applied human anatomy and...

Applied Human

Anatomy and

Biomechanics

Course Content

I. Introduction to the Course

II. Biomechanical Concepts Related to Human Movement

III. Anatomical Concepts & Principles Related to the Analysis of Human Movement

IV. Applications in Human Movement

V. Properties of Biological Materials

VI. Functional Anatomy of Selected Joint Complexes

Why study?

� Design structures that are safe against the

combined effects of applied forces and

moments

1. Selection of proper material

2. Determine safe & efficient loading conditions

Application

� Injury occurs when an imposed load exceeds the tolerance (load-carrying ability) of a tissue� Training effects

� Drug effects

� Equipment Design effects

Properties of Biological Materials

A. Basic Concepts

B. Properties of Selected Biological Materials

A. Bone

B. Articular Cartilage

C. Ligaments & Muscle-Tendon Units

Structural vs. Material

Properties

Structural Properties

� Load-deformation

relationships of like

tissues

Material Properties

� Stress-strain

relationships of

different tissues

Terminology

� load – the sum of all the external forces and

moments acting on the body or system

� deformation – local changes of shape within

a body

Load-deformation relationship

� Changes in shape (deformation) experienced

by a tissue or structure when it is subjected to

various loads

Extent of deformation

dependent on:

� Size and shape (geometry)

� Material� Structure

� Environmental factors (temperature, humidity)

� Nutrition

� Load application� Magnitude, direction, and duration of applied force

� Point of application (location)

� Rate of force application

� Frequency of load application

� Variability of magnitude of force

Types of Loads

Uniaxial Loads

� Axial

� Compression

� Tension

� Shear

Multiaxial Loads

� Biaxial loading

responses

� Triaxial loading

responses

� Bending

� Torsion

Types of Loads

Axial Loads

Whiting & Zernicke (1998)

Shear Loads


Axial Loads

Create

shear

load as

well


Biaxial & Triaxial Loads


Structural vs. Material

Properties

Structural Properties

� Load-deformation

relationships of like

tissues

Material Properties

� Stress-strain

relationships of

different tissues

Terminology – Stress (σ)

σ = F/A (N/m2 or Pa)

� normalized load

� force applied per unit area, where area is measured in the plane that is perpendicular to force vector (CSA)

Terminology – Strain (εεεε)

ε = ∆dimension/original

dimension

� normalized

deformation

� change in shape of a

tissue relative to its

initial shape

How are Stress (σ) and Strain

(εεεε) related?

� “Stress is what is done to an object, strain is

how the object responds”.

� Stress and Strain are proportional to each

other.

Modulus of elasticity = stress/strain

Typical Stress-Strain Curve

kxFe====

Elastic region & Plastic region

Stiffness

Fig. 3.26a, Whiting & Zernicke, 1998

Stiffness (Elastic Modulus)

Load (N)

Deformation (cm)

1 5 10 15 20 25

A

B C

1 2 3 4 5 6 7

Strength stiffness ≠ strength

•Yield

•Ultimate

Strength

•Failure

Apparent vs. Actual Strain

1. Ultimate Strength

2. Yield Strength

3. Rupture

4. Strain hardening

region5. Necking region

A: Apparent stress

B: Actual stress

Tissue PropertiesLoad (N)

Deformation (cm)

1 5 10 15 20 25

A

B C

Extensibility & Elasticity

ExtensibilityLoad (N)

Deformation (cm)

1 5 10 15 20 25

A

B C

1 2 3 4 5 6 7

ligament tendon

Rate of Loading

� Bone is stiffer, sustains a higher load to failure, and

stores more energy when it is loaded with a high

strain rate.

Bulk mechanical properties

� Stiffness

� Strength

� Elasticity

� Ductility

� Brittleness

� Malleability

� Toughness

� Resilience

� Hardness

Ductility

� Characteristic of a material that undergoes

considerable plastic deformation under

tensile load before rupture

� Can you draw???

Brittleness

� Absence of any plastic

deformation prior to

failure

� Can you draw???

Malleability

� Characteristic of a material that undergoes

considerable plastic deformation under

compressive load before rupture

� Can you draw???

Resilience

Toughness

Hardness

� Resistance of a material to scratching, wear,

or penetration

Uniqueness of Biological

Materials

� Anisotropic

� Viscoelastic

� Time-dependent behavior

� Organic

� Self-repair

� Adaptation to changes in mechanical demands

General Structure ofConnective Tissue

Cellular Component Extracellular Matrix

Protein Fibers

collagen, elastin

Ground

Substance(Fluid)

Resident Cells

fibroblasts,

osteocytes,chondroblasts, etc.

Circulating Cells

lymphocytes,

macrophages, etc.

synthesis &maintenance

defense &clean up

determines the functional characteristics of the connective tissue

Distinguishes CT from other tissues

…blast – produce matrix…clast – resorb matrix…cyte – mature cell

Collagen vs. Elastin

Collagen

� Great tensile strength

� 1 mm2 cross-section →

withstand 980 N tension

� Cross-linked structure →↑ stiffness

� Tensile strain ~ 8-10%

� Weak in torsion and bending

Elastin

� Great extensibility

� Strain ~ 200%

� Lack of creep

Types of Connective Tissue

Ordinary Special

Irregular Ordinary Regular Ordinary Cartilage Bone

Regular Collagenous

Regular Elastic

Loose

Adipose

Irregular Collagenous

Irregular Elastic

•Number & type of cells•Proportion of collagen, elastin, & ground substance

•Arrangement of protein fibers

•Bind cells•Mechanical links•Resist tensile loads

Why study?

� Design structures that are safe against the

combined effects of applied forces and

moments

1. Selection of proper material

2. Determine safe & efficient loading conditions

Application

� Injury occurs when an imposed load exceeds the tolerance (load-carrying ability) of a tissue� Training effects

� Drug effects

� Equipment Design effects


A. Basic Concepts


A. Bone



Mechanical Properties of Bone

� General

� Nonhomogenous

� Anisotropic

� Strongest

� Stiffest

� Tough

� Little elasticity

Material Properties: Bone Tissue

� Cortical: Stiffer, stronger, less elastic (~2% vs.

50%), low energy storage

Mechanical Properties of Bone

� Ductile vs. Brittle

� Depends on age and rate at which it is loaded

� Younger bone is more ductile

� Bone is more brittle at high speeds

Glass

Bone

Metal

σ

ε

•Stiffest?

•Strongest?

•Brittle?

•Ductile?

old

young

Tensile Properties: Bone

Ultimate

stress (MPa)

Modulus of

elasticity (GPa)

Strain to

Fracture (%)

Collagen 50 1.2 -

Osteons 38.8-116.6 - -

Axial

Femur (slow)

(fast)

78.8-144 6.0-17.6 1.4-4.0

Tibia (slow) 140-174 18.4 1.5

Fibula (slow) 146-165.6 - -

Transverse

Femur (fast) 52 11.5 -

Stiffness

Compressive Properties: Bone

Ultimate

stress (MPa)

Modulus of

elasticity (GPa)

Strain to

Fracture (%)

Osteons 48-93 - -

Axial

Mixed 100-280 - 1-2.4

Femur 170-209 8.7-18.6 1.85

Tibia 213 15.2-35.3 -

Fibula 115 16.6 -

Transverse

Mixed 106-133 4.2 -

140-174

146-165.6

78.8-144 1.4-4.06.0-17.6

18.4

Other: Bone

Ultimate

stress

(MPa)

Modulus of

elasticity

(GPa)

Strain to

Fracture

(%)

Shear 50-100 3.58 -

Bending 132-181 10.6-15.8 -

Torsion 54.1 3.2-4.5 0.4-1.2

Tension 78.8-174 6.0-18.4 1.4-4.0

Compression 100-280 8.7-35.3 1-2.4

From LeVeau (1992). Biomechanics of human motion (3rd ed.). Philadelphia: W.B. Saunders.

Ultimate

stress (MPa)

Modulus of

elasticity (GPa)

Strain to

Fracture (%)

Polymers (bone

cement)

20 2.0 2-4

Ceramic (Alumina) 300 350 <2

Titanium 900 110 15

Metals (Co-Cr alloy)

Cast

Forged

Stainless steel

600

950

850

220

220

210

8

15

10

Cortical bone 100-150 10-15 1-3

Trabecular bone 8-50 - 2-4

Bones (mixed) 100-280 8.7-35.3 1-2.4

Mechanical Properties of Selected Biomaterials

Viscoelastic Properties :

Rate Dependency of Cortical Bone

Fig 2-34, Nordin & Frankel, (2001)

•With ↑ loading rate:

� ↑ brittleness

� Energy storage ↑ 2X

(↑ toughness)

� Rupture strength ↑ 3X

� Rupture strain ↓100%

� Stiffness ↑ 2X


Rate Dependency of Cortical Bone

Fig 2-34, Nordin & Frankel, (2001)

•With ↑ loading rate:

� More energy to be

absorbed, so fx

pattern changes &

amt of soft tissue

damage ↑

Effect of Structure

� Larger CSA distributes force over larger area,

� ↓ stress

� Tubular structure (vs. solid)

� More evenly distributes bending & torsional stresses

because the structural material is distributed away from

the central axis

� ↑ bending stiffness without adding large amounts of bone

mass

� Narrower middle section (long bones)

� ↓ bending stresses & minimizes chance of fracture

Effects of Acute Physical Activity

Fig 2-32a, Nordin & Frankel (2001)

Acute Physical Activity

Fig 2-32b, Nordin & Frankel (2001)

•Tensile strength: 140-174 MPa

•Comp strength: 213 MPa

•Shear strength: 50-100 MPa


Fig 2-32b, Nordin & Frankel (2001)

•As speed ↑↑↑↑, εεεε and σσσσ ↑↑↑↑

•5X↑↑↑↑ in εεεε with speed

•εεεεwalk= 0.001/s

•εεεεslow jog = 0.03/s


Fig 2-33, Nordin & Frankel (2001)

•In vivo, muscle

contraction can

exaggerate or

mitigate the effect

of external forces

Chronic Physical Activity

� ↑ bone density,

� ↑ compressive strength

� ↑ stiffness (to a certain threshold)

Chronic Disuse

� ↓ bone density (1%/wk for bed rest)

� ↓ strength

� ↓ stiffnessFig 2-47, Nordin & Frankel (2001)

Repetitive Physical Activity

Injury

cycle

Muscle Fatigue

↓↓↓↓ Ability to Neutralize Stresses on Bone

↑↑↑↑ Load on Bone

↓↓↓↓ Tolerance for Repetitions

Repetitive Physical Activity

Fig 2-38, Nordin & Frankel (2001)

Applications for Bone Injury

� Crack propagation occurs more easily in the

transverse than in the longitudinal direction

� Bending

� For adults, failure begins on tension side, since

tension strength < compression strength

� For youth, failure begins on compression side,

since immature bone more ductile

� Torsion

� Failure begins in shear, then tension direction

Effects of Age

� ↑ brittleness

� ↓ strength

� (↓ cancellous bone & thickness of cortical bone)

� ↓ ultimate strain

� ↓ energy storage

Effects of Age on Yield & Ultimate

Stresses (Tension)

100

110

120

130

140

150

160

170

180

20-29 30-39 40-49 50-59 60-69 70-79 80-89

Age (yrs)

Stress (MPa)

Femur - Yield Tibia - Yield Femur - Ultimate Tibia - Ultimate

Effects of Age on Eelastic (Tension)

10.0

15.0

20.0

25.0

30.0

35.0

20-29 30-39 40-49 50-59 60-69 70-79 80-89

Age (yrs)

Elastic Modulus (GPa)

Femur Tibia

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

20-29 30-39 40-49 50-59 60-69 70-79 80-89

Age (yrs)

Ultim

ate Strain

Femur Tibia

Effects of Age on Ultimate Strain (Tension)

2

2.5

3

3.5

4

4.5

5

5.5

6

20-29 30-39 40-49 50-59 60-69 70-79 80-89

Age (yrs)

Energy (MPa)

Femur Tibia

Effects of Age on Energy (Tension)


A. Basic Concepts


A. Bone



� Deforms more than bone since is 20X less stiff than bone� ↑ congruency

� High water content causes even distribution of stress

� High elasticity in the direction of joint motion and where joint pressure is greatest

� Compressibility is 50-60%

Tensile Properties: Cartilage

Ultimate

stress (MPa)

Modulus of

elasticity (GPa)

Strain to

Fracture (%)

Tension 4.41 - 10-100

Superficial 10-40 0.15-0.5 -

Deep 0-30 0-0.2 -

Costal 44 - 25.9

Disc 2.7 - -

Annulus 15.68 - -

Compressive Properties:

Cartilage

Ultimate

stress (MPa)

Modulus of

elasticity (GPa)

Strain to

Fracture (%)

Compression 7-23 0.012-0.047 3-17

Patella - 0.00228 -

Femoral head - 0.0084-0.0153 -

Costal - - 15.0

Disc 11 - -

Other Loading Properties:

Cartilage

Ultimate

stress(MPa)

Modulus of

elasticity (GPa)

Strain to

Fracture (%)

Shear

Normal - 0.00557-0.01022 -

Degenerated - 0.00137-0.00933 -

Torsion

Femoral - 0.01163 -

Disc 4.5-5.1 - -

Tension

From LeVeau (1992). Biomechanics of human motion (3rd ed.). Philadelphia: W.B. Saunders.


A. Basic Concepts


A. Bone



D. Skeletal Muscle

Structure and Function:

Architecture

� The arrangement

of collagen fibers

differs between

ligaments and

tendons. What is

the functional

significance?

Biomechanical Properties and

Behavior

� Tendons: withstand

unidirectional loads

� Ligaments: resist

tensile stress in one

direction and smaller

stresses in other

directions.


Rate Dependent Behavior

� Moderate strain-rate sensitivity

� With ↑ loading rate:

� Energy storage ↑ (↑ toughness)

� Rupture strength ↑

� Rupture strain ↑

� Stiffness ↑

Viscoelastic Properties:

Repetitive Loading Effects

Enoka (2002), Figure 5.3, p. 219, From Butler et al. (1978)

•↑ stiffness

Enoka (2002), Figure 5.3, p. 219, From Butler et al. (1978)

Idealized

Stress-Strain

for

Collagenous

Tissue

Very small

plastic

region

Ligamentum flavum

Nordin & Frankel (2001), Figure 4-10, p. 110, From Nachemson & Evans (1968)

Tensile Properties: Ligaments

Ultimate

stress (MPa)

Modulus of

elasticity (GPa)

Strain to

Fracture (%)

Nonelastic 60-100 0.111 5-14

ACL 37.8 - 23-35.8

Anterior

Longitudinal

.0123

Collagen 50 1.2 -

Viscoelastic Behavior of Bone-

Ligament-Bone Complex

� Fast loading rate:

� Ligament weakest

� Slow loading rate:

� Bony insertion of ligament weakest

� Load to failure ↓ 20%

� Energy storage ↓ 30%

� Stiffness similar

As loading rate ↑↑↑↑, bone strength ↑↑↑↑ more

than ligament strength.

Ligament-capsule injuries

� Sprains

� 1st degree – 25% tissue failure; no clinical instability

� 2nd degree – 50% tissue failure; 50%↓ in strength & stiffness

� 3rd degree – 75% tissue failure; easily detectable instabilty

� Bony avulsion failure (young people –more likely if tensile load applied slowly)

Tensile Properties:

Muscles & Tendons

Ultimate

stress (MPa)

Modulus of

elasticity (GPa)

Strain to

Fracture (%)

Muscle 0.147-3.50 - 58-65

Fascia 15 - -

Tendon

Various 45-125 0.8-2.0 8-10

Various 50-150 - 9.4-9.9

Various 19.1-88.5 - -

Mammalian 0.8-2

Achilles 34-55 - -

Enoka (2002), Figure 5.12, p. 227, From Noyes (1977); Noyes et al. (1984)

Enoka (2002), Figure 3.9, p. 134,

From Schechtman & Bader (1997)

EDL Tendon

ECRB Achilles

Max muscle force (N) 58.00 5000.0

Tendon length (mm) 204.00 350.0

Tendon thickness (mm2) 14.60 65.0

Elastic modulus (MPa) 726.00 1500.0

Stress (MPa) 4.06 76.9

Strain (%) 2.70 5.0

Stiffness (N/cm) 105.00 2875.0

Muscle-Tendon Interaction

� Stiffer tendon → more brisk, accurate movements

� Less stiff, ↓ muscle contraction velocity, ↑ efficiency

� ↑ tendon compliance, small ∆ muscle length (as

compared to ∆ M-T unit length

� High resilience

� Limited viscoelastic behavior, therefore, tendon in

major site of storage of elastic energy in M-T unit

� Tensile strength of tendon 2X that of its muscle

Role of Elasticity in Human

Movement

� Elasticity of tendon

� responsible for force transfer from muscle to

bone

� enables storage and release of energy, reducing

metabolic cost

� Material & structural properties of tendon

determine the amount of resistance to

stretch and, thus, amount of elastic force

transferred to bone

Muscle – Mechanical Stiffness

� Instantaneous rate of change of force with length

� Unstimulated muscles are very compliant

� Stiffness increases with tension

� High rates of change of force have high muscle

stiffness, particularly during eccentric actions

� Stiffness controlled by stretch and tendon reflexes

Effects of Disuse

Nordin & Frankel (2001), Figure 4-15a, p. 110, From Noyes (1977)

Effects of Disuse

Nordin & Frankel (2001), Figure 4-15b, p. 110, From Noyes (1977)

Effects of corticosteroids

� ↓ stiffness

� ↓ rupture strength

� ↓ energy absorption

� Time & dosage dependent

Effect of Structure

Whiting & Zernicke (1998), Figure 4.8a,b, p. 104, From Butler et al. (1978).

Miscellaneous Effects

� Age effects

� More compliant / less strong before maturity

� Insertion site becomes weak link in middle age

� ↓ stiffness & strength in pregnancy in rabbits

� Hormonal?

Summary

� Mechanical properties of biological materials vary across tissues and structures due to material and geometry differences.

� Understanding how age, physical activity, nutrition, and disease alter mechanical properties enables us to design appropriate interventions and rehabilitations.

� Understanding these mechanical properties allows us to design appropriate prosthetic devices to for joint replacement and repair.

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