A rabbit model of implant-related osteomyelitis inoculated with biofilm after open femoral fracture

Current therapeutic interventions combating biofilm-related infections in orthopaedics : a systematic review of in vivo animal studies

Aims

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.

Methods

Literature research was performed on PubMed and Embase databases. Keywords used for search criteria were “bone AND biofilm”. Information on the species of the animal model, bacterial strain, evaluation of biofilm and bone infection, complications, key findings on observations, prevention, and treatment of biofilm were extracted.

Results

A total of 43 studies were included. Animal models used included fracture-related infections (ten studies), periprosthetic joint infections (five studies), spinal infections (three studies), other implant-associated infections, and osteomyelitis. The most common bacteria were Staphylococcus species. Biofilm was most often observed with scanning electron microscopy. The natural history of biofilm revealed that the process of bacteria attachment, proliferation, maturation, and dispersal would take 14 days. For systemic mono-antibiotic therapy, only two of six studies using vancomycin reported significant biofilm reduction, and none reported eradication. Ten studies showed that combined systemic and topical antibiotics are needed to achieve higher biofilm reduction or eradication, and the effect is decreased with delayed treatment. Overall, 13 studies showed promising therapeutic potential with surface coating and antibiotic loading techniques.

Conclusion

Combined topical and systemic application of antimicrobial agents effectively reduces biofilm at early stages. Future studies with sustained release of antimicrobial and biofilm-dispersing agents tailored to specific pathogens are warranted to achieve biofilm eradication.

Cite this article: Bone Joint Res 2022;11(10):700–714.

Role of Animal Models to Advance Research of Bacterial Osteomyelitis

Osteomyelitis is an inflammatory bone disease typically caused by infectious microorganisms, often bacteria, which causes progressive bone destruction and loss. The most common bacteria associated with chronic osteomyelitis is Staphylococcus aureus. The incidence of osteomyelitis in the United States is estimated to be upwards of 50,000 cases annually and places a significant burden upon the healthcare system. There are three general categories of osteomyelitis: hematogenous; secondary to spread from a contiguous focus of infection, often from trauma or implanted medical devices and materials; and secondary to vascular disease, often a result of diabetic foot ulcers. Independent of the route of infection, osteomyelitis is often challenging to diagnose and treat, and the effect on the patient's quality of life is significant. Therapy for osteomyelitis varies based on category and clinical variables in each case. Therapeutic strategies are typically reliant upon protracted antimicrobial therapy and surgical interventions. Therapy is most successful when intensive and initiated early, although infection may recur months to years later. Also, treatment is accompanied by risks such as systemic toxicity, selection for antimicrobial drug resistance from prolonged antimicrobial use, and loss of form or function of the affected area due to radical surgical debridement or implant removal. The challenges of diagnosis and successful treatment, as well as the negative impacts on patient's quality of life, exemplify the need for improved strategies to combat bacterial osteomyelitis. There are many in vitro and in vivo investigations aimed toward better understanding of the pathophysiology of bacterial osteomyelitis, as well as improved diagnostic and therapeutic strategies. Here, we review the role of animal models utilized for the study of bacterial osteomyelitis and their critically important role in understanding and improving the management of bacterial osteomyelitis.

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

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

Development of a large animal rabbit model for chronic periprosthetic joint infection

Aims

Periprosthetic joint infections (PJIs) and osteomyelitis are clinical challenges that are difficult to eradicate. Well-characterized large animal models necessary for testing and validating new treatment strategies for these conditions are lacking. The purpose of this study was to develop a rabbit model of chronic PJI in the distal femur.

Methods

Fresh suspensions of Staphylococcus aureus (ATCC 25923) were prepared in phosphate-buffered saline (PBS) (1 × 10⁹ colony-forming units (CFUs)/ml). Periprosthetic osteomyelitis in female New Zealand white rabbits was induced by intraosseous injection of planktonic bacterial suspension into a predrilled bone tunnel prior to implant screw placement, examined at five and 28 days (n = 5/group) after surgery, and compared to a control aseptic screw group. Radiographs were obtained weekly, and blood was collected to measure ESR, CRP, and white blood cell (WBC) counts. Bone samples and implanted screws were harvested on day 28, and processed for histological analysis and viability assay of bacteria, respectively.

Results

Intraosseous periprosthetic introduction of planktonic bacteria induced an acute rise in ESR and CRP that subsided by day 14, and resulted in radiologically evident periprosthetic osteolysis by day 28 accompanied by elevated WBC counts and histological evidence of bacteria in the bone tunnels after screw removal. The aseptic screw group induced no increase in ESR, and no lysis developed around the implants. Bacterial viability was confirmed by implant sonication fluid culture.

Conclusion

Intraosseous periprosthetic introduction of planktonic bacteria reliably induces survivable chronic PJI in rabbits.

Cite this article: Bone Joint Res 2021;10(3):156–165.

Innovations in osteomyelitis research: A review of animal models

Infection of bone tissue, or osteomyelitis, has become a growing concern in modern healthcare due in no small part to a rise in antibiotic resistance among bacteria, notably Staphylococcus aureus. The current standard of care involves aggressive, prolonged antibiotic therapy combined with surgical debridement of infected tissues. While this treatment may be sufficient for resolving a portion of cases, recurrences of the infection and associated risks including toxicity with long-term antibiotic usage have been reported. Therefore, there exists a need to produce safer, more efficacious options of treatment for osteomyelitis. In order to test treatment regimens, animal models that closely mimic the clinical condition and allow for accurate evaluation of therapeutics are necessary. Establishing a model that replicates features of osteomyelitis in humans continues to be a challenge to scientists, as there are many variables involved, including choosing an appropriate species and method to establish infection. This review addresses the refinement of animal models of osteomyelitis to reflect the clinical disease and test prospective therapeutics. The aim of this review is to explore studies regarding the use of animals for osteomyelitis therapeutics research and encourage further development of such animal models for the translation of results from the animal experiment to human medicine.

Antibacterial infection and immune-evasive coating for orthopedic implants

Bacterial infection and infection-induced immune response have been a life-threatening risk for patients having orthopedic implant surgeries. Conventional biomaterials are vulnerable to biocontamination, which causes bacterial invasion in wounded areas, leading to postoperative infection. Therefore, development of anti-infection and immune-evasive coating for orthopedic implants is urgently needed. Here, we developed an advanced surface modification technique for orthopedic implants termed lubricated orthopedic implant surface (LOIS), which was inspired by slippery surface of Nepenthes pitcher plant. LOIS presents a long-lasting, extreme liquid repellency against diverse liquids and biosubstances including cells, proteins, calcium, and bacteria. In addition, we confirmed mechanical durability against scratches and fixation force by simulating inevitable damages during surgical procedure ex vivo. The antibiofouling and anti-infection capability of LOIS were thoroughly investigated using an osteomyelitis femoral fracture model of rabbits. We envision that the LOIS with antibiofouling properties and mechanical durability is a step forward in infection-free orthopedic surgeries.

A systematic review on current osteosynthesis-associated infection animal fracture models

Objective

Osteosynthesis-associated infection is a challenging complication post fracture fixation, burdening the patients and the orthopaedic surgeons alike. A clinically relevant animal model is critical in devising new therapeutic strategies. Our aim was to perform a systematic review to evaluate existing preclinical models and identify their applications in aspects of animal selection, bacterial induction, fracture fixation and complications.

Methods

A systematic literature research was conducted in PubMed and Embase up to February 2020. A total of 31 studies were included. Information on the animal, bacterial induction, fracture fixation, healing result and complications were extracted.

Results

Animals selected included murine (23), rabbit (6), ewe (1) and goat (1). Larger animals had enabled the use of human-sized implant, however small animals were more economical and easier in handling. Staphylococcus aureus (S. aureus) was the most frequently chosen bacteria for induction. Bacterial inoculation dose ranged from 10^2-8 ​CFU. Consistent and replicable infections were observed from 10⁴ ​CFU in general. Methods of inoculation included injections of bacterial suspension (20), placement of foreign objects (8) and pretreatment of implants with established biofilm (3). Intramedullary implants (13), plates and screws (18) were used in most models. Radiological (29) and histological evaluations (24) in osseous healing were performed. Complications such as instability of fracture fixation (7), unexpected surgical death (5), sepsis (1) and persistent lameness (1) were encountered.

Conclusion

The most common animal model is the S. aureus infected open fracture internally fixated. Replicable infections were mainly from 10⁴ ​CFU of bacteria. However, with the increase in antibiotic resistance, future directions should explore polymicrobial and antibiotic resistant strains, as these will no doubt play a major role in bone infection. Currently, there is also a lack of osteoporotic bone infection models and the pathophysiology is unexplored, which would be important with our aging population.

The translational potential of this article

This systematic review provides an updated overview and compares the currently available animal models of osteosynthesis-associated infections. A discussion on future research directions and suggestion of animal model settings were made, which is expected to advance the research in this field.

Animal models of orthopaedic infections. A review of rabbit models used to induce long bone bacterial infections

The development of infections is one of the main complications in orthopaedics, especially in the presence of implants for the osteosynthesis of compound fractures and joint prosthesis. Indeed, foreign materials and implants act as substrates for the adhesion and proliferation of bacterial strains able to produce biofilm, causing peri-implant osteomyelitis. The eradication of biofilm remains a great challenge for the host immune system, as well as for medical and surgical approaches, thus imposing the need for new prophylactic and/or therapeutic strategies in which animal models have an essential role. In vivo orthopaedic models have mainly been used to study the pathogenesis of infections, biofilm behaviour and the efficacy of antimicrobial strategies, to select diagnostic techniques and test the efficacy of novel materials or surface modifications to impede both the establishment of bone infections and the associated septic loosening of implants. Among several models of osteomyelitis and implant-related infections described in small rodents and large animals, the rabbit has been widely used as a reliable and reproducible model of orthopaedic infections. This review examines the relevance of rabbits for the development of clinically representative models by analysing the pros and cons of the different approaches published in the literature. This analysis will aid in increasing our knowledge concerning orthopaedic infections by using this species. This review will be a tool for researchers who need to approach pre-clinical studies in the field of bone infection and have to identify the most appropriate animal model to verify their scientific hypothesis.