Aim. The current antibiotic treatment of periprosthetic joint infection (PJI) is optimized by measuring concentrations in plasma. However, it remains unclear whether effective concentrations of the antibiotics are reached at the site of PJI. Nonetheless, adequate target site concentrations are important to achieve effective eradication of the micro-organism. In order to determine the efficacy of cefuroxime and flucloxacillin in synovial fluid, synovial tissue and bone tissue in relation to the minimal inhibitory concentration (MIC) of the pathogen causing the PJI, we perform a pharmacokinetic/pharmacodynamic (PK/PD) study. Therefore, we aimed to develop validated analytical methods for analysis of cefuroxime and flucloxacillin in synovial fluid, synovial tissue and bone tissue. Method. Blank samples of synovial fluid, synovial tissue and bone tissue were obtained by orthopedic surgeons during surgery. For validation the samples of each matrix were spiked with both cefuroxime and flucloxacillin. Synovial tissue and bone tissue was pulverized with a mikro-dismembrator. Samples were kept frozen at −20°C until analysis. After a sample preparation quantification of cefuroxime and flucloxacillin in each matrix was performed on the ultra-performance convergence chromatography-tandem mass spectrometry (UPC2-MS/MS). Stable-isotope-labeled meropenem-d6 served as internal standard. The linearity, limits of quantification, accuracy and precision and carry-over were determined for all methods separately. The methods were validated according to the European Medicine Agency (EMA) and Food and Drug Administration (FDA) guidelines on bioanalytical method validation. Results. These methods were successfully validated for cefuroxime and flucloxacillin quantification in all matrices according to the EMA and FDA guidelines. The limits of quantification were adequate to cover potential cefuroxime and flucloxacillin concentration in synovial fluid, synovial tissue and bone tissue as described in literature, with a range of 1–100mg/L for synovial fluid and 1–20 µg/g for synovial tissue and bone tissue (r >0.995). Accuracy and within-run precision were validated according to acceptance values (RSD <15%). Carry over was less than 20%. Matrix effects and recovery were investigated for synovial fluid. The results were within the range of 80–120%. Conclusions. The results of the validation fall within the limits of quantification according to the EMA and FDA guidelines. Therefore, these methods can be applied during a PK/PD study to discover the exposure of antibiotics in synovial fluid, synovial tissue and bone tissue at the site of infection in patients with a PJI

Summary Statement. In this study, we observed that MR16-1, an interleukin-6 inhibitor, recovered phosphatidylcholine containing docosahexaenoic acid at the injury site after spinal cord injury in mice model by using imaging mass spectrometry. Introduction. The current drugs for improving motor function of the limbs lost due to spinal cord injury (SCI) are ineffective. Development of new drugs for spinal cord injury is desired. MR16-1, an interleukin-6 inhibitor, is found to be effective in improving motor function after spinal cord injury in mice model. Thus, we examined the molecular mechanism in more detail. Therefore, the purpose of this study was to analyze the molecular changes in the spinal cord of the SCI mice treated with MR16-1 using imaging mass spectrometry. Methods. All experiments were performed according to the guidelines for animal experimentation and care and use of laboratory animals established by Hamamatsu University School of Medicine (Shizuoka, Japan). We used 36 adult female C57BL/6J mice for laminectomy and contusion injury of the spinal cord that were performed at the T10 level using the Infinite Horizon Impactor (IH Impactor, 60 kdyn; Muromachi, Tokyo, Japan). Immediately after SCI, mice were intraperitoneally injected with a single dose of MR16-1 (Chugai, Tokyo Japan) (100 µg/g body weight, MR16-1 group) or a single dose of phosphate-buffered saline (PBS) of the same volume (control group). Motor function of the hind limbs was evaluated using the Basso Mouse Scale (BMS), an open-field locomotor test in which the scores range from 0 points (scored for no ankle movement) to 9 points (scored for complete functional recovery). BMS scores were recorded at 1, 7, 14, 21, 28, 35, and 42 days after SCI. The spinal cord tissues were flash frozen and were sliced to a thickness of 8 µm using a cryostat (CM1950; Leica, Wetzler, Germany). Imaging mass spectrometry was used to visualise 12 molecular species of phosphatidylcholine (PC) from thin slices of the spinal cords obtained at 7 days post-SCI. Results. The contusive SCI immediately resulted in complete paralysis. The MR16-1–treated group showed a significant improvement in the BMS locomotor score compared with the control group at both 7 days and 42 days after SCI (1.4 vs 0.2 points and 4.0 vs 1.4 points, respectively). Phospholipids at 7 days after SCI showed unique distribution patterns. In particular, PCs containing docosahexaenoic acid (DHA) localised in the gray matter region was significantly higher in the MR16-1–treated group than in the control group, at 7 days post-SCI. Discussion. MR16-1 treatment showed to improve locomotor BMS score after 7 days of SCI compared with that observed in the control group. Spinal cord injury had induced inflammation; injury sites showed changes in the lipid content. We had previously reported that PC containing DHA mostly expressed in neuron cells decrease on injury sites. In this study, we observed that MR16-1 recovered PC containing DHA at the injury site. This may be associated with the recovery of motor function

Aims. The metabolic variations between the cartilage of osteoarthritis (OA) and Kashin-Beck disease (KBD) remain largely unknown. Our study aimed to address this by conducting a comparative analysis of the metabolic profiles present in the cartilage of KBD and OA. Methods. Cartilage samples from patients with KBD (n = 10) and patients with OA (n = 10) were collected during total knee arthroplasty surgery. An untargeted metabolomics approach using liquid chromatography coupled with mass spectrometry (LC-MS) was conducted to investigate the metabolomics profiles of KBD and OA. LC-MS raw data files were converted into mzXML format and then processed by the XCMS, CAMERA, and metaX toolbox implemented with R software. The online Kyoto Encyclopedia of Genes and Genomes (KEGG) database was used to annotate the metabolites by matching the exact molecular mass data of samples with those from the database. Results. A total of 807 ion features were identified for KBD and OA, including 577 positive (240 for upregulated and 337 for downregulated) and 230 negative (107 for upregulated and 123 for downregulated) ions. After annotation, LC-MS identified significant expressions of ten upregulated and eight downregulated second-level metabolites, and 183 upregulated and 162 downregulated first-level metabolites between KBD and OA. We identified differentially expressed second-level metabolites that are highly associated with cartilage damage, including dimethyl sulfoxide, uric acid, and betaine. These metabolites exist in sulphur metabolism, purine metabolism, and glycine, serine, and threonine metabolism. Conclusion. This comprehensive comparative analysis of metabolism in OA and KBD cartilage provides new evidence of differences in the pathogenetic mechanisms underlying cartilage damage in these two conditions. Cite this article: Bone Joint Res 2024;13(7):362–371

Aims. The diagnosis of periprosthetic joint infection (PJI) continues to present a significant clinical challenge. New biomarkers have been proposed to support clinical decision-making; among them, synovial fluid alpha-defensin has gained interest. Current research methodology suggests reference methods are needed to establish solid evidence for use of the test. This prospective study aims to evaluate the diagnostic accuracy of high-performance liquid chromatography coupled with the mass spectrometry (LC-MS) method to detect alpha-defensin in synovial fluid. Methods. Between October 2017 and September 2019, we collected synovial fluid samples from patients scheduled to undergo revision surgery for painful total knee arthroplasty (TKA). The International Consensus Meeting criteria were used to classify 33 PJIs and 92 aseptic joints. LC-MS assay was performed to measure alpha-defensin in synovial fluid of all included patients. Sensitivity, specificity, positive predictive value, negative predictive value, and the area under the receiver operating characteristic curve (AUC) were calculated to define the test diagnostic accuracy. Results. The AUC was 0.99 (95% confidence interval (CI) 0.98 to 1.00). Receiver operating characteristic (ROC) analysis showed that the optimal cut-off value of synovial fluid alpha-defensin was 1.0 μg/l. The sensitivity of alpha-defensin was 100% (95% CI 96 to 100), the specificity was 97% (95% CI 90 to 98), the positive predictive value was 89.2% (95% CI 82 to 94), and negative predictive value was 100% (95% CI 96 to 100). ROC analysis demonstrated an AUC of 0.99 (95% CI 0.98 to 1.0). Conclusion. The present study confirms the utility of alpha-defensin in the synovial fluid in patients with painful TKA to select cases of PJI. Since LC-MS is still a time-consuming technology and is available in highly specialized laboratories, further translational research studies are needed to take this evidence into routine procedures and promote a new diagnostic approach. Cite this article: Bone Joint J 2022;104-B(9):1047–1051

Purpose Coagulase negative staphylococci (CNS) have been one of the major pathogens responsible for prosthetic joint infections, and are showing increasing multiple-antibiotics resistance. Intact cell mass spectrometry (ICMS), based on the analysis of bacterial surface proteins, has been recognised as a new technique for identification of micro-organisms. The aim of this study was to evaluate the ability of ICMS for species level identification of clinical CNS isolates. Method A total of 50 CNS strains from revision joint replacement operations were studied. ICMS and commercial identification kits were used for identification of those CNS. The commercial kits were used following the manufacturer’s recommendations. For ICMS, single colonies were smeared onto five spots on a sample slide. After drying, a 1 μl of aliquot of matrix solution was added to each spot. Analysis of strains was performed using a Kompact MALDI 2 linear, time of flight mass spectrometer and 3-ns pulse width nitrogen laser light. Combined spectra were constructed from 100 shots at each spot on the sample slide. Results In this study, the commercial kit did not require any special equipment, but required overnight incubation and could not identify at least seven strains. On the other hand, the ICMS method was rapid, accurate and highly reproducible. The mass: charge spectra produced by ICMS contained potential biomarker peaks that could be used for species level identification. Conclusions ICMS has the potential as a powerful tool for species level identification of clinical CNS isolates in terms of rapidity, accuracy and cost effectiveness. This study suggested that ICMS is a possible new method of identifying causative organism in infected joint replacements

Aims. The aim of this study was to determine the fracture haematoma (fxH) proteome after multiple trauma using label-free proteomics, comparing two different fracture treatment strategies. Methods. A porcine multiple trauma model was used in which two fracture treatment strategies were compared: early total care (ETC) and damage control orthopaedics (DCO). fxH was harvested and analyzed using liquid chromatography-tandem mass spectrometry. Per group, discriminating proteins were identified and protein interaction analyses were performed to further elucidate key biomolecular pathways in the early fracture healing phase. Results. The early fxH proteome was characterized by immunomodulatory and osteogenic proteins, and proteins involved in the coagulation cascade. Treatment-specific proteome alterations were observed. The fxH proteome of the ETC group showed increased expression of pro-inflammatory proteins related to, among others, activation of the complement system, neutrophil functioning, and macrophage activation, while showing decreased expression of proteins related to osteogenesis and tissue remodelling. Conversely, the fxH proteome of the DCO group contained various upregulated or exclusively detected proteins related to tissue regeneration and remodelling, and proteins related to anti-inflammatory and osteogenic processes. Conclusion. The early fxH proteome of the ETC group was characterized by the expression of immunomodulatory, mainly pro-inflammatory, proteins, whereas the early fxH proteome of the DCO group was more regenerative and osteogenic in nature. These findings match clinical observations, in which enhanced surgical trauma after multiple trauma causes dysbalanced inflammation, potentially leading to reduced tissue regeneration, and gained insights into regulatory mechanisms of fracture healing after severe trauma. Cite this article: Bone Joint Res 2024;13(5):214–225

Aims. There is a considerable challenge in treating bone infections and orthopaedic device-associated infection (ODAI), partly due to impaired penetration of systemically administrated antibiotics at the site of infection. This may be circumvented by local drug administration. Knowledge of the release kinetics from any carrier material is essential for proper application. Ceftriaxone shows a particular constant release from calcium sulphate (CaSO. 4. ) in vitro, and is particularly effective against streptococci and a large portion of Gram-negative bacteria. We present the clinical release kinetics of ceftriaxone-loaded CaSO. 4. applied locally to treat ODAI. Methods. A total of 30 operations with ceftriaxone-loaded CaSO. 4. had been performed in 28 patients. Ceftriaxone was applied as a single local antibiotic in 21 operations and combined with vancomycin in eight operations, and in an additional operation with vancomycin and amphotericin B. Sampling of wound fluid was performed from drains or aspirations. Ceftriaxone concentrations were measured by liquid chromatography with tandem mass spectrometry (LC-MS/MS). Results. A total of 37 wound fluid concentrations from 16 operations performed in 14 patients were collected. The ceftriaxone concentrations remained approximately within a range of 100 to 200 mg/l up to three weeks. The median concentration was 108.9 mg/l (interquartile range 98.8 to 142.5) within the first ten days. No systemic adverse reactions were observed. Conclusion. Our study highlights new clinical data of locally administered ceftriaxone with CaSO. 4. as carrier material. The near-constant release of ceftriaxone from CaSO. 4. observed in vitro could be confirmed in vivo. The concentrations remained below known local toxicity thresholds. Cite this article: Bone Joint Res 2022;11(11):835–842

Stratification is required to ensure that only those patients likely to benefit, receive Autologous Chondrocyte Implantation (ACI); ideally by assessing a biomarker in the blood. This study aimed to assess differences in the plasma proteome of individuals who respond well or poorly to ACI. Isobaric tag for relative and absolute quantitation (ITRAQ) mass spectrometry and label-free proteomics analyses were performed in tandem as described previously by our group (Hulme et al., 2017; 2018; 2021) using plasma collected from ACI responders (n=10) compared with non-responders (n=10) at each stage of surgery (Stage I, cartilage harvest and Stage II, cell implantation). iTRAQ using pooled plasma detected 16 proteins that were differentially abundant at baseline in ACI responders compared with non-responders (n=10) (≥±2.0 fold; p<0.05). Responders demonstrated a mean Lysholm (patient reported functional score from 0–100) improvement of 33±13 and non-responders a mean worsening of −13±13 points. The most pronounced plasma proteome shift was seen in response to Stage I surgery in ACI non-responders, with 48 proteins being differentially abundant between the two surgical procedures. We have previously noted this marked shift in response to initial surgery in the SF of ACI non-responders, several of these proteins were associated with the Acute Phase Response. One of these proteins, clusterin, could be confirmed in patients’ plasma using an independent immunoassay using individual samples. Label-free proteomic data from individual samples identified only cartilage acidic protein-1 (known to associate with osteoarthritis progression) to be significantly more abundant at Stage I in the plasma of non-responders. This study indicates that proteins can be identified within the plasma that have potential use in ACI patient stratification. Further work is required to validate the findings of this discovery-phase work in larger ACI cohorts

Introduction. Autologous fat grafting has favourable potential as a regenerative strategy and is the current gold-standard to repair large contour defects, as needed in breast reconstruction after mastectomy and traumatic soft tissue reconstruction. Clinically, there is a limit on the volume of lipoaspirate which can be utilised to repair a soft-tissue defect. Surgical complications are the result of poor structural fidelity of lipoaspirate and graft resorption as a filling material and are hindered further by poor graft vascularisation. This study aims to develop injectable lipoaspirate-derived adipose tissue grafts with enhanced biologically and clinically-admissible structural and functional properties adopting light photocrosslinking of unmodified lipoaspirate. Methods. Patient-derived lipoaspirate was harvested and crosslinked using novel photoinitiator and exposure to visible light (wavelength 450nm) in surgery, establishing bonds between extracellular matrix (ECM) proteins within the material. The degree of crosslinking was tuned (photoinitiator concentration, light exposure, light intensity) and covalent bond formation measured using mass spectrometry. To predict patient response, SWATH-MS was used to identify differences in patient ECM and crosslinked grafts were implanted in vivo using a subcutaneous mouse model. Functional vessel formation and resorption were quantified using micro-CT and tissue-remodelling was assessed via histology. Results. There was an increase in the relative abundance of covalent bonds present with increasing degree of crosslinking. When injected, crosslinked lipoaspirate had better shape fidelity compared with native lipoaspirate – demonstrated by a smaller fibre diameter. Crosslinked lipoaspirate remained viable over long term culture and resulted in more predictable resorption profiles when implanted in vivo. Conclusions. The crosslinking approach described here is tunable and functional across different patient samples. Improving the structural properties of lipoaspirate through minimal manipulation has clinical utility for the delivery of grafts with higher shape fidelity and therefore increased graft survival when implanted

Meniscal injuries affect over 1.5 million people across Europe and the USA annually. Injury greatly reduces knee joint mobility and quality of life and frequently leads to the development of osteoarthritis. Tissue engineered strategies have emerged in response to a lack of viable treatments for meniscal pathologies. However, to date, constructs mimicking the structural and functional organisation of native tissue, whilst promoting deposition of new extracellular matrix, remains a bottleneck in meniscal repair. 3D bioprinting allows for deposition and patterning of biological materials with high spatial resolution. This project aims to develop a biomimetic 3D bioprinted meniscal substitute. Meniscal tissue was characterised to effectively inform the design of biomaterials for bioprinting constructs with appropriate structural and functional properties. Histology, gene expression and mass spectrometry were performed on native tissue to investigate tissue architecture, matrix components, cell populations and protein expression regionally across the meniscus. 3D laser scanning and magnetic resonance imaging were employed to acquire the external geometrical information prior to fabrication of a 3D printed meniscus. Bioink suitability was investigated through regional meniscal cell encapsulation in blended hydrogels, with the incorporation of growth factors and assessed for their suitability through rheology, scanning electron microscopy, histology and gene expression analysis. Meniscal tissue characterisation revealed regional variations in matrix compositions, cellular populations and protein expression. The process of imaging through to 3D printing highlighted the capability of producing a construct that accurately replicated meniscal geometries. Regional meniscal cell encapsulation into hydrogels revealed a recovery in cell phenotype, with the incorporation of growth factors into the bioink's stimulating cellular re-differentiation and improved zonal functionality. Meniscus biofabrication highlights the potential to print patient specific, customisable meniscal implants. Achieving zonally distinct variations in cell and matrix deposition highlights the ability to fabricate a highly complex tissue engineered construct. Acknowledgements: This work was undertaken as part of the UK Research and Innovation (UKRI)-funded CDT in Advanced Biomedical Materials

Obesity is correlated with the development of osteoporotic diseases. Gut microbiota-derived metabolite trimethylamine-n-oxide (TMAO) accelerates obesity-mediated tissue deterioration. This study was aimed to investigate what role TMAO may play in osteoporosis development during obesity. Mice were fed with high-fat diet (HFD; 60 kcal% fat) or chow diet (CD; 10 kcal% fat) or 0.2% TMAO in drinking water for 6 months. Body adiposis and bone microstructure were investigated using μCT imaging. Gut microbiome and serum metabolome were characterized using 16S rRNA sequencing and liquid chromatography-tandem mass spectrometry. Osteogenic differentiation of bone-marrow mesenchymal cells was quantified using RT-PCR and von Kossa staining. Cellular senescence was evaluated by key senescence markers p16, p21, p53, and senescence association β-galactosidase staining. HFD-fed mice developed hyperglycemia, body adiposis and osteoporosis signs, including low bone mineral density, sparse trabecular microarchitecture, and decreased biomechanical strength. HFD consumption induced gut microbiota dysbiosis, which revealed a high Firmicutes/Bacteroidetes ratio and decreased α-diversity and abundances of beneficial microorganisms Akkermansiaceae, Lactobacillaceae, and Bifidobacteriaceae. Serum metabolome uncovered increased serum L-carnitine and TMAO levels in HFD-fed mice. Of note, transplantation of fecal microbiota from CD-fed mice compromised HFD consumption-induced TMAO overproduction and attenuated loss in bone mass, trabecular microstructure, and bone formation rate. TMAO treatment inhibited trabecular and cortical bone mass and biomechanical characteristics; and repressed osteogenic differentiation capacity of bone-marrow mesenchymal cells. Mechanistically, TMAO accelerated mitochondrial dysfunction and senescence program, interrupted mineralized matrix production in osteoblasts. Gut microbial metabolite TMAO induced osteoblast dysfunction, accelerating the development of obesity-induced skeletal deterioration. This study, for the first time, conveys a productive insight into the catabolic role of gut microflora metabolite TMAO in regulating osteoblast activity and bone tissue integrity during obesity

Preventing infections in joint replacements is a major ongoing challenge, with limited effective clinical technologies currently available for uncemented knee and hip prostheses. This research aims to develop a coating for titanium implants, consisting of a supported lipid bilayer (SLB) encapsulating an antimicrobial agent. The SLB will be robustly tethered to the titanium using self-assembled monolayers (SAMs) of octadecylphosphonic acid (ODPA). The chosen antimicrobial is Novobiocin, a coumarin-derived antibiotic known to be effective against resistant strains of Staphylococcus aureus. ODPA SAMs were deposited on TiO. 2. -coated quartz crystal microbalance (QCM) sensors using two environmentally friendly non-polar solvents (anisole and cyclopentyl methyl ether, CPME), two concentrations of ODPA (0.5mM and 1mM) and two processing temperatures (21°C and 60°C). QCM, water contact angle measurements, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and temperature-programmed desorption mass spectrometry (TPD-MS) were used to characterise the ODPA SAM. A SLB with encapsulated Novobiocin was subsequently developed on the surface of the ODPA SAM using fluorescent lipids and a solvent assisted method. The prototype implant surface was tested for antimicrobial activity against S. aureus. A well-ordered, uniform ODPA SAM was rapidly formed using 0.5 mM ODPA in CPME at 21°C during 10 min, as confirmed by high Sauerbrey mass (≍285-290 ng/cm. 2. ), high atomic percentage phosphorus (detected using XPS) and high water contact angles (117.6±2.5°). QCM measurements combined with fluorescence microscopy provided evidence of complete planar lipid bilayer formation on the titanium surface using a solvent assisted method. Incorporation of Novobiocin into the SLB resulted in reduced attachment and viability of S. aureus. Key parameters were established for the rapid, robust and uniform formation of an ODPA SAM on titanium (solvent, temperature and concentration). This allowed the successful formation of an antimicrobial SLB, which demonstrated potential for reducing attachment and viability of pathogens associated with joint replacement infections

Aim. Antibiotic concentration at the infected site is a relevant information to gain knowledge about deep-seated infections. The combination of antibiotic therapy and debridement is often indicated to treat these infections. At University Hospital Basel the most frequently administered antibiotic before debridement is amoxicillin in combination with clavulanic acid. Amoxicillin is a fragile beta-lactam antibiotic that brings multiple challenges for its quantification. As for many sample materials only little material is available, the aim of this work was to establish a sensitive and reliable quantification method for amoxicillin that only requires a small sample mass. We did not quantify clavulanic acid as we focused on the drug with antibiotic action. Method. Usually discarded sample material during debridement was collected and directly frozen. The thawed tissues were prepared using simple protein precipitation and manual homogenization with micro pestles followed by a matrix cleanup with online solid-phase extraction. Separation was performed by HPLC followed by heated electrospray ionization and tandem mass spectrometry. Results. During method development, amoxicillin showed partial formation of a covalent methanol adduct when performing protein precipitation. Furthermore, multiple in-source products of amoxicillin during ionization could be observed. Adding an aqueous buffer to the samples before protein precipitation and summing up the signals of amoxicillin and its in-source acetonitrile-sodium-adduct led to successful method validation for a calibration range of 1–51 mg/kg using 10 mg of each tissue sample. The imprecision was < 8% over the entire concentration range and the bias was ≤ 10 %. The quantitative matrix effect was < 6 % in six different tissue samples. Until now we measured amoxicillin in samples from nine patients with prosthetic joint infection, bursitis, or an abscess who obtained amoxicillin between 5 hours and 15 minutes before sampling and found concentrations between 1.4 and 35 mg/kg. Conclusions. With this method, we developed a fast, simple, and sensitive quantification assay for amoxicillin in tissue samples with little material that can now be applied to different study samples

Aim. Prosthetic joint infections (PJI) are a common reason for revisions in patients that underwent total arthroplasty of the hip (THA) or knee (TKA). Extensive antibiotic treatment follows while a clear understanding of target site concentrations is lacking. The aim is to investigate the target site concentrations, like bone and synovial tissue concentrations, which consequently may lead to an optimisation of the dosing regiments of cefuroxime of PJI patients suffering from pain and immobility. Dosing optimisation may lead to a reduced risk of (re-)infection and adverse effects like renal-insufficiency and therefore lower health-care costs. Method. Patients (n=26) with PJI of hip or knee undergoing a one- or two-stage revision treated with cefuroxime were included as part of the ASTERICS study. During implant removal two samples were collected 15-30 and 60-120 minutes after IV infusion of plasma, bone tissue and synovial tissue and one synovial fluid sample. Samples were analysed using a UltraPerformance Convergence Chromotography – quadruple mass spectrometry system (UPC. 2. -MS/MS). Bone tissue and synovial tissue were pulverized before analysis acquiring for bone tissue a homogenate of cortical and cancellous bone. Using nonlinear mixed effect modelling (NONMEM) a base model was developed to analyse the bone to plasma ratio of cefuroxime in osteomyelitis patients. Results. Mean bone concentrations (mg/L) of cefuroxime at 30-60 min after IV administration in the knee and hip are 21.29 (SD:11.86) and 19.06 (SD: 11.79) respectively and 8.23 (SD:4.90) and 9.67 (SD:9.75) respectively at 90-120 min after IV administration. The penetration of cefuroxime described by the bone:plasma ratio into knee and hip affected by osteomyelitis is 0.3 and 0.4 respectively within 1 hour and 0.1 for both joints within 2 hours. The results mentioned here were collected during knee operations without blood void conditions. Concentration data was used to develop a base pharmacokinetic model using NONMEM and was best described by a two-compartment model. Conclusions. Cefuroxime penetrates osteomyelitis affected bone tissue within the hour proving the usefulness of cefuroxime as prophylaxis of orthopaedic surgery and as treatment option for PJI. However, PK modelling and further simulations need to prove whether repeated cefuroxime dosing in this population is required to reach minimal inhibitory concentrations in target tissue

Aim. Dalbavancin is a lipoglycopeptide with a broad antimicrobial spectrum against Gram-positive bacteria and effect against microorganisms in biofilm in vitro. Its pharmacokinetic properties, with an exceptionally long half-life of approximately 300 hours, allow for simplified administration that may be of value in the long-term treatment of bone and joint infections, such as prosthetic joint infections (PJIs). Several case reports and case series with “off-lable” treatment with dalbavancin of PJIs exist, but the optimal dosing regimen remains to be defined. Therapeutic drug monitoring (TDM) is recommended for treatment with >2 doses of dalbavancin. In the absence of TDM, the Swedish national guidelines for bone and joint infections (2023, . www.infektion.net. ) recommends a loading dose of dalbavancin 1,500 mg on day 1 and 1,500 mg on days 8 – 14, after which from day 28 1,000 mg is given biweekly or 500 mg every week. The aim of the present study was to determine trough levels of dalbavancin in patients with long-term treatment of PJIs according to the national guidelines. Method. Twelve patients with PJI were treated with at least 6 doses of dalbavancin, of which the first two doses were 1500 mg and the following doses were 1000 every second week, and prospectively sampled biweekly for determination of serum concentrations (trough levels) of dalbavancin which was measured by liquid chromatography coupled to electrospray tandem mass spectrometry (LC-MS/MS). The renal function was also examined. Results. The median serum concentration 14 days after the first dose of dalbavancin 1500 mg was 36.3 mg/L (range 6.6 – 62.4 mg/L). The median value 14 days after the second dose of 1500 mg (day 27 – 28) was 48.2 mg/L (range 12.2 – 77.3 mg/L). The trough value after the last dose of a total of 6 – 7 doses was as median 43.1 mg/L (range 26.2 – 97.5 mg/L). Three patients showed a tendency towards successive accumulation of dalbavancin during treatment. None of the patients, including those three with increasing through levels during treatment, showed any significant alteration in creatinine nor glomerular filtration rate. Conclusions. TDM during long-term treatment with dalbavancin is recommended to avoid the risk of accumulation and unnecessarily high trough values. With TDM, the dosing interval can be extended in several cases. In addition, with the support of TDM, subtherapeutic serum concentrations, with the risk of developing resistance, can be avoided

Aim. S. aureus and S. epidermidis remain the leading biofilm-forming agents causing orthopedic implant-associated infections (OIAI), but other coagulase-negative Staphylococcus (CoNS) with clinical importance is emerging. Besides, few studies have assessed specific genomic traits associated with patient outcome. This is a preliminary descriptive study of phenotypic and genomic features identified in clinical isolates of S. aureus and CoNS isolates recovered from OIAIs patients that progressed to treatment failure. Methods. Ten isolates were identified by matrix-time-of-flight laser-assisted desorption mass spectrometry (MALDI-TOF-MS) and tested for antibiotic susceptibility and biofilm formation. Genotypic characteristics, including, MLST (Multi Locus Sequence Typing), SCCmec typing, virulence and resistance genes were assessed by whole-genome sequencing (WGS) that was performed on an Illumina HiSeq 2500 platform. Bioinformatics analyzes were performed using CGE, PATRIC, VFDB, CARD RGI, SnapGene, BLAST, and PubMLST. S. aureus (215, 260 and 371) isolates belonged to CC5 (ST5 and ST105, spa type t002) and carried SCCmec type I (1B), II (2A) and V(5C2), respectively. Results. They carried multiple resistance genes, with all resistant to methicillin (MRSA), and harboured mecA, blaZ. S. aureus 215 and 371 carried ermA gene and multiple genes for aminoglycosides resistance including aph(3’)-III, ant(9)-Ia, and ant(4)-Ib, and for quinolones. S. aureus 260 also carried resistance genes for tetracycline, quinolones and trimethoprim (dfrC). All MRSA were strong biofilm producers harboring the complete icaADBC and icaR operon, and also carried multiple adhesion and toxin-related virulence genes. Seven CoNS isolates comprising five species (S. epidermidis, S. haemolyticus, S. sciuri, S. capitis and S. lugdunensis) were analyzed, with mecA gene detection in five isolates. S. haemolitycus (95) and S. lugdunensis were unable to form biofilm and did not harbor the complete icaADBCR operon. S. epidermidis (216, 403) and S. haemolyticus (53,95) isolates belonged to the ST2/CC2, ST183, ST9 and ST3, respectively. High variability of adhesion genes was detected, with atl, ebp, icaADBC operon and IS256 being the most common. Conclusions. In conclusion, this study provides insights into the phenotypic and genomic analysis of Staphylococci allowing elucidation of MRSA and CoNS specific features that are associated with treatment failure in OIAIs, including genes associated with biofilm production, and resistance to β-lactam and aminoglycosides

Background. Surgical site infection following spine surgery is associated with increased morbidity, mortality and increased cost for the health care system. The reported pooled incidence is 3%. Perioperative antibiotic prophylaxis is a key factor in lowering the risk of acquiring an infection. Previous studies have assessed perioperative cefuroxime concentrations in the anterior column of the cervical spine with an anterior surgical approach. However, the majority of surgeries are performed in the posterior column and often involve the lumbar spine. Accordingly, the objective was to compare the perioperative tissue concentrations of cefuroxime in the anterior and posterior column of the same lumbar vertebra using microdialysis in an experimental porcine model. Method. The lumbar vertebral column was exposed in 8 female pigs. Microdialysis catheters were placed for sampling in the anterior column (vertebral body) and posterior column (posterior arch) within the same vertebra (L5). Cefuroxime (1.5 g) was administered intravenously over 10 min. Microdialysates and plasma samples were continuously obtained over 8 hours. Cefuroxime concentrations were quantified by Ultra High Performance Liquid Chromatography Tandem Mass Spectrometry. Microdialysis is a catheter-based pharmacokinetic tool, that allows dynamic sampling of unbound and pharmacologic active fraction of drugs e.g., cefuroxime. The primary endpoint was the time with cefuroxime above the clinical breakpoint minimal inhibitory concentration (T>MIC) for Staphylococcus aureus of 4 µg/mL as this has been suggested as the best predictor of efficacy for cefuroxime. The secondary endpoint was tissue penetration (AUC. tissue. /AUC. plasma. ). Results. Mean T>MIC 4 µg/mL (95% confidence interval) was 123 min (105–141) in plasma, 97 min (79–115) in the anterior column and 93 min (75–111) in the posterior column. Tissue penetration (95% confidence interval) was incomplete for both the anterior column 0.48 (0.40–0.56) and posterior column 0.40 (0.33–0.48). Conclusions. Open lumbar spine surgery often involves extensive soft tissue dissection, stripping and retraction of the paraspinal muscles which may impair the local blood flow exposing the lumbar vertebra to postoperative infections. A single intravenous administration of 1.5 g cefuroxime resulted in comparable T>MIC between the anterior and posterior column of the lumbar spine. Mean cefuroxime concentrations decreased below the clinical breakpoint MIC for S. aureus of 4 µg/mL after 123 min (plasma), 97 min (anterior column) and 93 min (posterior column). This is shorter than the duration of most lumbar spine surgeries, and therefore alternative dosing regimens should be considered in posterior open lumbar spine surgeries lasting more than 1.5 hours

We carried out metal artefact-reduction MRI, three-dimensional CT measurement of the position of the component and inductively-coupled plasma mass spectrometry analysis of cobalt and chromium levels in whole blood on 26 patients with unexplained pain following metal-on-metal resurfacing arthroplasty. MRI showed periprosthetic lesions around 16 hips, with 14 collections of fluid and two soft-tissue masses. The lesions were seen in both men and women and in symptomatic and asymptomatic hips. Using three-dimensional CT, the median inclination of the acetabular component was found to be 55° and its positioning was outside the Lewinnek safe zone in 13 of 16 cases. Using inductively-coupled plasma mass spectrometry, the levels of blood metal ions tended to be higher in painful compared with well-functioning metal-on-metal hips. These three clinically useful investigations can help to determine the cause of failure of the implant, predict the need for future revision and aid the choice of revision prostheses

In a recent phase 2 superiority clinical trial we demonstrated that a single dose of 60mg of the human monoclonal antibody denosumab inhibits osteolytic lesion activity in patients undergoing revision total hip arthroplasty (THA), demonstrating proof of biological efficacy for this clinical application. Here, we examined the effect that denosumab has on disease biology at the osteolysis tissue level. Osteolytic tissue taken from the prosthesis-bone lesion interface at revision surgery in patients with osteolysis (n=10 participants that had received a single 60 mg dose of denosumab 8 weeks prior to revision surgery and n=10 that had received placebo) was examined for total genetic message activity and protein levels using whole genome sequencing and mass spectrometry, respectively. The top five upregulated enriched pathways with denosumab treatment included inflammatory response, myeloid cell activation, myeloid leukocyte migration, neutrophil and granulocyte activation (p<6.26 × 10. −28. ). Cell morphogenesis was amongst the most downregulated pathways (p<3.42 ×10. −23. ). Finally, comparison of the trial mRNA and protein data versus mouse single cell RNA sequencing data of the same pathway blockade in mouse tibia showed the same direction of effect, suggesting that giving the drug causes then cells responsible for osteolysis to disperse into a more immature form (128 of 189 genes (z=4.87, P<0.0001) disease and functional pathways at the mRNA level and 10 of 11 (z=2.72, P=0.0065) at the protein level). In this first-in-man study we identify multiple genes and pathways within periprosthetic osteolysis tissue that are affected by denosumab treatment. The dominant pathways involved upregulation of innate inflammatory signaling and downregulation of cell morphogenesis. We also found enrichment of similar disease and functional pathways at both the mRNA and protein levels versus mRNA pathway enrichment found in mouse osteomorphs. These data provide the first human data of the mechanistic effect of denosumab treatment on inflammatory osteolytic lesion activity after joint replacement that is necessary to support its clinical application. ∗Winner of The Bone & Joint Journal prize∗

Aim. It is traditionally stated that around 80% of all periprosthetic joint infections (PJI) are caused by well-known gram-positive organisms such as Staphylococcus aureus. With the advances in diagnostic modalities and improved abilities to isolate infective organisms, we believe the organism profile causing PJI has changed over time and includes numerous other organisms that were either not recognized as pathogens and/or considered as contaminants. Method. We retrospectively reviewed the medical records of 1,363 patients with confirmed PJI (559 THA and 804 TKA) who received treatment at our institution between 2000 and 2019. Pertinent data related to demographics, microbiological findings, and outcome of treatment were collected. Organisms were differentiated using culture or confirmed by Matrix-Assisted Laser Desorption Ionization-time of flight (MALDI-tof) mass spectrometry. Statistical analysis included logistic regressions. Results. There was a total of 26 different species of organisms that resulted in PJI in our cohort. The rate of PJI caused by slow growing organisms, that are catalase negative, such as Streptococcal viridans (OR 1.244; 95% CI 1.036–1.494), Streptococcus agalactiae (OR 1.513; 95% CI 1.207–1.898), and Staphylococcus epidermidis (OR 1.321; 95% CI 1.191–1.466) has been increasing over time. In contrast, the incidence of PJI caused by coagulase-negative Staphylococcus (OR 0.954; 95% CI 0.927–0.981); resistant species (OR 0.962, 95% CI 0.931–0.995), and Gram-positive species (OR 0.94, 95% CI 0.914–0.966) decreased over time. Notably, there was a higher prevalence of Streptococcal PJI (OR 0.551, 95% CI 0.374–0.812) and culture-negative PJI (OR 0.652, 95% CI 0.478–0.890) seen in knees versus hips. The rate of culture negative PJI also increased from 20% in 2000 to 28% in 2019. In the latter years of the study, very unusual list of organisms causing PJI were also identified. Conclusions. This study reveals that the list of organisms causing PJI has expanded in recent years. The study also finds that some the slow growing organisms that were previously believed to be “contaminants” can and do cause PJI in a considerable number of patients. The number of culture negative cases of PJI has also increased at our institution over the years. There are a number of explanations for the latter finding, perhaps with the most important reason being liberal use of antibiotics that interferes with isolation of the infective organism