Articulations or Joints

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Articulations or Joints

• Articulation or Joint
• Place where two bones (or bone and cartilage)
  come together
• Arthrology study of the joints
• Functions of joints
• Give the skeleton mobility
• Hold the skeleton together
• Structure correlated with movement

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Classification of Joints

• Structural classes based on type of connective
  tissue type that binds bones and whether or not a
  joint cavity is present
• Fibrous
• Cartilaginous
• Synovial
• Functional classes based on degree of motion
• Synarthrosis non-movable
• Amphiarthrosis slightly movable
• Diarthrosis freely movable

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Fibrous Joints

• Characteristics
• United by fibrous connective tissue
• Have no joint cavity
• Move little or none
• Types
• Sutures
• Syndesmoses

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Fibrous Joints Syndesmoses

• Two bones joined by ligament
• Most moveable of fibrous joints
• Examples radioulnar joint and tibiofibular joints

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Cartilaginous Joints

• Bones are joined by cartilage
• Lack a joint cavity
• Types
• Synchondroses bound by hyaline cartilage
• Symphyses bound by fibrocartilage

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Cartilaginous Joints Synchondroses

• Joined by hyaline cartilage
• Little or no movement
• Some are temporary and are replaced by synostoses
• Some are permanent
• Some like costochondral joints develop into
  synovial joints
• Examples Epiphyseal plates, 1st sternocostal

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Cartilaginous Joints Symphyses

• Fibrocartilage uniting two bones
• Slightly movable
• Examples symphysis pubis, between the manubrium
  and the body of the sternum, intervertebral
  disks.

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Synovial Joints

• Contain synovial fluid in a joint cavity called
  the synovial cavity
• Allow considerable movement (diarthroses)
• Most joints that unite bones of appendicular
  skeleton reflecting greater mobility of
  appendicular skeleton compared to axial

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Structure of Synovial Joints

• Articular cartilage
• Hyaline cartilage that covers epiphysis
• Absorbs compression of joint
• Joint cavity (synovial cavity)
• Unique to synovial joints
• Cavity is a potential space that holds small
  amount of fluid
• Synovial fluid
• Viscous fluid similar to raw egg white
• A filtrate of blood from capillaries in synovial
  membrane
• Contains glycoprotein molecules secre-ted by
  fibroblasts
• Nerves in capsule help brain know position of
  joints (proprioception)

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Flexion and Extension

• Flexion movement of a body part anterior or
  posterior to the coronal plane
• Extension movement of a body part posterior or
  anterior to the coronal plane
• Dorsoflexion - foot lifted toward the shin
• Plantar flexion - pointing toes downward
• Abduction movement away from the midline
• Adduction movement toward the midline

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Types of Synovial JointsPlane Joints

• Plane or gliding joints
• Monaxial. One flat bone surface glides or slips
  over another similar surface
• Sometimes considered an amphiarthrosis
• Examples intervertebral, intercarpal,
  intertarsal acromioclavicular, carpometacarpal,
  tarsometatarsal,

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Hinge and Pivot Joints

• Hinge joints
• Monaxial
• Convex cylinder in one bone corresponding
  concavity in the other
• Example elbow, ankle, interphalangeal
• Pivot joints
• Monaxial. Rotation around a single axis.
• Cylindrical bony process rotating within a circle
  of bone and ligament
• Example articulation between dens of axis and
  atlas (atlantoaxial), proximal radioulnar

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Types of Synovial Joints

• Saddle joints
• Each articular surface is shaped like a saddle
• Trapeziometacarpal joint at base of the thumb
  

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Ball-and-Socket and Ellipsoid Joints

• Ball-and-socket
• Smooth heispherical head fits within a cuplike
  depression
• Multiaxial
• Examples shoulder and hip joints
• Condyloid (ellipsoid) joint
• Oval convex surface on one bone fits into a
  similarly shaped depression on the next
• Atlantooccipital joint (C1-C2)
• Metacarpophalangeal joints

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The Knee Joint

• Most complex diarthrosis
• patellofemoral gliding joint
• tibiofemoral gliding with slight rotation and
  gliding possible in flexed position
• Joint capsule anteriorly consists of patella and
  extensions of quadriceps femoris tendon
• Capsule strengthened by extracapsular and
  intracapsular ligaments

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Effects of Aging on Joints

• Tissue repair slows rate of new blood vessel
  development decreases
• Articular cartilages wear down and matrix becomes
  more rigid
• Production of synovial fluid declines
• Ligaments and tendons become shorter and less
  flexible decrease in range of motion (ROM)
• Muscles around joints weaken
• A decrease in activity causes less flexibility
  and decreased ROM