低弹性模量膨胀螺钉在骨质疏松绵羊的体内研究

Study of low elastic modulus expandable screws in osteoporotic sheep in vivo

目的观察应力作用下低弹性模量膨胀螺钉在骨质疏松绵羊体内生物学表现,探讨其是否能在普通膨胀螺钉的基础上进一步提高螺钉的稳定性。方法选用4只成年雌性绵羊,行去势手术12月后,以双能X线骨密度测量仪测定去势前后腰椎骨密度,确定骨质疏松模型建立成功。于L1-L5脊椎两侧椎弓根内随机植入两种弹性模量的膨胀螺钉,低弹膨胀螺钉(42GPa)为实验组,普通膨胀螺钉(110GPa)为对照组,术后3月处死动物,取材标本进行最大拔出力实验,Micro-CT检测以及组织学分析。结果去势1年后绵羊腰椎骨密度显著下降,差异具有统计学意义(P<0.05)。膨胀螺钉植入绵羊椎体3月后,实验组的最大拔力高于对照组(P<0.05),Micro-CT检测显示骨体积分数(BV/TV)骨小梁厚度(Tb.Th.)以及骨小梁分离度(Tb.Sp.)在实验组均优于对照组(P<0.05),同时骨小梁数量(Tb.N.)在两组无显著性差异(P>0.05)。组织学显示实验组螺钉周围新骨形成多于对照组,同时钉骨界面结合紧密,其间无纤维结缔组织。结论通过减小内植物与周围骨质弹性模量的差异,低弹性模量膨胀螺钉能进一步提高螺钉在骨质疏松绵羊体内的稳定性,从而减少螺钉内固定失败的发生。

Objective To observe the biological performance of the low elastic modulus expandable screw in osteoporotic sheep in vivo and to find out whether the stability of the screw can be improved. Methods Four adult female sheep were ovariectomized. After 12 months, the bone mineral density of the lumber vertebra was determined using dual energy X-ray absorptiometry to confirm the establishment of the osteoporosis model. Bilateral pedicles of the lumbar vertebrae （ L^-L5 ） were random fixed with two different elastic modulus expendable screws, low elastic module expandable screws （42GPa） for the experiment group and ordinary expandable screws （ll0GPa） for the control group. All the animals were sacrificed 3 months after the implantation. Maximal force testing, micro-CT measurement, and histology analysis were performed. Results BMD of the lumbar vertebrae of the sheep decreased significantly 1 year after ovariectomy （P 〈 0.05）. After 3 months implantation, the maximal axial pull-out strength in experimental group was significantly enhanced compared to that in the control group （P 〈 0.05 ）. Micro-CT analysis showed that BV/TV, Tb. Th and Tb. Sp improved in experimental group compare to those in the control group （P 〈 0. 05 ）, but no difference in Tb. N. between the two groups （P 〉 0. 05 ）. Histological observation showed that newly formed bone around the screws was more in the experimental group than in the control group. Meanwhile more tight contact and less fibrous connective tissue were observed on the screw-bone interface in the experimental group. Conclusion The low elastic modulus expandable screws can further improve the bionlechanical fixation strength in osteoporotic sheep and reduce the failure of the screw fixation, through reduction of the difference of elastic modulus between the screws and the surrounding bone tissue.