Gautier E, Perren S M, Cordey J
Department of Orthopaedic Surgery, Kantonsspital, Fribourg, Switzerland.
Injury. 2000 Sep;31 Suppl 3:C14-20. doi: 10.1016/s0020-1383(00)80027-3.
Mechanical unloading of the plated bone segment is observed after plate osteosynthesis because the implant takes over a part of the physiological loading. Strain reduction in the bony tissue depends on the rigidity of the plate (cross-sectional area, geometrical form, and modulus of elasticity). The aim of the present study was to calculate theoretically the effect of plate position relative to bending direction on the overall bending stiffness of the composite system plate-bone. To calculate the rigidity, a cylindrical bone model with mechanical characteristics similar to a sheep tibia and a rectangular plate cross-section corresponding to a DC-plate with either a modulus of elasticity of steel or titanium was used. Calculations under different bending directions were performed according to the laws of the linear bending theory and the composite beam theory. The bending stiffness of a plate osteosynthesis reaches a minimum and a maximum respectively, in cases in which the bending moment acts in the direction of the main axis of the area moment of inertia of the plate. The minimum is present with the plate bent vertically, the maximum with the plate bent horizontally, e.g. on the tension side of the composite system--on the assumption that the bone structure opposite the plate is capable of withstanding compressive loading. For steel and titanium plates, factors of 2 and 2.25 respectively were calculated between the minimum and the maximum bending stiffnesses of the osteosynthesis. The bending rigidity of the plate alone has only a minimal effect on the total stiffness of the osteosynthesis. With a plate bent vertically, the difference between steel and titanium plates was 18%, with the plate bent horizontally (situated on the tension side), it was only 7%. The bending stiffness of a plate osteosynthesis depends on the cross-section, the geometrical form, and the modulus of elasticity of the plate, as well as on the plate position relative to the bending direction of the composite system. The modulus of elasticity of the plate is relatively unimportant, while with a given plate the individual plate position relative to the bending direction is of crucial importance. Thus, changing the modulus of elasticity of the plate cannot solve the problem of implant induced unloading of the bone cortex because the bending stiffness of the composite system depends much more on the plate position relative to the bending direction.
钢板接骨术后可观察到接骨钢板段的机械性卸载，因为植入物承担了部分生理负荷。骨组织中的应变降低取决于钢板的刚度（横截面积、几何形状和弹性模量）。本研究的目的是从理论上计算钢板相对于弯曲方向的位置对钢板 - 骨复合系统整体弯曲刚度的影响。为计算刚度，使用了一个机械特性类似于绵羊胫骨的圆柱形骨模型以及一个对应于具有钢或钛弹性模量的动力加压钢板（DC - 钢板）的矩形钢板横截面。根据线性弯曲理论和复合梁理论对不同弯曲方向进行了计算。当弯矩作用于钢板惯性矩主轴方向时，钢板接骨术的弯曲刚度分别达到最小值和最大值。最小值出现在钢板垂直弯曲时，最大值出现在钢板水平弯曲时，例如在复合系统的张力侧——假设钢板对面的骨结构能够承受压缩负荷。对于钢和钛钢板，接骨术的最小和最大弯曲刚度之间分别计算出的系数为2和2.25。仅钢板的弯曲刚度对接骨术的总刚度影响极小。当钢板垂直弯曲时，钢和钛钢板之间的差异为18%，当钢板水平弯曲（位于张力侧）时，差异仅为7%。钢板接骨术的弯曲刚度取决于钢板的横截面、几何形状和弹性模量，以及钢板相对于复合系统弯曲方向的位置。钢板的弹性模量相对不重要，而对于给定的钢板，其相对于弯曲方向的具体位置至关重要。因此，改变钢板的弹性模量无法解决植入物引起的骨皮质卸载问题，因为复合系统的弯曲刚度更多地取决于钢板相对于弯曲方向的位置。
