Difference between revisions of "Joints - Anatomy & Physiology"

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|maplink = Musculoskeletal System (Content Map) - Anatomy & Physiology
 
|maplink = Musculoskeletal System (Content Map) - Anatomy & Physiology
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==Links==
 
==Links==
 
*[[Joints - Pathology|Joint Pathology]]
 
*[[Joints - Pathology|Joint Pathology]]
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[[Category:Musculoskeletal System]]

Revision as of 16:30, 29 August 2010

()Map MUSCULOSKELETAL SYSTEM (Map)



Introduction

Joints comprise broadly two categories:

  • Synarthroses form joints that are relatively rigid
  • Diarthroses form joints that are freely movable

Joint Function:

  • Absorb force of impact, transfer force via cartilage to bone
  • Allow a variable degree of movement

Fibrous Joints

Sutures of the skull- Copyright Thegreenj
  • Most occur in the skull: known as sutures
    • Key in development: allow extension of individual bones during growth
    • Gradually eliminated as ossification progresses
  • Syndesmoses: facing areas of two bones joined by connective tissue ligaments, very limited movement allowed
    • Eg. Joints of the metacarpus in the horse
  • Gomphosis: attachment of tooth to bone within its socket



Cartilaginous Joints

Pelvic Symphysis, Gray's Anatomy - Wikimedia Commons 2008
  • Synchondroses: eg. joints between epiphyses and diaphyses of juvenile long bones, disappear on maturity
    • Permanent synchondroses: the joint between the skull and hyoid
  • Symphysis: articulating bones are divided by a succession of tissues, with cartilage covering the bones or the tissue between
    • Eg. mandibular, pelvic, vertebral
    • Fibrocartilagenous joints
      • Form major union between vertebrae, except first two cervical vertebrae
      • Nucleus pulposus is position eccentrically within annulus fibrosis
      • Vertebrae in thoracic region have conjugal ligaments
        • Extend from rib to rib on opposite sides
        • Strenghten the area over the discs

Synovial Joints

File:Synovial Joint.jpg
Synovial Joint - Wikimedia Commons 2008
  • Articulating joints are separated by a fluid-filled joint cavity, which is bounded by a synovial membrane
    • Synovial membrane: pink connective tissue sheet, vascular and sensitive
      • Can be unsupported (membrane may pouch, allowing remote access), resting on an outer fibrous capsule, or separated from capsule by pads of fat
      • No continuous covering of cells
      • Where cells exist, they produce lubricant (aminoglycans) of synovial fluid
    • Synovial fluid: Nourishes and lubricates articular cartilage
      • Derived from synovial membrane cells and blood plasma
      • Normal amount in canine joint - 0.01 - 1.0 ml; possible in equine/bovine: 20-40mL
      • Transparent to light yellow (horses)
      • Usually very thick due to high hyaluronic acid, forms strands
      • Windrowing of cells on smear
      • Normal protein < 25g/l (all species)
      • Normal cell count: Large mononuclear cells, <12% neutrophils, <11% lymphocytes
        • Small animals - < 3 x 10e9/L
        • Horses - < 0.5 x 10e9/L
        • Cows - < 1 x 10e9/L
  • Often the synovial membrane is reinforced by a fibrous capsule and ligaments restricting joint movement and providing stability
    • Encloses bone and muscle insertions within joint capsule
    • Supplied by blood vessels and nerve endings
  • Articular cartilage covers the articular surfaces
    Normal joint cartilage (Image courtesy Bristol Biomed Image Archive)
    • Usually, this is Hyaline, although Fibrocartilage or fibrous tissue can substitute
    • Articular cartilage is avascular and insensitive
      • Nutrients via diffusion from synovial fluid and nearby vessels (adjoining tissue and marrow cavities)
  • Some joints possess intracapsular discs or menisci to provide congruence and enable complicated movements
    • Eg. Temperomandibular joint, paired menisci of the stifle joint
    • Limited response to injury, Little repair capacity



Joint Movements

File:Joint movements.jpg
Flexion and Extension - Wikimedia Commons 2008
  • Translation: Flat surfaces slide against each other, producing no change in orientation of their bodies
  • Rotation: Moving bone turns on an axis perpendicular to articulation
  • Swing: Moving bone turns on an axis parallel to articulation
  • Flexion:(aka palmar flexion) Angle between two segments of a limb is reduced
  • Extension: Angle between two segments of a limb is increased
  • Overextension: (aka dorsal flexion) Eg, Posture of equine fetlock standing at rest
  • Adduction: Pendular movement toward the median plane
  • Abduction: Pendular movement away from the median plane
  • Circumduction: Combination of flexion and extension that allows a limb to create a circular movement

Types of Joints

  • Plane Joint: describes translational movement; in reality, nonexistent, as all articular surfaces are curved
  • Hinge Joint: movement allowed in one plane only, inhibited by collateral ligaments and/or bony protuberances (eg. elbow joint)
  • Pivot Joint: comprises a peg fitted with a ring, movement occurs about the long axis of the peg (eg. radioulnar joint)
  • Condylar Joint: knuckle-shaped condyles vary in distance from one another allowing uniaxial movement with limited rotation (eg.femorotibial joint)
  • Ellipsoidal Joint: ovoid convex articulation allows movement in two planes at right angles with limited rotation (eg. radiocarpal joint)
  • Saddle Joint: also biaxial with a greater scope for rotation
  • Spheroidal Joint: (aka ball-and-socket) multiaxial movement allows for rotational movement in several planes (eg hip joint)

Links