpha-Defensin, results were 48%, 100%, 83%, and 0.74, respectively. When the IDSA criteria were applied, the sensitivity of the quantitative and qualitative alpha-defensin test was 83% and 75%, respectively; when the MSIS criteria were applied, the sensitivity of the quantitative and qualitative alpha-Defensin was 92% and 83%, respectively. The comparison between the qualitative and quantitative alpha-defensin tests showed no statistically significant difference regardless of the used infection classification (modified Zimmerli: [difference AUC −0.01; p = 0.792], IDSA: [difference AUC 0.04; p = 0.317], MSIS: [difference AUC 0.04; p = 0.264]). Conclusions. The sensitivity of the alpha-defensin test in synovial fluid showed poor sensitivity (48%) for diagnosing PJI when modified Zimmerli criteria were used. No difference were observed between the qualitative and quantitative alpha-defensin test

Aim. A key of success in the treatment of prosthetic joint infection (PJI) is the proper diagnosis. There is a lack of diagnostic tools able to diagnose a PJI with high accuracy. Alpha-defensin has been proposed as possible solution but the available literature is still limited. This prospective study was carried out in order to determine (1) what is the sensitivity, the specificity, the positive and the negative predictive value of the Alpha-defensin immunoassay test in diagnosing PJI; (2) which clinical features may be responsible for false positive and false negative results?. Method. Preoperative aspiration was performed in patients presenting with a painful hip/knee arthroplasty. Metallosis, other inflammatory comorbidities and previous/concomitant antibiotic therapy were not considered as exclusion criteria. Patients with inadequate amount of synovial fluid for culture were excluded. At time of revision synovial fluid samples were taken in the OR in order to perform Alpha-defensin assay. During surgical debridement tissue samples for cultures were obtained. Prospectively, 156 patients (65 knees and 91 hips) were included. A diagnosis of PJI was confirmed in 29 patients. Results. The sensitivity of the Alpha-defensin immunoassay was 97% (95% CI, 92% – 99%), the specificity was 97% (95% CI, 92% – 99%), the positive predictive value was 88% (95% CI, 81% – 92%) and the negative predictive value was 99% (95% CI, 96% – 99%). Among four false positive patients two had a metallosis and one had a polyethylene wear. The false negative case presented with a draining sinus, and intraoperative cultures were also negative. Conclusions. Alpha-defensin assay may have a significant role in PJI diagnosis. Negative tests may exclude the diagnosis of PJI. Positive tests are very much likely to confirm PJI, but other conditions (metallosis, poly wear) should be excluded

Introduction. Periprosthetic joint infection (PJI) can be difficult to diagnose. A variety of techniques have been described. The efficacy of the alpha-defensin laboratory test was examined and compared with other established modalities in the diagnostic workup of ‘real world’ arthroplasty patients. Methods. This was a retrospective review of 210 episodes (86 hips, 124 Knees) in 172 patients at one centre, and included samples from acute admissions, elective aspirations, and planned revisions. MSIS (musculoskeletal infection society) major and minor criteria were used for diagnosing PJI. Each patient was investigated using a standardised protocol with inflammatory markers, synovial fluid analysis for white cell count (SWCC) and polymorphonuclear leukoctyes percentage (PMN %), and synovial fluid/tissue culture. Synovial fluid was also tested for alpha-defensin. Results. Fifty-two (24.8%) episodes were defined as ‘PJI’ using MSIS criteria, and 158 ‘non-PJI’. Alpha-defensin had 71.2% (95% CI 56.9–82.9) sensitivity and 94.3% (89.5–97.4) specificity. The positive predictive value was 80.4% (68.1–88.8) with negative predictive value of 90.9% (6.6–93.9). Thirty-seven (of 52 PJI episodes) were ‘culture positive’ (identical microorganism on ≥2 samples). Eighty (of 158 non-PJI) satisfied none of the major or minor MSIS criteria, and none of these patients subsequently had a PJI. In this sub-set of 117, alpha-defensin had 64.9% (47.5–79.8) sensitivity and 98.7% (92.9–99.9) specificity, whilst the sensitivities of CRP (>20), SWCC (>3000) and PMN (>80%) were 94.6% (81.8–99.3), 86.5% (71.2–95.5) and 83.8% (68.0–93.8) respectively. There were 93 episodes where at least 1 minor criterion was satisfied and/or a sinus was present, but were not ‘culture positive’. In these, alpha-defensin had 85.7% (57.2–98.2) sensitivity and 88.4% (78.4–94.9) specificity. Discussion and conclusion. The alpha-defensin laboratory test has a lower sensitivity than previously reported, limiting its use for diagnosing PJI. SWCC and PMN % have similar sensitivity and are cheaper. We no use the alpha-defensin test

Prosthetic joint infection continues to remain a diagnostic challenge for unhappy primary arthroplasty of hip and knees. There is increasing dependence upon alpha-defensin test to make key decisions like whether to revise or not & to decide between one-stage versus two-stage. Aim. This study aims to assess diagnostic accuracy of alpha-defensin test in determining prosthetic hip & knee infection and to provide guidance for appropriate use of this novel but expensive investigation. Methods. Retrospective review of all alpha-defensin investigated patients in an orthopaedic institute between February 2015 & March 2017 was performed. Clinical and radiological outcomes including re-infections, re-operations were analysed and alpha-defensin outcomes were compared with that of other available investigations. Results. Of total 52 tests performed (17 hips & 35 knees), 3 were positive. On comparison with intra-operative culture (gold standard), sensitivity is 100%. All suspected prosthetic hip infections have good clinical outcomes following their decisions being made based upon alpha-defensin test. Among the negative knee test results, 6 patients developed signs of infection in the post-operative period, 4 of which have been revised with washout, poly exchange or full revision. Conclusion. No single clinical investigation can accurately predict prosthetic joint infection in revision for suspected infection. Alpha-defensin test, however, is a useful adjunct to intra-operative surgeon's findings & pre-operative investigations to decide for crucial decisions like whether to revise or not & for deciding between single and two stage

Aim. Alpha-defensin was recently introduced as a new biomarker having a very high accuracy to rule out periprosthetic joint infection (PJI). A new rapid lateral flow version of the Alpha-defensin test was developed and introduced to detect high levels of Alpha-defensin in synovial fluid quickly and with ease. We conducted a single-centre prospective clinical study to compare the results of the Alpha-defensin rapid test* against the conventional diagnostics according to MSIS criteria. Method. A total of 223 consecutive patients with painful total hip or knee arthroplasty were enrolled into the study. In all patients, blood C-reactive protein was measured and joint aspirations were performed. From the synovial fluid a leukocyte cell count with granulocyte percentage, microbiology cultures and Leukocyte Esterase tests were carried out according to the recommendation of MSIS for diagnosing PJI. At the same time, the Lateral Flow Test* was performed from the aspirate. 191 subjects with 195 joint aspirations (96 hips, 99 knees) were included in final clinical and statistical evaluation. We had 119 joints with an aseptic revision and 76 joints with PJI. Results. After statistical analysis the overall sensitivity of the Lateral Flow Test* was 92.1% (95% confidence interval [CI], 83.6% to 97.1%), the specificity was 100% (95% CI, 97.0% to 100%), the positive predictive value was 100% (95% CI, 94.9% to 100%), and the negative predictive value was 95.2% (95% CI, 89.9% to 98.2%). The overall accuracy of the Lateral Flow Test* was 96.9% (189 of 195, 95% CI, 93.4% to 98.9%). Conclusions. Our results suggest that the PJI test* has a very high accuracy in diagnosing infected THA and TKA. Though the Lateral Flow Test* does not provide information on the identity of the infectious pathogen, the test does have an important role in recognizing PJI early and enables surgeons to start proper therapy without delay. *Synovasure®

Purpose. Unexpected-positive-intraoperative-cultures (UPIC) in presumed aseptic revision-total-knee-arthroplasties (rTKA) are common, and the clinical significance is not entirely clear. In contrast, in some presumably septic rTKA, an identification of an underlying pathogen was not possible, so called unexpected-negative-intraoperative-cultures (UNIC). The purpose of this study was to evaluate alpha defensin (AD) levels in these patient populations. Methods. In this retrospective analysis of our prospectively maintained biobank, we evaluated synovial AD levels from 143 rTKAs. The 2018-Musculoskeletal Infection Society score (MSIS) was used to define our study groups. Overall, 20 rTKA with UPIC with a minimum of one positive intraoperative culture with MSIS 2-≥6 and 14 UNIC samples with MSIS≥6 were compared to 34 septic culture-positive samples (MSIS ≥6) and 75 aseptic culture-negative (MSIS 0–1) rTKAs. Moreover, we compared the performance of both AD-lateral-flow-assay (ADLF) and an enzyme-linked-immunosorbent-assay (ELISA) to test the presence of AD in native and centrifuged synovial fluid. Concentration of AD determined by ELISA and ADLF methods, as well as microbiological, and histopathological results, serum and synovial parameters along with demographic factors were considered. Results. AD was detected in 31/34 (91.2%) samples from the infected-group and in 14/14 (100%) samples in the UNIC group. All UPIC samples showed a negative AD result. Positive AD samples were highly (p<0.001) associated with culture positive and infection related histopathological results. Moreover, we found significantly (p=0.001) more high-virulent microorganisms 19/34 (55.9%) in the infected-group compared to the UPIC-group (0/20). Samples from the infected group with high virulent microorganisms 17/19 (89.5%) showed a positive AD. The presence of methicillin resistant Staphylococcus epidermis (MRSE) led to increased AD (p=0.003) levels when compared to those determined in samples positive for methicillin susceptible S. epidermdis (MSSE). ELISA and ADLF tests were positive with centrifuged (8/8) and native (8/8) synovial fluid. Conclusion. AD showed a solid diagnostic performance in infected and non-infected revisions, and it provided an additional value in the diagnostic of UPIC and UNIC associated to rTKAs. AD levels produced by patients with PJIs caused by high-virulent microorganisms and MRSE are significantly higher compared to those in patients with PJIs caused by either low-virulent or antibiotic susceptible microorganisms. Centrifugation of synovial fluid had no influence in the outcome of ADLF quantification. Keywords: Alpha-defensin, UPIC, UNIC, revision-knee-arthroplasty

Aim

The aim of the study was to assess the accuracy of the alpha defensin lateral flow test for diagnosis of periprosthetic joint infection (PJI) using an optimized diagnostic algorithm and three classification systems. In addition, we compared the performance with synovial fluid leukocyte count, the most sensitive preoperative test.

Aims. The diagnosis of periprosthetic joint infection (PJI) remains a challenge, as no single diagnostic test shows high diagnostic accuracy. Recently, the measurement of synovial biomarkers has shown promising results. The aim of this study was to present a novel multiplex micro-enzyme-linked immunosorbent assay (ELISA) method for the rapid and simultaneous measurement of alpha-defensin, interleukin (IL)-6, and calprotectin developed in a model buffer system and human spiked synovial fluid. Methods. A microfluidics- and chemiluminescence-based multiplex micro-ELISA point-of-care testing system was employed for the rapid and simultaneous measurement of alpha-defensin, calprotectin, and IL-6 developed in a model buffer system and spiked human synovial fluid. Cut-off values of 1.56 µg/ml for alpha-defensin, 50 µg/ml for calprotectin, and 0.031 µg/ml for IL-6 were extracted from the literature as optimal cut-off values for the diagnosis of PJI, and were used for comparison. Results. Limit of detection (LoD) was determined for each individual biomarker by means of calibration curves with serial dilutions in a model buffer system. LoDs of 0.008, 0.002, and 0.00014 µg/ml were determined for alpha-defensin, calprotectin, and IL-6, respectively. The spiked synovial fluid assay determined LoDs of 0.08, 0.31, and 0.004 µg/ml for alpha-defensin, calprotectin, and IL-6, respectively. Conclusion. These findings highlight the proposed platform’s unique features, including simultaneous measurement of three key synovial biomarkers, minimal sample volume requirements (5 to 50 µl), lower LoDs compared to conventional tests, and a short processing turnaround time of 22 minutes. Further validation studies are necessary to confirm its clinical utility. Cite this article: Bone Joint Res 2025;14(3):176–184

Aims. 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). Methods. 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. Results. 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. Conclusion. 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. Cite this article: Bone Joint J 2023;105-B(4):373–381

Aims. The diagnosis of periprosthetic joint infection can be difficult due to the high rate of culture-negative infections. The aim of this study was to assess the use of next-generation sequencing for detecting organisms in synovial fluid. Materials and Methods. In this prospective, single-blinded study, 86 anonymized samples of synovial fluid were obtained from patients undergoing aspiration of the hip or knee as part of the investigation of a periprosthetic infection. A panel of synovial fluid tests, including levels of C-reactive protein, human neutrophil elastase, total neutrophil count, alpha-defensin, and culture were performed prior to next-generation sequencing. Results. Of these 86 samples, 30 were alpha-defensin-positive and culture-positive (Group I), 24 were alpha-defensin-positive and culture-negative (Group II) and 32 were alpha-defensin-negative and culture-negative (Group III). Next-generation sequencing was concordant with 25 results for Group I. In four of these, it detected antibiotic resistant bacteria whereas culture did not. In another four samples with relatively low levels of inflammatory biomarkers, culture was positive but next-generation sequencing was negative. A total of ten samples had a positive next-generation sequencing result and a negative culture. In five of these, alpha-defensin was positive and the levels of inflammatory markers were high. In the other five, alpha-defensin was negative and the levels of inflammatory markers were low. While next-generation sequencing detected several organisms in each sample, in most samples with a higher probability of infection, there was a predominant organism present, while in those presumed not to be infected, many organisms were identified with no predominant organism. Conclusion. Pathogens causing periprosthetic infection in both culture-positive and culture-negative samples of synovial fluid could be identified by next-generation sequencing. Cite this article: Bone Joint J 2018;100-B:127–33

Background. The diagnosis of periprosthetic joint infection (PJI) remains a challenge in clinical practice and the analysis of synovial fluid (SF) is a useful diagnostic tool. Recently, two synovial biomarkers (leukocyte esterase (LE) strip test, alpha-defensin (AD)) have been introduced into the MSIS (MusculoSkeletal Infection Society) algorithm for the diagnosis of PJI. AD, although promising with high sensitivity and specificity, remains expensive. Calprotectin is another protein released upon activation of articular neutrophils. The determination of calprotectin and joint CRP is feasible in a routine laboratory practice with low cost. Purpose. Our objective was to evaluate different synovial biomarkers (calprotectin, LE, CRP) for the diagnosis of PJI. Methods. In this monocentric study, we collected SF from hip, knee, ankle and shoulder joints of 42 patients who underwent revision or puncture for diagnostic purposes. Exclusion criteria included a joint surgery in the previous 3 months and a diagnosis of a systemic inflammatory disease. PJI was diagnosed in a multidisciplinary consultation meeting (RCP) of the Reference Centers for Osteoarticular Infections of the Great West (CRIOGO). SF was analysed for LE, CRP and calprotectin. The cut-off values used were 50 mg/L for calprotectin, 8.8 mg/L for CRP and 125 WBC/µL for LE. The overall sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated for these different synovial markers. Results. Of the 42 patients included, 28 were considered as infected and 14 uninfected. The statistical parameters are presented in Table 1. Conclusion. The present study shows that the synovial calprotectin assay has an excellent sensitivity and a 100% NPV for the diagnosis of PJI, suggesting that a result < 50 mg/L could exclude PJI. This promising study suggests that calprotectin should be included with synovial CRP in a new decision algorithm for the diagnosis of PJI. For any tables or figures, please contact the authors directly

Introduction. Periprosthetic joint infection (PJI) is considered one of the most feared causes of implant failure, due to the difficulty in formulating a proper and timely diagnosis. In the diagnostic workup are often used test with a low specificity, such as the dosage of ESR and CRP, or sensitivity, such as cultures or the leukocyte count of the synovial fluid. Radiological investigations are expensive and unreliable to play a direct role in the diagnosis of PJI. The alpha-defensin is an antimicrobial peptide released by neutrophils in response to pathogens and it is an ideal biomarker for the diagnosis of PJI. It is now possible to verify the presence of alpha-defensin in periprosthetic synovial fluid with an ELISA (Synovasure® PJI, Zimmer) that provides results in 10 minutes, with a sensitivity of 97% and a specificity of 96%, without being affected by systemic inflammatory diseases or by the assumption of antibiotics. The purpose of this study is to assess the applicability and reliability of Synovasure® PJI, correlating its results with microbiological analyzes, laboratory tests and imaging studies of the patient. Materials and Methods. Patients recruited are those who have undergone a previous total hip or knee arthroplasty where there is suspicion of PJI. The test can be performed either during surgery or during the diagnostic iter, through the execution of an arthrocentesis. The synovial fluid is partly used for Synovasure® PJI and partly put in culture for microbiological analyzes. Once ready, culture results are compared with the results of the test to get a confirmation of its reliability or reference to identify the microorganism responsible for PJI. These data are then compared, with laboratory tests and radiological investigations performed by the patient. Results. Up to now we have full results in 10 patients (11 implants). In four cases, the test showed the presence of alpha-defensin in the synovial fluid, while in seven cases the test result were negative. In case of negative test culture of synovial fluid showed no growth of microorganisms that could indicate the presence of false negatives. All patients with positive test have arthrocentesis positive for pathogenic microorganisms. We are waiting for culture results of two other patients (one with positive test and one with negative test). In the next few months will be tested other patients with suspicion of PJI. Discussion. Timeliness and accuracy in the diagnosis are essential for the proper management of the patient with suspected PJI. Diagnostic tools currently available are often sensitive but not very specific or conversely, specific but insensitive. New synovial markers such as alpha-defensin and rapid ELISA tests for their dosage open new horizons in the diagnosis of periprosthetic infections. Conclusions. Synovasure® PJI is a practical and reliable tool in the diagnosis of periprosthetic joint infections. Thanks to the quick response and the ease of execution the test can be used both during the diagnostic iter and during the revision surgery helping the orthopedic to apply the most appropriate measures to each case

While advances in laboratory and imaging modalities facilitate the diagnosis of periprosthetic joint infection (PJI), clinical suspicion and a thorough history and physical remain the basis of evaluation. If clinical suspicion is high, the evaluation should be more vigorous, and vice versa. The erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are inexpensive as well as ubiquitous, and should be obtained as a preliminary screening tool. These tests have been found to be cost-effective and highly sensitive. If both tests are negative, there is a low risk of periprosthetic joint infection (i.e., good negative predictive value). Positive results on both tests, in contrast, are not as specific but again raise suspicion. When either the ESR or CRP is elevated, or if the clinical suspicion for infection is high, aspiration of the knee joint is suggested. Synovial fluid should be sent for a synovial fluid white blood cell count (WBC), differential and culture. Given the ability to get three data points from one intervention, arthrocentesis, is the best single maneuver the physician can perform to rule in or out PJI. The synovial fluid WBC count has demonstrated in multiple studies excellent specificity and sensitivity in the diagnosis of infection. Based on multiple recent studies, the proceedings of the International Consensus on PJI recommend cut-offs for the synovial fluid WBC count as >3000 cells/mL and > 80% neutrophils for the differential. Synovial fluid biomarkers represent an expanding area of clinical interests based on the unique cascade of gene expression that occurs in white blood cells in response to pathogens. Deirmegian et al. described the unique gene expression and biomarker production by neutrophils in response to bacteria that are detectable in synovial fluid. Specifically, alpha-defensin is one such antimicrobial peptide. Along with synovial CRP, alpha-defensin can be measured in a currently commercially-available immunoassays. The diagnosis of PJI can be difficult to make in spite of the variety of tests available. That being said, the diagnosis is easily made in our experience in 90% of patients by getting an ESR and CRP followed by selective aspiration of the joint if these values are elevated or if the clinical suspicion is high. Synovial fluid obtained should be sent for a synovial fluid WBC count, differential and cultures