Lecture 3 - Fracture and bone healing

Question 1

Summarise what happens when a bone breaks (5 stages)

Answer 1

1. Haematoma formation
2. Acute inflammation - neutrophil first then m.phage
3. Fibrocartilaginous callus formation
4. Bony callus formation
5. Bone remodelling

Question 2

Difference between centripetal and centrifugal blood supply to bone?

Answer 2

centripetal
- out to in, children

centrifugal
- in to out, adults

Question 3

Summarise bone healing

Answer 3

1. Primary —> woven bone
2. Secondary
   - —> endochondral ossification
   - —> intramembranous ossification
   - —> woven bone

Question 4

How is framework for bone set down?

Answer 4

• fibroblasts

- first collagen type 3 then collagen type 1

Question 5

Difference between endochondral and intramembranous ossification

Answer 5

1. endochondral, from cartilage

2. intramembranous, directly from mesenchyme

Question 6

Endochondral ossification

Answer 6

1. mesenchymal cells —differentiate —-> chondroblasts
2. chondroblasts —secrete—-> matrix —-> perichondrium
3. chondroblasts —-buried in matrix —-> mature to chondrocytes
4. Hypertrophy of middle chondrocytes
   
   • –> some burst
     - –> release of contents changes pH
5. this triggers calcification
6. as cartilage calcifies chondrocytes begin to die —> nutrients cannot diffuse

Question 7

Intramembranous ossification

Answer 7

1. mesenchymal stem cells — condense —- differentiate —-> osteogenic cell —-> osteoblasts
2. Osteoblasts —- secrete —- uncalcified bone matrix —–> osteoid
3. osteoid —- plus calcium —-> calcifies with help of alkaline phosphatase enzyme
4. OB when surrounded by bone matrix —> osteocyte
5. Lacunae form: hollowed out spaces
6. Bony spicules from matrix fuse around BV, increased nutrient delivery
7. Spongy bone remodelling
   - —> osteocyte organsies themselves into osteons —-> compact bone!

Question 8

Compare intracapsular and extracapsular fracture

Answer 8

Intracapsular

• poor BS
• replacement

Extracapsular

• BS okay
• replacement not necessary
• fixation

Question 9

Describe bisphosphonates as treatment

Answer 9

1. Analogues of pyrophosphate which is a molecule with decreases demineralisation of bone.
2. Inhibits osteoclasts by reducing recruitment and promoting apoptosis

Question 10

Bisphosphonates types

Answer 10

1. nitrogen containing (kills OB)

2. non nitrogen containing (stops OC)