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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