Detroit Medical Center - Biomech1

8/13/2019 Detroit Medical Center - Biomech1

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Concepts in OrthopaedicBiomechanics

Basic Science LecturesDepartment of Orthopaedic Surgery

Detroit Medical Center

Michele J. Grimm, Ph.D.Director of Orthopaedic Biomechanics


2/84

Mechanical Concepts -- Force

Force: A vector quantity that describes the

action of one body on another

Three attributes must be defined

Magnitude

Direction

Point of Action

Forces can either be normal or shear in

nature

Normal forces act perpendicularly

to a surface

Shear forces act tangentially to a

surface

Newton's Second Law:

F = m*a


3/84

Mechanical Concepts --

Compression and Tension

Compression: defined most simply as a "squeeze"

When a force is applied to an object to squeeze it, the

object is deformed (shortened) along the direction of

the compressive force while expanding perpendicular to

the force.

Tension: opposite of compression, or a "pull"

When a force is applied to pull a fixed object, the object

is lengthened along the direction of the tensile force

while being reduced in size in the direction

perpendicular to the force.


4/84

Mechanical Concepts -- Stress

Stress: Force normalized to cross-sectional area to

eliminate the effect of geometry

Units of force/area

Newtons/square meter (N/m2

) or pascals (Pa) Pounds/square inch (psi)

1 TON

Area

1 TON

Area

1 TON

Area


5/84

Mechanical Concepts -- Strain

Strain: The change in length of a material divided by its

original overall length

Strain is dimensionless and is often expressed as

percent strain

Ten percent strain means an object has been deformed

by one tenth of its original length

L D L L D L


6/84

Mechanical Concepts -- Elastic Modulus

Elastic Modulus: Ratio of stress to strain at any point in

the elastic (linear) region of deformation (small strains)

Also known as modulus of elasticity or Young's modulus

Units of stress/strain (Pascals/dimensionless = Pascals) Often (incorrectly) referred to as stiffness

True stiffness is defined as the change in force per

change in length and is given in units of force/length

Stiffness is dependent both on the material’s elasticmodulus and the object’s geometry


7/84

Mechanical Concepts -- Elastic Modulus

Determined as the slope of thelinear portion of the stress-strain

curve

Higher elastic modulus

indicates that more stress isrequired to deform a material

Ex: A compressive load is

applied to functional spinal unit

(a disc and 2 vertebral bodies).The vertebral body has a higher

elastic modulus than the disc.

Therefore, the disc deforms to a

greater extent than the vertebral

bodies.

Strain

Stress

Ds De

E = Ds De


8/84

Question 1

The deformation of a material as a result of an applied load

is referred to as:

(1) Stress

(2) Strain

(3) Plasticity

(4) Elasticity

(5) Viscoelasticity


9/84

Question 1

The deformation of a material as a result of an applied load

is referred to as:

(1) Stress

(2) Strain

(3) Plasticity

(4) Elasticity

(5) Viscoelasticity


10/84

Question 2

The stress produced when a force acts in line with a

surface is:

(1) Shear

(2) Torque

(3) Tension

(4) Elasticity

(5) Compression


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Question 2

The stress produced when a force acts in line with a

surface is:

(1) Shear

(2) Torque

(3) Tension

(4) Elasticity

(5) Compression


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Question 3

In the Figure, which material has the highest modulus of

elasticity?

Stress

Strain

5

4

1

2

3


13/84

Question 3

In the Figure, which material has the highest modulus of

elasticity?

Stress

Strain

5

4

1

2

3


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Mechanical Concepts -- Mechanical Models

Behavior of materials fits into a combination of three

categories

Elasticity is characterized by

Full recovery of deformation when a load is removed

Instantaneous reaction to a force application

Linear relationship between force and deformation

Time

0

ForceOn

ForceOff

Deformation

Time

Force

0

Deformation

Force


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Mechanical Models

Plasticity is characterized by

Resistance of a body to deformation after a critical

(yield) stress is reached

After deformation begins, it continues to occur withoutincreased stress

Plastic deformation is not recoverable

Time

0

Force

On

Force

Off Deformation Force

0

Critical Force

Time


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Mechanical Concepts -- Mechanical Models

Viscosity is characterized by

Time/rate dependence of stress-strain

response

Higher rate of force application

requires higher stress to give desired

deformation Conversely, a given deformation at a

higher strain rate results in an

increased force

Response to stress is not instantaneous

A constant load applied to a viscous

element will cause continuous

deformation until the load is

removed

Deformation is not recoverable

Force

Rate of Deformation

Force

Time

Deformation

F1 F2

F3 F1>F2>F3


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Question 4 The Figure represents the behavior of a material

characterized as

(1) linearly elastic

(2) linearly elastic, linearly plastic

(3) linearly elastic, perfectly plastic

(4) rigid, linearly plastic

(5) rigid, perfectly plastic s

e


18/84

Question 4 The Figure represents the behavior of a material

characterized as

(1) linearly elastic

(2) linearly elastic, linearly plastic

(3) linearly elastic, perfectly plastic

(4) rigid, linearly plastic

(5) rigid, perfectly plastic s

e


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Mechanical Concepts -- Strength and Failure

Ultimate Strength: Maximum stress amaterial supports before failure

NOTE: The elastic modulus and

ultimate strength of a material are not

necessarily related

Yield Strength: The stress at the pointwhere the stress-strain curve undergoes a

transition from linear to non-linear behavior

Typically the transition between elastic

and plastic behavior or the start of plastic deformation in a purely plastic

material

Rupture: Point at which failure occurs and

stress subsequently goes to zero

Rupture

su

sy X

e

s


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Question 5

The Figure shows the stress-strain relationship for a

material loaded in uniaxial tension. The ultimate tensile

strength of this material is defined by which point?

s

e

X

• • •

•

A B

C D E


21/84

Question 5

The Figure shows the stress-strain relationship for a

material loaded in uniaxial tension. The ultimate tensile

strength of this material is defined by which point?

s

e

X

• • •

•

A B

C D E


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Mechanical Concepts - Ductility

Ductility: Total strain to failure

A ductile material will undergo considerable plastic

deformation resulting in greater strains before rupture

occurs

A brittle material (low ductility) will fail soon after the

elastic limit is reached

X X

s

e

Brittle

Ductile


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Mechanical Concepts -- Energy Absorption

Energy Absorption: The area under a load-deformation

curve indicates the amount of strain energy absorbed by

the material during deformation

A portion of the energy may be stored in the material and

is recoverable once the stress is removed

For a purely elastic material, all of the stored strain energy

is recovered


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Most materials have a viscous component to their behavior, sosome of the absorbed energy is lost, through conversion to heat,

on removal of the stress

Lost energy is indicated by the area between the loading and

unloading curves on a stress-strain plot

This loss of a portion of energy for elastic deformation is

termed hysteresis

The greater the amount of viscous behavior in a material, the

greater the amount of energy lost

s

e

s

e

s

e


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Energy absorbed during plastic deformation is unrecoverable

If plastic deformation proceeds to fracture, the total area under the

load-deformation curve is the energy absorbed

If the load is removed, the material may return partially to its

original state, with recovery of the elastic deformation. However,the plastic deformation will not be recovered and the energy lost

will be greater than for only elastic deformation

F

L

F

L


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Question 6

The energy absorbed by a specimen during a load-to-

failure test is determined by calculating the

(1) slope of the load-deformation curve

(2) hysteresis of the stress-strain curve

(3) load at failure multiplied by strain at failure

(4) area under the load-elongation curve

(5) slope of the stress-strain curve


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Question 6

The energy absorbed by a specimen during a load-to-

failure test is determined by calculating the

(1) slope of the load-deformation curve

(2) hysteresis of the stress-strain curve

(3) load at failure multiplied by strain at failure

(4) area under the load-elongation curve

(5) slope of the stress-strain curve


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Mechanical Concepts -- Fatigue

Fatigue Fracture: Results from repetitive loading cyclesthat produce stresses at lower levels than the ultimate stress

Dependent both on level of stress and number of cycles

Begins with a set of microscopic cracks that propagate and

cause failure under repeated loading A material is defined by an endurance limit, a stress up to

which it can withstand an infinite number of cycles of

loading


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Mechanical Concepts -- Fatigue

Above the endurance limit, material behavior can beassessed by an S-n curve relating stress to number of

cycles

Based on experimental evidence

Fatigue can be exacerbated by processes such as corrosionand therefore cannot be expected to be the same for a

material in a physiological environment as it was in a

bench test

"S-n curve"

S t r e s s ( p s i )

125000

100 10 1 0.1 0.01

Endurance Limit

Number of Cycles (millions)


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Behavior of Materials

Bone can fracture as a result of a single, high stress (traumaticfracture)

Bone is also exposed in vivo to repetitive stresses of various

levels

Repeated loading of daily activities can result in microdamageMicro-cracks in both the cortical and trabecular bone

If microdamage accumulates faster than it can be repaired by

physiological processes, the cracks may propagate and result

in fracture of the bone This is fatigue fracture

This is the proposed mechanism behind stress fractures and

atraumatic fractures, such as occur in the vertebrae


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Behavior of Materials -- Viscoelasticity

Actual materials often exhibit viscoelastic behavior

A combination of purely elastic and viscous behavior discussed

above

Bone, cartilage, ligaments, and muscle are all viscoelastic to

varying extents

Ex. Bone or ligament is more likely to rupture or fracture if a

load is applied quickly, such as in an impact situation. The

deformation may be the same for other loading conditions;

however, the high strain-rate results in a higher stress being

required to produce the deformation and the stress may then be greater than the ultimate strength of the structure.

Stress is partially dependent on strain-rate and the strain itself

can change with time for a constant stress

Viscoelastic behavior can be described with two basic models


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Behavior of Materials -- Viscoelasticity Model 1: Maxwell Body

Creep: Slow, continuingdeformation with time

under a constant stress

Ex: The loss of spinal

height over the courseof a day is a result of

creep behavior in the

spine, primarily in the

intervertebral discs Stress Relaxation:

Reduction in measured

stress with time for a

constant strain

D e f o

r m a t i o n

Time

Force

On

Force

Off

ElasticRecovery

Force

Time

Force

On

Force

Off

D e f o r m a t i o n

Time

Structure Deformed

Time

Force

Structure Deformed


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Behavior of Materials -- Viscoelasticity Model 2: Kelvin Body or Voigt Element

No instantaneous response to stress due todash-pot effect

Deformation characterized by initial creep behavior

which is limited by the extension limit of the spring

for that loadRecovery after removal of the load is gradual but

complete due to the tendency of the spring to return to

its original length

Deformation

Time

ForceOn

ForceOff

0

Force

Time

ForceOn

ForceOff


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Question 7

Strain of a material beyond its elastic limit is defined as

(1) Fatigue

(2) Relaxation

(3) Plastic deformation

(4) Creep

(5) Stretching


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Question 7

Strain of a material beyond its elastic limit is defined as

(1) Fatigue

(2) Relaxation


(4) Creep

(5) Stretching


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Question 8

A material is subjected to a constant load and is found to

deform with time. The deformation-time curve for this

material approaches a steady state with time. The behavior

of this material is termed

(1) Elastic deformation


(3) Creep

(4) Anisotropic deformation

(5) Ductility


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Question 8

A material is subjected to a constant load and is found to

deform with time. The deformation-time curve for this

material approaches a steady state with time. The behavior

of this material is termed

(1) Elastic deformation


(3) Creep

(4) Anisotropic deformation

(5) Ductility


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Question 9

The deformation of a material with respect to its original

shape as a result of an applied load is referred to as:

(1) Stress

(2) Strain

(3) Elasticity

(4) Plasticity

(5) Viscoelasticity


39/84

Question 9

The deformation of a material with respect to its original

shape as a result of an applied load is referred to as:

(1) Stress

(2) Strain

(3) Elasticity

(4) Plasticity

(5) Viscoelasticity

(3, 4, 5) related to the modulus


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Question 10

The resistance of a material to deformation from an applied

load is called:

(1) Tolerance

(2) Stiffness

(3) Elasticity

(4) Viscoelasticity

(5) Plasticity


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Question 10

The resistance of a material to deformation from an applied

load is called:

(1) Tolerance

(2) Stiffness

(3) Elasticity

(4) Viscoelasticity

(5) Plasticity


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Behavior of Materials Actual materials are based on a

combination of elastic andviscoelastic elements

Biological materials such as

ligament, tendon, or other soft

tissues exhibit the followingdeformation-time response

This behavior can be explained

most simply by the following

model A plastic element should also be

added to the model to account

for plastic deformation at high

stresses

Time

D e f o r m a t i o nForce

On ForceOff


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Mechanical properties of a material can be dependent on the

direction of loading

Behavioral differences are typically related to the structural

organization of the material

Bone, ligaments, and other tissues have obvious fiber or

structural orientations

Properties are different for forces applied parallel and

perpendicular to those structural orientations

This directional dependence is termed anisotropy


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Mechanical properties can also vary depending upon the

mode of loading

Elastic modulus and strength can be different for the

same material when loaded in compression, tension,

and shear


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Question 11

Which of the following is a characteristic property of

viscoelastic materials:

(1) The material is anisotropic

(2) Deformational behavior is independent of time

(3) Deformational behavior is independent of the

applied strain rate

(4) During constant deformation, the internal stress is

gradually increased

(5) During application of a constant load, the material

gradually deforms


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Question 11

Which of the following is a characteristic property of

viscoelastic materials:

(1) The material is anisotropic

(2) Deformational behavior is independent of time

(3) Deformational behavior is independent of the

applied strain rate

(4) During constant deformation, the internal stress is

gradually increased

(5) During application of a constant load, the material

gradually deforms


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Question 12

A material that has the same mechanical properties in all

directions is referred to as:

(1) Plastic

(2) Ductile

(3) Elastic

(4) Isotropic

(5) Viscoelastic


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Question 12

A material that has the same mechanical properties in all

directions is referred to as:

(1) Plastic

(2) Ductile

(3) Elastic

(4) Isotropic

(5) Viscoelastic


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Properties of Bone

Bone is a two-phase, anisotropic and viscoelastic material

which can react to stresses with self-repair and self-

adaptation

Cortical and trabecular bone have different mechanical

properties, based predominantly on the different densitiesof the material

Cortical bone has an apparent density (mass of bone per

total unit volume) of approximately 1.8 g/cm^3

Trabecular bone has an apparent density ranging from0.1 to 1.0 g/cm^3 depending upon the porosity of the

bone, which varies based on anatomic site and between

individuals


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Properties of Bone

Both cortical and trabecular bone have a higher ultimatestrength in compression than in tension

Both cortical and trabecular bone are anisotropic, with

higher ultimate strength and higher elastic modulus in the

direction of predominant structure orientation Changes in bone composition due to disease affect

properties:

A reduction in bone mineralization results in more

ductile, less stiff bones with reduced compressivestrength and elastic modulus

A reduction in bone protein composition results in more

brittle, harder bones with reduced tensile strength and

increased elastic modulus


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Effect of Age on Bone Properties

Changes due to age can affect bone mechanical properties

through both structural changes and changes in material

properties

Aging results in both cortical and trabecular bone becoming

more porous

Strength and elastic modulus are both dependent on the

amount of bone present (increased porosity --> reduced

strength and modulus)

In trabecular bone, strength and elastic modulus are also

dependent on how the trabecular material is lost

An overall thinning of trabeculae will result in different

changes in mechanical properties than if some trabeculae

are lost completely while others maintain their thickness


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Effect of Age on Bone Properties

Aging also results in less ductile bone (more brittle)

The maximum strain to failure is reduced as is the

ability of bone to absorb energy


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Question 13

A long bone is anisotropic because

(1) its material properties are strongest in tension

(2) its material properties have a directional preference

along the long axis

(3) its dimensions are not the same in all directions

(4) it contains an intramedullary canal

(5) it is a porous structure


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Question 13

A long bone is anisotropic because

(1) its material properties are strongest in tension

(2) its material properties have a directional preference

along the long axis

(3) its dimensions are not the same in all directions

(4) it contains an intramedullary canal

(5) it is a porous structure


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Question 14

Which of the following is the best description of the

mechanical properties of wet compact bone in humans?

(1) Isotropic

(2) Brittle

(3) Fatigue-resistant

(4) Strain-rate dependent

(5) Strongest in tension


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Question 14

Which of the following is the best description of the

mechanical properties of wet compact bone in humans?

(1) Isotropic

(2) Brittle

(3) Fatigue-resistant

(4) Strain-rate dependent

(5) Strongest in tension


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Question 15

What effect does demineralization have on the

biomechanical properties of bone?

(1) Increases toughness

(2) Increases modulus of elasticity

(3) Increases brittleness

(4) Decreases stiffness

(5) Decreases ductility


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Question 15

What effect does demineralization have on the

biomechanical properties of bone?

(1) Increases toughness

(2) Increases modulus of elasticity

(3) Increases brittleness

(4) Decreases stiffness

(5) Decreases ductility

Mechanics of Soft Tissue --


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Ligament and Tendon

Ligaments and Tendons have a defined fiber orientation based on

the arrangement of the collagen fibers

Mechanical behavior is anisotropic with greater strength and

stiffness along the fiber direction

Strength and modulus higher in tension than in compression



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Ligament and Tendon

Deformation of ligaments and tendons has acharacteristic behavior due to the action of

the fibers

Initial "toe" region is a result of the

straightening of crimped collagen fibers

Linear, elastic region is due to theoverall elastic deformation of the

structure

Stiffness begins to decrease in the plastic

region where individual fibers begin tofail

Overall failure occurs when stress

experienced by the remaining fibers

exceeds their ultimate tensile strength

X

Deform.

Force



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Ligament and Tendon

Ligaments and tendons exhibit viscoelastic behavior

Stiffness and strength are dependent on the loading rate,

with increased rates of deformation resulting in

increased stiffness and stress

Comparison of properties:

Ultimate tensile strength:

Tendon = 1/2 Bone

Ligament < Tendon

Elastic modulus

Tendon = 5 - 10 % Bone

Ligament < Tendon


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Question 16

A ligament is subjected to a constant force well below that

required to cause its rupture. The ligament will respond to

these loading conditions by:

(1) Elongating instantly and remaining at that length

(2) Elongating instantly and continuing to do so until a

constant length is reached

(3) Elongating instantly and then shrinking slowly

back to its original length

(4) Elongating indefinitely

(5) Remaining the same length


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Question 16

A ligament is subjected to a constant force well below that

required to cause its rupture. The ligament will respond to

these loading conditions by:

(1) Elongating instantly and remaining at that length

(2) Elongating instantly and continuing to do so until a

constant length is reached

(3) Elongating instantly and then shrinking slowly

back to its original length

(4) Elongating indefinitely

(5) Remaining the same length


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Mechanics of Soft Tissue -- Cartilage

Cartilage is designed to be loaded predominantly in

compression and exhibits substantial anisotropy

Properties are highly dependent on the rate of loading

At high strain rates, collagen behaves almost elastically

At low strain rates, viscoelastic behavior such as creep

is very apparent independent of the direction of loading

Like ligaments and tendons, cartilage exhibits a toe region

in the tension stress-strain curve due to the allignment of

the collagen fibers

Cartilage has an ultimate tensile strength of approximately

5 % that of bone, while the compressive elastic modulus is

about 1 % of bone


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Mechanics of Soft Tissue -- Cartilage

The behavior of cartilage under compressive load is

influenced by its porous, fluid-filled structure

Cartilage can be seen as a matrix of collagen and

proteoglycans filled with a large amount of water

During the first phase of compression, water is expelled

from the gel-like structure and deformation occurs easily

resulting in low stiffness and a high level of creep under

constant loading

Once a large amount of water has been expressed, thestructural elements of the matrix support the load, the

material becomes stiffer, and creep occurs at a lower rate


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Mechanics of Biomaterials -- Metals

Commonly used metals for medical implants

Stainless Steel

Cobalt-Chromium Alloy

Titanium Alloy

Elastic moduli of metals are about 1 order of magnitude higher

than cortical bone

Titanium has an elastic modulus of approximately 1/2 that of

stainless steel or cobalt alloys


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Mechanics of Biomaterials -- Metals

Fatigue Fracture of metals is an important consideration

due to the cyclic loading of orthopaedic implants and the

inability of artificial materials to self-repair

The endurance limit of typical implant metals is

between 250 MPa (Stainless steel) and 400 MPa(Titanium Alloy)

Fatigue is quickened due to the effect of corrosion of

the metals

i


68/84

Corrosion

Corrosion is a chemical reaction that occurs to form metallic

ions and hydroxides. It is extremely common for metals placed

in electrolytic solutions, such as the physiological environment.

Implant metals rely on the existence of an inert protective layer

to resist corrosion

Passivation is a reaction that produces a surface coating,

typically a metal oxide, on the metallic material which results in

an equilibrium solution of metal ions

C i


69/84

Corrosion

Implant metals and surface coatings

Stainless steel -- chromium oxide

Titanium alloy -- titanium dioxide

Cobalt-chromium alloy -- none

corrosion resistance due to an immunity mechanism While an oxide layer may be generally inactive in vivo,

changes in pH -- due to variations in location or disease

processes -- may damage the layer and result in corrosion

Oxide layers can also be damaged due to mechanicaltrauma, such as scratching, which can then lead to

corrosion

Most oxide layers are self-repairing in the presence of

oxygen

C i


70/84

Corrosion

Multiple types of corrosion

Uniform attack: requires a bathing solution with considerable

ionic activity (eg. physiological solution)

Galvanic attack: when two different metals are in contact in an

electrolytic solution, one may tend to release ions to the other

anode --> cathode

Cathodic material gains protection against corrosion

C i


71/84

Corrosion

Stress corrosion: caused by rupture of the passive surface

layer as a result of high tensile stresses, allowing local

attack at the exposed site

If conditions favor passivation, repair of the crack will

occur by formation of the oxide layer

Continued cyclic loading or the presence of organic

molecules may interfere with the repair allowing for

continued local attack, resulting in stress concentrations

and possible failure

C i


72/84

Corrosion

Pitting: galvanic attack which occurs between two

adjacent locations on the same metal due to impurities in

the alloy which result in a galvanic reaction

Intergranular attack: similar to pitting, however the

impurities exist in the boundaries between the metalcrystals or grains. Results in grain-boundary cracks.

Crevice corrosion: A linear and local attack, similar to

stress corrosion, which occurs at sites where scratches,

seams, or fatigue cracks form defects in the metal oxidecoating. These areas typically have low oxygen

concentration and so passivation, and coating repair, is

inhibited.

Q ti 17


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Question 17

Which of the following will help prevent corrosion of an

implant?

(1) An oxide layer

(2) Repetitive axial loading

(3) Contact of two dissimilar metals

(4) Muscle over the implant

(5) A layer of fibrin

Q ti 17


74/84

Question 17

Which of the following will help prevent corrosion of animplant?

(1) An oxide layer

(2) Repetitive axial loading

(3) Contact of two dissimilar metals

(4) Muscle over the implant

(5) A layer of fibrin

M h i f Bi t i l P l


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Mechanics of Biomaterials -- Polymers

Polyethylene, polymethyl methacrylate (PMMA), and siliconesare commonly used polymers for orthopaedic applications

Polyethylene

Low friction coefficient reduces wear when used as a

bearing surface for joint replacements

Low strength

Limited resistance to wear which does occur

M h i f Bi t i l P l


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Mechanics of Biomaterials -- Polymers

PMMA

Typically used as bone cement

Low viscosity immediately following mixing, allowing

for insertion in the medullary canal

Low tensile strength, higher compressive strength

Silicones (rubber)

Very low strength, poor wear behavior

High energy absorption properties

Used as spacer for small, load-bearing joints

M h i f Bi t i l C i


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Mechanics of Biomaterials-- Ceramics

Include aluminum oxide, calcium phosphate, and various"bioglasses"

Investigated due to chemical inertness for use as implant

materials

Very brittle, hard, low tensile strength, high modulus

High resistance to wear, low friction coefficient when

polished, high compressive strength

Possibility exists for development of a bio-reactive ceramic

which induces bone growth

Mechanical Properties --


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p

Biomaterials

Cortical Bone

Cancellous Bone

Stainless Steel

Titanium Alloy

Cobalt-Chrome

Polymethylmethacrlyate

Polyethylene

Aluminum Oxide

ElasticModulus

(GPa)

15

1

200

100

200-230

2

1

350

100

2

>500

900

>450

40

40

175

3

80

20

3500

2%

10%

15-40%

10%

8-10%

500%

5%

minimal

Ultimate

Tensile

Strength

(MPa)

Ultimate

Compressive

Strength

(MPa)

Maximum

Elongation

Q ti 18


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Question 18

Which of the following is the best description of acomparison of mechanical properties of titanium and

cortical bone?

(1) Titanium is twice as stiff as bone

(2) Titanium has a higher modulus of elasticity than bone

(3) Bone has a higher modulus of elasticity than

titanium

(4) Titanium and bone have the same stiffness

(5) Titanium and bone have the same modulus of

elasticity

Q ti 18


80/84

Question 18

Which of the following is the best description of acomparison of mechanical properties of titanium and

cortical bone?

(1) Titanium is twice as stiff as bone

(2) Titanium has a higher modulus of elasticity than bone

(3) Bone has a higher modulus of elasticity than

titanium

(4) Titanium and bone have the same stiffness

(5) Titanium and bone have the same modulus of

elasticity

Q estion 19


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Question 19

Compared to a stainless steel bone plate that is the samesize, the rigidity of a titanium plate is:

(1) Two times greater

(2) The same

(3) Half as great

(4) One-fourth as great

(5) One-eighth as great

Question 19


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Question 19

Compared to a stainless steel bone plate that is the samesize, the rigidity of a titanium plate is:

(1) Two times greater

(2) The same

(3) Half as great

(4) One-fourth as great

(5) One-eighth as great

Question 20


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Question 20

The modulus of elasticity of methylmethacrylate bonecement is:

(1) The same as that of polyethylene

(2) Between the values of cortical bone and cancellous

bone

(3) Between the values for cobalt-chromium alloy and

cortical bone

(4) Less than that of cancellous bone

(5) Less than that of cortical bone but greater than that

of cobalt-chromium alloy

Question 20


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Question 20

The modulus of elasticity of methylmethacrylate bonecement is:

(1) The same as that of polyethylene

(2) Between the values of cortical bone and cancellous

bone

(3) Between the values for cobalt-chromium alloy and

cortical bone

(4) Less than that of cancellous bone

(5) Less than that of cortical bone but greater than that

of cobalt-chromium alloy

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Detroit Medical Center - Biomech1