The impact of walking posture on trabecular structure in the femur of Rattus norvegicus.

Bone responds to mechanical loads through growth. This response to external loading has been important for understanding skeletal form and function relationships. However, uncertainty still exists regarding how different locomotor behaviors, (e.g., bipedalism, quadrupedalism) are reflected in bone morphology. This study assesses the effects of locomotor posture on femoral bone structure in a rodent model (Rattus norvegicus). The study individuals come from a previously-executed experiment (Foster, 2019) that utilized a treadmill-mounted harness to induce bipedal walking postures in rats over 12-weeks. The sample includes individuals from two experimental groups plus a control: bipedal walking, quadrupedal walking, and no exercise controls. Proximal and distal femora were microCT scanned at 20µm and trabecular bone volume fraction (BV/TV) and degree of anisotropy (DA) were analyzed and compared among groups to assess the impacts of differences in hip loading. In the proximal femur, the bipedal group had higher DA inferior to the neck and greater trochanter than the quadrupedal group, suggesting more unidirectional loading in bipeds. However, the quadrupedal group had greater BV/TV throughout the proximal metaphysis; particularly at the greater trochanter, which may be due to a higher demand for hip extension. In the distal femur, the bipedal group had higher mean BV/TV (0.39) when compared to the quadrupedal group (0.36), with a larger concentration of BV/TV in the medial condyle. These results suggest that the femoral epiphyses are responsive to changes in hip postural angle due to locomotion, however cortical bone structure and a larger sample size may be more informative.