Although the proposition of Wolffs law as bones ability to adapt its structure to mechanical needs is nowadays hardly questioned, the consequences of adaption in mechanical terms resist a clear-cut description. To understand the interplay between the habitual loading conditions on the bone and the local bone structure, the proximal femora of four primates with dissimilar locomotor habits were imaged with high resolution micro-computed tomography. A previous study revealed different strategies of how the bone volume fraction (BV/TV) of the trabecular bone is locally adapted: high values of BV/TV are obtained by a thickening of the trabeculae with trabecular number (Tb.N) being relatively constant, while low BV/TV values are obtained by a reduction of Tb.N, whereas Tb.Th remains constant.1 Here we go beyond a structural analysis and calculate the local tissue strains using micro-finite element analysis. Proper boundary conditions reflecting prevalent loadings were estimated based on muscle insertion locations and pulling directions. The forces were applied on the femoral head and great trochanter with magnitudes proportional to the animal weight. The design of the computer experiment was to test the mechanical properties of all 16 combinations of the four proximal femora under the four different loading conditions. In all animals, the femoral neck always showed not only the highest strains but also the most heterogeneous strain distributions. The strain distributions did not provide features that clearly indicated when there was a match between bone structure and loading conditions. A comparison between the different scenarios further allows a consideration whether differences in bone structure or differences in the external loading has a stronger influence on the resulting strains.
Disclosure: The authors declared no competing interests.
1. P. Saparin et al., (2011) Anatomical Record 294 5567.