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Why Will a Fractured Bone Heal While AVN Usually Does Not?
Submitted by joel on 1 March, 2009 - 09:08

The key difference between a bone fracture and Avascular Necrosis (or Osteonecrosis) is that a fractured bone still has an intact network of cells and blood vessels necessary for regeneration where as Avascular Necrosis is the condition where blood supply to the bone cells is blocked and the regenerative bone cells die. 

 
Healthy bone is always undergoing constant change and process of regeneration. This regenerative process of the bone occurs primarily due to three types of cells within the bone, osteoblast, osteoclasts, and Osteocytes.[1]
 
  • Osteoblasts are primarily located on the surface of bone tissue and hold the important responsibility of forming new bone.[2] 
  • Osteoclasts are the cells which breakdown and resorb bone by secreting acid and enzymes.[3]
  • Osteocytes are simply mature osteoblasts that become trapped in the bone matrix. Osteocytes make up 90% of cells in mature bone.[4]
 
When healthy bones fracture, the osteoblasts and osteoclasts receive nutrients via blood vessels and the regenerative process is able to rebuild the matrix and eventually heal the bone. In contrast, “Avascular Necrosis” occurs when the blood circulation to the bone cells is compromised. As the bone cells die, they release “lysosomes” which acidify and harm the tissues, including the osteoblasts needed to form new bone. Researches believe this chemical processes that occurs when the cells die is the primary reason that the regenerative cells are often not able to rebound and heal and thus why necrotic bone often will not heal.[5]
 
References 
[1] “Bone Resorption by Osteoclasts”, Science Magazine. September 2000, Vol. 289. no. 5484, pp. 1504 – 1508. 
[2] "Osteoblast", Wikipedia. Retrieved on 2009-04-09.
[3] “Osteoclast”, Wikipedia. Retrieved on 2009-04-09.
[4] “Osteocytes”, Wikipedia. Retrieved on 2009-0409.
[5] Donnelly and Wynne. “Bone Injury, Regeneration, and Repair”, 2002-11-19.
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