Mills O S, Hull M L
Department of Mechanical Engineering, University of California, Davis 95616.
J Biomech. 1991;24(6):351-69. doi: 10.1016/0021-9290(91)90025-i.
The contributions of this paper are twofold. One is the design and performance evaluation of new equipment to determine the rotational flexibility of the human knee in vivo. Since determining knee flexibility requires the application of external loads and the measurement of knee rotations, the new equipment consists of a load application stand and a triaxial goniometer. The triaxial goniometer noninvasively mounts to the leg and directly measures the relative three degrees-of-freedom rotations of the knee sequentially and independently. The goniometer incorporates several unique design features which enhance measurement accuracy. The load stand applies pure varus/valgus and external/internal axial moments either individually or in combination through the use of motors controlled by the test subject. Unique to this design are features which enable the application of moments to the knee which minimise shear forces. Other unique design features permit the stand to control hip and knee flexion angles, muscle contraction, and axial loading. To assess the accuracy with which rotations are measured during experiments, three tests were conducted with the equipment. One test evaluated the inherent accuracy of the goniometer, a second test assessed the potential for goniometer slippage during loading, and a third explored the effect of goniometer mounting on the repeatability of results. A special verification apparatus facilitated evaluation of goniometer inherent accuracy. A second contribution of the paper is an investigation of the effect of foot constraints (i.e. boundary conditions) on flexibility results. To make this investigation, three subjects were tested with the knee at 15 degrees of flexion. Results revealed large differences in flexibility between constraining the foot in both external/internal and varus/valgus rotations and permitting the foot to rotate freely in the direction not being loaded. Further, constraint moments as high as 23 Nm were also recorded. These results emphasise that in order to obtain accurate flexibility results for isolated loads, the foot must be unconstrained by the loading apparatus.
本文的贡献有两个方面。一是设计并评估用于在体内测定人体膝关节旋转灵活性的新设备。由于测定膝关节灵活性需要施加外部负荷并测量膝关节旋转，因此新设备包括一个负荷施加架和一个三轴测角仪。三轴测角仪以无创方式安装在腿部，可依次独立地直接测量膝关节相对的三个自由度的旋转。该测角仪具有多个独特的设计特点，可提高测量精度。负荷架通过由测试对象控制的电机单独或组合施加单纯的内翻/外翻和外/内轴向力矩。该设计的独特之处在于能够向膝关节施加力矩，从而将剪切力降至最低。其他独特的设计特点使负荷架能够控制髋关节和膝关节的屈曲角度、肌肉收缩以及轴向负荷。为了评估实验过程中旋转测量的准确性，使用该设备进行了三项测试。一项测试评估了测角仪的固有准确性，第二项测试评估了加载过程中测角仪滑动的可能性，第三项测试探究了测角仪安装对结果可重复性的影响。一种特殊的验证装置有助于评估测角仪的固有准确性。本文的第二个贡献是研究足部约束（即边界条件）对灵活性结果的影响。为了进行这项研究，对三名受试者在膝关节屈曲15度时进行了测试。结果显示，在内外旋转和内翻/外翻旋转中约束足部与允许足部在未加载方向自由旋转时，灵活性存在很大差异。此外，还记录到高达23牛米的约束力矩。这些结果强调，为了获得孤立负荷下准确的灵活性结果，足部必须不受加载设备的约束。
