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

English Keywords:Cervical  Vertebrae screw  Pullout strength  Insertional torque  Biomechanical

English Abstract:

  【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.