Development and application of a six degree-of-freedom knee joint goniometer

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To quantify manual test of knee joint instability, we developed a six dgree-of-freedom goniometer and applied it to clinical use. first, we gave mathematical definition of internal-external rotation (axial rotation). Suppose that <phi> , <theta> , <psi> denote Eulerian angles respectively. According to our definition, net axial rotation is given by integrating angular velocity<omega> =-(d <phi> )/(dt)・sin <theta> +(d <psi> )/(dt)Second, we developed a six degree-of-freedom knee goniometer. We used four sensors which detect abduction-adduction, flexion-extention, internal-external rotation angles and anterior-posterior displacement. Outputs of these sensors correspond to above-mentioned angles and displacement directly and no processing and calculation is necessary.Using this goniometer, we tried anterior-posterior drawer test, varus-valgus stress test on normal ten knees and three injured knees. Though amount of data are not enough, results of injured knees were specific to injured ligaments. And good agreement was obtained between these results and roentgenographic measurement.We are now developing unrestrained measurement apparatus of knee joint motion which adopts two inclinometers and one magnetic sensor.