Purpose

Critical size long bone defects represent a clinical challenge in orthopaedic surgery. Various grafting techniques have been developed through the years, but they all present several downsides. A key requirement of all grafting techniques is the achievement of a continuous interface between host bone and graft to enhance both biological processes and mechanical stability. This study used a parametric in silico model to quantify the biomechanical effect of the inaccuracies inherent to current osteotomy techniques, and to test a new concept of accurate taper-fit junction that may improve the biomechanical parameters of the reconstruction under load.

Methods

A population-based in-silico 3D model of the reconstruction of a long bone defect was built to represent a defect of the femoral mid-diaphysis. To fix the reconstruction a titanium plate was placed on the lateral aspect of the reconstruction. The model was modified to (i) quantify the biomechanical consequences of actual inaccuracies in the realization of a flat host-graft interface, (ii) compare the contact behaviour and bone strains among different taper angles of the new design and the current host-graft flat interface, (iii) evaluate the robustness of the taper-fit design to inter-subject variability in bone geometry and defect length.

Results

The influence of 2° single-plane misalignments of the host-graft interface is highly dependent on the misalignment orientation with respect to the metal plate. For some misalignment orientations, tangential micromotions of contact interfaces exceeded alert thresholds. When the angle of the taper-fit host-graft junction is changed from 10° to 30° and the results obtained are compared with the planar case, the overall stiffness is almost preserved, the bone strains are almost unchanged with safety factors higher than five, and full contact closure around the host-graft junction is achieved at 20°. Similarly, contact pressures decrease almost linearly with a 20% decrease at 30°. The host-graft micro motions are almost unchanged in both value and distribution up to 20° and never exceed the warning threshold of 50 μm.

Conclusions

The present in silico study developed quantitative biomechanical evidence that an osteotomy performed with attention to the perpendicularity of the cut planes is needed to reduce the risk of mismatch and possible complications of long bone reconstructions, and that a new concept of a taper-fit junction may improve the biomechanical environment of the interface between the graft and the host bone. The optimal taper-fit configuration is suggested to be around a 20° taper angle. These results will serve as an input to conduct ex vivo experiments to further corroborate the proposed taper-fit junction concept and to refine its surgical implementation.

中文翻译：

---

改善长骨重建的锥形接头：参数化 In Silico 模型

目的

临界尺寸长骨缺损代表了骨科手术的临床挑战。多年来已经开发了各种嫁接技术，但它们都存在一些缺点。所有移植技术的一个关键要求是实现宿主骨和移植物之间的连续界面，以增强生物过程和机械稳定性。本研究使用计算机参数化模型来量化当前截骨技术固有的不准确性的生物力学影响，并测试可以改善负载下重建的生物力学参数的精确锥形配合接头的新概念。

方法

建立了基于人群的长骨缺损重建的计算机 3D 模型来表示股骨中骨干的缺损。为了固定重建，将钛板放置在重建的侧面。该模型被修改为 (i) 量化在实现平面宿主-移植物界面中实际不准确性的生物力学后果，(ii) 比较新设计和当前宿主移植物的不同锥角之间的接触行为和骨应变平面界面，（iii）评估锥形配合设计对骨骼几何形状和缺陷长度的受试者间变异性的稳健性。

结果

宿主-移植物界面的 2° 单平面错位的影响高度取决于相对于金属板的错位方向。对于某些未对准的方向，接触界面的切向微动超过了警报阈值。当锥度配合宿主-移植物交界处的角度从 10° 变为 30° 并与平面情况进行比较时，整体刚度几乎保持不变，骨应变几乎没有变化，安全系数高于 5 ，并且在 20° 处实现了围绕宿主移植结的完全接触闭合。同样，接触压力几乎呈线性下降，在 30° 时下降 20%。宿主移植物微运动在值和分布上几乎没有变化，直到 20°，并且从未超过 50 μm 的警告阈值。

结论

目前的计算机研究开发了定量的生物力学证据，表明需要进行截骨术时注意切面的垂直度，以降低长骨重建的不匹配风险和可能的并发症，并且锥形配合连接的新概念可能改善移植物与宿主骨界面的生物力学环境。建议最佳锥度配合配置为 20° 锥角左右。这些结果将作为进行体外实验的输入，以进一步 证实所提出的锥形配合连接概念并改进其手术实施。