Derincek Alihan, Wu Chunhui, Mehbod Amir, Transfeldt Ensor E
Twin Cities Spine Center, Minneapolis, MN 55404, USA.
J Spinal Disord Tech. 2006 Jun;19(4):286-91. doi: 10.1097/01.bsd.0000211203.31244.a0.
Many salvage options for failed thoracic pedicle screws exist including the use of a different trajectory or the augmentation of the screw with polymethylmethacrylate cement. Although polymethylmethacrylate immediately increases the construct stiffness and the pull-out strength, it may cause bone necrosis, toxin relaxation, and/or neural injury. On the other hand, calcium sulfate bone grafts have a high potential for biologic incorporation and no thermal damage effect. In the current study, polyaxial pedicle screws were first inserted with a straightforward approach on both sides in 17 fresh human cadaveric thoracic vertebrae. The maximal insertion torque for each screw was measured and then the pull-out strengths were recorded. Afterward, these pedicle screws were randomly assigned to be replaced either by graft augmentation or by anatomic trajectory technique for salvage. The graft-augmented screws were placed using the previous holes. The maximum insertional torque for each anatomic trajectory screw was measured. Finally, the pull-out strengths of the revision screws were recorded. The mean maximum insertional torque decreased with the anatomic trajectory salvage technique when compared with the straightforward approach, 0.23 versus 0.38 Nm, respectively (P=0.003). The anatomic trajectory revision resulted in decreased pull-out strength when compared with the pull-out strength of the straightforward technique, 297 versus 469 N, respectively (P=0.003). The calcium sulfate graft augmentation increased the pull-out strength when compared with the pull-out strength of the straightforward technique, 680 versus 477 N, respectively (P=0.017). The mean pull-out strength ratio of revised screw to original was 0.71 for anatomic trajectory and 1.8 for graft-augmented screws, a statistically significant difference (P=0.002).
对于失败的胸椎椎弓根螺钉存在多种挽救方法，包括采用不同的进钉轨迹或用聚甲基丙烯酸甲酯骨水泥增强螺钉。尽管聚甲基丙烯酸甲酯能立即增加内固定结构的刚度和拔出强度，但它可能导致骨坏死、毒素释放和/或神经损伤。另一方面，硫酸钙骨移植具有很高的生物融合潜力且无热损伤效应。在本研究中，首先采用直接入路在17个新鲜人尸体胸椎双侧插入多轴椎弓根螺钉。测量每个螺钉的最大插入扭矩，然后记录拔出强度。之后，这些椎弓根螺钉被随机分配采用植骨增强或解剖轨迹技术进行挽救替换。植骨增强螺钉通过先前的螺钉孔置入。测量每个解剖轨迹螺钉的最大插入扭矩。最后，记录翻修螺钉的拔出强度。与直接入路相比，采用解剖轨迹挽救技术时平均最大插入扭矩降低，分别为0.23 Nm和0.38 Nm（P = 0.003）。与直接技术的拔出强度相比，解剖轨迹翻修导致拔出强度降低，分别为297 N和469 N（P = 0.003）。与直接技术的拔出强度相比，硫酸钙植骨增强增加了拔出强度，分别为680 N和477 N（P = 0.017）。解剖轨迹翻修螺钉与原始螺钉的平均拔出强度比为0.71，植骨增强螺钉为1.8，差异有统计学意义（P = 0.002）。
