Identification of silent prosthetic joint infection: preliminary report of a prospective controlled study

In vitro models for studying implant-associated biofilms - A review from the perspective of bioengineering 3D microenvironments

Biofilm research has grown exponentially over the last decades, arguably due to their contribution to hospital acquired infections when they form on foreign body surfaces such as catheters and implants. Yet, translation of the knowledge acquired in the laboratory to the clinic has been slow and/or often it is not attempted by research teams to walk the talk of what is defined as 'bench to bedside'. We therefore reviewed the biofilm literature to better understand this gap. Our search revealed substantial development with respect to adapting surfaces and media used in models to mimic the clinical settings, however many of the in vitro models were too simplistic, often discounting the composition and properties of the host microenvironment and overlooking the biofilm-implant-host interactions. Failure to capture the physiological growth conditions of biofilms in vivo results in major differences between lab-grown- and clinically-relevant biofilms, particularly with respect to phenotypic profiles, virulence, and antimicrobial resistance, and they essentially impede bench-to-bedside translatability. In this review, we describe the complexity of the biological processes at the biofilm-implant-host interfaces, discuss the prerequisite for the development and characterization of biofilm models that better mimic the clinical scenario, and propose an interdisciplinary outlook of how to bioengineer biofilms in vitro by converging tissue engineering concepts and tools.

Risk of Periprosthetic Joint Infection after Posttraumatic Hip Arthroplasty following Acetabular Fractures

BACKGROUND

Raised complication rates have been reported for total hip arthroplasty (THA) in posttraumatic hip joints after acetabular fractures with prior open reduction and internal fixation (ORIF). The present study evaluated (I) postoperative surgical site infection and the risk of early infection following THA in posttraumatic hip joints after acetabular fractures and (II) the discriminatory ability of preoperative C-reactive protein (CRP) blood levels for periprosthetic joint infection (PJI).

MATERIALS AND METHODS

Patients were included who had undergone THA (2014-2019) after prior ORIF, and nonsurgically treated acetabular fractures. Patients' demographics and the duration between fracture and THA implantation were assessed. Preoperative diagnostic testing (laboratory results, hip aspirations) as well as the results of intraoperative microbiological swabs and sonication were also evaluated. Postoperative complications were recorded.

RESULTS

Sixty-seven patients (51 men/16 women) were included, with a mean age of 54.7 ± 14.0 years (range: 18.0-82.9). The mean time between acetabular fracture and THA was 13.5 ± 14.9 years (0.2-53.5). Four subgroups were classified: subgroup I (nonsurgical, n = 15), subgroup II (complete removal of osteosynthesis, n = 8), subgroup III (partial removal of osteosynthesis, n = 15), and subgroup IV (remaining osteosynthesis, n = 29). Preoperative CRP blood levels were normal. CRP levels had no discriminatory ability to predict PJI (AUC: 0.43). Positive microbiological swabs were assessed in subgroups III (n = 1) and IV (n = 2). Complications during follow-up occurred in subgroups I (one aseptic loosening [6.7%]), III (one wound revision [6.7%], two low-grade infections [13.3%]), and IV (three low-grade infections [10.3%]).

CONCLUSION

High infection rates were found in patients with THA after acetabular fracture with remaining implants or partial implant removal. Serum CRP alone seems to be a poor predictor. Therefore, an extensive diagnostic algorithm can help to detect an occult infection, including preoperative hip aspiration (microbiological samples and measurements of synovial CRP, WBC, and alpha-defensin levels). Intraoperative tissue samples and sonication results should be obtained during THA implantation.

Occult prosthetic aortic valve endocarditis caused by Propionibacterium acnes: a case report

We present an unusual case of occult mechanical aortic valve endocarditis caused by Propionibacterium acnes (P. acnes), which occurred five years after the initial cardiac surgical procedure. The only potential source of this infection from the patient's past medical history was a gastric band removal followed by a gastric bypass surgery, which was performed two years prior to her redo cardiac procedure. The patient's main presenting symptom was progressive dyspnoea with worsening of gradients across the mechanical aortic valve. Of note, she had no cardinal symptoms of infection. The patient underwent redo bioprosthetic aortic valve replacement with aortic root replacement. Prosthetic valve cultures grew P. acnes, while blood cultures remained negative. She was started on intravenous antibiotics for six weeks and her postoperative course was uneventful. She remained symptom-free six months postoperatively. This case opens the discussion for the importance of administering antibiotics prophylaxis for endocarditis in patients with prosthetic heart valves undergoing gastric procedures.

Single-stage total hip arthroplasty after failed fixation of proximal femoral fractures: an increased risk for periprosthetic joint infections?

BACKGROUND

Higher complication rates have been reported for total hip arthroplasty (THA) after osteosynthesis of proximal femur fractures (PFF). This study evaluated the infection risk for conversion of internal fixation of PFF to THA by a single-staged procedure in the absence of clear infection signs.

METHODS

Patients undergoing a one-staged conversion to THA (2013-2018) after prior internal fixation of the proximal femur were included. Preoperative diagnostics with laboratory results, hip aspirations as well as intraoperative microbiology and sonication were assessed. Postoperative complications were recorded as well as patient demographics, duration between initial and conversion to THA, explanted osteosynthesis and implanted THA.

RESULTS

Fifty-eight patients (24 male/34 female, 62.8 ± 14.5 years) were included with a mean time of 3.8 ± 7.5 years between internal fixation and conversion to THA (45 cementless, 3 cemented, 3 hybrid and 7 hybrid inverse THAs). Preoperative mean blood level CRP was 8.36 ± 14 mg/l (reference value < 5 mg/l) and leukocyte count was 7.11 ± 1.84^3/µl (4.5-10.000^3/µl). Fifty patients had intraoperative microbiological diagnostics, with either swabs in 86.2% and/or sonication in 29.3%. Positive microbiological results were recorded in 10% (5 of 50 patients), with pathogens identified being mainly Staphylococcus. Complications after conversion occurred in 9.6% including a postoperative low-grade infection rate of 5.8% after a mean of 2.5 years.

CONCLUSION

This study found a positive microbiological test result in 10% of a one-stage conversion of PFF fixation to THA. Moreover, we found a high infection rate (5.8%) for early postoperative periprosthetic joint infection. Interestingly, CRP has not been proven to be an adequate parameter for low-grade infections or occult colonized implants. Therefore, we recommend a comprehensive pre- and intraoperative diagnostic including hip aspiration, swabs and sonication when considering one-staged revision.

Long-term outcome of two-stage revision surgery after hip and knee prosthetic joint infections: an observational study

Introduction: Two-stage revision surgery is the most frequently performed procedure in patients with a chronic periprosthetic joint infection (PJI). The infection eradication rates in the current literature differ between 54 % and 100 %, which could be attributed to different treatment strategies. The aim of this study was to retrospectively evaluate the infection eradication rate in patients with chronic PJI treated with two-stage revision surgery of the hip or knee in primary and re-revision cases. Methods: All patients treated with a two-stage revision for chronic PJI between 2005 and 2011 were analysed. Patient and infection characteristics were retrieved. Primary outcome was successful infection eradication at last follow-up. Successful eradication is specified as no need for subsequent revision surgery or suppressive antibiotic treatment. Results: Forty-seven patients were treated with a two-stage revision. Infection eradication was achieved in 36 out of 47 cases. Thirty-eight patients had positive cultures: 35 monomicrobial infections and 3 polymicrobial infections. Nine cases of culture-negative infections were identified. Accompanying eradication rates were 26 out of 35 cases, 2 out of 3 cases, and 8 out of 9 cases respectively. Mean follow-up was 128 (27–186) months. For hip and knee revisions the eradication rates were 22 out of 31 cases and 14 out of 16 cases respectively. After primary arthroplasty the infection was eradicated in 29 out of 38 cases and after re-revision in 7 out of 9 cases. Conclusion: In this study, the infection eradication rate for two-stage revision surgery after PJI of the hip and knee in primary and re-revision cases was 77 %. No statistically significant patient, infection and micro-organism characteristics were found which influence the infection eradication rates at long-term follow-up of 128 (27–186) months.

Deciphering the low abundance microbiota of presumed aseptic hip and knee implants

16S rRNA gene sequencing of DNA extracted from clinically uninfected hip and knee implant samples has revealed polymicrobial populations. However, previous studies assessed 16S rRNA gene sequencing as a technique for the diagnosis of periprosthetic joint infections, leaving the microbiota of presumed aseptic hip and knee implants largely unstudied. These communities of microorganisms might play important roles in aspects of host health, such as aseptic loosening. Therefore, this study sought to characterize the bacterial composition of presumed aseptic joint implant microbiota using next generation 16S rRNA gene sequencing, and it evaluated this method for future investigations. 248 samples were collected from implants of 41 patients undergoing total hip or knee arthroplasty revision for presumed aseptic failure. DNA was extracted using two methodologies-one optimized for high throughput and the other for human samples-and amplicons of the V4 region of the 16S rRNA gene were sequenced. Sequencing data were analyzed and compared with ancillary specific PCR and microbiological culture. Computational tools (SourceTracker and decontam) were used to detect and compensate for environmental and processing contaminants. Microbial diversity of patient samples was higher than that of open-air controls and differentially abundant taxa were detected between these conditions, possibly reflecting a true microbiota that is present in clinically uninfected joint implants. However, positive control-associated artifacts and DNA extraction methodology significantly affected sequencing results. As well, sequencing failed to identify Cutibacterium acnes in most culture- and PCR-positive samples. These challenges limited characterization of bacteria in presumed aseptic implants, but genera were identified for further investigation. In all, we provide further support for the hypothesis that there is likely a microbiota present in clinically uninfected joint implants, and we show that methods other than 16S rRNA gene sequencing may be ideal for its characterization. This work has illuminated the importance of further study of microbiota of clinically uninfected joint implants with novel molecular and computational tools to further eliminate contaminants and artifacts that arise in low bacterial abundance samples.

hBMSC-Derived Extracellular Vesicles Attenuate IL-1β-Induced Catabolic Effects on OA-Chondrocytes by Regulating Pro-inflammatory Signaling Pathways

Background: Human bone marrow-derived mesenchymal stromal cells (hBMSCs) provide a promising therapeutic approach in the cell-based therapy of osteoarthritis (OA). However, several disadvantages evolved recently, including immune responses of the host and regulatory hurdles, making it necessary to search for alternative treatment options. Extracellular vesicles (EVs) are released by multiple cell types and tissues into the extracellular microenvironment, acting as message carriers during intercellular communication. Here, we investigate putative protective effects of hBMSC-derived EVs as a cell-free approach, on IL-1β-stimulated chondrocytes obtained from OA-patients.

Methods: EVs were harvested from the cell culture supernatant of hBMSCs by a sequential ultracentrifugation process. Western blot, scanning electron microscopy (SEM), and nanoparticle tracking analysis (NTA) were performed to characterize the purified particles as EVs. Intracellular incorporation of EVs, derived from PHK26-labeled hBMSCs, was tested by adding the labeled EVs to human OA chondrocytes (OA-CH), followed by fluorescence microscopy. Chondrocytes were pre-stimulated with IL-1β for 24 h, followed by EVs treatment for 24 h. Subsequently, proliferation, apoptosis, and migration (wound healing) were analyzed via BrdU assay, caspase 3/7 assay, and scratch assay, respectively. With qRT-PCR, the relative expression level of anabolic and catabolic genes was determined. Furthermore, immunofluorescence microscopy and western blot were performed to evaluate the protein expression and phosphorylation levels of Erk1/2, PI3K/Akt, p38, TAK1, and NF-κB as components of pro-inflammatory signaling pathways in OA-CH.

Results: EVs from hBMSCs (hBMSC-EVs) promote proliferation and reduce apoptosis of OA-CH and IL-1β-stimulated OA-CH. Moreover, hBMSC-EVs attenuate IL-1β-induced reduction of chondrocyte migration. Furthermore, hBMSC-EVs increase gene expression of PRG4, BCL2, and ACAN (aggrecan) and decrease gene expression of MMP13, ALPL, and IL1ß in OA-CH. Notably, COL2A1, SOX9, BCL2, ACAN, and COMP gene expression levels were significantly increased in IL-1β⁺ EV groups compared with those IL-1β groups without EVs, whereas the gene expression levels of COLX, IL1B, MMP13, and ALPL were significantly decreased in IL-1β⁺ EV groups compared to IL-1β groups without EVs. In addition, the phosphorylation status of Erk1/2, PI3K/Akt, p38, TAK1, and NF-κB signaling molecules, induced by IL-1β, is prevented by hBMSC- EVs.

Conclusion: EVs derived from hBMSCs alleviated IL-1β-induced catabolic effects on OA-CH via promoting proliferation and migration and reducing apoptosis, probably via downregulation of IL-1ß-activated pro-inflammatory Erk1/2, PI3K/Akt, p38, TAK1, and NF-κB signaling pathways. EVs released from BMSCs may be considered as promising cell-free intervention strategy in cartilage regenerative medicine, avoiding several adverse effects of cell-based regenerative approaches.

Understanding Biofilms and Novel Approaches to the Diagnosis, Prevention, and Treatment of Medical Device-Associated Infections

Treatment of medical device-related infections is challenging and recurrence is common. The main reason for this is that microorganisms adhere to the surfaces of medical devices and enter into a biofilm state in which they display distinct growth rates, structural features, and protection from antimicrobial agents and host immune mechanisms compared with their planktonic counterparts. This article reviews how microorganisms form biofilms and the mechanisms of protection against antimicrobial agents and the host immune system provided by biofilms. Also discussed are innovative strategies for the diagnosis of biofilm-associated infection and novel approaches to treatment and prevention of medical device-associated infections.

Two-stage revision for the culture-negative infected total hip arthroplasty : A comparative study

Aims

Periprosthetic joint infection (PJI) remains a challenging complication following total hip arthroplasty (THA). It is associated with high levels of morbidity, mortality and expense. Guidelines and protocols exist for the management of culture-positive patients. Managing culture-negative patients with a PJI poses a greater challenge to surgeons and the wider multidisciplinary team as clear guidance is lacking.

Patients and Methods

We aimed to compare the outcomes of treatment for 50 consecutive culture-negative and 50 consecutive culture-positive patients who underwent two-stage revision THA for chronic infection with a minimum follow-up of five years.

Results

There was no significant difference in the outcomes between the two groups of patients, with a similar rate of re-infection of 6%, five years post-operatively. Culture-negative PJIs were associated with older age, smoking, referral from elsewhere and pre-operative antibiotic treatment. The samples in the culture-negative patients were negative before the first stage (aspiration), during the first-stage (implant removal) and second-stage procedures (re-implantation).

Conclusion

Adherence to strict protocols for selecting and treating culture-negative patients with a PJI using the same two-stage revision approach that we employ for complex culture-positive PJIs is important in order to achieve control of the infection in this difficult group of patients.

Cite this article: Bone Joint J 2018;(1 Supple A)100-B:3–8.

A Review of the Literature on Culture-Negative Periprosthetic Joint Infection: Epidemiology, Diagnosis and Treatment

Purpose

The prevalence of periprosthetic joint infection (PJI) has increased with the increasing incidence of arthroplasty surgery. Considering identification of causative microorganisms is crucial for treatment of PJI, culture-negative (CN) PJI is a significant clinical issue. The purpose of the present study is to describe epidemiology, diagnosis and treatment of CN PJI based on review of the literature to help prevent delayed diagnosis and improve clinical outcomes of CN PJI.

Methods

MEDLINE, EMBASE, Cochrane Library and Scopus databases were searched for articles on CN PJI. Only clinical studies written in English were included. Basic science studies, letters to the editor, case reports and review articles on PJI were excluded.

Results

Seven studies were included in this study. The prevalence of CN PJI ranged from 0% to 42.1%. The major risk factors for CN PJI were prior antibiotic use and presence of postoperative wound drainage. Vancomycin and cephalosporins were the most commonly used antibiotics for CN PJI. Two-stage revision arthroplasty followed by 6 weeks of antibiotic therapy produced the most successful treatment outcomes.

Conclusions

In most clinical studies on CN PJI, a definite diagnostic method for identifying causative microorganisms or optimal treatment strategy for CN PJI were not clearly described. Therefore, further studies are needed to establish standard diagnostic methods for identifying infecting organisms and treatment strategies for CN PJI.

Sonication contribution to identifying prosthetic joint infection with Ralstonia pickettii: a case report and review of the literature

Background

In the context of an increase number of primary and revision total hip and total knee arthroplasty performed yearly, an increased risk of complication is expected. Prosthetic joint infection (PJI) remains the most common and feared arthroplasty complication. Ralstonia pickettii is a Gram-negative bacterium, that has also been identified in biofilms. It remains an extremely rare cause of PJI. There is no report of an identification of R. pickettii on an extracted spacer loaded with antibiotic.

Case presentation

We present the case of an 83-years-old Caucasian male patient, that underwent a right cemented total hip replacement surgery. The patient is diagnosed with an early PJI with no isolated microorganism. A debridement and change of mobile parts is performed. At the beginning of 2016, the patient in readmitted into the Orthopedic Department for sever, right abdominal and groin pain and elevated serum erythrocyte sedimentation rate and C-reactive protein. A joint aspiration is performed with a negative microbiological examination. A two-stage exchange with long interval management is adopted, and a preformed spacer loaded with gentamicin was implanted. In July 2016, based on the proinflammatory markers evolution, a shift a three-stage exchange strategy is decided. In September 2016, a debridement, and changing of the preformed spacer loaded with gentamicin with another was carried out. Bacteriological examination of the tissues sampled intraoperatively was positive for Pseudomonas aeruginosa. From the sonication fluid, no bacteria were isolated on culture or identified using the bbFISH assay. During the hospitalization period, the patient received i.v. ceftazidime 3x2g/day and p.o. ciprofloxacin 2x750mg/day, antibiotic therapy that was continued after discharge with p.o. ciprofloxacin 2x750mg/day for 6 weeks. In February 2017, a reimplantation of a revision prosthesis is performed. The retrieved spacer is sonicated, and after 4 days of incubation of the sonication fluid, R. pickettii is isolated. A long term antibiotic therapy with cotrimoxazole being prescribed.

Conclusions

Bacteria culture of sonication fluid remains the gold standard in diagnosing prosthetic joint infections. R. pickettii remains an extremely rare cause of prosthetic joint infection. Optimal management of R. pickettii prosthetic joint infections of has not been established.

Superiority of the sonication method against conventional periprosthetic tissue cultures for diagnosis of prosthetic joint infections

INTRODUCTION

Diagnosis of periprosthetic infections is challenging. The aim of this study was to compare the diagnostic accuracy of conventional periprosthetic tissue culture and culture of sonication fluid of the explanted prostheses.

METHODS

We prospectively enrolled 114 patients undergoing revision hip or knee arthroplasty because of loosening of the prostheses, at our institution, between July 2012 and July 2016. Patients' medical history and demographic characteristics were recorded. The explanted hardware was separated in sterile containers and sonicated under sterile conditions. At least five samples of periprosthetic tissue were sent for culture and histological examination. We compared the culture of samples obtained by sonication of explanted hip and knee prostheses with conventional culture of periprosthetic tissue for the microbiological diagnosis of prosthetic joint infection.

RESULTS

Infectious Diseases Society of America guidelines were used for the definition of prosthetic joint infection. Sixty-one patients had periprosthetic infection and 53 aseptic loosening (73 hip prostheses and 41 knee prostheses). The sensitivity of sonication fluid culture was 77.04%, and the sensitivity of conventional tissue cultures was 55.73% (p value = 0.012). The specificities of the two methods were 98.11 and 94.34%, respectively. The sensitivity of the histopathological examination of the periprosthetic tissue was 72.10%. There were 17 patients with PJI where the isolated pathogen was detected in SFC but not in PTC, while in five cases the pathogen was detected only in PTC. There were nine patients where no bacteria were detected by any microbiological method and the diagnosis was based on clinical and histological findings, according to the guidelines.

CONCLUSIONS

The sonication method represents a reliable test for the diagnosis of prosthetic joint infections with a greater sensitivity and specificity than the conventional periprosthetic tissue cultures.

Sonication culture improves microbiological diagnosis of modular megaprostheses

Modular megaprostheses are known for high infection rates followed by high rates of revisions. Microbial biofilms growing adherently on prosthetic surfaces may inhibit the detection of the pathogens causing prosthetic joint infections. We sought to answer the following questions: Does sonication culture (SC) improve the microbiological diagnosis of periprosthetic infections of megaprostheses compared to conventional tissue culture (TC)? Which pathogens were detected on the surface of megaprostheses with either SC or TC and do the findings help to identify low-grade infections? Included were 31 patients with modular megaprostheses, whose implant had been explanted due to suspected joint infection or revision surgery. SCs were performed according to the protocol by Trampuz et al. The diagnosis of infection was evaluated according to the definition of the Musculoskeletal Infection Society. The sensitivity of SC was 91.3% compared to 52.2% for TC and the specificity was 100% for SC and TC (p = 0.004). Under preoperative antibiotic therapy, the sensitivity of SC was 83.3% while the sensitivity of TC was 50%. Without preoperative antibiotic therapy the sensitivity of SC was 100% compared to 54.5% for TC. In nine cases, SCs detected microorganisms, while TC was negative. Detected bacteria were Staphylococcus epidermidis in four, Micrococcus species in one, Finegoldia magna in one, Brevibacterium casei in one, Pseudomonas fluorescens in one, and Enterococcus faecium in one. SC is a reliable method for dislodging pathogens from orthopedic implants. The SC of modular megaprostheses showed significantly higher pathogen detection than the periprosthetic TC, especially for low virulence pathogens. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1383-1387, 2017.

Prosthetic joint and implant contamination caused by Ralstonia pickettii: a report of three cases٭

We describe three cases of orthopaedic contamination caused by Ralstonia pickettii grown from prosthetic joint and implant material cultures following sonication in the microbiology laboratory. Given the temporal association between the cases, lack of clinical or intra-operative features of infection, growth of the organism in the water bath, and unlikely etiology of Ralstonia as a prosthetic joint or implant pathogen, the bacteria were judged to be contaminants.

Diagnosis of periprosthetic joint infection using alpha-defensin test or multiplex-PCR: ideal diagnostic test still not found

PURPOSE

Diagnosing periprosthetic infection remains a challenge. Multiplex-PCR and biomarkers such as alpha-defensin are potentially useful and fast methods for detecting periprosthetic infection. This study compared these new methods with clinical assessment, conventional microbiological methods and histo-pathological examination.

METHODS

Twenty-eight consecutive patients with 30 joints and a mean age of 67.7 years (range 39 to 88) with removal of total hip arthroplasty (THA) or total knee replacement (TKR) were included in this study. Patients were classified according to the modified Musculoskeletal Infection Society score (MSIS) for infected joints. Punction fluid and tissue specimens were taken for conventional microbiological examination, alphadefensin test was performed, a synovial membrane specimen was used for multiplex-PCR and histopathological examination was carried out.

RESULTS

The alpha-defensin test and multiplex-PCR showed a sensitivity of 76.9 vs. 30.8% and a specificity of 82.4 vs. 100%, respectively. We found a significant difference between the positive and negative results (p = 0.0023). The conventional microbiological methods were not significantly different from the alpha-defensin test (p = 0.244) with a sensitivity of 84.6% and a specificity of 100% but did differ significantly from the multiplex PCR (p = 0.0030). There was a significant difference between modified MSIS classification and multiplex PCR (p = 0.0007).

CONCLUSIONS

Neither alpha-defensin test nor multiplex-PCR could detect periprosthetic infection immediately and reliably. Multiplex-PCR was suitable for detecting the non-infected but not the truly infected. Alpha-defensin test was helpful but showed no satisfactory results. Conventional microbiological methods remain the most reliable for periprosthetic infection diagnosis.

Remote transient Lactobacillus animalis bacteremia causing prosthetic hip joint infection: a case report

Background

Lactobacillus spp. are uncommon pathogens in immunocompetent hosts, and even rarer causes of prosthetic device infections.

Case presentation

A case of chronic hip prosthetic joint infection (PJI) caused by L. animalis is described. This occurred 5 years after a transient bacteremia with the same organism. Whole genome sequencing of both isolates proved this PJI infection resulted from this remote bacteremia.

Conclusions

We document that prosthetic joint infections may be a consequence of bacteremia as much as 3 years before the onset of symptoms.

Accuracy of diagnostic tests for prosthetic joint infection: a systematic review

PURPOSE

There are few evidence-based recommendations on the most effective methods for diagnosing prosthetic joint infections (PJIs), and the potency of tests in relation to each other also remains vague. This systematic review aimed to (1) identify systematic reviews reporting accuracies of available approaches for diagnosing PJI, (2) critically appraise their quality and bias, and (3) compare the available approaches in terms of accuracy for diagnosing PJI.

METHODS

PubMed and EMBASE databases were searched for meta-analyses reporting accuracies of different diagnostic modalities for PJIs. Thirteen systematic reviews met the inclusion and exclusion criteria, and their data were extracted and tabulated by two reviewers in duplicate and independent manners.

RESULTS

The 13 articles reported diagnostic accuracy from 278 clinical studies comprising 27,754 patients and evaluating 13 diagnostic tests grouped into 7 broad categories. Implant sonication had the highest positive likelihood ratio (17.2), followed by bacteriology (15.3) and synovial fluid differentiated cytology (13.3). The highest negative likelihood ratio was for interleukin (IL)-6 serum marker (0.03) followed by synovial fluid cytology and differentiation (0.12 and 0.13, respectively).

CONCLUSION

The diagnostic tests that are most likely to rule out PJI include serum IL-6, serum C-reactive protein, and synovial fluid cytology. On the other hand, the diagnostic test that is most likely to confirm PJI is implant sonication. Nuclear imaging showed low overall accuracy as diagnostic tests for PJI. The findings of this study could enable clinicians to confirm or rule out PJIs using the most accurate, rapid, least invasive, and cost-effective tools available, thereby enabling fast treatment before formation of resistant biofilms and degradation of patient conditions.

LEVEL OF EVIDENCE

Systematic review, Level IV.

Oral, intestinal, and skin bacteria in ventral hernia mesh implants

Background

In ventral hernia surgery, mesh implants are used to reduce recurrence. Infection after mesh implantation can be a problem and rates around 6–10% have been reported. Bacterial colonization of mesh implants in patients without clinical signs of infection has not been thoroughly investigated. Molecular techniques have proven effective in demonstrating bacterial diversity in various environments and are able to identify bacteria on a gene-specific level.

Objective

The purpose of this study was to detect bacterial biofilm in mesh implants, analyze its bacterial diversity, and look for possible resemblance with bacterial biofilm from the periodontal pocket.

Methods

Thirty patients referred to our hospital for recurrence after former ventral hernia mesh repair, were examined for periodontitis in advance of new surgical hernia repair. Oral examination included periapical radiographs, periodontal probing, and subgingival plaque collection. A piece of mesh (1×1 cm) from the abdominal wall was harvested during the new surgical hernia repair and analyzed for bacteria by PCR and 16S rRNA gene sequencing. From patients with positive PCR mesh samples, subgingival plaque samples were analyzed with the same techniques.

Results

A great variety of taxa were detected in 20 (66.7%) mesh samples, including typical oral commensals and periodontopathogens, enterics, and skin bacteria. Mesh and periodontal bacteria were further analyzed for similarity in 16S rRNA gene sequences. In 17 sequences, the level of resemblance between mesh and subgingival bacterial colonization was 98–100% suggesting, but not proving, a transfer of oral bacteria to the mesh.

Conclusion

The results show great bacterial diversity on mesh implants from the anterior abdominal wall including oral commensals and periodontopathogens. Mesh can be reached by bacteria in several ways including hematogenous spread from an oral site. However, other sites such as gut and skin may also serve as sources for the mesh biofilm.

Histological analysis of surgical samples and a proposed scoring system for infections in intervertebral discs

Back pain remains one the most prevalent types of pain and disability worldwide. Infection is estimated to be the underlying cause in approximately 0.01% of patients. Despite recent evidence demonstrating prominent infection rates, a standardised algorithm for diagnosis of disc infection is lacking. Histopathological evaluation can aid in confirming inflammatory changes and also in identifying degenerative changes. Hence, standardising practice through a clear scoring system with regards to inflammation and degeneration may have some utility in the clinical setting. To our knowledge no such systems exist specifically for intervertebral disc infection. A literature review of current methods of scoring inflammation and degeneration in spine surgery and orthopaedic surgery was performed. Based on the current evidence, a scoring system for disc inflammatory and degenerative changes was proposed. We propose four domains for consideration: (1) granulation tissue, (2) dense fibrosis, (3) chronic inflammatory cells, and (4) neutrophil count. The non-standardised nature of diagnosing infections and degeneration in the spinal surgery literature means that this scoring system is currently of particular value. Based on a literature review, our proposed method for diagnosis incorporates a combination of histopathological criteria expected to increase diagnostic sensitivity in the setting of disc infection. Overall, scoring can be applied to surgically obtained material and integrated directly into routine pathological practice.

Propionibacterium prosthetic joint infection: experience from a retrospective database analysis

BACKGROUND

With improved diagnostic methods and longer prosthesis indwelling time, the frequency of diagnosed Propionibacterium prosthetic joint infections (PJI) is increasing. Data on clinical, microbiological, radiological and surgical treatment are limited, and importance of this organism in PJI is probably underestimated.

MATERIALS AND METHODS

We retrospectively analyzed patients with PJI caused by Propionibacterium spp. diagnosed at our institution between 2000 and 2012. Patient data were retrieved through chart review, and the outcome was evaluated at patient follow-up visits.

RESULTS

Of 15 included patients (median age 65 years, range 44-87), 8 hip, 4 shoulder, 2 knee and 1 ankle PJI were recorded. The median time from implantation to diagnosis of PJI was 44.2 months (range 2-180 months). Most PJI (8 patients, 53 %) were diagnosed late (>24 months after arthroplasty). Persistent pain was present in 13, local joint symptoms in 8, fever in 4 and sinus tract in 3 patients. Radiological signs of loosening were present in 11 patients (73 %). Organisms were detected in intraoperative biopsy (n = 5), sonication (n = 4) or preoperative joint puncture (n = 4). In three cases coinfection with a coagulase-negative staphylococcus was diagnosed. Revision surgery was performed in all cases. After a mean follow-up of 16 months after revision surgery (range 4-37 months), 14 patients (93 %) showed no signs or symptoms of infection and had a functional prosthesis; one patient experienced a new infection with another organism (Staphylococcus epidermidis).

CONCLUSION

Patients with persistent postoperative pain and/or loosening of implants should be screened for PJI with low-virulent organisms such as Propionibacterium, including.

Comparison of cultures and 16S rRNA sequencing for identification of bacteria in two-stage revision arthroplasties: preliminary report

BACKGROUND

The use of a prefabricated spacer in two-stage revision arthroplasty remains one of the few surgery strategies for infected-joint arthroplasty treatment, despite the many unidentified microorganisms in the infected joint replacements reported in some recent studies. The aim of this prospective survey was to investigate if the sonication followed by polymerase chain reaction (PCR) can improve bacterial identification on the surfaces of prefabricated spacers and if the systemic laboratory mediators of infection and positive microbiological results can take a role of predictive factors of infection and clinical failures in 2-years follow-up.

METHODS

Thirteen patients with prosthetic joint infection were investigated. Bacterial culture and deoxyribonucleic acid (DNA) sequencing were used to detect bacteria on the surface of prefabricated spacers removed during the second stage of revision arthroplasty. The results of pre- and intraoperative culture and DNA sequencing were compared. Minimum follow-up was 2 years.

RESULTS

The result of tissue cultures in second-stage revision arthroplasties revealed positive results in 15 % of patients with Coagulase-negative Staphylococci (CNS) growth. Bacterial DNA was found in over 90 % of patients with negative synovial fluid culture. Positive PCR results revealed potential pathogenic bacteria and species of human and environmental microflora with low virulence. Clinical failures at final follow-up were recorded in 2 (16.6 %) patients.

CONCLUSION

The lack of clinical signs of infection, negative culture of preoperative joint aspirate, and intraoperative specimens do not exclude the presence of bacteria on the surfaces of spacers. The positive results of sonication and molecular tests should be interpreted as real pathogenicity factors in the light of the clinical and laboratory data, especially for patients with immunodeficiency. We confirmed our previous results that sonication followed by PCR and sequencing improved bacterial identification.

Does Preoperative Antimicrobial Prophylaxis Influence the Diagnostic Potential of Periprosthetic Tissues in Hip or Knee Infections?

BACKGROUND

Undiagnosed low-grade prosthetic joint infections (PJI) are recognized as an important reason for early failure of presumably aseptic revisions. Preoperatively administered antimicrobial prophylaxis reduces the incidence of PJI but it may reduce the sensitivity of microbiologic periprosthetic tissue cultures and consequently increase the incidence of undiagnosed septic prosthetic joint failures, which can lead to catastrophic serial revisions.

QUESTIONS/PURPOSES

We wished to determine whether administration of preoperative antibiotics decreases the likelihood of diagnosing PJI in patients undergoing revision hip or knee arthroplasty in whom infection is suspected.

METHODS

We prospectively enrolled and evaluated 40 patients (29 with THAs and 11 with TKAs) who met the following inclusion criteria: older than 18 years, with suspected PJI of unknown cause, undergoing surgical revision. After arthrotomy, three tissue samples were obtained for microbiologic analysis and diagnosis, and antimicrobial prophylaxis (cefazolin 2 g intravenously) then was administered. Later during the procedure, but before débridement and irrigation, the second set of three tissue samples was obtained from the same surgical area and was cultured. Tissue concentration of prophylactic antibiotic was verified with the second set of samples. A positive culture result was defined as one or more positive cultures (growth on agar at or before 14 days). We then compared the yield on the microbiologic cultures obtained before administration of antibiotics with the yield on the cultures obtained after antibiotics were administered. An a priori analysis was performed; with the numbers available, we had 98% power to detect a difference in diagnostic sensitivity of 33%.

RESULTS

With the numbers available, we found no difference in the likelihood that an infection would be diagnosed between the samples obtained before and after administration of antimicrobial prophylaxis (odds ratio [OR] for positive microbial culture = 0.99; 95% CI, 0.40-2.48; p = 0.99). All measured tissue concentrations of cefazolin were greater than the minimum inhibitory concentration, therefore we found that antibiotic prophylaxis was adequate at the time of second-set tissue specimen recovery.

CONCLUSIONS

Results from this small, prospective series suggest that preoperative antimicrobial prophylaxis may be administered safely even in patients undergoing revision hip or knee arthroplasty in which microbiologic sampling is planned without compromising the diagnostic sensitivity of tissue sample cultures. However, before applying our results more generally, our findings need to be confirmed in larger, multicenter studies that would allow evaluation by sex, procedure, bacteriology, and other potentially important factors.

LEVEL OF EVIDENCE

Level I, diagnostic study.

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.

Polymerase Chain Reaction molecular diagnostic technology for monitoring chronic osteomyelitis

BACKGROUND

Osteomyelitis is a devastating condition whose treatment relies on the detection of bacteria. The current standard of microbiology culture may not be adequate. Molecular biology based diagnostic procedures for detecting bacteria in orthopaedic infections was previously established, but has not been applied to the setting of chronic osteomyelitis. We aim to determine the applicability of molecular diagnostic procedures for monitoring chronic osteomyelitis, and to evaluate if these procedures are superior to standard culture methods of osteomyelitis detection.

METHODS

A rabbit experimental model of chronic osteomyelitis was used; infection was induced in the proximal, medial aspect of the tibia with Staphylococcus aureus at titers ranging from 1 × 10(2) to 1 × 10(6) colony forming units. At 28 days post-infection, animals were sacrificed, and the tibias were examined radiographically, harvested, and assayed for the presence of bacteria. Two bacterial detection methods were used: (1) standard microbiological culturing, and (2) polymerase chain reaction (PCR) based diagnostic method to detect bacterial genomic DNA.

RESULTS

The molecular diagnostic method was highly sensitive and accurate, and detected low titer infections that were undetected by radiographic and microbiological methods. By using two sets of PCR primers, one for a universal bacterial gene (16S rRNA) and one for a species-specific gene (nuc), the molecular protocol allowed both the detection and speciation of the bacterial infection.

CONCLUSIONS

The use of the PCR-based method was effective for high-sensitivity detection and identification of bacteria associated with chronic osteomyelitis in a rabbit model. Our findings illustrate the applicability of PCR for monitoring chronic osteomyelitis, which may be useful for improved detection of osteomyelitis organisms in humans.

Isolated Lactobacillus chronic prosthetic knee infection

Lactobacillus is a gram-positive rod bacteria found primarily in the gastrointestinal and female genital tracts. Prosthetic infections in implants are being increasingly reported. The authors present a case of a 58-year-old patient with Lactobacillus septic prosthetic knee joint infection. To the authors’ knowledge, this is the first reported case of chronic prosthetic knee infection with isolated Lactobacillus species. Lactobacillus has been most commonly implicated with bacteremia and endocarditis and rarely with pneumonia, meningitis, and endovascular infection, and a vast majority of the cases are reported in immunocompromised patients. In the current case, diabetes mellitus, hepatitis, malnutrition, anemia, and liver failure were comorbid conditions, placing the patient at increased risk of infection. The findings suggest that further case series are necessary to establish the significance of Lactobacillus as an etiologic agent in chronic low-virulence, and potentially vancomycin-resistant, prosthetic joint infection. The need also exists for further research aimed at the risk of prosthetic joint infection with oral intake of certain probiotic foods and supplements. The goal of this case report is to bring to light the potential of this organism to be a cause of subtle chronic prosthetic joint infection.