The Rigid Framework
of the Body
THE
SKELETAL SYSTEM
CHAPTER 10:
Skeletal Anatomy
Skeletal System
• Mechanically, the skeletal system my be
thought of as an arrangement of rigid links
connected to each other at joints to allow
specific movements.
Knowledge of
the skeletal
system is
important for
ALL
movement
analysts
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).
Divisions of the Skeletal System (239):
• Central or axial skeleton
• skull, vertebrae, sternum, and
ribs
• Peripheral or appendicular
skeleton
• bones of the arms and legs
Bone Shape
• The mechanical stresses imposed a bone
and its function determine its shape.
Three point bending test of an intact rat femur.
The resulting force-deflection curve from a three point bend test provides
the biomechanical properties of bone
Types of Bones
• Short bones
• Limited gliding motions and shock absorption.
• Small, cubical structures (e.g., carpals, tarsals)
Types of bones
• Short bones
• Flat bones
• Protection, provide attachment sites
• Flat in shape (e.g., scapula)
Types of bones
• Short bones
• Flat bones
• Irregular bones
• Multi-functional
• odd shapes (e.g., 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 (e.g., tibia, femur,
humerus, radius, ulna, clavicle, fibula, metatarsals, and
the phalanges)
Material Constituents:
• Calcium carbonate
60 to 70%
of
mass
• calcium phosphate
• collagen
• water 25 to 30% of bone mass
Material Constituents:
•stiffness
• Calcium carbonate
•compressive
• calcium phosphate
strength
• collagen • flexibility (tensile strength)
• water • tensile & compressive strength
Varies from person to person
Structural Organization
Cortical bone
(compact)
Low porosity
5-30% of bone
volume nonmineralized tissue.
Trabecular
(spongy\cancellous)
High porosity
30 to > 90% volume
non-mineralized
tissue.
Load and Response
•Stress
• force per unit
area
• Strain
• deformation
• amount of
deformation
divided by
original length
Life is an ongoing
cycle of repeated
applied external
stresses, interrupted
by applications of
isolated stresses of
varying magnitudes.
Generic
Stress-Strain Relationship
Elastic
Limit
Strain (deformation)
Bone
Stress-Strain Relationship
Fracture
Threshold
Strain (deformation)
Tension
Compression
Stress to Fracture
Relative Bone Strength
Load Type
Fractures: with excessive loads, bone tends to
fracture on the side loaded in tension.
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
• most rapid change before adulthood.
• Osteoblasts
• Osteoclasts
• form new
bone
• resorb
existing bone
Critical factor in bone
modelling/remodelling:
balance of their action
Bone Response to Stress
• Wolff's law (1892)
•
tissue adapts to level of imposed stress
•
increased stress
•
•
decreased stress
•
•
hypertrophy (increase strength)
atrophy (decrease strength)
SHAPE REFLECTS FUNCTION
•
Genetics, Body weight, physical activity,
diet, lifestyle (see note clippings)
(review the stress continuum)
Protecting our Bones in Sport
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 in Bone
• Weight & strength decrease
• Calcium content diminishes
• reduced BMD
• trabecular integrity is lost
Bone stimulating factors
Rate of loading
Magnitude
Frequency
BMD and walking
Quartiles based on
miles walked/week
Krall et al, 1994, Walking is
related to bone density and rates
of bone loss. AJSM, 96:20-26
Is physical
decline
inevitable
with
aging?
No.
Genetics
dominates.
But
lifestyle
modulates.
Changing concept of old age.
How much
activity do
we need?
The synovial joint
You should be able to draw and label this diagram.
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.
Role of Meniscii
Meniscii effect on mechanical stress
Back pain 'starts in school
By Roger Highfield
Around half of all children are at risk of suffering a lifetime of back problems
because of awkward postures during lessons and using computers, furniture and other
equipment designed for adults.
Forty per cent of schoolchildren suffer health problems considered in adults to be
"work related” that could affect them for the rest of their lives, said Prof Peter Buckle, of the
University of Surrey's Robens Centre for Health Ergonomics in Guildford.
He said a Danish study showed that 51 per cent of children aged 13 to 16 reported
low back pain in the previous year, and 24 per cent of 11- to14-year-olds in the north-west of
England reported having back pain in the month prior to completing a questionnaire.
"Under European laws the health of workers is protected," he said. "But when we
start to look at young adults and children the picture is far less clear.
"Worryingly, evidence is starting to show that, for some health problems, we may
be leaving it too late before we start helping."
A study found that those reporting low back pain in school were more likely to report low
back pain as adults.
(Filed: 10/09/2002) © Copyright of Telegraph Group Limited 2002.
Joint Stability
• Joint stability - resist abnormal
displacement of the articulating bones.
• Dislocation - bones displace out of their normal
positions.
• Subluxation - a partial dislocation of a joint.
Joint Stability
• Dislocation - bones displace out of their
normal positions.
Impingement
Subluxation
Dislocation
Joint Stability
• 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
• Fatigue or improper use of the joints are major
contributing factors.
• Muscles add to joint stability.
Joint Stability
• Contributing factors
• 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
Joint Stability
• Rotary component - perpendicular
component of a muscle force.
• Stabilizing component - parallel component
of a muscle force acting toward the joint
center.
• Dislocating component - parallel
component of a muscle force acting away
from the joint center.
Joint Stability
• Fascia - fibrous connective tissue that
surrounds muscles and the bundles of
muscle fibers within muscles, providing
protection and support.
• Iliotibial band.
Flexibility: ROM at a joint
Flexibility and Injury
• Risk of injury is heightened when joint
flexibility is extremely low, extremely high,
or significantly imbalanced between
dominant and non-dominant sides of the
body.
• Although people usually become less
flexible with age, a large part is due to
inactivity.
Joint Flexibility
• Factors influencing joint flexibility:
• Shape of articulating bones
• other soft tissue: stiffness & mass
• 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?
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
Techniques for increasing
joint flexibility
• Review neural
innervation
• Golgi tendon organs
• 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
• 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???