环形外固定架对长骨斜形骨折断端固定效果的生物力学研究

Biomechanical study on the fixation effect of circular external fixators for oblique fractures of long bones

目的比较不同构型的环形外固定架对长骨斜形骨折断端固定效果的生物力学特性。方法选取15根同一批次的聚乙烯(polyethylene,PE)塑料棒制作长骨中段斜形骨折模型,根据PE棒与外固定架之间的连接方式随机分为五组,即单纯使用克氏针拉张固定组(克氏针组)、单纯使用橄榄针拉张固定组(橄榄针组)、单纯使用半针固定组(半针组)、橄榄针拉张固定结合两枚半针单皮质固定骨折断端组(橄榄针+半针组)、橄榄针拉张固定结合两枚橄榄针拉张固定骨折断端组(橄榄针+橄榄针组)。对各组模型进行轴向压缩试验,测定200 N、400 N、600 N、800 N轴向负荷下的断端位移并计算出断端的轴向刚度,再对各组模型进行扭转试验,测定4 N·m、7 N·m、10 N·m扭转负荷下的断端扭转角度,计算断端的扭转刚度。结果随着轴向负荷由200 N逐渐增至800 N,各组构型PE棒断端的位移均逐渐增加,各组断端轴向位移由小到大均依次为:橄榄针+橄榄针组、橄榄针+半针组、半针组、橄榄针组、克氏针组;在800 N轴向负荷下各组构型的轴向刚度由大到小依次为:橄榄针+橄榄针组[863.93(824.32,875.87)N/mm]、橄榄针+半针组[119.92(113.16,123.58)N/mm]、半针组[81.92(79.42,82.40)N/mm]、橄榄针组[76.83(72.45,79.47)N/mm]、克氏针组[70.80(67.49,71.59)N/mm],两两比较差异均有统计学意义(均P<0.05)。随着扭转负荷由4 N·m逐渐增至10 N·m,各组PE棒断端的扭转角度均逐渐增加,各组断端扭转角度由小到大均依次为:半针组、橄榄针+橄榄针组、橄榄针+半针组、橄榄针组、克氏针组;在10 N·m扭转负荷下各组构型扭转刚度由大到小依次为:半针组[1.80(1.63,1.85)N·m/°]、橄榄针+橄榄针组[1.05(1.02,1.07)N·m/°]、橄榄针+半针组[0.99(0.98,1.03)N·m/°]、橄榄针组[0.81(0.78,0.82)N·m/°]、克氏针组[0.75(0.74,0.76)N·m/°],两两比较差异均有统计学意义(均P<0.05)。结论使用橄榄针或半针固定斜形骨折断端均可以增加外固定架的轴向刚度和扭转刚度。由于斜形骨折断端之间无法提供足够的相互支撑,使用半针固定骨折断端时轴向位移和扭转角度仍较大;通过橄榄针对斜形骨折远、近端及骨折断端行拉张固定,可有效控制断端之间的剪切及位移,为骨折愈合提供理想的力学环境。

Objective To compare the biomechanical properties of different circular external fixators for the fracture site of oblique long bone fractures.Methods 15 polyethylene(PE)plastic rods with the same batch were selected to make the model of oblique fractures in the middle of long bones.According to the connection between PE rods and external fixators,the PE rods were randomly divided into:the group that was simply used kirschner wires(group kirschner wires),the group that was simply used olive wires(group olive wires),the group that was simply inserted half pins(group half pins),the group that was inserted single cortical fixed half pins at either side of the fracture site after being fixed by the tensioned olive wires(group olive wires+half pin),the group that was inserted tensioned trans-fracture olive wires after being fixed by the tensioned olive wires(group olive wires+olive wires).The axial compression tests were carried out,and the interfragmentary displacements under axial loads of 200 N,400 N,600 N and 800 N were measured and the axial stiffness was calculated.Then,the torsional tests were carried out,and the interfragmentary torsional angles were measured under torsional loads of 4 N·m,7 N·m and 10 N·m,and the torsional stiffness was calculated.Results With the increase of axial load from 200 N to 800 N,the axial interfragmentary displacement in each group gradually increased.The interfragmentary axial displacement of each group in ascending order was:group olive wires+olive wires,group olive wires+half pins,group half pins,group olive wires,group kirschner wires.The axial stiffness of each configuration under 800 N axial load in descending order was:group olive wires+olive wires[863.93(824.32,875.87)N/mm],group olive wires+half pins[119.92(113.16,123.58)N/mm],group half pins[81.92(79.42,82.40)N/mm],group olive wires[76.83(72.45,79.47)N/mm],group kirschner wires[70.80(67.49,71.59)N/mm].The pairwise comparisons of the axial stiffness data of each configuration had statistical significance(all P<0.05).With the increase of the torque load from 4 N·m to 10 N·m,the interfragmentary rotational angle in each configuration gradually increased.The interfragmentary torsion angle of each group in ascending order was:group half pins,group olive wires+olive wires,group olive wires+half pins,group olive wires,group kirschner wires.The torsional rigidity of each configuration under 10 N·m torsional load in descending order was:group half pins[1.80(1.63,1.85)N·m/°],group olive wires+olive wires[1.05(1.02,1.07)N·m/°],group olive wires+half pins[0.99(0.98,1.03)N·m/°],group olive wires[0.81(0.78,0.82)N·m/°],group kirschner wires[0.75(0.74,0.76)N·m/°].The pairwise comparisons of the torsional rigidity data of each configuration had statistical significance(all P<0.05).Conclusion The axial stiffness and torsional stiffness of circular external fixators can be increased by using tensioned olive wires or half pins at the fracture site.Due to the insufficient support between oblique fracture site,when the load is applied,the axial displacement and torsion angle of the fracture site will still be fairly large after being fixed the fracture site with half pins.Treating with tensioned trans-fracture olive wires after being fixed by the tensioned olive wires at either side of the fracture site can effectively control the interfragmentary shear and displacement,thus providing an ideal mechanical environment for fracture healing.