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BMSc > Biomechanics unit 2 > Flashcards

Biomechanics unit 2 Flashcards

1
Q

4 principle types of tissue

A

Epithelial, connective, muscle and nervous tissue

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2
Q

4 types of connective tissue

A

Bone tissue, articular cartilage, tendon, ligament

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3
Q

4 types of bone size/shape

A

long bones, short bones, flat bones and irregular bones

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4
Q

What are bones composed of

A

Osteophytes, non cellular component, inorganic component

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5
Q

What does non cellular component of bone consist of

A

v strong collagen fibres embedded in a jelly like matrix called ground substance

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6
Q

What does inorganic component of bone consist of

A

Calcium phosphate crystals deposited in the matrix- gives bone hardness and rigidity

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7
Q

Two types of bone tissue

A

compact bone

cancellous bone

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8
Q

Compact bone

A

Forms outer layer of bones and has a dense structure- also called cortical bone

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9
Q

cancellous bone

A

Forms inner part of short flat and irregular bones. In long bones it lines the inner surface and makes up the greater part of the metaphases and epiphyses

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10
Q

Cancellous bone structure

A

Mesh like structure- spongy bone- spaces between the mesh contain red bone marrow

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11
Q

Structure of compact bone

A

Haversian system (basic structural unit). These are arranged longitudinally in columns of about 200 micrometers diameter.

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12
Q

Haversian system

A

Bone tissue arranged in layers (lamellae) forming cylinders around a central canal. Small central channel, haversian canal, contains blood vessels and nerve fibres. Small cavities between lamellae called lacunae - that contain osteocytes

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13
Q

What links osteocytes to haversian canal and other lacunae

A

minute channels called canaliculi- along which nutrients are carried from the blood vessels

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14
Q

What interconnects the layers of lamellae within the haversian system

A

Collagen fibres.

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15
Q

What is the weakest part of the bones microstructure

A

haversian canal surrounded by a cement like ground substance, probably because it contains no collagen fibres

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16
Q

Basic structural unit in cancellous bone

A

Trabecula

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17
Q

How are trabecular arranged

A

In a latticework of branching sheets and columns

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18
Q

What do trabecullae consist of

A

layers of lamellae with lacunae containing osteocytes connected by canaliculi

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19
Q

main difference between trabecular and haversian system

A

Trabeculae dont contain haversian canals- they are not needed because blood vessels pass through the marrow filled spaces between the latticework of trabecular, supplying nutrients to the osteocytes through the canaliculi

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20
Q

Why does compact bone need haversian canals

A

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

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21
Q

Tension

A

Load acting to stretch a material

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22
Q

Compression

A

load acting to compress a material

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23
Q

Stress

A

force per cross sectional area (force/area)

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24
Q

Units for stress

A

N/m2 (Pa)

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25
Q

Strain

A

change in length/ original length

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26
Q

Units for strain

A

No units

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27
Q

Stress strain curve for cortical bone

A

stress increases with increasing strain - as the bone is increasingly deformed, it becomes harder to deform it further

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28
Q

Elastic region of stress strain curve

A

Linear- stress directly proportional to strain

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29
Q

Elastic behaviour

A

Provided bone specimen is not deformed beyond its yield point, it will return to its original size and shape once the load is removed

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30
Q

Yield stress and yield strain

A

amount of stress and strain at the yield point

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31
Q

yield point

A

division between the elastic and plastic regions of stress strain curve

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32
Q

Plastic region

A

curve not linear. For a small increase in stress, the bone deforms a lot

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33
Q

What happens when bone is stressed beyond its yield point

A

it is permanently deformed- plastic behaviour

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34
Q

Ultimate stress and strain

A

Stress and strain at the point at which the bone fractures

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35
Q

Youngs modulus eq

A

stress/strain

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36
Q

young modulus units

A

Pa

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37
Q

Small young modulus

A

only a small amount of stress to produce a large amount of strain

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38
Q

Shear loading

A

two forces acting in opposite directions- tend to cause layers within the materials to slip or shear

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39
Q

What load is cortical bone weakest in

A

Shear

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40
Q

Bending loading

A

Loads applied to a structure that tend to cause the structure to bend

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41
Q

Two types of bending

A

Cantilever bending and 3 point bending

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42
Q

Cantilever bending

A

e.g. diving board. one end fixed and load applied to other end- causing it to bend

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43
Q

3 point bending

A

3 forces applied to the object- see saw

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44
Q

Neutral axis

A

Between the two sides of a structure being bent- along which no deformation occurs

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45
Q

Neutral axis of femur

A

shape of femur causes it to be bent when it is loaded vertically- neutral axis runs approx along centre of the femur

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46
Q

Bone stronger under compression or tension

A

compression

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47
Q

Where does bone tend to fracture

A

the elongated side- under tensile stress

48
Q

e.g. of bending fracture

A

boot top fracture- skiing

49
Q

Torsional loading

A

bone twisted about longitudinal axis- often occur when one end of the bone is fixed and the other end is twisted

50
Q

What is most distorted in torsional load

A

No deformation along neutral axis, outer surface of the bar/bone is most distorted

51
Q

How are long bones designed to resist torsional loads

A

Hollow with strong cortical bone forming the outer layer- maximises strength to weight ratio

52
Q

Why do torsional fractures of tibia often occur distally

A

distal cross sectional area is smaller than proximal. Although the amount of bone tissue is the same, the distal part is less able to resist torsional loads

53
Q

Combined loading

A

Presence of more than one type of loading

54
Q

Muscle contraction affect on loading

A

Muscles can contract to alter the stress distribution within a bone- produce a compressive load on the bone to eliminate any tensile loads as bones are stronger in compression than tension

55
Q

Wolffs law

A

bone is laid down where needed and resorbed where not needed

56
Q

How to bones respond to increased levels of stress e.g. during exercise

A

They lay down more collagen fibres and mineral salts to strengthen the bone

57
Q

Bone atrophy

A

inactivity leads to resorption of bone tissue

58
Q

Stress shielding

A

During fracture healing- the plate will carry most of the load on the limb- if the plate isn’t removed soon after the fracture has healed, the bone will weaken as unstressed bone tissue is resorbed

59
Q

Bone hypertrophy

A

Increase in bone tissue. At points in the bone where screws are inserted, bone will strengthen as the bone tissue will be carrying a greater load than normal

60
Q

Fatigue fractures

A

fracture resulting from the repeated application of a load that is smaller than the ultimate strength

61
Q

What are fatigue fractures also known as

A

stress fractures or march fractures

62
Q

Small load

A

greater no. of repetitions required to produce a fatigue fracture

63
Q

Why is freq of repetitions important for fatigue fractures

A

Bone can remodel. If time between repetitions is long enough, bone can repair itself

64
Q

How do childrens bones differ from adults

A

Contain a greater proportion of collagen

65
Q

Why are greenstick fractures more common in children

A

Their bones are more flexible- due to increased collagen

66
Q

what is a greenstick fracture

A

incomplete fracture- one side of the bone is bent and the other side is buckled

67
Q

What kind of loads cause greenstick fractures

A

Excessive bending or torsional loads

68
Q

What happens to bones between ages of 35-40yrs

A

Bone tissue begins to be lost as resorption exceeds formation. Some thinning of compact bone and a larger reduction in the amount of cancellous bone due to the thinning of longitudinal trabeculae and the resorption of some transverse trabeculae

69
Q

Result of bone age related changes

A

bones that are slightly weaker but significantly more brittle

70
Q

Types of cartilage

A

hyaline, elastic, fibrocartilage

71
Q

Hyaline cartilage

A

covers articular surfaces of bones in synovial joints and forms tip of nose

72
Q

elastic cartilage

A

external ear, epiglottis

73
Q

fibrocartilage

A

symphysis pubis and the intervertebral discs

74
Q

articular cartilage

A

form of hyaline cartilage that is found on the articulating ends of bones in synovial joints

75
Q

How is articular cartilage adapted

A

adapted to withstand very large loads, it cushions bone while at the same time providing a smooth lubricated bearing surface with minimal wear

76
Q

Articular cartilage appearance

A

glassy smooth glistening blueish white.

77
Q

Articular cartilage properties

A

shock absorbing, allows it to distribute loads evenly over a large surface area, thus reducing contact stress

78
Q

Composition of articular cartilage

A

Organic matrix of non cellular material, interspersed with cells and fluid.

79
Q

Articular cartilage organic matrix of non cellular material composition

A

mainly made up of collagen- structured into strong, fine collagen fibrils. Collagen fibrils are enmeshed in a concentrated solution of proteoglycans.

80
Q

What do proteoglycans do

A

these large protein based molecules are important contributors to the mechanical properties of articular cartilage and make uo 3-10% of the wet weight of articular cartilage.

81
Q

where are proteoglycans most concentrated

A

the middle portion of articular cartilage

82
Q

Chondrocytes

A

sparsely distributed in articular cartilage - less than 10% of the tissues volume. Densely packed in the deeper layers adjacent to the bone

83
Q

what do chondrocytes do?

A

manufacture, secrete and maintain the organic matrix

84
Q

What is interstitial fluid of articular cartilage made up of

A

mostly water

85
Q

3 zones of articular cartilage

A

superficial tangential, middle and deep

86
Q

Arrangement of collagen fibres in superficial tangential zone

A

tightly woven into sheets arranged parallel to the articular surface and the chondrocytes are oblong with their longitudinal axes aligned parallel to the articular surface

87
Q

arrangement of collagen fibres in middle zone

A

more randomly but still parallel to the articular surface. less densely packed to accommodate the hugh conc of proteoglycans and the chondrocytes are circular and randomly distributed

88
Q

collagen and chondrocyte arrangement in deep zone

A

collagen arranged in larger fibre bundles that are anchored in the underlying bone tissue, thereby attaching articular cartilage to the bone. Chondrocytes arranged in loose columns aligned perpendicular to the line dividing articular cartilage and underlying bone

89
Q

Whats below the deep zone of articular cartilage

A

thin layer of calcified cartilage which gradually merges into the subchondral bone

90
Q

what is the interface between the articular cartilage and calcified cartilage beneath called

A

tidemark

91
Q

what is the role of the chondrocytes in articular cartilage

A

they manufacture, secrete and maintain the organic matrix

92
Q

Mechanical behaviour of articular cartilage

A

viscoelastic

93
Q

what is viscoelastic behaviour dependent on

A

time- response of the material varies according to the length of time that a load is applied and the rate at which a load is applied

94
Q

what happens to viscoelastic material once load is removed

A

it returns to its original size and shape- however the response is not immediate

95
Q

creep

A

occurs when viscoelastic material is subjected to a constant load. when the load is first applied the material will deform rapidly, followed by a slow (creeping) increasing deformation

96
Q

explanation of creep behaviour of articular cartilage

A

initial rapid deformation- fluid rapidly forced out. as the amount of fluid decreases, the rate of expellation decreases until it reaches equilibrium

97
Q

stress relaxation

A

stress is reduced over time as the material is maintained at a constant strain

98
Q

3 main types of lubrication

A

elastohydrodynamic lubrication
boosted lubrication
boundary lubrication

99
Q

elastohydrodynamic lubrication

A

2 surfaces, one of which is deformable, lubricated by a film of fluid as they move relative to each other

100
Q

do surfaces touch in elastohydrodynamic lubrication

A

no, film completely separates them

101
Q

2 ways in which 2 surfaces can move relative to each other

A

slide over each other (hydrodynamic), move closer together (squeeze film)

102
Q

hydrodynamic lubrication

A

two surfaces slide over each other forming a wedge of fluid. Pressure is generated as the surfaces slide- motion drags viscous lubricant into the narrowing gap between the surfaces.

103
Q

squeeze film lubrication

A

2 surfaces are forced together. viscous lubricant will not instantaneously be squeezed out from the gap between the two surfaces

104
Q

what happens if high loads are maintained in squeeze film lubrication

A

lubricant will eventually be depleted and the two surfaces will be in contact

105
Q

what happens if one/both of the surfaces in squeeze film is relatively soft

A

deformation- will increase the area over which the load is distributed. this occurs in synovial joints

106
Q

boosted lubrication

A

articular cartilage only permeable to molecules below a certain size. As the size of the gap between articular surfaces decreases, resistance to sideways flow of the lubricant eventually becomes greater than the resistance of flow go the small molecules into the articular cartilage. These small molecules include water that makes up the solvent component of synovial fluid. Water moves into articular cartilage leaving a thick viscose gel behind- enriched lubricant

107
Q

When does boundary lubrication occur

A

if film of fluid between two surfaces isn’t thick enough to keep surfaces apart

108
Q

what is boundary lubrication

A

lubricant molecules attach themselves chemically to the surfaces, creating a boundary layer

109
Q

Boundary lubricant molecules in synovial joints

A

lubricin

110
Q

What do tendons connect

A

muscle to bone

111
Q

what do ligaments connect

A

bone to bone

112
Q

composition of tendons and ligaments

A

dense fibrous connective tissue, fibroblasts embedded in mainly collagen fibre matrix

113
Q

how are collagen fibres arranged in tendons

A

in parallel - as they need to withstand large loads in one direction only

114
Q

collagen fibres in ligaments

A

not arranged completely in parallel, need to withstand large load in one direction and smaller loads in other directions

115
Q

where are collagen fibres branched and interwoven

A

cruciate ligaments of knee

116
Q

mechanical properties of tendons and ligaments

A

viscoelastic, are able to withstand large tensile forces and are very flexible

117
Q

Approx how far can the ACL be elongated before rupturing completely

A

7 mm

BMSc (9 decks)

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