Vangsness C T, Carter D R, Frankel V H
Clin Orthop Relat Res. 1981 Jun(157):279-86.
The heads of self-tapping and non-self-tapping screws in dog femurs were exposed to a cyclic shearing force of 110 N for 200 loading cycles. This cyclic shear loading created a decrease in pull-out strength for both screw types of approximately 11% (p less than 0.01). No statistically significant difference in pull-out strength was found between screw types either before or after cyclic loading. A linear relationship between pull-out force and cortical thickness was observed for both screw types. These tests corroborated past work which showed equal holding power for the self-tapping and non-self-tapping screw. The progressive loosening of the screws with cyclic shear loading was accompanied by increasing load-displacement hysteresis and screw head migration. Greater hysteresis suggested that the non-self-tapping screw might have loosened more than the self-tapping screw from this applied loading schedule. Bone microcracking around screw threads before and after cyclic loading was observed by scanning electron microscopy. Photomicrographs of one non-self-tapping screw type and two self-tapping screw types showed microcracks at the tip of the outer diameter of the screw thread. More microcracks were observed after application of cyclic shear loading.
将犬股骨中的自攻和非自攻螺钉头部置于110 N的循环剪切力下，进行200次加载循环。这种循环剪切加载使两种类型螺钉的拔出强度均降低了约11%（p小于0.01）。在循环加载前后，两种螺钉类型之间的拔出强度均未发现统计学上的显著差异。两种螺钉类型的拔出力与皮质厚度之间均观察到线性关系。这些测试证实了过去的研究结果，即自攻和非自攻螺钉具有相同的固定力。随着循环剪切加载，螺钉逐渐松动，同时载荷-位移滞后增加，螺钉头部移位。更大的滞后表明，按照这种加载方案，非自攻螺钉可能比自攻螺钉松动得更多。通过扫描电子显微镜观察了循环加载前后螺钉螺纹周围的骨微裂纹。一种非自攻螺钉类型和两种自攻螺钉类型的显微照片显示，在螺钉螺纹外径尖端处有微裂纹。在施加循环剪切加载后，观察到更多微裂纹。
