Shoes may change the structure of our ankle bones

Wearing shoes is linked to slight structural changes to the spongy bone of our ankles. This discovery affects our understanding of how human walking evolved, as fossils have often previously been compared to the ankle bones of modern, shoe-wearing people. But studying modern humans who don’t routinely wear shoes offers a “window into the past” as to how our extinct human relatives moved, says Zewdi Tsegai at the University of Chicago. Our ancestors habitually walked on two legs by about 4.2 million years ago, but that doesn’t mean they walked like we do today. Fossil bones and footprints suggest different hominins used different walking styles, foot positions and amounts of climbing, says Hannah Farrell at UNT Health Fort Worth in Texas. Advertisement Trabecular bone – the spongy network of tiny struts and plates inside bones – is particularly useful to study, because it remodels throughout an individual’s life in response to forces, she says. This leaves clues to how ancient humans used their feet and legs, she says. However, the modern populations used in such comparisons are usually people living in today’s industrial societies, who wear shoes throughout their lives. Farrell and Tsegai wondered how wearing shoes might skew these comparative results. To find out, the duo and their colleagues used high-resolution CT scans to create 3D maps of the trabecular bone in the talus – an ankle bone connecting the lower leg to the foot – in 56 modern humans. The majority of these individuals were shoe wearers, made up of adults in the US who died since 2000. There was also a barefoot group, composed of 13 Andaman Islanders, two Khoisan people from southern Africa and one Aka hunter-gatherer from Central Africa. They were all from the mid-19th century, and their skeletons are housed at the Natural History Museum, London. The team’s analyses revealed that the barefoot people had relatively dense trabecular bone towards the front of the ankle. That makes sense for an ankle position associated with a flexed foot, as in squatting or climbing, says Farrell. Their trabeculae also ran in a wider range of directions, suggesting their ankles experienced forces from a greater variety of angles. By contrast, the shoe wearers had a greater volume of trabecular bone overall, with relatively more of it towards the inside and back. The researchers say this could reflect the way shoes shift loading towards the inner ankle and hold the foot in a more extended position, particularly when they have heels. The shoe wearers’ struts and plates also tended to run more consistently in particular directions, suggesting footwear restricts ankle movement and channel forces through a narrower range of paths. “This is crucial baseline information to have for studies concerning the evolution of the foot,” says Malorie Albee at Northern Michigan University. “The study shows that something as culturally and behaviourally important as habitual footwear can be associated with measurable differences in internal bone architecture,” says Thomas Püschel at the University of Oxford. “That should make us think carefully about what our comparative samples actually represent.” But, like the authors, Püschel emphasises the importance of teasing out any compounding effects of body size, activity, terrain and other lifestyle differences through future studies. “Really, we’re just trying to do the footwork, so to say, to better inform more studies moving forward,” says Farrell. Journal of Anatomy DOI: 10.1111/joa.70236