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Block 4 Week 1 Meg > Robertson: Biomechanics of Tendon, Bone, Cartilage, and Muscle > Flashcards

Robertson: Biomechanics of Tendon, Bone, Cartilage, and Muscle Flashcards

1
Q

What is this: direction, magnitude, point of application

A

force

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2
Q

What is this: rotational force

A

torque

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3
Q

Equation for torque

A 
Torque = force * distance
T = rFsin(theta)
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4
Q

Equation for stress

A

stress = force/area

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5
Q

Two types of pressure and give an example of each

A
  1. solid pressure
    ex: 70kg male standing on two feet with 100cm surface surface area for each foot. How much pressure under each foot? 36mPA
  2. fluid pressure
    ex: compartment syndrome, blood pressure
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6
Q

This can depict the relationship between the stress and strain that a particular material displays

A

stress/strain curve

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7
Q

Three ways in which force can be applied to bone

A
  1. bending
  2. torsion (ends twisting in opposing directions)
  3. compression (longitudinal)
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8
Q

When plotting a curve of deformation vs load, what is the difference between the elastic region and the plastic region?

A

The elastic region is linear (it has a constant slope). The plastic region is when structural deformation occurs, and the slope of this portion of the curve changes.

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9
Q

This region of the stress/strain curve has a constant slope

A

elastic region

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10
Q

Two important points on a stress/strain curve

A

yield point

failure point

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11
Q

This point on the stress/strain curve signals the end of the elastic region, and is the point at which structural changes occur to the specimen

A

yield stress or yield point

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12
Q

This region on the stress/strain curve begins at the yield point and ends at the ultimate tensile strength. During this time, structural irreversible changes occur to the specimen.

A

plastic region

*think: plastic can undergo irreversible deformation, elastic does not

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13
Q

What is this: mechanical properties INDEPENDENT of direction of stress. Ex: metal sphere

A

isotropy

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14
Q

What is this: mechanical properties different in all directions of loading. Ex: typical of most living things.

A

anisotropy

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15
Q

What is this: mechanical properties symmetric within two planes. Ex: long bone, axial/transverse loading

A

orthotropy

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16
Q

What is this: cyclic loading leads to smaller differences between loading and unloading curves

A

hysteresis

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17
Q

What is the yield point?

A

The point along the strain curve at which you end the elastic response

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18
Q

What is the ultimate stress?

A

This is the failure point

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19
Q

Explain how brittle material and ductile material differ in terms of what occurs after the yield point.

A

With a brittle material, the material will fail shortly after the yield point. Yield point and ultimate stress point would be close together. However, with a ductile material, it will not reach its ultimate stress point for a while after the yield point.

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20
Q

What is failure strength?

A

As you increase number of cycles of loading, you will ultimately regress to fatigue strength.

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21
Q

Functions of bone

A

dynamic metabolic bank (Ca+, Pi)
protects vital organs (skull, rib cage)
framework for skeletal motions
hematopoiesis

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22
Q

What is the ratio of stress over strain, or the slope of the curve in the elastic region referred to as?

A

Youngs modulus

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23
Q

What is this: a principle of physics that states that the force needed to extend or compress a spring by some distance is proportional to that distance

A

Hooke’s law

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24
Q

What is this: bone remodels in response to stress placed on it

A

Wolff’s law

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25
Q

The proximal and distal ends of the femur are what type of bone? The diaphysis of the femur is what type of bone?

A

trabecular; lamellar/cortical

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26
Q

Which portion of the femur can bear axial loading and bending.

A

diaphysis

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27
Q

Which portion of the femur is good for force transmission and hematopoiesis?

A

proximal/distal ends

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28
Q

Which has a higher yield point: cortical bone or trabecular bone?

A

cortical bone

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29
Q

Which type of bone can absorb significant energy with minimal mass?

A

trabecular bone

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30
Q

Is bone strongest under compression or tension?

A

Strongest under compression, undergoes more of a change under tension

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31
Q

Is bone more resistant to a longitudinal or transverse load? Does bone undergo more of a change under a longitudinal or transverse load?

A

More resistant to transverse load. Undergoes more of a change under a longitudinal load

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32
Q

What is this: mechanical properties sensitive to strain rate and duration of applied loads

A

viscoelastic

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33
Q

Bone is (blank) with slow loading, but (blank) with rapid loading

A

ductile; brittle

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34
Q

What is this: continued deformation of a tissue that is subject to constant stress for an extended time

35
Q

What is this: the force necessary to maintain deformation decreases over time.

A

stress relaxation

36
Q

Give an example of stress relaxation

A

Imagine initially using a lot of force to hold a joint straight, but over time, as creep occurs and the fibers stretch, you’ll need less force to keep it straight.

37
Q

What is this: energy absorbed before ultimate failure

38
Q

What is this: ultimate strain substantially larger than yield strain

39
Q

Which has more toughness, a brittle fracture or a ductile fracture?

A

ductile fracture (more energy absorbed before ultimate failure, larger area under the stress/strain curve)

40
Q

What’s the difference between senile and postmenopausal osteoporosis?

A

senile affects both males and females and is a reduction in both cortical and trabecular bone; postmenopausal osteoporosis affects subset of females and is a disproportional loss of trabecular bone

41
Q

In response to aging, what happens to trabecula? Is there more of a reduction in vertical trabecula or horizontal?

A

reduction in number of trabeculae (greater reduction in vertical trabecula)
reduction in thickness of trabeculae
increase in length of trabeculae

42
Q

How does loss of bone density affect the modulus (stress/strain curve in elastic region)?

A

modulus is reduced to a 2:1 ratio, slope equals 2

43
Q

List ways in which bone responds to aging

A

Decreases in density
Decreases in cortical thickness
But increase in diameter of diaphysis!!

44
Q

How do the axial and bending strengths change in response to aging?

A

axial strengths remain similar, but bending strength increases with age related diaphyseal expansion

45
Q

Properties of bone

A

viscoelastic (strain rate/duration affect properties)
strong
tough
ductile or brittle

46
Q

Bone is strongest during (blank) and weakest in (blank)

A

compression; tension

47
Q

Bone volume (blank) with age, but (blank) with disuse

A

increases; decreases

48
Q

What happens to trabeculae with aging? What happens to diaphyseal bone?

A

trabeculae become fewer, longer, less vertical; diaphyseal bone enlarges and increases bending resistance

49
Q

Tendons have similar organization to a ligament. How do they differ in percentage of collagen? Percentage of ground substance? Longitudinal organization of collagen?

A

lower percentage of collagen
higher percentage of ground substance
less longitudinal organization of collagen

50
Q

What’s the ultimate tensile strength of human tendons?

What’s the ultimate strain?

A

50-105 MPa

9-35%

51
Q

What does the stress/strain curve look like for tendons? What are the three regions?

A

Toe region, in which uncrimping of collagen fibers.
Linear region in which slope is elastic modulus.
Failure region which is permanent stretching

52
Q

T/F: Tendons have rate, time, and history dependent behavior.

53
Q

Do tendons undergo creep? What is…creep?

A

yes; time dependent elongation of tissue that is under constant force

54
Q

Do tendons undergo stress relaxation? What is stress relaxation?

A

yes; time dependent decrease in load when deformation is held constant

55
Q

What is this: area between loading and unloading curve. Energy loss due to internal friction. Can be given off as heat.

A

hysteresis

56
Q

What happens to the hysteresis of a tendon after a few cycles of loading and unloading?

A

first few cycles of loading and unloading create larger hysteresis, but hysteresis becomes minimal with repetitive loading

57
Q

4 zones as tendon inserts into bone. What are they?!

A

Zone 1: parallel collagen fibers
Zone 2: unmineralized fibrocartilage
Zone 3: mineralized fibrocartilage
Zone 4: cortical bone

58
Q

In real life, tendons load less than (blank)% of ultimate stress

59
Q

How does tendon strength change with age?

A

Tendon strength increases to maturity and then is rather constant

60
Q

In the rabbit study, what happened to failed ligaments in immature rabbits? What happened to failed ligaments in mature rabbits?

A

in immature rabbits, ligament failed and pulled away with a piece of bone (avulsion)
in mature rabbits, ligament failed mid substance

61
Q

What happens to your ACL over time?

A

It gets weaker :(

62
Q

In the monkey ACL study in which monkeys were immobilized in a body cast, what happened to their strength over a years time?

A

With immobility ligament substance and ligament bone interface substantially weakened

8 wks immobilization resulted in 40% reduction in strength: one year to return to near normal

63
Q

What do corticosteroids do to maximum failure load?

A

After 15 wks, can reduce maximum failure load by 20%

64
Q

How does estrogen affect collagen production? What’s a clinical application of this?

A

reduces it; during pregnancy, pubic symphysis becomes relaxed

65
Q

What happens to tendons when ya have diabetes?

A

They become weaker

66
Q

Are bone ligament bone auto grafts useful?

A

After about three years, only about 1/2 as strong as initial ligament strength

67
Q

Tendons and ligaments are (blank)

A

viscoelastic

68
Q

The in vivo strain rate for tendons and ligaments is far below the (blank)

A

ultimate failure load

69
Q

Severe negative mechanical effects are the result of (blank) of tendons/ligaments. Increase in mechanical strength with activity is not linear.

A

immobilization

70
Q

Do reconstructed tendons/ligament grafts reach native strength?

71
Q

What’s this: muscle shortens against a constant load, muscle tension remains

A

isotonic contraction

72
Q

What’s this: muscle contracts at constant velocity.

A

isokinetic contraction

73
Q

What’s this: muscle length remains static as tension is generated.

A

isometric contraction

74
Q

What’s this: muscle contracture with decreasing muscle length.

A

concentric contraction

75
Q

What’s this: muscular contraction with increase in resting length. Resisting load is greater than muscle contraction force.

A

eccentric contraction

76
Q

What type of training increases oxidative capacity of type I fibers? What type of training increases cross sectional area of type II fibers?

A

endurance training; resistance training

77
Q

Articular cartilage is subject to high (blank) loads applied statically, cyclically, and repetitively over many years

A

compressive

78
Q

Properties of cartilage

A

must be fatigue resistant and tough
soft, permeable
65-80% water
biphasic: solid and fluid phase

79
Q

Three portions of cartilage architecture

A

superficial (tangential fibers)
middle (oblique)
deep (radial fibers - perpendicular)

80
Q

What does it mean that cartilage undergoes biphasic creep, or flow-dependent rate of creep?

A

rate of creep is governed by rate fluid is forced out of tissue

81
Q

Biphasic creep of cartilage is dependent on (blank) of tissue and stiffness of porous material

A

permeability

82
Q

What’s the coefficient of friction in human joints?

A

0.002 to 0.004

83
Q

Cartilage load bearing is (blank) and cartilage has (blank) dependent creep

A

biphasic; flow

84
Q

What occurs in cartilage where fluid film has been depleted?

A

boundary lubrication

Block 4 Week 1 Meg (13 decks)

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