The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

The Effect of the Achilles Tendon on Trabecular Structure in the Primate Calcaneus


1Anthropology, Boston University, 2Anthropology, University of Michigan

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Humans possess the longest Achilles tendon relative to total muscle length of any primate, an attribute that is likely beneficial for bipedal locomotion. Unfortunately, triceps surae muscles and Achilles tendons do not fossilize, so the only evidence of this anatomy is the insertion site on the calcaneal tuber, which is rarely preserved in the fossil record and, when present, is equivocal for reconstructing tendon morphology. To better understand how variation in Achilles morphology might affect the calcaneus, we analyzed the trabecular bone underlying the Achilles tendon insertion site in baboons, gibbons, chimpanzees, and humans to test the hypothesis that trabecular microarchitecture differs between primates with different tendon lengths. Though possessing very different Achilles tendon lengths, we were unable to find a statistically significant difference between the trabecular properties of chimpanzee and human calcanei in this specific region. There were regional differences within the calcaneus in the degrees of anisotropy (DA) in both chimpanzees and humans, though the patterns were similar between the two species (higher DA inferiorly). Our results suggest that while trabecular bone in the calcaneus varies, it does not respond to the tensile forces exerted on it by the Achilles tendon in the way we hypothesized. These results indicate that internal bone architecture is not an informative tool for reconstructing Achilles tendon anatomy in early hominins.

Funded by the Boston University Undergraduate Research Opportunities Program

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