Robertson: Biomechanics of Tendon, Bone, Cartilage, and Muscle

Question 1

What is this: direction, magnitude, point of application

Answer 1

force

Question 2

What is this: rotational force

Answer 2

torque

Question 3

Equation for torque

Answer 3

Torque = force * distance
T = rFsin(theta)

Question 4

Equation for stress

Answer 4

stress = force/area

Question 5

Two types of pressure and give an example of each

Answer 5

1. solid pressure
   ex: 70kg male standing on two feet with 100cm surface surface area for each foot. How much pressure under each foot? 36mPA
2. fluid pressure
   ex: compartment syndrome, blood pressure

Question 6

This can depict the relationship between the stress and strain that a particular material displays

Answer 6

stress/strain curve

Question 7

Three ways in which force can be applied to bone

Answer 7

1. bending
2. torsion (ends twisting in opposing directions)
3. compression (longitudinal)

Question 8

When plotting a curve of deformation vs load, what is the difference between the elastic region and the plastic region?

Answer 8

The elastic region is linear (it has a constant slope). The plastic region is when structural deformation occurs, and the slope of this portion of the curve changes.

Question 9

This region of the stress/strain curve has a constant slope

Answer 9

elastic region

Question 10

Two important points on a stress/strain curve

Answer 10

yield point

failure point

Question 11

This point on the stress/strain curve signals the end of the elastic region, and is the point at which structural changes occur to the specimen

Answer 11

yield stress or yield point

Question 12

This region on the stress/strain curve begins at the yield point and ends at the ultimate tensile strength. During this time, structural irreversible changes occur to the specimen.

Answer 12

plastic region

*think: plastic can undergo irreversible deformation, elastic does not

Question 13

What is this: mechanical properties INDEPENDENT of direction of stress. Ex: metal sphere

Answer 13

isotropy

Question 14

What is this: mechanical properties different in all directions of loading. Ex: typical of most living things.

Answer 14

anisotropy

Question 15

What is this: mechanical properties symmetric within two planes. Ex: long bone, axial/transverse loading

Answer 15

orthotropy

Question 16

What is this: cyclic loading leads to smaller differences between loading and unloading curves

Answer 16

hysteresis

Question 17

What is the yield point?

Answer 17

The point along the strain curve at which you end the elastic response

Question 18

What is the ultimate stress?

Answer 18

This is the failure point

Question 19

Explain how brittle material and ductile material differ in terms of what occurs after the yield point.

Answer 19

With a brittle material, the material will fail shortly after the yield point. Yield point and ultimate stress point would be close together. However, with a ductile material, it will not reach its ultimate stress point for a while after the yield point.

Question 20

What is failure strength?

Answer 20

As you increase number of cycles of loading, you will ultimately regress to fatigue strength.

Question 21

Functions of bone

Answer 21

dynamic metabolic bank (Ca+, Pi)
protects vital organs (skull, rib cage)
framework for skeletal motions
hematopoiesis

Question 22

What is the ratio of stress over strain, or the slope of the curve in the elastic region referred to as?

Answer 22

Youngs modulus

Question 23

What is this: a principle of physics that states that the force needed to extend or compress a spring by some distance is proportional to that distance

Answer 23

Hooke’s law

Question 24

What is this: bone remodels in response to stress placed on it

Answer 24

Wolff’s law

Question 25

The proximal and distal ends of the femur are what type of bone? The diaphysis of the femur is what type of bone?

Answer 25

trabecular; lamellar/cortical

Question 26

Which portion of the femur can bear axial loading and bending.

Answer 26

diaphysis

Question 27

Which portion of the femur is good for force transmission and hematopoiesis?

Answer 27

proximal/distal ends

Question 28

Which has a higher yield point: cortical bone or trabecular bone?

Answer 28

cortical bone

Question 29

Which type of bone can absorb significant energy with minimal mass?

Answer 29

trabecular bone

Question 30

Is bone strongest under compression or tension?

Answer 30

Strongest under compression, undergoes more of a change under tension

Question 31

Is bone more resistant to a longitudinal or transverse load? Does bone undergo more of a change under a longitudinal or transverse load?

Answer 31

More resistant to transverse load. Undergoes more of a change under a longitudinal load

Question 32

What is this: mechanical properties sensitive to strain rate and duration of applied loads

Answer 32

viscoelastic

Question 33

Bone is (blank) with slow loading, but (blank) with rapid loading

Answer 33

ductile; brittle

Question 34

What is this: continued deformation of a tissue that is subject to constant stress for an extended time

Answer 34

Creep

Question 35

What is this: the force necessary to maintain deformation decreases over time.

Answer 35

stress relaxation

Question 36

Give an example of stress relaxation

Answer 36

Imagine initially using a lot of force to hold a joint straight, but over time, as creep occurs and the fibers stretch, you’ll need less force to keep it straight.

Question 37

What is this: energy absorbed before ultimate failure

Answer 37

toughness

Question 38

What is this: ultimate strain substantially larger than yield strain

Answer 38

ductility

Question 39

Which has more toughness, a brittle fracture or a ductile fracture?

Answer 39

ductile fracture (more energy absorbed before ultimate failure, larger area under the stress/strain curve)

Question 40

What's the difference between senile and postmenopausal osteoporosis?

Answer 40

senile affects both males and females and is a reduction in both cortical and trabecular bone; postmenopausal osteoporosis affects subset of females and is a disproportional loss of trabecular bone

Question 41

In response to aging, what happens to trabecula? Is there more of a reduction in vertical trabecula or horizontal?

Answer 41

reduction in number of trabeculae (greater reduction in vertical trabecula) reduction in thickness of trabeculae increase in length of trabeculae

Question 42

How does loss of bone density affect the modulus (stress/strain curve in elastic region)?

Answer 42

modulus is reduced to a 2:1 ratio, slope equals 2

Question 43

List ways in which bone responds to aging

Answer 43

Decreases in density Decreases in cortical thickness But increase in diameter of diaphysis!!

Question 44

How do the axial and bending strengths change in response to aging?

Answer 44

axial strengths remain similar, but bending strength increases with age related diaphyseal expansion

Question 45

Properties of bone

Answer 45

viscoelastic (strain rate/duration affect properties) strong tough ductile or brittle

Question 46

Bone is strongest during (blank) and weakest in (blank)

Answer 46

compression; tension

Question 47

Bone volume (blank) with age, but (blank) with disuse

Answer 47

increases; decreases

Question 48

What happens to trabeculae with aging? What happens to diaphyseal bone?

Answer 48

trabeculae become fewer, longer, less vertical; diaphyseal bone enlarges and increases bending resistance

Question 49

Tendons have similar organization to a ligament. How do they differ in percentage of collagen? Percentage of ground substance? Longitudinal organization of collagen?

Answer 49

lower percentage of collagen higher percentage of ground substance less longitudinal organization of collagen

Question 50

What's the ultimate tensile strength of human tendons? | What's the ultimate strain?

Answer 50

50-105 MPa | 9-35%

Question 51

What does the stress/strain curve look like for tendons? What are the three regions?

Answer 51

Toe region, in which uncrimping of collagen fibers. Linear region in which slope is elastic modulus. Failure region which is permanent stretching

Question 52

T/F: Tendons have rate, time, and history dependent behavior.

Answer 52

True

Question 53

Do tendons undergo creep? What is...creep?

Answer 53

yes; time dependent elongation of tissue that is under constant force

Question 54

Do tendons undergo stress relaxation? What is stress relaxation?

Answer 54

yes; time dependent decrease in load when deformation is held constant

Question 55

What is this: area between loading and unloading curve. Energy loss due to internal friction. Can be given off as heat.

Answer 55

hysteresis

Question 56

What happens to the hysteresis of a tendon after a few cycles of loading and unloading?

Answer 56

first few cycles of loading and unloading create larger hysteresis, but hysteresis becomes minimal with repetitive loading

Question 57

4 zones as tendon inserts into bone. What are they?!

Answer 57

Zone 1: parallel collagen fibers Zone 2: unmineralized fibrocartilage Zone 3: mineralized fibrocartilage Zone 4: cortical bone

Question 58

In real life, tendons load less than (blank)% of ultimate stress

Answer 58

25%

Question 59

How does tendon strength change with age?

Answer 59

Tendon strength increases to maturity and then is rather constant

Question 60

In the rabbit study, what happened to failed ligaments in immature rabbits? What happened to failed ligaments in mature rabbits?

Answer 60

in immature rabbits, ligament failed and pulled away with a piece of bone (avulsion) in mature rabbits, ligament failed mid substance

Question 61

What happens to your ACL over time?

Answer 61

It gets weaker :(

Question 62

In the monkey ACL study in which monkeys were immobilized in a body cast, what happened to their strength over a years time?

Answer 62

With immobility ligament substance and ligament bone interface substantially weakened 8 wks immobilization resulted in 40% reduction in strength: one year to return to near normal

Question 63

What do corticosteroids do to maximum failure load?

Answer 63

After 15 wks, can reduce maximum failure load by 20%

Question 64

How does estrogen affect collagen production? What's a clinical application of this?

Answer 64

reduces it; during pregnancy, pubic symphysis becomes relaxed

Question 65

What happens to tendons when ya have diabetes?

Answer 65

They become weaker

Question 66

Are bone ligament bone auto grafts useful?

Answer 66

After about three years, only about 1/2 as strong as initial ligament strength

Question 67

Tendons and ligaments are (blank)

Answer 67

viscoelastic

Question 68

The in vivo strain rate for tendons and ligaments is far below the (blank)

Answer 68

ultimate failure load

Question 69

Severe negative mechanical effects are the result of (blank) of tendons/ligaments. Increase in mechanical strength with activity is not linear.

Answer 69

immobilization

Question 70

Do reconstructed tendons/ligament grafts reach native strength?

Answer 70

No

Question 71

What's this: muscle shortens against a constant load, muscle tension remains

Answer 71

isotonic contraction

Question 72

What's this: muscle contracts at constant velocity.

Answer 72

isokinetic contraction

Question 73

What's this: muscle length remains static as tension is generated.

Answer 73

isometric contraction

Question 74

What's this: muscle contracture with decreasing muscle length.

Answer 74

concentric contraction

Question 75

What's this: muscular contraction with increase in resting length. Resisting load is greater than muscle contraction force.

Answer 75

eccentric contraction

Question 76

What type of training increases oxidative capacity of type I fibers? What type of training increases cross sectional area of type II fibers?

Answer 76

endurance training; resistance training

Question 77

Articular cartilage is subject to high (blank) loads applied statically, cyclically, and repetitively over many years

Answer 77

compressive

Question 78

Properties of cartilage

Answer 78

must be fatigue resistant and tough soft, permeable 65-80% water biphasic: solid and fluid phase

Question 79

Three portions of cartilage architecture

Answer 79

superficial (tangential fibers) middle (oblique) deep (radial fibers - perpendicular)

Question 80

What does it mean that cartilage undergoes biphasic creep, or flow-dependent rate of creep?

Answer 80

rate of creep is governed by rate fluid is forced out of tissue

Question 81

Biphasic creep of cartilage is dependent on (blank) of tissue and stiffness of porous material

Answer 81

permeability

Question 82

What's the coefficient of friction in human joints?

Answer 82

0.002 to 0.004

Question 83

Cartilage load bearing is (blank) and cartilage has (blank) dependent creep

Answer 83

biphasic; flow

Question 84

What occurs in cartilage where fluid film has been depleted?

Answer 84

boundary lubrication