骨质疏松人工骨模块中膨胀式椎弓根螺钉与骨水泥强化螺钉稳定性的比较研究

Comparison on stability of expansive pedicle screw and polymethylmethacrylate-augmented pedicle screw in osteoporotic synthetic bone

目的:比较膨胀式椎弓根螺钉(expansive pedicle screw,EPS)与骨水泥强化螺钉(polymethylmethacrylate-augmented pedicle screw,PMMA-PS)在骨质疏松人工骨模块中的稳定性。方法:30块骨质疏松人工骨模块随机分为3组(n=10),普通椎弓根螺钉(conventional pedicle screw,CPS)组:直接置入CPS;PMMA-PS组:先向钉道内注入PMMA,再置入CPS;EPS组:直接置入EPS。24 h后进行X线及CT检查和轴向拔出实验、并测量最大拔出力(maximum pullout strength,Fmax)和能量吸收值(energy absorbed value,EAV),然后观察模块的破坏情况、并测量出口处直径(diameter of hole,DOH)。结果:CPS组中螺钉被人工骨材料直接包裹,PMMA-PS组中PMMA严密包裹螺钉,明显提高了螺钉周围的密度;EPS组中螺钉的前端在模块内膨胀形成一个"爪状"结构。CPS组、PMMA-PS组和EPS组的Fmax分别为(48.50±9.22)、(217.40±62.15)N和(84.50±11.36)N。PMMA-PS组和EPS组的Fmax均明显高于CPS组(P=0.000,P=0.038),而EPS组的Fmax明显低于PMMA-PS组(P=0.000),差异均具有统计学意义;CPS组、PMMA-PS组和EPS组的EAV分别为(0.11±0.04)、(0.41±0.08)J和(0.18±0.06)J,PMMA-PS组和EPS组的EAV均明显高于CPS组(P=0.000,P=0.016),而EPS组的EAV明显低于PMMA-PS组(P=0.000),差异均具有统计学意义。螺钉拔出后,PMMA-PS组的破坏最为严重,EPS组其次,CPS组的破坏最小。CPS组、PMMA-PS组和EPS组的DOH分别为(8.40±0.86)、(13.85±1.63)mm和(10.29±1.15)mm,PMMA-PS组和EPS组的DOH均明显大于CPS组(P=0.000,P=0.002),而EPS组的DOH明显小于PMMA-PS组(P=0.000),差异均具有统计学意义。结论:EPS和PMMA-PS均可以明显提高螺钉在骨质疏松人工骨模块中的稳定性,尽管EPS提高螺钉稳定性的效果不如PMMA-PS,但它为预防临床上骨质疏松条件下螺钉松动和避免传统方法中使用PMMA的诸多风险提供了一个新的研究方向。

Objective：To compare the stability of expansive pedicle screw（EPS）and polymethylmethacrylate-augmented pedicle screw（PMMA-PS）in osteoporotic synthetic bone blocks. Methods：Thirty osteoporotic synthetic bone blocks were randomly divided into three groups（10 in each group）. A pilot hole was prepared in advance using the same method in all samples. Then,the conventional pedicle screw（CPS）was inserted into the hole in CPS group,the pilot hole was filled with PMMA（2.5 ml）followed by CPS insertion in PMMA-PS group,and EPS was inserted into blocks in EPS group. Twenty-four hours later,X-ray and CT examination and axial pullout tests were performed on all samples. The maximam pullout strength（Fmax）and energy absorbed value（EAV）were measured.Then,the destruction of blocks was observed and the diameter of hole（DOH）was measured. Results：In CPS group,the screw was surrounded directly by synthetic bone without any other materials. In PMMA-PS group,the screw was wrapped up by PMMA totally. The PMMA was evenly distributed in synthetic bone around screw,which obviously improved the local density around track. In EPS group,anterior part of EPS presented an obvious expansion in synthetic bone and formed an unguiform structure which pressed surrounding synthetic bone. Results in the axial pull-out tests revealed that screw stability in both EPS group and PMMA-PS group were significantly enhanced compared with that in CPS group（P0.05）. But screw stability in PMMA-PS group was significant higher than that in EPS group（P 0.05）. After pullout of screw,the destructions of blocks were the most severe in PMMA-PS group and the lightest in CPS group. The DOH in PMMA-PS group and EPS group were significant bigger than that in CPS group（P0.05）. But the DOH in PMMA-PS group was significant bigger than that in EPS group（P0.05）. Conclusion：EPS and PMMA-PS can both significantly increase screw fixation strength in osteoporotic synthetic bone blocks. In addition,EPS can avoid the shortcomings caused by PMMA. Though,EPS shows less effect on augmentation of screw stability compared with PMMA-PS in osteoporotic synthetic bone blocks,it also provides a new study direction to prevent screw loosening in osteoporosis in clinic and avoid risks caused by PMMA in traditional method.