Orthopedic device-related infection (ODRI) preclinical models are widely used in translational research. Most models require induction of general anesthesia, which frequently results in hypothermia in rodents. This study aimed to evaluate the impact of peri anesthetic hypothermia in rodents on outcomes in preclinical orthopedic device-related infection studies.

A retrospective analysis of all rodents that underwent surgery under general anesthesia to induce an ODRI model with inoculation of Staphylococcus epidermidis between 2016 and 2020 was conducted. A one-way multivariate analysis of covariance was used to determine the fixed effect of peri anesthetic hypothermia (hypothermic defined as rectal temperature <35°C) on the combined harvested tissue and implant colonies forming unit counts, and having controlled for the study groups including treatments received duration of surgery and anesthesia and study period. All animal experiments were approved by relevant ethical committee.

A total of 127 rodents (102 rats and 25 mice) were enrolled in an ODRI and met the inclusion criteria. The mean lowest peri-anesthetic temperature was 35.3 ± 1.5 °C. The overall incidence of peri-anesthetic hypothermia was 41% and was less frequently reported in rats (34% in rats versus 68% in mice). Statistical analysis showed a significant effect of peri anesthetic hypothermia on the post-mortem combined colonies forming unit counts from the harvested tissue and implant(s) (p=0.01) when comparing normo- versus hypothermic rodents. Using Wilks’ Λ as a criterion to determine the contribution of independent variables to the model, peri-anesthetic hypothermia was the most significant, though still a weak predictor, of increased harvested colonies forming unit counts.

Altogether, the data corroborate the concept that bacterial colonization is affected by abnormal body temperature during general anesthesia at the time of bacterial inoculation in rodents, which needs to be taken into consideration to decrease infection data variability and improve experimental reproducibility.

Treatment of bone infection often includes a burdensome two-stage revision. After debridement, contaminated implants are removed and replaced with a non-absorbable cement spacer loaded with antibiotics. Weeks later, the spacer is exchanged with a bone graft aiding bone healing. However, even with this two-stage approach infection persists. In this study, we investigated whether a novel 3D-printed, antibiotic-loaded, osteoinductive calcium phosphate scaffold (CPS) is effective in single-stage revision of an infected non-union with segmental bone loss in rabbits.

A 5 mm defect was created in the radius of female New Zealand White rabbits. The bone fragment was replaced, stabilized with cerclage wire and inoculated with Staphylococcus aureus (MSSA). After 4 weeks, the infected bone fragment was removed, the site debrided and a spacer implanted. Depending on group allocation, rabbits received: 1) PMMA spacer with gentamycin; 2) CPS loaded with rifampin and vancomycin and 3) Non-loaded CPS. These groups received systemic cefazolin for 4 weeks after revision. Group 4 received a loaded CPS without any adjunctive systemic therapy (n=12 group1-3, n=11 group 4). All animals were euthanized 8 weeks after revision and assessed by quantitative bacteriology or histology. Covariance analysis (ANCOVA) and multiple regression were performed.

All animals were culture positive at revision surgery. Half of the animals in all groups had eliminated the infection by end of study. In a historical control group with empty defect and no systemic antibiotic treatment, all animals were infected at euthanasia. There was no significant difference in CFU counts between groups at euthanasia.

Our results show that treating an osteomyelitis with segmental bone loss either with CPS or PMMA has a similar cure rate of infection. However, by not requiring a second surgery, the use of CPS may offer advantages over non-resorbable equivalents such as PMMA.

Local antimicrobial therapy is an integral aspect of treating orthopaedic device related infection (ODRI), which is conventionally administered via polymethylmethacrylate (PMMA) bone cement. PMMA, however, is limited by a suboptimal antibiotic release profile and a lack of biodegradability.

In this study, we compare the efficacy of PMMA versus an antibioticloaded hydrogel in a single- stage revision for chronic methicillin-resistant Staphylococcus aureus (MRSA) ODRI in

sheep. Antibiofilm activity of the antibiotic combination (gentamicin and vancomycin) was determined in vitro. Swiss alpine sheep underwent a single-stage revision of a tibial intramedullary nail with MRSA infection. Local gentamicin and vancomycin therapy was delivered via hydrogel or PMMA (n = 5 per group), in conjunction with systemic antibiotic therapy. In vivo observations included: local antibiotic tissue concentration, renal and liver function tests, and quantitative microbiology on tissues and hardware post-mortem.

There was a nonsignificant reduction in biofilm with an increasing antibiotic concentration in vitro (p = 0.12), confirming the antibiotic tolerance of the MRSA biofilm. In the in vivo study, four out of five sheep from each treatment group were culture negative. Antibiotic delivery via hydrogel resulted in 10–100 times greater local concentrations for the first 2–3 days compared with PMMA and were comparable thereafter. Systemic concentrations of gentamicin were minimal or undetectable in both groups, while renal and liver function tests were within normal limits.

This study shows that a single-stage revision with hydrogel or PMMA is equally effective, although the hydrogel offers certain practical benefits over PMMA, which make it an attractive proposition for clinical use.

Aim

Antibiotic prophylaxis is critical for the prevention of fracture related infection (FRI) in trauma patients, particularly those with open wounds. Administration of prophylactic antibiotics prior to arrival at the hospital (e.g. by paramedics) may reduce intraoperative bacterial load and has been recommended; however scientific evidence for pre-hospital administration is scarce.

Aim

The treatment of chronic orthopedic device-related infection (ODRI) often requires multiple surgeries and prolonged antibiotic therapy. In a two-stage exchange procedure, the treatment protocol includes device removal and placement of an antibiotic-loaded bone cement spacer to achieve high local antibiotic concentrations. At the second stage, further surgery is required to remove the spacer and replace it with the definitive device. We have recently developed a thermo-responsive hyaluronan hydrogel (THH) that may be loaded with antibiotics and used as delivery system. Since the material is bio-resorbable, it does not require surgical removal and may therefore be suitable for use as treatment strategy in a single-stage exchange.

This aim of this study was to evaluate gentamicin sulphate (Genta)-loaded THH (THH-Genta) for treating a chronic Staphylococcus aureus ODRI in sheep using a single-stage procedure.

One of the most challenging complications in orthopedic trauma surgery is the development of infection. Improved infection prophylaxis could be achieved by providing local delivery of antibiotics directly to the tissue-implant interface. Especially implant-associated bone infections caused by antibiotic-resistant pathogens pose significant clinical challenges to treating physicians. Prophylactic strategies that act against resistant organisms, such as methicillin-resistant Staphylococcus aureus (MRSA), are urgently required.

The objective of this experimental study was to determine the efficacy of a biodegradable Polymer-Lipid Encapsulation MatriX (PLEX) loaded with the antibiotic doxycycline as a local prophylactic strategy against implant-associated osteomyelitis in a humeral non-fracture rabbit model.

Activity of the PLEX-doxycycline-coating was tested against both a doxycycline susceptible (doxyS) methicillin-susceptible S. aureus (MSSA) as well as a doxycycline-resistant (doxyR) MRSA. In a rabbit intramedullary (IM) nail-related infection model, twelve rabbits received an inoculum of a doxyS MSSA direct into the medullary cavity of the humerus. After inoculation, animals received either a PLEX-doxycycline-coated nail, or an uncoated nail. The animals were observed for four weeks. Upon euthanasia, quantitative bacteriology was performed to determine bacterial load in tissues and biofilm formation on the implant. A second study was performed with sixteen rabbits receiving a DoxyR MRSA inoculum, again in coated and uncoated groups.

In vitro elution studies revealed that 25% of the doxycycline was released from the PLEX-coated implants within the first day, followed by a 3% release per day up to day 28. Quantitative bacteriology revealed the presence of osteomyelitis in all animals receiving an uncoated nail in both the MSSA and the DoxyR MRSA studies (figure). All rabbits receiving a PLEX-doxycycline-coated nail were culture negative in the doxyS MSSA-group and the surrounding bone displayed a normal physiological appearance in both histological sections and radiographs. In the doxyR MRSA inoculated rabbits, a statistically significant reduction in the number of culture-positive samples was observed for the PLEX-doxycycline-coated group when compared to the animals that had received an uncoated nail, although the reduction in bacterial burden did not reach statistical significance.

Improved prophylaxis against infection in trauma and orthopedic implant surgery is clearly required today. In this study, we investigated a PLEX-doxycycline-coated IM nail in a humeral non-fracture rabbit model. The PLEX-doxycycline coating on titanium alloy implants provided complete protection against implant-associated MSSA osteomyelitis, and resulted in a significant reduction in the number of culture positive samples when challenged with a doxycycline-resistant MRSA.

Summary

The two-step labeling protocol using Lysostaphin and bio-orthogonal click chemistry for staining bacteria is described. The click protocol is efficient in labeling staphylococci and is non-toxic. This protocol promises the efficient of infections that are difficult to assess by conventional imaging.