Spatial distribution and remodeling of elastic modulus of bone in micro-regime as prediction of early stage osteoporosis

We assessed the local distribution of bone mechanical properties on a micro-nano-scale and its correlation to strain distribution. Left tibia samples were obtained from 5-month old female Sprague Dawley rats, including baseline control (n=9) and hindlimb suspended (n=9) groups. Elastic modulus was measured by nanoindentation at the dedicated locations. Three additional tibias from control rats were loaded axially to measure bone strain, with 6-10 N at 1 Hz on a Bose machine for strain measurements. In the control group, the difference of the elastic modulus between periosteum and endosteum was much higher at the anterior and posterior regions (2.6 GPa), where higher strain differences were observed (45 με). Minimal elastic modulus difference between periosteum and endosteum was observed at the medial region (0.2 GPa), where neutral axis of the strain distribution was oriented with lower strain difference (5με). In the disuse group, however, the elastic modulus differences in the anterior posterior regions reduced to 1.2 GPa from 2.6 GPa in the control group, and increased in the medial region to 2.7 GPa from 0.2 GPa. It is suggested that the remodeling rate in a region of bone is possibly influenced by the strain gradient from periosteum to endosteum. Such pattern of moduli gradients was compromised in disuse osteopenia, suggesting that the remodeling in distribution of micro-nano-elastic moduli among different regions may serve as a predictor for early stage of osteoporosis.