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First published online March 8, 2005
Journal of Experimental Biology 208, 899-905 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01475
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How does the relative wall thickness of human femora follow the biomechanical optima? An experimental study on mummies

Sándor Évinger1, Bence Suhai2, Balázs Bernáth2, Balázs Gerics3, Ildikó Pap1 and Gábor Horváth2,*

1 Department of Anthropology, Hungarian Natural History Museum, H-1083 Budapest, Ludovika tér 2, Hungary,
2 Department of Biological Physics, Eötvös University, H-1117 Budapest, Pázmány Péter sétány 1, Hungary
3 Department of Anatomy and Histology, Faculty of Veterinary Science, Szent István University, H-1078 Budapest, István u. 2, Hungary

* Author for correspondence (e-mail: gh{at}arago.elte.hu)

Accepted 22 December 2004

We studied how the ratio (K) of the internal:external diameter of human femora follows the biomechanical optima derived earlier by other researchers for marrow-filled tubular bones with circular cross section and minimum mass designed to withstand yield and fatigue, or stiffness, or bending fracture, or impact strengths. With evaluation of radiographs of 107 femora from 57 human mummies the values of K were measured. We found that Kposterior=0.498±0.085 for the posterior radiographic view, and Kmedial=0.589±0.070 for the medial view with Kmin=0.345 and Kmax=0.783. The theoretical optima for K depend on the ratio (Q) of the marrow:bone density. Accepting the assumption of earlier authors that Q=0.50, our data show that human femora are optimised to withstand bending fracture, or yield and fatigue strengths. There were no sex-, age- and length-specific differences in K, and the means of K of the right and left femora of individuals were statistically not significantly different. The biomechanical optimization for K of human femora is not finely tuned. Compared with fox femora, K of human femora follows the biomechanical optimum to a much lesser extent. Although the relative wall thickness W=1–K of human femora are optimised, the very low relative mass increment due to deviation of K from the optimum and the considerable intraspecific variance of K make it probable that an accurate optimization of the relative wall thickness is irrelevant in humans.

Key words: marrow-filled tubular bones, optimum bone-wall thickness, human femora, mummies, bone mechanics


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