Biomechanical Characteristics of Bone - Bone Tissue
Organic Components
(e.g. collagen)
Inorganic Components
(e.g., calcium and phosphate)
25-30%
65-70%
(dry wt)
H2O
(25-30%)
(dry wt)
ductile
one of the
body’s hardest
structures
brittle
viscoelastic
1
Strength and Stiffness of Bone Tissue
evaluated using relationship between
applied load and amount of deformation
LOAD - DEFORMATION CURVE
Bone Tissue Characteristics
Anisotropic
Viscoelastic
Elastic
Plastic
2
Stress = Force/Area
Strain = Change in Length/Angle
Note: Stress-Strain curve is a normalized Load-Deformation Curve
3
Elastic & Plastic responses
plastic region
Stress (Load)
fracture/failure
elastic
region
•elastic thru 3%deformation
•plastic response leads to fracturing
Dstress
Dstrain
•Strength defined by failure point
•Stiffness defined as the slope of the
elastic portion of the curve
Strain (Deformation)
4
Elastic Biomaterials (Bone)
•Elastic/Plastic characteristics
Brittle material fails before
permanent deformation
Ductile material deforms
greatly before failure
Bone exhibits both properties
Load/deformation curves
elastic
limit
ductile material
brittle material
bone
deformation (length)
5
Anisotropic response
behavior of bone is dependent
on direction of applied load
Bone is strongest along
long axis - Why?
6
Viscoelastic Response
behavior of bone is dependent
on rate load is applied
Bone will fracture sooner
when load applied slowly
Load
fracture
fracture
deformation
7
Mechanical Loading of Bone
Compression Tension Shear
Torsion
Bending
8
Compressive Loading
Vertebral fractures
cervical fractures
spine loaded through head
e.g., football, diving, gymnastics
once “spearing” was outlawed
in football the number of cervical
injuries declined dramatically
lumbar fractures
weight lifters, linemen, or gymnasts
spine is loaded in hyperlordotic
(aka swayback) position
9
Tensile Loading
Main source of tensile load is muscle
tension can stimulate tissue growth
fracture due to tensile loading is usually an avulsion
other injuries include sprains, strains, inflammation, bony deposits
when the tibial tuberosity experiences excessive loads from quadriceps
muscle group develop condition known as Osgood-Schlatter’s disease
10
Shear Forces
created by the application
of compressive, tensile or a
combination of these loads
11
Relative Strength of Bone
12
Bending Forces
Usually a 3- or 4-point
force application
13
Torsional Forces
Caused by a twisting force
produces shear, tensile, and
compressive loads
tensile and compressive loads are
at an angle
often see a spiral fracture develop
from this load
14
SKELETON
• axial skeleton
– skull, thorax, pelvis, &
vertebral column
• appendicular skeleton
– upper and lower
extremities
• should be familiar with
all major bones
15
Purposes of Skeleton
• protect vital organs
• factory for production of red blood cells
• reservoir for minerals
• attachments for skeletal muscles
• system of machines to produce movement in
response to torques
16
Bone Vernacular
• condyle
– a rounded process of a bone that
articulates with another bone
• e.g. femoral condyle
• epicondyle
– a small condyle
• e.g. humeral epicondyle
17
Bone Vernacular
• facet
– a small, fairly flat, smooth surface of a
bone, generally an articular surface
• e.g. vertebral facets
• foramen
– a hole in a bone through which nerves or
vessels pass
• e.g. vertebral foramen
18
Bone Vernacular
• fossa
– a shallow dish-shaped section of a bone
that provides space for an articulation with
another bone or serves as a muscle
attachment
• glenoid fossa
• process
– a bony prominence
• olecranon process
19
Bone Vernacular
• tuberosity
– a raised section of bone to which a
ligament, tendon, or muscle attaches;
usually created or enlarged by the stress of
the muscle’s pull on that bone during
growth
• radial tuberosity
20
Long Bones
• e.g. femur, tibia
• 1 long dimension
• used for leverage
• larger and stronger
in lower extremity
than upper extremity
– have more weight to
support
21
Short Bones
• e.g. carpals and
tarsals
• designed for
strength not mobility
• not important for us
in this class
22
Flat Bones
• e.g. skull, ribs,
scapula
• usually provide
protection
23
Irregular Bones
• e.g. vertebrae
• provide protection,
support and
leverage
24
Sesamoid Bones
• e.g. patella (knee cap)
• a short bone embedded
within a tendon or joint
capsule
• alters the angle of
insertion of the muscle
25
Long Bone Structure
cortical or compact bone
(porosity ~ 15%)
periosteum
outer cortical membrane
endosteum
inner cortical membrane
trabecular, cancellous,
or spongy, bone
(porosity ~70%)
26
Long Bone Structure
epiphyseal plate
metaphysis
either end of diaphysis
filled with trabecular bone
cartilage separating
metaphysis from epiphysis
diaphysis
shaft of bone
epiphysis
proximal and distal
ends of a long bone
27
Biomechanical Characteristics of Bone
Physical Activity
Gravity
Lack of Activity
Bone Tissue
Remodeling/Growth
Bone Deposits
(myositis ossificans)
Hormones
Age &
Osteoporosis
28
Longitudinal
Bone Growth
– occurs at the
epiphyseal or
“growth “ plate
– bone cells are produced on the
diaphyseal side of the plate
– plate ossifies around age 18-25 and
longitudinal growth stops
29
Circumferential
Bone Growth
– growth throughout the
lifespan
– bone cells are produced on the
internal layer of the periosteum by
osteoblasts
– concurrently bone is resorbed around
the circumference of the medullary
cavity by osteoclasts
30
Biomechanical Characteristics of Bone
Wolff’s Law
• bone is laid down where needed and
resorbed where not needed
• shape of bone reflects its function
– tennis arm of pro tennis players have
cortical thicknesses 35% greater than
contralateral arm (Keller & Spengler, 1989)
• osteoclasts resorb or take-up bone
• osteoblasts lay down new bone
31
Bone Deposits
• A response to regular activity
– regular exercise provides stimulation to maintain
bone throughout the body
– tennis players and baseball pitchers
develop larger and more dense bones in
dominant arm
– male and female runners have higher than
average bone density in both upper and
lower extremities
– non-weightbearing exercise (swimming,
cycling) can have positive effects on
BMD
32
Bone Resorption
• lack of mechanical stress
– Calcium (Ca) levels decrease
– Ca removed through blood via kidneys
• increases the chance of kidney stones
• weightless effects (hypogravity)
– astronauts use exercise routines to provide
stimulus from muscle tension
• these are only tensile forces - gravity is compressive
33
34
Typical Vertical GRF during running
30
Tip-Toe running pattern
Heel-toe running pattern
25
Fz (N/kg)
20
15
10
5
0
0
50
100
150
200
250
300
time (ms)
35
TVIS
Treadmill Vibration Isolation and
Stabilization System
36
Changes in bone over time
Early Years
• Osgood-Schlatter’s disease
• development of inflammation, bony deposits, or
an avulsion fracture of the tibial tuberosity
• muscle-bone strength imbalance
• “growth factor” between bone length and
muscle tendon unit (e.g., rapid growth of femur
and tibia places large strain on patellar tendon
and tibial tuberosity)
• during puberty muscle development
(testosterone) may outpace bone development
allowing muscle to pull away from bone
37
Changes in bone over time
Early Years
• overuse injuries
– repeated stresses mold skeletal structures
specifically for that activity
– Little Leaguer’s Elbow
• premature closure of epiphyseal disc
– Gymnasts
• 4X greater occurrence of low back pathology in
young female gymnasts than in general
population (Jackson, 1976)
38
Changes in bone over time
Adult Years
• little change in length
• most change in density
– lack of use decreases density
• DECREASE STRENGTH OF BONE
• activity
– increased activity leads to increased
diameter, density, cortical width and Ca
39
Changes in bone over time
Adult Years
• hormonal influence
– estrogen to maintain bone minerals
– previously only consider after menopause
– now see link between amenorrhea and
decreased estrogen - Female Athlete Triad
disordered
eating
amenorrhea
low body fat
excessive training
osteoporosis
low estrogen
levels
40
Changes in Bone Over Time
Older Adults
• 30 yrs males and 40 yrs females
– BMD peaks (Frost, 1985; Oyster et al., 1984)
– decrease BMD, diameter and
mineralization after this
• activity slows aging process
41
Osteopenia
Osteoporosis
Hormonal
Factors
Nutritional
Factors
Reduced BMD
slightly elevated risk
of fracture
Severe BMD reduction
very high risk of
fracture
(hip, wrist, spine, ribs)
Physical
Activity
28 million Americans affected – 80% of these are women
10 million suffer from osteoporosis
18 million have low bone mass
42
Osteoporosis
• age
– women lose 0.5-1% of their bone mass
each year until age 50 or menopause
– after menopause rate of bone loss
increases (as high as 6.5%)
43
Do you get shorter with age?
• Osteoporosis compromises structural
integrity of vertebrae
– weakened trabecular bone
– vertebrae are “crushed”
• actually lose height
• more weight anterior to spine so the
compressive load on spine creates wedgeshaped vertebrae
– create a kyphotic curve known as Dowager’s Hump
• for some reason men’s vertebrae increase in
diameter so these effects are minimized
44
Preventing Osteoporosis
• $13.8 billion in 1995 (~$38 million/day)
• Lifestyle Choices
– proper diet
• sufficient calcium, vitamin D,
• dietary protein and phosphorous (too much?)
• tobacco, alcohol, and caffeine
– EXERCISE, EXERCISE, EXERCISE
• 47% incidence of osteoporosis in sedentary population
compared to 23% in hard physical labor occupations
(Brewer et al., 1983)
45
Osteoporosis, Activity and the Elderly
Rate of bone loss (50-72 yr olds, Lane et al., 1990)
4% over 2 years for runners
6-7% over 2 years for controls
However - rate of loss jumped to 10-13%
after stopped running
suggest substitute activities should provide
high intensity loads, low repetitions
(e.g. weight lifting)
46
magnitude of loading
Injury - Repetitive v. Acute
Loading
injury tolerance
(above this line injury will occur)
frequency of loading
47
Articulations
• junction of 2 bones
• MOTION OCCURS AT A JOINT -- NOT
AT A LIMB
– i.e. elbow flexion NOT forearm flexion
48
Classification of joints
• Synarthroses - fibrous joint with little or
no movement
• Amphiarthroses - cartilaginous joints
with some motion
• Diarthroses - (aka synovial) - freely
movable joint
49
50
Joint Classification
• based on
– number of axes of rotation
– number of planes of motion
– e.g. uniaxial -- 1 axis of rotation so 1 plane
of motion
51
Ball and Socket = Triaxial
e.g., flexion & extension
internal & external rotation
abduction & adduction
Condyloid = Biaxial
e.g., flexion & extension
internal & external rotation
52
Hinge = uniaxial
e.g., flexion and extension
Pivot = uniaxial
e.g., supination
& pronation
53
Gliding = no axes
‘gliding between
2 flat bones’
Saddle = biaxial
same as condyloid
but greater ROM
Ellipsoidal = biaxial
e.g., flexion & extension
abduction & adduction
54
Structure of Synovial Joint
A - articular (hyaline)
cartilage (1-7 mm)
– smooth elastic tissue
on ends of bone
– 60-80% water
– no blood supply
– absorbs shock,
distributes force and
provides a low
friction surface
55
Structure of Synovial Joint
B - fibrous capsule
– very fibrous collagen
tissue used to hold
bones together
C - synovial
membrane
– lines the joint cavity
– secretes synovial fluid
to lubricate and
provide nutrition
NOTE: B & C combine to form the articular capsule
56
or joint capsule
Structure of Synovial Joint
D - ligaments
– connect bone-to-bone
– usually restrict ROM
at a joint
• tendons (not shown)
– connect muscle-tobone
A* - Joint cavity
57
Other Structures of Synovial
Joints
• bursa
– small capsules lined with
synovial membranes
– reduces friction between other
structures in the joint
Olecranon
bursa
• tendon sheaths
– fascia surrounding tendon to
reduce friction between
tendon and surrounding
structures
Digital
synovial
58
sheath
Other Structures of Synovial Joints
articular fibrocartilage
– different from articular cartilage
– takes the form of a
fibrocartilaginous disc or partial
disc
• distributes load over joint surface
• improve fit of articulating surfaces
• limit slipping of one bone relative to
other
• protect periphery of articulation
• lubricate articulation
• absorb shock
59
Arthritis
• Refers to more than 100
different diseases that
affect areas in or around
joints.
• The disease also can
affect other parts of the
body.
• Arthritis causes pain,
loss of movement and
sometimes swelling.
•Affects women more
than men
60
Source: Arthritis Foundation – www.arthritis.org
Osteoarthritis
20.7 million
Mostly after age 45
Rheumatoid
2.1 million
Mostly women
Juvenile
Arthritis
285,000
Under age 17
Juvenile Rheumatoid
Arthritis (JRA)
50,000
Arthritis
Fibromyalgia
3.7 million
Mostly women
Gout
2.1 million
Mostly men
Spondylarthropathies
412,000
Lupus
239,000
61
Source: Arthritis Foundation – www.arthritis.org
Osteoarthritis (OA), or degenerative
joint disease, is one of the oldest and
most common types of arthritis,
characterized by the breakdown of the
joint's cartilage. Cartilage is the part of
the joint that cushions the ends of bones.
Cartilage breakdown causes pain and
joint swelling. With time, there will be
limited joint movement.
• Most commonly affects middle-aged and older people
• Range from very mild to very severe
• Affects hands and weight-bearing joints (e.g., knees, hips, feet and back).
• OA is not an inevitable part of aging, although age is a risk factor
• Obesity may lead to osteoarthritis of the knees
• Joint injuries due to sports, work-related activity or accidents may be at
increased risk of developing OA.
Source: Arthritis Foundation – www.arthritis.org
62
Rheumatoid Arthritis (RA)
– a systemic disease that
affects the entire body.
• Characterized by the inflammation of the membrane lining the joint, which
causes pain, warmth, redness and swelling.
• The inflamed joint lining, the synovium, can invade and damage bone and
cartilage.
• Inflammatory cells release enzymes that may digest bone and cartilage.
• The involved joint can lose its shape and alignment, resulting in pain and
loss of movement.
• The disease usually begins in middle age, but can start at any age, and
affects two to three times more women than men.
Source: Arthritis Foundation – www.arthritis.org
63
Location of “Tender Points”
Fibromyalgia syndrome is a condition
with generalized muscular pain and
fatigue that is believed to affect
approximately 3.7 million people.
• The name fibromyalgia means pain in the muscles and the fibrous
connective tissues (the ligaments and tendons). The condition is known
as a syndrome because it is a set of signs and symptoms that occur
together.
• Fibromyalgia mainly affects muscles and their attachments to bones.
Although it may feel like a joint disease, it is not a true form of arthritis
and does not cause deformities of the joints. Fibromyalgia is, instead, a
form of soft tissue or muscular rheumatism.
64
Source: Arthritis Foundation – www.arthritis.org
Medicines
(e.g., analgesics, NSAIDS,
DMARDS, Disease Modifying
Anti-Rheumatic Drugs)
Use of Heat or Cold
Rest
Helpful before and after exercise
Many respond better
to cold packs than to heat
More rest and less activity are
needed during flares and the
opposite is true during periods of
improvement.
Exercise
(see next slide)
Surgery
joint replacement
Arthritis Treatments
Joint Protection
Use of Heat or Cold
Helpful before and after exercise
Many respond better
to cold packs than to heat
Careful use of joints to limit the pressure on the
involved joint
Simple and inexpensive devices available
Diet
Physical/Occupational Therapy
• Lack of vitamins associated with progression of
• recommend and teach prescribed muscle
OA of the knee
• Connection between obesity and OA of the knee
• Diet high in Omega 3 fatty acids may help reduce
inflammation in RA
• In general, people with arthritis are urged to
maintain a balanced diet and stay close to their
ideal weight.
strengthening and range-of-motion exercises
• teach non-medication ways to control pain
• suggest ways to make everyday and work
activities easier
65
Source: Arthritis Foundation – www.arthritis.org
Exercise
• Proper exercises performed on a daily basis are an important part of arthritis treatment.
• Exercise to help reduce weight can help prevent osteoarthritis in the knee.
• Proper exercise helps build and preserve muscle strength, keep joints flexible and help protect
joints from further damage.
Two categories of exercise:
• Therapeutic -- Prescribed by a doctor, physical therapist or an occupational therapist. These exercises are
based on individual needs and are designed to reach a certain goal.
• Recreational -- Includes any forms of movement, amusement or relaxation that refreshes the body and
mind. These exercises add to a therapeutic program, but do not replace it.
Three types of exercises:
•Range-of-motion -- Moving a joint as far as it comfortably will go and then stretching it a little further.
Range-of-motion exercises are designed to increase and maintain joint mobility that will decrease pain and
improve function.
•Strengthening -- Increases muscle strength to stabilize weak joints. These exercises use the muscle
without moving the joint.
•Endurance -- This type of exercise includes walking, swimming, bicycling, jogging, dancing and skiing.
These dynamic forms of exercise increase endurance, whereas range-of-motion and strengthening do not.
The most common risk in exercising is injury to joints and muscles. This usually happens from exercising
too long or too hard, especially if a person has not been active for some time.
66
Source: Arthritis Foundation – www.arthritis.org
close-packed vs. loose
packed
close packed
position
– maximum contact
area
– minimum mobility
– maximum stability
67
Bony Stability (cont.)
• amount of contact area
68
Joint Stability - Connective
Tissue
• ligamentous support
69
Properties of Connective
Tissue
• elasticity
– ability to return to normal state after stretch
– elastic limit
• stretch beyond this limit will cause permanent
damage
• plasticity
– stretched too far such that does not return
to its normal state
• ligament sprain (worse than bone fracture)
70
Exercise
will help
increase
the loads
a ligament
or tendon
can sustain
elastic
limit
Sprains occur in this region
plastic
Sprains result
in decrease of
joint stability
deformation (length)
71
Joint Stability - Muscles
• muscular
arrangement
– ability of muscle to
provide support
– muscle fatigue
• cruciate rupture more
likely when muscle is
fatigued
72
Mobility
• degree to which an articulation is
allowed to move before being restricted
by surrounding tissues
• ROM a.k.a. flexibility
73
Stability v. Mobility
• trade-off between stability and
mobility
–increase stability decrease
mobility
–vice-versa
74