Fracture Healing (and disruptors of this process)

Inflammatory Stage (0-7d)

 • Fracture disrupts local blood vessels -> formation of hematoma -> Inflammatory reaction & release of cytokines -> activation of osteoprogenitor cells and mesenchymal differentiation into cartilage-producing chondrocytes at fracture site

Soft Callus Stage (wks 1-3)

 • Chondrocytes lay down cartilage in place of the hematoma -> bridging the fracture site more stability

Hard Callus Stage (wk 3 - mo 3)

 • Mineralization of cartilaginous matrix by osteoblasts forms bony callus -> Incr fracture-site stability

Remodeling (mos - yrs)

 • Osteoclast-osteoblast coupled bone remodeling: Callus along the trajectory of mechanical forces is fortified, while callus not in line with mechanical forces is reabsorbed



Factors that may disrupt fracture healing

 - Tobacco & Alcohol abuse - Incr healing time, mechanisms unclear

 - Metabolic / Endocrine disorders

 - Corticosteroids & prolonged NSAlDs - Block the inflammatory response that promotes healing

 - Vascular Insufficiency / Compromise - Trauma or pre-existing vasculopathy

 - Fluoroquinolones - Causes formation of an immature callus

 - Infection - Increases risk for non-union

 - Inadequate fixation of fracture - Too loose = hypertrophic non-union, Too rigid = atrophic non-union

 - Rifampicin & topical gentamycin - Toxic to osteoblasts

 - Vitamin D Deficiency - Insufficient Ca2+ & PO4- absorption from GI tract, bone mineralization.



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