Chiu W K, Ong W H, Russ M, Tran T, Fitzgerald M
Department of Mechanical & Aerospace Engineering, Monash University, Melbourne, Australia.
The Alfred Hospital, Melbourne, Australia.
J Rehabil Assist Technol Eng. 2019 Apr 24;6:2055668319842806. doi: 10.1177/2055668319842806. eCollection 2019 Jan-Dec.
This paper aims to evaluate the effects of mass loading on the healing assessment of an internally fixated femur by vibrational means. The presence of soft tissue surrounding a femur increases damping and mass of a system, and hence affects the vibrational response of a mechanical structure by obscuring the coherent modes. This may compromise vibration-based monitoring strategies in identifying modes associated with fracture healing.
This paper presents a series of experimental works to address this issue. Two osteotomised composite femurs were internally fixated using a plate-screw system and an intramedullary nail. Soft tissue is approximated by surrounding an artificial Sawbone femur with modelling clay. The femur is excited by an instrumented impact hammer and instrumented with two accelerometers to record bending and torsion modes between 0 and 600 Hz. A 30-min epoxy was applied to simulate the healing of the fractured femur in the osteotomised region. The resonant frequencies and its modes are monitored while union is being formed and a healing index is calculated at various times to quantify the degree of healing.
The results demonstrate that the effect of modelling clay compressed the natural modes along the frequency axis. It is observed that frequency bandwidth in the vicinity of 150 Hz and 500 Hz is sensitive to the state of healing of the fixated femurs, which is due to the increase in stiffness of the osteotomised region. These findings were used to formulate the healing index which assists in identifying the initial, later and complete healing stages in conjunction with the index derivative.
In this study, a two-sensor measurement strategy to quantify fixated femur healing is investigated. It is shown that the mass loading effect did not affect this vibrational analysis method ability to assess the state of healing, and both coherent bending and twisting modes associated with healing were easily identified. The proposed healing index, its derivative, and the cross-spectra are a viable tool for quantitative healing assessment.
本文旨在评估质量加载对通过振动手段对内固定股骨愈合评估的影响。股骨周围软组织的存在增加了系统的阻尼和质量，从而通过模糊相干模态影响机械结构的振动响应。这可能会损害基于振动的监测策略识别与骨折愈合相关模态的能力。
本文提出了一系列实验工作来解决这个问题。两根截骨的复合股骨使用钢板螺钉系统和髓内钉进行内固定。通过用模型黏土围绕人工锯骨股骨来近似软组织。用仪器化的冲击锤激发股骨，并安装两个加速度计来记录0至600Hz之间的弯曲和扭转模态。应用一种30分钟固化的环氧树脂来模拟截骨区域骨折股骨的愈合。在愈合形成过程中监测共振频率及其模态，并在不同时间计算愈合指数以量化愈合程度。
结果表明，模型黏土的作用使自然模态沿频率轴压缩。观察到150Hz和500Hz附近的频率带宽对固定股骨的愈合状态敏感，这是由于截骨区域刚度增加所致。这些发现被用于制定愈合指数，该指数结合指数导数有助于识别初始、后期和完全愈合阶段。
在本研究中，研究了一种用于量化固定股骨愈合的双传感器测量策略。结果表明，质量加载效应并未影响这种振动分析方法评估愈合状态的能力，并且与愈合相关的相干弯曲和扭转模态都很容易识别。所提出的愈合指数、其导数和互谱是用于定量愈合评估的可行工具。
