Transcript Chapter 4: The Biomechanics of Human Bone Growth and

Chapter 13:
The Skeletal System
The rigid
framework
of the body
Clopton Havers (1691)
It is true, if we come
to torture a bone with
the Fire, it seems to
confess that it consists
of all the five
Chymical Principles...
Composition and Structure of Bone
Tissue
 Mechanical
functions of bone
provides a rigid skeletal framework
to support and protect other tissues.
– forms a system of rigid levers (links)
that can be moved by forces from the
attached muscles (rotated by torques
from the attached muscles).
–
Types of bones (206):
 Central
– skull,
or axial skeleton
vertebrae, sternum, and
ribs
 Peripheral
or appendicular
skeleton
– bones
of the arms and legs
Types of bones (overheads)

Short bones
–
–
limited gliding motions and shock absorption.
Small, cubical structures (carpals, tarsals)
Types of bones
Short bones
 Flat bones

–
–
Protection, provide attachment sites
Flat in shape (ie scapula)
Types of bones
Short bones
 Flat bones
 Irregular bones

–
–
Multi-functional
odd shapes (ie vertebrae)
Types of bones
Short bones
 Flat bones
 Irregular bones
 Long bones

–
–
long shaft and bulbous heads (condyles,
tubercles, or tuberosities)
serve as levers for movement (ie tibia, femur,
humerus, radius, ulna, clavicle, fibula,
metatarsals, and the phalanges)
Material Constituents:
 Calcium
-stiffness
carbonate
-compressive
 calcium phosphate
strength
 collagen -flexibility (tensile strength)
 water -tensile & compressive strength
Structural Organization (overhead)
 Cortical
»
bone (compact)--Low porosity
5-30% of bone volume non-mineralized
tissue.
 Trabecular
(spongy\cancellous) High
porosity
»
30 to > 90% volume non-mineralized tissue.
Structural Organization
Bone Comparison
 Cortical
–
–
low porosity
more stiff
»
–
–
 Trabecular
–
–
greater stress
casing of all bones
(epiphysis,
irregular)
diaphysis of long
bones
high porosity
more elastic
»
–
greater strain
interior of all bones
Load and Response
Stress
– force
area
per unit
Strain
– deformation
» amount
of
deformation
divided by
original
length
Generic Stress-Strain Relationship
Bone Stress-Strain Relationship
Fracture
Threshold
Strain (deformation)
Tension
Compression
Stress to Fracture
Relative Bone Strength
Load Type
Common bone injuries:

Fractures - with excessive loads, bone tends
to fracture on the side loaded in tension.
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–
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–
–
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Simple - no break in skin.
Compound - protrusion through the skin.
Comminuted - fragmentation of the bone.
Avulsions - bone chip pulled away
Spiral - twisting break.
Impacted - opposite ends compressed together.
Stress - repeated low magnitude loading
Site of Ankle Avulsion Fracture
Avulsion fracture of
the patella
following B-PT-B
repair of the
ispsilateral ACL
Comminuted
Fracture
Ankle Trouble
Three Biological Phases to
fracture healing
 Inflammatory
Phase
–3 to 7 days
–immobilize the bone
–activates cells for repair
–step by step process that is
critical to successful union
Three Biological Phases to
fracture healing
 Inflammatory
Phase
 Reparative Phase (bony union)
–about one month
–callus formation
»provisional ==> bony
Three Biological Phases to
fracture healing
 Inflammatory
Phase
 Reparative Phase (bony union)
 Remodelling Phase
–restoration of original contour
Bone Growth and Development

Living bone is dynamic
–

continually changes throughout lifespan.
Longitudinal growth
–
length increases occur at the epiphyses
»
–

epiphyseal plates.
produce new bone tissue until closing during
adolescence or early adulthood.
Circumferential growth
–
Bones alter diameter throughout lifespan, with
most rapid change before adulthood.
Osteoblasts
Osteoclasts
 form
 resorb
bone
new
existing bone
Critical factor in bone
modelling/remodelling:
balance of their action
Bone Response to Stress
Wolff's
–
tissue adapts to level of imposed stress
»
increased stress
•
»
hypertrophy (increase strength)
decreased stress
•
–
law (1892)
atrophy (decrease strength)
FORM FOLLOWS FUNCTION
»
Genetics, Body weight, physical activity,
diet, lifestyle (see note clippings)
The pattern of
trabecular bone
in the
greater trochanter
neck of the femur
head of the femur
reflects femur’s roles:
muscle attachment
flexibility
weight transfer
support
Atrophy
 Bone
weight & strength
decreases
–Calcium content diminishes
»reduced BMD
–trabecular integrity is lost
Bone stimulating factors
Rate
of loading
Magnitude
Frequency
Is physical
decline
inevitable
with
aging?
No.
Genetics
dominates.
But
lifestyle
modulates.
Changing concept of old age.
Osteoporosis slide presentation
(Aging(?), OA and OP)
Effect of Peak BMD on osteoporosis
Fracture Threshold
20
50
AGE (years)
80
Effect of Peak BMD on osteoporosis
Menopause
Fracture Threshold
20
50
AGE (years)
80
Effect of Peak BMD on osteoporosis
Fracture Threshold
20
50
AGE (years)
80
Effect of Peak BMD on osteoporosis
Fracture Threshold
20
50
AGE (years)
80
Effect of Peak BMD on osteoporosis
Fracture Threshold
20
50
AGE (years)
80
Effect of Peak BMD on osteoporosis
Can the rate
of BMD decrease
be altered?
Fracture Threshold
20
50
AGE (years)
80
DEXA Scans
Click here
to read
about
DEXA scans
Calcium Intake
Check out this site
with information on
calcium and osteoporosis
Joint Architecture &
Classification
 Synarthoses
(immovable)
 Amphiarthroses (slightly movable)
 Diarthroses or synovial (freely
movable)
–
Get our attention
William Hunter (1743)
[The bone ends] are covered with a
smooth elastic crust, to prevent
mutual abrasion; connected with
string ligaments, to prevent dislocation;
and enclosed in a bag that contains a
proper fluid deposited there for
lubricating the two contiguous surfaces.
Synovial Joint Features

Articular (hyaline) cartilage
– covers articulating surfaces
– no blood vessels
– no nerves
– Serves 3 purposes:
»
»
»
reduces friction
increases articulating area to
reduce stress
shock absorption
Synovial Joint Features


Articular (hyaline) cartilage
Articular (fibrous/joint)
capsule
– double layer membrane
surrounds synovial joint
– outer connects bones
– inner secretes synovial fluid
– may have definite ligaments
Synovial Joint Features



Articular (hyaline) cartilage
Articular capsule
Synovial fluid
– clear, slightly yellow liquid
– lubricates joint
– nourishes cartilage
Synovial Joint Features




Articular (hyaline) cartilage
Articular capsule
Synovial fluid
Fibrocartilage:
– disc or partial disc between
articulating bones.
»
–
–
–
–
Intervertebral discs; menisci
increase surface area: reduce stress
improve fit of articulating surfaces
limits translation or slip of bones
shock absorption
Synovial Joint Features





Articular (hyaline) cartilage
Articular capsule
Synovial fluid
Fibrocartilage
Tendon sheaths
– surround tendons located
close to bones
»
»
reduce stress on tendon
maintain low friction
Synovial Joint Features






Articular (hyaline) cartilage
Articular capsule
Synovial fluid
Fibrocartilage
Tendon sheaths
Bursae
– small synovial fluid filled
capsules
»
separate tendon from bone to
reduce friction
Mobility is a
very precious gift.
More complex than
the space shuttle.
Total Hip Implants
Acetabular Component
Polyethylene
Liner
Metal
Shell
Head
“Collar”
Stem
Osteotomy
Line
Femoral Component
Osteoarthritis Slide Show
Osteoarthritis Slide Show
Click on
the info
button to
read on
NSAIDs
Joint Stability

ability to resist abnormal displacement of
the articulating bones
–
Dislocation - bones displace out of their normal
positions.
Impingement
Subluxation
Dislocation
Joint Stability
ability to resist abnormal displacement of
the articulating bones
 Contributing factors

–
shape of articulating surfaces
»
close-packed position: position of max contact
•
•
»
knee, wrist, interphalangeal: full extension
ankle: full dorsiflexion
loose-packed position: position other than c-p
•
most prone to dislocation, cartilage damage
Joint Stability
ability to resist abnormal displacement of
the articulating bones
 Contributing factors

–
–
shape of articulating surfaces
arrangement of ligaments & muscles
»
concept of rotary & stabilizing components of
muscle/ligament tension
•
•
rotary: component that causes/tends to cause rotation
stabilizing: acts parallel to the bone
Flexibility: ROM at a joint
Joint Flexibility

Factors influencing joint flexibility:
–
–
Shape of articulating bones
other soft tissue: stiffness & mass
»
»
»
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–
–
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muscle: current ‘tone”
ligaments: arranged in direction of expected pull
fatty tissue
temperature: warmer = more pliant
past injury: collagen alignment integrity
clothing
AGE??? vs inactivity
Why is flexibility important?
 Basic
component of a fitness profile.
Why is flexibility important?
 Basic
–
component of a fitness profile.
allows for greater choice of movement patterns
»
»
slides of gymnasts
elderly shoulder ROM & independence
•
»
»
Osteoarthroses
contractures (ie cerrebral palsy)
sprain ankle & inflammation
Why is flexibility important?
 Basic
–
–
component of a fitness profile.
allows for greater choice of movement patterns
reduce risk of injury
»
»
absorb energy over a greater distance (time)
CAVEAT: Risk of injury increased with ROM high,
or low
•
slide & next overhead
From Cowan et al, 1988, ref #304
Why is flexibility important?
 Basic
–
–
–
component of a fitness profile.
allows for greater choice of movement patterns
reduce risk of injury
Increase forceful performance
»
apply force over a greater distance (time)
•
•
violation of principle of summation of joint force
violation of principle of IMPULSE
Techniques for increasing joint
flexibility
Best Advice:
Use It
Don’t Lose It
How best to stretch?
Techniques for increasing joint
flexibility

Review neural innervation
–
Golgi tendon organs (figure 5-11)
»
»
»
located in junctions between muscles and tendons
responsive to tension in tendon
inhibits tension development in active muscle
Techniques for increasing joint
flexibility

Review neural innervation
–
–
Golgi tendon organs
Muscle spindles (figure 5-12)
»
»
»
located parallel to the muscle fibers in the belly of
the muscle
responsive to lengthening of fibers (rate & length)
Stretch Reflex
activate stretched muscle, inhibit antagonist
(reciprocal inhibition)
Techniques for increasing joint
flexibility

Review neural innervation
–
–

Golgi tendon organs
Muscle spindles
Flexibility training goal
–
–
do not invoke stretch reflex (do not activate the
muscle group to be stretched) HOW???
activate golgi tendon organs (further inhibit the
muscle group to be stretched (reduce tonus))
HOW???
Types of stretching:
Active - stretching muscles, tendons, &
ligaments by active development of tension
in the antagonist muscles
 Passive - stretching muscles, tendons, &
ligaments by a force other than tension in
the antagonist muscles (gravity, another
segment, another person)

Types of stretching
Ballistic - a series of quick, bouncing
movements.
 Static - a slow controlled stretch held over
time (10-30s, 3 to 4 reps)
 Proprioceptive Neuromuscular Facilitation alternating contraction and relaxation of the
muscles being stretched.

–
Contract-relax& pull-contract