Richter M, Wilke H J, Kluger P, Claes L, Puhl W
Department of Orthopaedics, University of Ulm, Germany.
Spine (Phila Pa 1976). 1999 Feb 1;24(3):207-12. doi: 10.1097/00007632-199902010-00002.
The primary biomechanical stability of anterior internal fixation of the cervical spine obtained with a new monocortical expansion screw in vitro was evaluated.
To determine whether the anterior internal fixation of the spine obtained with the new monocortical expansion screw provides biomechanical stability comparable with that obtained with bicortical fixation.
The anterior plate instrumentation used with bicortical screw fixation in the cervical spine provides a primary stability superior to that associated with monocortical screw fixation. However, bicortical screws have the potential to perforate the posterior cortex. Therefore, monocortical instrumentation systems were developed, but without the biomechanical stability associated with bicortical systems. A new expansion screw for monocortical fixation was developed to improve biomechanical stability of monocortical systems.
Three different internal fixation systems were compared in this study: 1) H-plate with AO 3.5-mm bicortical screws, 2) cervical spine locking plate with monocortical screws, and 3) H-plate with the new monocortical expansion screws. Eight fresh human cadaver spine segments from C4 to C7 were tested in flexion-extension, axial rotation, and lateral bending using pure moments of +/- 2.5 Nm without axial preload. Five conditions were investigated consecutively: 1) intact spine; 2) uninstrumented spine with the segment C5-C6 destabilized; 3-5) instrumentation of the segment C5-C6 with the three implants mentioned above after removal of the disc and insertion of an interbody spacer.
Between bicortical and monocortical expansion screw H-plate fixation, no significant differences were observed in all load cases concerning range of motion and neutral zone. The neutral zone and range of motion were significantly larger for the cervical spine locking plate than for bicortical and monocortical expansion screw fixation in all load cases, except neutral zone for axial rotation versus bicortical screw fixation. The instrumented cases only had a significantly lower range of motion and neutral zone than the intact cases in extension-flexion, whereas for lateral bending and axial rotation no significant differences could be observed. Because the experimental design precluded any cyclic testing, the data represent only the primary stability of the implants.
In anterior instrumentation of the cervical spine using a H-plate, the new monocortical expansion screw provides the same biomechanical stability as the bicortical 3.5-mm AO screw and a significantly better biomechanical stability than the cervical spine locking plate. Therefore, the expansion screw may be an alternative to the bicortical fixation and does not involve the risk of penetration of the posterior vertebral body cortex.
评估一种新型单皮质扩张螺钉在体外获得的颈椎前路内固定的主要生物力学稳定性。
确定使用新型单皮质扩张螺钉进行的脊柱前路内固定是否能提供与双皮质固定相当的生物力学稳定性。
颈椎双皮质螺钉固定使用的前路钢板器械提供的初始稳定性优于单皮质螺钉固定。然而，双皮质螺钉有穿透后皮质的风险。因此，开发了单皮质器械系统，但缺乏与双皮质系统相关的生物力学稳定性。为提高单皮质系统的生物力学稳定性，研发了一种新型单皮质固定扩张螺钉。
本研究比较了三种不同的内固定系统：1）带AO 3.5毫米双皮质螺钉的H型钢板；2）带单皮质螺钉的颈椎锁定钢板；3）带新型单皮质扩张螺钉的H型钢板。使用±2.5 Nm的纯力矩且无轴向预载，对8个新鲜人尸体C4至C7脊柱节段进行屈伸、轴向旋转和侧方弯曲测试。连续研究了五种情况：1）完整脊柱；2）C5-C6节段失稳的未植入器械脊柱；3-5）在切除椎间盘并插入椎间融合器后，用上述三种植入物对C5-C6节段进行植入。
在双皮质和单皮质扩张螺钉H型钢板固定之间，在所有载荷情况下，关于活动范围和中性区均未观察到显著差异。在所有载荷情况下，除轴向旋转中性区与双皮质螺钉固定相比外，颈椎锁定钢板的中性区和活动范围均显著大于双皮质和单皮质扩张螺钉固定。在屈伸时，植入器械的情况仅比完整情况的活动范围和中性区显著更低，而在侧方弯曲和轴向旋转时未观察到显著差异。由于实验设计排除了任何循环测试，数据仅代表植入物的初始稳定性。
在使用H型钢板的颈椎前路内固定中，新型单皮质扩张螺钉提供的生物力学稳定性与3.5毫米双皮质AO螺钉相同，且比颈椎锁定钢板的生物力学稳定性显著更好。因此，扩张螺钉可能是双皮质固定的一种替代方法，且不涉及椎体后皮质穿透的风险。
