Fig. 1

Experimental imaging. Fig. 1a (left top) shows the view of the video camera that was synchronized with the MRI. Fig. 1b (right top) shows a non-constraining brace applied to the subject’s forearm. The position of the brace was not affected by pronation or supination of the forearm. Fig. 1c (left bottom) is a frame captured by the video camera, showing (1) the shoulder rotation angle. Fig. 1d (right  bottom), taken from an MRI scan, shows how translation of the humeral head and rotation angle on MRI are defined. (2) Center of the humeral head. (3) Center of the glenoid fossa. (4) Line from the center of the humeral head perpendicular to the glenoid. Translation of the humeral head is defined as the distance between (3) and (4). (5) Line parallel to a line connecting the anterior and posterior edges of the glenoid and crossing the center of the humeral head. (6) Line connecting the bicipital groove to the center of the humeral head. The rotation angle of the humeral head is defined as the angle between (5) and (6)