A rabbit humerus model of plating and nailing osteosynthesis with and without Staphylococcus aureus osteomyelitis

Implant retention in a rabbit model of fracture-related infection

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.

Exploring the role of bacterial virulence factors and host elements in septic arthritis: insights from animal models for innovative therapies

Septic arthritis, characterized as one of the most aggressive joint diseases, is primarily attributed to Staphylococcus aureus (S. aureus) and often results from hematogenous dissemination. Even with prompt treatment, septic arthritis frequently inflicts irreversible joint damage, leading to sustained joint dysfunction in a significant proportion of patients. Despite the unsatisfactory outcomes, current therapeutic approaches for septic arthritis have remained stagnant for decades. In the clinical context, devising innovative strategies to mitigate joint damage necessitates a profound comprehension of the pivotal disease mechanisms. This entails unraveling how bacterial virulence factors interact with host elements to facilitate bacterial invasion into the joint and identifying the principal drivers of joint damage. Leveraging animal models of septic arthritis emerges as a potent tool to achieve these objectives. This review provides a comprehensive overview of the historical evolution and recent advancements in septic arthritis models. Additionally, we address practical considerations regarding experimental protocols. Furthermore, we delve into the utility of these animal models, such as their contribution to the discovery of novel bacterial virulence factors and host elements that play pivotal roles in the initiation and progression of septic arthritis. Finally, we summarize the latest developments in novel therapeutic strategies against septic arthritis, leveraging insights gained from these unique animal models.

Comparative bone healing with induced membrane technique (IMT) versus empty defects in septic and aseptic conditions in a novel rabbit humerus model

BACKGROUND

Long bone defects resulting from primary trauma or secondary to debridement of fracture-related infection (FRI) remain a major clinical challenge. One approach often used is the induced membrane technique (IMT). The effectiveness of the IMT in infected versus non-infected settings remains to be definitively established. In this study we present a new rabbit humerus model and compare the IMT approach between animals with prior infection and non-infected equivalents.

METHODS

A 5 mm defect was created in the humerus of New Zealand White rabbits (n = 53) and fixed with a 2.5 mm stainless steel plate. In the non-infected groups, the defect was either left empty (n = 6) or treated using the IMT procedure (PMMA spacer for 3 weeks, n = 6). Additionally, both approaches were applied in animals that were inoculated with Staphylococcus aureus 4 weeks prior to defect creation (n = 5 and n = 6, respectively). At the first and second revision surgeries, infected and necrotic tissues were debrided and processed for bacteriological quantification. In the IMT groups, the PMMA spacer was removed 3 weeks post implantation and replaced with a beta-tricalcium phosphate scaffold and bone healing observed for a further 10 weeks. Infected groups also received systemic antibiotic therapy. The differences in bone healing between the groups were evaluated radiographically using a modification of the radiographic union score for tibial fractures (RUST) and by semiquantitative histopathology on Giemsa-Eosin-stained sections.

RESULTS

The presence of S. aureus infection at revision surgery was required for inclusion to the second stage. At the second revision surgery all collected samples were culture negative confirming successful treatment. In the empty defect group, bone healing was increased in the previously infected animals compared with non-infected controls as revealed by radiography with significantly higher RUST values at 6 weeks (p = 0.0281) and at the end of the study (p = 0.0411) and by histopathology with increased cortical bridging (80% and 100% in cis and trans cortical bridging in infected animals compared to 17% and 67% in the non-infected animals). With the IMT approach, both infected and non-infected animals had positive healing assessments.

CONCLUSION

We successfully developed an in vivo model of bone defect healing with IMT with and without infection. Bone defects can heal after an infection with even better outcomes compared to the non-infected setting, although in both cases, the IMT achieved better healing.

Skeletal infections: microbial pathogenesis, immunity and clinical management

Osteomyelitis remains one of the greatest risks in orthopaedic surgery. Although many organisms are linked to skeletal infections, Staphylococcus aureus remains the most prevalent and devastating causative pathogen. Important discoveries have uncovered novel mechanisms of S. aureus pathogenesis and persistence within bone tissue, including implant-associated biofilms, abscesses and invasion of the osteocyte lacuno-canalicular network. However, little clinical progress has been made in the prevention and eradication of skeletal infection as treatment algorithms and outcomes have only incrementally changed over the past half century. In this Review, we discuss the mechanisms of persistence and immune evasion in S. aureus infection of the skeletal system as well as features of other osteomyelitis-causing pathogens in implant-associated and native bone infections. We also describe how the host fails to eradicate bacterial bone infections, and how this new information may lead to the development of novel interventions. Finally, we discuss the clinical management of skeletal infection, including osteomyelitis classification and strategies to treat skeletal infections with emerging technologies that could translate to the clinic in the future.

A Journey into Animal Models of Human Osteomyelitis: A Review

Osteomyelitis is an infection of the bone characterized by progressive inflammatory destruction and apposition of new bone that can spread via the hematogenous route (hematogenous osteomyelitis (HO)), contiguous spread (contiguous osteomyelitis (CO)), and direct inoculation (osteomyelitis associated with peripheral vascular insufficiency (PVI)). Given the significant financial burden posed by osteomyelitis patient management, the development of new preventive and treatment methods is warranted. To achieve this objective, implementing animal models (AMs) of infection such as rats, mice, rabbits, avians, dogs, sheep, goats, and pigs might be of the essence. This review provides a literature analysis of the AMs developed and used to study osteomyelitis. Historical relevance and clinical applicability were taken into account to choose the best AMs, and some study methods are briefly described. Furthermore, the most significant strengths and limitations of each species as AM are discussed, as no single model incorporates all features of osteomyelitis. HO’s clinical manifestation results in extreme variability between patients due to multiple variables (e.g., age, sex, route of infection, anatomical location, and concomitant diseases) that could alter clinical studies. However, these variables can be controlled and tested through different animal models.

Patient and Surgical Factors Affecting Fusion Rates After Arthroscopic and Open Ankle Fusion: A Review of a High-Risk Cohort

ABSTRACT

We present a case series with the objective of identifying risk factors for nonunion after open and arthroscopic primary ankle arthrodesis. Eighty-seven patients who underwent primary ankle arthrodesis and met inclusion criteria were divided into open (N = 46) and arthroscopic (N = 41) groups. Patient and operative characteristics were retrospectively analyzed as possible risk factors for nonunion within each technique. The nonunion rate was 11% in the open and 12% in the arthroscopic group. Obesity, smoking, and ASA class 3 were highly prevalent in both groups. In the arthroscopic group, a remote history of infection and the use of headed screws had notably higher risk of nonunion, though not statistically significant. In the open group, use of bone graft trended toward lower risk of nonunion, though also not statistically significant. The results of this study demonstrated, nonunion rates are comparable between open and arthroscopic ankle arthrodesis in high-risk patients. For patients with a remote history of infection, open ankle arthrodesis may be preferable, and bone graft importance may vary with open versus arthroscopic technique.

LEVEL OF EVIDENCE

III.

Bacteriophage Therapy for the Prevention and Treatment of Fracture-Related Infection Caused by Staphylococcus aureus: a Preclinical Study

Although several studies have shown promising clinical outcomes of phage therapy in patients with orthopedic device-related infections, questions remain regarding the optimal application protocol, systemic effects, and the impact of the immune response. This study provides a proof-of-concept of phage therapy in a clinically relevant rabbit model of fracture-related infection (FRI) caused by Staphylococcus aureus. In a prevention setting, phage in saline (without any biomaterial-based carrier) was highly effective in the prevention of FRI, compared to systemic antibiotic prophylaxis alone. In the subsequent study involving treatment of established infection, daily administration of phage in saline through a subcutaneous access tube was compared to a single intraoperative application of a phage-loaded hydrogel and a control group receiving antibiotics only. In this setting, although a possible trend of bacterial load reduction on the implant was observed with the phage-loaded hydrogel, no superior effect of phage therapy was found compared to antibiotic treatment alone. The application of phage in saline through a subcutaneous access tube was, however, complicated by superinfection and the development of neutralizing antibodies. The latter was not found in the animals that received the phage-loaded hydrogel, which may indicate that encapsulation of phages into a carrier such as a hydrogel limits their exposure to the adaptive immune system. These studies show phage therapy can be useful in targeting orthopedic device-related infection, however, further research and improvements of these application methods are required for this complex clinical setting. IMPORTANCE Because of the growing spread of antimicrobial resistance, the use of alternative prevention and treatment strategies is gaining interest. Although the therapeutic potential of bacteriophages has been demonstrated in a number of case reports and series over the past decade, many unanswered questions remain regarding the optimal application protocol. Furthermore, a major concern during phage therapy is the induction of phage neutralizing antibodies. This study aimed at providing a proof-of-concept of phage therapy in a clinically relevant rabbit model of fracture-related infection caused by Staphylococcus aureus. Phage therapy was applied as prophylaxis in a first phase, and as treatment of an established infection in a second phase. The development of phage neutralizing antibodies was evaluated in the treatment study. This study demonstrates that phage therapy can be useful in targeting orthopedic device-related infection, especially as prophylaxis; however, further research and improvements of these application methods are required.

Alterações hematológicas após implante de matriz óssea desmineralizada caprina em modelo de defeito ulnar crítico em coelhos

Objetivo Diversos modelos animais têm sido usados em estudos sobre enxertos ósseos e o tratamento de fraturas, mas as respostas hematológicas são raramente relatadas. Este estudo descreveu as alterações hematológicas observadas em coelhos submetidos a xenoenxertos de matriz óssea desmineralizada caprina (MODC).

Métodos Vinte e quatro (24) coelhos machos (2,5 ± 0,5 kg) foram adquiridos para este estudo e divididos aleatoriamente em três grupos: enxerto ósseo autólogo (EOA); controle negativo sem preenchimento (SP) e matriz óssea desmineralizada caprina (MODC). Amostras de sangue foram coletadas por punção cardíaca sob anestesia com xilazina-quetamina no dia 0 (para estabelecimento dos valores basais) e aos dias 28 e 56 após a cirurgia; essas amostras foram submetidas à análise manual em até 2 horas após a coleta. A análise estatística foi composta por análise de variância (ANOVA) de dois fatores com medidas repetidas, e o valor de p < 0,05 foi considerado significativo.

Resultados Houve uma diferença geral significativa nos números de leucócitos totais (p = 0,0043), neutrófilos (p < 0,0001), monócitos (p = 0,0184) e hemácias (p = 0,003), na concentração de hemoglobina (p < 0,0001) e no hematócrito (p < 0,0001) ao longo dos dias e entre os grupos de tratamento. No entanto, não houve diferença global significativa no número de linfócitos (p = 0,4923), basófilos (p = 0,4183) e eosinófilos (p = 0,4806) entre os dias.

Conclusão A resposta ao enxerto de MODC em coelhos é, portanto, caracterizada por leucocitose intensa com neutrofilia, linfocitose e monocitose no 28° dia após o procedimento. Esses dados podem basear a utilização da hematologia no monitoramento da resposta corporal em modelos animais de enxerto ósseo.

Copper coating formed by micro-arc oxidation on pure Mg improved antibacterial activity, osteogenesis, and angiogenesis in vivo and in vitro

Micro-arc oxidation (MAO) was used to improve the resistance of pure magnesium (Mg). Copper (Cu), a good antibacterial, angiogenic, and osteogenic element, was added by reaction in a Cu-containing electrolyte to improve the osteogenic and pro-angiogenic activities of Mg. The surface microstructures of the resulting MAO were evaluated by a scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) mapping. The release of Cu ions was detected by ICP-OES. The antibacterial activity of films with different concentrations of Cu ions was assessed against Staphylococcus aureus (S. aureus). The osteogenesis of films was confirmed by cell morphology and proliferation, ALP activity, alizarin red staining, and osteogenic-related gene expression in the MC3T3-E1 cell line. The angiogenesis of the films was tested in human umbilical vein endothelial cells (HUVECs) by cell migration, tube formation, and VEGF quantification in vitro, and by a chicken embryo chorioallantoic membrane (CAM) assay in vivo. The results showed that the microporous structure was shaped by MAO, and the Cu group was denser and more uniform. The Cu coating showed effective antibacterial activity against S. aureus while also enhancing osteogenesis and angiogenesis in vitro. According to the CAM assay, the Cu group showed not only biocompatibility but also a significant angiogenic response, which was consistent with in vitro studies. The findings indicate that a Cu coating on Mg-MAO enhances osteogenesis and angiogenesis.

An Improved 2-Aminoimidazole Based Anti-Biofilm Coating for Orthopedic Implants: Activity, Stability, and in vivo Biocompatibility

Orthopedic device-related infections remain a serious challenge to treat. Central to these infections are bacterial biofilms that form on the orthopedic implant itself. These biofilms shield the bacteria from the host immune system and most common antibiotic drugs, which renders them essentially antibiotic-tolerant. There is an urgent clinical need for novel strategies to prevent these serious infections that do not involve conventional antibiotics. Recently, a novel antibiofilm coating for titanium surfaces was developed based on 5-(4-bromophenyl)-N-cyclopentyl-1-octyl-1H-imidazol-2-amine as an active biofilm inhibitor. In the current study we present an optimized coating protocol that allowed for a 5-fold higher load of this active compound, whilst shortening the manufacturing process. When applied to titanium disks, the newly optimized coating was resilient to the most common sterilization procedures and it induced a 1 log reduction in biofilm cells of a clinical Staphylococcus aureus isolate (JAR060131) in vitro, without affecting the planktonic phase. Moreover, the antibiofilm effect of the coating in combination with the antibiotic cefuroxime was higher than cefuroxime treatment alone. Furthermore, the coating was successfully applied to a human-scale fracture fixation device resulting in a loading that was comparable to the titanium disk model. Finally, an in vivo biocompatibility and healing study in a rabbit osteotomy model indicated that these coated implants did not negatively affect fracture healing or osteointegration. These findings put our technology one step closer to clinical trials, confirming its potential in fighting orthopedic infections without compromising healing.

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.

An overview of de novo bone generation in animal models

Some of the earliest success in de novo tissue generation was in bone tissue, and advances, facilitated by the use of endogenous and exogenous progenitor cells, continue unabated. The concept of one health promotes shared discoveries among medical disciplines to overcome health challenges that afflict numerous species. Carefully selected animal models are vital to development and translation of targeted therapies that improve the health and well-being of humans and animals alike. While inherent differences among species limit direct translation of scientific knowledge between them, rapid progress in ex vivo and in vivo de novo tissue generation is propelling revolutionary innovation to reality among all musculoskeletal specialties. This review contains a comparison of bone deposition among species and descriptions of animal models of bone restoration designed to replicate a multitude of bone injuries and pathology, including impaired osteogenic capacity.

Focused high-energy extracorporeal shockwaves as supplemental treatment in a rabbit model of fracture-related infection

Focused high-energy extracorporeal shockwave therapy (fhESWT) is used to improve fracture healing in cases of nonunion. In addition, it has been shown to have direct antibacterial effects. We evaluated fhESWT as an adjunct to conventional treatment in a clinically relevant rabbit model of fracture-related infection (FRI). A humeral osteotomy in 31 rabbits was fixed with a seven-hole locking compression plate. FRI was established with a clinical Staphylococcus aureus isolate. After 2 weeks, a revision surgery was performed with debridement, irrigation, and implant retention. Rabbits then received: no further treatment (controls); shockwaves (4000 impulses with 23 kV at days 2 and 6 after revision); systemic antibiotics (rifampin and nafcillin); or the combination of antibiotics and shockwaves. Treatments were applied over 1 week. Blood cultures were taken before and after shockwave sessions. After another week without treatment, rabbits were euthanized and quantitative bacteriology was performed on implants and tissues to determine infection burden. Indicator organs (brain, heart, liver, lungs, kidneys, and spleen) were cultured to assess possible bacteremia. All the rabbits were infected at revision surgery as determined by the bacteriological culture of debrided materials. fhESWT in combination with antibiotic treatment lowered the bacterial burden 100-fold compared with antibiotic treatment alone in all samples (P = .38). This effect was most prevalent for the implant sample (P = .08). No significant effect was seen for fhESWT alone compared with untreated controls. No signs of bacteremia occurred in blood cultures and organs. fhESWT appears safe and could be a helpful adjunct to conventional treatment in certain difficult-to-treat FRIs.

Local Application of a Gentamicin-Loaded Hydrogel Early After Injury Is Superior to Perioperative Systemic Prophylaxis in a Rabbit Open Fracture Model

OBJECTIVES

Open fractures are at significant risk of developing a fracture-related infection, despite the routine administration of perioperative antibiotic prophylaxis. Early application of antibiotic prophylaxis is known to reduce infection rates; however, most international guidelines focus on postoperative duration rather than prehospital administration. We compared conventional perioperative prophylaxis against early prehospital prophylaxis either as a systemic single shot of cefuroxime or a locally applied gentamicin-loaded hydrogel in a laboratory animal model.

METHODS

Thirty New Zealand white rabbits underwent a first surgical procedure to create an open wound, bone damage and contamination with Staphylococcus aureus. After a 4-hour observation period mimicking the time-to-treatment, the animals underwent a second procedure to irrigate the wound and apply a fracture fixation device. The 5 groups (n = 6 per group) received (1) no treatment; (2) conventional 24-hour cefuroxime; (3) an early single shot of cefuroxime 15 minutes after trauma; (4) a combined early and standard systemic prophylaxis; and (5) early application of a gentamicin-loaded hydrogel that was removed during irrigation.

RESULTS

Untreated animals displayed high numbers of bacteria in irrigation fluid and were all highly culture positive at euthanasia. Three of 6 animals were culture positive at euthanasia after conventional prophylaxis. Early systemic prophylaxis reduced bacterial burden in irrigation fluid by up to 100-fold, but 5/6 animals were culture positive at euthanasia. The combined prophylaxis displayed greater efficacy with only 1/6 rabbits culture positive at euthanasia. Local application of the gentamicin-loaded hydrogel reduced bacteria recovered by irrigation to just above our detection limit, and at euthanasia, all animals were culture negative at euthanasia.

CONCLUSIONS

Early systemic antibiotic administration can significantly reduce bacterial burden in the operative field and reduce culture positivity at euthanasia when continued for 24 hours after injury. The early application of a gentamicin-loaded hydrogel that was removed during irrigation displayed superior efficacy to early systemic therapy alone and postoperative conventional gold standard 24-hour systemic therapy alone. These experimental results highlight the importance of early antibiotic administration in fracture care.

Antimicrobial silver-coating for locking plates shows uneventful osteotomy healing and good biocompatibility results of an experimental study in rabbits

Infections after internal fixation of fractures remain a challenge. Silver is known for its antimicrobial activity, including activity against multi-resistant strains. The aim of the current study was to analyze the biocompatibility and potential influence on the osteotomy healing process of a silver-coating technology for locking plates compared to silver-free locking plates in an established rabbit model. The implants used in this study were 7-hole titanium locking plates, and plasma electrolytic oxidation (PEO) silver-coated equivalents. A total of 24 rabbits were used in this study (12 coated, 12 non-coated). An osteotomy of the midshaft of the humerus was created and the humerus stabilized with the 7-hole locking plates with a total of 6 screws. Radiographs were taken on day 0, week 2, 4, 6, 8, and 10 for continuous radiographical evaluation. All animals were euthanized after 10 weeks and further assessment was performed using X-rays, micro-CT, non-destructive four-point bending biomechanical testing and semi-quantitative histopathological evaluation. Furthermore, silver concentration was measured in the blood, kidney, liver, spleen, brain, feces and soft tissue around the plate. Radiographs showed normal undisturbed and completed healing of the osteotomy in all animals without any differences between the two groups over the entire observation period. Micro-CT analysis revealed overall tissue volume as well as tissue density to be comparable between the two groups. Mechanical testing showed comparable stiffness with an average stiffness relative to contralateral bones of 75.7 ± 16.1% in the silver-free control group compared to 69.7 ± 18.5% (p-value: 0.46). Semi-quantitative histopathological evaluation showed no remarkable difference in the analysis of the osteotomy gap healing or in the surrounding soft tissue area. There were detectable silver concentrations in the soft tissue around the plate after 10 weeks. Silver in the blood was only found in 3 animals within the first two weeks and all animals were free of silver afterwards. There were no detectable silver concentrations in the brain, liver, spleen, axillary lymph nodes and kidney. This study shows undisturbed osteotomy healing of the presented antimicrobial silver surface coating and a good biocompatibility in this rabbit model.

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.

Releasing Behavior of Lipopolysaccharide from Gelatin Modulates Inflammation, Cellular Senescence, and Bone Formation in Critical-Sized Bone Defects in Rat Calvaria

Lipopolysaccharide (LPS) is a well-known strong inducer of inflammation. However, there is little information regarding how LPS-release behavior affects cellular senescence at the affected area. In this paper, we demonstrate that a vacuum-heating technique (dehydrothermal treatment) can be utilized to prepare an LPS sustained-release gelatin sponge (LS-G). LPS sustained release from gelatin leads to the long-term existence of senescent cells in critical-sized bone defects in rat calvaria. Three types of gelatin sponges were prepared in this study: a medical-grade gelatin sponge with extremely low LPS levels (MG), LS-G, and a LPS rapid-release gelatin sponge (LR-G). Histological (H-E) and immunohistochemical (COX-2, p16, and p21) staining were utilized to evaluate inflammatory reactions and cellular senescence one to three weeks after surgery. Soft X-ray imaging was utilized to estimate new bone formation in the defects. The LR-G led to stronger swelling and COX-2 expression in defects compared to the MG and LS-G at 1 week. Despite a small inflammatory reaction, LS-G implantation led to the long-term existence of senescent cells and hampered bone formation compared to the MG and LR-G. These results suggest that vacuum heating is a viable technique for preparing different types of materials for releasing bacterial components, which is helpful for developing disease models for elucidating cellular senescence and bone regeneration.

Impact of Bacterial Infections on Osteogenesis: Evidence From In Vivo Studies

The clinical impact of bacterial infections on bone regeneration has been incompletely quantified and documented. As a result, controversy exists about the optimal treatment strategy to maximize healing of a contaminated defect. Animal models are extremely useful in this respect, as they can elucidate how a bacterial burden influences quantitative healing of various types of defects relative to non-infected controls. Moreover, they may demonstrate how antibacterial treatment and/or bone grafting techniques facilitate the osteogenic response in the harsh environment of a bacterial infection. Finally, it a well-known contradiction that osteomyelitis is characterized by uncontrolled bone remodeling and bone loss, but at the same time, it can be associated with excessive new bone apposition. Animal studies can provide a better understanding of how osteolytic and osteogenic responses are related to each other during infection. This review discusses the in vivo impact of bacterial infection on osteogenesis by addressing the following questions (i) How does osteomyelitis affect the radiographic bone appearance? (ii) What is the influence of bacterial infection on histological bone healing? (iii) How do bacterial infections affect quantitative bone healing? (iv) What is the effect of antibacterial treatment on the healing outcome during infection? (v) What is the efficacy of osteoinductive proteins in infected bones? (vi) What is the balance between the osteoclastic and osteoblastic response during bacterial infections? (vii) What is the mechanism of the observed pro-osteogenic response as observed in osteomyelitis? © 2019 The Authors. Journal of Orthopaedic Research^© published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 37:2067-2076, 2019.

Exotic Mammal Orthopedics

Orthopedic disorders are a common clinical presentation for the exotic clinician. Before treating the fracture it is vital to stabilize the patient. Small exotic mammals are characterized by relatively thinner bones, adding to the difficulty the small size already represents. A combination of conservative and surgical treatment options are available. The principles of orthopedic surgery and ideas behind the treatment options remain the same as for small mammals, but not all techniques can be directly extrapolated. Historically, the tie-in fixator has been the preferred surgical choice whenever feasible, but further development in bone plates represents a promising advancement.

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.

Recommendations for design and conduct of preclinical in vivo studies of orthopedic device-related infection

Orthopedic device-related infection (ODRI), including both fracture-related infection (FRI) and periprosthetic joint infection (PJI), remain among the most challenging complications in orthopedic and musculoskeletal trauma surgery. ODRI has been convincingly shown to delay healing, worsen functional outcome and incur significant socio-economic costs. To address this clinical problem, ever more sophisticated technologies targeting the prevention and/or treatment of ODRI are being developed and tested in vitro and in vivo. Among the most commonly described innovations are antimicrobial-coated orthopedic devices, antimicrobial-loaded bone cements and void fillers, and dual osteo-inductive/antimicrobial biomaterials. Unfortunately, translation of these technologies to the clinic has been limited, at least partially due to the challenging and still evolving regulatory environment for antimicrobial drug-device combination products, and a lack of clarity in the burden of proof required in preclinical studies. Preclinical in vivo testing (i.e. animal studies) represents a critical phase of the multidisciplinary effort to design, produce and reliably test both safety and efficacy of any new antimicrobial device. Nonetheless, current in vivo testing protocols, procedures, models, and assessments are highly disparate, irregularly conducted and reported, and without standardization and validation. The purpose of the present opinion piece is to discuss best practices in preclinical in vivo testing of antimicrobial interventions targeting ODRI. By sharing these experience-driven views, we aim to aid others in conducting such studies both for fundamental biomedical research, but also for regulatory and clinical evaluation. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:271-287, 2019.

Collagen scaffolds functionalised with copper-eluting bioactive glass reduce infection and enhance osteogenesis and angiogenesis both in vitro and in vivo

The bone infection osteomyelitis (typically by Staphylococcus aureus) usually requires a multistep procedure of surgical debridement, long-term systemic high-dose antibiotics, and - for larger defects - bone grafting. This, combined with the alarming rise in antibiotic resistance, necessitates development of alternative approaches. Herein, we describe a one-step treatment for osteomyelitis that combines local, controlled release of non-antibiotic antibacterials with a regenerative collagen-based scaffold. To maximise efficacy, we utilised bioactive glass, an established osteoconductive material with immense capacity for bone repair, as a delivery platform for copper ions (proven antibacterial, angiogenic, and osteogenic properties). Multifunctional collagen-copper-doped bioactive glass scaffolds (CuBG-CS) were fabricated with favourable microarchitectural and mechanical properties (up to 1.9-fold increase in compressive modulus over CS) within the ideal range for bone tissue engineering. Scaffolds demonstrated antibacterial activity against Staphylococcus aureus (up to 66% inhibition) whilst also enhancing osteogenesis (up to 3.6-fold increase in calcium deposition) and angiogenesis in vitro. Most significantly, when assessed in a chick embryo in vivo model, CuBG-CS not only demonstrated biocompatibility, but also a significant angiogenic and osteogenic response, consistent with in vitro studies. Collectively, these results indicate that the CuBG-CS developed here show potential as a one-step osteomyelitis treatment: reducing infection, whilst enhancing bone healing.

An antibiofilm coating of 5-aryl-2-aminoimidazole covalently attached to a titanium surface

Biofilms, especially those formed by Staphylococcus aureus, play a key role in the development of orthopedic implant infections. Eradication of these infections is challenging due to the elevated tolerance of biofilm cells against antimicrobial agents. In this study, we developed an antibiofilm coating consisting of 5-(4-bromophenyl)-N-cyclopentyl-1-octyl-1H-imidazol-2-amine, designated as LC0024, covalently bound to a titanium implant surface (LC0024-Ti). We showed in vitro that the LC0024-Ti surface reduces biofilm formation of S. aureus in a specific manner without reducing the planktonic cells above the biofilm, as evaluated by plate counting and fluorescence microscopy. The advantage of compounds that only inhibit biofilm formation without affecting the viability of the planktonic cells, is that reduced development of bacterial resistance is expected. To determine the antibiofilm activity of LC0024-Ti surfaces in vivo, a biomaterial-associated murine infection model was used. The results indicated a significant reduction in S. aureus biofilm formation (up to 96%) on the LC0024-Ti substrates compared to pristine titanium controls. Additionally, we found that the LC0024-Ti substrates did not affect the attachment and proliferation of human cells involved in osseointegration and bone repair. In summary, our results emphasize the clinical potential of covalent coatings of LC0024 on titanium implant surfaces to reduce the risk of orthopedic implant infections. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1908-1919, 2019.

Time-dependent differences in management and microbiology of orthopaedic internal fixation-associated infections: an observational prospective study with 229 patients

OBJECTIVES

Little information has been published on orthopaedic internal fixation-associated infections. We aimed to analyse time-dependent microbiology, treatment, and outcome.

METHODS

Over a 10-year period, all consecutive patients with internal fixation-associated infections at the University Hospital of Basel, were prospectively followed and clinical, microbiological and outcome data were acquired. Infections were classified as early (0-2 weeks after implantation), delayed (3-10 weeks), and late (>10 weeks).

RESULTS

Two hundred and twenty-nine patients were included, with a median follow-up of 773 days (IQR 334-1400). Staphylococcus aureus was the most prevalent pathogen (in 96/229 patients, 41.9%). Enterobacteriaceae were frequent in early infections (13/49, 26.5%), whereas coagulase-negative staphylococci (36/92, 39.1%), anaerobes (15/92, 16.3%) and streptococci (10/92, 10.9%) increased in late revisions. Failure was observed in 27/229 (11.7%). Implants were retained in 42/49 (85.7%) in early, in 51/88 (57.9%) in delayed, and in 9/92 (9.8%) in late revisions (p < 0.01). Early revisions failed in 6/49 (12.2%), delayed in 9/88 (10.2%), and late in 11/92 (13.0%) (p 0.81). Debridement and retention failed in 6/42 (14.3%) for early, in 6/51 (11.8%) for delayed, and in 3/9 (33.3%) for late revisions (p 0.21). Biofilm-active antibiotic therapy tailored to resistance correlated with improved outcome for late revisions failure (6/72, 7.7% versus 6/12, 50.0%; p < 0.01) but not for early revisions failure (5/38, 13.2% versus 1/11, 9.1%; p 1.0).

CONCLUSIONS

Treatment of internal fixation-associated infections showed a high success rate of 87-90% over all time periods. Implant retention was highly successful in early and delayed infections but only limited in late infections.

Antibiotic Prophylaxis With Cefuroxime: Influence of Duration on Infection Rate With Staphylococcus aureus in a Contaminated Open Fracture Model

OBJECTIVES

The optimal duration of perioperative antibiotic prophylaxis (PAP) for open fractures remains controversial because of heterogeneous or unclear guidelines and highly variable prophylactic regimens in clinical practice. We aimed at testing different PAP durations under controlled conditions in a contaminated rabbit fracture model.

METHODS

A complete humeral osteotomy in 18 rabbits was fixed with a 7-hole locking compression plate and inoculated with Staphylococcus aureus. Cefuroxime was administered in a weight-adjusted dosage equivalent to human medicine (18.75 mg/kg). PAP was administered as a single shot only; for 24 hours; or for 72 hours in separate groups of rabbits (n = 6 per group). Infection was assessed after 2 weeks by quantitative bacteriological evaluation of the tissues and hardware.

RESULTS

Postoperative duration of PAP had a significant impact on the success of antibiotic prophylaxis in this model. Whereas the single-shot regimen completely failed to prevent infection, the 24-hour regimen showed a reduced infection rate (1 of 6 rabbits infected), but only the 72-hour course was able to prevent fracture-related infection in all animals in our model.

CONCLUSIONS

When contamination with high bacterial loads is likely (eg, in an open fracture situation), a 72-hour course of intravenous cefuroxime seems to be superior in preventing fracture-related infection in our rabbit model compared with a single-shot or 24-hour antibiotic regimen.

Infection after fracture fixation: Current surgical and microbiological concepts

One of the most challenging complications in trauma surgery is infection after fracture fixation (IAFF). IAFF may result in permanent functional loss or even amputation of the affected limb in patients who may otherwise be expected to achieve complete, uneventful healing. Over the past decades, the problem of implant related bone infections has garnered increasing attention both in the clinical as well as preclinical arenas; however this has primarily been focused upon prosthetic joint infection (PJI), rather than on IAFF. Although IAFF shares many similarities with PJI, there are numerous critical differences in many facets including prevention, diagnosis and treatment. Admittedly, extrapolating data from PJI research to IAFF has been of value to the trauma surgeon, but we should also be aware of the unique challenges posed by IAFF that may not be accounted for in the PJI literature. This review summarizes the clinical approaches towards the diagnosis and treatment of IAFF with an emphasis on the unique aspects of fracture care that distinguish IAFF from PJI. Finally, recent developments in anti-infective technologies that may be particularly suitable or applicable for trauma patients in the future will be briefly discussed.

Definition of infection after fracture fixation: A systematic review of randomized controlled trials to evaluate current practice

INTRODUCTION

One of the most challenging musculoskeletal complications in modern trauma surgery is infection after fracture fixation (IAFF). Although infections are clinically obvious in many cases, a clear definition of the term IAFF is crucial, not only for the evaluation of published research data but also for the establishment of uniform treatment concepts. The aim of this systematic review was to identify the definitions used in the scientific literature to describe infectious complications after internal fixation of fractures. The hypothesis of this study was that the majority of fracture-related literature do not define IAFF.

MATERIAL AND METHODS

A comprehensive search was performed in Embase, Cochrane, Google Scholar, Medline (OvidSP), PubMed publisher and Web-of-Science for randomized controlled trials (RCTs) on fracture fixation. Data were collected on the definition of infectious complications after fracture fixation used in each study. Study selection was accomplished through two phases. During the first phase, titles and abstracts were reviewed for relevance, and the full texts of relevant articles were obtained. During the second phase, full-text articles were reviewed. All definitions were literally extracted and collected in a database. Then, a classification was designed to rate the quality of the description of IAFF.

RESULTS

A total of 100 RCT's were identified in the search. Of 100 studies, only two (2%) cited a validated definition to describe IAFF. In 28 (28%) RCTs, the authors used a self-designed definition. In the other 70 RCTs, (70%) there was no description of a definition in the Methods section, although all of the articles described infections as an outcome parameter in the Results section.

CONCLUSION

This systematic review shows that IAFF is not defined in a large majority of the fracture-related literature. To our knowledge, this is the first study conducted with the objective to explore this important issue. The lack of a consensus definition remains a problem in current orthopedic trauma research and treatment and this void should be addressed in the near future.

Examining the association of MMP-1 gene -1607 (2G/1G) and -519 (A/G) polymorphisms with the risk of osteomyelitis: A case-control study

To investigate the effects of matrix metalloproteinase-1 (MMP-1) gene polymorphisms on the onset of osteomyelitis in Chinese Han population.In all, 80 osteomyelitis patients (case group) and 81 healthy people (control group) were recruited into this case-control study. Polymerase chain reaction-restriction fragment length polymorphism method was utilized to examine the genotypes of MMP-1 polymorphisms (-1607 2G/1G and -519A/G) in the 2 groups. Genotype and allele differences between the case and control groups were analyzed by chi-square test. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated to present the association strength between MMP-1 gene polymorphisms and osteomyelitis.Frequencies of -1607 2G/2G genotype between the case and control groups were statistically significant (P = .025). Compared with 1G/1G genotype carriers, the 2G/2G genotype carriers had 1.605 times risk of developing osteomyelitis (OR 2.605, 95% CI 1.116-6.082). Meanwhile, the 2G allele significantly associated with the risk of osteomyelitis (OR 1.735, 95% CI 1.115-2.701). In addition, frequency of -519GG genotype was obviously higher in case group than that in control group (P = .024), and GG genotype related to an increased risk of osteomyelitis (OR 2.792, 95% CI 1.127-6.917). Whereas, the -519G allele may be a susceptible factor for osteomyelitis (OR 1.622, 95% CI 1.038-2.536).The MMP-1 -1607 (2G/1G) and -519 (A/G) polymorphisms may contribute to the onset of osteomyelitis.

Injectable gentamicin-loaded thermo-responsive hyaluronic acid derivative prevents infection in a rabbit model

Despite the use of systemic antibiotic prophylaxis, the surgical fixation of open fractures with osteosynthesis implants is associated with high infection rates. Antibiotic-loaded biomaterials (ALBs) are increasingly used in implant surgeries across medical specialties to deliver high concentrations of antibiotics to the surgical site and reduce the risk of implant-associated infection. ALBs which are either less or not restricted in terms of spatial distribution and which may be applied throughout complex wounds could offer improved protection against infection in open fracture care. A thermo-responsive hyaluronic acid derivative (hyaluronic acid-poly(N-isopropylacrylamide) (HApN)) was prepared by a direct amidation reaction between the tetrabutyl ammonium (TBA) salt of hyaluronic acid and amine-terminated poly(N-isopropylacrylamide) (pN). The degree of grafting, and gelation properties of this gel were characterized, and the composition was loaded with gentamicin. The rheological- and release properties of this gentamicin-loaded HApN composition were tested in vitro and its efficacy in preventing infection was tested in a rabbit model of osteosynthesis contaminated with Staphylococcus aureus. The gentamicin-loaded HApN composition was able to prevent bacterial colonization of the implant site as shown by quantitative bacteriology. This finding was supported by histopathological evaluation of the humeri samples where no bacteria were found in the stained sections. In conclusion, this gentamicin-loaded HApN hydrogel effectively prevents infection in a complex wound, simulating a contaminated fracture treated with plating osteosynthesis.

STATEMENT OF SIGNIFICANCE

Fracture fixation after trauma is associated with high infection rates. Antibiotic loaded biomaterials (ALBs) can provide high local concentrations without systemic side effects. However, the currently available ALBs have limited accessibility to contaminated tissues in open fractures because of predetermined shape. Thus, a novel thermo-responsive hyaluronan based hydrogel with control over gelation temperature is reported. The efficacy of this gentamicin loaded hyaluronan derivative is demonstrated in an in vivo fracture model in the presence of fracture fixation hardware. The bacterial burden is cleared in all of the inoculated rabbits in the presence of the ALB. Thus, the proposed injectable thermo-responsive hyaluronan presents an effective ALB for the prevention of infection.

Titanium and steel fracture fixation plates with different surface topographies: Influence on infection rate in a rabbit fracture model

INTRODUCTION

Implant-related infection is a challenging complication in musculoskeletal trauma surgery. In the present study, we examined the role of implant material and surface topography as influencing factors on the development of infection in an experimental model of plating osteosynthesis in the rabbit.

METHODS

The implants included in this experimental study were composed of: standard Electropolished Stainless Steel (EPSS), standard titanium (Ti-S), roughened stainless steel (RSS) and surface polished titanium (Ti-P). Construct stability and load-to-failure of Ti-P implants was compared to that of Ti-S implants in a rabbit cadaveric model. In an in vivo study, a rabbit humeral fracture model was used. Each rabbit received one of three Staphylococcus aureus inocula, aimed at determining the infection rate at a low, medium and high dose of bacteria. Outcome measures were quantification of bacteria on the implant and in the surrounding tissues, and determination of the infectious dose 50 (ID50).

RESULTS

No significant differences were observed between Ti-S and Ti-P regarding stiffness or failure load in the cadaver study. Of the 72 rabbits eventually included in the in vivo study, 50 developed an infection. The ID50 was found to be: EPSS 3.89×10(3) colony forming units (CFU); RSS 8.23×10(3) CFU; Ti-S 5.66×10(3) CFU; Ti-P 3.41×10(3) CFU. Significantly lower bacterial counts were found on the Ti-S implants samples compared with RSS implants (p<0.001) at the high inoculum. Similarly, lower bacterial counts were found in the bone samples of animals in the Ti-S group in comparison with both RSS and EPSS groups, again at the high inoculation dose (p<0.005).

CONCLUSION

No significant differences were seen in susceptibility to infection when comparing titanium and steel implants with conventional or modified topographies. Ti-P implants, which have previously been shown in preclinical studies to reduce complications associated with tissue adherence, do not affect infection rate in this preclinical fracture model. Therefore, Ti-P implants are not expected to affect the infection rate, or influence implant stability in the clinical situation.

Animal Models of Implant-Related Low-Grade Infections. A Twenty-Year Review

The demand for joint replacement and surgical treatment is continuously increasing, thus representing a clinical burden and a cost for the healthcare system. Among several pathogens involved in implant-related infections, staphylococci account for the two-thirds of clinically isolated bacteria. Despite most of them are highly virulent microorganisms (Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa), low virulent bacteria (Staphylococcus epidermidis, Propionibacterium acnes) are responsible for delayed, low-grade infections without specific clinical signs and hardly distinguishable from aseptic prosthetic failure. Therefore, there is a real need to study the pathogenesis of orthopedic infections through in vivo animal models. The present review of the literature provides a 20-year overview of animal models of acute, subclinical or chronic orthopedic infections according to the pathogen virulence and inocula. Through this analysis, a great variety of conditions in terms of bacterial strains and inocula emerged, thus encouraging the development of more reproducible in vivo studies to provide relevant information for a translational approach to humans.