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PT 511 Biomechanics > L7 Introduction to mechanical behavior of biological materials- Biomechanics of Bones > Flashcards

L7 Introduction to mechanical behavior of biological materials- Biomechanics of Bones Flashcards

1
Q

How many bones are present in the adult human body?

A

206

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2
Q

How many bones are present in a new born?

A

270

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3
Q

Smallest bone in the human body?

A

Stapes

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4
Q

Stress (σ)

  • Define
  • Units
A
  • Force applied to deform a structure
    ◦ Force per unit area
    ◦ Measured in N/m2 or pascals
    ◦ σ = F/A
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5
Q

Strain (ε)

  • Define
  • Units
A

◦ Deformation caused by applied stress

◦ ε = ΔL/L

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6
Q

Elastic modulus (k)

  • Define
  • Formula
A

Stress-Strain Curve

  • Stiffness of a material
  • k = stress/strain (σ/ε )
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7
Q

Yield point

- Describe

A
  • Up to yield point, structure is in its elastic region

- Past the yield point is the structure’s plastic region

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8
Q

Failure

- Describe

A
  • If the applied force continues past the plastic region, the tissue will eventually fail.
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9
Q

Describe the Stress-Strain Curve

A
  • Stress is on the Y-axis
  • Strain is on the X-axis
  • The elastic region is mainly linear and is followed by the yield pt, which indicates the initiation of the plastic region
  • The end of the curve is failure.
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10
Q

Modulus of elasticity/Young’s modulus

- Define

A
  • Modulus of elasticity is a property of the material,
    not of the structure
  • Slope of the stress/strain plot = Modulus of
    elasticity
  • Can also be called Young’s modulus
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11
Q

Residual strain

A
  • Difference between original length and length resulting from stress into the plastic region
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12
Q

Safety factor

A
  • Engineers usually design structures to be able to withstand 5–10× typical stress on structure.
  • Similarly, the stresses placed on biological structures in everyday activities are much less than the
    structure can handle.
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13
Q

How many bones are in the spine?

A
  • 32 consisting of 7 cervical, 12 thoracic, 5 lumbar, 5 sacrum, 3 coccyx
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14
Q

If the weight of a person is 200lbs, the weight of bones is

A

~30lbs

Bones are 15% of body wt.

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15
Q

What are the degrees of freedom?

A 
3 linear
- Up/ Down
- Right/ Left
- Back/ Forward
Rotation
- Pitch
- Yaw
- Roll
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16
Q

Functions of the Skeleton

A
  • Leverage*
  • Support*
  • Protection
  • Storage
  • Blood cell formation
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17
Q

Which functions of the Skeleton are critical for movement?

A
  • Leverage*

- Support*

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18
Q

Describe protection (related to bone functions)

A
  • Brain

- Internal organs

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19
Q

Describe storage (related to bone functions)

A
  • Fat

- Minerals

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20
Q

Blood cell formation

- Where does it occur?

A
  • (Hematopoiesis)

- Occurs inside cavities of bone

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21
Q

Describe the architecture of bone

A
  • Bone: matrix of inorganic salts and collagen
  • Osteocytes
  • Osseous
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22
Q

Osteocytes

  • Define
  • What do they include?
A
  • bone cells
  • Osteoblasts: cells that create bone
  • Osteoclasts: cells that resorb bone
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23
Q

Osseous

  • Define
  • What does it include?
  • Describe each
A
  • bone tissue
  • Cortical: compact, very dense, outer layer, porosity = 5-30%
  • Cancellous: spongy, very porous, inner layer, porosity= 30-90%
24
Q

Types of Bones

A

Long
◦ Ulna, clavicle, femur

Short
◦ Tarsals, carpals

Flat
◦ Ribs, scapula, sternum

Irregular
◦ Skull, vertebrae

Sesamoid
◦ Patella

25
Q

Wolff’s Law

A

Bone is deposited and resorbed in accordance to the stresses placed upon it

  • resorption
  • deposition
26
Q

Describe Resorption

A

◦ Response to decreased stress
◦ Osteoclasts dominate
◦ Disuse, immobilization, microgravity

27
Q

Describe Deposition

A

◦ Response to increased stress
◦ Osteoblasts dominate
◦ Weight-bearing exercise

28
Q

Describe bones & Physical Activity

A
  • Bones require mechanical stress to grow and strengthen. - Loading → Deposition → Increased Density
29
Q

Which activities provide substantial mechanical stress to bones?

A

◦ Weight lifting
◦ Running
◦ Swimming
◦ Football

30
Q

Describe Osteoporosis

A
  • Resorption exceeds deposition
  • Increases risk of fracture
  • less density – reduction of 10 – 20% every decade after 55 years
  • more mineralized
  • more brittle
31
Q

What is osteoporosis related to?

A 
Hormonal factors (i.e., menopause)
◦ Nutritional imbalances (i.e., calcium intake)
◦ Lack of exercise
32
Q

What are the locations for likely fractures?

A

Results in fractures during low or moderate impacts: wrist, hip, vertebrae

33
Q

What is the female athlete triad ?

A

Disordered eating, amenorrhea, osteoporosis

34
Q

Bone is both ___ & ___

A

Ansiotropic and viscoelastic

35
Q

Anisotropic

A
  • Response depends on direction of load application
36
Q

Viscoelastic

A
  • Response depends on rate and duration of loading
37
Q

What are anisotropic properties of bone?

A
  • Compression (best), tension (intermediate), & shear (worst)
38
Q
  • What are the 2 types of materials?

- Describe them.

A

Elastic
- Linear relationship between stress and strain
Viscoelastic
- Nonlinear relationship between stress and strain
- Hysteresis: energy lost in a viscoelastic material

39
Q

Describe the types of materials curve

A
  • stress is on the y-axis
  • strain is on the x-axis
  • energy lost is in between the 2 arrows and energy recovered is underneath the curve
40
Q

Behavior of viscoelastic tissues is rate-dependent

A
  • If you apply a different rate of loading, you will see different elastic properties.
  • Viscoelastic tissues demonstrate creep and stress relaxation
41
Q

Creep

A
  • progressive strain under constant stress
42
Q

Stress/load relaxation

A
  • decreasing stress under constant strain
43
Q

Stress-Strain Curve for Human Bone

  • describe how it affects bone
  • describe how it behaves past its loading pt
A
  • Bone initially exhibits an elastic response
    ◦ Deformation in response to loading
    ◦ Load removed → Return to original shape/length
  • Continued loading past yield point → Plastic response
    ◦ Microtears and debonding
    ◦ Load removed → Permanently deformed

-Continued loading → Eventual fracture

44
Q

What are 2 ways that bone can fracture?

A
  • sudden increase in rate

- sudden increase in wt

45
Q

Define strength

A
  • Failure point or load sustained before failure
46
Q

Failure is caused by:

A
  • Single traumatic event

- Accumulation of microfractures

47
Q

Assessed by:

A
  • Energy storage

- Area under stress-strain curve

48
Q

Stiffness

A
  • Modulus of elasticity
  • Slope of the load deformation curve
  • Bone is flexible and weak
49
Q

Desc materials in terms of flexible/ strong; stiff/ strong; flexible/ weak; stiff/ weak

A

Flexible/ strong: fiberglass, silk

Stiff/ strong: steel, iron, gold

Flexible/ weak: spiderweb, BONE, oak, lead

Stiff/ weak: copper, glass

50
Q

Types of Loading

A

Compression
◦ Presses ends of bones together

Tension
◦ Pulls or stretches bone apart

Shear
◦ Parallel to the surface of object

Bending
◦ Applied to area having no direct support

Torsional
◦ Twisting force

51
Q

Describe bone structure

A
  • Made up of osteons/Haversian systems
  • Concentric lamellae of mineralized ground substance
    note rich blood supply
  • Note constant dynamic process of remodeling
52
Q

Desc loading in relation to bone, mm, and injury risk.

A
  • Bone adapts to changes in loading
  • High rate of loading → Injury risk
  • Muscles apply compression and tension
53
Q

What do Stress Fractures result from?

A
  • Resorption weakens bone
  • Deposition occurs too slowly
  • Results from:
    ◦ Repetitive muscle forces pulling on bone
    ◦ Muscle fatigue → Reduced shock absorption
  • 10% of injuries to athletes
54
Q

Bending

  • What does this result in?
  • Desc 3 pt bending.
A
  • Results in both tensile and compressive forces
  • Greatest stress in the middle of the bone
  • Boot-top fracture
55
Q

Describe the injury threshold.

A
  • load is on the y-axis and repetition is on the x-axis.

- high load & more repetitions = high injury risk

56
Q

What is cartilage?

A
  • Skeletal tissue–maintains certain shape and form
  • Very resilient (bouncy or rubbery), mostly water
  • Grows fast–forms embryonic skeleton
57
Q

Kinds of cartilage

A
  • Hyaline cartilage–most common, found in joints
  • Elastic cartilage–epiglottis, ear
  • Fibrocartilage–annular fibrosis of intervertebral disk, menisci of knee

PT 511 Biomechanics (1 decks)

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