PCR-hybridization after sonication improves diagnosis of implant-related infection

Diagnostic accuracy of sonication fluid cultures from prosthetic components in periprosthetic joint infection: an updated diagnostic meta-analysis

BACKGROUND

Periprosthetic joint infection (PJI) is the most serious complication following total joint arthroplasty (TJA) and has a significant impact on patients and the national healthcare system. To date, the diagnosis of PJI is still confronted with dilemmas. The present study investigated the validity of sonication fluid culture (SFC) for removing implants in the diagnosis of PJI after joint replacement.

METHODS

From database establishment to December 2020, relevant literature was retrieved from the PubMed, Web of Science, Embase and Cochrane Library databases. Two reviewers independently performed quality assessment and data extraction to calculate the pooled sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), area under the curve (AUC) and diagnostic odds ratio (DOR) to evaluate the diagnostic value of overall SFC for PJI.

RESULTS

A total of 38 eligible studies including 6302 patients were selected in this study. The pooled sensitivity, specificity, PLR, NLR, and DOR of SFC for PJI diagnosis were 0.77 (95% confidence interval [CI], 0.76-0.79), 0.96 (95% CI, 0.95-0.96), 18.68 (95% CI, 11.92-29.28), 0.24 (95% CI, 0.21-0.29), and 85.65 (95% CI, 56.46-129.94), respectively, while the AUC was 0.92.

CONCLUSION

This meta-analysis showed that SFC was of great value in PJI diagnosis, and the evidence of SFC on PJI was more favorable but not yet strong. Therefore, improvement of the diagnostic accuracy of SFC is still necessary, and the diagnosis of PJI continues to warrant a multiplex approach before and during a revision procedure.

Advances in the Microbiological Diagnosis of Prosthetic Joint Infections

A significant number of prosthetic joint infections (PJI) are culture-negative and/or misinterpreted as aseptic failures in spite of the correct implementation of diagnostic culture techniques, such as tissue sample processing in a bead mill, prolonged incubation time, or sonication of removed implants. Misinterpretation may lead to unnecessary surgery and needless antimicrobial treatment. The diagnostic value of non-culture techniques has been investigated in synovial fluid, periprosthetic tissues, and sonication fluid. Different feasible improvements, such as real-time technology, automated systems and commercial kits are now available to support microbiologists. In this review, we describe non-culture techniques based on nucleic acid amplification and sequencing methods. Polymerase chain reaction (PCR) is a frequently used technique in most microbiology laboratories which allows the detection of a nucleic acid fragment by sequence amplification. Different PCR types can be used to diagnose PJI, each one requiring the selection of appropriate primers. Henceforward, thanks to the reduced cost of sequencing and the availability of next-generation sequencing (NGS), it will be possible to identify the whole pathogen genome sequence and, additionally, to detect all the pathogen sequences present in the joint. Although these new techniques have proved helpful, strict conditions need to be observed in order to detect fastidious microorganisms and rule out contaminants. Specialized microbiologists should assist clinicians in interpreting the result of the analyses at interdisciplinary meetings. New technologies will gradually be made available to improve the etiologic diagnoses of PJI, which will remain an important cornerstone of treatment. Strong collaboration among all specialists involved is essential for the correct diagnosis of PJI.

The Diagnostic Value of Blood Next-Generation Sequencing in Early Surgical Site Infection After Spine Surgery

Objective

To determine the diagnostic value of blood next-generation sequencing (NGS) in early surgical site infection after spine surgery. Because the blood is sterile in healthy individuals, it is expected that blood NGS is both sensitive and specific for the detection of infection.

Methods

A total of 28 patients with definitive spinal surgical site infections and controls (n=30) were retrospectively included. The postoperative results of NGS and culture on different samples, such as blood and drainage fluid, were obtained and compared to evaluate the diagnostic value of blood NGS. The diagnostic value parameters (sensitivity, specificity, etc.) were calculated.

Results

Among the four bacteriological exam methods, blood NGS was both sensitive and specific for the determination of infection after spine surgery. The sensitivities of blood and drainage fluid NGS were similar (0.82 vs 0.89, P=0.617). However, the specificities of the two assessments differed, which were 0.97 for blood NGS and 0.40 for drainage fluid NGS (P<0.001). The sensitivities of bacterial culture were lower than those of NGS (blood: 0.82 vs 0.25, P<0.001; drainage fluid: 0.89 vs 0.61, P<0.001), regardless of the sample type. However, the specificities of bacterial culture were equal to or higher than those of NGS (blood: 0.97 vs 0.97, P=1.000; drainage fluid: 0.40 vs 0.80, P=0.002).

Conclusion

This article emphasizes the superiority of blood NGS in infection detection and bacterial determination in patients undergoing spine surgery. Compared with traditional drainage fluid bacterial culture and NGS, blood NGS was more sensitive and specific, and its extensive application could be expected.

Molecular Diagnosis of Osteoarticular Implant-Associated Infection: Available Techniques and How We Can Use Them

Despite recent advances during the last few years, microbiological diagnosis of prosthetic joint infections remains a challenge. Molecular biology techniques have been developed to try to overcome this problem, and recently, many of them have become available for many laboratories. Some of them, especially commercial multiplex PCR-based assays and universal 16S rDNA homemade PCR assays, are now available in many laboratories. Moreover, new technologies have appeared, especially metagenomics and next-generation sequencing. These techniques have demonstrated their potential in many studies but appear to be experimental at present. A few studies have evaluated the possible use of these methods in the clinical routine, and a review of the critical aspects for the selection of a molecular method (accuracy, complexity, cost) was performed. Finally, a proposal for a protocol that includes molecular biology techniques was made according to the literature published in this field. In conclusion, molecular biology techniques are ready to be used in the clinical routine of a microbiology laboratory, but their use must be carried out in accordance with the many special characteristics of each laboratory. In all cases, the interpretation of the results must be conducted by a multidisciplinary team with experience in the management of these patients.

An update about molecular biology techniques to detect orthopaedic implant-related infections

Despite different criteria to diagnose a prosthetic joint infection (PJI), aetiological diagnosis of the causing microorganism remains essential to guide treatment.Molecular-biology-based PJI diagnosis is progressing (faster, higher specificity) in different techniques, from the experimental laboratory into clinical use.Multiplex polymerase chain reaction techniques (custom-made or commercial) provide satisfactory results in clinical series of cases, with specificity close to 100% and sensitivity over 70-80%.Next-generation metagenomics may increase sensitivity while maintaining high specificity.Molecular biology techniques may represent, in the next five years, a significant transformation of the currently available microbiological diagnosis in PJI. Cite this article: EFORT Open Rev 2021;6:93-100. DOI: 10.1302/2058-5241.6.200118.

Sampling challenges in diagnosis of chronic bacterial infections

In recent decades there has been an increase in knowledge of the distribution, species diversity and growth patterns of bacteria in human chronic infections. This has challenged standard diagnostic methods, which have undergone a development to both increase the accuracy of testing as well as to decrease the occurrence of contamination. In particular, the introduction of new technologies based on molecular techniques into the clinical diagnostic process has increased detection and identification of infectious pathogens. Sampling is the first step in the diagnostic process, making it crucial for obtaining a successful outcome. However, sampling methods have not developed at the same speed as molecular identification. The heterogeneous distribution and potentially small number of pathogenic bacterial cells in chronic infected tissue makes sampling a complicated task, and samples must be collected judiciously and handled with care. Clinical sampling is a step in the diagnostic process that may benefit from innovative methods based on current knowledge of bacteria present in chronic infections. In the present review, we describe and discuss different aspects that complicate sampling of chronic infections. The purpose is to survey representative scientific work investigating the presence and distribution of bacteria in chronic infections in relation to various clinical sampling methods.

Disinfection of contaminated metal implants with an Er:YAG laser

Infections related to orthopedic procedures are considered particularly severe when implantation materials are used, because effective treatments for biofilm removal are lacking. In this study, the relatively new approach for infection control by using an erbium:yttrium-aluminum-garnet (Er:YAG) laser was tested. This laser vaporizes all water containing cells in a very effective, precise, and predictable manner and results in only minimal thermal damage. For preliminary testing, 42 steel plates and 42 pins were seeded with mixed cultures. First, the minimally necessary laser energy for biofilm removal was determined. Subsequently, the effectiveness of biofilm removal with the Er:YAG laser and the cleansing of the metal implants with octenidine-soaked gauze was compared. Then, we compared the effectiveness of biofilm removal on 207 steel pins from 41 patients directly after explantation. Sonication and scanning electron microscopy were used for analysis. Laser fluences exceeding 2.8  J/cm² caused a complete extinction of all living cells by a single-laser impulse. Cleansing with octenidine-soaked gauze and irradiation with the Er:YAG laser are both thoroughly effective when applied to seeded pins. In contrast, when explanted pins with fully developed biofilms were analyzed, we found a significant advantage of the laser procedure. The Er:YAG laser offers a secure, complete, and nontoxic eradication of all kinds of pathogens from metal implants without damaging the implant and without the possible development of resistance. The precise noncontact removal of adjacent tissue is a decisive advantage over conventional disinfectants. Therefore, laser irradiation could become a valuable method in every debridement, antibiotics, and implant retention procedure.

Advantages of 16S rRNA PCR for the diagnosis of prosthetic joint infection

16S ribosomal RNA (rRNA) PCR has been reported to be an effective diagnostic means in patients with prosthetic joint infection (PJI). The aim of the present meta-analysis is to establish the overall diagnostic accuracy of the measurement of 16S rRNA PCR for diagnosing PJI. PubMed, Web of Science, Cochrane Library, EMBASE and Wiley Online Library were searched for studies on 16S rRNA PCR in the diagnosis of PJI. The search incorporated all literature published up until December 2018 and the QUADAS-2 checklist were used for quality assessment. The sensitivity, specificity and other measures of accuracy of 16S rRNA PCR in the diagnosis of PJI were pooled. Statistical analysis was performed by employing Meta-Disc 1.4 and Stata 12.0 software. A total of 15 studies met the inclusion criteria. The summary estimates for 16S rRNA PCR in the diagnosis of PJI in these studies were pooled: Sensitivity, 0.70 (95% CI, 0.67-0.73); specificity, 0.93 (95% CI, 0.91-0.94); positive likelihood ratio, 10.93 (95% CI, 5.55-21.51); negative likelihood ratio, 0.33 (95% CI, 0.28-0.40); diagnostic odds ratio, 41.77 (95% CI, 19.90-87.68); and the area under the curve, 0.89. Subgroup analysis showed that the use of sonicate fluid and periprosthetic tissue has higher sensitivity (0.76; 95% CI, 0.69-0.82; and 0.73; 95% CI, 0.68-0.78, respectively), specificity (0.93, 95% CI, 0.90-0.96; and 0.95; 95% CI, 0.90-0.98, respectively) and area under the curve (0.93 and 0.98, respectively). 16S rRNA PCR assay plays an important role in the diagnosis of PJI. The results of 16S rRNA PCR assays should be interpreted in parallel with clinical findings, the results of microbiological, and other laboratory tests.

The Impact of EBM-Manufactured Ti6Al4V ELI Alloy Surface Modifications on Cytotoxicity toward Eukaryotic Cells and Microbial Biofilm Formation

Electron beam melting (EBM) is an additive manufacturing technique, which allows forming customized implants that perfectly fit the loss of the anatomical structure of bone. Implantation efficiency depends not only on the implant's functional or mechanical properties but also on its surface properties, which are of great importance with regard to such biological processes as bone regeneration or microbial contamination. This work presents the impact of surface modifications (mechanical polishing, sandblasting, and acid-polishing) of EBM-produced Ti6Al4V ELI implants on essential biological parameters. These include wettability, cytotoxicity toward fibroblast and osteoblast cell line, and ability to form biofilm by Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans. Obtained results indicated that all prepared surfaces exhibited hydrophilic character and the highest changes of wettability were obtained by chemical modification. All implants displayed no cytotoxicity against osteoblast and fibroblast cell lines regardless of the modification type. In turn, the quantitative microbiological tests and visualization of microbial biofilm by means of electron microscopy showed that type of implant's modification correlated with the species-specific ability of microbes to form biofilm on it. Thus, the results of the presented study confirm the relationship between such technological aspects as surface modification and biological properties. The provided data are useful with regard to applications of the EBM technology and present a significant step towards personalized, customized implantology practice.

Sonication Leads to Clinically Relevant Changes in Treatment of Periprosthetic Hip or Knee Joint Infection

Background: Diagnosis of periprosthetic joint infection (PJI) can be troublesome. Sonication can be a helpful tool in culturing bacteria that are difficult to detect with standard tissue cultures. Aim of this study is to evaluate the clinical importance of our standardized sonication protocol in detecting periprosthetic joint infection. Materials and methods: All patients with revision surgery of a hip or knee prosthesis between 2011 and 2016 were retrospectively reviewed and divided in two groups: clinically suspected of infection or not suspected of infection. For both tissue culture and implant sonication, calculations of sensitivity and specificity were performed. Clinical relevance of sonication was evaluated by calculating in which percentage of patients' sonication influenced clinical treatment. Results: 226 patients with revision of a total hip prosthesis (122 patients) or a total knee prosthesis (104 patients) were included. Sensitivity of perioperatively taken tissue cultures was 94.3% and specificity was 99.3%. For sonication sensitivity was 80.5% and specificity was 97.8%. In the infection group eight patients (9%) with only one positive tissue culture and a positive sonication fluid culture with the same pathogen were found. Interpretation: Although sensitivity and specificity of sonication was lower compared to tissue cultures, periprosthetic joint infection could only be established in 8 patients (9%) suspected of infection because of a positive result of the sonication fluid culture. Sonication leads to clinically relevant changes in treatment and seems therefore to be a helpful diagnostic tool in clinical practice.

Value of multiplex PCR for detection of antimicrobial resistance in samples retrieved from patients with orthopaedic infections

Background

The performance of multiplex PCR (mPCR) for detection of antimicrobial resistance from clinical isolates is unknown. We assessed the ability of mPCR to analyse resistance genes directly from clinical samples.

Patients with orthopedic infections were prospectively included. Phenotypical and genotypical resistance was evaluated in clinical samples (synovial and sonication fluid) where identical pathogens were identified by culture and mPCR.

Result

A total of 94 samples were analysed, including 60 sonication fluid and 34 synovial fluid samples. For coagulase-negative staphylococcus strains, mPCR detected resistance to oxacillin in 10 of 23 isolates (44%) and to rifampin in none of 6 isolates. For S. aureus isolates, detection rate of oxacillin and rifampin-resistance was 100% (2/2 and 1/1, respectively). Fluoroquinolone-resistance was confirmed by mPCR in all 3 isolates of Enterobacteriaceae, in enterococci resistance to aminoglycoside-high level was detected in 1 of 3 isolates (33%) and in streptococci resistance to macrolides/lincosamides in none of 2 isolates. The overall sensitivity for different pathogens and antimicrobials was 46% and specificity 95%, the median concordance was 80% (range, 57–100%). Full agreement was observed for oxacillin in S. aureus, vancomycin in enterococci, carbapenems/cephalosporins in Enterobacteriaceae and rifampin in Cutibacterium species.

Conclusion

The overall sensitivity for detection of antimicrobial resistance by mPCR directly from clinical samples was low. False-negative mPCR results occurred mainly in coagulase-negative staphylococci, especially for oxacillin and rifampin. However, the specificity of mPCR was high and a positive result reliably predicted antimicrobial resistance. Including universal primers in the PCR test assay may improve the detection rate but requires additional sequencing step.

Trial registration

www.clinicaltrials.gov No. NCT02530229, registered at 21 August 2015 (retrospectively registered).

Infection Protocols for Implants

Infection can be a devastating complication of surgically inserted prosthetic implants and intramedullary rods, plates and pins. About 2 million implants were inserted in the United States in 2004, and, despite appropriate perioperative antibiotics, approximately 5% of internal fixation devices became infected. Infection rates in fractures that pierce the skin can be as high as 22.7%. Complications of infection include excessive antibiotic use, implant removal, reoperation, and potential amputation. Infections caused by colonized prosthetic implants are often difficult to predict, diagnose, and treat, because they form biofilms. This article explores the approach to infected implants.

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.

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.

Impacts and Challenges of Advanced Diagnostic Assays for Transplant Infectious Diseases

The advanced technologies described in this chapter should allow for full inventories to be made of bacterial genes, their time- and place-dependent expression, and the resulting proteins as well as their outcome metabolites. The evolution of these molecular technologies will continue, not only in the microbial pathogens but also in the context of host-pathogen interactions targeting human genomics and transcriptomics. Their performance characteristics and limitations must be clearly understood by both laboratory personnel and clinicians to ensure proper utilization and interpretation.

High percentage of microbial colonization of osteosynthesis material in clinically unremarkable patients

Stabilization of fractures with internal fixation devices is a common procedure and implant‐associated infections are a dreaded complication. The exact pathomechanism is not completely understood; however, microbial colonization of osteosynthesis material is considered a trigger for infection. This study aimed to determine the colonization rate of osteosynthesis implants in patients with no clinical or laboratory signs of infection, using two methods, conventional culture and polymerase chain reaction (PCR) of sonication fluid. Fifty‐seven patients aged between 18 and 79 years without signs of infection who underwent routine removal of osteosynthesis devices between March 2015 and May 2017 were included in this study. Osteosynthesis material was investigated by sonication followed by cultivation of the sonication fluid in blood culture bottles and PCR analysis, simultaneously. Additionally, electron scanning microscopy was performed in nine representative implants to evaluate biofilm production. Thirty‐two (56.1%) implants showed a positive result either by culture or PCR with coagulase‐negative staphylococci being the most commonly identified microorganism (68.1%). Furthermore, the detection rate of the culture (50.9%) was significantly higher compared to PCR (21.1%). The scanning electron microscopy imaging demonstrated biofilm‐like structures in four of six culture and/or PCR‐positive samples. This study is the first, to the best of our knowledge, to demonstrate bacterial colonization of osteosynthesis implants in healthy patients with no clinical or laboratory signs of infection. Colonization rate was unexpectedly high and conventional culture was superior to PCR in microbial detection. The common understanding that colonization is a trigger for infection underlines the need for strategies to prevent colonization of implant material like antibiotic‐loaded coating or intraoperative gel application.

What Is the Role of Diagnostic and Therapeutic Sonication in Periprosthetic Joint Infections?

BACKGROUND

Periprosthetic joint infection (PJI) is one of the most dreaded complications in joint replacement surgery. Diagnosis and treatment can be difficult and biofilms are of major concern due to their low susceptibility toward antibiotics.

METHODS

This review focuses on the use of sonication as an evolving diagnostic and adjunct treatment modality in the context of PJI. Therapeutic application of sonication is discussed separately for its (i) direct action on bacteria, (ii) synergistic effects with antibiotics, and (iii) effects on release of antibiotics from bone cement.

RESULTS

Used as a diagnostic tool, sonication shows promising results with respect to sensitivity and specificity when compared to conventional methods, notably after previous administration of antibiotics. As an adjunct treatment modality, the chemical, physical, and mechanical effects of sonication are primarily driven by cavitation and recognized as the main cause for bactericidal effects but the exact underlying mechanisms have not been identified yet. Sonication alone does not have the ability to completely eradicate biofilms but synergistic effects when used in conjunction with antibiotics have been reported. There is also evidence for enhanced antibiotic release from bone cement.

CONCLUSION

Sonication is as an evolving modality in the context of PJIs. As a diagnostic tool, it has not been introduced in routine clinical practice and sonication as a treatment modality in PJIs is still in an experimental stage. Factors such as frequency, pressure, chemical activity, intensity, and exposure time need to be evaluated for optimal application of sonication and may also improve study comparison.

Comparison of Genus Specific PCR and Culture with or without Sonication for Microbiological Diagnosis of Vascular Graft Infection

OBJECTIVES

Vascular graft infections (VGIs) are severe and require prolonged adequate antimicrobial therapy. However, up to 45% of conventional cultures are negative. Sonication and genus specific PCRs for microbiological diagnosis of VGI was evaluated.

METHODS

Samples were prospectively obtained from explanted vascular grafts in Bordeaux University Hospital. Conventional bacterial cultures with and without prior sonication of samples were performed. A genus specific PCR assay panel, targeting the most frequent bacteria involved in VGI (Staphylococcus, Streptococcus, Enterococcus, and Enterobacteriaceae), was also applied to sonicate fluids. The performance of these three diagnostic strategies was compared.

RESULTS

Forty-five patients (118 samples) were included between July 2014 and October 2015. Six patients had no infection and 39 had a VGI. Sensitivities of graft culture, sonicate fluid culture, and genus specific PCR were 85.7%, 89.7%, and 79.5%, respectively. Specificities were 100%, 100%, and 83.3%, respectively. Sonicate fluid culture was positive for five graft samples (from four patients) with negative culture without sonication. Four VGIs were detected by PCR only (3 patients had previously received antibiotics). For 15 patients with positive graft cultures, PCR identified at least one additional bacterium compared with culture, thus 30 additional bacteria for all included patients. By combining sonicate fluid culture and PCR, a microbiological diagnosis was obtained for all patients with VGI.

CONCLUSIONS

There was no statistical difference between performances of culture with and without sonication and genus specific PCR. However, combining sonicate fluid cultures and PCR may be the best strategy for microbiological diagnostic of VGI.

Meta-analysis of sonication prosthetic fluid PCR for diagnosing periprosthetic joint infection

Periprosthetic joint infection (PJI) is a catastrophic complication following total joint arthroplasty. Until now, the diagnosis of PJI is still confronted with difficulties, which is characterized by technical limitations. The question of whether sonication fluid PCR can provide high value in the diagnosis of PJI remains unanswered. This meta-analysis included 9 studies that evaluated PCR assays of sonication fluid for the diagnosis of PJI. The pooled sensitivity, specificity, Positive likelihood ratio (PLR), Negative likelihood ratio (NLR) and Diagnostic odds ratio (DOR) were 0.75 (95% confidence interval [CI], 0.71 to 0.81), 0.96 (CI, 0.94 to 0.97), 18.24 (CI, 6.07 to 54.78), 0.27 (CI, 0.20 to 0.36) and 86.97 (CI, 37.08 to 203.97), respectively. The AUC value of the SROC was 0.9244 (standard error, 0.0212). Subgroup analyses showed that use of multiplex PCR and may improve sensitivity and specificity. The results of this meta-analysis showed that PCR of fluid after sonication is reliable and of great value in PJI diagnosis.

Combination of conventional culture, vial culture, and broad-range PCR of sonication fluid for the diagnosis of prosthetic joint infection

We assessed the value of conventional culture, vial culture, and broad-range PCR of the sonication fluid (SF), individually or in combinations, for the diagnosis of prosthetic joint infection (PJI). We studied 114 consecutive patients (median age:72.5 years, males: 28.07%) undergoing removal of a total knee or hip prosthesis. By non-microbiologic criteria, 87 patients had aseptic failure, and 27 PJI. All patients had periprosthetic tissue culture, sonication of prosthesis, and study of SF by conventional and vial culture, and PCR. Compared to tissue culture, each test was significantly more sensitive and less specific. If only one test was positive, the sensitivity was 88.46% and specificity 64.29%. If all three SF tests were positive, sensitivity, and NPV were decreasing (34.6% and 80.23%), but specificity and PPV were increasing up to 98.57% and 90.9%, respectively, outperforming tissue culture. A triple negative test practically excluded PJI.

Value of PCR in sonication fluid for the diagnosis of orthopedic hardware-associated infections: Has the molecular era arrived?

INTRODUCTION

Bone healing disturbance following fracture fixation represents a continuing challenge. We evaluated a novel fully automated polymerase chain reaction (PCR) assay using sonication fluid from retrieved orthopedic hardware to diagnose infection.

PATIENTS AND METHODS

In this prospective diagnostic cohort study, explanted orthopedic hardware materials from consecutive patients were investigated by sonication and the resulting sonication fluid was analyzed by culture (standard procedure) and multiplex PCR (investigational procedure). Hardware-associated infection was defined as visible purulence, presence of a sinus tract, implant on view, inflammation in peri-implant tissue or positive culture. McNemar's chi-squared test was used to compare the performance of diagnostic tests. For the clinical performance all pathogens were considered, whereas for analytical performance only microorganisms were considered for which primers are included in the PCR assay.

RESULTS

Among 51 patients, hardware-associated infection was diagnosed in 38 cases (75%) and non-infectious causes in 13 patients (25%). The sensitivity for diagnosing infection was 66% for peri-implant tissue culture, 84% for sonication fluid culture, 71% (clinical performance) and 77% (analytical performance) for sonication fluid PCR, the specificity of all tests was >90%. The analytical sensitivity of PCR was higher for gram-negative bacilli (100%), coagulase-negative staphylococci (89%) and Staphylococcus aureus (75%) than for Cutibacterium (formerly Propionibacterium) acnes (57%), enterococci (50%) and Candida spp. (25%).

CONCLUSION

The performance of sonication fluid PCR for diagnosis of orthopedic hardware-associated infection was comparable to culture tests. The additional advantage of PCR was short processing time (<5 h) and fully automated procedure. With further improvement of the performance, PCR has the potential to complement conventional cultures.

Evaluation of the use of sonication of retrieved implants for the diagnosis of prosthetic joint infection in a routine setting

In order to evaluate the usefulness of sonication of retrieved implants for the diagnosis of prosthetic joint infection (PJI) in a large group of patients in a routine setting, we designed a 3-year retrospective study. Patients were classified into two groups: those meeting the clinical criteria of PJI and those that did not (control group). Two hundred patients and 276 samples were included. The types of infection were early (n = 44), delayed (n = 53), positive intraoperative cultures (n = 13) and late-acute (n = 8). The culture sensitivities of sonicate fluid, periprosthetic tissue, synovial fluid and combination of periprosthetic tissue and/or synovial fluid were 69.5, 52.8, 54.8 and 60.2%, respectively. The specificities were 97.6, 90.3, 93.0 and 89.9%, respectively. Sonicate fluid culture of implants was more sensitive than peri-implant tissue, synovial fluid and combination of periprosthetic tissue and/or synovial fluid for all infection types, though it was especially useful in delayed infection: 91.3% vs. 60.0% (p = 0.0015), 63.2% (p = 0.0005) and 66.7% (p = 0.0001), respectively. When sonicate fluid culture of implants was performed in addition to conventional cultures, the sensitivity increased significantly in total (from 60.2 to 77.1%) and delayed PJI (from 45.1 to 71.7%). On the other hand, for early PJI, sonicate fluid culture of prosthesis was not superior to conventional diagnostic methods.

Performance of automated multiplex PCR using sonication fluid for diagnosis of periprosthetic joint infection: a prospective cohort

PURPOSE

Sonication of explanted prostheses improved the microbiological diagnosis of periprosthetic joint infections (PJI). We evaluated the performance of automated multiplex polymerase chain reaction (PCR) using sonication fluid for the microbiological diagnosis of PJI.

METHODS

In a prospective cohort using uniform definition criteria for PJI, explanted joint prostheses were investigated by sonication and the resulting sonication fluid was analyzed by culture and multiplex PCR. McNemar's Chi-squared test was used to compare the performance of diagnostic tests.

RESULTS

Among 111 patients, PJI was diagnosed in 78 (70%) and aseptic failure in 33 (30%). For the diagnosis of PJI, the sensitivity and specificity of periprosthetic tissue culture was 51 and 100%, of sonication fluid culture 58 and 100%, and of sonication fluid PCR 51 and 94%, respectively. Among 70 microorganisms, periprosthetic tissue culture grew 52 (74%), sonication fluid culture grew 50 (71%) and sonication fluid PCR detected 37 pathogens (53%). If only organisms are considered, for which primers are included in the test panel, PCR detected 37 of 58 pathogens (64%). The sonication fluid PCR missed 19 pathogens (predominantly oral streptococci and anaerobes), whereas 7 additional microorganisms were detected only by PCR (including Cutibacterium spp. and coagulase-negative staphylococci).

CONCLUSIONS

The performance of multiplex PCR using sonication fluid is comparable to culture of periprosthetic tissue or sonication fluid. The advantages of PCR are short processing time (< 5 h) and fully automated procedure. However, culture technique is still needed due to the low sensitivity and the need of comprehensive susceptibility testing. Modification of primers or inclusion of additional ones may improve the performance of PCR, especially of low-virulent organisms.

Assessment of the automated multiplex-PCR Unyvero i60 ITI® cartridge system to diagnose prosthetic joint infection: a multicentre study

OBJECTIVES

Prosthetic joint infections (PJI) are responsible for significant morbidity and mortality and their number continues to rise. Their management remains complex, especially the microbiological diagnosis. Besides 'homemade' tests developed by several teams, new molecular biology methods are now available with different analytical performance and usability.

METHODS

We studied the performances of one of these tests: ITI^® multiplex PCR (mPCR) by the Curetis^® company and compared it to either 'optimized' culture or 16S rRNA PCR. We performed a retrospective multicentre study to assess the contributions of mPCR in the diagnosis of PJI. We randomly selected 484 intraoperative specimens among 1252 of various types (biopsy, bone, tissue around the prosthesis, synovial fluid) from 251 patients in seven different hospitals. Each sample was treated according to the recommendations of the manufacturer.

RESULTS

In all, 154 out of 164 (93.9%) samples negative in culture were negative with the mPCR. Among the 276 positive samples in culture, 251 (90.9%) were monomicrobial, of which 119 (47.4%) were positive with the mPCR, and 25 (9.1%) were polymicrobial, of which 12 (48%) were positive with the mPCR. The concordance rate of mPCR with culture was 58.1% (53.6%-62.7%) and the concordance rate with 16S rRNA PCR was 70.1% (65.5%-74.6%).

CONCLUSION

This new standardized molecular test showed a lack of detection when the bacterial inoculum was low (number of positive media per sample and number of colonies per media) but can be useful when patients have received antibiotic therapy previously.

Use of an experimental model to evaluate infection resistance of meshes in abdominal wall surgery

BACKGROUND

Staphylococcal species are the most common organisms causing prosthetic mesh infections, however, infections due to rapidly growing mycobacteria are increasing. This study evaluates the resistance of biomaterial for abdominal wall prostheses against the development of postoperative infection in a rat model.

MATERIAL AND METHODS

In 75 rats, we intramuscularly implanted three different types of prostheses: (1) low-density polypropylene monofilament mesh (PMM), (2) high-density PMM, and (3) a composite prosthesis composed of low-density PMM and a nonporous hydrophilic film. Meshes were inoculated with a suspension containing 10⁸ colony-forming units of Staphylococcus aureus, Staphylococcus epidermidis, Mycobacterium fortuitum, or Mycobacterium abscessus before wound closure. Animals were sacrificed on the eighth day postoperatively for clinical evaluation, and the implants were removed for bacteriologic analyses.

RESULTS

Prostheses infected with S aureus showed a higher bacterial viability, worse integration, and clinical outcome compared with infection by other bacteria. Composite prostheses showed a higher number of viable colonies of both M fortuitum and Staphylococcus spp., with poorer integration in host tissue. However, when the composite prosthesis was infected with M abscessus, a lower number of viable bacteria were isolated and a better integration was observed compared with infection by other bacteria.

CONCLUSIONS

Considering M abscessus, a smaller collagen-free contact surface shows better resistance to infection, however, depending on the type of bacteria, prostheses with a large surface, and covered with collagen shows reduced resistance to infection, worse integration, and worse clinical outcome.

Evaluation of a commercial multiplex PCR (Unyvero i60®) designed for the diagnosis of bone and joint infections using prosthetic-joint sonication

BACKGROUND

The development of sonication protocols over the last few years has improved the sensitivity of conventional cultures for the diagnosis of prosthetic-joint infection (PJI). However, the development of a new, specifically designed kit for the molecular diagnosis of PJI could provide a major improvement in this field.

METHODS

Prostheses retrieved from patients who underwent implant removal from May 2014 to May 2015 were sent for culture, and processed according to a previously defined protocol that included sonication. Furthermore, 180 microlitres of sonication fluid were used to carry out the multiplex PCR test (Unyvero i60 system^®). A comparison of the sensitivity, specificity, positive (PPV) and negative (NPV) predictive value, was performed. The study was approved by the Clinical Research Ethics Committee.

RESULTS

The analysis included 88 prostheses from 68 patients (1.29 prostheses/patient). The type of prostheses studied were knee (n=55), total hip (n=26), partial hip (n=5), and shoulder (n=2). Twenty-nine patients were diagnosed with a PJI (15 delayed, 12 acute, and 2 haematogenous infections). In 24 cases, the result of the PCR was positive, all but 1 corresponding to patients with clinical criteria of PJI. Nine resistance mechanisms were detected from 5 samples. The Unyvero i60 system^® showed slightly better results than traditional culture in terms of specificity and PPV.

CONCLUSIONS

The Unyvero i60 system^® may play a role in rapid diagnosis of PJI, due to its high specificity and PPV. However, despite these results, cultures have to be performed to detect organisms not detected by the system.

Diagnostic performance of swab PCR as an alternative to tissue culture methods for diagnosing infections associated with fracture fixation devices

BACKGROUND

Molecular procedures could potentially improve diagnoses of orthopaedic implant-related infections, but are not yet clinically implemented. Analysis of sonication fluid shows the highest sensitivity for diagnosing implant infections in cases of revision surgery with implant removal. However, there remains controversy regarding the best method for obtaining specimens in cases of revision surgery with implant retention. Tissue culture is the most common diagnostic method for pathogen identification in such cases. Here we aimed to assess the diagnostic performance of swab PCR analysis compared to tissue culture from patients undergoing revision surgery of fracture fixation devices.

METHODS

We prospectively investigated 62 consecutive subjects who underwent revision surgery of fracture fixation devices during a two-year period. Tissue samples were collected for cultures, and swabs from the implant surface were obtained for 16S rRNA PCR analysis. Subjects were classified as having an implant-related infection if (1) they presented with a sinus tract or open wound in communication with the implant; or (2) purulence was encountered intraoperatively; or (3) two out of three tissue cultures tested positive for the presence of the same pathogen. Tissue culture and swab PCR results from the subjects were used to calculate the sensitivity, specificity, accuracy, positive predictive value (PPV), negative predictive value (NPV), and area under the ROC curve (AUC) for identifying an orthopaedic implant-related infection.

RESULTS

Orthopaedic implant-related infections were detected in 51 subjects. Tissue culture identified infections in 47 cases, and swab PCR in 35 cases. Among the 11 aseptic cases, tissue culture was positive in 2 cases and swab PCR in 4 cases. Tissue culture showed a significantly higher area under the ROC curve for diagnosing infection (AUC=0.89; 95% CI, 0.67-0.96) compared to swab PCR (AUC=0.66; 95% CI, 0.46-0.80) (p=0.033).

CONCLUSIONS

Compared to swab PCR, tissue culture showed better performance for diagnosing orthopaedic implant-related infection. Although molecular methods are expected to yield higher diagnostic accuracy than cultures, it appears that the method of obtaining specimens plays an important role. Improved methods of specimen collection are required before swab PCR can become a reliable alternative to tissue-consumptive methods.

Obtaining High Quality DNA from Diverse Clinical Samples

Nucleic acids can be obtained in numerous ways from clinical specimens; however, the quality of the nucleic acid is only as good as the sampling and isolation protocol. While nucleic acids may be extracted they may not be representative of the original source. Large areas of tissue and explanted hardware must be successfully surveyed to reflect the overall clinical picture. Once good sampling technique has been established, successful bacterial nucleic acid isolation is essential. Clinical samples may be difficult to process because of the presence of scar tissue, bone, implants, and bacterial biofilms. The following protocols provide details on sampling techniques and DNA isolation from a variety of clinical samples which can then be used in downstream molecular applications including PCR-MS-ESI-TOF technology.

Diagnosis of Periprosthetic Infection: Novel Developments

The diagnosis of periprosthetic joint infection (PJI) has been performed by obtaining a history and physical examination, blood tests, and analysis of the synovial fluid and tissue samples. The measurement of serum biomarkers are routinely used to diagnose PJI. These markers may be elevated in other inflammatory conditions, necessitating the need for more specific biomarkers to diagnose PJI. Serum biomarkers may be more specific to PJI. Synovial CRP, α-defensin, human β-defensin-2 and -3, leukocyte esterase, and cathelicidin LL-37 biomarkers hold promise for the diagnosis of PJI.

Missed low-grade infection in suspected aseptic loosening has no consequences for the survival of total hip arthroplasty

BACKGROUND AND PURPOSE

Aseptic loosening and infection are 2 of the most common causes of revision of hip implants. Antibiotic prophylaxis reduces not only the rate of revision due to infection but also the rate of revision due to aseptic loosening. This suggests under-diagnosis of infections in patients with presumed aseptic loosening and indicates that current diagnostic tools are suboptimal. In a previous multicenter study on 176 patients undergoing revision of a total hip arthroplasty due to presumed aseptic loosening, optimized diagnostics revealed that 4-13% of the patients had a low-grade infection. These infections were not treated as such, and in the current follow-up study the effect on mid- to long-term implant survival was investigated.

PATIENTS AND METHODS

Patients were sent a 2-part questionnaire. Part A requested information about possible re-revisions of their total hip arthroplasty. Part B consisted of 3 patient-related outcome measure questionnaires (EQ5D, Oxford hip score, and visual analog scale for pain). Additional information was retrieved from the medical records. The group of patients found to have a low-grade infection was compared to those with aseptic loosening.

RESULTS

173 of 176 patients from the original study were included. In the follow-up time between the revision surgery and the current study (mean 7.5 years), 31 patients had died. No statistically significant difference in the number of re-revisions was found between the infection group (2 out of 21) and the aseptic loosening group (13 out of 152); nor was there any significant difference in the time to re-revision. Quality of life, function, and pain were similar between the groups, but only 99 (57%) of the patients returned part B.

INTERPRETATION

Under-diagnosis of low-grade infection in conjunction with presumed aseptic revision of total hip arthroplasty may not affect implant survival.

Efficacy of Single-stage Revision with Aggressive Debridement Using Intra-articular Antibiotics in the Treatment of Infected Joint Prosthesis

Prosthetic joint infections (PJI) of the hip and knee are uncommon, but result in significant morbidity and mortality when they do occur. Current management consists of a combination of either single- or two-stage exchange of the prosthesis and/or exchange of polymer components with intravenous (IV) antibiotics (4–6 weeks) and intraoperative debridement of the joint prior to reimplantation. However, failure rate, morbidity, and expense associated with current management are high, especially if the infection involves resistant pathogens and/or osteomyelitis. Also, the current use of systemic antibiotics does not allow for high local concentrations of the drug and biofilm penetration of the infected prosthesis. To overcome these difficulties, we examined the outcomes of aggressive operative debridement of the infected prosthesis. This was achieved through the use of a single-stage revision and administration of high concentrations of local intra-articular antibiotics via Hickman catheters. We present 57 patients with PJI who were treated with intra-articular antibiotics and single-stage revisions. Minimal systemic toxicity was observed along with a 100% microbiologic cure rate and 89% without relapse at 11-month follow-up despite isolation of multidrug resistant pathogens. This is the largest study to date using this method in the treatment of PJI.

The role of microbial biofilms in prosthetic joint infections

Prosthetic joint infection (PJI) still remains a significant problem. In line with the forecasted rise in joint replacement procedures, the number of cases of PJI is also anticipated to rise. The formation of biofilm by causative pathogens is central to the occurrence and the recalcitrance of PJI. The subject of microbial biofilms is receiving increasing attention, probably as a result of the wide acknowledgement of the ubiquity of biofilms in the natural, industrial, and clinical contexts, as well as the notorious difficulty in eradicating them. In this review, we discuss the pertinent issues surrounding PJI and the challenges posed by biofilms regarding diagnosis and treatment. In addition, we discuss novel strategies of prevention and treatment of biofilm-related PJI.

Do crosslinking and vitamin E stabilization influence microbial adhesions on UHMWPE-based biomaterials?

BACKGROUND

Microorganism adhesion on polyethylene for total joint arthroplasty is a concern. Many studies have focused on vitamin E-stabilized ultrahigh-molecular-weight polyethylene (UHMWPE), whereas first-generation, highly crosslinked UHMWPE, which is the most commonly used in clinical practice, has been scarcely evaluated.

QUESTIONS/PURPOSES

We aimed (1) to compare the adherence of Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli, and Candida albicans with virgin (untreated) UHMWPE (PE) and crosslinked UHMWPE (XLPE); (2) to correlate the results with the biomaterial surface properties; and (3) to determine whether the decreased adhesion on vitamin E-stabilized UHMWPE (VE-PE) previously recorded for bacteria can also be confirmed for C albicans.

METHODS

Microbial adhesion of biofilm-producing American Type Culture Collection (ATCC) and clinical strains on XLPE and VE-PE were compared with PE at 3, 7, 24, and 48 hours of incubation and quantified, as colony forming units (CFU)/mL, using a sonication protocol. Sample surfaces were characterized by scanning electron microscopy, roughness and contact angle measurements, attenuated total reflection-Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy (XPS) to reveal qualitative differences in surface composition and topography that could influence the microbial adhesion. The results were analyzed by descriptive statistics and tested by unpaired t-tests.

RESULTS

All microorganisms, both ATCC and clinical strains, showed lower adhesion (p < 0.05) on XLPE with adhesion percentages ranging from 18% to 25%, compared with PE with adhesion percentages ranging from 51% to 55%, after 48 hours. Only the ATCC S epidermidis showed a reduced adhesion profile even at 3 hours (adhesion ratio of 14% on XLPE versus 50% on PE) and 24 hours (19% on XLPE versus 55% on PE) of incubation. ATCC and clinical C albicans were less adherent to XLPE than to PE (p < 0.05) showing even at the earlier incubation time points adhesion values always of 10(3) CFU/mL and 10(4) CFU/mL, respectively. Roughness and contact angle were 0.8 ± 0.2 μm and 92° ± 3°, respectively, with no differences among samples. Qualitative differences in the surface chemical composition were revealed by XPS only. A confirmation of the decreased adhesion on VE-PE respect to PE was also registered here for C albicans strains (p < 0.05).

CONCLUSIONS

Vitamin E stabilization and crosslinking of UHMWPE are capable of reducing microbial adhesion. Further studies are needed to fully elucidate the mechanisms of modulation of microbial adhesion to medical-grade UHMWPE.

CLINICAL RELEVANCE

Our results suggest that VE-PE and XLPE may have an added benefit of being more resistant to bacterial adhesion, even fungal strains.

Human beta-defensin-3 producing cells in septic implant loosening

Human β-defensin-3 (hBD-3) has been found in synovial fluid and later in periprosthetic tissues in septic joint implant loosening. The aim of the present study was to identify its cellular sources. Tissue samples from 12 patients were analyzed. A fully automatic Leica BOND MAX staining robot was used. Affinity-purified rabbit anti-human hBD-3 IgG was applied in a two-layer horse radish peroxidase/anti-rabbit-labeled polymer method. Double immunofluorescence of hBD3 together with CD68, CD31, heat shock protein 47 (HSP47) and mast cell tryptase (MCT) staining was done. Human BD-3 was found in monocyte/macrophage-like cells, vascular endothelial cells and fibroblasts-like cells, but was weakly expressed in foreign body giant cells and negative in neutrophils. Human BD-3 was found in CD68 and CD31 immunoreactive cells, whereas HSP47 and MCT positive cells were hBD-3 negative. Immunostaining of hBD-3 was strong in some tissue areas but weak or absent in others. Monocyte/macrophages and endothelial cells were established in this study as the major cellular sources of hBD-3 in septic loosening, but fibroblasts and foreign body giant cells can also contribute to its production. The heterogeneous topological staining of hBD-3 suggests local regulation, possibly by bacterial products, damage-associated molecular patterns and cytokines. The results explain the increased synovial fluid/tissue concentrations of hBD-3 in septic loosening.

Bacterial and fungal DNA extraction from blood samples: manual protocols

A critical point of molecular diagnosis of systemic infections is the method employed for the extraction of microbial DNA from blood. A DNA isolation method has to be able to fulfill several fundamental requirements for optimal performance of diagnostic assays. First of all, low- and high-molecular-weight substances of the blood inhibitory to downstream analytical reactions like PCR amplification have to be removed. This includes human DNA which is a known source of false-positive results and factor decreasing the analytical sensitivity of PCR assays by unspecific primer binding. At the same time, even extremely low amounts of microbial DNA need to be supplied to molecular diagnostic assays in order to detect low pathogen loads in the blood. Further, considering the variety of microbial etiologies of sepsis, a method should be capable of lysing Gram-positive, Gram-negative, and fungal organisms. Last, extraction buffers, reagents, and consumables have to be free of microbial DNA which leads to false-positive results. Here, we describe manual methods which allow the extraction of microbial DNA from small- and large-volume blood samples for the direct molecular analysis of pathogen.

PCR diagnostic system in the treatment of prosthetic joint infections

In our prospective study, we examined whether a multiplex PCR diagnostic method is suitable for the primary detection of pathogens. We also examined the possibility and sensitivity of detecting genes responsible for biofilm production and methicillin resistance. From 2007 to 2009, 94 patients were included in the study. A UNB (universal detection of 16S ribosomal bacterial DNA) and UNF (universal detection of pathogenic fungi) were used in the primary detection. A multiplex assay for biofilm production, methicillin resistance allowed us to distinguish between Gram positivity and negativity and to detect Staphylococci. From all the samples, the culture was positive in 53.2 % of cases, and by using the UNB method, we detected bacteria in 79.8 % of cases-the UNF detection of fungi was positive in 10.6 % of cases. In 75 % of positive findings, we detected a Gram-negative bacterium in 65.3 % of cases. In 47.2 % of Staphylococci detected, the ability to produce biofilm was confirmed. 61.1 % of the Staphylococci exhibited a methicillin resistance. Our multiplex scheme cannot yet fully replace microbial cultivation but can be a rational guide when choosing an appropriate antibiotic therapy in cases where the microbial culture is negative.

Periprosthetic joint infections: a clinical practice algorithm

PURPOSE

periprosthetic joint infection (PJI) accounts for 25% of failed total knee arthroplasties (TKAs) and 15% of failed total hip arthroplasties (THAs). The purpose of the present study was to design a multidisciplinary diagnostic algorithm to detect a PJI as cause of a painful TKA or THA.

METHODS

from April 2010 to October 2012, 111 patients with suspected PJI were evaluated. The study group comprised 75 females and 36 males with an average age of 71 years (range, 48 to 94 years). Eighty-four patients had a painful THA, while 27 reported a painful TKA. The stepwise diagnostic algorithm, applied in all the patients, included: measurement of serum C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) levels; imaging studies, including standard radiological examination, standard technetium-99m-methylene diphosphonate (MDP) bone scan (if positive, confirmation by LeukoScan was obtained); and joint aspiration with analysis of synovial fluid.

RESULTS

following application of the stepwise diagnostic algorithm, 24 out of our 111 screened patients were classified as having a suspected PJI (21.7%). CRP and ESR levels were negative in 84 and positive in 17 cases; 93.7% of the patients had a positive technetium-labeled bone scan, and 23% a positive LeukoScan. Preoperative synovial fluid analysis was positive in 13.5%; analysis of synovial fluid obtained by preoperative aspiration showed a leucocyte count of > 3000 cells μ/l in 52% of the patients.

CONCLUSIONS

the present study showed that the diagnosis of PJI requires the application of a multimodal diagnostic protocol in order to avoid complications related to surgical revision of a misdiagnosed "silent" PJI.

LEVEL OF EVIDENCE

Level IV, therapeutic case series.

Improved diagnosis of infection associated with osteosynthesis by use of sonication of fracture fixation implants

Previous studies have shown that sonication fluid cultures from removed orthopedic devices improved the microbiological diagnosis of orthopedic implant-associated infections; however, few of these investigations have applied sonication to the removed fracture fixation devices to evaluate its utility for the diagnosis of osteosynthesis-associated infection (OAI). We compared sonication fluid to conventional tissue cultures from 180 subjects with different sizes of plates and screws (n = 156), spinal implants (n = 26), and intramedullary nails (n = 3), of whom 125 and 55 subjects had OAI and noninfected osteosynthesis (NIO), respectively. The sensitivity for detecting OAI was 90.4% for sonication fluid culture and 56.8% for periprosthetic tissue cultures (P < 0.05), and the specificities were 90.9% and 96.4%, respectively. Sonication fluid culture detected more pathogens than peri-implant tissue culture (113 versus 71; P < 0.001), while polymicrobial infections were diagnosed by sonication fluid cultures and tissue cultures in 20.8% and 8% (P < 0.001), respectively. Microbiological diagnosis was achieved exclusively by sonication fluid cultures for 47 (90.4%) subjects, and among them, 18 (38.3%) had previously received antibiotics, whereas in five (9.6%) infected subjects, tissue culture was positive and the sonication fluid culture was negative. Among 39 (31.2%) OAI cases receiving antibiotics, the identification of the organisms occurred in 38.5% and 82.1% of the tissue and sonication fluid cultures, respectively (P < 0.049). We demonstrated that sonication fluid culture from removed osteosyntheses has the potential for improving the microbiological diagnosis of OAI.

Characterization of denaturation and renaturation of DNA for DNA hybridization

OBJECTIVES

The present study was designed to systematically characterize the denaturation and the renaturation of double stranded DNA (dsDNA), which is suitable for DNA hybridization.

METHODS

A series of physical and chemical denaturation methods were implemented on well-defined 86-bp dsDNA fragment. The degree of each denaturation was measured and the most suitable denaturation method was determined. DNA renaturation tendency was also investigated for the suggested denaturation method.

RESULTS

Heating, beads mill, and sonication bath did not show any denaturation for 30 minutes. However probe sonication fully denatured DNA in 5 minutes. 1 mol/L sodium hydroxide (alkaline treatment) and 60% dimethyl sulfoxide (DMSO) treatment fully denatured DNA in 2-5 minutes.

CONCLUSIONS

Among all the physical methods applied, the direct probe sonication was the most effective way to denature the DNA fragments. Among chemical methods, 60% DMSO was the most adequate denaturation method since it does not cause full renaturation during DNA hybridization.