Department for Traumatology and Sports Injuries, Paracelsus Medical University, Muellner Hauptstrasse 48, 5020 Salzburg, Austria.
Eur Spine J. 2013 Jan;22(1):46-53. doi: 10.1007/s00586-012-2461-2. Epub 2012 Aug 28.
With increasing usage within challenging biomechanical constructs, failures of C2 posterior cervical pedicle screws (C2-pCPSs) will occur. The purpose of the study was therefore to investigate the biomechanical characteristics of two revision techniques after the failure of C2-pCPSs.
Twelve human C2 vertebrae were tested in vitro in a biomechanical study to compare two strategies for revision screws after failure of C2-pCPSs. C2 pedicles were instrumented using unicortical 3.5-mm CPS bilaterally (Synapse/Synthes, Switzerland). Insertion accuracy was verified by fluoroscopy. C2 vertebrae were potted and fixed in an electromechanical testing machine with the screw axis coaxial to the pullout direction. Pullout testing was conducted with load and displacement data taken continuously. The peak load to failure was measured in newtons (N) and is reported as the pullout resistance (POR). After pullout, two revision strategies were tested in each vertebra. In Group-1, revision was performed with 4.0-mm C2-pCPSs. In Group-2, revision was performed with C2-pedicle bone-plastic combined with the use of a 4-mm C2-pCPSs. For the statistical analysis, the POR between screws was compared using absolute values (N) and the POR of the revision techniques normalized to that of the primary procedures (%).
The POR of primary 3.5-mm CPSs was 1,140.5 ± 539.6 N for Group-1 and 1,007.7 ± 362.5 N for Group-2; the difference was not significant. In the revision setting, the POR in Group-1 was 705.8 ± 449.1 N, representing a reduction of 38.1 ± 32.9 % compared with that of primary screw fixation. For Group-2, the POR was 875.3 ± 367.9 N, representing a reduction of 13.1 ± 23.4 %. A statistical analysis showed a significantly higher POR for Group-2 compared with Group-1 (p = 0.02). Although the statistics showed a significantly reduced POR for both revision strategies compared with primary fixation (p < 0.001/p = 0.001), the loss of POR (in %) in Group-1 was significantly higher compared with the loss in Group-2 (p = 0.04).
Using a larger-diameter screw combined with the application of a pedicle bone-plastic, the POR can be significantly increased compared with the use of only an increased screw diameter.
随着在具有挑战性的生物力学结构中使用的增加，C2 颈椎后路椎弓根螺钉（C2-pCPS）将会失效。因此，本研究的目的是研究两种 C2-pCPS 失效后修复螺钉的生物力学特性。
在一项体外生物力学研究中，对 12 个人类 C2 椎体进行了测试，以比较两种策略用于修复 C2-pCPS 失效后的螺钉。双侧使用单皮质 3.5 毫米 CPS 对 C2 椎弓根进行了器械固定（Synapse/Synthes，瑞士）。透视验证了插入的准确性。C2 椎体用盆钵固定在机电测试机中，使螺钉轴与拔出方向同轴。连续采集加载和位移数据进行拔出试验。以牛顿（N）为单位测量失效时的峰值负载，并报告为拔出阻力（POR）。拔出后，在每个椎骨中测试了两种修复策略。在第 1 组中，使用 4.0 毫米 C2-pCPS 进行修复。在第 2 组中，使用 C2 椎弓根骨-塑料修复并结合使用 4 毫米 C2-pCPS 进行修复。为了进行统计分析，使用绝对值（N）比较螺钉之间的 POR，并将修复技术的 POR 归一化为主要程序的 POR（%）。
第 1 组中，原始 3.5 毫米 CPS 的 POR 为 1140.5 ± 539.6 N，第 2 组为 1007.7 ± 362.5 N；差异不显著。在修复设置中，第 1 组的 POR 为 705.8 ± 449.1 N，与原始螺钉固定相比，降低了 38.1 ± 32.9%。对于第 2 组，POR 为 875.3 ± 367.9 N，降低了 13.1 ± 23.4%。统计分析显示，第 2 组的 POR 明显高于第 1 组（p = 0.02）。尽管统计分析显示两种修复策略与主要固定相比 POR 明显降低（p < 0.001/p = 0.001），但第 1 组的 POR 损失（%）明显高于第 2 组（p = 0.04）。
与仅增加螺钉直径相比，使用较大直径的螺钉并结合椎弓根骨-塑料应用，可显著增加 POR。
