振动促进骨愈合系统的参数识别及动力学特征

Parameter identification and kinetics of thevibration in promoting bone healing system

背景:骨折愈合是一个极其复杂的生物学修复重建过程,骨折端局部的力学环境在骨折愈合过程中起着调控作用。目的:设计一部骨应力刺激仪并进行动力学建模及参数的识别。方法:基于振动促进骨愈合的机制,设计了一部骨应力刺激仪。简化成了二自由度带阻尼的弹簧系统强迫振动模型,对振动促进骨愈合系统进行了主要参数的识别(橡胶弹簧的总刚度的识别,足底肌肉刚度的识别,足底肌肉阻尼的识别,克氏针弯曲刚度′的识别),得到了模拟骨痂处的振幅并进行振动促进骨愈合系统实验。结果与结论:(1)通过理论分析及试验研究并结合样机的稳定工作区间,确定了该系统在激振频率为26-40 Hz、激振力为100-350N的条件下可使胫骨骨折断端产生轴向微动,在断骨界面产生了一定的力学刺激;(2)由于仿真时忽略了外固定架对骨痂处振幅的应力遮挡作用,所以仿真结果略高于测试结果。通过拆开外固定架进行测试,拆开后骨痂处的振幅大于完全固定的振幅;(3)结果表明,骨应力刺激仪可使骨折断端产生有利于骨愈合的微动。在临床上建议使用轴向刚度可调、径向刚度不变外固定支架,可以有效的克服应力遮挡。

BACKGROUND： Fracture healing is an extremely complex process in biological repair and reconstruction. Local mechanical environment of thefracturesite plays a regulatory role in the process of fracture healing. OBJECTIVE：To design a bone stress stimulator and to carry out the dynamics modeling and parameter identification.METHODS： Based on the mechanism of vibration in promoting bone healing, a bone stress stimulator was designed.A two-degree-of-freedom damped spring system forced vibration model was simplified. Five healthymale volunteers（about 25 years old） were recruited to identify the main parameters of the vibration in promoting bone healing system（the identification of the total stiffness of the rubber spring K1, the plantar muscle stiffness K2, theplantar muscle damping r1, andthe kirschner wire bending stiffness K＇）.The simulated callus amplitude was obtained and the experiments of vibration to promote bone healing wereperformed. RESULTS AND CONCLUSION：According to the theoretical analysis, and experimental research combined with the stable working range of the prototype, the system could generate axial fretting at tibial fragment and the bone fracture interface produced a certain mechanical stimulation under the conditions of excitation frequency of 26-40 Hz and excitation force of 100-350 N. Due to the omission of the stress shielding effect of the external fixator on the amplitude of the callus, the simulation results were slightly higher than the test results. The amplitude of the callus after disassembled was greater than that of the complete fixation. These results show that the stress-stimulator can make the tibial fragment to produce fretting which is beneficial to bone healing. Inthe clinic, it is recommended to use external stent with adjustable axial stiffness, constant external stiffness, which can effectively overcome the stress shielding.