Department of Neurosurgery, VKV Amerikan Hastanesi, Istanbul, Turkey.
J Neurosurg Spine. 2010 Feb;12(2):183-9. doi: 10.3171/2009.9.SPINE0951.
It is unclear how the biomechanics of dynamic posterior lumbar stabilization systems and traditional rigid pedicle screw-rod systems differ. This study examined the biomechanical response of a hinged-dynamic pedicle screw compared with a standard rigid screw used in a 1-level pedicle screw-rod construct.
Unembalmed human cadaveric L3-S1 segments were tested intact, after L4-5 discectomy, after rigid pedicle screw-rod fixation, and after dynamic pedicle screw-rod fixation. Specimens were loaded using pure moments to induce flexion, extension, lateral bending, and axial rotation while recording motion optoelectronically. Specimens were then loaded in physiological flexion-extension while applying 400 N of compression. Moment and force across instrumentation were recorded from pairs of strain gauges mounted on the interconnecting rods.
The hinged-dynamic screws allowed an average of 160% greater range of motion during flexion, extension, lateral bending, and axial rotation than standard rigid screws (p < 0.03) but 30% less motion than normal. When using standard screws, bending moments and axial loads on the rods were greater than the bending moments and axial loads on the rods when using dynamic screws during most loading modes (p < 0.05). The axis of rotation shifted significantly posteriorly more than 10 mm from its normal position with both devices.
In a 1-level pedicle screw-rod construct, hinged-dynamic screws allowed a quantity of motion that was substantially closer to normal motion than that allowed by rigid pedicle screws. Both systems altered kinematics similarly. Less load was borne by the hinged screw construct, indicating that the hinged-dynamic screws allow less stress shielding than standard rigid screws.
动态腰椎稳定系统的生物力学与传统刚性椎弓根螺钉-棒系统的生物力学有何不同尚不清楚。本研究比较了铰链式动力椎弓根螺钉与标准刚性螺钉在 1 节段椎弓根螺钉-棒固定中的生物力学反应。
完整的、L4-5 椎间盘切除后的、刚性椎弓根螺钉-棒固定后的以及铰链式动力椎弓根螺钉-棒固定后的未防腐的人体尸体 L3-S1 节段进行了测试。标本通过纯力矩加载，在记录运动的光电仪的情况下诱发屈伸、侧屈和轴向旋转。然后，在生理屈伸状态下，在连接棒上安装的应变片对仪器施加 400 N 的压缩力。通过安装在连接棒上的应变片测量穿过仪器的力矩和力。
铰链式动力螺钉在屈伸、侧屈和轴向旋转时允许的运动范围平均比标准刚性螺钉大 160%（p < 0.03），但比正常情况下小 30%。在使用标准螺钉时，在大多数加载模式下，杆上的弯矩和轴向载荷都大于使用动力螺钉时的弯矩和轴向载荷（p < 0.05）。在两种装置中，旋转轴都从正常位置向后显著移位超过 10 毫米。
在 1 节段椎弓根螺钉-棒固定中，铰链式动力螺钉允许的运动幅度与刚性椎弓根螺钉相比，更接近正常运动。两种系统的运动学变化相似。铰链式螺钉固定结构的负荷较小，表明铰链式动力螺钉比标准刚性螺钉的应力屏蔽作用更小。
