[An analysis of the rotational motion in three dimensional motion of the shoulder complex]

An apparatus was developed using a personal computer to measure three dimensional motion including rotation of the shoulder complex quantitatively. Euler angles were introduced to describe three dimensional motions. The rotation angle was calculated by integrating the components of angular velocity vectors of the Euler angles around the long axis of the humerus. Two kinds of measurements were performed on both the normal and contracted shoulders; One is measurement of the rotational motion accompanying abduction, flexion, extension, horizontal flexion and horizontal extension. The other is measurement of three dimensional range of motion and the rotational motion when the shoulder moves as far as possible in three dimensional space (maximum circumduction). External rotation occurred during abduction, and internal rotation occurred during flexion. In maximum circumduction, a linear relationship was found between three dimensional range of motion and the amount of rotational motion.