Kinematical Investigation of Triaxial Goniometer.

Abstract

Chao (1980) and Mills (1991), according to Grood (1979) developed a link mechanism goniometer composed of three rods connected perpendicular to each other by collars. They claimed that three relative rotational angles of the rods correspond to three-dimensional clinical angles, that is, the flexion-extension, abduction-adduction and external rotation-internal rotation. However, the three angles are equal to Euler's angles obtained by using the three axis method proposed by Panjabi (1971). It is well known that Euler's angle obtaind by using this method has six cases and it is understood that the goniometer by Chao et al gives only one case of the six because three angles obtained have different values depending on the way of making the correspondence of local coordinate axis of two bones to the rods of the link. This paper describes kinematics of a goniometer using a link mechanism based on the similarity transformation and investigates the three-dimensional expression of the rotation angle.