Body Joints

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Body Joints

• Every bone in the body is connected to or forms a
  joint with at least one other bone

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Joints perform two functions in the body

• they hold the skeletal bones together and
• they allow the rigid skeleton some flexibility so
  that gross movements can occur.

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Joints are points of union between bones.

• They may be more or less freely moveable,
• or fixed, allowing no movement whatsoever
  between the bones they join.

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Functionally joints are classified as

• Immovable Joints ( synarthroses
  arthrosejoint, syntogether - bone stuck
  together),
• Slightly Movable Joints ( amphiarthroses
  arthrosejoint, amphiboth - in between
  immovable and freely movable ),
• Freely Movable Joints ( diarthroses
  arthrosejoint, diaapart - bone apart, can move
  easily).

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Structurally joints are classified as

• fibrous joints
• cartilaginous joints
• synovial joints

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FIBROUS JOINTS

• There is NO JOINT CAVITY.
• Most of the fibrous joints are immovable - a few
  are slightly movable.

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There are three subtypes of fibrous joints

• Sutures
• Syndesmosis
• Gomphosis

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Sutures

• The connecting fibers holding bones together are
  short.
• This type of joint occurs only in the skull
  cranial sutures

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Syndesmosis

• Long connecting fibers holding two bones
  together.
• tibia/fibula joint and the interosseous membrane
  connecting the radius and ulna along their length

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Gomphosis

• It is a peg-in-socket fibrous joint.
• The only examples are the articulations of teeth.

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CARTILAGINOUS JOINTS

• In cartilaginous joints the bones are united with
  each other by cartilage.
• Again, there is NO JOINT CAVITY.

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There are two types of cartilaginous joints

• Primary cartilaginous joints
• Secondary cartilaginous joints

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Primary cartilaginous joints

• A plate of hyaline cartilage connects the bones
  at the joint.
• Only hyaline cartilage is involved, and the
  joints are immoveable.

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Secondary cartilaginous joints

• The articular surface of each bone is covered
  with a thin layer of hyaline cartilage, and
  fibrocartilage unites these two layers.
• Limited movement is permitted.

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SYNOVIAL JOINTS

• freely moveable joints
• A closed space or CAVITY between the bones the
  joint cavity ( synovial cavity).

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The articulating surfaces of the bones is

• Covered by a thin layer of very smooth hyaline
  cartilage (articular cartilage)
• Lubricated by a special fluid, the synovial fluid
  secreted by the synovial membrane which lines the
  cavity.

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Bursae

• are small sacs filled with synovial fluid that
  reduce friction in the joint.
• lined with synovial membrane
• The knee joint contains 13 bursae

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Synovial joints are classified according

• to the shape of the articulating surfaces
• and the range of movement permitted.

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They can be classified into six major categories

• 1. Plane ( gliding)
• 2. Hinge
• 3. Pivot
• 4. Ellipsoidal
• 5. Saddle
• 6. Ball and socket

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Plane ( gliding)

• Opposite bone surfaces are flat or slightly
  curved.
• Only sliding motion in all directions are
  allowed. Examples Carpal and Tarsal  

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Hinge

• Convex surface of one bone fits smoothly into
  concave surface of the second bone
• Examples Elbow and Ankle joints

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Pivot

• only movement allowed is the rotation of one bone
  around its own axis
• Examples Atlanto axial and proximal Radio ulna
  joints

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Ellipsoidal (biaxial)

• Oval-shaped surface fits into an oval-shaped
  cavity (ellipse means oval).
• Examples the Radio carpal and Metacarpophalangeal
  joints.

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Saddle

• The articular surface of one bone is grooved to
  accommodate the articular surface of the other
  bone.
• Example the Carpophalangeal joint of the thumb.

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Ball and socket

• Ball-shaped head fits into a cup-shaped
  depression
• Most freely moving of all synovial joints.
• These joints are multiaxial.
• Examples the Hip and the Shoulder

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