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Implant technology > Fractures, fracture healing + non-surgical fixation > Flashcards

Fractures, fracture healing + non-surgical fixation Flashcards

1
Q

to what type of force is a long bone generally weakest

A

shear

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2
Q

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

A

cross sectional area

- larger the area, stronger and stiffer the bone

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3
Q

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

A

cross sectional area
distribution of bone tissue around neutral axis

second moment of area takes both of these into account

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4
Q

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

A

at a distance

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5
Q

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

A

same as for bending

  • cross sec area
  • distribution of bone around neutral axis

polar moment of inertia

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6
Q

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

A

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

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7
Q

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?

A

bending:
convex side in tension
concave side in compression

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

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8
Q

what is the likely fracture pattern from bending loading on bone

A

transverse

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9
Q

fracture pattern of compressive force

A

oblique

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10
Q

under what circumstances does a butterfly fracture pattern occur

A

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
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11
Q

what type of load results in a spiral fracture

A

pure torsion

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12
Q

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

A

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

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13
Q

is bone stronger if loaded slowly or fast

A

stronger at faster loading rate

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14
Q

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

A

long bone

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15
Q

how long do long bones take to heal roughly

A

6 - 12 weeks

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16
Q

when would union be referred to as atrophic or fibrous

A

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

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17
Q

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

A

cartilage

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18
Q

what is ‘elephants foot’ appearance

A

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

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19
Q

fracture healing

- weeks 0-2

A

macrophages mop up the haematoma and dead cells

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20
Q

fracture healing

- weeks 2-6

A

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

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21
Q

fracture healing

- weeks 6-12

A

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

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22
Q

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

A

woven bone which gradually remodels to form a cortex

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23
Q

how does the provisional callus appear on X-ray

A

dense area

24
Q

what do fibroblasts form

A

fibrin (scar tissue)

25
Q

what is another name for secondary bone healing

A

natural bone healing

26
Q

what happens in primary bone healing

A

new Haversian systems grow directly across the fracture gap

27
Q

what is the problem with primary bone healing

A

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

28
Q

what is Wolffs law

A

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

29
Q

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

A

the second moment of area is increased

30
Q

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

A 
R = E I 
although E (yougs modulus) is lower for the callus, I (second moment of area) is higher
31
Q

along what axis does loading encourage bone union

A

along its long axis

32
Q

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

A

it develops an electric charge when loaded

33
Q

what hormone is thought to be produced at fracture sites

A

substance P

34
Q

how is pain relief achieved in fracture mx

A

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

35
Q

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

A

femoral - about 1 litre

pelvic - up to 3 litres

36
Q

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

A 
reduction of displacement 
minimise deformation (/movement)
37
Q

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

A

they help resist bending forces

little use in resisting torsional and compression forces

38
Q

what material is plaster of paris

A

calcium sulphate

39
Q

why does care need to be taken with plaster of paris

A

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

40
Q

what type of solvent are commercial plaster bandages made with

A

an organic solvent such as ether, which contains no water

41
Q

what is added to help the calcium sulphate ‘hold on’ to the bandage

A

starch

42
Q

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

A

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

43
Q

how can plaster setting be slowed down

A
  • reducing the amount of starch added
  • adding a retarder
  • altering the temp of the water used to wet the bandages
44
Q

examples of retarders

A

alum and borax

45
Q

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

A

long - occur naturally as alabaster - give a hard quality

short - give the cast a softer feel

46
Q

plaster functions in 2 ways - describe them

A
  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
47
Q

how do standard casts control rotation

A

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

48
Q

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

A

prolongs rehab due to making joints stiff and muscles waste

overcome with careful moulding and the application of hinges to the cast - FUNCTIONAL BRACING -

49
Q

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

A

moulding around upper third of tibia

extensions which encapture the femoral condyles in knee flexion

50
Q

principle disadvantage of skeletal traction

A

bone infection risk

51
Q

advantages of skeletal traction

A

can be used to apply large loads

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

52
Q

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

A

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

53
Q

What age group is a Thomas splint usually used for

A

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

54
Q

what is the purpose of balanced traction

A

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

55
Q

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

A

requires prolonged hospitalisation

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

Implant technology (10 decks)

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