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BMSc > biomechanics module 2 - sem1 > Flashcards

biomechanics module 2 - sem1 Flashcards

(91 cards)

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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
other names for fatigue fracture
stress / march fractures
26
when do fatigue fractures usually occur
usually sustained during a continuous period of strenuous activity
27
How will the fracture occur in fatigue fractures
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
28
characteristic of a green-stick fracture
incomplete fracture with one side bent and the other side buckled
29
why are children more prone to green-stick fractures
children's bones contain a greater proportion of collagen than adult bones, which gives their bones a greater amount of flexibility
30
Is the process of bone formation and reabsorption balanced in adults
Yes
31
List characteristics of bones in children
formation > resorption increased collagen increased flexibility greenstick fractures common
32
list characteristics of bones in elderly
resorption > formation compact bone thinning, decrease in cancellous bone brittle bones due to decreased flexibility slightly weaker bones
33
list the 3 groups of cartilage
hyaline (articular) elastic fibrocartilage
34
what type of tissue is cartilage
connective
35
what does hyaline cartilage form
the articular surfaces of bones in synovial joints also forms tip of the nose
36
what does elastic cartilage form
external ear and epiglottis
37
what does fibrocartilage form
symphysis pubis intervertebral discs
38
where is articular cartilage found
in synovial joints (mobile joints such as the hip and knee)
39
2 main roles of articular cartilage
shock absorber / cushion the bones, provide a smooth, lubricated, bearing surface
40
Function of chondrocytes
manufacture, secrete and maintain the organic matrix
41
How many layers does articular cartilage have and what are the names
3 main layers - superficial tangential - middle - deep
42
what solution are collagen fibrils found in
solution of proteoglycans large protein based molecules which are important for the mechanical properties of articular cartilage
43
how are collagen fibrils arranged in the superficial tangential zone
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
how are collagen fibrils arranged in the middle zone?
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
how are collagen fibrils arranged in the deep zone?
collagen fibrils are arranged in large fibre bundles that are anchored to the underlying bone tissue , attaching the articular cartilage to the bone
46
how is articular cartilage attached to bone?
attached by the collagen fibrils which extend from the deep zone into underlying bone tissue
47
what behaviour does articular cartilage demonstrate
viscoelastic mechanical behaviour
48
characteristics of viscoelastic behaviour
- time dependent - once a load is removed, it will return to its original size and shape - response is not immediate - stress relaxation - creep
49
why is the viscoelastic behaviour important for articular cartilage
gives articular cartilage the ability to cushion the high loads that occur between the bones in joints, reducing potential damage
50
what is creep
Creep is an increase in strain under a constant stress
51
what is stress relaxation
stress relaxation is is a reduction in stress under a constant strain
52
is the coefficient of friction low or high in synovial joints
very low made by the combined action of the articular cartilage and the synovial fluid
53
what determines the way in which lubrication is brought about
magnitude of the load length of time that the load is maintained
54
list the 3 types of lubrication
- elastohydrodynamic lubrication - boosted lubrication - boundary lubrication
55
when does hydrodynamic lubrication occur
occurs when the two surfaces are moving over one another
56
when does squeeze firm lubrication occur
occurs as the two surfaces are forced together
57
two types of elastrohydrodynamic lubrication
hydrodynamic squeeze firm lubrication
58
when does elastohydrodynamic lubrication occur
occurs when two surfaces, one of which is deformable, are lubricated by a film of fluid as they move relative to one another.
59
what occurs in boosted lubrication
small molecules including water are forced into the articular cartilage relies on permeability of articular cartilage
60
what occurs in boundary lubrication
fluid film is completely depleted lubricant molecules attach themselves chemically to the surfaces
61
example of boundary lubrication in synovial joints
the protein lubricin coats the surface of the articular cartilage
62
what are tendon and ligament cells called
fibroblasts
63
how are collagen fibres arranged in tendons and ligaments
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
what is the basic mechanical behaviour of tendons and ligaments
viscoelastic
65
what are bone cells called
ostocytes
66
what gives bones their characteristic hardness and rigidity
The inorganic component, which consists mainly of crystals of calcium phosphate, gives bone its characteristic hardness and rigidity.
67
what are the 4 types of connective tissue
bone articular tendon ligament
68
what are the 2 different types of bone tissue
compact and cancellous
69
describe compact bone
forms outer layer of bone and has a dense structure cortical bone
70
describe cancellous bone
forms inner part of short, flat and irregular bones mesh structure --> spongey bone spaces between mesh contain red bone marrow
71
basic structural unit in compact bone
Haversian system
72
how is bone tissue arranged
arranged in layers called lamellae forming concentric cylinders around a central canal
73
what is in the central canal / haversian canal
blood vessels and nerve fibres
74
basic structural unit in cancellous bone
trabecula
75
difference between trabecular and the haversian system
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
what happens to a material under tensile load
it will elongate
77
what is strain
Strain is defined as the change in length divided by the original length
78
what is stress
Stress is defined as the force per cross-sectional area stress = F/A
79
SI units of stress
N m-2
80
SI unit of strain
strain has no units
81
what regions make up the stress-strain curve
elastic plastic
82
what is the point inbetween the elastic and plastic region
yield point A where the yield stess and yield strain exist
83
describe the curve in the elastic region
linear - stress is directly proportional to strain
84
what is elastic behaviour
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
describe the curve in the plastic region
not linear - a small increase in stress will cause a large increase in strain, deforming the bone
86
what happens when a bone is deformed beyond it's yield point
it will not return to it's original shape and size, even when load is removed
87
what is plastic behaviour
a bone will be permanently deformed once it passes it's yield point
88
what happens to the bone at ultimate strain / stress
fracture
89
what is young's modulus
ratio of stress to strain describes how stiff / flexible a material is youngs modulus = stress / strain
90
what does a small young's modulus mean
a material requires a small amount of stress to produce a large amount of strain i.e it is flexible
91
what does a large young's modulus mean
a material requires a large amount of stress to produce a small strain, the material is stiff

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