Bone Biomechanics

Front 1

Biomechanical behavior of bone:

Loading Mode - bending

In bending the failure mechanism is the same as for what other two loading modes?

Back 1

tensile loading (one side)

compressive loading (other side)

Front 2

Biomechanical behavior of bone:

Loading Mode - bending

Is there stress or strain along the neutral axis in bending?

Back 2

there is NO stress or strain

Front 3

Biomechanical behavior of bone:

Loading Mode - bending

In bending where is the site of initial failure?

Back 3

differs based on the type of bending

Front 4

Biomechanical behavior of bone:

Loading Mode - bending

In bending tension stress occurs and compressive stress occurs. Which side do each of these stresses occur?

Back 4

tension stress occurs on convex side

compressive stress occurs on concave

Front 5

Biomechanical behavior of bone:

Loading Mode - bending

Where is stress the greatest and the least during bending?

Back 5

stress is the greatest at the periphery of the bone

stress decreases toward the center neutral axis

Front 6

Biomechanical behavior of bone:

Loading Mode - bending

What is 3-point bending?

Back 6

caused by the action of three parallel forces

(skiing boot-top fracture)

Front 7

Biomechanical behavior of bone:

Loading Mode - bending

What is 4-point bending?

Back 7

caused by two pairs of parallel forces

(muscle-force system)

Front 8

Biomechanical behavior of bone:

Loading Mode - bending

What is cantilever bending?

Back 8

caused by compressive loading offset from the longitudinal axis

(e.g. eccentric forces)

Front 9

Biomechanical behavior of bone:

Loading Mode - bending

Where does the failure occur in four-point bending?

Back 9

failure occurs at the weakest point between the two forces on the convex side, not necessarily at the midpoint

Front 10

Biomechanical behavior of bone:

Loading Mode - bending

Where does failure occur in cantilever bending?

Back 10

failure occurs at the weakest location or the location of greatest stress on the tension side

Front 11

Biomechanical behavior of bone:

Loading Mode - Torsion

During torsion shear stresses are distributed where?

Back 11

over the entire structure

Front 12

Biomechanical behavior of bone:

Loading Mode - Torsion

What does a torsion fracture pattern suggest?

Back 12

fails first in shear

initial crack forming parallel to neutral axis

secondary cracks form along the plane of maximal tensile stress

Front 13

Biomechanical behavior of bone:

Loading Mode - combined loading

In weight bearing on a single limb, why would there be a tension load on the tibia?

Back 13

The tibia is bending

probably cantilever bending

Front 14

Biomechanical behavior of bone:

Loading Mode - influence of muscle activity

What influence does muscle activity have on the bone?

Back 14

decreases tensile stress

increases compressive stress

absorbs energy

Front 15

Biomechanical behavior of bone:

Loading Mode - influence of muscle activity

How can muscle contraction protect bone?

Back 15

converts tensile stresses due to bending into compressive stress

Front 16

Biomechanical behavior of bone:

Loading Mode - strain rate dependency

Bone is stiffer, stronger & stores more energy at __________________

Back 16

faster strain rates

Front 17

Biomechanical behavior of bone:

Loading Mode - fatigue (load - repetition) curve

a mechanism of high load and a low number of repetitions

Back 17

acute injury

Front 18

Biomechanical behavior of bone:

Loading Mode - fatigue (load - repetition) curve

a mechanism of low or low-moderate load and high number of repetitions

Back 18

overuse injury

Front 19

Biomechanical behavior of bone:

Loading Mode - fatigue (load - repetition) curve

Common sites of stress fracture

Back 19

lumbar vertebrae

femoral head

proximal tibia

calcaneus

metatarsals

Front 20

What type of bone is considered layered mature bone?

Back 20

lamellar bone

Front 21

What is the difference between collagen fibers in lamellar bone and woven bone?

Back 21

- collagen fibers within a lamella are organized and aligned

- woven bone contains relatively few number of collagen fibers that are randomly oriented

Front 22

which bone is stronger lamellar bone or woven bone?

Back 22

lamellar bone

Front 23

In lamellar bone, collagen in adjacent lamellae are oriented in an opposing patter to assist the bone in resisting _________ forces

Back 23

torsional

Front 24

In modeling (new bone formation) when does lamellar bone begin to form?

Back 24

1 month after birth and it replaces woven bone

Front 25

In remodeling ( reorganization of existing bone) does lamellar bone replace woven bone?

Back 25

yes, it slowly replaces woven bone

- e.g. replaces a fracture callus

Front 26

What is required for lamellar bone to form?

Back 26

a pre-existing structure or model of either cartilage or woven bone on which to form

Front 27

Which, Cortical or Cancellous bone is considered lamellar bone?

Back 27

both are considered lamellar bone

Front 28

Considered immature bone

Back 28

woven bone

Front 29

How are collagen fibers organized in woven bone? ( 3 characteristics)

Back 29

there are few # of collagen fibers

less organized

randomly oriented

Front 30

What is required for woven bone to form?

Back 30

it doesn't require pre-existing cartilage model to form

Front 31

Where can woven bone be found?

Back 31

in embryo, newborn, fracture callus, metaphysis of growing bone and sometimes diseased bone

Front 32

Biomechanically, bone tissue behaves as a two-phase (biphasic) composite material.

Describe the two phases.

Back 32

phase 1 = mineral

phase 2 = collagen and ground substance

Front 33

What are the 3 most important mechanical properties of bone?

Back 33

1. strength

2. stiffness

3. energy storage

Front 34

Bone is viscoelastic tissue. Making it's mechanical behavior time-dependent.

What 4 characteristics does it exhibit

Back 34

1. hysteresis

2. strain-rate dependency

3. creep

4. stress relaxation

Front 35

Relative to stress-strain, strength can be viewed in different ways.

Name the different ways (3)

Back 35

1. stress at ultimate failure

2. strain at ultimate failure

3. energy stored

Front 36

Cortical bone tested in tension exhibits what about the elastic region, plastic region, energy stored and stiffness

Back 36

1. elastic region - nearly linear

2. plastic region - significant

3. energy - a lot of energy stored

4. stiffness - considered stiff

Front 37

Under compression forces, cortical bone vs. cancellous bone have some differences in regards to stress and strain.

What are those differences?

Back 37

Stress - cortical bone is more dense and harder, thus making it stiffer and stronger than cancellous bone. Meaning cortical bone can handle a greater amount of stress than cancellous

Strain - cancellous can handle a greater amount of strain and stores more energy

Front 38

Strain values for cancellous bone and cortical bone, in vitro?

Back 38

Cancellous bone = 50%

Cortical bone = 1.5%

Front 39

When comparing the values of strength (stress) for cortical, cancellous and tendon/ligament

rank them from greatest strength to least.

Back 39

1. cortical bone

2. tendon/ligament

3. cancellous bone

Front 40

When comparing the values of modulus (stiffness) for cortical, cancellous and tendon/ligament

rank them from greatest strength to least.

Back 40

1. cortical bone

2. tendon/ligament

3. cancellous bone

Front 41

When comparing the values of elongation (strain) for cortical, cancellous and tendon/ligament

rank them from greatest strength to least.

Back 41

1. tendon/ligament

2. cancellous bone

3. cortical bone

Front 42

Cortical bone demonstrates anisotropic behavior when tested in tension on different axes.

When does cortical bone stronger, stiffer and stores the most energy?

Back 42

When the load is parallel to the long axis

Front 43

Cortical bone demonstrates anisotropic behavior when tested with different modes of loading.

Under what mode of loading is cortical bone the strongest. Rank from strongest to weakest.

Back 43

1. compression

2. tension

3. shear

Front 44

Cancellous bone demonstrates anisotropic behavior when tested with different modes of loading.

Under what mode of loading is cancellous bone the strongest. Rank from strongest to weakest.

Back 44

1. compression

2. tension

Front 45

when does cortical bone and cancellous bone demonstrate anisotropic behaviors?

Back 45

Cortical bone - along different axes & different modes of loading

Cancellous bone - different modes of loading

Front 46

What are the 5 factors that influence biomechanical behavior of bone?

Back 46

1. loading mode

2. muscle activity

3. rate of loading

4. repetitive loading & fatigue

5. bone geometry

Front 47

Biomechanical behavior of bone:

Loading Mode - Tension

- maximal tensile stress occurs on a plane _____to the applied load (axial stress)

Back 47

perpendicular

Front 48

Biomechanical behavior of bone:

Loading Mode - Tension

in cortical bone, failure is due to what?

Back 48

debonding at cement lines, pulling out of osteons, and microfracture

Front 49

Biomechanical behavior of bone:

Loading Mode - Tension

Tensile fractures are most common in what type of bone?

Back 49

cancellous bone

e.g. muscle contraction

Front 50

What are two common sites of tensile fractures?

Back 50

5th metatarsal at the peroneus brevis attachment

calcaneus at the calcaneal tendon attachment

Front 51

Biomechanical behavior of bone:

Loading Mode - Compression

maximal compressive stress occurs on a plane _____ to the applied load (axial stress)

Back 51

perpendicular

Front 52

Biomechanical behavior of bone:

Loading Mode - Compression

in cortical bone, failure is due to what?

Back 52

oblique cracking of osteons or cracking of interstitial lamellae

Front 53

Biomechanical behavior of bone:

Loading Mode - Compression

Compression fractures commonly occur?

Back 53

in elderly vertebrae

any bone under extreme load

Front 54

Compression failure of bone results in a stable or unstable fracture?

Back 54

stable

Front 55

Tensile fractures of bone results in a stable or unstable fracture?

Back 55

unstable

Front 56

Biomechanical behavior of bone:

Loading Mode - shear

maximal shear stress occurs on a plane _____ to the applied load

Back 56

parallel

Front 57

Biomechanical behavior of bone:

Loading Mode - shear

During compressive and tensile loading shear stress also occurs. This is an example of ____

Back 57

angular deformation

Front 58

Biomechanical behavior of bone:

Loading Mode - shear

In cortical bone, failure is due to what?

Back 58

perpendicular cracking of osteons

Front 59

Biomechanical behavior of bone:

Loading Mode - shear

Where does a shear fracture most often occur?

Back 59

in cancellous bone

e.g. shear injuries to femoral condyles and tibial plateau

Front 60

Shear failure of bone results in a stable or unstable fracture?

Back 60

unstable

Front 61

Biomechanical behavior of bone:

Loading Mode - Bending

During 3-point bending where does the fracture (failure) occur?

Back 61

occurs on the tension side at a point opposite the middle force application

Front 62

What determines a bone's strength in bending?

Back 62

it's size and shape

Front 63

In torsion, maximal shear stress act on planes _____ and _______ to the neutral axis

Back 63

parallel and perpendicular

Front 64

At faster strain rates the bone will demonstrate what property?

Back 64

brittle

Front 65

Explain how strain rate influences injury pattern

Back 65

at fast strain rates, bone stores a lot of energy. When the tissue fails, the energy is released and influences the amount and pattern of soft tissue damage. The bone fragments under high energy loading to failure cause more damage of the surrounding soft tissue

Front 66

Biomechanical behavior of bone:

Loading Mode - fatigue (load - repetition) curve

When does chronic injury occur?

Back 66

if the frequency of loading results in the rate of failure proceeding faster than the rate of repair

Front 67

Biomechanical behavior of bone:

Effects of Geometry - Interaction w/loading mode

A larger _______ results in a stronger and stiffer bone in tension and compression.

Back 67

a larger cross sectional area

Front 68

Biomechanical behavior of bone:

Effects of Geometry - Interaction w/loading mode

A larger __________results in a stronger and stiffer bone in bending

Back 68

a larger area moment of inertia

Front 69

Biomechanical behavior of bone:

Effects of Geometry - Interaction w/loading mode

What is polar moment of inertia?

Back 69

the resistance to torsional loading about the longitudinal axis ( for a hollow tube)

Front 70

Biomechanical behavior of bone:

Effects of Geometry - Interaction w/loading mode

A larger __________ results in less stress for the same externally applied torque

Back 70

a greater polar moment of inertia

Front 71

A torsional fracture of the tibia commonly occurs at what part of the tibia?

Back 71

at the distal part because the radius and smaller polar moment of inertia

Front 72

After a fracture, callus formation(woven bone) plays what role in the healing of the bone?

Back 72

acts to stabilize the area and increase both the area and polar moments of inertia;

the healing bone can now maintain strength and stiffness in bending and torsion

Front 73

Biomechanical behavior of bone:

Effects of Geometry - Length

A longer bone will have a greater bending moment and thus experience __________ stress

Back 73

greater stress

Front 74

Biomechanical behavior of bone:

Effects of Geometry - discontinuity (stress risers)

discontinuities cause what to occur in bone?

Back 74

cause concentrations of stress called stress risers

Front 75

How can a bone develop stress risers?

Back 75

occur naturally (e.g. tendon/ligament attachments)

caused due to injury

caused due to surgery (e.g. bone section removed or fixator screw inserted)

Front 76

What affect can a stress riser due to surger have on a bone?

Back 76

weakens the bone especially under torsional loading possibly decreasing bone strength up to 60%

Front 77

What happens to the energy storage in bone with discontinuity?

Back 77

reduced energy storage (strength)

Front 78

How long does it take to recover full strength after screws or holes present in rabbit femur?

Back 78

up to 7-8 weeks due to bone remodeling

Front 79

An open defect in bone weakens the bone especially with what type of loading?

Back 79

torsional

Front 80

How much does the load - deformation relationship change in bone with an open defect?

Back 80

up to 90% decrease in energy storage and load to failure

up to 70% decrease in deformation at failure

Front 81

Net increase in bone mass that occurs during the growth process

Back 81

modeling

Front 82

the adaptation of bone to maintain, increase or decrease bone mass in response to the loading environment

Back 82

remodeling

Front 83

Modeling is driven by ______________ factors

Remoding is driven by ______________

Back 83

modeling = systemic factors

remodeling = local strain state detected by osteocytes

Front 84

Describes the nature of remodeling in response to the mechanical (strain) environment

Back 84

Wolff's Law

Front 85

3 main components of Wolff's Law

Back 85

1. bone will attempt to maintain optimal strength with minimal stress

2. bone adapts to its functional environment

3. bone adaptation is ordered and can be described mathematically

Front 86

what affect does bed rest have on bone?

Back 86

bed rest decreases bone mass by 1% / week

but limited to an overall loss of 32%

full recovery of bone mass may not occur even after 1 year of return to activity

Front 87

After being immobilized for 60 days there is a notable difference in what bone properties

Back 87

strength, stiffness and energy storage

Front 88

during bed rest where does the greatest loss of BMD occur

Back 88

in weight bearing bones

Front 89

A normal part of the aging process to bone is what?

Back 89

bone loss

Front 90

Osteoporosis has what affect on bone loss

Back 90

accelerates bone loss

Front 91

What is actually happening to the trabeculae of bone?

Back 91

longitudinal trabeculae becomes thinner

some transverse trabeculae becomes reabsorbed

Front 92

peak bone mass occurs at about what age

Back 92

30-35 in both men and women

Front 93

At what rate is bone mass lost

Back 93

men lose bone mass .5-.75% per year

women lose bone mass 1.5% per year

Front 94

Over several decades of life, how much does cancellous and cortical bone mass decrease?

Back 94

cancellous = 50%

cortical = 25%

Front 95

At the same BMD which type of bone is better in quality? older bone or younger bone

Back 95

younger bone

Front 96

What % of bone is inorganic, water and organic?

Back 96

inorganic = 60%

Water = 10%

organic = 30%

Front 97

What type of collagen is in bone?

Back 97

type 1 collagen

Front 98

What determines if bone's mechanical behavior

Back 98

composition and organization

Front 99

What makes bone one of the hardest structures?

Back 99

it's high concentration of inorganic mineral salts makes tissue hard and rigid

Front 100

What is harder than bone?

Back 100

dentin and enamel in teeth

Front 101

Bones are highly vascular and metabolically active (T/F)

Back 101

true

Front 102

Bone composition can vary. What factors influence bone composition?

Back 102

bone site

individuals' age

dietary history

disease

Front 103

There is a gelatinous ground substance that surrounds the mineralized collagen fibers, acting as a cementing agent.

What does this ground substance consist of ?

Back 103

protein polysaccarides called glycosaminoglycans

Front 104

What are glycosaminoglycans?

Back 104

primarily in the form of complex macro-molecules called proteoglycans

Front 105

Name two types of bone

Back 105

cortical and cancellous

Front 106

Concentric rings of mineralized matrix

Back 106

lamellae

Front 107

system of lamellae surrounding a central channel containing blood vessels and nerves

Back 107

osteon or haversian system

Front 108

cavities in the tissue where mature bone cells reside

Back 108

lacunae

Front 109

where do osteocytes reside

Back 109

lacunae

Front 110

name 3 types of bone cells

Back 110

osteocytes, osteoblasts, osteoclasts

Front 111

join adjacent osteons;

Back 111

cement lines

Front 112

Why are cement lines weaker than surrounding tissue?

Back 112

weaker than surrounding tissue because collagen fibers do no cross cement lines

Front 113

lamellae that span the regions between complete osteons; they are comprised of the same material but in a different geometric configuration

Back 113

interstitial lamellae

Front 114

rod or plate like structures that make up bone

Back 114

trabeculae

Front 115

what fills the inner space of trabeculae

Back 115

red marrow

Front 116

Name 2 bone coverings

Back 116

periosteum

endosteum

Front 117

two layer dense fibrous membrane that covers the outside of the bone everywhere except the joint surfave

Back 117

periosteum

Front 118

Describe the two layers of the periosteum

Back 118

outer layer= fibrous containing blood vessels and nerves

Inner layer = is osteogenic and contains osteoblasts

Front 119

the connective tissue layer that covers the trabeculae; it contains the osteoclasts and osteoblasts

Back 119

endosteum

Front 120

does trabeculae have haversian canals?

Back 120

No

Front 121

How is trabeculae arranged?

Back 121

in concentric lacunae - containing lamelle

Front 122

middle or main section of the shaft of long bone

Back 122

diaphysis

Front 123

end of long bone

Back 123

epiphysis

Front 124

region joining the diaphysis to the epiphysis

Back 124

metaphysis