Huang Tsung-Jen, Hsu Robert Wen-Wei, Tai Ching-Lung, Chen Weng-Pin
Biomechanical Laboratory, Department of Orthopaedic Surgery, Chang Gung Memorial Hospital at Chia-Yi, College of Medicine, Chang Gung University, No. 6, West Section, Chia Pu Road, Putz City, Chia-Yi 613, Taiwan, ROC.
Clin Biomech (Bristol). 2003 Jul;18(6):S40-5. doi: 10.1016/s0268-0033(03)00083-4.
This study tested the hypothesis that triangulation of two anterior vertebral screws without penetration of the cortex offers more resistance to pullout than two screws placed in parallel and penetrated.
The pullout strength for two parallel or two triangulated anterior vertebral screws fixation, with a uni-cortical or bi-cortical purchase, were tested and compared to the strength of a single-screw fixation with a bi-cortical purchase. Four porcine spines (six months old) were used for biomechanical test and bone mineral density was measured for each specimen before testing.
The potential hazards from penetration by anterior vertebral cortex screws including neurovascular and organs injuries are well documented. However, bi-cortical screw penetration is widely recognized as necessary for good anterior spinal stabilization. The authors are not aware of any biomechanical study on the anterior placement of triangulated vertebral screws without penetration and its effect on the fixation strength of anterior vertebral device remains unclear.
In this study five modes of screw fixations in lateral vertebral bodies were performed: Group A, triangulated screws with one screw penetration; Group B, triangulated screws without penetration; Group C, parallel penetrating screws; Group D, parallel nonpenetrating screws; and Group E, a single-screw with bi-cortical purchase. Biomechanical analysis with a material testing system machine was performed to determine the pull out strength of each configuration.
The results showed that the pullout strength in the various double-screw fixation modes were statistically increased as compared to that of the single-screw with bi-cortical purchase mode. There existed statistical differences (P<0.05) between Groups A and B, Groups C and D and Groups D and E, respectively. However, no significant difference was found between Groups B and C (P=0.144).
Based on the current data, triangulation of two anterior vertebral screws without penetration of the cortex (Group B) achieved pullout strengths similar to that of two-parallel double-cortical screws (Group C). The authors believe that this is an attractive alternative in anterior spinal instrumentation avoiding the potential risks of cortical penetration. However, in the event of pullout failure, the triangulation configuration will produce a more disastrous consequence.
Triangulation of two anterior vertebral screws without penetration of the cortex achieve pullout strengths similar to that of two-parallel double-cortical screws. This is an attractive alternative in anterior spinal instrumentation that avoids the potential risks of cortical penetration.
本研究验证了以下假设，即两枚未穿透皮质骨的前路椎体螺钉呈三角形排列比两枚平行且穿透皮质骨的螺钉具有更强的抗拔出力。
测试并比较了两枚平行或呈三角形排列的前路椎体螺钉固定方式（单皮质或双皮质植入）的拔出强度，并与双皮质植入的单枚螺钉固定强度进行比较。使用四个六个月大的猪脊柱进行生物力学测试，并在测试前测量每个标本的骨密度。
前路椎体皮质骨螺钉穿透造成的潜在危害，包括神经血管和器官损伤，已有充分记录。然而，双皮质螺钉穿透被广泛认为是实现良好前路脊柱稳定所必需的。作者未发现任何关于未穿透皮质骨的三角形排列椎体螺钉前路置入及其对前路椎体固定装置固定强度影响的生物力学研究。
本研究在椎体侧面进行了五种螺钉固定方式：A组，一枚螺钉穿透的三角形排列螺钉；B组，未穿透的三角形排列螺钉；C组，平行穿透螺钉；D组，平行未穿透螺钉；E组，双皮质植入的单枚螺钉。使用材料测试系统机器进行生物力学分析，以确定每种构型的拔出强度。
结果表明，与双皮质植入的单枚螺钉固定方式相比，各种双螺钉固定方式的拔出强度在统计学上均有所增加。A组与B组、C组与D组、D组与E组之间分别存在统计学差异（P<0.05）。然而，B组与C组之间未发现显著差异（P=０．１４４）。
根据目前的数据，两枚未穿透皮质骨的前路椎体螺钉呈三角形排列（B组）的拔出强度与两枚平行双皮质螺钉（C组）相似。作者认为，这是前路脊柱内固定的一种有吸引力的替代方法，可避免皮质骨穿透的潜在风险。然而，如果发生拔出失败，三角形排列构型将产生更严重的后果。
两枚未穿透皮质骨的前路椎体螺钉呈三角形排列的拔出强度与两枚平行双皮质螺钉相似。这是前路脊柱内固定的一种有吸引力的替代方法，可避免皮质骨穿透的潜在风险。
