Schematic representation of the fracture areas used for quantification. For cell counting analyses, regions of the fracture callus were designated as shown. The fracture gap (F) was defined as the area between the bone ends where the initial impact that broke the endogenous bone occurred. The peri-cortical bone (P) was defined as the area 150 μm above the endogenous bone and stretched along the length of the endogenous bone in the four quadrants shown. The callus area (C) was defined as the rest of the newly formed bone that enveloped the endogenous bone at the breakage point.