Advances in the laboratory diagnosis of prosthetic joint infection:

Acidity Is an Excellent Marker of Infection in Hip and Knee Arthroplasty

BACKGROUND

The diagnosis of joint replacement infection is a difficult clinical challenge that often occurs when the implant cannot be salvaged. We hypothesize that the pH value of synovial fluid could be an important indicator of the inflammatory status of the joint. However, in the literature, there is a lack of data on the pH changes in hip and knee joint replacements and their relation to infection and implant failure. In this study, we aimed to measure the pH levels of synovial fluid in patients with hip and knee joint replacements. We also investigated the potential of pH measurement as a diagnostic tool for joint replacement infection. In this study, we recorded the pH values to be 7.55 and 7.46 in patients where Pseudomonas aeruginosa was identified as the cause of the prosthetic joint infection. We attribute this to the different environments created by this specific bacterium. In other cases where the pH was higher, chronic mitigated infections were diagnosed, caused by strains of Staphylococcus aureus, Streptococcus agalactiase, and coagulase negative staphylococcus.

MATERIALS AND METHODS

In our cohort of 155 patients with implanted hip (THA; n = 85) or knee (TKA; n = 70) joint replacements, we conducted a prospective study with a pH measurement. Out of the whole cohort, 44 patients had confirmed joint replacement infection (28.4%) (44/155). In 111 patients, infection was ruled out (71.6%) (111/155). Joint replacement infection was classified according to the criteria of the Musculoskeletal Infection Society (MSIS) from 2018. Based on the measured values, we determined the cut-off level for the probability of ongoing inflammation. We also determined the sensitivity and specificity of the measurement.

RESULTS

The group of patients with infection (n = 44) had a significantly lower synovial fluid pH (pH = 6.98 ± 0.48) than the group of patients with no infection (n = 111, pH = 7.82 ± 0.29, p < 0.001). The corresponding median pH values were 7.08 for the patients with infection and 7.83 for the patients with no infection. When we determined the cut-off level of pH 7.4, the sensitivity level of infected replacements was 88.6%, and the specificity level of the measurement was 95.5%. The predictive value of a positive test was 88.6%, and the predictive value of a negative test was 95.5%.

CONCLUSIONS

Our results confirm that it is appropriate to include a pH measurement in the diagnostic spectrum of hip and knee replacements. This diagnostic approach has the potential to provide continuous in vivo feedback, facilitated by specialized biosensors. The advantage of this method is the future incorporation of a pH-detecting sensor into intelligent knee and hip replacements that will assess pH levels over time. By integrating these biosensors into intelligent implants, the early detection of joint replacement infections could be achieved, enhancing proactive intervention strategies.

Synovial fluid pH sensor for early detection of prosthetic hip infections

We describe an implantable sensor developed to measure synovial fluid pH for noninvasive early detection and monitoring of hip infections using standard-of-care plain radiography. The sensor was made of a pH responsive polyacrylic acid-based hydrogel, which expands at high pH and contracts at low pH. A radiodense tantalum bead and a tungsten wire were embedded in the two ends of the hydrogel in order to monitor the change in length of the hydrogel sensor in response to pH via plain radiography. The effective pKa of the hydrogel-based pH sensor was 5.6 with a sensitivity of 3 mm/pH unit between pH 4 and 8. The sensor showed a linear response and reversibility in the physiologically relevant pH range of pH 6.5 and 7.5 in both buffer and bovine synovial fluid solutions with a 30-minute time constant. The sensor was attached to an explanted prosthetic hip and the pH response determined from the X-ray images by measuring the length between the tantalum bead and the radiopaque wire. Therefore, the developed sensor would enable noninvasive detection and studying of implant hip infection using plain radiography.

Bacterial DNA screening to characterize surgical site infection risk in orthopaedic patients

Purpose

To provide an initial characterization of relevant bacterial DNA profiles for patients undergoing closed-fracture fixation or total joint arthroplasties.

Patients and methods

Swabs were collected and analyzed using Polymerase Chain Reaction from adult patients undergoing closed-fracture fixation or total shoulder, knee, or hip arthroplasties.

Results

Bacterial DNA profiles varied across the different orthopaedic patient populations, and produced uncharacteristic profile shifts with direct relevance to each clinical infection.

Conclusion

Findings provide a foundational dataset regarding bacterial colonization of relevant anatomic sites that can act as sources of surgical site infections for patients.

Periprosthetic joint infection: current concepts and outlook

Periprosthetic joint infection (PJI) is a serious complication occurring in 1% to 2% of primary arthroplasties, which is associated with high morbidity and need for complex interdisciplinary treatment strategies.

The challenge in the management of PJI is the persistence of micro-organisms on the implant surface in the form of biofilm. Understanding this ability, the phases of biofilm formation, antimicrobial susceptibility and the limitations of host local immune response allows an individual choice of the most suitable treatment.

By using diagnostic methods for biofilm detection such as sonication, the sensitivity for diagnosing PJI is increasing, especially in chronic infections caused by low-virulence pathogens.

The use of biofilm-active antibiotics enables eradication of micro-organisms in the presence of a foreign body. The total duration of antibiotic treatment following revision surgery should not exceed 12 weeks.

Cite this article: EFORT Open Rev 2019;4:482-494. DOI: 10.1302/2058-5241.4.180092

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.

The dissolvable bead: A novel in vitro biofilm model for evaluating antimicrobial resistance

In vitro biofilm assays are a vital first step in the assessment of therapeutic effectiveness. Current biofilm models have been found to be limited by throughput, reproducibility, and cost. We present a novel in vitro biofilm model, utilising a sodium alginate substratum for surface biofilm colony formation, which can be readily dissolved for accurate evaluation of viable organisms. The dissolving bead biofilm assay was evaluated using a range of clinically relevant strains. The reproducibility and responsiveness of the assay to an antimicrobial challenge was assessed using standardised methods. Cryo-scanning electron microscopy was used to image biofilm colonies. Biofilms were grown for 20h prior to testing. The model provides a reproducible and responsive assay to clinically-relevant antimicrobial challenges, as defined by established guidelines. Moreover cryo-scanning electron microscopy demonstrates that biofilm formation is localised exclusively to the alginate bead surface. Our results suggest that this simple model provides a robust and adaptable assay for the investigation of bacterial biofilms.

Comparison of 99mTc-UBI 29-41, 99mTc-ciprofloxacin, 99mTc-ciprofloxacin dithiocarbamate and 111In-biotin for targeting experimental Staphylococcus aureus and Escherichia coli foreign-body infections: an ex-vivo study

BACKGROUND

Diagnosis of implant-associated infection is challenging. Several radiopharmaceuticals have been described but direct comparisons are limited. Here we compared in vitro and in an animal model 99mTc-UBI, 99mTc-ciprofloxacin, 99mTcN-CiproCS2 and 111In-DTPA-biotin for targeting E. coli (ATCC 25922) and S. aureus (ATCC 43335).

METHODS

Stability controls were performed with the labelled radiopharmaceuticals during 6 hours in saline and serum. The in vitro binding to viable or killed bacteria was evaluated at 37 °C and 4 °C. For in vivo studies, Teflon cages were subcutaneously implanted in mice, followed by percutaneous infection. Biodistribution of i.v. injected radiolabelled radiopharmaceuticals were evaluated during 24 h in cages and dissected tissues.

RESULTS

Labelling efficiency of all radiopharmaceuticals ranged between 94% and 98%, with high stability both in saline and in human serum. In vitro binding assays displayed a rapid but poor bacterial binding for all tested agents. Similar binding kinetic occurred also with heat-killed and ethanol-killed bacteria. In the tissue cage model, infection was detected at different time points: 99mTc-UBI and 99mTcN-CiproCS2 showed higher infected cage/sterile cage ratio at 24 hours for both E. coli and S. aureus; 99mTc-Ciprofloxacin at 24 hours for both E. coli and at 4 hours for S. aureus; 111In-DTPA-biotin accumulates faster in both E. coli and S. aureus infected cages.

CONCLUSIONS

99mTc-UBI, 99mTcN-CiproCS2 showed poor in vitro binding but good in vivo binding to E. coli only. 111In-DTPA-biotin showed poor in vitro binding but good in vivo binding to S. aureus and poor to E. coli. 99mTc-Ciprofloxacin showed poor in vitro binding but good in vivo binding to all tested bacteria. The mechanism of accumulation in infected sites remains to be elucidated.

The role of biofilm on orthopaedic implants: the "Holy Grail" of post-traumatic infection management?

The development of post-traumatic infection is potentially a limb threatening condition. The orthopaedic trauma literature lags behind the research performed by our arthroplasty colleagues on the topic of implant-related infections. Surgical site infections in the setting of a recent ORIF are notoriously hard to eradicate due to biofilm formation around the implant. This bacteria-friendly, dynamic, living pluri-organism structure has the ability to morph and adapt to virtually any environment with the aim to maintain the causative organism alive. The challenges are twofold: establishing an accurate diagnosis with speciation/sensitivity and eradicating the infection. Multiple strategies have been researched to improve diagnostic accuracy, to prevent biofilm formation on orthopaedic implants, to mobilize/detach or weaken the biofilm or to target specifically bacteria embedded in the biofilm. The purpose of our paper is to review the patho-physiology of this mysterious pluri-cellular structure and to summarize some of the most pertinent research performed to improve diagnostic and treatment strategies in biofilm-related infections.

Management of infection following reconstruction in bone tumors

Limb salvage surgery in bone tumors has evolved in recent years and includes all of the surgical procedures designed to accomplish removal of a malignant tumor and reconstruction of the limb with an acceptable oncologic, functional, and cosmetic result. This dramatic change came about as the result of three important developments, i.e. effective chemotherapy, improved precision imaging techniques and advances in reconstructive surgery. Reconstruction with a modular custom-made oncological endoprosthesis (megaprosthesis) has become a common procedure nowadays. These large foreign bodies make infection a common and feared complication. However, the occurrence of complications may be multifactorial, including a poor nutritional and compromised immune status due to chemotherapy and/or radiotherapy, a lengthy operation, extensive dissection and resection of soft tissues, inadequate soft-tissue coverage, a longer exposure of the wound resulting in infection, etc. Management of postoperative infection in these cases remains a challenge. This article analyses the current literature available for these cases and summarizes the cause and different available methods of treatment.

Biofilms in periprosthetic orthopedic infections

As the number of total joint arthroplasty and internal fixation procedures continues to rise, the threat of infection following surgery has significant clinical implications. These infections may have highly morbid consequences to patients, who often endure additional surgeries and lengthy exposures to systemic antibiotics, neither of which are guaranteed to resolve the infection. Of particular concern is the threat of bacterial biofilm development, since biofilm-mediated infections are difficult to diagnose and effective treatments are lacking. Developing therapeutic strategies have targeted mechanisms of biofilm formation and the means by which these bacteria communicate with each other to take on specialized roles such as persister cells within the biofilm. In addition, prevention of infection through novel coatings for prostheses and the local delivery of high concentrations of antibiotics by absorbable carriers has shown promise in laboratory and animal studies. Biofilm development, especially in an arthoplasty environment, and future diagnostic and treatment options are discussed.

The host response: Toll-like receptor expression in periprosthetic tissues as a biomarker for deep joint infection

BACKGROUND

Toll-like receptors (TLRs) 1 and 6 are consistent molecular indicators of the host inflammatory response against bacterial infection. Our aims were to determine whether TLR elevation could be detected in infected periprosthetic tissues and to assess the utility of these biomarkers as tests for detecting a periprosthetic joint infection.

METHODS

Fifty-nine patients undergoing revision total joint arthroplasty (twenty-seven hips and thirty-two knees) were prospectively evaluated for periprosthetic joint infection according to currently recommended diagnostic criteria. Nine patients were excluded because of insufficient work-up, leaving fifty available for study. Of these, twenty-one were categorized as infected and twenty-nine as noninfected. Periprosthetic tissues were collected intraoperatively, and total RNA was extracted by standard techniques. Expression of TLR messenger RNAs was assessed by first-strand complementary DNA synthesis from 1 μg of total RNA followed by real-time PCR (polymerase chain reaction). Results were normalized relative to the housekeeping gene GAPDH (glyceraldehyde 3-phosphate dehydrogenase). Expression of TLRs 1, 6, and 10 in the infected and noninfected groups was compared with use of the Student t test. The receiver operating characteristic curve, area under the curve (AUC), sensitivity, specificity, positive likelihood ratio (LR+), and negative likelihood ratio (LR-) were calculated to determine the accuracy of each TLR for predicting periprosthetic joint infection at its optimal diagnostic threshold.

RESULTS

Mean TLR1 mRNA expression was significantly elevated in infected compared with noninfected samples (0.600 compared with 0.005, p = 0.0003); the same was true of TLR6 (0.208 compared with 0.0165, p = 0.0059) but not of TLR10 (0.00019 compared with 0.00014, p = 0.6238). The AUC was 0.995 for TLR1, 0.883 for TLR6, and 0.546 for TLR10. The optimal threshold for diagnosing periprosthetic joint infection was 0.0924 for TLR1 (sensitivity = 95.2%, specificity = 100%, LR+ = 13.80, LR- = 0.91) and 0.0215 for TLR6 (sensitivity = 85.7%, specificity = 82.8%, LR+ = 4.98, LR- = 0.83).

CONCLUSIONS

In our pilot study, TLR1 expression in periprosthetic tissues most accurately predicted periprosthetic joint infection. This measure of the host response may be particularly helpful in detecting culture-negative infections and avoiding false positives resulting from contamination.

LEVEL OF EVIDENCE

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

Rapid isolation and diagnosis of live bacteria from human joint fluids by using an integrated microfluidic system

Arthroplasty is a general approach for improving the life quality for patients with degenerative or injured joints. However, post-surgery complications including periprosthetic joint infection (PJI) poses a serious drawback to the procedure. Several methods are available for diagnosing PJI, but they are time-consuming or have poor sensitivity and specificity. Alternatively, reverse-transcription PCR can detect live bacteria and reduce false-positive results but cannot avoid the cumbersome RNA handling and human contamination issues. In response, an integrated microfluidic system capable of detecting live bacteria from clinical PJI samples within 55 minutes is developed in this study. This system employs an ethidium monoazide (EMA)-based assay and a PCR with universal bacterial primers and probes to isolate and detect only the live bacteria that commonly cause PJI. The experimental results indicated that the developed system can detect bacteria in human joint fluids with a detection limit of 10(4) colony formation unit mL(-1). Furthermore, nine clinical samples were analyzed using the microfluidic system. The results obtained from the microfluidic system were negative for all culture-negative cases, indicating that the proposed system can indeed reduce false-positive results. In addition, experimental results showed that the EMA sample pre-treatment process was crucial for successful detection of live bacteria. The culture-positive cases were diagnosed as positive by the proposed system only when the clinical samples were treated with EMA immediately after being sampled from patients. Based on these promising results, the developed microfluidic system can be a useful tool to detect PJI and potentially be applied in other clinical situations.

The diagnosis of periprosthetic infection

Periprosthetic infection (PJI) is the most serious joint replacement complication, occurring in 0.8-1.9% of knee arthroplasties and 0.3-1.7% of hip arthroplasties. A definition of PJI was proposed in the November 2011 issue of the journal Clinical Orthopedics and Related Research. The presence of a fistula or of local inflammatory signs is indicative of PJI, but in many cases local pain is the only symptom. In the absence of underlying inflammatory conditions, C-reactive protein measurement is the most useful preoperative blood test for detecting infection associated with a prosthetic joint. The most useful preoperative diagnostic test is the aspiration of synovial joint fluid to obtain a total and differential cell count and culture. Intraoperative frozen sections of periprosthetic tissues produce excellent accuracy in predicting a diagnosis of PJI but only moderate accuracy in ruling out the diagnosis. In this process, obtaining a quality sample is the first step, and determines the quality of microbiological results. Specimens for culture should be obtained prior to the initiation of antibiotic treatment. Sonication of a removed implant may increase the culture yield. Plain radiography has low sensitivity and low specificity for detecting infection associated with a prosthetic joint. Computed tomography and magnetic resonance imaging may be useful in the evaluation of complex cases, but metal inserts interfere with these tests, and abnormalities may be non-specific. Labelled-leucocyte imaging (e.g., leucocytes labelled with indium-111) combined with bone marrow imaging with the use of technetium-99m-labelled sulphur colloid is considered the imaging test of choice when imaging is necessary.

Diagnosis of periprosthetic joint infections in clinical practice

The diagnosis of a periprosthetic joint infection (PJI) can be challenging, either because of the variable clinical presentation or because of previous antimicrobial treatment interfering with the detection of the pathogen. In recent years, various means to diagnose PJI have been analyzed. These include invasive and non-invasive laboratory tests, imaging procedures, and novel techniques such as sonication of implants and the use of molecular microbiology. In this review, both established and novel diagnostic procedures are presented. An algorithm for detecting PJI in patients with acute and chronic symptoms is proposed.

Treatment strategies for periprosthetic infections after primary elbow arthroplasty

BACKGROUND

The goal of this study was to investigate the outcome of different surgical procedures (debridement and retention vs 1- or 2-stage exchange) together with a well-defined antimicrobial regimen.

MATERIALS AND METHODS

A total of 236 consecutive patients underwent 262 primary elbow arthroplasties between January 1994 and December 2007. We observed 20 episodes of periprosthetic infections in 19 patients and placed them into 3 groups according to the occurrence of infection after index surgery. A total of 9 early infections (<3 months), 1 delayed infection (3-24 months), and 10 late infections (>24 months) were observed. The treatment among those 3 groups was compared, and the outcome was assessed with a mean follow-up of 60.2 months.

RESULTS

In the group with early infections (n = 9), 8 cases were treated by irrigation and debridement and 1 case was treated by a 2-stage exchange without recurrence of infection. The mean Mayo Elbow Performance Score improved from 48.3 points (range, 30-75 points) to 91.7 points (range, 85-100 points). The delayed infection was treated by 1-stage exchange without recurrence of infection. For late infections (n = 10), 3 cases presented recurrence of infection after debridement and irrigation, and the mean Mayo Elbow Performance Score remained nearly unchanged, from 60 points (range, 45-80 points) to 65 points (range, 50-80 points). Eradication of infection could be achieved by staged revision and in 3 cases by debridement.

CONCLUSION

Both debridement with retention and staged reimplantation are highly successful for appropriate indications. Staged revisions are successful even against biofilm-active microorganisms, but a prosthesis-free interval of at least 3 months is recommended.

Role of universal 16S rRNA gene PCR and sequencing in diagnosis of prosthetic joint infection

The etiological diagnosis of prosthetic joint infection (PJI) requires the isolation of microorganisms from periprosthetic samples. Microbiological cultures often yield false-positive and false-negative results. 16S rRNA gene PCR combined with sequencing (16SPCR) has proven useful for diagnosing various infections. We performed a prospective study to compare the utility of this approach with that of culture to diagnose PJI using intraoperative periprosthetic samples. We analyzed 176 samples from 40 patients with PJI and 321 samples from 82 noninfected patients using conventional culture and 16SPCR. Three statistical studies were undertaken following a previously validated mathematical model: sample-to-sample analysis, calculation of the number of samples to be studied, and calculation of the number of positive samples necessary to diagnose PJI. When only the number of positive samples is taken into consideration, a 16SPCR-positive result in one sample has good specificity and positive predictive value for PJI (specificity, 96.3%; positive predictive value, 91.7%; and likelihood ratio [LR], 22), while 3 positive cultures with the same microorganism are necessary to achieve similar specificity. The best combination of results for 16SPCR was observed when 5 samples were studied and the same microorganism was detected in 2 of them (sensitivity, 94%; specificity, 100%; and LR, 69.62). The results for 5 samples with 2 positive cultures were 96% and 82%, respectively, and the likelihood ratio was 1.06. 16SPCR is more specific and has a better positive predictive value than culture for diagnosis of PJI. A positive 16SPCR result is largely suggestive of PJI, even when few samples are analyzed; however, culture is generally more sensitive.

Infected tumor prostheses

Infection of tumor prostheses has been a major concern because of the extensive soft tissue dissection, long operating times, and patients' immunosuppression by cancer and adjuvant treatments. Infections most often present within 2 years postoperatively, with approximately 70% of postoperative deep infections presenting within 12 months after surgery. They are typically low organism burden infections, the pathogenesis of which is related to bacteria growing in biofilms. Staphylococci are the most common pathogens involved in prosthetic joint infections, accounting for approximately 50% of infections overall, followed by streptococci, enterococci, Enterobacteriaceae species, Pseudomonas aeruginosa, and anaerobe species. Multiple pathogens may be isolated in approximately 25% of cases, with the most common combination being coagulase-negative Staphylococcus and group-D Streptococcus. Early diagnosis and appropriate treatment are necessary. However, diagnosis may be challenging because clinical symptoms are highly variable and numerous preoperative and intraoperative diagnostic laboratory tests are nonspecific. In most cases, a 1- or 2-stage revision surgery is necessary for eradicating the megaprosthetic infection. Prevention of infection is important. The future will see technical advances for infections of tumor prostheses in areas such as microbiological diagnostics and biofilm-resistant prostheses.

Preformed gentamicin spacers in two-stage revision hip arthroplasty: functional results and complications

Two-stage revisions with antibiotic-loaded spacers have gained popularity for treating infected hip-joint arthroplasties. The aim of this prospective study was to assess patient functionality between stages and treatment impact on duration of hospital stay and to describe related complications. Sixty-one consecutive patients with infected hip arthroplasties underwent two-stage revision with preformed spacer implantation. Mean Harris Hip and Merle d'Aubigné scores between the two stages were 39.9 and 7.6, respectively. Forty-six patients (75.4%) were able to leave hospital between stages. Spacer dislocation occurred in 16.4%. No cases of spacer breakage were noted. Preformed cement spacers provide acceptable functional outcome between revision hip arthroplasty stages and facilitate the surgical procedure without increasing mechanical complication rates.

Consensus document on controversial issues in the diagnosis and treatment of prosthetic joint infections

BACKGROUND

Joint replacement surgery has been on the increase in recent decades and prosthesis infection remains the most critical complication. Many aspects of the primary prevention and clinical management of such prosthesis infections still need to be clarified.

CONTROVERSIAL ISSUES

The aim of this GISIG (Gruppo Italiano di Studio sulle Infezioni Gravi) working group - a panel of multidisciplinary experts - was to define recommendations for the following controversial issues: (1) Is a conservative surgical approach for the management of prosthetic joint infections effective? (2) Is the one-stage or the two-stage revision for the management of prosthetic joint infections more effective? (3) What is the most effective treatment for the management of prosthetic joint infections due to methicillin-resistant staphylococci? Results are presented and discussed in detail.

METHODS

A systematic literature search using the MEDLINE database for the period 1988 to 2008 of randomized controlled trials and/or non-randomized studies was performed. A matrix was created to extract evidence from original studies using the CONSORT method to evaluate randomized clinical trials and the Newcastle-Ottawa Quality Assessment Scale for case-control studies, longitudinal cohorts, and retrospective studies. The GRADE method for grading quality of evidence and strength of recommendation was applied.

Amplification-based DNA analysis in the diagnosis of prosthetic joint infection

Microbiological cultures are moderately sensitive for diagnosing prosthetic joint infection (PJI). This study was conducted to determine whether amplification-based DNA methods applied on intraoperative samples could enhance PJI diagnosis compared with culture alone in routine surgical practice. Revision arthroplasty was performed for suspected PJI (n = 41) and osteoarthrosis control (n = 28) patients, and a diagnosis of PJI was confirmed in 34 patients. Amplification by polymerase chain reaction was performed on both 16S ribosomal DNA universal target genes and femA Staphylococcus-specific target genes. Species identification was achieved through amplicon sequencing. Amplification of the femA gene led to subsequent testing for methicillin resistance by amplification of the mecA gene. Microbiological and molecular assays identified a causative organism in 22 of 34 patients (64.7%) and in 31 of 34 patients (91.2%), respectively. In 18 of the 22 culture-positive patients, molecular and microbiological results were concordant for bacterial genus, species, and/or methicillin resistance. Bacterial agents were identified only by molecular methods in nine PJI patients, including seven who were receiving antibiotics at the time of surgery and one with recent but not concomitant antibiotherapy. DNA-based methods were found to effectively complement microbiological methods, without interfering with existing procedures for sample collection, for the identification of causative pathogens from intraoperative PJI samples, especially in patients with recent or concomitant antibiotherapy.

Prosthetic joint infections: microbiology, diagnosis, management and prevention

Infections associated with prosthetic joints occur less frequently than aseptic failures but represent the most devastating complication, with high morbidity and substantial cost. The most important risk factors are co-morbidity and prior joint replacement (revision surgery). No single routinely used clinical or laboratory test has been shown to achieve ideal sensitivity, specificity and accuracy for the diagnosis of prosthetic joint infection (PJI). Therefore, only the sum of clinical signs and symptoms, blood tests, histopathology, radiography, bone scans and a microbiological work-up can provide an accurate diagnosis. Antimicrobial therapy must always be combined with the correct surgical treatment, which is chosen according to the duration of the infection and co-morbidities of the patient. This review will briefly discuss the microbiology, diagnosis, management and prevention of PJI.

The treatment of deep shoulder infection and glenohumeral instability with debridement, reverse shoulder arthroplasty and postoperative antibiotics

We retrospectively reviewed 21 patients (22 shoulders) who presented with deep infection after surgery to the shoulder, 17 having previously undergone hemiarthroplasty and five open repair of the rotator cuff. Nine shoulders had undergone previous surgical attempts to eradicate their infection. The diagnosis of infection was based on a combination of clinical suspicion (16 shoulders), positive frozen sections (> 5 polymorphonuclear leukocytes per high-power field) at the time of revision (15 shoulders), positive intra-operative cultures (18 shoulders) or the pre-operative radiological appearances. The patients were treated by an extensive debridement, intravenous antibiotics, and conversion to a reverse shoulder prosthesis in either a single- (10 shoulders) or a two-stage (12 shoulders) procedure. At a mean follow-up of 43 months (25 to 66) there was no evidence of recurrent infection. All outcome measures showed statistically significant improvements. Mean abduction improved from 36.1 degrees (sd 27.8) pre-operatively to 75.7 degrees (sd 36.0) (p < 0.0001), the mean forward flexion from 43.1 degrees (sd 33.5) to 79.5 degrees (sd 43.2) (p = 0.0003), and mean external rotation from 10.2 degrees (sd 18.7) to 25.4 degrees (sd 23.5) (p = 0.0037). There was no statistically significant difference in any outcome between the single-stage and the two-stage group.

Infection and musculoskeletal conditions: Prosthetic-joint-associated infections

In patients with osteoarthritis or arthritis, prosthetic joint replacement is increasingly used to alleviate pain and to improve mobility. The most important risk factors are comorbidity and prior joint replacement (revision surgery). Diagnosis of prosthetic-joint-associated infection is difficult, because the infecting agent may be missed in synovial fluid due to its exclusive presence as a device-associated biofilm. Implant-associated infections are difficult to treat because of their resistance to natural host defence mechanisms and to most antibiotics. In staphylococcal implant-associated infections a rifampin combination should be used, because this drug has an excellent efficacy on surface-adhering microorganisms. Antimicrobial therapy must always be combined with the correct surgical treatment which is chosen according to an algorithm. The use of antibiotics during procedures with potential bacteraemia is controversial because evidence for its need is lacking. In contrast, during sepsis rapid antibiotic therapy is needed to prevent haematogenous seeding on the artificial joint.

[Infected knee arthroplasty. A treatment algorithm at the Kantonsspital Liestal, Switzerland]

The algorithm differentiates between several surgical treatment options depending on the duration of the infection, on the amount of soft tissue damage, on the stability of the implant and the type of micro-organism. If the symptoms of infection exist for less then 3 weeks, a radical debridement is indicated under the condition of a stable implant and good soft tissue conditions. A one-stage exchange is possible with satisfactory conditions of soft tissue and the absence of difficult-to-treat, resistant micro-organisms. In patients with sinustracts or compromised soft tissue, a two-stage exchange is necessary. The placement of a spacer combined with a short interval of 2-3 weeks until reimplantation is possible for easy-to-treat bacteria. For difficult-to-treat micro-organisms, an interval of 8 weeks without spacer until reimplantation is necessary. While stabilised by a fixateur extern, antimicrobial treatment is administered for the first 6 weeks. If the tissue specimens at reimplantation two weeks later do not show growth of bacteria or signs of acute inflammation, antimicrobial treatment can be discontinued. For all other above-mentioned treatment protocols, we administer antimicrobial treatment for a total of 6 months. We present the results of 40 consecutive infected total knee arthroplasties treated according to our algorithm, including a detailed presentation of the two-stage revision procedure.

Infections associated with orthopedic implants

PURPOSE OF REVIEW

We review recent advances in the prevention, diagnosis and treatment of infections associated with joint prostheses and internal fixation devices.

RECENT FINDINGS

The perioperative antimicrobial prophylaxis should be administered 60-30 min before incision or before inflation of the tourniquet. New diagnostic approaches include sonication of removed implants to dislodge adherent microorganisms growing in biofilms and the use of molecular techniques to improve diagnostic yield. Treatment of implant-associated infections without removal of the device is an established option for selected patients. Treatment with rifampin combinations in staphylococcal infections is crucial for success. As demonstrated in vitro, in animal studies and in clinical trials, quinolones are suitable combination agents with rifampin against susceptible staphylococci, but increasing antimicrobial resistance requires evaluation of alternative combination agents, such as quinpristin-dalfopristin, linezolid, and daptomycin, although clinical experience is limited. New antimicrobial agents, such as dalbavancin, tigecycline, iclaprim, and novel rifamycin derivatives are studied.

SUMMARY

Better understanding of the interaction between microorganisms, the implant and the host may improve our current approach to the diagnosis and treatment of implant-associated infections. The treatment modality depends on duration of infection, stability of the implant, antimicrobial susceptibility of the pathogen and condition of the surrounding soft tissue.

[Diagnosis and treatment of prosthetic joint infections]

Prosthetic replacement surgery for hip, knee, shoulder, and elbow joints has become commonplace due to the great success of these procedures in restoring function to persons disabled by arthritis. One of the most feared complications is prosthetic joint infection, which is associated with significant morbidity and health care costs. The pathogenesis of prosthetic joint infections is influenced by microorganisms growing in biofilms, making these infections difficult to diagnose and eradicate. Low-grade infections are often manifest as early loosening with or without pain. They are therefore difficult to distinguish from aseptic failure. For an accurate diagnosis of prosthetic joint infections, a combination of preoperative and intraoperative tests is usually needed. Underlying rheumatologic disease can lead to periprosthetic inflammatory changes in tissue. Therefore, only the culture of the microorganism is definitive proof of infection. Successful treatment requires long-term antimicrobial therapy, ideally with an agent acting on adhering stationary-phase microorganisms, combined with an adequate surgical procedure. In this article, the epidemiology, pathogenesis, diagnosis and treatment of prosthetic joint infections are reviewed. We focus on difficult diagnostic aspects in the context of underlying rheumatologic disease.

Management of infections of osteoarticular prosthesis

Prosthetic joint infections are an uncommon complication of joint replacement surgery, but are associated with significant morbidity and costs when they do occur. Gram-positive cocci, in particular Staphylococcus aureus and Staphylococcus epidermidis, are the most commonly recovered microorganisms (>or=50% of all isolates). About 60% of prosthetic joint infections probably occur by direct contamination during the operative procedure. Certain systemic conditions in the patients, as well as foreign material, have been identified as risk factors for prosthetic joint infection. The clinical diagnosis is only certain when there are sinus tracts that reach the prosthesis or purulent secretion is obtained from joint aspiration or during open surgery. The treatment of an infected joint prosthesis must be individualised, but it generally involves both systemic antibiotics and surgical intervention. Exchange arthroplasty in one or two stages continues to be the standard approach to management. Prosthesis retention, in conjunction with debridement and prolonged (for at least 3 months) oral antibiotic therapy, can be an alternative for early postoperative or late acute haematogenous infections, when the duration of symptoms is less than 1 month, the implant is stable, and the pathogen is relatively avirulent and sensitive to an orally well absorbed antibiotic. Good results have been achieved under these conditions in staphylococcal infections with rifampin associated with quinolones and other antibiotics, e.g., cotrimoxazole, fusidic acid, and linezolid.

Sonication of explanted prosthetic components in bags for diagnosis of prosthetic joint infection is associated with risk of contamination

Explanted orthopedic implants from 54 patients with aseptic failure and 24 patients with prosthetic knee or hip infection were sonicated in polyethylene bags. The sensitivities of periprosthetic tissue and sonicate fluid cultures for the diagnosis of prosthetic joint infection were 54% and 75%, whereas the specificities were 98% and 87%, respectively. Sonication in bags improved bacterial recovery from the surface of orthopedic implants; however, it lacked specificity, due to bag leakage.

The role of swab and tissue culture in the diagnosis of implantable cardiac device infection

BACKGROUND

The isolation of a pathogen is vital in the diagnosis and treatment of a device infection. A swab culture, despite poor sensitivity, is the most common method used in specimen collection.

OBJECTIVE

To determine the relative value of swab and tissue specimen cultures in patients with implantable cardiac pacemakers and defibrillators.

DESIGN

Prospective patient cohort study.

SETTING

A 1,000-bed tertiary referral center in Cleveland, Ohio.

PATIENTS

Consecutive patients with implantable cardiac pacemaker or defibrillator presenting for lead extraction from October 1, 2000 to March 31, 2001.

METHODS

Tissue and swab cultures were prospectively collected during pacemaker and implantable defibrillator surgeries that required lead extraction. Clinical manifestations, microbiology, and echocardiographic data were recorded in patients with and without a clinical diagnosis of device system infection.

RESULTS

Seventy-one patients with implantable pacemaker (n = 49, 69%), implantable defibrillator (n = 18, 25%), or both devices (n = 4, 6%) requiring lead extraction had pocket swab and tissue cultures for analysis. Infection was evident clinically in 35 (49%) of the patients and absent in the remainder. The most common bacteria isolated were coagulase-negative Staphylococcus (37%) and Staphylococcus aureus (10%). Patients with clinical infection had positive cultures more frequently (P = 0.002) by pocket tissue culture (n = 24, 69%) than by swab culture (n = 11, 31%). However, patients without clinical infections had positive cultures at similar rates by pocket tissue culture (n = 10, 28%) and by swab culture (n = 8, 22%; P = 0.48). Patients without clinical infection were not treated with other than perioperative antibiotics, and did not develop clinical infections.

CONCLUSION

Pocket tissue cultures are more effective than pocket swab cultures for the isolation and identification of the infectious pathogens in cardiac device infections. Positive cultures by pocket swab or tissue cultures in the absence of clinical signs and symptoms of infection does not imply infection or the need for specific therapy.

Universal primers for detection of common bacterial pathogens causing prosthetic joint infection

The diagnosis of low grade prosthetic joint infection is difficult and time consuming. Nested-PCR for universal bacterial DNA segments detection of "orthopaedic" bacteria was tested in a laboratory setting. This method is based on amplification of the 16S bacterial ribosomal RNA coding sequences. 11 species of the most frequent bacterial pathogens (Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pyogenes, Streptococcus agalactiae, Enterococcus faecium, Enterococcus faecalis, Klebsiella pneumoniae, Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa, Serratia marcescens) involved in prosthetic joint infections were studied. All could be detected rapidly and sensitively by this method.

Molecular diagnosis of prosthetic joint infection. A review of evidence

Prosthetic joint infection (PJI) diagnosis includes several classes of verification. Among them, only a few have a stronger independent value, namely intraarticular purulence and communicating fistulas. Other diagnostic methods require careful test combinations, analysis, and interpretation. Molecular based techniques using the polymerase chain reaction (PCR) seem to be a promising PJI diagnostic modality due to its excellent sensitivity, specificity, positive predictive value, and speed. Most of the recent reviewers are in agreement that molecular diagnosis has enough potential for future application in orthopaedics even if there are only a few heterogeneous studies fully supporting this concept. Conversely, at least one study has been published with significantly worse results (sensitivity and specificity less than 0.75). The lack of supporting evidence in the published studies may be closely related to varying PCR laboratory procedures, inappropriate reference standards, and other methodological shortcomings among research centers. It is not yet justifiable to firmly include molecular methods into the present PJI diagnostic schemes. The orthopaedic community must await the results of well-organized ongoing studies before considering inclusion of molecular diagnostics as a PJI diagnostic method. The aim of this paper was to make a survey of current PJI molecular diagnostic techniques in orthopaedics.

Quinolone-resistant Haemophilus influenzae in a long-term-care facility: nucleotide sequence characterization of alterations in the genes encoding DNA gyrase and DNA topoisomerase IV

Fluoroquinolone-resistant isolates of Haemophilus influenzae, obtained from a long-term care facility, were examined for nucleotide sequence differences in the quinolone-resistance-determining regions of gyrA, gyrB, parC, and parE. Similarities among the resistant isolates, plus multiple differences with susceptible isolates, suggest clonal dissemination involving two resistant subclones.

Molecular and antibiofilm approaches to prosthetic joint infection

The majority of patients with prosthetic joint replacement (arthroplasty) experience dramatic relief of pain and restoration of satisfactory joint function. In the United States, more than.5 million people have a primary arthroplasty each year. Less than 10% of prosthesis recipients have complications develop during their lifetime, commonly as a result of aseptic biomechanical failure, followed by prosthetic joint infection. The pathogenesis of prosthetic joint infection is related to bacteria in biofilms, in which they are protected from antimicrobial killing and host responses rendering these infections difficult to eradicate. Current microbiology laboratory methods for diagnosis of prosthetic joint infection depend on isolation of a pathogen by culture. However, these methods have neither ideal sensitivity nor ideal specificity. Therefore, culture-independent molecular methods have been used to improve the diagnosis of prosthetic joint infection. In the research setting, detection of 16S ribosomal deoxyribonucleic acid by polymerase chain reaction has been used in the molecular diagnosis of prosthetic joint infection. Various antibiofilm strategies directed at disruption of adherent bacteria are the focus of intense research to improve the detection of biofilm organisms and their eradication. In this article, molecular and antibiofilm approaches to prosthetic joint infection are reviewed.