Meyers Nicholaus, Schülke Julian, Ignatius Anita, Claes Lutz
Institute of Orthopedic Research and Biomechanics, Center of Musculoskeletal Research Ulm, University Hospital Ulm, Ulm, Baden-Württemberg, Germany.
PLoS One. 2017 Dec 11;12(12):e0189432. doi: 10.1371/journal.pone.0189432. eCollection 2017.
Distraction osteogenesis is a procedure widely used for the correction of large bone defects. However, a high complication rate persists, likely due to insufficient stability during maturation. Numerical fracture healing models predict bone regeneration under different mechanical conditions allowing fixation stiffness optimization. However, most models apply a linear elastic material law inappropriate for the transient stresses/strains present during limb lengthening or segment transport. They are also often validated using in vivo osteotomy models lacking precise mechanical regulation due to the unavoidable stimulation of secondary interfragmentary motion during ambulation under finitely stiff fixation. Therefore, in order to create a robust numerical model of distraction osteogenesis, it is necessary to both characterize the new tissue's viscoelasticity during distraction and determine the influence of strictly isolated stimulation in each loading mode (tension, compression, and shear) to account for potential differences in mechanical and histological response.
Two electromechanical fixators with integrated load cells were designed to precisely perform and monitor in vivo lateral distraction and isolated stimulation in sheep tibiae using a mobile, hydroxyapatite-coated titanium plate. The novel surgical procedure circumvents osteotomy, eliminating the undesirable and unquantifiable mechanical stimulation during ambulation.
After a 10-day post-surgery latency period, two 0.275 mm distraction steps were performed daily for 10 days. The load cell collected data before, during, and after each distraction step and was terminated after no less than one minute from the time of distraction. A 7-day consolidation period separated the distraction phase and 18-day stimulation phase. Stimulation was carried out in isolated tension, compression, or shear while recording force/time data. Each stimulation session consisted of 120 cycles with a magnitude of either 0.1 mm or 0.6 mm in the tension and compression groups and 1.0 mm in the shear group. The animals were euthanized after a 3-day holding period following stimulation.
Our initial results show that the tissue progressively stiffens and maintains an increasingly large residual traction. The force curves during compressive stimulation show a progressive drift from compression toward tension. We hypothesize that this behavior may be due to the preferential flow of fluid outward from the tissue and a greater resistance to reabsorption during the plate's return to the starting position.
牵张成骨术是一种广泛用于矫正大的骨缺损的手术方法。然而，并发症发生率仍然很高，这可能是由于成熟过程中稳定性不足所致。数值骨折愈合模型可预测不同力学条件下的骨再生情况，从而实现固定刚度的优化。然而，大多数模型采用线性弹性材料定律，不适用于肢体延长或节段转移过程中出现的瞬态应力/应变。这些模型还常常使用体内截骨模型进行验证，由于在有限刚度固定下行走过程中不可避免地会刺激继发性骨间运动，导致缺乏精确的力学调节。因此，为了创建一个强大的牵张成骨数值模型，有必要在牵张过程中表征新组织的粘弹性，并确定每种加载模式（拉伸、压缩和剪切）中严格隔离刺激的影响，以考虑力学和组织学反应的潜在差异。
设计了两种带有集成测力传感器的电动固定器，用于使用可移动的羟基磷灰石涂层钛板在绵羊胫骨中精确进行和监测体内横向牵张和隔离刺激。这种新颖的手术方法避免了截骨，消除了行走过程中不必要且无法量化的力学刺激。
术后10天的潜伏期后，每天进行两个0.275毫米的牵张步骤，持续10天。测力传感器在每个牵张步骤之前、期间和之后收集数据，并在牵张后不少于1分钟时终止。7天的巩固期将牵张阶段与18天的刺激阶段分开。在记录力/时间数据的同时，分别在孤立的拉伸、压缩或剪切状态下进行刺激。每个刺激疗程包括120个周期，拉伸和压缩组的幅度为0.1毫米或0.6毫米，剪切组为1.0毫米。刺激后3天的观察期结束后对动物实施安乐死。
我们的初步结果表明，组织逐渐变硬并保持越来越大的残余牵引力。压缩刺激期间的力曲线显示出从压缩向拉伸的逐渐漂移。我们推测，这种行为可能是由于流体从组织中优先向外流动，以及在钢板回到起始位置时对再吸收的更大阻力所致。
