Joints
Definition:
Joint is the articulation between any of
rigid component parts of the skeleton
whether bones or cartilage by different
tissues.
Functions of the joints:
1) Allowing movements of body segments by
providing the bones with a mean of moving or
rather of being moved.
2) Providing stability without interfering with the
desired motion.
The function of the joints depends upon:
A. The shape of the contours of the contacting
surfaces.
B. How well it fits together.
Classification of human
Joints according to structure
Synarthoroses
Diarthroses
Limeted or no movement
Free movement
Synostoses
Bone is connected to bone by bone
Synovial
There is synovial membrane and
Synovial fluid
Synchonroses
Bone is connected to bone by
Cartilage or fibrocartilage
Syndesmoses
Bone is connected to bone by a fibrous
Connective tissues
• According to the degree of freedom of
movement
• One degree of freedom of movement.
• Two degree of freedom of movement.
• Three degree of freedom of movement.
• According to the number of axes of rotation:
• Uniaxial.
• Biaxial.
• Multiaxial.
Classification of synovial joints
Anatomical classification Mechanical
Classification
Example
Hinge joint
Uniaxial
Elbow joint
Pivot joint
Uniaxial
Atlanto axial joint,
Superior radio-ulnar joint
Codyloid joint
Biaxial
Knee joint
Saddle joint
Biaxial
Carpometacarpal joint of
the thumb
Elbsoid joint
Triaxial
Wrist joint
Ball and socket
Triaxial
hip joint and shoulder
joint
Gliding joint
Nonaxial
Midtarsal joints of foot
Classification of motion
• Rotation
• Is motion about an axis,
causing points on the
rotating body to travil
different distances
depending upon their
distance from the point of
rotation
• Translation
• Produces a linear
movement in which all
points in the body travel
the same distance
regardless of their
location in the body, most
cartilaginous and fibrous
joints allow translation, or
linear movements.
• Synovial joints allow
rotation and translation
movements
Terminology
Concave : hollowed or rounded inward.
Convex : curved or rounded outward.
Congruent: The surfaces of the joint are
equal
Incongruent : The surfaces of the joint are
not equal
Joint Shapes
• Ovoid – one surface is convex, other surface is concave
– What is an example of an ovoid joint?
• Sellar (saddle) – one surface is concave in one direction
& convex in the other, with the opposing surface convex
& concave respectively
– What is an example of a sellar joint?
Relationship Between Physiological &
Accessory Motion
• Biomechanics of joint motion
– Physiological motion
• Result of concentric or eccentric active muscle contractions
• Bones moving about an axis or through flexion, extension,
abduction, adduction or rotation
– Accessory Motion
•
•
•
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Motion of articular surfaces relative to one another
Generally associated with physiological movement
Necessary for full range of physiological motion to occur
Ligament & joint capsule involvement in motion
Arthrokinematics
• Arthrokinematics means motions of
bone surfaces within the joint are :
Roll, Slide, Spin, Compression
and Distraction
(5 motions)
Roll
• A series of points on one articulating surface come into contact with
a series of points on another surface
– Rocking chair analogy; ball rolling on ground
– Example: Femoral condyles rolling on tibial plateau
– Roll occurs in direction of movement
– Occurs on incongruent (unequal) surfaces
– Usually occurs in combination with sliding or spinning
• In rolling, equidistant points touch each other in the
course of motion.
Spin
• Occurs when one bone rotates around a stationary longitudinal
mechanical axis
• Same point on the moving surface creates an arc of a circle
as the bone spins
• Example: Radial head at the humeroradial joint during
pronation/supination; shoulder flexion/extension; hip
flexion/extension
– Spin does not occur by itself during normal joint motion
In spinning, the contact point of one surface rotates around
a longitudinal axis.
Slide
Specific point on one surface comes into contact with a
series of points on another surface
In sliding, a point of a shallow concave gliding surface sweeps over a larger
surface of the other convex joint body. (sometimes referred to as a GLIDE)
Surfaces are congruent
.
Combined rolling-sliding in a joint
The more congruent the surfaces are, the more sliding
there is
The more incongruent the joint surfaces are, the more
rolling there is
Slide (glide)
• Compression –
– Decrease in space between two joint surfaces
– Adds stability to a joint
– Normal reaction of a joint to muscle contraction
• Distraction – Two surfaces are pulled apart
– Often used in combination with joint mobilizations to
increase stretch of capsule.
CONGRUENCE OF ARTICULAR
SURFACES
• a) CLOSE-PACKED POSITION OF THE
JOINT .
• b) LOOSE- PACKED POSITION
Kinematic chain
• It is a combination of several successively
arranged joints constituting a complex
motor system.
• Kinematic chain is when a number of links
are united in series.
Body link System and Kinematic
Chains:
• Body link system:
• Body link is the distance between joint axes and it unites
joint axes.
• A body link is the central straight link that extends
between two joint axes of rotation. In the case of hands
and feet, the terminal links are considered to extend from
the wrist and ankle joint centers to the center of the
mass of these so- called and members.
• Link systems are interconnected by joints that
predetermine the particular type of motion permitted to
the functional segments.
• The link system is used to make calculations regarding
different body segments in different positions.
The kinematic chain may be open or closed.
• In a closed kinematic chain,
the distal segment is fixed and
the end segments are unite to
form a ring or a circuit.
• When one link moves all the
other links will move in a
predictable pattern. e.g. the rib
cage.
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•
•
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In an open kinematic chain, the
distal segment terminates free in
space.
Each segment of an open chain
has a characteristic degree of
freedom of motion; the distal
possessing a higher degree of
freedom than the proximal ones.
Such linkage system allows the
degrees of freedom of the many
joints in the chain to be pooled
giving the segments (particularly
those more distal) greater
potential for achieving a variety of
movements than any one joint
could possibly have on its own.
e.g. when reaching forward to pick
up a small object from a high
shelf.
Kinematic chains
OPEN CHAIN
The distal end terminates free in
space.
It has a characteristic degree of
freedom.
The distal segments possess higher
degrees of freedom than the proximal
one.
Such linkage system allows the degree
of freedom of many joints in the chain
to be pooled giving the segments
greater potential for achieving a variety
of movements than can any one joint
could possibly have on its own
CLOSED CHAIN
The distal segment is fixed and
the terminal joint meets with great
resistance which restraints its
free motion.
e.g. chinning oneself on horizontal
bar or stance phase of gait
cycle.
2) end segments are united to form a
ring when one link moves, the other
links will move in a predictable
pattern e.g. rib cage
• Walking and ascending and descending
stairs are examples of alternation between
open and closed chains
• Open kinematic chains are the most
common type in the human body
Factors Affecting Joint Stability
( Resistance to Displacement)
1.
Shape of the bony structure: e.g. depth of the acetabulum of the hip joint
and shallowness of the glenoid fossa of the shoulder joint.
2.
Ligaments Arrangement: the ligaments attach the ends of the bones that
form a movable joint and help in maintaining them in the right relationship
to each other.They check the movement when it reaches its normal limits
and the resist the movements for which the joint is not constructed, e.g
collateral ligament of the knee. The importance of this factor remains as
long as the ligaments remain undamaged.
3.
Fascia: Accordingly to the location and function of the fascia, it may vary
from thin to tough and fibrous membranes.
4.
Muscular Arrangement: They play part in the stability of joints especially in
those joints whose bony structure contribute little to stability; e.g. rotator
cuff of the shoulder have strong inwards pull on the humeral head toward
the glenoid fossa.
5.
Atmospheric Pressure: It plays a role mainly in the hip joint.
Factors Affecting Range of
Motion:
1. Shape of articular surfaces.
2. Restraining effect of the ligaments and muscles crossing the joint as well as
overlying skin.
3. Controlling and restraining action of the muscles e.g. hamstring muscles
tightness when attempting to touch the floor.
4. Body build: Mesomorph and ectomorph have usually a greater flexibility
than endomorph.
5. The bulk of tissue in the adjacent segments.
6. Personal exercise habits.
7. Current state of physical fitness.
8. Age.
9. Heredity.
•
N.B.: Apparent range of motion can be affected by the close relationship
that exists between certain joints. E.g. relationship of pelvic tilting to
movement of the hip and relationship of the shoulder girdle articulation to
movement of the shoulder joint