| The functional adaptation model suggests that differences in biomechanical forces resulting from habitual loading will be reflected in the trabecular architecture of cancellous bone. Increasingly, trabecular architecture is used to compare habitual loading history in both extant and extinct animals. Yet, most research is limited to comparisons of differences in architectural measures between species, as it is not currently known exactly how trabecular architecture differs with varying principal loading conditions. This study analyzed the cancellous bone of the artiodactyl calcaneus (sheep and deer) to examine if and how trabecular architecture varies with respect to habitual loading in compression and tension. The artiodactyl calcaneus has been shown to be habitually loaded in bending with compression predominant in the dorsal aspect of the bone and tension predominant in the plantar aspect of the bone. Architectural measures analyzed included bone volume fraction, trabecular thickness, trabecular separation, trabecular number, connectivity density, and degree of anisotropy. Trabecular architecture was assessed across the length of the bone, between the dorsal and plantar aspects of the bone, with variation of cortical bone thickness and geometry, and between the two species to assess how cancellous bone may specifically adapt to habitual compression and tension. Across the length of the calcaneus the cancellous bone was shown to become less dense and less connected with greater trabecular separation and fewer trabeculae for both the sheep and deer. The data from the dorsal and plantar regions of both species indicate that alteration in trabecular architecture occurs at a localized level rather than across each region as a whole. Cortical thickness and geometry were shown to have a significant effect on trabecular architecture in both species. Significant differences were found between the sheep and the deer cancellous bone specifically in the planter region and in concordance with predicted loading magnitudes for each species. While some significant differences in trabecular architectural were identified, much of the variation in the trabecular architecture across the length of the bone and between the dorsal and planar regions was not significant suggesting that loading regime alone may not be sufficient to explain trabecular architectural variation. |
