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ME498 Midterm > Tissue Mechanics - Bone > Flashcards

Tissue Mechanics - Bone Flashcards

1
Q

What is the base material for bone?

A

Collagen Fibrils

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2
Q

What is the 2 structures collagen fibrils can form that create the basis of bone structure?

A

Lamellar: stacked, thin sheets with unidirectional fibrils
Woven: random orientation fibrils, common in growing organisms and initial stages of fracture healing

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3
Q

What are the different structures of bone? (0.5-1mm)

A

Primary lamellar: concentric rings of lamellae
Haversian (Osteonal): 10-15 lamellae arranged in concentric cylinders about the Haversian canal (for blood vessels, nerves, bone cells)
Laminar: Constructions of layered lamellae around blood vessels, contain woven bone
Woven

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4
Q

What are the 2 types of bone and how do their structures differ?

A

Cortical: tightly packed lamellae, Haversian, Laminar, and Woven

Trabecular: highly porous cellular solid, lamellae arranged in packets with rods and plates with marrow spaces

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5
Q

What is an osteon and what type of bone is it found in?

A

Primary unit of cortical bone: substructure of 10-15 concentric lamellae

  • Represent the primary unit of adult cortical bone
  • Can be removed which are then filled over time
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6
Q

What is the process of breaking down patrons and replacing them by different types of bone cells referred to as?

A

Remodelling

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7
Q

What is a cement line?

A

Weak interface between osteons surrounding interstitial lamellar bone thought to help dissipate energy during crack propagation

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8
Q

What are osteocytes?

A

Osteoblasts (cells) trapped between lamellae with processes reaching through to other osteocytes through canaliculi

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9
Q

What surrounds osteocytes?

A

Lacunae: Thin layer of fluid surrounding osteocytes

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10
Q

What is the purpose of osteocytes?

A

Sense mechanical deformation and transmit signals to other cells which can start remodeling

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11
Q

What is an osteoclast?

A

A cell which dissolves bone by secreting acid

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12
Q

What is an osteoblast?

A

A cell which secretes osteoids that mineralized to form bone

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13
Q

What is a bone lining cell?

A

Dormant osteoblasts which line trabecular bone surfaces, periosteal surfaces and Haversian canals, thought to start repair processes

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14
Q

What is a BMU?

A

Basic Multicellular Units, which coordinate the formation of secondary osteons

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15
Q

What are the processes in BMU’s and how long do they take on average?

A

Activation: osteoclasts are signalled by osteocytes - 3 days
Resorption and Reversal: bone is dissolved - 30 days
Formation: osteoblasts lay down osteoid - 90 days
Mineralization: 10 days for sufficient calcium and phosphorus, 60% occurs in 24hrs, rest over 6 months - 180 days

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16
Q

How does remodeling differ for trabecular bone?

A

Less organized than cortical bone
Osteoclasts attach themselves at the surface and eat a small region, then osteoblasts follow

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17
Q

What is Frost’s mechanical theory?

A
  • Stipulates that bone remodeling responds to strain at specific biological setpoints
18
Q

What happens to bone if it it’s usage is trivial (low usage of the bone)?

A

The body is thought to remodel the bone, decreasing its mass

19
Q

What happens if the Repair MES is exceeded?

A

The bone is repaired with woven structure which is more susceptible to fracture

20
Q

What are the 2 mechanical properties of bone that differentiate it from steel and other metals?

A

Anisotropic: bone strength varies with direction
Heterogenous: strength varies with spatial location

21
Q

What is typically defined as the longitudinal axis?

A

The diaphyseal axis of long bone

22
Q

Is the strength of bone similar in tension and compression?

A

No

23
Q

Why is the transverse tensile strength of bone so low?

A

Has not adapted due to rarely occurring during normal physiological loading

24
Q

What is the typical failure criteria for bone?

A

Excessive strain

25
Q

Why does drilling into the femur as part of a hip replacement cause fracture of the femur?

A

Transverse tensile strength is quite low due to rare occurrence in normal physiological loading

26
Q

What are mechanical properties of bone typically attributed to?

A

Ash density differences, not age

27
Q

What is the conversion from bone volume fraction to apparent density?

A

1.8g/cm3

28
Q

What is the relationship between ash density and yield strain and what are its implications?

A

No correlation suggesting that it controls failure

29
Q

Does bone have a greater resistance to fatigue and creep in tension or compression?

A

Compression

30
Q

How is fatigue for bone typically plotted?

A

Strain vs time (as opposed to stress vs time for steels and other materials)

31
Q

What is an important caveat regarding our understanding of fatigue in bones?

A

It is based on cadaveric bone, so high cycle fatigue actually occurs

32
Q

What happens to bone post-yield?

A

The elastic modulus decreases - a biological response is triggered

33
Q

How is the elastic modulus and strength of cortical bone related to the stress rate?

A

Proportional, it is a visco-elastic material

34
Q

Why can bone be assumed to behave elastically?

A

Normal loading is within a narrow range of strain rates

35
Q

How is the ultimate strength affected by aging? How is the ultimate strain?

A

Strength: unaffected
Strain: Reduces with age

36
Q

What difference is noteworthy between anisotropy in trabecular bone when compared to cortical bone?

A

The main longtudinal axis exhibits various positions throughout the structure

37
Q

What are mechanical properties of trabecular bone characterized as?

A

A function of density (usually apparent)

38
Q

Is the fatigue behaviour of trabecular bone similar to cortical?

A

Yes, it exhibits fatigue and experiences a reduction in elastic modulus and strength when loaded beyond yield

39
Q

How does the anisotropy of trabecular bone change with age?

A

The degree of anisotropy increases with age

40
Q

What is the primary failure mode for trabecular bone at later ages?

A

Buckling

ME498 Midterm (4 decks)

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