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Hmmm. I have the unpleasant feeling this is going to be one where my post is peering all trusting and baby seal like at the descending club of your insight. ;) However my thoughts on the above.
I was, speaking of the planal dominance in the sub talar joint. The planal dominance, so far as I know is not especially time Dependant from a practical viewpoint and is a quality of the morphology of the articular surfaces. The primary factor is the inclination of the STA in the saggital plane. A foot with an axis nearer the horizontal will exhibit more movement in the frontal plane and the navicular will drop more and drift less. A foot with an axis nearer vertical will exhibit more movement in the transverse plane and the navicular will drift more than it drops.
Best way I can recommend to understand this, for anyone wondering what the hell I am talking about, is to get a cast of a foot, A knitting needle, and a 30 cm masonry drill bit. Drill holes in the cast first where manter described the axis (42 degrees from horizontal and 16 from transverse)then vertical, horizontal, and if you have space at points in between. Then hold the needle still and rotate the foot around it in various axial positions observing the way the nav moves.
That worked for me anyhow. I have a nice one which I varnished so it doesn't shed bits everywhere. Good teaching aid.
So far as prescription variables I try to consider the most efficient way in which to exert supination moments across these joints. A foot with a navicular which tends to drop more than drift should be easier to control as this movement can be countered by GRF, in plain language, one can use the ground to brace an insole and push straight up against the foot. A foot which drifts more is harder to control because to put force directly opposed to the way the nav moves (sideways) one has nothing to brace against, save the side of the shoe and the medial flange of the orthotic. Of course there will still be SOME drop to control from beneath but if this is a smaller movement it will generate more lbs / sq inch of pressure and can cause problems with tolerance. As in trying to hold a sprung door nearer the hinge rather than by the handle, same force, shorter distance.
Prescription wise, depending on what I'm trying to achieve of course, I tend to use devices with less arch fill on the cast, more medial flange and higher friction covers on the transverse PD (drifty) ones. I'm also more likely to use Medial heel skives with these and I tend to nag the patients about their shoes more.
The frontal plane dominance ones seem to respond to a much wider range of treatments so they tend to get more pre fabs, simples, less of a hard time over shoes and lower profile devices. I find these easier to treat.
I sometimes compare it to catching a ball. Consider the movement of the nav, on its own (get rid of the rest of the bones for a sec. If that was a ball and I wanted to arrest its movement (catch it) I would angle my hand to be perpendicular to the angle it was coming in at. If I could do this I would not worry if my hand was slippy. If it was coming in horizontally and I could only hold my hand at a 45 degree angle I might still be able to catch it but it would be harder than if it was coming straight down and also easier if I had a glove with a high friction cover.
I'm rambling now but hopefully somebody has got some idea from this.
Regards
Robeer
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Re: HELP !!! MTSS revisited
The spatial location of the STJ axis of an individual is dependent upon the position of their STJ, and the position of the STJ during gait will vary with time during the gait cycle. Therefore, the planal dominance of the STJ will also vary with time during the gait cycle.
Questions: why do we use the navicular drift and drop as an indicator of STJ planal dominance? Why does the navicular drift and drop with STJ motion? And, from later in your post, why are we trying change the kinetics and kinematics of the navicular and not the STJ?
We are orientated here in the frontal plane slicing through the foot. Let 1, 2, and 3 be axial positions and a, b and c orthosis reaction force (ORF) vectors. Now re-orientate yourself so you a looking down on this in the transverse plane.
Take axial position 1, and force vector a, now re-orientate this in your imagination so that we are now looking at this from a transverse plane view, does this vector pass medially or laterally to the axis? Now consider axial position 1, but ORF vector b, has it's mechanical effect changed? Now consider the relationships between the other axial positions and the ORF vectors.
Alternatively, if you find this difficult to do in your mind, take your knitting needle model and use one needle to represent an ORF vector and another to represent the STJ axis- try sticking the needles through at different angles.
Hope you can see the relationship between axial position and ORF here and how this might be applied clinically.Attached Files:
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Re: HELP !!! MTSS revisited
Hey Simon.
And splat;)
I thought you had something like this in mind! Great stuff.:drinks Lets chew.
Again, from a purist point of view I accept that the Nav Kinematics are an imperfect means of infering sub talar kinematics. But speaking practically is there a better one?
Here is fun. I (for one) tend to find myself reverting to thinking of the axal shadow in the trans plane (if I'm not careful). What if we take the shadow an move it several slices up through the foot (say, a few cms), then consider where the ORF vector now falls. The axis is a shadow so will be the same regardless of the level of slice but the ORF comes in at an angle and so will hit the slice at a different point to the lumpy bit of the orthotic. An orthotic which exerts a more vertical orf vector will have the ORF intersect the high slice more lateral than the COF of the orthotic but not much. An orthotic with a more horizontal vector will have the ORF intersect the slice in a far more lateral position, moving it closer to, or past the axis and thus reduce the moments until it intersects and then move into pronation moment territory.
I know thats extrapolating 3d Data into two sets of 2d data but thats the best I can do right now...
No. Brain just went fizzle. I'm going to bed. Vectors don't happen well after 11pm for me. But I'll leave on this. I think we agree that the ORF vector is important. The ORF, in an inert material, will be a quality of the angle / morphology of the surface and the friction co-efficient. Increasing the friction of an orthotic is something we can practically do to make the orf more vertical. A slippy surface will have a more vertical vector if the foot is contained and held directly onto it (I think). What are the PRACTICAL implications of this in relation to insole cover choice, insole width and shoe style?
Regards
Robeer
Sorry Tek, Simon and I seem to have hijacked your thread. We'll get back to MTSS at some point I'm certain, but this is just too much fun. -
I've started a new thread on this subject. Robert and I were discussing this last night in the MTSS thread. Craig it would be helpful if you could move those posts to the head of this thread to make more sense of the context.
While the medial to lateral deviation of the STJ axis has been much discussed and described thanks to the work of Kevin and others, discussion of the "height" of the STJ axis seem to have fallen out of favour. Indeed, this last post by Michael Weber indicates that it is perhaps not being examined so frequently now.
"6. An estimation of the sagittal plane inclination ('pitch') of the STJ axis.
This clinical assessment method is based on the single axis model of the subtalar joint proposed by Manter and Root. It is not biomechanical reality but a model used to enhance our understanding of subtalar joint planal dominance. A clinical estimation of the sagittal plane pitch of the STJ axis as 'high'. 'average' or 'low' is absolutely essential biomechanical information without which an accurate prescription cannot be written.
Conceptually, the patient's individual sagittal plane STJ axis inclination determines the relationship between the degree of frontal plane (calcaneal) motion and the degree of transverse plane (talar) motion during STJ function. Basically, patients with a low STJ axis produce greater amounts of calcaneal eversion to talar adduction during closed chain STJ pronation than those with an average axis. Patients with a high axis will produce a small degree of calcaneal eversion but large degrees of talar adduction and therefore more internal leg rotation during closed chain STJ pronation. Considering this very important concept, it should be appreciated that the degree of rearfoot post motion (pronation skive) is directly related to the amount of calcaneal eversion required for the individual during the contact phase of gait and this is determined by the clinical estimation of the sagittal plane pitch of the STJ axis.
The STJ axis is clinically checked as follows:
a. The patient is placed in a prone position with both feet extending over the edge of the examination couch.
b. The foot is placed around talo-navicular congruency (rearfoot neutral) with the mid-tarsal joint fully pronated.
c. Using the thumb under the 4th and 5th metatarsal heads, the foot is gently dorsiflexed to ankle joint
resistance and then moved smoothly through its full range of pronation and supination.
d. During the motion, the forefoot is examined to appreciate its arc of motion. If there is more adduction/abduction of the forefoot as compared to the degree of inversion/eversion, the axis is deemed to be high (Fig. 1). If there is more inversion/eversion motion to adduction/abduction, the axis is deemed to be low (Fig. 2). Should the degree of inversion/eversion be equal to the degree of adduction/abduction, the axis is considered to be average (Fig. 3).
See Fig. 1 Fig. 2 Fig. 3 below.
It is essential for the practitioner of orthotic therapy to appreciate that, during foot orthosis manufacture, the degree of rearfoot post and the degree of pronation skive must be the same. Also, it must be understood that the degree of rearfoot posting is chosen on how much calcaneal eversion is required during the contact phase of gait and not on how much correction to the RRSP is required. For a full discussion of these very important concepts, refer to The Manufacture and Use of the Functional Foot Orthosis by Ray Anthony, published by Karger (1991).
As a basic rule, a 4° rearfoot post with a 4° pronation skive is prescribed for a foot with an average STJ axis. A 2° rearfoot post with a 2° pronation skive is used on an orthosis for a patient with a high axis and a 6° post with 6° of 'motion' for a patient with a low axis.
References:
Root M.L., Weed J.H., Sgarlato T.E., Bluth D.R.: Axis of Motion of the STJ. JAPA 1966, Vol.56, No.4.
Green D.R., Carol A.: Planal Dominance. JAPA 1984, Vol.74, No.2.
Phillips R.D., Christeck R., Phillips R.L.: Clinical Measurement of the Axis of the STJ. JAPMA 1985,
Vol.74, No.3."
What say you?
Robert, I'll come back to the points we were discussing later, ideally when Craig has moved the posts from the MTSS thread here- thanks Craig.Attached Files:
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Question Its this more to do with calcaneal inclination angle effecting where the motion occurs.
ie low calc inclination angle ( low axis) more calcaneal movement available, High calc inclination (high axis) less calcaneal movemnent therefore talus must move to allow motion at the STJ ? or have I completely missed the boat
Michael Weber -
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Ive just read the posts again for the 4th time and somethings clicked I did miss the boat I´ll be quiet and read now and not write.
Hopefully people can add to this as I find it very intersting.
Michael Weber -
The subject of the degree inclination of the subtalar joint (STJ) axis was taught to our class by Dr. John Weed while I was a student at CCPM from 1979-1983. Also Dr. Merton Root lectured on this while I attended his seminars during the late 1980s. (Ray Anthony came over to CCPM to learn from the Biomechanics Professors at CCPM during the mid 1980s.) The notion that we should assess for whether the STJ axis was a "high-pitched axis" or "low-pitched axis" was considered to be "advanced biomechanics" at the time.
Basically, we were taught by Drs. Root and Weed that a high-pitched axis would allow more tibial internal-external rotation for every degree or rearfoot inversion-eversion and a low-pitched axis would allow less tibial internal-external rotation for every degree of rearfoot inversion-eversion. This seemed at the time, and still seems to this day, to be a reasonable biomechanical assumption and seems to hold true after a quarter-century of analyzing these patients.
One of the problems with looking at just the inclination of the STJ axis to the sagittal plane (which Root and Weed emphasized), without considering where the STJ axis is located spatially relative to the osseous structures of the foot (which root and Weed did not emphasize) is that medial and lateral deviation of the STJ axis will change the relative motion of the foot relative to the tibia. I first wrote about this in my paper from 22 years ago on two methods of how to determine STJ axis location (Kirby KA: Methods for determination of positional variations in the subtalar joint axis. JAPMA, 77: 228-234, 1987).
The most popular method, which is now widely recognized within podiatric circles, is the method where I pushed on the plantar aspect of the foot to determine the STJ axis location. The second method briefly described at the end of the paper, which I have never heard anyone else talk about, involves watching the path of the forefoot relative to the tibia to determine STJ axis location while placing a dorsiflexion load on the distal 5th metatarsal against the passive ankle plantarflexion moment from the Achilles tendon.
When moving the STJ from the neutral position to the maximally pronated position with a plantar load on the 5th metatarsal head, the 5th metatarsal head will move more in the sagittal plane (i.e. will dorsiflex more relative to the tibia) when there is a medially deviated STJ axis, whereas the 5th metatarsal head will move more within the transverse plane (i.e. will dorsiflex very little relative to the tibia) when the STJ axis is laterally deviated. These spatial alterations in STJ axis location (which Drs. Root and Weed never talked about to my knowledge) complicates the ability of using the motion of the foot relative to the leg to determine the angle of inclination of the STJ axis. However, once an examiner is trained in this technique, they can basically get a very good idea of the amount of STJ axis medial or lateral devation just by moving the foot relative to the tibia with no visual input (i.e. the technique may be done while blindfolded with relatively good accuracy).
Excellent discussion! -
Re: STJ planal dominance and navicular drop /drift
If you think about it, you already consider time in several of your prescription variables (or you should- what are you trying to achieve and when?). When does the reafoot post "work"; when does a forefoot post "work"; when does a forefoot extension "work"? Are these all working at the same time and for the same duration during gait?
When we talk of planal dominance of the STJ we are really just talking about STJ axis spatial location and vice versa. Lets say we had an individual who's STJ axis was medially deviated during the first half of stance and laterally deviated during the latter half, how might you use your knowledge of orthoses prescription to reduce pronation moment during the first half and reduce supination moment during the second half of stance?
Now, lets say the same individuals axis was "low" and medial during the first half of stance and "high"and lateral during the later half, might this change your prescription?
I asked:
:drinksLast edited: Jun 5, 2009 -
Hey Simon.
I take your point about the navicular not being part of the STJ and therefore a poor tool for assessing the STA. You are, of course, correct.
However.
I think there is a question of WHY do we assess the STA as part of a clinical assessment. For me, the answer is the same as for why we assess any biometric factor, to better understand how the foot functions in vivo.
As you say, there are other factors which affect drift and drop. But these extraneous factors will also affect the function of the foot In vivo. For the purposes of assessing how the foot will move in closed chain I offer that the drift and drop is more predictive than an open chain test.* And for the purposes of maximising the efficiency of the orthotic to exert the desired force surely this is the important part!
Perhaps it is more accurate to consider drift and drop as reflective of the vector of navicular motion and nothing more. But I opine that this is of considerable relevance to orthotic prescription, perhaps, (pause for the torch and pitchfork bearing mob to assemble) even more inportant that the sagittal plane orientation of the STA :eek:
I'm off to hide under the table.
Cheers
Robert
* no evidence obviously ;) -
Reliable?
http://biblioteca.universia.net/ficha.do?id=42398364
Predictive?
https://www.amrms.com/ssl/gcmas/2008Abstracts/FB8F5931-AFDC-DE37-9CBD3080E206311C.pdf
We also know that factors such as muscle fatigue are important:
http://www.labmeeting.com/paper/280...trinsic-foot-muscles-increases-navicular-drop
Spooner's half time verdict? Static assessment of navicular drift and drop, do not appear to be reliable predictors of dynamic function.
I think before you can say whether or not "this is of considerable relevance to orthotic prescription", you first need to answer the questions I previously posed: why does the navicular drift and drop? What tissues are restraining this so called "drift" and "drop?" i.e., how does this relate to the stresses within the tissues of the foot? Then, you need to show that your foot orthoses have a kinematic effect on these kinematic variables or at least a kinetic effect on the restraining tissues- do they?
Here's the answer to at least part of this for you:
http://www.asbweb.org/conferences/2004/pdf/277.pdf
This study suggests that addressing navicular drop in isolation, i.e. reducing it, tends to increase rearfoot eversion. I'm not saying this either a good thing nor a bad thing, but it is counter-intuitive. Anyone know of an arch support without a rearfoot post? ;):D This probably takes us back to our discussion of vectors...Last edited: Jun 7, 2009 -
See attached image:
Let the image be a frontal plane section and 1-4 be spatial locations of the STJ axis.
Take axial positions 1 and 3, their orientation relative to the transverse plane is identical but their relationship to the sagittal plane differs, given the orthosis reaction force (ORF) vector illustrated by the arrow, we get two different moments produced by this vector. Similarly, if we look at axial positions 1 and 2, these have identical "height" in the sagittal plane, but one again the ORF vector will result in different moments about these axial positions. The comparison of axial positions 3 and 4 provides similar results.Attached Files:
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I believe that you should make CorelDraw your next purchase. You can get the older version, CorelDraw X3, fairly cheaply now and it will have more functions than you could ever use. It will greatly improve the appearance of your illustrations.:drinks
By the way, great references above!!Last edited: Jun 7, 2009 -
In regards to navicular drop and drift, these measures of the kinematics of the foot will probably never be as predictive of injury as will measures of the kinetics of the foot. Unless the forces requred to prevent navicular drop and to prevent navicular drift are reliably measured to produce mathematically quanifiable load vs. deformation curves of these motions, then there is little use, in my opinion, of even performing these measurements.
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I'm going to scan in a foot skeleton so that I can create 3d diagrams on my CAD software just for you.
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I get the diagrams. They're better than mine!
The SNA / feiss line is predictive isn't it?
I'm not saying its not, but I do think that the lack of good repeatability studies render a clinical observation without value.
Good fun
Robert -
The rest of your quotes were from Kevin, so I'll leave those for him, but I will ask you the same question I asked Kevin (which he didn't answer), why do you think the study that used insoles to "block" navicular drop, found an increase in rearfoot eversion with decreased navicular drop?Last edited: Jun 9, 2009 -
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Last edited: Jun 10, 2009
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That's a 10-4, big buddy (said with a Southern States twang....which the last time you tried.....you still didn't get it right.....):rolleyes::pigs::drinks -
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