Figure 3.

For each histological section, a grid of points was defined in the (A) anterior, (B) central, and (C) posterior regions of the portion of the callus located between the two inner pins. The anterior and posterior boundaries of each region were defined by the periosteal surface of the cortex and by the anterior and posterior boundaries of the callus. A fixed number of grid points (N1, N2, and N3 for the anterior, central and posterior regions, respectively) was used for each region. For POD 17 sections, N1=55×15, N2=55×30, and N3=55×15. For POD 24 and 38 sections, N1=55×30, N2=55×35, and N3=55×35. These were the minimum numbers of points that reproduced the trends in tissue areas measured previously via histomorphometry (Salisbury Palomares, et al., 2009). For each region in each histological section, each rectangular grid of points was made to conform to the shape of the region via projection of the grid onto the boundaries of the region (TrueGrid, XYZ Scientific, Livermore, CA). During the segmentation process that was carried out in the previous histomorphometric analyses, the digital images of the histological sections were converted to grayscale with each tissue type represented by a single grayvalue. No fibrocartilage was present in this section. The tissue type “Other” included any tissue other than cartilage, fibrocartilage, cortical bone, and woven bone as well as void space. (D) The strain fields computed from the SMLE technique were sampled at corresponding points. Correspondence was determined by using the digital camera images (Figure 1B) to identify the locations of the periosteal surface of the cortex; these locations allowed subdivision of the strain fields into anterior, central, and posterior regions (boundaries shown with black lines). The locations of the grid points were defined using the same boundary projection method that was used for the histological sections.