Unit of Biomechanics, Department of Mechanics, School of Applied Mathematical and Physical Sciences, National Technical University of Athens, 5 Heroes of Polytechnion Avenue, Athens, Greece.
Spine (Phila Pa 1976). 2010 Apr 20;35(9):E332-7. doi: 10.1097/BRS.0b013e3181ba0b0c.
The pullout strength of a typical pedicle screw was evaluated experimentally for different screw insertion techniques. OBJECTIVE.: To conclude whether the self-tapping insertion technique is indeed the optimum one for self-tapping screws, with respect to the pullout strength.
It is reported in the literature that the size of the pilot-hole significantly influences the pullout strength of a self-tapping screw. In addition it is accepted that an optimum value of the diameter of the pilot-hole exists. For non self-tapping screw insertion it is reported that undertapping of the pilot-hole can increase its pullout strength. Finally it is known that in some cases orthopedic surgeons open the threaded holes, using another screw instead of a tap.
A typical commercial self-tapping pedicle screw was inserted into blocks of Solid Rigid Polyurethane Foam (simulating osteoporotic cancellous bone), following different insertion techniques. The pullout force was measured according to the ASTM-F543-02 standard. The screw was inserted into previously prepared holes of different sizes, either threaded or cylindrical, to conclude whether an optimum size of the pilot-hole exists and whether tapping can increase the pullout strength. The case where the tapping is performed using another screw was also studied.
For screw insertion with tapping, decreasing the outer radius of the threaded hole from 1.00 to 0.87 of the screw's outer radius increased the pullout force 9%. For insertion without tapping, decreasing the pilot-hole's diameter from 0.87 to 0.47 of the screw's outer diameter increased its pullout force 75%. Finally, tapping using another screw instead of a tap, gave results similar to those of conventional tapping.
Undertapping of a pilot-hole either using a tap or another screw can increase the pullout strength of self-tapping pedicle screws.
通过实验评估了不同螺钉插入技术对典型椎弓根螺钉拔出强度的影响。目的：确定自攻丝插入技术是否确实是自攻螺钉的最佳选择，就拔出强度而言。
文献报道称，导孔的尺寸显著影响自攻螺钉的拔出强度。此外，人们普遍认为导孔的最佳直径存在。对于非自攻螺钉插入，导孔的浅攻丝可以增加其拔出强度。最后，众所周知，在某些情况下，矫形外科医生会使用另一个螺钉而不是丝锥来打开螺纹孔。
按照不同的插入技术，将典型的商业自攻椎弓根螺钉插入模拟骨质疏松松质骨的固体刚性聚氨酯泡沫块中。根据 ASTM-F543-02 标准测量拔出力。螺钉插入不同尺寸的预先制备的孔中，无论是螺纹孔还是圆柱形孔，以确定是否存在最佳的导孔尺寸，以及攻丝是否可以增加拔出强度。还研究了使用另一个螺钉进行攻丝的情况。
对于带攻丝的螺钉插入，将螺纹孔的外半径从螺钉外半径的 1.00 减小到 0.87 会增加拔出力 9%。对于不带攻丝的插入，将导孔直径从螺钉外径的 0.87 减小到 0.47 会增加拔出力 75%。最后，使用另一个螺钉而不是丝锥进行攻丝，得到的结果与传统攻丝相似。
使用丝锥或另一个螺钉进行浅攻丝可以增加自攻椎弓根螺钉的拔出强度。
