Chiro.Org Blog:

The shoulder girdle is a multiaxial intricately synchronized joint complex that has considerable power and an extreme range of motion. The anterior, superior, and posterior shoulder muscles provide the great power, and the collateral ligaments do not appreciably limit motion in any plane. Thus, stability must be provided by muscles: essentially the rotator cuff and subscapularis muscles of the arm, which are aided slightly by the glenohumeral ligaments.