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Biomechanics > Lecture 6 > Flashcards

Lecture 6 Flashcards

1
Q

Role & Function of Bone

A
  1. Provides a rigid framework which
    supports & protects body tissues
  2. Forms a system of rigid levers that can be moved by forces from the attaching muscles
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2
Q

The composition & structure of bone yield a material that is

A

strong despite its relatively light weight

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3
Q

Composition of bone

A

Mineral
Collagen
Water

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4
Q

Minerals composition of bone weight

A

60-70% of bone weight

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5
Q

Minerals that make up the bone

A

Calcium carbonate, calcium phosphate
Also Mg2+, Na2+, Fl

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6
Q

Functions of Minerals that make up the bone

A

Also Mg2+, Na2+, Fl contribute to growth & development

Give the bone its stiffness; primary determiners of bone’s compressive strength

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7
Q

What type of collagen primarily makes up bone

A

Type 1

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8
Q

Describe the collagen compostion of bone and teh function

A

ype 1 collagen, cross-links; protein provides bone with flexibility and contributes to its tensile strength.

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9
Q

What does breakdown of collagen with age decrease?

A

s bone toughness & strength by up to 60%

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10
Q

Howe much water makes up the bone composition

A

25-30%

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11
Q

What is the fuction of water in the bone

A

contributes to bone strength, medium for nutrient diffusion, viscoelasticity

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12
Q

What modulus is tied to collagen of. bone?

A

Low Young’s modulus of elasticity- meaning?, good tensile strength, poor compressive strength

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13
Q

Why are minerals good for bone

A

stiff & brittle, good compressive strength

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14
Q

All bones are composed of 2 types of osseous tissue at the macroscopic level name them.

A

Cortical (compact bone)
Cancellouis bone (trabecular)

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15
Q

Compact bone describe

A

forms the outer shell/cortex of bone, dense structure similar to ivory

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16
Q

Cancellous (trabecular) bone

A

within the ‘shell’, honeycomb structure, composed of thin rods/plates (trabeculae) in a loose mesh network; spaces between trabeculae are filled with red bone marrow, porous

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17
Q

Which type of bone is more porous, cancellous or cortical bone?

A

Cancellous bone is more porous than cortical bone.

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18
Q

How does the porosity of bone affect its composition

A

The more porous the bone, the smaller the proportion of minerals and greater the proportion of collagen.

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19
Q

What is the main difference between cortical and cancellous bone in terms of mechanical characteristics?

A

Cortical bone is stiffer and can withstand greater stress but less strain compared to cancellous bone.

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20
Q

What is the advantage of trabecular bone over cortical bone in terms of strain before fracturing?

A

Trabecular bone, being more spongy, can undergo more strain before fracturing, indicating a large capacity for energy storage.

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21
Q

: Describe the structural characteristics of cortical and cancellous bone in terms of strength and flexibility.

A

Cortical bone is strong but brittle, while cancellous bone is weak but flexible.

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22
Q

What determines the structure of a bone?

A

The function of a bone determines its structure.

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23
Q

Which type of bone forms the shafts of long bones?

A

The shafts of long bones are composed of strong cortical bone.
Question:

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24
Q

How does the relatively high trabecular bone content contribute to the vertebrae?

A

The relatively high trabecular bone content of the vertebrae contributes to their shock-absorbing capability.

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25
Q

How does trabecular bone adapt to different forces and loading conditions?

A

Trabecular bone develops different types of structure depending on whether it must withstand relatively high vs. low forces and whether the primary loading is axial or asymmetric.

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26
Q

What determines the direction in which new bone tissue is formed?

A

The direction in which new bone tissue is formed is in line with the loads most habitually encountered, particularly in regions of high stress

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27
Q

What is anisotropy in the context of bone biomechanics?

A

Anisotropy refers to the property where bone exhibits different strength and stiffness in response to forces applied from different directions due to differences in bone structure.

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28
Q

What is the strength of bone in resisting compressive stress and shear stress?

A

Bone is strongest in resisting compressive stress and weakest in resisting shear stress.

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29
Q

What causes different stress/strain behaviors in bone specimens taken in different orientations within the human cortical femur?

A

The different stress/strain behaviors are due to the anisotropic biomechanical property of long bones, where bone structure differs in the transverse and longitudinal directions.

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30
Q

What is indicated by the initial straight line of the stress-strain curve in bone?

A

The initial straight line represents the elasticity of the bone, indicating temporary deformation where the structure recovers its original shape when unloaded.

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31
Q

What happens as loading continues beyond the elastic region of the stress-strain curve in bone?

A

Beyond the elastic region, the outermost fibers of the bone structure begin to yield, reaching the yield point which is the elastic limit of the structure. Further loading results in plastic behavior where some deformation becomes permanent.

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32
Q

What does the ultimate failure point on the stress-strain curve in bone indicate?

A

The ultimate failure point indicates bone fracture, occurring when loading is progressively increased beyond the yield point.

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33
Q

How is strength in terms of energy storage indicated in bone biomechanics?

A

The strength in terms of energy storage is indicated by the size of the area under the entire stress-strain curve, known as the modulus of toughness. A larger area indicates greater energy buildup in the structure as the load is applied.

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34
Q

How is the stiffness of bone structure indicated in the stress-strain curve?

A

The stiffness of bone structure is indicated by the slope of the curve in the elastic region. The steeper the slope, the stiffer the material

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35
Q

What percentage of the compressive load on the vertebrae is carried by the cortical shell?

A

The cortical shell of the vertebra carries only 10% of the compressive load.

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36
Q

What part of the vertebra absorbs the majority of the compressive load?

A

The trabecular bone absorbs the majority of the compressive load.

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37
Q

How does the distribution of load on the vertebrae change with age?

A

The load carried by the cortex increases with age.

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38
Q

Where is the trabecular bone strength the greatest within the vertebral body when the disc is healthy?

A

The trabecular bone strength is the greatest in the center of the vertebral body when the disc is healthy.

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39
Q

How does the distribution of compressive stresses change as the disc degenerates?

A

As the disc degenerates, the compressive stresses are more uniformly distributed over the disc.

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40
Q

How does the strength of trabecular bone adapt with degeneration of the disc?

A

As the disc degenerates, the trabecular bone strength adapts accordingly to the change in distribution of compressive stresses.

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41
Q

What are the types of various loading modes that effect Bone behavior (6)

A

Tension
-Compression
-Shear
-Bending
-Torsion
-Combined loading

42
Q

What happens during tensile loading?

A

During tensile loading, equal and opposite loads are applied outward from the surface of the structure, resulting in tensile stress and strain inside the structure.

43
Q

Where are fractures produced by tensile loading usually seen?

A

Fractures produced by tensile loading are usually seen in bones with a large proportion of cancellous bone.

44
Q

Can you provide an example of a fracture caused by tensile loading?

A

An example is the avulsion fracture of the calcaneus adjacent to the attachment of the Achilles tendon.

45
Q

What happens to the bone during intense contraction of the triceps surae muscle?

A

Intense contraction of the triceps surae muscle produces abnormally high tensile loads on the bone.

46
Q

Why is tensile loading problematic for bones?

A

Tensile loading is problematic for bones because bone is usually weaker in tension than in compression.

47
Q

What happens during compressive loading?

A

During compressive loading, equal and opposite loads are applied towards the surface of the structure, resulting in compressive stress and strain inside the structure.

48
Q

How does the structure respond under compressive loading?

A

Under compressive loading, the structure shortens and widens.

49
Q

Where are compression fractures commonly found?

A

Compression fractures are commonly found in the vertebrae, which are subjected to high compressive loads.

50
Q

Who is most commonly affected by compression fractures?

A

Compression fractures are most often seen in the elderly with osteoporotic bone tissue.

51
Q

What happens during shear loading?

A

During shear loading, a load is applied parallel to the surface of the structure, resulting in shear stress and strain inside the structure.

52
Q

How does a structure respond under shear loading?

A

A structure subjected to shear loading deforms internally in an angular manner.

53
Q

Where are shear fractures most often seen?

A

Shear fractures are most often seen in cancellous bone.

54
Q

How do fractures of shear loading type appear?

A

Fractures of shear loading type snap like a transverse fracture.

55
Q

What happens in bending?

A

In bending, loads are applied to a structure in a manner that causes it to bend about an axis.

56
Q

What combination of stresses and strains does a bone experience during bending?

A

When a bone is loaded in bending, it is subjected to a combination of tension and compression. Tensile stresses and strains act on one side of the neutral axis, while compressive stresses and strains act on the other side.

57
Q

Which strength is greater, compression or tensile strength, and how does it relate to bone failure in bending?

A

Compression strength is greater than tensile strength. Bone tends to fail in tension because it is weaker in tension than in compression.

58
Q

How does a boot top fracture occur?

A

In a boot top fracture, one bending moment acts on the proximal tibia as the skier falls forward over the top of the ski boot. An equal moment produced by the fixed foot and ski acts on the distal tibia. As the proximal tibia bends forward, tensile stresses and strains act on the posterior side of the bone, and compressive stresses and strains act on the anterior side, leading to fracture at the top of the boot.

58
Q

What is a typical example of a bending fracture?

A

The boot top fracture sustained by skiers is a typical bending fracture.

59
Q

What happens in torsion?

A

In torsion, a load is applied to a structure in a manner that causes it to twist about an axis, producing a torque within the structure.

60
Q

What additional stress is developed when a structure is loaded in torsion?

A

When a structure is loaded in torsion, it also develops internal shear stress.

61
Q

What is the typical pattern of a torsional fracture?

A

The typical pattern of a torsional fracture is a spiral, which is perpendicular to the maximum tensile strength applied.

62
Q

Why is loading of bone considered complex?

A

Loading of bone is complex because bones are constantly subjected to multiple indeterminate loads, and their geometric structure is irregular.

63
Q

What is viscoelasticity, and how does it affect bone biomechanical behavior?

A

Viscoelasticity refers to the property where the biomechanical behavior of bone varies with the rate at which it is loaded. Bone is stiffer and sustains a higher load before failure when loads are applied at higher rates.

64
Q

How does the strain rate affect bone strength during different activities?

A

Bone is approximately 30% stronger for brisk walking than for slow walking, indicating that bone strength is influenced by the strain rate during different activities.

65
Q

What happens to bone at very high strain rates, such as during impact trauma?

A

At very high strain rates, bone becomes more brittle.

66
Q

How does the loading rate influence fracture patterns and soft tissue damage?

A

The loading rate influences both the fracture pattern and the amount of soft tissue damage at fracture. At low loading rates, energy can dissipate through the formation of a single crack, resulting in minimal soft tissue damage. At high loading rates, however, the greater energy stored may result in comminution of bone and extensive soft tissue damage.

67
Q

What happens when a bone fractures?

A

When a bone fractures, the stored energy is released. At low loading rates, the energy can dissipate through the formation of a single crack, whereas at high loading rates, the greater energy stored may lead to comminution of bone and extensive soft tissue damage.

68
Q

How does the loading rate influence fracture pattern and soft tissue damage at fracture?

A

The loading rate influences both the fracture pattern and the amount of soft tissue damage at fracture.

69
Q

What happens when a bone fractures in terms of energy release?

A

When a bone fractures, the stored energy is released.

70
Q

What occurs at a low loading rate during bone fracture?

A

At a low loading rate, the energy can dissipate through the formation of a single crack, resulting in minimal displacement of bone fragments and relatively intact soft tissues.

71
Q

What occurs at a high loading rate during bone fracture?

A

At a high loading rate, the greater energy stored cannot dissipate rapidly enough through a single crack, leading to comminution of bone and extensive soft tissue damage.

72
Q

How can bone fractures occur under repetitive loading?

A

Bone fractures under repetitive loading can occur either by a single load that exceeds the ultimate strength of the bone or by repeated applications of a lower magnitude load, resulting in a fatigue fracture.

73
Q

What is a fatigue fracture?

A

A fatigue fracture is a fracture caused by repeated load application, often resulting from many repetitions of a relatively normal load leading to microdamage and eventual failure.

74
Q

Why does bone fatigue rapidly when the load approaches its yield strength?

A

Bone fatigues rapidly when the load or deformation approaches its yield strength because the number of repetitions needed to produce a fracture diminishes rapidly.

75
Q

What is a common example of stress fractures related to repetitive loading?

A

Stress fractures are often reported among military recruits undergoing strenuous training involving marching and running over a short period of time.

76
Q

How can muscle contraction affect stress patterns on bone during physical activity?

A

Muscle contraction affects stress patterns on bone by producing compressive stress that works to neutralize the tensile stress acting on the bone.

77
Q

What happens when sustained strenuous physical activity leads to muscle fatigue?

A

Sustained strenuous physical activity leading to muscle fatigue can result in the inability of muscles to effectively contract, reducing their ability to store energy and neutralize stresses imposed on the bone, thus increasing the risk of fatigue fracture.

78
Q

What is Wolff’s Law?

A

Wolff’s Law states that bone has the ability to remodel by altering its size, shape, and structure in response to the mechanical demands placed on it.

79
Q

How is bone remodeling influenced according to Wolff’s Law?

A

Bone remodeling is influenced and modulated by mechanical stresses, meaning that bone adapts its mass and shape based on the mechanical signals it senses.

80
Q

What happens to bone when loading on it increases according to Wolff’s Law?

A

If loading on a bone increases, it will remodel itself over time to become stronger and resist that sort of loading by laying down more bone.

81
Q

How does decreased loading affect bone density and strength according to Wolff’s Law?

A

If loading on a bone decreases, the bone will become less dense and weaker due to the lack of stimulus required for continued remodeling.

82
Q

What are some examples of Wolff’s Law in action?

A

Gravity is a significant load on the skeleton, and a positive correlation exists between bone mass and body weight. Conversely, prolonged weightlessness in space results in decreased bone mass. Disuse or inactivity also negatively affects the skeleton, leading to bone resorption and decreased mechanical properties.

83
Q

What were the findings of the 1969 experiment involving monkeys in full-body casts?

A

Monkeys immobilized in full-body casts for 60 days showed a three-fold decrease in load to failure, stiffness, and toughness, demonstrating the negative effects of immobilization on bone strength and stiffness.

84
Q

What are osteoblasts and osteoclasts, and how do they relate to Wolff’s Law?

A

Osteoblasts are bone-forming cells responsible for laying down new bone tissue, while osteoclasts are bone-resorbing cells responsible for breaking down bone tissue. These cells play a crucial role in bone remodeling in response to mechanical stresses, as mediated by Wolff’s Law.

85
Q

How does exercise influence bone adaptation according to Wolff’s Law?

A

Exercise, especially weight-bearing and resistance exercises, stimulates bone remodeling by subjecting bones to mechanical stresses. This leads to the activation of osteoblasts, resulting in bone formation and increased bone density, strength, and resilience.

86
Q

What is the role of nutrition in bone adaptation and remodeling?

A

Adequate nutrition, particularly calcium, vitamin D, and protein intake, is essential for bone health and adaptation. These nutrients provide the building blocks for bone formation and repair, supporting the process of remodeling in response to mechanical stresses.

87
Q

How do age and hormonal factors affect bone adaptation?

A

Bone adaptation and remodeling are influenced by age-related changes in hormonal levels, such as estrogen and testosterone. Hormonal imbalances, particularly during menopause or andropause, can accelerate bone loss and weaken bone structure, affecting its ability to adapt to mechanical stresses.

88
Q

What are some clinical implications of Wolff’s Law in orthopedics and rehabilitation?

A

Understanding Wolff’s Law is essential in orthopedic surgery and rehabilitation to optimize bone healing and recovery. Surgeons may apply mechanical principles to promote bone fusion and stability, while rehabilitation specialists may prescribe exercise programs tailored to enhance bone adaptation and prevent disuse-related bone loss

89
Q

What is the piezoelectric effect in bones?

A

The piezoelectric effect in bones is a phenomenon where mechanical stress or pressure applied to a bone generates an electrical charge.

90
Q

How does the piezoelectric effect occur in bones?

A

When a mechanical force pushes atoms closer together or further apart in a bone, it upsets the electrical balance, causing positive and negative charges to appear on opposite ends of the bone, thus forming an electric field.

91
Q

What happens as a result of the accumulation of charges and the generation of a small current due to the piezoelectric effect in bones?

A

The accumulation of charges and the generation of a small current trigger a cascade of signaling pathways that ultimately promote bone formation.

92
Q

What degenerative changes occur in bone associated with aging

A

With aging, there is a progressive loss of bone density, resulting in thinner longitudinal trabeculae and resorption of some transverse trabeculae. This leads to a marked reduction in cancellous bone and thinning of cortical bone.

93
Q

How do stress-strain curves for bone specimens from different age groups compare?

A

Stress-strain curves for bone specimens from different age groups show that while the ultimate stress may be similar, older bone specimens can withstand only half the strain or deformation compared to younger bone. This indicates greater brittleness and a reduction in bone toughness with age.

94
Q

What factors contribute to increased bone fragility with aging?

A

The reduction in collagen cross-linking, bone density, strength, stiffness, and toughness contribute to increased bone fragility with aging.

95
Q

What role does collagen cross-linking play in bone strength and stiffness?

A

Collagen cross-linking contributes to the strength and stiffness of bone. With aging, there is a reduction in collagen cross-linking, which contributes to decreased bone strength and stiffness.

96
Q

How does the reduction in bone density affect bone fragility?

A

The reduction in bone density with aging contributes to bone fragility. As bone density decreases, there is less structural support, making bones more susceptible to fractures.

97
Q

What are some consequences of thinning cortical bone with aging?

A

Thinning cortical bone with aging reduces bone strength and stiffness, as cortical bone provides structural support and resistance to mechanical stress. This can increase the risk of fractures.

98
Q

How does the loss of trabecular bone affect bone integrity?

A

The loss of trabecular bone with aging compromises bone integrity, leading to decreased bone strength and increased susceptibility to fractures, particularly in weight-bearing bones.

99
Q

What interventions can help mitigate the degenerative changes in bone associated with aging?
Answer:

A

Exercise, particularly weight-bearing and resistance exercises, along with adequate calcium and vitamin D intake, can help mitigate the degenerative changes in bone associated with aging. Additionally, medications such as bisphosphonates may be prescribed to slow bone loss and reduce fracture risk in older individuals.

Biomechanics (6 decks)

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