The rotator interval is a confluence of tissue in a triangular shape located between the anterior supraspinatus leading edge and the upper border of the subscapularis tendon. The apex of the rotator cuff interval is located at the margin of the transitional ligament where the biceps sulcus is located. The rotator interval includes the coracohumeral ligament, the superior glenohumeral ligament, and the anterior-superior capsule. Contracture of these structures, the most commonly affected in frozen shoulder, results clinically in loss of flexion and external rotation in adduction [6, 10, 14, 17, 18] (Fig. 9.2).

Clinically, the rotator interval may be obliterated by fronding synovitis or inflammation, making initial appreciation difficult during arthroscopy (Fig. 9.3).

The anterior-inferior quadrant of the glenohumeral joint contains the anterior-inferior capsule and the middle glenohumeral ligament (MGHL). These structures are also almost invariably involved in frozen shoulder. The anterior capsule is frequently scarred to the middle glenohumeral ligament and the subscapularis. This results in further limitations of external rotation at the side and with increasing degrees of shoulder abduction [6, 11, 16].

In Neer’s original description based upon open surgical dissection, he described scarring of the axillary fold to itself and to the anatomic neck of the humerus [15]. However, newer research based on arthroscopic findings suggests that no such scarring of the axillary recess exists and that instead there is contracture of the inferior capsular tissues [25].

Nonetheless, this results in significant losses of abduction, forward flexion, and both external and internal rotation due to involvement of the anterior and posterior bands of the inferior glenohumeral ligaments (AIGHL/PIGHL) as well as the remainder of the capsular tissue [6].

Clinically, internal rotation is less affected in frozen shoulder. When involved, the posterior capsule results in loss of internal rotation of the adducted arm. Because this tissue frequently appears to be less involved, the need for surgical release of the posterior capsule during surgical treatment has been debated [2, 6, 24].

There has been recent evidence to suggest the existence of a posterior-superior glenohumeral ligament (PSGHL) [19]. Whether this represents a discrete structure or simply a thickening of the capsule is unclear [3, 20]. The relevance of this finding and its relevance to frozen shoulder are unknown. The expected effect of contracture would be a loss of internal rotation in adduction – an uncommon clinical finding.