Characterization of strains induced by in vivo locomotion and axial tibiotarsal loading in a chukar partridge model

Rodent models have offered valuable insights into the mechanobiological mechanisms that regulate bone adaptation responses to dynamic mechanical stimuli. However, using avian models may provide new insights into the mechanisms of bone adaptation to dynamic loads, as bird bones have distinct features that differ from mammalian bones. This paper illuminates these aspects by evaluating the mechanical environment in a novel avian, chukar partridge tibiotarsus (TBT), during fast locomotion and in cortical and cancellous tissue under in vivo dynamic compressive loading within the TBT. We measured in vivo mechanical strains at the TBT midshaft on the anterior, medial, and posterior surfaces during locomotion at various treadmill speeds. The mean in vivo strains measured on the anterior, medial, and posterior surfaces of the TBT midshaft were 154 με, -397 με, and -438 με, respectively, at a treadmill speed of 2 m/s. The mean experimentally measured strains on the anterior, medial, and posterior surfaces of the TBT were 114.7 με, -952.6 με, and -593.7 με under an in vivo dynamic compressive load of 130 N. The study, which employs a micro-computed tomography (microCT) based finite element model in combination with diaphyseal strain gauge measures, found that cancellous strains were greater than those in the midshaft cortical bone. Sensitivity analyses revealed that the material property of cortical bone was the most significant model parameter. In the midshaft cortical volume of interest (VOI), daily dynamic loading increased the maximum moment of inertia and reduced the bone area in the loaded limb compared to the contralateral control limb after three weeks of loading. Despite the strong correlations between the computationally modeled strains and experimentally measured strains at the medial and posterior gauge sites, no correlations existed between the computationally modeled strains and strain gradients, and histologically measured bone formation thickness at the mid-diaphyseal cross-section of the TBT.