Figure 1.

Glenohumeral joint force couples in the transverse plane (A) and coronal plane (B). Anterosuperior rotator cuff tears decrease posterior forces on the humerus, while posteropsuperior rotator cuff tears decrease anterior forces on the humerus (A). Both predispose to laxity in the saggital plane. An insufficient supraspinatus muscle or tendon leads to superior laxity and upward migration of the humeral head. Conditioning the deltoid (B) can restore downward forces on the humerus to minimize such laxity and improve joint kinematics and function.