骨水泥椎体强化椎弓根钉置入对骨质疏松脊柱生物力学稳定性的影响

背景：伴有骨质疏松患者的脊柱内固定松动、脱落是脊柱外科一个复杂而棘手的问题。用聚甲基丙烯酸甲酯骨水泥强化椎弓根螺钉可增加伴有骨质疏松患者的椎弓根螺钉防止椎弓根钉的松动及脱落。目的：评价聚甲基丙烯酸甲酯骨水泥椎体强化后椎弓根钉固定对不稳定骨质疏松脊柱的生物力学稳定性影响。设计、时间及地点：体外生物力学实验，于2008-03在上海大学生物力学实验室完成生物力学实验。材料：12具新鲜老年女性尸体T10~L3椎体标本，制成T12、L1间的不稳定模型，采用椎弓根螺钉系统固定。方法：将标本按照不同的处理方式分为4组。①对照组：为完整标本，只进行生物力学性能的测试。②一次固定组：对照组测试后随机选取6具不稳定模型，行T11~L2椎弓根钉固定。③二次固定组：一次固定组标本完成稳定性测试后，取出所有椎弓根螺钉，分别用注射器向T11~L2椎弓根钉道注入配制好的聚甲基丙烯酸甲酯骨水泥骨水泥2.0 mL后再次拧入螺钉固定。④强化固定组：将余下的6具标本于T11~L2双侧椎弓根分别以直径3.5 mm的钻头导孔，沿孔道插入直径3.5 mm的穿刺导管，插入深度为40 mm，用加压注射器经导管缓慢向椎体内加压注射配制好的聚甲基丙烯酸甲酯骨水泥3.5 mL后拧入螺钉固定。主要观察指标：进行轴向压缩、前屈/后伸、左/右侧弯、左/右旋转7项非损伤性加载，比较上述4组不同状态下脊柱的相对运动范围变化。结果：与一次固定组比较，二次固定组及强化固定组脊柱的相对运动范围增加(P < 0.05)，强化固定组与二次固定组组间比较，差异无统计学意义(P > 0.05)。结论：椎体成形强化椎弓根钉固定及钉道强化固定均可明显增强不稳定骨质疏松脊柱的稳定性。

Effect of pedicle screw fixation following vertebral augmentation with bone cement on biomechanical stability of osteoporotic spine

BACKGROUND: Screw loosening or pullout has been a challenging problem to pedicle screw fixation in the osteoporotic spine. Augmentation with polymethylmethacrylate (PMMA) in pedicle screw fixation can prevent screw loosening or pullout in osteoporotic spine.OBJECTIVE: To investigate the stability effect of pedicle screw fixation after augmentation with PMMA bone cement on unstable osteoporotic spine. DESIGN, TIME AND SETTING: The in vitro biomechanical experiment was performed at the Biomechanical Laboratory of Shanghai University in March 2008.MATERIALS: Twelve fresh osteoporotic spines (T10-L3) from old females were harvested to establish unstable models between T12 and L1, which were fixed by pedicle screw. METHODS: The specimens were divided into four groups: control group, normal specimens without any intervention; once fixation group, six unstable models were randomly selected and T12-L3 were fixed with pedicle screw with no augmentation; secondary fixation group, after stability testing, the pedicle screw of once fixation group was removed and 2 mL PMMA was injected into pedicle pole. Then the specimens were fixed with pedicle screw again; augmentation fixation group, pilot holes were prepared with a 3.5-mm drill at T11-L2 of the rest six specimens. Then a pipe was inserted into the vertebral body through the holes to a depth of 40-mm respectively and 3.5-mL PMMA was injected into each vertebral body of T12-L3. After vertebral augmentation, the models were fixed with pedicle screw. MAIN OUTCOME MEASURES: The specimens were tested in a nondestructive manner load, axial compression, flexion, extension, torsion right/left and lateral bending right/left. The change of relative range of motion was compared.RESULTS: Compared with once fixation group, secondary fixation and augmentation fixation significantly increased relative range of motion (P < 0.05). But there were no significant differences between second fixation and augmentation fixation groups (P > 0.05). CONCLUSION: Pedicle screw fixation after vertebral augmentation and pedicle augmentation with bone cement can greatly strengthen stability of the unstable osteoporotic spine.