JOINTS

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JOINTS
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Joints

• Joints or articulations sites where two or more
  bones meet
• Gives our skeleton mobility and holds it together
• Weakest parts of the skeleton
• Yet, their structure resists various forces, such
  as crushing or tearing, that threaten to force
  them out of alignment

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Structural Classification

• Focuses on the material binding the bones
  together and whether or not a joint cavity is
  present
• In fibrous joints the bones are joined together
  by fibrous tissue and lack a joint cavity
• In cartilaginous joints the bones are joined
  together by cartilage and they lack a joint
  cavity
• In synovial joints, the articulating bones are
  separated by a fluid-containing joint cavity

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Functional Classification

• Is based on the amount of movement allowed at the
  joint
• Synarthroses are immovable joints
• Amphiarthroses are slightly movable joints
• Diarthroses are freely movable joints

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Fibrous Joints

• Bones joined by fibrous tissue
• No joint cavity
• Amount of movement allowed depends on the length
  of the connective tissue fibers uniting the bones
• A few are slightly movable, most are immovable
• Three types
• Sutures
• Syndesmoses
• Gomphoses

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Fibrous JointsSutures

• Occur only between bones of the skull
• Wavy articulating bone edges interlock, and the
  junction is completely filled by a minimal amount
  of very short connective tissue fibers that are
  continuous with the periosteum
• During middle age, the fibrous tissue ossifies
  and the skull bones fuse into a single unit
• At this stage, the sutures are more precisely
  called synostoses (bony junctions)
• Because movement of the cranial bones would
  damage the brain, the immovable nature of sutures
  is a protective adaptation

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FIBROUS JOINT
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Fibrous JointsSyndesmoses

• Bones are connected by a ligament (cord or band
  of fibrous tissue)
• Connecting fibers vary in length amount of
  movement allowed depends on the length of the
  connecting fibers

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Fibrous JointsSyndesmoses

• Slight to considerable movement is possible
• Examples
• 1. Ligament connecting the distal ends of the
  tibia and fibula is short, and this joint allows
  only slight movement
• True movement is still prevented, so the joint is
  classed functionally as an immovable joint, or
  synarthrosis (amphiarthrosis)
• 2. Ligament (interosseous membrane) connecting
  the radius and ulna along their length are long
  enough to permit rotation of the radius around
  the ulna

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FIBROUS JOINT
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Fibrous JointsSyndesmoses
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Fibrous JointsGomphoses

• Gompho Greek for nail/bolt
• Peg-in-socket fibrous joint
• Refers to the way teeth are embedded in their
  sockets (as if hammered in)
• Only example is the articulation of a tooth with
  its bony alveolar socket
• Fibrous connection is the short periodontal
  ligament

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Fibrous JointsGomphoses
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Cartilaginous Joints

• Articulating joints are united by cartilage
• Lack joint cavity
• Two types
• Synchondroses
• Symphyses

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Cartilaginous JointsSynchondroses

• A bar or plate of hyaline cartilage unites the
  bones at a synchondrosis (junction of cartilage)
• Virtually all synchondroses are synarthrotic
  (immovable)
• Examples
• Epiphyseal plates connecting diaphysis and
  epiphysis regions in long bones of children
• (a)Epiphyseal plates are temporary joints and
  eventually become synostoses (bony junctions)
• (b)Immovable joint between the costal cartilage
  of the first rib and the manubrium of the sternum

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Cartilaginous JointsSymphyses
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Cartilaginous JointsSymphyses

• Symphyses (growing together)
• Articular surfaces of the bones are covered with
  articular (hyaline) cartilage, which in turn is
  fused to an intervening pad, or plate, of
  fibrocartilage
• Since fibrocartilage is compressible and
  resilient, it acts as a shock absorber and
  permits a limited amount of movement at the joint
• Amphiarthrotic joints (synarthrosis immovable)
  designed for strength with flexiblity
• Examples
• Intervertebral joints
• Pubic symphysis of the pelvis

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Cartilaginous JointsSymphyses
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Cartilaginous JointsSymphyses
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Synovial Joints

• Articulating bones are separated by a
  fluid-containing joint cavity
• This arrangement permits substantial freedom of
  movement, and all synovial joints are freely
  movable diarthroses (freely movable)
• All joints of the limbsindeed, most joints of
  the bodyfall into this class

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SYNOVIAL JOINT
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Synovial JointsGeneral Structure

• Contains five distinguishing features
• 1.Glassy-smooth articular (hyaline) cartilage
  covers the ends of the opposing articulating
  bones
• Thin but spongy cushions absorb compression
  placed on the joint and thereby keep the bone
  ends from being crushed
• 2.The joint (synovial) cavity is a space that is
  filled with synovial fluid

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SYNOVIAL JOINT
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Synovial JointsGeneral Structure

• 3.The two-layered articular capsule encloses the
  joint cavity
• The external layer is a tough fibrous capsule,
  composed of dense irregular connective tissue,
  that is continuous with the periostea of the
  articulating bones
• It strengthens the joint so that the bones are
  not pulled apart
• The inner layer of the joint capsule is a
  synovial membrane composed of loose connective
  tissue
• Besides lining the fibrous capsule internally, it
  covers all internal joint surfaces that are not
  hyaline cartilage

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SYNOVIAL JOINT
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Synovial JointsGeneral Structure

• 4.Synovial (joint egg) fluid is a viscous
  egg-white consistency, slippery fluid that fills
  all free space within the joint cavity
• Derived largely by filtration from blood flowing
  through the capillaries in the synovial membrane
• Viscous egg-white consistency due to its content
  of hyaluronic acid secreted by cells in the
  synovial membrane, but thins, becoming less
  viscous, as it warms during joint activity

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SYNOVIAL JOINT
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Synovial JointsGeneral Structure

• 4.Synovial fluid
• Also found within the articular cartilage
  providing a slippery weight-bearing film that
  reduces friction between the cartilages
• Forced from the cartilage when a joint is
  compressed weeping lubrication (lubricates the
  free surfaces of the cartilages and nourishes
  their cells)
• Seeps back into the articular cartilages like
  water into a sponge, ready to be squeezed out
  again the next time the joint is put under
  pressure
• Contains phagocytic cells that rid the joint
  cavity of microbes and cellular debris

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SYNOVIAL JOINT
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Synovial JointsGeneral Structure

• 5.Reinforcing ligaments cross synovial joints to
  strengthen the joint
• Capsular, or intrinsic ligaments thickened parts
  of the fibrous capsule
• Extracapsular ligaments outside the capsule
• Intracapsular ligaments deep to the capsule
• Since they are covered with synovial membrane,
  they do not actually lie within the joint cavity
• Double jointed
• People whose joint capsules and ligaments are
  more stretchy and looser than average
• They have the same number of joints

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SYNOVIAL JOINT
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Synovial JointsGeneral Structure

• Richly supplied with sensory nerve endings that
  monitor joints position and help maintain muscle
  tone
• Richly supplied with blood vessels, most of which
  supply the synovial membrane
• Other specific structures
• Hip, knee joints
• Fatty pads between the fibrous capsule and the
  synovial membrane or bone
• Knee, jaw, sternum and clavicle, shoulder, distal
  radioulnar
• Wedge of fibrocartilage separating the articular
  surfaces
• Called articular dics, or menisci
• Extends inward from the articular capsule and
  partially or completely divides the synovial
  cavity in two
• Improve the fit between articulating bone ends,
  making the joint more stable and maintaining wear
  and tear on the joint surfaces

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KNEE JOINT
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KNEE JOINT
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Bursae and Tendon Sheaths

• Not strictly part of the synovial joint, BUT
  often found closely associated with the joint
• Bags of lubricant that reduce friction at
  synovial joints during joint activity
• Bursae (purse) flattened fibrous sacs lined with
  synovial membrane and containing a thin film of
  synovial fluid
• Common where ligaments, muscles, skin, tendons,
  or bones rub together
• Example
• Bunion enlarged bursa at the base of the big
  toe, swollen from rubbing of a tight or poorly
  fitting shoe

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Bursae and Tendon Sheaths

• Tendon sheath
• Essentially an elongated bursa that wraps
  completely around a tendon subjected to friction
• Like a bun around a hot dog

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BURSAE
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Factors Influencing the Stability of Synovial
Joints

• Because joints are constantly stretched and
  compressed, they must be stabilized so that they
  do not dislocate (come out of alignment)
• Stability of a synovial joint depends chiefly on
  three factors
• 1.The shapes of the articular surfaces of bones
  found at a synovial joint
• Determines the movements that occur at the joint
• Play a minimal role in stabilizing the joint
• Example ball and deep socket of the hip joint
  provides the best example of a joint made
  extremely stable by the shape of its articular
  surfaces

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Factors Influencing the Stability of Synovial
Joints

• 2.Number and positioning of ligaments
• Ligament band of regular fibrous tissue that
  connects bones
• Capsules and ligaments of synovial joints unite
  the bones and prevent excessive or undesirable
  motion
• As a rule the more ligaments a joint has, the
  stronger it is
• When other stabilizing factors are inadequate,
  undue tension is placed on the ligaments and they
  stretch
• Stretched ligaments stay stretched (like taffy)
• A ligament can stretch only about 6 of its
  length before it snaps
• When ligaments are the major means of bracing a
  joint, the joint is not very stable

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Factors Influencing the Stability of Synovial
Joints

• 3.Muscle tone low levels of contractile activity
  in relaxed muscles
• Keeps the muscles healthy and ready to react to
  stimulation
• For most joints, the muscle tendons that cross
  the joint are the most important stabilizing
  factor
• Tendon cord of dense fibrous tissue attaching
  muscle to bone
• Kept taut at all times by the tone of their
  muscles
• Extremely important in reinforcing the shoulder
  and knee joints and the arches of the foot

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Movements Allowed by Synovial Joints

• Every skeletal muscle of the body is attached to
  bone or other connective tissue structures at no
  fewer than two points
• The muscles origin is attached to the immovable
  (or less movable) bone
• The other end, the insertion, is attached to the
  movable bone
• Body movement occurs when muscles contract across
  joints and their insertion moves toward their
  origin
• Movements can be described in directional terms
  relative to the lines, or axes, around which the
  body part moves and the planes of space along
  which movement occurs, that is, along the
  transverse, frontal, or sagittal plane

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Movements Allowed by Synovial Joints

• Range of motion
• Nonaxial slipping movements only
• No axis around which movement can occur
• Uniaxial
• Movement in one plane
• Biaxial
• Movement in two planes
• Multiaxial
• Movement in or around all three planes of space
  and axes

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Movements Allowed by Synovial Joints

• Three general types of movement
• 1. Gliding
• 2. Angular
• 3. Rotation

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Movements Allowed by Synovial Joints

• In gliding movements
• Also known as translation
• One flat, or nearly flat, bone surface glides or
  slips over another (back-and-forth or
  side-to-side) without appreciable angulation or
  rotation
• Examples
• Intercarpal and intertarsal joints
• Flat articular processes of the vertebrae

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Synovial MovementGliding
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Movements Allowed by Synovial Joints

• Angular movements
• Increase or decrease the angle between two bones
• May occur in any plane of the body and include
• Flexion
• Extension
• Hyperextension
• Abduction
• Adduction
• Circumduction

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Movements Allowed by Synovial Joints

• Angular Flexion
• Bending movement, usually along the sagittal
  plane
• Decreases the angle of the joint and brings the
  articulating bones closer together
• Examples
• (b) Bending the knee from a straight to an
  angled position
• (b) Arm flexed at the shoulder when the arm is
  lifted in an anterior direction
• (c) Bending the body trunk from a straight to an
  angled position
• (d) Bending the head forward on the chest

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Movements Allowed by Synovial Joints

• Angular Flexion
• (b) Bending the knee from a straight to an
  angled position
• (b) Arm flexed at the shoulder when the arm is
  lifted in an anterior direction

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SYNOVIAL MOVEMENT
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Movements Allowed by Synovial Joints

• Angular Flexion
• (c) Bending the body trunk from a straight to an
  angled position
• Lateral Flexion lateral bending of the trunk
  away from the body midline in the frontal plane

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Movements Allowed by Synovial Joints

• Angular Flexion
• (d) Bending the head forward on the chest

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SYNOVIAL MOVEMENT
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Movements Allowed by Synovial Joints

• Angular Extension
• Reverse of flexion and occurs at the same joints
• Involves movement along the sagittal plane that
  increases the angle between the articulating
  bones
• Examples
• Straightening a flexed elbow or knee
• (c) straightening a flexed body trunk
• (d) straightening a flexed neck

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Movements Allowed by Synovial Joints

• Angular Extension
• (c) straightening a flexed body trunk
• Angular Hyperextension
• Bending backward beyond its straight (upright)
  position

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SYNOVIAL MOVEMENT
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Movements Allowed by Synovial Joints

• Angular Extension
• (d) straightening a flexed neck
• Angular Hyperextension
• Bending backward beyond its straight (upright)
  position

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SYNOVIAL MOVEMENT
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Movements Allowed by Synovial Joints

• Up-and-down movements of the foot at the ankle
  joint are given more specific names
• (e) Dorsiflexion
• Lifting the foot so that its superior surface
  approaches the shin
• Decreases the angle between the top of the foot
  (dorsal surface) and the anterior surface of the
  tibia
• Corresponds to wrist extension
• (e) Plantar flexion
• Depressing the foot
• Decreases the angle between the sole of the foot
  (plantar surface) and the posterior side of the
  tibia
• Corresponds to wrist flexion

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SYNOVIAL MOVEMENT
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Movements Allowed by Synovial Joints

• Angular Abduction (f)
• Moving away
• Movement of a limb (or fingers) away from the
  midline or median plane of the body (or of the
  hand), along the frontal plane
• Examples
• Raising the arm laterally
• Raising the thigh laterally
• When the term is used to indicate the movement of
  the fingers or toes, it means spreading them
  apart
• In this case midline is the longest digit (third
  finger or second toe)

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SYNOVIAL MOVEMENT
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Movements Allowed by Synovial Joints

• Angular Adduction (f)
• Moving toward
• Opposite of abduction
• Movement of a limb (or fingers) toward the
  midline of the body (or the hand)
• In the case of digits, toward the midline of the
  hand or foot (In this case midline is the
  longest digit (third finger or second toe)

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Movements Allowed by Synovial Joints

• Circumduction (f)
• Is moving a limb so that it describes a cone in
  the air
• Distal end of the limb moves in a circle, while
  the point of the cone (shoulder or hip joint) is
  more or less stationary
• Because circumduction consists of flexion,
  abduction, extension, and adduction performed in
  succession, it is the quickest way to exercise
  the many muscles that move the hip an shoulder
  ball-andsocket joints
• Example
• Pitcher winding up to throw a ball

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SYNOVIAL MOVEMENT
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Movements Allowed by Synovial Joints

• Rotation (g)
• Is the turning of a bone along its own long axis
• Only movement allowed between the first two
  cervical vertebrae and is common at the hip and
  shoulder joints
• Examples
• Medial rotation of the thigh
• Femurs anterior surface moves toward the median
  plane of the body
• Lateral rotation of the thigh
• Femurs anterior surface moves away from the
  median plane of the body

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SYNOVIAL MOVEMENT
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Special Movements

• Certain movements do not fit into any of the
  categories previously listed

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Special Movements

• Supination and Pronation refer to the movements
  of the radius around the ulna
• (a) Supination (turning backward) is rotating
  the forearm laterally so that the palm faces
  anteriorly or superiorly
• In the anatomical position, the hand is supinated
  and the radius and ulna are parallel
• Example
• Lifting a cup of soup up to your mouth on your
  palm

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Special Movements

• (a) Pronation (turning forward) is rotating the
  arm medially so that the palm faces posteriorly
  or inferiorly
• Moves the distal end of the radius across the
  ulna so that the two bones form an X
• Forearm position when we are standing in a
  relaxed manner
• Example
• Dribbling a basketball

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BODY MOVEMENTS
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Special Movements

• (b)Inversion and Eversion are special movements
  of the foot
• Inversion turns the sole of the foot so that it
  faces medially
• Eversion turns the sole of the foot so that it
  faces laterally

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BODY MOVEMENTS
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Special Movements

• (c)Protraction and Retraction nonangular
  anterior and posterior movements in a transverse
  plane
• Examples
• Protraction moves the mandible anteriorly, juts
  the jaw forward
• Retraction returns the mandible to its original
  position

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BODY MOVEMENTS
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Special Movements

• (d)Elevation and Depression
• Elevation means lifting a body part superiorly
• Example
• When you shrug your shoulders you are elevating
  the scapulae
• Depression means to move an elevated body part
  inferiorly
• Example
• During chewing, the mandible is alternately
  elevated and depressed

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BODY MOVEMENTS
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Special Movements

• Opposition occurs when you touch your thumb to
  the tips of the other fingers on the same hand
• Makes the human hand a fine tool for grasping and
  manipulating objects
• The saddle joint between metacarpal 1 and the
  carpals allows this movement

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BODY MOVEMENTS
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Types of Synovial Joints

• Although all synovial joints have structural
  features in common, they do not have a common
  structural features
• Based on the shape of their articular surfaces,
  which in turn determine the movements allowed,
  synovial joints can be classified further into
  six major categories
• 1. Plane
• 2. Hinge
• 3. Pivot
• 4. Condyloid
• 5. Saddle
• 6. Ball-and-socket

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Types of Synovial JointsPlane (a)

• Have flat articular surfaces and allow gliding
  and transitional movements
• Does not involve rotation around any axis
• Only example of nonaxial joints
• Examples
• Intercarpal and intertarsal joints
• Joints between vertebral articular processes

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SYNOVIAL JOINTS
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Types of Synovial JointsHinge (b)

• (b) Consist of a cylindrical projection on a
  bone that fits into a trough-shaped structure on
  another bone
• Movement is along a single plane and resembles
  that of a mechanical hinge
• Uniaxial hinge permits flexion and extension only
• Examples
• Bending and straightening the elbow
• Interphalangeal joints

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SYNOVIAL JOINTS
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Types of Synovial JointsPivot (c)

• Consist of a rounded structure that protrudes
  into a sleeve or ring composed of bone (and
  possibly ligaments) of another bone
• Only movement allowed is uniaxial rotation of one
  bone around its own long axis
• Examples
• Joint between the atlas and dens of the axis,
  which allows you to move your head from side to
  side to indicate NO
• Proximal radioulnar joint
• Head of the radius rotates within a ringlike
  ligament secured to the ulna

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SYNOVIAL JOINTS
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Types of Synovial JointsCondyloid (d)

• Knuckle-like
• Ellipsoidal joint
• Consist of an oval articular surface of one bone
  that fits into a complementary depression in
  another bone
• Both articular bones are oval
• Biaxial joint that permits all angular movements
  (flexion, extension, abduction, adduction, and
  circumduction)
• Examples
• Radiocarpal (wrist) joints
• Metacarpophalangeal (knuckle) joints

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SYNOVIAL JOINTS
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Types of Synovial JointsSaddle (e)

• Resemble condyloid joints, but they allow greater
  freedom of movement
• Saddle joints consist of each articular surface
  bearing complementary concave and convex areas
  (shaped like a saddle)
• Allow more freedom of movement than condyloid
  joints
• Examples
• Carpometacarpal joints of the thumbs
• Movements allowed by these joints are clearly
  demonstrated by twiddling your thumbs

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SYNOVIAL JOINTS
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Types of Synovial JointsBall-and-Socket (f)

• Consist of a spherical or hemispherical head
  structure that articulates with a cuplike socket
  structure
• They are the most freely moving joints
• Allow multiaxial movements
• Universal movement is allowed (in all axes and
  planes, including rotation)
• Examples
• Shoulder
• Hip

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SYNOVIAL JOINTS
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Knee Joint

• Knee joint is the largest and most common complex
  joint in the body
• It allows extension, flexion, and some rotation
• Despite its single joint cavity, the knee
  consists of three joints in one
• An intermediate
• One between the patella and the lower end of the
  femur (femoropatellar joint)
• Lateral and medial joints (collectively known as
  the tibiofermoral joint) between the femoral
  condyles above and the C-shaped menisci, or
  semilunar cartilages, of the tibia below
• Besides deepening the shallow tibial articular
  surfaces, the menisci help prevent side-to-side
  rocking of the femur on the tibia and absorb
  shock transmitted to the knee joint

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KNEE JOINT
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KNEE JOINT
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Knee JointAnterior View

• Many different types of ligaments stabilize and
  strengthen the capsule of the knee joint
• The patellar ligament and retinacula are actually
  continuations of the tendon of the bulky
  quadriceps muscles of the anterior thigh
• Physicians tap the patellar ligament to test the
  knee-jerk reflex

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KNEE JOINT
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KNEE JOINT
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Knee JointLateral View

• The synovial cavity of the knee joint has a
  complicated shape, with several extensions that
  lead into blind alleys
• At least a dozen bursae are associated with this
  joint
• The subcutaneous perpatellar bursa is often
  injured when the knee is bumped

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KNEE JOINTLateral View
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Knee Joint

• All three types of joint ligaments stabilize and
  strengthen the capsule of the knee joint
• The capsular and extracapsular ligaments all act
  to prevent hyperextension of the knee and are
  stretched taut when the knee is extended

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Knee JointAnterior View

• Extracapsular fibular and tibial collateral
  ligaments
• Prevent lateral or medial rotation when knee is
  extended

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KNEE JOINT
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Knee JointPosterior View

• Oblique popliteal ligament
• Is actually part of the tendon of the
  semimembranous muscle that fuses with the capsule
  and strengthens the posterior aspect of the knee
  joint

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KNEE JOINT
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Knee JointPosterior View

• Arcuate popliteal ligament
• Arcs superiorly from the head of the fibula and
  reinforces the joint capsule posteriorly

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KNEE JOINT
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Knee Joint

• Intracapsular ligaments are called cruciate
  ligaments because they cross each other, forming
  an X in the notch between the femoral condyles
• Help prevent anterior-posterior displacement of
  the articular surfaces and secure the
  articulating bones when we stand

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KNEE JOINT
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HOMEOSTATIC IMBALANCE

• Of all body joints, the knees are most
  susceptible to sports injuries because of their
  high reliance on nonarticular factors for
  stability and the fact that they carry the bodys
  weight
• The knee can absorb a vertical force equal to
  nearly seven times body weight
• However, it is very vulnerable to horizontal
  blows, such as those that occur during blocking
  and tackling in football

110
HOMEOSTATIC IMBALANCEAnterior View of Medial
Knee Injury

• When thinking of common knee injuries, remember
  the 3 Cs
• 1. Collateral ligaments
• Most dangerous are lateral blows to the extended
  knee
• These forces tear the tibial collateral ligament
  and the medial meniscus attached to it, as well
  as the anterior cruciate ligament

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KNEE INJURY
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HOMEOSTATIC IMBALANCE

• 2. Cruciate ligaments Anterior Cruciate Ligament
  (ACL)
• Most ACL injuries occur when a runner changes
  direction quickly, twisting a hyperextended knee
• A torn ACL heals poorly, so repair usually
  requires a ligament graft using connective tissue
  taken from one of the larger ligaments (e.g.,
  patellar, Achilles, or semitendinosus)

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Shoulder (Glenohumeral ) Joint

• Stability has been sacrificed to provide the most
  freely moving joint in the body
• Is a ball-and-socket joint
• Large hemispherical head of the humerus fits in
  the small, shallow glenoid cavity of the scapula
  (like a golf ball setting on a tee)

114
Shoulder (Glenohumeral ) Joint

• The ligaments that help to reinforce the shoulder
  joint are the coracohumeral ligament and the
  three glenohumeral ligaments

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SHOULDER JOINT
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SHOULDER JOINT
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Shoulder (Glenohumeral ) Joint

• The tendons that cross the shoulder joint
  provide the most stabilizing effect on the joint
• These tendons and associated muscles
  (subscapularis, supraspinatus, infraspinatus, and
  teres minor) make up the rotator cuff
• This cuff encircles the shoulder joint and blends
  with the articular capsule

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SHOULDER MUSCLES
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SHOULDER MUSCLES
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SHOULDER JOINT
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SHOULDER JOINT
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SHOULDER JOINT
123
Shoulder (Glenohumeral ) Joint

• The rotator cuff can be severely stretched when
  the arm is vigorously circumducted (movement of a
  body part so that it outlines a cone in space)
• This is a common injury of baseball pitchers
• Dislocation
• Because the shoulders reinforcements are weakest
  anteriorly and inferiorly, the humerus tends to
  dislocate in the forward and downward direction

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Hip (Coxal) Joint

• The hip joint is a ball-and-socket joint that
  provides a good range of motion
• Not nearly as wide as the shoulders range of
  motion
• Movements occur in all possible planes but are
  limited by the joints strong ligaments and its
  deep sockets
• The hip joint is formed by the articulation of
  the spherical head of the femur with the deeply
  cupped acetabulum of the hip bone
• The depth of the acetabulum is enhanced by a
  circular rim of fibrocartilage called the
  acetabular labrum

125
HIP JOINT
126
Hip (Coxal) Joint

• (c) anterior view (b) posterior view
• Several strong ligaments reinforce the capsule of
  the hip joint
• These ligaments are arranged in such a way that
  they screw the femur head into the acetabulum
  when a person stands up straight, thereby
  providing more stability
• The muscle tendons that cross the joint
  contribute to the stability and strength of the
  joint, BUT the majority of the stability of the
  hip joint is due to the deep socket of the
  acetabulum and the ligaments

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HIP JOINT
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Elbow Joint

• The elbow joint provides a stable and smoothly
  operating hinge joint that ONLY allows flexion
  and extension
• Within the joint, both the radius and ulna
  articulate with the condyles of the humerus but
  it is the close gripping of the trochlea by the
  ulnas trochlear notch that forms the hinge and
  stabilizes this joint
• (b) lateral view

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ELBOW JOINT
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Elbow Joint

• The ligaments involved in providing stability to
  the elbow joint are the annular ligament, the
  ulnar collateral ligament, and the radial
  collateral ligament
• Tendons of several arm muscles, the biceps and
  the triceps, also provide additional stability by
  crossing the elbow joint
• The radius is a passive onlooker in the angular
  elbow movements
• However, its head rotates within the angular
  ligament during supination and pronation of the
  forearm

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ELBOW JOINT
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Common Joint Injuries

• Sprains
• The ligaments reinforcing a joint are stretched
  or torn
• Partially torn ligaments will repair themselves,
  but they heal slowly because ligaments are so
  poorly vascularized
• Tend to be painful and immobilizing
• Completely ruptured ligaments require prompt
  surgical repair because inflammation in the joint
  will break down the neighboring tissues and turn
  the injured ligament to mush
• Surgery requires sewing hundreds of fibrous
  strands (NOT EASY)
• Examples
• Lumbar region of the spine, the ankle, and the
  knee are common sprain sites

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Common Joint Injuries

• Cartilage
• Although most cartilage injuries involve tearing
  of the knee menisci, overuse damage to the
  articular cartilages of other joints is becoming
  increasingly common in competitive young athletes
• Is avascular and it rarely can obtain sufficient
  nourishment to repair itself thus, it usually
  stays torn
• Because cartilage fragments (called loose bodies)
  can interfere with joint function by causing the
  joint to lock or bind, most sports physicians
  recommend that the central (nonvascular) part of
  a damaged cartilage be removed

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Common Joint Injuries

• Cartilage
• Arthroscopic surgery
• A small instrument bearing a tiny lens and
  fiber-optic light source, enables the surgeon to
  view the joint interior
• Repair ligament
• Remove cartilage fragments
• Removal of part of a meniscus
• Removal of part of a meniscus does not severely
  impair joint mobility, but the joint is
  definitely less stable
• Minimizes tissue damage and scarring

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JOINT INJURY
136
Common Joint Injuries

• Dislocation luxation
• Occurs when bones are forced out of alignment
• Usually accompanied by sprains, inflammation, and
  joint immobilization
• Like fractures, dislocations must be reduced
  (bone ends must be returned to their proper
  positions)
• Examples
• Jaw
• Shoulder
• Fingers
• Thumb
• Subluxation partial dislocation of a joint

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Inflammatory and Degenerative Conditions

• Bursitis
• Inflammation of the bursa
• Is usually caused by a blow or friction
• Severe cases are treated by injecting
  anti-inflammatory drugs into the bursa
• If excessive fluid accumulates, removing some
  fluid by needle aspiration may relieve the
  pressure
• Examples
• Falling on ones knee may result in a painful
  bursitis of the prepatellar bursa (housemaids
  knee / water on the knee)
• Prolonged leaning on ones elbow may damage the
  bursa close to the olecranon process (students
  elbow / olecranon bursitis)

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Inflammatory and Degenerative Conditions

• Tendonitis
• Is inflammation of the tendon sheaths, and is
  usually caused by overuse
• Symptoms pain and swelling
• Treatment rest, ice, anti-inflammatory drugs

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Inflammatory and Degenerative Conditions

• Arthritis
• Describes many inflammatory or degenerative
  diseases (over 100) that damage the joints
• Resulting in pain, stiffness, and swelling of the
  joint
• Acute forms
• Usually result from bacterial invasion and are
  treated with antibiotics
• Synovial membrane thickens and fluid production
  decreases, causing increased friction and pain
• Chronic (long-term) forms osteoarthritis,
  rheumatoid arthritis, and gouty arthritis

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Inflammatory and Degenerative Conditions

• Osteoarthritis (OA)
• Most common chronic arthritis
• Often called wear-and-tear arthritis
• Probably related to aging
• But a genetic basis
• Slow and irreversible
• It is the result of breakdown of articular
  cartilage (by enzymes but in healthy people
  replaced) and subsequent thickening of bone
  tissue, which may restrict joint movement
• Cartilage softened, roughened, pitted, and eroded
• Treatment
• Aspirin, acetaminophen, magnetic therapy (assumed
  to stimulate the growth and repair of articular
  cartilage), glucosamine (nutritional supplement
  decrease pain and inflammation, preserve
  articular cartilage)
• Examples cervical and lumbar spines, fingers,
  knuckles, knees, hips

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Inflammatory and Degenerative Conditions

• Rheumatoid arthritis
• Chronic inflammatory disorder that is an
  autoimmune disease
• Disorder in which the bodys immune system
  attacks its own tissues
• Microorganisms that bear chemicals similar to
  some naturally present in the joints
• BOTH are attacked by the immune system
• Any age
• Examples
• Many joints, particularly the small joints of the
  fingers, wrists, ankles, and feet
• Afflicted at the same time and bilaterally (right
  and left sides)
• Treatment anti-inflammatory and
  immunosuppressant drugs

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ARTHRITIS
143
Inflammatory and Degenerative Conditions

• Gouty Arthritis gout
• Uric acid, a normal waste product of nucleic acid
  metabolism, is ordinarily excreted in urine
  without any problems
• However, when blood levels of uric acid rise
  excessively (due to its excessive production or
  slow excretion), it may be deposited as
  needle-shaped urate crystals in the soft tissues
  of joints
• Inflammatory response follows
• Genetic factors are definitely implicated
• Untreated
• Articular bone ends fuse and immobilizes the
  joints
• Treatment
• Anti-inflammatory drugs
• Avoid alcohol promotes uric acid overproduction
• Avoid foods high in purine-containing nucleic
  acids (liver, kidneys, sardines)

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ARTIFICIAL JOINT
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DEVELOPMENTAL ASPECTS OF JOINTS

• Joints develop at the same time as bones,
  resembling adult form by eight weeks gestation
• At late middle age and beyond, ligaments and
  tendons shorten and weaken, intervertebral discs
  become more likely to herniate, and there is
  onset of osteoarthritis