Luk Keith D K, Chen Liang, Lu William W
Department of Orthopaedics and Traumatology, The University of Hong Kong, Pokfulam, Hong Kong.
Spine (Phila Pa 1976). 2005 Mar 1;30(5):525-9. doi: 10.1097/01.brs.0000154649.55589.bf.
The insertion torque and pull-out force after cyclic loading of the bicortical sacral pedicle screw through the S1 endplate were tested using human cadaveric specimens.
The purpose of this study was to (1) evaluate the effect of cyclic loading on the pull-out force of two different techniques of bicortical sacral pedicle screw fixation and (2) to correlate the pull-out force after cyclic loading with the screw insertion torque.
Biomechanical studies using conventional sacral pedicle screw fixation techniques have demonstrated reduction in stiffness and strength after cyclic loading. Technical difficulties with anterior sacral cortex penetration and frequent screw loosening have been reported in clinical studies. In the authors' center, a new method of sacral pedicle screw fixation bicortically through the S1 endplate has been used successfully in the clinical setting. However, the mechanical stability of this new technique after undergoing cyclic loading has not been documented in the literature.
Seven-millimeter compact Cotrel-Dubousset sacral screws were randomly assigned by side (left vs. right) and inserted bicortically either anteromedially through the anterior sacral cortex or superiorly through the S1 endplate of 17 fresh frozen human sacrum. The tk;4maximum insertion torque for each screw was measured. Cyclic loading from 40 N to 400 N was applied to each screw at a frequency of 2 Hz for 20,000 cycles. Pull-out tests were conducted after completion of the cyclic tests.
The mean maximum insertion torque and mean pull-out force following cyclic loading were significantly higher for bicortical fixation through the S1 endplate (mean 3.17 N.m and 1457 N) than bicortical fixation through the anterior sacral cortex (mean 1.98 N.m and 1122 N). Both S1 endplate and anterior cortical fixation techniques demonstrated significant correlations between insertion torque and pull-out force following cyclic loading.
In sacral pedicle screw fixation, screw trajectory through the S1 endplate was significantly stronger than screws penetrating the anterior sacral cortex. Insertion torque was a good intraoperative indicator of screw pull-out force after cyclic loading.
使用人体尸体标本测试双皮质骶椎弓根螺钉经S1终板循环加载后的插入扭矩和拔出力。
本研究的目的是（1）评估循环加载对两种不同双皮质骶椎弓根螺钉固定技术拔出力的影响，以及（2）将循环加载后的拔出力与螺钉插入扭矩相关联。
使用传统骶椎弓根螺钉固定技术的生物力学研究表明，循环加载后刚度和强度会降低。临床研究报道了骶前皮质穿透的技术困难和频繁的螺钉松动。在作者所在的中心，一种通过S1终板双皮质固定骶椎弓根螺钉的新方法已在临床中成功应用。然而，这种新技术在循环加载后的机械稳定性在文献中尚未有记载。
将7毫米紧凑型Cotrel-Dubousset骶椎螺钉按侧别（左对右）随机分配，经17个新鲜冷冻人骶骨的骶前皮质从前内侧或经S1终板从上方双皮质插入。测量每个螺钉的最大插入扭矩。以2赫兹的频率对每个螺钉施加40牛至400牛的循环载荷，持续20000次循环。循环测试完成后进行拔出试验。
经S1终板双皮质固定的平均最大插入扭矩和循环加载后的平均拔出力（平均3.17牛·米和1457牛）显著高于经骶前皮质双皮质固定（平均1.98牛·米和1122牛）。S1终板和前皮质固定技术在循环加载后的插入扭矩和拔出力之间均显示出显著相关性。
在骶椎弓根螺钉固定中，经S1终板的螺钉轨迹明显强于穿透骶前皮质的螺钉。插入扭矩是循环加载后螺钉拔出力的良好术中指标。
