The frequency of os acromiale in the Robert J. Terry Collection

AbstractNormal fusion of the acromion process in humans begins at about age 15 and should complete ossification by age 22–25. Os acromiale occurs when fusion of the acromial epiphysis does not follow its normal ossification pattern, resulting in the retention of a separate epiphyseal end to the acromial process. Depending on how the metaphyseal junctures fuse, differential size and shape of the unattached acromial segment is produced. As a result of shoulder anatomy and the mobile epiphysis, os acromiale is associated with shoulder impingement and rotator cuff problems. The purpose of this study is to document the frequency of os acromiale in the Robert J. Terry Collection and gain a perspective on the occurrence of os acromiale in this specific US population. The overall frequency of os acromiale in the sample of 1594 skeletons was 8.34%. This study also evaluates the prevalence of os acromiale between sexes and ancestral groups in the Terry Collection. Significant frequency differences in the expression of os acromiale were found between both ancestry and sex; the black male sample has the highest frequency (12.47%), with a lower occurrence in the black female sample (9.22%). The white sample exhibited observably lower frequencies, with the white males at 6.8%, and white females at 3.2%. Size and shape and side expression (laterality) showed no significant differences between the sexes. However, significant differences in laterality by ancestry were observed; black males exhibited 48.3% bilateral expression, while white males exhibited bilateral expression only 29% of the time and 54.8% had a right lateral expression. Based on the results presented in this study, it is suggested that there is a genetic causation for os acromiale, which may or may not be exacerbated by physical activity. The use of this anomaly as an additional non‐metric feature in inferring familial relationships and personal identification is discussed. Copyright © 2006 John Wiley & Sons, Ltd.