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Articular Cartilage
articular cartilage notes
103
Anatomy
Graduate
10/02/2013

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Term
what is the composition of articular cartilage
Definition
60-80% water, 20-40% solid matrix (matrix is 60% type II collagen, 40% ground substance, <2% chondrocytes)
Term
describe vascularity of cartilage
Definition
avascular
Term
describe neurality of articular cartilage
Definition
aneural
Term
what are the implications for AC being aneural
Definition
pain free
Term
what are the implications for AC being avascular
Definition
potential for injury repair is poor with no blood supply and few reparative cells
Term
what 2 main things determine the mechanics of articular cartilage
Definition
1. lots of water, 2. collagen ground structure creates just the right amount of permeability to move water around in the AC
Term
describe how water and collagen ground structre affect the mechanics of AC
Definition
The time it takes to move water in loading increases the time of loading and therefore reduces contact forces.
Term
Describe how the amount of permeability is just right in AC
Definition
If it was too permeable, water would squeeze right out like a sponge and Δt wouldn't really be any bigger. If it wasn't permeable enough, it would be like concrete (hard to move water through) There is just the right amount of permeability to move water around and decrease contact forces crossing the joint.
Term
What is the job of articular cartilage
Definition
Protect underlying bone.
Term
How does articular cartilage protect underlying bone?
Definition
Increases time of loading to decrease contact force crossing the joint. F = mv/Δt. Also increases contact area. Decreasing force and increasing area reduces contact pressure.
Term
describe how AC increases contact area
Definition
Movement of water deforms cartilage to create increase in contact area.
Term
Describe the architecture of AC
Definition
superficial zone up top, middle zone in the middle, columnar orientation next to the bone
Term
Describe the superficial zone of AC
Definition
collagen fibers and chondrocytes are oriented horizontally, parallel to the surface.
Term
What is the purpose of the horizontal orientation of collagen fibers and chondrocytes in the superficial layer of AC
Definition
decrease shearing stress and tensile forces that want to create an opening in the AC
Term
describe the middle zone of AC
Definition
chondrocytes and collagen fibers going every which way
Term
What is the purpose of the random orientation of collagen fibers and chondrocytes in the middle layer of AC
Definition
to decrease stress concentrataion between the superficial and bottom layers of cartilage
Term
is the random orientation of the middle layer of AC foolproof?
Definition
No. sometimes people get delamination injuries where the top surface lifts off the bottom surface
Term
Describe the bottom layer of AC
Definition
Columnar orientation of cells next to the bone
Term
what is the purpose of the columnar orientation of cells in the bottom layer of AC
Definition
The columnar orientation mimics orientation of cells in subchondral bone to minimize stress concentration
Term
what is the problem with the different layers having different orientation in AC
Definition
can cause stress concentration which can lead to failure
Term
how does Mike describe AC?
Definition
dense fluid filled sponge with normal degree of relatively low permeability
Term
how do most pathologies tend to affect the permeability of AC?
Definition
most pathologies act to increase permeability of AC, resulting in decreased loading time
Term
why don't we see lots of frictional abrasion on AC
Definition
low coefficient of friction with synovial fluid
Term
what are 3 things that destroy articular cartilage
Definition
contact pressure, repetitive impact loading, frictional abrasion
Term
what causes increased contact pressure in AC
Definition
increased contact forces or decreased contact area
Term
why is repetitive impact loading bad for AC
Definition
makes subchondral bone too stiff causing destruction of the AC between bones
Term
what causes friction
Definition
one object sliding on another
Term
what is the formula for friction
Definition
F = μN
Term
what is μ
Definition
coefficient of friction = how rough the two surfaces are
Term
what is N
Definition
normal force = how vigorously the surfaces are pressed together
Term
thinking of the formula for friction, what increases frictional abrasion?
Definition
rough surfaces, too much pressure
Term
how to control N?
Definition
keep muscles quiet so that joint surfaces are not compressed too vigorously together
Term
how to control μ?
Definition
usually is low because of synovial fluid. There is a large range though, which could cause some problems.
Term
what happens when AC is loaded slowly such as in sitting
Definition
with constant low level loading, there is temporary creep as fluid is continually displaced from loaded areas of AC to unloaded areas of AC to intraarticular space.
Term
what happens when AC is loaded slowly such as in sitting and it continues to be loaded for a long time
Definition
subchondral bone will eventually feel the loss of fluid from the AC = moviegoer's sign
Term
Describe what happens to cause moviegoer's sign
Definition
When you sit with your knees in flexion, there is passive tension throughout the entire extensor mechanism crossing the knee. Patellar tendon and quadriceps tendon forces drive the patella into the trochlear groove. The 2 articulating surfaces are undergoing low level, constant deformation until the subchondral bone really feels it. When you go to stand, those forces become HUGE because the AC is already deformed and standing quickly deforms it the rest of the way. You feel TREMENDOUS contact pressure. Ouch!
Term
How to avoid moviegoer's sign
Definition
Before standing, you need to reform the articular cartilage: straighen your knees so that osmotic pressure can drive fluid back into AC to reform it. This way, when you stand again, the AC will be in a position to receive the high magnitude contact force because the AC is back to increasing contact area and increasing Δt to decrease force and decrease contact pressure
Term
If you stand up fast after sitting for a long time is that better or worse and why
Definition
worse because the increased speed of loading will increase stiffness. Stiff subchondral bone pounding AC leads to OA
Term
what should a person do who has been doing a lot of repetitive loading of a joint before then loading it in a big time way?
Definition
give the AC time to reform by removing the repetitive loading
Term
what are the two methods of exercising joints that have influence on lubricating the joints and minimizing friction?
Definition
Boundary lubrication, fluid film lubrication
Term
is the μ for boundary lubrication or fluid film lower (better)?
Definition
μ for fluid film lubrication is less than μ for boundary lubrication
Term
what is fluid film lubrication?
Definition
large volume of synovial fluid trapped between 2 joint surfaces
Term
what is boundary lubrication
Definition
hyaluronic acid/glycoprotein molecule complex layer on each articulating surfce
Term
what is Newton's 2nd law?
Definition
F=mA
Term
if you put a patient on a machine with high resistance and tell her to move her joints, will she move fast or slow?
Definition
slow because she has to overcome a large force. High load => low velocity
Term
what lubrication method results from the high load, low velocity scenario and why?
Definition
Most of the synovial fluid is squeezed out from between the 2 articulating surfaces, and you're left with two layers of molecules = boundary layer lubrication
Term
what is the name of the molecules that provide boundary layer lubrication
Definition
lubricin molecules
Term
if you have a patient on a machine with low resistance and ask them to move slowly, what happens?
Definition
they don't encounter much resistance
Term
if you have a patient on a machine with low resistance and you ask them to move quickly, what happens?
Definition
the joint behaves like a hydraulic piston: if you push it slowly, you don't encountermuch resistance. If you push it quickly, you feel a lot of resistance because the hydraulic fluid becomes entrapped in the cylinder. Synovial fluid performs the same way. It gets entrapped = fluid film lubrication
Term
if someone has problems with articular cartilage, is it better from them to do high load, low velocity or low load, high velocity and why?
Definition
Low load, high velocity is better to reduce articular disrepair through fluid film lubrication. Ex: Ride a bike at low resistance , high velocity
Term
what to do when someone says their joint hurts
Definition
have them show you the motion, tell you when they have the pain. Then you tell the patient NOT to go into the position that hurts.
Term
what is a surgical way to promote AC healing that Mike has had done?
Definition
drill hole into subchondral bone (microfracture)
Term
What is the purpose of microfracture for AC injury healing
Definition
Communication with vascularized bone tissue and migration of cells that end up producing fibrocartilage in the injured AC
Term
What is the problem with microfracture
Definition
Fibrocartilage is an inferior shock absorber to articular cartilage.
Term
why is fibrocartilage an inferior shock absorber to AC?
Definition
fibrocartilage has less water and a denser matrix that acts as a barrier to diffusion, which is necessary for nutrition of articular cartilage. Also, time of loading will be shorter so the contact force will increase. Also without the water of AC, the fibrocartilage can't deform as much and therefore you won't have as much contact area. increased force and decreased contact area means increased contact pressure. ALSO fibrocartilage has only 10% of the GAGs as articular cartilage, so it has a greater chance of failure.
Term
With fibrocartilage in place of AC after microfracture, how can you prevent/delay failure?
Definition
you have to re-hypertrophy the muscles and change the malalignment and/or the activity: stop running, wear orthotics. The good tissue has already failed, so unless you change something you know the inferior fibrocartilage will fail. We have to figure out what made the AC fail initially in order to change that and give the fibrocartilage a chance to survive.
Term
since fibrocartilage reduces the nutritonal flow into AC, how will surrounding AC survive?
Definition
without blood supply, AC relies on synovial fluid being pushed around to give it nutrition
Term
how to promote healing of articular cartilage?
Definition
protected weightbearing to give it a chance to recover.
Term
are chondrocytes metabolically fast or slow
Definition
slow, poor for healing
Term
is there a good blood supply to AC?
Definition
no
Term
what is the prognosis for injury to large volumes/surface areas of AC
Definition
poor
Term
how does location of the injury play a role in AC healing
Definition
healing prognosis is worse if the defect is subject to weightbearing that elicits high contact pressures
Term
how do you know what positions should have limited WB for AC healing?
Definition
listen to the joint. Limit WB positions in the ROM for which the joint "talks"
Term
what to do if you can't limit ROM because of functional reasons.
Definition
figure out how to keep contact pressures low for that point in the ROM: attenuate contact force
Term
how to attenuate contact force at specific points in ROM
Definition
keep the muscles quiet. Muscles have short moment arms, and weight force/GRF has a long moment arm. This means the muscle force is large.
Term
If someone has articular damage, will joint reaction forces be large or small?
Definition
large.
Term
How to reduce force through the knees in standing
Definition
Rise from the chair with knees directly above ankles rather than knees in front of toes. Knees in front of toes produces high forces though the quads tendon. This can cause severe muscle force at the joint. With knees behind toes, the GRF goes through the knee joint center, keeping quads quiet and therefore 0 moment arm in the knee so 0 force from the quads. THis does require more force from the hip extensors.
Term
what is the surface like on damaged AC?
Definition
irregular. Feels like stepping on little stones. Reduced contact area
Term
can shaving off the irregular surfaces help AC repair?
Definition
yes. Increases contact area. Short term effects
Term
is drilling through AC to subchondral bone a short or long term fix?
Definition
short term unless you make major changes
Term
has early CPM shown some promise in facilitating AC repair process?
Definition
yes, in animal studies
Term
has chondrocyte implantation shown promise for AC repair?
Definition
yes, we have good results so far early on
Term
Why must intra-articular fractures have strong reduction?
Definition
to inhibit migration of fibroblasts from subchondral bone
Term
describe the osteochondral autograft transfer system
Definition
hollow chisle pulls cores of AC from a NWB area and places it into the damaged tissue. NWB for 6-8 weeks after
Term
what is another name for osteochondral autograft transfer system
Definition
autologous osteochondral transplantation
Term
is OATS better than microfracture
Definition
seems to be
Term
how is OATS better than microfracture
Definition
more people return to play, less fibrocartilage and more AC
Term
what is Autologous Chondrocyte Implantation?
Definition
remove chondrocytes with a big needle, grow them in a lab. Put the cells back in underneath periosteum
Term
does autologous chondrocyte implantation show good results?
Definition
yes
Term
will a patient be NWB after ACI?
Definition
yes, for a bit
Term
does autologous chondrocyte implantation show good long term results
Definition
yes, starting to
Term
what are the two types of glucosamine
Definition
hydrochloride and sulfate
Term
which of the two types of glucosamine is more helpful
Definition
sulfate
Term
is chondroitin helpful
Definition
for some people yes, in combination with glucosamine
Term
what are the benefits/functions of glucosamine
Definition
facilitate GAG production, rebuild AC, improve lubrication by synovial fluid
Term
is glucosamine or chondroitin better absorbed?
Definition
glucosamine
Term
what is one concern of glucosamine consumption
Definition
insulin regulation issues in diabetic patients
Term
is glucosamine supplementation effective for people with severe OA?
Definition
no
Term
what is the problem of immobilization and AC
Definition
immobilization/reduced activity leads to atrophy. This means less cross sectional area. This means more stress inside the tissue. This can happen to AC. Recovery is possible through gradual return to activity.
Term
what if you try to increase activity too quickly after immobilization
Definition
post-rehabilitation OA
Term
what are some conservative ways to facilitate cartilage repair
Definition
glucosamine sulfate, chondroitin sulfate, growth hormone, electromagnetic fields, laser stimulation
Term
how does growth hormone facilitate cartilage repair process
Definition
causes chondrocytes to become more metabolically active
Term
how do electromagnetic fields and laser stimulation facilitate cartilage repair process?
Definition
they provide mechanical stimuli to stimulate reparative cells and make them do more business
Term
talk about contact pressure through a knee with varus
Definition
The varus angle creates a long moment arm from the center of the knee joint to the line of the GRF. This long moment arm and the GRF force = STF force and short STF moment arm. Therefore, the STF must be sky high. There is decreased contact area because of the malalignment. Decreased contact area and increased force, so CP = CF/CA will be huge on the medial side of the joint that is touching. Further force is added if the person stands with knees flexed: the patellar tendon will add to the force.
Term
what are some evidence based ways to reduce varus?
Definition
teach medial thrust gait, remove heel lift, give a lateral wedge, give poles
Term
how does a lateral wedge reduce varus?
Definition
causes increased GRF on lateral foot, which drives pronation, moving tibia medially and reducing varus angle
Term
why does heel lift increase varus loading at the knee
Definition
plantarflexion is a component of supination (plantarflexion, inversion, adduction). Supination puts you into varus. ALSO ankle PF causes knee and hip flexion. With knee flexion, the quads have to work. When the quads have to work, CF and CP increase.
Term
why do you not want a menisectomy
Definition
leads to loss of contact area and increased contact pressure in focal areas. Greatly increases risk of OA
Term
what are the effects of ligamentous instability on AC?
Definition
with ligamentous instability, we have an absence of restraint to shearing forces, primarily shearing forces imposed by soft tissues. This causes abrasive wear of AC and leads to OA
Term
what is a dramatic way to decrease CP in someone with a malalignment
Definition
decrease the malalignment with orthotics. When you decrease CF and increase CA, the decrease in CP is dramatic
Term
what are ways to decrease contact force?
Definition
stretch tight soft tissues that cross the joint. Decrease body weight. Shock absorption change via change in ground surface, shoes, orthotics, stronger muscles, change in movement patterns
Term
how to protect AC in someone with adhesive capsulitis
Definition
weight force already causes the joint reaction force to be very large. If the patient has adhesive capsulitis, inferior soft tissues will also be very tight,pulling the humeral head into the glenoid. This further increases joint reaction force and can hurt AC. Don't ask the patient to abduct against gravity. Do abduction in supine, do mobilizations to increase movemnet.
Term
what are initial PT recommendations for AC problems
Definition
avoid locations in the ROM where it hurts, protect weightbearing, decrease running velocity, avoid downhill running, increase shock absorption, reduce tightness in soft tissues that cross the joint, redirect activities, slow down, exercise with low load high velocity to take advantage of fluid film lubrictaion
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