Neonatal and adult cadaveric studies, as well as radiological, MRI and other studies, have been undertaken to try to establish whether different acromial shapes are acquired with age or congenital. The diverse results have led to continued debate about age-related changes in acromial morphology.

In this study to test the hypothesis that the acromial arch changes with age, 571 dry bone scapulae were examined. The specimens were divided into 10 groups according to age and gender. At least 50 specimens of each group were examined and classified according to the acromial types described by Bigliani. Height (h), length (l), thickness, acromial arch distance and coracoid height were measured. Because of interobserver differences in the interpretation of different acromial types, a statistical tool was devised to classify the types according to fixed parameters. This was done by calculating the acromial index (AI) with the formula AI =h/l.

Type-I and type-II acromions were found in all age groups. Type-III acromions were found only in age groups above 41 years, with the incidence peaking in the over 51-year group. Type-III acromions were more common in men than woman by 8:1. Type-II acromions were the most common in both genders and all age groups, followed by type-I and then by type-III. An os acromiale was found in 12.26% of specimens.

Looking at the results of this study, one has to agree with Edelson (JBJS (Br) 1995; 77-B) that type-I and type-II acromions seem to be inherited, while type-III hooked acromions are acquired.