Hsu Chia-Hao, Wang Chih-Kuang, Wang Yan-Hsiung, Lin Sung-Yen, Lu Cheng-Chang, Fu Yin-Chih, Huang Hsuan-Ti, Chen Chung-Hwan, Chou Pei-Hsi
Graduate Institute of Clinical Medicine, College of Medicine, Kaohsiung Medical University, No. 100, Shih-Chuan 1st Road, Sanmin District, Kaohsiung 80708, Taiwan.
Department of Orthopedics, Kaohsiung Medical University Hospital, No. 100, Tzyou 1st Road, Sanmin District, Kaohsiung 80756, Taiwan.
Bioengineering (Basel). 2025 May 1;12(5):483. doi: 10.3390/bioengineering12050483.
This novel compression screw design offers potential benefits due to its two-part structure and can be used for various bone types, much like a conventional single-piece compression screw. However, full engagement may not always occur after final compression in clinical practice. This study aimed to verify the hypothesized optimal mechanical strength when the two parts are nearly fully combined and to determine a recommended engagement range based on stress distribution and concentration using finite element analysis. Ten models representing different combinations of the two screw parts (ranging from 10% to 100% of the engagement length, at 10% intervals) were simulated to determine the acceptable engagement percentage. Pull-out and bending load simulations were performed using finite element models. Extreme clinical loading conditions were simulated, including 1000 N pull-out forces and a 1 Nm bending moment at the screw head. Finite element analysis revealed two stress concentration points. The pull-out load simulation showed that combinations with 100% engagement merged the two stress concentrations into one without force superposition, while combinations with less than 30% engagement should be avoided. In the bending load simulation, higher stress was observed for combinations with less than 90% engagement. A lower level of engagement increases the bending moment, which might be the major factor affecting the von Mises stress. Surgeons should be instructed on how to use the screw correctly and select the most appropriate screw size or length for the two parts to achieve an effective combination. Excessive bending or pull-out forces, or improper use with poor combinations, may cause the middle interval to strip or the screw to break or pull out. An engagement of more than 90% is recommended, while less than 30% is considered dangerous. This study provides biomechanical insights into this novel two-part screw design and its important clinical implications.
这种新型加压螺钉设计因其两部分结构而具有潜在优势，并且可用于多种骨类型，这与传统的一体式加压螺钉非常相似。然而，在临床实践中，最终加压后可能并非总能实现完全啮合。本研究旨在验证两部分近乎完全结合时假设的最佳机械强度，并使用有限元分析根据应力分布和集中情况确定推荐的啮合范围。模拟了代表螺钉两部分不同组合（啮合长度从10%到100%，间隔为10%）的十个模型，以确定可接受的啮合百分比。使用有限元模型进行拔出和弯曲载荷模拟。模拟了极端临床载荷条件，包括1000 N的拔出力和螺钉头部1 Nm的弯矩。有限元分析揭示了两个应力集中点。拔出载荷模拟表明，100%啮合的组合将两个应力集中合并为一个，且没有力的叠加，而应避免啮合小于30%的组合。在弯曲载荷模拟中，啮合小于90%的组合观察到更高的应力。较低的啮合水平会增加弯矩，这可能是影响冯·米塞斯应力的主要因素。应指导外科医生如何正确使用螺钉，并为两部分选择最合适的螺钉尺寸或长度，以实现有效组合。过度的弯曲或拔出力，或与不良组合的不当使用，可能会导致中间间隔脱扣或螺钉断裂或拔出。建议啮合超过90%，而小于30%则被认为是危险的。本研究为这种新型两部分螺钉设计提供了生物力学见解及其重要的临床意义。
