Joints

Objectives

• define the term “joint”

• explain the differences between synovial joint, fibrous joint and cartilaginous joint

• list typical features of all synovial joints

• describe major synovial joint types

• describe three basic motion axes permitted at ball and socket joints

joints (articulations): the union between 2+ bones or cartilage. classified depending on the type of connective tissue uniting the bones

• fibrous connective tissue unites bones meeting at fibrous joints and fills the spaces between them

  • unites bones of the skull

  • attach teeth to jaws

  • form substantial membranes between the radius and ulna in upper limbs and fibula and tibia in lower limbs

• cartilage unites bones meeting at cartilaginous joints and fills the spaces between them

  • joins hip bones at pubic symphysis

  • form part of inner vertebral disks joining vertebrae

    • epiphysis (cartilaginous growth plates) form temporary joints in developing long bones

• compression, stretching, bending and twisting of fibrous connective tissue in fibrous joints, or cartilage in cartilaginous joints, allow motion between bones meeting at the joint

• synovial joints allow for greater mobility. features include:

  • joint cavity

    • allows greater mobility

    • bone slide against each other rather than having a plate of tissue form

  • hyaline articular cartilage

    • cap bone ends

  • synovial membrane

    • secretes slippery synovial fluid

    • lines outer fibrous capsule

      • consists of dense connective tissue

      • two layer capsule: finrous connective tissue outside, synovial lining inside

  • internal/external ligaments

    • pieces of connective tissue limiting motion at the joints

• synovial joints are classified according to the shapes of the bones meeting at the joint

  • plane:

    • two flat surfaces

    • gliding occurs when articular surfaces of the bones meeting at a synovial joint slide across one another with little or no angulation between the bones

    • found between arches of the vertebrae, behind the articular disks

      • flexing and extending your spine changes the intervertebral disks shape and the bones meeting at the synovial joints will slide across one another

  • hinged

    • located in elbow and knee

    • motion in one axis (flexion + extension)

  • ball and socket

    • most mobile

      • located in shoulder and hip

    • permit motion in three axes

      • other joints have one or two axes

      • flexion + extension

        • flexion: the angle between the bones meeting at a joint decreases (becomes more acute)

        • extension: the angle between the bones meeting at a joint increases (becomes more obtuse)

      • abduction + adduction

        • abduction: a limb or limb segment moves away from the body midline

        • adduction: a limb or limb segment moves towards the body midline

      • internal + external rotation

        • internal rotation: a limb or limb segment turns around its longitudinal axis toward the midline (backward)

        • external rotation: a limb or limb segment turns around its longitudinal axis away from the midline (forward)

  • condyloid

  • saddle

  • pivot

• bone congruence at joints is the degree which bone surfaces are in contact

• most limb joints are synovial joints

• the motions permitted at a synovial joint are determined by the shapes of the bone articulations ends meeting at the joint and the ligaments and other structures limiting motion at the joint