Changes

**Ruptured blood vessels -> haemorrhage and clot formation, some ischaemic necrosis

**Ruptured blood vessels -> haemorrhage and clot formation, some ischaemic necrosis

***Dead marrow liquefies and is phagocytosed  

***Dead marrow liquefies and is phagocytosed  

***Dead bone is removed by [[Bones - normal#Normal structure|osteoclasts]]

***Dead bone is removed by [[Bones - Anatomy & Physiology|osteoclasts]]

****Continues long after bone has been united by callus

****Continues long after bone has been united by callus

**[[Bones - normal#Periosteum and blood supply|Periosteum]] tears, fragments displaced

**[[Bones - Anatomy & Physiology|Periosteum]] tears, fragments displaced

*-> Haematoma formation, necrosis of any isolated fragments

*-> Haematoma formation, necrosis of any isolated fragments

*-> Mesenchymal cells proliferate in haematoma - [[Granulation Tissue|granulation tissue]]  

*-> Mesenchymal cells proliferate in haematoma - [[Granulation Tissue|granulation tissue]]  

**Invading cells: endothelial, fibroblasts, osteoprogenitor

**Invading cells: endothelial, fibroblasts, osteoprogenitor

*-> Loose collagenous tissue (primary callus)

*-> Loose collagenous tissue (primary callus)

*-> Mesenchymal cells differentiate to [[Bones - normal#Normal structure|osteoblasts]] and chondroblasts

*-> Mesenchymal cells differentiate to [[Bones - Anatomy & Physiology|osteoblasts]] and chondroblasts

*-> [[Bones - normal#Bone organisation|Woven bone]] (secondary callus)

*-> [[Bones - Anatomy & Physiology|Woven bone]] (secondary callus)

**External callus - from periosteum

**External callus - from periosteum

***Periosteal growth eventually bridges the gap between the fracture ends

***Periosteal growth eventually bridges the gap between the fracture ends

***Blood supply is outstripped

***Blood supply is outstripped

***Cartilage is produced instead of osteoid

***Cartilage is produced instead of osteoid

***Blood vessels invade cartilage -> [[Bones - normal#Bone development|endochondral ossification]]

***Blood vessels invade cartilage -> [[Bone & Cartilage Development - Anatomy & Physiology|endochondral ossification]]

***Osteoid becomes ossified

***Osteoid becomes ossified

**Internal callus - from endosteum

**Internal callus - from endosteum

***Rarely forms cartilage

***Rarely forms cartilage

***May occlude the medullary cavity

***May occlude the medullary cavity

**Osteoid remodelled by [[Bones - normal#Normal structure|osteoclastic resorption]]  

**Osteoid remodelled by [[Bones - Anatomy & Physiology|osteoclastic resorption]]  

*-> Mature [[Bones - normal#Bone organisation|lamellar bone]]

*-> Mature [[Bones - Anatomy & Physiology|lamellar bone]]