Diagnosing periprosthetic joint infection: has the era of the biomarker arrived?

Synovial D-dimer is a novel and accurate test for diagnosis of chronic knee periprosthetic joint infection

BACKGROUND

Despite numerous tests and guidelines, diagnosing periprosthetic joint infection (PJI) remains challenging. The study aimed to determine the value of synovial D-dimer, rather than serum, in diagnosing PJI.

METHODS

This prospective study enrolled 17 patients with chronic knee PJI (the PJI group) and 52 with primary knee osteoarthritis (the control group). PJI was defined using the 2018 International Consensus Meeting Criteria. Synovial D-dimer, plasma D-dimer, serum erythrocyte sedimentation rate, and serum C-reactive protein levels were measured. Synovial fluid D-dimer levels were determined using an enzyme-linked fluorescence assay. The performance of each biomarker in diagnosing PJI was evaluated using receiver operating characteristic (ROC) curves.

RESULTS

The median synovial D-dimer level was significantly higher in the PJI group at (927,095 ng/ml, IQR 566,882-1,215,066) than in the control group (20,954 ng/ml, IQR 10,350-46,493) (P < 0.001). When the synovial D-dimer threshold value was determined to be 236,804 ng/ml, the sensitivity was 100% (CI 93.2-100%), and the specificity was 94.12% (95% CI 71.3-99.9). The area under the curve determined by ROC analysis was 0.992 (95% CI 0.992-1.000, P < 0.0001).

CONCLUSIONS

Patients with chronic knee PJI have significantly high synovial D-dimer levels, demonstrating that an increase in fibrinolytic activity coexists with an infection-induced inflammatory response. Synovial D-dimer levels appear to be valuable biomarkers for diagnosing PJI. However, further studies are required to evaluate the role of this novel biomarker.

Inflammatory Marker Changes Following Total Knee Arthroplasty for Rheumatoid Arthritis with Vancomycin-Loaded Calcium Sulfate Bone Filling

Rheumatoid arthritis (RA) patients undergoing total knee arthroplasty (TKA) face infection risk. The study evaluates vancomycin-loaded calcium sulfate bone as infection prevention. Patients with RA treated with TKA who had their femoral canal filled using either vancomycin-loaded calcium sulfate bone (experimental group [n = 35]) or the patient's own excised autologous bone (control group [n = 30]) at the Qingdao University Affiliated Hospital, Qingdao, China from January 1, 2017, to March 1, 2023, were retrospectively enrolled in this study. An experienced surgeon used midvastus approach. Surgeries included disinfection, antibiotics, and femoral filling. The age, gender, body mass index (BMI), comorbidities, and intraoperative details were extracted from the patient's medical records. Preoperation and postoperation markers (C-reactive protein [CRP], erythrocyte sedimentation rate [ESR]), pain scale (Visual Analog Scale [VAS]), infection rate, and Knee Society Score (KSS) were collected. Groups matched in age, gender, and BMI. No preoperative inflammatory marker differences were observed. However, compared to the control group, the postoperative inflammatory markers were significantly lower in the experimental group at 1-week postsurgery (CRP: 40.80 ± 23.17 vs. 60.80 ± 43.12 mg/L, p = 0.021; ESR: 72.06 ± 17.52 vs. 83.87 ± 21.52 mm/h, p = 0.012) and at 1-month postsurgery (CRP: 15.63 ± 6.56 vs. 21.17 ± 13.16 mg/L, p = 0.032; ESR: 25.25 ± 20.44 vs. 38.40 ± 25.26 mm/h, p = 0.024). There were no significant differences in the VAS (2.79 ± 0.90 vs. 2.70 ± 0.84 score, p = 0.689) and KSS (64.31 ± 17.88 vs. 66.57 ± 12.36) at 1-month postsurgery. Experimental group: zero infections; control group: only one infection. Administering vancomycin and calcium sulfate during TKA in RA patients reduces postoperative inflammation, but does not significantly affect infection risk; further research may be necessary for validation.

Periprosthetic joint infections: state-of-the-art

In general, periprosthetic joint infection (PJI) is regarded as one of the most common complications of total joint arthroplasty (TJA) and may lead to surgical failure, revision surgery, amputation or death. Nowadays, PJI has become a global health concern, which brings a great burden to public healthcare. In addition, there are still obstacles to achieve high success rates in the prevention, diagnosis and treatment of PJI. However, promising studies are also available with the advancements in biotechnology. This article will present an overview of the current methods used in the prevention, diagnosis and management of PJI while underlining the new technologies utilized.

What Are the Research Highlights of Periprosthetic Joint Infections From the 100 Most Cited Studies?

Background

Periprosthetic joint infections (PJIs) are a serious complication after total joint arthroplasty. Our study aimed to analyze the characteristics and research highlights of the top 100 most cited studies on PJI from an orthopaedic standpoint. Moreover, we sought to assess whether there has been a change in the level of evidence (LOE) throughout time.

Methods

We conducted a search of the PubMed, Embase, and Web of Science databases to identify the top 100 studies primarily focusing on PJI. Study characteristics assessed included publication year, LOE, journal of publication, and type of study. Research highlights of the included studies were classified into 6 sections. Linear regression was employed to assess correlation between LOE and publication year.

Results

The aggregated citation count of all studies was 19,558 and the median citation number was 129.5. While cohort studies were the most prevalent, articles focusing on analysis of costs associated with PJI care or PJI definition garnered the highest yearly citation counts. The bulk of included studies were concentrated in 3 orthopaedic journals and published in the 2010s. The majority of studies had a LOE II (30%) or III (34%). On regression analysis, LOE was not correlated with publication year (Pearson's r = 0.013, P = .61).

Conclusions

The most cited PJI articles assessed the definition of PJI and PJI cost. Despite growing interest in PJI, the majority of studies had LOE II or III, highlighting the difficulty of conducting prospective randomized controlled trials in PJI patients.

Level of evidence

IV.

β-Defensin versus conventional markers of inflammation in periprosthetic joint infection: a retrospective study

Background

Diagnosing periprosthetic joint infection (PJI) remains a significant challenge for healthcare professionals. Commonly utilized inflammatory markers include erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and white blood cells (WBC). Human β-defensin 1 (β-defensin) is an antimicrobial peptide elevated in infection, yet its diagnostic value for PJI has not been explored. The purpose of this study was to evaluate the efficacy of synovial β-defensin as a diagnostic marker for PJI and to compare its performance with ESR, serum CRP, and WBC.

Methods

We conducted a single-center retrospective study from October 2022 to June 2023. A total of 105 joint fluid samples from revision patients at the Instituto Nacional de Rehabilitación Luis Guillermo Ibarra Ibarra were collected intraoperatively (71 hips, 34 knees) and frozen. According to MSIS criteria, 64 patients were defined as positive for PJI and the remaining 41 were negative. Synovial β-defensin levels were quantified using ELISA, serum CRP levels by immunoturbidimetry, and blood ESR and WBC were analyzed. Sensitivity and specificity were determined using ROC curves, and diagnostic performance was compared using the area under the curve (AUC). Cut-off values for diagnosing PJI were established.

Results

Levels of synovial β-defensin, ESR, serum CRP, and WBC were significantly higher in the PJI group compared to the non-PJI (P < 0.0001). The AUCs were 0.948 for β-defensin, 0.884 for ESR, 0.902 for CRP, and 0.767 for WBC, with a combined AUC of 0.994. Sensitivity/specificity for β-defensin, ESR, CRP, and WBC were 0.966/0.830, 0.887/0.791, 0.930/0.771, and 0.820/0.682, respectively. Optimal predictive cut-off values were 1105.8 pg/mL for β-defensin, 11.5 mm/h for ESR, 5.55 mg/L for CRP, and 7.3 × 103/mm3 for WBC.

Conclusion

The synovial β-defensin assay demonstrated greater sensitivity and specificity for the diagnosis of PJI compared to ESR, serum CRP and WBC. Therefore, β-defensin shows promise as a diagnostic marker for PJI. Simultaneous determination of all markers may increase diagnostic confidence.

Analysis of Serum and Synovial Inflammatory Markers in Periprosthetic Joint Infections: A Narrative Review

Periprosthetic joint infection (PJI) is considered a rare but devastating complication after total joint arthroplasty (TJA). The problem lies in the fact that there is a paucity of "gold standard" diagnostic tests that make the diagnosis of PJI extremely challenging. Recently, there have been increasing evidence-based guidelines that have been introduced to standardise the approach to a patient with a suspected PJI. Diagnosing a case of PJI traditionally involves initial screening for elevated serum inflammation markers C-reactive protein (CRP) (mg/dL) and erythrocyte sedimentation rate (ESR), and aspiration remains the sole confirmatory investigation. However, several factors would affect the values of the aforementioned markers, such as gender, age, and the presence of inflammatory circumstances. Serum D-dimer that detects fibrinolytic activities during infection has high sensitivity, but the specificity was not persuasive as it would elevate during other conditions, such as venous thromboembolism. Therefore, there is also a need for a simultaneous and secondary marker. There are also several synovial biomarkers, including ESR, CRP, alpha-defensin, and synovial fluid leukocyte count and differential for the detection of PJI. In this narrative review, we want to sum up the serum and inflammatory markers that have been introduced so far for detecting PJI.

Assessing the predictive value of pre- and post-operative inflammatory markers in patients undergoing total knee arthroplasty

BACKGROUND AND OBJECTIVE

Total Knee Arthroplasty (TKA) has proven highly effective in improving quality of life for patients with severe knee conditions. Despite advancements, surgical complications such as periprosthetic joint infections (PJIs) pose risks. The potential predictive value of pre- and post-operative inflammatory markers like neutrophil-to-lymphocyte ratio (NLR), D-dimer, and albumin levels on surgical outcomes is garnering attention. There is a growing interest in leveraging these markers to enhance patient selection and outcome prediction in the context of TKA.Focusing on the natural course of these markers, and the incidence of PJIs and to refine perioperative care strategies, improve patient outcomes, and identify high-risk patients for targeted intervention.

METHODS

The study included 94 patients who underwent total knee arthroplasty (TKA) between 2019 and 2023. Blood tests were conducted before surgery and at 1, 3, 7, and 15 days after surgery to assess various parameters including white blood cell count, neutrophils, lymphocytes, platelets, hemoglobin, C-reactive protein, D-dimers, total protein, albumin, and total cholesterol values and ratios.

RESULTS

Following total knee arthroplasty (TKA), key observations in blood markers included a sharp rise in white blood cell (WBC) counts from 5.81 to 10.22 (*10^9/L) on the first day post-surgery, with levels returning close to preoperative values by day-15. Neutrophil counts similarly increased from 3.46 to 8.50 (*10^9/L) on day-1, decreasing to 4.01 by day-15. Hemoglobin levels significantly decreased from 115.70 g/L to 90.62 by day-3 before improving to 100.30 by day-15. C-reactive protein (CRP) levels also saw a significant rise from 6.15 mg/L to a peak of 47.07 on day-3, then reducing to 10.55 by day-15, indicating a response to inflammation.

CONCLUSION

Following total knee arthroplasty (TKA), a significant initial postoperative increase in white blood cell count, neutrophils, and C-reactive protein levels, indicative of an acute inflammatory response, before returning towards baseline values by day 15. Hemoglobin levels displayed a notable dip post-surgery, gradually improving by the study's end. These patterns emphasize the dynamic nature of inflammatory and hematological responses after TKA, highlighting their potential role in predicting surgical outcomes and guiding postoperative care.

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

BACKGROUND

To 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.

METHODS

Patients 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.

RESULTS

Patients 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.

CONCLUSIONS

Synovial 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.

Multiplex cytokine analysis for the identification of novel potential synovial fluid biomarkers for periprosthetic joint infections

INTRODUCTION

Periprosthetic joint infections (PJIs) are a devastating complication of total hip (THA) and knee (TKA) arthroplasty. The use of novel techniques like multiplex cytokine analysis could contribute immensely to the identification of potential novel biomarkers.

PATIENTS AND METHODS

This is a single-centre study of patients that were treated with revision TKA, THA or hemiarthroplasty. Serum's white blood cells (WBCs), erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) and synovial fluid's WBCs, percentage of polymorphonuclear neutrophils (%PMNs) and CRP were measured. Proteomic analysis targeting the secreted cytokines in synovial fluid was conducted using a 73-plex assay panel. The results were statistically compared between the septic and aseptic cases and ROC analysis to establish the area under the curve (AUC), sensitivity and specificity of each biomarker.

RESULTS

The study included 30 patients (18 revision THA cases; 3 conversion of hemiarthroplasty to THA and 9 revision TKA cases); 14 cases were considered infected, 1 likely infected and 15 not infected. The results showed statistically significant differences (p < 0.05) between infected and not infected cases in serum's ESR, CRP and synovial fluid's%PMNs, growth-regulated oncogene alpha (GROA), interleukin-8, interleukin-5, S100-A8/calprotectin and resistin (RETN) with AUCs of 0.75, 0.72, 0.95, 0.75, 0.72, 0.95, 0.83, 0.73, 0.75, 0.81 and 0.76 respectively.

CONCLUSIONS

In the present study, serum ESR and CRP as well as synovial %PMNs, GROA, IL-8, IL-5, calprotectin and RETN protein levels were identified as potential biomarkers. Further studies are needed to further investigate their diagnostic utility and optimal cut-off values.

Serum and Synovial Markers in the Diagnosis of Periprosthetic Joint Infection of the Hip, Knee, and Shoulder: An Algorithmic Approach

➤ No single test has demonstrated absolute accuracy for the diagnosis of periprosthetic joint infection (PJI).➤ Physicians rely on a combination of serological tests, synovial markers, and clinical findings plus clinical judgment to help to guide preoperative decision-making.➤ Several organizations have proposed criteria for the diagnosis of hip or knee PJI on which we now rely.➤ Given that shoulder arthroplasty has only recently become popular, it is possible that a shoulder-specific definition of PJI will be introduced in the coming years.➤ Although a number of serum and synovial markers have demonstrated high accuracy for the diagnosis of PJI of the hip and knee, further research is needed in order to identify markers that may be more suitable for the diagnosis of shoulder PJI and for the potential development and identification of specific serological tests as screening tools for PJI.

An overview of the current diagnostic approach to Periprosthetic Joint Infections

The diagnosis of periprosthetic joint infections (PJI) presents a formidable challenge to orthopaedic surgeons due to its complex and diverse manifestations. Accurate diagnosis is of utmost importance, as even mild pain following joint replacement surgery may indicate PJI in the absence of a definitive gold standard diagnostic test. Numerous diagnostic modalities have been suggested in the literature, and international societies have continually updated diagnostic criteria for this debilitating complication. This review article aims to comprehensively examine the latest evidence-based approaches for diagnosing PJI. Through a thorough analysis of current literature, we explore promising diagnostic strategies that have demonstrated effectiveness in identifying PJI. These strategies encompass the utilization of laboratory markers, such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), alongside imaging techniques such as magnetic resonance imaging (MRI) and leukocyte scintigraphy. Additionally, we highlight the importance of synovial fluid analysis, including the potential role of alpha-defensin as a biomarker, and examine evolving international diagnostic criteria to standardize and improve diagnostic accuracy.

Interleukin-1β Polymorphisms Are Genetic Markers of Susceptibility to Periprosthetic Joint Infection in Total Hip and Knee Arthroplasty

Periprosthetic joint infections (PJIs) are serious complications of prosthetic surgery. The criteria for the diagnosis of PJI integrate clinical and laboratory findings in a complex and sometimes inconclusive workflow. Host immune factors hold potential as diagnostic biomarkers in bone and joint infections. We reported that the humoral pattern-recognition molecule long pentraxin 3 (PTX3) predicts PJI in total hip and knee arthroplasty (THA and TKA, respectively). If and how genetic variation in PTX3 and inflammatory genes that affect its expression (IL-1β, IL-6, IL-10, and IL-17A) contributes to the risk of PJI is unknown. We conducted a case-control study on a Caucasian historic cohort of THA and TKA patients who had prosthesis explant due to PJI (cases) or aseptic complications (controls). Saliva was collected from 93 subjects and used to extract DNA and genotype PTX3, IL-1β, IL-6, IL-10, and IL-17A single-nucleotide polymorphisms (SNPs). Moreover, the concentration of IL-1β, IL-10, and IL-6 was measured in synovial fluid and plasma. No association was found between PTX3 polymorphisms and PJI; however, the AGG haplotype, encompassing rs2853550, rs1143634, and rs1143627 in IL-1β, was linked to the infection (p = 0.017). Also, synovial levels of all inflammatory markers were higher in cases than in controls, and a correlation emerged between synovial concentration of PTX3 and that of IL-1β in cases only (Spearman r = 0.67, p = 0.004). We identified a relationship between rs2853550 and the synovial concentration of IL-1β and PTX3. Our findings suggest that IL-1β SNPs could be used for the early identification of THA and TKA patients with a high risk of infection.

Update on the role of pathology and laboratory medicine in diagnosing periprosthetic infection

Technological and implant design advances have helped reduce the frequency of aseptic total joint arthroplasty failure, but periprosthetic joint infections (PJI) remain a clinical important problem with high patient morbidity. Misinterpreting PJI as aseptic mechanical loosening commonly leads to unsatisfactory revision arthroplasty, persistent infection, and poor long-term results. While there is no single "gold standard" diagnostic test for PJI, recent collaborative efforts by Orthopaedic and Infectious Disease Societies have developed algorithms for diagnosing PJI. However, the efficacy of individual tests as well as diagnostic thresholds are controversial. We review the recommended thresholds for commonly used screening tests as well as tissue histopathology and confirmatory tests to diagnose periprosthetic infection. We also update lesser-known laboratory tests, and we briefly summarize rapidly evolving molecular tests to diagnose periprosthetic infection. Pathologists hold a critical role in assisting with PJI diagnosis, maintaining laboratory test quality and interpreting test results. Collaboration between clinicians and pathologists is essential to provide optimal patient care and reduce the burden of PJI.

Advancing the Diagnosis of Periprosthetic Joint Infections: Integrated Microfluidic Platform for Alpha-Defensins-Specific Aptamer Selection and Its Analytical Applications

Periprosthetic joint infections (PJIs) pose a significant challenge in orthopedic surgery, particularly total joint arthroplasty (TJA), due to the potential for implant failure and increased patient morbidity. Early and accurate detection of PJIs is crucial for timely intervention and better patient prognosis. Herein, we successfully screened a high-affinity aptamer targeting alpha-defensin complex human neutrophil protein 1-3 (HNP 1-3; potential PJI biomarkers in synovial fluid [SF]) for the first time using systematic evolution of ligands by exponential enrichment (SELEX) on an integrated microfluidic platform. The compact microfluidic device enabled efficient screening, with each round completed within <2 h, comprising five rounds of positive selection, two rounds of negative selection, and one round of competitive selection. A novel one-aptamer-one-antibody assay was further developed from the optimal aptamer screened, and it could accurately quantify HNP 1-3 in SF within 3 h with only ∼50 μL of SF. The assay demonstrated strong binding affinity and specificity for the target protein in SF. Thirteen PJI SF samples were accurately diagnosed and the assay was accurate over a wide dynamic range (0.32-100 mg/L). This study has showcased a rapid and accurate diagnostic tool for PJI detection, which should see widespread use in the clinic, holding promise for potential analytical applications in orthopedic surgery and improving patient care.

Diagnostics in Late Periprosthetic Infections-Challenges and Solutions

The rising number of arthroplasties is combined with a rising number of periprosthetic joint infections, which leads to life-concerning consequences for the patients, including extended antibiotic treatment, further surgery and increased mortality. The heterogeneity of the symptoms and inflammatory response of the patients due to, e.g., age and comorbidities and the absence of a single diagnostic test with 100% accuracy make it very challenging to choose the right parameters to confirm or deny a periprosthetic joint infection and to establish a standardized definition. In recent years, additional diagnostic possibilities have emerged primarily through the increasing availability of new diagnostic methods, such as genetic techniques. The aim of the review is to provide an overview of the current state of knowledge about the various tests, including the latest developments. The combination of different tests increases the accuracy of the diagnosis. Each physician or clinical department must select the tests from the available methods that can be best implemented for them in organizational and technical terms. Serological parameters and the cultivation of the samples from aspiration or biopsy should be combined with additional synovial tests to create an accurate figure for the failure of the prosthesis, while imaging procedures are used to obtain additional information for the planned therapeutic procedure.

Diagnostic Evaluation of Prosthetic Joint Infections of the Shoulder: What Does the Literature Say?

The total number of patients with a total shoulder arthroplasty (TSA) is increasing, and the number of patients experiencing a (TSA) prosthetic joint infection (PJI) also will increase. It is important that physicians know how to identify signs of infection, know the common pathogens, and know how to work up a shoulder PJI. This publication reviewed the current literature about presenting signs and symptoms, common shoulder pathogens and how they differ from total knee and hip pathogens, and what images, tests, and procedures can aid in identification of infection.

Diagnosis and Management of Infected Total Ankle Replacements

As the number of primary total ankle replacements increases for treatment of end-stage ankle arthritis, failures are also expected to rise. Periprosthetic joint infection is among the causes of failures and has been reported to be as high as 5%. Diagnosis is usually made by a combination of clinical examination findings, imaging, laboratory, and microbiological workup. Management is generally separated into limb salvage or amputation. Limb salvage can be challenging and may involve a single versus staged approach. Options include revision arthroplasty or arthrodesis procedures (ankle versus tibiotalocalcaneal), and a multidisciplinary approach is sought to eradicate infection before definitive management.

Synovial Fluid C-reactive Protein Clinical Decision Limit and Diagnostic Accuracy for Periprosthetic Joint Infection

Introduction C-reactive protein (CRP) has long served as a prototypical biomarker for periprosthetic joint infection (PJI). Recently, synovial fluid (SF)-CRP has garnered interest as a diagnostic tool, with several studies demonstrating its diagnostic superiority over serum CRP for the diagnosis of PJI. Although previous studies have identified diagnostic thresholds for SF-CRP, they have been limited in scope and employed various CRP assays without formal validation for PJI diagnosis. This study aimed to conduct a formal single clinical laboratory validation to determine the optimal clinical decision limit of SF-CRP for the diagnosis of PJI. Methods A retrospective analysis of prospectively collected data was performed using receiver operating characteristic (ROC) and area under the curve (AUC) analyses. Synovial fluid samples from hip and knee arthroplasties, received from over 2,600 institutions, underwent clinical testing for PJI at a single clinical laboratory (CD Laboratories, Zimmer Biomet, Towson, MD) between 2017 and 2022. Samples were assayed for SF-CRP, alpha-defensin, white blood cell count, neutrophil percentage, and microbiological culture. After applying selection criteria, the samples were classified with the 2018 ICM PJI scoring system as "infected," "not infected," or "inconclusive." Data were divided into training and validation sets. The Youden Index was employed to optimize the clinical decision limit. Results A total of 96,061 samples formed the training (n = 67,242) and validation (n = 28,819) datasets. Analysis of the biomarker median values, culture positivity, anatomic distribution, and days from aspiration to testing revealed nearly identical specimen characteristics in both the training set and validation set. SF-CRP demonstrated an AUC of 0.929 (95% confidence interval (CI): 0.926-0.932) in the training set, with an optimal SF-CRP clinical decision limit for PJI diagnosis of 4.45 mg/L. Applying this cutoff to the validation dataset yielded a sensitivity of 86.1% (95% CI: 85.0-87.1%) and specificity of 87.1% (95% CI: 86.7-87.5%). No statistically significant difference in diagnostic performance was observed between the validation and training sets. Conclusion This study represents the largest single clinical laboratory evaluation of an SF-CRP assay for PJI diagnosis. The optimal CRP cutoff (4.45 mg/L) for PJI, which yielded a sensitivity of 86.1% and a specificity of 87.1%, is specific to the assay methodology and laboratory performing the assay. We propose that an SF-CRP test with a laboratory-validated optimal clinical decision limit for PJI may be preferable, in a clinical diagnostic setting, to serum CRP tests that do not have laboratory-validated clinical decision limits for PJI.

Are C-reactive protein (CRP) and neutrophil to lymphocyte ratio (NLR) predictive markers of successful two-stage prosthetic joint infection management?

The treatment of prosthetic joint infections (PJI) regularly involves a two-stage surgical strategy. The second stage is generally performed when the surgeon estimates that the infection is under control based on either the treatment length or clinical and biological data. We have raised the question whether standardization of C-reactive protein (CRP) and neutrophil to lymphocyte ratio (NLR) values could be either indicative of infection control or predictive of infection recurrence. This was an analytical retrospective and monocentric cross-sectional observational study. The CRP and NLR values were recorded prior to the second-stage surgery in a sample of 100 patients who underwent a two-stage revision arthroplasty following a PJI, and these values were correlated with the absence of infectious recurrence within a 2-year follow-up. The statistical analysis consisted of evaluating the diagnostic validity of each marker, first individually, and then in combination. CRP was shown associated with a 68% sensitivity, 40% specificity, 27% positive predictive value (PPV), and 79% negative predictive value (NPV). The ROC curve was 51.1%. The NLR displayed a 12% sensitivity, 89% specificity, 27% PPV, and 75% NPV. The ROC curve was 47.9%. The combination of the two markers did not fundamentally improve the statistical results, with only a 43% concordance of the two markers, 27% sensitivity, 84% specificity, 37% PPV, and 77% NPV. Measuring CRP and NLR values, either individually or in combination, before the second-stage revision arthroplasty did not turn out to be predictive of either infection recurrence or cure within two years of follow-up. Therefore, an absolute test is still lacking, which would enable us to predict without failure the absence of control or the control of a PJI before or after second-stage revision. Level of evidence: Level III, retrospective cross-sectional study.

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.

A paper-based aptamer-sandwich assay for detection of HNP 1 as a biomarker for periprosthetic joint infections on an integrated microfluidic platform

BACKGROUND

Total joint arthroplasty (TJA) has significantly improved the quality of life for millions suffering from end-stage arthritis. However, periprosthetic joint infections (PJI) remain a serious complication, necessitating extensive interventions and prolonged antimicrobial treatments. The aging population is expected to lead to a rise in TJA cases, subsequently increasing the incidence of PJI, particularly in the elderly who face higher mortality rates. Current diagnostic methods for suspected PJI, such as radiographs and biochemical markers like CRP and ESR, exhibit limited sensitivity. Therefore, there is a critical need for a specific synovial fluid biomarker assay to enhance PJI diagnosis using specific SF-based assay.

RESULTS

This study introduces a novel microfluidic chip with a paper-based aptamer-sandwich assay for the quantitative detection of HNP 1, a crucial PJI biomarker, in synovial fluid. The assay leverages the advantages of aptamers over antibodies, demonstrating high selectivity and affinity for target molecules. The integration of a nitrocellulose (NC) membrane onto the microfluidic platform represents a significant advancement, reducing background signals and simplifying the assay procedure without intricate procedure and pre-treatment. The NC membrane-based microfluidic device offers rapid, cost-effective, and highly sensitive detection of HNP 1, with a limit of detection of 0.5 mg L-1. The microfluidic device demonstrates exceptional performance, detecting up to four clinical samples in approximately 42 min on a single chip with 100 % accuracy, as confirmed by analysis of 12 clinical samples and comparison with "gold-standard". Moreover, the assay exhibits a wide dynamic range of 0.5-100 mg L-1, underscoring its potential as a powerful tool for PJI diagnosis in clinical settings.

SIGNIFICANCE

This work introduces a paper-based microfluidic system tailored for rapid HNP 1 detection using synovial fluid near joint region (and not serum via blood) for better diagnosis. The innovative paper-based aptamer-sandwich assay yields results within 42-min. Significantly, it boasts a wide dynamic range, detecting levels from an impressive 0.5 mg L-1, crucial in the 2.6 mg L-1 threshold region. This heightened sensitivity and expansive detection capability establish our assay as a leader in PJI diagnostics, promising unmatched precision and efficiency in clinical applications.

ACR Appropriateness Criteria® Imaging After Total Knee Arthroplasty: 2023 Update

Total knee arthroplasty is the most commonly performed joint replacement procedure in the United States. This manuscript will discuss the recommended imaging modalities for six clinical variants; 1. follow-up of symptomatic or asymptomatic patients with a total knee arthroplasty. Initial imaging, 2. Suspected infection after total knee arthroplasty. Additional imaging following radiographs, 3. Pain after total knee arthroplasty. Infection excluded. Suspect aseptic loosening or osteolysis or instability. Additional imaging following radiographs, 4. Pain after total knee arthroplasty. Suspect periprosthetic or hardware fracture. Additional imaging following radiographs, 5. Pain after total knee arthroplasty. Measuring component rotation. Additional imaging following radiographs, and 6. Pain after total knee arthroplasty. Suspect periprosthetic soft-tissue abnormality unrelated to infection, including quadriceps or patellar tendinopathy. Additional imaging following radiographs. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

Utility of Blood Cell Ratio Combinations for Diagnosis of Periprosthetic Joint Infection

Background

Periprosthetic joint infection (PJI) is a serious complication following joint replacement surgery, and its diagnosis can be challenging due to the similarity of symptoms to other conditions and the lack of confirmatory imaging tests. Platelet/mean platelet volume ratio (PVR), platelet/lymphocyte ratio, monocyte/lymphocyte ratio, and neutrophil/lymphocyte ratio have been proposed as potential markers to aid in the diagnosis of PJI. This study aimed to further assess the utility of these blood cell ratio combinations for the diagnosis of PJI.

Methods

A retrospective chart review was conducted on patients who presented to a university hospital for evaluation for PJI or underwent aseptic revision surgery. All patients were reviewed for inclusion in the study. Data were collected on several markers, including complete blood counts, synovial fluid white blood cell count, and polymorphonuclear percentage. Receiver operator characteristic curve analysis was used to evaluate the diagnostic capabilities of the markers and marker combinations.

Results

The combination of erythrocyte sedimentation rate, C-reactive protein, synovial white blood cell count, and synovial polymorphonuclear percentage, with PVR, had the highest area under the curve of 0.97, with a sensitivity of 94.3% and a specificity of 88.9%, and a positive predictive value of 97.1% and a negative predictive value of 80.0%.

Conclusions

This study further supports the use of PVR calculated from complete blood count commonly ordered laboratory values obtained during routine complete blood counts when combined with established serum and synovial markers to increase the diagnostic accuracy for diagnosing PJI.

Periprosthetic Joint Infection Diagnosis: A Narrative Review

Replacement of native joints aims to restore patients' quality of life by relieving pain and improving joint function. While periprosthetic joint infection (PJI) affects a small percentage of patients, with an estimated incidence of 1-9% following primary total joint replacement, this postoperative complication necessitates a lengthy hospitalisation, extended antibiotic treatment and further surgery. It is highlighted that establishing the correct diagnosis of periprosthetic infections is critical in order for clinicians to avoid unnecessary treatments in patients with aseptic failure. Of note, the PJI diagnosis could not purely rely upon clinical manifestations given the fact that heterogeneity in host factors (e.g., age and comorbidities), variability in infection period, difference in anatomical location of the involved joint and discrepancies in pathogenicity/virulence of the causative organisms may confound the clinical picture. Furthermore, intra-operative contamination is considered to be the main culprit that can result in early or delayed infection, with the hematogenous spread being the most prevalent mode. To elaborate, early and hematogenous infections often start suddenly, whereas chronic late infections are induced by less virulent bacteria and tend to manifest in a more quiescent manner. Last but not least, viruses and fungal microorganisms exert a role in PJI pathogenesis.

Joint aspiration for diagnosis of chronic periprosthetic joint infection: when, how, and what tests?

Diagnosing chronic periprosthetic joint infection (PJI) requires clinical suspicion in combination with both serological and synovial fluid tests, the results of which are generally applied to validated scoring systems or consensus definitions for PJI. As no single "gold standard" test exists, the diagnosis becomes challenging, especially in the setting of negative cultures or equivocal test results. This review aims to address the workup of chronic PJI and considerations for clinical evaluation to guide treatment. Following aspiration of the joint in question, a multitude of tests has been developed in an attempt to assist with diagnosis, including cell synovial white blood cell count, gram stain, cultures, leukocyte esterase, alpha-defensin, synovial C-reactive protein, multiplex polymerase chain reaction, next-generation sequencing, and interleukins. Each test has advantages and disadvantages and should be used in conjunction with the overall clinical picture to guide further clinical evaluation and treatment in this complex patient population.

Current relevance of biomarkers in diagnosis of periprosthetic joint infection: an update

With a significant rise in the number of arthroplasty procedures performed worldwide, the increasing revision burden posed by periprosthetic joint infection (PJI) is a matter of growing concern. In spite of various attempts to diagnose PJI, there are no defined tests that can be called a gold standard. Given the importance of early diagnosis in PJI, newer tests and biomarkers have been introduced to improve cumulative diagnostic accuracy. Novel biomarkers like calprotectin, lipocalcin, monocyte-to-lymphocyte ratio, neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio and platelet-to-mean platelet volume ratio have demonstrated a potential as diagnostic biomarkers for PJI. This article discusses the relevance of available and newly described diagnostic biomarkers to provide a perspective on the practical applicability in current medical practice, as well as highlights some recent advances in biomarkers for the diagnosis of PJI.

Emerging Technologies in Diagnosing Periprosthetic Joint Infections

Periprosthetic joint infection (PJI) is a well-known serious complication following joint replacement surgeries and is responsible for high failure rates of implanted devices. Any delay in the diagnosis can compromise treatment success, putting a huge burden on the patients' wellness and healthcare systems. Diagnosing PJIs is quite complex as there is still no gold standard test to reach the definitive diagnosis in a timely manner. A number of laboratory tests and radiological imaging inventions have evolved in the past few years, requiring consistent updates of the available guidelines to keep up with the latest advances in the field. This article highlights the recent advances in diagnosing PJIs and discusses their validity for use in clinical practice.

Mitigating Concerns Over Transport Delays: An Analysis of Synovial Fluid Culture Results in Arthroplasty

INTRODUCTION

 There is a concern in the field of arthroplasty that synovial fluid transport delays may reduce the accuracy of synovial fluid culture. However, synovial fluid samples collected in the office, and sometimes in a hospital setting, often require transport to a third-party central or specialty laboratory, causing delays in the initiation of culture incubation. This study investigated the impact of transportation delays on synovial fluid culture results.

METHODS

 A retrospective review of prospectively collected data at one clinical laboratory, from 2016 to 2022, was conducted. A total of 125,270 synovial fluid samples from knee arthroplasties, from 2,858 different US institutions, were transported to a single clinical laboratory for diagnostic testing including synovial fluid culture (blood culture bottles). Synovial fluid to be cultured was transported in red top tubes without additives. Samples were grouped into six-time cohorts based on the number of days between aspiration and culture initiation (1-day-delay to 6-day-delay). Metrics such as culture positivity, false-positive culture rate, culture sensitivity, and proportional growth of top genera of organisms were assessed across the cohorts.

RESULTS

 Of the 125,270 samples in this study, 71.2% were received the day after aspiration (1-day-delay), with an exponential decrease in samples received on each subsequent day. Culture-positive rates for synovial fluid samples received after 1, 2, 3, 4, 5, and 6 days of transport time were 12.2%, 13.3%, 13.5%, 13.1%, 11.6%, and 11.0%, respectively. The maximum absolute difference in culture-positive rate compared to the 1-day-delay cohort was an increase of 1.3% in the 3-day-delay cohort, which was not considered a clinically meaningful difference. The estimated false-positive culture rate remained relatively consistent across time cohorts, with values of 0.3%, 0.4%, 0.3%, 0.2%, 0.5%, and 0.5% for 1, 2, 3, 4, 5, and 6 days of transport time, respectively. None of the cohorts showed a statistically significant difference after adjustment for multiplicity compared to the 1-day-delay cohort. Culture sensitivity was estimated at 68.2%, 67.2%, 70.5%, 70.7%, 65.9%, and 70.7% for 1, 2, 3, 4, 5, and 6 days of transport time, respectively. None of the cohorts showed a statistically significant difference after adjustment for multiplicity compared to the 1-day-delay cohort. Organism proportions were consistent across time cohorts, with Staphylococcus being the most commonly identified organism. No statistically significant differences were found in the proportional contribution of major genera across the cohorts.

CONCLUSIONS

 Synovial fluid culture exhibited surprisingly consistent results despite variable transport time to the destination laboratory, with differences that have minimal clinical importance. While the authors of this study advocate for short transport times as a best practice to expedite diagnosis, it appears that concerns regarding the rapid degradation of culture results due to synovial fluid transportation is unwarranted.

Two-stage revision in periprosthetic knee joint infections

Periprosthetic joint infection (PJI) following total knee arthroplasty is one of the most catastrophic and costly complications that carries significant patient wellness as well as economic burdens. The road to efficiently diagnosing and treating PJI is challenging, as there is still no gold standard method to reach the diagnosis as early as desired. There are also international controversies with respect to the best approach to manage PJI cases. In this review, we highlight recent advances in managing PJI following knee arthroplasty surgery and discuss in depth the two-stage revision method.

Host Immune Regulation in Implant-Associated Infection (IAI): What Does the Current Evidence Provide Us to Prevent or Treat IAI?

The number of orthopedic implants for bone fixation and joint arthroplasty has been steadily increasing over the past few years. However, implant-associated infection (IAI), a major complication in orthopedic surgery, impacts the quality of life and causes a substantial economic burden on patients and societies. While research and study on IAI have received increasing attention in recent years, the failure rate of IAI has still not decreased significantly. This is related to microbial biofilms and their inherent antibiotic resistance, as well as the various mechanisms by which bacteria evade host immunity, resulting in difficulties in diagnosing and treating IAIs. Hence, a better understanding of the complex interactions between biofilms, implants, and host immunity is necessary to develop new strategies for preventing and controlling these infections. This review first discusses the challenges in diagnosing and treating IAI, followed by an extensive review of the direct effects of orthopedic implants, host immune function, pathogenic bacteria, and biofilms. Finally, several promising preventive or therapeutic alternatives are presented, with the hope of mitigating or eliminating the threat of antibiotic resistance and refractory biofilms in IAI.

The Challenge of Periprosthetic Joint Infection Diagnosis: From Current Methods to Emerging Biomarkers

Due to the increase in the life span and mobility at older ages, the number of implanted prosthetic joints is constantly increasing. However, the number of periprosthetic joint infections (PJIs), one of the most severe complications after total joint arthroplasty, also shows an increasing trend. PJI has an incidence of 1-2% in the case of primary arthroplasties and up to 4% in the case of revision operations. The development of efficient protocols for managing periprosthetic infections can lead to the establishment of preventive measures and effective diagnostic methods based on the results obtained after the laboratory tests. In this review, we will briefly present the current methods used in PJI diagnosis and the current and emerging synovial biomarkers used for the prognosis, prophylaxis, and early diagnosis of periprosthetic infections. We will discuss treatment failure that may result from patient factors, microbiological factors, or factors related to errors during diagnosis.

An aptamer-based sandwich assay for detection of alpha-defensin human neutrophil protein 1 on a microfluidic platform

The diagnosis of periprosthetic joint infection (PJI) remains a labor-intensive and challenging issue, with life-threatening complications associated with misdiagnoses. Superior diagnostic approaches are therefore urgently needed, and synovial biomarkers are gaining substantial attention in this capacity. A new aptamer-based sandwich assay was developed where the aptamer probes specific to one such biomarker, alpha-defensin human neutrophil protein 1 (HNP 1), was integrated herein into a new microfluidic platform. The magnetic beads coated with the primary aptamer probe were able to bind the target protein with high affinity and high specificity in synovial fluid and a fluorescent-labelled secondary aptamer were further used to quantify HNP 1 in a sandwich approach. Up to four clinical samples with low volume (∼50 μL each) in a much faster assay including detection within <60 min with 100% accuracy (with totally 13 clinical samples without the need of sample pretreatment) through the use of the aptamer-based sandwich assay were automatically detected on a single chip. The wide dynamic range of this compact device, 0.5-100 mg/L, highlights its utility for future PJI diagnostics in the clinic.

Wound alpha defensin levels are significantly higher in patients with fracture related infection: A pilot, prospective cohort study

BACKGROUND

In absence of frank purulence, wound cultures represent 'gold-standard' for diagnosis of fracture related infection (FRI). However, these are time-intensive, and may be falsely negative, necessitating the need for accurate and rapid biomarker-based diagnosis. We conducted this study to determine the accuracy of 3 wound-based biomarkers for the diagnosis of FRI.

METHODS

This was a prospective cohort study on adult patients who underwent an operative procedure for an upper or lower limb fracture. Wound fluid levels of alpha-defensin (AD), neutrophil elastase (NE) and IL-6 were evaluated on post-operative day 2, and patients were followed up for one month. Patients were categorized as cases (FRI) or controls (no FRI), on the basis of the consensus definition of FRI. Univariate analysis, along with receiver operating characteristic (ROC) analysis was performed.

RESULTS

48 patients were included. AD levels showed a 2.6-fold elevation in cases (n = 26, Median = 23.74 µg/ml) as compared to controls (n = 22, Median = 8.78 µg/ml). The area under the curve for this variable was 0.71 (95% Confidence Intervals = 0.56 - 0.86). The levels of NE and IL-6 were not significantly different between cases and controls.

CONCLUSION

Wound AD levels are significantly elevated in patients with FRI. However, these results need to be validated in a larger cohort of patients before it can be used as a biomarker of FRI.

Profiling the Immune Response to Periprosthetic Joint Infection and Non-Infectious Arthroplasty Failure

Arthroplasty failure is a major complication of joint replacement surgery. It can be caused by periprosthetic joint infection (PJI) or non-infectious etiologies, and often requires surgical intervention and (in select scenarios) resection and reimplantation of implanted devices. Fast and accurate diagnosis of PJI and non-infectious arthroplasty failure (NIAF) is critical to direct medical and surgical treatment; differentiation of PJI from NIAF may, however, be unclear in some cases. Traditional culture, nucleic acid amplification tests, metagenomic, and metatranscriptomic techniques for microbial detection have had success in differentiating the two entities, although microbiologically negative apparent PJI remains a challenge. Single host biomarkers or, alternatively, more advanced immune response profiling-based approaches may be applied to differentiate PJI from NIAF, overcoming limitations of microbial-based detection methods and possibly, especially with newer approaches, augmenting them. In this review, current approaches to arthroplasty failure diagnosis are briefly overviewed, followed by a review of host-based approaches for differentiation of PJI from NIAF, including exciting futuristic combinational multi-omics methodologies that may both detect pathogens and assess biological responses, illuminating causes of arthroplasty failure.

C9 immunostaining as a tissue biomarker for periprosthetic joint infection diagnosis

Background

Culture-negative periprosthetic joint infections (PJI) are often false diagnosed as aseptic implant failure leading to unnecessary revision surgeries due to repeated infections. A marker to increase the security of e PJI diagnosis is therefore of great importance. The aim of this study was to test C9 immunostaining of periprosthetic tissue as a novel tissue-biomarker for a more reliable identification of PJI, as well as potential cross-reactivity.

Method

We included 98 patients in this study undergoing septic or aseptic revision surgeries. Standard microbiological diagnosis was performed in all cases for classification of patients. Serum parameters including C-reactive protein (CRP) serum levels and white blood cell (WBC) count were included, and the periprosthetic tissue was immunostained for C9 presence. The amount of C9 tissue staining was evaluated in septic versus aseptic tissue and the amount of C9 staining was correlated with the different pathogens causing the infection. To exclude cross-reactions between C9 immunostaining and other inflammatory joint conditions, we included tissue samples of a separate cohort with rheumatoid arthritis, wear particles and chondrocalcinosis.

Results

The microbiological diagnosis detected PJI in 58 patients; the remaining 40 patients were classified as aseptic. Serum CRP values were significantly increased in the PJI cohort. Serum WBC was not different between septic and aseptic cases. We found a significant increase in C9 immunostaining in the PJI periprosthetic tissue. To test the predictive value of C9 as biomarker for PJI we performed a ROC analyses. According to the Youden's criteria C9 is a very good biomarker for PJI detection with a sensitivity of 89% and a specificity of 75% and an AUC of 0.84. We did not observe a correlation of C9 staining with the pathogen causing the PJI. However, we observed a cross reactivity with the inflammatory joint disease like rheumatoid arthritis and different metal wear types. In addition, we did not observe a cross reactivity with chondrocalcinosis.

Conclusion

Our study identifies C9 as a potential tissue-biomarker for the identification of PJI using immunohistological staining of tissue biopsies. The use of C9 staining could help to reduce the number of false negative diagnoses of PJI.

Serum versus synovial fluid interleukin-6 for periprosthetic joint infection diagnosis: a systematic review and meta-analysis of 30 diagnostic test accuracy studies

BACKGROUND

Early and accurate detection of periprosthetic joint infection (PJI) after hip and/or knee arthroplasty remains challenging. This systematic review and meta-analysis of diagnostic test accuracy studies aimed to evaluate the diagnostic accuracy of serum and synovial fluid interleukin (IL)-6 in detecting PJI.

METHODS

We searched 3 databases for studies through December 31, 2021, using medical sub-headings terms and keywords. Studies reported sensitivity and specificity of serum and synovial fluid IL-6 in detecting PJI were considered. We calculated the pooled sensitivity, specificity, positive and negative likelihood ratio, diagnostic odds ratio (DOR), and the area under the summary receiver operating characteristic curve (AUC) to evaluate the diagnostic accuracy of serum and synovial fluid IL-6.

RESULTS

Thirty studies were included. The pooled sensitivity, specificity, positive and negative likelihood ratio, DOR, and AUC of serum IL-6 in detecting PJI were 0.76 (0.69-0.81), 0.88 (0.82-0.92), 6.2 (4.3-9.0), 0.28 (0.22-0.35), 22 (14-36), and 0.88 (0.85-0.91), respectively. However, synovial fluid IL-6 achieved a pooled sensitivity of 0.87 (0.75-0.93), specificity of 0.90 (0.85-0.93), positive and negative likelihood ratio of 8.5 (5.3-13.6) and 0.15 (0.08-0.29), DOR of 57 (21-156), and AUC of 0.94 (0.92-0.96), which were higher than serum IL-6.

CONCLUSIONS

Synovial fluid IL-6 test may be a promising test for PJI after hip and/or knee arthroplasty. However, considering the limited volume of synovial fluid and invasive acquisition of synovial fluid IL-6, serum IL-6 test may be also considered.

Neutrophil Gelatinase-Associated Lipocalin in Synovial Fluid from Horses with and without Septic Arthritis

Neutrophil gelatinase-associated lipocalin (NGAL) has been suggested to be a highly sensitive and specific marker of joint infection in humans. The aim of the study was to investigate NGAL concentrations in synovial fluid (SF) from horses with septic synovitis, horses without septic synovitis, and horses with uncertain status. NGAL was measured in 177 admission samples obtained from 152 horses. From a subset of horses (n = 35), additional samples obtained sequentially over the course of treatment were available. Concentrations of NGAL were significantly higher in septic synovitis (n = 47 samples) than in samples classified as non-septic (n = 103) or samples with uncertain status (n = 27), with median NGAL concentrations in the three groups being 1236, 16.8, and 266.4 µg/L, respectively. NGAL discriminated nearly perfectly between septic and non-septic (area under the receiver operating characteristic curve 0.98, 95% confidence interval 0.95-1.00). The optimal cut-off value for maximal sensitivity (87.2%) and specificity (75.0%) to discriminate septic samples from those with uncertain status was 444.6 µg/L, with an area under the receiver operating characteristic curve of 0.85 (95% confidence interval 0.74-0.93). Concentrations declined over time in horses undergoing treatment. NGAL is a novel biomarker that seems to have great potential for identifying septic synovitis and for monitoring the response to treatment of synovial infection in horses.

Synovial C-Reactive Protein is a Useful Adjunct for Diagnosis of Periprosthetic Joint Infection

BACKGROUND

The diagnostic utility of synovial C-reactive protein (CRP) has been debated for a while. Existing studies are limited by small sample sizes and using outdated criteria for periprosthetic joint infection (PJI). Furthermore, the relationship between synovial and serum CRP has rarely been investigated in the setting of PJI. This study aimed to evaluate the diagnostic utility of synovial CRP and to assess its relationship with serum CRP and other common biomarkers.

METHODS

We reviewed 621 patients who underwent evaluation for PJI prior to revision arthroplasty from 2014 to 2021. Biomarkers, including serum CRP and erythrocyte sedimentation rate, synovial CRP, polymorphonuclear leukocyte percentage, white blood cell count, and alpha-defensin, were evaluated using the 2018 International Consensus Meeting criteria.

RESULTS

In total, 194 patients had a PJI; 394 were considered aseptic failures and 33 were inconclusive. Synovial CRP showed an area under the curve (AUC) of 0.951 (95% CI, 0.932-0.970) with 74.2% sensitivity and 98.0% specificity, whereas, serum CRP had an AUC of 0.926 (95% CI, 0.903-0.949) with 83.5% sensitivity and 88.3% specificity. There was a good correlation between synovial and serum CRP (R = 0.703; 95% CI, 0.604-0.785). The combination of serum and synovial CRP yielded a significantly higher AUC than that obtained when using serum CRP alone (AUC 0.964 versus 0.926, P = .016).

CONCLUSION

Synovial CRP demonstrated excellent accuracy when used to determine the presence of PJI. There was a good correlation between serum and synovial CRP levels in revision arthroplasty patients and the combined use of serum and synovial CRP proved to be more accurate than the serum test alone. These findings support the use of synovial CRP as an adjunct in the workup of PJI.

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

Objective

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.

Methods

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.

Results

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.

Conclusions

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.

The quality of diagnostic studies used for the diagnostic criteria of periprosthetic joint infections

BACKGROUND

Although periprosthetic joint infection (PJI) is a serious complication following a total joint arthroplasty procedure, there remains uncertainty regarding the diagnosis of PJI due to the lack of a globally accepted, standardized definition. The goal of this review is to critically analyze the quality of the evidence used for the novel 2018 MSIS PJI definition and identify gaps and limitations with using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool.

METHODS

References from the modified 2018 MSIS definition for PJI by Parvizi et al. were retrieved and manually reviewed. A total of 11 studies were assessed using a validated QUADAS-2 tool.

RESULTS

Many included studies had an unclear or high risk of bias for the Index Test domain due to a lack of blinding and lack of prespecified thresholds. A majority of studies utilized Youden's J statistic to optimize the thresholds which may diminish external validity. Likewise, several studies were assessed to have an unclear and high risk of bias for the Flow and Timing domain primarily due to a lack of reporting and a large number of exclusions. Overall, there was a low risk of bias for the choice of reference standard, its conduct and interpretation, as well as for the Patient Selection domain.

CONCLUSION

Although the literature used for the MSIS 2018 PJI definition is fraught with potential sources of bias, there may be a trend toward an improvement in the quality of evidence when compared to the earlier definition of PJI.

Quantitative alpha-defensin testing: Is synovial fluid dilution important?

BACKGROUND

Alpha-defensin has been widely studied for the diagnosis of periprosthetic joint infection (PJI). However, there is a lack of detailed information regarding the proper laboratory technique of the enzyme-linked immunosorbent assay (ELISA) method, such as sample dilution.

AIM

To assess the influence of dilution in the synovial fluid during ELISA for the diagnosis of knee PJI; and determine which dilution presents a better performance.

METHODS

Forty samples of synovial fluid from arthroplasty knees were included, 17 in the infected group and 23 in the aseptic group, according to Musculoskeletal Infection Society criteria. Initially, five synovial fluid samples from each group were assessed for quantitative analysis of alpha-defensin using ELISA. Different dilution ratios (1:10, 1:100, 1:500, 1:1000 and 1:5000) were tested based on the predetermined cutoff value of 5.2 mg/L. The dilutions that performed better were used to compare the results of all samples.

RESULTS

For infected cases, a gradual increase in the dilution of synovial fluid samples led to an equivalent increase in alpha-defensin level. The same was not observed in the aseptic cases. Both 1:1000 and 1:5000 dilutions presented satisfactory results to differentiate infected and aseptic cases. Further analyses were performed using 1:1000 and 1:5000 for all 40 samples. The 1:1000 dilution resulted in a sensitivity of 88.2% (95%CI, 66%-98%) and specificity of 95.7% (95%CI, 79%-99%), whereas the 1:5000 dilution presented a sensitivity of 94.1% (95%CI, 73%-99%) and a specificity of 100% (95%CI, 86%-100%).

CONCLUSION

The synovial fluid dilution had an important influence on the alpha-defensin ELISA results. Dilutions of 1:5000 showed the best performance for the diagnosis of knee PJI. The results of this study set the basis for a more reliable and reproducible alpha-defensin ELISA during the investigation of PJI, contributing to the expansion of this technique in different treatment centers worldwide.

Synovial Fluid Neutrophil Gelatinase-Associated Lipocalin Can be Used to Accurately Diagnose Prosthetic Joint Infection

BACKGROUND

Neutrophil gelatinase-associated lipocalin (NGAL)¹ in synovial fluid (SF) may have potential diagnostic value for prosthetic joint infection (PJI). The purpose of this study was to study (1) the diagnostic performance of SF-NGAL level for diagnosing PJI and (2) the impact of prior antibiotic use on the SF-NGAL levels.

METHODS

Consecutive 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 (AF) group. An enzyme-linked immunosorbent assay was used to determine the SF-NGAL level.

RESULTS

Fifty of 78 included patients were diagnosed with PJI. The median SF-NGAL level was 3633 ng/ml (interquartile range (IQR), 1332-10737) in the PJI group and 26.8 ng/ml (IQR, 12.4-52.5) in the AF group (p < 0.0001). When the SF-NGAL threshold was 263 ng/ml, the AUC was 0.98, the sensitivity was 92.9%, and the specificity was 98%. The median level was 5779 ng/ml (IQR, 1425-13072) in the antibiotic group and 2590 ng/ml (IQR, 932-8970) in the nonantibiotic group (p = 0.1).

CONCLUSION

SF-NGAL level can be used as a diagnostic indicator of PJI. The use of antibiotics prior to sampling does not affect the SF-NGAL level.

Skeletal infections: microbial pathogenesis, immunity and clinical management

Osteomyelitis remains one of the greatest risks in orthopaedic surgery. Although many organisms are linked to skeletal infections, Staphylococcus aureus remains the most prevalent and devastating causative pathogen. Important discoveries have uncovered novel mechanisms of S. aureus pathogenesis and persistence within bone tissue, including implant-associated biofilms, abscesses and invasion of the osteocyte lacuno-canalicular network. However, little clinical progress has been made in the prevention and eradication of skeletal infection as treatment algorithms and outcomes have only incrementally changed over the past half century. In this Review, we discuss the mechanisms of persistence and immune evasion in S. aureus infection of the skeletal system as well as features of other osteomyelitis-causing pathogens in implant-associated and native bone infections. We also describe how the host fails to eradicate bacterial bone infections, and how this new information may lead to the development of novel interventions. Finally, we discuss the clinical management of skeletal infection, including osteomyelitis classification and strategies to treat skeletal infections with emerging technologies that could translate to the clinic in the future.

Human transcriptomic response to periprosthetic joint infection

Periprosthetic joint infection (PJI), a devastating complication of total joint replacement, is of incompletely understood pathogenesis and may sometimes be challenging to clinically distinguish from other causes of arthroplasty failure. We characterized human gene expression in 93 specimens derived from surfaces of resected arthroplasties, comparing transcriptomes of subjects with infection- versus non-infection-associated arthroplasty failure. Differential gene expression analysis confirmed 28 previously reported potential biomarkers of PJI, including bactericidal/permeability increasing protein (BPI), cathelicidin antimicrobial peptide (CAMP), C-C-motif chemokine ligand 3 (CCL3), 4(CCL4) and C-X-C-motif chemokine ligand 2 (CXCL2), colony stimulating factor 2 receptor beta (CSF2RB), colony stimulating factor 3 (CSF3), alpha-defensin (DEFA4), Fc fragment of IgG receptor 1B (CD64B), intercellular adhesion molecule 1 (ICAM1), interferon gamma (IFNG), interleukin 13 receptor subunit alpha 2 (IL13RA2), interleukin 17D (IL17D), interleukin 1 (IL1A, IL1B, IL1RN), interleukin 2 receptors (IL2RA, IL2RG), interleukin 5 receptor (IL5RA), interleukin 6 (IL6), interleukin 8 (IL8), lipopolysaccharide binding protein (LBP), lipocalin (LCN2), lactate dehydrogenase C (LDHC), lactotransferrin (LTF), matrix metallopeptidase 3 (MMP3), peptidase inhibitor 3 (PI3), and vascular endothelial growth factor A (VEGFA), and identified three novel molecules of potential diagnostic use for detection of PJI, namely C-C-motif chemokine ligand CCL20, coagulation factor VII (F7), and B cell receptor FCRL4. Comparative analysis of infections caused by staphylococci versus bacteria other than staphylococci and Staphylococcus aureus versus Staphylococcus epidermidis showed elevated expression of interleukin 13 (IL13), IL17D, and MMP3 in staphylococcal infections, and of IL1B, IL8, and platelet factor PF4V1 in S. aureus compared to S. epidermidis infections. Pathway analysis of over-represented genes suggested activation of host immune response and cellular maintenance and repair functions in response to invasion of infectious agents. The data presented provides new potential targets for diagnosis of PJI and for differentiation of PJI caused by different infectious agents.

Usefulness of serum D-dimer and platelet count to mean platelet volume ratio to rule out chronic periprosthetic joint infection

Background: Diagnosing periprosthetic joint infection (PJI) is challenging and usually requires the evaluation of several biomarkers. Our main aim was to evaluate the usefulness of D-dimer levels as well as the platelet count (PC) to mean platelet volume (MPV) ratio serum as biomarkers to rule out chronic knee and hip infection. Methods: The study enrolled a prospective cohort of 93 patients undergoing hip or knee revision. D-dimer values, PC to MPV ratio, C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) were preoperatively determined and evaluated as a predictor of PJI. The definitive diagnosis of PJI was established according to the 2018 International Consensus Meeting criteria. Results: A total of 24 (25.8 %) cases were postoperatively diagnosed with PJI. The median D-dimer value was significantly higher ( p   <  0.001) for patients with PJI (1950 ng mL- 1 ) than for patients with aseptic failure (700 ng mL- 1 ). The area under the receiver operating characteristic curves for D-dimer, CRP and ESR was 0.820, 0.793 and 0.791 respectively. D-dimer  ≥  950 ng mL- 1 (91 % sensitivity, 64 % specificity), CRP  ≥  1.95 mg dL- 1 (61 % sensitivity, 90 % specificity) and ESR  >  20 (74 % sensitivity, 82 % specificity) were identified as the values with the best balance between sensitivity and specificity. The mean PC to MPV ratio was 37.0 for PJI patients and 29.8 for patients in the aseptic revision cohort ( p = 0 .067). Conclusions: Serum D-dimer levels appear very unlikely to remain normal in the presence of chronic PJI. The 91 % sensitivity when considering 950 ng mL- 1 as the threshold highlights D-dimer as the most accurate initial test to rule out chronic PJI. Conversely, the PC to MPV ratio may be of limited value for accurately diagnosing PJI.

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.

Utility of Human Neutrophil Lipocalin as a Diagnosing Biomarker of Prosthetic Joint Infection: A Clinical Pilot Study

Purpose

The discrimination of prosthetic joint infection (PJI) from aseptic failure is regarded as a major clinical challenge. The key function of human neutrophil lipocalin (HNL) in regulating bacterial infection rationalizes its potential as a biomarker to diagnose PJI. This work evaluated the accuracy of serum human neutrophil lipocalin as a biomarker to diagnose PJI.

Methods

This prospective cohort study enrolled altogether 58 patients suffering from miserable knee or hip arthroplasty and receiving revision surgery from 2018 to 2020. Related laboratory and clinical information of these patients were retrieved. Following the Musculoskeletal Infection Society (MSIS) criteria, the diagnosis of PJI was conducted. Collecting preoperative blood samples, we measured HNL by the standard assay. Thereafter, plotting the receiver-operating characteristic curve (ROC), the area under the curve (AUC) values were calculated to analyze the diagnosis accuracy.

Results

According to the MSIS criteria, 38 cases (65.5%) were classified into the PJI group, while 20 (34.5%) into the aseptic loosening group, with age ranging from 38 to 87 (median, 66.9) years. The median serum HNL level of the PJI patients was 199.01 (range, 85.34–357.79) ng/mL, significantly higher as compared with that of 64.81 (range, 20.73–157.89) ng/mL of the aseptic loosening group. Using the Youden index, the optimal threshold value was 105.1ng/mL, while the specificity, sensitivity, and AUC were 85.0%, 81.6%, and 0.919, respectively.

Conclusion

Serum HNL is the creditable test that can be employed as the laboratory biomarker to screen PJI. The threshold HNL level is 105.1 ng/mL, which may distinguish PJI from aseptic failure.

Serum calprotectin: a potential biomarker to diagnose chronic prosthetic joint infection after total hip or knee arthroplasty

The preoperative detection of prosthetic joint infection (PJI) prior to revision of total hip or knee arthroplasty is still a challenge. Serum Calprotectin (CP) is a heterodimer of two calcium-binding proteins present in the cytoplasm of neutrophils that is released in inflammatory processes and infections. The objective of this study is to determine the reliability of serum CP in the diagnosis of chronic PJI. 81 patients (40 women, 41 men) that presented a potential indication for revision arthroplasty of the hip (THA; n = 18) or knee (TKA, n = 63) at a single institution were prospectively evaluated. The joints were diagnosed as chronically infected or aseptic based on the musculoskeletal infection society (MSIS) criteria of 2018. Receiver operating characteristics and the Youden's index were used to define an ideal cutoff value. The median serum CP level was significantly higher in the group with chronic PJI (15,120 vs. 4980 ng/ml; p < 0.001) compared to the aseptic cases. The calculated optimal cut-off value was 9910 ng/ml (AUC 0.899, 95% CI 0.830-0.968) with a specificity of 91% and sensitivity of 81%. The present investigation suggests that serum CP has a high specificity and good sensitivity to diagnose chronic PJI after TJA of the knee or hip.