Table 4.

Stages of bone graft incorporation.

Stage	Events
Inflammation & Revascularization	Week 1: Haematoma formation with presence of lymphocytes, plasma cells, osteoclasts, mononuclear and polynuclear cells
	Week 2: Increased osteoclastic activity with formation of fibrous granulation tissue. Macrophages remove necrotic debris and release intra-cellular substances that attracts mesenchymal stem cells (MSCs)
	Revascularization allows for MSCs from donor and recipient to reach the marrow spaces
	Greater inflammatory response in allograft incorporation
Osteogenesis	MSCs differentiate into bone forming cells in the marrow spaces
Osteoinduction	Both cortical and cancellous autologous bone graft allows for bone growth to occur on its surface, pores or channels
Osteoconduction	Cortical Grafts	Cancellous Graft	Allografts
	Initial resorbed by osteoclasts before new osteoid are laid down by osteoblasts (“cutting cones”), thus leading to initial reduction in mechanical strength	Creeping substitution occurs where new bone is laid down by osteoblasts on a necrotic bed that is simultaneously resorbed by osteoclasts. This leads to an initial increase in mechanical strength	Intra-membranous and endochondral ossification occurs on the surface, forming a bridging external callus. Creeping substitution of cortical bone occurs.
Remodelling	Incomplete incorporation with no remodelling phase	Occurs along lines of force with complete incorporation of bone graft	Fusion occurs only at the bone-graft interface with deeper layers of the grafted bone containing dead trabeculae