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Lateral Arch

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Robertisaacs, Aug 22, 2007.

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    I was looking at a prefab system t'other day (the Vectorthotic if you're interested) and i noticed it had a very high lateral arch. In fact measured with a calliper from 5mm in from the two edges the lateral side measured 12mm and the medial 18mm (only 6 mm difference).

    This is something i have observed with several different pre fabs, a lateral arch only slightly lower than the medial. This seems strange in devices which are usually attempting to invert the foot. Surely raising the insole lateral to the STA will increase the pronatary moment.

    When i do casting for an insole (presuming i'm trying to increase supination moments and not specifically trying to do something in the sagital plane) i examine the height of the lateral arch when the patient is in relaxed stance and cast correct to that level for the orthotic. More often than not the lateral side of the foot is flat to the ground so most devices i issue have little or no lateral arch.

    Am i missing something here? What do other people do with lateral arch? Is there a reason for so many prefabs to have such a chunky lateral componant?

  2. Bruce Williams

    Bruce Williams Well-Known Member

    excellent point you raised and could make for a very interesting discussion.
    When I cast now, and I"ve been doing this for the past 2-3 years utilizing my AMFIT digitizer, I always shoot for the highest lateral arch I can get.

    I've also argued several times that the act of dorsiflexing the 5th ray in nwbing neutral position casting is wrong.

    My reasoning for creating a higher lateral arch is fairly simple, to me anyway! :) When teh lateral column is higher at the 5th metabase-cuboid junction it will also tend to be in an internally rotated position if you are looking from the heel. This position will compact the cuboid against the lateral cuneiform which will then support the medial column and stabilize it so that it too can be as high as necesary.

    These two columns need to be in the most stable positions so that they can support each other. Simply plantarflexing the 1st ray is not enough, because it will not stabilize without support from the lateral column structures.

    When I use the AMFIT program, I add on average 5 degrees of arch height to the lateral column, which also acts as a lateral FF valgus wedge. I say this because I've tried both and seen the same results utilizing F-Scan.

    With an OTC device, they can build both the lateral and medial arches very high, as most devices are so weak that they will collapse very quickly with use anyway. But, I think they are moving in the right direction, whether they know it or not.

    Bruce Williams, D.P.M.
  3. Thanks for your reply bruce.

    Ok i've read this about 16 times and i'm staring at a skeleton foot with the intensity of a chimp studying the rosetta stone and it still makes no sense to me. Perhaps you could clarify for the hard of thinking.

    1. When you say the lateral column is inverted what exactly do you mean? given the shape of the 5th met base a higher lat arch would seem to evert the 5th met to me.

    2. re the inversion of the cuboid compacting it against the cuniform, how? surely if the cuboid is inverted the effect will be to elevate the lat cuniform. I can't grasp how it will push the two bones together. For inversion of the cuboid to push the cuboid medially the axis around which it inverts would need to be higher than the midline of the cuboid would'nt it?

    3. What do you mean when you talk about the medial column "stabilizing" and how is this acheived with the lateral column.

    Sorry if i'm being dense here!

  4. Bruce Williams

    Bruce Williams Well-Known Member

    you are not being dense at all. My explanation was lacking and you've pointed that out. That being said...

    First, put the foot bones on the table as if the foot is in midstance. Now, both plantarflex the 1st and 5th metatarsals, or hold them against the table and slightly squeeze them towards each other. Finally, to mimic the action of the plantar fascia, dorsiflex the calcaneus and slightly draw the rearfoot towards the forefoot. ( this might work best for you if you put your hand over the midfoot and squeeze the midshafts of the 1st and 5th rays together and down. This really stabilizes the midfoot)

    After you've tried this a few times, see what positions the 1st and 5th rays are in, as well as the relative arch heights medial and lateral.

    You should see both a plantarflexed and supinated position of the 5th ray, and a plantarflexed and pronated position of the 1st ray. Keep in mind I did not create the nomenclature for the positions of the midfoot and forefoot. I would say PF'd and inverted for the 5th ray and PF'd and everted for the 1st ray. My positioning statements in relation to inverted and everted are using the reference of the calcaneus in stance and looked at from behind or posterior to the heel.

    Also, as you stabilize these columns in that position, the bones of the mid foot artculate as they were meant to and stabilize this area so that the rays 1-5 will have maximum dorsiflexion stiffness! Kevin K. is correct here for the most part. I feel that you can put the foot into position to maximize DFion stiffness with proper casting technique.

    Try this and see if that makes any more sense.

  5. efuller

    efuller MVP

    Hi Robert,

    One of John Weed's teachings was not to evert the foot farther than it can go. He tried to figure out how far it can go by looking at calcaneal eversion to leg, tibial varum, and RCSP, and forefoot to rearfoot relationship. I prefer looking directly at the foot and asking the patient to evert their foot in static stance without moving their leg. Some people can get their lateral column off the ground about 2cm and others cannot lift it off of the ground because of lack of range of motion. A 12mm lateral arch would have the tendency to evert someone farther than they have range of motion.

    If you try to evert the foot farther than it can go you can get sinus tarsi pain or you can get lateral column pain.

    Having the really high part around the cc joint and then tapering to nothing at the distal end of the device is less likely to cause problems because the point of application of force relative to the STJ axis. Because the STJ axis is, on average, angled away from the distal part of the foot, the distal part of the foot will be farther from the axis than the proximal part of the foot.

    Birkenstock also has a little bump in their sandals around the CC joint. I've seen a few people with really low lateral arches who don't like the bump. However, there must be a lot of people who like it or don't notice it, because they do sell a lot of shoes.

    I agree, I really don't understand why a lot of devices have that thick lateral component.


    Eric Fuller
  6. efuller

    efuller MVP

    Bruce, are you talking about real foot with ligaments or are you talking about a skeleton with fishing line holding it together?

    I don't see what plantar flexing, or not dorsiflexing, the 5th ray has to do with your example of the bones above. Standing on a device with the fifth ray plantar flexed does not squeeze the 1st and 5th mets together.

    Could you elaborate further on how plantar flexing the 5th met when casting increases dorsiflexion stiffness of any part of the foot when you stand on the orthotic made from the cast with plantarflexed 5th ray?

    Regards from another monkey staring at the rosetta stone (or was it the obelisk in 2001 a space odysey? Did I miss your reference Robert?)

    Eric Fuller
  7. Bruce Williams

    Bruce Williams Well-Known Member

    do you cast using a foam box, or utilizing plaster on a foam block with the patient in full weight bearing?

    My point is that if you don't care about positioning of the foot other than at the STJ, then you might as well cast full weight bearing. I doubt that you do that, and I would not suggest it in most instances.

    If you don't cast as above, then you already do much of what I do, though I attempt to do more as far as positioning of teh foot during casting is concerned.

    It is not a matter of what the foot can do or does do at midstance, ie the foot will move as it needs to no matter what it is standing on or in. The foot can be put into its most stable position purely by putting the STJ into a close to neutral position and dorsiflexing the toes 1-5 to fully engage the plantar fascia. This is what I do with my casting technique plain and simple.

    What matters is how the foot is positioned due to the CFO from contact, into midstance and then into propulsion.

    I see the CFO as a conforming platform that can potentially allow the foot to be positioned in a stable a position as possible as it contacts and rolls thru midstance and into propulsion.

    To do that I put the foot into what I see is its most stable position. The 1st and 5th mets plantarflexed and in- or everted as I stated previously.

    The foot is a mobile adaptor, and because of this if we give it a very stable platform on which to best adapt we should tend to see better outcomes. I do anyway! ;-)

  8. Glad it's not just me. I was just referring to an utter lack of comprehension but the 2001 obelisk works better as an analogy.

    Speaking for myself i do care a great deal about the positioning of the foot. I use foam box casting for most people, semi wb. I aim (so far as possible) for the 25% of patients body mass needed to acheive 70 odd% of foot shape change / soft tissue deviation. I used to rely on that and do very little "cast correction but because of the nature of FRF (foam reaction force :cool: , like GRF and ORF only different) creating loads of lateral arch i was getting a lot of lateral arch problems as described by Eric. This is in spite of the fact that the lateral arch of the orthotic is obviously not "everted farther than it would go". Switched to leaving only the lateral arch i saw in NCSP and the problems went away.

    Again i'm not 100% sure what you mean here. Two things trouble me. One is the desire to put the foot in the most stable position. I've never thought of my orthotics as devices to lock the foot into a fixed configuration thus to better resist the ravages of gravity so much as to manipulate the effects of gravity in such a way as to minimise any patholgical tissue loading. Or have i misunderstood again?

    The other is the dosiflexing the toes bit. Engage PF and windlass to get the desired position, no argument there. Having great fun with Craigs Plantar fascial grooves at the mo as well. However i'm not too sure about the concept that when the toes are released the "stability" inherent in the shape of the foot remains.

    Sounds a bit bio tensitegrity to me.


  9. User7

    User7 Active Member


    By scanning with the forefoot plantarflexed on the rearfoot and the subtalar joint slightly pronated, I bet you get a device with a rather high arch, medial and lateral. I wonder: does a device that can more or less do the same job as the plantar fascia in mid-stance (prevent dorsiflexion of the rays, collapse of the arch, maybe even some energy return, etc.) put the plantar fascia itself at risk of damage from orthotic reaction forces that could lead to creep and consequent weakening or even loss of structural integrity?
  10. Bruce Williams

    Bruce Williams Well-Known Member

    Well if it does then all the shoe companies are screwed in the next 5 years! According to Simon Barthold adn Craig Payne they are all experimenting with a shoe that will become rigid at the midfoot and heel as the mpj's extend.
    Sounds like the plantar fascia to me!!!

    Finally, you must keep in mind that even though I cast with the toes dorsiflexed to capture a more stable foot position, this does not automaticall load the plantar fascia. It gives the foot a more ideal position to slip into that will potentially allow more stability as it moves from midstance to active propulsion.

    If we don't tend to blow out the plantar fascia barefoot, why would an orthotic blow out the plantar fascia?

    I consider the load of the plantar fascia wiht the toes dorsiflexed to be a good load, as opposed to when the fascia is tight and loaded with the 1st ray not dorsiflexed.

    my thoughts.
  11. Bruce Williams

    Bruce Williams Well-Known Member

    be careful, we don't want the tensigrity gods ****** off again do we?! :)

    I'm not talking about "locking" the foot into position. If you put the foot into neutral position, you are altering the foots position as it will stand on the floor, in a shoe and on an orthotic device.

    I'm just taking that farther. If you dorsiflex the toes 1-5 you will see the foot increase in arch height at the medial and lateral columns adn the foot is very stable, like it is supposed to be as the heel starts to lift off the ground.

    Why should we not then consider casting the foot in this more stable position in hopes that it will allow for a more uniform transition from midstance to propulsion? To me it makes perfect sense. But, I may need a more effective translator! Any volunteers? ;)
    Last edited by a moderator: Aug 24, 2007
  12. User7

    User7 Active Member

    But these devices (will) become rigid only"as the mpjs extend". My question relates to weather a device that resembles a foot in propulsion, with the arch at its maximum height, would be too large a lump underfoot during midstance, when the arch height is at it's minimum. Wouldn't such a lump impose forces on the plantar fascia that are not encountered while wearing a more conservatively contoured device? The plantar fascia is under tension in midstance and more or less runs parallel to the ground. Any pressure from below would seem to me to provide forces capable of causing injury.

    That's hard for me to understand. Ground reaction forces on the heel and forefoot automatically load the plantar fascia; what I'm worried about are orthotic reactions forces imposed on that loaded fascia.

    That makes lots of sense. I'm intrigued by the concept and I think I understand how you've explained it. Lateral column support has been discussed on this forum before, and seems to be on the minds of many. I think you're on the right track.

    Probably, to be more precise, your method needs to be explained in terms of moments acting about the "midtarsal joint axis",etc. Although, based on what you've written, I think there is probably a "neuromuscular" component to the success you're having with these devices that could not be easily explained by,nor reduced to, moments. No small task I think.

    While barefoot there are no ground or orthotic reaction forces that act directly upon the length of the plantar fascia in directions roughly perpedicular to it's length.

    Bruce, I'm not saying that your devices do cause plantar fascia injury or creep. But it seems to me that they could. And I'm not convinced that they couldn't. Could you convince me otherwise?
  13. Robert:

    Of course, if the lateral arch of a prefab orthosis is higher than normal, this can create problems for a foot wearing it especially if the foot has a low lateral arch. A high lateral arch orthosis could cause increased subtalar joint (STJ) pronation moments and could cause increased lateral midfoot plantar compression forces in the low lateral arch foot.

    However, there is a paradoxical effect seen with foot orthoses in that lateral forefoot wedging, even though this will cause an increase in STJ pronation moments in static stance, may also cause an increase in STJ supination motion during late midstance and propulsion when the foot functions dynamically in gait. In order to achieve this effect, the lateral forefoot wedging is best done as a forefoot extension plantar to either metatarsal heads 2-5 or or plantar to metatarsal heads 4-5 (I generally start with a 3 mm thickness of adhesive felt or korex). This effect can also be achieved by increasing the thickness in the distal lateral forefoot of the orthosis and this effect is minimal if the lateral forefoot wedging is placed proximally at at the calcaneo-cuboid joint. I believe I discussed this effect previously on Pod Arena at Forefoot Valgus Wedge Effect. .

    One of the potential benefits of a higher lateral arch in an orthosis is that it will increase the rearfoot dorsiflexion moment and increase the forefoot plantarflexion moment acting along the lateral foot. This will tend to cause the lateral component of the plantar aponeurosis and the short and long plantar ligaments to have less tensile force within them and the dorsal joint surfaces of the calcaneo-cuboid joints and cuboid-4th and 5th metatarsal joints to have less compression forces during weightbearing activities. Of course, this effect must be weighed against the increase in STJ pronation moment that the high lateral arch will also cause. The only time I use this "high lateral arch" orthosis modification is when the patient has lateral column symptoms caused by a excessive tensile forces within the lateral component of the plantar aponeurosis or the short and long plantar ligaments or symptoms caused by excessive dorsal joint compression forces at the calcaneo-cuboid or cuboid-4th and 5th metatarsal joints.
  14. Bruce Williams

    Bruce Williams Well-Known Member

    Beleive it or not I have very few complaints from my patients on the degree of arch height. That's because the devices tend to match up to the arch heights quite closely, often closer than my previous plaster cast devices, especially in teh lateral column.

    When the fascia is finally under load, accelerations and timing come into play. The forces tend to stay the same, but if they are stopped at any of the pivots of the heel, AJ, or MPJ's then the force load will cause a problem. If however the timing of teh force has no stoppages of motion, you will see far fewer problems in tension. It's not about force alone, you have to figure in rotations at the primary pivots of teh foot and ankle.

    From my perspective, setting the foot up to be as stable and effective as possible for pivoting at the mpj's leads to much less plantar fascia stress.

    Again, try to look past the forces and loads and understand we are rolling over the foot, pivoting is better. If that motion stops some where, then it is constant load w/ no movement that causes problems. That's why force vs time curves are very important, its a kinematic issue.

    I agree with you. If any of my explanations were worth a damn, more people would understand me. I very much need to work on it from every angle for it to be accepted over time.

    I can't convince you, you have to do that yourself!:) I understand where you are coming from though. I think that if you appreicate the differing positioning of the foot like I am ineptly explaining, and appreciate the force loads OVER TIME then you will eventually appreciate where I'm coming from.
  15. Bruce Williams

    Bruce Williams Well-Known Member

    thank you for this wonderful explanation on the effects of the lateral column's arch height on the rearfoot and forefoot. You stated what I wanted very easily.

    I would contend with you somewhat on the location of the forefoot valgus wedging.

    If a practitioner is utilizing a rigid or moslty rigid plastic CFO, then using a forefoot extension with a valgus wedge is really all you can do. If you put a wedge anywhere else on a rigid device you will valgus the entire device.

    In instance where a practitioner utilizes a more malleable device, such as EVA or Cork/leather, then I would suggest the use of the valgus wedging proximal to the mpj's 4-5 back to the cuboid.

    I have found that this last modification in general gives a much more obvious outcome pattern utilizing in-shoe pressure, than just the FF extension.

    You could also consider a soft cuboid pad or topcover valgus wedging as well on a hard device.

  16. Bruce:

    Since I don't use the Amfit system as you do, then I will defer to your experience with the EVA orthoses. However, I have used plastazote #3 and polypropylene shells extensively over the past 20 years and , therefore, I have experimented quite a bit with both shank dependent and shank independent materials. It has been my experience that the forefoot valgus wedge effect (i.e. increased orthosis reaction force plantar to the lateral column) works more effectively and is more comfortable for the patient if placed plantar to the metatarsal heads, rather than more proximally alone.
  17. Bruce Williams

    Bruce Williams Well-Known Member

    Kevin, I would agree with you when utilizing more rigid shell of poly and with some more rigid plastazote.

    That said, my experience with in-shoe pressure has shown me better results when utilizing the valgus wedging more proximal, at least in softer shelled devices.

    I used a FF extension of 3mm of korex as a reverse morton's extension a lot when I first started working with my temporary devices, and with my rigid poly's. Once I was able to change my casting technique to achieve a higher lateral arch height I started to see much better FF force time curves and less Midfoot blockage of motion on the F-Scan.

    Thanks for your input Kevin. Your ability at positional description has always exceeded mine adn I do very much appreciate that. I hope you are well and maybe we will see each other soon.
  18. efuller

    efuller MVP

    I use the classic method where you cast close to STJ neutral and then maximally dorsiflex the MTJ in this position. When I have looked at cadaver range of motion I have not seen a lot of dorsiflexion of the forefoot when moving from STJ neutral to a more pronated position. From your description, it sounds like you are casting the foot with the forefoot more plantarflexed than I do. I doubt that there is much difference in lateral arch height with the way I cast and the full weight bearing position.

    It seems that both of us get good results. Maybe it doesn't matter so much what is done to the lateral column. Although, I have seen problems when the lateral arch of the orthosis is too high. This can occur with both of our methods. Your method would be more likely to cause the arch to be too high. With my method the lateral arch is raised when either an intrinsic or extrinsic forefoot post is used. From your writings I'm not sure if you understand how an intrinsic forefoot valgus works. Am I misinterpreting your writings?

    From the previous paragraph, and the paragraphs below, it seems that you are making the assumption that when the foot stands on the orthosis it attains the same position that you casted it in. I'll ask my question again. What forces cause the foot to change position when the foot is on the orthosis?

    So, do you feel the foot is more stable when standing on an orthosis made from a cast with the toes dorsiflexed? Even when the toes of the foot are parallel with the ground when the foot is on the orthosis? If the toes are parallel with the ground and the arch is as high as the cast this is not a stable position. Stable in this sense I'm defining as the effort required to maintain the foot in the same position. So, we have too arch heights: H1 static stance with the toes on the ground. H2 Static stance with the toes dorsiflexed. H2 is higher than H1. A foot is unstable when it is in a position to attain H2 and the toes are parallel to the ground, because the plantar fascia will have no tension. To achieve H2 with the toes parallel to the ground some other forces will have to be present to hold the arch in this position. The need for these forces is what makes the foot unstable. Ground reaction force on the forefoot and heel and body weight applied to top of the talus will tend to flatten the foot until something stops
    When the foot is on the top of this high arched orthosis what forces maintain the arch in this position?

    Bruce, what is your definition of stable?
  19. efuller

    efuller MVP

    An intrinsic forefoot valgus post can be used at the same time a medial heel skive is used. The whole device will be everted, but the heel will not get that effect because of the medial heel skive.

    An intrinsic forefoot valgus post lifts the cuboid and 5th met base and shaft, but not the head. A cast balanced with an intrinsic forefoot valgus post will evert the lateral forefoot regardless of what material it is made out of. Of course, an extension can be added to an orthosis with an intrinsic forefoot valgus post.

    Eric Fuller
  20. Hey if i pick up this bone i can hit stuff with it!

    That makes a bit more sense now in terms of line of force etc. Also makes more sense if i think of the lateral arch as a forefoot valgus extention put a little more proximal to function earlier in the gait cycle. The only thing there is that a forefoot valgus extension is rarely used at the same time as a forefoot varus extention. Lateral arch is used at the same time as medial arch.

    I use Shank dependant FFO's (rather similar to the amfit type devices) EVA 2/3's length devices and rigid polyprop type devices. Certainly i agree that lateral arch causes less problems on the SD devices than on polyprop. However i'm still mildly confused re the whole line of force thing. Bruce, any chance you could do us a quick sketch of line of force type results you expect get with lat arch, ff valgus extentions and neither of the above? A picture might tell a thousand words.

  21. efuller

    efuller MVP

    Robert, Bruce,

    I'm not sure what you mean by line of force. Here are a couple of definitions

    Line of force, or more accurately line of action of a force is a line that extends infinately in both directions from the point of application of the force. It is used to calculate moments.

    The line you see on an F-scan printout is called a center of pressure path (or center of force path). The Fscan measures pressure at a specified time interval. If I remember correctly it measures 50/sec. Each of the pressure pictures (frame) can have its center of pressure calculated to a single point. You can project all of these points onto any single frame or to a picture that shows the maximum pressure achieved at each location over the step. (aka maximum pressure picture) You connect the dots and you get the center of pressure path.


    Eric Fuller
  22. I meant that one. ;)
    Last edited: Aug 29, 2007
  23. Bruce Williams

    Bruce Williams Well-Known Member

    I agree with you.

    Eric, if I have casted a foot withing the limits of its own boney and soft tissue structure how can this cause the arch to be too high? You are misinterpreting my writings. I understand the workings of intrinsic posts. Do you understand that an extrinsic post must in a rigid orthotic must be balanced at the FF to RF relationship or it will rock back and forth?

    You misinterpret again Eric. If you will read again I most definitely do not state that. I said that the foot will fully pronate to whatever level it will no matter what it is standing on. That is at full midstance though. As soon as the foot begins to transition into late midstance and early propulsion the foot is supposed to supinate. It is at this time frame that I think the foot can now accept a more stable orthotic position to maximize It's function. I do not talk about standing on orthotics much. I talk about dynamic gait and in-shoe effects of orthoses.

    In your final paragraph you talk of toes being parallel to the ground. Indeed in dynamic gait this will be true throughout midstance to toe-off. It is the foot that must dorsiflex around the toes.

    Therefore my thought is to mimic the position of the foot, in the midfoot particularly, with the metatarsals plantarflexed and the toes dorsiflexed so that as the foot transitions into midstance and the heel begins to lift the foot will be more able to dorsiflex around the toes.

    Cheers Eric;
  24. Bruce Williams

    Bruce Williams Well-Known Member

    I make no promises on this one. I will be working with a lot of F-scan data this weekend and if I find some examples I will copy and paste them.

    If you think about it though, the more stable portions of the foot tend to have the greatest pressures regardless of foot function. What I mean is that to get a high pressure you need equal and opposite resistance from the foot against the ground.

    So, if the lateral column is dorsiflexed like Eric casts, and I used to as well, then the pressures can be higher because like it or not, maximally dorsiflexed is a more resistant position.

    This is why the CoP (center of pressure) tends to move from central heel to lateral column to metatarsals 2-3 in patients with FnHL. They don't load the medial column becuase it wont' hold a stable plantarflexed or dorsiflexed position at the 1st metahead, and because the foot chooses a different path because the 1st mpj extension will not occur.

    After using a 1st ray cutout though, the CoF will tend to move midline from the heel and end up sub 1-2 mets because now that the medial column can plantarflex, the pressures can increase. This is interesting as well, because before I started using metapads and plantarflexing the lateral colunn in casting, I got straight midline transitions from the heel. Now I see more pressure under the lateral column. I think that once the medial column was more effective it moved the CoF under the central portion of the foot. Acceptable, but possibly not the best intended function of the foot.

    What I see with a lhigher ateral arch is a more curved CoP from the heel to the lateral column that then transitions towards the 1-2nd metaheads. Similar to what is in Roots book, but not as drastic or linear under the medial column.

    I think the plantarflexed position of the 5th metahead stabilizes the lateral column similar to plantarflexing the medial column. But, the difference is that plantarflexing the 5th metatarsal head ( increasing the lateral column height) often positions the cuboid in such a way that it stabilizes the lateral cuneiform which then lends proximal stability to the medial column while stabilizing the lateral column as well.

    So you should see a more uniform transition from the heel to the midfoot to the mpj's and then toe-off with much less delay in motion.

  25. efuller

    efuller MVP

    Bruce, I don't understand your point about rocking back and forth with an intrinsic post.

    Just because you cast someone within the limits of their bony and soft tissue structure does not mean that the orthosis will be comfortable. I have tried to wear orthoses made from a casting position with the medial column plantar flexed and they were extremely uncomfortable because of high pressure in the arch.

    Say you put a 2 inch dowel under the lateral part of the calcaneus, the forefoot will attempt to plantar flex to reach the ground, because gravity will pull it down. This is an extreme, but we can make it less extreme by choosing smaller dowels. We can find a dowel where the forefoot just touches the ground (just above 0 load) and there is a high amount of foce at the anterior end of the calcaneus and the forefoot is plantar flexed. This is not necessarilly a comfortable position, nor is it a stable position.

    I agree that you never stated that you are making the assumption that the foot attains the casted position. However, some of the things that you are saying seem to be implying that without saying it. Could explain further your mimic comment in the first line of the last paragraph above?

    In terms of the forces involved, the midstance phase of gait is very similar static stance. At some point in gait, the forefoot has to load to the same amount as it is in static stance. If you have a dowel under the lateral forefoot (or an orthotic made from a cast with a plantar flexed forefoot) there will be high load at the anterior calcaneus and little load on the forefoot. In gait, tension in the Achilles tendon will increase causing the heel to lift, as the heel lifts more force will be placed on the forefoot. Ground reaction force on the forefoot will be greater than the force of gravity acting just on the forefoot and the forefoot will dorsiflex until something stops it. The structures that can stop it are the muscles or plantar ligaments. The more stable position is where the forefoot is dorsiflexed to the point where the plantar ligaments become tight. So, I disagree with your assumption that the plantar flexed metatarsal position is more stable and I don't see how an orthosis can hold it in that position as the heel lifts in gait.


  26. Stanley

    Stanley Well-Known Member

    Great discussion. I just wanted to add my 2 cents (2 pence).
    I have used shank dependent orthoses for over 30 years, and what I have found out, is there is no way to predict the perfect arch height that is required for a patient. If you add more height to the arch, the patient will tolerate it, until you go too far. The difference between maximum arch height and the patient feeling a "rock in the shoe pressing up on my arch" is 1/16" (1-2mm). The same principle also holds true for semi-flexible plastic foot orthoses.
    Bruce you bring up an excellent point about pronating the fifth ray. At propulsion all the metatarsals are plantarflexed due to the windlass effect which means that the fifth ray has to supinate. A lateral arch pad would press up on the base of the fifth and rotate the fifth metatarsal into eversion and hence pronation. It would seem that the most lateral part of the lateral arch pad should end on the medial half of the base of the fifth metatarsal and in line with the lateral edge of the cuboid. Hence a "cuboid pad". I'll start doing it this way and see what happens. Also for the podiatric historians, Ralph Dye would take his Campbell's rest strap and apply it in the "squeeze" position, which would effectively supinate the fifth ray. Just a thought.

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