Biomechanical evaluation of rotation torque with polygonal and round rod on pedicle screw fixations

English Keywords:Pedicle screw  Polygonal rod  Rotation  Correction torque

English Abstract:

  【Abstract】 Objective：To compare rotation torque between round rod and polygonal rod on Legacy，USSⅡ and RF pedicle screw instrument.Method：Six test groups were designed as follows：（1）Legacy screw plus Legacy round rod（group A）；（2）Legacy screw plus polygonal rod（group B）；（3）USSⅡ screw plus USSⅡ round rod（group C）；（4）USSⅡ screw plus polygonal rod（group D）；（5）RF screw plus RF round rod（group E）；（6）RF screw plus polygonal rod（group F）.Each group had 7 monoaxial pedicle screws and one round or polygonal rod，each time one screw was tightened on rod with constant torque.MTS 858 testing system was used to record the rotation torque，MNOVA was used for analysis.Result：The average of rotational torque of group A and B was 12.3±1.9Nm and 16.9±2.1Nm respectively，3.9±0.8Nm and 4.6±0.7Nm respectively for group C and D，6.7±0.4Nm and 17.6±0.7Nm for group E and F respectively.The rotational torque of polygonal rod plus Legacy screw and RF screw were significantly higher than round rod（P<0.05）.The rotational torque between polygonal and round rod plus USSⅡ screw showed no significant difference（P>0.05）.Conclusion：Polygonal rod can significantly increase the rotation torque of Legacy and RF pedicle screw system.