聚甲基丙烯酸甲酯强化对骨质疏松椎弓根螺钉固定的生物力学作用

目的探讨聚甲基丙烯酸甲酯 (polymethylmethacrylate,PMMA)骨水泥强化椎弓根螺钉的方法和评价 PMMA强化骨质疏松椎弓根螺钉后的生物力学性质。方法 6具新鲜老年女性胸腰段骨质疏松脊柱标本 (T10～ L5)，使用双能 X线骨密度吸收仪测试每个椎体的骨密度，随机取 16个椎体 (32侧椎弓根 )，一侧椎弓根拧入 CCD螺钉，测量最大旋入力偶矩后拔出螺钉作为正常对照组，用 PMMA骨水泥强化椎弓根螺钉作为修复固定组，行螺钉拔出试验；另一侧经导孔直接强化椎弓根螺钉后拔出作为强化固定组，记录三组螺钉的最大轴向拔出力。结果椎体平均骨密度为 (0.445± 0.019)g/cm2；螺钉最大旋入力偶矩为（ 0.525± 0.104） Nm；正常对照组螺钉最大轴向拔出力为 (271.5± 57.3)N；修复固定组为 (765.9± 130.7)N；强化固定组为 (845.7± 105.0)N。 PMMA骨水泥强化或修复骨质疏松椎弓根螺钉后最大抗压力明显高于强化前，差异有非常显著性意义 (P< 0.01)。结论 PMMA骨水泥强化骨质疏松椎弓根螺钉能显著增加螺钉在椎体内的稳固性。

Augmentation of pedicle screw fixation with polymethylmethacrylate in the osteoporotic spine:an in vitro biomechanical study

Objective To ascertain whether augmentation with polymethylmethacrylate(PMMA) bone cement can enhance pedicle screw fixation in the osteoporotic spine. Methods Sixteen cadaveric thoracolumbar vertebral bodies were obtained from 6 fresh frozen old females spines(T10－ L5)at random and BMD were evaluated using DEXA. One pedicle screw of 6mm diameter (CCD) was implanted (one side). The maximum torque force was measured using torque wrench. The screws were pulled out from the vertebrae at 5 mm/min. A pedicle pilot hole was created using 3.5mm drill (the other side) and vertebral body was augmented with PMMA bone cement. Two CCD screws were implanted bilaterally. The screws were pulled out two hours later and pull out force were recorded. Results Average BMD was (0.445± 0.019)g/cm2 and the maximum torque force was (0.525± 0.104)Nm. The pull out strength of pedicle screw fixation following augmentation and restoration with PMMA averaged 310％ greater than that of not augmented. Conclusion Augmentation or restoration with PMMA offered a significantly increase of strength for pedicle screw fixation in the osteoporotic spine, people with osteoporosis who must use pedicle screw fixation should augment pedicle screw with PMMA bone cement.