One thing for sure, Craig's excellent Boot Camps certainly get you thinking - the only problem is you leave with more questions than answers! Perhaps some patient, kind soul might assist with this one.
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When considering your orthotic prescription - for simplicity a Root device from a STJ neutral cast - what correlation (if any) exists between the mechanisms used - posts, skives, extensions etc., and the damaged tissue the device intends to heal? For example, can you calculate the forces generated from various inclination angles on rearfoot posts in the same subject - if so, how? If this has been discussed before - I'd appreciate a pointer in the right direction.
Cheers
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If you want a full copy PM with an email address and it will appear in your inbox. -
Thanks Mike - bedtime reading. Not sure it's what I'm after though. Let's make it simple.....
Patient complaines of plantar faciitis and an examination reveals a medially deviated STJn axis with FnHL and delayed windlass. High supination resistance. She responds well to a course of inversion strapping and icing but there's a Hx of PF occurring over the last 20 years so we're considering bespoke orthoses.
Ordinarily I would be looking at the differential between her relaxed and neutral stance positions and trying to get her everted calcaneus as close to the neutral position as possible. Let's say a 5 degrees medial wedge for argument's sake.
Am I correct in thinking that if I increase the inclination angle - either directly or by adding a medial skive or removing the lateral heel cup - then I would be increasing the supination moments and facilitating the reduction of pronatory moments by a greater factor than if I were to post the devices to the old prescription? Most clinicians won't have in-shoe pressure measuring systems or the like - so calculating the GRF vectors will be difficult if not impossible for the average podiatrist. But if the foot pathology results in an abnormal force of say 40N and we try to counteract that force with medial wedging - what correlation is there (if any) between the inclination angle and the orthotic reaction force? Is it simply, higher angle = higher force? -
Mark
You wrote
The better way to think about this is not by force change but by how the CoP vector will change relative to the axis of interest e.g. the STJ axis. So in simple 2D terms, lets say reductionist terms, the medial wedge moves the CoP medially and the higher the incline of the wedge the more medial the CoP becomes (up to a certain point of slippage in the shear plane, where the foot slides onto the lateral aspect of the foot.
The medial skive works slightly differently, it is like a chock under a wheel, as the foot tries to roll over it the force vector from the skive becomes more vertical and higher in magnitude and therefore more medial, plus and at the same time, the force acting on the lateral aspect of the foot reduces in magnitude, and so the total CoP vector again moves more medially. Also the placement of the medial skive enables an initial condition of a more medial force to be applied to the foot than a normal wedge would, again the analogy with a chock under a wheel show this well.
Determining exactly how much change in CoP position you might require will not be precise but consideration of the STJ axis position (for instance) thru the stance phase will help considerably in terms of the pathology of interest.
The problem with using in shoe pressure insoles to make a reasonable estimate of change in CoP relative to the STJ axis for instance, is that the curved surface of the orthosis is characterised as a flat surface on the PC screen and so the force vector that appears vertical and medial (and causing supination moments) to the STJ axis may in fact be oblique and lateral (or rather as if lateral & causing pronation moments) to the STJ axis. You'll have to read the paper Mike quoted to get the full picture of this proposition.
Does this help?
Regards Dave -
Mark
Reading between the lines of your last two posts: are you thinking, if you can't calculate forces then it might be reasonable to observe change in position.
Change in position might indicate change in internal force applied but no change in position does not imply the converse i.e. no change in internal force.
This is because the position can remain the same but the internal forces that held the foot in a certain position can be replaced by external forces e.g. orthotic reaction forces. So because the design of the orthosis means the CoP moves medially the stress on internal structures are reduced and the force on external structures are increased. In other words the same angular or rotational equilibrium is achieved but by utilising plastic materials instead of biological tissue.
Regards Dave -
Use a forefoot extension to reduce load on the medial forefoot and increase load on the lateral forefoot.
Then adjust as symptoms warrant. There's way too many factors to calculate it all out. You just have to go by the level of symptoms to see if you changed things enough.
Eric -
In order to calculate these thing you need a 3d force plate + in-shoe pressure + 3d kinematic analysis with multi-segment foot modelling. Can you imagine how long this would take on all patients and how much you'd have to charge them. Anyway the best evidence suggests a prefab will do the trick:rolleyes:
Like Eric and Dave, I think more in terms of the position and direction of the forces, rather than their exact magnitude. -
This seems relevant here: http://matacq.free.fr/Publis/sheep.pdf :D
And some of us realise that shamopody is weird, can you imagine this at an international conference with your mates and peers:
"So what you working on at the moment?"
"Sheep dragging kinetics"
"Really?"
"You bet your ass".
"No, really?"
"Sheep dragging kinetics"
"So, what are you benching these days?"
"two-twenty"....... etc. -
Okay - firstly thanks for the replies - as always, much appreciated. Now by and by I think for the most part, I can understand exactly where your thinking leads and it makes a lot of sense. I've had any number of cases in the past who present with navicular/fascia/MTPj symptoms and yet my clinical examination didn't reveal immediately what pathology was at play to cause the symptoms in the first place. I guess it's only when you start thinking about the effectiveness of lever arms, resistance, elasticity etc., as well as alignment issues, you begin to see much more of the bigger picture! Oh happy days.
So coming back to my original point - and thinking along what you said about position and direction of forces - we have a patient with a medially deviated STJn axis and we can see that there is adequate medial space on the calcaneus for a R/F post (lets forget about skives/MOSI/MASS devices for now) - should we post to the maximum amount we can - to where the patient finds it comfortable and doesn't slide off the device - and not worry about rearfoot alignment or inclination angle? -
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Thanks Simon - makes a lot of sense. I can see my head's going to hurt over the next few weeks.... Has anyone written any protocols for determining prescription values yet, taking into account force vectors, loading, ZOOS, resistance etc?
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we started talking about variables, but it kind of got nowhere.
http://www.podiatry-arena.com/podiatry-forum/showthread.php?t=35482
but the how much will be very individual and even activity to activity. -
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Mike - you're a wizard! That's the conversation I was looking for. Simon et al., I guess when we eventually manage to construct a protocol that takes into account all the variables in vivo/in vitro then we might come close to understanding exactly how our interventions actually work. Until then it's the ET technique and some informed reasoning.....
ET = Eyeball Technique. -
Just because there is "inadequate" medial space to cause supination doesn't mean that you should not add the varus wedge effect to your device. You have to remember this is a matter of leverage of the center of pressure relative to the STJ axis. Just because you cannot create a supination moment does not mean that you should not reduce the pronation moment as much as possible. (Increasing supination moment = decreasing pronation moment) The higher the pronation moment from the ground the greater the internal supination moment must be. The higher the internal supination moment the higher the stress in those tissues that are resisting the pronation moment from the ground.
Eric -
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If the center of pressure without treatment is 6mm lateral to the STJ axis. Then with a varus wedge the center of pressure is 4 mm lateral to the STJ axis you have improved the situation. If you shifted the center of pressure to 8mm lateral to the axis then you would be making it worse. So, I don't see how the medial wedge could possibly increase the pronation moment.
Eric -
It helps with the image of the axis moving during gait, http://www.youtube.com/watch?v=Fn9Uujfo3iA
hope that helps -
Simon Solomon Spooner wrote in the thread 'Orthotic precrition Variables'
This is well kept in mind as we might try to become more prescriptive as opposed to descriptive
Regards Dave -
Ian -
This is actually my daughter-in-law, Keira, who is married to my oldest son, Keegan, and is the mother of my three grandchildren. Yes, this is our kitchen table she is standing on in our current home.
She also was the subject for my midtarsal joint video up on YouTube which was also shot in our house on the couch with a black sheet backdrop.
We're currently paying off her modelling fee by Pam and I babysitting her kids as much as possible.:rolleyes:Last edited by a moderator: Sep 22, 2016 -
This was Solomon:
http://en.wikipedia.org/wiki/Solomon
"blessings are not just for the ones who kneel, luckily." U2- City of Blinding Lights
"City Of Blinding Lights"
The more you see the less you know
The less you find out as you go
I knew much more then than I do now
Neon heart, day glow eyes
A city lit by fireflies
They're advertising in the skies
For people like us
And I miss you when you're not around
I'm getting ready to leave the ground
Oh you look so beautiful tonight
In the city of blinding lights
Don't look before you laugh
Look ugly in a photograph
Flash bulbs, purple irises
The camera can't see
I've seen you walk unafraid
I've seen you in the clothes you made
Can you see the beauty inside of me
What happened to the beauty I had inside of me
And I miss you when you're not around
I'm getting ready to leave the ground
Oh, you look so beautiful tonight
In the city of blinding lights
Time, time, time, time
Time won't leave me as I am
But time won't take the boy out of this man
Oh, you look so beautiful tonight
Oh, you look so beautiful tonight
Oh, you look so beautiful tonight
Yeah, the city of blinding lights
The more you know the less you feel
Some pray for, others steal
Blessings are not just for the ones who kneel
Luckily
You know who you are and that this is for you. x
For you Dave because I love you too: Yahweh
Take these shoes
Click clacking down some dead end street
Take these shoes
And make them fit
Take this shirt
Polyester white trash made in nowhere
Take this shirt
And make it clean, clean
Take this soul
Stranded in some skin and bones
Take this soul
And make it sing
Yahweh, Yahweh
Always pain before a child is born
Yahweh, Yahweh
Still I'm waiting for the dawn
Take these hands
Teach them what to carry
Take these hands
Don't make a fist no
Take this mouth
So quick to critisize
Take this mouth
Give it a kiss
Yahweh, Yahweh
Always pain before a child is born
Yahweh, Yahweh
Still I'm waiting for the dawn
Still waiting for the dawn, the sun is coming up
The sun is coming up on the ocean
His love is like a drop in the ocean
His love is like a drop in the ocean
Yahweh, Yahweh
Always pain before a child is born
Yahweh, tell me now
Why the dark before the dawn?
Take this city
A city should be shining on a hill
Take this city
If it be your will
What no man can own, no man can take
Take this heart
Take this heart
Take this heart
And make it brave -
You have started a very good thread here since I'm sure a lot of others following along here have similar questions but are not willing to ask them on this forum.
As the others have stated so far, it would be very difficult to actually calculate the external moments acting from ground reaction force acting across the subtalar joint (STJ) without a force plate and without a very good idea of the spatial location of the STJ axis.
The good news is that when using Tissue Stress Theory to prescribe foot orthoses, you don't need to know the absolute magnitudes of moments acting across the STJ. All you need to know is which direction one should change the STJ moments in order to produce the reduction in stress acting within the injured tissue in order to produce the desired therapeutic results.
For example, let's take the example of the runner with medial ankle pain and see how one would use Tissue Stress Theory to design an orthosis that would make the runner less symptomatic.
First of all, after taking the history of the runner, one should determine which of the structural components of the medial ankle area of the runner is symptomatic. Palpation reveals that the runner is most tender at the posterior tibial (PT) tendon. If the runner relates no history of direct trauma (i.e. an external compression force) to the PT tendon, then one must assume that the most likely cause of PT tendon pain is excessive magnitudes of tensile stress within the PT tendon.
Now, since we know that the function of the PT tendon is to increase internal STJ supination moment, then the most reasonable way to reduce PT tendon tension is to decrease the contractile activity within the PT muscle. It makes sense if we can increase the external STJ supination moment with a properly designed foot orthosis, then the central nervous system (CNS) will recognize the increase in external STJ supination moment from the orthosis from its afferent joint/tissue receptors and reduce the efferent contractile activity to the PT muscle. This reduction in PT muscle contractile activity will also likely reduce the pain in the PT tendon and allow it to heal uneventfully.
How do we then increase external STJ supination moment with a foot orthosis? There are many ways to accomplish this task from a technical aspect. Orthosis modifications which may increase external STJ supination moment include adding a medial heel skive, inverting the orthosis, increasing the medial longitudinal arch height, stiffening the medial longitudinal arch of the orthosis, adding a rearfoot post, adding a varus forefoot extension or lowering the lateral arch of the orthosis. Basically, any orthosis modification which reduces the ground reaction force (GRF) on the more lateral aspect of the plantar foot and/or increases the GRF on the more medial aspect of the plantar foot will increase the external STJ supination moment and will likely produce a therapeutic effect for the runner with PT tendinitis.
Mark, I would have to say that the most difficult task in prescribing orthoses is not in the decision of which direction to "push the foot" with the orthosis. Rather, the most difficult task is knowing how much "correction" and which orthosis modification one should use so that our example of the runner with PT tendinitis is given the proper amount of external STJ supination moment so that 1) the abnormal magnitudes of excessive PT tensile stress are reduced so that proper healing may occur, 2) the gait function of the runner is optimized, and 3) the increase in external STJ supination moment is not too little to produce insufficient reduction in PT tensile stress but also not too great that it may cause pathologies from excessive STJ supination moments such as iliotibial band syndrome, peroneal tendinitis, lateral ankle instability, or plantar fascial compression irritation.
For most clinicians who are highly skilled with foot orthoses, it takes years upon years of trial and error experimentation to find which combination of foot orthosis modifications work best for each patient. Unfortunately, due to a lack of proper training, or being taught improper orthosis theory, many clinicians are unable to achieve the full potential of custom foot orthosis therapy.
However, for the clinician that has worked to obtain a better understanding of how the foot works by studying and using mechanically coherent theories, and has worked to better understand how foot orthoses work by the alteration of GRF into orthosis reaction force (ORF), such a clinician can become one of the most valuable foot-health clinicians in their community and provide their patients with a medical service that can not be obtained from any other medical professional.
I suggest, Mark, that if you spend time reading my first book and then, if you so desire, spend time reading my second and third books as time allows, that you will gain a much better understanding of the process I have outlined above. My first book has now been reprinted is now available again at the Precision Intricast Website.
Kirby KA: Foot and Lower Extremity Biomechanics: A Ten Year Collection of Precision Intricast Newsletters. Precision Intricast, Inc., Payson, Arizona, 1997.
Kirby KA: Foot and Lower Extremity Biomechanics II: Precision Intricast Newsletters, 1997-2002. Precision Intricast, Inc., Payson, AZ, 2002.
Kirby KA: Foot and Lower Extremity Biomechanics III: Precision Intricast Newsletters, 2002-2008. Precision Intricast, Inc., Payson, AZ, 2009.
Hope this helps.:drinks -
All the best -
No matter how much we are convinced that a certain orthosis prescription should be the "optimum orthosis formula" for a patient, if their gait function deteriorates with application of our "optimum orthosis formula", then the orthosis must be adjusted to optimize their gait function. This is why it is so important to develop a better understanding of how the CNS controls gait function since, without the CNS, there would be no gait function.
As an aside to this great discussion, we are driving this morning up to Lake Tahoe to a cabin on the lake for our family Thanksgiving celebration. I'll take some photos and send them along to make everyone jealous. Lake Tahoe just got about 5 feet of snow in the last few days!
Happy Thanksgiving everyone! -
Simon
http://www.youtube.com/watch?v=GkEQS5SJZPU
Great song
Amazing Yahweh Thank you
DaveLast edited: Nov 26, 2010 -
Even when you have the "3d force plate + in-shoe pressure + 3d kinematic analysis with multi-segment foot modelling" that's only the forces at the orthoses/skin interface. What happens to those forces between skin and bone through the soft tissue, are those forces transmitted in straight lines? Bone surfaces, and that's where we're interested in with the forces, isn't smooth, even and equidistant from the skin surface.
Have we covered this? or isn't this relevant?
And goodaye to you all, it's been a beautiful day. -
Sometimes I think we over think things a little, while interesting discussion do come from them there must be a point where clinically we say here is the sum of a forces being too much on this tissue, add a device to change the COP to move the force from the stress tissue to another tissues , and if it doesn´t work make adjustments. -
Great discussion!
Greetings from a snowy but clear Lake Tahoe. Today is the annual Kirby Christmas Photo Shoot and sledding with the grandchildren/children. Tomorrow, we expect about 4-6" of new snow. Fun!Attached Files:
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Ah man - you get a lake named after you and all I get is a pond in Massachusetts... says it all really...
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http://www.youtube.com/watch?v=VmalWbUXaD0 -
National Lampoons and golf... you spoil me.
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Beautiful day here in Aus mate! -
And here's the results of the 32nd annual Kirby Christmas Card Photo Shoot.....expecting 4-8 inches of snow tomorrow, wind gusts to 25 mph....starting to feel like winter up here! (Do you know how hard it is to get 5 adults, 3 children and 3 dogs to all be looking toward a camera at any one time?!)
Attached Files:
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