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Prescription advice - heavy supination.

Discussion in 'Biomechanics, Sports and Foot orthoses' started by williac, Feb 5, 2009.

  1. williac

    williac Active Member


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    Hi Pod Community,

    I'm after some advice regarding suitable orthoses prescription parameters for a heavily supinated foot. I'm concerned predominately as to tolerance and footwear fit.

    The story so far.....

    Active male - electrician, late 40's.
    Hx of repetitive lateral ankle sprains. Mild cuboid pain (syndrome?). HD's plantar 1st and 5th MPJ's - very painful. General foot/ankle stiffness. Heavily supinated, pes cavus foot type - irritation HK focal to base of 5th bilaterally. Retracted extensor tendons. Plantarflexed first rays (semi-rigid). Blows out the lateral aspect of all footwear quickly.

    The main reason that this bloke has come in is his annoyance at having to buy so many pairs of shoes/boots.

    Any thoughts about effective management for this fellow. He had been previously issued custom devices that were a bog standard Mod Root. Needless to say this course of action provided no relief whatsoever.

    No problems with extensions to balance the forefoot - more concerned regarding everting the lateral column.

    I'd really appreciate some useful prescription tips on this one.

    Thanks in advance.

    Chris Williams
     
  2. CraigT

    CraigT Well-Known Member

    Do you mean balanced the FF deformity? So there was a lateral FF platform built up?
    If this is the case, then why do you think they provided no relief whatsoever?

    At the end of the day, you are the one who has seen his feet, so you have to assess what you want to acheive with the orthoses.
    With the information you have provided, the sort of modification commonly prescribed would be-
    - Intrinsic ot extrinsic valgus posting of the forefoot (ie- the the level of the MTPJ)
    - Valgus FF extensions
    - lateral heel skive

    I personally always use a rigid shell, but the fit and balance (ie how the orthosis sits in the shoe) must be absolutely spot on.
     
  3. LuckyLisfranc

    LuckyLisfranc Well-Known Member

    Do the same as for a 'heavy pronator', but in reverse...

    Caveat: rigid cavo-varus confirmed with Coleman Block Test. This means the STJ cannot pronate to compensate for the forefoot valgus - like a supinatus in some respects. Then is becomes very hard, short of a DFWO of the 1st metatarsal, to bring the hindfoot out of varus.

    LL
     
  4. Griff

    Griff Moderator

    Hi Chris

    I agree with Craig - lateral FF posting (possibly combined with a FF extension) is probably your best option as this is where the STJ supination moment lever arm is at its longest. If the STJ axis is laterally deviated it may be of little to no use posting the rearfoot.

    What footwear is he in generally? As he is an electrician I am correct in assuming he is in rigid toed work boots which lace up above the ankle? Do you feel this wearing of the lateral heel is happening due to foot position/kinematics in the stance phase or a varus foot position in the swing phase?
     
  5. David Smith

    David Smith Well-Known Member

    Chris

    Not picking on you just pointing out that to give useful replies to your query you need to post useful data about your patient and what your question actually is.
    Random thoughts hastily typed are not good enough. Remember we have no other clues to your meaning than the words you write, there are no hand gestures is no body language or intonation or inflection to judge the precise meaning of a statement.

    To answer your question in general.

    To reduce Supination moments that cause excessive internal (or external) forces on the tissues (or materials) that resist supination you must RELATIVELY increase pronation moments. How this is done is entirely a matter for you to decide depending on the presentation of your patient.

    NB it is possible to reduce supination moments without increasing absolute forces that induce pronation moments. There is however a relative increase in forces that produce pronation moments.

    This is where the skill and knowledge of the clinician really pays off, IE no paradigm just deductive reasoning combined with experience.

    Without more precise info this is as far as I can go with advice.

    All the best Dave Smith
     
  6. Johnpod

    Johnpod Active Member

    You might try a laterally flared heel on the shoe. Use a neutral othotic to offload the cuboid (take a segment out of the shell beneath the cuboid). Pronatory moments would be increased immediately following heel strike.

    Defend against excessive wear of the flare with those metal 'spraggs' that cobblers apply to heels.
     
  7. Chris:

    Even though I don't know what a "bog standard Mod Root" is, and don't know what the sentence "No problems with extensions to balance the forefoot - more concerned regarding everting the lateral column" means, and am assuming that "HK" means hyperkeratosis, I will try to help you out here.

    I see this type of patient frequently in my practice and I have published papers on this subject. This patient likely has a laterally deviated subtalar joint (STJ) axis due the his cavus foot, where the talar head and neck or more laterally angulated relative to the calcaneus and forefoot than normal, creating excessive STJ supination moments from ground reaction force (GRF).

    1. Kirby KA: Methods for determination of positional variations in the subtalar joint axis. JAPMA, 77: 228-234, 1987.
    2. Kirby KA: Rotational equilibrium across the subtalar joint axis. JAPMA, 79: 1-14, 1989.
    3. Kirby KA: Subtalar joint axis location and rotational equilibrium theory of foot function. JAPMA, 91:465-488, 2001.

    Since the patient has "HDs" (I'm assuming this is means heloma dura which are dorsally occurring lesions, not plantarly occurring skin lesions) on the plantar 1st and 5th metatarsophalangeal joints (MPJs), then he likely also has a high first ray dorsiflexion stiffness along with his plantarflexed first ray. The "cuboid pain" you mention could possibly be some form of internal damage within the peroneus longus tendon, which would not be uncommon in this type of foot.

    You need to put some form of in-shoe padding and/or custom foot orthosis design that will increase the external STJ pronation moments which will, in turn, decrease the external STJ supination moments that are acting on the foot from GRF acting across a laterally deviated STJ axis. Both the plantar forefoot and plantar rearfoot need to have some form of valgus wedging applied to achieve optimal gait function and symptom relief for your patient. And, don't worry, like 95% of podiatrists trained using Root's neutral position theory, that you will "over pronate" the patient's foot since this foot is will be highly resistant to external STJ pronation moments but will have little resistanve to external STJ supination moments.

    Here is an excerpt from a PowerPoint lecture I have been giving on this type of foot for the last decade. Hope this helps.

     
  8. williac

    williac Active Member

    Thankyou one and all for replying to the thread. Your thoughts have been much appreciated. David, I know the info was a little/lot short on details - quickly scrawled down between appointments....piss-weak excuse I know however I the time you spent on your reply was great. Thanks....Chris
     
  9. Please, for us Yankees who don't completely understand Australian podiatry terminology, what does "bog standard Mod Root" mean?!
     
    Last edited: Feb 6, 2009
  10. williac

    williac Active Member

    Hi Kevin,

    Let me clarify....

    "Bog standard Mod Root" = general anti-pronatory device to MTPJ's, no forefoot/rearfoot additions/postings. Now you can speak Aussie mate!

    Chris
     
  11. bkelly11

    bkelly11 Active Member

    Kevin, quick question.


    Reducing the suppination moments with this patient with 2-5 valgus wedge on the F/F and 2-4mm lateral skive (assuming R/F), would this not increase the force going through the 1st and 5th Met heads assuming its a rigid foot type and and increased D/F stiffness at the first Met therefore increasing pain??

    I'm thinking F/F plantar met extension with a double wing to off load the H/D would be of great benefit.

    Now if Ive missed something guys go easy on me.

    Hi Chris. What about seeing a footwear specialist. Extended rigid heen counter above malleoli with good retaining medium sounds the way to go.
     
  12. LuckyLisfranc

    LuckyLisfranc Well-Known Member

    I will attempt to answer this, though Kevin will possibly correct me.

    Any significant posting of the forefoot into valgus (either intrinsic or extrinsic) will provide a dorsiflexory porce on the distal shafts of the lesser MTs, increasing towards the 5th.

    What this achieves is a reduction in ground reaction force under the lesser metatarsal heads, increasing laterally.

    This is what a Coleman block test is essentially doing. Stick a 1/2 to 1 inch thick book under the lateral forefoot, proximal to the MT heads. See if the hindfoot everts or not. Voila!

    LL
     
  13. efuller

    efuller MVP

    That description gave me a pretty good picture of what you are dealing with. I would pretty much agree with comments up to this point. You need to increase the pronation moment on this foot. This is counter to Root theory.

    The only thing that I would add is a clinical measurement and what to do with the results of that measurement. Have the patient stand and attempt to evert their foot without moving their knees. Note how far the lateral forefoot lifts off of the ground. Some of these feet can lift a couple of inches and others cannot lift at all. Do not make a forefoot valgus wedge higher than the height that they can lift their foot off of the ground. If they can't lift their lateral forefoot off of the ground then the only thing you can do with a standard orthotic is a rearfoot valgus wedge (lateral heel skive) I've put valgus wedge in patients who cannot lift their forefoot off of the ground and the get a sensation of too much pressure under the lateral forefoot.

    Beyond orthotics, high top shoes, lace up ankle braces, aircast stirrups, and an AFO are all things that might help.

    Regards,

    Eric
     
  14. The forefoot valgus extension is made with the korex most thick under the 5th metatarsal head and skived down to no thickness at the 1st intermetatarsal space (i.e. no korex plantar to the 1st metatarsal head). This creates a "2-5 valgus wedge" that accommodates the 1st metatarsal head to help reduce ground reaction force (GRF) plantar to the 1st metatarsal head. If the patient has too much pressure with this modification plantar to the 1st metatarsal head (which they generally don't), I may increase the korex thickness plantar to the 2nd and 3rd metatarsal heads to locally decrease the GRF at the 1st metatarsal head. If the patient has too much pressure with this modification plantar to the 5th metatarsal head (which they generally don't), I may grind the korex plantar to the 5th metatarsal head to half thickness to locally decrease the GRF at the 5th metatarsal head.

    Balancing the cast with the heel everted is something I have done regularly with these feet for about the past 15-20 years and is something that the Root purists think will harm patients (of course none of the Root purists that have told me I should never do this to a patient have never tried this on a patient before, but simply assume that because Mert Root said you shouldn't do this, it shouldn't be done:bang:). Balancing the cast everted will increase the intrinsic forefoot valgus correction, decrease the medial longitudinal arch height, increase the lateral longitudinal arch height and evert the plantar heel cup of the resultant orthosis, all modifications that will increase the external subtalar joint (STJ) pronation moment acting on the foot.

    The filler material plantar to the lateral longitudinal arch is necessary to prevent bending of the polypropylene plate in the lateral arch. Bending of the lateral orthosis arch downward will decrease the STJ pronation effect of the orthosis.

    The extra thick medial expansion on the positive cast decreases the medial longitudinal arch height on the orthosis. In addition, when negative casting these patients, I also fully dorsiflex the medial column during casting to further decrease the medial arch of the resultant cast and orthosis.

    It is now the evening here at my home in beautiful Fair Oaks, California and this afternoon, after writing my first message on this subject, I had a patient come in to me, referred for foot orthoses, with nearly the same set of feet described in this posting. She has right greater than left peroneus brevis tendinitis, right greater than left cavus foot and right greater than left laterally deviated STJ axis with about a 6 degree of forefoot valgus bilaterally. I expect the foot orthoses I am making for her (similar to the ones I have described above) will make her nearly asympotomatic within 3 weeks of receiving them (if she is like the many other patients I have used these specially constructed foot orthoses on).

    Below is a photograph of some orthoses constructed with a similar prescription as mentioned above that has temporary adhesive felt valgus wedging on the side that was the most symptomatic and was also the most supinated foot. This orthosis ultimately received a permanent korex wedge once I had completed the adjusment process of the orthosis for the patient.
     

    Attached Files:

  15. williac

    williac Active Member

    Again,

    Thanks to everyone who has contributed their thoughts and experience on this thread. As a solo practitioner this resource (forum) is a wonderfully valuable tool for me - and indirectly my patients. I have read another thread regarding people not posting in fear of being made a fool of. I had a lot of respect for a particular lecturer at university. I once asked a question to which he could not answer confidently. Instead of bluffing or blowing me off he said "I don't know Chris, but when you find out could you come and let me know".
    When you stop needing to ask questions..... it's time to bail out - the challenge is dead!

    With kind Regards,

    Chris Williams
     
  16. Phil Wells

    Phil Wells Active Member

    Kevin

    Hope you don't mind but I would like to challenge a couple of points about your treatment approach based on a few assumptions I make about foot function. (These may be erroneus so please feel free to set me right)(They are also not specific to this patient)

    I have always assumed that the non weight bearing plantar Stj axis location is in part caused by forces acting on the ligamentous structures of the foot causing shortening/lengthening. (I have seen the axis move medial to lateral over a 6 month period when appropriate supination moment causing interventions have been used).
    Therefore do we need to assess why the lateral axis is lateral?
    It may be a bit chicken and egg but could a more proximal cause be creating an inverted heel strike leading to inversion /supination moments (Pathology?) leading to the lateral stjt axis.
    If this is the case, can the ORF ever be enough to resolve symptoms.
    If an extrinsic force (to the foot) is causing the inverted heel strike, the deformation of the shoe could then be the pathomechanical cause of all the symptoms.

    Regards

    Phil
     

  17. Phil:

    Good questions. The subtalar joint (STJ) axis spatial location will, of course, change as the rotational position of the STJ changes in response to any long-term changes in ligamentous structure of the foot. Let's say for example, a patient has a plantar fascial rupture of the medial band that attaches to the sesamoids. This patient over time may develop more medial deviation of the STJ axis due to the increased STJ pronation moments that may develop from the loss of GRF plantar to the first metatarsal head and hallux (from the plantar fascial rupture).

    The "chicken-or-egg" question is important here. The STJ axis spatial location is nothing more than the position of the STJ axis in space, relative to the osseous structures of the foot, for that point in time and in that position of the foot you are evaluating the STJ axis in. If you evaluate the STJ axis in the standing position, a more pronated STJ will cause a more medial STJ axis location and the more supinated the STJ, the more lateral the STJ axis location. The STJ axis spatial location should not be thought of as a permanent or non-changing structural feature of the foot, but simply one important mechanical factor for that foot that will determine how external forces acting on the foot and internal forces acting within the foot may cause alteration in STJ moments.

    Even though there is some correlation between the Root system and Subtalar Joint Axis Location/Rotational Equilibrium (SALRE) Theory of Foot Function, they don't always match up since they use two very different reference systems. The Root system uses STJ neutral position as its evaluation reference and the SALRE theory uses the STJ axis location as its reference for evaluation of the foot.

    For example, if there is an excessive amount of rearfoot varus deformity, combined along with a "rigid forefoot valgus deformity", then the patient will likely have a laterally deviated STJ axis. However, if the patient has a rearfoot varus deformity with a forefoot varus/supinatus deformity, they may have a medially deviated STJ axis. However, a patient with a mild rearfoot varus deformity with a slight forefoot valgus deformity may have a completely normal STJ spatial location.

    In regards to orthosis reaction force (ORF), ORF is an external force acting on the foot from the reaction force between the orthosis and the foot that may, as a result of its mechanical actions, change the internal forces acting within the foot. We, as foot-health clinicians, use the concept that we may alter the ORF with various foot orthosis designs to alter the magnitudes, temporal patterns and plantar locations of ground reaction force (GRF) so that we may achieve the goal of reducing the stress on the injured structural components of the foot and/or lower extremity, optimize gait function and prevent future pathologies from occurring in our patients. Evaluation of STJ axis spatial location is only one tool of many that clinicians may use to improve the orthosis therapy for their patients....but it is a very important one.
     
  18. Lucky, I may be reading you wrong but I think this statement above is incorrect.
    2004: Van Gheluwe Bart; Dananberg Howard J
    Changes in plantar foot pressure with in-shoe varus or valgus wedging.
    Journal of the American Podiatric Medical Association 2004;94(1):1-11.
    Varus and valgus wedging are commonly used by podiatric physicians in therapy with custom-made foot orthoses. This study aimed to provide scientific evidence of the effects on plantar foot pressure of applying in-shoe forefoot or rearfoot wedging. The plantar foot pressure distribution of 23 subjects walking on a treadmill was recorded using a pressure insole system for seven different wedging conditions, ranging from 3 degrees valgus to 6 degrees varus for the forefoot and from 4 degrees valgus to 8 degrees varus for the rearfoot. The results demonstrate that increasing varus wedging magnifies peak pressure and maximal loading rate at the medial forefoot and rearfoot, whereas increasing valgus wedging magnifies peak pressure and maximal loading rate at the lateral forefoot and rearfoot. As expected, the location of the center of pressure shifts medially with varus wedging and laterally with valgus wedging. However, these shifts are less significant than those in peak load and maximal loading rate. Timing variables such as interval from initial impact to peak load do not seem to be affected by forefoot or rearfoot wedging. Finally, rearfoot wedging does not significantly influence pressure variables of the forefoot; similarly, rearfoot pressure remains unaffected by forefoot wedging.
     
  19. LuckyLisfranc

    LuckyLisfranc Well-Known Member

    Simon,

    Thanks for bringing the above to my attention. I do not have a copy of the paper immediately to hand, but I would be interested to read it.

    I can understand that peak pressures may be increased immediately underneath the actual forefoot valgus wedging, which I assume the authors placed just proximal to the MT heads. Was there mention of changes in MT head pressure distal to the wedging?

    I will have to dig it out.

    I find cavo-varus deformity and its 'correction', including surgical, the most challenging and interesting of orthopaedic deformities that we manage.

    LL
     
  20. Lucky,
    I too will need to pull the full paper to know where the wedges were positioned versus where the pressure sensor masks were applied, as it's been many moons since I read this- someone save me and LL the effort!- don't look at it as an arduous task, think of it as CPD ;) I take the point that regarding a valgus wedging beneath the met necks holding the actually met head clear of the interface with a wedge ending proximal to the MPJ's. I've always thought that if you want to alter pressure beneath a met head, posting is best positioned beneath the met head to achieve this.

    Time for bed.
     
  21. Simon and LL:

    You deserve only the best.......:drinks
     
  22. LuckyLisfranc

    LuckyLisfranc Well-Known Member

    Thanks Kevin,

    So it would appear that the forefoot wedging is positioned directly under the MT heads...

    Certainly would create more leverage...not so helpful if there is pain around the 5th MTP joint itself me thinks? Not what I would do for one of my neuropathic victims with cavo-varus and 5th MT head breakdown.

    Obviously diff'rent strokes for diff'rent fokes..

    LL
     

    Attached Files:

  23. drsha

    drsha Banned

    In Neoteric language.
    This is a poster boy Rigid Rearfoot, Rigid Forefoot Functional Foot Type.

    I would suggest utilizing a semi rigid plastic shell (polypro 3mm for example) negative cast corrected for The Rigid/Rigid Functional Foot Type with an aggressive first and fifth ray cutout, B/L.
    I would utilize rearfoot varus correction technique to create a pronatory moment and post the rearfoot in zero or as much valgus as clinically tolerated.
    I would add 3+ mm of heel lift, B/L (Boots may tolerate more) in order to compensate for the huge equinus influence.
    I would post the forefoot with a 4mm 2/3/4 Bar post (more if tolerated). This when combined with the ray cutouts will offload 1 and 5 and relieve peroneal stress.
    I would use a low durometer crepe (35 or less) for postings for shock absorption and refurbish these materials frequently as they compress.
    Finally, I would advise the patient to get Boots with as much positive heel height as possible (or consider a perQ TAL) and
    I would add additional lift to the short side if TIP is in play.

    You did not mention his lower back problems and his tight posture in general and his inability to stretch out which should be in play in this foot type but I would consider ancillary aggressive physical therapy with a therapist with a heavy dance background for these sequellae.

    "He who rejects change is the architect of decay. The only human institution which rejects progress is the cemetery". ~Harold Wilson

    and to all of you who think you have me pegged.
    "I'm Glad I'm Not Me!!
    Bob Dylan

    Dennis
     
  24. Phil Wells

    Phil Wells Active Member

    Kevin

    Thanks for the clarification and help.
    One extra question. If the axis is outside the foot, would you still try to apply a countering moment via the orthotic - every little helps?
    Obviously there are other devices that may be more appropriate but is there a threshold when we have to say the ORF are too small or are counter productive?

    Cheers

    Phil
     
  25. Phil,

    As far as I am aware, all the research on STJ axial position show an axis/ axial bundle that passes through the foot, specifically through the talar neck, hence it appears unlikely that the STJ axis should ever be "outside the foot".
     
  26. efuller

    efuller MVP

    Simon and all,

    I agree the above was from a good paper, but all subjects were treated as if they were the same. This is one of the points that Root made when he tried to classify feet. Not all feet will respond the same to the same treatment. I would like a repeat of the study separating out groups of feet with a different maximum eversion height. Maximum eversion height is a measurement where you have the patient stand and attempt to evert their forefoot without moving their legs or knees. For those subjects who cannot evert their forefoot off of the ground I would expect a greater increase in lateral forefoot pressure than if a patient was able to lift their lateral forefoot off of the ground. In my experience, the overly supinated foot, with lots of eversion range of motion is rarer than a foot with little eversion range of motion. Therefore, when averaged across all subjects I would expect to see an increase in lateral forefoot loading with a valgus wedge. In my clinical experience, I would agree with Kevin's observation that you would see a decrease in pressure for the foot type discussed.

    Regards,
    Eric
     
  27. efuller

    efuller MVP


    Hi Phil,

    Some joints create their axis/axes by the tightening of ligaments. The MPJ is a good example of this. The head of the metatarsal is close to spherical and the ligaments on the sides of the metatarsal limit ab/aduction to give a horizontal axis. On the other hand the ankle joint is under compression and the trochlear surface of the talus is rounded and articulates with the bottom of a similarly shaped surface of the tibia. When compressed together the bones will glide along those surfaces and the axis of this motion will be described by the center of the radius of curvature of the joint. Inman described how the talar dome describes part of a surface of a cone. A cone has an axis as well and this is how one could find the axis of the ankle joint by looking at the joint surfaces. So, other joints have their axis determined by bony surfaces.

    At the STJ, Cahil described how the posterior facet of the talocalcaneal joint on the calcaneus forms a convex surface of a cone and the anterior and middle facets, on the calcaneus, form the concave surface of a cone. This explains the average of 42 degree angulation of the axis from the transverse plane as viewed in the sagittal plane. As someone else pointed out the literature has found that the STJ axis passes through the talar neck. This is also consistent with articular surface as part of the cone observation. (If you have one axis with two cones pointing toward each other you can draw a surface on each cone, one convex and one concave that will use the same axis) When loaded the joint surfaces are pressed together and then you can expect the joint surfaces to determine the location of the axis.

    The above also explains how the axis moves relative to the plantar surface of the foot with motion of the foot. As the talus adducts, the axis will adduct relative to the rest of the foot.


    If the intervention holds the foot in a more supinated position then the axis position relative to the foot will be more lateral. However, because the axis position is determined by the shape of the bones the axis will not change relative to the talus, unless the shape of the bone changes. 6 months seems too short for that to happen.



    I remember seeing a spina bifida patient who had almost zero peroneal strength. Placing a valgus wedge under this forefoot did not prevent end of range of motion in the direction of inversion. (Lat dev STJ axis. The patient was able to bear weight while staying plantigrade with a very high top stiff shoe. You can apply moments to the STJ through other means than just orthotics.

    A foot with an extremely medially deviated STJ axis may have very little plantar surface of the foot medial to the axis. Looking from behind this foot will appear almost lateral to the leg. In this foot you can still do something with an orhtotic. The pronation moment is determined by the location of the center of pressure of ground reaction force relative to the STJ axis. Any movement of the center of pressure more medially (varus wedge effect) will decrease the pronation moment from the ground and then reduce the stress on the structures that resist pronation.

    Regards,

    Eric
     
    Last edited: Feb 9, 2009
  28. Phil:

    I think some clarification of terminology is in order here. The subtalar joint (STJ) has an axis of rotation that can be best described as a "bundle of axes" that, as Simon stated, has its anterior exit point at the dorsal talar neck, and posteriorly exits the foot at the superior-lateral quadrant of the posterior calcaneus.

    If one were to project the STJ axis past these exit points anteriorly and/or posteriorly, of course, then the STJ axis would be "outside the foot". However, I think you mean, in this case, if the STJ axis anterior projection was lateral to the lateral border of the foot then would foot orthoses still be effective?

    As Eric mentioned in one of his posts, the simple fact that one can move the center of pressure (CoP) laterally in these feet with a valgus wedged foot orthosis will decrease the external STJ supination moment acting on the foot from ground reaction force (GRF), which will, even if the "STJ axis anterior projection is lateral to the foot" tend to reduce the external STJ supination moment from GRF.

    When I teach these concepts, I find that it is often helpful to mechanically model the STJ as a see-saw. A boy sitting at the left hand end of a see-saw, when no one is on the right hand side of the see-saw, will force the left hand end of the see-saw into the ground with a given force due to a large amount of counterclockwise moments acting on the see-saw from the boy and a large amount of clockwise moments from GRF acting on the left side end of the see-saw.

    Now, as the boy scoots more forward toward the fulcrum of the see-saw, away from the left end of the board, the counter-clockwise moment from the boy reduces which, in turn, reduces the clockwise moment from GRF acting on the left end of the see-saw still siting on the ground (GRF on left side of board is reduced with boy shifting toward the right toward the fulcrum of the see-saw). Therefore, to apply this mechanical analogy to rotational forces acting across the the STJ, just because a force applied by an orthosis does not cross over the STJ axis to the other side of the axis (e.g. CoP moves from the medial side of foot to a point 1 cm more lateral, but still on the medial side of the STJ axis) the external force from the orthosis will still have a significant mechanical effect on rotational forces acting on the foot and will still have a significant mechanical effect on the rotational forces acting within the foot (i.e. internal moments) which resist the external moments from GRF.

    Hope this helps.
     
  29. Phil Wells

    Phil Wells Active Member

    Simon

    Thanks for the clarification.
    With this in mind, do you know the mechanism behind those feet that evert where ever you press via the Stjt method?

    Cheers

    Phil
     
  30. Phil Wells

    Phil Wells Active Member

    Kevin, Simon and Eric

    Thanks for the explanations.
    I think the need to understand the CoP in relation to potential moments is the key aspect when dealing with the StJt axis.

    If you don't mind, could you just clarify the variability in StJt axes.
    Does this come from GRF and vectors loading the articular surfaces of the joint at different magnitudes leading to variable moments being generated in the rest of the foot?

    Thanks

    Phil
     
  31. Think vectors, i.e. you can have a point of application of a force that is medial to the STJ axis, but still cause pronation moment due to the direction of the force vector. Robert Isaacs gave a very nice explanation of this elsewhere. I'm sure he'll link us to it.
     
  32. It comes from the variation in the surface geometry and the variation in the "packing" of the articular surfaces as they rotate and translate relative to each other throughout the range of motion. Also, to an extent the tension in the soft tissues surrounding the joint will have a role. I've probably missed something, but that's my quick answer after a couple of minutes thought. Which I think is kind of what you are saying.

    This study demonstrates how the contact area changes as the joint is moved:
    http://www.ncbi.nlm.nih.gov/pubmed/18701029

    This is an interesting view:
    http://www.ncbi.nlm.nih.gov/pubmed/...nel.Pubmed_DefaultReportPanel.Pubmed_RVDocSum
    "Recent studies have described the subtalar joint as a structure with no degrees of unresisted freedom, i.e., motion from the single neutral position is attained only by deformation of the ligaments and of the articular surfaces."
     
    Last edited: Feb 10, 2009
  33. drsha

    drsha Banned

    1. I realize where your focus is (The STJ) but what about the midfoot axes (The Vault)? What about the forefoot axes? What about balancing one foot to the other?
    2. Dr. Kirby's valgus orthotic (I'm trying to include a copy and hope I figured it out) is so unprofessional and cheap looking. How can he dispense it in good faith as representative of an orthotic to patients and the medical commuity?
    3. His device has a rearfoot valgus post, no vault conformity(is lower than the patients high arch), has a 3-4 mm forefoot bar post with an aggresive first ray cutout. It's similarities to my prescription as per my posting on this thread is more than coincidental.
    4. I am trying to download a similar Centirng for this rigid/rigid type. It has a varus post instead of a bar post (different foot type) but it is a first strike, professional looking product. I can understand why sarcastically Dr. Kirby turned down my challenge to evaluate and produce an orthotic for the same patient. I would win for esthetics/cosmetics/professionalim, even if his device IS better (and its not!).
    Dr Shavelson
     

    Attached Files:

  34. efuller

    efuller MVP

    Hi Phil,

    Some of the variation, I believe is genetic in that the articular facets are angled differently in different people. Some people are tall, others are short. Some variation is from "Forefoot to Rearfoot" relationship. Even though I find this measurement very unsatisfactory in terms of repeatability, there is some merit in the extremes. A forefoot to rearfoot relationship with a high degree of valgus will behave different than one with a forefoot varus. In the average foot, the foot will tend to pronate until something stops it. To some degree one of those things that stops the foot from pronating is the medial forefoot hitting the ground. If, you started in neutral position, then as you pronate the STJ there will be internal rotation of the talus and since the axis position is determined by the articular facets of the talus the axis will internally rotate as well. The axis will internally rotate until the pronation is stopped. With all else being equal, the forefoot valgus foot will have the medial forefoot hit sooner (in a more supinated position) than the forefoot varus foot. So, the axis will not have internally rotated as far in the forefoot valgus foot as compared to the forefoot varus foot.

    The above tells you why it is important to assess the location of the axis when the STJ is in the position seen in static stance as opposed to neutral position.

    Phil, I believe you asked about the foot that seems to pronate no matter where you push it. Tthere are some feet that have everted so far that the vast majority of the plantar surface of the foot is lateral to the STJ axis. These feet will often have abduction of the forefoot on the rearfoot. There is usually a small sliver of surface area on the medial calcaneus that wont cause pronation. If you invert the foot you can increase the area in which you will see supination in response to plantar pressure.

    I hope this helps.

    Eric
     
  35. efuller

    efuller MVP

    Dennis, I believe we discussed some of these, but could explain why midfoot and forefoot axes are important, and why one should balance one foot to the other.


    Dennis, did you notice in his post that he described that modification as a temporary modification?


    Dennis, did you know your tone is very confrontational? Is it necessary to call someone unprofessional when you disagree with them?

    You point out the dfferences between yours and Kevin's devices. Why do you think your modifications are better?

    Regards,

    Eric
     
  36. Phil:

    I just so happened to give a lecture on this subject this morning at the California School of Podiatric Medicine to the second year podiatry students.

    The variability in subtalar joint (STJ) axis spatial location can be due to a number of structural variations with the human foot or may be due to changes in rotational position of the STJ or midtarsal/midfoot joints. For example, a metatarsus adductus deformity will tend to make the STJ axis be more laterally deviated relative to the forefoot whereas a metatarsus abductus deformity will tend to make the STJ axis be more medially deviated relative to the forefoot. In addition, a maximally pronated STJ will always have a more medially deviated STJ axis than the same foot when it is supinated at the STJ.

    Once the forefoot is loaded by ground reaction force (GRF), the plantar ligaments and plantar fascia tighten, the STJ, midtarsal and midfoot joints all compress and basically, the foot becomes relatively more rigid than when GRF is not acting on the plantar forefoot. Then, if, for example, the center of pressure (CoP) is moved laterally on the forefoot, then either the STJ pronation moments will increase or the STJ supination moments will decrease, depending on the spatial location of the STJ axis relative to the GRF vector. In other words, the GRF acting now on the forefoot is transmitted directly back to the rearfoot, from the forefoot, so that either increased STJ pronation moment, or increased STJ supination moments, and/or increased STJ interosseous compression force results from the mechanical action of GRF on the plantar forefoot. Even if the patient only has GRF acting on the forefoot, such as during the propulsive phase of walking, the GRF is still causing a direct STJ pronation or supination moment due to the relative rigidity of the forefoot on the rearfoot. In physics and biomechanics, this is called the "rigid body effect".

    A chapter of my third Precision Intricast Newsletter book is devoted toward explaining how forces are transmitted through the foot with ligamentous tensile forces causing joint compression forces, joint stability, etc. These are basic mechanical concepts that, unfortunately, are not taught thoroughly in most podiatry school biomechanics programs. These concepts need to be understood before one can fully appreciate the subtalar joint axis location and rotational equilibrium (SALRE) theory of foot function (Kirby KA: Subtalar joint axis location and rotational equilibrium theory of foot function. JAPMA, 91:465-488, 2001).
     
    Last edited: Feb 11, 2009
  37. drsha

    drsha Banned

    Eric:
    I called his DEVICE unprofessional, NOT THE MAN!
    but here we are twisting and avoiding the issue. Let's close another thread editor.

    I seriously think his device is a shabby, patched-up, created on the fly, UNPROFESSIONAL looking orthotic. Can you really argue that it does not!

    But look at how skillfully The Arena avoided my suggestion for an orthotic casting and prescription to solve the thread and look how skillfully you changed the topic and made it personal.

    Why wouldn't one of you open minded blokes say "I'll try this other method just to prove Shavelson wrong", espeically the bloke who posted the question in the first place.

    “Every clique is a refuge for incompetence. It fosters corruption and disloyalty, it begets cowardice, and consequently is a burden upon and a drawback to the progress of the country. Its instincts and actions are those of the pack.” Madame Chiang Kai-Shek
    dennis
     
  38. Phil Wells

    Phil Wells Active Member

    Dear all

    Thanks for all of your excellent work in answering my questions. I now feel as though it has filled the gaps in my knowledge in relation to rotational equilibrium approach.

    Onto Dennis's comments about device cosmetics etc.
    I run an orthotic lab that makes orthoses to customer specifications and consequently see over 200 different style and approaches. Some are similar approaches to your 'Vault' approach and others are very different. Therefore I have no axe to grind in any direction.

    The technology I use is VERY advanced resulting in my devices being much prettier than yours so consequently that makes me a better person, practitioner and all round hero.

    I hope you see how ridiculous my comment seems and maybe how your similar comment is to it.
    Lets try and be a bit more professional or I will post piccies of orthoses that are so pretty you will weep with envy!

    Phil
     
  39. drsha

    drsha Banned

    Phil:
    I appreciate your genuine words but I hope you realize that away from The Arena, I have a different personna. The Arena members are probably more civil to "those that don't work with STJ axis theory" away from the Arena, I am sure.
    My theory and work is denergrated before inspecting it (I know that none of you has taken a serious look at it )
    I simply implied that Dr. Kirby's device when seen by other patients in a gym or at a doctors office or at a conference or seminar would have less importance, impact and marketability because they (to use your sarcastic term) aren't pretty.
    Dr. Kirby is a fine person (as is the editor) whom I respect, quote and monitor, he is an excellent practitioner and the hero of The Arena. That doesn't make his orthotics any more digestable as eye candy.
    Phil: As a lab director, I am sure I can talk you through my suggested casting and prescription for this patient (or another) so that you can make a Foot Centring to compare to the one rotational equilibrium will produce and I believe we will both learn something by the process, come what may.

    Please visit www.foothelpers.com and maybe you can share your website with me so we can get a foundational feel of where we are coming from.

    "The bend in the road is not the end of the road unless you refuse to take the turn". -Anon.
    Dennis
     
  40. efuller

    efuller MVP

    For those who missed the earlier discussion of Dennis' theories, can we get a link back to that thread?

    Link
     
    Last edited by a moderator: Feb 11, 2009
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