去卵巢大鼠不同时期皮质骨与松质骨变化的显微CT观察

Micro-CT analysis of cortical and cancellous bone on left tibial in ovariectomized rats

目的应用显微CT观察去卵巢大鼠胫骨近端皮质骨与松质骨骨密度和骨微结构差异。方法40只7月龄SD大鼠,随机分为去卵巢（OVX）组和假手术（SHAM）组,每组20只,于手术后第3周及第15周处死。处死后剥离左侧胫骨,行显微CT三维扫描,扫描完成后选取距生长板远端2.5 mm、层厚0.4 mm骨组织为皮质骨感兴趣区域,选取距生长板远端0.7 mm、层厚1.2 mm骨组织为松质骨感兴趣区域行三维重建。获取二维最大密度投射图像及三维结构图像,并对感兴趣区的皮质骨和松质骨进行定量分析。结果3周时,OVX和SHAM组大鼠皮质骨面积分别为（0.43±0.13）、（0.31±0.06）mm^2;骨髓腔面积（10.31±1.98）、（8.44±1.25）mm^2,截面总面积（10.74±2.05）、（8.75±1.26）mm^2,截面惯性矩（4.10±0.73）、（3.49±0.37）mm^4,两组比较差异有统计学意义（均为P〈0.05）。第15周时,除OVX组皮质骨平均厚度低于SHAM组外（P〈0.05）,其余各参数两组比较差异无统计学意义。15周OVX组大鼠左侧胫骨骨丢失敏感区域内皮质骨平均厚度和皮质骨面积较3周OVX组大鼠下降（P〈0.05）。SHAM组15周大鼠骨内径周长、骨外径周长和截面惯性矩增大,与3周比较,差异有统计学意义（P〈0.05）。3周时,OVX和SHAM组体积骨密度分别为（288.2±48.2）mg/mm^3和（408.4±51.6）mg/mm^3、组织骨密度（604.5±45.3） mg/mm^3和（686.7±40.0）mg/mm^3、骨体积分数（25.1±5.1）%和（33.6±4.1）%、骨小梁数量（6.04±2.94）个/mm和（9.85±2.83）个/mm,两组比较差异有统计学意义（均为P〈0.05）,结构模型指数（分别为3.11±0.36）和2.58±0.36）,小梁间隔为（0.37±0.22）mm和（0.14±0.10）mm,明显高于SHAM组（P〈0.05）。第15周时,OVX组体积骨密度、骨体积分数、骨小梁数量、结构模型指数和骨小梁间隔改变与SHAM组比较,差异有统计学意义（均为P〈0.05）,但组织骨密度差别消失。OVX组大鼠15周较3周组织骨密度增加、骨小梁厚度增厚、骨小梁数量减少和骨小梁间隔增宽（P〈0.05）。结论大鼠去卵巢后,胫骨近端皮质骨与松质骨具有不同的骨量丢失方式和不同的微结构改变。早期松质骨骨密度明显下降,骨微结构发生退变;皮质骨厚度减少,其微结构改变则先于骨密度的下降,骨量在去卵巢后15周变化不大。

Objective To observe the changes of bone mass and microarchitecture in ovariectomized rat left tibia by Micro CT（μCT）.Methods Forty seven-month-old SD rats were randomly divided into ovariectomized（OVX）and sham-operated（SHAM）groups,twenty in each group.After killed at 3^rdweek and 15^thweek aftersurgery,μCT scanning were performed in the left tibia in vitro.After scanning,the regions involving 0.4 mm slice thickness and 2.5 mm distance at the far end from tibial growth plate were selected as the region of interest（ROI）for cortical bone analysis.The regions selected as ROI of cancellous analysis,were involved in 1.2 mm slice thickness and 0.7 mm distance at the far end from tibial growth plate.After three dimension（3D） reconstruction,2D images of the maximum intensity projection and pictures of 3D microarchitecture were obtained,and bone mineral density（BMD）and microarchitectural parameters were quantitively identified.Results There were significant increases in Ct.Ar〔（0.43±0.13）mm^2 vs.（0.31±0.06）mm^2〕,Ma.Ar〔（10.31±1.98）mm^2 vs.（8.44±1.25）mm^2〕,Tt.Ar〔（10.74±2.05）mm^2 vs. （8.75±1.26）mm^2〕,and Mm〔（4.10±0.73）mm^2 vs.（3.49±0.37）mm^4〕in OVX group,compared with SHAM group at the 3^rdweek（all P〈0.05）.While at the 15^thweek,only Ct.Th showed a decrease in OVX group（P〈0.05）.In OVX group,Ct.Th and Ct.Ar were lower at 15 weeks than at 3 weeks.In SHAM group,In.Pro,Ot.Pm and Mm at 15 weeks were higher than those at 3 weeks （P〈0.05）.At the 3^（rd）week OVX rats had much lower vBMD〔（288.2±48.2）mg/mm^3 vs（408.4±51.6）mg/mm3〕,tBMD〔（604.5±45.3）mg/mm^3 vs.（686.7±40.0）mg/mm^3〕,BVF〔（25.1±5.1）%vs.（33.6±4.1）%〕,and Tb.N〔（6.04±2.94）mm^（-1）vs.（9.85±2.83）mm^（-1）〕,but higher SMI〔（3.11±0.36）vs.（2.58±0.36）〕and Tb.Sp〔（0.37±0.22）vs.（0.14±0.10）〕mm than SHAM had（P〈0.05）.At the 15th week,vBMD,BVF and Tb.N were still lower in OVX than in SHAM.SMI and Tb.Sp in OVX were also higher than in SHAM rats,but no significant difference of tBMD was found.In OVX group,the scores of tBMD,Tb.Th,Tb.N,Tb.Sp in the 15^thweek were higher than those in the 3^rdweek（P〈0.05）.Conclusions The cortical bone and cancellous bone have different ways of bone mass losing and microarchitecture changing in proximal tibia of post-OVX rat.At early period,BMD and microarchitecture of cancellous are decreased obviously.The thickness of cortical bone is reduced,the microarchitecture change is earlier than BMD decreasing while bone mass has no obvious changing during 15 weeks post-OVX.