VCU DPT - Biomechanics (Lecture 14)

hyaline cartialge will deform to ____________, and is slippy to ______

distribute joint loads

decrease friction

the composition of articular cartialge is 25% _________ and 75% __________

collagen-PG matrix

interstitial fluid

the _____ provides structural components to support internal mechanical stress from loads applied to joint cartialge

matrix

______ are sparsely disperesed and is less than 10% of the volume of articular cartialge

responsible for making/maintiang matrix

chondrocytes

2 types of lubrication are

boundary

fluid film

what describes cartialge more, and which is reliant upon pressure

fluid film x2

_________ = fluid volume/total volume

porosity

matrix is made out of what things

collagen

proteoglycans

water

_______ is most abudnat protein in body

collagen

t/f: collagen has high level of structural organization

true

the direction of collagen fibers in the ______ section are ????

a) superficial

b) middle

c) deep

a) parallel to surface

b) random

c) perpindicular to surface

what is the tidemark with collagen

part where the collagen fuses to the calcified cartialge and bone

collagen is stronger in ___(tension/compression)___ than in ___(tension/compression)_____

tension

compression

cartialge is 'anisotropic'

what does this mean

that it has different mechanical properites when loaded along different axes

proteoglycan is WHAT

large protein molecules, structurally arranged like bottle brsh

chondrotin sulfate:keratin sulfate ratio is higher when we are adults or kids?

if we ingest chondrotin sulfate, what is effectq

kids

- do not really know why

it will go to blood stream, not cartialge bc cartialge does not get blood! so largely nothing

what is the most abundant component of articular cartialge

water

where is water concentrated the most in articular cartialge

near the surface

water makes up a majority of the intermolecular space in cartialge

it is there to help ____________

controls joint ____________

moves when ___________

diffusion of materials and waste to/from cartialge

lubrication and movement

pressure is applied

synovial fluid is not just lubricant but is also ????

a means to transport waste and nutrients in/out

what is the normal charge of GAGs

what is the normal charge of Na and CA

what does this mean

Gags are negative, so repulse each other

both positive, attracted to Gags

this refers to the fact that we have swelling pressure that pre-stresses the collagen network, and compression results in increased repulsion (helping cycle fluid)

articular cartialge = __________, _________ material = water + sponge

fluid filled, porous-permeable

articular cartialge is VISCOELASTIC, due to:

intestitial fluid flow

intrinsic behavior of solid matrix

when subjected to stress, two things happen to cartialge

name them

creep

stress relaxation

difference in creep and stress relaxation

creep: with a constant load, cartialge will deform over time

stress relaxation: lot of force inititally when put into a new position, but if that positon is held, the force decreases

__________ refers to characterisitc of cartialge in that when put in a position and held, the resistant force will decrease over time

stress relaxation

______ refers to charactersitic of cartialge in that when given a constant froce over time, the cartialge will physically deform

creep

fluid flow (exudate) controls ________

fluid redistribution controls _______

creep

stress relaxation

with creep, there is a rapid period of deformation, then a slow period where it begins to almost stop

explain this

the water rushes out of cartialge, and does so really quickly (hence the quick part)

however, once water is gone now the mechanical components are all that is left and that takes longer

once the rapid fluid exudation has occured, with creep, we are in equilibrium

what now supports the load

solid matrix

rate of creep is governed by the ________________

rate of water leaving

- related to permeability

constant deformation leads to _____ initial stress but over time _______ stress

high

less

with stress relaxation, describe the stress time curve

initially there is a big spike in stress as the object resists deformation

then, it slowly decreases as it relaxes

why, when applying a load over long time, may it be hard to maintain a high force

stress relaxation

articlar cartialge has ___ permeability

low

- difficult to push liquid through

with high loads, we ________ frictional drag on the water leaving the tissue

this makes the tissue ________ and ____ difficult to cause movement

increase

stiffer, more

fluid in the joint space stays in ___(low/high)___ load areas and is reabosrbed in ___(low/high)____ load areas

high

low

when we load a system fast, it provides ???

resistance

why is it important we load the whole joint

because as we load it, the joint exudes fluid in front of the compression and is reabsorbed behind it

- to get a full joint fluid exchange, you need to load the entire thing so it all exudes and reabsorbs

what does the toe region represent in collagen articular cartialge, with tension

it represents the fiber "pull out", aka taking slack out and putting it on tension

what hapens to the collagen net work with OA? what does this mean

it gets loosened

the cartialge does not get tight with stress and can not longer support system

under unilateral SLOW tension, articular cartilage ______ effect of fluid flow

negates

disruption of the collagen network (w/ OA) leads to:

decreased tensile strength

increased swelling of articular cartialge (bad)

as we age, increased water content leads to _______ compressive streength and _______ permeability

decreased

increased

what is a PG washout, resulting from interstitial fluid moving

repetitive and massive movement of fluid at high speeds can cause holes to be put in cartilage, making it lose its ability over time

and becoming more permeable

does the cumulative stress of impact loading need to just be high, or does low also have long term effect

both do

with excessive stress concentrations, what do we see

too much force being loaded in one spot; not good

congential acetabular dysplasia

slipped capital femoral epiphysis

intrarticular fracture

meniscectomy

ligament rupture

RA/joint space hemorage

WHAT HAPPENS WITH ALL THESE

disrutpion of cartialge and joint space, leading to long term issues

what does it mean saying articular cartialge is "biphasic"

has the matrix and the fluid