Transcript Basic Biomechanics, (5th edition) by Susan J. Hall, Ph.D.

The Biomechanics of Human
Skeletal Articulations
Explain the functions of articular, fibro cartilage and articular
connective tissue.
Define joint stability and explain factors influencing its.
Define joint flexibility and Explain the advantages and
disadvantages of different techniques for increasing or
maintaining joint flexibility.
Describe the biomechanical contributions to common joint
injuries and pathologies.
Classification of Joints based on Functions
Immovable
Slightly Moveable
(Synarthroses)
(Amphiarthroses)
Freely Movable
(Diarthroses or
Synovial)
Absorb shock but permit
little or no movement
Sut
ure
s–
Sk
ulls
Sy
nd
es
mo
ses
Tibi
ofi
bul
Synchondroses –
Sternocostal joint,
epiphyseal plates
Symphyses –
Vertebral joints and
the pubic symphysis
The articulating
bone surfaces are
covered with
articular cartilage,
an articular capsule
and synovial
membrane.
Synovial membrane
lining the interior
articular capsule
secretes a lubricant
known as synovial
fluid.
SUTURES
T
h
e
o
n
l
y
e
x
a
m
p
l
e
i
n
SYNDESMOSES
Dense fibrous tissue binds the bone
together
AMPHIARTHROSES - SYMPHYSIS
Thin plates of hyaline cartilage separate a disc of fibrocartilage from
the bones.
SYNCHONDROSES
Articulating bones are held together by a thin layer of
hyaline cartilage
DIARTHROSES OR SYNOVIAL
Articular capsule consist of double
layered membrane Synovial
membrane (stratum) and Fibrous
membrane.
Synovial fluid -a clear, slightly yellow
liquid that provides lubrication inside
the articular capsule.
Associated bursae - small capsules
filled with synovial fluid that cushion
the structures they separate
DIARTHROSES – CATEGORIZED BASED ON
NUMBER OF AXES OF ROTATION PRESENT
(a)Athrodial;(b)Sellar;(c)Ginglymus;(d)Trochoid;(e)Spherodial (f) Condyloid
Articular or Hyaline Cartilage
Articular cartilage is
a white connective
tissue
It covers the ends of
bones.
FUNCTIONS OF ARTICULAR CARTILAGE
What are the functions of articular cartilage?
• It provides a protective lubricants that
minimizes frictions and mechanical wear.
• It spreads loads over a wide area, thereby
reducing contact stress.
• It has no blood supply and nerves.
• Anisotropic, it deforms instantaneously to a
low or moderate load. If rapidly loaded, it will
become stiffer and deforms over a longer
period.
ARTICULAR CARTILAGE
• It is 1 to 5 mm thick, depending on the
stress and the incongruity of the joint
surfaces.
• The force distributions depend on the
cartilage thickness. Ankle and elbow, thin;
hip and knee, thick.
• It has a very low coefficient of frictions,
range from 0.01 to 0.04, ice at 0º is about
0.1. Almost frictionless, allows gliding.
Functions of Articular Fibrocartilage
Lateral
meniscus
Transverse
ligament
Medial
meniscus
Posterior cruciate
ligament
Anterior cruciate
ligament
Superior view
What?
It is a fibrocartilaginous disc or partial discs known
as menisci that intervene between articulating
bones.
ARTICULAR FIBROCARTILAGE
Examples are the intervertebral disc and the
knee joint.
It is where both tensile strength and the
ability to withstand high pressure are
necessary.
What are the possible functions of
articular fibrocartilage?
• Distributing loads over joint surfaces
• Protecting the joint periphery
• Lubricating the joint
• Absorbing shock at the joint
• Improving the fit of articulations
• Limiting slip between articulating bones
What are articular connective tissues?
• Tendons - connect muscles to bones
• Ligaments - connect bones to other
bones
Do not have ability to contract like muscle
tissue but slightly extensible, elastic. Like
bone it responds to mechanical stress by
hypertrophying and atrophying. Therefore,
regular exercises, increase size and strength
of both tendon and ligaments.
What is joint stability?
Ability of a joint to resist
abnormal displacement
(dislocation) of the
articulating bones.
What factors effect joint stability?
Orientation or joint position
• Stability is maximal when joints are
in the close-packed position
(maximum contact surface between
the articulating bone).
• Loosed-packed position - any joint
orientation other than the closed
packed position.
What factors effect joint stability?
Shape of the articulating
surface
– Acetabulum has relatively
deep socket for the head of
femur and large amount of
contact area.
– The small glenoid fossa has
lesser contact area and
diameter than humeral head,
therefore contribute to
relatively instable joint.
What factors effect joint stability?
A strong array of ligaments and muscle tendons
crossing the joint
Strong ligaments and muscle contributes significantly
to joint stability by holding the articulating bone ends
together (E.g. Strengthening the quadriceps and
hamstring groups enhance the stability of the knee).
The angle of attachment of most tendons to bones
contributes to joint stability. The articulating ends of the
bones at the joint are pulled closer together.
Absence of muscle fatigue
Since muscle strength effect joint stability, when muscle
fatigues, joint stability also affected.
Other Connective tissue
Fascia and the bundles of muscle fiber within provide
protections and support.
What is Joint Flexibility?
• A description of the relative ranges of motion
(ROM) allowed at a joint in different directions
• ROM: the angle through which a joint moves from
anatomical position to the extreme limit of segment
motion in a particular direction.
• Static flexibility – An indicator of the relative
tightness or laxity of a joint. It refers to the ROM
present when a body segment is passively moved
(by an exercise partner or clinician).
• Dynamic flexibility – It refers to the ROM achieve
by virtue of muscle contraction.
Joint Flexibility
Range of motion is measured directionally
from anatomical position (zero).
What factors influence joint flexibility?
• Shape of the articulating bone surface and an
intervening muscle tissue or fat terminate
movement at extreme ROM.
• Tightness in the muscle and collagenous
tissue crossing a joint. When these tissues are
not stretched, their extensibility usually
diminishes (Collagenous tissue - extensibility
increase with temperature elevation).
Joint Flexibility and Injury
If the joint flexibility is extremely low or
extremely high, the risk of injury is also
increased. Too tight, possibility of tearing
and rupturing are high. Too loose, it is
prone to displacement-related injuries.
People with less physical activity will have
less flexibility.
Stretching increase flexibility and avoid
injury.
AGONIST AND ANTAGONIST
Agonist
The muscle that responsible for moving the body
part to contracts or shortens.
Antagonist
The muscle that responsible for moving the body
part back to its original position.
HOW TO INCREASE JOINT FLEXIBILITY?
Stretching the ligaments and muscles
that limit the ROM at joint will increase or
maintain flexibility.
Certain type of stretching being more
effective than the other due to different
neuromuscular responses.
The proprioreceptors which transform
mechanical distortion in the muscle or joint
into nerve impulses that enter the spinal
cord and stimulate the motor response.
NEURALMUSCULAR RESPONSE THAT INFLUENCING
THE JOINT FLEXIBILITY
Golgi Tendon Organs (GTO)
What?
It is a sensory receptors that influence extensibility.
Where?
It is located in the muscle-tendon junction and in the
tendons at both ends of muscles.
How?
It is stimulated by tension either produce by muscle
contraction or by passive muscle stretch. It inhibit tension in
agonist muscle (promote relaxation) & initiate tension
development in antagonists.
GTO MECHANISM
Contractions of quadriceps muscle increases the tension in the
patellar tendon which stimulates the Golgi tendon organ.
The impulse travel to the spinal cord and some of them head
upward to the higher centers of the nervous system for
further interpretation and integration.
The remaining messages excite either, interneurons that
inhibit quadriceps function (extension of the knee), or
interneurons that activate hamstring function (flexion of the
knee).
NEURALMUSCULAR RESPONSE THAT INFLUENCING
THE JOINT FLEXIBILITY
Muscle Spindles
What?
It is a sensory receptors that are respond to the
amount of muscle (static response) and rate of
muscle lengthening (dynamic response).
Where?
It is interspered throughout and parallel to the
fibers of muscles.
How?
Muscle spindles will provoke reflex contraction in
stretched muscle & inhibit tension in
antagonists..
KNEE JERK TEST
A tap on the patellar tendon initiates
the stretch reflex, resulting in the
jerk caused by the immediate
tension development in the
quadriceps group.
KNEE JERK TEST MECHANISM
Tapping the tendon stretches the
quadriceps femoris muscle group.
This activates stretch receptors within
the muscle called muscle spindles.
Stretching a spindle fiber initiates a
volley of impulses in the sensory
neuron (called an "I-a" neuron)
attached to it. Impulse from muscle
spindle travel to spinal cord. Some
impulse are carried back to the same
muscle causing it to contract. The leg
straightens.
KNEE JERK TEST MECHANISM
Some of the branches of the I-a
axons synapse with inhibitory
interneurons in the spinal
cord. These, in turn, synapse
with motor neurons leading
back to the antagonistic
muscle that inhibits tension
development in antagonist
muscle.
Golgi Tendon Organs and Muscle
Spindles: How do they Compare?
Golgi Tendon Organs
Muscle Spindles
Location
Within tendons near the
muscle-tendon junction in
series with muscle fibers
Interspersed among muscle
fibers in parallel with the
fibers
Stimulus
Increase in muscle tension Increase in muscle length
1) inhibit tension
development in stretched
Response
muscle, 2) initiate tension
development in antagonist
muscle
Overall
Promote stretch in muscle
Effect
being stretched
1) initiate rapid contraction
of stretched muscle, 2)
inhibit tension development
in antagonist muscles
Inhibit stretch in muscle
being stretched
BETWEEN GTO’S AND MUSCLE SPINDLE
GTO promotes relaxation in muscle
developing tension, whereby Muscle
Spindles inhibit stretch in muscle
being stretch. Therefore, maximizing
GTO and minimizing the muscle
spindle effect is the general goals in
increasing joint flexibility
Techniques for Increasing Joint Flexibility
What are active and passive stretching?
• Active stretching is produced by contraction of the
antagonist muscles (Quadriceps contract so that
Harmstring is stretched). It provides the advantage of
exercising the muscle group used to develop force.
• Passive stretching is produced by a force other than
tension (Gravitational force, force applied by another
body segment or by another person) in the antagonist
muscles. Movement can be carried out father beyond
the ROM (compare to active stretching)
Techniques for Increasing Joint Flexibility
What are ballistic and static stretching?
• Ballistic stretching - a series of quick, bouncing-type
stretches. The potential for injuries is heightened.
• Static stretching - maintaining a slow, controlled,
sustained stretch over time-usually about 30 seconds.
This type of stretching is preferred because ballistic
activate the muscle spindle respond that inhibits
stretching. Why static stretching did not activate
muscle spindle?
Techniques for Increasing Joint Flexibility
What is PNF?
Proprioceptive neuromuscular facilitation
is a group of stretching procedures
involving alternating contraction and
relaxation of the muscles being
stretched
COMMONT JOINT INJURIES AND PATHOLOGIES
Sprains – abnormal displacement or twisting of
the articulating bones results in stretching or
tearing of ligaments, tendons, and connective
tissues crossing joints.
DISLOCATION
Dislocation - Displacement of the articulating
bones at a joint. Result from fall or
involving large magnitude of force.
Symptoms include pain, swelling and loss
of joint movement capability.
BURSITIS
Bursitis – Overuse
injury caused by
excessive use of a
joint that produces
frictional irritation
and inflammation of
one or more bursae.
Pain and some
swelling are
symptoms of bursitis.
ARTHRITIS
Arthritis - an inflammation of a bone
joint accompanied by pain and
swelling.
Rheumatoid Arthritis- Type of arthritis
where body’s autoimmune system
attack healthy tissue. the synovium
becomes inflamed. This
inflammation causes chemicals to
be released that thicken the
synovium and damage the cartilage
and bone of the affected joint. This
leads to inflammation of the
synovium causing pain and swelling
Osteoarthritis
What is osteoarthritis?
• a common, degenerative disease of
articular cartilage
• symptoms include pain, swelling, ROM
restriction, and stiffness
• cause is unknown
• both too little and too much mechanical
stress seem to promote development
Cartilage that cushions the bones of the hip starts
to erode, eventually allowing the bones to grind or
rub together and causing hip pain and
stiffness.The exact cause of osteoarthritis is
unknown.