卵巢切除骨质疏松小鼠骨折愈合不同时期骨微结构及力学性能变化★

背景：骨组织力学性能除受其自身的材料力学性能影响外，与骨量及结构形态等密切相关。骨质疏松的发病机制、微结构和力学性能还不是很清楚。目的：检测骨质疏松性骨折愈合不同时期骨密度、骨微结构与力学性能的变化，以期能为临床治疗提供科学指导与理论依据。 设计、时间及地点：随机对照动物实验，于2005年在上海第二医科大学实验室完成。材料：选择6周龄雌性C57 BL/6J小鼠, 体质量25 g，共40只。方法：将小鼠分别行双侧卵巢切除的骨质疏松组与行假手术的对照组，每组20只，3周后所有小鼠行右侧股骨横断骨折建立骨质疏松性骨折模型，采用髓内钉固定，并与对照侧比较。 主要观察指标：于术后1，2，4和8周采用X射线检测骨折愈合情况,采用双能X射线检测骨痂组织骨密度；Micro-CT测定骨痂形成和矿化；3点弯曲法测定力学性能。结果：①卵巢切除组骨痂骨密度明显低于对照组。②与对照组比较，卵巢切除组骨痂体积在骨折后1，2周明显减少，骨折后4，8周没明显改变。卵巢切除组在骨折后2周有明显高的矿化比例，在1，4和8周没有明显改变。③骨折后2，8周，对照组小鼠股骨最后负载和最后压力大于卵巢切除组。结论：骨质疏松性骨折修复过程中，显微结构、骨密度等随愈合时间而不断改变，并最终影响着骨痂组织的力学性能。

Changes of microstructure and mechanical properties in osteoporotic fracture healing in ovariectomized mice

BACKGROUND: Mechanical properties of bone are closely related to bone mass and structural morphology besides mechanics of materials. The pathogenesis, microstructure and mechanical properties of osteoporosis are not clear.OBJECTIVE: To provide an evidence for clinical practice by detecting changes of bone density, microarchitecture and mechanical property in different periods of osteoporotic fracture healing. DESIGN, TIME AND SETTING: The randomized control experiment was completed in the Laboratory of Shanghai Second Medical University in 2005.MATERIALS: Forty female C57 BL/6J mice, weighing 25 g with 6-week-old, were adopted in this study.METHODS: The mice were divided into 2 groups, twenty mice in each group. Mice in the ovariectomized group were underwent two-side ovariectomy and in the control group with sham operation. 3 weeks after operation, all mice were cut down right femurs and fixed by intramedullary nail to create osteoporotic fracture models.MAIN OUTCOME MEASURES: X-ray imaging and Micro-CT were performed to assess the healing of fracture and bone density of callus at 1, 2, 4 and 8 weeks postoperative. Three-point flexural test was used to evaluate the mechanical property.RESULTS: Density of callus mineralization in the ovariectomized group was obvious lower than that of the control group. Compared with control group, the volume of callus in the ovariectomized group were decreased significantly at 1 and 2 weeks after surgery, and there were no change in 4 and 8 weeks. Proportion of callus mineralization were higher 2 weeks post-fracture, but there were no obvious changes at 1, 4, and 8 weeks. The maximum load and ultimate stress in the control group were larger than that of the ovariectomized group at the 2 and 8 weeks after fracture.CONCLUSION: The microstructure and bone density change with time and ultimately influence the mechanical property of callus in the process of osteoporotic fracture healing.