MEASUREMENT OF MULTI-AXIS JOINT ANGLES USING FLEXIBLE ELECTROGONIOMETERS

Abstract

A system is developed to measure multi-axis joint angles by using improved flexible electrogoniometers. The weight and shape of the goniometer is smaller than the usual one which was developed in our laboratory a few years ago. Two pieces of specially designed strain gauge which are extra long are plastered on the two opposite sides of a metal thin beam with uniform section, to form a Wheatstone bridge circuit. The total amount of elongation of each strain gauge changes in proportion to the angle between the two ends of the beam and does not depend on the deformation curves of the beam. Thus, the output voltage of the bridge circuit changes in proportion to the angle between the two ends of the beam. The weight of the measuring part is under 1g; its width is under 3mm, thickness is under 0.1mm, and the length is variable up to 100mm. It is very easy to flex and to attach on the joint without considering alignment. It has no convex part to side direction, and can be used without taking off the clothes. These are great advantage for application in the clinical fields. The two goniometers are attached on the multi-axis joint perpendicular to each other to detect the flexed angle of the joint in the corresponding plane. The outputs of the goniometers are stored in a microcomputer through A/D converter, the joint angles on the two measuring planes are calculated with correction of the interference effect between the outputs. The correction of the interference is rather simple compared with other multi-axis electrogoniometers. These are processed in a very short time, and the result is displayed graphically on the CRT of the microcomputer in real time. This measuring system is applied to the human wrist joint of a normal subject. The result is displayed in real time as the relative motion of the hand segment against the forearm segment in three-dimensional space on the CRT display. The precise phenomena of motion can be observed, and the range of motion to the direction of dorsal, palmar, radial and ulnar flexion can be easily grasped quantitatively.