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Biomechanics III > Biomech > Flashcards

Biomech Flashcards

1
Q

What is injury a result of?

A

Tissue macro or micro failure under load

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2
Q

What determines whether or not ther will be tissue damage?

A

Nature of the load and properties of tissue.

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3
Q

How are we injured? (5)

A

1) High load (single traumatic event)
2) Repetitive loads (end range)
3) Sustained loads (end range) ie: postural syndromes
4) Sudden unguarded movement
5) Normal activity coupled with a failure of segmental coordination (especially in an unstable joint)

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4
Q

Joints are protected by what at mid range and end range?

A

Mid range- Muscles. End range- Ligaments.

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5
Q

What is Load?

A

The amount of force on an object.

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6
Q

What are the 3 types of Load?

A
  1. Tensile.
  2. Compressive.
  3. Shear.
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7
Q

What is tensile or tension?

A

It is like pulling the head up.

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8
Q

What is stress?

A

A load divided by the cross sectional areas. Like stepping on someone’s foot in flat shoes vs high heels.

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9
Q

What are the 3 types of stress?

A

1) Tensile stress
2) Compressive Stress
3) Shear Stress

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10
Q

What type of stress is tissue most susceptible to?

A

Shear Stress

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11
Q

What is deformation?

A

A change in length in response to a load.

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12
Q

What happens with tensile deformation?

A

Stretch an object to be longer.

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13
Q

What happens with compressive deformation?

A

Compress an object to be smaller.

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14
Q

The amount of deformation is known as what?

A

Strain.

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15
Q

What is strain?

A

A change in length divided by the original length. Or the % of change.

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16
Q

What is shear strain?

A

The angle of deformation in radians.

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17
Q

What is tensile strain?

A

The % of length change.

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18
Q

What is a muscle strain?

A

Muscle tear.

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19
Q

Is a biomechanical strain the same as a muscle strain?

A

No, a muscle strain is a muscle tear whereas a biomechanical strain is the change in legth divided by the original length

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20
Q

What happens when there is a loss of energy in tissue?

A

A tissue gets weaker and the damage caused can be permanent or transient

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21
Q

What is involved in a sprain?

A

Ligaments and disks.

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22
Q

What is elasticity?

A

The ability of a substance to return to its original form following the removal of a deforming load.

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23
Q

What happens to energy with elastic material?

A

No loss of energy in one cycle of load and unload.

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24
Q

What is plasticity?

A

The property of a material to permanently deform if loaded beyond its elastic range.

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25
Q

What is an example of plasticity?

A

Tearing a ligament that causes instability due to permanent deformation

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26
Q

What happens to energy with plasticity?

A

Loses original form and material loses energy after one cycle of loading or unloading.

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27
Q

What is stiffness?

A

A measure of resistance offered to external loads by a material as it deforms.

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28
Q

Does a stiffer material need more or less stress to deform?

A

More stress.

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29
Q

How is stiffness calculated?

A

the amount of stress/the amount of strain.

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30
Q

What parts in biomechanics need to be stiff?

A

Bones and spine for stability

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31
Q

What is flexibility?

A

Measure of compliance offered to external loads by a material as it deforms.

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32
Q

Does a flexible material needs more or less stress to deform?

A

Less stress.

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33
Q

How is flexibility calculated?

A

the amount of strain (deformation)/the amount of stress (load).

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34
Q

What is brittleness?

A

The quality whereby a material exhibits little plastic deformation before failure.

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35
Q

What is failure in regards to brittleness?

A

< 5% of total elongation of material.

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36
Q

What is ductility?

A

The quality whereby a material exhibits large plastic deformaitn before failure.

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37
Q

What is failure in regards to ductility?

A

> 5% of total elongation of material.

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38
Q

What is viscoelasticity of tissue?

A

The property of a material that links how it will deform to how the load is applied.

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39
Q

What 4 things will change how a viscoelastic material will deform?

A

rate, speed, quantity and duration of loading.

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40
Q

What is a deformation of a viscoelastic material with time, when the load remains constant?

A

Creep.

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41
Q

What type of viscoelasticity is when overtime tissue relaxes into new lengths. This results in a decreased load overtime to maintain fixed derfomation?

A

Relaxation.

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42
Q

What type of viscoelasticity is when loss of energy during a loading cycle despite returining to its original form than its weaker ?

A

Hysteresis.

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43
Q

What type of viscoelasticity occurs when the process of plastic deformation or failure of material happens from repeated loading?

A

Fatigue.

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44
Q

What is the resistance to speed where the faster the load, the greater the load is created to deform an object of a given amount?

A

Damping.

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45
Q

What is the reduction in the viscosity of a fluid following movements?

A

Thixotropy.

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46
Q

What is the composition of ligaments? (4)

A

1) Collagen and elastin
2) reticular fibers
3) ground substance
4) Cells (fibroblasts)

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47
Q

What makes up 80-90 % of connective tissue?

A

COLLAGEN and elastin.

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48
Q

What type of links break first in connective tissue?

A

Cross links.

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49
Q

With what type of trauma (micro or macro) do tissues tend to fail more?

A

Microtrauma

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50
Q

What does a micro trauma entail?

A

Repeated incidence, doesn’t allow body time to heal

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51
Q

What is the first indicator of microtrauma?

A

Pain

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52
Q

What is the half life of collagen?

A

Could be as old as the individual, but time can be accelerated in young animals, injured tissues, and immobilized tissues.

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53
Q

A tendon or ligament behaves according to what 3 things?

A
  1. properties ( collagen and elastin).
  2. Proportion of collagen to elastin.
  3. Fiber orientation.
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54
Q

What does the Strength of tendons or ligaments depends on?

A

Fiber composition, size, and shape.

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55
Q

What are some ways to increase strength in tendons and ligaments? (3)

A

1) Increase number of fibers
2) Increase fiber diameter
3) Increased number of fibers parallel to direction of tension

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56
Q

Tendons and ligaments normaly have how much stress on them?

A

1/3 of their capacitiy.

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57
Q

What type of loads can cause injury to tendons and ligaments? (3)

A

High loads (trauma), repetitive loads, or sustained loads.

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58
Q

What direction do the fibers run in Tendons and what type of load do they resist?

A

Parallel and tensile loads.

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59
Q

What direction do the fibers of Ligaments run in?

A

Parallel and some non parallel

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60
Q

Where is the distrubtion of force in a tendon?

A

Directly through the tendon

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61
Q

Where is the distrubtion of force in a ligament?

A

Ligaments can move in more than one direction so the force distribution runs muliple directions

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62
Q

What is stronger skin, tendons, or ligaments?

A

Tendons are stronger than skin and ligaments.

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63
Q

Collagen will have a slight elongation without much muscle tension then it is followed by what?

A

A region of stiffness.

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64
Q

What is the strength of collagen like with tension?

A

One half cortical bone strength.

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65
Q

How much strain can collagen fibers withstand?

A

6-8%. This makes it ductile. (>5%)

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66
Q

How flexible are elastic fibers?

A

200 % elongation in elastic range.

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67
Q

What happens after elastic fibers are elongated as long as they can?

A

They become suddenly stiff and then brittle and then no further deformation before failure.

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68
Q

What is enthesis?

A

Bone-ligament or bone tendon complex.

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69
Q

A progressive change from ligament to bone protects against injury how?

A

By allowing better stress absorption and transmission.

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70
Q

What are sharpeys fibers?

A

Fibers that sink into bone that connect the ligament to bone

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71
Q

What are the structural jobs of ligaments? (3)

A

stabalize joints, guide joint motion, prevent excessive motion.

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72
Q

What are the functional jobs of ligaments? (2)

A

Detect rate and vectors of load, detect tissue damage.

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73
Q

What is the Toe region of a stress strain curve for ligaments?

A

Straightening out the wavey ligament fibers.

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74
Q

What happens with strain when stress is increased on ligaments in the toe region?

A

The strain remains at zero until the end of the toe region when it starts to go up.

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75
Q

What range comes after the toe region in a stress strain curve for a ligament?

A

Elastic range.

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76
Q

What is the elastic range like in a stress strain curve for a ligament?

A

The strain goes up proportionatly to the stress that is placed on the ligaments while in the elastic region.

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77
Q

What happens to tissues that were under elastic strain?

A

They distort and then go back to orignal form.

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78
Q

What region comes after the elastic range in a stress strain curve for a ligament?

A

Plastic range.

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79
Q

What is the plastic range like for an stress strain curve of a ligament?

A

This is wherethe ligament is permanently deformed if loaded beyond the elastic range. Tearing of the ligament and loss of energy.

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80
Q

What type of fibers is the ligamentum flavum made of?

A

2/3 elastic fibers.

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81
Q

What is the function of the ligamentum flavum?

A

Absorb shock of flexion and protect nerve roots and spinal cord.

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82
Q

How far can the ligamentum flavum elongate before stiffness increases?

A

50%.

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83
Q

At what percetage of elongation does the ligamentum flavum fail?

A

70%.

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84
Q

What is the plastic phase like for the ligamentum flavum?

A

There’s no real plastic phase so the ligamentum flavum fails abruptly after stiffness.

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85
Q

What is the failure point?

A

The point of maximum strength of the material.

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86
Q

What happens to energy with a failure point?

A

Large or complete energy loss.

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87
Q

What is the anterior drawer test?

A

Pull tibia anterior while patient is supine and knee is bent and this should feel nice and snugg not lose.

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88
Q

Clinical tests of ligaments should be in what region?

A

Toe region and the first part of the elastic range.

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89
Q

The more fibers that are _______ to the load the stronger the structure?

A

Parallel.

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90
Q

What region will the beginning of a grade 1 ligament sprain happen in?

A

At the end of the elastic range.

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91
Q

What are some additional deformations that occur with ligament sprains?

A

1) Failure of internal structure
2) decrease in strength
3) a sudden relaxation

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92
Q

What is a failure point?

A

Point of maximum strenght of the material

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93
Q

Which fibers sustain greater force in a ligament?

A

Fibers that are parallel to the load straighten out first and sustain greater force

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94
Q

What makes a ligament a stronger structure, more parallel or more perpendicular fibers to a load?

A

More parallel fibers

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95
Q

In the clinical test region of a joint (first region), what occurs in the ligaments?

A

A small load is enough to cause elongation while the ligament’s wavy fibers straigten out

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96
Q

In the clinical test region of a joint (first region), what joint motion is occurring?

A

Joint motion what occurs without locking bones together

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97
Q

In the Physiological loading region of a joint (second region), what is it characterized by?

A

Stiffness, mostly a linear elastic region

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98
Q

In the Physiological loading region of a joint (second region), what is the function?

A

Stability and limitation of motion

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99
Q

In regards to a joint, when does the beginning of injury occur?

A

The physiological loading stage

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100
Q

When injury begins in the physiological loading (second region), what is happening microscopically?

A

Microfailure of collagen fibers

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101
Q

What type of sprain begins in the physiological loading stage (second region) of a joint?

A

Beginning of grade 1 sprains

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102
Q

How many “regions” is the injury portion of joint motion split into?

A

3 regions (on the graph it is known as third, fourth and fifth region)

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103
Q

What is the “third region” or beginning of injury in a joint also known as?

A

Plastic region

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104
Q

What occurs in this “third region” or beginning of injury in a joint?

A

Progressive failure of collagen fiber bundles with no change in gross appearance

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105
Q

What type of sprain occurs in this “third region” or beginning of injury in a joint?

A

A grade 1 sprain where microfailure, slight pain, minimal signs and no instability occurs

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106
Q

What is occuring in the ligament during the “third region” or beginning of injury in a joint?

A

The ligament is stretched and the joint moves more than it should

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107
Q

What occurs “fourth region” in joint motion? (3)

A

1) Gross failure with ultimate loading (ultimate strain is 6-8 %)
2) tensile failure of collagen fibers
3) shear failure between fibers

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108
Q

What extent of injury occurs in the “fourth region” of injury in a joint?

A

A Grade 2 Sprain: Partial rupture, joint instability, 50% decrease of stregth and severe pain and swelling

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109
Q

What grade of sprain does instability occur?

A

Grade 2 sprain

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110
Q

What occurs “fifth region” in joint motion?

A

Complete failure of the ligaments

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111
Q

What injury occurs “fifth region” in joint motion?

A

Grade 3 sprain : Complete rupture, complete instability and dislocation with severe pain at injury followed by decreased pain/no pain afterwards

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112
Q

Where will a grade 1,2,3 sprain happen at?

A

1- in the end of the elastic range, and start of the plastic range.
2-the end of the plastic range.
3- after the plastic range with failure.

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113
Q

What is pain like with a grade 3 sprain or failure of a ligament?

A

severe pain at injury followed by decreased pain at injury followed by decreased pain and sometimes no pain.

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114
Q

What is a residual effect of a significant sprain?

A

Hypermobility and instability (empty feel on endplay, palpatory pain, repeated dislocation, excessive motion)

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115
Q

Hypermobility and instability following a significant sprian can lead to what?

A

Degeneration of joints, and susceptibility to further the injury.

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116
Q

How will loading speed affect the degree injury and what are the 2 factors it is dependent on?

A

With viscoelastic material, the degree of injury depends on the magnitude of the load and the rate that the load is applied.

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117
Q

How much will the strength of tissue increase with a 4 times speed increase of a load?

A

50% in strength, 30% in energy storage capacity and 30% increase in strain to failure.

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118
Q

With high speed loads what tears first?

A

Ligaments (2/3 times and bone 1/3 times)

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119
Q

With low speed loads what tears first?

A

Bone avulsion-pull a chunck of bone off with the ligament.

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120
Q

What gets stronger with increased speed of a load bones or ligaments?

A

both.

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121
Q

Since both bones and ligaments get stronger with increased speed of a load which one gets stronger?

A

Bone strength is increased more than ligaments with speed so the ligament will fail first with a fast load.

122
Q

Why will slower loading make bone fail first?

A

Slow loading makes bone more brittle.

123
Q

After slouching what load is created?

A

Flexion at the Lumbosacral junction.

124
Q

What happens in about 20-30 minutes when ligaments and the posterior disc is placed under sustained flexion (like with bad posture from sitting)?

A

Creep and Hysteresis.

125
Q

What is creep ?

A

Creep- a deformation of viscoelastic material with time when load remains CONSTANT.

126
Q

What is hysteriesis?

A

Distortion over time but without loss of energy, tissue is temporarily weaker

127
Q

What type of tissues can creep occur in?

A

Almost any type.

128
Q

What is relaxation?

A

Over time the tissue relaxes into its new length. So this results in a decrease of load over time to maintain a fixed deformation.

129
Q

Creep/relaxation take how long to occur?

A

Some take place within a few minutes, but most take place in the first 6-8 hours.

130
Q

Creep/relaxation continues for how long?

A

At a slow rate for months.

131
Q

What happens to a structure after hysteresis?

A

when unloaded a structure regains shape at a different rate compared to when it was deformed.

132
Q

With hysteresis what makes the spine more susceptible to injury?

A

Ligaments are a little longer and they have lost some energy and they no longer act as shock absorbers.

133
Q

Hysteresis on the spine lasts for how long?

A

1-2 hours.

134
Q

What is “set” from a stress strain graph for hysteresis?

A

The amount of tissue length change after the load is removed. Hysteresis will lengthen the tissues and the set should be a positive number.

135
Q

After hysteresis and even after the material returns to its original length what happens to the energy?

A

There is still a loss of energy.

136
Q

What type of loads even within the physiological range can eventually cause microfailure due to hysteresis?

A

Repetitive or sustained.

137
Q

What is fatigue?

A

The process of plastic deformation or failure of a material from repeated loading.

138
Q

Less external load is necessary to cause tissue failure with what type of stress?

A

Prolonged cycles of repetitive stress.

139
Q

What will repeated loading even in the elastic range cause?

A

Fatigue cracks, general weakening of material and ultimate load capacity decreases.

140
Q

Low back can have a micro failure with what % of strain (elongation)?

A

4%.

141
Q

4% strain on the low back can cause a micro failure so the low back is what?

A

Brittle.

142
Q

What is more commonly seen in practice repetitive microtraumas or a single traumatic event?

A

Repetitive microtraumas.

143
Q

How often should breaks be taken in order to reduce the exposure to repetitive or sustained overloading?

A

20 minutes.

144
Q

What will help a recovering ligament/tendon become stronger and stiffer?

A

Increased stress.

145
Q

What happens to ligaments and tendons with less stress?

A

They become less stiff and weaker.

146
Q

What can cross friction massage theoreticaly do?

A

Promotes paralleled collagen deposition and coss links.

147
Q

How many weeks will a broken bone be in a cast?

A

6-8 weeks.

148
Q

What happened to the monkeys who had their knees immobilized for 8 weeks?

A

40% decrease of maximum load to failur of their ACL, and a 30% decrease of energy storage capacity, and a loss of stiffness.

149
Q

What happened to the monkeys after 5 months of rehab?

A

They load to failure was 80% of normal and energy storage was 80% of normal.

150
Q

What happened to the monkeys after 12 months of rehab?

A

The load to failure was 90% of normal. And energy storage capacity was 90% of normal.

151
Q

What duration of strenuous exercise might be required to rehabilitate ligaments?

A

A year

152
Q

What does aging do to ligaments and tendons?

A

Causes loss of strength, stiffness and energy storage capacity

153
Q

What is a sprain?

A

A tear of a ligament.

154
Q

What is the function of a tendon?

A

Attach muscle to bone and transmit tensile loads from muscle to bone for the purpose of joint motion and stabilization.

155
Q

What are tendon fibers made of?

A

Nearly 100% collagen.

156
Q

How are the collagen fibers traveling in tendons?

A

Parallel arrangement.

157
Q

What is a paratendon?

A

Loose arelar connective tissue that surrounds the tendon

158
Q

What is the function of the paratendon?

A

Aids in gliding

159
Q

Where does the paratendon run on the tendon?

A

May run the entire length of the tendon or just where it rubs against the bone

160
Q

What is an epitendon?

A

Points of high friction on the paratendon

161
Q

Where are epitendons found and what is the function?

A

Surrounds the paratendon and produces synovial fluid

162
Q

What are the 2 major factors that will determine the amount of stress a tendon can handle?

A

1) Relative size of muscle and tendon.

2) Whether the muscle is contracting.

163
Q

Normal activity produces how much load on a tendon?

A

Only 1/4 of its capacity.

164
Q

Can a muscle contraction alone rupture a tendon?

A

No.

165
Q

How is a tendon usually injured?

A

The muscle is contracted and tensile force rapidly extends the muscle before it can relax.

166
Q

What is stronger muscles or tendons?

A

Tendos may be 2 times stronger therefore muscle strains are more common than tendon tears

167
Q

What is a torn muscle called?

A

strain.

168
Q

What is more common muscle strains or torn tendons?

A

Muscle tear.

169
Q

Is stress good for a torn tendon to remodel?

A

Yes.

170
Q

What is the healing time like for tendons and ligaments?

A

Slow.

171
Q

Why is the healing time slow for tendons and ligaments?

A

Poor blood supply.

172
Q

What muscle in our shoulder has poor vascularization?

A

Supraspinatus.

173
Q

What are some resulting dysfunction of muscle strains? (6)

A

1) Weakness
2) Palpatory pain
3) hypermobility and instability
4) aberrant motion
5) subluxation (medical)
6) increased susceptibility to joint injury

174
Q

What will aging do to tendons?

A

Collagen fibers get smaller.

175
Q

What will mobilization exercises do to tendons?

A

They increase the tensile strength of tendons and the tendon-bone interface.

176
Q

What do corticosteroids do to tendons?

A

They inhibit collagen synthesis, and can prevent early strenous rehab.

177
Q

What percentage of microfailure in ligaments occur with repetitive micro-trauma.

A

4%.

178
Q

With what condition does, tissue returns to pre-strain status yet it is still weaker because of loss of energy.

A

Hysteresis.

179
Q

What is the strongest and stiffest Connective tissue?

A

Bones.

180
Q

Does a stiffer material need more or less stress to deform?

A

More Stress.

181
Q

What is stiffness?

A

the amount of stress/the amount of strain.

182
Q

After a bone fracture heals what % of the height may return?

A

95% so 5% is lost to plastic deformation.

183
Q

What happens to bone with compression?

A

It shortens and widens.

184
Q

What is a bone deformation without a fracture?

A

Osteromalacia.

185
Q

What is a schmorl’s node?

A

Protrusions of the cartilage of the intervertebral disc through the vertebral body enplate and into the adjacent vertebra

186
Q

What are the two different types of fractures due to compression forces?

A

Compression fracture and end plate fracture

187
Q

Are compression bone fractures typically stable or unstable?

A

They are stable.

188
Q

What are 3 times to suspect a traumatic compression fracture?

A
  1. Fall on buttock.
  2. Land on heels.
  3. Lift a heavy load.
189
Q

What is spinal percussion how is it done and why?

A

Tap on SP’s with a reflex hammer as a screen for a fracture. If a fractures has occurred then a sharp pain occurs

190
Q

What is an avulsion?

A

Pulling a piece of bone off.

191
Q

What happens with game keepers thumb?

A

The thumb is forced into abduction and extension and sprains ulnar ligament and may cuase a small avulsion from proximal phalange

192
Q

What is the failure mechanism in tension forces on bone?

A

Debonding and separation of osteons

193
Q

What is the anisotropic property?

A

Response of cortical bone is dependent on direction of a tension strength

194
Q

What are bone fractures like with tensile conditions?

A

Avulsion.

195
Q

What occurs with structure of bone under tensile conditions?

A

It lengthens and narrows

196
Q

Fractures under tensile stress tend to be stable or unstable?

A

Unstable.

197
Q

What type of bone is tensile forces seen in?

A

Cancellous bone

198
Q

What are the 3 types of load?

A

Compression, tensile and shear

199
Q

In what type of bone is shear stress found in?

A

Cancellous bone

200
Q

Are shear stress fractures typically stable or unstable?

A

Unstable.

201
Q

What type of loads does shear stress occur with?

A

Compressive and twisting loads

202
Q

Shear strain is measured by in what units?

A

The angle (in radians) created by deformation.

203
Q

What would cause compression of the spinpous processes in the cervical region?

A

Hyperextension.

204
Q

Cortical bone can handle what type of stress more than others?

A

Compression> Tension > shear.

205
Q

With bending stress will the convex or concave side be under tensile or compressive stress?

A

Convex- Tensile. Concave- Compressive.

206
Q

What is the theory behind 3 point bending?

A

Fracture occurs at the point of application of the middle force

207
Q

A boot top fracture happens while skiing where will the fracture occur?

A

ON the convex side (posterior side) because it is where tensile stress will be and tensile stress is weaker in bones than compressive stress.

208
Q

What is torsion?

A

A combination of shear and tensile and compressive stress.

209
Q

Where does twisting cause shear stress?

A

Around the axis

210
Q

Where is there greater shear stress, closer or farther from the axis?

A

The further from the axis, the greater the shear stress

211
Q

In what plane does maximum compression and tension stress act on in the neutral axis?

A

a plane diagonal to the neutral axis

212
Q

*When a bone breaks under torsional stress what part breaks first and second?

A

first will be from shear and second will be from tensile.

213
Q

In a picture of a torsional fracture what will shear and tensile fractures look like?

A

Shear parallel to the bone. Tensile will travel acrossed the bone.

214
Q

What are the complications with end plate fractures?

A

schmorls nodes, may cause loss of disc height, if enough disk height is lost then the nerve root may be compromised in IVF.

215
Q

What stress can muscle groups produce on bone?

A

Compression stress

216
Q

What does the compression caused by muscles on bone do in regards to tensile stress?

A

Reduce or neutralize the tensile stress of bending

217
Q

How much stronger is bone with brisk walking than slow walking?

A

30% d/t faster load with faster walking therefore it needs more protection

218
Q

What happens to energy storage when speed and load is increased?

A

The energy storage capacity can double

219
Q

With increased speed and load it is said that “load to failure doubles” what does this mean?

A

Doubling the load if the load is applied quickly it can be supported however the same load applied slowly might cause the bone to fail or break

220
Q

What kind of fracture is caused in low speed fractures?

A

A stable, single crack with little soft tissue damage

221
Q

What kind of fracture is caused in high speed fractures?

A

A comminuted fracture (explosion of bone) that may be unstable with ore tissue damage

222
Q

What can occurs in regards to the disk in an end plate fracture?

A

May allow nucleus pulpsis to migrate through cracks in the end plate

223
Q

With end plate fractures, what occurs with the disk height?

A

May cause a loss of disc height at that level

224
Q

If there is loss of disc height due to end plate fractures what can occur?

A

Nerve roots may be compromised in the IVF

225
Q

What does repetitive loading due to bone strength?

A

It causes a decreased strength

226
Q

When do fatigue fractures occur?

A

with high repetitions and low load or low repetitions and high loads. AND when fatigue outpaces remodeling.

227
Q

Microfractures of trabeculae can occur with repetitive loading _____% of maximum failure rate.

A

20-30%.

228
Q

When bones fatigue and are under repetitive stress what happens to stiffness and shock absorption?

A

The bone loses it’s stiffness and shock absorption

229
Q

What happens to bones with muscle fatigue?

A

When muscles are fatigued they don’t protect the bones from stress.

230
Q

How will density of bones change?

A

Increases with use and decreased with disues.

231
Q

What are some adaptive changes by bone under mechanical demand? (3)

A

1) Density changes: increases with use, decreases with disuse
2) Remodeling
3) spurring

232
Q

What is wolff’s law?

A

Bone is laid down or resorbed where needed, and load on bone is caused by muscle action or gravity. The greater the body mass the greater the bone mass.

233
Q

How much bone mass is lost per week with bed rest?

A

1%.

234
Q

Over decades, how much reduction will the skeletal mass (trabecular and cortical mass) undergo?

A

Trabecular = 50% and Cortical = 25%.

235
Q

How much bone mass will women lose from the 4th decade on?

A

1.5-2%.

236
Q

How much bone mass will men lose from the 4th decade on?

A

About half of women.

237
Q

What is brittleness?

A

The quality whereby a material exhibits little plastic deformation before FAIURE. Failure < 5% total elongation of material.

238
Q

What are some common sites of fracture with age?

A

lumbar vertebra, femoral head, proximal tibia.

239
Q

X-rays should be ordered in what 3 cases?

A
  1. Osteoporosis.
  2. Patients over 50.
  3. Spontaneous fracture or with slight load.
240
Q

How many people that break their hip can regain their independence?

A

1/3 of them.

241
Q

How many people with hip fractures die within the first year?

A

1/4 of them.

242
Q

What % of people that survive hip fractures will be able to walk without aid?

A

50% of them.

243
Q

What is the second leading cause of admissions to nursing homes?

A

Broken hips

244
Q

What % of people that use corticosteroids get hip fractures?

A

25%of them.

245
Q

what will the prevalence of vertebral fractures be for asthma patients that use corticosteroids for less than a year ?

A

11%.

246
Q

What is a good thing to do to keep bones strong?

A

Exercise.

247
Q

What type of cartilage make up the nose and ear?

A

Elastic cartilage.

248
Q

Where is fibrocartilage found in the body? (3)

A

1) annular fibers of the disc
2) iliac surface of SI joints
3) menisci of the knee

249
Q

Where is hyaline cartilage found?

A

In synovial joints

250
Q

What is the purpose of cartilage in joints?

A

To decrease contact stress on articular surfaces by spreading the load over a larger area. AND to alow movement of articular surfaces with minimal wear and friction.

251
Q

What is the composition of hyaline cartilage be like?

A

No nerve, No blood supply, No lymph supply and low density so not visible on x-ray

252
Q

How fast can cartilage heal and why?

A

Not fast because there is nothing supporting it like blood, lymph and nerves.

253
Q

What are the 3 parts of cartilage?

A
  1. Solid matrix (collagen and proteoglycan gel).
  2. Chondrocytes.
  3. Water.
254
Q

Of the 3 parts of cartilage what is the largest part?

A

Water.

255
Q

What makes up the solid matrix of cartilage?

A

Collagen and proteoglycan gel.

256
Q

What is the function of collagen in cartilage?

A

Provides ultrastructure for cartilage. AND provides tensile stiffness and strength.

257
Q

What directional pattern do the lines of force move in occurs when cartilage is compressed?

A

Lines of force, when compressed, move in horizontal pattern

258
Q

How will collagen be arranged in the 3 layers of cartilage?

A

Layer1- Random packed and random orientation in planes parallel to the surface.
Layer 2- Random orientation loosely packed.
Layer 3- Perpendicular orientation to anchor bone and fibrocartialge.

259
Q

What is proteoglycan gel made of?

A

Protein core, aggrecans (condroitin sulfate, keratin sulfate).

260
Q

What type of force will proteoglycan gel resists and how?

A

Compression and the anions on the proteoglycan gel will repeal the other parts of the proteoglycan gel. Cations create a cloud around the proteoglycan gel as they get pulled in by the anions and creates an osmotic pressure.

261
Q

Are proteoglycan gels hydrophylic or hydrophobic?

A

Hydrophylic.

262
Q

Cartilage swells and gets stiff due to what 2 things?

A
  1. Repulsive forces of the agrrecan.

2. Osmotic-pressure attracting water.

263
Q

What happens to water under increasing stress of a joint?

A

It is pushed out, and produces increased swelling pressure and equilibrium is re-established when the swelling pressures balances the stress.

264
Q

What part of the cartilage will the water be in?

A

Most of it is in the superficial zone.

265
Q

What is creep?

A

Under a constant load, a viscoelastic material will deform quickly at first and then more slowly over time

266
Q

What is most of the creep in cartilage due to?

A

Most of the creep in cartilage is due to the exudation of fluid (partly based on the permeability of the solid phase of cartilage

267
Q

With creep, how does it work to resist deformation of the cartilage?

A

Copious exudation of fluid, then exudation slows and finally stops as swelling pressure balalnces the load and the swelling pressure and matrix strength resist futher deformation to a large degree

268
Q

How does cartilage swell back up once the pressure/load is reduced?

A

The cations have stayed inside the cartilage and when the pressure is reduced it swells back up with water like a sponge

269
Q

What are the properties that determine the effectiveness of the biomechanical properties? (2)

A

1) material properties of the matrix

2) Permeability of the matrix

270
Q

What is permeability?

A

Measure of resistance to fluid flow

271
Q

Does cartilage have low or high permeability?

A

Low permeability

272
Q

Under which circmstances does permeability decrease? (2)

A

1) increased pressure gradient

2) compression deformation which doesn’t allow the last drops of fluid to be squeezed out of the cartilage

273
Q

What is the function of permeability in cartilage?

A

Important for nutrition, lubrication and wear to prevent total loss of fluid

274
Q

Under which circumstances does permeability increase?

A

In athological conditions due to collagen fiber defects and loss of proeoglycan

275
Q

What happens to cartilage with high speed loading?

A

1) insufficient time to squeeze water out of the tissue causing the cartilage to be very stiff and little deformation

276
Q

What is damping?

A

An increase in stiffness when a load is applied with increased speed

277
Q

Is high speed loading due to damping a good or bad shock absorber ?

A

It is an excellent shock absorber and absorbs compressive shock that would otherwise overload the bone

278
Q

What happens with the unloading following slow loading of cartilage?

A

1) Immediate restoration to 90% original thickness via elastic recoil
2) slower restoration via swelling pressure to original thickness

279
Q

What is lubrication?

A

Protection from wear and tear

280
Q

What acts as a lubricant between articular surfaces?

A

Synovial fluid

281
Q

What are the two types of lubrication?

A

Fluid film and boundary

282
Q

What is fluid film?

A

A thick film of lubricant that separates the surfaces

283
Q

When does fluid film lubrication occur?

A

In physiologic loading and unlike man-made material, there is almost zero friction at the joint surfaces

284
Q

What are the types of fluid film lubrication? (2)

A

Hydrodynamic and squeeze film

285
Q

Where is hydrodynamic lubrication found?

A

Non-parallel surfaces

286
Q

What kind of movement and action is hydrodynamic lubrication?

A

Tangential movement that creates a lifting action, keeping surfaces apart and reducing friction

287
Q

What is squeeze lubrication?

A

Keeps surfaces apart and provides a perpendicular force

288
Q

How is the lubricant held together and prevented from escaping from the surfaces?

A

The viscosity holds the lubricant together so that it doesn’t escae from between the surfaces allowing it to be sufficient for high loads for short durations

289
Q

What is a boundary lubrication?

A

Last resort for cartilage as it is a monolayer of synovial fluid and important in severe loading

290
Q

What is cartilaginous wear?

A

The unwanted removal of material from solid surfaces by mechanical action

291
Q

What are the two types of cartilage wear?

A

Interfacial and fatigue wear

292
Q

What is interfacial wear?

A

Due to interaction of articular surfaces caused by adhesion and abrasion

293
Q

Is interfacial wear likely in healthy cartilage?

A

No, because of effective lubrication

294
Q

What does interfacial wear cause?

A

Surface defect leading to softing and increased permeability -> fluid leakage -> loss of lubrication -> further wear and degeneration

295
Q

What is fatigue wear?

A

Occurs with repetitive cyclic loading and reloading before the cartilage has time to fully reload

296
Q

What does fatigue wear cause?

A

Collagen fiber disruption (perhaps due to tesile failure) and rapid high impact loads don’t allow the fluid to redistribute rapidly enough causing high internal fluid pressure at the PG-collagen matrix

297
Q

What are some high reptitive load examples?

A

Football player’s knees, ballet dancer’s ankles

298
Q

What are is an example of loss of muscle balance?

A

Loss of flexibility that prevents loads from being evenly distributed throughout joint surface and causes a defect that focuses load into one area

299
Q

What are some disease that can cause matrix destruction? (3)

A

RA, joint space hemorrhage and collagen disorders

300
Q

What does immobility do to synovial fluid circulation?

A

It decrease it

301
Q

What does degeneration lead to?

A

Promotes further degeneration yielding deterioration of tensile properties which can lead to progressive breakdown and OA

302
Q

Is the repair capcity of the body limited or unlimited?

A

Limited

Biomechanics III (2 decks)

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