Equine or porcine synovial fluid as a novel ex vivo model for the study of bacterial free-floating biofilms that form in human joint infections

Bacterial invasion of synovial joints, as in infectious or septic arthritis, can be difficult to treat in both veterinary and human clinical practice. Biofilms, in the form of free-floating clumps or aggregates, are involved with the pathogenesis of infectious arthritis and periprosthetic joint infection (PJI). Infection of a joint containing an orthopedic implant can additionally complicate these infections due to the presence of adherent biofilms. Because of these biofilm phenotypes, bacteria within these infected joints show increased antimicrobial tolerance even at high antibiotic concentrations. To date, animal models of PJI or infectious arthritis have been limited to small animals such as rodents or rabbits. Small animal models, however, yield limited quantities of synovial fluid making them impractical for in vitro research. Herein, we describe the use of ex vivo equine and porcine models for the study of synovial fluid induced biofilm aggregate formation and antimicrobial tolerance. We observed Staphylococcus aureus and other bacterial pathogens adapt the same biofilm aggregate phenotype with significant antimicrobial tolerance in both equine and porcine synovial fluid, analogous to human synovial fluid. We also demonstrate that enzymatic dispersal of synovial fluid aggregates restores the activity of antimicrobials. Future studies investigating the interaction of bacterial cell surface proteins with host synovial fluid proteins can be readily carried out in equine or porcine ex vivo models to identify novel drug targets for treatment of prevention of these difficult to treat infectious diseases

Mast cells and hypoxia drive tissue metaplasia and heterotopic ossification in idiopathic arthrofibrosis after total knee arthroplasty

ABSTRACT: BACKGROUND: Idiopathic arthrofibrosis occurs in 3-4% of patients who undergo total knee arthroplasty (TKA). However, little is known about the cellular or molecular changes involved in the onset or progression of this condition. To classify the histomorphologic changes and evaluate potential contributing factors, periarticular tissues from the knees of patients with arthrofibrosis were analyzed for fibroblast and mast cell proliferation, heterotopic ossification, cellular apoptosis, hypoxia and oxidative stress. RESULTS: The arthrofibrotic tissue was composed of dense fibroblastic regions, with limited vascularity along the outer edges. Within the fibrotic regions, elevated numbers of chymase/fibroblast growth factor (FGF)-expressing mast cells were observed. In addition, this region contained fibrocartilage and associated heterotopic ossification, which quantitatively correlated with decreased range of motion (stiffness). Fibrotic, fibrocartilage and ossified regions contained few terminal dUTP nick end labeling (TUNEL)-positive or apoptotic cells, despite positive immunostaining for lactate dehydrogenase (LDH)5, a marker of hypoxia, and nitrotyrosine, a marker for protein nitrosylation. LDH5 and nitrotyrosine were found in the same tissue areas, indicating that hypoxic areas within the tissue were associated with increased production of reactive oxygen and nitrogen species. CONCLUSIONS: Taken together, we suggest that hypoxia-associated oxidative stress initiates mast cell proliferation and FGF secretion, spurring fibroblast proliferation and tissue fibrosis. Fibroblasts within this hypoxic environment undergo metaplastic transformation to fibrocartilage, followed by heterotopic ossification, resulting in increased joint stiffness. Thus, hypoxia and associated oxidative stress are potential therapeutic targets for fibrosis and metaplastic progression of idiopathic arthrofibrosis after TKA

Numerical processing in the human parietal cortex during experimental and natural conditions

Human cognition is traditionally studied in experimental conditions wherein confounding complexities of the natural environment are intentionally eliminated. Thus, it remains unknown how a brain region involved in a particular experimental condition is engaged in natural conditions. Here we use electrocorticography to address this uncertainty in three participants implanted with intracranial electrodes and identify activations of neuronal populations within the intraparietal sulcus region during an experimental arithmetic condition. In a subsequent analysis, we report that the same intraparietal sulcus neural populations are activated when participants, engaged in social conversations, refer to objects with numerical content. Our prototype approach provides a means for both exploring human brain dynamics as they unfold in complex social settings and reconstructing natural experiences from recorded brain signals

Reactive oxygen and nitrogen species induce protein and DNA modifications driving arthrofibrosis following total knee arthroplasty

BACKGROUND: Arthrofibrosis, occurring in 3%-4% of patients following total knee arthroplasty (TKA), is a challenging condition for which there is no defined cause. The hypothesis for this study was that disregulated production of reactive oxygen species (ROS) and nitrogen species (RNS) mediates matrix protein and DNA modifications, which result in excessive fibroblastic proliferation. RESULTS: We found increased numbers of macrophages and lymphocytes, along with elevated amounts of myeloperoxidase (MPO) in arthrofibrotic tissues when compared to control tissues. MPO expression, an enzyme that generates ROS/RNS, is usually limited to neutrophils and some macrophages, but was found by immunohistochemistry to be expressed in both macrophages and fibroblasts in arthrofibrotic tissue. As direct measurement of ROS/RNS is not feasible, products including DNA hydroxylation (8-OHdG), and protein nitrosylation (nitrotyrosine) were measured by immunohistochemistry. Quantification of the staining showed that 8-OHdg was significantly increased in arthrofibrotic tissue. There was also a direct correlation between the intensity of inflammation and ROS/RNS to the amount of heterotopic ossification (HO). In order to investigate the aberrant expression of MPO, a real-time oxidative stress polymerase chain reaction array was performed on fibroblasts isolated from arthrofibrotic and control tissues. The results of this array confirmed the upregulation of MPO expression in arthrofibrotic fibroblasts and highlighted the downregulated expression of the antioxidants, superoxide dismutase1 and microsomal glutathione S-transferase 3, as well as the significant increase in thioredoxin reductase, a known promoter of cell proliferation, and polynucleotide kinase 3\u27-phosphatase, a key enzyme in the base excision repair pathway for oxidative DNA damage. CONCLUSION: Based on our current findings, we suggest that ROS/RNS initiate and sustain the arthrofibrotic response driving aggressive fibroblast proliferation and subsequent HO

(iv) Managing bone loss of the femur and tibia in revision total knee arthroplasty

The number of primary and revision knee arthroplasty procedures performed yearly is steadily increasing. The management of bone loss at the time of revision surgery will play an integral role in the longevity and function of these knees into the future. There are a variety of options for addressing these defects varying from the use of polymethylmethacrylate bone cement, metal augments, sleeves, cones and large allograft replacements. This manuscript discusses the evaluation, classification and management of bone loss of the distal femur and proximal tibia

Revision Total Knee Arthroplasty: Infection should be Ruled Out in All Cases

We hypothesized that some aseptic revision total knee arthroplasty failures are indeed caused by occult infection. This prospective study recruited 65 patients undergoing revision total knee arthroplasty. The mean follow-up period was 19 months. Collected synovial fluid was analyzed by Ibis T5000 biosensor (Abbott Molecular Inc, Ill; a multiplex polymerase chain reaction technology). Cases were considered as infected or aseptic based on the surgeon\u27s judgment and Ibis findings. Based on Ibis biosensor, 17 aseptic cases were indeed infected that had been missed. Of these 17 cases, 2 developed infection after the index revision. A considerable number of so-called aseptic failures seem to be occult infections that were not adequately investigated and/or miscategorized as aseptic failure. We recommend that all patients undergoing revision arthroplasty be investigated for periprosthetic joint infection. Copyright © 2012 Elsevier Inc. All rights reserved

Risk factors for surgical site infection following total joint arthroplasty.

BACKGROUND: Currently, most hospitals in the United States are obliged to report infections that occur following total joint arthroplasty to the Centers for Disease Control and Prevention through the National Healthcare Safety Network surveillance. The objective of this study was to identify the risk factors of surgical site infections that were reported to the Centers for Disease Control and Prevention from a single institution. METHODS: For this study, 6111 primary and revision total joint arthroplasties performed from April 2010 to June 2012 were identified. Surgical site infection cases captured by infection surveillance staff on the basis of the Centers for Disease Control and Prevention definition were identified. Surgical site infection cases with index surgery performed at another institution were excluded. All cases were followed up for one year for development of surgical site infection. The model for predictors of surgical site infection was created by logistic regression and was validated by bootstrap resampling. RESULTS: Of all performed total joint arthroplasties, surgical site infection developed in eighty cases (1.31% [95% confidence interval, 1.02% to 1.59%]). The highest rate of surgical site infection was observed in revision total knee arthroplasty (4.57% [95% confidence interval, 2.31% to 6.83%]) followed by revision total hip arthroplasty (1.94% [95% confidence interval, 0.75% to 3.13%]). Among the variables examined, the predictive factors of surgical site infection were higher Charlson Comorbidity Index (odds ratio for a Charlson Comorbidity Index of ≥2, 2.29 [95% confidence interval, 1.32 to 3.94] and odds ratio for a Charlson Comorbidity Index of 1, 2.09 [95% confidence interval, 1.06 to 4.10]), male sex (odds ratio, 1.79 [95% confidence interval, 1.11 to 2.89]), and revision total knee arthroplasty (odds ratio, 3.13 [95% confidence interval, 1.17 to 8.34]), and a higher level of preoperative hemoglobin (odds ratio, 0.85 per point [95% confidence interval, 0.73 to 0.98 per point]) was protective against surgical site infection. The C-statistic of the model was 0.709 without correction and 0.678 after bootstrap correction, indicating that the model has fair predictive power. CONCLUSIONS: Low preoperative hemoglobin level is one of the risk factors for surgical site infection and preoperative correction of hemoglobin may reduce the likelihood of postoperative surgical site infection. LEVEL OF EVIDENCE: Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence