Joints

• Arthrology


  The study of joints (articulations)
• Classification of joints by type of tissue

  • Fibrous
  • Cartilagenous
  • Synovial
• Classification of joints by degree of movement


  • Immovable
  • Limited movement
  • Freely movable
• Joints


  Connections between 2 or more bones that are capped, surrounded and hold the bones together, and determine the type and degree of movement between them
• Functional classification of joints

  • Immovable or slightly moveable (Synarthroses)
  • Freely moveable (Diarthroses)
• Synarthroses


  • Serve to protect internal organs, give stability to the body and allow for limited body movement
• Diarthroses


  • Allow for much more extensive movements of the body and limbs
• Fibrous joints


  Bones held together by dense collagenous elastic connective tissue (fibrous tissue)
• Sutures


  • Irregular interlocking margins of the bones, with narrow strips of fibrous tissue between the margins
• The wider sutures of the fetal skull allow some useful passive deformation during birth in some species, e.g. humans and primates
• Syndesmoses


  Relatively broad areas of bone united by short ligaments, allowing very restricted movement
• Gomphosis


  The attachment of a tooth to the bone of its socket
• Cartilaginous joints


  Adjacent bones are united by hyaline or fibrocartilage
• Types of cartilaginous joints

  • Synchondroses (united by hyaline cartilage, appreciable movement)
  • Symphyses (united by fibrocartilage, limited movement)
• Temporary cartilaginous joints


  Disappear with ossification of the cartilage, becoming synostoses (bones united by bone tissue)
• Temporary cartilaginous joints


  • Between epiphyses and diaphysis (epiphyseal plate) of growing long bones
• Permanent cartilaginous joints


  • Between bodies of the vertebrae, pelvic girdle, between the symmetrical halves of the mandible, between the skull and hyoid apparatus, costochondral junctions
• Synovial joints


  The articulating bones are separated by a fluid-filled space, the synovial cavity, surrounded by a joint capsule
• Components of the synovial joint capsule

  • Synovial membrane (delicate connective tissue)
  • Fibrous layer (strengthened externally by ligaments)
• Synovial membrane


  • Has no junctional complexes or continuous covering of cells, and no basement membranes
• Composition of the synovial membrane

  • Synovial cells (of mesenchymal origin)
  • Loose fibrous tissue
  • Adipose tissue
  • Dense irregular connective tissue
• Synovial cavity


  Contains synovial fluid, a viscous, colourless to pale straw-medium brown fluid in small amounts
• Synovial fluid


  • Lubricates and nourishes the articular cartilage, and contains hyaluronic acid, aminoglycans, and glycoproteins
• Ligaments in synovial joints


  • Intracapsular (e.g. cruciate ligaments)
  • Extracapsular (e.g. collateral ligaments)
• Ligaments


  • Contain both white fibrous tissue and some elastic tissue
• Accessory structures in synovial joints

  Articular disks or menisci, composed of hyaline cartilage, fibrocartilage, or fibrous tissue
• Accessory structures


  • Means of resolving complicated movements into simpler components
• Types of synovial joints based on number of surfaces

  • Simple (2 articular surfaces)
  • Compound (more than 2 articular surfaces)
• Types of synovial joints based on shape of articular surfaces

  • Plane
  • Hinge
  • Pivot
  • Ball and socket
  • Condylar
• Plane joint


  Articular surfaces are essentially flat, permitting slight movement
• Hinge joint


  Permits flexion and extension with a limited degree of rotation, with the most movable surface usually concave
• Pivot joint


  Chief movement is around a longitudinal axis through the bones forming the joint
• Ball and socket joint

  Formed by a convex hemispherical head that fits into a shallow or deep cavity
• Condylar joint


  Resembles a hinge joint in movement, but has rounded prominences or condyles that fit into depressions or condyles of the adjacent bone
• Stifle joint


  • A complex condylar joint that possesses an intra-articular fibrocartilage that partially subdivides the intraarticular cavity