Lin Chen-Huei, Chao Ching-Kong, Tang Yi-Hsuan, Lin Jinn
Department of Mechanical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan.
Department of Orthopedics, National Taiwan University Hospital, Taipei, Taiwan.
Injury. 2018 Mar;49(3):585-592. doi: 10.1016/j.injury.2018.01.036. Epub 2018 Feb 3.
Reports of driver slippage leading to difficult locking screw removals have increased since the adoption of titanium for screw fabrication; the use of titanium is known to cause cross-threading and cold welding. Such problems occur most frequently in screws with hex sockets, and may cause serious surgical complications. This study aimed to improve screw socket design to prevent slippage and difficult screw removal.
Three types of small sockets (hex, Torx, and cruciate) and six types of large sockets (hex, Torx, Octatorx, Torx+ I, Torx+ II, and Torx+ III) with screw head diameters of 5.5 mm were manufactured from titanium, and corresponding screwdrivers were manufactured from stainless steel. The screw heads and drivers were mounted on a material testing machine, and torsional tests were conducted to simulate screw usage in clinical settings at two insertion depths: 1 and 2 mm. Ten specimens were tested from each design, and the maximum torque and failure patterns were recorded and compared.
For small sockets in 2 mm conditions, the hex with the largest driver core had the highest torque, followed by Torx and cruciate. In these tests, the drivers were twisted off in all specimens. However, under the 1 mm condition, the hex slipped and the torque decreased markedly. Overall, torque was higher for large sockets than for small sockets. The Octatorx, with a large core and simultaneous deformation of the driver and socket lobes, had the highest torque at almost twice that of the small hex. The hex had the lowest torque, a result of slippage in both the 1 and 2 mm conditions. Torx plus designs, with more designed degrees of freedom, were able to maintain a higher driving angle and larger core for higher torque.
The hex design showed slipping tendencies with a marked decrease in torque, especially under conditions with inadequate driver engagement. Large sockets allowed for substantial increases in torque. The Torx, Octatorx, and Torx plus designs displayed better performance than the hexes. Improvements to the socket design could effectively prevent slippage and solve difficult screw removal problems.
自采用钛制造螺钉以来，因螺丝刀打滑导致锁定螺钉难以取出的报告有所增加；已知使用钛会导致螺纹交叉和冷焊。此类问题在六角槽螺钉中最为常见，可能会引发严重的手术并发症。本研究旨在改进螺钉槽设计，以防止打滑和螺钉难以取出的情况。
用钛制造了三种类型的小槽（六角、梅花和十字）以及六种类型的大槽（六角、梅花、八角梅花、梅花 + I、梅花 + II 和梅花 + III），螺钉头部直径为 5.5 毫米，并用不锈钢制造了相应的螺丝刀。将螺钉头部和螺丝刀安装在材料试验机上，在两个插入深度（1 毫米和 2 毫米）下进行扭转试验，以模拟临床环境中螺钉的使用情况。每种设计测试 10 个样本，记录并比较最大扭矩和失效模式。
对于 2 毫米条件下的小槽，螺丝刀芯最大的六角槽扭矩最高，其次是梅花槽和十字槽。在这些测试中，所有样本中的螺丝刀都被拧断。然而，在 1 毫米条件下，六角槽打滑且扭矩显著下降。总体而言，大槽的扭矩高于小槽。八角梅花槽的芯大，螺丝刀和槽瓣同时变形，其扭矩最高，几乎是小六角槽的两倍。六角槽扭矩最低，这是 1 毫米和 2 毫米条件下均出现打滑的结果。梅花 + 设计具有更多的设计自由度，能够保持更高的驱动角度和更大的芯以获得更高的扭矩。
六角槽设计表现出打滑倾向，扭矩显著降低，尤其是在螺丝刀啮合不足的情况下。大槽可大幅提高扭矩。梅花、八角梅花和梅花 + 设计的性能优于六角槽。改进槽设计可有效防止打滑并解决螺钉难以取出的问题。
