Representative H&E stained sections at the 7-day time point in the BMP-2 treated groups (groups I, II, IV and V). Within each panel, the left image is a longitudinal section of the femoral defect (2× magnification) and the image on the right is a 20× magnification of the black rectangle showing hypercellular areas of acute inflammation and cartilaginous tissue. This tissue forms a superior bridge over the bone ends/bone defect in the area where the bony bridge will later be formed in groups I, II, IV and V.