Transcript Introduction to the Skeletal System

Applied Human
Anatomy and
Biomechanics
Course Content
I.
II.
Introduction to the Course
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 (loadcarrying 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
Multiaxial Loads


Shear


Biaxial loading
responses
Triaxial loading
responses
Bending
Torsion
Types of Loads
Axial Loads
Whiting & Zernicke (1998)
Shear Loads
Whiting & Zernicke (1998)
Axial Loads
Create
shear
load as
well
Whiting & Zernicke (1998)
Biaxial & Triaxial Loads
Whiting & Zernicke (1998)
Structural vs. Material
Properties
Structural Properties
 Load-deformation
relationships of like
tissues

Material Properties
Stress-strain
relationships of
different tissues
Terminology – Stress ()
 = 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 ()
 = dimension/original
dimension


normalized
deformation
change in shape of a
tissue relative to its
initial shape
How are Stress () and Strain
() 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
Fe  kx
Elastic region & Plastic region
Stiffness
Fig. 3.26a, Whiting & Zernicke, 1998
Stiffness (Elastic Modulus)
25
5
10
15
B
1
Load (N)
20
A
1
2
3
4
5
Deformation (cm)
6
7
C
Strength
stiffness ≠ strength
•Yield
•Ultimate
Strength
•Failure
Apparent vs. Actual Strain
1. Ultimate Strength
2. Yield Strength
3. Rupture
4. Strain hardening
region
5. Necking region
A: Apparent stress
B: Actual stress
25
Tissue Properties
5
10
15
B
1
Load (N)
20
A
Deformation (cm)
C
Extensibility & Elasticity
25
Extensibility
ligament
5
10
15
B
1
Load (N)
20
A
1
2
3
4
5
Deformation (cm)
6
7
tendon
C
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
…blast – produce matrix
…clast – resorb matrix
…cyte – mature cell
General Structure of
Connective Tissue
Cellular Component
Resident Cells
fibroblasts,
osteocytes,
chondroblasts, etc.
synthesis &
maintenance
Circulating Cells
lymphocytes,
macrophages, etc.
defense &
clean up
Distinguishes
CT from other
tissues
Extracellular Matrix
Protein Fibers
collagen, elastin
Ground
Substance
(Fluid)
determines the
functional characteristics
of the connective tissue
Collagen vs. Elastin
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

Great extensibility

Strain ~ 200%
Lack of creep

•Bind cells
•Mechanical links
•Resist tensile loads
Types of
Connective Tissue
Ordinary
Irregular Ordinary
Special
Regular Ordinary
Cartilage
Loose
Regular Collagenous
Adipose
Regular Elastic
Bone
Irregular Collagenous
Irregular Elastic
•Number & type of cells
•Proportion of collagen, elastin, & ground substance
•Arrangement of protein fibers
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 (loadcarrying 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
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
Metal
•Stiffest?
•Strongest?
•Brittle?
•Ductile?
Glass

young
old
Bone

Tensile Properties: Bone
Stiffness
Ultimate
stress (MPa)
Modulus of
elasticity (GPa)
Strain to
Fracture (%)
Collagen
50
1.2
-
Osteons
38.8-116.6
-
-
Femur (slow)
(fast)
78.8-144
6.0-17.6
1.4-4.0
Tibia (slow)
140-174
18.4
1.5
146-165.6
-
-
52
11.5
-
Axial
Fibula (slow)
Transverse
Femur (fast)
Compressive Properties: Bone
Osteons
Ultimate
stress (MPa)
Modulus of
elasticity (GPa)
Strain to
Fracture (%)
48-93
-
-
100-280
-
1-2.4
Axial
Mixed
Femur78.8-144 170-209 6.0-17.6 8.7-18.6 1.4-4.0 1.85
18.4 15.2-35.3
Tibia 140-174 213
Fibula 146-165.6 115
16.6
-
4.2
-
Transverse
Mixed
106-133
Other: Bone
Shear
Ultimate
stress
(MPa)
50-100
Modulus of
elasticity
(GPa)
3.58
Strain to
Fracture
(%)
-
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.
Mechanical Properties of Selected Biomaterials
Ultimate
Modulus of
Strain to
stress (MPa) elasticity (GPa) 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
100-150
10-15
1-3
8-50
-
2-4
100-280
8.7-35.3
1-2.4
Cortical bone
Trabecular bone
Bones (mixed)
Viscoelastic Properties :
Rate Dependency of Cortical Bone
•With  loading rate:





Fig 2-34, Nordin & Frankel, (2001)
 brittleness
Energy storage  2X
( toughness)
Rupture strength  3X
Rupture strain 100%
Stiffness  2X
Viscoelastic Properties :
Rate Dependency of Cortical Bone
•With  loading rate:

Fig 2-34, Nordin & Frankel, (2001)
More energy to be
absorbed, so fx
pattern changes &
amt of soft tissue
damage 
Effect of Structure

Larger CSA distributes force over larger area,


Tubular structure (vs. solid)



 stress
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
•Tensile strength: 140-174 MPa
•Comp strength: 213 MPa
•Shear strength: 50-100 MPa
Fig 2-32b, Nordin & Frankel (2001)
Acute Physical Activity
•As speed ,  and  
•5X in  with speed
•walk = 0.001/s
•slow jog = 0.03/s
Fig 2-32b, Nordin & Frankel (2001)
Acute Physical Activity
•In vivo, muscle
contraction can
exaggerate or
mitigate the effect
of external forces
Fig 2-33, Nordin & Frankel (2001)
Chronic Physical Activity



 bone density,
 compressive strength
 stiffness (to a certain threshold)
Chronic Disuse



 bone density (1%/wk for bed rest)
 strength
 stiffness
Fig 2-47, Nordin & Frankel (2001)
Repetitive Physical Activity
Muscle Fatigue
Injury
cycle
 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)
180
170
Stress (MPa)
160
150
140
130
120
110
100
20-29
30-39
40-49
50-59
60-69
70-79
80-89
Age (yrs)
Femur - Yield
Tibia - Yield
Femur - Ultimate
Tibia - Ultimate
Effects of Age on Eelastic (Tension)
35.0
Elastic Modulus (GPa)
30.0
25.0
20.0
15.0
10.0
20-29
30-39
40-49
50-59
60-69
Age (yrs)
Femur
Tibia
70-79
80-89
Effects of Age on Ultimate Strain (Tension)
0.045
0.040
Ultim ate Strain
0.035
0.030
0.025
0.020
0.015
0.010
0.005
0.000
20-29
30-39
40-49
50-59
60-69
Age (yrs)
Femur
Tibia
70-79
80-89
Effects of Age on Energy (Tension)
6
5.5
Energy (MPa)
5
4.5
4
3.5
3
2.5
2
20-29
30-39
40-49
50-59
60-69
Age (yrs)
Femur
Tibia
70-79
80-89
Properties of Biological Materials
A. Basic Concepts
B. Properties of Selected Biological Materials
A. Bone
B. Articular Cartilage
C. Ligaments & Muscle-Tendon Units

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 (%)
4.41
-
10-100
Superficial
10-40
0.15-0.5
-
Deep
0-30
0-0.2
-
Costal
44
-
25.9
Disc
2.7
-
-
15.68
-
-
Tension
Annulus
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
11
-
-
Disc
Other Loading Properties:
Cartilage
Ultimate
stress(MPa)
Modulus of
elasticity (GPa)
Strain to
Fracture (%)
Normal
-
0.00557-0.01022
-
Degenerated
-
0.00137-0.00933
-
-
0.01163
-
4.5-5.1
-
-
Shear
Torsion
Femoral
Disc
Tension
From LeVeau (1992). Biomechanics of human motion (3rd ed.). Philadelphia: W.B. Saunders.
Properties of Biological Materials
A. Basic Concepts
B. Properties of Selected Biological Materials
A.
B.
C.
D.
Bone
Articular Cartilage
Ligaments & Muscle-Tendon Units
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.
Viscoelastic Properties :
Rate Dependent Behavior


Moderate strain-rate sensitivity
With  loading rate:




Energy storage  ( toughness)
Rupture strength 
Rupture strain 
Stiffness 
Viscoelastic Properties:
Repetitive Loading Effects
• stiffness
Enoka (2002), Figure 5.3, p. 219, From Butler et al. (1978)
Very small
plastic
region
Enoka (2002), Figure 5.3, p. 219, From Butler et al. (1978)
Idealized
Stress-Strain
for
Collagenous
Tissue
Ligamentum flavum
Nordin & Frankel (2001), Figure 4-10, p. 110, From Nachemson & Evans (1968)
Tensile Properties: Ligaments
Nonelastic
ACL
Ultimate
stress (MPa)
Modulus of
elasticity (GPa)
Strain to
Fracture (%)
60-100
0.111
5-14
37.8
-
23-35.8
Anterior
Longitudinal
Collagen
.0123
50
1.2
-
Viscoelastic Behavior of BoneLigament-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
-
-
Various
45-125
0.8-2.0
8-10
Various
50-150
-
9.4-9.9
Various
19.1-88.5
-
-
Tendon
Mammalian
Achilles
0.8-2
34-55
-
-
Enoka (2002), Figure 5.12, p. 227, From Noyes (1977); Noyes et al. (1984)
EDL Tendon
Enoka (2002), Figure 3.9, p. 134,
From Schechtman & Bader (1997)
ECRB
Achilles
Max muscle force (N)
58.00
5000.0
Tendon length (mm)
204.00
350.0
14.60
65.0
726.00
1500.0
Stress (MPa)
4.06
76.9
Strain (%)
2.70
5.0
105.00
2875.0
Tendon thickness (mm2)
Elastic modulus (MPa)
Stiffness (N/cm)
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.