Wähnert D, Lenz M, Schlegel U, Perren S, Windolf M
AO Research Institute Davos, Davos, Switzerland.
Acta Chir Orthop Traumatol Cech. 2011;78(3):208-14.
Twisting is clinically the most frequently applied method for tightening and maintaining cerclage fixation. The twisting procedure is controversially discussed. Several factors during twisting affect the mechanical behaviour of the cerclage. This in vitro study investigated the influence of different parameters of the twisting procedure on the fixation strength of the cerclage in an experimental setup with centripetal force application.
Cortical half shells of the femoral shaft were mounted on a testing fixture. 1.0 mm, 1.25 mm and 1.5 mm stainless ste- el wire cerclages as well as a 1.0mm cable cerclage were applied to the bone. Pretension of the cerclage during the installation was measured during the locking procedure. Subsequently, cyclic testing was performed up to failure.
Higher pretension could be achieved with increasing wire diameter. However, with larger wire diameter the drop of pre- tension due to the bending and cutting the twist also increased. The cable cerclage showed the highest pretension after locking. Cerclages twisted under traction revealed significantly higher initial cerclage tension. Plastically deformed twists offered higher cerclage pretension compared to twists which were deformed in the elastic region of the material. Cutting the wire within the twist caused the highest loss of cerclage tension (44% initial tension) whereas only 11 % was lost when cutting the wire ends separately. The bending direction of the twist significantly influenced the cerclage pretension. 45% pretension was lost in forward bending of the twist, 53% in perpendicular bending and 90% in backward bending.
Several parameters affect the quality of a cerclage fixation. Adequate installation of cerclage wires could markedly improve the clinical outcome of cerclage.
在临床上，扭转是收紧和维持环扎固定最常用的方法。对于扭转操作存在争议。扭转过程中的几个因素会影响环扎的力学性能。本体外研究在施加向心力的实验装置中，研究了扭转操作的不同参数对环扎固定强度的影响。
将股骨干的皮质半壳安装在测试夹具上。将1.0毫米、1.25毫米和1.5毫米的不锈钢丝环扎带以及1.0毫米的缆线环扎带应用于骨。在锁定过程中测量安装过程中环扎带的预紧力。随后，进行循环测试直至失效。
随着钢丝直径的增加，可以实现更高的预紧力。然而，钢丝直径越大，由于弯曲和切割扭转导致的预紧力下降也越大。缆线环扎带在锁定后显示出最高的预紧力。在牵引下扭转的环扎带显示出明显更高的初始环扎带张力。与在材料弹性区域变形的扭转相比，塑性变形的扭转提供了更高的环扎带预紧力。在扭转内切割钢丝导致环扎带张力损失最大（初始张力的44%），而分别切割钢丝末端时仅损失11%。扭转的弯曲方向显著影响环扎带预紧力。扭转向前弯曲时预紧力损失45%，垂直弯曲时损失53%，向后弯曲时损失90%。
几个参数会影响环扎固定的质量。环扎钢丝的适当安装可以显著改善环扎的临床效果。
