Ying Szu-Han, Kao Hung-Chan, Chang Ming-Chau, Yu Wing-Kuang, Wang Shih-Tien, Liu Chien-Lin
Department of Orthopaedics, Taipei Veterans General Hospital, Beitou District, Taipei City, Taiwan.
Orthopedics. 2012 Oct;35(10):e1511-6. doi: 10.3928/01477447-20120919-21.
The purpose of this study was to determine the change of fixation strength after adjusting the height of polymethylmethacrylate (PMMA)-augmented pedicle screws.Cement-augmented cannulated pedicle screws with or without PMMA augmentation with a radial hole in the distal third of the screw thread were inserted into synthetic bone blocks used to model osteoporosis. Screws were left unchanged (in situ), screwed in 3 threads, or screwed out 3 threads. The change in screw height was made 24 hours after cement placement. Radiographs of the samples were taken before and after screw adjustment, and pullout strength testing was performed. In the cement group, a radiolucent cavity was present after screwing in due to the screw-cement complex migrating downward, whereas no obvious change in the boneicement complex existed after screwing out. Mean pullout strength was significantly higher in the groups with cement as compared to those without cement. However, in the cement groups, the screw-in group had the lowest mean pullout strength among 3 groups, and the mean pullout strength in the screw-out group was also significantly lower than that in the in situ group (P<.05).Adjustment of pedicle screw height after cement augmentation in a severely osteoporotic spine can significantly reduce the pullout strength of the screw.
本研究的目的是确定调整聚甲基丙烯酸甲酯（PMMA）增强椎弓根螺钉高度后固定强度的变化。将带有或不带有PMMA增强且在螺纹远端三分之一处有径向孔的骨水泥增强空心椎弓根螺钉插入用于模拟骨质疏松症的合成骨块中。螺钉保持不变（原位）、拧入3个螺纹或拧出3个螺纹。在骨水泥置入24小时后改变螺钉高度。在螺钉调整前后对样本进行X线摄影，并进行拔出强度测试。在骨水泥组中，拧入后由于螺钉-骨水泥复合体向下迁移出现了一个透亮腔，而拧出后骨水泥复合体无明显变化。与无骨水泥组相比，骨水泥组的平均拔出强度显著更高。然而，在骨水泥组中，拧入组的平均拔出强度在3组中最低，拧出组的平均拔出强度也显著低于原位组（P<0.05）。在严重骨质疏松的脊柱中，骨水泥增强后调整椎弓根螺钉高度会显著降低螺钉的拔出强度。
