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Ortho BMSc > Mechanics: Unit 2 Skeletal tissue (online) > Flashcards

Mechanics: Unit 2 Skeletal tissue (online) Flashcards

1
Q

What is bone composed of?

A

osteocytes
non-cellular component: collagen and ground substance
inorganic component: calcium phosphate crystals

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2
Q

Describe collagen fibres

A

strong and flexible but don’t allow stretching

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3
Q

Describe ground substance

A

jelly-like cement

weak

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4
Q

What gives bone its hardness and rigidity?

A

inorganic component

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5
Q

What makes up
a) 25-30%
b) 65-70%
of bone’s dry weight?

A

a) collagen

b) inorganic component

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6
Q

Name the 2 types of bone

A

compact

cancellous

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7
Q

Give another name for

a) compact bone
b) cancellous bone

A

a) cortical

b) spongy

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8
Q

What does compact bone form?

A

outer layer of bone as it is a dense structure

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9
Q

What does cancellous bone form?

A

inner part of short, flat and irregular bones

liner inner part of long bones + metaphyses + epiphyses

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10
Q

What is the basic structural unit of

a) compact bone?
b) cancellous bone?

A

a) haversion system

b) trabecula

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11
Q

Describe cancellous bone

A

mesh-like

spaces have red bone marrow

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12
Q

How is a haversion system formed?

A

laminae form cylinders around haversion canal

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13
Q

Where are osteocytes found?

A

in lacunae ( the spaces between laminae)

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14
Q

What does a haversion canal contain?

A

blood vessels and nerve fibres

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15
Q

Which structure links lacunae to the canal?

A

canaliculi

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16
Q

What connects lamellae?

A

collagen fibres

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17
Q

What structures
a) do
b) don’t
trabeculae have?

A

a) lamellae, lacunae, canaliculi

b) canals

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18
Q

Which type of bone tissue contains haversian canals and why are they needed?

A

cortical bone

contain blood vessels which are needed to supply the bone tissue with nutrients

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19
Q

What is a tensile load? + example

A

a load that acts to stretch a material like in a rope

eg radius and ulna when lifting an object

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20
Q

What is a compressive load? + example

A

a load that acts to compress a material

eg vertebrae carrying upper body weight

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21
Q

What is stress?

A

a measure of the concentration of a load

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22
Q

How do we calculate stress?

A

force/area

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23
Q

What are the units for stress?

A

n/m2

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24
Q

What is strain?

A

a measure of the amount of deformation a material has undergone.

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25
Q

How do we calculate strain?

A

change in length/ original length

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26
Q

What does a strain-stress curve show?

A

how a material deforms as it is loaded

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27
Q

What are the 2 regions of the strain stress curve? and what separates them?

A

elastic region and plastic region

separated by yield point

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28
Q

Describe the elastic region of the stress-strain curve

A

linear ie. stress is proportional to strain

will return to original shape/size once load is removed

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29
Q

Describe the plastic region of the stress-strain curve

A

small inc in stress = large deformity

will not return to original

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30
Q

What is Young’s modulus?

A

ratio of stress to strain tells us how flexible or stiff a material is

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31
Q

What does a small young’s modulus indicate?

A

material is flexible

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32
Q

What is a shearing force?

A

when two forces act in the opposite direction

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33
Q

Give an example of a shearing force

A

screw on fracture fixation plate

bone cement by hip prosthesis

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34
Q

Is cortical bone stronger in shear, compression or tension?

A

compression then tension then shearing

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35
Q

Give an example of a fracture caused by shearing

A

intra-articular fracture of the femoral condyle

36
Q

Give the two types of bending force and an example of each

A

cantilever ie. one side fixed eg. diving board

3 point eg seesaw

37
Q

describe the sides of a bent structure

A

one elongated side due to tension
one compressed side

and a neutral axis with no distortion between the two

38
Q

Along which surface will a fracture most likely occur when an excessive bending load is applied to a long bone?

A

elongated side

39
Q

Describe a torsion load

A

twist along a longitudial axis ie. one side of bone fixed and one twisted

40
Q

What type of fracture results from an excessive torsion load?

A

spiral fracture

41
Q

When considering torsional loads, do hollow or solid bars have the best strength-to-weight ratio?

A

hollow

42
Q

How do muscles affect stress distribution of bones?

A

attach via tendons and change the loads when they contract

43
Q

Why is it sometimes desirable for muscles to contract even when it is not to produce movement?

A

muscles contract when bone subject to large tensile load to make the overall load compressive

this is because the bone is stronger in compression

44
Q

What is Wolff’s law?

A

bone is laid down where needed and resorbed where it is not

45
Q

What affect does
a) exercise
b) inactivity
have on bone?

A

a) increases stress so bone lays down more collagen and minerals and is stronger
b) bone is resorbed causing bone atrophy

46
Q

How does fracture fixation affect bone remodelling?

A

plates cause bone immobility and stress shielding ie they take most of the stress, this makes bone weaker

47
Q

How do screws affect bone remodelling?

A

increase the stress causing hypertrophy

48
Q

What is a fatigue/stress fracture?

A

fracture caused by a repeated application of a load that is smaller than the ultimate strength of the bone over a short period of time

49
Q

Why are children prone to greenstick fractures but not adults?

A

their bones contain a greater proportion of collagen than adult bones which gives their bones a greater amount of flexibility

50
Q

How would you recognise a greenstick fracture?

A

an incomplete fracture with one side bent and the other buckled

51
Q

How is cancellous bone tissue affected by ageing?

A

affected more so than cortical bone

thinning of the longitudinal trabeculae and the resorption of some transverse trabeculae

52
Q

What age is bone lost quicker than it is made? What qualities does this change make?

A

35-40

bone only loses a little strength but becomes a lot more brittle

53
Q

What does cartilage consist of?

A

cartilage cells, fibres and ground substance

54
Q

Name the 3 types of cartilage and give an example of each

A

hyaline eg articular, tip of nose
elastic eg external ear, epiglottis
fibrocartilage eg pubis symphysis, intervertebral discs

55
Q

In what type of joints is articular cartilage found?

A

synovial eg hip and knee

56
Q

What are the two main roles of articular cartilage?

A

to cushion the bones and to provide a smooth, lubricated, bearing surface.

57
Q

What consistency is articular cartilage and what function does this provide?

A

firm but pliable means shock is absorbed evenly to reduce contact stress

58
Q

What is articular cartilage composed of?

A

organic matrix of non-cellular material (collagen)
chondrocytes
interstitial fluid (water)
proteoglycans

59
Q

What forms the organic matrix of non-cellular material in articular cartilage ?

A

collagen structures in strong fibrils

60
Q

Where are proteoglycans found in articular cartilage?

A

middle zone

61
Q

Where are chondrocytes most densely packed?

A

deep layer

62
Q

what function do chondrocytes have?

A

they maintain, manufacture and secrete the organic matrix

63
Q

How many layers (or zones) does articular cartilage have?

Name them

A

3: superficial tangential, middle and deep

64
Q

How is articular cartilage attached to bone?

A

the collagen fibrils that extend from the deep zone into the underlying bone tissue

65
Q

how are collagen fibrils arranged in

a) superficial zone of articular cartilage?
b) deep zone of articular cartilage?

A

a) parallel sheets

b) large bundles anchored perpendicular to bone

66
Q

What shape are chondrocytes in

a) superficial layer?
b) middle layer?
c) deep layer?

A

a) oblong
b) circular
c) circular in columns

67
Q

What does the tidemark in articular cartilage divide?

A

deep zone from calcified cartilage

68
Q

How does articular cartilage behave mechanically

A

viscoelastic

69
Q

What is the difference between creep and stress relaxation?

A

Creep is an increase in strain under a constant stress whilst stress relaxation is a reduction in stress under a constant strain.

70
Q

Will viscoelastic material return to its original size and shape when a load is removed?

A

yes but not immediately

71
Q

Why does stress relaxation occur in articular cartilage?

A

initially as fluid is forced out there is a large frictional drag that needs a large force to compress the tissue but then once fluid is all in the surface layer which is the most compacted the stress needed to compress it is decreased

72
Q

Give the 3 types of lubrication

A

elastohydrodynamic
boosted
boundary

73
Q

What is elastohydrodynamic lubrication?

A

when 2 surfaces, one of which is deformable, are lubricated by a film of fluid so that they do not touch

74
Q

Summarise the differences between hydrodynamic and squeeze film lubrication in terms of when they occur

A

hydrodynamic: when surfaces slide over each other

squeeze film: when surfaces are forced together

75
Q

describe boosted lubrication

A

as two surfaces are forced together the gap between them decreases and the resistance to lubricant is greater than the resistance of small molecules like water flowing through permeations into articular cartilage

so solvent of synovial fluid is lost and leave behind a viscose gel that can withstand the increased load

76
Q

Which type of lubrication stops direct contact of articulating surfaces when large loads completely deplete the fluid film?

A

boundary

77
Q

describe boundary lubrication

A

molecules in lubricant attach chemically to the surfaces to stop them touching when the fluid is depleted completely

78
Q

which molecule allows for boundary lubrication in humans?

A

lubricin

79
Q

What are tendons and ligaments?

A

dense and fibrous connective tissues
tendons connect muscles to bones
ligaments connect bone to bone

80
Q

What are the cells in tendons and ligaments called?

A

fibroblasts

81
Q

How are the collagen fibres arranged in tendons and ligaments? why?

A

In tendons collagen fibres are aligned in parallel and in ligaments collagen fibres are aligned nearly in parallel.

tendons have one large load in one direction but ligaments have this and also smaller loads in other directions

82
Q

What is the basic mechanical behaviour of tendons and ligaments?

A

viscoelastic

83
Q

What tensile properties must
a) a ligament
b) a tendon
withstand?

A

a) the forces that could split joints

b) muscle contraction

84
Q

What happens when a tensile load is applied to move tibia and femur apart?

A

ACL elongates up to 7mm before it fails

85
Q

If the compressive load on a bone is doubled, how will the stress and strain be affected?

A

the stress doubles

the strain doubles if it is in the linear elastic range

86
Q

What happens to the distribution of pressure in elastohydrodynamic lubrication when we consider the surface as deformable not rigid?

A

distribution of pressure increases so the magnitude decreases and the film of fluid remains relatively thick

Ortho BMSc (14 decks)

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