Pedicle screw loosening is still observed in clinical practice. Therefore, the understanding of the interaction between screw and bone is evermore subject of research. However, complex relationships between screw design and anchorage are rarely examined. For this reason, it is investigated whether screw fixation is predictable by a parameter that maps the thread. Two types of pedicle screws, 6.5 mm and 7.5 mm in major diameter, respectively, are pulled out from synthetic polyurethane foam. Representative design parameters were evaluated with regard to their influence on the insertion torque and pull-out strength. A correlation between the insertion torque and the degree of compacting of the bone was observed. In addition, the pull-out strength was found to be related to the contact area of the bone-screw interface, the bone volume displaced during screwing, and the displaced diameter. The relationship between insertion torque and pull-out strength was also linear. In addition, a relational equation was derived for the pull-out strength versus the insertion torque with the major diameter as scaling factor. Thus, the pull-out strength from cancellous bone is predictable by a representative design parameter. Furthermore, the derived relation equation opens a new perspective for the evaluation of screw fixation.

中文翻译：

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预测松质骨椎弓根螺钉固定的新参数-合成泡沫的生物力学研究。

在临床实践中仍观察到椎弓根螺钉松动。因此，对螺钉与骨骼之间相互作用的理解一直是研究的主题。但是，很少检查螺钉设计和锚固之间的复杂关系。因此，通过映射螺纹的参数来研究螺钉固定是否可预测。从合成聚氨酯泡沫中分别拉出两种直径分别为6.5 mm和7.5 mm的椎弓根螺钉。评估了代表性的设计参数对插入扭矩和拉出强度的影响。观察到插入扭矩与骨的紧实度之间的相关性。此外，发现拉出强度与骨螺钉界面的接触面积有关，拧紧过程中移位的骨体积和移位的直径。插入扭矩和拉出强度之间的关系也是线性的。此外，以大直径为比例因子，得出了抗拉强度与插入扭矩的关系方程。因此，可以通过代表性的设计参数来预测松质骨的拔出强度。此外，推导的关系方程式为螺钉固定的评估开辟了新的视角。从松质骨中拔出的强度可以通过代表性的设计参数来预测。此外，推导的关系方程式为螺钉固定的评估开辟了新的视角。从松质骨中拔出的强度可以通过代表性的设计参数来预测。此外，推导的关系方程式为螺钉固定的评估开辟了新的视角。