Joints

Joints Overview

  • A joint is a point of contact between:
    • Two or more bones
    • Cartilage and bone
    • Teeth and bone
  • Also called articulation or arthrosis

Classification of Joints

  • Structurally
    • Is there a joint cavity?
    • What type of connective tissue is involved?
  • Functionally
    • What degree of movement is permitted?

Structural Classification of Joints

  • Fibrous: No articular cavity; little or no movement.
    • Articulating bones held together by dense irregular connective tissue.
    • Types: Sutures, Syndesmoses.
  • Cartilaginous: No articular cavity; little or no movement.
    • Articulating bones held together by hyaline or fibrous cartilage.
    • Types: Synchondrosis, Symphysis.
  • Synovial: Have articular capsule; permit a large range of movement.
    • Characterized by synovial cavity and articular cartilage; may contain accessory ligaments, articular discs, and bursae.
    • Types: Hinge, Ball-and-socket, Condyloid (ellipsoid).

Movements at Synovial Joints

  • Gliding: Movement of relatively flat bone surface back-and-forth and side-to-side over another; little change in angle between bones.
  • Angular: Increase or decrease in angle between bones.
    • Flexion: Decrease in angle between articulating bones.
    • Lateral flexion: Movement of trunk in frontal plane.
    • Extension: Increase in angle between articulating bones.
  • Abduction: Movement of bone away from midline.
  • Adduction: Movement of bone toward midline.
  • Circumduction: Flexion, abduction, extension, adduction, and rotation in succession; distal end of body part moves in circle.
  • Rotation: Movement of bone around longitudinal axis; may be medial or lateral.
  • Special: Occurs at specific joints.
    • Elevation: Superior movement of body part.
    • Depression: Inferior movement of body part.
    • Protraction: Anterior movement of body part in transverse plane.
    • Retraction: Posterior movement of body part in transverse plane.
    • Inversion: Medial movement of sole.
    • Eversion: Lateral movement of sole.
    • Dorsiflexion: Bending foot in direction of dorsum.
    • Plantar flexion: Bending foot in direction of plantar surface.
    • Supination: Movement of forearm that turns palm anteriorly.
    • Pronation: Movement of forearm that turns palm posteriorly.
    • Opposition: Movement of thumb across palm to touch fingertips on same hand.

Structural and Functional Classification of Synovial Joints

  • Plane: Articulated surfaces flat or slightly curved; biaxial or triaxial.
  • Hinge: Convex surface fits into concave surface; uniaxial (flexion-extension).
  • Pivot: Rounded or pointed surface fits into ring; uniaxial (rotation).
  • Ellipsoid: Oval-shaped projection fits into oval-shaped depression; biaxial (flexion-extension, abduction-adduction).
  • Saddle: Saddle-shaped articular surface; biaxial (flexion-extension, abduction-adduction).
  • Ball-and-socket: Ball-like surface fits into cuplike depression; triaxial (flexion-extension, abduction-adduction, rotation).

Factors Affecting Contact and Range of Motion at Synovial Joints

  1. Structure and shape of articulating bones
  2. Strength and tension of joint ligaments
  3. Arrangement and tension of muscles
  4. Contact of soft parts
  5. Hormones
  6. Disuse

Selected Joints of the Body

  • Temporomandibular: Depression, elevation, protraction, retraction, lateral displacement, slight rotation.
  • Shoulder: Flexion, extension, hyperextension, abduction, adduction, medial and lateral rotation, circumduction.
  • Elbow: Flexion and extension.
  • Hip: Flexion, extension, abduction, adduction, medial and lateral rotation, circumduction.
  • Knee: Flexion, extension, slight medial and lateral rotation.

Aging and Joints

  • Decreased production of synovial fluid
  • Thinning of articular cartilage
  • Loss of ligament length and flexibility
  • Arthroplasty: Joint replacement surgery.

Disorders

  • Rheumatism and arthritis
  • Lyme disease
  • Sprain and strain
  • Tenosynovitis
  • Dislocated mandible