在同一钉道二次置入颈椎椎体螺钉对螺钉拔出力的影响

The biomechanical effect of cervical vertebra body screw reinsertion by using previous pilot hole and trajectory

中文关键词:  颈椎  椎体螺钉  拔出力  扭矩  生物力学

英文关键词:Cervical  Vertebrae screw  Pullout strength  Insertional torque  Biomechanical

中文摘要:

  【摘要】 目的：评价在同一钉道二次置入颈椎椎体螺钉对螺钉拔出力的影响。方法：取5具成人新鲜尸体颈椎标本（C3~C7），游离出25个完整颈椎椎骨。在椎体两侧分别置入直径4.0mm的颈椎椎体螺钉，测量螺钉置入时的最大扭矩，并将两侧的最大扭矩进行比较。随机选取任意一侧的椎体螺钉（即试验组，另一侧即对照组），将其旋出，然后再将螺钉旋入原钉道，再次测量螺钉旋入时的最大扭矩，并与同侧螺钉首次置入时的最大扭矩进行比较。在生物力学试验机上行最大轴向拔出力试验，比较同一椎体两侧螺钉固定的最大轴向拔出力，分析初次旋入扭矩、二次旋入扭矩及最大轴向拔出力之间的关系。结果：试验组最大轴向拔出力为372.86±171.44N，对照组为343.91±169.90N，两者比较差异无统计学意义（P＞0.05）。试验组螺钉初次置入的最大扭矩为2.47±1.04kgf·cm，对照组为2.35±1.00kgf·cm，两者比较差异无统计学意义（P＞0.05）。试验组螺钉二次置入的最大扭矩为1.36±0.77kgf·cm，与试验组螺钉初次置入的最大扭矩比较差异有统计学意义（P＜0.05）。对照组螺钉置入的最大扭矩与最大轴向拔出力显著相关（r=0.784，P=0.00），试验组螺钉初次置入的最大扭矩与二次置钉的最大轴向拔出力显著相关（r=0.800，P=0.00），试验组螺钉二次置入的最大扭矩与最大轴向拔出力显著相关（r=0.732，P=0.00）。结论：在同一钉道二次置入颈椎椎体螺钉时的最大扭矩显著减小，但螺钉的最大拔出力并无明显减小，因此，当需要二次置钉时，在原钉道未被破坏的情况下，理论上可以选择将原螺钉旋入原钉道。

英文摘要:

  【Abstract】 Objectives: To evaluate the biomechanical consequence of vertebra screw reinsertion in the cervical spine. Methods: Twenty-five cervical vertebral levels from five fresh-frozen cadaveric cervical spine specimens(C3-C7) were instrumented bilaterally with 4.0mm titanium vertebra screws, and insertional torque(IT) was measured with each revolution. A paired comparison was performed for each level. Screw reinsertion was performed by completely removing the vertebra screw, and then reinserting the screws along the same trajectory. Screws were subjected to load to failure test, and pullout strength(POS) was measured, a paired comparison was performed for each level. The relationship among initial IT, reinsertion torque, and pullout strength were analyzed. Results: There was no significant difference in cervical vertebra screw pullout strength(POS) between reinserted and control screws(372.86±171.44N vs. 343.91±169.90N, respectively; P＞0.05). There was no significant difference in IT for initial insertion between the test group(INI)(2.47±1.04 kgf.cm) and control(2.35±1.00kgf·cm)(P＞0.05). IT for reinserted screws(1.36±0.77kgf·cm) decreased significantly compared with INI screws(P＜0.05). The initial IT of control group screws in the cervical spine had significant correlations with POS(r=0.784, P=0.00), the initial IT of test group screws in the cervical spine had significant correlations with POS of reinserted screw(r=0.800, P=0.00), and significant correlations between reinsertion IT and POS in test group (r=0.732, P=0.00). Conclusions: On the premise of original screw trajectory being maintained intact, reinsertion along the same trajectory can be performed theoretically.