Disruption of the Gut Microbiome Increases the Risk of Periprosthetic Joint Infection in Mice

A translational murine model of aseptic loosening with osseointegration failure

An in vivo animal model of a weight-bearing intra-articular implant is crucial to the study of implant osseointegration and aseptic loosening caused by osseointegration failure. Osseointegration, defined as a direct structural and functional attachment between living bone tissue and the surface of a load-carrying implant, is essential for implant stability and considered a prerequisite for the long-term clinical success of implants in total joint arthroplasty. Compared to large animal models, murine models offer extensive genetic tools for tracing cell differentiation and proliferation. The 18- to 22-week-old C57BL/6J background mice underwent either press-fitted or loose implantation of a titanium implant, achieving osseointegration or fibrous integration. A protocol was developed for both versions of the procedure, including a description of the relevant anatomy. Samples were subjected to microcomputed tomography and underwent biomechanical testing to access osseointegration. Lastly, samples were fixed and embedded for histological evaluation. The absence of mineralized tissue and weakened maximum pull-out force in loose implantation samples indicated that these implants were less mechanically stable compared to the control at 4 weeks postoperation. Histological analysis demonstrated extensive fibrotic tissue in the peri-implant area of loose implantation samples and excellent implant osseointegration in press-fitted samples at 4 weeks. Both mechanically stable and unstable hemiarthroplasty models with either osseous ingrowth or a robust periprosthetic fibrosis were achieved in mice. We hope that this model can help address current limitations for in vivo study of aseptic loosening and lead to necessary translational benefits.

Duration of cefazolin prophylaxis did not impact infection risk in a murine model of joint arthroplasty

To minimize periprosthetic joint infection (PJI) risk, some clinicians prescribe extended antibiotic prophylaxis (EAP) following total joint arthroplasty (TJA). Given the limited evidence supporting EAP, we sought to evaluate impact of prophylactic antibiotic duration on PJI risk in a murine TJA model. A titanium prosthesis was implanted into the proximal tibia of 89 mice and inoculated with 102 colony forming units (cfu) of Staphylococcus aureus Xen36. Control mice (n = 20) did not receive antibiotics. Treated mice received either 24 h (n = 35) or 4 days (n = 34) of cefazolin prophylaxis. Cultures were obtained from the prostheses, tibia, femur, and knee tissues 3 weeks after surgery. All mice in the control group developed PJI. Both prophylaxis regimens reduced the rate of PJI relative to the control, with only 2/35 mice in the 24-h cohort (p < 0.0001) and 1/34 in 4-day cohort developing PJI (p < 0.0001). CFU counts from the prostheses, bone and knee tissues were reduced for the 24-h and 4-day prophylaxis cohorts relative to the control (p < 0.0001 for both). There was no difference in rates of PJI or CFU counts between the two prophylaxis cohorts (p = 0.58). Prophylactic cefazolin profoundly reduced rates of PJI in a murine model of TJA in which all control animals developed PJI. Extending cefazolin prophylaxis duration from 24 h to 4 days did not result in improved PJI rates or decreased bacterial loads in infected cases. While these results strongly support use of antibiotic prophylaxis for TJA, EAP did not appear to add benefit in the described mouse model.

Clostridium difficile Infection Prior to Total Hip Arthroplasty Independently Increases the Risk of Periprosthetic Joint Infection

BACKGROUND

Periprosthetic joint infection (PJI) following total hip arthroplasty (THA) is associated with major morbidity. There may be a link between the gut microbiome and an individual's overall immune system. A Clostridium difficile (C. difficile) infection portends poor gut microbiome health and has been previously associated with increased 90-day complication rates in total joint arthroplasty (TJA). The purpose of this study was to determine the effect of a previous history of C. difficile infection within 2 years of undergoing THA on PJI within 2 years postoperatively.

METHODS

Patients undergoing THA from 2010 to 2021 were identified in a patient claims database (n = 770,075). Patients who had active records 2 years before and after THA as well as a history of C. difficile infection within 2 years prior to THA (n = 1,836) were included and propensity matched to a control group using age, sex, and Elixhauser comorbidity index. The primary outcome was the 2-year incidence of postoperative PJI. The exposed C. difficile infection cohort was stratified into 4 groups based on the time proximity of the C. difficile infection. Chi-square tests and logistic regressions were used to compare the groups.

RESULTS

A C. difficile infection anytime within 2 years prior to total hip arthroplasty was independently associated with higher odds of PJI (OR [odds ratio]: 1.49 [95% CI (confidence interval) 1.09 to 2.02, P = .014]). Proximity of C. difficile infection to arthroplasty was associated with increased risk of PJI (infection 0 to 3 months before THA: OR 2.01 [95% CI 1.23 to 3.20], infection 3 to 6 months before THA: OR 1.84 [95% CI 1.06 to 3.04], infection 6 to 12 months before THA: OR 1.10 [95% CI 0.65 to 1.77], infection 1 to 2 years before THA: OR 1.40 [95% CI 0.94 to 2.06]).

CONCLUSIONS

A C. difficile infection prior to THA is an independent risk factor for PJI. Proximity of C. difficile infection is associated with increased risk of PJI. Future investigations should evaluate how to adequately optimize patients prior to THA and pursue strategies to determine appropriate timing for proceeding with THA.

Wireless Optogenetic Targeting Nociceptors Helps Host Cells Win the Competitive Colonization in Implant-Associated Infections

The role of nociceptive nerves in modulating immune responses to harmful stimuli via pain or itch induction remains controversial. Compared to conventional surgery, various implant surgeries are more prone to infections even with low bacterial loads. In this study, an optogenetic technique is introduced for selectively activating peripheral nociceptive nerves using a fully implantable, wirelessly rechargeable optogenetic device. By targeting nociceptors in the limbs of awake, freely moving mice, it is found that activation induces anticipatory immunity in the innervated territory and enhances the adhesion of various host cells to the implant surface. This effect mediates acute immune cell-mediated killing of Staphylococcus aureus on implants and enables the host to win "implant surface competition" against Staphylococcus aureus. This finding provides new strategies for preventing and treating implant-associated infections.

Effects of antiseptic irrigation solutions on osseointegration in a cementless tibial implantation mouse model

Despite the success of standard antiseptic irrigation solutions in reducing periprosthetic joint infection (PJI) rates, there is still a need for more effective solutions. Synergistic use of povidone-iodine (PI) and hydrogen peroxide (H2O2) has shown promising results; however, the optimal solution concentration balancing bactericidal activity and osseointegration remains unknown. This study aims to evaluate the impact of these antiseptic irrigation solutions on osseointegration and the bone-implant interface strength in vivo. Forty C57BL/6 mice underwent bilateral tibial implantation surgery and were randomly allocated into three groups receiving 0.3% PI, 10% PI mixed with 3% H2O2, or saline as irrigation solutions intraoperatively. Assessments were performed on postoperative Days 1 and 28, including plain radiographs, microcomputed tomography (microCT) evaluation, histological analysis, immunohistochemistry, and biomechanical pull-out testing. No wound complications were observed. MicroCT scans revealed no differences in peri-implant trabecular bone parameters. Biomechanical pull-out testing showed no differences in the bone-implant interface strength across groups. Histological analysis indicated no differences in bone and bone marrow percentage areas among treatment groups. Immunohistochemical analysis demonstrated no differences among groups in peri-implant osteocalcin, osterix, or endomucin-positive cells. In conclusion, using either antiseptic irrigation solution showed no differences in osseointegration parameters compared to the control group, demonstrating safety and the absence of toxicity. CLINICAL RELEVANCE: Dilute 0.3% povidone-iodine and a 1:1 combination of 10% povidone-iodine mixed with 3% hydrogen peroxide can be safely used during primary and revision total joint arthroplasty without compromising osseointegration or causing wound complications.

The influence of gut microbiome on periprosthetic joint infections: State-of-the art

Early periprosthetic joint infection constitutes one of the most frightening complications of joint replacement. Recently, some evidence has highlighted the potential link between dysregulation of the gut microbiota and degenerative diseases of joints. It has been hypothesized that microbiome dysbiosis may increase the risk of periprosthetic joint infection by facilitating bacterial translocation from these sites to the bloodstream or by impairing local or systemic immune responses. Although the processes tying the gut microbiome to infection susceptibility are still unknown, new research suggests that the presurgical gut microbiota-a previously unconsidered component-may influence the patient's ability to resist infection. Exploring the potential impact of the microbiome on periprosthetic joint infections may therefore bring new insights into the pathogenesis and therapy of these disorders. For a successful therapy, a proper surgical procedure in conjunction with an antibacterial concept is essential. As per the surgical approach, different treatment strategies include surgical irrigation, debridement, antibiotic therapy, and implant retention with or without polyethylene exchange. Other alternatives could be one-stage or two-stage revisions surgery. Interventions that either directly target gut microbes as well as interventions that modify the composition and/or function of the commensal microbes represent an innovative and potentially successful field to be explored. In recent times, innovative therapeutic methods have arisen in the realm of microbiome restoration and the management of gut-related ailments. These progressive approaches offer fresh perspectives on tackling intricate microbial imbalances in the gastrointestinal tract. These emerging therapies signify a shift towards more precise and individualized approaches to microbiome restoration and the management of gut-related disorders. Once a more advanced knowledge of the pathways linking the gut microbiota to musculoskeletal tissues is gained, relevant microbiome-based therapies can be developed. If dysbiosis is proven to be a significant contributor, developing treatments for dysbiosis may represent a new frontier in the prevention of periprosthetic joint infections.

The Microbial Revolution in the World of Joint Replacement Surgery

Background

The prevalence of revision surgery due to aseptic loosening and periprosthetic joint infection (PJI) following total hip and knee arthroplasty is growing. Strategies to prevent the need for revision surgery and its associated health-care costs and patient morbidity are needed. Therapies that modulate the gut microbiota to influence bone health and systemic inflammation are a novel area of research.

Methods

A literature review of preclinical and clinical peer-reviewed articles relating to the role of the gut microbiota in bone health and PJI was performed.

Results

There is evidence that the gut microbiota plays a role in maintaining bone mineral density, which can contribute to osseointegration, osteolysis, aseptic loosening, and periprosthetic fractures. Similarly, the gut microbiota influences gut permeability and the potential for bacterial translocation to the bloodstream, increasing susceptibility to PJI.

Conclusions

Emerging evidence supports the role of the gut microbiota in the development of complications such as aseptic loosening and PJI after total hip or knee arthroplasty. There is a potential for microbial therapies such as probiotics or fecal microbial transplantation to moderate the risk of developing these complications. However, further investigation is required.

Clinical Relevance

Modulation of the gut microbiota may influence patient outcomes following total joint arthroplasty.

Bacteria Invade the Brain Following Sterile Intracortical Microelectrode Implantation

Brain-machine interface performance is largely affected by the neuroinflammatory responses resulting in large part from blood-brain barrier (BBB) damage following intracortical microelectrode implantation. Recent findings strongly suggest that certain gut bacterial constituents penetrate the BBB and are resident in various brain regions of rodents and humans, both in health and disease. Therefore, we hypothesized that damage to the BBB caused by microelectrode implantation could amplify dysregulation of the microbiome-gut-brain axis. Here, we report that bacteria, including those commonly found in the gut, enter the brain following intracortical microelectrode implantation in mice implanted with single-shank silicon microelectrodes. Systemic antibiotic treatment of mice implanted with microelectrodes to suppress bacteria resulted in differential expression of bacteria in the brain tissue and a reduced acute inflammatory response compared to untreated controls, correlating with temporary improvements in microelectrode recording performance. Long-term antibiotic treatment resulted in worsening microelectrode recording performance and dysregulation of neurodegenerative pathways. Fecal microbiome composition was similar between implanted mice and an implanted human, suggesting translational findings. However, a significant portion of invading bacteria was not resident in the brain or gut. Together, the current study established a paradigm-shifting mechanism that may contribute to chronic intracortical microelectrode recording performance and affect overall brain health following intracortical microelectrode implantation.

The Role of the Gut Microbiome in Orthopedic Surgery-a Narrative Review

PURPOSE OF REVIEW

The importance of the gut microbiome has received increasing attention in recent years. New literature has revealed significant associations between gut health and various orthopedic disorders, as well as the potential for interventions targeting the gut microbiome to prevent disease and improve musculoskeletal outcomes. We provide a broad overview of available literature discussing the links between the gut microbiome and pathogenesis and management of orthopedic disorders.

RECENT FINDINGS

Human and animal models have characterized the associations between gut microbiome dysregulation and diseases of the joints, spine, nerves, and muscle, as well as the physiology of bone formation and fracture healing. Interventions such as probiotic supplementation and fecal transplant have shown some promise in ameliorating the symptoms or slowing the progression of these disorders. We aim to aid discussions regarding optimization of patient outcomes in the field of orthopedic surgery by providing a narrative review of the available evidence-based literature involving gut microbiome dysregulation and its effects on orthopedic disease. In general, we believe that the gut microbiome is a viable target for interventions that can augment current management models and lead to significantly improved outcomes for patients under the care of orthopedic surgeons.

The Human Microbiome and Its Role in Musculoskeletal Disorders

Musculoskeletal diseases (MSDs) are characterized as injuries and illnesses that affect the musculoskeletal system. MSDs affect every population worldwide and are associated with substantial global burden. Variations in the makeup of the gut microbiota may be related to chronic MSDs. There is growing interest in exploring potential connections between chronic MSDs and variations in the composition of gut microbiota. The human microbiota is a complex community consisting of viruses, archaea, bacteria, and eukaryotes, both inside and outside of the human body. These microorganisms play crucial roles in influencing human physiology, impacting metabolic and immunological systems in health and disease. Different body areas host specific types of microorganisms, with facultative anaerobes dominating the gastrointestinal tract (able to thrive with or without oxygen), while strict aerobes prevail in the nasal cavity, respiratory tract, and skin surfaces (requiring oxygen for development). Together with the immune system, these bacteria have coevolved throughout time, forming complex biological relationships. Changes in the microbial ecology of the gut may have a big impact on health and can help illnesses develop. These changes are frequently impacted by lifestyle choices and underlying medical disorders. The potential for safety, expenses, and efficacy of microbiota-based medicines, even with occasional delivery, has attracted interest. They are, therefore, a desirable candidate for treating MSDs that are chronic and that may have variable progression patterns. As such, the following is a narrative review to address the role of the human microbiome as it relates to MSDs.

The Potential Role of Gut Bacteriome Dysbiosis as a Leading Cause of Periprosthetic Infection: A Comprehensive Literature Review

(1) Background: Periprosthetic joint infections (PJIs) represent a small yet important risk when undertaking a joint arthroplasty; they occur in approximately 1-2% of treatments. These infections create a medical and financial burden for patients and healthcare systems. Despite the introduction of recognized best clinical practices during arthroplasty operations, it is not yet possible to further reduce the risk of infection after surgery. The purpose of this review is to raise awareness of the potential role of gut dysbiosis in the development of PJIs and to highlight the potential of the gut bacteriome as a possible target for preventing them. (2) Methods: We compiled all the available data from five databases, examining the effects of gut dysbiosis in human and murine studies, following PRISMA guidelines, for a total of five reviewed studies. (3) Results: One human and one murine study found the Trojan horse theory applicable. Additionally, inflammatory bowel diseases, gut permeability, and oral antibiotic ingestion all appeared to play a role in promoting gut dysbiosis to cause PJIs, according to the other three studies. (4) Conclusions: Gut dysbiosis is linked to an increased risk of PJI.

Gut permeability may be associated with periprosthetic joint infection after total hip and knee arthroplasty

A growing number of recent investigations on the human genome, gut microbiome, and proteomics suggests that the loss of mucosal barrier function, particularly in the gastrointestinal tract, may substantially affect antigen trafficking, ultimately influencing the close bidirectional interaction between the gut microbiome and the immune system. This cross-talk is highly influential in shaping the host immune system function and ultimately affecting the outcome of interventions. We hypothesized that the loss of mucosal barrier in the gut may be associatedto acute and chronic periprosthetic joint infections (PJI). Zonulin, soluble CD14 (sCD14), and lipopolysaccharide (LPS) were tested in plasma as part of a prospective cohort study of patients undergoing primary arthroplasty or revision arthroplasty because of an aseptic failure or PJI (as defined by the 2018 criteria). All blood samples were collected before antibiotic administration. Samples were tested using commercially available enzyme-linked immunosorbent assays as markers for gut permeability. A total of 134 patients were included in the study of which 44 patients had PJI (30 chronic and 14 acute), and the remaining 90 patients were categorized as non-infected that included 64 patients revised for aseptic failure, and 26 patients undergoing primary total joint arthroplasty. Both Zonulin (7.642 ± 6.077 ng/mL vs 4.560 ± 3.833 ng/mL; p < 0.001) and sCD14 levels (555.721 ± 216.659 ng/mL vs 396.872 ± 247.920 ng/mL; p = 0.003) were significantly elevated in the PJI group compared to non-infected cases. Higher levels of Zonulin were found in acute infections compared to chronic PJI (11.595 ± 6.722 ng/mL vs. 5.798 ± 4.841 ng/mL; p = 0.005). This prospective study reveals a possible link between gut permeability and the ‘gut-immune-joint axis’ in PJI. If this association continues to be borne out with a larger cohort and more in-depth analysis, it will have a clinically significant implication in managing patients with PJI. It may be that in addition to the administration of antimicrobials, patients with PJI and other orthopaedic infections may benefit from administration of gastrointestinal modulators such as pro and prebiotics.

Periprosthetic Joint Infection and the Trojan Horse Theory: Examining the Role of Gut Dysbiosis and Epithelial Integrity

BACKGROUND

Periprosthetic joint infection (PJI) is an uncommon yet dreadful complication after total joint arthroplasty. Emerging evidence suggested a role for the gut microbiome in the pathogenesis of such infections as a reservoir of opportunistic pathogens.

METHODS

A secondary analysis of an ongoing trial looking at gut dysbiosis and PJI was performed on patients that had next-generation sequencing done as part of their workup. Gut permeability and dysbiosis were measured using known biomarkers such as Zonulin. Statistical analysis consisted of descriptive statistics and logistic regression modeling.

RESULTS

Among the cohort of 46 (47.8% female) patients, with a mean age of 68.47 years (range, 40 to 91) and a mean BMI 31.15 ± 6.49 kg/m², 38 patients underwent a revision for PJI (29 chronic and 9 acute infections), and 8 patients were classified as aseptic failures. Then, a review of each of the bacteria retrieved was performed. Those known to be gut commensal based on available literature were noted. When regression modeling was performed, Zonulin levels were found to be associated with an increased probability of a similar finding (Estimate: 0.377, OR: 1.458; P = .001).

CONCLUSION

In our study, we report the first clinical evidence of the translocation of bacteria from the gut to the joint in patients with PJI. In particular, when evaluating the microbiological profile of the NGS signal, a great number of known gut commensals were seen in patients with a highly permeable dysbiotic gut. Manipulation of the gut microbiome may become part of an essential and comprehensive approach for management of patients with PJI.

Dysbiotic relationship between arthritis and the oral-gut microbiome. A critical review

Arthritis and prosthetic joint infections (PJIs) overall are associated with reduced quality of life and limited work capacity. Multiple, overlapping factors contribute to these conditions. Some investigations have suggested a dysbiotic association between the oral-gut microbiome and pathogenesis of arthritis and PJIs. A better understanding of the role of the oral-gut microbiota in arthritis and PJI pathophysiology can shed light into how its disequilibrium can discharge a pro-inflammatory response, and impact the health of patients susceptible to arthritis or with established joint disease. A review of published in vivo and clinical data suggested that alterations in oral and gut microbiota can lead to a disturbance of immunoregulatory properties, and may be associated with joint infections and arthritis. This review brings new insights into the current status of the evidence on the potential molecules and inflammatory biomarkers disrupted by an oral-gut microbial dysbiosis. Normal commensals and pathogenic oral and gut microflora homeostasis are important not only to prevent infections per se but also its potential progression. Further experiments, especially controlled clinical trials, are needed to ascertain how microbiome manipulation and other microbiota-directed approaches can help control inflammation and effectively prevent and treat arthritic diseases. Additionally, studies on the effects of the long-term oral diseases, such as chronic periodontitis, on arthritis and PJIs need to be conducted.

Staphylococcus aureus and Acinetobacter baumannii Inhibit Osseointegration of Orthopedic Implants

Bacterial infections routinely cause inflammation and thereby impair osseointegration of orthopedic implants. Acinetobacter spp., which cause osteomyelitis following trauma, on or off the battlefield, were, however, reported to cause neither osteomyelitis nor osteolysis in rodents. We therefore compared the effects of Acinetobacter strain M2 to those of Staphylococcus aureus in a murine implant infection model. Sterile implants and implants with adherent bacteria were inserted in the femur of mice. Bacterial burden, levels of proinflammatory cytokines, and osseointegration were measured. All infections were localized to the implant site. Infection with either S. aureus or Acinetobacter strain M2 increased the levels of proinflammatory cytokines and the chemokine CCL2 in the surrounding femurs, inhibited bone formation around the implant, and caused loss of the surrounding cortical bone, leading to decreases in both histomorphometric and biomechanical measures of osseointegration. Genetic deletion of TLR2 and TLR4 from the mice partially reduced the effects of Acinetobacter strain M2 on osseointegration but did not alter the effects of S. aureus. This is the first report that Acinetobacter spp. impair osseointegration of orthopedic implants in mice, and the murine model developed for this study will be useful for future efforts to clarify the mechanism of implant failure due to Acinetobacter spp. and to assess novel diagnostic tools or therapeutic agents.

The soil microbiome increases plant survival and modifies interactions with root endosymbionts in the field

Evidence is accumulating that the soil microbiome-the community of microorganisms living in soils-has a major effect on plant traits and fitness. However, most work to date has taken place under controlled laboratory conditions and has not experimentally disentangled the effect of the soil microbiome on plant performance from the effects of key endosymbiotic constituents. As a result, it is difficult to extrapolate from existing data to understand the role of the soil microbiome in natural plant populations. To address this gap, we performed a field experiment using the black medick Medicago lupulina to test how the soil microbiome influences plant performance and colonization by two root endosymbionts (the mutualistic nitrogen-fixing bacteria Ensifer spp. and the parasitic root-knot nematode Meloidogyne hapla) under natural conditions. We inoculated all plants with nitrogen-fixing bacteria and factorially manipulated the soil microbiome and nematode infection. We found that plants grown in microbe-depleted soil exhibit greater mortality, but that among the survivors, there was no effect of the soil microbiome on plant performance (shoot biomass, root biomass, or shoot-to-root ratio). The soil microbiome also impacted parasitic nematode infection and affected colonization by mutualistic nitrogen-fixing bacteria in a plant genotype-dependent manner, increasing colonization in some plant genotypes and decreasing it in others. Our results demonstrate the soil microbiome has complex effects on plant-endosymbiont interactions and may be critical for survival under natural conditions.

Recent Advances in the Evaluation of Antimicrobial Materials for Resolution of Orthopedic Implant-Associated Infections In Vivo

While orthopedic implant-associated infections are rare, revision surgeries resulting from infections incur considerable healthcare costs and represent a substantial research area clinically, in academia, and in industry. In recent years, there have been numerous advances in the development of antimicrobial strategies for the prevention and treatment of orthopedic implant-associated infections which offer promise to improve the limitations of existing delivery systems through local and controlled release of antimicrobial agents. Prior to translation to in vivo orthopedic implant-associated infection models, the properties (e.g., degradation, antimicrobial activity, biocompatibility) of the antimicrobial materials can be evaluated in subcutaneous implant in vivo models. The antimicrobial materials are then incorporated into in vivo implant models to evaluate the efficacy of using the material to prevent or treat implant-associated infections. Recent technological advances such as 3D-printing, bacterial genomic sequencing, and real-time in vivo imaging of infection and inflammation have contributed to the development of preclinical implant-associated infection models that more effectively recapitulate the clinical presentation of infections and improve the evaluation of antimicrobial materials. This Review highlights the advantages and limitations of antimicrobial materials used in conjunction with orthopedic implants for the prevention and treatment of orthopedic implant-associated infections and discusses how these materials are evaluated in preclinical in vivo models. This analysis serves as a resource for biomaterial researchers in the selection of an appropriate orthopedic implant-associated infection preclinical model to evaluate novel antimicrobial materials.

Interactions between the foreign body reaction and Staphylococcus aureus biomaterial-associated infection. Winning strategies in the derby on biomaterial implant surfaces

Biomaterial-associated infections (BAIs) are an increasing problem where antibiotic therapies are often ineffective. The design of novel strategies to prevent or combat infection requires a better understanding of how an implanted foreign body prevents the immune system from eradicating surface-colonizing pathogens. The objective of this review is to chart factors resulting in sub-optimal clearance of Staphylococcus aureus bacteria involved in BAIs. To this end, we first describe three categories of bacterial mechanisms to counter the host immune system around foreign bodies: direct interaction with host cells, modulation of intercellular communication, and evasion of the immune system. These mechanisms take place in a time frame that differentiates sterile foreign body reactions, BAIs, and soft tissue infections. In addition, we identify experimental interventions in S. aureus BAI that may impact infectious mechanisms. Most experimental treatments modulate the host response to infection or alter the course of BAI through implant surface modulation. In conclusion, the first week after implantation and infection is crucial for the establishment of an S. aureus biofilm that resists the local immune reaction and antibiotic treatment. Although established and chronic S. aureus BAI is still treatable and manageable, the focus of interventions should lie on this first period.

Musculoskeletal Microbiology: The Microbiome in Orthopaedic Biomechanics

Orthopaedic biomechanics and bioengineering is a founding discipline of biomedical engineering that focuses on the effects of mechanical stress and strain on musculoskeletal tissues during growth, function and repair. In the past decade the gut microbiome has emerged as a contributor to disease processes throughout the body, but only recently has been shown to influence orthopaedic biomechanics. Here I review emergent findings showing that the gut microbiome can regulate important aspects of the musculoskeletal system including growth and development; tissue failure and disease; and orthopaedic surgery. These early findings suggest that the microbiome may help answer questions in orthopaedic biomechanics that are not well addressed by current interventions, and highlights the promise of the emerging field of "Musculoskeletal Microbiology".

Is Preoperative Staphylococcus aureus Screening and Decolonization Effective at Reducing Surgical Site Infection in Patients Undergoing Orthopedic Surgery? A Systematic Review and Meta-Analysis With a Special Focus on Elective Total Joint Arthroplasty

BACKGROUND

Staphylococcus aureus is a major pathogen implicated in orthopedic infections worldwide. Preoperative decolonization has been promoted but different strategies present mixed results. Thus, the goals of this study are to determine (1) whether S aureus screening and/or decolonization is effective at reducing surgical site infection in orthopedic surgery, (2) with a special focus on elective total joint arthroplasty (TJA), and (3) which preoperative S aureus screening/treatment strategy is most cost-effective for TJA.

METHODS

PubMed, Ovid MEDLINE, and Cochrane databases were searched on January 1, 2020, using a systematic strategy. We included papers with data comparing surgical site infection and periprosthetic joint infection rate in orthopedic surgery and/or elective total hip and knee arthroplasty patients before/after S aureus screening and/or decolonization protocol and papers evaluating the cost-effectiveness of different S aureus screening/treatment strategies.

RESULTS

A total of 1260 papers were screened, and 32 papers were ultimately included. Results showed an increased risk of developing any infection (relative risk [RR] = 1.71 ± 0.16) and S aureus infection (RR = 2.79 ± 0.45) after orthopedic surgery without previous nares and whole-body decolonization. Focusing exclusively on elective TJA, there was an increased risk of developing any infection (RR = 1.70 ± 0.17) and S aureus infection (RR = 2.18 ± 0.41) if no decolonization is performed. All strategies appeared to be cost-effective, although universal decolonization without screening seemed to be the most advantageous.

CONCLUSION

Preoperative S aureus screening/decolonization protocol lowered the risk of infection after elective orthopedic and TJA surgeries. However, further studies are needed to determine optimal clinical and cost-effective methodologies.

Musculoskeletal microbiology: The utility of the microbiome in orthopedics

The past 15 years have witnessed a renaissance in the study of the microbes that colonize the human body. The vast majority of the human microbiome resides within the gut. Alterations to the gut microbiome have been associated with the pathogenesis and progression of wide-ranging diseases throughout the body-including atherosclerosis, depression, and obesity. Our understanding of the effects of the gut microbiome on the musculoskeletal system remains in its infancy, but preclinical work has demonstrated an effect of the gut microbiome on the success of orthopedic surgical procedures, osteoporosis, osteoarthritis, and muscle mass. In this perspective I review preclinical findings demonstrating that an impaired presurgical gut microbiome can increase the likelihood of developing periprosthetic joint infection and how alterations in the gut microbiome can reduce bone strength by impairing bone tissue material properties. In addition to discussing these examples, I review the hypothesis that many chronic non-communicable diseases have become more prevalent in modern industrialized societies as a result of changes in the composition of the gut microbiome resulting from changes in environment/lifestyle (diet, sanitation, antibiotic use). The most burdensome musculoskeletal disorders are chronic and non-communicable and may therefore be related to generational shifts in the composition of the gut microbiome, a possibility I illustrate by reviewing changes in the prevalence of osteoarthritis over the last century. Microbiome-based therapeutics are potentially innocuous, inexpensive, and have the potential to be effective with only occasional use, making them attractive for addressing the needs of chronic and/or slowly progressing musculoskeletal disorders.

Association of Antibiotic Alterations in Gut Microbiota With Decreased Osseointegration of an Intramedullary Nail in Mice With and Without Osteomyelitis

Treatment of osteomyelitis requires prolonged antibiotic therapy which significantly alters the gut microbiota. While the influences on bone mass and microstructure have been extensively studied, it is poorly understood what impact the changes in gut microbiota may have on the host response to osseointegration around an intramedullary nail implanted. Here, we explored the influence of gut microbiota on the bone osseointegration process around an implant under two conditions: implantation of an intramedullary nail in the bone marrow cavity and chronic osteomyelitis (CO) induced by Staphylococcus aureus infection. Body weight, hepatorenal functions, serum levels of proinflammatory cytokines were monitored. The composition of gut microbiota was assessed via 16S rRNA sequencing, and the bone condition was analyzed via micro-computed tomography, hematoxylin and eosin staining, Safranin O-fast green and Goldner's trichrome staining. Osteoblastogenesis and osteoclastogenesis were assessed by detecting tartrate-resistant acid phosphatase and osterix expression. We found that perturbation of gut microbiota (increase in Proteobacteria and decrease in Bacteroidetes) associated with delayed osseointegration and increased levels of proinflammatory cytokines in the serum (p<0.05), lower bone mass (p<0.05), deficient endochondral ossification and bone formation, reduced osteoblastogenesis (p<0.05) and enhanced osteoclastogenesis (p<0.001). Survival rates (p=0.002) and bacterial loads (p=0.0363) in bone differed significantly between the CO and antibiotic-treated CO mice, but cytokines levels, bone mineral density, and bone formation did not differ, likely because of the severely damaged bone structure. In summary, antibiotic treatment perturbed the gut microbiota and significantly interfered with the bone osseointegration around the nail by increasing proinflammatory cytokine levels in circulation, inhibiting osteoblastogenesis, enhancing osteoclastogenesis, and thus leading to higher pathogen colonization as well as higher mortality postinfection. This report of ours is the first to demonstrate antibiotic-induced alterations in the gut microbiota affect bone osseointegration, helping us understand the role of gut microbiota disorders in osteoblastogenesis and osteoclastogenesis following implant insertion with or without infection.

Bone mineral as a drug-seeking moiety and a waste dump

Bone is a dynamic tissue with a quarter of the trabecular and a fifth of the cortical bone being replaced continuously each year in a complex process that continues throughout an individual's lifetime. Bone has an important role in homeostasis of minerals with non-stoichiometric hydroxyapatite bone mineral forming the inorganic phase of bone. Due to its crystal structure and chemistry, hydroxyapatite (HA) and related apatites have a remarkable ability to bind molecules. This review article describes the accretion of trace elements in bone mineral giving a historical perspective. Implanted HA particles of synthetic origin have proved to be an efficient recruiting moiety for systemically circulating drugs which can locally biomodulate the material and lead to a therapeutic effect. Bone mineral and apatite however also act as a waste dump for trace elements and drugs, which significantly affects the environment and human health. Cite this article: Bone Joint Res 2020;9(10):709-718.

Adaptive and innate immune cell responses in tendons and lymph nodes after tendon injury and repair

Tendon injuries are a common clinical condition with limited treatment options. The cellular components of the innate immune system, such as neutrophils and macrophages, have been studied in tendon injuries. However, the adaptive immune system, comprising specialized lymphocytes, plays an important role in orchestrating the healing of numerous tissues, but less is known about these cells in tendon healing. To gain a greater understanding of the biological processes that regulate tendon healing, we determined how the cellular components of the adaptive and innate immune system respond to a tendon injury using two-month-old male mice. We observed that lymphatic vasculature is present in the epitenon and superficial regions of Achilles tendons, and that the lymphatics drain into the popliteal lymph node. We then created an acute Achilles tenotomy followed by repair, and collected tendons and popliteal lymph nodes 1, 2, and 4 wk after injury. Tendon injury resulted in a robust adaptive immune cell response that followed an initial innate immune cell response in tendons and lymph nodes. Monocytes, neutrophils, and macrophages initially accumulated at 1 wk after injury in tendons, while dendritic cells and CD4⁺ T cells peaked at 2 wk after injury. B cells and CD8⁺ T cells progressively increased over time. In parallel, immune cells of the popliteal lymph node demonstrated a similarly coordinated response to the injury. These results suggest that there is an adaptive immune response to tendon injury, and adaptive immune cells may play a role in regulating tendon healing.NEW & NOTEWORTHY While the innate immune system, consisting of macrophages and related hematopoietic cells, has been studied in tendon injury, less is known about the adaptive immune system. Using a mouse model of Achilles tendon tenotomy and repair, we observed an adaptive immune cell response, consisting of CD4⁺ and CD8⁺ T cells, and B cells, which occur through 4 wk after tendon injury. This response appeared to be coordinated by the draining popliteal lymph node.