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Post by robertisaacs on Jul 14, 2008 19:39:02 GMT
I've moved this here from Biomechanics education because it IS going to cause debate. Much of my view on this will be anathema to many. Still, lets have a go. Ian et al Firstly i would echo Bills sentiments about Roots contribution to podiatry. He was the trailblazer who really moved biomechanics into the realm that we understand it today. All which has been done since has built on that and the terminology is still used today. The Sub talar neutral position, for example, is arguable the single most important referance point in biomechanics, still used in almost all assessment models and we have Root and his co workers to thank for it. It is also true that Root did not work alone and that Messers Orien and Weed were equally involved. Like Flory and Chain their contributions are in danger of being forgotton. However for the sake of brevity we shall refer to the work of all three as "Rootian". I think Ian's choice of words when he asked what it (rootian docterine) has evolved into was a good one. It should also be noted that there is no "current thinking" as such. Biomechanics exists in a state of glorious chaos. There is no single view, just a spectrum of opinion. That is what makes it so fun . That said. Lets begin. Rootian docterine states that Sub talar neutral is the "position of maximal functionality". In other words, the position in which the foot works most effectivly. We still use the phrase "functional orthotic" to describe an orthotic which seeks to hold the foot in this position. Much of the rest of Rootian docterine is concerned with how to acheive this position. So, we must ask. [glow=red,2,300]1. Does the STJ have a single "position of maximum functionality" or is it rather that it has a "functional range" or "zone od optimum stress" as described by KK? [/glow] Personally i feel that if there is a joint with such available range and two obvious functions (shock absorbtion and adaptation) we should think carefully before blockading it in one position or considering that there is a single position the joint SHOULD be in. Secondly, of RSCP and NSCP. Standard Rootian docterine teaches these two measurements as key to assessment. The protocol is to bisect the calcaneum via palpation and skin markings. The STJ is then Placed in STN. The angle of this line on the ground in this position is the NSCP. If the line is at 90 degrees to the flat the rearfoot is considered "normal. If the line is tilted to the outside of the foot the rearfoot is considered to be in varus. If to the inside, valgus. The foot is allowed to relax and the angle measured again this is the RSCP. If the rearfoot is found to be Varus it is suggested that the rearfoot of the orthotic should be posted to the degree needed to support the heel with the STJ in neutral. Two questions i would ask here. 1. 2. On 1 there is a significant body of research which shows that even the intra rater (same tester, same subject same day, different readings) repeatability varies by at least 3 degrees from the true bisection measured using calipers. That means the line used to calculate the posting vary by 6 degrees (3 either side) That is a LOT of variation!!! If you cannot be sure of the accuracy of a bisection can we say our prescriptions are accurate? On 2. Consider the following pictures. One is a cadaver heel, the other is from a plastic "normal" skeleton. With the planter lobes on the ground the actual bisection of the heels is outwards. In varus to use Rootian terminolgy. To get the bisection lines to be perpendicular to the ground the rearfoot MUST pronate! If the heel is square on the ground the bisection line will, assuming these calcs are representative (and i think they are), always be in varus. This has obvious implications If an STN position finds the calcaneum square on the ground, does this mean a "normal" position appears as a reafoot varus? Thats enough for tonight. Comments? Robert
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Post by lawrencebevan on Jul 15, 2008 11:28:02 GMT
"Rootian docterine states that Sub talar neutral is the "position of maximal functionality" ".
Dont think this is actually a correct translation of what is said that Mert Root said - STJN is a reference position for ff-rf measurement not a position of function.
Mert Root DID NOT use RCSP and NCSP to write orthotic rx's - big and common misconception I think stemming from the Langer educational days. He would simply balance the positive cast to vertical with intrinsic ff posting. The rf post was always ground 4deg inverted on the lateral side and level with the front edge on the medial side. He would probably accept the foot would not be functioning in STJN when on this device, the aim of the orthotic was to "lock the MTJ" - in modern speak to prevent MTJ pronation.
I dont think the Podiatric Biomech world is in chaos. Whilst there may be competing points of view on foot biomech to me the views overlap a lot and the observations are often the same but just described differently. There are references to functional hallux limitus and medially deviated STJ axes in Root Weed and Orien Vol2, just as there are many discussions on functional hallux limitus in Kevin Kirby's books and Howard Dananberg uses heel skives!
In the main IMO what has changed is a shift from measuring angles to measuring (or thinking about) forces. The big "hole" in the STJ neutral/Root/Weed/Orien concepts is the lack of actually explaing why a structure hurts. How does a forefoot deformity make my plantar fascia hurt? Answer that without slipping into a discussion on forces. Once you accpet that the high longitudinal strain is the reason for pain in the fascia you start thinking about how to lower that strain not just about rf and ff angles. Ones rx goals become more "focussed".
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ians
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Post by ians on Jul 17, 2008 7:54:12 GMT
in your pics of the skeletal foot Robert, you have the lobes sat flat on the surface. I have a plastic model foot in front of me. If you apply a downward pressure to the top of the calcaneous as you say when the lobes level and are flat on the surface the whole foot moves to a varus or rotates anticlockwise. It would seem that by asserting this pressure that the foot moves to a varus position. However if you stop applying that pressure it rotates back to rest on the medial lobe. Bulk of bones weighting the medial aspect. My point is that the whole of the body's vertical force pushing down on the talus would keep that calcaneous resting in a less varus position wouldn't it? Is the inaccuracy of the intra rater(unsure of this equipment)due to the differing vertical loading on the talus /calcaneous? could it be, just maybe the downward forces of a persons weight and their complete stillness would affect that rock from lateral lobe to medial lobe a very hard target to measure with anything.
If you put a downward pressure on the model skeletal foot in a way that one finger is on the top of the calcaneous and one finger on the top of the talus it rocks in a range of degrees from varus to vertical. Is this a valid point or am i being very naive. Regards Ian
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Post by robertisaacs on Jul 17, 2008 8:03:19 GMT
Sorry i have not got back to folks on this one, Jude sprang a speaking engagement on me with all of 24 hours notice so i've been burning the midnight oil on that!
You might be right, i forget now where i read that. It might well have been on one of those courses you mentioned.
Sorry if i'm being dense here but i don't follow. How can it be inverted on the lateral side?
He might well. However the presumption remains that the position the MTJ should function in is based on a rearfoot neutral. I'm not sure thats accurate particularly considered in context of the bisections shown above.
I would have to disagree. Not that chaos is a bad thing. Most of the best and most educational threads / discussions i have been involved in have been on subjects where the protagonists disagree. I think the dynamism and interest of an argument brings out the best in people, it certainly motivates well. There are areas where MOST people agree but even here there are usually differences in how these areas should be treated.
Perhaps a better term would be contention.
Agreed! For me thats where the interplay of the models becomes useful. Kinetics is definatly the new kinematics!
Regards Robert
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Post by lawrencebevan on Jul 17, 2008 10:40:29 GMT
Classically, the rf post is ground to 4 degrees inverted and then ground level to the medial ff of the shell. This gives a rf post that has 2 surfaces - the so-called biplanar post that rocks on the work surface. Classically the rf post was about allowing movement not preventing it, the "control" came from the forefoot post.
Where you see the areas of disagreement, I see the large areas of agreement. Howard talks about the kinematic effects of functional hallux limitus, Kevin Kirby talks about the kinetic and Eric Fuller hypothesises that its due to pain avoidence. They all agree it exists and has AN effect. Contention is a better word!
"He might well. However the presumption remains that the position the MTJ should function in is based on a rearfoot neutral. I'm not sure thats accurate particularly considered in context of the bisections shown above."
Indeed. However the presumption is that the STJN position is the correct position to take a cast and the resultant FF-RF position captured is the one that requires posting varus or more commonly valgus. The measure of the FF-RF is then dependent on the bisection of the HEEL of the cast, not the bisection of calcaneus of the patient.
Either way up, these days I wuld be thinking about the pt's symptoms and I need a valgus force from a lateral forefoot post or a medial force from a varus rearfoot post or both! I would not concern myself with FF-RF or RF-leg measurements at all.
this is a stump I love to go around! thankyou!
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Post by ianl on Jul 17, 2008 16:39:27 GMT
Just a quick dip in here. At one level it does not matter where the lobes are?!. Each calcaneum is likely a different shape anyway with some lobes being more square some more round and some more angled. All affect how they might sit on the ground and if one lobe on a calcaneum was a different shape to the other might this also alter how the heel sits to the ground so affecting ideas of measurement?
Cheers Ian
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Post by robertisaacs on Jul 18, 2008 7:38:19 GMT
Me too! Thats why i put this in discussion, i was hoping we might get a good debate going. Lets play! There is something i have always been a bit unclear on with rootian casting. Just so we are talking about the same thing (and i might be wrong here because i don't do as much POP casting as i used to) can we clarify the method you use for casting? My understanding of Rootian casting is that one gets the foot in STJN then maximully pronates the midfoot by applying Y+ force through the 4th met head. I have heard it preached that this should only be done to the point where the forefoot is plantergrade relative to the midfoot. From your post you seem to be pronating the forefoot beyond this and using valgus forefoot posting to balance the FF with the RF. Have i got that about right? I'm partially with you on the last bit. I always consider the angle on inclination of the tibia from tibial varum or Genu varum but i don't bother with rearfoot / leg measurements any more. Regarding Valgus forefoot / varus rearfoot posting. This is something I use for mild intoeing in infants but rarely in "standard" pronation controll insoles. Couple of reasons. 1. a valgus forefoot wedge exerts a pronation moment around the sub talar axis. I get the idea that this will "lock" the mid tarsal joint increasing supination moments from the 1st PMA balancing this. However that presumes that the rearfoot can be held stable by the back end of the orthotic. Given the kinematic studies carried out on the function of orthotics i'm not sure we can say that. 2. Orthotics must be considered in 4 dimensions. Assuming the rearfoot of the device controlls the pronatiory moments during midstance what effect will the valgus forefoot have on late stage pronation after heel lift (when the rearfoot ceases functioning.) Will the pronation moments be balanced by the windlass effect and could the additional load on the windlass cause FnHL or PF. Always a pleasure lawrence! Regards Robert
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Post by robbloxsom on Jul 21, 2008 22:07:53 GMT
robertissacs: "a valgus forefoot wedge exerts a pronation moment around the sub talar axis."[sorry...don't know how to do the 'Quote' thingy ] ...not always, according to Our Lord KK[!] looking at some of his Intricast newsletters (2002), & I quote, "One might think that a forefoot valgus wedge would tend to cause increased midstance pronation of the subtalar joint (STJ) during walking, but this is simply not the case in most individuals...the result can actually be that the patient will have decreased midstance pronation of the STJ"
robertissacs: "I get the idea that this will "lock" the mid tarsal joint increasing supination moments from the 1st PMA balancing this."KK also says elsewhere , "To this day, I don't know what "locking the midtarsal joint" means."
I think this means we are all doomed!! robertissacs: "what effect will the valgus forefoot have on late stage pronation after heel lift"KK: "The biomechanical effect of the forefoot valgus wedge is to allow the lateral forefoot to become a more significant weightbearing structure in the latter half of stance of gait...the body's proprioceptive mechanisms sense that it can begin to initiate propulsion more "actively" in the late midstance phase of gait without causing supination instability at the STJ."PS: do the 'lobes' of the calcaneus necessarily 'sit' in a horizontal plane in the living foot? There's a whole load of squishy stuff underneath it ...Again, I believe KK suggests medial tubercle sits lower than lateral (have another look at all his diagrams of his foot model.) This might affect my calcaneal bisections...(if I did them !!) Any thoughts? Rob
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Post by robertisaacs on Jul 22, 2008 7:50:26 GMT
Hey Rob! Quotes are found bottom row of buttons second from right. Oh dear. Going to be burned as a heretic . I think this depends very much on the foot it goes in. I cannot see how a lateral FF wedge could not exert a pronatory moment, particularly if the mid tarsal joint is stiff. If you read on i then said So i'm with Kevin on this. I can't see how "locking" the joint works! Interesting question. For the Lateral part of the foot to become more significantly WB there would need to be balancing moments to prevent the foot from pronating away from the wedge. If they exist or can be generated by increased muscular activity then fine. However if the active structures + windlass are not adequate or are pathological i cannot see how placing more demands on them is appropriate. Also Kevin talks about "supination instability" during propulsion. This sounds to me like something one would find in a pathological supinator rather than a pathological pronator (in which case lateral modification is, of course, the way forward.) Whilst the Triceps surae do, of course, exert a mild supinatory moment, i don't tend to find it needs balancing with anything more than the force of gravity lateral to the STA. No, they don't. My point was that we cannot view the foot in angular terms whether by the bisection of the heel or the perpendicular line to the ground. Another reason i cannot see the relevance of RSCP and NSCP. We're going to have some fun with this Regards Robert
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Post by lawrencebevan on Jul 22, 2008 12:15:31 GMT
I used to have sleepless nights over this to. Funny how even though we deny it a valgus wedge upsets us a little bit...
A valgus forefoot wedge on a flat insole = pronation moment in most people = good for over-supinators, 1st ray elevation in pronated/normal feet (also read = MTJ pronation or "unlocked" MTJ) A valgus forefoot wedge WITH varus rearfoot wedge = balanced supination and pronation moments = ineffective in supinators, theoretically 1st ray plantaflexion in normal/pronated feet.
For varus rearfoot wedge also read medial heel cup and arch of a custom/prefab shell or heel skive.
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Post by robertisaacs on Jul 22, 2008 16:15:58 GMT
At which point during gait? Can see it during midstance. Not so sure during late midstance / heel lift.
It might help the slow of mind (ie me) to understand where you are going with this if you could sketch me out a force diagram. I can't get my head around how a valgus wedge will enhance the device! What exactly, is it doing?
Also unsure how it would planterflex the 1st ray. Explain please. I would think that it would, if anything make the navicular sit lower relative to the rest of the foot (or the rest of the foot higher to be accurate) and the position of the 1st MPJ relative to the ground would appear to be unchanged.
Much ta
Robert
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Post by davidsmith on Jul 22, 2008 17:39:00 GMT
Robert
You wrote
If the forefoot is valgus then it is possible that the 1st ray will have early ground contact relative to the lesser rays. Therefore there may be early dorsiflexion and large RoM of the 1st ray. This may cause excessive stretching of the plantar fascia which in turn will cause excessive plantarflexion moments of the hallux. This will result in high pressure sub hallux and rel;atively low pressure sub 1st MPJ. This, according to Dananberg and my research is the precurser for FncHL. Moments due to excessive dorsiflexion stiffness caused by FncHL will tend to slow the velocity of the CoM prior to its optimal position for the Lamda model of gait progression IE, due to the force of gravity, the CoM is still falling backwards . In this case there are several compensation options open to the CNS operating system - one is to allow the foot to pronate (perhaps by toeing out more) and increase RoM thru the saggital plane. By adding a valgus post to the fore foot this will change the relative timing of the 1st ray to lesser ray dorsiflexions and take force off the 1st MPJ thus reducing hallux plantarflexion moments and therefore reducing or resolving FncHL and the later compensations. Therefore, in this case, a valgus wedge will reduce pronation.
Cheers Dave
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Post by robertisaacs on Jul 22, 2008 19:43:34 GMT
Much like a reverse mortons extension. That makes sense i suppose. When would you use a valgus extension in preference to a reverse mortons / ist met head cutout?
Also are we speaking here of a forefoot valgus proper or a forefoot which is in valgus when held in maximal proonation during casting? I ask because the model you outline speaks of a 1st ray in which
If there is a true forefoot valgus than i can se that being true. Most forefeet, however, are in a supinated or varus position particularly if we are inverting the rearfoot. That being so would not the lesser mets load early and first anyway?
Regards Robert
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Post by lawrencebevan on Jul 22, 2008 21:45:15 GMT
"Also are we speaking here of a forefoot valgus proper or a forefoot which is in valgus when held in maximal proonation during casting?"
Surely the cast should capture the true deformity and thus be the same??
Eric Fuller sets out a simple way of deciding on this : Ask pt to pronate their feet in weight bearing - how much can they lift their lateral forefeet? cant? = no valgus post (read or reverse mortons/2-5 pad) can? number of millimetres = amount of pad/post. With normal/pronated rearfoot add rearfoot wedge, supinated rearfoot dont. If that aint KISS the you can KMA!!!
"Most forefeet, however, are in a supinated or varus position particularly if we are inverting the rearfoot" Aaah the old problem - depends on your heel bisection!!!
I always plantarflex the 1st ray when taking a cast, I see v few varus forefeet
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Post by robertisaacs on Jul 23, 2008 7:27:32 GMT
Which, of course, brings us back to where we started! If we cannot repeatably and therefore accuratly bisect the heel, how can we base our prescription on it?
Something else i have a problem with. What is the "true deformity"?
Presuming my understanding of the rootian casting method is correct (hold STJ in neutral, maximally pronate forefoot) this will capture the forefoot at the end of its eversion range. Is this the "true deformity"? Is this the "neutral position"? What, in fact is the significance of this position?
What of feet in which the MTJ has a "normal" neutral position but an excessive range?
I guess what this boils down to is what position are we trying to acheive in the MTJ. If the object is to hold it at the end range of eversion i can see the sense in this. In which case the question becomes, should we?
Perhaps i am have been hanging around David H too much but i am uncomfortable with the concept of the FF position being a "deformity" without we have a firm idea of normal. Which brings us on to...
What is the "normal" position of a forefoot relative to a "neutral" (say, STJ neutral during WB) rearfoot?
Is this the position we try to recreate during casting?
Really enjoying this guys!
Robert
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