Aims. The aim of this study was to analyze the prevalence of culture-negative periprosthetic joint infections (PJIs) when adequate methods of culture are used, and to evaluate the outcome in patients who were treated with antibiotics for a culture-negative PJI compared with those in whom antibiotics were withheld. Methods. A multicentre observational study was undertaken: 1,553 acute and 1,556 chronic PJIs, diagnosed between 2013 and 2018, were retrospectively analyzed. Culture-negative PJIs were diagnosed according to the Muskuloskeletal Infection Society (MSIS), International Consensus Meeting (ICM), and European Bone and Joint Society (EBJIS) definitions. The primary outcome was recurrent infection, and the secondary outcome was removal of the prosthetic components for any indication, both during a follow-up period of two years. Results. None of the acute PJIs and 70 of the chronic PJIs (4.7%) were culture-negative; a total of 36 culture-negative PJIs (51%) were treated with antibiotics, particularly those with histological signs of infection. After two years of follow-up, no recurrent infections occurred in patients in whom antibiotics were withheld. The requirement for removal of the components for any indication during follow-up was not significantly different in those who received antibiotics compared with those in whom antibiotics were withheld (7.1% vs 2.9%; p = 0.431). Conclusion. When adequate methods of culture are used, the incidence of culture-negative PJIs is low. In patients with culture-negative PJI, antibiotic treatment can probably be withheld if there are no histological signs of infection. In all other patients, diagnostic efforts should be made to identify the causative microorganism by means of serology or molecular techniques. Cite this article: Bone Joint J 2022;104-B(1):183–188

Aims. Bacterial infection activates neutrophils to release neutrophil extracellular traps (NETs) in bacterial biofilms of periprosthetic joint infections (PJIs). The aim of this study was to evaluate the increase in NET activation and release (NETosis) and haemostasis markers in the plasma of patients with PJI, to evaluate whether such plasma induces the activation of neutrophils, to ascertain whether increased NETosis is also mediated by reduced DNaseI activity, to explore novel therapeutic interventions for NETosis in PJI in vitro, and to evaluate the potential diagnostic use of these markers. Methods. We prospectively recruited 107 patients in the preoperative period of prosthetic surgery, 71 with a suspicion of PJI and 36 who underwent arthroplasty for non-septic indications as controls, and obtained citrated plasma. PJI was confirmed in 50 patients. We measured NET markers, inflammation markers, DNaseI activity, haemostatic markers, and the thrombin generation test (TGT). We analyzed the ability of plasma from confirmed PJI and controls to induce NETosis and to degrade in vitro-generated NETs, and explored the therapeutic restoration of the impairment to degrade NETs of PJI plasma with recombinant human DNaseI. Finally, we assessed the contribution of these markers to the diagnosis of PJI. Results. Patients with confirmed PJI had significantly increased levels of NET markers (cfDNA (p < 0.001), calprotectin (p < 0.001), and neutrophil elastase (p = 0.022)) and inflammation markers (IL-6; p < 0.001) in plasma. Moreover, the plasma of patients with PJI induced significantly more neutrophil activation than the plasma of the controls (p < 0.001) independently of tumour necrosis factor alpha. Patients with PJI also had a reduced DNaseI activity in plasma (p < 0.001), leading to a significantly impaired degradation of NETs (p < 0.001). This could be therapeutically restored with recombinant human DNaseI to the level in the controls. We developed a model to improve the diagnosis of PJI with cfDNA, calprotectin, and the start tail of TGT as predictors, though cfDNA alone achieved a good prediction and is simpler to measure. Conclusion. We confirmed that patients with PJI have an increased level of NETosis in plasma. Their plasma both induced NET release and had an impaired ability to degrade NETs mediated by a reduced DNaseI activity. This can be therapeutically restored in vitro with the approved Dornase alfa, Pulmozyme, which may allow novel methods of treatment. A combination of NETs and haemostatic biomarkers could improve the diagnosis of PJI, especially those patients in whom this diagnosis is uncertain. Cite this article: Bone Joint J 2024;106-B(9):1021–1030

Background. Increasing evidence suggests a link between the bearing surface used in total hip arthroplasty (THA) and the occurrence of infection. It is postulated that polyethylene has immunomodulatory effects and may influence bacterial function and survival, thereby impacting the development of periprosthetic joint infection (PJI). This study aimed to investigate the association between polyethylene type and revision surgery for PJI in THA using data from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR). We hypothesized that the use of XLPE would demonstrate a statistically significant reduction in revision rates due to PJI compared to N-XLPE. Methods. Data from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) spanning September 1, 1999, to December 31, 2021, were used to compare the infection revision rates between THA using N-XLPE and XLPE. We calculated the Cumulative Percentage Revision rate (CPR) and Hazard Ratio (HR) while controlling for factors like age, sex, body mass index (BMI), American Society of Anesthesiologists’ (ASA) grade, and head size. Results. From the total 361,083 primary THAs, 26,827 used N-XLPE and 334,256 used XLPE. Excluding data from the first 6 months post-surgery, 220 revisions occurred in the N-XLPE group and 1,055 in the XLPE group for PJI. The HR for infection revision was significantly higher in N-XLPE compared to XLPE, at 1.64 (95% CI, 1.41–1.90, p<0.001). Conclusions. This analysis provides evidence of an association between N-XLPE and revision for infection in THA. We suspect that polyethylene wear particles contribute to the susceptibility of THA to PJI, resulting in a significantly higher risk of revision for infection in N-XLPE hips compared to those with XLPE. Level of Evidence. Therapeutic Level III

Aims. Despite numerous studies on periprosthetic joint infections (PJI), there are no robust data on the risk factors and timing of metachronous infections. This study was performed to answer the following questions: 1) Is there any difference of manifestation time of metachronous PJIs between different localizations of multiple artificial joints? 2) Can we identify any specific risk factor for metachronous PJIs for different localizations of multiple artificial joints?. Methods. Between January 2010 and December 2018, 661 patients with more than one prosthetic joint at the time of PJI surgical treatment were recruited. Seventy-one developed metachronous PJI after a mean time interval of 101.4 months (range 37.5 to 161.5 months). The remaining patients were chosen as control group. The diagnosis of the PJI, including the metachronous PJI, was made according to the Muscoloskeletal Infection Society (MSIS) criteria. The metachronous infections were divided in group 1: metachronous infections in the same extremity (e.g. right hip and right knee); group 2: metachronous infections of the other extremity (e.g. right knee and left hip); group 3: metachronous infections of the lower extremity and upper extremity (e.g. right knee and left shoulder). Results. We identified 32 PJI cases in group 1, 38 in group 2 and 1 in group 3. Diabetes mellitus was found higher in the metachronous infections (p<0.05). Rate of same side infection was significantly higher compared to contralateral and upper and lower infection (p<0.05). Time interval of metachrononous infection development was faster in same-side infections. Same bacteria sample rate between primary PJI and metachronous PJI in same side infections (21/32) was significantly higher than in the contralateral PJI group (13/38, p<0.05). Conclusions. The current study underlined that the risk of metachronous infections are relatively high, particularly in the cases of prostheses on the same side

Aim. A substantial portion of periprosthetic joint infections (PJI) literature is comprised of observational studies. The Strengthening the Reporting of Observational Studies in Epidemiology guidelines emphasize the importance of clearly defining variables and providing diagnostic criteria. Well-defined variables in these studies play a crucial role in ensuring data consistency, fostering comparability among studies, and laying a robust foundation for evidence-based decision-making. We aimed to determine the definition of these variables and determine the objectivity of the definitions. Method. We reviewed observational studies on hip or knee PJI that focused on variables and their association with treatment outcomes. The inclusion criteria comprised studies from Jan 2017 to Jan 2023. We focused on 13 variables that were possibly subjective. These were smoking, alcohol use, diabetes mellitus, hypertension, lung disease, rheumatoid arthritis, liver diseases, kidney diseases, cardiovascular diseases, malignancy, immunosuppression, use of antibiotics, and type of infection. The reviewers examined the text of the articles, along with any available online supplements or protocols, for definitions of the selected variables. We classified a definition as objective if there was the presence of time element, severity, staging, frequencies, laboratory cut-off, medication dependence, among others. Chart review was deemed subjective. Results. We included 75 studies in the analysis. The most common factors studied were diabetes mellitus (79%), cardiovascular disease, smoking history, and rheumatoid arthritis (47% each). The variables that were objectively defined most often were antibiotic use (100%) and type of infection (95%). Smoking history (16%) and alcohol use (20%) were the least frequently objectively defined variables. Further analysis revealed that a considerable number of studies incorporated variables into their primary analyses without clear definitions. For instance, out of the 59 studies where diabetes was considered a variable, 41 studies (70%) included diabetes in their main analyses as a factor for PJI treatment outcomes, despite only 34 studies having defined this variable. Moreover, of the 34 provided definitions of diabetes mellitus, only 12 provided objective criteria for diagnosis. The rest of the provided definitions relied on “chart review” without further specification. Table 1 outlines the proportion of studies with variables defined and included in their analysis. Conclusions. Study variables were not clearly defined in most of the observational studies raising concerns about the reproducibility and reliability of findings. Our study underscores the vital need for standardized variable definitions in PJI research. Professional societies may play a crucial role in setting standards for the definition of variables. For any tables or figures, please contact the authors directly

Aim. As the populations of patients who have multiple prosthetic joints increase these years, the fate of a single joint periprosthetic joint infection in these patients is still unknown. Risk factors leading to a subsequent infection in another prosthetic joint are unclear. Our goal is to identify the risk factors of developing a subsequent infection in another prosthetic joint and describe the organism profile to the second prosthetic infection. Method. We performed a retrospective cohort study of all PJI cases underwent surgical intervention at our institute, a tertiary care referral center over 11 years, during January 2006 to December 2016. We identified 96 patients with periprosthetic joint infection who had another prosthetic joint in place at the time of presentation. The comorbidity, number of prosthetic joints, date and type of each arthroplasty, times of recurrent infection at each prosthetic joint with subsequent debridement or 2-stage resection arthroplasty, organisms from every infection episode, the outcome of each periprosthetic joint infection in these patients were analyzed. Results. During January 2006 to May 2017, we retrospective collected 294 PJI cases (159 hips, 135 knees) in our institute. Patients with single prosthetic joint were excluded and finally 96 patients were included. Of the 96 patients, 19 (19.79%) developed a periprosthetic joint infection in a second joint. The type of organism was the same as the first infection in 12 (63.16%) of 19 patients. The time to developing a second infection averaged 2.16 years (range, 0–9.3 years). The risk factors leading to a subsequent infection in another prosthetic joint are albumin level (< 3.5 mg/dl), long-term steroid usage (> 5mg/day, > 3 months), history of necrotizing fasciitis, history of invasive dental procedure (> Grade IV procedure), 3-stage resection arthroplasty or more, and PJI caused by vacomycin-resistent enterococcus (VRE). Conclusions. A PJI might predispose patients to subsequent PJI in another prosthesis. Patients and surgeons must be aware of the risk factors contribute to this devastating complication. Most organisms in the second PJI are identical to the first one, and we believe the bacteremia may be the pathogenesis, but need further proved. The preventive policy may be needed in the future for this population who has multiple prosthetic joints

Background. The diagnosis of periprosthetic joint infection (PJI) remains a challenge in clinical practice and the analysis of synovial fluid (SF) is a useful diagnostic tool. Recently, two synovial biomarkers (leukocyte esterase (LE) strip test, alpha-defensin (AD)) have been introduced into the MSIS (MusculoSkeletal Infection Society) algorithm for the diagnosis of PJI. AD, although promising with high sensitivity and specificity, remains expensive. Calprotectin is another protein released upon activation of articular neutrophils. The determination of calprotectin and joint CRP is feasible in a routine laboratory practice with low cost. Purpose. Our objective was to evaluate different synovial biomarkers (calprotectin, LE, CRP) for the diagnosis of PJI. Methods. In this monocentric study, we collected SF from hip, knee, ankle and shoulder joints of 42 patients who underwent revision or puncture for diagnostic purposes. Exclusion criteria included a joint surgery in the previous 3 months and a diagnosis of a systemic inflammatory disease. PJI was diagnosed in a multidisciplinary consultation meeting (RCP) of the Reference Centers for Osteoarticular Infections of the Great West (CRIOGO). SF was analysed for LE, CRP and calprotectin. The cut-off values used were 50 mg/L for calprotectin, 8.8 mg/L for CRP and 125 WBC/µL for LE. The overall sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated for these different synovial markers. Results. Of the 42 patients included, 28 were considered as infected and 14 uninfected. The statistical parameters are presented in Table 1. Conclusion. The present study shows that the synovial calprotectin assay has an excellent sensitivity and a 100% NPV for the diagnosis of PJI, suggesting that a result < 50 mg/L could exclude PJI. This promising study suggests that calprotectin should be included with synovial CRP in a new decision algorithm for the diagnosis of PJI. For any tables or figures, please contact the authors directly

Aim. Diagnosing periprosthetic joint infection after total joint arthroplasty is often challenging. The alpha defensin test has been recently reported as a promising diagnostic test for periprosthetic joint infection. The goal of this study was to determine the diagnostic accuracy of alpha defensin testing. Method. One hundred and eighty-three synovial alpha defensin and synovial fluid C-reactive protein (CRP) tests performed in 183 patients undergoing evaluation for periprosthetic joint infection were reviewed. Results were compared with the Musculoskeletal Infection Society (MSIS) criteria for periprosthetic joint infection. Results. Alpha defensin tests were performed prior to surgical treatment for infection, and 37 of these patients who had these tests were diagnosed by MSIS criteria as having infections. Among this group, the alpha defensin test had a sensitivity of 81.1% (95% confidence interval [CI], 64.8% to 92.0%) and a specificity of 95.9% (95% CI, 91.3% to 98.5%). There were 6 false-positive results, 4 of which were associated with metallosis. There were 7 false negatives, all of which were associated with either draining sinuses (n = 3) or low-virulence organisms (n = 4). A combined analysis of alpha defensin and synovial fluid CRP tests was performed in which a positive result was represented by a positive alpha defensin test and a positive synovial fluid CRP test (n = 28). Among this group, the sensitivity was calculated to be 73.0% (95% CI, 55.9% to 86.2%) and the specificity was calculated to be 99.3% (95% CI, 96.2% to 99.9%). An additional combined analysis was performed where a positive result was represented by a positive alpha defensin test or positive synovial fluid CRP test (n = 64). Among this group, the sensitivity was calculated tobe91.9%(95%CI, 78.1%to98.3%) andthe specificitywas calculated tobe79.5%(95%CI, 72.0%to85.7%). Conclusions. Alpha defensin in combination with synovial fluid CRP demonstrates very high sensitivity for diagnosing periprosthetic joint infection, but may yield false-positive results in the presence of metallosis or false-negative results in the presence of low-virulence organisms. When both alpha defensin and synovial fluid CRP tests are positive, there is a very high specificity for diagnosing periprosthetic joint infection

Aim. Periprosthetic joint infections follow 1-3% of arthroplasty surgeries, with the biofilm nature of these infections presenting a significant treatment challenge. 1. Prevention strategies include antibiotic-loaded bone cement; however, increases in cementless procedures means there is an urgent need for alternative local antimicrobial delivery methods. 2. A novel, ultrathin, silica-based sol-gel technology is evaluated in this research as an anti-infective coating for orthopaedic prosthetic devices, providing local antibiotic release following surgery. Method. Reduction in clinically relevant microbial activity and biofilm reduction by antimicrobial sol-gel coatings, containing a selection of antibiotics, were assessed via disc diffusion and microdilution culture assays using the Calgary biofilm device. 3. Proliferation, morphology, collagen, and calcium production by primary bovine osteoblasts cultured upon antibiotic sol-gel surfaces were examined, and cytotoxicity evaluated using Alamar blue staining and lactate dehydrogenase assays. Concentrations of silica, calcium and phosphorus compounds within the cell layer cultured on sol-gel coatings and concentrations eluted into media, were quantified using ICP-OES. Furthermore, cellular phenotype was assessed using alkaline phosphatase activity with time in culture. Results. Low antibiotic concentrations within sol-gel had an inhibitory effect on clinically relevant biofilm growth, for example 0.8 mg ml. -1. tobramycin inhibited clinically isolated S. aureus (MRSA) growth with an 8-log reduction in viable colony forming units. There was no significant difference in metabolic activity between untreated and sol-gel exposed primary bovine osteoblasts in elution-based assays. Reduction (2-fold) in metabolic activity in direct contact assays after 48 hours exposure was likely to be due to increased osteoinduction, whereas no impact upon cell proliferation were observed (p=0.92 at 14 days culture). The morphology of primary osteoblasts was unaffected by culture on sol-gel coatings and collagen production was maintained. Calcium containing nodule production within bovine osteoblastic cells was increased 16-fold after 14 days culture upon sol-gel. Conclusions. The ultrathin sol-gel coating showed low cytotoxicity, strong biofilm reducing activity and antimicrobial activity, which was comparable to antibiotics alone, demonstrating that sol-gel delivery of antibiotics could provide local antimicrobial effects to inhibit PJI growth without the need for bone cement. Future work will develop and evaluate sol-gel performance in an ex vivo explant bone infection model which will reduce the need for animal experimentation

Aim. Serum parameters continue to be a focus of research in diagnosing periprosthetic joint infections (PJI). Several workgroups have recently proposed serum Albumin-Globulin-Ratio (AGR) as a potential new biomarker. Due to controversies in the literature, its usability in clinical practice remains uncertain. The aim of this study was to assess the value of serum AGR in diagnosing PJI preoperatively, especially in comparison with the well-established marker C-reactive Protein (CRP). Method. From January 2015 to June 2022, patients with indicated revision hip (rTHA) and knee (rTKA) arthroplasty were included in this retrospective cohort study of prospectively collected data. A standardized diagnostic workup was performed using the 2021 European Bone and Joint Infection Society (EBJIS) definition of PJI, excluding CRP. Diagnostic accuracies of serum AGR and CRP were calculated by receiver operating characteristic curve (ROC) analysis. A z-test was used to compare the area under the curves (AUC). Results. A total of 275 patients with rTHA and rTKA were included, 144 joints (52.4%) were identified as septic. Decreased AGR and elevated CRP were strongly associated with PJI, optimal diagnostic thresholds were calculated with 1.253 and 9.4 mg/L, respectively. Sensitivities were 62.5% (95%-confidence interval: 54.3–70.0) and 73.6% (65.8–80.1), and specificities 84.7% (77.5–89.9) and 87.8% (80.9–92.4), respectively. CRP showed a significantly higher AUC than AGR (0.807 (0.761–0.853) and 0.736 (0.686–0.786); p<0.0001). Subgroup analysis of acute versus chronic infections yielded significantly higher diagnostic accuracies in acute PJI for both parameters (p<0.0001). Similar results were observed when focusing on the causative microorganism; a better diagnostic performance was observed in high-virulence PJI compared to low-virulence PJI (p≤0.005). Furthermore, higher AUCs were calculated in knee PJI compared with hip PJI, with a significant difference for AGR (p=0.043). Conclusions. Due to its limited diagnostic accuracy, serum AGR cannot be recommended as an additional marker for diagnosing PJI. Serum parameters are generally unspecific and can be influenced by comorbidities and other foci of infection. Additionally, parameters may remain within normal levels in low-grade PJI. Evaluating AGR, further possible pitfalls must be considered, for example an increased latency until bottom values are reached and the impact of malnutrition

Background. Fungal infection at an arthroplasty site is rare and poses a therapeutic challenge. To the best of our knowledge, no reports have been published thus far on the success rate of prosthesis reimplantation after fungal prosthetic joint infections. Questions/purposes. We asked: (1) What is the success rate in terms of infection eradication using a two-stage exchange arthroplasty in patients with hip or knee fungal periprosthetic joint infections, particularly focusing on Candida infections? (2) What patient-, infection-, and treatment-related variables are associated with the success or failure of treatment?. Methods. From January 2000 to December 2010, 16 patients with hip or knee candidal periprosthetic joint infections were treated with two-stage exchange arthroplasty at our institute. Treatment success was defined as a well-functioning joint without relapse of candidal infection after prosthesis reimplantation, while treatment failure was defined as uncontrolled or a relapse of candidal infection or mortality. Variables, including age, sex, comorbidities, microbiology, antimicrobial agents used, and operative methods, were analyzed. Minimum followup was 28 months (mean, 41 months; range, 28–90 months). Results. At latest followup, the treatment failed to eradicate the infection in eight of the 16 patients, and there were four deaths related to fungemia. Four patients required permanent resection arthroplasty owing to uncontrolled or recurrent candidal infections. All eight patients (50% successful rate) who had their infections eradicated and successful prosthesis reimplantation had prolonged treatment with oral fluconazole before (mean, 8 months) and after (mean, 2.2 months) prosthesis reimplantation. The antifungal therapy correlated with successful treatment. Renal insufficiency, hypoalbuminemia, anemia, and chronic obstructive pulmonary disease were significantly more prevalent in the treatment-failure group than in the treatment-success group. Conclusions. Half of the patients treated with two-stage exchange arthroplasty for fungal periprosthetic joint infections had recurrence or lack of control of the infection. A prolonged antifungal therapy appeared to be essential for successful treatment of candidal periprosthetic joint infections. The presence of renal insufficiency, hypoalbuminemia, anemia, or chronic obstructive pulmonary disease might be associated with a poor outcome

Aim. This study aimed to externally validate promising preoperative PJI prediction models in a recent, multinational European cohort. Method. Three preoperative PJI prediction models (by Tan et al., Del Toro et al., and Bülow et al.) which previously demonstrated high levels of accuracy were selected for validation. A multicenter retrospective observational analysis was performed of patients undergoing total hip arthroplasty (THA) and total knee arthroplasty (TKA) between January 2020 and December 2021 and treated at centers in the Netherlands, Portugal, and Spain. Patient characteristics were compared between our cohort and those used to develop the prediction models. Model performance was assessed through discrimination and calibration. Results. A total of 2684 patients were included of whom 60 developed a PJI (2.2%). Our patient cohort differed from the models’ original cohorts in terms of demographic variables, procedural variables, and the prevalence of comorbidities. The c-statistics for the Tan, Del Toro, and Bülow models were 0.72, 0.69, and 0.72 respectively. Calibration was reasonable, but precise percentage estimates for PJI risk were most accurate for predicted risks up to 3-4%; the Tan model overestimated risks above 4%, while the Del Toro model underestimated risks above 3%. Conclusions. In this multinational cohort study, the Tan, Del Toro, and Bülow PJI prediction models were found to be externally valid for classifying high risk patients for developing a PJI. These models hold promise for clinical application to enhance preoperative patient counseling and targeted prevention strategies. Keywords. Periprosthetic Joint Infection (PJI), High Risk Groups, Prediction Models, Validation, Infection Prevention

INTRODUCTION. Total joint arthroplasty continues to gain acceptance as the standard of care for the treatment of severe degenerative joint disease, and is considered one of the most successful surgical interventions in the history of medicine. However, infection of these implants, called Periprosthetic Joint Infection (PJI), remains one of the biggest challenges facing orthopaedics today. PJI can lead to additional surgeries, revision, fusion and amputation. Diagnosis of PJI. It is important to accurately diagnose PJI because its management differs from that of other causes of arthroplasty failure. In acute infection, the local signs and symptoms (e.g., severe pain, swelling, erythema, and warmth at the infected joint) of inflammation are generally present. On the other hand, chronic infection usually has a more subtle presentation, with pain alone, and is often accompanied by loosening of the prosthesis at the bone-implant interface. The diagnosis of PJI has proven quite challenging, as both acute and chronic infections can be difficult to differentiate from other forms of inflammation. The reported literature on the diagnosis of PJI has focused on evaluated laboratory tests that were never developed specifically for the diagnosis of PJI. These include the erythrocyte sedimentation rate (ESR), the serum C-reactive protein (CRP), the synovial fluid white blood cell count and the leukocyte differential. Because these tests were not made for the purpose of diagnosing PJI, it has been the responsibility of the orthopaedic community to evaluate and recommend their interpretation. This has resulted in significant confusion regarding the appropriate thresholds and optimal combination of these tests. These difficulties were the motivation for the development of a specific test for the detection of PJI. The Synovasure® Test for Periprosthetic Joint Infection (PJI). The promising diagnostic capabilities of synovial fluid biomarkers for PJI have already been reported in the literature. These biomarkers include inflammatory proteins, cytokines, and microbicidal peptides / proteins that are known to be involved in the host response to infection. Studies have demonstrated that the alpha-defensin microbicidal peptide present in human neutrophils is an ideal biomarker for PJI due to the distinct separation it achieves between positive and negative results. A specific test allowing to measure the concentration of the alpha-defensin in the synovial fluid has been developed. The specificity and the sensitivity of this test for the detection of a PJI are respectively 96% and 97%. This test has been proven to have also a high reproducibility, its results not being influenced by antibiotics. DISCUSSION. A lateral flow version of this test (Synovasure PJI, distributed exclusively in Europe by Zimmer GmbH) has been recently developed. It allows reading the results in 10 minutes and it doesn't require any laboratories for its interpretation. Currently, this test device is in clinical evaluation in more than 200 European hospitals. CONCLUSIONS. In case that the clinical evaluation of this test device is positive, this method will be a new paradigm for the diagnosis of periprosthetic joint infection

Aim. Patients with late acute periprosthetic joint infections (PJI) and treated with surgical debridement have a high failure rate. Previous studies have shown that rheumatoid arthritis (RA) is an independent risk factor for treatment failure. We conducted a case-control study to identify predictors for failure in late acute PJI treatment in RA patients. We hypothesize that patients with RA have a higher failure rate compared to controls due to the use of immunosuppressive drugs. Method. Data of an international multicenter retrospective observational study was used. Late acute PJI was defined as a sudden onset of symptoms and signs of a PJI, more than 3 months after implantation. Failure of treatment was defined as persistent signs of infection, relapse with the same or reinfection with a different micro-organism, need for prosthesis removal or death. Cases with RA were matched with cases without RA based on the affected joint. A Cox survival analyses, stratified for RA, was used to calculate hazard ratio's (HR) for failure. Subgroup analyses were used to explore other predictors for treatment failure in RA patients. Results. A total of 40 patients with RA and 80 controls without RA were included. Treatment failure occurred in 65% patients with RA compared to 45% for controls (p= .052). 68% of patients with RA used immunosuppressive drugs at time of PJI diagnosis. The use or continuation of immunosuppressive drugs in PJI was not associated with a higher failure rate; neither were the duration of symptoms and causative microorganism. The time between implantation of the prosthetic joint and diagnosis of infection was longer in RA patients: median 110 (IQR 41-171) vs 29 months (IQR 7.5–101.25). Exchange of mobile components was associated with a lower risk of treatment failure (HR 0.489, 95% CI 0.242–0.989, p-value .047). Conclusions. The use of immunosuppressive drugs does not seem to be associated with a higher failure rate in patients with RA. Mobile exchange in RA patients is associated with a lower risk of failure. This might be due to the significantly older age of the prosthesis in RA patients. Future studies are needed to explore these associations and its underlying pathogenesis

Aim. Rifampicin as a biofilm-active antibiotic drug has a significant role in the treatment of periprosthetic joint infection (PJI). However, rifampicin resistance is an increasing threat to PJI treatment. This study aimed to evaluate the prevalence of rifampicin resistant staphylococci over time and its association with infection-free survival after PJI in a single centre in Sweden. Methods. We included 238 PJIs in 238 patients who had undergone PJI revision surgery from 2001 to 2020 on whom the causative bacteria were staphylococci, and the agent was tested for rifampicin resistance. Data regarding agents, rifampicin resistance, treatment and outcome was obtained. Kaplan-Meier survival analysis and a Cox regression model with adjustment for age, sex, localisation (hip or knee) and type of prosthesis (primary or revision) were used to calculate infection-free survival rates and adjusted risk ratios (HRs) of the risk of treatment failure. Treatment failure was defined as any reoperation or suppression treatment with antibiotics due to prolonged infection. Results. Among the included 238 PJIs, 40 rifampicin-resistant staphylococci [93% Coagulase Negative Staphylococci (CoNS)] and 29 treatment failures were identified. The proportion of rifampicin resistant agents decreased from 25% in 2010–2015 to 12% in 2016–2020. The 2-year infection-free survival rates were 79.0% (95% CI 0.66–0.92) for the rifampicin resistant and 90% (95% CI 0.86–0.94) for the rifampicin sensitive group. Patients with PJI caused by rifampicin resistant bacteria had a significantly higher risk of treatment failure than those caused by sensitive bacteria (HR 2.5; 95% CI 1.0–6.2). Conclusions. The incidence of PJI caused by rifampicin resistant staphylococci decreased in Uppsala, Sweden over the past 20 years. PJI caused by rifampicin-resistant staphylococci has a two-fold risk for treatment failure compared to PJI caused by rifampicin-sensitive staphylococci, which stresses the importance of retaining rifampicin resistance low. Additionally, the increased risk of treatment failure when PJI is caused by a rifampicin-resistant bacteria warrants consideration of a more conservative treatment strategy

Aim. Periprosthetic joint infection (PJI) is a serious complication after joint arthroplasty. Diagnosing PJI can be challenging as preoperative screening and conventional cultures may be inconclusive. Sonication fluid culturing stands out as a valuable adjunct technique to improve microbiological PJI diagnosis. This study aims to determine the clinical relevance of routinely using sonication for all septic and aseptic revisions. Method. All patients who underwent (partial) hip or knee revision arthroplasty for all causes between 2012 and 2021 at our institution were retrospectively reviewed. Based on the European Bone and Joint Society PJI criteria, we categorized them into three groups: infection confirmed, infection likely, and infection unlikely. We analyzed the clinical, laboratory, and radiological screening that could confirm or refute suspicion of PJI. We analyzed microbiology cultures and the most frequently detected microorganisms. Sensitivity and specificity were calculated for synovial fluid cultures (preoperative), tissue cultures, and sonication fluid cultures. We determined the clinical relevance of sonication as the percentage of patients for whom sonication confirmed (microbiological) PJI diagnosis. Results. 429 patients who underwent (partial) revision of hip (246 patients) or knee (183 patients) arthroplasty were included. Sensitivity and specificity were 69% and 99% for preoperative synovial fluid cultures, 76% and 92% for intraoperative tissue cultures, and 80% and 89% for sonication fluid cultures, respectively. Sonication fluid cultures improved tissue culture sensitivity and specificity to 83% and 99%, respectively. In 12 (11%) out of 110 PJIs, sonication fluid cultures were decisive for confirming the causative pathogen. This was applicable to acute and chronic infections. In 29 (9%) out of 319 aseptic cases, a negative sonication fluid culture could confirm contamination of tissue cultures. Conclusions. Routine sonication fluid cultures enhanced the sensitivity and specificity of PJI diagnostics. In 11% of PJI cases, causative pathogens were confirmed by sonication fluid culture results. Routine sonication may be helpful in confirming contamination of synovial fluid cultures and tissue cultures. Routine sonication fluid culture should be performed in all revision arthroplasties

Aim. Periprosthetic joint infections (PJI) are severe complications after total joint arthroplasty (TJA). Up to now, a gold standard in the diagnostics of PJI is missing. Small extracellular vesicles (sEVs) are secreted by all types of cells and play a key role in immune response in presence of infection (1). In this prospective study, the diagnostic accuracy of sEVs in the synovial fluid to detect PJI of knee, hip and shoulder joints was investigated. We hypothesized increased surface markers of sEVs in PJI compared to aseptic complications (e.g. implant loosening, stress shielding related pain). Method. Synovial fluid from 48 patients with painful arthroplasty was examined. The distinction between aseptic and infectious cases was made on the basis of the 2018 Definition of Periprosthetic Hip and Knee Infection (2). 35 (72,9%) probands assigned to aseptic and 13 patients (27,1%) to PJI group. Immuno-fluorescence flow cytometry served to document the concentrations of CD9, CD63, CD66b, CD82 and HLA-DR on sEVs. Results. The concentration of CD9 surface marker on sEVs in synovial fluid was significantly lower (p=0.002) in PJI group than in aseptic group. In contrast, the levels of CD82 on sEVs in synovial fluid was significantly higher (p<0.0001) in the PJI group than in aseptic group. The concentrations of CD63, CD66b and HLA-DR on sEVs in synovial fluid did not differ significantly between the two cohorts (CD63: p=0.372; CD66b: p=0.634; HLA-DR: p=0.558). Conclusions. Overall, the significance of sEVs in the diagnostics of PJI is not well enough understood and the subject of current research and scientific discussion. Our data suggest, that CD82 and CD9 on sEVs in synovial fluid are promising biomarkers to differentiate between PJI and aseptic complications

Aim. Periprosthetic joint infection (PJI) is one of the main reasons for revision surgery after primary unicompartmental knee arthroplasty (UKA), total knee arthroplasty (TKA) or total hip arthroplasty (THA). Currently the MSIS and EBJIS criteria sets are considered to be the gold standards in determining PJI. These criteria sets are complex and contain tests that are time-consuming and many are rather costly. Therefore, further research is indicated to find a simpler but equally reliable diagnostic test. In this study we evaluated the additional value of calprotectine measurement in synovial fluid in patients undergoing hip and knee (revision) arthroplasty following routine work-up. Method. In a retrospective cohort study, we analyzed 182 synovial fluid samples from 143 patients with suspected PJI after UKA, TKA, THA or revision arthroplasty. Twenty-six of those cases were classified as PJI according to the MSIS and EBJIS criteria. Subsequently, synovial calprotectin was determined, using a lateral flow assay and two cut-off thresholds of ≥14 mg/L and ≥50 mg/L. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of synovial calprotectin was determined. Results. When applying the MSIS and EBJIS criteria and a calprotectin level ≥14 mg/L, synovial calprotectin revealed an area under the curve of 0.96 (95% CI 0.90-1.00), with 92.3% sensitivity and 100% specificity. The PPV and NPV were 100% and 92.9% respectively. When applying the MSIS and EBJIS criteria and a calprotectin level ≥ 50 mg/L, synovial calprotectin revealed an area under the curve of 0.94 (95% CI 0.87-1.00), with 88.5% sensitivity and 100% specificity. The PPV and NPV were 100% and 89.7% respectively. Conclusions. The value of calprotectin in synovial fluid gives valuable information with a single test result, resulting in high predictive value in the diagnosis of PJI after hip or knee arthroplasty and should seriously be considered as part of PJI diagnostics in an outpatient clinical setting. The high specificity can help rule in patients that are suspected of PJI. Therefor this test can be helpful in a preop diagnostic work-up to avoid unnecessary revisions in patients with well-placed and well-fixed arthroplasties with a suspected PJI. These conclusions are independent of which criteria set was used as a gold standard

Aim. Periprosthetic joint infection (PJI) is a devastating complication of total joint arthroplasty. While research has focused on developing better tests for disease diagnosis, treatment options have stayed relatively constant over the years with high failure rates ranging from 30%–50% and are due in part to the protective biofilm produced by some bacterial species. Current treatment options are compromised by the presence of biofilm, emphasizing the need for novel treatment strategies to be developed. Our group has developed a novel treatment (PhotothermAA) which has demonstrated in vitro its ability to target bacterial biofilm. The purpose of this study was to test this PhotothermAA technology in vivo in a rabbit model of PJI for its efficacy in eradicating biofilm. Method. Rabbits were fitted with a titanium implant into the tibial plateau and inoculated with 5×10. 6. CFU Xen36 (luminescent Staphylococcus aureus). At two weeks, rabbits underwent irrigation and debridement and treatment with PhotothermAA gel for two hours and subsequently laser heated using an 808 nm laser for 10 minutes. Gel was washed out and implant was removed for quantitative biofilm coverage analysis via scanning electron microscopy (SEM, n=3 for control and n=2 for PhotothermAA treated). Periprosthetic tissue was collected before and after treatment for toxicity studies via hemotoxylin and eosin (H&E) staining and scored for necrosis by three blinded reviewers (n=5 per group). Student's t-test was used for statistical analysis. Results. Implants isolated after PhotothermAA gel treatment had less biofilm coverage on the surface of the implant compared to non-treated control via SEM analysis (36.9% vs. 55.2%, p<0.14). PhotothermAA gel treatment and subsequent laser treatment was not harmful to surrounding tissue as no increase in necrotic tissue was observed. Conclusions. PhotothermAA gel and laser treatment safely decreases biofilm coverage on infected knee implants in a rabbit PJI model

Aim. The aim of this study was to investigate the metabolomic profile of synovial fluid in periprosthetic joint infection (PJI) cases regarding a possible diagnostic approach. Also, further information about the metabolic composition of synovial fluid in PJI may point to future diagnostic and therapeutic approaches. Method. Patients with a clinical suspicion of a prosthesis infection who underwent a joint puncture in our outpatient department or ward were included. After sample preparation, the nuclear magnetic resonance (NMR) experiments were performed at 310 K on an AVANCE™ NeoBruker Ultrashield 600 MHz spectrometer. Bruker Topspin version 4.0.2 was used for NMR data acquisition. The spectra for all samples were automatically processed (exponential line broadening of 0.3 Hz), phased, and referenced using TSP at 0.0 ppm. In total, 37 metabolites were analysed using a volume of 200 µl per synovial sample. The PJI and aseptic cases were assigned according to the EBJIS criteria. Results. In total, 76 samples were included in the final analysis with 48 PJI cases and 28 aseptic cases. Five measured metabolites have shown an area under the curve (AUC) over 0.8, with Taurine (AUC 0.8558, p<0.0001) and Glutamine (AUC 0.8333, p<0.0001) showing the best diagnostic performance. When combining two metabolites, the AUC indicated even higher diagnostic performance: Glucose/Glycogen (AUC 0.9073, p<0.0001), Taurine/Mannose (AUC 0.9073, p<0.0001), Mannose/Glycogen (AUC 0.8992, p<0.0001) and Taurine/Glucose (AUC 0.8956, p<0.0001). Conclusions. While NMR as a method in PJI diagnostics is currently not broadly available for daily clinical work, our results indicate that certain synovial metabolites and their combinations can be used for PJI diagnosis