Kinesiology of the Musculoskeletal System

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Kinesiology of the Musculoskeletal System

• Chapter 2
• Basic Structure Function of the Joints

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Classification Description of Joints

• Synarthrosis a junction between bones that is
  held together by dense irregular connective
  tissue (CT) little or no movement at this
  junction. i.e. sutures of skull, teeth embedded
  in mandible, distal tibiofemoral joint,
  interosseous membranes of forearm and lower leg.
  
• This type of joint functions to disperse
  stress over a large surface area.

• Amphiarthrosis junction between bones formed by
  fibrocartilage and/or hyaline cartilage
  functions to allow but restrain motion, disperse
  stress. i.e. intervertebral disc, pubic symphysis

Intervertebral disc made of fibrocartilage
example of an amphiarthrosis
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Classification Description of Joints (cont.)

• Diarthrosis a.k.a. Synovial joint this
  articulation contains a fluid filled joint cavity
  located between two boney surfaces much greater
  degree of motion allowed
• Synovial fluid provides lubrication and
  nutrition to articular cartilage
• Articular cartilage covers the ends of the
  bones protects bone
• Articular capsule a.k.a. joint capsule
  internal layer is the synovial membrane which
  produces synovial fluid membrane also acts as a
  barrier external fibrous layer of capsule
  provides support reinforced by capsular
  ligaments
• Diarthrotic joints may contain
• Intraarticular disc or menisci, i.e. knee,
  sternoclavicular acromioclavicular joints, TMJ
  functions to increase congruency, disperse stress
• Labrum, i.e. glenohumeral and hip joints
  functions to deepen and stabilize the joint

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Joint Classification
Diarthrosis
Synarthrosis
Amphiarthrosis
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Classification of Synovial Joints by Analogy

• Hinge Joint largely allows uni-planar motion of
  flexion/extension, i.e. humeroulnar joint
  analogous to a door hinge
• Pivot Joint allows angular motion of spin,
  analogous to a doorknob, i.e. proximal radioulnar
  joint or atlanto-axial joint (C1-C2 vertebrae)

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Synovial Joints by Analogy (cont.)

• Ellipsoid Joint the union of an elongated
  convex surface with an elongated concave surface,
  i.e. radiocarpal joint allows bi-planar
  movement, restricted from spinning by elliptical
  shape
• Ball and Socket Joint a spherical convex
  surface paired with a cuplike socket provides
  for tri-planar movement, allowing spin i.e.
  glenohumeral and hip joints

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Synovial Joints by Analogy (cont.)

• Plane Joint pairing of two relatively flat
  surfaces allows for sliding and some rotation,
  analogous to a book on a desk i.e. zygapophyseal
  (posterior vertebral) joints, inter-carpal joints
• Saddle Joint comprised of a convex surface and
  a concave surface at right angles to each other
  and are reciprocally curved analogous to a
  saddle and rider i.e. sternoclavicular joint
• Condyloid Joint similar to a ball and socket
  joint, but the concave surface is very shallow
  allows bi-planar movement, 3rd plane of motion
  restricted by ligaments and bony incongruity
  i.e. tibiofemoral (knee) joint

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Simplifying Synovial Joint Classification

• An alternative classification can be made by
  general joint surface shape. With the exception
  of planar joints, the articulating surfaces can
  be classified by either ovoid or saddle.
• Ovoid paired mating surfaces that are
  imperfectly spherical, or egg-shaped, with
  adjacent parts possessing a changing surface
  curvature one surface is concave, one is convex
• Saddle paired curved surfaces that are opposite
  in direction and oriented at 90 degrees to each
  other.

• Ovoid and Saddle joint structure
• classification allows for Roll, Slide
• Spin arthrokinematics

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Axis of Rotation

• A of R an imaginary line extending through a
  joint about which rotation occurs
• A joints A of R is a non-anatomical axis
• In anatomic joints, the A or R is not a fixed
  axis
• IAR Instantaneous A of R the A of R at a
  given point within the joints ROM
• IAR changes through joint ROM
• Evolute the path of the serial locations of the
  IAR
• The path of the evolute is longer and more
  complex when mating joint surfaces are less
  congruent or have greater changes in their radii
  of curvature, i.e. knee.
• For practical purposes, the IAR can be estimated
• based on the average IAR evolute
• Goniometry
• Prosthetic joint
• Orthopedic brace sizing
• Athletic taping to support or restrict joint
  motion

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Migrating IAR
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Biological Materials

• Four primary tissues of the body
• Muscle
• Nerve
• Epithelium
• Connective Tissue
• Connective Tissue (CT)
• Dense irregular CT
• Articular cartilage
• Fibrocartilage
• Bone
• Loose areolar CT not a significant component of
  joints
• Blood - not a significant component of joints

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Fundamental Materials of Joint CT

• Fibers various types of collagen fibers and
  elastic fibers
• Collagen short helical fibers grouped together
  and formed into strands
• Type 1 collagen thick rugged fibers gathered
  into bundles these fibers do not appreciably
  elongate when stretched designed for support
  i.e. ligaments, fascia, joint capsules, tendons
• Type 2 collagen thinner, less stiff than type 1
  fibers provide a flexible framework for
  maintaining shape and consistency of tissues that
  require less stiffness, i.e. hyaline cartilage
• Elastin comprised of interwoven elastin fibrils
  that resist tensile (stretching) forces but tend
  to give when elongated return to original
  shape when force is removed from the tissues
  i.e. ear

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Fundamental Materials of Joint CT (cont.)

• Ground substance water saturated substance in
  which collagen and elastin fibers are embedded
  cells also embedded in the ground substance
• Glycosaminoglycans (GAG) a glucose/protein
  molecule found within the ground substance
  responsible for binding water GAG cause tissue
  swelling due to high binding affinity held in
  check by collagen and elastin fiber network,
  providing structure and rigidity of the tissue
• Clinical Note GAGs are often prescribed and
  supplemented as an attempt to maintain connective
  tissue integrity and viscosity of synovial fluid
• Cells located within the ground substance
  responsible for maintenance and repair i.e.
  fibroblast, chondrocyte, osteoblasts

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CT Structure of Joints

• Dense irregular CT joint capsule, ligaments,
  tendons fascia high type 1 collagen content, low
  elastin low ground substance content sparse
  cell content
• Articular cartilage articular (hyaline)
  cartilage high type 2 collagen content high
  ground substance content moderate cell content
  resists and distributes compressive forces low
  coefficient of friction
• Fibrocartilage intervertebral disc (IVD)
  menisci of knee glenoid and acetabular labrums
  high type 1 collagen content arranged in multiple
  directions moderate ground substance and cell
  content provides some support and stabilization
  of joints, shock absorption
• Bone specialized type 1 collagen content is
  high low GAG content moderate cell content
  resists deformation, provides rigid lever for
  motion

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Effects of Aging on CT

• Rate and process by which aging effects the body
  is highly individual
• Fiber and GAG replacement and repair is slowed
• Effects of microtrauma accumulate over time,
  resulting in sub-clinical damage, and possibly
  tissue failure
• GAG produced by aging cells are fewer in number
  and smaller in size, resulting in diminished
  water binding and tissue hydration
• Less hydrated tissue is more susceptible to
  compression forces
• Fiber bundles within ligaments become loosely
  formed, lowering their ability to resist applied
  forces
• CT adhesions form joints lose ROM
• Less hydrated cartilage becomes brittle, and less
  able to attenuate and distribute imposed forces
• Tissue injury results in greater healing times

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Immobilization and CT Health

• Amount and arrangement of fibers and GAG in CT is
  influenced by physical activity
• Joint immobilization for extended periods results
  in diminished strength of the tissues, due to the
  lack of force production of the injured or
  immobilized tissues normal response to an
  abnormal condition
• Immobilization results in a marked decrease in
  the tensile strength of ligaments that is
  measurable within days of immobilization, and
  which may never return to the pre-immobilization
  level
• Bone and cartilage show losses of mass, volume
  and strength
• Connective tissues respond to the demands, or
  lack thereof placed upon them

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The Evolution of Posture
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Joint Pathology

• Acute Trauma damage to a joint resulting from a
  single overwhelming event
• Joints frequently affected by acute trauma are
  often associated with the longest lever arms, and
  therefore, are exposed to high external torques
• Acute trauma of a joint may result in fracture of
  bone or tearing of cartilage, ligaments, tendons
  or capsules
• Fibrocartilage repair is poor, and depends on the
  extent of blood supply to the tissue, i.e. knee,
  IVD

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Chronic Trauma

• Chronic Trauma damage to a joint resulting from
  an accumulation of lesser injuries over an
  extended period of time
• Chronic trauma is often classified as Overuse
  Syndromes

• Overuse syndromes involve a cyclical pattern in
  which many episodes of minor, microtrauma to the
  tissues results in constant inflammation with
  poor, incomplete healing of the tissue tissue
  strength diminishes and the likelihood of tissue
  failure increases

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Fibrocartilage
Articular Cartilage
Dense Irregular CT
Loose Areolar CT
Bone
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References

• Neumann, DA. Kinesiology of the Musculoskeletal
  System. Elsevier. 2002