Fracture Healing

Question 1

WHat are the two major types of bone?

Answer 1

cortical = compact

trabelcular = cancellous = spongy

Question 2

What is primary bone? What is secondary bone?

Answer 2

primary bone is woven bone (it’s what’s layed down first, but it’s weaker)

secondary bone - lamellar bone

Question 3

WHat are the important differences between woven and lamellar bone?

Answer 3

woven is immature, lamellar is mature

woven is laid down rapidly while lamellar takes time

woven is put down first

lamellar is stronger

Question 4

What are the three general steps in the sequence in fracture healing?

Answer 4

1. inflammation
2. repair
3. remodelling

Question 5

What happens first after the actual fracture?

Answer 5

you get injury to the cells, blood vessles, matrix and surrounding ST

This results in a hematoma (swelling) and osteocyte death with necrotic material at the fracture site

Question 6

How does the inflammation period start? What happens in it?

Answer 6

the platelets in the hematoma and the injured cells will release inflammatory mediators

this gives you vasodilation and edema

you get migration of inflammatory cells including PMNs, followed by macrophages and lymphocytes

Question 7

What do the inflammatory cells do ?

Answer 7

they release cytokines that promote angiogenesis to bring in important things for healing.

Question 8

WHy is angiogenesis so important in fracture healing?

Answer 8

Because the blood brings with it the fibroblasts, osteoblasts, and chondrocytes that are needed to fix the fracture

they will produce new osteoid = new matrix

the blood also brings the monocytes which will become osteoclasts that resorb necrotic tissue

Question 9

Why does the fracture actually look bigger on x-ray after a few weeks?

Answer 9

because the healing process includes having the osteoclasts eat up the dead stuff, so the space actually does get bigger

Question 10

THe structure first formed by the fibroblasts, chondroblasts and osteoblasts is called what? Will it show up on x-ray?

Answer 10

the soft callus 0 it’s a bridging structure between the fracture site ends

it will not show up on x-ray because it’s not calcified yet

Question 11

Which of the following is NOT a descendant of a pluripotent mesenchymal cell? Which is NOT involved in callus formation?

osteoblasts

osteoclasts

osteocytes

chondrocytes

fibroblasts

Answer 11

Osteoclasts are not from mesenchyme 0 they’re from monocytes

osteocytes are not involved in callus formation

Question 12

What is the soft callus made of in general?

Answer 12

fibrous tissue

cartilage

woven bone

Question 13

What does the soft callus mature into? How?

Answer 13

hard callus

you get intramembranous bone formation at the periphery and the woven bone envelopes the fracture ends and beocomes ossified

then endochondral ossification hardens the soft callus from the inside

Question 14

Why did we evolve to have an external callus and not an internal callus in fracture healing?

Answer 14

because the ability of a bone to resist torsional and bending loads is proportionate to the radius⁴

so the wider the bone, the stronger it will be while it heals

Question 15

What is the difference between clinical union and radiographic union?

Answer 15

clincal union occurs when the fracture site become sstable and pain free (this happens first)

radiographic union is when the x-ray shows cortical bone crossing the fracture site - so actually healed solid.

Question 16

What happens after the hard callus is matured?

Answer 16

remodeling - the woven bone gets completely replaced by lamellar bone and the unneeded callus gets resorbed by the osteoclasts

Question 17

What is a hugely important injury variable that hinders healing?

Answer 17

damage to the blood supply

Question 18

What is an important patient variable that plays a role in healing?

Answer 18

age - kids heal super fast and old people don’t

Question 19

What are two tissue variables that play a role in how well a fracture heals?

Answer 19

where the bone is located and whether there is a bone disease involved

Question 20

What are two treatment variables that play a role in how a fracture heals?

Answer 20

1. whether the fracture fragments are placed in the right apposition
2. if you use plates/screws

Question 21

What effect will placing a plate have on healing?

Answer 21

they have to suck out the hematoma to put in the plate, which means they take out the blood and cells that brought in the inflammatory phase

this means you skip the external callus entirely!!! You go directly to lamellar bone formation, which is a very slow process

so the only stability for the bone during repair will be the plate

Question 22

What are the three zones of the plate that we should know?

Answer 22

proliferative zone (where the pluripotent cells are)

hypertrophic zone (where the cartilage is becoming ossified)

metaphasis (the bone just pass the growth plate)

Question 23

Which zone is the weakest zone and most likely to fracture?

Answer 23

the hypertrophic zone

Question 24

Why is it bad if a fracture goes through the proliferative zone?

Answer 24

you can get a growth arrest or malgrowth