The purpose of this study was to estimate the three-dimensional position and orientation of the scapula on the scapular plane. We measured 12 right shoulders of asymptomatic male volunteers.12 reflective markers were attached to the subject's skin surface over various landmarks(the thorax 4, scapula 5, humerus 3). The subjects were asked to elevate their arms from 0 deg. to 150 deg. at every 15 deg. on the scapular plane. At each humeral elevation, the markers were relocated to the correct positions with palpation of the bony landmarks and recorded with a motion-capture system for two seconds. The scapula shifted 16,0 mm medially,27.9 mm upward and 11.3 mm posteriorly, tilted 5.5 deg. posteriorly, adducted 8.6 deg. horizontally and elevated 52.8 deg. laterally through from 0 to 150 deg. elevation. The scapulohumeral rhythm was 1: 2.9 at 15 deg.,1: 1.9 at 90 deg. and 1: 1.5 at 150 deg. This system possesses various merits; 1)it is non-invasive,2)we are able to measure it continuously and 3)it is capable of being estimated in any position. It enabled us to evaluate some trouble for throwing athletes or patients who have shoulder joint diseases. We believe that this system could make shoulder morbidity clearer by comparing accumulated data concerning normal shoulders.
