[24] Bone and Fracture Physiology

Question 1

What is bone made up of?

Answer 1

Cells

Matrix

Question 2

What cells are found in bone?

Answer 2

Osteoblasts
Osteoclasts
Osteocytes
OPCs

Question 3

What are the components of bone matrix?

Answer 3

Organic (osteoid)

Inorganic

Question 4

What proportion of the bone matrix is organic?

Answer 4

40%

Question 5

What is the organic component of the bone matrix made up of?

Answer 5

Collagen type I

Question 6

What are the properties of the organic component of the bone matrix?

Answer 6

Resists tension, twisting, and bending

Question 7

What % of the bone matrix is inorganic?

Answer 7

60%

Question 8

What is the inorganic component of the bone matrix made up of?

Answer 8

Calcium hydroxyapatite

Question 9

What are the properties of the inorganic component of the bone matrix?

Answer 9

Resists compressive forces

Question 10

What are the classifications of different types of bone?

Answer 10

Woven bone

Lameller bone

Question 11

What is woven bone?

Answer 11

Disorganised bone that forms the embryonic skeleton and fracture callus

Question 12

What is lamellar bone?

Answer 12

Mature bone

Question 13

What are the two types of lamellar bone?

Answer 13

Cortical/compact

Cancellous/trabecular

Question 14

What does the cortical lamellar bone form?

Answer 14

The dense outer layer

Question 15

What does the cancellous lamellar bone form?

Answer 15

The porous central layer

Question 16

How does bone form?

Answer 16

Intramembranous ossification

Endochondral ossification

Question 17

What is intramembranous ossification?

Answer 17

Direct ossification of mesenchymal bone models formed during embryonic development

Question 18

What bone is formed by intramembranous ossification?

Answer 18

Skull bones
Mandible
Clavicle

Question 19

What happens in endochondral ossification?

Answer 19

Mesnechyme -> cartilage -> bone

Question 20

Do most bones form by endochondral ossification or intramembranous ossification?

Answer 20

Endochondral

Question 21

What are the phases in fracture healing?

Answer 21

Reactive phase
Reparative phase
Remodelling phase

Question 22

When does the reactive phase of fracture healing occur?

Answer 22

Injury time - 48 hours

Question 23

What happens in the reactive phase of fracture healing?

Answer 23

There is bleeding into the fracture site, causing a haematoma, and there is inflammation

Question 24

What happens in the ‘inflammation’ in the reactive phase of fracture healing?

Answer 24

Cytokines, growth factors, and vasoactive mediators are released, leading to recruitment of leukocytes and fibroblasts, leading to granulation tissue

Question 25

When does the reparative phase of fracture healing occur?

Answer 25

2 days to 2 weeks

Question 26

What happens in the reparative phase of fracture healing?

Answer 26

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

Question 27

When does the remodelling phase of fracture healing occur?

Answer 27

1wk - 7 years

Question 28

What happens in the remodelling phase of fracture healing?

Answer 28

Remodelling of lamellar bone to cope with mechanical forces applied to it

Question 29

How long does a simple fracture take to heal?

Answer 29

3 weeks

Question 30

What are considered ‘complicating factors’ in fracture healing?

Answer 30

Adult
Lower limb
Diaphyseal
Open

Question 31

By how much does a ‘complicating’ factor increasing fracture healing time?

Answer 31

Doubles it