Structure and Types of Joints in the Human Body

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  • A joint, also known as articulation is the place where two adjacent bones or cartilages meet.
  • Although most joints are movable, some are not.
  • Movable joints provide the mechanism that allows the body to move through coordination of nervous, skeletal and muscular systems.
  • Joints are classified on two bases:

I. On the basis of their function (Degree of movement):

  • This classification is based on the degree of movement of bones in a joint.
  • According to this system, a joint may be;
    • Immovable (Synarthrosis):
      • Such joints don’t allow movement because bones are rigidly joined together.
      • e.g. Manubriosternal joint, the joints between the skull bones (Sutures)
    • Slightly movable (Amphiarthrosis):
      • They allow limited or slight movement.
      • e.g. Pubic symphysis of the pelvis, intervertebral joints
    • Freely movable (Diarthrosis):
      • They permit a great deal of movement.
      • e.g. Elbow, shoulder and ankle joints

II. On the basis of their structure:

  • This classification is based on the presence or absence of a joint cavity and the kind of supporting tissue that binds the bones together.
  • According to this system, there are three types of joints;
    • Fibrous joints
    • Cartilaginous joints
    • Synovial joints

1. Fibrous joints:

  • Lack a joint cavity
  • Fibrous connective tissue unites the articulating bones tightly
  • Mostly immovable and some are slightly movable
  • Usually synarthroses
  • They are of three types;
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a. Sutures:

  • Found only in the skull
  • Fibrous tissue connects the articulating bones in children
  • Bones are permanently fused in adults
  • Some movement in fetuses and young children but immovable in adults
  • e. g. Cranial sutures

b. Syndesmoses:

  • Articulating bones are held together (without touching each other) by fibrous or interossoeus ligaments.
  • Allow slight movement: twisting of forearm (pronation and supination)
  • e.g. Inferior tibiofibular joint, interosseous ligament between shafts of radius and ulna

c. Gomphoses:

  • A peg fits into a socket.
  • Mostly immovable and some may have very slight movement of teeth in their sockets.
  • e. g. roots of teeth in alveolar processes of mandible and maxillae

2. Cartilaginous joints:

  • The articulating bones are united by a plate of hyaline cartilage or fibro-cartilaginous disk.
  • They also lack a joint cavity.
  • Most of them are slightly movable while some are immovable.
  • Usually amphiarthroses
  • They are of two types;
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a. Synchondroses:

  • Also called a primary cartilaginous joint.
  • It is a temporary joint composed of an epiphyseal plate of hyaline cartilage that joins the diaphysis and epiphysis of a growing long bone.
  • Chief function is to permit growth of the bones, not their movement.
  • Immovable joints
  • e. g. epiphyseal plate of femur, union of manubrium and the body of sternum

b. Symphyses:

  • Also called secondary synchondrosis
  • The two articulating bony surfaces are covered by thin layers of hyaline cartilage.
  • Between them are disks of fibro-cartilage (collagenous fibers with cartilage cells) that serve as shock absorbers.
  • Allow slight movement
  • e. g. pubic symphysis, manubriosternal joint, intervertebral joints

3. Synovial joints:

  • The ends of the articulating bones are covered with a smooth hyaline articular cartilage and the joint is enclosed by a flexible articular capsule.
  • Joint cavity is present which is also called a synovial cavity.
  • The joint is lubricated by a thick fluid called synovial fluid.
  • Articular capsules that are reinforced with collagenous fibers are called fibrous capsules, which are further reinforced at certain portions with collagenous fibers to form a ligament.
  • Allow more free movements than any other type of joint, i.e. usually diarthroses
  • Synovial joints are classified according to the shape of their articulating surfaces and the type of joint movements those shapes permit.
  • Six types of synovial joints are recognized;

Also see in detail: Structure of a Typical Synovial Joint

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a. Hinge joints:

  • The convex surface of one bone fits into the concave surface of another bone.
  • Allows uniaxial movement like flexion and extension (back and forth movement occurs around a single transverse axis)
  • e. g. joints in elbow, interphalangeal joints in fingers, knee and ankle

b. Pivot joints:

  • Central bony pivot is surrounded by a collar of bone and ligament.
  • Allows uniaxial movement like supination, pronation and rotation around a central axis through the center of the pivot.
  • e. g. proximal radioulnar joint, atlantoaxial joint

c. Ball and socket joints:

  • Globe-like head of one bone fits into a cup-like concavity of another bone.
  • This is the most freely movable of all the joints allowing multiaxial movement
  • Allows movements like flexion, extension, medial (internal) rotation, lateral (external) rotation, abduction, adduction and circumduction.
  • e. g. shoulder joint and hip joint

d. Condyloid or Ellipsoidal joints:

  • They are the modifications of multiaxixal ball and socket joints.
  • However, because the ligaments and muscles around the joint limit the rotation to two axes, the joint is classified as biaxial joint.
  • Allows movements like flexion and extension of the hinge joints as well as abduction, adduction and circumduction.
  • No rotational movement in permitted.
  • e. g. metacarpophalangeal (knuckle) joints except thumb

e. Gliding joints (Plane joints):

  • They are almost always small and are formed by essentially flat articular surfaces.
  • One bone slides on another bone with a minimal axis of rotation, if any.
  • Allows multiaxial movement like simple gliding within narrow limits.
  • e. g. between articular processes of vertebrae, acromioclavicular joint, some carpal and tarsal bones

f. Saddle joints:

  • The opposing articular surfaces of both bones are shaped like a saddle, i.e. they have both concave and convex areas that fit into one another at right angles to each other.
  • Allows multiaxial movements like abduction, adduction, opposition and reposition.
  • e. g. carpometacarpal joint of thumb

Structure and Types of Joints in the Human Body