Karaarslan Ahmet Adnan, Karakaşlı Ahmet, Aycan Hakan, Ertem Fatih, Sesli Erhan
Department of Orthopedics and Traumatology, Medical Faculty of Şifa University, 35100 Bornova, İzmir, Turkey.
Eklem Hastalik Cerrahisi. 2015;26(3):145-50. doi: 10.5606/ehc.2015.30.
This study aims to investigate whether there is any significant difference in bending resistance between titanium and stainless steel locking screws of femur nails and to review deformation of locking screws which is a common problem in interlocking nailing.
In this study, a total of 60 pieces of 5 mm major diameter titanium and stainless steel locking screws were used as six groups in three different thread depth structures (high threaded, low threaded, and unthreaded). Three-point bending tests were conducted on steel screws placed inside stainless steel tube with 30 mm inner diameter, which imitated the level of lesser trochanter. We used an axial compression testing machine in order to determine the yield points that permanent deformation occurred in the locking screws.
For low threaded locking screws, which are the most frequently used thread type for locking screws, the mean bending yield points were 1413 N on the titanium screws and this level was below 1922 N (2.8 BW) of level walking loading on femur for 70 kg person. On low threaded stainless screws, bending resistance was 2071 N, which was above the value of 1922 N. For high threaded locking screws, the mean bending yield points were 874 N on the titanium screws and 556 N on stainless screws.
In comminuted femur shaft fractures (in full load bearing conditions), using stainless steel locking screws is better instead of titanium screws to avoid locking screw deformation since low threaded stainless steel screws were 46.5% more resistant to bending deformation than titanium ones. Stainless steel or titanium high threaded locking screws may only be carefully used in non-comminuted fractures.
本研究旨在调查股骨钉的钛合金锁定螺钉和不锈钢锁定螺钉在抗弯曲性能上是否存在显著差异，并探讨锁定螺钉变形这一交锁髓内钉常见问题。
本研究共使用60枚直径5mm的钛合金和不锈钢锁定螺钉，分为三组，每组两种材质，分别具有三种不同的螺纹深度结构（高螺纹、低螺纹和无螺纹）。将螺钉置于内径30mm的不锈钢管内进行三点弯曲试验，模拟小转子水平。使用轴向压缩试验机测定锁定螺钉发生永久变形时的屈服点。
对于最常用的低螺纹锁定螺钉，钛合金螺钉的平均弯曲屈服点为1413N，低于70kg体重者股骨水平行走负荷1922N（2.8倍体重）。低螺纹不锈钢螺钉的抗弯曲力为2071N，高于1922N。对于高螺纹锁定螺钉，钛合金螺钉的平均弯曲屈服点为874N，不锈钢螺钉为556N。
在粉碎性股骨干骨折（全负荷承重情况下），使用不锈钢锁定螺钉比钛合金螺钉更好，可避免锁定螺钉变形，因为低螺纹不锈钢螺钉的抗弯曲变形能力比钛合金螺钉高46.5%。不锈钢或钛合金高螺纹锁定螺钉仅可在非粉碎性骨折中谨慎使用。
