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Navicular drop + navicular drift = planal dominance?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Simon Spooner, Jan 10, 2011.

  1. Members do not see these Ads. Sign Up.
    All, in another thread Robert wrote:
    Here is a reliability study: http://www.japmaonline.org/cgi/content/abstract/91/5/262, regardless of their moderate reliability in the hands of these testers, what do the tests actually show? Hylton Menz assumed they were measures of foot pronation: http://www.japmaonline.org/cgi/content/abstract/88/3/119 Robert appears to be assuming that some inference can be made from these to planal dominance? Planal dominance, described by Don Green http://www.japmaonline.org/cgi/content/citation/74/2/98 relates to the relationship between a joints axial position and the amount of motion that should occur about that axis in the cardinal body planes. What does navicular drift / drop tell us about planal dominance, if anything, and if so, the planal dominance of which joint? Talonavicular joint? Navicular-cuboid joint? Navicular-medial cuneiform joint? Navicular-intermediate cuneiform joint? Navicular-lateral cuneiform joint? All of these? None of these? Given the relatively unconstrained nature of some of these joints, and Nesters contention that the axis is created by the motion, not vice versa, is the concept of planal dominance even valid and worthy of consideration for these joints?

    P.S. edit the title please Craig, typo on the word navicular!
  2. Admin2

    Admin2 Administrator Staff Member

  3. bob

    bob Active Member

    Hello Simon,

    'Planal dominance' is a term often used in surgical circles in the context of planning flatfoot surgery. When planning which particular operation the surgeon feels will provide the best chance of success (which I hope is a happy, pain-free patient) you assess the flatfoot deformity's dominant plane and offer a particular operation or combination of operations to address that as the major component of the painful flatfoot. An example of this would be a transverse plane dominant flatfoot, where you might perform an Evan's calcaneal osteotomy in an attempt to achieve a more 'rectus' foot - and hopefully that coincides with a patient with a functioning, more comfortable foot.

    I guess Navicular drift (where I presume the assessor sees medial motion of the navicular?) would be one clinical sign of a transverse plane dominant flatfoot. Increased navicular drop I'm guessing would be one sign of a sagittal plane dominant flatfoot. So, in answer to your question as to what do they show - my best guess is that they are clinical signs that you could use to justify what type of surgery you will offer (in combination with other clinical signs, x-ray charting, etc...).

    Your point on Nester et al's work is interesting. In between being totally overworked and severely lacking in motivation I have read one of that group's papers and it seems to me that their conclusions that the axis is created by motion (if that is their conclusion?) is based on the technology they have available to them - they seem to use a system for measuring relative motion of body segments that relies on a set of infra-red tracking cameras. Forgive me if I'm being a bit slow here, but they use a measurement tool that displays 3d motion of markers applied to different bit of the surface of the foot and ankle so I can't see what other conclusions they can draw from this? Even the bone pin study that I read didn't really tell me a great deal more than 'this bone moves this way relative to this one' etc... Can these 3d tracking systems tell you much more than that? I have not read that much around the area, but all they seem to churn out in that paper is angular motion of segments of the foot from what I recall. It did not seem all that clinically relevant, so I had a short attention span for the paper in all honesty, so I'd appreciate anyone's thoughts on that (probably in a different thread if it's not too relevant here).
  4. markjohconley

    markjohconley Well-Known Member

    I grasp the calcaneus and apply inversion/eversion forces observing the forefoot to 'roughly' estimate the STJ planal dominance, fully realising there's multiple other joints and soft tissue structures affecting the motion of the distal forefoot.
    I tried the drop/drift once at a boot camp and didn't fancy grovelling on the floor (dodgy knees).
    Although the same criticism could be made for this method, I can't comprehend why I wouldn't use it to determine certain characteristics of the shape of the orthoses.
    Looking forward to Michael and Robert with quick responses then in 24-36 hours time Kevin's.
  5. A couple of thoughts/Questions

    As I remember the measurements of Navicular drift and drop are part of FPI and it too much (whatever that is ) is seen as a bad thing or poor score as part of FPI.

    We never seem to discuss drift as medial or lateral - can there be lateral Navicular drift ?, I guess there could when the compression forces cuboid-navicular increase.

    We also never discuss Navicular lift, but tend to discuss the whole MLA , should we discuss Navicular lift ?

    The point to these Questions all comes back to some of the discussion on the Midtarsal Joint Equilibrium thread, if we are going to look at the Midtarsal joint and surrounding soft tissue are we better to look at the forces acting on tissue and use free body diagrams.

    Eric wrote this in the above midtarsal joint thread.

    Hope that makes some sense, very jet lagged and at work :mad:
  6. Anyone got a copy of Don Greens planal dominance article - JAPMA don´t seem to have a copy on the website.
  7. B. Englund

    B. Englund Active Member

    not really

    The FPI item assessing navicular position looks at the “bulging” or congruence of the Talo-Nav joint, meaning only the transverse plane. More bulging = higher score = more pronated. If this is a bad thing…I´m not going into deep water.

    talking about deep water, hope you and the family had a nice holiday is AUS.
  8. I'm presently quite stoned and in a fair amount of pain so you might have to bear with me for mine. This ain't gonna be a simple thread. Can I beg 24 hours to reply please?
  9. The little Button is your Friend Remember that.

    Hope your on the improve soon Mate.
  10. Griff

    Griff Moderator

    I got it on my machine at home. Will be in your inbox tonight.
  11. Thanks Björn went to do some re-reading of FPI stuff.

    Was a nice Holiday, hope yours was good. Good luck with the Dr studies hope if goes fast.
  12. RobinP

    RobinP Well-Known Member


    Could I have a copy of that too please. Also, you wouldn't happen to have the Hylton Menz one would you?

    many thanks

  13. RobinP

    RobinP Well-Known Member

  14. So, here you appear to be talking about the planal dominance of the entire foot which would suggest a singular axis which the whole foot rotates about? That is an interesting way of modelling weightbearing foot motion, but I guess Nester lumped a whole load of joints together to give a single resultant MTJ axis, so why not the whole foot?

    What influence does the state of the spring ligament have on this "planal dominance"? Moreover, what influence does the state of the spring ligament have on navicular drop and drift? Or, on the spatial orientation of helical axes of the joints I mentioned in the original post?

    How do you assess the "planal dominance" of a flat foot deformity? Once the navicular hits the ground (sagittal plane), it can't go any further, but the transverse plane motion is somewhat less constrained.

    As an aside, do surgeons repair spring ligaments in the same way that surgeons repair, for example, cruciate ligaments when performing flat foot surgery in feet in which this ligament is torn / elongated?

    Bob, that's kind of what happens. Adjacent bony segments rotate and translate relative to each other and from that we can calculate the instantaneous axes of rotation. If we know the axial position and we combine that with force plate data, we can then calculate the joint moments, accelerations etc etc.

    As another aside, when you perform an Evan's procedure, how do you work out how far you need to slide the calcaneus?

    If we go back to your "surgical" definition of planal dominance and added markers to all of the bones of the foot, we should need to see all of the markers rotating and or translating about a single helical axis at given time in order to demonstrate a valid model of whole foot planal dominance. Do you think this is possible? I thought the point of some of the research Chris did with Erin Ward using the cadaver simulator was to work out which segments of the foot you could "lump" together, and which segments you could not?
  15. Griff

    Griff Moderator

    To all those who asked for a copy of the Don Green paper via this thread and PM - check your inboxes

  16. Quick thought: we have navicular drop, i.e we measure the translation of the navicular in the sagittal plane; we have navicular drift, i.e. translation of the navicular in the frontal plane, put them together and we have a 2-dimensional translation axis for the navicular (whatever significance that may have), i.e. we can calculate the angulation of this translational axis for the navicular and hence its (the navicular translation axis) planal dominance in 2- dimensions. Why not measure anterior / posterior displacement of the navicular relative to the transverse plane too, and call it "navicular slide", put all three together and get a 3-dimensional translation vector for the navicular; call this composite measure "navicular translation"; get a 3-dimensional translational axis; work out the 3-dimensional planal dominance of this net translational axis and then work out its clinical significance? ;) If nothing else, if foot pronation and supination are triplanar motions it should give a better measure of foot pronation/ supination than measuring only navicular drop and drift as was Menz's contention to include "drift" with the "drop" measure. You can quote me on that and use this post in your references ;);):cool:

    Then, I'll spoil your fun and tell you that foot position doesn't necessarily predict pathology, and ask you why you are measuring this anyway? Yet, if I can apply a "braking" force in a direction directly opposite the translational vector of the navicular, via a foot orthosis, should this not be the most efficient point and direction to apply such a force... assuming deceleration of navicular motion is important? Knock yourselves out.
  17. So, the butterfly thoughts of a madman on a Tuesday evening leads to this conclusion: we have spent the last too many years trying to control the position of joints with foot orthoses, when really we stand better chance of controlling the motion of the individual bones which make up the joints by applying forces to these bony segments (the joint is a fluid filled space between the bony segments) with our foot orthoses. So, if we assume that it is the deceleration of the motion of the segments that is important, if we work out the translational/ rotational motions of each bony segment in 3-dimensions, but within dynamic function, you should be able to apply forces via a foot orthosis which should be optimised to decelerate the motion of each segment by designing the orthoses to apply directly opposing, "countering" forces to decelerate the motions of the foot's bony segments with the minimal internal stress to the soft tissues by angulation of the orthosis surface geometry. Yet, we still have to allow enough stress to maintain the tissues within their zones of optimal stress, by manipulating the orthosis stiffness... Then it turns into a bummer, when we realise that the magnitude and direction of the translations and rotations etc, will be environmental and task dependent.... doh.
  18. bob

    bob Active Member

    Hello Simon,
    The state of the spring ligament is often investigated pre-operatively using MR scans. It is not uncommon to find spring ligament attenuation/ tears in patients with tibialis posterior tendon dysfunction and associated flatfoot deformity. I guess it depends on the individual as to how much influence the spring ligament has on either drop or drift of the navicular. I have seen patients with both sagittal and/ or transverse plane dominant flatfeet having spring ligament attenuation (for some reason I see more transverse and sagittal than frontal plane flatfeet) and can not really say for sure how much influence attenuation of the ligament truly has on planal dominance – especially since I can not remember a single case where spring ligament rupture/ attenuation has occurred in isolation. And the same goes for the helical axis question. Very basically, if the spring ligament is rupture or attenuated, I repair it as part of the surgery.

    You assess planal dominance by checking clinical signs such as ‘too many toes’ (transverse plane), valgus heel (frontal plane) or loss of medial longitudinal arch (sagittal plane) – you can already see that there will be cross-over between all of these and they are only simple examples of each. These, along with other clinical signs will be combined with x-ray measurements such as calcaneal inclination, talar declination, talar head coverage, cuboid abduction, Kite’s angle, etc... to help determine specific points where you might offer surgery – looking for an apex of deformity to aim your surgery at. Soft tissue scans will also be used to assess integrity of the tib post tendon, spring ligament, etc... so you can repair any pathology as needed. So as said before, if I see a ruptured or attenuated spring ligament, I’ll repair it.

    With an Evans, it’s an opening osteotomy of the calcaneus where you seek to ‘lengthen the lateral column’. You are essentially increasing length of the anterior aspect of the calcaneus which will push the forefoot medially through the cuboid. The general rule is to use a graft less than 10mm long, or the patient will most likely get CCJ OA/ pain. Alternatively, you can do a distraction fusion of the CCJ if you need more length than that.

    I am not completely familiar with the methodology for using these markers and tracking systems for assessing foot function, but my best guess is that it may well be possible to determine an overall dominant plane of motion of a defined ‘foot’ segment. How clinically relevant (in terms of surgery) this would be is something I don’t know. The good thing about looking at an x-ray or a scan is that I can feel more confident to offer surgery to a certain area of the foot.

    I must confess that I am not aware of the paper you mention, so if you could provide a reference I’d appreciate it. Did they have any conclusions that could affect the way we manage painful flatfeet?
  19. I'll need to look it up. My recollection of this research is based on personal conversations with Erin, he might have presented it a PFOLA meeting? As I recall, what they were trying to do was to work out the functional units of the foot. It may or may not have implications for flat-foot surgery.

    I'll try to find it tomorrow, if not you could contact Erin or Chris, I'm sure they could put you in the frame regarding their research and its conclusions.

    10mm, you can't beat a round figure ;) ( http://www.youtube.com/watch?v=WzF26HRjfBw ). How do we know that more than 10mm results in calcaneo-cuboid joint osteoarthritis/ pain? Is this "limit" the same for all foot lengths? Why not shorten the medial column which will pull the forefoot medially?
  20. Erin talks about it here:

    among the references he gives are these:
  21. bob

    bob Active Member

    I’ll have to google Erin Ward and find the paper. Who is this Chris person? Does he/ she have a surname? The majority of fusions are performed in arthritic joints, but I suppose it would be nice to know how much motion is available at the surrounding joints to take up the slack if you are to sacrifice a healthy joint in order to attempt to ‘correct’ the flatfoot.

    As far as the 10mm thing goes, I can not remember a reference for this leading to CCJ pain/ compression, but I seem to think that there is one somewhere in my past reading. Probably in the bible, old testament of course ;) It’s a generalisation and some people will need less, some more. As previously discussed in our arthroeresis conversation on here, the eyeball and hit and hope will come in to play to an extent. There are some wedges available from certain companies that sell allogenic bone grafts for the Evans. These kits have a sizer set of varying width wedges to help you assess how big the graft needs to be which helps the eyeball process. http://www.youtube.com/watch?v=zH18_dZIYOE

    Why don’t you shorten the medial column – lateral column is easier to lengthen. Medial column shortening also generally means fusions which could mean losing a ‘healthy’ joint (I’d rather preserve where I can). Hoke fusions do this to a point, but I prefer to offer these for sagittal plane dominant flatfeet, especially in the presence of OA.
  22. Yep, "The Neste[o]r" http://en.wikipedia.org/wiki/Battle_Beyond_the_Stars He really is five alien clones.

    How do you decide who needs more and who needs less and how does this relate to foot length at the time of surgery?
  23. bob

    bob Active Member

    From wikipedia regarding 'Chris' Nestor:

    "Shad is then approached by a set of five alien clones who share a group consciousness named Nestor. These aliens say their life is incredibly dull, since their whole race shares one mind. In order to be entertained, they have sent five members in a ship to join Shad's cause. Nestor asks no payment, saying they are completely self sufficient having developed a rubbish insole to peddle to intergalactic chiropractors with little or no knowledge of foot function."

    Sounds an interesting fellow :D

    Eyeball ;) Sorry, it's easier to show you than describe it. I distract the osteotomy site with a certain type of surgical tool to the point where the foot is in a suitably rectus position upto the magic 10mm. You can use general clinical impression of the foot (eyeballing an improvement by simply looking at the relative lengths of the medial and lateral column, checking improvement in arch height, etc...) and/ or checking intra-operative x-rays for improvement in your pre-measured angles (as mentioned in a post further down this thread).
  24. That's not what it says, as well you know. Chris is interesting, if your interested. Although, he does have a tendency to put his hand upon his chin when thinking. Regardless, I'm interested in this carpentry thing, so... if you use this surgical "planal dominance" notion pre-operatively, you then lengthen the lateral column, you then presumably must re-measure this planal dominance thing post-operatively? And conclude that since the foot is now a more pleasing shape and stands in a nicer position, everything in garden is now flowery, so long as in the next month or two they heal well and don't complain? I'm joking, of course. Yet am I am trying to learn something at the same time. How does foot position relate to pathology?
  25. bob

    bob Active Member

    Yes, you measure the same things post operatively. You may joke about the flowery garden thing, but that's not all that far from the truth. Healing is good for the short term, but long term reduction of pain is the goal. In the NHS, long term is 6 or 12 months maximum (budgetary constraints on post-op follow up). I do not do a lot of flatfoot surgery (podiatric surgeons the world over will no doubt perform lots of the usual surgery such as bunions, etc...) so maybe my 'conservative' approach to these patients has helped me achieve good results with the majority of flatfoot surgery over the years - or maybe they went to see someone else when it didn't work a few years down the line? Things like that are the great unknowns in all our practices. Of course, it doesn't always work and any surgeon who says it does is either lying or seriously deluded, but I guess this applies to all interventions.

    How does foot position relate to pathology - a fairly simple example of this would be a medial displacement calcaneal osteotomy. Pre-surgery, you have a valgus heel with ground reaction force consistently increasing pronation moments about your rearfoot which probably contributes to the common pathology of tibialis posterior tendon tears. Post surgery, you've fixed your tendon tear and medialised the posterior aspect of the calcaneus to prevent future recurrence of tib post pathology by increasing supination moments about the rearfoot (or reducing pronation moments, depending on how you look at it).
  26. Thank you for your time and honesty, Bob. And goodnight- b-byes time for me at least. When you find time I should be interested in your and other peoples answers to my final question above. To reiterate: How does foot position relate to pathology? If any one says it doesn't, I'll have to send "the boys 'round"- think about y'all, before you answer.
  27. markjohconley

    markjohconley Well-Known Member

    In Erin Ward's 'cadaver' article it says, "have also indicated that custom Root-type orthotics appear to ..., as well as decreasing the subtalar eversion." Is that position or magnitude of motion or ..?
    And thanks for the articles, mark
  28. bob

    bob Active Member

    No problem. I attempted a short reply to this as an edit to my previous post after I re-read your post and realised I hadn't answered your question. Apologies for the oversight but I too am very tired and should be in bed!
  29. Maybe the question should read how does a change in foot position relate to pathology - if the foot doesn't move from one position to the other ie standing completely still ( which is different from standing with no locomotion) there is unlikely to be pathology.

    But say we take the navicular , we have navicular at point X and we have -x to any degree which would represent one or more of the following navicular lateral drift, lift and your posterior slide. On the X+ side we have medial drift,drop and anterior slide of the navicular.

    Now during gait we will have the navicular be in mutipule positions from -X to X to +X, in this change of position we will have changes in force on bone and soft tissue ie increase bone compression force or increased tension in ligaments or tendons. If these changes in position are too great we may have cartilage damage or plastic deformation and then pathology.

    So if we have -X motion or +X motion which is too great, we will have a new position of the navicular which may mean pathology.

    Zones of optimal stress, which was my thinking with free body diagrams and looking at the forces at play.

    And with plastic deformation we may over time have more of X+ position ie more navicular drop or drift or anterior slide which may lead to even greater pathology
  30. Right then. Still a bit punchy so you'll have to forgive me if I'm a bit more "fighty" than usual.

    I'm going to start from the top if I may, rather than try to piggyback in on Simon and Bob's debate.

    First off. I think there is a dissonance here between biomechanics (as a theoretical study) and MSK Podiatry (as a clinical discipline). As I have ranted many a time, I think that they are profoundly different.

    Can one derive, with any degree of accuracy, the position of the sub talar axis by observing the navicular drift / drop? I'd say no. Several reasons. Firstly, as Simon points out, this assumes that the sub talar axis is biplanar. The further the axis from the sagittal plane the more movement there will be in the frontal plane from that orientation.

    Far more significantly, there is the issue of midfoot stiffness. If the midfoot is munted, and can dorsiflex freely and far, the navicular could be weight bearing with little or no sub talar motion at all! And just to really confuse matters, Sub talar pronation involves dorsiflexion so in the sagital plane, sub talar pronation could actually be raising the navicular in the sagittal plane, even as it lowers it in the other two.:wacko:.

    And of course we are measuring the position of the navicular. The amount (if any) of navicular movement relative to the other tarsal bones may also be a confounding factor.

    So no. In a biomechanical sense, I don't believe we can make any profound observations about the location of the sub talar axis based on nav drift / drop.

    And here is the MSK Podiatry bit. Why is the position of the axis important at the sharp end of the process? Lets keep in mind that from an MSK podiatry perspective the purpose of all our biomechanics is to make the right shaped bit of bent plastic (or, with a respectful nod to Bob, to know which bits to cut and which bits to leave alone and suchlike).

    As Simon observed, knowing the direction of travel of the navicular, and its start and end point, offer a very useful piece of information when deriving prescription, both the shape of the device and potentially the covering material as well. From this perspective one might consider the movement of the gross morphology of the foot to be as important as the details of the axial componants of that movement. There are a limited number of places and ways we control the foot. Knowing what percentage of movement is originating from which of the tarsal joints is interesting from a theoretical, and perhaps diagnostic viewpoint. But if you were to know that the movement was 60% Talonavicular joint and 40% Navicular-medial cuneiform joint as opposes to 40% / 60% would it make a vast difference to the way you shaped the arch of your orthotic?

    Here is another point to consider. I am a great fan of the "directly opposing force" concept Simon mentioned. If the navicular was a cricket ball and I want to control its fall, I want to hold my hand / orthotic perpendicular to its direction of travel right? But there is another element. As Simon and Kevin's recent paper illustrated, the effect of a force is not just about its location, but also its vector. The vector of the ORF, the equal and opposite reaction force, will, I suspect, depend significantly on the vector of the incoming force.

    The idea of measuring navicular slide is a great one from a biomechanical point of view. But how much would that inform our treatment? We can't put anything in front of the navicular to stop it sliding forward, the cuniform gets in the way!
    Thats why I use the two dimensional test to derive a two dimensional vector.

    The drift / drop test may not tell me, with any degree of accuracy, the planal dominance of the sub talar joint axis, the mid tarsal axis, or any other axis. But these axes are theoretical constructs designed to help us reach a goal, that being the shape of the device. So far as that is concerned, when I talk about planal dominance, I am happy enough to think in terms of the planal dominance of the movement of the arch as measured from its peak, the navicular. Its crude, but then so are orthoses. While biomechanics, as a pure science, has no room for pragmatism, I believe MSK podiatry does, provided it does not masquerade as other than it is. If I have, in the past, inferred such then I shan't do so again.

    And if you made it to the bottom of that ramble you're a better man / woman than I!!

  31. I'm still not sure why the subtalar joint axis is even being discussed with regard to the navicular drop and drift, is the navicular part of the subtalar joint?

    That's why you need to measure the slide: to work out the 3D movement vector. The slide measures the anterior/ posterior component and will ultimately influence the net vector of movement. So while you may not be able to directly stop the anterior / posterior component in isolation, it should influence the required opposing 3D surface angulation to decelerate the net movement.
  32. Its attatched to the talus. Not firmly, I'll grant you, but I think it gives you some inclination about what the talus is doing.

    Certainly it will influence the net vector of movement. But not, I suspect (no evidence), so much as the position of the body over the foot.

    Help me out. Give me an example. Foot 1 has no slide and a 45 degree movement medial/plantar of, say, 1cm. Foot 2 has a 0.5 cm anterior slide at the same medial plantar vector. So we have 2 parts drift, 2 parts drop and 1 part anterior slide. How would I make my insole differently to take this into account?

    I suppose higher friction cover would make a difference, but I tend to use those anyway....
  33. we are talking about the movement of the navicular so the slide component is part of that movement. What drives the motion is something completely different.

    Draw it out as a vector diagram, that will give you the resultant translational axis, your orthotic shell would be best able to decelerate translation along that axis if it were normal to it.

    A quick analogy, you drive your car along a horizontal surface into a concrete wall (orthotic) which is vertical and perpendicular to the direction of motion; you then drive you car into a concrete wall which is a wedge shaped inclined plane and therefore at an angle <90 degrees to the direction of motion. Which wall will decelerate the car more effectively?

    Missed the bit about the talus. But you are not measuring the movement of the talar head, you are measuring the navicular displacement, and while the navicular articulates with the talar head, it also articulates with a host of other bones. Lets say I fused the navicular at all of its articulations other than the talonavicular joint and then moved the subtalar joint in isolation, what motion of the navicular might we observe?
  34. This I understand. Much as the cricket ball analogy (which I had to include because its seasonal). This is how I apply the drift / drop. But I can't see how one can make the orthotic surface normal to the X+ element because to do so would require the orthotic to occupy space which is occupied by the medial cuniform. To take a hypothetical, if we made our foot 1:1:1 movement, forward, down and sideways, it would require an orthotic surface at 45 degrees to the ground in all planes. But that space is occupied.

    I'm not explaining this well. I feel a video with a skeleton and some cardboard coming on...
  35. I think you are looking at it as individual components rather than a single resultant motion. When I put an orthotic under a pes pancake foot, with the navicular touching the ground, I'm introducing the orthotic into a space which is "occupied" too. Can I suggest that rather than cardboard you start with a cube of foam, from this create a triplane wedge angled 45 degrees to each plane, then slip this under the arch of your foot.
  36. The cardboard video is uploading as we speak but I tried it with foam and that illustrated the point rather better. If I get time I'll do that one this PM.

    Good thread BTW. Thanks for starting it.
  37. Here's an even easier illustration, palpate and mark the navicular tuberosity, as you would if you were about to measure navicular drop, drift and slide. Then take a tack nail and place the flat head of the nail against the navicular tuberosity, let this be a portion of the orthotic shell and the spike part of the nail be the net translational axis, change the angulation of the nail relative to the cardinal planes such that it simulates an axis roughly 45 degrees to each plane along which the marked point of the navicular should move plantarly, medially and anteriorly, you should be able to do this and keep the head of the nail pretty much in contact with the foot. Now try varying the angulation of the nail..
  38. ignore, going mad.
  39. Here Ya go.

    Its not just for you simon. In fact its mainly for those folk following along (I hope there are a few) who are wondering what the hell we are talking about.

    For some reason, try as I might, I cannot get these things to embed. Craig, would you mind? Thanks.

    Here is number 1

    Last edited by a moderator: Sep 22, 2016

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