Fig. 1

(A) Displaying a right shoulder specimen mounted to the shoulder testing rig. The scapula is fixed to a vertical linear bearing translator and lever arm system on top of an X-Y table, allowing for glenohumeral translation in the anteroposterior and superoinferior direction. During testing, an axial compression load of 40 N is constantly applied via the lever arm of the X-Y table to center the joint. As the humerus is fixed in the testing rig, the oppositely directed force of 30 N is consequently applied to the X-Y table (glenoid) in the posterior direction during external rotation (green arrow) and in the anterior direction (red arrow) during internal rotation. The force is applied via a friction-less cable, which is attached to a servohydraulic testing system or 30 N hanging weight, depending on the direction of force. (B) The rotator cuff muscles are loaded based on physiological cross-sectional area ratios with multiple lines of pull. Specifically, two lines of pull are used for the supraspinatus (orange), three for the subscapularis (blue), two for the infraspinatus (red), and one for the teres minor (yellow). Each line of pull is loaded with 5 N, resulting in a total load of 40 N