Bone healing. A regenerative process leading to bone formation with restored form/ function if successful. A: Intramembranous bone formation along osteomized cortical bone (CB) clearly shows the newly formed woven bone (WB) on the left. Further from the bone edge connective tissue is visible, that remains in the osteotomy gap at this healing stage. B: The difference between lamellar bone (CB) on the right is clearly visible when compared to the heterogeneous newly formed woven bone (WB) on the left. Important cells in bone formation: C: Cells depositing new bone are osteoblasts. The small black and white image explains this image. The arrow indicates an osteoblast in typical palisade form sitting in a row with other osteoblasts on the surface of newly synthesized bone. The region marked with a line and stained blue in “C” shows osteoid (OI), the extracellular matrix, yet unmineralized, synthesized by the osteoblasts. Freshly embedded in the newly formed woven bone at least 4 osteocytes can be seen, surrounded by mineralized matrix (★). D: Endochondral bone formation is initiated by a cartilaginous phase, with chondrocytes becoming hypertrophic and then being replaced by osteoblasts and woven bone. E: Osteoclasts (OC) are multinuclear bone resorbing cells, sitting on the bone surface. Clearly visible is the ruffled border, which is the actual bone resorbing area of the active osteoclast. (Images are taken from a large animal bone healing model in sheep, 3 mm osteotomy gap, stable external fixation, staining: Alcian blue).