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BMSc > biomechanics module 2 - sem1 > Flashcards

biomechanics module 2 - sem1 Flashcards

1
Q

What are the 5 types of loading?

A

Tensile, compressive, shearing, bending, torsional

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2
Q

What is combined loading?

A

When more than one type of loading is present

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3
Q

What causes combined loading?

A

results from irregular geometry of bones, combined actions of gravitational forces, muscle forces, ligament forces,

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4
Q

describe shear loading

A

two forces act in opposite directions

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5
Q

what type of tensile force can human cortical bone withstand (is stronger against)

A

Withstand tensile and compressive loads
weaker against shear loads

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6
Q

describe bending loading

A

load is applied to a structure causing it to bend

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7
Q

2 types of bending loading

A

cantilever
3 point bending

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8
Q

Describe cantilever loading

A

One end of the object is fixed and a load is applied to the opposite end, causing the object to bend
e.g. diving board

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9
Q

Describe 3 point bending

A

Three forces are applied to an object
e.g. see-saw

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10
Q

What is the neutral axis?

A

The neutral axis is the line through a structure along which no distortion occurs

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11
Q

Which force is bone stronger under? Compression or tension

A

Compression > tension

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12
Q

What happens when an object is subject to a large bending load?

A

The object will fracture on the elongated side (which is under tension) / outer surface

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13
Q

Describe torsional loads

A

Bone is twisted about it’s longitudinal axis
Occurs when one end of the bone is fixed and the other is twisted.

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14
Q

What is the characteristic appearance of torsional loads

A

Spiral

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15
Q

What type of structure maximizes the strength-weight ratio

A

Hollow structures

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16
Q

What do tendons connect

A

muscle to bone

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17
Q

What do ligaments connect

A

bone to bone

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18
Q

What is another reason for muscle contraction, other than for movement

A

alter stress distribution in bones to reduce amount of tensile stress and potentially prevent any damage

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19
Q

What is Wolff’s law

A

Compact and cancellous tissue is constantly gained or lost in response to the amount of stress placed on the bone
/ bone is laid down when needed, and reabsorbed when not needed

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20
Q

what can lead to bone atrophy

A

inactivity

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21
Q

Describe stress shielding

A

Fixation plate is carrying more load than bone, causing unstressed bone tissue to be reabsorbed

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22
Q

examples of bone remodelling problems in orthopaedics

A

stress shielding
bone hypertrophy

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23
Q

Describe bone hypertrophy

A

increase in bone tissue, bone strengthens at points carrying a greater load than normal

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24
Q

What is a fatigue fracture

A

A fracture caused by a load being applied repeatedly over a short period of time
load is smaller than ultimate strength of the bone

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25
Q

other names for fatigue fracture

A

stress / march fractures

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26
Q

when do fatigue fractures usually occur

A

usually sustained during a continuous period of strenuous activity

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27
Q

How will the fracture occur in fatigue fractures

A

will occur if the repetition / frequency is too fast for the remodeling process
if the repetitions were spaced out, the bone would have time to remodel itself and repair any damage

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28
Q

characteristic of a green-stick fracture

A

incomplete fracture with one side bent and the other side buckled

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29
Q

why are children more prone to green-stick fractures

A

children’s bones contain a greater proportion of collagen than adult bones, which gives their bones a greater amount of flexibility

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30
Q

Is the process of bone formation and reabsorption balanced in adults

A

Yes

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31
Q

List characteristics of bones in children

A

formation > resorption
increased collagen
increased flexibility
greenstick fractures common

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32
Q

list characteristics of bones in elderly

A

resorption > formation
compact bone thinning,
decrease in cancellous bone
brittle bones due to decreased flexibility
slightly weaker bones

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33
Q

list the 3 groups of cartilage

A

hyaline (articular)
elastic
fibrocartilage

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34
Q

what type of tissue is cartilage

A

connective

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35
Q

what does hyaline cartilage form

A

the articular surfaces of bones in synovial joints
also forms tip of the nose

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36
Q

what does elastic cartilage form

A

external ear and epiglottis

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37
Q

what does fibrocartilage form

A

symphysis pubis
intervertebral discs

38
Q

where is articular cartilage found

A

in synovial joints
(mobile joints such as the hip and knee)

39
Q

2 main roles of articular cartilage

A

shock absorber / cushion the bones, provide a smooth, lubricated, bearing surface

40
Q

Function of chondrocytes

A

manufacture, secrete and maintain the organic matrix

41
Q

How many layers does articular cartilage have and what are the names

A

3 main layers
- superficial tangential
- middle
- deep

42
Q

what solution are collagen fibrils found in

A

solution of proteoglycans
large protein based molecules which are important for the mechanical properties of articular cartilage

43
Q

how are collagen fibrils arranged in the superficial tangential zone

A

collagen fibrils are tightly woven into sheets, arranged parallel to the articular surface and the chondrocytes
oblong with longitudinal axis parallel to the articular surface

44
Q

how are collagen fibrils arranged in the middle zone?

A

collagen fibrils are more randomly arranged but are still broadly parallel to the articular surface.
less densly packed to accommodate for proteoglycans
circular chondrocytes

45
Q

how are collagen fibrils arranged in the deep zone?

A

collagen fibrils are arranged in large fibre bundles that are anchored to the underlying bone tissue , attaching the articular cartilage to the bone

46
Q

how is articular cartilage attached to bone?

A

attached by the collagen fibrils which extend from the deep zone into underlying bone tissue

47
Q

what behaviour does articular cartilage demonstrate

A

viscoelastic mechanical behaviour

48
Q

characteristics of viscoelastic behaviour

A
  • time dependent
  • once a load is removed, it will return to its original size and shape
  • response is not immediate
  • stress relaxation
  • creep
49
Q

why is the viscoelastic behaviour important for articular cartilage

A

gives articular cartilage the ability to cushion the high loads that occur between the bones in joints, reducing potential damage

50
Q

what is creep

A

Creep is an increase in strain under a constant stress

51
Q

what is stress relaxation

A

stress relaxation is is a reduction in stress under a constant strain

52
Q

is the coefficient of friction low or high in synovial joints

A

very low
made by the combined action of the articular cartilage and the synovial fluid

53
Q

what determines the way in which lubrication is brought about

A

magnitude of the load
length of time that the load is maintained

54
Q

list the 3 types of lubrication

A
  • elastohydrodynamic lubrication
  • boosted lubrication
  • boundary lubrication
55
Q

when does hydrodynamic lubrication occur

A

occurs when the two surfaces are moving over one another

56
Q

when does squeeze firm lubrication occur

A

occurs as the two surfaces are forced together

57
Q

two types of elastrohydrodynamic lubrication

A

hydrodynamic
squeeze firm lubrication

58
Q

when does elastohydrodynamic lubrication occur

A

occurs when two surfaces, one of which is deformable, are lubricated by a film of fluid as they move relative to one another.

59
Q

what occurs in boosted lubrication

A

small molecules including water are forced into the articular cartilage
relies on permeability of articular cartilage

60
Q

what occurs in boundary lubrication

A

fluid film is completely depleted
lubricant molecules attach themselves chemically to the surfaces

61
Q

example of boundary lubrication in synovial joints

A

the protein lubricin coats the surface of the articular cartilage

62
Q

what are tendon and ligament cells called

A

fibroblasts

63
Q

how are collagen fibres arranged in tendons and ligaments

A

tendons - collagen fibres are arranged in parallel, withstand large load in one direction

ligaments - collagen fibres are branched and interwoven, withstand smaller loads in multiple directions

64
Q

what is the basic mechanical behaviour of tendons and ligaments

A

viscoelastic

65
Q

what are bone cells called

A

ostocytes

66
Q

what gives bones their characteristic hardness and rigidity

A

The inorganic component, which consists mainly of crystals of calcium
phosphate, gives bone its characteristic hardness and rigidity.

67
Q

what are the 4 types of connective tissue

A

bone
articular
tendon
ligament

68
Q

what are the 2 different types of bone tissue

A

compact and cancellous

69
Q

describe compact bone

A

forms outer layer of bone and has a dense structure
cortical bone

70
Q

describe cancellous bone

A

forms inner part of short, flat and irregular bones
mesh structure –> spongey bone
spaces between mesh contain red bone marrow

71
Q

basic structural unit in compact bone

A

Haversian system

72
Q

how is bone tissue arranged

A

arranged in layers called lamellae forming concentric cylinders around a central canal

73
Q

what is in the central canal / haversian canal

A

blood vessels and nerve fibres

74
Q

basic structural unit in cancellous bone

A

trabecula

75
Q

difference between trabecular and the haversian system

A

The main difference is that trabeculae do not contain haversian canals
Haversian canals are not needed in cancellous bone as blood vessels pass though the marrow filled spaces between the latticework of trabeculae, supplying nutrients to the osteocytes through the canaliculi.

76
Q

what happens to a material under tensile load

A

it will elongate

77
Q

what is strain

A

Strain is defined as the change in length divided by the original length

78
Q

what is stress

A

Stress is defined as the force per cross-sectional area
stress = F/A

79
Q

SI units of stress

A

N m-2

80
Q

SI unit of strain

A

strain has no units

81
Q

what regions make up the stress-strain curve

A

elastic
plastic

82
Q

what is the point inbetween the elastic and plastic region

A

yield point A
where the yield stess and yield strain exist

83
Q

describe the curve in the elastic region

A

linear - stress is directly proportional to strain

84
Q

what is elastic behaviour

A

a bone will return to its original shape and size once a load is removed, if it is not deformed beyond it’s yield point

85
Q

describe the curve in the plastic region

A

not linear - a small increase in stress will cause a large increase in strain, deforming the bone

86
Q

what happens when a bone is deformed beyond it’s yield point

A

it will not return to it’s original shape and size, even when load is removed

87
Q

what is plastic behaviour

A

a bone will be permanently deformed once it passes it’s yield point

88
Q

what happens to the bone at ultimate strain / stress

A

fracture

89
Q

what is young’s modulus

A

ratio of stress to strain
describes how stiff / flexible a material is
youngs modulus = stress / strain

90
Q

what does a small young’s modulus mean

A

a material requires a small amount of stress to produce a large amount of strain i.e it is flexible

91
Q

what does a large young’s modulus mean

A

a material requires a large amount of stress to produce a small strain, the material is stiff

BMSc (4 decks)

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