• Osteoinduction: recruitment, proliferation, and differentiation of osteoprogenitor cells into osteoblasts
  
• Osteoconduction: three-dimensional scaffold promotes bone formation along its surface
  
• Osteogenesis: formation of new bone by osteoblasts
  
• Stability: required for adequate ingrowth of bone

• Definition: Cancellous and/or cortical bone harvested from the same individual. The source of autogenous bone is most commonly the iliac crest, ribs, and bone chips collected during the surgical approach (spinous processes, laminae). While cortical bone grafts provide initial stability to the spinal fusion, cancellous bone grafts have superior osteoinductive, osteoconductive, and osteogenic properties. The formation of a fusion mass is radiographically first noted 1 month after grafting. The majority of patients show radiographic fusion after 6 months. Incorporation of autogenous bone graft occurs in three phases:
  
  
  
  
  • Inflammatory phase (1 to 3 weeks): The initial hematoma induces the accumulation of inflammatory cells. Progressively mesenchymal cells appear and transform the clot into a fibrovascular stroma. Membranous bone formation is initially observed at decorticated surface of host bone. Endochondral bone formation occurs between grafted bone fragments.
    
  • Reparative phase (4 to 5 weeks): Membranous and endochondral bone formation lead to the formation of an early bone fusion mass. During this phase, implanted graft is revascularized and necrotic graft tissue is reabsorbed.
    
  • Remodeling phase (6 to 10 weeks): The early fusion mass consists of a thin cortical rim surrounding a center composed of secondary spongiosa and bone marrow. During the remodeling phase, the cortical rim thickens and newly formed trabeculae extend toward the center of the fusion.

• Gold standard among fusion promoting materials
  
• Optimal osteoinductivity
  
• Osteoconductivity and osteogenic properties
  
• No risk of disease transfer
  
• No risk of immunologic rejection
  
• Inexpensive

Cons

• Possible intraoperative bleeding at the harvest site
  
• Postoperative local hematoma and prolonged pain at the harvest site
  
• Possible iliac crest fractures and nerve injury at the harvest site
  
• Limited availability

• Definition: Cortical and/or cancellous bone tissue from another human. The bone is available as machined bone, tricortical strips, and cortical/cancellous chips and either frozen or freeze-dried. Allograft bone promotes osteoconduction. Frozen specimens that still contain viable host cells and bone morphogenic proteins promote osteoinduction. Freeze-dried specimens exhibit a lower degree of osteoinduction because of the lack of viable cells and growth factors; however, they may offer a lower risk of infectious disease transmission.