Joints

• a joint point of contact between two bones,

  cartilage and bone, or teeth and bone.
• Structural classification is based on the presence or absence of a

  synovial cavity and the type of connecting tissue.
• Structurally,

  joints are classified as fibrous, cartilaginous, or synovial.
• Structurally,

  joints are classified as fibrous, cartilaginous, or synovial.
• Joints may be synarthroses (immovable),

  amphiarthroses (slightly movable), or diarthroses (freely

  movable).
• There is no joint cavity and the bones are held together by

  dense irregular connective tissue in fibrous joints.
• These joints include slightly movable or immovable sutures

  (found between skull bones), slightly movable syndesmoses

  (such as the distal joint between the tibia and fibula), immov-

  able gomphoses (roots of teeth in alveoli of the mandible and

  maxilla), and slightly movable interosseous membranes (found

  between the radius and ulna and tibia and fibula).
• There is no joint cavity and the bones are held together by car-

  tilage in cartilaginous joints.
• These joints include immovable synchondroses united by hya-

  line cartilage (epiphyseal plates) and slightly movable symphy-

  ses united by fibrocartilage (pubic symphysis)
• A synovial joint contains a synovial cavity. All synovial joints

  are diarthroses
• Other characteristics of a synovial joint are the presence of ar-

  ticular cartilage and an articular capsule, made up of a fibrous

  membrane and a synovial membrane.
• The synovial membrane secretes synovial fluid, which forms a

  thin, viscous film over the surfaces within the articular capsule.
• Many synovial joints also contain accessory ligaments and ar-

  ticular discs.
• Bursae are saclike structures, similar in structure to joint cap-

  sules, that reduce friction in joints such as the shoulder and

  knee joints.
• In a gliding movement, the nearly flat surfaces of bones move

  back-and-forth and side-to-side.
• In angular movements, there is a change in the angle be-

  tween bones. Examples are flexion–extension, hyperextension,

  abduction–adduction, and circumduction
• In rotation, a bone moves around its own longitudinal axis.
• Special movements occur at specific synovial joints in the body.

  Examples are as follows: elevation–depression, protraction-

  retraction, inversion–eversion, dorsiflexion–plantar flexion, and

  supination–pronation.
• Types of synovial joints are planar, hinge, pivot, condyloid, sad-

  dle, and ball-and-socket.
• In a planar joint the articulating surfaces are flat, and the bones

  glide back-and-forth and side-to-side (many are biaxial); exam-

  ples are joints between carpals and tarsals.
• In a hinge joint, the convex surface of one bone fits into the

  concave surface of another, and the motion is angular around

  one axis (monaxial); examples are the elbow, knee (a modified

  hinge joint), and ankle joints
• In a pivot joint, a round or pointed surface of one bone fits into

  a ring formed by another bone and a ligament, and movement

  is rotational (monaxial); examples are the atlanto-axial and ra-

  dioulnar joints
• In a condyloid joint, an oval projection of one bone fits into an

  oval cavity of another, and motion is angular around two axes

  (biaxial); examples include the wrist joint and metacarpopha-

  langeal joints of the second through fifth digits.
• In a saddle joint, the articular surface of one bone is shaped like

  a saddle and the other bone fits into the “saddle” like a sitting

  rider; motion is angular around three axes (triaxial). An exam-

  ple is the carpometacarpal joint between the trapezium and the

  metacarpal of the thumb.
• In a ball-and-socket joint, the ball-shaped surface of one bone fits

  into the cuplike depression of another; motion is around three

  axes (triaxial). Examples include the shoulder and hip joints.
• The knee joint is a diarthrosis that illustrates the complexity of

  this type of joint.
• It contains an articular capsule, several ligaments within and

  around the outside of the joint, menisci, and bursae
• Arthroplasty refers to the surgical replacement of severely

  damaged natural joints with artificial joints
• With aging, a decrease in synovial fluid, thinning of articular

  cartilage, and decreased flexibility of ligaments occur.
• Most individuals experience some degeneration in the knees,

  elbows, hips, and shoulders due to the aging process