Steele C R, Zhou L J, Guido D, Marcus R, Heinrichs W L, Cheema C
Department of Mechanical Engineering, Stanford University, Calif. 94305.
J Biomech Eng. 1988 May;110(2):87-96. doi: 10.1115/1.3108423.
An approach referred to as Mechanical Response Tissue Analysis (MRTA) has been developed for the noninvasive determination of mechanical properties of the constituents of the intact limb. Of specific interest in the present study is the bending stiffness of the ulna. The point mechanical impedance properties in the low frequency regime, between 60 and 1,600 Hz are used. The procedure requires a proper design of the probe for good contact of the skin at midshaft and proper support of the proximal and distal ends of the forearm to obtain an approximation to "simple support" of the ulna. A seven-parameter model for the mechanical response is then valid, which includes the first mode of anterior-posterior beam bending of the ulna, the damping and spring effect of the soft tissue between probe and bone, and the damping of musculature. A dynamic analyzer (HP3562A) provides in seconds the impedance curve and the pole-zero curve fit. The physical parameters are obtained from a closed-form solution in terms of the curve-fit parameters. The procedure is automated and is robust and analytically reliable at about the five percent level. Some 80 human subjects have been evaluated by this mechanical response system and by the Norland single photon absorptiometer, providing for the first time in vivo, a comparison of elastic bending stiffness (ulna) and bone mineral content (radius). Three functional parameters of potential clinical value are the cross-sectional bending stiffness EI, the axial load capability Pcr (Euler buckling load) and the bone "sufficiency" S, defined as the ratio of Pcr to body weight. The correlation between EI and bone mineral (r = 0.81) is only slightly less than previous in vitro results with both measurements on the same bone (r = 0.89). When sufficiency is taken into consideration, the correlation of Pcr and bone mineral content is improved (r = 0.89). An implication is that "quality" of bone is a factor which is not indicated by bone mineral content but which is indicated by stiffness. Bone mineral is necessary for proper stiffness but not sufficient. Therefore mechanical measurement should provide a new dimension to be used toward a better understanding of the factors related to bone health and disease.
一种被称为机械响应组织分析（MRTA）的方法已被开发出来，用于无创测定完整肢体各组成部分的力学性能。本研究特别感兴趣的是尺骨的弯曲刚度。使用的是60至1600赫兹低频范围内的点机械阻抗特性。该过程需要对探头进行适当设计，以便在骨干中部与皮肤良好接触，并对前臂的近端和远端进行适当支撑，从而获得接近尺骨“简支”的状态。然后一个七参数的机械响应模型是有效的，它包括尺骨前后梁弯曲的第一模态、探头与骨骼之间软组织的阻尼和弹簧效应以及肌肉组织的阻尼。一台动态分析仪（HP3562A）能在数秒内提供阻抗曲线和零极点曲线拟合。物理参数是根据曲线拟合参数通过闭式解获得的。该过程是自动化的，在约5%的水平上是稳健且分析可靠的。约80名人类受试者已通过这种机械响应系统和诺兰德单光子吸收仪进行了评估，首次在体内比较了弹性弯曲刚度（尺骨）和骨矿物质含量（桡骨）。具有潜在临床价值的三个功能参数是横截面弯曲刚度EI、轴向承载能力Pcr（欧拉屈曲载荷）和骨“充足性”S，S定义为Pcr与体重的比值。EI与骨矿物质之间的相关性（r = 0.81）仅略低于之前在同一根骨上进行两种测量的体外结果（r = 0.89）。当考虑充足性时，Pcr与骨矿物质含量的相关性得到改善（r = 0.89）。这意味着骨的“质量”是一个不由骨矿物质含量体现但由刚度体现的因素。骨矿物质对于适当的刚度是必要的，但不是充分的。因此，力学测量应该为更好地理解与骨骼健康和疾病相关的因素提供一个新的维度。
