Woo S L, Lothringer K S, Akeson W H, Coutts R D, Woo Y K, Simon B R, Gomez M A
J Orthop Res. 1984;1(4):431-49. doi: 10.1002/jor.1100010412.
In the application of "rigid" plates for diaphyseal fractures, lack of callus healing and overprotection of the underlying bone are viewed by many investigators as undesirable consequences. Potential solutions offered to overcome these deficiencies include modification of the timing of plate removal, use of biologically degradable materials for plates so that stress-shielding can be minimized, and use of less rigid plate fixation systems. This study emphasizes the selection of appropriate design criteria for less rigid plate-fixation systems. To accomplish this goal, the axial, bending, and torsional stiffness parameters are considered in place of the oversimplified terms such as "flexible plate" or "elastic fixation." With the aid of finite element modeling and simplified bench experiments, we performed parametric studies and singled out the plate axial stiffness as the dominant factor in altering the bone stresses. As a result, we designed two experimental plates, one a thin Ti-6Al-4V (titanium with 6% aluminum and 4% vanadium) alloy plate with low stiffness in axial and bending directions, and the other a tubular stainless steel plate with low stiffness in the axial direction but moderate stiffness in bending and torsional directions. The low-stiffness Ti-6Al-4V alloy plate was first tested in a demanding bilateral canine midshaft osteotomy, and proved to be inadequate. Both experimental plates were successful in the unilateral osteotomies, with the tubular plate yielding the best results. After 6 months of plating, the bones beneath the tubular plate had superior mechanical and structural properties as compared to those of the control "rigid" stainless steel and the Ti-6Al-4V alloy plates. Application of this plate prolonged for 9 months did not cause reduction in bone properties and strength. The success of the tubular plate is due to its moderate bending and torsional stiffnesses, which provide adequate fixation to achieve callus union, while its low axial stiffness permits the underlying bone to share the physiological stresses needed for bone remodeling. These drastic changes in mechanical demands on the internal fixation plate during the early healing phase and the postunion remodeling phase are discussed.
在将“刚性”钢板应用于骨干骨折时，许多研究者认为缺乏骨痂愈合以及对下方骨骼的过度保护是不良后果。为克服这些缺陷而提出的潜在解决方案包括改变钢板取出时间、使用生物可降解材料制作钢板以尽量减少应力遮挡，以及使用刚性较小的钢板固定系统。本研究强调为刚性较小的钢板固定系统选择合适的设计标准。为实现这一目标，考虑了轴向、弯曲和扭转刚度参数，以取代诸如“柔性钢板”或“弹性固定”等过于简化的术语。借助有限元建模和简化的台架实验，我们进行了参数研究，并确定钢板轴向刚度是改变骨应力的主导因素。结果，我们设计了两种实验性钢板，一种是轴向和弯曲方向刚度较低的薄钛 - 6Al - 4V（含6%铝和4%钒的钛）合金钢板，另一种是轴向刚度低但弯曲和扭转方向刚度适中的管状不锈钢板。低刚度的钛 - 6Al - 4V合金钢板首先在要求苛刻的双侧犬股骨干中段截骨实验中进行测试，结果证明并不理想。两种实验性钢板在单侧截骨实验中均取得成功，其中管状钢板效果最佳。钢板固定6个月后，与对照的“刚性”不锈钢板和钛 - 6Al - 4V合金钢板相比，管状钢板下方的骨骼具有更好的力学和结构性能。应用这种钢板9个月也未导致骨性能和强度下降。管状钢板的成功归因于其适中的弯曲和扭转刚度，这为实现骨痂愈合提供了足够的固定，而其低轴向刚度使下方骨骼能够分担骨重塑所需的生理应力。文中还讨论了在早期愈合阶段和愈合后重塑阶段对内固定钢板力学需求的这些剧烈变化。
