Fractures

Question 1

how is the structure of bone assessed?

Answer 1

DEXA scans

Question 2

what are the scores used in the DEXA scan and what do they mean?

Answer 2

T and Z scores

T score= how much your bone mass differs from the bone mass of an average healthy 30 year old adult.

Z score= compares your bone density to the average bone density of people your own age and gender

Question 3

what T scores indicate pathology?

Answer 3

T score 2.5 SD below normal (score < -2.5)–> osteoporosis

T score 1.0-2.5 SD below normal (score between -1.0 and -2.5) –> osteopenia, low bone mass

Question 4

what is main composition of bone?

Answer 4

• matrix and cells

- matrix is organic (e.g. collagen) and inorganic (Ca, P)

Question 5

what are the cells that make up bone?

Answer 5

o Osteoclasts
– break down bone
– big and have a ruffled border

o Osteoblasts
– lay down new bone

o Osteocytes
– mature osteoblasts
– act as mechanoreceptors.

o Osteoprogenitors

Question 6

what is the bone remodelling cycle?

Answer 6

1) resorption: osteoclasts break down bone
2) reversal: osteoclasts apoptose while preosteoblasts line the bone
3) formation: mature osteoblasts form osteoid and mineralisation occurs
4) resting: osteocytes line the bone

Question 7

what is contained in the ruffled borders of osteoclasts?

Answer 7

the digestive bone enzymes

Question 8

what are bisphosphonates, what do they do?

Answer 8

induce osteoclast apoptosis:

destroy the osteoclast cytoskeleton which breaks down the ruffled border so they no longer can release digestive enzymes

inhibit the constant bone remodelling (so limit the bone reabsorption)

Question 9

name an example of a bisphosphonate

Answer 9

alendronate

Question 10

what is the negative effect of using bisphosphonates over time?

Answer 10

build-up of microfractures that can lead to spontaneous fractures (of the shaft typically)

Question 11

what drug inhibits osteoclast activation?

Answer 11

Denosumab

an RANK/OPG analogue

Question 12

what cell normally exhibits the RANK receptor?

Answer 12

osteoclast

Question 13

what cells normally exhibits the RANK ligand (RANKL)?

Answer 13

osteoblasts

Question 14

what effect does osteoprotegrin have?

Answer 14

acts to supress osteoclast activation.

Question 15

what period of someone life is most bone laid down?

Answer 15

pre-pubertal

Question 16

what does Wolff’s Law describe? how can this be applied to remodelling

Answer 16

bone remodels according to the stresses applied to it

bone can remodel according to the stresses applied to e.g exercises

Question 17

what are the 4 stages of fracture healing?

Answer 17

1. Haematoma/Inflammation 
– up-to 1 week.
2. Soft callus formation 
– 1-4 weeks.
3. Hard callus formation 
– 1-4 months
4. Remodelling 
– up-to several years.

Question 18

what happens at the haematoma stage of fracture healing?

Answer 18

a. Macrophages, leucocytes, IL-1-6, BMPs to promote healing
b. Granulation tissue formation.
c. Progenitor cell invasion

Question 19

what happens in soft callus formation in fracture healing?

Answer 19

a. Chondroblasts –> collagen, fibroblasts –> fibrous tissue.
b. Proteoglycans produced (prevent mineralisation).
c. Chondrocytes release calcium + enzymes to break down proteoglycans (allows mineralisation).

soft callous stabilises the disorganised bone
the bone is not yet at optimal strength but can have some use

Question 20

what happens in hard callous formation in fracture healing?

Answer 20

a. Blood vessel invasion of soft callus.
b. Chondroclasts break down calcified callus and this is replaced by osteoid (T1 collagen) from osteoblasts.
c. Osteoid calcified into WOVEN bone.

Question 21

what happens in remodelling in fracture healing?

Answer 21

a. Woven –> lamellar bone.
b. Shapes according to Wolff’s law.
c. Medullary canals form.

Question 22

how do children compare to adults in bone healing ability?

Answer 22

children are much quicker in the healing process

Question 23

what are 4 types of general fracture?

Answer 23

o Spiral fracture (twist)
o Oblique fracture (compressive on bone)
o Butterfly fragment fracture – blow to one side.
o Transverse fracture (perpendicular to long axis)

Question 24

What is a typical children’s bone fracture?

Answer 24

o Greenstick (one side broken, the other intact)

visually like slumped tree trunk