Type I = Flat inferiorly (12%)
Type II = Curved (56%)
• parallel to the humeral head with concave undersurface
• considered most common type
Type III = Hooked (29%)
• most anterior portion of the acromion has a hooked shape
• associated with increased incidence of
Type IV = Convex (upturned) (3%)
• most recent classification of acromion process shape
• the undersurface of the acromion is convex near the distal end
• no convincing correlation between a type IV acromion and impingement syndrome exists
Overview of parameters of acromial morphology.
A. Acromial slope (d) according to and .
B. Acromial tilt (b) according to and .
C. Lateral acromial angle (a) according to .
D. Acromion index (AI) according to .
The acromial type according to Bigliani was not associated with any particular cuff lesion.
A statistically significant difference between controls and impingement patients was found for AS.
AT of controls was significantly smaller than that of impingement patients and cuff-tear patients.
LAA of cuff-tear patients differed significantly from that of controls and impingement patients, but LAA of controls was not significantly different from that of impingement patients. Differences between impingement patients and cuff-tear patients were also significant.
AI of controls was significantly lower than of impingement patients and of cuff-tear patients. A good correlation was found between acromial type and AS.
A low lateral acromial angle and a large lateral extension of the acromion were associated with a higher prevalence of impingement and rotator cuff tears. An extremely hooked anterior acromion with a slope of more than 43° and an LAA of less than 70° only occurred in patients with rotator cuff tears.