Polymerase chain reaction can detect bacterial DNA in aseptically loose total hip arthroplasties

Occurrence of Rare Pathogens at the Site of Periprosthetic Hip and Knee Joint Infections: A Retrospective, Single-Center Study

The frequency and clinical relevance of rare pathogens at the site of periprosthetic infections of the hip and knee joint and their antibiotic resistance profiles have not yet been assessed in-depth. We retrospectively analyzed all periprosthetic hip and knee joint infections that occurred between 2016 and 2020 in a single center in southwest Germany. Among 165 infections, 9.7% were caused by rare microorganisms such as Veilonella sp., Pasteurella sp., Pantoea sp., Citrobacter koseri, Serratia marcescens, Parvimonas micra, Clostridium difficile, Finegoldia magna, Morganella morganii, and yeasts. No resistance to piperacillin/tazobactam, carbapenemes, fluoroquinolones, or gentamicin was observed. Some bacteria displayed resistance to ampicillin, ampicillin/sulbactam, and cefuroxime. We present follow-up data of patients with infections due to rare pathogens and discuss the importance of close, interdisciplinary collaboration between orthopedic surgeons and clinical microbiologists to carefully select the most appropriate anti-infective treatment regimens for the increasing number of patients with such infections.

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

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

Positive Microbiological Findings at the Site of Presumed Aseptic Revision Arthroplasty Surgery of the Hip and Knee Joint: Is a Surgical Revision Always Necessary?

Little is known about patients that undergo presumed aseptic revision arthroplasty surgery of the hip and knee joint and having positive microbiological findings of the intraoperatively taken tissue samples. 228 “aseptic” operations were retrospectively analyzed from prospectively collected data with regard to the following parameters: demographic data; reasons for primary and revision surgery, respectively; time between primary and revision surgery; preoperative laboratory findings; microbiological and histopathological findings; type and length of systemic antibiotic therapy; clinical outcome; and follow-up. Identification of microorganisms was present in 8.8% of the cases (9.3% of the hip and 7.8% of the knee cases). Preoperatively, the median CRP value was 8.4 mg/l (normal values 0-5.0 mg/l) and the median WBC count 8,100 × 10⁶/l (normal values 3, 700‐10,100 × 10⁶/l). The most common identified organism was methicillin-resistant Staphylococcus epidermidis in 30%, followed by viridans streptococci in 15% of the cases. In 7 cases, the microbiological findings were interpreted as a contamination, and no antibiotic therapy was administered. In the other cases, a systemic antibiotic therapy was applied for a time period between 2 weeks and 3 months. 68.4% of the patients did not have any infectious complications at a median follow-up of 20 (3-42) months. The present study indicates that more than 2/3 of the cases with positive microbiological findings at the site of presumed aseptic revision arthroplasty surgery of the hip and knee joint can be successfully treated conservatively and they do not require any further surgical therapy.

Higher sensitivity of swab polymerase chain reaction compared with tissue cultures for diagnosing periprosthetic joint infection

PURPOSE

The aim of this study was to assess the diagnostic accuracy of swab polymerase chain reaction (PCR) compared with tissue culture as the current gold standard.

METHODS

Forty-one consecutive patients were prospectively enrolled undergoing revision arthroplasty due to septic and aseptic reasons. Infection classification was done according to the criteria of the Musculoskeletal Infection Society. Intraoperatively, tissue samples of the periprosthetic membrane were collected for culture analysis, and swabs were taken from the accessible implant surface to perform 16S ribosomal RNA PCR. The diagnostic performance of swab PCR and tissue cultures was determined.

RESULTS

Of the 41 patients, 53.7% ( n = 22) had a periprosthetic joint infection (PJI) and 46.3% ( n = 19) an aseptic loosening. Swab PCR showed a higher sensitivity than tissue cultures (86.4% vs. 68.2%), while the specificity was equal (89.5%). The area under the curve was 0.79 for tissue cultures and 0.88 for swab PCR.

CONCLUSIONS

In this first investigation of swab PCR for diagnosing PJI, this procedure revealed a higher sensitivity for diagnosing PJI compared with tissue cultures. Because swab PCR is easily implementable and does not require special equipment, it can potentially improve the diagnosis of PJI.

Identifying Common Pathogens in Periprosthetic Joint Infection and Testing Drug-resistance Rate for Different Antibiotics: A Prospective, Single Center Study in Beijing

OBJECTIVE

The aim of this study is to identify the common microorganisms causing PJI as well as the drug-resistant spectrum for each microorganism, to help orthopaedic surgeons to choose appropriate antibiotics.

METHOD

One hundred and sixty patients who suffered from failure of primary or revision total hip or knee arthroplasty for different reasons were prospectively recruited. These patients underwent revision or re-revision total hip or knee arthroplasty in our institution between August 2013 to August 2016. The details of patients' medical history and comprehensive physical examination, as well as demographic data were recorded precisely. Routine blood test results, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), high sensitive C-reactive protein (hs-CRP), interleukin-6 (IL-6) levels, and synovial leukocyte counts were collected. Additionally, aspiration was conducted during surgery to avoid pollution unless when PJI was strongly suspected, in which case, joint puncture and aspiration were conducted before surgery. Intraoperatively, the implant-surrounding tissue and the prosthesis were collected under aseptic conditions. Postoperatively, the prosthesis, implant-surrounding tissue and synovium were sent to the laboratory immediately. The sonicate extraction (the prosthesis was sent for ultrasound sonication first), implant surrounding tissue and synovium were sent for microbiologic culture, and the implant-surrounding tissue was also sent for pathological examination. The isolated bacteria strains and drug-resistance rates for each pathogen for different antibiotics were presented.

RESULTS

There were 59 PJI cases in the infectious group and 101 cases in the non-infectious group (PJI is diagnosed according to the diagnosing criteria from the Workgroup of the Musculoskeletal Infection Society). Of 69 strains of pathogens isolated, Gram-positive bacterium is the most common pathogenic bacteria causing PJI (60, 86.96%). Staphylococcus epidermidis and Staphylococcus aureus played an important role as well, followed by Gram-negative bacteria (8, 11.59%) and fungus (1, 1.45%). Penicillin (78.57%), erythromycin (66.67%) and clindamycin (44.74%) showed high antibiotic resistance rate. In addition, the second-generation cephalosporin, usually as the prophylactic antibiotic, resistance rate was high (20%) as well. Fortunately, no vancomycin-resistant bacteria were discovered in the current study.

CONCLUSION

This study provides some information on the most common pathogens in our institution and the selection of antibiotics in the perioperative period in northern China. Cefuroxime and clindamycin might not be appropriate for use as prophylactic antibiotics in revision total knee or hip arthroplasty. Vancomycin is ideal for empiric antibiotic use in suspected PJI cases because of the low drug-resistance rate.

Diagnostic challenges and future perspectives in fracture-related infection

Fracture-related infection (FRI) is one of the most challenging complications in orthopaedic trauma surgery. It has severe consequences for patients and an important socio-economic impact. FRI has distinct properties and needs to be addressed interdisciplinary. Since criteria for the diagnosis of FRI are not standardized, an expert panel recently proposed a definition for FRI. In this review the current diagnostic modalities and an interdisciplinary diagnostic algorithm based on this recently published definition, are presented and future diagnostic techniques discussed. Since to date, there is no single universal diagnostic test available that gives the clinician the definitive diagnosis of FRI, it is mandatory to follow a standardized diagnostic algorithm to correctly diagnose FRI.

Diagnosis of Periprosthetic Infection: Novel Developments

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

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

BACKGROUND AND PURPOSE

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

PATIENTS AND METHODS

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

RESULTS

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

INTERPRETATION

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

Innate immune reactions in septic and aseptic osteolysis around hip implants

According to the long-standing definition, septic and aseptic total joint replacement loosening are two distinct conditions with little in common. Septic joint replacement loosening is driven by bacterial infection whereas aseptic loosening is caused by biomaterial wear debris released from the bearing surfaces. However, recently it has been recognized that the mechanisms that drive macrophage activation in septic and aseptic total joint replacement loosening resemble each other. In particular, accumulating evidence indicates that in addition to mediating bacterial recognition and the subsequent inflammatory reaction, toll-like receptors (TLRs) and their ligands, pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPS), play a key role in wear debris-induced inflammation and macrophage activation. In addition, subclinical bacterial biofilms have been identified from some cases of seemingly aseptic implant loosening. Furthermore, metal ions released from some total joint replacements can activate TLR signaling similar to bacterial derived PAMPs. Likewise, metal ions can function as haptens activating the adaptive immune system similar to bacterial derived antigens. Thus, it appears that aseptic and septic joint replacement loosening share similar underlying pathomechanisms and that this strict dichotomy to sterile aseptic and bacterial-caused septic implant loosening is somewhat questionable. Indeed, rather than being two, well-defined clinical entities, peri-implant osteolysis is, in fact, a spectrum of conditions in which the specific clinical picture is determined by complex interactions of multiple local and systemic factors.

Postoperative Deep Infection After Cemented Versus Cementless Total Hip Arthroplasty: A Meta-Analysis

Periprosthetic joint infection (PJI) is a serious complication of total hip arthroplasty (THA). The objective of this meta-analysis was to compare the PJI rate between cemented and cementless THAs. Eight clinical studies (2 randomized controlled trials and 6 observational studies) were available for the analysis. Meta-analysis (with a fixed-effects model) and subgroup analysis were performed by research design and meta-regression was performed by continuous moderator. The overall incidence of PJI was 0.4% (357/84,200). The incidence was 0.5% (310/67,531) in cemented group, and 0.3% (47/16,669) in cementless group (P=0.008). The meta-analysis revealed that the use of cement in THA was associated with an increased risk of PJI (odds ratio 1.53; 95% confidence interval 1.120 to 2.100; P=0.008).

Diagnosis of prosthetic joint infections using UMD-Universal Kit and the automated multiplex-PCR Unyvero i60 ITI(®) cartridge system: a pilot study

BACKGROUND

Prosthetic joint infections (PJI) are associated with high morbidity and costs. Various efforts have been made to improve the diagnosis of PJI over the past years, but only few studies have assessed the diagnostic utility of nucleic acid amplification test (NAAT) techniques in this context. Here, we report our experience with a commercial 16S rRNA gene PCR and an automated multiplex-PCR cartridge system in identifying pathogens causing PJI.

MATERIALS AND METHODS

A prospective single-centre study was performed including 54 patients with either septic or aseptic prosthetic joint replacement or surgical revision between February 2012 and April 2013. Conventional cultures of periprosthetic tissue samples were compared with the results of broad-range 16S rRNA gene real-time PCR (UMD-Universal Pathogen DNA Extraction and PCR Analysis, Molzym GmbH, Germany) and the multiplex-PCR Unyvero ITI(®) cartridge system (U-ITI; Curetis AG, Germany). Conventional culture and broad-range 16S rRNA gene real-time PCR were performed on all samples. U-ITI was used in a subgroup of 28 cases including all culture-positive cases. The agreement of the results from the methods was assessed.

RESULTS

Of 54 cases, seven were culture-positive. Broad-range 16S rRNA gene real-time PCR gave 6, U-ITI 3 concordant positive results. Of the 47 culture-negative samples, 46 were also negative by broad-range 16S rRNA gene real-time PCR resulting in a 96 % (52/54) agreement between 16S rRNA gene PCR and culture. Of the 21 culture-negative samples analysed with U-ITI, 20 gave negative results, including the single 16S rRNA gene PCR-positive/culture-negative specimen. The rate of agreement between U-ITI and culture results was 82 % (23/28).

CONCLUSION

This pilot study gave no indication of superiority of the used NAATs over conventional culture methods for the microbiological diagnosis of PJI. Drawbacks are susceptibility to contamination in the case of 16S rRNA gene real-time PCR, labour-intensive DNA extraction and limited pathogen panel in the case of the multiplex cartridge PCR system. More prospective trials are needed to evaluate the diagnostic performance of NAATs and their impact on the clinical management of PJI.

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

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

Sensitivities, specificities, and predictive values of microbiological culture techniques for the diagnosis of prosthetic joint infection

Background. Identifying the microorganism in a prosthetic joint infection is the key to appropriately targeting antimicrobial treatment. Despite the availability of various techniques, no single test is considered the definitive gold standard. Aim. Our aim was to determine the sensitivity, specificity, and positive/negative predictive values for a variety of culture techniques. Methods. We performed a retrospective case series of 219 patients undergoing revision surgery of their hip or knee replacement between May 2004 and February 2013. The patients were classified as either infected or noninfected according to criteria set out by the Musculoskeletal Infection Society. The number and type of samples taken intraoperatively varied between cases but included tissue samples and fluid sent in either blood culture vials or sterile containers. Results. The highest sensitivity was found with blood culture vials (0.85) compared to fluid in sterile containers (0.26) and tissues samples (0.32). Blood culture vials also had a better specificity and positive and negative predictive values profile. Conclusion. We conclude that, of the techniques studied, fluid in blood culture vials had the best profile for the correct identification of microorganisms and advocate its use.

Different diagnostic properties of C-reactive protein, real-time PCR, and histopathology of frozen and permanent sections in diagnosis of periprosthetic joint infection

BACKGROUND AND PURPOSE

There are several diagnostic tests for periprosthetic joint infection (PJI). We evaluated the properties of preoperative serum C-reactive protein (CRP), real-time polymerase chain reaction (PCR), and histopathological evaluation of frozen and permanent sections in clinical cases with culture-positive PJI.

PATIENTS AND METHODS

63 joints involving 86 operations were analyzed using serum CRP measurement prior to operation and tissue samples were collected intraoperatively for real-time PCR and histopathology. We calculated the sensitivity, specificity, likelihood ratio of positive test results (PLR), and likelihood ratio of negative test results (NLR) for each test in relation to positive microbiological culture results as the gold standard.

RESULTS

The sensitivity and specificity of diagnosis with serum CRP were 90% and 85%, respectively. The corresponding values for real-time PCR and histopathology of frozen and paraffin tissue sections were 90% and 45%, 71% and 89%, and 90% and 87%, respectively. Serum CRP had a PLR of 5.8 and an NLR of 0.12, and real-time PCR had a PLR of 1.6 and an NLR of 0.18. The corresponding figures for frozen tissue sections were 6.6 and 0.32, and those for paraffin sections were 7.1 and 0.11, respectively.

INTERPRETATION

The results suggest that real-time PCR and histopathology of frozen sections is a good combination. The former is suitable for screening, with its high sensitivity and good NLR, while the latter is suitable for definitive diagnosis of infection, with its excellent specificity and good PLR.

The response of macrophages to titanium particles is determined by macrophage polarization

Aseptic loosening of total joint replacements is driven by the reaction of macrophages to foreign body particles released from the implant. It was hypothesized that the macrophages' response to these particles is dependent, in addition to particle characteristics and contaminating biomolecules, on the state of macrophage polarization as determined by the local cytokine microenvironment. To test this hypothesis we differentiated M1 and M2 macrophages from human peripheral blood monocytes and compared their responses to titanium particles using genome-wide microarray analysis and a multiplex cytokine assay. In comparison to non-activated M0 macrophages, the overall chemotactic and inflammatory responses to titanium particles were greatly enhanced in M1 macrophages and effectively suppressed in M2 macrophages. In addition, the genome-wide approach revealed several novel, potentially osteolytic, particle-induced mediators, and signaling pathway analysis suggested the involvement of toll-like and nod-like receptor signaling in particle recognition. It is concluded that the magnitude of foreign body reaction caused by titanium particles is dependent on the state of macrophage polarization. Thus, by limiting the action of M1 polarizing factors, e.g. bacterial biofilm formation, in peri-implant tissues and promoting M2 macrophage polarization by biomaterial solutions or pharmacologically, it might be possible to restrict wear-particle-induced inflammation and osteolysis.

Macrophages-Key cells in the response to wear debris from joint replacements

The generation of wear debris is an inevitable result of normal usage of joint replacements. Wear debris particles stimulate local and systemic biological reactions resulting in chronic inflammation, periprosthetic bone destruction, and eventually, implant loosening, and revision surgery. The latter may be indicated in up to 15% patients in the decade following the arthroplasty using conventional polyethylene. Macrophages play multiple roles in both inflammation and in maintaining tissue homeostasis. As sentinels of the innate immune system, they are central to the initiation of this inflammatory cascade, characterized by the release of proinflammatory and pro-osteoclastic factors. Similar to the response to pathogens, wear particles elicit a macrophage response, based on the unique properties of the cells belonging to this lineage, including sensing, chemotaxis, phagocytosis, and adaptive stimulation. The biological processes involved are complex, redundant, both local and systemic, and highly adaptive. Cells of the monocyte/macrophage lineage are implicated in this phenomenon, ultimately resulting in differentiation and activation of bone resorbing osteoclasts. Simultaneously, other distinct macrophage populations inhibit inflammation and protect the bone-implant interface from osteolysis. Here, the current knowledge about the physiology of monocyte/macrophage lineage cells is reviewed. In addition, the pattern and consequences of their interaction with wear debris and the recent developments in this field are presented.

Defining peri-prosthetic infection: do we have a workable gold standard?

Peri-prosthetic infection remains a leading cause of revision surgery. Recent publications from the American Musculoskeletal Infection Society have sought to establish a definition of peri-prosthetic infection based on clinical findings and laboratory investigations. The limitations of their approach are discussed and an alternative definition is proposed, which it is felt may better reflect the uncertainties encountered in clinical practice.

Presence of interleukin-17C in the tissue around aseptic loosened implants

PURPOSE

The most common long-term complication of joint arthroplasty is aseptic loosening. The proinflammatory cytokines secreted by macrophages are involved in aseptic loosening. Recently, a novel proinflammatory cytokine IL-17C was reported to participate in inflammatory diseases by synergising with proinflammatory cytokines. However, the relationship between IL-17C and the aseptic loosening is unclear.

METHODS

The tissues around aseptic loosened implants were collected during revision surgery and handled by formalin fixation and embedded in paraffin. The presence of IL-17C in the tissues around the aseptic loosened implants was investigated in 12 aseptic loosening patients using immunofluorescence.

RESULTS

The presence of IL-17C protein in the tissues around aseptic loosened implants was detected by immunofluorescence. There are no statistical differences between optical density of IL-17C in aseptic loosening samples and in rheumatoid arthritis samples (positive control).

CONCLUSIONS

These results suggest the presence of IL-17C in aseptic loosening. Interleukin-17C was related to the inflammation of aseptic loosening, possibly by contributing to the inflammation and osteolysis in the tissues surrounding aseptic loosened implants.

Prosthetic joint infection diagnosis using broad-range PCR of biofilms dislodged from knee and hip arthroplasty surfaces using sonication

Periprosthetic tissue and/or synovial fluid PCR has been previously studied for prosthetic joint infection (PJI) diagnosis; however, few studies have assessed the utility of PCR on biofilms dislodged from the surface of explanted arthroplasties using vortexing and sonication (i.e., sonicate fluid PCR). We compared sonicate fluid 16S rRNA gene real-time PCR and sequencing to culture of synovial fluid, tissue, and sonicate fluid for the microbiologic diagnosis of PJI. PCR sequences generating mixed chromatograms were decatenated using RipSeq Mixed. We studied sonicate fluids from 135 and 231 subjects with PJI and aseptic failure, respectively. Synovial fluid, tissue, and sonicate fluid culture and sonicate fluid PCR had similar sensitivities (64.7, 70.4, 72.6, and 70.4%, respectively; P > 0.05) and specificities (96.9, 98.7, 98.3, and 97.8%, respectively; P > 0.05). Combining sonicate fluid culture and PCR, the sensitivity was higher (78.5%, P < 0.05) than those of individual tests, with similar specificity (97.0%). Thirteen subjects had positive sonicate fluid culture but negative PCR, and 11 had negative sonicate fluid culture but positive PCR (among which 7 had prior use of antimicrobials). Broad-range PCR and culture of sonicate fluid have equivalent performance for PJI diagnosis.

Quantitative evaluation of periprosthetic infection by real-time polymerase chain reaction: a comparison with conventional methods

Several recent studies have demonstrated the limited accuracy of conventional culture methods for diagnosing periprosthetic infections. We have applied real-time polymerase chain reaction (PCR) assays for the rapid identification of bacteria around implants and reported its utility. However, the capability of quantification is also a useful feature of this type of assay. The aim of our study was to validate the usefulness of quantitative analyses using real-time PCR of cases with clinical periprosthetic infections in comparison with more established tests, such as C-reactive protein (CRP) levels, microbiologic cultures, and histopathology. Fifty-six joints with suspected infections were reviewed retrospectively. A universal PCR assay was used to perform the quantitative analyses. The differences in the threshold cycles between clinical samples and a negative control (∆Ct) in each case were calculated. The results of the quantitative PCR assay were compared with CRP levels, microbiologic cultures, and histopathology. There was a significant correlation found between the CRP and ∆Ct values. There were also significant differences found in the ∆Ct values according to CRP levels, with higher CRP levels showing higher ∆Ct values. Similarly, there were significant differences in the ∆Ct measurements in our culture results and among our pathologic evaluations. We confirmed that quantification by universal PCR based on the ∆Ct correlated with preoperative CRP levels and was associated with the microbiologic culture results and pathologic severity. This quantification method may be valuable for assessing infection severity.

[Prevention of periprosthetic joint infections]

High numbers of primary joint replacement procedures lead to increasing numbers of revision surgeries due to periprosthetic joint infections. Several studies revealed different patient-associated and intervention-associated risk factors. Importance should be pointed on short operating times to avoid intraoperative colonisation of the implant with microorganisms. Patient-associated diseases such as diabetes and obesity should be influenced positively in the preoperative setting. Cessation of smoking should be started two months before surgery and continued until wound healing is completed. Intraoperative single-shot antibiotic prophylaxis has become clinical routine. Prolonged perioperative antibiotic prophylaxis is often conducted but has not shown to be effective in lowering infection rates.

Molecular techniques to detect biofilm bacteria in long bone nonunion: a case report

BACKGROUND

Biofilms cause chronic infections including those associated with orthopaedic hardware. The only methods that are Food and Drug Administration-approved for detecting and identifying bacterial infections are cultures and selected DNA-based polymerase chain reaction methods that detect only specific pathogens (eg, methicillin-resistant Staphylococcus aureus). New DNA-based technologies enable the detection and identification of all bacteria present in a sample and to determine the antibiotic sensitivities of the organisms.

CASE DESCRIPTION

A 34-year-old man sustained an open tibia fracture. He experienced 3 years of delayed healing and episodic pain. In addition to his initial treatment, he underwent three additional surgeries to achieve fracture healing. During the last two procedures, cultures were taken and samples were tested with the IBIS T5000 and fluorescence in situ hybridization (FISH). In both cases, the cultures were negative, but the IBIS and FISH confirmed the presence of a biofilm within the tibial canal.

LITERATURE REVIEW

Examinations of tissues from biofilm infections, by DNA-based molecular methods and by direct microscopy, have often found bacteria present despite negative cultures. Infections associated with orthopaedic hardware may be caused by bacteria living in biofilms, and these biofilm organisms are particularly difficult to detect by routine culture methods.

PURPOSES AND CLINICAL RELEVANCE

Rapid DNA-based detection methods represent a potentially clinically useful tool in the detection of bacterial biofilms. The sensitivity and clinical impact of the technology has yet to be established.

IRAK-M in macrophages around septically and aseptically loosened hip implants

The most common long-term complication of joint arthroplasty is loosening, which is mediated by chronic inflammatory cytokines produced by macrophages stimulated by implant-derived debris and eventually bacterial components adherent to such debris. In this study, antiinflammatory interleukin-1 receptor-associated kinase-M (IRAK-M) was studied in macrophages in interface membranes in vivo using immunohistochemical staining and in titanium particle-stimulated macrophages in vitro using reverse transcriptase-polymerase chain reaction. Results show that the interface membranes of septically and aseptically loosened prosthesis express more IRAK-M protein than control membranes from osteoarthritic patient and that IRAK-M mRNA-levels increase upon particle stimulation. These findings suggest that, the upregulation of IRAK-M in macrophages is involved in the local immunosuppression around implants, and may contribute to septic and aseptic implant loosening.

Incidence of low-grade infection in aseptic loosening of total hip arthroplasty

PURPOSE

We investigated the hypothesis that many total hip arthroplasty revisions that are classified as aseptic are in fact low-grade infections missed with routine diagnostics.

METHODS

In 7 Dutch hospitals, 176 consecutive patients with the preoperative diagnosis of aseptic loosening of their total hip arthroplasty were enrolled. During surgery, between 14 and 20 tissue samples were obtained for culture, pathology, and broad-range 16S rRNA PCR with reverse line blot hybridization. Patients were classified as either not being infected, suspected of having infection, or infected according to strict, predefined criteria. Each patient had a follow-up visit after 1 year.

RESULTS

7 patients were classified as infected, 4 of whom were not identified by routine culture. 15 additional patients were suspected of having infection. 20 of these 22 patients received a cemented prosthesis, fixated with antibiotic-loaded bone cement. All 22 patients received prophylactic systemic antibiotics. 7 of them reported complaints one year after surgery, but only one showed signs of early loosening. However, additional surgery was not performed in any of the patients.

INTERPRETATION

Although the proportions were not as high as previously reported in the literature, between 4% and 13% of patients with the preoperative diagnosis of aseptic loosening were infected. However, as thorough debridement was performed during surgery and prophylactic antibiotics were used, the diagnosis of infection did not have any obvious clinical consequences, as most patients performed well at the 1-year follow-up. Whether this observation has implications for long-term implant survival remains to be seen.

Molecular detection of transcriptionally active bacteria from failed prosthetic hip joints removed during revision arthroplasty

The purpose of this study was to use microbiological culture and bacterial 16S rRNA gene sequencing methods to detect transcriptionally active bacteria present on the surface of failed prosthetic hip joints removed during revision arthroplasty. Five failed prosthetic hip joints were sonicated to dislodge adherent bacteria and subjected to microbiological culture. Bacterial RNA was extracted from each sonicate, cDNA prepared by reverse transcription and the 16S rRNA gene amplified using universal primers. Polymerase chain reaction (PCR) products were cloned, assigned to distinct groups by restriction fragment length polymorphism (RFLP) analysis and one representative clone from each group was sequenced. Bacteria were identified by comparison of the obtained 16S rRNA gene sequences with those deposited in public access sequence databases. All five specimens were positive for the presence of bacteria by both culture and PCR. Culture methods identified species from eight genera. Molecular detection of transcriptionally active bacteria identified a wider range of species. A total of 42 phylotypes were identified, of which Lysobacter gummosus was the most abundant (31.6%). Thirty-four clones (14.5%) represented uncultivable phylotypes. No potentially novel species were identified. It is concluded that a diverse range of transcriptionally active bacterial species are present within biofilms on the surface of failed prosthetic hip joints.

Toll-like receptors and aseptic loosening of hip endoprosthesis-a potential to respond against danger signals?

Bacterial remnants and subclinical biofilms residing on prosthesis surfaces have been speculated to play a role in hip implant loosening by opsonizing otherwise relatively inert wear particles. The innate immune system recognizes these microbial pathogen-associated molecular patterns (PAMPs) using Toll-like receptors (TLRs). Our objective was to evaluate the possible presence of TLRs in aseptic synovial membrane-like interface tissue. Bacterial culture-negative, aseptic (n = 4) periprosthetic synovial membrane-like tissue was compared to osteoarthritis synovial membrane (n = 5) for the presence of cells positive for all known human functional TLRs, stained using specific antibodies by immunohistochemistry, and evaluated using morphometry. In comparison to osteoarthtritic synovium, the number of TLR-positive cells was found to be increased in the aseptic setting, reflecting the considerable macrophage infiltration to the tissues investigated. Thus aseptic periprosthetic tissue seems to be very reactive to PAMPs. It has been recently recognized that TLR do not only respond to traditional PAMPs, but also to endogenous alarmings or danger signals released from necrotic and activated cells. Alarming-TLR interaction in the periprosthetic tissue might be a novel mechanism of aseptic loosening of endoprosthesis.

[Applications of molecular pathology in the diagnosis of joint infections]

The diagnosis of infections in patients with arthritis and/or joint prostheses requires interdisciplinary cooperation and the use of up-to-date methods. Massive bacterial infection can be identified by bacterial culture, and minimal infection can be detected by molecular pathological methods. These processes include specific enrichment of bacterial and fungal DNA, amplification, and identification of the DNA by gel electrophoresis, sequencing techniques, and chip technologies.Anamnesis (enteral or urogenital infection), the clinical picture (oligoarthritis), and further parameters (e.g., HLA B27 status) are important for the diagnosis of reactive arthritis. In many cases of reactive arthritis, molecular methods allow detection of bacterial DNA or RNA in synovial fluid or tissue. Molecular pathological methods allow the fast and reliable differential diagnosis of granulomatous synovialitis without prior cultivation of bacteria or fungi. The development of new molecular pathological methods for detecting bacterial and fungal nucleic acids will increase diagnostic accuracy.

Molecular identification of bacteria from aseptically loose implants

Polymerase chain reaction (PCR) assays have been used to detect bacteria adherent to failed orthopaedic implants, but some PCR assays have had problems with probable false-positive results. We used a combination of a Staphylococcus species-specific PCR and a universal PCR followed by DNA sequencing to identify bacteria on implants retrieved from 52 patients (92 implants) at revision arthroplasty. We addressed two questions in this study: (1) Is this method able to show the existence of bacterial DNA on presumed aseptic loosed implants?; and (2) What proportion of presumed aseptic or culture-negative implants was positive for bacterial DNA by PCR? Fourteen implants (15%) were believed infected, whereas 74 implants (85%) were believed aseptic. Each implant was sonicated and the resulting solution was submitted for dual real-time PCR assay and culture. All implants believed aseptically loose were culture-negative, but nine of the 74 (12%) had bacterial DNA by PCR; two (2.7%) were PCR-positive and also showed histologic findings suggestive of infection. Uniquely developed PCR and bacterial sequencing assays showed bacterial DNA on 12% of implants removed for presumed aseptic loosening. Additional studies are needed to determine the clinical importance of bacterial DNA detected by PCR but not by conventional culture.

LEVEL OF EVIDENCE

Level III, diagnostic study.

Simulated joint infection assessment by rapid detection of live bacteria with real-time reverse transcription polymerase chain reaction

BACKGROUND

Although microbiological bacterial culture is currently considered the gold standard for diagnosis of septic arthritis, many studies have documented substantial false-negative and false-positive rates. The objective of this study was to determine whether real-time quantitative reverse transcription polymerase chain reaction can be used to detect bacterial messenger RNA (mRNA) in synovial fluid as a way to distinguish live and dead bacteria as an indicator of active infection.

METHODS

Synovial fluid samples were obtained from twelve consecutive patients who presented with knee pain and effusion but no evidence of infection. Following assurance of sterility with plate cultures, each sample was inoculated with clinically relevant bacteria and incubated for twenty-four hours to simulate septic arthritis. Bacterial viability and load were assessed with cultures. Selected samples were also treated with a single dose of a combination of two antibiotics, vancomycin and gentamicin, and sampled at several time points. Total RNA isolated from each sample was analyzed in triplicate with one-step real-time quantitative reverse transcription polymerase chain reaction to detect mRNA encoding for the genes groEL or femC. Controls included sterile, uninoculated samples and inoculated samples analyzed with quantitative polymerase chain reaction without reverse transcription. mRNA content was estimated on the basis of detection limits as a function of serial dilutions and was expressed as a function of colony number in bacterial cultures and RNA content as determined spectrophotometrically.

RESULTS

All synovial fluid samples that had been inoculated with one of the four bacterial species, and analyzed in triplicate, were identified (distinguished from aseptic synovial fluid) with real-time quantitative reverse transcription polymerase chain reaction; there were no false-negative results. All inoculated samples produced bacterial colonies on culture plates, while cultures of the aseptic samples were negative for growth. The detection limit of the one-step bacterial mRNA-based real-time quantitative reverse transcription polymerase chain reaction varied depending on the bacterial species. A time-dependent decrease in the concentration of detectable bacterial mRNA was seen after incubation of bacteria with antibiotics.

CONCLUSIONS

The direct quantification of the concentration of viable bacterial mRNA with real-time quantitative reverse transcription polymerase chain reaction allows identification of both culture-positive bacterial infection and so-called unculturable bacterial infection in a simulated septic arthritis model. In contrast to conventional polymerase chain reaction, real-time quantitative reverse transcription polymerase chain reaction minimizes false-positive detection of nonviable bacteria and thus provides relevant information on the success or failure of antibiotic therapy.

Identification of orthopaedic infections using broad-range polymerase chain reaction and reverse line blot hybridization

BACKGROUND

Culture remains the gold standard in the diagnosis of bacterial infection, but molecular biological techniques have yielded promising results. In this study, we validated a combined polymerase chain reaction and reverse line blot hybridization protocol for identifying musculoskeletal infections.

METHODS

Samples were obtained from seventy-six patients undergoing orthopaedic surgery for various aseptic and septic indications. The diagnosis of infection was based on a review of all available clinical and culture data. In addition to routine culture for aerobic and anaerobic growth, samples were analyzed with a broad-range 16S rRNA polymerase chain reaction and subsequent reverse line blot hybridization with use of twenty-eight group, genus, and species-specific oligonucleotide probes.

RESULTS

An infection was diagnosed on the basis of patient data in thirty-one patients. All but one of the patients with a clinical diagnosis of infection had a positive result of the polymerase chain reaction-reverse line blot hybridization. Five of the forty-five patients in whom an infection was not suspected on the basis of patient data had at least one positive result of the polymerase chain reaction-reverse line blot hybridization. Cultures demonstrated microorganisms in twenty-five patients with an infection and in two patients in whom an infection was not suspected on the basis of the patient data. Staphylococcus aureus was the most common organism grown on culture. The species identified by the polymerase chain reaction-reverse line blot hybridization was in full accordance with that grown on culture in all but one patient.

CONCLUSIONS

Polymerase chain reaction-reverse line blot hybridization performed well in detecting and identifying the various bacterial species and was more sensitive than routine culture. It identified Staphylococcus aureus as the most frequently found microorganism. Five patients in whom an infection was not suspected on the basis of the patient data had a positive result of the polymerase chain reaction, which may have been caused by contamination of the samples. However, three of these patients had aseptic loosening of a total hip prosthesis, suggesting the presence of a low-grade bacterial infection that remained undetected by the culture but was detected by the polymerase chain reaction-reverse line blot hybridization.

LEVEL OF EVIDENCE

Diagnostic Level III.

Brief ultrasonication improves detection of biofilm-formative bacteria around a metal implant

Biofilms are complex microenvironments produced by microorganisms on surfaces. Ultrasonication disrupts biofilms and may make the microorganism or its DNA available for detection. We determined whether ultrasonication could affect our ability to detect bacteria adherent to a metal substrate. A biofilm-formative Staphylococcus aureus strain was used for an in vitro implant infection model (biofilm-formative condition). We used quantitative culture and real time-polymerase chain reaction to determine the influence of different durations of ultrasound on bacterial adherence and viability. Sonication for 1 minute increased the yield of bacteria. Sonication longer than 5 minutes led to fewer bacterial colonies by conventional culture but not by polymerase chain reaction. This suggests short periods of sonication help release bacteria from the metal substrate by disrupting the biofilm, but longer periods of sonication lyse bacteria prohibiting their detection in microbiologic cultures. A relatively short duration of sonication may be desirable for maximizing detection of biofilm-formative bacteria around implants by culture or polymerase chain reaction.

[Diagnostic strategies in cases of suspected periprosthetic infection of the knee. A review of the literature and current recommendations]

Reliable confirmation of periprosthetic infection after total knee arthroplasty is a diagnostic challenge. The present work reviews published data evaluating the available diagnostic tools. Erythrocyte sedimentation rate and C-reactive protein serum levels are relatively sensitive methods with rather low specificity towards periprosthetic infection and are mainly applied to exclude infection. Studies evaluating scintigraphic methods--especially white cell scans--provide inconsistent data with varying accuracy. Consequently, white cell scans cannot be recommended as standard methods. Immunoscintigraphy with antigranulocyte antibodies and FDG-PET scans demonstrated promising results with particularly high sensitivities, but have to be validated in larger studies. Microbiological evaluation of joint aspirates proved high specificity for periprosthetic infection. However, an average of 20% of infected cases remained undetected. Nevertheless, aspiration is widely recommended for preoperative isolation of the infecting organism. Intraoperative frozen sections demonstrated excellent specificity with good sensitivity. The real accuracy of intraoperative culture and permanent histology cannot be determined due to the missing golden standard; however, a combination of both methods is recommended to define the final diagnosis. Large studies validating both methods and criteria for the final diagnosis of periprosthetic infection are necessary to optimize the diagnostic algorithm.

Dry reagent dipstick test combined with 23S rRNA PCR for molecular diagnosis of bacterial infection in arthroplasty

Periprosthetic joint infections present a challenging problem in orthopaedics. Conventional methods for detection of arthroplasty infections rely on bacterial culture of synovial fluid aspirates. During recent years, however, molecular tests that are based on DNA amplification by the polymerase chain reaction (PCR), followed by electrophoretic analysis of the products, have been introduced. We report a simple and inexpensive assay that allows visual detection and confirmation of the PCR-amplified sequences by hybridization within minutes. The assay is performed in a dry reagent dipstick format (strip) and does not require special instrumentation. Universal primers are used for PCR of the 23S ribosomal RNA (rRNA) gene. The biotinylated amplification product is hybridized with dA-tailed probes that are specific for six pathogens commonly involved in periprosthetic joint infections. The mixture is applied to the strip, which is then immersed in the appropriate buffer. The buffer migrates along the strip by capillary action and rehydrates gold nanoparticles with oligo(dT) strands attached to their surface. The nanoparticles bind to the target DNA through hybridization, and the hybrids are captured by immobilized streptavidin at the test zone of the strip, producing a characteristic red line. Unbound nanoparticles are captured by immobilized oligo(dT) strands at the control zone of the strip, generating a second line. The dipstick test was applied to the detection of Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumoniae, Enterococcus faesium, and Haemophilus influenza. Twelve samples of synovial fluids from patients were analyzed for the detection and identification of the infection caused by the six pathogens. The results were compared with bacterial cultures.

The comparison of pyrosequencing molecular Gram stain, culture, and conventional Gram stain for diagnosing orthopaedic infections

We have developed a combined real-time PCR and pyrosequencing assay that successfully differentiated the vast majority of gram-positive and gram-negative bacteria when bacterial isolates were tested. The purpose of this study was to evaluate this assay on clinical specimens obtained from orthopedic surgeries, and to prospectively compare the results of "molecular Gram stain" with culture and conventional direct Gram stain. Forty-five surgical specimens were obtained from patients who underwent orthopedic surgery procedures. The DNA was extracted and a set of broad-range PCR primers that targeted a part of the 16S rDNA gene was used for pan-bacterial PCR. The amplicons were submitted for pyrosequencing and the resulting molecular Gram stain characteristics were recorded. Culture and direct Gram staining were performed using standard methods for all cases. Surgical specimens were reviewed histologically for all cases that had a discrepancy between culture and molecular results. There was an 86.7% (39/45) agreement between the traditional and molecular methods. In 12/14 (85.7%) culture-proven cases of bacterial infection, molecular Gram stain characteristics were in agreement with the culture results, while the conventional Gram stain result was in agreement only for five cases (35.7%). In the 31 culture negative cases, 27 cases were also PCR negative, whereas 4 were PCR positive. Three of these were characterized as gram negative and one as gram positive by this molecular method. Molecular determination of the Gram stain characteristics of bacteria that cause orthopedic infections may be achieved, in most instances, by this method. Further studies are necessary to understand the clinical importance of PCR-positive/culture-negative results.