Tendinopathy is a debilitating musculoskeletal condition which can cause significant pain and lead to complete rupture of the tendon, which often requires surgical repair. Due in part to the large spectrum of tendon pathologies, these disorders continue to be a clinical challenge. Animal models are often used in this field of research as they offer an attractive framework to examine the cascade of processes that occur throughout both tendon pathology and repair. This review discusses the structural, mechanical, and biological changes that occur throughout tendon pathology in animal models, as well as strategies for the improvement of tendon healing. Cite this article: Bone Joint Res 2014;3:193–202

Aim. Treatment of infected and non-infected non-unions remain a major challenge after orthopedic fracture-related surgery. In clinical practice, several revision surgeries are usually required, including a radical debridement and exchange of implants, to control or even eradicate the infection to finally achieve bone healing. However, a clear treatment algorithm in clinical practice may be difficult to follow due to the heterogeneous patient population. Thus, so controlled settings for research purposes is better achieved in standardized animal studies. So far, there exists no multi-stage animal model that can be realistically transferred to the clinical situation in humans. The importance of such a model is obvious in order to be able to investigate different therapy concepts for infected and non-infected non unions. Methods. In 20 female Sprague-Dawley rats, a critical size defect by a femur osteotomy with 5 mm width was done. The periosteum at the fracture zone was cauterized proximal and distal to the osteotomy to achieve an hypovascularized situation. After randomization, 10 animals were intramedullary infected with a multisensible Staph. aureus strain (10. 3. CFU). After 5 weeks, a second surgery was performed with removing the K-wire, debridement of the osteotomy-gap and re-osteosynthesis with an angle-stable plate. After further 8 weeks all rats were euthanized and underwent biomechanical testing to evaluate bone consolidation or delayed union, respectively. Additional micro-CT analysis, histological, and histomorphometric analysis were done to evaluate bone consolidation or delayed union, respectively, by the score of Lane and Sandhu and to quantify callus formation and the mineralized area of the callus. Results. 5 weeks after the first surgery a non-union had formed in all septic and aseptic animals. According to the Lane and Sandhu score a significantly higher callus formation was found in the infected group. In all infected animals, the inoculated Staph. aureus strain was detected during the revision surgery. 8 weeks after the second surgery no bone healing could be detected in the µ-CT analysis in both groups and biomechanical testing showed a significant lower maximum torque in both groups as compared to the untreated contralateral femura. Conclusion. Here we show first results of a new two-stage pseudarthrosis animal model, which reflects a very realistic clinical situation of an infection-related non-union model. Based on this model, various therapeutic strategies in the treatment of infectious and non-infectious pseudarthrosis, such as the use of bone substitutes, can be evaluated in further studies

The Masquelet or induced membrane technique (IMT) is a two-stage surgical procedure used for the treatment of segmental bone defects. In this technique, the defect is first filled with a polymethyl methacrylate (PMMA) spacer, which triggers the formation of a membrane that will encapsulate the defect. During the second surgery, the spacer is carefully removed and replaced by autologous bone graft while preserving the membrane. This membrane is vascularized, contains growth factors, and provides mechanical stability to the graft, all of which are assumed to prevent graft resorption and promote bone healing. The technique is gaining in popularity and several variations have been introduced in the clinical practice. For instance, orthopaedic surgeons now often include antibiotics in the spacer to treat or prevent infection. However, the consequences of this approach on the properties of the induce membrane are not fully understood. Accordingly, in a small animal model, this study aimed to determine the impact on the induced membrane of impregnating spacers with antibiotics frequently used in the IMT. We surgically created a five-mm segmental defect in the right femur of 25 adult male Sprague Dawley rats. The bone was stabilized with a plate and screws before filling the defect with a PMMA spacer. Animals were divided into five equal groups according to the type and dose of antibiotics impregnated in the spacer: A) no antibiotic (control), B) low-dose tobramycin (1.2 g/40 g of PMMA), C) low-dose vancomycin (1 g/40 g of PMMA), D) high-dose tobramycin (3.6 g/40 g of PMMA), E) high-dose vancomycin (3 g/40 g of PMMA). The animals were euthanized three weeks after surgery and the induced membranes were collected and divided for analysis. We assessed the expression of selected genes (Alpl, Ctgf, Runx2, Tgfb1, Vegfa) within the membrane by quantitative real-time PCR. Moreover, frozen sections of the specimens were used to quantify vascularity by immunohistochemistry (CD31 antigen), proliferative cells by immunofluorescence (Ki-67 antigen), and membrane thickness. Microscopic images of the entire tissue sections were taken and analyzed using FIJI software. Finally, we measured the concentration of vascular endothelial growth factor (VEGF) in the membranes by ELISA. No significant difference was found among the groups regarding the expression of genes related to osteogenesis (Alpl, Runx2), angiogenesis (Vegfa), or synthesis of extracellular matrix (Ctgf, Tgfb1) (n = four or five). Similarly, the density of proliferative cells and blood vessels within the membrane, as well as the membrane thickness, did not vary substantially between the control, low-dose, or high-dose antibiotic groups (n = four or five). The concentration of VEGF was also not significantly influenced by the treatment received (n = four or five). The addition of tobramycin or vancomycin to the spacer, at the defined low and high doses, does not significantly alter the bioactive characteristics of the membrane. These results suggest that orthopaedic surgeons could use antibiotic-impregnated spacers for the IMT without compromising the induced membrane and potentially bone healing

Aim. A gentamicin-eluting biocomposite consisting of hydroxyapatite and calcium sulfate. 1. can provide effective dead space management in chronic osteomyelitis. However, radiographic follow-up after implantation of this novel material has consistently shown evidence of several unique imaging features previously not described with other comparable bone graft substitutes. Conclusive interpretation of these newly described imaging features is difficult as long term follow-up and histological correlation is not yet available. The aim of this study was to establish a large animal model, closely simulating the clinical situation in order to permit further analysis of imaging features in correlation with histological progression of bone remodelling. Method. Standardised bone defects were created in ten Merino-wool sheep (age: two to four years). Large drill holes (diameter 2.5cm, depth 2cm, volume approx. 10ml) were placed in the medial femoral condyles of both hind legs and filled with a gentamicin antibiotic eluting bone graft substitute. *. Initially surgery was carried out on the right hind leg. Three months later, an identical intervention was performed on the contralateral side. With sacrifice planned after six or twelve months, bone voids three, six, nine and twelve months post-implantation are obtained for evaluation. The study was approved by the Animal Care Committee of Thuringia, Germany. Results. We present our preliminary radiographic results after a follow-up of six months. The bio-composite was clearly visible on all initial post-operative radiographs, showing intimate contact to the surrounding cancellous bone of the distal femur. At one month, a radio-dense ring around the bone void (the so called “halo sign”) was found in four of six bone voids treated with the biocomposite. From 2 months onwards this “halo” typically appeared to progress towards the centre of the treated defects, where spherical remnants of the composite often become increasingly apparent. This pattern has been termed “marble sign” and often appears in combination with the halo-sign. Between three to six months bone remodelling appears to continue, halo- and marble sign increasingly disappear and the composite becomes more and more indistinct from surrounding cancellous bone. Conclusions. We have established a large animal model, which appears to mimic the clinical situation very well and reproduces comparable radiographic post implantation features previously observed and described in clinical cases (including the “halo” and the “marble” sign). We expect that this model will provide valuable information regarding the correlation between histological and basic & advanced imaging features (including MRI, CT and Dexa scans) in the future

Aim. A gentamicin-eluting biocomposite consisting of hydroxyapatite (HA) and calcium sulphate (CaS)*1 can provide effective dead space management and bone formation in chronic osteomyelitis. However, radiographic follow-up after implantation of this biomaterial has shown imaging features previously not described with other comparable bone graft substitutes. Last year we presented preliminary results with a follow-up of 6 months. Now we present the radiographic, µCT and histological one-year follow-up of the critical-size bone defect model in sheep. The aim of this study was to simulate the clinical situation in a large animal model to correlate different imaging techniques used in the clinic (Radiography, CT and MRI scans) with histological finding. Methods. Standardised bone defects were created in ten Merino-wool sheep (age two to four years). Large drill holes (diameter 2.5cm, depth 2cm, volume approx. 10ml) were placed in the medial femoral condyles of both hind legs and filled with gentamicin-eluting biocomposite. Initially surgery was carried out on the right hind leg. Three months later, an identical intervention was performed on the contralateral side. Animals were sacrificed at three and six weeks and 4.5, six and twelve months. Radiographs and MRI scans were taken immediately after sacrifice. Filled bone voids were harvested en-block and analysed using µCT, and histology. Results. We present our radiographic, µCT and histological results after a follow-up of twelve months. The bio-composite was clearly visible on all post-operative radiographs and resorbed over the next four months following the before described pattern of “halo sign” and “marble sign”. µCT images of the “halo sign” show degradation of the biocomposite starting at its surface, with the degradation products CaS and HA carried into the periphery of the bone void. µCT images of the “marble sign” showed the further degradation of the biocomposite from the surface to its core, leaving a “marble shaped” remnant of the biocomposite behind. These remnants are completely resorbed at 4.5 months. µCT scans at twelve and six months' reveal progression of trabecula bone formation. The histological results confirm the µCT findings. Conclusion. We have established a large animal model, which mimics the clinical situation and reproduces comparable radiographic post implantation features previously observed in clinical cases (including the “halo” and the “marble” sign). Using µCT imaging and histology we can describe and understand the biodegradation process and the bone formation capacity of the biocomposite in detail. *1 CERAMENTTM|G, BONESUPPORT, Lund, Sweden. *2 CERAMENTTM|G

Aim. Implant-associated osteomyelitis is a devastating complication with poor outcomes following treatment, especially when caused by antibiotic-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA). A large animal model of a two-stage revision to treat MRSA implant-associated osteomyelitis has been developed to assess novel treatments. A bioresorbable, thermo-responsive hyaluronan hydrogel (THH) loaded with antibiotics has been developed and our aim was to investigate it´s in vivo efficacy as a local antibiotic carrier compared to the current standard of care i.e. antibiotic-loaded polymethylmethacrylate (PMMA) bone cement. Method. 12 female, 2 to 4 year old, Swiss Alpine Sheep were inoculated with MRSA at the time of intramedullary nail insertion in the tibia to develop chronic osteomyelitis. After 8 weeks sheep received a 2-stage revision protocol, with local and systemic antibiotics. Group 1 received the gold standard clinical treatment: systemic vancomycin (2 weeks) followed by rifampicin plus trimethoprim/sulfamethoxazole (4 weeks), and local gentamicin/vancomycin via PMMA. Group 2 received local gentamicin/vancomycin delivered via THH at both revision surgeries and identical systemic therapy to group 1. Sheep were euthanized 2 weeks following completion of antibiotic therapy. At euthanasia, soft tissue, bone, and sonicate fluid from the hardware was collected for quantitative bacteriology. Results. Sheep tolerated the surgeries and both local and systemic antibiotics well. Gold standard of care successfully treated 3/6 sheep with a total of 10/30 culture-positive samples. All 6 sheep receiving antibiotic-loaded THH were successfully treated with 0/30 culture-positive samples, p=0.0008 gold-standard vs. hydrogel (Fisher's Exact). Conclusions. The clinical gold standard treatment was successful in 50% of sheep, consistent with outcomes reported in the literature treating MRSA infection. The antibiotic-loaded THH clearly outperformed the gold standard in this model. Superior efficacy of the THH is likely due to 1) the ability to administer local antibiotics at the both revision surgies due to the bioresorbable nature of the hydrogel, and 2) complete antibiotic release compared to bone cement, which is known to retain antibiotics. Our results highlight the potential of local delivered, biodegradable systems for antibiotics for eradicating implant-related infection caused by antibiotic-resistant pathogens. Acknowledgement. Funding provided by AO Trauma

Aim

In trauma surgery, the development of biomaterial-associated infections (BAI) is one of the most common complications affecting trauma patients, requiring prolonged hospitalization and the intensive use of antibiotics. Following the attachment of bacteria on the surface of the biomaterial, the biofilm-forming bacteria could initiate a chronic implant-related infection. Despite the use of conventional local and systemic antibiotic therapies, persistent biofilms involve various resistance mechanisms that contribute to therapeutic failures. The development of in vivo chronic BAI models to optimize antibiofilm treatments is a major challenge. Indeed, the biofilm pathogenicity and the host response need to be finely regulated, and compatible with the animal lifestyle. Previously, a Galleria mellonella larvae model for the formation of an early-stage biofilm on the surface of a Kirschner (K)-wire was established. In the present study, two models of mature biofilm using clinical Staphylococcus aureus strains were assessed: one related to contaminated K-wires (in vitro biofilm maturation) and the second to hematogenous infections (in vivo biofilm maturation). Rifampicin was used as a standard drug for antibiofilm treatment.

Purpose

Nucleus pulposus (NP) replacements represent a less invasive alternative for treatment of early stage degenerative disc disease (DDD). Hydrogel based NP replacements are of particular interest as they can be injected/implanted using minimally invasive surgical (MIS) techniques to re-establish mechanical integrity and as a scaffold for regeneration. A thiol-modified hyaluronan elastin-like polypeptide (TMHA/EP) hydrogel crosslinked using polyethylene diacrylate has shown promise as a potential NP replacement for DDD in vitro. This study aims to assess the mechanical properties of this hydrogel when injected into an induced early stage DDD porcine model and to determine the optimal injection method for delivery. It is hypothesized that minimally invasive injection of the TMHA/EP material can restore mechanical behaviour of spinal motion segments in early stage DDD.

Ten percent of fractures end in delayed or non-union. NSAIDs have been linked to an inhibitory action on fracture repair for three decades yet the mechanism of action remains to be elucidated. Cancer research has identified that NSAIDs impede cell proliferation by inhibiting angiogenesis. It is proposed that a similar mechanism occurs in the induction of NSAID induced non-union. We have investigated this hypothesis in a randomised placebo control trial of the NSAID rofecoxib using a murine femoral fracture.

All animals had an open femoral fracture treated using an external fixator. Outcomes measures included x-ray, histology and biomechanical testing, with laser Doppler used to assess blood flow across the fracture gap.

Radiology showed similar healing patterns in both groups; however, at the later stages (day 32) the NSAID group had significantly poorer healing. Histological analysis showed that controls healed quicker (days 24 and 32), with more callus (day 8) and less fibrous tissue (Day 32). Biomechanical testing showed controls were stronger at day 32. Both groups exhibited a similar pattern of blood flow; however NSAIDs exhibited a lower median flow from day 4 onwards (significant at days 4, 16 and 24).

Positive correlations were demonstrated between both histological and radiographic assessments of healing, with increasing blood flow. NSAID animals exhibited lower flows and poorer healing by all outcomes. Regression analysis demonstrates, however, that the negative effect of NSAIDs on fracture repair is independent of its inhibitory action on blood flow.

COX-2 inhibitors are marketed as having cleaner side effect profiles and are widely used in trauma patients. Following development of a novel method of analysing functional vascularity across a fracture gap, we have demonstrated that the COX-2 inhibitor rofecoxib has a significant negative effect on blood flow at the fracture gap alongside inhibiting fracture repair.

In patients with conventional metal-on-Polyethylene (MoP) hip replacements, osteolysis can occur in response to wear debris. During revision hip surgery, surgeons usually remove the source of osteolysis (polyethylene) but cannot always remove all of the inflammatory granulomatous tissues in the joint. We used a human/rat xenograft model to evaluate the effects of polyethylene granuloma tissues on bone healing. Human osteoarthritic and periprosthetic tissues collected during primary and revision hip arthroplasty surgeries were transplanted into the distal femora of athymic (nude) rats. The tissues were assessed before and after implantation and the bone response to the tissues was evaluated after 1 week and 3 weeks using micro-computed tomography, histology, and immunohistochemistry. After 3 weeks, the majority (70%) of defects filled with osteoarthritic tissues healed, while only 21% of defects with polyethylene granuloma tissues healed. Polyethylene granuloma tissues in trabecular bone defects inhibited bone healing. Surgeons should remove polyethylene granuloma tissues during revision surgery when possible, since these tissues may slow bone healing around a newly implanted prosthesis. This model provides a method for delivering clinically relevant sized particles into an in vivo model for investigation.

Purpose

There are concerns with regard to the physiological effects of reamed intramedullary femoral fracture stabilisation in patients who have received a pulmonary injury. This large animal study used invasive monitoring techniques to obtain sensitive cardiopulmonary measurements and compared the responses to Early Total Care (reamed intramedullary femoral fracture fixation) to Damage Control Orthopaedics (external fixation), after the induction of acute lung injury. We hypothesised a greater cardiopulmonary response to intramedullary fracture fixation.

Currently, there is no animal model in which to evaluate the underlying physiological processes leading to the heterotopic ossification (HO) which forms in most combat-related and blast wounds. We sought to reproduce the ossification that forms under these circumstances in a rat by emulating patterns of injury seen in patients with severe injuries resulting from blasts. We investigated whether exposure to blast overpressure increased the prevalence of HO after transfemoral amputation performed within the zone of injury. We exposed rats to a blast overpressure alone (BOP-CTL), crush injury and femoral fracture followed by amputation through the zone of injury (AMP-CTL) or a combination of these (BOP-AMP). The presence of HO was evaluated using radiographs, micro-CT and histology. HO developed in none of nine BOP-CTL, six of nine AMP-CTL, and in all 20 BOP-AMP rats. Exposure to blast overpressure increased the prevalence of HO. This model may thus be used to elucidate cellular and molecular pathways of HO, the effect of varying intensities of blast overpressure, and to evaluate new means of prophylaxis and treatment of heterotopic ossification. Cite this article: Bone Joint J 2015;97-B:572–6

Introduction. Major trauma during military conflicts involve heavily contaminated open fractures. Staphylococcus aureus (S. aureus) commonly causes infection within a protective biofilm. Lactoferrin (Lf), a natural milk glycoprotein, chelates iron and releases bacteria from biofilms, complimenting antibiotics. This research developed a periprosthetic biofilm infection model in rodents to test an Lf based lavage/sustained local release formulation embedded in Stimulin beads. Method. Surgery was performed on adult rats and received systemic Flucloxacillin (Flu). The craniomedial tibia was exposed, drilled, then inoculated with S. aureus biofilm. A metal pin was placed within the medullary cavity and treatments conducted. Lf in lavage solutions: The defect was subject to 2× 50 mL lavage with 4 treatment groups (saline only, Lf only, Bactisure with Lf, Bactisure with saline). Lf embedded in Stimulin beads: 4 bead types were introduced (Stimulin only, Lf only, Flu only, Lf with Flu). At day 7, rats are processed for bioluminescent and X-ray imaging, and tibial explants/pins collected for bacterial enumeration (CFU). Results. Rats without treatments established a mean infection of 2×106 CFU/tibia. 4 treatment groups with a day 0, one-off lavage demonstrated >95% reduction in bacterial load 7 days post-op, with a reduction in CFU from 1×106/tibia down to 1×104/tibia. There was no statistically significant difference between each group (p = 0.55 with one way ANOVA). The stimulin bead experiments are ongoing and complete results will be obtained in the end of July. Conclusions. This research demonstrated a clinically relevant animal model of implanted metalware that establishes infection. No additional benefit was observed with a one-off, adjuvant Lf lavage during the initial decontamination of the surgical wound, compared with saline alone, and in combination with the antiseptic Bactisure. This animal model provides the foundation for future antibiofilm therapies

Aim. To provide proof of concept in an in vivo animal model for the prevention of prosthetic joint infection prevention using electric fields along with conventional antibiotic prophylaxis. Corresponding Author: Marti Bernaus. Method. First, we standardized the animal model to simulate implant contamination during the surgical procedure. We then implanted cobalt-chrome prostheses adapted to both knees of two New Zealand White rabbits, under standard aseptic measures and antibiotic prophylaxis with cefazolin. Prior to implantation, we immersed the prostheses in a 0.3 McFarland inoculum of S. aureus (ATCC 25923) for 30 seconds. In the first animal (control), the joint was directly closed after washing with saline. In the second animal (case), both prostheses were treated with electric current pulses for 30 seconds, washed with saline, and the joint was closed. After 72 hours, both animals were reoperated for the collection of periprosthetic tissue and bone samples, and prosthesis removal. In all samples, we performed quantitative cultures prior to vortexing and sonication, as well as prolonged cultures of the sonication broth. We confirmed the absence of contamination by identification with MALDI-TOF (VITEK-MS) and automated antibiotic susceptibility testing of the isolated colonies (VITEK-2). Results. In the “control” animal, we isolated S. aureus in all studied samples. The bacterial count expressed as log10 (cfu/cm2) in the prostheses of the right and left legs was 9.38 and 8.86, respectively. The bacterial count expressed as log10 (cfu/mL) in bone and periprosthetic tissue biopsies was 2.70 and 2.72 in the right leg and 3.24 and 3.87 in the left leg, respectively. In the “case” animal, where an electric field was applied to the implant after placement in addition to cefazolin prophylaxis, all samples (prosthesis, bone, and periprosthetic tissue) were negative, and no isolation of the inoculated strain of S. aureus was obtained after incubation of the sonication broth for 14 days. Conclusions. This in vivo model suggests the potential effectiveness of applying an electric field to a prosthetic implant in combination with cefazolin for the prevention of PJI development, after exposure of the implant to an inoculum of S. aureus (ATCC 25923). Our findings need to be confirmed using a larger sample size

Prosthetic joint infection (PJI) is a complex disease that causes significant damage to the peri-implant tissue. Developing an animal model that is clinically relevant in depicting this disease process is an important step towards developing novel successful therapies. In this study, we have performed a thorough histologic analysis of peri-implant tissue harvested post Staphylococcus aureus (S. aureus) infection of a cemented 3D-printed titanium hip implant in rats. Sprague-Dawley rats underwent left hip cemented 3D-printed titanium hemiarthroplasty via posterior approach under general anesthesia. Four surgeries were performed for the control group and another four for the infected group. The hip joint was inoculated with 5×10. 9. CFU/mL of S. aureus Xen36 prior to capsule closure. The animals were scarified 3 weeks after infection. The femur was harvested and underwent micro-CT and histologic analysis. Hematoxylin and eosin (H&E), as well as Masson's trichrome (MT) stains were performed. Immunohistochemistry (IHC) using rabbit antibody for S. aureus was also used to localize bacterial presence within femur and acetabulum tissue . The histologic analysis revealed strong resemblance to tissue changes in the clinical setting of chronic PJI. IHC demonstrated the extent of bacterial spread within the peri-implant tissue away from the site of infection. The H&E and MT stains showed 5 main features in infected bone: 1) increased PMNs, 2) fibrovascular inflammation, 3) bone necrosis, and 4) increased osteoclasts 5) fibrosis of muscular tissue and cartilage. Micro CT data showed significantly more osteolysis present around the infected prosthesis compared to control (surgery with no infection). This is the first clinically relevant PJI animal model with detailed histologic analysis that strongly resembles the clinical tissue pathology of chronic PJI. This model can provide a better understanding of how various PJI therapies can halt or reverse peri-implant tissue damage caused by infection

Aim. Debridement, Antibiotics, Irrigation, and implant Retention (DAIR) is a surgical treatment protocol suitable for some patients with fracture related infection (FRI). Clinically relevant pre-clinical models of DAIR are scarce and none have been developed in large animals. Therefore, this project aimed to develop a large animal model for FRI including a DAIR approach and compare outcomes after 2 or 5 weeks of infection. Method. Swiss Alpine sheep (n=8), (2–6 years, 50–80 kg) were included in this study. This study was approved by cantonal Ethical authorities in Chur, Switzerland. A 2 mm osteotomy was created in the tibia and fixed with a 10-hole 5.5 mm steel plate. Subsequently, 2.5 mL of saline solution containing 10. 6. CFU/mL of Staphylococcus aureus MSSA (ATCC 25923) was added over the plate. Sheep were observed for 2 (n=3) or 5 weeks (n=5) until revision surgery, during which visibly infected or necrotic tissues were removed, and the wound flushed with saline. All samples were collected for bacterial quantification. After revision surgery, the sheep were treated systemically for 2 weeks with flucloxacillin and for 4 weeks with rifampicin and cotrimoxazole. After 2 further weeks off antibiotics, the animals were euthanized. Bacteriological culture was performed at the end of the study. Bone cores were isolated from the osteotomy site and processed for Giemsa & Eosin and Brown and Brenn staining. A radiographical examination was performed every second week. Results. Bacteriological evaluation of the retrieved samples during revision surgery showed no significant difference between the 2 vs 5 weeks infection periods in term of total CFU counts. At the end of the study, radiographical examination showed callus formation over the osteotomy site in both groups, although the osteotomy was not completely healed in either group. At euthanasia, the 2 weeks infection group showed a higher soft tissue burden compared to the 5 weeks group, whereby the infection in the 5 weeks group was primarily located in the bone and bone marrow. Conclusions. The large animal model of FRI and DAIR was successfully established. Bacteriological outcomes highlight that the increasing duration of the infection does not change the outcome but the location of the infection from a predominantly soft tissue infection to a deeper bone and intramedullary (IM) channel infection. The debridement of the IM channel could potentially reduce the infection burden by eliminating those bacteria not easily reached by systemic antibiotics, though is not practical using conventional techniques

Aim. To conduct a systematic review of non-rodent animal models (rabbit, pig, dog, goat and sheep) of bone infection. In the future, anti-infective technologies aiming to fight bone infections are depending on evaluation in reliable animal models. Therefore, it is highly relevant to evaluate the scientific quality of existing bone infection models. Method. PubMed and Web of Science were searched systematically. To be included in the systematic review, publications had to deal with bacterial inoculation of non-rodent animals in order to model bone infections in humans. Data was extracted on study design e.g. bacterial inoculation dose and infection time, methodological quality and post-mortem evaluation with respect to registration and quantification of pathology and microbiology. Results. In total, 316 publications were included in the systematic review. A substantial lack of study design information (e.g. bacterial identity and infection time) was demonstrated in many of the papers, which hampers reproducibility and continuation of the established work. Furthermore, the methodological study quality was found to be low as definition of infection, randomization, power analysis and blinding were only seldom reported. The use of histology has increased in recent years, but a semi-quantitative scoring of the lesions was often missing, i.e. no objective quantification of outcome. Most of the studies focused on whether the inoculated bacteria were present within the bone tissue post mortem or not. However, very often the bacterial burden was not quantified. In many of the models, different antimicrobial interventions were examined, and the lack of quantitative microbiology makes it difficult to estimate and reproduce the effects objectively. Although, antimicrobial effects were described for most interventions, a lack of sterile outcome was observed in many models. Failure to report a sterile outcome reduces the possibility for obtaining valuable knowledge regarding effective antibiotic doses in-vivo. Based on the present review a standard study template guideline for animal models of bone infections was established. The guideline describes details related to the animal, pathogen, animal + pathogen (infected animal) and post mortem analysis that are of crucial importance for validation of results and reproducibility. Conclusions. Due to a substantial lack of uniformity we miss the opportunity to get maximal knowledge from the preclinical literature. The new guideline will improve reproducibility of future models and translation of findings to the clinical setting. Bone infection organisations/societies and journal editors should encourage compliance with the new guideline. Reference: JBJS, 2019, In press

No animal model currently exists for hip abductor tendon tears. We aimed to 1. Develop a large animal model of delayed abductor tendon repair and 2. To compare the results of acute and delayed tendon repair using this model. Fourteen adult Romney ewes underwent detachment of gluteus medius tendon using diathermy. The detached tendons were protected using silicone tubing. Relook was performed at six and 16 weeks following detachment, histological analysis of the muscle and tendon were performed. We then attempted repair of the tendon in six animals in the six weeks group and compared the results to four acute repairs (tendon detachment and repair performed at the same time). At 12 weeks, all animals were culled and the tendon–bone block taken for histological and mechanical analysis. Histology grading using the modified Movin score confirmed similar tendon degenerative changes at both six and 16 weeks following detachment. Biomechanical testing demonstrated inferior mechanical properties in both the 6 and 16 weeks groups compared to healthy controls. At 12 weeks post repair, the acute repair group had a lower Movin's score (6.9 vs 9.4, p=0.064), and better muscle coverage (79.4% of normal vs 59.8%). On mechanical testing, the acute group had a significantly improved Young's Modulus compared to the delayed repair model (57.5MPa vs 39.4MPa, p=0.032). A six week delay between detachment and repair is sufficient to produce significant degenerative changes in the gluteus medius tendon. There are significant histological and mechanical differences in the acute and delayed repair groups at 12 weeks post op, suggesting that a delayed repair model should be used to study the clinical problem

Restoration a joint's articular surface following degenerative or traumatic pathology to the osteochondral unit pose a significant challenge. Recent advances have shown the utility of collagen-based scaffolds in the regeneration of osteochondral tissue. To provide these collagen scaffolds with the appropriate superstructure novel techniques in 3D printing have been investigated. This study investigates the use of polyɛ-caprolactone (PCL) collagen scaffolds in a porcine cadaveric model to establish the stability of the biomaterial once implanted. This study was performed in a porcine cadaveric knee model. 8mm defects were created in the medial femoral trochlea and repaired with a PCL collagen scaffold. Scaffolds were secured by one of three designs; Press Fit (PF), Press Fit with Rings (PFR), Press Fit with Fibrin Glue (PFFG). Mobilisation was simulated by mounting the pig legs on a continuous passive motion (CPM) machine for either 50 or 500 cycles. Biomechanical tensile testing was performed to examine the force required to displace the scaffold. 18 legs were used (6 PF, 6 PFR, 6 PFFG). Fixation remained intact in 17 of the cohort (94%). None of the PF or PFFG scaffolds displaced after CPM cycling. Mean peak forces required to displace the scaffold were highest in the PFFG group (3.173 Newtons, Standard deviation = 1.392N). The lowest peak forces were observed in the PFR group (0.871N, SD = 0.412N), while mean peak force observed in the PF group was 2.436N (SD = 0.768). There was a significant difference between PFFG and PFR (p = 0.005). There was no statistical significance in the relationship between the other groups. PCL reinforcement of collagen scaffolds provide an innovative solution for improving stiffness of the construct, allowing easier handling for the surgeon. Increasing the stiffness of the scaffold also allows press fit solutions for reliable fixation. Press fit PCL collagen scaffolds with and without fibrin glue provide dependable stability. Tensile testing provides an objective analysis of scaffold fixation. Further investigation of PCL collagen scaffolds in a live animal model to establish quality of osteochondral tissue regeneration are required

Gram-negative prosthetic joint infections (GN-PJI) present unique challenges in management due to their distinct pathogenesis of biofilm formation on implant surfaces. To date, there are no animal models that can fully recapitulate how a biofilm is challenged in vivo in the setting of GN-PJI. The purpose of this study is to establish a clinically representative GN-PJI in vivo model that can reliably depict biofilm formation on titanium implant surface. We hypothesized that the biofilm formation on the implant surface would affect the ability of the implant to be osseointegrated. The model was developed using a 3D-printed, medical-grade titanium (Ti-6Al-4V), monoblock, cementless hemiarthroplasty hip implant. This implant was used to replace the femoral head of a Sprague-Dawley rat using a posterior surgical approach. To induce PJI, two bioluminescent Pseudomonas aeruginosa (PA) strains were utilized: a reference strain (PA14-lux) and a mutant strain that is defective in biofilm formation (DflgK-lux). PJI development and biofilm formation was quantitatively assessed in vivo using the in vivo imaging system (IVIS), and in vitro using the viable colony count of the bacterial load on implant surface. Magnetic Resonance Imaging (MRI) was acquired to assess the involvement of periprosthetic tissue in vivo, and the field emission scanning electron microscopy (FE-SEM) of the explanted implants was used to visualize the biofilm formation at the bone-implant interface. The implant stability, as an outcome, was directly assessed by quantifying the osseointegration using microCT scans of the extracted femurs with retained implants in vitro, and indirectly assessed by identifying the gait pattern changes using DigiGaitTM system in vivo. A localized prosthetic infection was reliably established within the hip joint and was followed by IVIS in real-time. There was a quantitative and qualitative difference in the bacterial load and biofilm formation between PA14 and DflgK. This difference in the ability to persist in the model between the two strains was reflected on the gait pattern and implant osseointegration. We developed a novel uncemented hip hemiarthroplasty GN-PJI rat model. This model is clinically representative since animals can bear weight on the implant. PJI was detected by various modalities. In addition, biofilm formation correlated with implant function and stability. In conclusion, the proposed in vivo GN-PJI model will allow for more reliable testing of novel biofilm-targeting therapetics