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Ortho Implant technology > Unit 6a: Fractures, fracture healing & non-surgical fixation > Flashcards

Unit 6a: Fractures, fracture healing & non-surgical fixation Flashcards

1
Q

What are the most important mechanical properties of bone?

A

strength and stiffness

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2
Q

Which type of loading is a long bone most resistant under?

A

best resistance to compression, then tension, and is weakest in shear.

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3
Q

What determines the location and type of fracture?

A
  1. geometry + structure of the bone
  2. type of loading (eg. tension, compression, shear)…
  3. rate of loading
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4
Q

Under an axial load, what is the stiffness of the bone proportional to?

A

its cross sectional area

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5
Q

Under a bending load, which two factors affect stiffness of a bone? what term describes this?

A

cross sectional area and the distribution of bone around a neutral axis

= second moment of area

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6
Q

Under a torsional load, which two factors affect stiffness of a bone? what term describes this?

A

cross sectional area and the distribution of bone around a neutral axis

= polar second moment of area

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7
Q

How does the geometry of the tibia affect fracture location when subjected to a torsional load?

A

fracture occurs distally

because distally there is more bone located close to the neutral axis so the polar second moment of area is low

whereas proximally there is less bone distributed further so the polar second moment of area is high

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8
Q

Is cortical or cancellous bone weaker under axial loading?

A

cancellous

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9
Q

Which parts of a long bone are made of cortical and which parts are made of cancellous bone?

A 
mid-diaphysis = cortical 
metaphyses = cancellous
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10
Q

Which fracture pattern is the result of pure bending?

A

transverse

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11
Q

In a transverse fracture, which side is loaded in tension and which side in compression?

A

convex side in tension

concave side in compression

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12
Q

In a transverse fracture, which side fails in

a) adults ?
b) children?

A

a) convex/tension side as it is weaker in tension than compression
b) concave/ compression

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13
Q

Which fracture pattern is the result of pure compression?

A

oblique

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14
Q

Which fracture pattern is the result of bending and compression?

A

butterfly segment

  • bending causes transverse crack on tension side of bone
  • compression causes an oblique fracture
  • results in fragment on compression side of bone
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15
Q

Which fracture pattern is the result of pure torsion?

A

spiral

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16
Q

Why does a spiral fracture pattern form?

A

the fracture line at about 45° to the axis about which the torque is applied
failure of the bone in tension, perpendicular to the crack

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17
Q

Which portion of the bone fractures under a compressive load?

A

close to or within the metaphyses

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18
Q

How does rate of loading determine bone strength?

A

it is stronger at a higher loading rate than at a lower loading rate

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19
Q

Describe the fracture process

A
  1. energy to limb
  2. energy soft tissues to bone
  3. bone absorbs energy
  4. bone fractures releasing energy into soft tissues
  5. damaged bone and soft tissues bleed causing a haematoma
  6. acute inflammatory response causes pain and healing
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20
Q

How does the size of gap affect bone healing?

A

If the gap is small it heals but if large it does not

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21
Q

What characterises fracture healing?

A

callus formation

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22
Q

What is secondary bone healing?

A

callus developing, around the fracture site, from mesenchymal (primitive) tissue then chondroid (cartilage) and then osseous (bone) tissue. Later, remodelling takes place and the external callus gradually disappears as the bone regains its original strength, shape and internal architecture.

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23
Q

How long does it take for most long bone fractures to heal?

A

6-12 weeks

24
Q

What happens to fracture if blood supply is not re-established?

A

bony union will not take place. This may be described as an “atrophic” or fibrous union

25
Q

What happens if there is excessive movement during fracture healing?

A 
cartilage laid down instead of bone
or pseudoarthrosis (false joint) may form
26
Q

What happens if there is no relative movement (or micromovement) taking place between fracture fragments during the healing process?

A

primary bone healing with no callus formation

27
Q

Is primary or secondary bone healing quicker?

A

primary gets its structure back quicker but not its strength

28
Q

What is the disadvantage of primary bone healing?

A

rigid fixation deprives bone of its natural loads causing stress shielding and weakness

29
Q

“Bone has the ability to remodel, by altering its size, shape, and structure, to meet the mechanical demands placed on it” describes which term…

A

Wolff’s law

30
Q

How does callus formation give structural support to a healing bone?

A

increases the second moment of area which compensates for the lower strength and rigidity of the material of the callus

31
Q

How does loading encourage bone union?

A

loading bone along long axis

32
Q

Name three possible factors which may explain why movement at the fracture site influences bone healing.

A

Electrical effects caused by moving crystals of hydroxyapatite, which are the basic mineral constituents of bone. Hydroxyapatite is known to be piezoelectric, that is it develops an electric charge when loaded.

Hormonal factors (there is some evidence of a hormone “Substance P” being produced at fracture sites).

Electro-magnetic effects produced through electron flow away from the fracture site.

33
Q

How much blood is lost from

a) femoral fracture?
b) pelvic fracture?

A

a) 1 litre

b) 3 litres

34
Q

What is the first step in fracture management?

A

reduction

35
Q

What is the second step in fracture management?

A

holding

36
Q

What are the two types of reduction?

A

open

closed

37
Q

What are the two types of holding?

A

internal and external fixation

38
Q

Give 3 methods of external fixation

A

plaster of paris
traction
external fixator

39
Q

What is the primary objective of all kind of fixation devices?

A

to minimise deformation (or movement) between the fracture fragments.

40
Q

How do splints work? when are they suitable?

A

stabilise soft tissues of a stable fracture to resist bending forces after reduction but are of little use in resisting torsional and compression forces

41
Q

What material is plaster of paris?

A

calcium sulphate

42
Q

What risk is there when using a plaster of paris cast?

A

produces heat when the crystal sets to a solid which may damage patient

43
Q

How is a plaster of paris cast made?

A

using cotton bandages, hard-coated with crystals of calcium sulphate hemihydrate

getting wet and putting around splint

44
Q

In a plaster of paris cast what does

a) the bandage provide?
b) the starch provide?

A

a) vehicle

b) accelerates drying

45
Q

Give the two ways that plaster functions

A
  1. hydraulic theory - rigid exoskeleton supports soft tissues which support the bone
  2. periosteal hinge - three point bending fixates bone
46
Q

How do casts have to control the position of the bone?

A
  1. length - prevent shortening
  2. prevent A/P or medial/lateral tilt
  3. rotation about long axis of bone
47
Q

In which way do externally applied splints struggle to control bone position? How is this controlled?

A

struggle with controlling rotation

by applying to joint above and below

48
Q

Describe an advantage of a functional brace, compared to a full- leg cast.

A

dont immobilise the limb so muscles dont waste

49
Q

How is traction as a holding device difference to using traction to reduce a fracture?

A

traction reduces a fracture by controlled use of force on a relaxed limb in order to position bones

Traction as a holding technique depends on altering muscle tone in order to maintain a position achieved at reduction.

50
Q

What role do the muscles play in holding a fracture, in traction?

A

The muscles increase in tone if subject to an increased load in traction, maintaining the position of the broken bone fragments.

51
Q

What is Static (fixed) traction?

A

load is applied to the limb and attached to a splint eg. Thomas’ splint

52
Q

What is the disadvantage of using Static (fixed) traction?

A

immobilises the joint so there is no movement at fracture site + muscle weakness

53
Q

What is dynamic traction?

A

pulleys allow joint to move but with the net force along the axis of the bone

54
Q

Why is balanced traction used?

A

to offset the pressure effects caused by splints

55
Q

Give some general disadvantages of traction

A

prolonged hospitalisation + immobilisation
Bed sores
chest and urinary infections
disuse atrophy of muscles and bone

56
Q

Name the factors taken into consideration when deciding on the method that will be used to hold a fracture.

A

the patient’s age and functional requirements

the method and character of injury: open/closed, high/low energy, soft tissue injuries

available facilities

skills of the operator

Ortho Implant technology (7 decks)

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