Apparatus for Measuring the Shoulder Complex Motion

A new apparatus for measuring the motion of the shoulder complex has been developed. The system is composed of four portions, i. e., a mechanism part which consists of a gimbal and a sliding free arm with three optical rotary encoders, a counter circuit which decodes the outputs of the rotary encoders, a personal computer system and two holding gears for the subject's trunk and elbow. The loci of the end of the free arm, which are mapped on each of the horizontal plane, the sagittal plane and the frontal plane of the subject, are displayed on real time. The apparatus has abilities in calculating conventional ranges of motion of the shoulder complex. In addition, a concept of the three-dimensional range of the motion (3D ROM) of the shoulder is introduced. This index is defined as the area which is enclosed by the path of the maximum motion described on a sphere, the center of which corresponds to the shoulder joint. The 3D ROM observed from any viewpoint can be displayed. Moreover, another index of the three-dimensional percent range of the motion (3D% ROM), which is defined as a percent ratio of the whole spherical surface to the 3D ROM, quantitatively explains a three-dimensional mobility of the shoulder complex. As a result of experiments on 19 persons, involving 3 patients using the apparatus, the normal value of the 3D% ROM has been found to exceed the range of 40%.