Louise Kruse Jensen

Background: Antibiotic-loaded ceramic bone grafts (ACBGs) are widely assumed to provide extended local antimicrobial protection, maintaining concentrations above the minimum inhibitory concentration (MIC) for 28 to 42 days. However, this time frame is mainly based on in vitro elution assays with simplified washout models, and its relevance to in vivo performance is uncertain. This study compared the in vivo and in vitro release and behavior of gentamicin from 2 commercial ACBGs. Methods: Gentamicin-loaded hydroxyapatite/calcium sulfate (HA-CS) and calcium sulfate (CS) composites were investigated using a murine implantation model and in vitro elution assays. Gentamicin content in recovered depot material and elution media was quantified by liquid chromatography with tandem mass spectrometry. Model calculations evaluated how the assay design affects the estimated time above the MIC. Results: Both ACBGs released >98% of gentamicin within 6 hours and >99% within 24 hours in vivo. In vitro assays likewise indicated early depot depletion, with concentration-time profiles beyond 48 hours driven by serial dilution rather than release. Model calculations suggested that the apparent prolonged antibiotic activity in previous in vitro assays was largely due to the assay design, not to sustained release, implying that freely administered antibiotics could produce similar profiles. Conclusions: Neither ACBG demonstrated measurable sustained release beyond an initial 24-hour burst phase. This may have important clinical implications, as expectations of prolonged local antimicrobial protection are not supported by the cumulative-release data showing rapid antibiotic depot depletion.

Microbiological culture and histology of deep tissue specimens are independent diagnostic criteria in fracture-related infection (FRI). However, the association between these tests has rarely been investigated, particularly in relation to clinical outcome after treatment. Patients undergoing surgery for International Consensus-confirmed FRI were included. All had ≥5 tissue specimens taken for microbiological culture and 2–3 for histology. The correlation between cultured pathogen, histological positivity (defined as ≥5 polymorphonuclear neutrophils/high power field), and outcome at one year after surgery was explored. FRI was confirmed in 430 patients, predominantly in the tibia (194), femur (111), upper limb (70), and ankle (40). A total of 321 (74.7%) were culture-positive and 334 (77.7%) were histology positive, while 265 (61.6%) were positive for both tests. Staphylococcus aureus was cultured in 169 (42.5%), coagulase-negative Staphylococci (CoNS) in 61 (15.3%), and Gram-negatives in 145 (36.3%) cases. Virulent microorganisms were strongly associated with positive histology (odds ratio 2.72; 95% CI 1.61–4.58) but not with clinical failure (OR 1.08; 0.42–2.75). Isolation of S. aureus was significantly associated with positive histology compared to other microorganisms (OR 2.21; 1.27–3.87). Surgery succeeded in 390 (90.7%) patients. Treatment failure was weakly associated with positive microbiology alone (OR 2.03; 0.83–4.96) or positive histology alone (OR 2.13; 0.81–5.6). Combined positive culture and histology was strongly associated with clinical failure (OR 2.3; 1.06–4.96). There was no difference in outcome between virulent and non-virulent bacteria when histology was positive, but both had higher failure rates compared to patients with negative culture or histology. A pronounced inflammatory response, as seen in histology, is a feature of virulent bacterial FRI. However, the presence of virulent infection alone does not dictate clinical outcome without marked inflammation. This suggests that outcome is at least as much related to the host response as to the bacterium. When the pathological response is prominent, this may lead to tissue necrosis, further bacterial invasion of adjacent tissues, osteolysis and loss of fracture stability, contributing to treatment failure. This deserves further study to understand the mechanisms behind this interplay and clinical outcome.

Aims: Cardiac implantable electronic device (CIED)-related infective endocarditis (IE) is associated with morbidity and mortality. Current guidelines recommend complete CIED extraction; however, the optimal timing for reimplantation remains uncertain. We aimed to evaluate CIED reimplantation rates, and outcomes in patients with non-surgically treated IE who underwent CIED extraction. Methods and results: We included all Danish residents ≥18 years diagnosed with first-time IE (2010–2021), with a pre-existing CIED, who underwent CIED extraction without concurrent valve surgery. Data were obtained from Danish nationwide registries. The primary variable of interest was CIED reimplantation within 90 days after extraction. Reimplantation rates were described, and reimplantation status was used to stratify patients for analysis of secondary outcomes, including recurrent IE-related bacteraemia and all-cause mortality within 6 months. Among 661 patients with CIED extraction due to IE, 396 (59.9%) underwent reimplantation within 3 months, with a median of 29 days (IQR:19–42 days). There was no significant difference in the 6 month cumulative incidence of recurrent bacteraemia with IE (2.5% [95% CI:0.95–5.5] vs. 1.8% [95% CI:0.8–3.6] P = 0.55) or mortality (11.2% [95% CI:7.0–16.4] vs. 7.0% [95% CI:4.7–10.0]; P = 0.11) between non-reimplanted and reimplanted patients. Conclusion: In IE patients who underwent CIED extraction, 60% of patients were reimplanted within 3 months with substantial variation in timing. No significant differences in outcomes were found by reimplantation status.

Background: Microbiological culture and histology are gold standards for diagnosing chronic osteomyelitis (cOM) and fracture-related infection (FRI). This study investigated whether combining these modalities within a single tissue sample provides additional insight into disease severity. We hypothesized that high neutrophil and osteoclast numbers correlate with culture-positive microbiology and that double-positive samples may indicate more severe disease. Methods: In this prospective single-centre study, adults undergoing surgery for confirmed FRI or cOM were included. Clinical and disease classification data (FRI and BACH) were recorded. Five deep-tissue samples were collected intraoperatively and divided for paired microbiological culture and histological assessment of neutrophil infiltration, according to international diagnostic guidelines. Results: Forty-one patients were included (11 cOM, 30 FRI) of whom 68% received preoperative antibiotics. Nineteen patients (46%) were identified as culture-positive, while 32 patients (78%) were histologically positive according to international diagnostic guidelines, respectively. Among the 205 samples, 31% were culture-positive, 56% histology-positive, and 26% double-positive. Histological scores were significantly higher in culture-positive samples (p < 0.001). Treatment failure occurred in seven patients (18%), all with FRI. Paired positive samples were associated with increased odds of clinical failure and earlier revision, with odds increasing 1.68-fold for each additional paired positive sample (95% CI, 1.10–2.77). Conclusions: The paired analysis demonstrated a strong concordance between culture-positivity and suppurative inflammation within the same sample. Combining microbiology and histology may help identify patients at increased risk of revision and enhance diagnostic certainty, particularly in patients identified as culture-negative.

In 2018, the Centrum fOr translational Medicine on Bone and joint INfEctions (COMBINE) was created to facilitate collaboration among Danish scientists and researchers dedicated to bone and joint infection research. The COMBINE approach was developed to ensure successful collaboration, and this publication aims to share this successful approach.