It has been difficult to improve the intramedullary nail technique because of the lack of consistency in the procedures used to evaluate the bone-implant stiffness. The goal of this study was to develop a simple methodology for determining the stiffness of a bone implant that considers the physiological loads and bone orientation, and allows a finite element analysis and its validation using mechanical experimentation. Finite element models for a composite tibia before and after an intramedullary nail was implanted were created and validated using the results of a set of mechanical experiments, in which the stiffness values of the model were measured and compared under axial compression, 4-point bending, shear, and torsional loads considering the patient’s condition in the early healing phase. Grips with personalized bone interfaces were developed to guarantee the physiological loads and bone orientation. In the 4-point bending, torsional, and shear loading modes, the developed bone-implant finite element model showed a satisfactory level of predictive potential in relation to the experimental observations, with a percentage variation of less than 35%. This study also demonstrated that despite the high stiffness of the bone-implant construct, motion was always generated at the interfragmentary site during the early healing phase. In addition, during this stage, the nail supported most of the load applied to the lower limb (up to 85%). This strategy could contribute to the future determination of the ideal mechanical environment at a fracture site and how this environment evolves throughout the healing process.

中文翻译：

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骨植入物刚度评估方法

由于用于评估骨植入物刚度的程序缺乏一致性，因此很难改进髓内钉技术。本研究的目标是开发一种简单的方法来确定骨植入物的刚度，该方法考虑了生理负荷和骨骼方向，并允许使用机械实验进行有限元分析和验证。使用一组力学实验的结果创建并验证了髓内钉植入前后复合胫骨的有限元模型，其中在轴向压缩、4 点弯曲、考虑到患者在早期愈合阶段的状况，剪切和扭转载荷。开发了带有个性化骨骼接口的手柄，以保证生理负荷和骨骼方向。在 4 点弯曲、扭转和剪切载荷模式下，开发的骨植入物有限元模型显示出与实验观察相关的令人满意的预测潜力，百分比变化小于 35%。该研究还表明，尽管骨植入结构具有很高的刚度，但在早期愈合阶段总是在碎片间部位产生运动。此外，在这个阶段，钉子支撑了施加到下肢的大部分负荷（高达 85%）。该策略可能有助于未来确定骨折部位的理想机械环境以及该环境如何在整个愈合过程中演变。