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Foot posture index versus navicular drop

Discussion in 'Biomechanics, Sports and Foot orthoses' started by proud, Jan 5, 2010.

  1. proud

    proud Member

    Members do not see these Ads. Sign Up.
    I am wondering what tool is "better" to determine pronation/supination in the minds of the experts on this site:

    The foot posture index or the navicular drop test?
  2. Admin2

    Admin2 Administrator Staff Member

  3. Apples and oranges.

    FPI is a test of foot posture and looks at lots of things. Nav drop (or SNA) only tells you what one bone is doing in a single plane.

    For eg, I've seen feet in which there is a strong transverse planal dominance with heaps of pronation but not much nav drop. There again a foot with a very hypermobile midfoot / 1st ray might have Heaps of nav drop with relativly little pronation.

    Nav drop measures arch height. Arch height is not the same as pronation / supination.
  4. proud

    proud Member

    Thank you guys very much for your attention.

    You'll have to excuse me...but if looking at what the arch is doing is not in your terms "supination/pronation...what is?

    Perhaps if I ensure we have the definitions equalized...I could engage in a better analysis of what people are telling me.

    All I can see from the FPI is that it tells you if someone is a pronator or supinator( the index's definition based upon scores).

    I gather you are saying someone can pronate at different loactions within the foot?

  5. Same answer to both questions. Pronation and supination happen at the sub talar joint. This may cause an effect further down but it happens at the joint.

    Put it this way. You can see if the knee bends by looking at the shins... but it happens at the knee.
  6. To enlarge my earlier post, lets take three people with an identical number of degrees sub talar pronation. One has a drift drop ratio of 1:1. The second is 2:1. The last is 1:2.

    The first has a nav drop of 1cm. The second might have 0.5 cm and the last 1.5 cms. Completely different feet. Different functions, different insoles probably required. Same amount of pronation at the joint. Is the Nav drop significant? Yes, particularly considered as half of the drift / drop test for planal dominance. But does it determine degrees of pronation? No. Because a foot with HALF the amount of pronation could have the SAME nav drop as the drifting foot and a foot with DOUBLE the pronation could have the same drop as the foot with greater nav drop than drift.

    Consider the arch by all means, but remember it has three planes of movement not just the one. And a foot with a big ass nav drift will have all sorts of badness going on with the ST axis even if the nav drops by a tiny amount.
  7. proud

    proud Member

    Really really helpful everyone. Thank you.

    So from the "drift" article above...I'm gathering that a ratio of drop/drift is a good indicator? Pretty reliable.

    So Robertisaacs when you say apples and oranges....both are seeking to tell us the same thing though correct?

    It seems to me based on the research provided above...the drop/drift is more reliable so in my mind a better tool?

    If not....I'd like to know why and what others do objectively and in evidence based format to determine pronation/supination.

    Thanks again
  8. Asher

    Asher Well-Known Member

    Hi Proud,

    I'm not sure you could say navicular drift / drop is better than the FPI?

    The FPI looks at the three segments of the foot: rearfoot, midfoot and forefoot. And it looks at bony positions in all three planes: frontal, sagittal and transverse.

    Navicular drift / drop looks at bony position of only one bone in two planes only.

  9. Thia might answer some of your questions Proud.
  10. Nope. You're not quite there yet.

    Drift / drop ratio tells you nothing about the the amount of pronation / supination, it tells you the planal dominance. The planal dominance is needed to interpret the amount of sub talar movement from the amount of movement you actually see on a point of the foot (like the navicular).

    So no, not correct. They are completely different animals. Altogether.

    If you want to make a consistant and repeatable observation of static weight bearing pronation then FPI is probably your best bet. But what does that even tell you? It's not as if that is consistantly predictive of dynamic function.

    Craig has a saying, only take a measurement if you are going to use it for something. What are you going to use it for?

    We may be able to guide you better if we knew the reason for your enquiry.

  11. proud

    proud Member


    Sure. Well being a Physiotherapist, I am generally in the clinic treating such beasts as PFS, Shin splints, Plantar fascitis, low back pain etc.

    In terms of foot biomechanics I am more a generalist of course. But I do let current evidence formulate my practice. As it stands now from most systemmatic reviews that I've read( cochrane collaborative being just one).....custom orthotics have no net benefit over the off the shelf variety......

    I'll wait for the stones to start flying.....

    Now....as such, it does appear that excessive pronation or lack of pronation( so called pes cavus foot architecture) can contribute to various NMSK conditions( Plantar fascitis, shin spints for example). I've read quite a bit of the literature.

    Therefore, I often utilize an off the shelf product( Vasyli) in cases that I can document either excessive pronation or limited pronation. I need to substantiate why I might use a 40$ item on a patient. I have been using the navicular drop as a test but recently was sent the FPI.

    I have a funny feeling I'm about to be schooled here but thats why I signed in. To learn as much as I can. I just like it to be supported by high quality RCT's. Theories are great, we have our share in the Physiotherapy world as well, but I think professions must be held to a higher standard. I'm hoping to learn more about how you guys practice in an evidence based manner.

    The input has been great and I appreciate the education.

  12. Ah, all becomes clear now. Now I suspect I can help you more.

    The relationship between pronation and pathology is rather more complex than one might think. Pronation is not the root of all evil and whilst some studies have shown pronation to be predictive of some conditions, many of the conditions often attributed to pronation have no evidence supporting a correlation. Also most of the studies are cross sectional which means they do not show causation, merely correlation.

    For example we may find that tibialis posterior pathology correlates to increased degrees of pronation. But does that prove that the pronation caused the TP pain or that the TP dysfunction caused the pronation? Either seems plausible.

    To use an analogy closer to home, if you looked at 100 people with severe back pain and compared activity levels with those without one might find that those with back pain did less salsa dancing. Does that prove that salsa dancing prevents back pain or that one struggles to salsa with a slipped disk?

    Also you need to remember that a measure of pronation taken in static weight bearing is not necessarily predictive of how the foot will behave in vivo. I've seen patients who stand in an eye wateringly pronated position which disappears when they walk!

    LOL, no stones from here. This ain't that kind of forum. However you should consider carefully the nature of those studies. They tend to compare a certain type of pre fab with a neutrally casted shell. But CUSTOM orthotics are not simply neutral shells. There is an unfortunate confusion as to the precise definition of a "custom" orthotic.

    To give another example, it would be akin to comparing one of those shiatsu machines you get in airports to a particular type of back massage from a physio for a diagnosis of "lower back pain". They might work the same. But of course a physio is not limited to a single type of treatment for "lower back pain", they will investigate what specifically is hurting and what is causing it. They will take into account lifestyle and such. They have access to a broad range of manual techniques. You get the gist.

    From your perspective then, If you want a simple, bumper sticker answer, the FPI is probably a decent tool to use to decide whether to try an off the peg orthotic. If it works then great. If not it would probably be worth referring to a podiatrist, preferably one who does lots of Biomechanics. If you can find such a Podiatrist you may even be able to develop a reciprocal arrangement wherein you refer your tougher biomechanics cases and they refer to you where they feel physiotherapy can help their patients.

    Kind regards
  13. proud

    proud Member

    Yes, static versus what happens dynamically. I don't think there is a system that has any validity/reliability for dynamic evaluation...(?).

    Now that is something I never considered. Thanks for that. Having said that....it is suprising that after all this time....there has not been any study then that looks at appropriately prescribed custom orthotics( presumably by a certified ped) versus off the shelf. To me anyway that screams of the claims of acupuncture. Acupuncture has been around for years yet the verdict is still out on it's efficacy. Eventually lack of evidence suggests something.

    Or is there such research and I'm just not locating it?

    I never massage patients.....Physiotherapists don't massage;)
  14. It is a bit of a pickle! I could do a study comparing my choice of all the weird and wonderful variations on in shoe orthotic vs a pre fab but all that it would show was that I could do that. Wouldn't show what anyone else could do. Whereas acupuncture could so easily be double blinded. N=1. Its a bitch.

    However can I invite you to consider the difference between inductive and deductive evidence? Just because something has no direct inductive evidence does not mean it has NO evidence. Good biomechanics is based largely on deductive evidence.

    Are you familiar with the concept?
  15. proud

    proud Member

    That would imply that podiatrists have no reliable way of determining what type of orthotic is best....

    Are you suggesting that if 500 people with say....plantar fasciitis entered into a study. 250 were placed in the "custom orthotic" group( wherein the patients were assessed by chosen experts within the podiatry field) and the other 250 were simply provided with "off the shelf".....this would not be a decent study?

  16. proud

    proud Member

    Are you suggesting orthotic prescription could not be blinded?

    I think I know what you are speaking of RE: inductive verus deductive evidence.

    Absence of proof is not proof of absence? That sort of idea?
  17. I'm suggesting that the 250 people in the custom group each received different foot orthoses. Moreover, foot orthoses, be they custom or prefabricated ultimately transmit the load from the body above via the shoe to the ground, they do this by developing stress and strain within their structures. The stress and strain that they develop is dependent upon their geometry, material properties and loading pattern. Since each of the custom devices have unique geometry and material properties (the two are linked) and loading is unique to the individual and task, then neither custom nor prefabricated foot orthoses will behave the same under the feet of two individuals performing the same task.

    Would you perform an RCT and give everyone different dosses of the drug? This is what your trial above did.
  18. proud

    proud Member

    Although I understand what you are trying to say...it still makes little sense.

    Let me pose the question this way. Is there any way that you( or any podiatrist) would suggest constructing a well designed research protocol that would compare special orthotics as prescribed by a podiatrist against off the shelf?

    Surely this is not an impossible research design. Is there such research available?

    Thanks again.
  19. Why do you think it makes little sense?

    Let me ask you this question: how do foot orthoses exert their therapeutic effects?

    Its a difficult problem, which I have no real answer to at the moment. We have considered analysing the data in terms of multiple single case designs, but we ultimately have an n=1 problem as Robert intimated. One way to better match the subjects between groups might be to use MZ twins. At best the current RCT's examine the prescription protocol, not the orthoses per se. But the researchers are doing their best. The key to this is understanding how orthoses work, which is why it is important that you attempt to answer my question above, then it may make more sense to you. And not least to understand the limitations of the published research.

    BTW, how would you design a study to compare prefabricated foot orthoses with custom foot orthoses for the treatment of X?
  20. proud

    proud Member


    To you first question:

    By offloading a tissue structure via altering the mechanical forces?

    Interesting take. Okay, let me clarify. The research would look at how effective podiatrists are. In other words, even with an N=1 situation, you could still have 500 people with plantar fasciitis evaluated by a podiatrist and subsequently prescribed what they feel is best suited.

    Then 500 with the same diagnosis simply provided with an off the shelf( after a full evaluation...blinded by the patient...they are not aware that there "orthotic" is off the shelf).

    Does that make sense?

    Let's take an area known to me. Low back pain. If 100 people are sent to Physiotherapy for treatment, and 100 people are sent to any person on the street for advice....technically we would hope the Physiotherapy group would have a better outcome...

    The problem we have currenetly is that the PT profession is way to varied. The treatment options are huge and much of it is not evidence based. So.....much research designed that way end up with poor outcomes for Physiotherapy.

    However( and this is huge)....recently we have discovered that patients with LBP often have "clusters"' of tests that match them to a specific type of treatment( spinal manipulation, spinal stabilization, fear avoidance education etc). As a result, treatment-based classification for low back pain has resulted in markedly better outcomes. We are truly evolving as a profession by adhering to high quality research.

    What I am saying is that from what I'm gathering here, my notion that using the navicular drop to determine pronation to guide my clinical descision too use Vasyli as an augmentative treatment to offload a tissue structure may not be taken well by podiatrists, but it's equally valid when compared to the current state of the research into custom orthotics.

    To be clear, often I think a patient could benefit from something more customized and as pointed out above, I might want to locate a podiatrist to assist along the way. But I have to know a little more about the evidence to support and substantiate why I might do this.

    Thanks again
  21. You seem to have altered your research question, initially you said:

    Now you want to know if podiatrists are better than prefabricated devices?

    No, your notion to use navicular drop is flawed because: navicular drop test does not provide you with a) a diagnosis b) a valid measure of dynamic function and c) a means to decide if Vasyli device is required and with what modifications?

    What is the current state of the research into foot orthoses?

    A little bit of knowledge.........

    I'll leave this discussion to me colleagues.
  22. Hey Proud

    Hmmm. Could possibly help you there. If you PM me you're email address I can send you an article on the evidence for the efficacy of orthoses in the broader sense. Can't give you a direct comparison but if you are looking for metasearch type information you could come up with some.

  23. proud

    proud Member


    I agree I modified my question. Based upon the information you provided that's all.

    a) I know it's not a diagnosis

    b) is there a way to measure dynamically? That has any reliability or validity?

    c) It does tell me something....and this is the point of me being here. Right now if I note a navicular drop greater than 13mm....I use the vasyli to offload while I tape, stretch or whatever else. But I'm open to modify this approach if better evidence based information exists.

    Robert, thanks for that. I'll PM you my email as soon as I get a chance. Your offer is much appreciated of course.

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