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Biomechanics 2D > Bones > Flashcards

Bones Flashcards

1
Q

What does morphological mean?

A

Relating to the form or structure of things

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2
Q

What does anisotropic mean?

A

Having a physical property which has a different value when measured in different directions

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3
Q

What two types of bone structure are found in long bones?

A

Cortical (compact) bone

Cancellous/trabecular (spongy) bone

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4
Q

What are the two phases or bone remodelling?

A

Resorption (break down of old bone)

Ossification (formation of new bone)

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5
Q

What are the 3 types of cell related to bone creation and remodelling?

A

Osteoblasts

Osteoclasts

Osteocytes

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6
Q

Osteoblasts:

  • what is their function?
  • where are they found (in relation to the bone)?
A

Ossification (formation) of new bone)

Found near the surface of bones

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7
Q

How do osteoblasts create new bone?

A

They:
- make osteoid (mainly collagen)
- secrete alkaline phosphatase (creates sites for calcium and phosphate deposition)
- allows crystals of bone mineral to grow
- osteoid becomes mineralised and forms bone
-

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8
Q

What is osteoid?

A

Osteoid is an unmineralized organic tissue (mainly comprised of collagen) that eventually undergoes calcification and is deposited as lamellae or layers in the bone matrix

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9
Q

Where are osteoclasts found?

How do they break down bone?

A

On the surface of bones

They secrete acid phosphatase which un-fixes calcium in mineralised bone, breaking it down.

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10
Q

What are osteocytes?

Where are they found?

What is their function?

A

Osteoblasts which are no longer on the bone surface

Found in lacunae between lamellae

Maintain oxygen and mineral levels in bone

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11
Q

What are lacunae in bones?

A

Gaps within the lamellae (rings) of bone tissue in which osteocytes are to be found

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12
Q

What are the 2 mechanisms for creating bone in foetal development and what type of bone do they create?

A
  1. Endochronal ossification (long bones)
  2. Intramembraneous ossification (flat bones)
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13
Q

What are the stages of endochronal ossification?

A
  1. Development of cartilage model (rough shape of bone being formed)
  2. Osteoid calcifies, blood vessels grow into cavities within matrix
  3. Osteoblasts use calcified matrix as support structure to lay down more osteoid and form trabecullae
  4. Osteoclasts break down spongy bone to create medullary cavity
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14
Q

How does bone strength over time (from initial formation)?

A

Initially bone material deposited with collagen fibres in random directions (called woven bone)

Overtime, converted into lamellar bone (stronger due to aligned fibres)

Osteoid initially calcifies to produce cancellous bone

Where cortical bone required, more deposition of osteoid increeases bone density

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15
Q

What is woven bone?

What is the reason for its name?

A

Bone material initially deposited with collagen fibres in random directions

Collagen fibres woven together randomly

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16
Q

Where do secondary ossification centres appear in long bones?

A

At either end of bone

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17
Q

What is found between the primary and secondary ossification centres in long bones?

What is this made of?

What happens to this as the bone grows?

What eventually happens to this as bone growth ceases?

A

Epiphyseal plate

Cartilage

Continues to form new cartilage and replaced by bone (the bone increases in length)

Mid 20’s : the plate is replaced by bone and no further growth

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18
Q

What are the reasons for remodelling of bone?

A
  1. Reshape skeleton during growth
  2. Maintain calcium levels in body
  3. Repair microfractures caused by stress
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19
Q

What are the 5 stages of bone remodelling?

A
  1. Quiesence - resting state of bone surface (lining cells - inactive osteoblasts on bone surface)
  2. Activation - osteoclasts on bone surface in small resorption pits (Howships lacunae)
  3. Resorption - osteoclasts remove old bone by removing the the mineral matrix and break down collagen fibres
  4. Reversal - resorption process ends. Osteoclasts replaced by osteoblasts
  5. Formation - osteoblasts lay down new bone:
    i. create a matrix of collagen (osteoid)
    ii. osteoblasts mineralise the matrix to form new bone
  6. Quiescence
20
Q

How does the process of remodelling cortical bone compare to remodelling trabecular bone?

A

Same process

Different geometry to form concentric lamellae in osteons

21
Q

Why is bone considered a responsive material?

A

Continuous resorption and formation of bone

Body responds to stress levels in different areas to ensure right amount of healthy bone is maintained and reshaped

22
Q

What factors cause a variation in bone properties?

A
  1. Age
  2. Gender
  3. Location in body
  4. Temperature
  5. Mineral content
  6. Amount of water present
  7. Disease e.g. osteoperosis
23
Q

What category of material does bone fall within?

A

Fibre composite (collagen fibres and inorganic matrix)

24
Q

What are the 5 types of loading (of bone)?

A
  1. Tension
  2. compression
  3. Torsion
  4. Bending
  5. Shear
25
Q

Explain stress

How is it calculated?

What are its units?

A

Load acting on material in body

Force/cross sectional area

Pascal or N/m2

26
Q

Explain strain

How is it calculated

What are its units?

A

Deformation experienced by material in a body

Change in dimension/Original dimension

No units

27
Q

What are 3 prefixes for increasing orders of numbers?

A

Kilo (k) - 1,000

Mega (M) - 1,000,000

Giga (G) - 1,000,000,000

28
Q

Define yield stress/strain

A

The level of stress/strain up to which strain is proportional to stress

29
Q

What is the name for the region for which strain is proportional to stress?

A

Elastic region

30
Q

Define ultimate stress/strain

A

Fracture point

The level of stress/strain at which fracture of the material occurs

31
Q

What measure is often used to define the strength of a material?

A

Ultimate stress

32
Q

What is the measure of stiffness of a material?

How is it calculated?

What are its units?

A

Young Modulus

Change in stress/Change in strain (within the elastic region)

Pa or N/m2

33
Q

How does osteoporosis affect the Youngs Modulus of bone?

What causes this?

A

Higher Young’s Modulus

More brittle

Lower bone mineral and therefore collagen content (which would otherwise allow bone to flex and bend)

34
Q

What does the Young’s Modulus of trabecular bone vary with?

A

Bone density squared

35
Q

What is the dominant form of linear elastic deformation in both high and low density trabecular bone?

A

Bending

36
Q

What two factors account for 70-95% of the variance in elastic constant of trabecular bone?

A

Density

Architecture

37
Q

What is the strength of trabecular bone proportionate to?

A

Density to the power of 3/2

38
Q

What does certain evidence suggest the mechanism of compressive failure by trabecular bone result from?

A

Elastic buckling rather than brittle crushing

39
Q

How does osteoporosis affect trabeculae in relation to modulus and strength?

A

10% reduction in trabeculae

leads to

70% reduction in modulus and strength

40
Q

What are the 2 mechanisms whereby osteoporosis affects modulus and strength of bone.

How do these two mechanisms compare in terms of impact?

A

Trabecular thinning as well as resorption

Resorption more severely reduces modulus and strength than uniform thinning

41
Q

What are the 3 methods of measuring bone density?

A
  1. Dual energy x-ray absorpitometry (DEXA)
  2. Ultrasound
  3. Quantitative computed tomography (QCT)
42
Q

What is the most common method of measuring bone density?

A

DEXA

43
Q

How is ultrasound used to measure bone density?

How does ultrasound compare to DEXA?

A

Usually performed at calcaneus (not poss. to measure at hip or spine).

Mainly measures bone mass rather than quality

Measurement at hip can predict hip fracture nearly as well ass DEXA

Using in combination with DEXA does not improve prediction of fractures

44
Q

What are the pros and cons of QCT compared to other methods of measuring bone density?

A
  1. Must be done following strict protocols in lab. (In-community setting reproducibility of results is poor)
  2. Greater radiation exposure
  3. Worse precision (partic. in older individuals)
  4. Can be used to study changes in cortical vs trabecular bone
45
Q

What are the 2 measure of bone quality?

A

T-score
- number of standard deviations for bone mineral density (e.g. as measured by DEXA) below average for young adult at peak bone density (differs depending on group of adults used as reference)

Z-score
- as above but with ref to average for a person of same age

46
Q

What is the WHO categorisation of bone density

What population is this based on?

A

Normal bone: T-score > -1

Osteopenia: T-score between -2.5 and -1

Osteoporosis: T-score < -2.5

Based on bone density in white women

Biomechanics 2D (6 decks)

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