Cortical Bone Morphological and Trabecular Bone Microarchitectural Changes in the Mandible and Femoral Neck of Ovariectomized Rats

Objective
This study used microcomputed tomography (micro-CT) to evaluate the effects of ovariectomy on the trabecular bone microarchitecture and cortical bone morphology in the femoral neck and mandible of female rats.
Materials and Methods
Twelve female Wister rats were divided into two groups: the control and ovariectomized groups. The rats in the ovariectomized group received ovariectomy at 8 weeks of age; all the rats were sacrificed at 20 weeks of age, and their mandibles and femurs were removed and scanned using micro-CT. Four microstructural trabecular bone parameters were measured for the region below the first mandibular molar and the femoral neck region: bone volume fraction (BV/TV), trabecular thickness (TbTh), trabecular separation (TbSp), and trabecular number (TbN). In addition, four cortical bone parameters were measured for the femoral neck region: total cross-sectional area (TtAr), cortical area (CtAr), cortical bone area fraction (CtAr/TtAr), and cortical thickness (CtTh). The CtTh at the masseteric ridge was used to assess the cortical bone morphology in the mandible. The trabecular bone microarchitecture and cortical bone morphology in the femoral necks and mandibles of the control group were compared with those of the ovariectomized group. Furthermore, Spearman’s correlation (rs) was conducted to analyze the correlation between the osteoporosis conditions of the mandible and femoral neck.
Results
Regarding the trabecular bone microarchitectural parameters, the BV/TV of the trabecular bone microarchitecture in the femoral necks of the control group (61.199±11.288%, median ± interquartile range) was significantly greater than that of the ovariectomized group (40.329±5.153%). Similarly, the BV/TV of the trabecular bone microarchitecture in the mandibles of the control group (51.704±6.253%) was significantly greater than that of the ovariectomized group (38.486±9.111%). Furthermore, the TbSp of the femoral necks in the ovariectomized group (0.185±0.066 mm) was significantly greater than that in the control group (0.130±0.026mm). Similarly, the TbSp of the mandibles in the ovariectomized group (0.322±0.047mm) was significantly greater than that in the control group (0.285±0.041mm). However, the TbTh and TbN trends for the mandibles and femoral necks were inconsistent between the control and ovariectomized groups. Regarding the cortical bone morphology parameters, the TtAr of the femoral necks in the ovariectomized group was significantly smaller than that in the control group. There was no significant difference in the TtAr, CtAr, or CtTh of the femoral necks between the control and ovariectomized groups, and no significant difference in the CtTh of the mandibles between the control and ovariectomized groups. Moreover, the BV/TV and TbSp of the mandibles were highly correlated with those of the femurs (rs = 0.874 and rs = 0.755 for BV/TV and TbSp, respectively). Nevertheless, the TbTh, TbN, and CtTh of the mandibles were not correlated with those of the femoral necks.
Conclusion
After the rats were ovariectomized, osteoporosis of the trabecular bone microarchitecture occurred in their femurs and mandibles; however, ovariectomy did not influence the cortical bone morphology. In addition, the parametric values of the trabecular bone microarchitecture in the femoral necks were highly correlated with those of the trabecular bone microarchitecture in the mandibles.

研究目的
本研究采用显微计算机断层扫描（microcomputed tomography, micro-CT），评估卵巢切除术对雌性大鼠股骨颈及下颌骨的骨小梁微结构与皮质骨形态的影响。

材料与方法
将12只雌性Wister大鼠分为两组：对照组与卵巢切除术组。卵巢切除术组大鼠于8周龄时接受卵巢切除术；所有大鼠均于20周龄时处死，摘取其下颌骨与股骨，采用micro-CT进行扫描。针对下颌第一磨牙下方区域及股骨颈区域，测定4项骨小梁微结构参数：骨体积分数（BV/TV, bone volume fraction）、骨小梁厚度（TbTh, trabecular thickness）、骨小梁分离度（TbSp, trabecular separation）及骨小梁数量（TbN, trabecular number）。此外，针对股骨颈区域测定4项皮质骨参数：总横截面积（TtAr, total cross-sectional area）、皮质骨面积（CtAr, cortical area）、皮质骨面积分数（CtAr/TtAr, cortical bone area fraction）及皮质骨厚度（CtTh, cortical thickness）。以咬肌嵴处的皮质骨厚度（CtTh）评估下颌骨的皮质骨形态。将对照组与卵巢切除术组大鼠的股骨颈及下颌骨的骨小梁微结构与皮质骨形态进行对比。此外，采用斯皮尔曼相关系数（rs, Spearman’s correlation）分析下颌骨与股骨颈的骨质疏松状态间的相关性。

结果
就骨小梁微结构参数而言，对照组大鼠股骨颈骨小梁的骨体积分数（61.199±11.288%，中位数±四分位数间距）显著高于卵巢切除术组（40.329±5.153%）。同理，对照组大鼠下颌骨骨小梁的骨体积分数（51.704±6.253%）亦显著高于卵巢切除术组（38.486±9.111%）。进一步分析显示，卵巢切除术组大鼠股骨颈的骨小梁分离度（0.185±0.066 mm）显著高于对照组（0.130±0.026 mm）；卵巢切除术组大鼠下颌骨的骨小梁分离度（0.322±0.047 mm）同样显著高于对照组（0.285±0.041 mm）。但对照组与卵巢切除术组大鼠下颌骨及股骨颈的骨小梁厚度与骨小梁数量变化趋势并不一致。
关于皮质骨形态参数，卵巢切除术组大鼠股骨颈的总横截面积显著小于对照组。两组大鼠股骨颈的总横截面积、皮质骨面积及皮质骨厚度均无显著差异，且两组大鼠下颌骨的皮质骨厚度亦无显著差异。此外，下颌骨的骨体积分数与骨小梁分离度与股骨的对应参数呈高度相关（骨体积分数的rs=0.874，骨小梁分离度的rs=0.755）。然而，下颌骨的骨小梁厚度、骨小梁数量及皮质骨厚度与股骨颈的对应参数并无相关性。

结论
大鼠接受卵巢切除术后，其股骨与下颌骨的骨小梁微结构均出现骨质疏松改变，但卵巢切除术并未对皮质骨形态产生影响。此外，股骨颈的骨小梁微结构参数值与下颌骨的骨小梁微结构参数值呈高度相关。