Unidirectional instability (anterior, posterior, or inferior) may be the result of physiological laxity of the connective tissues, but is more often the result of trauma and usually involves rotator cuff tears.

Internal impingement is associated with a combination of posterior GH capsule tightness and scapula kinematic alterations.

Extrinsic impingement is believed to occur as a result of mechanical compression of the rotator cuff against the anteroinferior one-third of the acromion in the suprahumeral space during arm elevation (Fig. 17.15).

The superior glenohumeral ligament and its associated rotator interval capsule structures contribute most to anterior and inferior joint stability by limiting anterior and inferior translations of the humeral head when the arm is at the side (0° abduction) (Fig. 7–31A).