Inzana Jason A, Schwarz Edward M, Kates Stephen L, Awad Hani A
Center for Musculoskeletal Research, University of Rochester Medical Center, 601 Elmwood Avenue, Box 665, Rochester, NY 14642, United States; Department of Biomedical Engineering, University of Rochester, 207 Robert B. Goergen Hall, Rochester, NY 14642, United States.
Center for Musculoskeletal Research, University of Rochester Medical Center, 601 Elmwood Avenue, Box 665, Rochester, NY 14642, United States; Department of Biomedical Engineering, University of Rochester, 207 Robert B. Goergen Hall, Rochester, NY 14642, United States; Department of Orthopaedics, University of Rochester Medical Center, 601 Elmwood Avenue, Rochester, NY 14642, United States.
Bone. 2015 Mar;72:128-36. doi: 10.1016/j.bone.2014.11.019. Epub 2014 Nov 29.
Mice are the small animal model of choice in biomedical research due to the low cost and availability of genetically engineered lines. However, the devices utilized in current mouse models of implant-associated bone infection have been limited to intramedullary or trans-cortical pins, which are not amenable to treatments involving extensive debridement of a full-thickness bone loss and placement of a segmental antibiotic spacer. To overcome these limitations, we developed a clinically faithful model that utilizes a locking fracture fixation plate to enable debridement of an infected segmental bone defect (full-thickness osteotomy) during a revision surgery, and investigated the therapeutic effects of placing an antibiotic-laden spacer in the segmental bone defect. To first determine the ideal time point for revision following infection, a 0.7 mm osteotomy in the femoral mid-shaft was stabilized with a radiolucent PEEK fixation plate. The defect was inoculated with bioluminescent Staphylococcus aureus, and the infection was monitored over 14 days by bioluminescent imaging (BLI). Osteolysis and reactive bone formation were assessed by X-ray and micro-computed tomography (micro-CT). The active bacterial infection peaked by 5 days post-inoculation, however the stability of the implant fixation became compromised by 10-14 days post-inoculation due to osteolysis around the screws. Thus, day 7 was defined as the ideal time point to perform the revision surgery. During the revision surgery, the infected tissue was debrided and the osteotomy was widened to 3mm to place a poly-methyl methacrylate spacer, with or without vancomycin. Half of the groups also received systemic vancomycin for the remaining 21 days of the study. The viable bacteria remaining at the end of the study were measured using colony forming unit assays. Volumetric bone changes (osteolysis and reactive bone formation) were directly measured using micro-CT image analysis. Mice that were treated with local or systemic vancomycin did not display gross pathology at the end of the study. While localized vancomycin delivery alone tended to decrease the bacterial burden and osteolysis, these effects were only significant when combined with systemic antibiotic therapy. This novel mouse model replicates key features of implant-associated osteomyelitis that make treatment extremely difficult, such as biofilm formation and osteolysis, and imitates the clinical practice of placing an antibiotic-laden spacer after infected tissue debridement. In addition, the model demonstrates the limitations of current PMMA spacers and could be an invaluable tool for evaluating alternative antimicrobial treatments for implant-associated bone infection.
由于基因工程品系成本低且易于获得,小鼠是生物医学研究中首选的小动物模型。然而,目前植入相关骨感染小鼠模型中使用的装置仅限于髓内针或经皮质针,这些装置不适用于涉及全层骨质缺损广泛清创和放置节段性抗生素间隔物的治疗。为了克服这些限制,我们开发了一种临床逼真的模型,该模型利用锁定骨折固定板在翻修手术期间对感染的节段性骨缺损(全层截骨术)进行清创,并研究在节段性骨缺损中放置载抗生素间隔物的治疗效果。为了首先确定感染后翻修的理想时间点,在股骨干中段进行0.7mm的截骨术,并用可透射线的聚醚醚酮固定板固定。在缺损处接种生物发光金黄色葡萄球菌,并通过生物发光成像(BLI)在14天内监测感染情况。通过X射线和微型计算机断层扫描(micro-CT)评估骨质溶解和反应性骨形成。接种后5天,活跃的细菌感染达到峰值,但由于螺钉周围的骨质溶解,接种后10-14天植入物固定的稳定性受到损害。因此,第7天被定义为进行翻修手术的理想时间点。在翻修手术期间,对感染组织进行清创,并将截骨术扩大至3mm,以放置含或不含万古霉素的聚甲基丙烯酸甲酯间隔物。一半的组在研究的剩余21天内还接受了全身万古霉素治疗。使用菌落形成单位测定法测量研究结束时剩余的活菌。使用micro-CT图像分析直接测量体积骨变化(骨质溶解和反应性骨形成)。在研究结束时,接受局部或全身万古霉素治疗的小鼠未显示明显的病理学变化。虽然单独局部递送万古霉素倾向于降低细菌负荷和骨质溶解,但这些效果仅在与全身抗生素治疗联合使用时才显著。这种新型小鼠模型复制了植入相关骨髓炎的关键特征,这些特征使得治疗极其困难,如生物膜形成和骨质溶解,并模仿了在感染组织清创后放置载抗生素间隔物的临床实践。此外,该模型展示了当前聚甲基丙烯酸甲酯间隔物的局限性,可能是评估植入相关骨感染替代抗菌治疗的宝贵工具。