Periprosthetic infection: where do we stand with regard to Gram stain?

Isothermal microcalorimetry improves accuracy and time to bacterial detection of periprosthetic joint infection after total joint arthroplasty

Isothermal microcalorimetry (IMC) was evaluated compared to conventional cultures to determine the clinical performance for diagnosing periprosthetic joint infection (PJI) of hip/knee replacements. We prospectively collected three to five deep tissue samples per patient from 152 patients undergoing conversion or revision hip/knee arthroplasty from July 2020 to November 2022. Cultures and IMC for each sample were compared for concordance, median time to detection (TTD), and diagnostic performance based on 2013 Musculoskeletal Infection Society criteria. Secondary analyses involved patients on antibiotics at sampling. The 152 total patients had 592 tissue samples (mean 3.9 ± 0.3) with sample concordance between cultures and IMC of 90%. IMC demonstrated a sensitivity of 83%, specificity of 100%, negative predictive value (NPV) of 89%, and positive predictive value (PPV) of 100% for PJI. Cultures resulted in 69% sensitivity, 100% specificity, 81% NPV, and 100% PPV. The accuracy of IMC was 93% compared to 87% for cultures (P < 0.001). The median TTD of PJI by cultures was 51 (21-410) hours compared to 10 (0.5-148) hours for IMC (P < 0.001). For 39 patients on chronic antibiotics, sensitivity in PJI detection was 93%, specificity 100%, NPV 85%, and PPV 100% by IMC compared to 79% sensitivity, 100% specificity, 65% NPV, and 100% PPV for cultures. The accuracy was 95% for IMC compared to 85% for cultures (P < 0.001) with median TTD of 12 (0.5-127) hours compared to 52 (21-174) hours (P < 0.001). Utilizing IMC for PJI detection improves TTD by nearly 2 days while improving diagnostic accuracy compared to cultures, particularly in patients on chronic antibiotics.

How well does synovial fluid gram staining correlate with cultures in native joint infections?

To evaluate the sensitivity and specificity of Gram staining of synovial fluid aspirated from native joints suspected to be infected, we reviewed results of synovial fluid Gram stain and cultures. The sensitivity and specificity of the synovial Gram stain were then calculated. From the 1067 consecutive synovial fluid samples evaluated, 830 samples fulfilled the set criteria. From these 830 synovial fluid samples, organisms were detected by culture technique in only 100 samples; most of which were Gram-positive bacteria (78%). The other 22% comprised Gram-negative bacteria, Fungi and a mixture of growth. Of these, concomitant Gram stain test revealed sensitivity and specificity of 17.0% and 99.7% respectively. Our study demonstrates that the Gram stain technique has low sensitivity in detecting organisms in presumed native joint infections. Our findings demonstrate that the Gram stain test is an unreliable investigation in diagnosing native joint infections.

Diagnosis of peripheral bone and prosthetic joint infections: overview on the consensus documents by the EANM, EBJIS, and ESR (with ESCMID endorsement)

OBJECTIVES

Peripheral bone infection (PBI) and prosthetic joint infection (PJI) are two different infectious conditions of the musculoskeletal system. They have in common to be quite challenging to be diagnosed and no clear diagnostic flowchart has been established. Thus, a conjoined initiative on these two topics has been initiated by the European Society of Radiology (ESR), the European Association of Nuclear Medicine (EANM), the European Bone and Joint Infection Society (EBJIS), and the European Society of Clinical Microbiology and Infectious Diseases (ESCMID). The purpose of this work is to provide an overview on the two consensus documents on PBI and PJI that originated by the conjoined work of the ESR, EANM, and EBJIS (with ESCMID endorsement).

METHODS AND RESULTS

After literature search, a list of 18 statements for PBI and 25 statements for PJI were drafted in consensus on the most debated diagnostic challenges on these two topics, with emphasis on imaging.

CONCLUSIONS

Overall, white blood cell scintigraphy and magnetic resonance imaging have individually demonstrated the highest diagnostic performance over other imaging modalities for the diagnosis of PBI and PJI. However, the choice of which advanced diagnostic modality to use first depends on several factors, such as the benefit for the patient, local experience of imaging specialists, costs, and availability. Since robust, comparative studies among most tests do not exist, the proposed flowcharts are based not only on existing literature but also on the opinion of multiple experts involved on these topics.

KEY POINTS

• For peripheral bone infection and prosthetic joint infection, white blood cell and magnetic resonance imaging have individually demonstrated the highest diagnostic performance over other imaging modalities. • Two evidence- and expert-based diagnostic flowcharts involving variable combination of laboratory tests, biopsy methods, and radiological and nuclear medicine imaging modalities are proposed by a multi-society expert panel. • Clinical application of these flowcharts depends on several factors, such as the benefit for the patient, local experience, costs, and availability.

Diagnostic Accuracy of Serum, Synovial, and Tissue Testing for Chronic Periprosthetic Joint Infection After Hip and Knee Replacements: A Systematic Review

BACKGROUND

Chronic periprosthetic joint infection (PJI) is a devastating complication that can occur following total joint replacement. Patients with chronic PJI report a substantially lower quality of life and face a higher risk of short-term mortality. Establishing a diagnosis of chronic PJI is challenging because of conflicting guidelines, numerous tests, and limited evidence. Delays in diagnosing PJI are associated with poorer outcomes and morbid revision surgery. The purpose of this systematic review was to compare the diagnostic accuracy of serum, synovial, and tissue-based tests for chronic PJI.

METHODS

This review adheres to the Cochrane Collaboration's diagnostic test accuracy methods for evidence searching and syntheses. A detailed search of MEDLINE, Embase, the Cochrane Library, and the grey literature was performed to identify studies involving the diagnosis of chronic PJI in patients with hip or knee replacement. Eligible studies were assessed for quality and bias using the Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) tool. Meta-analyses were performed on tests with sufficient data points. Summary estimates and hierarchical summary receiver operating characteristic (HSROC) curves were obtained using a bivariate model.

RESULTS

A total of 12,616 citations were identified, and 203 studies met the inclusion criteria. Of these 203 studies, 170 had a high risk of bias. Eighty-three unique PJI diagnostic tests were identified, and 17 underwent meta-analyses. Laboratory-based synovial alpha-defensin tests and leukocyte esterase reagent (LER) strips (2+) had the best performance, followed by white blood-cell (WBC) count, measurement of synovial C-reactive protein (CRP) level, measurement of the polymorphonuclear neutrophil percentage (PMN%), and the alpha-defensin lateral flow test kit (Youden index ranging from 0.78 to 0.94). Tissue-based tests and 3 serum tests (measurement of interleukin-6 [IL-6] level, CRP level, and erythrocyte sedimentation rate [ESR]) had a Youden index between 0.61 to 0.75 but exhibited poorer performance compared with the synovial tests mentioned above.

CONCLUSIONS

The quality of the literature pertaining to chronic PJI diagnostic tests is heterogeneous, and the studies are at a high risk for bias. We believe that greater transparency and more complete reporting in studies of diagnostic test results should be mandated by peer-reviewed journals. The available literature suggests that several synovial fluid-based tests perform well for diagnosing chronic PJI and their use is recommended in the work-up of any suspected case of chronic PJI.

LEVEL OF EVIDENCE

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

Is Gram staining still useful in prosthetic joint infections?

Introduction: Staphylococcus aureus is an independent risk factor for DAIR failure in patients with a late acute prosthetic joint infection (PJI). Therefore, identifying the causative microorganism in an acute setting may help to decide if revision surgery should be chosen as a first surgical approach in patients with additional risk factors for DAIR failure. The aim of our study was to determine the sensitivity of Gram staining in late acute S. aureus PJI.

Material and methods: We retrospectively evaluated all consecutive patients between 2005-2015 who were diagnosed with late acute PJI due to S. aureus. Late acute PJI was defined as the development of acute symptoms and signs of PJI, at least three months after the index surgery. Symptoms existing for more than three weeks were excluded from the analysis. Gram staining was evaluated solely for synovial fluid.

Results: A total of 52 cases were included in the analysis. Gram staining was positive with Gram positive cocci in clusters in 31 cases (59.6%). Patients with a C-reactive protein (CRP) > 150 mg/L at clinical presentation had a significantly higher rate of a positive Gram stain (30/39, 77%) compared to patients with a CRP ≤ 150 mg/L (4/10, 40%) (p=0.02). A positive Gram stain was not related to a higher failure rate (60.6% versus 57.9%, p 0.85).

Conclusion: Gram staining may be a useful diagnostic tool in late acute PJI to identify S. aureus PJI. Whether a positive Gram stain should lead to revision surgery instead of DAIR should be determined per individual case.

Consensus document for the diagnosis of prosthetic joint infections: a joint paper by the EANM, EBJIS, and ESR (with ESCMID endorsement)

Background

For the diagnosis of prosthetic joint infection, real evidence-based guidelines to aid clinicians in choosing the most accurate diagnostic strategy are lacking.

Aim and Methods

To address this need, we performed a multidisciplinary systematic review of relevant nuclear medicine, radiological, orthopaedic, infectious, and microbiological literature to define the diagnostic accuracy of each diagnostic technique and to address and provide evidence-based answers on uniform statements for each topic that was found to be important to develop a commonly agreed upon diagnostic flowchart.

Results and Conclusion

The approach used to prepare this set of multidisciplinary guidelines was to define statements of interest and follow the procedure indicated by the Oxford Centre for Evidence-based Medicine (OCEBM).

Electronic supplementary material

The online version of this article (10.1007/s00259-019-4263-9) contains supplementary material, which is available to authorized users.

Normal CRP and WBC values in total hip arthroplasty (THA) with signs of loosening. Do we need a joint aspiration?

PURPOSE

Overall Total hip arthroplasty (THA) is a very successful procedure. However, in case of complication dedicated management is required. Two major complications of THA failures are aseptic loosening (AL) and periprosthetic joint infection (PJI). The primary hypothesis of this study was that joint aspirations in patients with signs of loosening after THA are capable to detect PJI in suspected AL with negative serologic testing.

METHODS

In this study a total of 108 symptomatic patients with radiographic signs of prosthetic loosening and hip pain in THA were included. Based on a standardized algorithm all patients underwent serological testing followed by joint aspiration preoperatively. Intraoperatively harvested samples were subjected to microbiological testing and served as the gold standard in differential diagnosis. Demographics, as well as the results of serologic and microbiological testing were collected from the medical records.

RESULTS

Of the included patients 85 were finally diagnosed with an AL and 23 with PJI. Within the patients with PJI 13 (56%) patients demonstrated elevated CRP and WBC counts, as well as positive synovial cultures after joint aspiration. In ten patients (44%) diagnosed with PJI neither CRP nor WBC were abnormal.

CONCLUSION

The diagnosis of PJI can be difficult in THA with radiographic signs of loosening. Clinical features including pain, fever, and local sings of infection are uncommon especially a long period after index operation. First-line screening testing relies on serological evaluation of CRP and WBC. However, normal CRP and WBC values cannot rule out a PJI. These cases can be detected by joint aspiration and synovial cultures reliably.

Clinical usefulness of multiplex PCR-lateral flow for the diagnosis of orthopedic-related infections

Objectives: Polymerase chain reaction (PCR)-based assays are being increasingly used for the diagnosis of orthopedic-related infections. Unfortunately, classical PCR requires imaging devices that are expensive and complex. We previously developed the PCR-lateral flow (PCR-LF) method, which does not require any additional imaging device. In the present study, the objective was to determine whether PCR-LF tests could be used to effectively diagnose orthopedic-related infections. Methods: In this study, we used PCR-LF to diagnose common causes of orthopedic-related infections and compared the results to those from conventional bacterial cultures of the same samples. Results: Notably, for 228 synovial fluid or pus specimens, the sensitivity and specificity of bacterial cultures were 53.5% and 97.7%, respectively, compared to 61.6% and 89.9% for PCR-LF. Although the difference in sensitivity between bacterial cultures and PCR-LF was not significant, when our analysis was limited to cases with suspected periprosthetic joint infection, the sensitivity of PCR-LF (66.1%) was superior to that of bacterial cultures (42.9%). Conclusion: This study indicates that PCR-LF is a useful method for diagnosing orthopedic-related infections.

Multidrug-Resistant Organisms in the Setting of Periprosthetic Joint Infection-Diagnosis, Prevention, and Treatment

BACKGROUND

Periprosthetic joint infection (PJI) is a rare yet challenging problem in total hip and knee arthroplasties. The management of PJI remains difficult primarily due to the evolution of resistance by the infecting organisms.

METHODS

This review profiles acquired mechanisms of bacterial resistance and summarizes established and emerging techniques in PJI diagnosis, prevention, and treatment.

RESULTS

New techniques in PJI diagnosis and prevention continue to be explored. Antibiotics combined with 1 or 2-stage revision are associated with the higher success rates and remain the mainstay of treatment.

CONCLUSION

With higher prevalence of antibiotic-resistant organisms, novel antibiotic implant and wound care materials, improved methods for organism identification, and well-defined organism-specific treatment algorithms are needed to optimize outcomes of PJI.

Leukocyte Esterase Strip Test Can Predict Subsequent Failure Following Reimplantation in Patients With Periprosthetic Joint Infection

BACKGROUND

Leukocyte esterase (LE) strip test is an accurate marker for diagnosing periprosthetic joint infection (PJI). This study aims to determine if LE is a good predictor of persistent infection and/or subsequent failure in patients undergoing reimplantation.

METHODS

This single-institution study prospectively recruited and retrospectively analyzed 109 patients who underwent two-stage exchange treatment of PJI, from 2009-2016, and had an LE test performed at time of reimplantation. LE results of "2+" were considered positive. Ninety-five patients had 90-day minimum follow-up to assess treatment failure, defined by Delphi criteria. Eighteen patients were excluded due to blood contamination of LE test, resulting in a final cohort of 77 patients (mean follow-up 1.76 years).

RESULTS

Of the final cohort, 19 patients (24.7%) experienced subsequent failure. At reimplantation, LE test was positive in 22.2% of culture-positive and 4.4% of culture-negative cases. The LE test was negative in all patients who had not failed at latest follow-up, yielding sensitivity, specificity, positive predictive value, negative predictive value, and AUC of 26.3%, 100%, 100%, 87.5%, and 0.632, respectively; in comparison, MSIS criteria respectively yielded 25.0%, 87.3%, 27.6%, 85.8%, and 0.562 (P = .01 for specificity). Kaplan-Meier curves revealed higher failure rate in patients who had a positive LE test at time of reimplantation (P < .001).

CONCLUSION

There is a dire need for an accurate diagnostic test to determine optimal timing of reimplantation in patients undergoing surgical treatment for PJI. The current study suggests that a positive LE test may be indicative of persistence of infection and results in a higher rate of subsequent failure.

Qualitative α-defensin test (Synovasure) for the diagnosis of periprosthetic infection in revision total joint arthroplasty

AIMS

The diagnosis of periprosthetic joint infection (PJI) remains demanding due to limitations of all the available diagnostic tests. The synovial fluid marker, α-defensin, is a promising adjunct for the assessment of potential PJI. The purpose of this study was to investigate the qualitative assessment of α-defensin, using Synovasure to detect or exclude periprosthetic infection in total joint arthroplasty.

PATIENTS AND METHODS

We studied 50 patients (28 women, 22 men, mean age 65 years; 20 to 89) with a clinical indication for revision arthroplasty who met the inclusion criteria of this prospective diagnostic study. The presence of α-defensin was determined using the qualitative Synovasure test and compared with standard diagnostic methods for PJI. Based on modified Musculoskeletal Infection Society (MSIS) criteria, 13 cases were categorised as septic and 36 as aseptic revisions. One test was inconclusive.

RESULTS

The Synovasure test achieved a sensitivity of 69% and a specificity of 94%. The positive and negative likelihood ratios were 12.46 and 0.33, respectively. A good diagnostic accuracy for PJI, with an area under the curve of 0.82, was demonstrated. Adjusted p-values using the method of Hochberg showed that Synovasure is as good at diagnosing PJI as histology (p = 0.0042) and bacteriology with one positive culture (p = 0.0327).

CONCLUSION

With its ease of use and rapid results after approximately ten minutes, Synovasure may be a useful adjunct in the diagnosis of PJI. Cite this article: Bone Joint J 2017;99-B:66-72.

Microbiological Diagnosis of Implant-Related Infections: Scientific Evidence and Cost/Benefit Analysis of Routine Antibiofilm Processing

Prosthetic joint infection is one of the most severe complication following joint arthroplasty, producing a significant worsening of patient's quality of life. Management of PJIs requires extended courses of antimicrobial therapy, multiple surgical interventions and prolonged hospital stay, with a consequent economic burden, which is thought to markedly increase in the next years due to the expected burden in total joint arthroplasties. The present review summarizes the present knowledge on microbiological diagnosis of prosthetic joint infections, focusing on aethiological agents and discussing pros and cons of the available strategies for their diagnosis.Intra-operative clinical diagnosis and pathogen identification is considered the diagnostic benchmark, however the presence of bacterial biofilm makes pathogen detection with traditional microbiological techniques highly ineffective. Diagnosis of PJIs is a rather complex challenge for orthopedics and requires a strict collaboration between different specialists: orthopaedics, infectivologists, microbiologists, pathologists and radiologists. Diagnostic criteria have been described by national and international association and scientific societies. Clinicians should be trained on how to use it, but more importantly they should know potential and limitation of the available tests in order to use them appropriately.

The value of intraoperative Gram stain in revision spine surgery

BACKGROUND CONTEXT

Intraoperative cultures and Gram stains are often obtained in cases of revision spine surgery even when clinical signs of infection are not present. The clinical utility and cost-effectiveness of this behavior remain unproven.

PURPOSE

The aim was to evaluate the clinical utility and cost-effectiveness of routine intraoperative Gram stains in revision spine surgery.

STUDY DESIGN

This was a retrospective clinical review performed at an academic center in an urban setting.

PATIENT SAMPLE

One hundred twenty-nine consecutive adult revision spine surgeries were performed.

OUTCOME MEASURES

The outcome measures included intraoperative Gram stains.

METHODS

We retrospectively reviewed the records of 594 consecutive revision spine surgeries performed by four senior surgeons between 2008 and 2013 to identify patients who had operative cultures and Gram stains performed. All revision cases including cervical, thoracic, and lumbar fusion and non-fusion, with and without instrumentation were reviewed. One hundred twenty-nine (21.7%) patients had operative cultures obtained and were included in the study.

RESULTS

The most common primary diagnosis code at the time of revision surgery was pseudarthrosis, which was present in 41.9% of cases (54 of 129). Infection was the primary diagnosis in 10.1% (13 of 129) of cases. Operative cultures were obtained in 129 of 595 (21.7%) cases, and 47.3% (61 of 129) were positive. Gram stains were performed in 98 of 129 (76.0%) cases and were positive in 5 of 98 (5.1%) cases. Overall, there was no correlation between revision diagnosis and whether or not a Gram stain was obtained (p=.697). Patients with a history of prior instrumentation were more likely to have a positive Gram stain (p<.0444). Intraoperative Gram staining was found to have a sensitivity of 10.9% (confidence interval [CI] 3.9%-23.6%) and specificity of 100% (CI 93.1%-100%). The positive and negative predictive values were 100% (CI 48.0%-100%) and 57.3% (CI 45.2%-66.2%), respectively. Kappa coefficient was calculated to be 0.1172 (CI 0.0194-0.2151). The cost per discrepant diagnosis (total cost/number discrepant) was $172.10.

CONCLUSIONS

This study demonstrates that while very specific for infection, the sensitivity of intraoperative Gram staining is low, and agreement between positive cultures and Gram stains is very poor. Gram staining demonstrated limited cost-effectiveness because of the low prevalence of findings that altered patient management.

Limitations of Gram staining for the diagnosis of infections following total hip or knee arthroplasty

The diagnosis of prosthetic joint infection (PJI) following total joint arthroplasty is difficult for clinicians to make decisions due to the similar symptoms presented by aseptic loosening and infection. Gram staining (GS) is a widely used test but its value remains controversial due to conflicting results in the diagnosis of PJI. The aim of the present study was therefore to evaluate the value of GS in the diagnosis of PJI. Searches using MEDLINE, EMBASE and OVID databases were conducted for data published between January 1990 and December 2013. Meta-analysis was used to pool the sensitivity, specificity, diagnostic odd ratios (DORs), area under the receiver-operating characteristic curve (AUC), positive-likelihood ratios (PLRs), negative-likelihood ratios (NLRs) and post-test probability. The heterogeneity and publication bias were assessed, and subgroup and meta-regression analyses were conducted. A total of 18 studies, including a total of 4,647 patients, were selected for analysis. The pooled sensitivity and specificity values for the diagnosis of PJI were 0.19 and 1.00, respectively. The AUC, PLR and NLR were 0.89, 41.6 and 0.82, respectively. Subgroup analyses indicated that the sensitivity/specificity for total hip arthroplasty was 0.14/0.99, whereas that for total knee arthroplasty was 0.14/1.00. Synovial fluid best reflected accurate GS-based diagnoses, with the highest DOR of 242, whereas tissue had the highest AUC of 0.96 (95% CI, 0.94-0.97). GS had a poor clinically acceptable diagnostic value for detecting PJI. These data do not support the routine use of GS, without additional proof of infection, for diagnosing PJI; instead, GS could be used as an adjuvant tool to support the results of other investigations.

Treatment of acute periprosthetic infections with prosthesis retention: Review of current concepts

Periprosthetic joint infection (PJI) is a devastating complication after total joint arthroplasty, occurring in approximately 1%-2% of all cases. With growing populations and increasing age, PJI will have a growing effect on health care costs. Many risk factors have been identified that increase the risk of developing PJI, including obesity, immune system deficiencies, malignancy, previous surgery of the same joint and longer operating time. Acute PJI occurs either postoperatively (4 wk to 3 mo after initial arthroplasty, depending on the classification system), or via hematogenous spreading after a period in which the prosthesis had functioned properly. Diagnosis and the choice of treatment are the cornerstones to success. Although different definitions for PJI have been used in the past, most are more or less similar and include the presence of a sinus tract, blood infection values, synovial white blood cell count, signs of infection on histopathological analysis and one or more positive culture results. Debridement, antibiotics and implant retention (DAIR) is the primary treatment for acute PJI, and should be performed as soon as possible after the development of symptoms. Success rates differ, but most studies report success rates of around 60%-80%. Whether single or multiple debridement procedures are more successful remains unclear. The use of local antibiotics in addition to the administration of systemic antibiotic agents is also subject to debate, and its pro’s and con’s should be carefully considered. Systemic treatment, based on culture results, is of importance for all PJI treatments. Additionally, rifampin should be given in Staphylococcal PJIs, unless all foreign material is removed. The most important factors contributing to treatment failure are longer duration of symptoms, a longer time after initial arthroplasty, the need for more debridement procedures, the retention of exchangeable components, and PJI caused by Staphylococcus (aureus or coagulase negative). If DAIR treatment is unsuccessful, the following treatment option should be based on the patient health status and his or her expectations. For the best functional outcome, one- or two-stage revision should be performed after DAIR failure. In conclusion, DAIR is the obvious choice for treatment of acute PJI, with good success rates in selected patients.

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

BACKGROUND

The diagnosis of periprosthetic joint infection (PJI) remains a serious clinical challenge. There is a pressing need for improved diagnostic testing methods; biomarkers offer one potentially promising approach.

QUESTIONS/PURPOSES

We evaluated the diagnostic characteristics of 16 promising synovial fluid biomarkers for the diagnosis of PJI.

METHODS

Synovial fluid was collected from 95 patients meeting the inclusion criteria of this prospective diagnostic study. All patients were being evaluated for a revision hip or knee arthroplasty, including patients with systemic inflammatory disease and those already receiving antibiotic treatment. The Musculoskeletal Infection Society (MSIS) definition was used to classify 29 PJIs and 66 aseptic joints. Synovial fluid samples were tested by immunoassay for 16 biomarkers optimized for use in synovial fluid. Sensitivity, specificity, and receiver operating characteristic curve analysis were performed to assess for diagnostic performance.

RESULTS

Five biomarkers, including human α-defensin 1-3, neutrophil elastase 2, bactericidal/permeability-increasing protein, neutrophil gelatinase-associated lipocalin, and lactoferrin, correctly predicted the MSIS classification of all patients in this study, with 100% sensitivity and specificity for the diagnosis of PJI. An additional eight biomarkers demonstrated excellent diagnostic strength, with an area under the curve of greater than 0.9.

CONCLUSIONS

Synovial fluid biomarkers exhibit a high accuracy in diagnosing PJI, even when including patients with systemic inflammatory disease and those receiving antibiotic treatment. Considering that these biomarkers match the results of the more complex MSIS definition of PJI, we believe that synovial fluid biomarkers can be a valuable addition to the methods utilized for the diagnosis of infection.

LEVEL OF EVIDENCE

Level II, diagnostic study. See Instructions for Authors for a complete description of levels of evidence.

Performance characteristics of broth-only cultures after revision total joint arthroplasty

BACKGROUND

Surgeons frequently obtain intraoperative cultures at the time of revision total joint arthroplasty. The use of broth or liquid medium before applying the sample to the agar medium may be associated with contamination and false-positive cultures; however, the degree to which this is the case is not known.

QUESTIONS/PURPOSES

We (1) calculated the performance characteristics of broth-only cultures (sensitivity, specificity, positive predictive value, and negative predictive value) and (2) characterized the organisms identified in broth to determine whether a specific organism showed increased proclivity for true-positive periprosthetic joint infection (PJI).

METHODS

A single-institution retrospective chart review was performed on 257 revision total joint arthroplasties from 2009 through 2010. One hundred ninety (74%) had cultures for review. All culture results, as well as treatment, if any, were documented and patients were followed for a minimum of 1 year for evidence of PJI. Cultures were measured as either positive from the broth only or broth negative. The true diagnosis of infection was determined by the Musculoskeletal Infection Society criteria during the preoperative workup or postoperatively at 1 year for purposes of calculating the performance characteristics of the broth-only culture.

RESULTS

The sensitivity, specificity, positive predictive value, and negative predictive value were 19%, 88%, 13%, and 92%, respectively. The most common organism identified was coagulase-negative Staphylococcus (16 of 24 cases, 67%). Coagulase-negative Staphylococcus was present in all three true-positive cases; however, it was also found in 13 of the false-positive cases.

CONCLUSIONS

The broth-only positive cultures showed poor sensitivity and positive predictive value but good specificity and negative predictive value. The good specificity indicates that it can help to rule in the presence of PJI; however, the poor sensitivity makes broth-only culture an unreliable screening test. We recommend that broth-only culture results be carefully scrutinized and decisions on the diagnosis and treatment of infection should be based specifically on the Musculoskeletal Infection Society criteria.

LEVEL OF EVIDENCE

Level IV, diagnostic study. See Instructions for Authors for a complete description of levels of evidence.

Contributions of human tissue analysis to understanding the mechanisms of loosening and osteolysis in total hip replacement

Aseptic loosening and osteolysis are the most frequent late complications of total hip arthroplasty (THA) leading to revision of the prosthesis. This review aims to demonstrate how histopathological studies contribute to our understanding of the mechanisms of aseptic loosening/osteolysis development. Only studies analysing periprosthetic tissues retrieved from failed implants in humans were included. Data from 101 studies (5532 patients with failure of THA implants) published in English or German between 1974 and 2013 were included. "Control" samples were reported in 45 of the 101 studies. The most frequently examined tissues were the bone-implant interface membrane and pseudosynovial tissues. Histopathological studies contribute importantly to determination of key cell populations underlying the biological mechanisms of aseptic loosening and osteolysis. The studies demonstrated the key molecules of the host response at the protein level (chemokines, cytokines, nitric oxide metabolites, metalloproteinases). However, these studies also have important limitations. Tissues harvested at revision surgery reflect specifically end-stage failure and may not adequately reveal the evolution of pathophysiological events that lead to prosthetic loosening and osteolysis. One possible solution is to examine tissues harvested from stable total hip arthroplasties that have been revised at various time periods due to dislocation or periprosthetic fracture in multicenter studies.

Synovial IL-6 as inflammatory marker in periprosthetic joint infections

We analyzed serum and synovial biomarkers of 69 patients. 31 of them suffered from a periprosthetic joint infection (PJI) and 38 from aseptic arthralgia after total joint arthroplasty. We used Receiver-Operating-Characteristic-curves to calculate the Area-under-the-curve (AUC), cutoff-values, positive (+LR), negative (-LR) and interval-Likelihood-Ratios (iLR) for predicting a PJI. The most significant parameter was synovial interleukin-6 (IL-6) (cutoff-value ≥ 30,750 pg/ml, AUC = 0.959, SE = 90.0%, SP = 94.7%, +LR = 17.27), followed by synovial lactate (cutoff-value ≥ 8.3 mmol/l, AUC = 0.844, SE = 71.4%, SP=88.0%, +LR = 5.95), and synovial glucose (cutoff-value ≤ 44 mg/dl, AUC = 0.829, SE = 79.2%, SP = 78.6%, +LR = 3.69). IL-6 ≥ 30,750 pg/ml and lactate ≥ 10 mmol/l make a PJI very likely, IL-6 <10,000pg/ml or lactate <4.3 mmol/l makes a PJI very unlikely. If none of these thresholds are met, physicians should use the iLR of IL-6, glucose and lactate to estimate the likelihood of PJI.

Leukocyte esterase reagent strips for the rapid diagnosis of periprosthetic joint infection

A total of 223 consecutive total hip or total knee arthroplasties were evaluated for periprosthetic joint infection (PJI) using leukocyte esterase reagent (LER) strips. Fifty-two LER strips were read as positive (23.3%), 106 were read as negative (47.5%), and 65 strips (29.2%) were unable to be read secondary to debris or blood in the aspiration. Using a synovial fluid white blood cell count of greater than 3000 white blood cell per microliter as an indicator of PJI, the sensitivity and specificity were 92.9% and 88.8%, respectively. When using positive cultures for diagnosis of PJI, sensitivity and specificity were 93.3% and 77.0% and 100% and 86.8% for the cases where a reoperation was performed and a combination of factors were used to define PJI. Leukocyte esterase reagent strips represent a rapid, inexpensive, and sensitive tool for the diagnosis of PJI. Their utility is limited, however, by blood or debris in the synovial fluid rendering them unreadable in one-third of cases.

Management of periprosthetic joint infection: the current knowledge: AAOS exhibit selection

Periprosthetic joint infection continues to frustrate the medical community. Although the demand for total joint arthroplasty is increasing, the burden of such infections is increasing even more rapidly, and they pose a unique challenge because their accurate diagnosis and eradication can prove elusive. This review describes the current knowledge regarding diagnosis and treatment of periprosthetic joint infection. A number of tools are available to aid in establishing a diagnosis of periprosthetic joint infection. These include the erythrocyte sedimentation rate, serum C-reactive protein concentration, synovial white blood-cell count and differential, imaging studies, tissue specimen culturing, and histological analysis. Multiple definitions of periprosthetic joint infection have been proposed but there is no consensus. Tools under investigation to diagnose such infections include the C-reactive protein concentration in the joint fluid, point-of-care strip tests for the leukocyte esterase concentration in the joint fluid, and other molecular markers of periprosthetic joint infection. Treatment options include irrigation and debridement with prosthesis retention, one-stage prosthesis exchange, two-stage prosthesis exchange with intervening placement of an antibiotic-loaded spacer, and salvage treatments such as joint arthrodesis and amputation. Treatment selection is dependent on multiple factors including the timing of the symptom onset, patient health, the infecting organism, and a history of infection in the joint. Although prosthesis retention has the theoretical advantages of decreased morbidity and improved return to function, two-stage exchange provides a lower rate of recurrent infection. As the burden of periprosthetic joint infection increases, the orthopaedic and medical community should become more familiar with the disease. It is hoped that the tools currently under investigation will aid clinicians in diagnosing periprosthetic joint infection in an accurate and timely fashion to allow appropriate treatment. Given the current knowledge and planned future research, the medical community should be prepared to effectively manage this increasingly prevalent disease.

Mark B. Coventry Award: synovial C-reactive protein: a prospective evaluation of a molecular marker for periprosthetic knee joint infection

BACKGROUND

C-reactive protein (CRP) serum assays are a standard element of the diagnostic workup for periprosthetic joint infection (PJI). However, because CRP is a marker for systemic inflammation, this test is not specific to PJI.

QUESTIONS/PURPOSES

Our purpose was to assess whether synovial fluid and serum assays alone could differentiate between infected and uninfected revision knee arthroplasties and to determine which of these methods had the greatest diagnostic accuracy.

METHODS

We collected synovial fluid specimens from 66 patients undergoing revision total knee arthroplasty. Patients were judged uninfected or infected by standardized criteria. Synovial CRP levels were measured using an individual CRP assay (15 samples; 10 infected, five uninfected) and a multiplex immunoassay platform (59 samples; 25 infected, 34 uninfected). Results from preoperative standard serum CRP assays conducted were also collected (55 samples; 25 infected, 30 uninfected). Sensitivity, specificity, and receiver operating characteristic curve analyses were performed for each assay with a diagnosis of infection based on previously established criteria.

RESULTS

Synovial CRP concentrations differed between infected and uninfected joints in the multiplex and serum analyses. The area under the curve was 0.84 for the individual assay, 0.91 for the multiplex assay, and 0.88 for the serum CRP assay. Sensitivity and specificity were 70.0% and 100.0% for the individual enzyme-linked immunosorbent assay, 84.0% and 97.1% for the multiplex assay, and 76.0% and 93.3% for the serum CRP assay.

CONCLUSIONS

An assay measuring CRP in synovial fluid may be more accurate in diagnosing PJI than the standard serum CRP assay. We believe such an assay holds promise as a new diagnostic marker for PJI.

Diagnosis of periprosthetic joint infection: the utility of a simple yet unappreciated enzyme

BACKGROUND

The white blood-cell count and neutrophil differential of the synovial fluid have been reported to have high sensitivity and specificity in the diagnosis of periprosthetic infection following total knee arthroplasty. We hypothesized that neutrophils recruited into an infected joint secrete enzymes that may be used as markers for infection. In this prospective study, we determined the sensitivity and specificity of one of these enzymes, leukocyte esterase, in diagnosing periprosthetic joint infection.

METHODS

Between May 2007 and April 2010, synovial fluid was obtained preoperatively from the knees of patients with a possible joint infection and intraoperatively from the knees of patients undergoing revision knee arthroplasty. The aspirate was tested for the presence of leukocyte esterase with use of a simple colorimetric strip test. The color change (graded as negative, trace, +, or ++), which corresponded to the level of the enzyme, was noted after one or two minutes.

RESULTS

On the basis of clinical, serological, and operative criteria, thirty of the 108 knees undergoing revision arthroplasty were infected and seventy-eight were uninfected. When only a ++ reading was considered positive, the leukocyte esterase test was 80.6% sensitive (95% confidence interval [CI], 61.9% to 91.9%) and 100% specific (95% CI, 94.5% to 100.0%), with a positive predictive value of 100% (95% CI, 83.4% to 100.0%) and a negative predictive value of 93.3% (95% CI, 85.4% to 97.2%). The leukocyte esterase level correlated strongly with the percentage of polymorphonuclear leukocytes (r = 0.7769) and total white blood-cell count (r = 0.5024) in the aspirate as well as with the erythrocyte sedimentation rate (r = 0.6188) and C-reactive protein level (r = 0.4719) in the serum.

CONCLUSIONS

The simple colorimetric strip test that detects the presence of leukocyte esterase in synovial fluid appears to be an extremely valuable addition to the physician's armamentarium for the diagnosis of periprosthetic joint infection. The leukocyte esterase reagent strip has the advantages of providing real-time results, being simple and inexpensive, and having the ability to both rule out and confirm periprosthetic joint infection. However, additional multicenter studies are required to substantiate the results of our preliminary investigation before the reagent strip can be used confidently in the clinic or intraoperative setting.

The Role of the Pathologist in Diagnosing Periprosthetic Infection

Most patients who undergo total joint arthroplasty experience dramatic relief of pain and improved ambulation for many years, but some eventually develop pain, often accompanied by radiographic evidence of bone resorption around their implants. The most frequent cause of device failure is osteolysis, but infection is another important cause of pain and arthroplasty failure. The distinction between infection and aseptic loosening is important because the 2 conditions are treated very differently. The purpose of this article is to summarize the role of the anatomic and clinical pathologist in helping distinguish aseptic loosening from infection.

New definition for periprosthetic joint infection

Diagnosis of periprosthetic joint infection (PJI) remains a real challenge to the orthopedic community. Currently, there is no single standard definition for PJI. This communication presents the diagnostic criteria that have been proposed by a workgroup convened by the Musculoskeletal Infection Society. The diagnostic criteria were developed after the evaluation of available evidence. The role of every diagnostic test was examined, and the literature was reviewed in detail to determine the threshold for each test. It is hoped that the proposed definition for PJI will be adopted universally, bringing standardization into a field that has suffered extensive variability and heterogeneity.

Molecular markers for diagnosis of periprosthetic joint infection

Despite a battery of tests available for diagnosing periprosthetic joint infection, as yet, no gold standard has been identified. Our purpose was to measure inflammatory proteins in synovial fluid from patients undergoing revision arthroplasty for septic or aseptic failure. We analyzed 74 synovial fluid samples: 31 infected and 43 uninfected, based on clinical and laboratory criteria. Proteomics analysis and receiver operating characteristic curve analyses were conducted on 46 inflammatory proteins for each sample. Of 46 proteins, 5 (interleukin 6, interleukin 8, α(2)-macroglobulin, C-reactive protein, and vascular endothelial growth factor) had an area under the curve greater than 0.90. This prospective study has demonstrated promising results for the use of molecular markers in diagnosis of periprosthetic joint infection. Future studies will focus on designing assays with these proteins in mind.

[Hip joint infections - Results of a questionnaire among 28 university orthopedic departments]

BACKGROUND

Despite numerous prophylactic measures infections still remain a hazardous complication in orthopedic surgery.

MATERIAL AND METHODS

A questionnaire about hip joint infections was sent to all university orthopedic departments in Germany and Austria. The questionnaire included 33 questions with respect to demographic data, causative organisms, diagnostic measures, treatment options for early and late infections, antibiotic therapy and prosthesis reimplantation.

RESULTS

The participation rate was 70%. The most frequent primary surgical indication was primary total hip replacement and Staphylococcus aureus and S. epidermidis were the most common pathogens identified. All departments performed a joint aspiration for diagnosis confirmation but for other diagnostic measures a great discrepancy could be observed. In the treatment of early infections removable components were always exchanged, whereas a local antibiotic therapy was not always employed. With regard to late infections a two-stage protocol was more frequently used than a one-stage treatment, whereby the implantation of a cement spacer was more commonly performed than a resection arthroplasty. The time between stages varied between 6 and 12 weeks and systemic antibiotics were administered for a mean time of 6 weeks. For prosthesis reimplantion cementless components were mostly used but no clear tendency could be determined for systemic antibiotic therapy.

CONCLUSION

Treatment of hip joint infections among German and Austrian university orthopedic departments is only partly carried out in a similar manner.

Gram stains have limited application in the diagnosis of infected total knee arthroplasty

BACKGROUND

The diagnosis of periprosthetic knee infections can present a challenge to surgeons, especially in the case of chronic presentation. Gram stains are regularly performed as part of the microbiological evaluation of suspected infected total knee arthroplasties. Recently, the utility of this test in diagnosing infections has been questioned. The purpose of this study was to assess the effectiveness of Gram stains performed from surgical site samples by comparing their results to the final diagnosis of infection.

METHODS

The results of 347 Gram stains performed at a single center at the time of revision total knee arthroplasty for both septic and aseptic reasons were compared to the final diagnosis based on intra-operative findings and histological evaluation.

RESULTS

Gram staining demonstrated a low sensitivity of 7% (95% confidence interval 4-12%), a specificity of 99% (95% confidence interval 97-100%), and positive and negative predictive values of 92% and 57%, respectively.

CONCLUSIONS

This study confirmed previous findings of the poor utility of this test for the diagnosis of periprosthetic knee infections. The authors recommend that Gram staining no longer be performed at the time of suspected periprosthetic knee arthroplasty infection.

Diagnosing periprosthetic infection: false-positive intraoperative Gram stains

BACKGROUND

Intraoperative Gram stains have a reported low sensitivity but high specificity when used to help diagnose periprosthetic infections. In early 2008, we recognized an unexpectedly high frequency of apparent false-positive Gram stains from revision arthroplasties.

QUESTIONS/PURPOSES

The purpose of this report is to describe the cause of these false-positive test results.

METHODS

We calculated the sensitivity and specificity of all intraoperative Gram stains submitted from revision arthroplasty cases during a 3-month interval using microbiologic cultures of the same samples as the gold standard. Methods of specimen harvesting, handling, transport, distribution, specimen processing including tissue grinding/macerating, Gram staining, and interpretation were studied. After a test modification, results of specimens were prospectively collected for a second 3-month interval, and the sensitivity and specificity of intraoperative Gram stains were calculated.

RESULTS

The retrospective review of 269 Gram stains submitted from revision arthroplasties indicated historic sensitivity and specificity values of 23% and 92%, respectively. Systematic analysis of all steps of the procedure identified Gram-stained but nonviable bacteria in commercial broth reagents used as diluents for maceration of periprosthetic membranes before Gram staining and culture. Polymerase chain reaction and sequencing showed mixed bacterial DNA. Evaluation of 390 specimens after initiating standardized Millipore filtering of diluent fluid revealed a reduced number of positive Gram stains, yielding 9% sensitivity and 99% specificity.

CONCLUSIONS

Clusters of false-positive Gram stains have been reported in other clinical conditions. They are apparently rare related to diagnosing periprosthetic infections but have severe consequences if used to guide treatment. Even occasional false-positive Gram stains should prompt review of laboratory methods. Our observations implicate dead bacteria in microbiologic reagents as potential sources of false-positive Gram stains.

Should gram stains have a role in diagnosing hip arthroplasty infections?

BACKGROUND

The utility of Gram stains in diagnosing periprosthetic infections following total hip arthroplasty has recently been questioned. Several studies report low sensitivity of the test, and its poor ability to either confirm or rule out infection in patients undergoing revision total hip arthroplasty. Despite this, many institutions including that of the senior author continue to perform Gram stains during revision total hip arthroplasty.

QUESTIONS/PURPOSES

We assessed the sensitivity, specificity, accuracy, and positive and negative predictive values of Gram stains from surgical-site samplings taken from procedures on patients with both infected and aseptic revision total hip arthroplasties.

METHODS

A review was performed on patients who underwent revision total hip arthroplasty between 2000 and 2007. Eighty-two Gram stains were performed on patients who had infected total hip arthroplasties and underwent revision procedures. Additionally, of the 410 revision total hip arthroplasties performed on patients who were confirmed infection-free, 120 Gram stains were performed. Patients were diagnosed as infected using multiple criteria at the time of surgery. Sensitivity, specificity, positive and negative predictive values, and accuracy were calculated from these Gram stain results.

RESULTS

The Gram stain demonstrated a sensitivity and specificity of 9.8% and 100%, respectively. In this series, the Gram stain had a negative predictive value of 62%, a positive predictive value of 100%, and an accuracy of 63%.

CONCLUSIONS

Gram stains obtained from surgical-site samples had poor sensitivity and poor negative predictive value. Based on these findings, as well as those of other authors, we believe that Gram stains should no longer be considered for diagnosing infections in revision total hip arthroplasty.

LEVEL OF EVIDENCE

Level III, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

[Replacement of infected knee and hip endoprostheses]

Infections occur in 0.5-5% of cases after implantation of an endoprosthesis and represent one of the most severe complications of artificial joint replacements. Approximately 300,000 primary implantations for hip and knee prostheses are carried out in Germany annually with a corresponding number of early and late infections. This means that approximately 4,000-6,000 cases are to be expected annually. Periprosthetic infections normally lead to a significant loss of function and quality of life for patients and the complex remediation is costly. Therefore, preventive measures, such as perioperative prophylaxis with antibiotics, maintaining highly sterile conditions during operations and an expedient selection of patients are of substantial importance. The basic principles of an adequate restoration include identification of the pathogen, local eradication of the infection mostly after removal of the prosthesis, pathogen-oriented systemic and local antibiotic therapy and finally re-implantation of the revision prosthesis under infection-free conditions. The standard procedure for revision surgery is a two-phase replacement with maintenance of an infection-free interval before renewal of the prosthesis. The use of single-phase or multi-phase strategies, as well as the selection of cemented or cement-free revision, varies between centers as a definitive evaluation is not yet available.The most important parameters for successful treatment of periprosthetic infections have been identified as the earliest possible diagnosis, radical surgical cleansing with an adequate antibiotic therapy and successful restoration has been reported in approximately 80% of cases. Because of the complex therapy regime, treatment in specialized centers is generally recommended especially under the aspect of a demanding patient monitoring.