Cartilage Flashcards
function of cartilage
movement, gliding, limiting friction, distribute loads over a wide area and absorb shock
structure of articular cartilage
has specialized form of hyaline cartilage that covers the ends of all bones, surface appears smooth but actually has pits and ridges
Chondrocytes
account for 10% of tissue volume and are responsible for producing and maintaining the organic composition of articular cartilage (collagen, proteoglycans and glycoproteins)
Collagen makes up what net weight of cartilage
10-30%
Proteoglycans make up what net weight of cartilage
3-10%
what is the predominant factor to net weight in cartilage
water, 60-87% (along with inorganic salts)
what is the predominant collagen type in articular cartilages
type II, resists compression
Collagen function in cartilage
provides the ECM framework and tensile strength of articular cartilage
are proteoglycans positive or negatively charged?!
negative they are polyionic
compression of PGs results in
increased repulsive forces between the PGs and increased compressive stiffness
when tissue is loaded… up to ____ % of water can be moved
70
Nutrition of cartilage means
cartilage becomes less stiff and more permeable due to increased water content
Superficial/tangential zone
structure: sheets of fine, densely packed fibers randomly woven in planes PARALLEL to the articular surface
function: resists shearing forces on the surface by decreasing friction and distributing the force
resists compression with type 1 collagen
Middle zone
fibers are randomly oriented and homogenously dispersed to surround the chondrocytes
deep zone
collagen fibers are oriented with pattern in tightly packed bundles, fibers are perpendicular to the surface
tidemark
interface b/w articular cartilage and the calcified cartilage beneath is, anchors the cartilage to the underlying bone
where does articular cartilage show less healing when injured
above the tidemark
why does below the tidemark heal faster?
the healing/inflammation from the subchondral bone occurs so there is increased blood flow and faster healing than a superficial wound
Subchondral bone
highly organized
trabecular bone interlocks and align in a matrix configuration
designed to counteract the line of application of the average load to the joint
What provides the nutrition to articular cartilage
synovial fluid through compression and decompression of the cartilage surface (we need non-destructive motion of the joint) AKA MOVEMENT
where is permeability of AC the highest
near the joint line
where is permeability the lowest in AC
in the deep zone
Permeability changes with deformation
as it is compressed, the permeability decreases
articular cartilage is highly porous but very low in permeability
how much synovial fluid is in the synovial space of the knee
about 4 mL
Function of synovial fluid
exchange metabolites with the vasculature in synovial lining, nutrients, contains Lubrican and hyaluronic acid to add viscosity
decreases friction, nutrition and distributes forces
Rapid loading
there is no time for the fluid to flow out so pressure from the interstitial fluid rather than the solid matrix, supports a significant portion of the load
slow loading
fluid pressure decreases and STRESS increases in the solid matrix
the negatively charged GAGS push away
CREEP
sustained load
articular cartilage deforms under a constant load (like braces)
as the rate of displacement slows, fluid flow slows too
equilibrium= displacement is constant and fluid flow has stopped (takes a several thousand seconds 4-6 hours
what contributes to the stress rise
associated with fluid exudation
stress relaxation=
fluid redistribution within the porous solid matrix
Where does the collagen resist TENSION
collagen in the superficial tangential zone
extracellular framework and tensile strength
provides the joint cartilage with a tough, wear resistant, protective skin
Monolayer of synovial fluid
it is absorbed on each surface so there is no direct contact surface to surface which prevents surface wear
Fluid Film
thin layer of freestanding lubricant between sliding surfaces to decrease surface to surface contact area
what does fluid film rely on
viscosity
Hydrodynamic fluid film
occurs when rigid bearing surfaces which are not parallel and are separated by a fluid film
SLIDING IS TANGENTIAL
Squeeze film
occurs when the bearing surfaces are moving PERPENDICULARLY towards each other
viscosity of fluid produces pressure that tends to force the lubricant out
weeping
joint load is borne by hydrostatic pressure of the synovial fluid escaping from the cartilage
boosted lubrication
as the load is applied, synovial fluid is trapped in the cartilage, toward the subchondral bone at the point of contact
causes to articular cartilage degeneration
increased stress wear and tear high load over extended period of time chemical insults metabolic factors
Histological changes of articular cartilage
increased water content secondary to freeing of GAGs
loss of PGs leading to decreased mechanical properties
PGs less dense between fibers (poor matrix support)
Interfacial adhesive wear
fragments stick and pull away from the surface
interfacial abrasive wear
soft material scraped by harder material
fatigue wear
accumulation of microscopic damage under repetitive stresses
superficial cartilage trauma
no inflammatory response
minimal healing
healing of deep cartilage lesion
local bleeding from subchondral bone produces hematoma that becomes organized and invaded by granulation tissue
flakes of the cartilage break away into the joint space
which decreases the energy absorbing function and stimulating the subchondral bone plate
immobilization on articular cartilage
decreased PG aggregation
increased water content
AC is softer and weaker
