Download Joints Notes

Joints (articulations), Fibrous and Cartilaginous Joints
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A joint is formed where 2 or more bones meet (study of joints is arthrology)
2 functions- mobility, holds skeleton together
Although they are designed to resist forces that threaten to force them out of alignment, they are the
weakest points in our skeleton
Classification- by structure and function
 Structural- based on what holds them together and whether a (synovial) cavity present or not
 Fibrous, cartilaginous and synovial
 Functional- based on amount of movement allowed
 Synarthroses- (syn=together, artho= joint)- immovable, mostly in axial skeleton
 Amphiathroses- (amphi- on both sides)- slightly movable, mostly in axial skeleton
 Diarthroses- (di- through, apart)- freely movable joints, predominant in limbs
 In general- fibrous joints are immovable, synovial freely movable, cartilaginous can be either
Fibrous joints- bones joined by fibrous tissue, no synovial cavity is present- amount of movement
depends on length of connecting tissues joining the bones- few are slightly movable, most immobile
- 3 types
 Sutures- only between skull bones- wavy edges of bones interlock, junction filled completely by
very minimal amount of connective tissue fibers continuous with periosteum
 Result= nearly rigid spaces bind bones, yet allow growth in youth
 Middle age fibrous tissue ossifies, skull bones fuse into single unit= synostosesfunctionally same as synarthroses
 Syndesmoses (desmos – to join or bind)- fibrous joint with more fibrous connective tissue than in
a suture- bones joint by ligament cord or by a band of fibrous tissue- vary in length and amount of
movement varies with length
 E.g.- ligament between tibia and fibula is short, true movement prevented= synarthrosis,
but interosseous membrane between rad and ulna long enough to allow rotation rad
around ulna
 Gomphoses- peg in socket fibrous joint, only example= tooth in alveolar socket (‘gompho’ greek=
nail/bolt)- periodontal ligament= short fibrous connection
Cartilaginous joints- articulating bones united by cartilage- fibrocartilage or hyaline cartilage (also lack
synovial cavity), 2 types
 Synchondroses- bar or plate of hyaline cart unite, they are synarthrotic meaning they are
immovable. Examples - epiphseal plates connecting dia and epi regions in long bones of children
(temporary joints that become synostoses), immovable joint between costal cart of 1st rib and
manubrium
 Symphyses- articular surfaces of bone covered with articular (hyaline) cart- in turn fused to a pad
or plate of fibrocartilage (compressible and resistant= shock absorber). They allow limited
movement in joint, or are amphiarthrotic. Examples are intervertebral joints and pubic symphysis
Synovial Joints, Sprains, Strains, Bursae and Tendon Sheaths and Types of Movement
o Synovial joints- have fluid containing synovial cavity between articulating bones and are freely movable or
diarthrotic- all joints of limbs (most joints in body)
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General structure- 5 features
 Articular cartilage- glassy-smooth hyaline covers opposing bone surfaces- thin but
spongy take some shock, prevent ends from being crushed, reduces friction
o To replace when worn down- chondrocytes are removed from patient, grown in
culture and then placed in damaged joint
o Sometime eroded cartilage replaced with synthetic materials
o Also examining use of stem cells to replace cartilage
 Joint (synovial) cavity- space with small amount synovial fluid
 Articular capsule- two layers that enclose joint cavity
o external fibrous capsule (dense irregular tissue) - continuous with periosteum of
bones- strengthens joint
 flexibility permits movement, tensile strength keeps it together (prevents
dislocation)
o internal- synovial membrane- loose connective tissue- lines capsule and covers
all internal joint surfaces not covered by hyaline- secretes lubing and joint
nourishing synovial fluid
o also contain ligaments and articular fat pads
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Synovial fluid- occupies all free space in joint capsule- derived largely by filtration from
blood in capillaries in synovial membrane
o Viscous- egg white- consistency (synovi= joint egg) due to hyaluronic acid
secreted by cells in membrane
o Also seen in articular cartilages
o Provides slippery weight-bearing film, reduces friction between cartilages
o Also have phagocytes rid joint cavity of microbes and cellular debris (metabolic
wastes)
o Disease/injury can lead to build-up of fluid- may be aspirated (drained) and
medications can be injected
 Reinforcing ligaments- strengthens synovial joints- band like ligaments- can be part of
fibrous capsule or outside or deep to the capsule (distinct)
o Most diarthroses have accessory ligaments and articular discs (menisci)
o Ligaments hold bone to bone
o Articular discs modify shape of joint surfaces of articulating bones, help maintain
stability of joint, direct the flow of synovial fluid to areas of greatest friction
 Torn cartilage- frequent in knees of athletes- damage to articular discs
between ends of some bones- usually use arthroscopy to remove to
prevent erosion and arthritis
o Double-jointed- do not really have extra joints- joint capsules and ligaments are
stretchy and looser than average
 Blood and nerve supply- nerves that supply joints same as those that supply skeletal
muscles that move joint
o Articular capsule and ligaments richly supplied with sensory nerve endings to
monitor joint position and help maintain muscle tone
o Numerous arteries and veins supply joints and surrounding structures, most
supply synovial membrane
How joints move or how much they can move not only depends on their basic structure, but also how they
are stabilized
Since they are constantly being stretched and compressed they must be stabilized so they don’t dislocate
(come out of alignment)
Stability determined by 3 factors:
 Shapes of articular surfaces- determine what movements are possible at a joint but play
minor role in stability- many joints have shallow sockets or articulating surfaces that don’t
really fit together that great
 Number of positioning ligaments- capsules and ligaments unit bones to prevent
excessive or undesirable movement, generally the more lig.s a joint has, the more stable
it is
 Muscle tone- for most joints the muscle tendons that cross the joints= most important
stabilizing factor- tendons are kept taut at all times by tone of muscles
Sprain and Strain
 Sprain= forcible wrenching or twisting of joint that stretches or tears its ligaments but does not
dislocate the bone
 Strain= stretched or partially torn muscle
Bursae and Tendon sheaths- bags of lubricant, act as ball bearings to reduce friction during activity
 Not strictly part of synovial joint, but often associated with them
 Bursae- flattened fibrous sacs lined with synovial membrane and thin film of fluid, common where
ligaments, muscles, skin, tendons or bones rub together
 Tendon sheath- elongated bursae that wraps completely around a tendon subject to friction (like
a hot dog bun)
 Like tendon of biceps brachii at shoulder joint
 Bursitis= chronic inflammation of bursae (tendonitis later)
Types of Movements
o In which types of joints would we be defining movement? Synovial! (diarthroses)
o How joints move or how much they can move not only depends on their basic structure, but also how they
are stabilized
o every skeletal muscle (our next unit) in the body is attached to bone or other connective tissue at no
fewer than 2 points- origin= immovable (or less movable) bone, insertion= attached to movable bonewhen muscles contract across joints, insertion moves towards origin- creating movement
o range of motion differs in different people
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movement can be described as directional in terms of lines (axes) around which the body part moves and
planes of space along which movement occurs (transverse, frontal or sagittal plane)
 nonaxial- slipping movements only since no axis around which movement can occur
 uniaxial- movement in one plane
 biaxial- movement in 2 planes
 multiaxial- movement in or around all 3 planes of space and axes
3 general types of movement: (most common types of movement allowed in fig 8.5
 gliding movements- occur when relatively flat bone surfaces move back and forth and from side
to side with respect to one another (glide or slip over each other, nonaxial)
 simplest joint motion, no significant alteration of angle between bones
 occur at plantar joints (intercapral and intertarsal joints, between flat processes of vert,
and in combos with other movements)
 everyone wave  you are doing carpal glides!
 angular movements-increase or decrease in the angle between articulating bones, can occur in
any plane (uniaxial) 3 principle movements:
 flexion- results in decrease in angle between articulating bones- along sagital plane)
o everyone, flex your biceps and show me those guns! See how forarm became
much smaller angle with arm?
o Same when flex hami!
o Nod head down toward chest, bend body at waist, flex at shoulder, arm comes
forward
o Weird flexion= lateral flexion- involves moving trunk sideways to R or L at waist,
movement in frontal plane and involves intervertrebral joints
 Extension- results in increase in angle between articulating bones- also along sagittal
plane)
o Reverse of flexion in same joints (flex tris, flex quads) – straighten a joint
o Hyperextenion- bend past straight, look at ceiling, neck is hyperextened- at
shoulder or hip, brings limb posterior to joint
o Often prevented by arrangement of ligaments and alignment of bones (knee,
elbow, etc)
 Also- abduction- movement of bone away from body (midline)- along frontal plane- raise
arm/leg to side, spread fingers/toes (midline= middle finger/toe) NOTE: bending body= lat
flexion, not abduction!
o Adduction- movement of bone towards body (midline)- “adding” back to your
body (again frontal plane)
 Circumduction- movement of distal end of body in circle (circum=around, duco- draw 
draw a circle or cone in space)- joints stays relatively stationary, limb does flexion,
extension, abduction, adduction, all to make circle
 Rotation- turning of bone along long axis- only movement allowed between1st to cervical vertcommon at hip and shoulder (pivot and ball-and-socket joints allow)
 If anterior surface rotates toward midline (inward)= medial rotation, outward= lateral
rotation
special movements:
 elevation- upward motion of body part, depression- downward motion of body part- shrug
shoulders, chewing something
 protraction- movement body part anterior on transverse plane, retraction- movement posterior on
transverse plane- stick shoulders front and back, project jaw, retract in horror!
 Special names for movements of radius and ulna- Supination-movement of forearm at proximal
and distal radioulnar joints, palm turned anteriorly or superiorly, in anatomical position hand is
supinated, ulna and radius are parallel, pronation- moves forearm at proximal and distal
radioulnar joints so palm turns posteriorly or inferiorly and radius crosses ulna
 Special names for foot motions up and down of ankle- lifting foot so superior surface goes toward leg= dorsiflexion (like
wrist extension), go on toes= plantar flexion (wrist flexion), flexion plantar area
 inversion- sole of foot turns medially, eversion soles laterally at intertarsal joints, face
away (new for me!)
 Opposition- movement of thumb at carpometacarpal joint in which thumb moves across
palm to touch tips of fingers on same hand, saddle joint between metacarpal 1 and
carpals allow,
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Types of Joints and Select joints of the body
o Types of joints that allow movement
 Synovial joints all have 5 common features (articular cartilage, synovial cavity, articular capsule,
synovial fluid, reinforcing ligaments) but different structures that allow different types of
movement, 6 types:
 Plane joints- articular surfaces are flat, allow only short gliding motions (side to side, back and
forth, nonaxial)
 E.g. intercarpal, intertarsal, sternoclavicular, acromioclaviular, sterncostal, and
vertebrocostal
 Hinge joints- convex surface of one bone fits in concave surface of other- movement primary
flexion and extension (uniaxial)
 E.g. elbow, knee, ankle, interphalangeal joints
 Selected Synovial Joint- The Elbow- hinge joint formed by trochlea of humerus, trochlear
notch of ulna, and head of radius
o Movement= flexion-extension of forearm
o Tennis elbow (lateral epicondylitis) and dislocation of the radial head are
common injuries of this joint
 Pivot joints-round or pointed surface of one bone fits into ring formed by another bone and
ligament (radial head into radial notch)- movement is rotational (also primarily uniaxial)
 E.g. atlas rotating about axis, supination/pronation
 Condyloid joint- oval-shaped condyle of one bone fits into an elliptical cavity of another (condyles
of humerus and tibia)- movements are flex-ext, abd-add, and circumduction (multiaxial)
 Joint between carpals and radius
 Saddle joint- one bone whose articular surface is saddle-shaped and another whose articular
surface is shaped like a rider sitting in the saddle (metacarpal 1 and carpal bones- trapezium)movements= flex-ext, abd-add, and circumduction
 Ball-and-socket- ball-shaped surface of one bone fits into cuplike depression of another (only 2=
shoulder and hip)- movements= flex-ext, abd-add, rotation and circumduction
 Selected Synovial Joint- The Shoulder- ball-and-socket formed by head of humerus and
glenoid cavity of scapula
o Movement= flex-ext, abd-add, medial and lateral rotation, and circumduction
o Extreme freedom of movement at expense of stability
o Rotator cuff injuries (injury to 1 or more of 4 muscles/tendons of shoulder),
dislocation (humerus dislocates), or separated shoulder (separation of
acromioclavicular joint) are common injuries
 Selected Synovial Joint- The Hip- ball-and-socket formed by head of femur and
acetabulum of coxal bone
o Movement= flex/ext, abd/add, circumduction, and medial and lateral rotation of
thigh
o Extremely stable joint due to bones making up the joint and many accessory
ligaments and muscles
 TMJ- Temporomandibular Joint- jaw joint- where condylar process of mandible, the
mandibular fossa (depression posterior) of temporal bone and articular tubercle (dense
knob on anterior) of temporal bone come together- the joint is enclosed laterally by a
ligament- an articular disc (menisci) divides synovial cavity into sup an inf parts
o Combo hinge and planar joint
o Movements- opening and closing mouth (elevation and depression- allowed by
condyle and fossa) and protraction and retraction of jaw (glide side to side too,
helpful in chewing hard stuff)
o Because socket is so shallow, most easily dislocated joint on body.
o A deep yawn can even do it!
o When dislocation occurs, mouth remains open
 Also, at least 5% of people have pain associated with this joint- often affect people that
grind their teeth! Heat or ice, stress reduction techniques and bite plates help reduce