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Bones – one size doesn’t fit all

9 March 2011

Microscopic adaptations allow bones to cope in all creatures great and small.

Research funded by BBSRC shows that the internal spongy structure of bone as is typically found near joints can take on different forms to cope with an animal's size. This has important evolutionary implications as it suggests that animals adapt their bone microstructure as they evolve toward larger or smaller size without needing fundamental changes to their overall skeletal shape.

Scientists led by Dr Sandra Shefelbine of Imperial College London studied bones from 90 different mammals and birds, from a tiny shrew to an Asian elephant, and found that the overall density of bone near the joints was remarkably uniform but that the internal struts that give it its foamy appearance got thicker and further apart as species got larger

The research is published today (Wednesday 9 March) In Proceedings of the Royal Society B and suggests that bone structures are flexible at a wide range of organizational scales and across a vast range of animal sizes. Almost all previous studies had focused on the gross macrostructure of bones; this is the first comprehensive, microscopic scale study of land animals' trabecular bone.

Dr Michael Doube, the post-doctoral researcher on the project explains: "Our team studies a special type of spongy bone called trabecular bone that is found mostly near joints. You often see it in pork chops and it basically acts as a shock absorber cushioning the impact that bones are put under during loading in life.

"In this research we used an image analysis program that we developed ourselves to study trabecular bone from the thighs of 90 different species of animals, mostly mammals but also some birds and a reptile. We found that in larger animals the overall amount of bone per unit volume stayed roughly the same as in smaller animals, but the struts that criss-cross it to give it its spongy shock absorbing properties got thicker, further apart and less numerous to the extent that a single trabecular strut within an elephant is bigger than the whole thigh bone of a shrew.

"This is an intriguing finding as it suggests that as animals evolve into larger or smaller species spongy bone might adapt to carry the load without needing to get heavier or lighter overall."

This study increases our understanding of the mechanics of bone structures and could prove insightful in a range of areas, not least in underpinning work to combat fractures and osteoporosis.

Professor Douglas Kell, BBSRC Chief Executive said: "Bones are remarkably versatile structures able to produce intricate mechanisms in the ear and to support the weight of an elephant. However, in elderly people bones can become fragile and prone to breakages which can lead to serious health problems and drastically reduce quality of life. This research has increased our understanding of how bones have evolved across the animal kingdom and may lead to new insights about how to keep them strong and healthy."



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