Yang L, Saleeh M, Nayagam S
Division of Clinical Sciences, University of Sheffield, Northern General Hospital Trust, UK.
Proc Inst Mech Eng H. 2000;214(6):669-76. doi: 10.1243/0954411001535697.
Hybrid external fixators that use tensioned wires in the metaphysis and screws in the diaphysis combine the advantages of both unilateral and circular fixators and provide considerable flexibility in frame construction. This study aims to determine the effects of wire and screw combinations on the mechanical characteristics of such systems. Acrylic rods were used to simulate a long bone with a transverse fracture gap. A standard hybrid fixator design was used to stabilize the fracture in accordance with modern concepts with wires being used on one side of the fracture and screws on the other side. Twelve different wire and screw combinations were tested in axial compression and four-point bending in two planes. All the fixators tested demonstrated stiffening under increasing axial load, the extent of which appeared to correlate inversely with the number of wires used. Increasing the number of wires by one increased the axial stiffness by 7-16 N/mm (average 11 N/mm). The bending stiffness was largely controlled by the number of wires and increased by 0.42-1.03 N m/mm (average 0.74 N m/mm) for each additional wire. The axial stiffness of fixators with three screws was 4-7 N/mm (average 6 N/mm) higher than those with two screws if the offset screw was not in use. When the offset screw was used no stiffness advantages were found for three screws over two screws. The use of an offset screw substantially increased axial stiffness (by 12-26 N/mm, average 20 N/mm) and is recommended for unstable fractures. The two-ring hybrid fixators with four wires in one ring and three screws in the other had stiffness characteristics similar to the conventional four-ring Ilizarov fixator. Knowledge gained regarding the effects of wire and screw combinations on overall stiffness will be helpful both in the construction of frames and in destabilization during fracture healing.
混合式外固定器在干骺端使用张紧的钢丝，在骨干使用螺钉，结合了单侧和环形固定器的优点，并在框架构建方面提供了相当大的灵活性。本研究旨在确定钢丝和螺钉组合对这类系统力学特性的影响。使用丙烯酸棒模拟有横向骨折间隙的长骨。采用标准的混合固定器设计，根据现代理念稳定骨折，在骨折的一侧使用钢丝，另一侧使用螺钉。对12种不同的钢丝和螺钉组合进行了轴向压缩和两个平面的四点弯曲测试。所有测试的固定器在轴向载荷增加时均表现出刚度增加，其增加程度似乎与所用钢丝数量成反比。钢丝数量增加一根，轴向刚度增加7 - 16 N/mm（平均11 N/mm）。弯曲刚度在很大程度上由钢丝数量控制，每增加一根钢丝，弯曲刚度增加0.42 - 1.03 N·m/mm（平均0.74 N·m/mm）。如果不使用偏置螺钉，有三个螺钉的固定器的轴向刚度比有两个螺钉的固定器高4 - 7 N/mm（平均6 N/mm）。当使用偏置螺钉时，三个螺钉相对于两个螺钉没有刚度优势。使用偏置螺钉可大幅增加轴向刚度（增加12 - 26 N/mm，平均20 N/mm），推荐用于不稳定骨折。一个环有四根钢丝、另一个环有三个螺钉的双环混合固定器的刚度特性与传统的四环伊里扎洛夫固定器相似。关于钢丝和螺钉组合对整体刚度影响的知识，将有助于框架构建以及骨折愈合过程中的去稳定化。
