Fig. 1

Rotation angle of the glenohumeral joint. The glenoid axis (dotted line) was defined as a line perpendicular to the surface of the glenoid fossa at its midpoint (a). The humeral head axis (white line) was defined as a line connecting the midpoint of the articular surface (black ×) to the center of the humeral head (white dot), which was the center of the best-fit circle (white circle) applied to the humeral head (b). The articular surface was identified by the articular cartilage (bold white line). The rotation angle was defined as the angle formed by the glenoid and humeral head axes (c)