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

Imaging approach to prosthetic joint infection

The diagnosis of prosthetic joint infection (PJI) remains challenging, despite multiple available laboratory tests for both serum and synovial fluid analysis. The clinical symptoms of PJI are not always characteristic, particularly in the chronic phase, and there is often significant overlap in symptoms with non-infectious forms of arthroplasty failure. Further exacerbating this challenge is lack of a universally accepted definition for PJI, with publications from multiple professional societies citing different diagnostic criteria. While not included in many of the major societies' guidelines for diagnosis of PJI, diagnostic imaging can play an important role in the workup of suspected PJI. In this article, we will review an approach to diagnostic imaging modalities (radiography, ultrasound, CT, MRI) in the workup of suspected PJI, with special attention to the limitations and benefits of each modality. We will also discuss the role that image-guided interventions play in the workup of these patients, through ultrasound and fluoroscopically guided joint aspirations. While there is no standard imaging algorithm that can universally applied to all patients with suspected PJI, we will discuss a general approach to diagnostic imaging and image-guided intervention in this clinical scenario.

Noncontact Diffuse Reflectance Spectroscopy of Synovial Fluid Samples for Rapid Identification of Infections

Severe joint infections, such as septic arthritis, require rapid diagnostic testing of the synovial fluid aspirated from joints level so that a surgical team can be assembled quickly. We present a diffuse reflectance spectroscopy (DRS) system for noncontact determination of infection. Using a light-tight syringe holder and fiber optic probe, diffusely reflected light from 475 to 655 nm was acquired from 18 patient samples through the wall of a syringe in a noncontact and sterile manner. We determined the reflectance ratios at two different wavelengths-R490/R600 and R580/R600 and found statistically significant differences (p < 0.05) in both ratios between the infected and noninfected groups. Critically, the R490/R600 and R580/R600 ratios were significantly correlated with clinical biomarkers-the white blood cell (WBC) and red blood cell (RBC) counts, respectively. This study demonstrates the potential of DRS as a rapid diagnostic tool for joint infections.

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.

The diagnosis and treatment of septic hip with osteonecrosis of the femoral head

This article aims to provide clinical doctors with references for the diagnosis and treatment of osteonecrosis of the femoral head (ONFH) accompanied with septic hip by summarizing and analyzing clinical data and postoperative follow-up information of patients treated with two-stage arthroplasty. We retrospectively analyzed ten patients who underwent two-stage arthroplasty in our hospital due to ONFH accompanied with septic hip. The diagnosis of septic hip includes erythrocyte sedimentation rate (ESR) > 30 mm/h, C-reactive protein (CRP) > 10 mg/L, pus-like synovial fluid, positive microbiological culture, and the findings of septic arthritis on magnetic resonance imaging (MRI) scan. Patient's information was evaluated based on the review of medical records, including gender, age, symptoms, risk factor of ONFH and septic arthritis, blood test, radiograph, MRI scan, microbiological culture, treatment, follow-up period and outcome. A total of ten patients were diagnosed with ONFH accompanied with septic hip. The average follow-up period was 43.5 months. None of the patients experienced failure during the follow-up period. The risk factor of ONFH was alcohol-related (60%), steroid-related (20%) and idiopathic (20%). Nine patients (90%) have no risk factor of septic arthritis and one patient (10%) has nephrotic syndrome. All patients did not experience any fever symptoms before surgery, but all showed worsening symptoms of pain. There were three patients (30%) with abnormal WBC count > 10 × 109/L. All patients had elevated ESR and/or CPR. Nine patients (90%) had positive MRI findings, and seven patients (70%) had positive microbiological culture. When patients with ONFH experience worsening hip joint pain accompanied by unexplained elevated CRP and/or ESR, it should be suspected whether ONFH is accompanied with septic hip. In these cases, MRI scans should be performed to exclude septic hip. Patients with ONFH accompanied with septic hip showed satisfactory results after two-stage arthroplasty.

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.

Achieving High Accuracy in Predicting the Probability of Periprosthetic Joint Infection From Synovial Fluid in Patients Undergoing Hip or Knee Arthroplasty: The Development and Validation of a Multivariable Machine Learning Algorithm

Background and objective The current periprosthetic joint infection (PJI) diagnostic guidelines require clinicians to interpret and integrate multiple criteria into a complex scoring system. Also, PJI classifications are often inconclusive, failing to provide a clinical diagnosis. Machine learning (ML) models could be leveraged to reduce reliance on these complex systems and thereby reduce diagnostic uncertainty. This study aimed to develop an ML algorithm using synovial fluid (SF) test results to establish a PJI probability score. Methods We used a large clinical laboratory's dataset of SF samples, aspirated from patients with hip or knee arthroplasty as part of a PJI evaluation. Patient age and SF biomarkers [white blood cell count, neutrophil percentage (%PMN), red blood cell count, absorbance at 280 nm wavelength, C-reactive protein (CRP), alpha-defensin (AD), neutrophil elastase, and microbial antigen (MID) tests] were used for model development. Data preprocessing, principal component analysis, and unsupervised clustering (K-means) revealed four clusters of samples that naturally aggregated based on biomarker results. Analysis of the characteristics of each of these four clusters revealed three clusters (n=13,133) with samples having biomarker results typical of a PJI-negative classification and one cluster (n=4,032) with samples having biomarker results typical of a PJI-positive classification. A decision tree model, trained and tested independently of external diagnostic rules, was then developed to match the classification determined by the unsupervised clustering. The performance of the model was assessed versus a modified 2018 International Consensus Meeting (ICM) criteria, in both the test cohort and an independent unlabeled validation set of 5,601 samples. The SHAP (SHapley Additive exPlanations) method was used to explore feature importance. Results The ML model showed an area under the curve of 0.993, with a sensitivity of 98.8%, specificity of 97.3%, positive predictive value (PPV) of 92.9%, and negative predictive value (NPV) of 99.8% in predicting the modified 2018 ICM diagnosis among test set samples. The model maintained its diagnostic accuracy in the validation cohort, yielding 99.1% sensitivity, 97.1% specificity, 91.9% PPV, and 99.9% NPV. The model's inconclusive rate (diagnostic probability between 20-80%) in the validation cohort was only 1.3%, lower than that observed with the modified 2018 ICM PJI classification (7.4%; p<0.001). The SHAP analysis found that AD was the most important feature in the model, exhibiting dominance among >95% of "infected" and "not infected" diagnoses. Other important features were the sum of the MID test panel, %PMN, and SF-CRP. Conclusions Although defined methods and tools for diagnosis of PJI using multiple biomarker criteria are available, they are not consistently applied or widely implemented. There is a need for algorithmic interpretation of these biomarkers to enable consistent interpretation of the results to drive treatment decisions. The new model, using clinical parameters measured from a patient's SF sample, renders a preoperative probability score for PJI which performs well compared to a modified 2018 ICM definition. Taken together with other clinical signs, this model has the potential to increase the accuracy of clinical evaluations and reduce the rate of inconclusive classification, thereby enabling more appropriate and expedited downstream treatment decisions.

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.

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.

The role of biopsy in diagnosing infection after hip and knee arthroplasty: a meta-analysis

INTRODUCTION

Early diagnosis of periprosthetic hip and knee infection still represents a major challenge, as no single test can achieve ideal results. Currently, multiple preoperative indicators were performed to diagnose periprosthetic joint infection (PJI) to confirm or exclude infection in the early stage. However, the diagnostic value of biopsy-related tests in diagnosing periprosthetic hip and knee infection remains unclear.

MATERIALS AND METHODS

Publications in PubMed, Embase, and the Web of Science databases were searched systematically until October 2020. Inclusion and exclusion criteria were used for screening biopsy-related studies of the diagnosis of periprosthetic hip and knee infection.

RESULTS

Three biopsy-related tests were identified in 14 articles and further analyzed in the present meta-analysis. The combined method had the highest value for the area under the curve (0.9805), followed by histology (0.9425) and microbiological tests (0.9292). In the subgroup, statistical differences were identified in sensitivity and specificity for PJI diagnosis between the synovial fluid culture and biopsy culture group, as well as in the biopsy-related combined method and serum C-reactive protein.

CONCLUSIONS

Biopsy culture does not appear to be advantageous compared to synovial fluid culture in the preoperative diagnosis of periprosthetic hip and knee infection. In contrast, combined biopsy microbial culture with histology analysis shows great potential in improving the preoperative diagnosis of PJI. The standard procedure of biopsy needs to be further explored. Further research is required to verify our results.

Nationwide Results of Microorganism Antigen Testing as a Component of Preoperative Synovial Fluid Analysis

BACKGROUND

Antigen immunoassays to detect synovial fluid (SF) microorganisms have recently been made available for clinical use. The purpose of this study was to determine the sensitivity and specificity of an SF microorganism antigen immunoassay detection (MID) panel, evaluate the panel's capability to detect microorganisms in the setting of culture-negative periprosthetic joint infection (PJI), and determine diagnostic predictive values of the MID panel for PJI.

METHODS

This study included 67,441 SF samples obtained from a hip or knee arthroplasty, from 2,365 institutions across the United States, submitted to 1 laboratory for diagnostic testing. All data were prospectively compiled and then were analyzed retrospectively. Preoperative SF data were used to classify each specimen by the International Consensus Meeting (2018 ICM) definition of PJI: 49,991 were not infected, 5,071 were inconclusive, and 12,379 were infected. The MID panel, including immunoassay tests to detect Staphylococcus, Candida, and Enterococcus, was evaluated to determine its diagnostic performance.

RESULTS

The MID panel demonstrated a sensitivity of 94.2% for infected samples that yielded positive cultures for target microorganisms (Staphylococcus, Candida, or Enterococcus). Among infected samples yielding positive cultures for their respective microorganism, individual immunoassay test sensitivity was 93.0% for Staphylococcus, 92.3% for Candida, and 97.2% for Enterococcus. The specificity of the MID panel for samples that were not infected was 98.4%, yielding a false-positive rate of 1.6%. The MID panel detected microorganisms among 49.3% of SF culture-negative infected samples. For PJI as a diagnosis, the positive predictive value of the MID panel was 91.7% and the negative predictive value was 93.8%. Among MID-positive PJIs, 16.2% yielded a discordant cultured organism instead of that detected by the antigen test.

CONCLUSIONS

SF microorganism antigen testing provides a timely adjunct method to detect microorganisms in the preoperative SF aspirate, yielding a low false-positive rate and enabling the detection of a microorganism in nearly one-half of SF culture-negative PJIs.

LEVEL OF EVIDENCE

Prognostic Level II . See Instructions for Authors for a complete description of levels of evidence.

How Does a "Dry Tap" Impact the Accuracy of Preoperative Aspiration Results in Predicting Chronic Periprosthetic Joint Infection?

BACKGROUND

Periprosthetic joint infection (PJI) after total hip arthroplasty (THA) is challenging to diagnose. We aimed to evaluate the impact of dry taps requiring saline lavage during preoperative intra-articular hip aspiration on the accuracy of diagnosing PJI before revision surgery.

METHODS

A retrospective review was conducted for THA patients with suspected PJI who received an image-guided hip aspiration from May 2016 to February 2020. Musculoskeletal Infection Society (MSIS) diagnostic criteria for PJI were compared between patients who had dry tap (DT) vs successful tap (ST). Sensitivity and specificity of synovial markers were compared between the DT and ST groups. Concordance between preoperative and intraoperative cultures was determined for the 2 groups.

RESULTS

In total, 335 THA patients met inclusion criteria. A greater proportion of patients in the ST group met MSIS criteria preoperatively (30.2% vs 8.3%, P < .001). Patients in the ST group had higher rates of revision for PJI (28.4% vs 17.5%, P = .026) and for any indication (48.4% vs 36.7%, P = .039). MSIS synovial white blood cell count thresholds were more sensitive in the ST group (90.0% vs 66.7%). There was no difference in culture concordance (67.9% vs 65.9%, P = .709), though the DT group had a higher rate of negative preoperative cultures followed by positive intraoperative cultures (85.7% vs 41.1%, P = .047).

CONCLUSION

Our results indicate that approximately one third of patients have dry hip aspiration, and in these patients cultures are less predictive of intraoperative findings. This suggests that surgeons considering potential PJI after THA should apply extra scrutiny when interpreting negative results in patients who require saline lavage for hip joint aspiration.

Factors predicting hip joint aspiration yield or “dry taps” in patients with total hip arthroplasty

Background

Image-guided joint aspirations used to assist the diagnosis of periprosthetic joint infection (PJI) may commonly result in a dry tap–or insufficient fluid for culture and cell count analysis. Dry tap aspirations are painful and invasive for patients and often utilize a subsequent saline lavage to obtain a microbiology sample. Currently, there is a paucity of the literature addressing predictors that could suggest whether a dry tap will occur. The purpose of this study was to examine the effects of various factors on “dry tap” occurrence in patients with suspected PJI following total hip arthroplasty (THA).

Methods

A retrospective review was performed among THA patients suspected for PJI who received image-guided joint aspiration procedures at our institution from May 2016 to February 2020. The procedural factors included the imaging modality used for aspiration, anatomic approach, needle gauge size used, and the presence of a trainee. The patient-specific factors included number of prior ipsilateral hip surgeries, femoral head size, ESR/CRP values, and BMI.

Results

In total, 336 patients met our inclusion criteria. One hundred and twenty hip aspirations resulted in a dry tap (35.7%) where the patients underwent a saline lavage. Among the procedural and patient-specific factors, none of the factors were found to be statistically different between the two cohorts nor conferred any greater odds of a dry tap occurring.

Conclusion

No associations with dry tap occurrence were found among the procedural and patient-specific factors studied. Further research is needed to identify additional factors that may be more predictive of dry taps.

Value of ultrasound-guided aspiration of hip arthroplasties performed in an orthopedic clinic by orthopedic surgeons

Background: Total joint arthroplasties continue to increase as do periprosthetic joint infections (PJIs). Ultrasound-guided aspiration can yield useful synovial fluid for analysis while avoiding radiation exposure. This study presents a high-yield, ultrasound-guided technique with analysis of aspiration results. Methods: All consecutive ultrasound-guided aspirations of hip arthroplasties performed from May 2016 through to April 2019 were retrospectively reviewed. Patient demographic information, component specifics, presence of draining sinus, and inflammatory markers were recorded. Results of aspiration including volume, appearance, lavage use, synovial fluid differential leukocyte count, synovial neutrophil percent, and culture results were recorded. Surgical results, specimen cultures, and surgeon description of purulence were recorded. Aspiration results were compared to the surgical specimen results in all patients who underwent reoperations. Results: Review of 349 hip aspirations demonstrated accuracy of 87 %, sensitivity of 83 %, specificity of 89 %, positive predictive value of 79 %, and negative predictive value 91 %. Surgical and aspiration cultures matched in 81 % of cases. Bloody aspirates and aspirates obtained after lavage had less accuracy at 69 % and 60 %, respectively. Specificity was 100 % for cultures obtained with lavage and 91 % for bloody aspirates. Synovial leukocyte count and neutrophil percentage was obtained in 85 % of aspirations, and cultures were obtained in 98 % of aspirates. Contamination rate was 2 %. Conclusion: Ultrasound-guided aspirations aid in the diagnosis of PJI. The use of lavage to obtain fluid is helpful when aspiration cultures are positive. Bloody aspirates are less accurate but have high specificity. A low contamination rate and 88 % accuracy results with this meticulous technique.

“Unexpected” Infections in Revision Arthroplasty for Aseptic Loosening

Background. Data from the national registers of arthroplasty showed that about 12% of hip and knee arthroplasty undergo revision within 10 years after the primary surgery. The leading cause of hip revisions is aseptic loosening of components, knee joint periprosthetic infection (PPI). Some of the infectious complications, including those related to mechanical causes, remain out of sight. The aim of the study was to identify the frequency of unexpected infections during revision knee and hip arthroplasty performed for aseptic complications of any etiology. Materials and Methods. 839 cases of revision arthroplasty of knee and hip joints were analyzed, including 485 aseptic revisions in 450 patients. Clinical, X-ray, laboratory (complete blood count and comprehensive metabolic panel, coagulation panel) methods, synovial fluid analysis and microbiological examination of punctures, including intraoperative ones, were used. The ICM and EBJIS (European Bone and Joint Infections Society) consensus recommendations were used as criteria for assessing the presence of infection. Results. The average age of patients at the time of the revision was 61.7 years. The hip joint prevailed (59.4%), knee joint 40.6%. The growth of microorganisms in the intraoperative biomaterial was detected in 2.08% of observations: in 10 out of 287 patients after aseptic revision of the hip joints and in none of the 198 revisions of the knee joints. In 8 out of 10 cases, the causative agents were coagulase-negative staphylococci, including 6 MRSE; in two cases, anaerobic bacteria. All revisions were carried out by a one-stage method. Patients with detected PPI underwent systemic antibacterial therapy. At the stage of catamnesis, reinfection was assumed in one of the 10 identified cases of PPI, the patient did not show up for revision. In control 63% of the group of the other (aseptic) 470 patients, PPI developed in 4 cases, two-stage revisions were carried out. Conclusions. The frequency of infections accidentally detected during aseptic revisions of large joints was 2.08%. Three-time examination of joint punctures, including intraoperative, provides additional opportunities for the diagnosis of PPI during aseptic revision, and also allows you to choose the optimal stage of revision treatment. The experience gained makes it possible in certain cases to perform one-stage revision in the treatment of PPI.

“Unexpected” Infections in Revision Arthroplasty for Aseptic Loosening

Background. Data from the national registers of arthroplasty showed that about 12% of hip and knee arthroplasty undergo revision within 10 years after the primary surgery. The leading cause of hip revisions is aseptic loosening of components, knee joint periprosthetic infection (PPI). Some of the infectious complications, including those related to mechanical causes, remain out of sight. The aim of the study was to identify the frequency of unexpected infections during revision knee and hip arthroplasty performed for aseptic complications of any etiology. Materials and Methods. 839 cases of revision arthroplasty of knee and hip joints were analyzed, including 485 aseptic revisions in 450 patients. Clinical, X-ray, laboratory (complete blood count and comprehensive metabolic panel, coagulation panel) methods, synovial fluid analysis and microbiological examination of punctures, including intraoperative ones, were used. The ICM and EBJIS (European Bone and Joint Infections Society) consensus recommendations were used as criteria for assessing the presence of infection. Results. The average age of patients at the time of the revision was 61.7 years. The hip joint prevailed (59.4%), knee joint 40.6%. The growth of microorganisms in the intraoperative biomaterial was detected in 2.08% of observations: in 10 out of 287 patients after aseptic revision of the hip joints and in none of the 198 revisions of the knee joints. In 8 out of 10 cases, the causative agents were coagulase-negative staphylococci, including 6 MRSE; in two cases, anaerobic bacteria. All revisions were carried out by a one-stage method. Patients with detected PPI underwent systemic antibacterial therapy. At the stage of catamnesis, reinfection was assumed in one of the 10 identified cases of PPI, the patient did not show up for revision. In control 63% of the group of the other (aseptic) 470 patients, PPI developed in 4 cases, two-stage revisions were carried out. Conclusions. The frequency of infections accidentally detected during aseptic revisions of large joints was 2.08%. Three-time examination of joint punctures, including intraoperative, provides additional opportunities for the diagnosis of PPI during aseptic revision, and also allows you to choose the optimal stage of revision treatment. The experience gained makes it possible in certain cases to perform one-stage revision in the treatment of PPI.

Accuracy and Cost-Effectivenss of a Novel Method for Alpha Defensins Measurement in the Diagnosis of Periprosthetic Joint Infections

BACKGROUND

Two methods for detecting synovial fluids alpha defensins are available: the enzyme-linked immunosorbent assay and the lateral flow test. For both, the proper role and accuracy remain uncertain. The purpose of this study was to assess the accuracy of the matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) for alpha defensin detection in synovial fluids of patients with total knee arthroplasty/total hip arthroplasty failures. The hypothesis was that the alpha defensin measurement through MALDI-TOF MS assay could be a high sensitive and specific test for periprosthetic joint infections (PJI) diagnosis as compared with Musculoskeletal Infection Society (MSIS) criteria.

METHODS

The study included 138 patients. The 2018 MSIS criteria were used to diagnose PJIs. Synovial fluids were assessed for routinely synovial fluid tests and alpha defensin measurement through MALDI-TOF MS. Sensitivity, specificity, overall diagnostic accuracy, positive and negative predictive values, receiver operator curves, and area under the curve were calculated.

RESULTS

As per the 2018 MSIS criteria, 59 PJIs (43%) and 79 aseptic failures (57%) were diagnosed. The MALDI-TOF MS assay showed an overall accuracy of 94.9%. The sensitivity was 93%, the specificity was 96%, the positive predictive value was 95%, and the negative predictive value was 95%. Receiver operator curves analysis demonstrates an area under the curve of 0.95 (P < .001).

CONCLUSION

The MALDI-TOF MS assay showed high sensitivity and specificity for alpha defensin detection in case of total knee arthroplasty/total hip arthroplasty failures. The advantages of the technology, such as the few milliliters of sample needed, the rapidity of obtaining results, and the cost-effectiveness of the procedure could make the MALDI-TOF MS alpha defensin assay a useful and widespread test in clinical practice.

Does the alpha-defensin lateral flow test conserve its diagnostic properties in a larger population of chronic complex periprosthetic infections? Enlargement to 112 tests, from 42 tests in a preliminary study, in a reference center

BACKGROUND

Diagnosis of periprosthetic infection (PPI) is crucial for management of bone and joint infection. The preoperative gold-standard is joint aspiration, providing results after 2-14 days' culture, with non-negligible false negative rates due to the fragility of certain micro-organisms and/or prior antibiotic treatment. The Synovasure™ alpha-defensin lateral flow test (Zimmer, Warsaw, IN, USA) contributes within minutes to joint fluid diagnosis of almost all infectious agents, including in case of concomitant antibiotic therapy. Validity remains controversial, notably in complex microbiological situations: multi-operated patients, diagnostic doubt despite iterative sterile culture, long-course antibiotic therapy. We extended a prospective study reported in 2018, to determine whether the test maintained diagnostic value in a larger population, assessing 1) negative (NPV) and positive (PPV) predictive value, and 2) sensitivity and specificity.

HYPOTHESIS

Synovasure™ maintains NPV above 95% in a broader population of microbiologically complex suspected PPI.

MATERIAL AND METHODS

Synovasure™'s performance was assessed between October 2015 and October 2019 in 106 patients (112 tests) in complex diagnostic situations: 37 discordant cultures (discordant findings between 2 samples), 65 cases with clinically or biologically suspected infection but iterative sterile culture, 10 emergencies (requiring surgery, precluding antibiotic window, or mechanical failure in suspected infection), including 5 with ongoing antibiotic therapy for infection in another organ. Six tests were repeated in the same patient and same joint at >6 months' interval for strong clinical suspicion of infection. The main endpoint was the MSIS score (MusculoSkeletal Infection Society, 2018).

RESULTS

NPV was 98.8%, PPV 72.4%, sensitivity 95.5% and specificity 91%. Prevalence of infection was 19.6%. Only 1 of the 22 infected patients had negative Synovasure™ tests, compared to 81 of the 84 non-infected patients.

CONCLUSION

Synovasure™ is a reliable novel diagnostic test, contributing mainly to ruling out infection thanks to its strong NPV. The cost imposes sparing use, but medico-economic assessment would be worthwhile.

LEVEL OF EVIDENCE

III; prospective of diagnostic performance.

The Graphical Representation of Cell Count Representation: A New Procedure for the Diagnosis of Periprosthetic Joint Infections

Aim: This study was designed to answer the question whether a graphical representation increase the diagnostic value of automated leucocyte counting of the synovial fluid in the diagnosis of periprosthetic joint infections (PJI). Material and methods: Synovial aspirates from 322 patients (162 women, 160 men) with revisions of 192 total knee and 130 hip arthroplasties were analysed with microbiological cultivation, determination of cell counts and assay of the biomarker alpha-defensin (170 cases). In addition, microbiological and histological analysis of the periprosthetic tissue obtained during the revision surgery was carried out using the ICM classification and the histological classification of Morawietz and Krenn. The synovial aspirates were additionally analysed to produce dot plot representations (LMNE matrices) of the cells and particles in the aspirates using the hematology analyser ABX Pentra XL 80. Results: 112 patients (34.8%) had an infection according to the ICM criteria. When analysing the graphical LMNE matrices from synovia cell counting, four types could be differentiated: the type “wear particles” (I) in 28.3%, the type “infection” (II) in 24.8%, the “combined” type (III) in 15.5% and “indeterminate” type (IV) in 31.4%. There was a significant correlation between the graphical LMNE-types and the histological types of Morawietz and Krenn (p < 0.001 and Cramer test V value of 0.529). The addition of the LMNE-Matrix assessment increased the diagnostic value of the cell count and the cut-off value of the WBC count could be set lower by adding the LMNE-Matrix to the diagnostic procedure. Conclusion: The graphical representation of the cell count analysis of synovial aspirates is a new and helpful method for differentiating between real periprosthetic infections with an increased leukocyte count and false positive data resulting from wear particles. This new approach helps to increase the diagnostic value of cell count analysis in the diagnosis of PJI.

Validation of the Alpha Defensin Lateral Flow Test for Periprosthetic Joint Infection

BACKGROUND

The synovial fluid test for alpha defensin has been reported to have an excellent performance in diagnosing periprosthetic joint infection (PJI). The purpose of this study was to evaluate the performance of the lateral flow test for synovial fluid alpha defensin by using the methods of a formal diagnostic accuracy study and to compare its performance with that of the laboratory-based alpha defensin test for PJI.

METHODS

We conducted a diagnostic accuracy study of the index lateral flow immunoassay for synovial fluid alpha defensin relative to the reference 2013 Musculoskeletal Infection Society (MSIS) multicriteria definition of PJI. The study included a prospective multicenter cohort of outpatients with a failed hip or knee arthroplasty and a supplemental control cohort of fresh synovial fluid specimens submitted by physicians for diagnostic PJI testing.

RESULTS

Among 57 patients with PJI and 248 patients without PJI in the overall prospective patient cohort, the sensitivity and specificity of the alpha defensin lateral flow test were 89.5% (95% confidence interval [CI]: 78.5% to 96.0%) and 94.8% (95% CI: 91.2% to 97.2%), respectively. The sensitivity increased to 94.3% (95% CI: 84.3% to 98.8%) after exclusion of 17 patients with grossly bloody aspirates (>1 million red blood cells/µL). Among the supplemental control cohort of fresh synovial fluid samples, including 65 samples from patients with PJI and 397 from patients without PJI, the sensitivity and specificity of the alpha defensin lateral flow test were 98.5% (95% CI: 91.7% to 100.0%) and 98.2% (95% CI: 96.4% to 99.3%), respectively. A comparison of the sensitivity and specificity of the alpha defensin lateral flow test with those of the alpha defensin enzyme-linked immunosorbent assay (ELISA) in the combined cohort did not demonstrate a significant difference in sensitivity (94.3% [95% CI: 88.5% to 97.7%] compared with 93.0% [95% CI: 87.1% to 96.7%]) or specificity (96.9% [95% CI: 95.3% to 98.1%] compared with 97.8% [95% CI: 96.4% to 98.8%]) (both p > 0.05).

CONCLUSIONS

The results of this study demonstrate the solid diagnostic performance of the alpha defensin test and have resulted in the U.S. Food and Drug Administration (FDA) authorization of the lateral-flow test with an intended use as an aid in the clinical diagnosis of PJI.

LEVEL OF EVIDENCE

Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Preoperative Skin Cultures Predict Periprosthetic Infections in Revised Shoulder Arthroplasties: A Preliminary Report

Current approaches do not provide a practical method for the accurate prediction of a Cutibacterium periprosthetic joint infection (PJI) in failed arthroplasties. Thus, surgeons revising failed arthroplasties must decide whether to exchange the implants and to institute antibiotic treatment without knowing the results of cultures of deep specimens obtained at the revision procedure. This study tests the hypothesis that the results of preoperative culture specimens of the skin surface obtained in the clinic can predict the presence of culture-positive Cutibacterium PJIs.

METHODS

Revision shoulder arthroplasties performed between October 3, 2017, and February 4, 2020, that had both preoperative clinic culture specimens and surgical culture specimens were included in this analysis. Culture results were assigned a value from 0 to 4. The percentage of the total skin bacterial load contributed by Cutibacterium (Cutibacterium percentage) was determined. To reduce concern about contamination, a robust criterion for culture-positive Cutibacterium PJI was applied: ≥2 surgical specimens with a Cutibacterium value of ≥1. The predictive values for a culture-positive Cutibacterium PJI were determined for a clinic skin culture Cutibacterium value of >1 and a clinic skin percentage of Cutibacterium of ≥75%.

RESULTS

Eighteen cases met the inclusion criteria; of these, 7 (6 male patients) met our criterion for a culture-positive Cutibacterium PJI. For all patients, a preoperative clinic skin Cutibacterium value of >1 predicted the presence of a culture-positive Cutibacterium PJI with an accuracy of 89%, and a clinic skin Cutibacterium percentage of ≥75% predicted the presence of a culture-positive Cutibacterium PJI with an accuracy of 94%. For male patients, a preoperative clinic skin Cutibacterium value of >1 predicted the presence of a culture-positive Cutibacterium PJI with an accuracy of 91%, and a clinic skin Cutibacterium percentage of ≥75% predicted the presence of a culture-positive Cutibacterium PJI with an accuracy of 100%.

CONCLUSIONS

A simple culture specimen of the unprepared skin surface obtained in a clinic prior to revision shoulder arthroplasty may provide valuable assistance to surgeons planning a revision arthroplasty.

LEVEL OF EVIDENCE

Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.