Fractures, fracture healing + non-surgical fixation

Question 1

to what type of force is a long bone generally weakest

Answer 1

shear

Question 2

in tension and compression, what are stiffness and load required to cause failure of a bone proportional to?

Answer 2

cross sectional area

- larger the area, stronger and stiffer the bone

Question 3

what 2 things affect mechanical behaviour of bone in bending loading and what quantity takes these into account?

Answer 3

cross sectional area
distribution of bone tissue around neutral axis

second moment of area takes both of these into account

Question 4

to resist bending is it best to have bone close to or at a distance from the neutral axis?

Answer 4

at a distance

Question 5

what factors affect bone strength and stiffness in torsional loading? what is the quantity that takes these into account?

Answer 5

same as for bending

• cross sec area
• distribution of bone around neutral axis

polar moment of inertia

Question 6

are the tibia and fibula more prone to fracture proximally or distally?

Answer 6

tibia - more prone distally
fibula - more prone proximally
(they have diff geometry to one another)

Question 7

in bending, which side of a bone (convex/concave) is in compression and which is in tension? which will fail first in adults and children?

Answer 7

bending:
convex side in tension
concave side in compression

convex will fail first in adults and concave will fail first in children

Question 8

what is the likely fracture pattern from bending loading on bone

Answer 8

transverse

Question 9

fracture pattern of compressive force

Answer 9

oblique

Question 10

under what circumstances does a butterfly fracture pattern occur

Answer 10

compressive force coupled with bending force

• the bending force causes a transverse crack on the side in tension
• the compressive force causes an oblique fracture

Question 11

what type of load results in a spiral fracture

Answer 11

pure torsion

Question 12

where in the bone will the fracture occur in pure axial compression

Answer 12

close to or within the metaphases because the cancellous bone is weaker

Question 13

is bone stronger if loaded slowly or fast

Answer 13

stronger at faster loading rate

Question 14

what takes longer to heal, long bone fractures or cancellous bone fractures?

Answer 14

long bone

Question 15

how long do long bones take to heal roughly

Answer 15

6 - 12 weeks

Question 16

when would union be referred to as atrophic or fibrous

Answer 16

bony union not taking place due to no blood supply being re-established

Question 17

what is laid down instead of bone cells at the fracture site if there is excessive movement

Answer 17

cartilage

Question 18

what is ‘elephants foot’ appearance

Answer 18

a lot of movement at the fracture site causing a false joint (or pseudo arthritis) to form between rapidly proliferating cartilage cells at either end

Question 19

fracture healing

- weeks 0-2

Answer 19

macrophages mop up the haematoma and dead cells

Question 20

fracture healing

- weeks 2-6

Answer 20

new capillaries grow into the fracture haematoma bringing fibroblasts and osteoblasts
surviving periosteum begins to regenerate and grow

Question 21

fracture healing

- weeks 6-12

Answer 21

new bone tissue laid down and eventually the 2 ends reunite as a provisional callus

Question 22

under the right circumstances what will the provisional callus continue to form up until about 12 months

Answer 22

woven bone which gradually remodels to form a cortex

Question 23

how does the provisional callus appear on X-ray

Answer 23

dense area

Question 24

what do fibroblasts form

Answer 24

fibrin (scar tissue)

Question 25

what is another name for secondary bone healing

Answer 25

natural bone healing

Question 26

what happens in primary bone healing

Answer 26

new Haversian systems grow directly across the fracture gap

Question 27

what is the problem with primary bone healing

Answer 27

although faster at healing the fracture, it does not quickly recover its original strength

Question 28

what is Wolffs law

Answer 28

the ability of bone to remodel itself depending upon the mechanical demands placed upon it

Question 29

what makes up for the fact that the callus has lower strength and rigidity than bone

Answer 29

the second moment of area is increased

Question 30

what maintains the rigidity of the callus (back up with an equation)

Answer 30

``` R = E I although E (yougs modulus) is lower for the callus, I (second moment of area) is higher ```

Question 31

along what axis does loading encourage bone union

Answer 31

along its long axis

Question 32

Hydroxyapatite is known to be piezoelectric, what does this mean?

Answer 32

it develops an electric charge when loaded

Question 33

what hormone is thought to be produced at fracture sites

Answer 33

substance P

Question 34

how is pain relief achieved in fracture mx

Answer 34

strong opioids usually justified - added benefit of reduced anxiety and fear splint reduces muscle spasm

Question 35

how much blood is roughly lost from a femoral fracture and a pelvic fracture

Answer 35

femoral - about 1 litre | pelvic - up to 3 litres

Question 36

what are the 2 primary objectives of all kinds of fixation device

Answer 36

``` reduction of displacement minimise deformation (/movement) ```

Question 37

what types of force does a splint allow bone to resist / not resist

Answer 37

they help resist bending forces | little use in resisting torsional and compression forces

Question 38

what material is plaster of paris

Answer 38

calcium sulphate

Question 39

why does care need to be taken with plaster of paris

Answer 39

heat is produced from the calcium sulphate hemihydrate (the more of this compound in the bandage, the more heat)

Question 40

what type of solvent are commercial plaster bandages made with

Answer 40

an organic solvent such as ether, which contains no water

Question 41

what is added to help the calcium sulphate 'hold on' to the bandage

Answer 41

starch

Question 42

why is starch referred to as an accelerator in plaster cast setting

Answer 42

it speeds up the chemical reaction and therefore influences the speed of setting

Question 43

how can plaster setting be slowed down

Answer 43

- reducing the amount of starch added - adding a retarder - altering the temp of the water used to wet the bandages

Question 44

examples of retarders

Answer 44

alum and borax

Question 45

whats the difference between long and short crystals in plaster of paris

Answer 45

long - occur naturally as alabaster - give a hard quality short - give the cast a softer feel

Question 46

plaster functions in 2 ways - describe them

Answer 46

1. forms a rigid exoskeleton which support the soft tissues, which in turn supports the broken bone 2. gentle 3 point fixation achieved by moulding the cast against the fracture - giving a so called periosteal hinge

Question 47

how do standard casts control rotation

Answer 47

by incorporating the whole of the broken bone and limb segment in the cast including the joints

Question 48

what is the disadvantage of prolonged casting and how can it be overcome

Answer 48

prolongs rehab due to making joints stiff and muscles waste overcome with careful moulding and the application of hinges to the cast - FUNCTIONAL BRACING -

Question 49

how does Sarmiento's below the knee cast achieve rotary control

Answer 49

moulding around upper third of tibia extensions which encapture the femoral condyles in knee flexion

Question 50

principle disadvantage of skeletal traction

Answer 50

bone infection risk

Question 51

advantages of skeletal traction

Answer 51

can be used to apply large loads load can be precisely relative to the long axis of the bone (important in dynamic traction)

Question 52

why is a Thomas splint only used for a week or two

Answer 52

the immobility prevents joint movement, does not induce axial movement at the fracture site, and leads to muscle disuse

Question 53

What age group is a Thomas splint usually used for

Answer 53

children because their fractures usually heal quickly and they dont cope well with complicated traction

Question 54

what is the purpose of balanced traction

Answer 54

principally used to offset pressure effects caused by splints e.g. thomas splint with small load applied to the splint as a whole to offset the pressure at the groin

Question 55

traction is the safest method of treating fractures, why then is it not commonly used?

Answer 55

requires prolonged hospitalisation clinical complications include bed sores, chest and urinary unfections, muscle and bone atrophy