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Fracture Healing

Inflammatory response 

– Time of injury to 24-72 hours

  • Injured tissues and platelets release vasoactive mediators, growth factors and other cytokines.  

  • These cytokines influence cell migration, proliferation, differentiation and matrix synthesis.  

  • Growth factors recruit fibroblasts, mesenchymal cells & osteoprogenitor cells to the fracture site.

  • Macrophages, PMNs & mast cells (48hr) arrive at the fracture site to begin the process of removing the tissue debris. 

 

Important cytokines in bone healing: 

BMP

Osteoinductive, induces metaplasia of mesenchymal cells into osteoblasts

Target cell for BMP is the undifferentiated perivascular mesenchymal cell

TGF-b

Induces mesenchymal cells to produce type II collagen and proteoglycans

Induces osteoblasts to produce collagen

PDGF

Attracts inflammatory cells to the fracture site

FGF

Stimulates fibroblast proliferation

IGF-II

Stimulates type I collagen production, cartilage matrix synthesis and cellular proliferation

IL-1

Attracts inflammatory cells to the fracture site

IL-6

Attracts inflammatory cells to the fracture site

 

Reparative response 

– 2 days to 2 weeks

  • Vasoactive substances (Nitric Oxide & Endothelial Stimulating Angiogenesis Factor) cause neovascularisation & local vasodilation

  • Undifferentiated mesenchymal cells migrate to the fracture site and have the ability to form cells which in turn form cartilage, bone or fibrous tissue.  

  • The fracture haematoma is organised and fibroblasts and chondroblasts appear between the bone ends and cartilage is formed (Type II collagen).

  • The amount of callus formed is inversely proportional to the amount of immobilisation of the fracture.

  • In fractures that are fixed with rigid compression plates there can be primary bone healing with little or no visible callus formation.

 

Types of callus:

External (bridging) callus

From the fracture haematoma

Ossifies by endochondral ossification to form woven bone

Internal (medullary) callus

Forms more slowly and occurs later

Periosteal callus

Forms directly from the inner periosteal cell layer. 

Ossifies by intramembranous ossification to form woven bone

 



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