Rowlands A, Duck F A, Cunningham J L
Department of Mechanical Engineering, University of Bath & Medical Physics Department, Royal United Hospital, Bath, UK.
Med Eng Phys. 2008 Apr;30(3):278-84. doi: 10.1016/j.medengphy.2007.04.017. Epub 2007 Jun 22.
Hip prosthesis loosening can be determined in vivo using a vibration-based technique called vibrometry. In this technique, a low frequency (<1000Hz) sinusoidal vibration is applied to the femoral condyles and the resulting vibration is measured at the greater trochanter. If the prosthesis is securely fixed, the output vibration signal matches that of the input vibration, whereas if the prosthesis is loose, the output vibration signal is distorted and shows the marked presence of harmonics of the input frequency. One of the main problems with this application of this technique is in measuring the output vibration where significant amounts of soft tissue cover the measurement site. In order to circumvent this problem, an ultrasound probe, normally used for the measurement of blood flow, has been used to measure the output vibration. This has been evaluated by comparing the results obtained from the ultrasound probe with those from a conventional accelerometer in models representing a tight and loose hip prosthesis under simulated clinical conditions. The ultrasound probe was able to consistently detect the output vibration, for both the loose and secure prostheses. Under the test conditions used (which attempted to simulate a large thickness of soft tissue), the ultrasound probe was able to produce a greatly enhanced output vibration signal compared to the accelerometer. This suggests that the use of an ultrasound probe to detect mechanically induced vibration through significant amounts of soft tissue appears to be viable and could lead to enhanced detection of prosthesis loosening using this technique.
髋关节假体松动可以通过一种称为振动测量法的基于振动的技术在体内进行测定。在该技术中，向股骨髁施加低频（<1000Hz）正弦振动，并在大转子处测量产生的振动。如果假体固定牢固，输出振动信号与输入振动信号匹配，而如果假体松动，输出振动信号会失真，并显示出输入频率谐波的明显存在。该技术应用的一个主要问题在于测量输出振动，因为测量部位被大量软组织覆盖。为了解决这个问题，一种通常用于测量血流的超声探头已被用于测量输出振动。通过在模拟临床条件下，将超声探头获得的结果与传统加速度计在代表紧密和松动髋关节假体的模型中获得的结果进行比较，对其进行了评估。超声探头能够始终检测到松动和牢固假体的输出振动。在所使用的测试条件下（试图模拟较厚的软组织），与加速度计相比，超声探头能够产生大大增强的输出振动信号。这表明使用超声探头通过大量软组织检测机械诱导振动似乎是可行的，并且可能会提高使用该技术检测假体松动的能力。
