Improving the Socket Design of Locking Screw Head to Prevent Screw Head Stripping
| Autor: | Yuan-Tsung Hsu, 徐源聰 |
|---|---|
| Rok vydání: | 2016 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 104 Locking plates have widely been used to treat different kinds of fractures in the body during surgical operation, for it can strengthen the bone-plate structures to make the fixation more rigid. However, the screw head slippage happened frequently during insertion and removal of the screws. Slippage may occur when the screws are well-bonded with the bone, and when a screw cannot be driven since the user’s power or torque is not transmitted properly and is commonly seen in small size hexagonal screws made of titanium. There have been no studies with comparisons of different kinds of screw head designs on the slippage of screw head. Therefore, the purpose of this study is to improve the socket design of locking screw head to prevent screw head stripping. In this study, seven types of screw head designs were investigated, including small Hexagon, small Torx, small Cross, 3.93mm-Hexagon, big Hexa-torx, big Octa-torx and Torx PLUS. We used Finite Element Method (FEM) and biomechanical experimental testing to validate the results in order to evaluate which type of screw head produces better torque to avoid screw slippage. We simulated incomplete engagement screw driver during the insertion and removal of screw was also observed. In this study, Titanium and SUS420 stainless steel were utilized in the manufacturing of screw head and screw driver, and torque of each designs were measured and calculated after torsion tests were applied to all specimens. The results of FEM revealed that the torque obtained from model one had the best consistency with the torque of the big Hexa-torx, Octa-torx and Torx PLUS obtained from the biomechanical test, but not in the case of the big Hexagon and the small screw. The results of the biomechanical test revealed that Octa-torx screws head had the highest torque in both engaged conditions, while all the drivers warped and broke during the biomechanical test in well-engaged condition and the lobes of most of the drivers broke during the biomechanical test in incomplete-engaged condition. In the mathematical simulations, the driver with the structure as close as round shape could achieve higher torque. After enlarging the size of the socket of the screws, the torque is much higher than the torque of the small ones obtained from previous studies. Furthermore, the big Hexa-torx, Octa-torx and Torx PLUS screws can actually prevent screw head stripping. We proved that Torx is a better design than Hexagon is and that there is a better design than Torx, which is Octa-torx. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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