Leukocyte esterase and alpha-defensin in periprosthetic joint infection: predictive quality and correlation in a prospective study

PURPOSE

Periprosthetic joint infection (PJI) is a rare but serious complication of total joint arthroplasty (TJA). An accurate diagnosis of PJI preoperatively does not exist. Alpha-defensin (AD) is a proven and common indicator. The diagnostic marker of leukocyte esterase (LE) promises some advantages: feasibility, availability, and fast result reporting. The aim of this study was the evaluation of the predictive quality and correlation between both diagnostic tools in the diagnosis of PJI.

METHODS

A prospective study was conducted between April 2018 and August 2022. All patients with suspicion of PJI on hip and knee joint were included and underwent a routine and standardized joint punction. For laboratory diagnostics of AD, the synovial liquid was analyzed by ELISA. The sample was additionally applied to a LE test strip (Combur 10 Test, Roche Diagnostics, Mannheim, Germany).

RESULTS

A total of 249 patients were examined (mean age 67.12 ± 11.89; gender distribution man/woman 139 (55.8%)/110(44.2%), hip/knee 71(28.5%)/178 (71.5%). According to EBJIS criteria, PJI was diagnosed in 54 (21.7%) patients. AD showed excellent results with an AUC of 0.930 (sensitivity/specificity 0.870/0.990). LE yielded very good results with an AUC of 0.820 (sensitivity/specificity 0.722/0.918). Both parameters showed a strong positive correlation.

CONCLUSION

LE is a rapidly available alternative in PJI diagnostics. The simultaneous determination of both markers may enhance diagnostic reliability. A routine usage may shorten the time from diagnosis to treatment of PJI.

It can be unnecessary to combine common synovial fluid analysis and alpha-defensin tests for periprosthetic joint infection diagnosis

BACKGROUND

Periprosthetic joint infection is a serious complication after total joint arthroplasty. Despite that alpha-defensin was used as diagnostic test in the 2018 ICM (international consensus meeting) criteria, its position in the PJI diagnostic pipeline was controversial. Therefore, we performed a retrospective pilot study to identify whether synovial fluid alpha-defensin test was necessary when corresponding synovial fluid analysis (WBC count, PMN% and LE tests) was performed.

METHODS

Between May 2015 and October 2018, a total of 90 suspected PJI patients who underwent revisions after TJA were included in this study. Based on the 2018 ICM criteria, the interobserver agreements between preoperative diagnostic results and postoperative diagnostic results and the interobserver reliability between preoperative diagnostic results and postoperative diagnostic results with or without synovial fluid alpha-defensin tests were calculated. After that, the ROC analysis, and the direct cost-effectiveness of adding alpha-defensin was performed.

RESULTS

There were 48,16 and 26 patients in the PJI group, inconclusive group and non-PJI group, respectively. Adding the alpha-defensin tests into 2018 ICM criteria can't change the preoperative diagnostic results, postoperative diagnostic results, and the concordance between preoperative and postoperative diagnostic results. Moreover, the Risk-benefit Ratio is over 90 per changed decision and the direct cost-effectiveness of alpha-defensin was more than $8370($93*90) per case.

CONCLUSIONS

Alpha-defensin assay exhibit high sensitivity and specificity for PJI detection as a standalone test based on the 2018 ICM criteria. However, the additional order of Alpha-defensin can't offer additional evidence for PJI diagnosis when corresponding synovial fluid analysis was performed (synovial fluid WBC count, PMN% and LE strip tests).

EVIDENCE LEVEL

Level II, Diagnostic study.

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

BACKGROUND

Various organizations have published definitions for periprosthetic joint infection (PJI) with significant differences in the cut-offs of white blood cell (WBC) count and polymorphonuclear (PMN) leukocyte cells. Herein, we aim to analyze optimal cut-offs in patients which are planned to undergo a prosthesis revision and compare them with the actual published thresholds of the International Consensus Meeting (ICM) and European Bone and Joint Infection Society (EBJIS).

METHODS

A test kit was compiled in a monocentric prospective study, according to the ICM criteria (2018) and 2021 EBJIS criteria. The kit was implemented using: blood samples (including leukocyte count and C-reactive protein); samples for examining the synovial fluid (WBC count, PMN cell differentiation, microbiological culture for incubation over 14 days, alpha-defensin ELISA laboratory test, and leukocyte-esterase test). The cut-offs for WBC and PMN counts were investigated using ROC analyses and Youden index. The ICM 2018 criteria were applied, using alpha-defensin in all cases. Patients which have to undergo a prosthesis revision were included, a pre-operative joint aspiration had been performed, and the patients had been followed up prospectively.

RESULTS

405 patients were examined with the compiled test kit; 100% had a complete dataset with respect to alpha-defensin; 383 patients, according to WBC count; and 256, according to PMN cell differentiation The cut-off of 2478.89 cells/µl in the WBC count (sensitivity: 87.70%; specificity: 88.10%) and the cut-off of 66.99% in PMN differentiation showed the best accuracy (sensitivity: 86.00%; specificity: 88.80%). Other published cut-offs for WBC were tested in this cohort and showed the following accuracy: 3000/µl (EBJIS/ICM; sensitivity: 82.10%; specificity: 91.00%), 2000/µl (sensitivity: 89.60%; specificity: 83.40%), and 1500/µl (sensitivity: 91.50%; specificity: 75.00%). The published cut-offs for PMN had the following accuracy in this cohort: 80% (ICM; sensitivity: 66.3%; specificity: 96.50%), 70% (sensitivity: 82.6%; specificity: 90%), and 65% (EBJIS, sensitivity: 86%; specificity: 88.8%).

CONCLUSIONS

This study aims to improve current cut-offs for PMN- and WB-Count, even though PJI diagnosis is based on the combination of all defined tests. The optimal diagnostic cut-off of WBC and PMN counts was found to be 2479/µL and 67%, respectively, whereas ICM cut-offs in this cohort seem too high, as they provide high specificity but very low sensitivity. On the other hand, a cut-off for WBC count of 1500/µl alone would be very low, leading to low specificity and very high suspicion of PJI. The current consensus guidelines could be actualized considering these results to significantly improve the diagnostic quality.

LEVEL OF EVIDENCE

II.

Alpha-defensin as a diagnostic tool in revision total knee arthroplasties with unexpected positive intraoperative cultures and unexpected culture negative intraoperative cultures

PURPOSE

Unexpected-positive-intraoperative-cultures (UPIC) are common in presumed aseptic revision-total-knee-arthroplasties (rTKA). However, the clinical significance is not entirely clear. In contrast, in some presumably septic rTKA, identification of an underlying pathogen was not possible, so-called unexpected-negative-intraoperative-cultures (UNIC). The purpose of this study was to evaluate the potential use of synovial alpha-defensin (AD) levels in these patients.

METHODS

Synovial AD levels from 143 rTKAs were evaluated retrospectively from our prospectively maintained institutional periprostetic joint infection (PJI) biobank and database. The 2018-International Consensus Meeting (ICM) criteria was used to define the study groups. Samples from UPICs with a minimum of one positive intraoperative culture (ICM 2- ≥ 6) (n = 20) and UNIC's (ICM ≥ 6) (n = 14) were compared to 34 septic culture-positive samples (ICM ≥ 6) and 75 aseptic culture-negative (ICM 0-1). Moreover, AD-lateral-flow-assay (ADLF) and an enzyme-linked-immunosorbent-assay (ELISA) in detecting the presence of AD in native and centrifuged synovial fluid specimens was performed. Concentration of AD determined by ELISA and ADLF methods, as well as microbiological, and histopathological results, serum and synovial parameters along with demographic factors were analysed.

RESULTS

AD was positive in 31/34 (91.2%) samples from the septic culture-positive group and in 14/14 (100%) samples in the UNIC group. All UPIC samples showed a negative AD result. Positive AD samples were highly associated with culture positive and histopathological results (p < 0.001). No high-virulent microorganisms (0/20) were present in the UPIC group, compared to infected-group (19/34; 55.9%). High virulent microorganisms showed a positive AD result in 89.5% (17/19) of the cases. Methicillin resistant Staphylococcus epidermis (MRSE) infections had significantly higher AD levels than with methicillin susceptible S. epidermdis (MSSE) (p = 0.003). ELISA and ADLF tests were positive with centrifuged (8/8) and native (8/8) synovial fluid.

CONCLUSION

AD showed a solid diagnostic performance in infected and non-infected revisions, and it provided an additional value in the diagnosis of UPIC and UNIC associated to rTKAs. Pathogen virulence as well as antibiotic resistance pattern may have an effect on AD levels. Centrifugation of synovial fluid had no influence on ADLF results.

Are Accuracy Studies for Periprosthetic Joint Infection Diagnosis Inherently Flawed? And What to Do with Schrödinger's Hips? A Prospective Analysis of the Alpha Defensin Lateral-Flow Test in Chronic Painful Hip Arthroplasties

Purpose

The most recent diagnostic criteria for periprosthetic joint infection (PJI) include the use of the alpha-defensin (AD) lateral-flow (LF) test, but hip and knee arthroplasties were usually combined in previous studies. This prospective study was designed to examine the accuracy of the AD-LF test for diagnosis of PJI in chronic painful total hip arthroplasties (THA).

Materials and Methods

Patients with chronic painful hip arthroplasties were prospectively enrolled between March 2018 and May 2020. Exclusion criteria included acute PJI or an insufficient amount of synovial fluid. The modified Musculoskeletal Infection Society (MSIS) criteria were primarily used for PJI diagnosis. Fifty-seven patients were included in the analysis group. Revision surgery was not performed in 38 patients, for different reasons (clinical group); these patients remain "Schrödinger's hips": in such cases PJI cannot be excluded nor confirmed until you "open the box".

Results

The result of the AD-LF test was positive in nine patients and negative in 48 patients. Six patients were diagnosed with PJI. AD-LF sensitivity (MSIS criteria) was 83% (95% confidence interval [CI] 36-100%) and specificity was 92% (95% CI 81-98%). The positive and negative predictive value were 56% and 98%, respectively.

Conclusion

The AD test is useful in addition to the existing arsenal of diagnostic tools, and can be helpful in the decision-making process. Not all patients with chronical painful THA will undergo revision surgery. Consequently, in order to determine the reliable diagnostic accuracy of this test, future PJI diagnostic studies should include a second arm of "Schrödinger's hips".

Synovial fluid alpha-defensin in periprosthetic knee infection workup : liquid chromatography-mass spectrometry detection of alpha-defensin in synovial fluid

AIMS

The diagnosis of periprosthetic joint infection (PJI) continues to present a significant clinical challenge. New biomarkers have been proposed to support clinical decision-making; among them, synovial fluid alpha-defensin has gained interest. Current research methodology suggests reference methods are needed to establish solid evidence for use of the test. This prospective study aims to evaluate the diagnostic accuracy of high-performance liquid chromatography coupled with the mass spectrometry (LC-MS) method to detect alpha-defensin in synovial fluid.

METHODS

Between October 2017 and September 2019, we collected synovial fluid samples from patients scheduled to undergo revision surgery for painful total knee arthroplasty (TKA). The International Consensus Meeting criteria were used to classify 33 PJIs and 92 aseptic joints. LC-MS assay was performed to measure alpha-defensin in synovial fluid of all included patients. Sensitivity, specificity, positive predictive value, negative predictive value, and the area under the receiver operating characteristic curve (AUC) were calculated to define the test diagnostic accuracy.

RESULTS

The AUC was 0.99 (95% confidence interval (CI) 0.98 to 1.00). Receiver operating characteristic (ROC) analysis showed that the optimal cut-off value of synovial fluid alpha-defensin was 1.0 μg/l. The sensitivity of alpha-defensin was 100% (95% CI 96 to 100), the specificity was 97% (95% CI 90 to 98), the positive predictive value was 89.2% (95% CI 82 to 94), and negative predictive value was 100% (95% CI 96 to 100). ROC analysis demonstrated an AUC of 0.99 (95% CI 0.98 to 1.0).

CONCLUSION

The present study confirms the utility of alpha-defensin in the synovial fluid in patients with painful TKA to select cases of PJI. Since LC-MS is still a time-consuming technology and is available in highly specialized laboratories, further translational research studies are needed to take this evidence into routine procedures and promote a new diagnostic approach.Cite this article: Bone Joint J 2022;104-B(9):1047-1051.

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.

Performance of alpha-defensin lateral flow test after synovial fluid centrifugation for diagnosis of periprosthetic knee infection

BACKGROUND

The quantitative alpha-defensin enzyme-linked immunosorbent assay (ELISA) demands a prior synovial fluid centrifugation, whereas this processing is not routinely required prior to the alpha-defensin lateral flow test.

AIM

To evaluate whether a prior synovial fluid centrifugation could lead the lateral flow performance to achieve comparable results to ELISA during periprosthetic joint infection (PJI) diagnosis.

METHODS

Fifty-three cases were included in this study: 22 classified as PJI and 31 classified as aseptic cases, according to Musculoskeletal Infection Society 2013 criteria. Synovial fluid samples were submitted to centrifugation, and the supernatant was evaluated by ELISA and lateral flow tests. The sensitivity (SE), specificity (SP) and accuracy of each method were calculated as well as the agreement between those two methods.

RESULTS

In all of the 31 samples from aseptic patients, alpha-defensin ELISA and lateral flow tests showed negative results for infection. Regarding the 22 infected patients, the lateral flow test was positive in 19 cases (86.4%) and the ELISA was positive in 21 (95.5%). Sensibility, SP and accuracy were, respectively, 86.4% (95%CI: 65.1%-97.1%), 100% (95%CI: 88.8%-100%) and 93.2% (95%CI: 82.8%-98.3%) for the lateral flow test and 95.5% (95%CI: 77.2%-99.9%), 100% (95%CI: 88.8%-100%) and 98.1% (95%CI: 89.9%-100%) for ELISA. An agreement of 96.2% between those methods were observed. No statistical difference was found between them (P = 0.48).

CONCLUSION

Alpha-defensin lateral flow test showed high SE, SP and accuracy after a prior synovial fluid centrifugation, achieving comparable results to ELISA. Considering the lower complexity of the lateral flow and its equivalent performance obtained in this condition, a prior centrifugation might be added as a valuable step to enhance the PJI diagnosis.

Implementation of a standardized clinical test kit for diagnostics of periprosthetic infections in the clinical routine

BACKGROUND

The number of primary arthroplasties is increasing and the proportion of revision arthroplasties is becoming increasingly more important. The need for standardized and guideline-based diagnostics for the safe detection of a periprosthetic joint infection (PJI) is becoming apparent. In the past 10 years various organizations have published definitions and diagnostic guidelines. The implementation of an inhouse standard test kit could help to simplify the process and could improve the diagnostic quality.

METHOD

In 2016 a test kit was compiled in a monocentric prospective study, taking the International Consensus Meeting (ICM) criteria 2014 and the Infectious Diseases Society of America (IDSA) criteria into account, which also fulfils the definitions of the ICM criteria 2018 and criteria of the European Bone and Joint Infection Society 2021. The test kit was implemented in the clinical setting of a special department for aseptic and septic revision arthroplasty. The usability and accuracy of the test kit were examined.

RESULTS

The test kit was implemented using blood samples (leukocyte count; C‑reactive protein, CRP), samples for examining the synovial fluid (white blood cell count, PMN cell differentiation, microbiological culture for incubation over 14 days, alpha-defensin enzyme-linked immunosorbent assay, ELISA, leukocyte esterase test strips) together with information and request forms. Between April 2016 and February 2020 a total of 405 patients were investigated. Within 3 calendar years, the use of the test kit increased from 59% initially to 86%, and finally to 96% of cases in the third calendar year. The leukocyte esterase test strip was reliable in only 72%, due to undifferentiated readability or blood contamination. The costs increased by the only commercially available alpha-defensin ELISA test by approx. 52€ per puncture. The best individual test showed a sensitivity/specificity of 92.8%/95.2% with alpha-defensin. It was calculated which combinations showed a similar test quality and different combinations, such as CRP+ cell count+ microbiology showed a sensitivity/specificity both of around 90%. Metallosis is a challenge for preoperative PJI diagnostics.

DISCUSSION

In a prospective study it was shown, that the implementation of the standardized test kit lead to a guideline based PJI diagnostic in all cases and thus to a significantly increase of the diagnostic quality. There is currently no single test that reliably excludes or proves an infection. The alpha-defensin laboratory ELISA test showed the best test accuracy, whereby the consideration of test combinations is obligatory and at the same time safe.

[Implementation of a standardized clinical test kit for diagnostics of periprosthetic infections in the clinical routine. German version]

BACKGROUND

The number of primary arthroplasties is increasing and the proportion of revision arthroplasties is becoming increasingly more important. The need for standardized and guideline-based diagnostics for the safe detection of a periprosthetic joint infection (PJI) is becoming apparent. In the past 10 years various organizations have published definitions and diagnostic guidelines. The implementation of an inhouse standard test kit could help to simplify the process and could improve the diagnostic quality.

METHOD

In 2016 a test kit was compiled in a monocentric prospective study, taking the International Consensus Meeting (ICM) criteria 2014 and the Infectious Diseases Society of America (IDSA) criteria into account, which also fulfils the definitions of the ICM criteria 2018 and criteria of the European Bone and Joint Infection Society 2021. The test kit was implemented in the clinical setting of a special department for aseptic and septic revision arthroplasty. The usability and accuracy of the test kit were examined.

RESULTS

The test kit was implemented using blood samples (leukocyte count; C‑reactive protein, CRP), samples for examining the synovial fluid (white blood cell count, PMN cell differentiation, microbiological culture for incubation over 14 days, alpha-defensin enzyme-linked immunosorbent assay, ELISA, leukocyte esterase test strips) together with information and request forms. Between April 2016 and February 2020 a total of 405 patients were investigated. Within 3 calendar years, the use of the test kit increased from 59% initially to 86%, and finally to 96% of cases in the third calendar year. The leukocyte esterase test strip was reliable in only 72%, due to undifferentiated readability or blood contamination. The costs increased by the only commercially available alpha-defensin ELISA test by approx. 52€ per puncture. The best individual test showed a sensitivity/specificity of 92.8%/95.2% with alpha-defensin. It was calculated which combinations showed a similar test quality and different combinations, such as CRP+ cell count+ microbiology showed a sensitivity/specificity both of around 90%. Metallosis is a challenge for preoperative PJI diagnostics.

DISCUSSION

In a prospective study it was shown, that the implementation of the standardized test kit lead to a guideline based PJI diagnostic in all cases and thus to a significantly increase of the diagnostic quality. There is currently no single test that reliably excludes or proves an infection. The alpha-defensin laboratory ELISA test showed the best test accuracy, whereby the consideration of test combinations is obligatory and at the same time safe.

Synovial Alpha-defensin at Reimplantation in Two-stage Revision Arthroplasty to Rule Out Persistent Infection

BACKGROUND/AIM

Owing to the lack of a diagnostic gold standard, ruling out persistent periprosthetic joint infection (PJI) before second-stage surgery in the setting of two-stage revision arthroplasty constitutes a major challenge. We evaluated if the alpha-defensin-1 (AD-1) test could predict successful infection eradication before reimplantation of a new prosthesis.

PATIENTS AND METHODS

Our prospective study included 20 patients who underwent two-stage revision arthroplasty for treatment of PJI. A standard quantitative enzyme AD-1 immunoassay of synovial fluid, the synovial leukocyte esterase test and routine laboratory blood testing were performed prior to explantation and reimplantation. Treatment failure was defined according to the Delphi-based consensus criteria after a minimum follow-up of 1 year.

RESULTS

A 15% of our patients met the Delphi Criteria within 1 year. None of the markers investigated were significantly different in patients with and without reinfection.

CONCLUSION

Further research is necessary to identify biomarkers more suitable for indicating persistent infection before reimplantation.

Leukocyte esterase test and alpha-defensin test have similar accuracy for the diagnosis of periprosthetic joint infection

BACKGROUND

The diagnosis of periprosthetic joint infection (PJI) after total joint replacement remains challenging. Synovial biomarkers are recommended as the major diagnostic criteria for PJI. The purpose of this study was to test the accuracy of the alpha-defensin test and compare it with that of the leukocyte esterase (LE) test for the diagnosis of PJI.

METHODS

We obtained 130 hip or knee aspirates from May 2015 to September 2018. PJI was defined according to the European Bone and Joint Infection Society (EBJIS) criteria. Synovial fluid samples were tested with the alpha-defensin ELISA and a LE strip. For the LE strip test, besides using the traditional threshold 500 (equal to ++), we are also using an improved one, with 500 (equal to ++) serving as the threshold for the tests before centrifugation and both 250 and 500 indicating positive results after centrifugation. The receiver operating characteristic (ROC) curves, sensitivity, specificity, positive predictive value, negative predictive value, and Cohen's Kappa value were calculated for the LE and alpha-defensin tests.

RESULTS

The area under the curve (AUC) of alpha-defensin, LE strip test with traditional, and improved interpretation strategy were 0.875, 0.854, and 0.877, respectively. The Cohen's Kappa value for the alpha-defensin tests was 0.826 with the traditional LE interpretation strategy and 0.875 with the improved strategy.

CONCLUSION

The present study shows that the use of the LE strip to test synovial fluid yielded an accuracy similar to that of the alpha-defensin immunoassay for the diagnosis of PJI; this finding supports the 2018 ICM PJI definition, which considers positive alpha-defensin and LE test results to be equivalent.

Good accuracy of the alpha-defensin lateral flow test for hip periprosthetic joint infection: A pilot study in a retrospective cohort of 52 patients

BACKGROUND

The alpha-defensin lateral flow (ADLF) test is a new diagnostic tool for periprosthetic joint infection (PJI). Test accuracy for combined cohorts of hip and knee PJI has been reported to be good.

AIM

To assess the accuracy of the ADLF test for hip PJI, and to compare three different diagnostic criteria for PJI.

METHODS

A cohort of 52 patients was identified, with a painful or poorly functioning total hip- or hemi-arthroplasty, that underwent aspiration and a subsequent ADLF test. PJI was diagnosed with Musculoskeletal Infection Society (MSIS) criteria, and sensitivity, specificity, overall accuracy, positive predictive value and negative predictive value were calculated. Furthermore, test specifics were compared with the European Bone and Joint Infection Society (EBJIS) and 2018 International Consensus Meeting (ICM) criteria for PJI.

RESULTS

Using MSIS criteria, sensitivity was 100% (CI: 54%-100%) and specificity was 89% (CI: 76%-96%). Six true positives and 5 false positives were found, including one case of metallosis. Using EBJIS criteria, more PJIs were found (11 vs 6), sensitivity was lower (71%, CI: 42%-92%) and specificity was higher (97%, CI: 86%-100%), with 4 false negatives and one false positive result. Using 2018 ICM criteria, sensitivity was 91% (62%-100%) and specificity 100% (91%-100%). The results in this cohort are comparable to previous studies.

CONCLUSION

Overall test accuracy of the ADLF test was good in this cohort, with a sensitivity of 100% and specificity of 89%. Using different PJI definition criteria, sensitivity and specificity changed slightly but overall accuracy remained around 90%. Using the ADLF test in metallosis cases can result in false positive results and should be performed with caution.

The Impact of α-Defensin Test in Diagnosing Periprosthetic Infection After Total Ankle Arthroplasty

Periprosthetic joint infection (PJI) after total ankle arthroplasty (TAA) is a serious complication, and a reliable diagnostic test to identify PJI is needed. The purpose of this study was to investigate the use of synovial α-defensin levels in identifying PJI of the ankle. Data from 33 patients were retrospectively collected between September 2015 and May 2018. Patients who had pain or suspected loosening after TAA and who had undergone joint aspiration were included in the study. Aspiration was performed in a semisterile theatre. Synovial fluid was processed in descending order for microbiological cultures, α-defensin, leukocyte esterase strip test, and cell count. A periprosthetic infection was defined by Musculoskeletal Infection Society criteria. The sensitivity, specificity, and overall accuracy were calculated, and based on a receiver operating characteristic curve, the quality of the α-defensin test was determined. The calculated area under the curve was 0.97 ± 0.32. Two of 33 patients fulfilled the 2014 Musculoskeletal Infection Society criteria and were scheduled for septic revision arthroplasty. Sensitivity, specificity, and overall accuracy of the α-defensin test were 100% (95% confidence interval [CI], 15.8% to 100%), 93.5% (95% CI, 78.6% to 99.2%), and 93.9% (95% CI, 79.8% to 99.3%), respectively. The positive predictive value was 50% (95% CI, 20.7% to 79.3%), and the negative predictive value was 100%. The α-defensin test seems to be the best available synovial test to detect a late-onset PJI after total ankle arthroplasty. Further prospective studies with a larger number of patients are required.

New diagnostic tools for prosthetic joint infection

The diagnosis of peri-prosthetic bone and joint infections relies on converging information from clinical, laboratory and imaging assessments. Clinical findings alone may suffice: a sinus tract is a major criterion that establishes the diagnosis of infection. Identifying the causative organism is crucial and requires the early collection of high-quality samples from sites in contact with the prosthetic material. The bacteriological samples may be obtained by aspiration or open surgery. Imaging techniques have undergone remarkable improvements over the last two decades. Ultrasonography can be performed early and can be used to guide a needle biopsy if appropriate. Computed tomography or magnetic resonance imaging shows the extent of bone and/or soft-tissue involvement, provided effective artefact-suppression techniques are applied. Nuclear medicine methods have an undefined place in the diagnostic strategy and their possible role must be evaluated during a multidisciplinary discussion. The array of new laboratory methods introduced in recent years includes microbiological culture techniques, molecular biology tests, antigen and antibody assays and tests for immune markers in blood and/or joint fluid. When the first-line investigations fail to provide a definitive diagnosis, a multidisciplinary discussion at a referral centre for complex osteo-articular infections makes a major contribution to defining the subsequent diagnostic strategy. This lecture focusses on the following six questions: does the clinical assessment still have diagnostic relevance? What is the diagnostic contribution of imaging studies? Must the infection be documented pre-operatively and if so, how? Which microbiological techniques should be used? Which non-microbiological investigations help to diagnosis peri-prosthetic bone and joint infections? What role do referral centres for complex bone and joint infections play in the diagnostic strategy?

A meta-analysis of synovial biomarkers in periprosthetic joint infection: Synovasure™ is less effective than the ELISA-based alpha-defensin test

PURPOSE

(1) To determine the overall accuracy of synovial alpha-defensin, synovial C-reactive protein (sCRP), interleukin-6 (sIL-6), and leukocyte esterase (sLE) as diagnostic markers for periprosthetic joint infection (PJI) and (2) to independantly evaluate the accuracy of both the laboratory-based ELISA alpha-defensin test and the Synovasure™ alpha-defensin test kit.

METHODS

An EMBASE and MEDLINE (PubMed) database search was performed using a set of professionally set search terms. Two independent reviewers rated eligible articles. Sensitivity and specificity were meta-analysed using a bivariate random-effects model.

RESULTS

Accuracy values were extracted from 42 articles. Pooled sensitivity and specificity of the represented biomarkers were: alpha-defensin ELISA 0.97 (95% CI 0.91-0.99) and 0.97 (95% CI 0.94-0.98), respectively; Synovasure™ test kit assay 0.80 (95% CI 0.65-0.89) and 0.89 (95% CI 0.76-0.96), respectively; sLE 0.79 (95% CI 0.67-0.87) and 0.92 (95% CI 0.87-0.92), respectively; sIL-6 0.76 (95% CI 0.65-0.84) and 0.91 (95% CI 0.88-0.94), respectively; sCRP 0.86 (95% CI 0.81-0.91) and 0.90 (95% CI 0.86-0.93), respectively.

CONCLUSION

The labararory-based alpha-defensin ELISA test showed the highest ever reported accuracy for PJI diagnosis. However, this did not apply for the Synovasure™ alpha-defensin test, which was comparable in its overall diagnostic accuracy to sCRP, sIL-6 and sLE. The later biomarkers also did not yield an overall diagnostic accuracy higher than that previously reported for synovial white cell count (sWBC) or culture bacteriology. Based on current evidence, no synovial biomarker should be applied as a standalone diagnostic tool. Furthermore, the use of the laboratory-based alpha-defensin ELISA test should be encouraged, still, the Synovasure™ alpha-defensin test kit should be critically appreciated.

LEVER OF EVIDENCE

III.

Current Recommendations for the Diagnosis of Acute and Chronic PJI for Hip and Knee-Cell Counts, Alpha-Defensin, Leukocyte Esterase, Next-generation Sequencing

PURPOSE OF REVIEW

Despite significant progress in recent years, the diagnosis of periprosthetic joint infection (PJI) remains a challenge and no gold standard test exists. A combination of serological, synovial, microbiological, histological, and radiological investigations is performed that are expensive, often invasive, and imperfect. Novel biomarkers and molecular methods have shown promise in recent years. The purpose of this review is to provide an update about the diagnostic recommendations for PJI and cover a selection of emerging diagnostic tools.

RECENT FINDINGS

Recent literature highlights a new evidence-based definition for diagnosing hip and knee PJI that shows excellent performance on formal external multi-institutional validation. There is also increasing evidence to support the measurement of selected biomarkers in serum and synovial fluid, such as alpha-defensin, D-dimer, and interleukin-6. Finally, the emerging utility of next-generation sequencing for pathogen identification is discussed. In summary, we describe current recommendations and emerging tests for the diagnosis of PJI. Residual limitations and directions for future research are also discussed.

Qualitative Alpha-defensin Versus The Main Available Tests For The Diagnosis Of Periprosthetic Joint Infection: Best Predictor Test?

Introduction: Biomarkers such as α-defensin demonstrated to be a potentially useful option in periprosthetic joint infection (PJI) diagnosis. Recently, a new point-of-care test for α-defensin level detection in synovial fluid has been commercialized in Europe. The aim of this study is to compare the α-defensin test (SynovasureTM) diagnostic ability with the main available clinical tests for periprosthetic joint infection diagnosis in a practical clinical setting of a Bone Infection Unit. Methods: Between 2015 and 2017, 146 patients with suspected chronic PJI were screened with SynovasureTM. Seventy-three of these met the Musculoskeletal Infection Society (MSIS) criteria and were included in the analysis. According to MSIS criteria, 40 patients (54.7%) were classified as infected and 33 (45.3%) as not infected. The results obtained with SynovasureTM were recorded and compared with standard diagnostic methods for PJI diagnosis. Results: SynovasureTM showed a sensitivity of 85.0 % (95% CI 70.2 to 94.3) and a specificity of 96.9 % (95% CI 83.8 to 99.9) for PJI detection. The positive likelihood ratio of SynovasureTM was 27.2 (95% CI 3.9 to 188.1) and the negative likelihood ratio was 0.2 (95% CI 0.1 to 0.3). The diagnostic odds ratio was 181.3 (95% CI 20.7 to 1590.4). SynovasureTM demonstrated a statistical significant difference when compared to Erythrocyte Sedimentation Rate (ESR) and C-reactive Protein (CRP) specificity (at least one positive test) and preoperative culture sensitivity (1 positive culture). Conclusion: Our findings show that SynovasureTM sensitivity is lower than quantitative α-D test, but when compared to the main available tests shows a good specificity and the highest DOR. On the SF it is the easier test to do, due to the fact that it needs a minimal amount of SF and it is not limited by blood contamination or antibiotic use. Whereas there is no single standalone test, SynovasureTM should be considered a reliable additional test for periprosthetic joint infection diagnosis in everyday clinical practice.

Diagnostic accuracy of alpha-defensin in periprosthetic joint infection: a systematic review and meta-analysis

BACKGROUND

Alpha-defensin, a novel biomarker, has shown great potential for the accurate diagnosis of periprosthetic joint infection (PJI) in recent years: many published studies have presented encouraging results. Nevertheless, the diagnostic accuracy of alpha-defensin is inconsistent across published studies. Moreover, the optimum value of the diagnostic threshold urgently needs to be ascertained. This meta-analysis sought to estimate the precision of alpha-defensin for the diagnosis of PJI and, where possible, to confirm the threshold.

METHOD

We systematically searched PubMed, Embase, Cochrane, Web of Knowledge, and ClinicalTrials.gov for relevant literature on alpha-defensin in the diagnosis of PJI (searching publications from the inception of each database until February 2017, with no language restriction). Pooled sensitivity, specificity, diagnostic odds ratios, and likelihood ratios were the indexes used for assessment, with the use of a random-effects model.

RESULT

Eleven of the 426 studies that evaluated the diagnostic accuracy of alpha-defensin in periprosthetic joint infection (PJI) were included in this analysis. The pooled diagnostic sensitivity of alpha-defensin for PJI was 0.96 (95% confidence interval [CI], 0.87 to 0.99) and the specificity was 0.95 (95% CI, 0.91 to 0.97). Since there was substantial heterogeneity among studies, based on the inconsistency index (I²), threshold, site of arthroplasty, study design and techniques for the alpha-defensin test, subgroup analyses were performed to estimate the impacts of these variables on heterogeneity.

CONCLUSION

In summary, this meta-analysis clearly lends support to the conclusion that alpha-defensin is a promising addition to the current methods for diagnosis of PJI.

Diagnosis of prosthetic joint infection with alpha-defensin using a lateral flow device: a multicentre study

AIMS

The purpose of this current multicentre study is to analyse the presence of alpha-defensin proteins in synovial fluid using the Synovasure lateral flow device and to determine its diagnostic reliability and accuracy compared with the prosthetic joint infection (PJI) criteria produced by the Musculoskeletal Infection Society (MSIS).

PATIENTS AND METHODS

A cohort of 121 patients comprising 85 total knee arthroplasties and 36 total hip arthroplasties was prospectively evaluated between May 2015 and June 2016 in three different orthopaedic centres. The tests were performed on patients with a chronically painful prosthesis undergoing a joint aspiration in a diagnostic pathway or during revision surgery.

RESULTS

Based on the MSIS criteria, 34 patients (28%) would have had a PJI, and 87 patients had no PJI. Testing with the lateral flow device had a sensitivity of 97.1% (95% confidence intervals (CI) 84.5 to 99.9) and a specificity of 96.6% (95% CI 90.3 to 99.2). The positive predictive value was 91.7% (95% CI 77.7% to 98.3), and the negative predictive value was 98.8% (95% CI 93.6 to 99.9). Receiver operator characteristics analysis demonstrated an area under the curve for the Synovasure test of 0.97 (95% CI 0.93 to 1.00).

CONCLUSION

Our findings suggest that the Synovasure test has an excellent diagnostic performance to confirm or reject the diagnosis of a PJI. The results are promising for the care of the painful or problematic knee and hip joint arthroplasty and the test should be considered as part of the diagnostic toolbox for PJIs. Cite this article: Bone Joint J 2017;99-B:1176-82.