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BMSc > Biomechanics Unit 2 Part 2 > Flashcards

Biomechanics Unit 2 Part 2 Flashcards

1
Q

Describe torsional loading and example

A

When objected is twisted about its longitudinal axis eg one end of bone is fied and other end twisted

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2
Q

Describe a torsional fracute

A

spiral

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3
Q

where is stress and strain greatest in a object undergoing torsion

A

the outside as it takes the most load

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4
Q

How do long bones resist torsional load

A

They are hollow with strong cortical bone forming the outer layer - maximise their strength to weight ratio

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5
Q

Why does the distal end of tibia fracture easier than proximal

A

same amount of bone tissue but cross section of distal is smaller therefore less able to resist torsional load

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6
Q

Why do bones undergo combined loading?

A

thier irrgular geometry and combined actions of gravity, muscles and ligaments

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7
Q

How do muscles prevent fractures?

A

Put compressive load on the bone as oen is stronger in this state than in otrsion or tension

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8
Q

What is Wolffs Law

A

bone is lard down where needed and resorbed where not needed

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9
Q

What happens when there is a lack of exercise

A

bone atrophy - resorption of bone

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10
Q

Why is bone remodeling an issue with fixation plates?

A

they cause stress sheilding if not removed soon after the bone is healed -> they take all the stress so bones start to resorb
However where screws are place the opposite will happen as those areas will be carrying a heavier laod - bone hypertrophy

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11
Q

What causes a fatigue fracture?

A

When a load smaller than the ultimate strength of the bone is applied repeatedly.

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12
Q

Other names for fatigue fractures

A

stress or march fractures

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13
Q

How might continuous strenuous physical activity cause a fatigue fracture?

A

The breaks inbetween the repetitive laods is too small to allow the bone to remodel - bone is weakened. The muscles are also weakened therefore they cannot reduce the tensile stress on the bone.

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14
Q

Describe bone in children

A

Children: more formation than resporption, more collagen therefore more flexible (less brittle)

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15
Q

What is a greenstick fracture?

A

more common in children due to their flexible bones –> incomplete fracture caused by torsion or excessive bending where one side is bent and hthe other side is buckled

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16
Q

Describe bone between 35 and 40 years

A

resorption > formation
- some thining in compact bone
- big reduction in cancellous –> thinning of longitudinal trabeculae and resorption of transver trabeculae
therefore bones are wekaer and more brittle

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17
Q

Name the three types of cartilage

A

Hyaline, elastic, fibrocartilage

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18
Q

Which covers the articular surfaces of bones in synovial joints and tip of nose?

A

Hyaline cartialge

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19
Q

Which forms the exernal ear and epiglottis?

A

Elastic

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20
Q

Which froms the symphsis pubis and IV discs?

A

fibrocartilage

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21
Q

Describe a synovial joint give examples

A

very mobile joints (hip and knee) held together by muscles and ligaments - enclosed in a capsule lined with synovial membrane containing synovial fluid

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22
Q

Two roles of articular cartilage

A

cuchions bones

provides smooth lubricated surface with minimal wear

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23
Q

describe articular cartilages appearance and why

A

glassy smooth, glistening and blueish white - firm but pliable consistency - allows for shock absorbing and even load distribution (reduce stress)

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24
Q

Articular cartilage is made up of…

A

an organic matrix of non-cellular material interperesed with cells and fluid

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25
Q

What is the organic matrix made up of

A

collagen fibrils (strong and fine)

26
Q

Wjat are collagen fibrils enmeshed in

A

proteoglycans - most concentrated in middle articular cartialge and not near the bone

27
Q

What are chondrocytes and where are they found

A

cells in articular cartilage - densely packed in deeper layers ajacent to bone

28
Q

What is the role of chondrocytes

A

make, secrete and maintain the organic matrix

29
Q

Name the layers of articualr cartilage

A

superficial tangential, middle, deep

30
Q

Describe the superficial tangential zone

A

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

31
Q

Describe the middle zone

A

collagen fibrils are randomly arrange but still broadly parallel to AS, less densely packed to accommodate the high conc of proteoglycans
chrondocytes are circular and random

32
Q

Describe the deep zone

A

collagen fibrils are in larger fibre bundles - anchored to the underlying bone tissue, attaching the articular cartilage to the bone
chondrocytes are in loose columns perpendicular to the line dividing articular cartilage and underlying bone

33
Q

What is the tidemark

A

interface between articular cartilage and calcified cartilage

34
Q

The mechanical behaviour of articular cartilage?

A

viscoelastic - will return to original shape but takes time

35
Q

Viscoelastic behavious is ? dependent

A

time (depends on length of time and rate)

36
Q

What is creep

A

Creep is when the object is subjected to a constant load - it will deform rapidly then increasingly deform slowly

37
Q

Describe a creep graph

A 
1             \_\_\_\_\_\_\_\_ deform
1          /
1        i
1       i
1\_\_\_i\_\_\_\_\_\_\_\_\_\_\_ time 
the load would be constant
38
Q

Explain the creep characterisitc of artiuclar cartilage

A

initial: fluid rapidly is expelled out causing rapid deformation but as fluid decreases so does deformation - until no fluid left and held just by solid matrix (equilibrium0

39
Q

WHich characteristic occurs when object is kept at constant deformation

A

stress relaxation

40
Q

Describe stress relaxation

A

When an objecct is subjected to a constant deformation (strain) then the load required to maintain it will decrease (aka stress)

41
Q

Explain stress relaxation in articualr cartillage

A

inital deformation: interstitial fluid escapes through the solid matrix causing a frictional drag (this requires a large load to overcome). Once fluid is no longer pushed out it redistributed from most copacted to least compacted areas - less laod is required therefore less stress

42
Q

Name the three lubrication found in synovial joints

A

elastohydrodynamic ,boosted and boundary

43
Q

Synovial joints have a high coefficinet of Fr than articifical joints

A

FALSE other way round - meaning artifcal joitns wear out quickly

44
Q

Two factors that bring about lubrication are…

A

magnitude of load on joint pressing the surfaces together and the length of time the load is maintained

45
Q

What is elastohydrodynamic lubrication

A

When two surfaces- one of which is derfomable - are lubricated by fluid as they move about eahc other

46
Q

? lubrication is when the surfaces slide over each other

A

hydrodynamic

47
Q

? lubrication is when they move closer to one another

A

squeeze film

48
Q

Describe hydrodynamic lubriaction

A

the sliding surfaces cause a lifting pressure as motion drags the viscous fluid into the narrowing gap of the surfaces

49
Q

Describe squeeze film lubrication and why is it useful

A

When two surfaces are pressed together the fluid wont instantaneously be depelted therefore cushioning the two surfaces

50
Q

If high loads are added then…

A

the fluid will be depeleted the two surfaces will come into contact

51
Q

Elastohydrodynamic lubrication is when a surface is deformable - why is this important

A

the pressure distribution is increases so the laod pressure is decreases and the film of fluid remians thick

52
Q

When does boosted lubrication come in to play?

A

When a laod is placed over a long period of time to prevent complete depeltion of the fluid

53
Q

Describe boosted lubrication

A

Surface of AC is permeable to small molecules only. As size of gap decreases the resistance to sideways movement of fluid becomes greater than the resistance of movement of small molecules through the articular surface they escape but larger molecules remain behind leaving a thick viscose gel layer - this is capable of supporting large loads

54
Q

Draw the diagrams of boosted lubricant and the elastohydrodynamic lubricant

A

look at notes soz

55
Q

Describe boundary lubrication

A

This occurs when a large load acts over a long enough period of time to deplete the fluid film completely between articular surfaces. Lubricant molescules (lubricin) attach themselve chemically to the AS creating a boundary layer. It has low shear strength therefore less friction that bare surfaces.

56
Q

Ligaments connect muscle to bone

A

FALSE tendons do.

Ligaments connect bone to bone

57
Q

What cell do ligametns and tendons contain and how are they arranged

A

fibroblasts - long length of collagen fibre

58
Q

How are collagen dibres arranged in tendons and why

A

parallel bundles - they need to be able to support large loads in one direction

59
Q

How are ligament collagen fibres arranged

A

Mainly parallel but are often branced and interwoven as they need to support larage loads in mostly one direction but also need to withstand smaller loads in other directions.

60
Q

What mechanical behaviour do ligaments nad tendons exert

A

viscoelastic

61
Q

What two factors are important for ligaments and tendons

A

must be able to withstand large tensile loads (tendon) or withstand forces wrenching them apart ligament) but also flexible enough to move around bone or allow joints to move normally

62
Q

How far can the ACL elongate before rupture

A

7mm

BMSc (8 decks)

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