Modern Frequency and the Significance of Acromial Shape in the Etiological Debate of Os Acromiale

• Main Author: Villao, Lorena
• Published: Trace: Tennessee Research and Creative Exchange 2007
• Subjects: Anthropology
• Online Access: http://trace.tennessee.edu/utk_gradthes/329

Os acromiale was first described by the anatomist Grüber in 1859. In later anthropological studies, os acromiale has subsequently been referred to as a genetic marker among African-American populations. However, Blakey (2000) and Rankin-Hill (1997) point out that biomechanical stress should be considered as a possible cause of this trait. This population has a harsh history, which is evidenced in the skeletal remains via nutritional deficiency, disease, and markers of occupational stress. A trait interpreted as genetic, may in fact be another stress marker. Frequency rates (%) in the William M. Bass donated skeletal collection, representing a modern sample, were compared to data from African-American skeletal samples spanning the last 300+ years. A lower frequency among modern samples may support a functional argument as a result of technological advancements leading to reduced physiological stress. The comparative African-American samples, examined here, include (in chronological order): New York African Burial Ground (7.6%), First African Baptist Church (20%), Mother United African Methodist Episcopalian Church (2.9%), Terry (11.1%), and the Hamann-Todd Collection (13.2%). Both the New York African Burial Ground and Mother UAME are samples presented for the first time. Unlike other samples, their frequency is not high. The Bass data, collected from a sample of 420 individuals, yielded an overall frequency of os acromiale at 3.3%. This is a decrease from the average frequency of 7% cited in the clinical literature. However, the frequency rate among the African-American component of this collection is a high os acromiale frequency, of 10.8% (n=4/37). The European- American frequency of the William M. Bass collection is quite low at 2.6% (n=10/383). In general, the African-American os acromiale frequencies are not always high as they have been presented. Further investigation may reveal that the underlying cause of the high os acromiale frequencies may involve additional factors. One factor may be acromial shape. The shape categories as classified by Edelson and Taitz (1992), is argued to reveal the underlying genetic cause of high os acromiale frequencies. If certain acromial shapes prove to be positively correlated to specific ancestral groups, then this could illustrate the genetic cause is a result of variation. However, if acromial shape varies in spite of ancestry, other mechanical arguments should be examined. While this research is not meant to present the last word on the etiology of this trait, it is meant to examine modern os acromiale frequencies, specifically in reference to acromial shape. The former is to test a mechanical etiology and the latter to test a genetic etiology.