The failure of fracture healing represents a substantial clinical problem. Moreover, aged patients demonstrate an elevated risk for failed bone healing. However, murine models to study the failure of fracture healing are established only in young adult animals. Therefore, the aim of this study was to develop a reliable model to study failed fracture healing in aged mice. After creation of a 1.8-mm segmental defect and periosteal resection, femora of aged mice (18–20 months) and young adult control mice (3–4 months) were stabilized by pin-clip fixation. Segmental defects were analyzed by means of biomechanics, x-ray, and micro-computed tomography, as well as histomorphometric, immunohistochemical, and Western blot analysis. After 10 weeks, all animals showed a complete lack of osseous bridging, resulting in fracture healing failure. Segmental defects in aged mice revealed a reduced bone formation and vascularization when compared to young adult mice. This was associated with a decreased expression of bone formation markers. In addition, we detected a reduced number of tartrate-resistant acid phosphatase-positive osteoclasts and an elevated osteoprotegerin/receptor activator of NF-ĸB ligand ratio in aged animals, indicating a reduced osteoclast activity. Moreover, aged animals showed also an enhanced inflammatory response, characterized by an increased infiltration of macrophages within the callus tissue. Taken together, we herein report for the first time a reliable model to study fracture healing failure in aged mice. In the future, the use of this model enables us to study novel therapeutic strategies and molecular mechanics of failed fracture healing during aging.

中文翻译：

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建立研究老年小鼠骨折愈合失败的可靠模型

骨折愈合失败代表了一个重要的临床问题。此外，老年患者表现出骨愈合失败的风险升高。然而，研究骨折愈合失败的小鼠模型仅在年轻成年动物中建立。因此，本研究的目的是开发一个可靠的模型来研究老年小鼠骨折愈合失败的情况。在创建 1.8 毫米节段性缺损和骨膜切除后，通过针夹固定稳定老年小鼠（18-20 个月）和年轻成年对照小鼠（3-4 个月）的股骨。通过生物力学、X 射线和微型计算机断层扫描以及组织形态计量学、免疫组织化学和蛋白质印迹分析来分析节段性缺陷。10 周后，所有动物都表现出完全缺乏骨桥，导致骨折愈合失败。与年轻成年小鼠相比，老年小鼠的节段性缺陷显示骨形成和血管化减少。这与骨形成标志物的表达减少有关。此外，我们在老年动物中检测到抗酒石酸酸性磷酸酶阳性破骨细胞数量减少和 NF-ĸB 配体比率的骨保护素/受体激活剂升高，表明破骨细胞活性降低。此外，老年动物还表现出增强的炎症反应，其特征是愈伤组织内巨噬细胞的浸润增加。总之，我们在此首次报告了一种研究老年小鼠骨折愈合失败的可靠模型。将来，该模型的使用使我们能够研究衰老过程中骨折愈合失败的新治疗策略和分子力学。