Term
| what is the composition of articular cartilage |
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Definition
| 60-80% water, 20-40% solid matrix (matrix is 60% type II collagen, 40% ground substance, <2% chondrocytes) |
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Term
| describe vascularity of cartilage |
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Definition
|
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Term
| describe neurality of articular cartilage |
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Definition
|
|
Term
| what are the implications for AC being aneural |
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Definition
|
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Term
| what are the implications for AC being avascular |
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Definition
| potential for injury repair is poor with no blood supply and few reparative cells |
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Term
| what 2 main things determine the mechanics of articular cartilage |
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Definition
| 1. lots of water, 2. collagen ground structure creates just the right amount of permeability to move water around in the AC |
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Term
| describe how water and collagen ground structre affect the mechanics of AC |
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Definition
| The time it takes to move water in loading increases the time of loading and therefore reduces contact forces. |
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Term
| Describe how the amount of permeability is just right in AC |
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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. |
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Term
| What is the job of articular cartilage |
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Definition
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Term
| How does articular cartilage protect underlying bone? |
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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. |
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Term
| describe how AC increases contact area |
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Definition
| Movement of water deforms cartilage to create increase in contact area. |
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Term
| Describe the architecture of AC |
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Definition
| superficial zone up top, middle zone in the middle, columnar orientation next to the bone |
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Term
| Describe the superficial zone of AC |
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Definition
| collagen fibers and chondrocytes are oriented horizontally, parallel to the surface. |
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Term
| What is the purpose of the horizontal orientation of collagen fibers and chondrocytes in the superficial layer of AC |
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Definition
| decrease shearing stress and tensile forces that want to create an opening in the AC |
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Term
| describe the middle zone of AC |
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Definition
| chondrocytes and collagen fibers going every which way |
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Term
| What is the purpose of the random orientation of collagen fibers and chondrocytes in the middle layer of AC |
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Definition
| to decrease stress concentrataion between the superficial and bottom layers of cartilage |
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Term
| is the random orientation of the middle layer of AC foolproof? |
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Definition
| No. sometimes people get delamination injuries where the top surface lifts off the bottom surface |
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Term
| Describe the bottom layer of AC |
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Definition
| Columnar orientation of cells next to the bone |
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Term
| what is the purpose of the columnar orientation of cells in the bottom layer of AC |
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Definition
| The columnar orientation mimics orientation of cells in subchondral bone to minimize stress concentration |
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Term
| what is the problem with the different layers having different orientation in AC |
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Definition
| can cause stress concentration which can lead to failure |
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Term
| how does Mike describe AC? |
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Definition
| dense fluid filled sponge with normal degree of relatively low permeability |
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Term
| how do most pathologies tend to affect the permeability of AC? |
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Definition
| most pathologies act to increase permeability of AC, resulting in decreased loading time |
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Term
| why don't we see lots of frictional abrasion on AC |
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Definition
| low coefficient of friction with synovial fluid |
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Term
| what are 3 things that destroy articular cartilage |
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Definition
| contact pressure, repetitive impact loading, frictional abrasion |
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Term
| what causes increased contact pressure in AC |
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Definition
| increased contact forces or decreased contact area |
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Term
| why is repetitive impact loading bad for AC |
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Definition
| makes subchondral bone too stiff causing destruction of the AC between bones |
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|
Term
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Definition
| one object sliding on another |
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|
Term
| what is the formula for friction |
|
Definition
|
|
Term
|
Definition
| coefficient of friction = how rough the two surfaces are |
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Term
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Definition
| normal force = how vigorously the surfaces are pressed together |
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Term
| thinking of the formula for friction, what increases frictional abrasion? |
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Definition
| rough surfaces, too much pressure |
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Term
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Definition
| keep muscles quiet so that joint surfaces are not compressed too vigorously together |
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Term
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Definition
| usually is low because of synovial fluid. There is a large range though, which could cause some problems. |
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Term
| what happens when AC is loaded slowly such as in sitting |
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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. |
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Term
| what happens when AC is loaded slowly such as in sitting and it continues to be loaded for a long time |
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Definition
| subchondral bone will eventually feel the loss of fluid from the AC = moviegoer's sign |
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Term
| Describe what happens to cause moviegoer's sign |
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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! |
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Term
| How to avoid moviegoer's sign |
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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 |
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Term
| If you stand up fast after sitting for a long time is that better or worse and why |
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Definition
| worse because the increased speed of loading will increase stiffness. Stiff subchondral bone pounding AC leads to OA |
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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? |
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Definition
| give the AC time to reform by removing the repetitive loading |
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Term
| what are the two methods of exercising joints that have influence on lubricating the joints and minimizing friction? |
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Definition
| Boundary lubrication, fluid film lubrication |
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Term
| is the μ for boundary lubrication or fluid film lower (better)? |
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Definition
| μ for fluid film lubrication is less than μ for boundary lubrication |
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Term
| what is fluid film lubrication? |
|
Definition
| large volume of synovial fluid trapped between 2 joint surfaces |
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Term
| what is boundary lubrication |
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Definition
| hyaluronic acid/glycoprotein molecule complex layer on each articulating surfce |
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|
Term
| what is Newton's 2nd law? |
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Definition
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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? |
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Definition
| slow because she has to overcome a large force. High load => low velocity |
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Term
| what lubrication method results from the high load, low velocity scenario and why? |
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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 |
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Term
| what is the name of the molecules that provide boundary layer lubrication |
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Definition
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Term
| if you have a patient on a machine with low resistance and ask them to move slowly, what happens? |
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Definition
| they don't encounter much resistance |
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Term
| if you have a patient on a machine with low resistance and you ask them to move quickly, what happens? |
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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 |
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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? |
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Definition
| Low load, high velocity is better to reduce articular disrepair through fluid film lubrication. Ex: Ride a bike at low resistance , high velocity |
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Term
| what to do when someone says their joint hurts |
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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. |
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Term
| what is a surgical way to promote AC healing that Mike has had done? |
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Definition
| drill hole into subchondral bone (microfracture) |
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Term
| What is the purpose of microfracture for AC injury healing |
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Definition
| Communication with vascularized bone tissue and migration of cells that end up producing fibrocartilage in the injured AC |
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Term
| What is the problem with microfracture |
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Definition
| Fibrocartilage is an inferior shock absorber to articular cartilage. |
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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. |
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Term
| With fibrocartilage in place of AC after microfracture, how can you prevent/delay failure? |
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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. |
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Term
| since fibrocartilage reduces the nutritonal flow into AC, how will surrounding AC survive? |
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Definition
| without blood supply, AC relies on synovial fluid being pushed around to give it nutrition |
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|
Term
| how to promote healing of articular cartilage? |
|
Definition
| protected weightbearing to give it a chance to recover. |
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|
Term
| are chondrocytes metabolically fast or slow |
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Definition
|
|
Term
| is there a good blood supply to AC? |
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Definition
|
|
Term
| what is the prognosis for injury to large volumes/surface areas of AC |
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Definition
|
|
Term
| how does location of the injury play a role in AC healing |
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Definition
| healing prognosis is worse if the defect is subject to weightbearing that elicits high contact pressures |
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Term
| how do you know what positions should have limited WB for AC healing? |
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Definition
| listen to the joint. Limit WB positions in the ROM for which the joint "talks" |
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Term
| what to do if you can't limit ROM because of functional reasons. |
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Definition
| figure out how to keep contact pressures low for that point in the ROM: attenuate contact force |
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Term
| how to attenuate contact force at specific points in ROM |
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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. |
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Term
| If someone has articular damage, will joint reaction forces be large or small? |
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Definition
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Term
| How to reduce force through the knees in standing |
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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. |
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Term
| what is the surface like on damaged AC? |
|
Definition
| irregular. Feels like stepping on little stones. Reduced contact area |
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|
Term
| can shaving off the irregular surfaces help AC repair? |
|
Definition
| yes. Increases contact area. Short term effects |
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|
Term
| is drilling through AC to subchondral bone a short or long term fix? |
|
Definition
| short term unless you make major changes |
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|
Term
| has early CPM shown some promise in facilitating AC repair process? |
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Definition
|
|
Term
| has chondrocyte implantation shown promise for AC repair? |
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Definition
| yes, we have good results so far early on |
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|
Term
| Why must intra-articular fractures have strong reduction? |
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Definition
| to inhibit migration of fibroblasts from subchondral bone |
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|
Term
| describe the osteochondral autograft transfer system |
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Definition
| hollow chisle pulls cores of AC from a NWB area and places it into the damaged tissue. NWB for 6-8 weeks after |
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Term
| what is another name for osteochondral autograft transfer system |
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Definition
| autologous osteochondral transplantation |
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|
Term
| is OATS better than microfracture |
|
Definition
|
|
Term
| how is OATS better than microfracture |
|
Definition
| more people return to play, less fibrocartilage and more AC |
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|
Term
| what is Autologous Chondrocyte Implantation? |
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Definition
| remove chondrocytes with a big needle, grow them in a lab. Put the cells back in underneath periosteum |
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|
Term
| does autologous chondrocyte implantation show good results? |
|
Definition
|
|
Term
| will a patient be NWB after ACI? |
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Definition
|
|
Term
| does autologous chondrocyte implantation show good long term results |
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Definition
|
|
Term
| what are the two types of glucosamine |
|
Definition
| hydrochloride and sulfate |
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|
Term
| which of the two types of glucosamine is more helpful |
|
Definition
|
|
Term
|
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? |
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Definition
|
|
Term
| what is one concern of glucosamine consumption |
|
Definition
| insulin regulation issues in diabetic patients |
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|
Term
| is glucosamine supplementation effective for people with severe OA? |
|
Definition
|
|
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. |
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|
Term
| what if you try to increase activity too quickly after immobilization |
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Definition
|
|
Term
| what are some conservative ways to facilitate cartilage repair |
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Definition
| glucosamine sulfate, chondroitin sulfate, growth hormone, electromagnetic fields, laser stimulation |
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|
Term
| how does growth hormone facilitate cartilage repair process |
|
Definition
| causes chondrocytes to become more metabolically active |
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|
Term
| how do electromagnetic fields and laser stimulation facilitate cartilage repair process? |
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Definition
| they provide mechanical stimuli to stimulate reparative cells and make them do more business |
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Term
| talk about contact pressure through a knee with varus |
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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. |
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|
Term
| what are some evidence based ways to reduce varus? |
|
Definition
| teach medial thrust gait, remove heel lift, give a lateral wedge, give poles |
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|
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 |
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|
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. |
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|
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 |
|
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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 |
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|
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 |
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|
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. |
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|
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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