The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)

Relationships between muscle architectural anatomy and the morphology of entheses in the thenar and hypothenar regions of modern humans


1Department of Biology, Chatham University, 2Center for the Advanced Study of Hominid Paleobiology, The George Washington University, 3Evolutionary Anthropology, Duke University

March 26, 2015 3:00, Grand Ballroom E/F/G Add to calendar

Paleontologists and bioarcheologists frequently use muscle markings (entheses) on bones to infer behavior during life. One region which relies strongly on entheses for functional interpretation is the hand. In particular, anthropologists have relied on entheses of the thenar and hypothenar regions of hominin remains to evaluate whether the individuals engaged in stone tool behaviors. Little is known, however, about the relationship between the mechanics of these muscles and their entheses; the effects of frequent or strenuous muscle recruitment on the morphology of these insertion sites are also poorly understood.

Here we test the hypothesis that aspects of muscle architecture and mechanics including overall muscle belly length, fiber lengths, and physiological cross-section area positively correlate with a size and shape change of the enthesis. Gross and microscopic measurements were taken on thenar and hypothenar muscles as well as the flexor pollicis longus (7 muscles total) and the associated entheses from twenty human cadavers of both sexes, ages 60 to 100 years old. Contrary to our hypothesis, preliminary results show no consistent patterns between muscle architecture and entheseal change. However, a similar study using mice as the test organism discovered that the underlying cortical bone thickness of an attachment site is more informative of the associated muscle anatomy. Results of these studies together caution the use of entheseal surfaces to interpret past hominin behaviors, such as stone tool making. Instead, internal bone structures and cross-sectional properties of the entheses may be more reliable for making inferences from skeletal and fossil remains.

This project has generously been funded by Chatham University