Fracture Union
https://jorthoptraumatol.springeropen.com/articles/10.1186/s10195-019-0528-0
How does a fracture unite ?
Secondary union occurs via five phases
1. Haematoma formation 2.Inflammatory Reaction 3. Soft tissue callus formation
4. Hard callus formation 5. Remodelling
Haematoma Phase- Last for hours.
immediate vasoconstriction, platelet plug formation and activated platelets degranulate PDGF
Clotting cascade and complement system both activated.
Activation of cytokines and signalling molecules which are chemotactic to inflammatory cells and angiogenic to blood vessels.
BMP-7 also released from bone - Osteoinductive, mitogenic and angiogenic.
Inlfammatory Phase - lasts for days.
begins with arrival of PMNs followed by macrophages
Repair Phase
begins with arrival of fibroblasts
fibrous tissue makes gap less mobile, angiogenesis continues
less than 15 % strain and chondrocytes proliferate laying down collagen matrix and soft callus in fracture gap.
soft callus becomes harder with mineralization.
Remodelling Phase
woven bone oriented into hard denser lamellar bone.
Bone Development in Human Body
Intramembranous Ossification
- foetal bone development
- day to day bone development
- fracture repair
- formation of bone in fibrous connective tissue
- flat bones - Mandible and skull
Encohndral Ossification
- Replacement of cartilage by bone
- Development of long bones e.g. femur and humerus
How do bones grow wider ?
Increase in diameter is via appositional growth.
Osteoblasts in the periosteum form compact bone around external bone surface.
At the same time, osteoclasts in endosteum break down bone on internal bone surface around medullary cavity.
These two processes increase diameter of bone.
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