MOTION ANALYSIS OF THE SHOULDER COMPLEX

Abstract

The shoulder complex is composed of the scapula, clavicle and humerus. Shoulder motion is the result of cooperation of these elements. So far motion analysis of the shoulder complex has been carried out by means of X-ray photography. However, it is difficult to measure the three-dimensional motion of each element by this method. Using a magnetic sensor system (3 SPACE), we tried to measure three-dimensional motion of the scapula and humerus in elevation in the sagittal, scapular and frontal planes. This magnetic sensor system is composed of a source coil which generates a magnetic field and a sensor coil which detects electromotive force corresponding to attitude and distance of the sensor coil with respect to the source coil. The source coil was attached on the chest and the first sensor coil was attached to the humerus. We tried to fix the second sensor coil to the scapula by grasping the spine of the scapula together with the sensor. This method is not so accurate but it is safe and easy. We measured Euler angles of the scapula (scapulothoracic angle) and humerus and excursion of the scapula with respect to the reference coordinate attached to the trunk. And we calculated relative Euler angles between the scapula and humerus (glenohumeral angle). The ratio of glenohumeral to scapulothoracic angle during elevation was not constant, as has been reported so far. Instead this ratio varied considerably. In elevation in the sagittal and scapular plane, the scapula moved posteriorly and inferiorly at maximal elevation. However, in abduction the scapula moved medially and posteriorly.