Karaarslan Ahmet Adnan, Karakaşlı Ahmet, Karcı Tolga, Aycan Hakan, Sesli Erhan
Şifa University Faculty of Medicine, Department of Orthopedics and Traumatology, İzmir, Turkey.
Dokuz Eylül University Faculty of Medicine, Department of Orthopedics and Traumatology, İzmir, Turkey.
Acta Orthop Traumatol Turc. 2015;49(5):552-7. doi: 10.3944/AOTT.2015.14.0439.
A frequent problem for interlocking nailing that affects the treatment of the fracture is locking screw deformation. The aim of this study is to determine whether bending resistance is different between high, low, and unthreaded locking screws of interlocking femoral nails.
Ninety screws were used in this experimental study, with 10 screws used in each of 9 groups. Three-point bending tests were performed on 6 groups of 5 mm screws (titanium, stainless steel, crossed with unthreaded, low threaded, and high threaded) and the same 3 thread types of 5.5 mm stainless steel screws in a 30-mm inner diameter steel tube, imitating the level of the lesser trochanter. An axial compressor was used to determine the yield points for permanent deformation in the locking screws by way of 3-point bending tests.
The mean yield point value of the 3-point bending tests of 5-mm low threaded stainless steel locking screws was 2071 N, 53% less than that of unthreaded screws (3169 N). The mean yield point value of 5-mm high threaded stainless steel locking screws was 556 N, 272% less than that of low threaded screws (2071 N).
To avoid locking screw deformation, high threaded screws must not be used as locking screws. In cases of unreliable patients, 5-mm low threaded screws should not be used in the nailing of comminuted or oblique femur shaft fractures. All 5-mm unthreaded screws and 5.5-mm low threaded stainless steel screws can be used safely in full weight-bearing conditions of unreliable patients.
交锁髓内钉治疗骨折时经常出现的一个影响治疗效果的问题是锁定螺钉变形。本研究的目的是确定交锁股骨髓内钉的高、低螺纹及无螺纹锁定螺钉的抗弯曲性能是否存在差异。
本实验研究共使用90枚螺钉，9组，每组10枚。在一根内径30 mm的钢管内，对6组5 mm的螺钉（钛合金、不锈钢，包括无螺纹、低螺纹和高螺纹交叉的）以及同样3种螺纹类型的5.5 mm不锈钢螺钉进行三点弯曲试验，模拟小转子水平。使用轴向压缩机通过三点弯曲试验确定锁定螺钉发生永久变形的屈服点。
5 mm低螺纹不锈钢锁定螺钉三点弯曲试验的平均屈服点值为2071 N，比无螺纹螺钉（3169 N）低53%。5 mm高螺纹不锈钢锁定螺钉的平均屈服点值为556 N，比低螺纹螺钉（2071 N）低272%。
为避免锁定螺钉变形，不得使用高螺纹螺钉作为锁定螺钉。对于不可靠的患者，在粉碎性或斜形股骨干骨折的髓内钉固定中不应使用5 mm低螺纹螺钉。所有5 mm无螺纹螺钉和5.5 mm低螺纹不锈钢螺钉在不可靠患者完全负重的情况下均可安全使用。
