To clarify the shoulder movement, changes of the tilting angle of the scapula were elevated radiographically in three dimensions during arm elevation. Utilizing data of the tilt of the glenoid fossa against the plane of scapula measured in dry bones, the direction of the glenoid fossa during arm elevation in living subjects was evaluated. The medial tilting angle was nearly constant at about 40 degrees from the resting position to an elevation of the arm to 150 degrees position. The average downward tilt was 12.46 degrees in the resting position; thereafter it gradually tilted backward. Horizontal tilt of the glenoid fossa following arm elevation was 46.15 degrees in the resting position, 46.15 degrees at 90 degrees of elevation, 38.79 degrees at 150 degrees of elevation, and 33.0 degrees at maximum elevation. These findings suggest that the "scapular plane" is the plane 40 degrees against the frontal plane in the range from 0 degrees to 150 degrees elevation of the arm, and that "zero position" is at 150 degrees elevation position in the scapular plane.
