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

Introduction. Gram-negative prosthetic joint infections (GN-PJI) present unique challenges in management due to their distinct pathogenesis of biofilm formation on implant surfaces. The purpose of this study is to establish a clinically representative GN-PJI model that can reliably recapitulate biofilm formation on titanium implant surface in vivo. We hypothesized that biofilm formation on an implant surface will affect its ability to osseointegrate. Methods. The model was developed using 3D-printed titanium hip implants, to replace the femoral head of male Sprague-Dawley rats. GN-PJI was induced using two bioluminescent Pseudomonas aeruginosa strains: a reference strain (PA14-lux) and a mutant biofilm-defective strain (ΔflgK-lux). Infection was monitored in real-time using the in vivo imaging system (IVIS) and Magnetic Resonance Imaging (MRI). Bacterial loads on implant surface and in periprosthetic tissues were quantified utilizing viable-colony-count. Field-emission scanning-electron-microscopy 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 in vitro using microCT scan, and indirectly assessed by identifying the gait pattern changes using DigiGait. TM. system in vivo. Results. Localized infection was 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-lux and ΔflgK-lux. This difference in the ability to persist in the model between the two strains was reflected in the gait pattern and implant osseointegration. Conclusions. We developed a novel uncemented hip hemiarthroplasty, GN-PJI rat model. To date, the proposed in vivo biofilm-based model is the most clinically representative for GN-PJI since animals can bear weight on the implant and poor osseointegration correlates with biofilm formation. In addition, localized PJI was detected by various modalities. Clinical Relevance. The proposed in vivo GN-PJI model will allow for more reliable testing of novel biofilm-targeting therapeutics

Aims

Delayed postoperative inoculation of orthopaedic implants with persistent wound drainage or bacterial seeding of a haematoma can result in periprosthetic joint infection (PJI). The aim of this in vivo study was to compare the efficacy of vancomycin powder with vancomycin-eluting calcium sulphate beads in preventing PJI due to delayed inoculation.

Purpose. To achieve 3D kinematic analysis of total knee arthroplasty (TKA), 2D/3D registration techniques, which use X-ray fluoroscopic images and computer-aided design model of the knee implants, have been applied to clinical cases. In previous feature-based registration methods, only edge contours originated from knee implants are assumed to be extracted from X-ray images before 2D/3D registration. Due to the influence of bone and bone-cement close to knee implants, however, edge detection methods extract unwanted spurious edges and noises in clinical images. Thus, time-consuming and labor-intensive manual operations are often necessary to remove the unwanted edges. It has been a serious problem for clinical applications, and there is a strong demand for development of improved method. The purpose of this study was to develop a pose estimation method to perform accurate 2D/3D registration even if spurious edges and noises exist in knee images. Methods. Our 2D/3D registration technique is based on a feature-based algorithm, and contour points from X-ray images are extracted by Gaussian Laplacian filter and zero crossing methods. The basic principle of the algorithm is that the 3D pose of a model can be determined by projecting rays from contour points in an image back to the X-ray focus and noting that all of these rays are tangential to the model surface. Therefore, 3D poses are estimated by minimizing the sum of Euclidean distances between all projected rays and the model surface. Additionally, we introduce robust statistics into the 3D pose estimation method to perform accurate 2D/3D registration even if spurious edges and noises exist in knee images. The robust estimation method employs weight functions to reduce the influence of spurious edges and noises. The weight functions are defined for each contour point, and optimization is performed after the weight functions are multiplied to a cost function. Experimental results. The accuracy and stability validation were performed using in vivo images. The effects of robust estimation were evaluated by comparison with non-robust estimation. One image contained spurious edges and noises, and the other image didn't (they were erased manually). We applied robust and non-robust methods to each image (300 frames). As correct poses, we used the poses which were got by applying previous method to the contour images which spurious edges and noises didn't exist. The root mean square errors (RMSE) and success rate were calculated, and the success rate was defined as the rate of satisfying clinical required accuracy (error is less than 1mm, 1 degree). As results of the experiments, when non-robust method was applied to contour images in which spurious edges and noises exist, RMSE was too large and success rate was 0 %. However, when robust method was applied to the same images, RMSE was less than 1 mm, 1 degree, and the success rate was about 60 percent. Fig. 1 shows typical result of the experiment. Conclusions. We have developed a robust 3D kinematic estimation method of TKA from X-ray images, and the method was found to be helpful for analyzing TKA kinematics without labor-intensive operations

INTRODUCTION. Trabecular Titanium. ™. (TT) is a novel material with a structure similar to trabecular bone, already used for prosthetic clinical applications. Being the bone-implant interface the weakest point during the initial healing period, the association of TT with a hydrogel enriched with progenitor cells and osteoinductive factors may represent a promising strategy to improve prosthesis osteointegration. In a previous in vitro study we evaluated the ability of an ammidated carboxymethylcellulose hydrogel (CMCA) and of TT enriched with CMCA to support bone marrow mesenchymal stem cells (BMSCs) viability and osteogenic differentiation [1]. The aim of this study was to evaluate in vivo if the association of TT with CMCA enriched with strontium chloride (SrCl. 2. ) and BMSCs could ameliorate TT osteointegration. METHODS. This study combines TT with CMCA, SrCl. 2. and BMSCs. To mimic prosthesis-bone implants, TT discs were seeded with human BMSCs predifferentiated in osteogenic medium, then press-fit into engineered bone. A total of 36 athymic mice were implanted subcutaneously, each animal received 2 constructs as un-seeded TT and TT+CMCA or cell seeded TT+BMSCs and TT+CMCA+BMSCs. After 4, 8 and 12 weeks, osteodeposition, bone mineral density (BMD) and osteointegration were evaluated by fluorescence imaging, micro-CT, SEM, histology and pull-out tests. RESULTS. Micro-CT analysis demonstrated the homogeneity of the engineered bone in all experimental groups, supporting the reproducibility of our novel engineered model. Macroscopic evaluation of explanted constructs after 4 weeks revealed their integration with mice subcutaneous structures. In pull-out biomechanical tests, increases in extraction energy and peak force from 4 to 12 weeks were observed in all the experimental groups, except TT+CMCA. TT+CMCA+BMSCs showed the highest value of peak force and the greatest increase in comparison to samples explanted at 4 weeks. In vivo fluorescence imaging showed osteodeposition activity inside the constructs, observation confirmed by the ex-vivo analyses revealing a higher activity in TT+BMSCs and in TT+CMCA+BMSCs in comparison to acellularized TT samples. SEM evaluation of ECM deposition at the interface between bone scaffolds and TT disks revealed a significant difference between TT+CMCA+BMSCs and the other experimental groups with the former showing an almost complete filling of the space between the integration surfaces already after 4 weeks. In histomorphometric analyses of tissue ingrowth at 8 weeks, TT+BMSCs and TT+CMCA+BMSCs showed a greater tissue ingrowth compared to TT and TT+CMCA samples. DISCUSSION. Several efforts have been made to improve osteointegration with particular attention to critical cases such as implant revision surgeries. The association of porous structures with osteoinductive factors enriched hydrogels and stem cells represents a novel and promising strategy for more effective osteointegration to reduce prosthesis mobilization risks. Our results demonstrate that the association of Trabecular Titanium. ™. with a SrCl. 2. enriched hydrogel and BMSCs increases the production of ECM and may thus represent a valid approach to accelerate prosthesis osteointegration. Further validation of these data will include construct implantation in large animal orthotopic models to better mimic surgical procedures