It contains the coracohumeral ligament superficially, the tendon of the long head of the biceps and the superior glenohumoral ligament at the deep aspect. This is a common site for arthroscopic entry into the glenohumeral joint since it does not compromise the rotator cuff. During abduction of the arm, the greater tuberosity of humerus can impinge on acromion and put pressure on the contents of the subacromial space. Normally when the arm is abducted, external rotation also occurs to diminish impingement. The shape of the acromion exhibits variability which affects the area of the subacromial space.
Acromial spurs can also form by ossification of the acromial end of the coracoacromial ligament.
The acromial angle is between 0-12 o . The acromial angle is between 13-27 o . Acromion with a hooked undersurface. The acromial angle is greater than 27 o . The occurrence of os acromiale is thought to decrease the area of the subacromial space, predisposing an individual to impingement and rotator cuff tear.