Objective To biomechanically compare the stability of the short and long iliae screw fixation constructs in lumboiliac reconstruction. Methods Seven adult human embalmed cadavers (L3- pelvis) were used. Using posterior spinal fixation system, L4-S1 pedicle screw fixation was performed. This was defined as intact state of the sacroiliac joint. After the intact test, total sacrum resection and L4-L5- pelvis reconstruction by pediele screw and iliac screw with different lengths were performed as follow: short screw group (as the length of exceeding 2 mm over ischial notch) and long screw group (as the length of exceeding 2 mm over anterior inferior iliac spine ). Using the 858 MTS material testing machine, biomechanical testing was performed under 800 N compression and 7 Nm torsion loading modes. At last, the axial pullout test of two iliac screws was executed. Construct stiffness in compression and torsion test, and maximum pullout force were analyzed. Results Insertion lengths of the short and long iliac screw were (70±2) mm and (138±4) mm respectively. The lumbopelvic reconstruction using short and long iliac screw, respectively restored 53.3%±13.6% and 57.6%±16.2% of the initial stiffness in compression testing, and respectively harvested 55.1%±11.9% and 62.5%±9.2% of the initial stiffness in torsion testing. No significant difference was detected between the two reconstructions (P>0.05), however, the compressive and torsional stiffness of the two techniques were markedly less than the intact condition (P< 0.05). The maximum pullout strength of long iliac screw was significantly higher than short screw ( P< 0.05). Conclusions Under the physical loading, lumbopelvic fixation construct using the short iliac screw may obtain mechanical stability comparable to that by long iliac screw. The short iliac screw is only the half of the long iliac screw by length, could reduce the implantation risk. However, the long iliac screw behaves greater axial pullout force, should be applied as far as possible in the osteoporosis patient. The lumbopelvic reconstruction utilizing any lenght of iliac screw is difficult to restore the local stability.%目的 比较髂骨长钉和短钉对腰椎-骨盆重建结构的生物力学影响.方法 7具成年防腐尸体L3-骨盆标本用于实验.使用脊柱椎弓根钉后路系统对L4-S1椎间活动度进行固定,并将这一状态定义为骶髂关节完整状态.完整状态测试后,将骶骨全部切除,联合髂骨钉行L4-L5-骨盆的稳定重建.根据髂骨钉置入长度顺序分为短钉组和长钉组.其中短钉长度定义为过坐骨切迹水平2 mm,长钉长度定义为穿透髂前下棘前方皮质2 mm.在858型MTS材料实验机上,给标本施加800N轴向压缩和7 Nm轴向旋转载荷后,行髂骨钉轴向拔出实验,记录压缩和旋转刚度、最大拔出力,并加以分析.结果 髂骨短钉和长钉的置入长度分别为(70±2)mm和(138±4)mm.髂骨短钉和长钉的重建结构,在压缩实验中分别获得脊柱.骨盆间初始刚度的53.3%±13.6%和57.6%±16.2%;在旋转实验中,分别恢复脊柱-骨盆间初始刚度的55.1%±11.9%和62.5%±9.2%;长钉和短钉结构间的压缩和旋转刚度均无显著差异(P>0.05);但是,两者的轴向压缩及旋转刚度均显著低于完整状态组(P<0.05).髂骨长钉的最大拔出力显著高于髂骨短钉(P<0.05).结论 在生理载荷下,髂骨短钉的脊柱-骨盆重建结构可获得与髂骨长钉同等的力学稳定性;髂骨短钉的置入深度仅为长钉的一半,可降低置入的风险.但是,无论髂骨长钉或短钉的脊柱.骨盆重建装置均难以恢复局部的初始稳定性.
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