Bone fracture repair is a complex process which is divided into an inflammatory, reparative, and remodeling phase. Only few studies focus on the remodeling phase of healing. However, behavior during the remodeling phase is important because that is when strength of bone returns and chance of re-fracture decreases. Small animal models are more frequently used in studies of fracture healing. Although their patterns of healing during the inflammatory and reparative phases are similar to that in larger animals including humans, remodeling has been noted to be different. During remodeling, rapidly laid down woven bone is replaced by highly organized lamellar bone. In large animals, the periosteal and the endosteal callus slowly resorb until the original shape of the cortex is restored. In mice, another behavior is observed [1]. Similar to large animals, at the end of the reparative phase (day 21), a large callus bridges the fracture gap both periosteally and endosteally. During remodeling (day 28 to 42) the callus gradually transforms into a double cortex (Figure 1a-c). Then the two equally thick and dense cortices merge together into one cortex. This contrasting response could be due to biological differences in species, or to differences in mechanical loading. We postulate that the latter is true and in this study explore if these patterns of remodeling could be explained by known differences in loading. For this purpose, a generally recognized bone remodeling algorithm [2-3], in which adaptation of bone mass and geometry over time are modulated through osteocyte mechano-sensing and signaling, is used.
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