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This study aimed to investigate the clinical characteristics and outcomes associated with culture-negative limb osteomyelitis patients.

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Chronic osteomyelitis (COM) of the lower limb in adults can be surgically managed by either limb reconstruction or amputation. This scoping review aims to map the outcomes used in studies surgically managing COM in order to aid future development of a core outcome set.

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Biofilm-related infection is a major complication that occurs in orthopaedic surgery. Various treatments are available but efficacy to eradicate infections varies significantly. A systematic review was performed to evaluate therapeutic interventions combating biofilm-related infections on in vivo animal models.

Aims. With the ageing population, fragility fractures have become one of the most common conditions. The objective of this study was to investigate whether microbiological outcomes and fracture-healing in osteoporotic bone is worse than normal bone with fracture-related infection (FRI). Methods. A total of 120 six-month-old Sprague-Dawley (SD) rats were randomized to six groups: Sham, sham + infection (Sham-Inf), sham with infection + antibiotics (Sham-Inf-A), ovariectomized (OVX), OVX + infection (OVX-Inf), and OVX + infection + antibiotics (OVX-Inf-A). Open femoral diaphysis fractures with Kirschner wire fixation were performed. Staphylococcus aureus at 4 × 10. 4. colony-forming units (CFU)/ml was inoculated. Rats were euthanized at four and eight weeks post-surgery. Radiography, micro-CT, haematoxylin-eosin, mechanical testing, immunohistochemistry (IHC), gram staining, agar plating, crystal violet staining, and scanning electron microscopy were performed. Results. Agar plating analysis revealed a higher bacterial load in bone (p = 0.002), and gram staining showed higher cortical bone colonization (p = 0.039) in OVX-Inf compared to Sham-Inf. OVX-Inf showed significantly increased callus area (p = 0.013), but decreased high-density bone volume (p = 0.023) compared to Sham-Inf. IHC staining showed a significantly increased expression of TNF-α in OVX-Inf compared to OVX (p = 0.049). Significantly reduced bacterial load on bone (p = 0.001), enhanced ultimate load (p = 0.001), and energy to failure were observed in Sham-Inf-A compared to Sham-Inf (p = 0.028), but not in OVX-Inf-A compared to OVX-Inf. Conclusion. In osteoporotic bone with FRI, infection was more severe with more bone lysis and higher bacterial load, and fracture-healing was further delayed. Systemic antibiotics significantly reduced bacterial load and enhanced callus quality and strength in normal bone with FRI, but not in osteoporotic bone. Cite this article: Bone Joint Res 2022;11(2):49–60

Periprosthetic infection with extensive bone loss is a complex situation. The appropriate management of large bone defects has not been established. Without reconstruction amputation/disarticulation is the likely outcome. Aim of the study was to Analyse preliminary results of direct exchange endoprosthetic reconstruction for periprosthetic infection associated with segmental bone defects. Study of patients with periprosthetic infection and severe osteolysis treated by direct exchange tumour prostheses between June, 2005 and May, 2008 (4 – Distal femoral & 2 – Total femoral Replacements). Microbiological evidence of infection was confirmed with regular monitoring of radiograph, crp, esr and wcc. Community based antibiotic therapy was provided by infectious disease team based in our institution. The mean age and follow up were 74.2 years and 26.5 months respectively. Mean duration of antibiotics was 6 weeks intravenous(community based) and 3.5 months oral. 1 patient required intervention by plastic surgeons at index procedure. Radiographs at 6, 12 & 24 months showed no changes from immediate post-op. CRP, ESR and WBC count were within normal limits at the end of antibiotic therapy. One patient required prolonged pain relief with poor mobility due to instability in the opposite knee. One patient had infection recurrence. Knee range of movements averaged full extension to 95 degrees. The mean oxford knee scores pre and post operatively were 58 and 39.4 respectively. We conclude that salvage endoprosthetic reconstruction has provided effective pain relief, stability and improved mobility in our experience. It has provided an oppourtunity to avoid amputation. Multidisciplinary support from plastic surgeons and specialist microbiologists is essential

Introduction: Periprosthetic infection with extensive bone loss is a complex situation. The appropriate management of large bone defects has not been established. Without reconstruction amputation/disarticulation is the likely outcome. Aim: To Analyse preliminary results of direct exchange endoprosthetic reconstruction for periprosthetic knee infection associated with segmental bone defects. Methods: Study of patients with periprosthetic knee infection and severe osteolysis treated by direct exchange tumour prostheses between June, 2005 and May, 2008 (4 - Distal femoral & 2 - Total femoral Replacements). Exclusion criteria included polymicrobial infection, resistant organisms, depressed immunity and poor peripheral perfusion. At each clinical visit they were monitored for clinical, microbiological, haematological and radiological evidence of infection. Community based antibiotic therapy was provided by specialist microbiologists. All patients were counselled and consented by the operating surgeon and specialist microbiologist prior to surgery. Results: The mean age and follow up were 70.2 years and 30.5 months respectively. The most common infecting organism was Staphylococcus epidermidis (four), followed by Streptococcus species. Mean duration of antibiotics was 6 weeks intravenous(community based) and 8 weeks oral. 1 patient required intervention by plastic surgeons at index procedure. Radiographs showed no changes at final followup. One patient had superficial wound infection, which was successfully debrided. Knee range of movements averaged full extension to 95 degrees. The mean oxford knee scores pre and post operatively were 58 and 39.4 respectively. Conclusion: Salvage direct exchange endoprosthetic reconstruction has provided effective pain relief, stability and improved mobility in our experience. Isolation of sensitive organism, specialist microbiologist input, availability of specialist physiotherapy and plastic surgery service, appropriate community care, good patient compliance and surgeon’s experience are key to success in these patients. Morbidity was significantly reduced due to early mobilisation

Aims. We aimed to evaluate the long-term impact of fracture-related infection (FRI) on patients’ physical health and psychological wellbeing. For this purpose, quality of life after successful surgical treatment of FRIs of long bones was assessed. Methods. A total of 37 patients treated between November 2009 and March 2019, with achieved eradication of infection and stable bone consolidation after long bone FRI, were included. Quality of life was evaluated with the EuroQol five-dimension questionnaire (EQ-5D) and German Short-Form 36 (SF-36) outcome instruments as well as with an International Classification of Diseases of the World Health Organization (ICD)-10 based symptom rating (ISR) and compared to normative data. Results. With a mean follow-up of 4.19 years (SD 2.7) after the last surgery, the mean SF-36 score was 40.1 (SD 14.6) regarding the physical health component and 48.7 (SD 5.1) regarding the mental health component, compared to German normative values of 48.4 (SD 9.2) (p < 0.001) and 50.9 (SD 8.8) (p = 0.143). The mean EQ-5D index reached 0.76 (SD 0.27) with a mean EQ-5D visual analogue scale (VAS) rating of 65.7 (SD 22.7) compared to reference scores of 0.88 (p < 0.001) and 72.9 (p < 0.001). Mean scores of the ISR did not reveal significant psychological symptom burden, while an individual analysis showed moderate to severe impairments in 21.6% (n = 8) of the patients. Conclusion. Even a mean 4.2 years (SD 2.7) after surgically successful treatment of FRI of long bones, patients report significantly lower quality of life in comparison to normative data. Future clinical studies on FRIs should focus on patient-related outcome measures enabling best possible shared treatment decision-making. Prevention methods and interdisciplinary approaches should be implemented to improve the overall quality of life of FRI patients. Cite this article: Bone Joint Res 2021;10(5):321–327

Purpose: We reviewed all isolated tibial shaft fractures treated by operative means, with focus on prolonged healing and infection. Design; Retrospective Case Control Study; level of evidence; Prognostic level III.

Methods: Patients: 821 isolated tibial shaft fractures, with a drop-out of 5.6% Open fractures: 400 (grade I & II 280, grade IIIa,b,c 120) Type A,B fractures: 597 Type C fractures: 224 Skeletal Fixation Modes: Ex;Fix (unilateral-one plane): 192, UTN(Synthes): 337, Plate(LCDCP): 129, RTN(Synthes): 163

Outcome measurements: Union time, requirement for secondary treatment, and development of deep infection.

Results: Infections: 94 (11,4%), Closed # which became infected: 21 (5%) Open # which became infected: 73 (18%) Ex.Fix: 56 (29%) Plate: 15 (12%) UTN: 16 (5%) RTN: 7 (5%) In a multiple logistic regression analysis, only Soft tissue damage had a statistical significant interference with the outcome infection (point estimate 0.117, 95% CI 0.053–0.262) Prolonged healing: 285 (34%)? Delayed union 191 ? Non-union 94 Closed fractures which develop a delayed healing: 56 (13%) Open fractures which develop a delayed healing: 135 (34%) Closed fractures which develop a non-union: 20 (5%) Open fractures which develop a non-union: 74 (19%) In a multiple logistic regression analysis, infection & fracture type had a statistical significant interference with the outcome prolonged healing.

Conclusions: The use of an unilateral external fixator as a definitive treatment for tibial fractures is obsolete. For a contaminated tibial fracture the use of the UTN diminish the risk of infection. Looking for the healing time, UTN & Ex.Fix. are associated with a significant prolonged bone healing time.

Complex acetabular reconstruction for oncology and bone loss are challenging for surgeons due to their often hostile biological and mechanical environments. Titrating concentrations of silver ions on implants and alternative modes of delivery allow surgeons to exploit anti-infective properties without compromising bone on growth and thus providing a long-term stable fixation. We present a case series of 12 custom acetabular tri-flange and custom hemipelvis reconstructions (Ossis, Christchurch, New Zealand), with an ultrathin plasma coating of silver particles embedded between layers of siloxane (BioGate HyProtect™, Nuremberg, Germany).

At the time of reporting no implant has been revised and no patient has required a hospital admission or debridement for a deep surgical site infection. Routine follow up x-rays were reviewed and found 2 cases with loosening, both at their respective anterior fixation. Radiographs of both cases show remodelling at the ilium indicative of stable fixation posteriorly. Both patients remain asymptomatic. 3 patients were readmitted for dislocations, 1 of whom had 5 dislocations within 3 weeks post-operatively and was immobilised in an abduction brace to address a lack of muscle tone and has not had a revision of their components.

Utilising navigation with meticulous implant design and construction; augmented with an ultrathin plasma coating of silver particles embedded between layers of siloxane with controlled and long-term generation of silver ion diffusion has led to outstanding outcomes in this series of 12 custom acetabular and hemipelvis reconstructions. No patients were revised for infection and no patients show signs of failure of bone on growth and incorporation. Hip instability remains a problem in these challenging mechanical environments and we continue to reassess our approach to this multifaceted problem.

Aim. Staphylococcus aureus (SA) chronic bone and joint infections (BJI) are characterized by a progressive destruction of bone tissue associated to SA persistence which results in a large number of relapses (10–20%). The main factors proposed for these failures are: i) a weak diffusion of antibiotics in bone tissue, ii) formation of biofilm, iii) the bacterial internalization by the cells responsible for bone mineralization, namely the osteoblasts (OB). Our in vitro and in vivo work aimed at providing new information on the impact of SA, more specifically of internalized SA, on bone homeostasis. Method. Effect of SA infection (8325–4/FnBP+; DU5883/FnBP-) on the viability, differentiation and mineralization of an OB cell line was measured in vitro by MTT and Phosphatase Alcaline (PAL) activity assays and quantification of calcium deposits using Alizarin red, respectively. A gentamicin protection assay (GPA) confirmed that the effects observed are due solely to the internalized SA. In vivo, X-ray microtomography (μCT) and 3D reconstruction was used to evaluate the impact of SA infection on bone formation and bone resorption in a mouse model of femur infection. Results. In vitro, the infection of pre-OB decreases their capacity of differentiation into mature OB displaying a PAL activity. This effect depends on both the multiplicity of infection and invasion capacities of the strains used (8325–4 (invasion competent) vs DU5883 (invasion incompetent)). The infection delays mineralization after 5 days (p <0.0001), likely due to a cytotoxic effect. Indeed, after bacterial clearance at J21, this delay is made up (no difference between infected and uninfected cells). These results are consistent with the preliminary in vivo observations (μCT) showing a significant decrease in the thickness of trabecular of infected femurs with 8325–4 compared to DU5883 and non-infected femurs (p< 0, 0041). Conclusions. These results suggest that the internalization of SA leads to an imbalance of bone remodeling, in particular by a cytotoxic effect on the pre-OB and a slowed-down formation of bone tissue by OB, leading to a significant bone loss. The ongoing study of the cellular and bacterial mechanisms involved in this internalization should allow a better management of chronic BJI

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To characterize the intracellular penetration of osteoblasts and osteoclasts by methicillin-resistant Staphylococcus aureus (MRSA) and the antibiotic and detergent susceptibility of MRSA in bone.

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The optimal treatment of displaced intra-articular calcaneal fractures (DIACF) remains controversial. The operative treatment group has better anatomical recovery, functional outcome scores and less pain than non operative treatment patients, but it may lead to a higher incidence of complications, such as delayed wound healing and surgical site infections. The aim of this study was to analyze the prophylactic effect using a biphasic bone substitute (BS) eluting antibiotic on calcaneal implant-related infections.

Two patients with acute osteomyelitis of the foot caused by mixed aerobic organisms are described; sources of infection and predisposing factors are discussed. Serratia marcescens was isolated in each instance. Antimicrobial therapy which did cover this organism failed; a change to treatment directed against it succeeded.

Introduction: The National Bone Bank of Ireland was established in June 1996 at Cappagh National Orthopaedic Hospital, Dublin in response to the increased demand of allogenic bone grafts in Ireland. We reviewed the Bone Bank performance since it started with special emphasis on Microbiological monitoring of bone allograft as infection is the main complication of bone allograft (Chapman and Villar 1992). Material and Methods: The femoral head allograft is harvested from living volunteer donors who are undergoing primary total hip replacement at Cappagh Hospital and have been assessed by the Bone Bank Co-Ordinator. Harvesting: The bone is retrieved and harvested at the time of total hip replacement according to a strict protocol. Storage: The bone is stored in the “Quarantine” freezer at −80 degrees C for a minimum period of 180 days. Each specimen is subjected to a full technical review by the Bone Bank Co-Ordinator and Medical Director and only when results of screening confirmed negative, the bone designated suitable for “Issue Stock” freezer. Issue of Allografts: Bone is supplied for use, only after receiving full details of recipient to allow tracking. The results of the culture swab taken at the time of implantation and details of any post operative infection in recipients are forwarded to the bone bank. Results: From June 1996 to December 2003, 5089 Primary Total Hip Replacements done at Cappagh Hospital and 1921 (38%) femoral heads were harvested. 109 (5.7%) of grafts had initial positive swabs/chips and 22 of these were discarded because of second positive chips. 1457 femoral head grafts supplied to 876 recipients and were used in Revision Total Hip Replacement (60%), Spine Surgeries (15%), Revision Total Knee (12%), Fractures, Tumours, Foot and Ankle (12%). 6 swabs at the time of grafting in recipients grew Staphylococcus Epidermidis but no clinical infection reported in our follow-up system. To double check, we posted a questioner to all consultants with list and details of their recipient patients and only 2 cases of suspected grafts related infection reported. Discussion and Conclusion: Microbiological surveillance of bone grafts protect recipients from infection and is useful as a quality control of the process of bone banking (Farrington et al 1998). Our study showed contamination rate of 5.7%. Minimum infection rate post Revision Hip Replacement has been reported by Tomford in 1990, but after massive femoral allograft, infection has been reported 4% – 5% (Tomford 1990) and over 11% by Lord et al in 1988. Our experience showed only 2 cases in spite of strict follow-up protocol. We follow the policy of discarding the heavily contaminated grafts (Chapman 1992). The quality performance of a Bone Bank depend on a full time bone bank co-ordinator, identification of donors, retrieval and harvesting of grafts, blood and microbiological assessment, medical supervision for decisions about contaminated grafts, a strict follow-up protocol and a regular audit of bone bank (Ivory and Thomas 1993). We also suggest that regular correspondence to the consultant using the bone grafts will improve the accuracy of follow-up

Aims. Fracture-related infection (FRI) is commonly classified based on the time of onset of symptoms. Early infections (< two weeks) are treated with debridement, antibiotics, and implant retention (DAIR). For late infections (> ten weeks), guidelines recommend implant removal due to tolerant biofilms. For delayed infections (two to ten weeks), recommendations are unclear. In this study we compared infection clearance and bone healing in early and delayed FRI treated with DAIR in a rabbit model. Methods. Staphylococcus aureus was inoculated into a humeral osteotomy in 17 rabbits after plate osteosynthesis. Infection developed for one week (early group, n = 6) or four weeks (delayed group, n = 6) before DAIR (systemic antibiotics: two weeks, nafcillin + rifampin; four weeks, levofloxacin + rifampin). A control group (n = 5) received revision surgery after four weeks without antibiotics. Bacteriology of humerus, soft-tissue, and implants was performed seven weeks after revision surgery. Bone healing was assessed using a modified radiological union scale in tibial fractures (mRUST). Results. Greater bacterial burden in the early group compared to the delayed and control groups at revision surgery indicates a retraction of the infection from one to four weeks. Infection was cleared in all animals in the early and delayed groups at euthanasia, but not in the control group. Osteotomies healed in the early group, but bone healing was significantly compromised in the delayed and control groups. Conclusion. The duration of the infection from one to four weeks does not impact the success of infection clearance in this model. Bone healing, however, is impaired as the duration of the infection increases. Cite this article: Bone Joint Res 2024;13(3):127–135

Aim. Galleria mellonella larvae is a well-known insect infection model that has been used to test the virulence of bacterial and fungal strains as well as for the high throughput screening of antimicrobial compounds against infections. Recently, we have developed insect infection model G. mellonella larvae to study implant associated biofilm infections using small K-wire as implant material. Here, we aimed to further expand the use of G. mellonella to test other materials such as bone cement with combination of gentamicin to treat implant-associated infections. Method. The poly methyl methacrylate (PMMA) with and without gentamicin and liquid methyl methacrylate (MMA) were kindly provided by Heraeus Medical GmbH, Wehrheim. To make the bone cement implants as cubes, Teflon plate (Karl Lettenbauer, Erlangen) with specified well size was used. The Radiopaque polymer and monomer were mixed well in a bowl, applied over on to the Teflon plate and pressed with spatula to form fine and uniform cubes. After polymerization, the bone cement implants were taken out of the Teflon well plate with the help of pin. For the infection process, bone cement cubes were pre-incubated with S. aureus EDCC 5055 culture at 5×10. 6. CFU/ml for 30 min at 150 rpm shaking conditions. Later, these implants were washed with 10ml PBS and implanted in the larvae as mentioned. Survival of the larvae were observed at 37°C in an incubator. To analyze the susceptibility of the bacterial infections towards gentamicin, survival of the larvae compared with control group implanted only with bone cement. The effect of gentamicin was also measured in terms of S. aureus load in larvae on 2. nd. day. SEM analysis was performed to see the effect of gentamicin on biofilm formation on bone cement. Results. Our experiments established the G. mellonella as an excellent model to screen bone cement with antimicrobial compounds against bacterial infections. The gentamicin bone cement samples showed excellent S. aureus bacterial load reduction after the implantation in G. mellonella model. The bone cement with gentamicin showed better survival of larvae infected with S. aureus compared to control. Finally, the gentamicin also affected the biofilm formation on the bone cement surface with S. aureus. Conclusions. Thus, our work showed G. mellonella is a rapid, cheap economical pre-clinical model to study the bone cement associate bacterial infections as well as screening of the various antimicrobial compounds

The Cierny and Mader classification assists with decision-making in the management of osteomyelitis by strafying the host status and the pathoanatomy of disease. However the anatomical type IV represents a heterogenous group with regards to treatment requirements and outcomes. We propose that modification of the Cierny and Mader anatomical classification with an additional type V classifier (diffuse corticomedullary involvement with an associated critical bone defect) will allow more accurate stratification of patients and tailoring of treatment strategies. A retrospective review of 83 patients undergoing treatment for Cierny and Mader anatomical type IV osteomyelitis of the appendicular skeleton at a single centre was performed. Risk factors for the presence of a critical bone defect were female patients (OR 3.1 (95% CI 1.08– 8.92)) and requirement for soft tissue reconstruction (OR 3.35 (95% CI 1.35–8.31)); osteomyelitis of the femur was negatively associated with the presence of a critical bone defect (OR 0.13 (95% CI 0.03–0.66)). There was no statistical significant risk of adverse outcomes (failure to eradicate infection or achieve bone union) associated with the presence of a critical-sized bone defect. The median time to bone union was ten months (95% CI 7.9–12.1 months). There was a statistically significant difference in the median time to bone union between cases with a critical bone defect (12.0 months (95% 10.2–13.7 months)) and those without (6.0 months (95% CI 4.8–7.1 months)). This study provided evidence to support the introduction of a new subgroup of the Cierny and Mader anatomical classification (Type V). Using a standardised approach to management, comparable early outcomes can be achieved in patients with Cierny and Mader anatomical type V osteomyelitis. However, to achieve a successful outcome, there is a requirement for additional bone and soft tissue reconstruction procedures with an associated increase in treatment time

Paediatric bone and joint infections remain common in low- and middle-income countries (LMICs). We aimed to determine the complication rate and incidence of disseminated infection in paediatric bone and joint infections in an LMIC setting. Secondly, we aimed to elucidate factors associated with complications and disseminated disease. We retrospectively reviewed our database for children that presented with bone and joint infections between September 2015 and March 2019. Data were extracted to identify factors that were associated with development of complications and disseminated infection. We analysed 49 children. The median age at presentation was 6 years (range 1 month to 12 years). Locally advanced disease was present in 13 children (27%). The remaining 36 children were evenly divided (18/49 each, 37%) between isolated AHOM and SA, respectively. Disseminated disease was present in 16 children (33%) and was associated with locally advanced disease, an increase in number of surgeries and an increased length of stay. Twenty-six complications were documented in 22 (45%) children. Chronic osteomyelitis developed in 15/49 (31%) cases, growth arrest in 5/49 (10%), and pathological fracture, DVT and septic shock in 2/49 (4%) each. Complicated disease was associated with locally advanced disease, a higher number of surgeries, disseminated disease and an increased length of stay. Sixty five percent of cases cultured Staphylococcus aureus, while 25% (12/49) were culture negative. The median time from admission to surgery was one day, and the median time from onset of symptoms to surgery was seven days. We found a high complication rate. One third of patients had locally advanced disease, and this was associated with the development of complications and disseminated disease. Further studies are needed to be able to predict which children will have poor outcomes

Introduction. The Cierny and Mader classification assists with decision-making by stratifying host status and the pathoanatomy of the disease. However, the anatomical type IV represents a heterogenous group with regards to treatment requirements and outcomes. We propose that modification of the Cierny and Mader anatomical classification with an additional type V classifier (diffuse corticomedullary involvement with an associated critical bone defect) will allow more accurate stratification of patients and tailoring of treatment strategies. Materials & Methods. A retrospective review of 83 patients undergoing treatment for Cierny and Mader anatomical type IV osteomyelitis of the appendicular skeleton at a single centre was performed. Results. Risk factors for the presence of a critical bone defect were female patients (OR 3.1 (95% CI 1.08–8.92)) and requirement for soft tissue reconstruction (OR 3.35 (95% CI 1.35–8.31)); osteomyelitis of the femur was negatively associated with the presence of a critical bone defect (OR 0.13 (95% CI 0.03–0.66)). There was no statistically significant risk of adverse outcomes (failure to eradicate infection or achieve bone union) associated with the presence of a critical-sized bone defect. The median time to bone union was ten months (95% CI 7.9–12.1 months). There was a statistically significant difference in the median time to bone union between cases with a critical bone defect (12.0 months (95% 10.2–13.7 months)) and those without (6.0 months (95% CI 4.8–7.1 months)). Conclusions. This study provided evidence to support the introduction of a new subgroup of the Cierny and Mader anatomical classification (Type V). Using a standardised approach to management, comparable early outcomes can be achieved in patients with Cierny and Mader anatomical type V osteomyelitis. However, to achieve a successful outcome, there is a requirement for additional bone and soft tissue reconstruction procedures with an associated increase in treatment time

Aim. Osteomyelitis (OM) is a debilitating infection of the bone that originates from hematogenous spreading of microbes or contamination after surgery/fracture. OM is mainly caused by the opportunistic bacterium Staphylococcus aureus (SA), which can evade the host immune response, acquire antibiotic resistance and chronically colonize the musculoskeletal tissue . 1,2. , yet the underlying molecular and cellular processes are largely unclear. This study aimed to characterize the pathogenetic mechanisms of SA-OM with a focus on the long pentraxin 3 (PTX3), a soluble pattern recognition molecule and bone tissue component that is emerging as a new player in osteoimmunology . 3. and a diagnostic marker of periprosthetic joint infections, a common form of OM. 4. . Method. A murine model of OM based on intra-bone injection of SA was developed that closely mimicked surgery/trauma-related OM in humans and allowed addressing the role of PTX3 in gene-modified (Ptx3-/-) animals. Local and systemic infection and inflammation were assessed via microbiology, flow cytometry, histochemistry and microCT techniques. Results. SA-injected mice developed chronic infection with measurable levels of viable bone-resident bacteria up until 30 days from microbial challenge. The infection was confined to the treated limbs only and accompanied by extensive tissue remodelling. The bacterial load was higher in WT than Ptx3. -/-. animals at 6 and 14 days from SA injection. Accordingly, WT mice had enhanced systemic inflammation with expanded innate immune compartment in the spleen and increased serum levels of inflammatory cytokines and chemokines. PTX3 levels were higher in SA- than vehicle (PBS)-injected WT animals both in the serum and bone tissue. Furthermore, administration of a PTX3-targeting antibody reduced the bacterial burden in the bones of SA-injected WT mice. Conclusions. In a mouse model of SA-OM, genetic deficiency of PTX3 protected from infection and inflammation, pointing to this pentraxin as a crucial player in OM pathogenesis and a novel therapeutic target in bone infections. The study was approved by the Italian Ministry of Health (approval n. 520/2019-PR issued on 19/07/2019) and supported by Fondazione Beppe and Nuccy Angiolini