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Post by lawrencebevan on Jul 23, 2008 12:16:11 GMT
Yep the classical approach would be to cast maximally pronating the MTJ and the orthotic is posted to whatever is needed to maintain the appropriate forefoot to rearfoot relationship. Some would argue that they can repeatably measure this. I dont include myself but its not beyond the realms of possibility?
re normal mtj position but excessive range perhaps you allude to to things such as the previously known animal the "high MTJ oblique axis". There are variations on classical prescriptions passed on for these alledgedly such as no motion in the rf post and deep heel cups etc.
this all falls down largely on measurement problems and validity issues such as diurnal variation.
this huge variability has oft led me to concluded that our "expensive arch supports" for most people are just that !
The skill or trick is knowing how to do it without making more people worse than better and knowing a little mechanics so that if it doesnt go to plan you have an idea why and how to fix it in those people who need it to be "just so".
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Post by ianl on Jul 23, 2008 12:59:58 GMT
Ah. Diurnal variation.
Sssshhhh. Don't let Dvid H hear you mention this phrase, we'll be here for years!
Ian
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Post by robertisaacs on Jul 23, 2008 13:19:46 GMT
But what IS the appropriate forefoot - rearfoot relationship? Perpendicular to a neutral rearfoot? Mid range? End range of eversion? Is is deduced from the position of best congruance in the mid tarsal joint or reference to an absolute transverse plane (perhaps a hard flat one). The thing i struggle with is that there is such a formula which decides the most appropriate for all regardless of pathology or function. Don't worry ian, Studies have shown that David is much calmer about these things when he reads the post in the evening . Mind you we're in trouble if he reads it in the morning! Regards Robert
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Post by davidsmith on Jul 23, 2008 13:53:38 GMT
Robert
You wrote
Have you seen the case where a person presents with severe apparent genu valgum, and yet has severe pronation and pronation related pathology eg plantar fasiitis. Often the medial forefoot / 1st ray contacts the ground first. Similar scenario as my last post, in this case the knee is usually flexed and internally rotated (apparent genu valgum) and as the hip progresses forward there are increased internal rotation moments about the TC joint and so the tibia and fibula malleolous internally rotate and the STJ pronates, when by obsevation of stance one might intuitively expect the foot to supinate. Here again a valus f.foot post will reduce pronation. The addition of a 1st ray c/o etc may help if you measure a low/dorsiflexed 1st ray/mPJ As you say Robert with a valgus foot the lateral rays usually will have increased GRF but not always. Can we be sure our definition of valgus is reliable? maybe not. Again tho, with reference to 'normal' bisection and relative position of the calcaneous, it is only a reference point for use by the attending clinician. The secret to true custom orthoses that reduce tissue strain is to diagnose which tissue is traumatised and design an orthsosis that facillitates its rehabilitation and induces no further trauma, regardless of the 'normal' position.
Cheers Dave
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Post by ianl on Jul 23, 2008 15:31:29 GMT
Hi Rob
You ask: "But what IS the appropriate forefoot - rearfoot relationship? Perpendicular to a neutral rearfoot? Mid range? End range of eversion?"
In relation to what?
Ian
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Post by robertisaacs on Jul 23, 2008 19:13:03 GMT
Well quite! I then said
That is the question!
I thought i said that would be the case in a foot with a varus forefoot (relative to rearfoot)
I'd say not.
Thats fair. Although it is well to bear that in mind because when lines get drawn and angles measured gross observations tend to masquerade as precise biometrics.
YES YES YES!
And that is where the root model falls on its bum somewhat. Root starts from its "criteria for biomechanical normalcy" Root, M.L., W.P. Orien, J.H. Weed and R.J. Hughes: Biomechanical Examination of the Foot, Volume 1. Deviation from these norms is presumed to cause pathological compensations and rootian casting / biomechanics is built around looking for and accomodating these "deformities".
Three problems i see
1. Some of these "criteria for normalcy" have little basis beyond enthusiastic assertion (such as the assertion that the Calc should be straight to the tibia when in stjN). Can we say that there is a "normal" situation we should return to? Is that what we do?
2. We struggle to quantify or measure many / any of these criteria with any degree of repeatability.
3. This method of "returning to normal function" does not take specific account of the presenting injury. For Eg, in a foot with a peroneal pathology do we want to return the foot to a more inverted position?
Regards Robert
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Post by ianl on Jul 23, 2008 22:26:16 GMT
Hi "But what IS the appropriate forefoot - rearfoot relationship? Perpendicular to a neutral rearfoot? Mid range? End range of eversion?"
In relation to what?
The above question remains.
Indeed does there have to be a definitive "relationship" between fore and rearfoot or is this something that allows us to place function into a category we can conveniently manage or deal with.
Is not the Relationship of the foot to do with the surfaces it walks on and that as that varies so does the role (in a broad sense) of rear and forefoot alter. Indeed in the case of some surfaces can we really discuss the foot in terms of two distinct aspects?
Just reflecting on my own ignorance really as usual.
Ian
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Post by robertisaacs on Jul 24, 2008 7:40:20 GMT
Well put.
We might want to consider the idea of a ZOOS, A la STJ. We might want to consider a "position of maximum functionality" individual to each individuals pathology, function and circumstances. To bring us back to the OP i don't think we can say there is a single "right position" as laid out in Root's "criteria for normalcy" and i think a model which is based on returning the foot to this "normal" position is flawed.
Nothing wrong with using catagories, at the end of the day one has to do that. But there is a risk that instead of examining function in an open way and then assigning to a catogory for conveniance we start thinking in catagories and prescribing accordingly?
Regards Robert
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Post by davidsmith on Jul 24, 2008 15:57:04 GMT
Robert
Oh! ok then but - Only an un or semi compensated forefoot varus, a compensated varus tends to load the 1st ray and off load the 5th. This is why a valgus post can reduce 1st ray loading and enhance windlass action, which in turn reduces compensations that result in pronation ie reduced pronation.
Dave
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Post by kevinakirby on Oct 21, 2008 3:28:20 GMT
Good to read some of the comments on biomechanics on this website. There have been some very good discussions here and I'm very impressed by the comments of those such as Robert Isaacs and David Smith who seem to have a very good grasp on the biomechanics of the foot. Good job!
We have progressed much in our knowledge since the days of Mert Root and coworkers and certainly shouldn't throw out what they have provided to us. However, we need to move on to more scientific, biomechanically sound principles if we are to, as a profession, progress forward. Keep up the good work.
By the way, Dave Holland....great site!!
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Post by Admin on Oct 21, 2008 7:30:26 GMT
Thank you Kevin - and welcome!
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Post by billliggins on Oct 21, 2008 9:43:10 GMT
It's only fair to point out that Root, in the introduction to Clincal Biomechanics Vol. 2 stated: " The truth of this text is based primarily upon coherence" - and it is coherent. Further "The practitioner must have the best possible basis upon which to make treatment decisions. He cannot wait until sufficient research has been conducted to conclusively prove how the foot functions."
Root clearly understood that his theories were just that, theories, but logical theories. It is well to remember that his concepts were brought into a coherent whole in the 1960's and that was getting on for 50 years ago. Concepts move on, and whilst acknowledging Root's huge contribution (and I was weaned on it), no-one now takes the definition of normalcy as accurate. Neither, I hazard a guess, would Root if he were still with us.
All the best
Bill
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Post by robertisaacs on Oct 21, 2008 10:49:58 GMT
I'm not so sure that is true!
I can still think of more than a few Podiatrists who have not yet moved on from this as gospel.
As has been observed recently it is far easier to draw your own "normal" target then hit it than to actually consider each case!
Regards Robert
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