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BMSc > Biomechanics Unit 2 Part 2 > Flashcards

Biomechanics Unit 2 Part 2 Flashcards

(62 cards)

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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
What is the organic matrix made up of
collagen fibrils (strong and fine)
26
Wjat are collagen fibrils enmeshed in
proteoglycans - most concentrated in middle articular cartialge and not near the bone
27
What are chondrocytes and where are they found
cells in articular cartilage - densely packed in deeper layers ajacent to bone
28
What is the role of chondrocytes
make, secrete and maintain the organic matrix
29
Name the layers of articualr cartilage
superficial tangential, middle, deep
30
Describe the superficial tangential zone
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
Describe the middle zone
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
Describe the deep zone
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
What is the tidemark
interface between articular cartilage and calcified cartilage
34
The mechanical behaviour of articular cartilage?
viscoelastic - will return to original shape but takes time
35
Viscoelastic behavious is ? dependent
time (depends on length of time and rate)
36
What is creep
Creep is when the object is subjected to a constant load - it will deform rapidly then increasingly deform slowly
37
Describe a creep graph
``` 1 ________ deform 1 / 1 i 1 i 1___i___________ time the load would be constant ```
38
Explain the creep characterisitc of artiuclar cartilage
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
WHich characteristic occurs when object is kept at constant deformation
stress relaxation
40
Describe stress relaxation
When an objecct is subjected to a constant deformation (strain) then the load required to maintain it will decrease (aka stress)
41
Explain stress relaxation in articualr cartillage
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
Name the three lubrication found in synovial joints
elastohydrodynamic ,boosted and boundary
43
Synovial joints have a high coefficinet of Fr than articifical joints
FALSE other way round - meaning artifcal joitns wear out quickly
44
Two factors that bring about lubrication are...
magnitude of load on joint pressing the surfaces together and the length of time the load is maintained
45
What is elastohydrodynamic lubrication
When two surfaces- one of which is derfomable - are lubricated by fluid as they move about eahc other
46
? lubrication is when the surfaces slide over each other
hydrodynamic
47
? lubrication is when they move closer to one another
squeeze film
48
Describe hydrodynamic lubriaction
the sliding surfaces cause a lifting pressure as motion drags the viscous fluid into the narrowing gap of the surfaces
49
Describe squeeze film lubrication and why is it useful
When two surfaces are pressed together the fluid wont instantaneously be depelted therefore cushioning the two surfaces
50
If high loads are added then...
the fluid will be depeleted the two surfaces will come into contact
51
Elastohydrodynamic lubrication is when a surface is deformable - why is this important
the pressure distribution is increases so the laod pressure is decreases and the film of fluid remians thick
52
When does boosted lubrication come in to play?
When a laod is placed over a long period of time to prevent complete depeltion of the fluid
53
Describe boosted lubrication
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
Draw the diagrams of boosted lubricant and the elastohydrodynamic lubricant
look at notes soz
55
Describe boundary lubrication
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
Ligaments connect muscle to bone
FALSE tendons do. | Ligaments connect bone to bone
57
What cell do ligametns and tendons contain and how are they arranged
fibroblasts - long length of collagen fibre
58
How are collagen dibres arranged in tendons and why
parallel bundles - they need to be able to support large loads in one direction
59
How are ligament collagen fibres arranged
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
What mechanical behaviour do ligaments nad tendons exert
viscoelastic
61
What two factors are important for ligaments and tendons
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
How far can the ACL elongate before rupture
7mm

BMSc (8 decks)

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