[24] Bone and Fracture Physiology Flashcards
What is bone made up of?
Cells
Matrix
What cells are found in bone?
Osteoblasts
Osteoclasts
Osteocytes
OPCs
What are the components of bone matrix?
Organic (osteoid)
Inorganic
What proportion of the bone matrix is organic?
40%
What is the organic component of the bone matrix made up of?
Collagen type I
What are the properties of the organic component of the bone matrix?
Resists tension, twisting, and bending
What % of the bone matrix is inorganic?
60%
What is the inorganic component of the bone matrix made up of?
Calcium hydroxyapatite
What are the properties of the inorganic component of the bone matrix?
Resists compressive forces
What are the classifications of different types of bone?
Woven bone
Lameller bone
What is woven bone?
Disorganised bone that forms the embryonic skeleton and fracture callus
What is lamellar bone?
Mature bone
What are the two types of lamellar bone?
Cortical/compact
Cancellous/trabecular
What does the cortical lamellar bone form?
The dense outer layer
What does the cancellous lamellar bone form?
The porous central layer
How does bone form?
Intramembranous ossification
Endochondral ossification
What is intramembranous ossification?
Direct ossification of mesenchymal bone models formed during embryonic development
What bone is formed by intramembranous ossification?
Skull bones
Mandible
Clavicle
What happens in endochondral ossification?
Mesnechyme -> cartilage -> bone
Do most bones form by endochondral ossification or intramembranous ossification?
Endochondral
What are the phases in fracture healing?
Reactive phase
Reparative phase
Remodelling phase
When does the reactive phase of fracture healing occur?
Injury time - 48 hours
What happens in the reactive phase of fracture healing?
There is bleeding into the fracture site, causing a haematoma, and there is inflammation
What happens in the ‘inflammation’ in the reactive phase of fracture healing?
Cytokines, growth factors, and vasoactive mediators are released, leading to recruitment of leukocytes and fibroblasts, leading to granulation tissue
When does the reparative phase of fracture healing occur?
2 days to 2 weeks
What happens in the reparative phase of fracture healing?
Proliferation of osteoblasts and fibroblasts leads to cartilage and woven bone formation, leading to callus formation.
Consolidation (endochondrial ossification) of woven bone forms lamellar bone
When does the remodelling phase of fracture healing occur?
1wk - 7 years
What happens in the remodelling phase of fracture healing?
Remodelling of lamellar bone to cope with mechanical forces applied to it
How long does a simple fracture take to heal?
3 weeks
What are considered ‘complicating factors’ in fracture healing?
Adult
Lower limb
Diaphyseal
Open
By how much does a ‘complicating’ factor increasing fracture healing time?
Doubles it
