Joints

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Joints
Biomechanics of the joint

• Definition
• Joint is the articulation between any of rigid
  component parts of the skeleton whether bones or
  cartilage by different tissues.

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Functions of the joints

• 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
• The shape of the contours of the contacting
  surfaces.
• How well it fits together.

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• 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.

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Classification of synovial joints
Example Mechanical Classification Anatomical classification
Elbow joint Uniaxial Hinge joint
Atlanto axial joint, Superior radio-ulnar joint Uniaxial Pivot joint
Knee joint Biaxial Codyloid joint
Carpometacarpal joint of the thumb Biaxial Saddle joint
Wrist joint Triaxial Elbsoid joint
hip joint and shoulder joint Triaxial Ball and socket
Midtarsal joints of foot Nonaxial Gliding joint
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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

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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

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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?

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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
• 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

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Arthrokinematics

• Arthrokinematics means motions of
• bone surfaces within the joint are
• Roll, Slide, Spin, Compression
• and Distraction
• (5 motions)

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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.

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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.

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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
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Slide (glide)
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• 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.

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CONGRUENCE OF ARTICULAR SURFACES

• a) CLOSE-PACKED POSITION OF THE
• JOINT .
• b) LOOSE- PACKED POSITION

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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.

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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.

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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.

• 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.

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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
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• 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

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Factors Affecting Joint Stability ( Resistance
to Displacement)

• 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.
• 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.
• Fascia Accordingly to the location and function
  of the fascia, it may vary from thin to tough and
  fibrous membranes.
• 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.

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Factors Affecting Range of Motion

• Shape of articular surfaces.
• Restraining effect of the ligaments and muscles
  crossing the joint as well as overlying skin.
• Controlling and restraining action of the
  muscles e.g. hamstring muscles tightness when
  attempting to touch the floor.
• Body build Mesomorph and ectomorph have usually
  a greater flexibility than endomorph.
• The bulk of tissue in the adjacent segments.
• Personal exercise habits.
• Current state of physical fitness.
• Age.
• 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