OA Mechanisms and Treatment

what 2 main factors increase joint stress?

what 2 main factors increase joint stress?

increased force and decreased area

what is underneath the cartilage

subchondral plate

what are the 4 zones of articular cartilage from superficial to deep?

superficial, transitional, radial, calcified

what happens to the fibers and cells as you move down through the articular cartilage layers?

fibers become less organized and chondrocytes become fatter

how are superficial cartilage fibers oriented?

based on the patterns of motions and mechanical stress

does hyaline cartilage have nerve, blood, and lymph supply?

no

how does hyaline cartilage receive its nutrition and remove waste?

diffusion

__________ are key to adequate diffusion, why?

mechanical forces, develop pressure gradients

what can cause problems with the nutrition of hyaline carilage?

immobilization, trauma

does immobilization affect contact or non-contact areas of cartilage?

both

how is cartilage thickness related to bony congruity?

inversely (less cartilage where there is more congruency)

does cartilage work more by load distribution or load attenuation?

load distribution

does rate of loading affect the cartilage?

yes

what loading rate is most damaging to articular cartilage?

impulse loading (high rate)

why is high rate loading damaging to cartilage?

does not allow adequate force distribution

are non contact areas of cartilage loaded? if so how?

yes, tension

initiating event in OA

trauma

series of microscopic events throughout the progression of OA

release of enzymes, release of proteoglycans, disruption of collagen fiber network, surface fibrillation (foreign substances escape into synovial fluid)

what happens in the cells with OA

initial attempt to proliferate, cell clustering or clones, increased lysososomes, RER, goilgi, or mitochondria

what are proteoglycans highly correlated with?

degree of stiffness

roles of proteoglycans

mechanical integrity, physically limit diffusion

what properties of proteoglycans provide mechanical integrity?

electrostatic and osmotic properties

what gives proteoglycans their electrostatic properties?

high negative charge that repel each other

describe the osmotic properties of proteoglycans

proteoglycans hold water, this means that cartilage with more proteoglycans will be stiffer and push out more than cartilage with less

immobilization leads to a ________ of proteoglycans that can take up to a year to restore. The ______ zone is most effective

loss, superficial

what physically contains proteoglycans, how does OA affect thsi?

fibers, surface fibrillation due to OA allows PGs to escape the fiber net

what is the effect on the tissue caused by surface fibrilation?

remaining PGs spread out and hold more water, resulting tissue is mechanically inferior

what directions of movement are hardest on the superficial cartilage fibers?

movements in new directions

what happens to the subchondral bone during OA?

the subchondral plate thickens

how does thickening of the subchondral plate affect the cartilage?

perpetuates the degenerative process

in a joint with OA, applied stress is ________ stress attenuating mechanisms

greater than

how can force on a joint be increased?

body weight, external load, quick loading rate, muscle weakness, joint instability, tight tissues

how can area where force is applied on a joint be decreased?

high loading rate, joint incongruence, degenerative changes, limited joint motion, fractured joint surface

is exercise recommended for people with OA?

yes

why is exercise good for OA patients?

muscle for shock absorption and stabilization, maintaining normal joint mobility, anti-inflammatory effects, mechanotransduction

is there higher force when stepping down in footwear or in bare feet? why?

footwear, rely on shoes to support so less muscle activation

to change momentum from max to 0 over the _________ amount of time creates the least force

greatest

what is required in order for muscle to act a shock absorber?

joint motion and eccentric control

what injuries greatly increase prevalence of knee OA?

ACL and meniscus

consequences of hypomobility

loss of normal motion leads to increased articular pressures

consequences of hypermobility

loss of normal center of rotation and creates abnormal surface stress, excess shear stress and rotational instability