Whitney Kluk Augusta, Zhang Tina, Russell Joseph P, Kim Hyunchul, Hsieh Adam H, O'Toole Robert V
Orthopedics. 2017 Mar 1;40(2):e238-e241. doi: 10.3928/01477447-20161006-03. Epub 2016 Oct 13.
Orthopedic dogma states that external fixator stiffness is improved by placing 1 pin close to the fracture and 1 as distant as possible ("near-far"). This fixator construct is thought to be less expensive than placing pins a shorter distance apart and using "pin-bar" clamps that attach pins to outriggers. The authors therefore hypothesized that the near-far construct is stiffer and less expensive. They compared mechanical stiffness and costs of near-far and pin-bar constructs commonly used for temporary external fixation of femoral shaft fractures. Their testing model simulated femoral shaft fractures in damage control situations. Fourth-generation synthetic femora (n=18) were used. The near-far construct had 2 pins that were 106 mm apart, placed 25 mm from the gap on each side of the fracture. The pin-bar construct pins were 55 mm apart, placed 40 mm from the gap. Mechanical testing was performed on a material test system machine. Stiffness was determined in the linear portion of the load-displacement curve for both constructs in 4 modes: axial compression, torsional loading, frontal plane 3-point bending, and sagittal plane 3-point bending. Costs were determined from a 2012 price guide. Compared with the near-far construct, the pin-bar construct had stiffness increased by 58% in axial compression (P<.05) and by 52% in torsional loading (P<.05). The pin-bar construct increased cost by 11%. In contrast to the authors' hypothesis and existing orthopedic dogma, the near-far construct was less stiff than the pin-bar construct and was similarly priced. Use of the pin-bar construct is mechanically and economically reasonable. [Orthopedics. 2017; 40(2):e238-e241.].
骨科教条认为，通过将1根针靠近骨折处放置，另一根尽可能远离（“近-远”），可提高外固定器的刚度。人们认为这种固定器结构比将针放置得更近并使用将针连接到支腿的“针-杆”夹更便宜。因此，作者假设“近-远”结构更坚固且成本更低。他们比较了常用于股骨干骨折临时外固定的“近-远”结构和“针-杆”结构的机械刚度和成本。他们的测试模型模拟了损伤控制情况下的股骨干骨折。使用了第四代合成股骨（n = 18）。“近-远”结构有2根针，相距106 mm，在骨折两侧距间隙25 mm处放置。“针-杆”结构的针相距55 mm，距间隙40 mm。在材料测试系统机器上进行机械测试。在4种模式下，针对两种结构在载荷-位移曲线的线性部分测定刚度：轴向压缩、扭转载荷、额面三点弯曲和矢状面三点弯曲。成本根据2012年价格指南确定。与“近-远”结构相比，“针-杆”结构在轴向压缩时刚度增加了58%（P <.05），在扭转载荷时增加了52%（P <.05）。“针-杆”结构成本增加了11%。与作者的假设和现有的骨科教条相反，“近-远”结构比“针-杆”结构刚度更低，且价格相近。使用“针-杆”结构在机械和经济上是合理的。[《骨科》。2017；40(2):e238 - e241。]
