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The 'Keystone Device' for Measuring Supination Resistance

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Craig Payne, May 8, 2017.

  1. Craig Payne

    Craig Payne Moderator


    Members do not see these Ads. Sign Up.

    This is not my device, but I have obviously been aware of it during development and given a little feedback.
    For those been on my Boot Camp's this is the product that I said was coming.

    There is a patent on it (patent here)
    Its finally on the market.
    More info here

    At this stage, its only available from Amazon.com and direct from Interpod (will post back if other distributors have it)

    Podiatry Arena is taking some $ to advertise the product.
    The 'More info here' page is sponsored content.

    Attached Files:

  2. Admin2

    Admin2 Administrator Staff Member

  3. Sinex

    Sinex Member

    Oddly, after having followed your first two lessons of your online bootcamp, this morning i built up this supination resistance device using the same luggage case i see in your picture!
    As soon as i tried it the first time, i quickly realize there was the need to prevent the risk of leg abduction during testing .
    It's such a coincidence for me to find your patent as a direct solution to a problem i discoverd only 12 hours ago... Great job Craig!
  4. Craig Payne

    Craig Payne Moderator


    Just to be clear; this is NOT my device.
    I was obviously aware of it during its development and provided a little feedback.
    The biggest cost and problem during development was the blue bit to attach the strap to.
  5. Dieter Fellner

    Dieter Fellner Well-Known Member

    The unit looks like an adaptation of a baggage scale (sells for $10) complete with luggage strap. The addition of the blue plastic prop can be helpful, I guess. I put in an order, always the tech-toy fan.

    My questions:

    1. What is the unit of measurement
    2. Can we correlate the measured supination resistance with orthotic modifications.
  6. Craig Payne

    Craig Payne Moderator

    Of course! The biggest part of the cost was the blue bit - it went through many iterations to get right and is injection model; costs reflect that development costs.

    The prototype that they sent me was in kg, so assume it still is
    Theoretically. The higher the force to supinate the foot, the more force that has to come from the foot orthotic.
  7. Dieter Fellner

    Dieter Fellner Well-Known Member

    Thanks Craig, spoke like a true entrepreneur (ref. blue plastic). I had wondered if the luggage strap was simply looped around the foot it might achieve the same purpose, but anywho ....

    I guess what I hoped for was a formula to translate supination resistance into 2mm/4mm/6mm Kirby skive, used with XYZ density shell etc. or some such similar (but I didn't truly expect that). Perhaps sometime / someone in the future that can be figured out.
  8. Craig Payne

    Craig Payne Moderator

    The formula may come one day! No one has looked at anything like that yet.
    I "just know" from my own experience when using my hands to do the test what I want from a device to achieve the force I think I need.... how do you teach that????

    But, yes, evidence and data needed.
  9. Dieter Fellner

    Dieter Fellner Well-Known Member

    Indeed. In the meantime I tip my hat to those smart guys working on the problem.
  10. Craig Payne

    Craig Payne Moderator

    One of the problems with the device is even if there was a formula, how useful will it be.
    While no one done an intra- or Intertester reliability study on the device, I suspect strongly based on my experiences with devices that we have developed that the intra-tester reliability will be adequate to good --> so within ourselves it can be pretty reliable.
    However, I suspect the inter-tester reliability is not be so good --> that is a problem transferring number from you to me etc.
    The reason I suspect that is that the device measurement will be affected by the speed that you use it at. If you pull the strap faster, then you will get a higher value.
    But what I have seen, is that people tend to pull the strap at a consistent speed themselves (hence the probably good intra-tester).

    You just have to use the device yourself, get a feel for what is high and low and get a feel for how feet respond to different orthotics with the different design features
  11. BEN-HUR

    BEN-HUR Well-Known Member

    Just got it & tested it on myself... should be interesting to test on a variety of patients & then start acquiring/developing an element of correlation to orthotic material stiffness/flexibility (i.e. for my scenario, this being shell thickness [i.e. poly. 2.5mm, 3mm] in association/combination with EVA hardness [i.e. 240, 300] at plantar MLA of orthotic shell) to counteract desired degree of patient pronation force... whilst also keeping in mind arch contour & length (hence, not as straight forward as orthotic material stiffness/flexibility alone i.e. longer lessor profile orthotic arch contour will deform easier than a shorter higher orthotic arch profile). If needed, I then grind EVA MLA fill to meet patient tolerance (i.e. to gain more orthotic flex/give).

    I do have 1 query. The following diagram is straight forward (i.e. measure unit device, strap, hook & blue plastic anchor device)... but within the package also came a smaller blue plastic thingy. Any views on what that is... another version of an anchor device?

  12. Dieter Fellner

    Dieter Fellner Well-Known Member


    I suspect this will be very difficult to determine a meaningful algorithm to know if this works. There are no objective measures to understand the 'correction' achieved. It's all subjective patient feedback. Truly, the Hyprocure approach is my go to for managing the problem but I will try orthotic therapy first. This device can hopefully improve on the two-finger test.
  13. Griff

    Griff Moderator

    I think before we get carried away thinking about correlations with prescription variables we need to know if this device is reliable.

    I have rather large suspicions it is not.
  14. BEN-HUR

    BEN-HUR Well-Known Member

    Thanks Dieter for your views.

    Yes... this is why I'm (as I'm sure others are) interested in testing the device out within a clinic setting. I too have some reservations... but the data & feedback will be interesting all the same... even if it is within the confines of a (as Craig put it)... "intra-tester reliability" (usefulness) context. Hence the potential usefulness of threads likes this... in discussing devices like this... in nutting out issues & better solutions.
  15. Ian Drakard

    Ian Drakard Active Member

    How come Griff- did you have a chance to compare it with your jig? Is it speed of application or the way the device interacts with the foot that's a problem?

    Little bit surprised if there was no validation testing on it before release?
  16. Griff

    Griff Moderator

    I was sent one of these about a year ago to test along with Craig and a few others. I've not compared it to my jig as I donated that to a University sadly. I have had a play with it though, and whilst not run any formal statistics (yet) just a glance at the spread of my intra-tester data (and I like to think I'm ok at this stuff) does not paint a great picture...
  17. Dieter Fellner

    Dieter Fellner Well-Known Member

    I want to know why one device would be better than a similar device - measures the same thing , no?
  18. Griff

    Griff Moderator

    All devices which have been made to quantify supination resistance to date (I am aware of 4 including this one) are constructed of different materials, are of differing design, and there is a requirement for them to be operated slightly differently.

    Would your expectation be that they are the same Dieter??
  19. Dieter Fellner

    Dieter Fellner Well-Known Member

    My question is do they not measure the same thing, not if they are constructed in the same way, irrespective of how they are operated.

    A more useful response will be to offer an explanation why one of those four devices would perform better than another, wouldn't you agree, Griff??
  20. Griff

    Griff Moderator

    They are all designed to quantify the same thing (supination resistance) yes. That doesn't mean they do though does it? Can we be certain this is what we are measuring? What do we know about their validity? Hopefully it is obvious to most that they way they are constructed (and operated) will be a significant factor here.

    To put it another way, a machine that quantifies supination resistance with a 'sling' that traverses the width of the plantar foot has been designed (and therefore needs to be operated) very differently from a machine that applies point loading at the navicular in a plantar-dorsal fashion. Would you expect their values to be the same? Do you think that because they "measure the same thing" we should just accept and assume that are all equal without employing further scientific enquiry?
  21. Dieter and Colleagues:

    The various supination resistance machines that have been used do not measure the same exact thing due to their different constructions. The original supination resistance test which I first experimented with during my Biomechanics Fellowship in 1984-1985, was done by manually pulling directly upwards on the medial aspect of the plantar navicular (Kirby KA, Green DR: Evaluation and Nonoperative Management of Pes Valgus, pp. 295-327, in DeValentine, S.(ed),
    Foot and Ankle Disorders in Children. Churchill-Livingstone, New York, 1992). My manual supination resistance test will produce a different set of result from the devices which use a strap that pulls upwards on the whole plantar aspect of the midfoot, such as Noakes and Payne used in their study (Noakes H, Payne C: The reliability of the manual supination resistance test. JAPMA, 93:185-189, 2003). Their device is nearly identical to the "Keystone Device" that is now being sold commercially.

    Then there is also the device that Griffiths and McEwan used in their publication in 2012 (Griffiths IB, McEwan I: Reliability of a new supination resistance measurement device and validation of the manual supination resistance test. JAPMA, 102(4):278-289, 2012). This was the same device that Simon Spooner used in his unpublished study mentioned earlier in this thread. The device used by Simon and Ian is much more similar to my manual test, but since again the external force is being applied to a slightly different area of the foot, the results may be different from the manual supination resistance test.

    Certainly, if you wanted to best quantify how much tension force the posterior tibial muscle would need to supinate the foot, a device which pulled upward on the medial navicular with a sticky "J hook" under the medial navicular would, in my estimation, be a more accurate way and quite inexpensive device to make. This type of device would likely be better than either of the supination resistance machines that I have described above for trying to determine how much tension force is required within the posterior tibial tendon to initiate STJ supination in the foot. However, if one was more interested in supination resistance from a foot orthosis mechanics standpoint, I would think the Spooner/Griffiths device has more potential.

    How much do all these two techniques vary? I don't know. However, I do know that they all measure the external force required to supinate the STJ. The problem is that these various "supination resistance tests" apply external forces to different areas of the plantar foot (and lateral foot in the Payne/Noakes and Keystone device) and thus would be expected to give different values for supination resistance.

    I believe much more research will be necessary to determine which test has the most clinical significance. For now, using any of these tests in an attempt to better understand foot kinetics seems much more reasonable than simply ignoring these important biomechanical concepts.


    Kevin A. Kirby, DPM
    Adjunct Associate Professor
    Department of Applied Biomechanics
    California School of Podiatric Medicine at Samuel Merritt College
    E-mail: kevinakirby@comcast.net
    Website: www.KirbyPodiatry.com
    Private Practice:
    107 Scripps Drive, Suite 200
    Sacramento, CA 95825 USA
    Voice: (916) 925-8111 Fax: (916) 925-8136
  22. Griff

    Griff Moderator

    Hi Kevin,

    Agree with most of your post, but just one correction that is important regarding the machines - the one I used in my paper was not the same as the one Simon designed and built. His is a depressingly (for me) brilliant improvement on mine as it has the rearfoot platform which can be tilted in the frontal plane.

    I've attached an image for all following so they can see the design differences between the device built by Craig and colleagues, my device and Simons device, and thus gain a better appreciation of how it is inappropriate to compare them or consider them the same just because their aim was/is to quantify the same thing.



    Attached Files:

  23. Griff:

    Thanks for the correction. I thought you and Simon had used the same device. Have you and Simon compared your two devices on the same feet to see if the values between your two devices match up pretty well?


  24. Griff

    Griff Moderator

    Kevin: We have not (nor is it now possible to do so) unfortunately.
  25. Dieter Fellner

    Dieter Fellner Well-Known Member

    Thank you for the additional information. Ian, you have an uncanny/irritating knack of putting words in my mouth - no; I do not 'think' so - nor did I say that.

    Seeing the pictures, and reading Kevin's explanation, certainly clarifies the issue. The other devices seem to fit better in the research arena as opposed to the busy office environment. That said, a numerical value can, perhaps, still be a little more objective as opposed to my aging fingers hoisting on the foot for a 'suck- it- and- see' evaluation. With the device it's still a suck-it-and-see but it is heading in a better direction. The package arrived yesterday, so I guess I will put it to use and Putz around some, to see how useful this can be.

    Craig has provided a useful numerical range and perhaps this an provide a baseline assessment to direct orthotic Rx variables.
  26. Griff

    Griff Moderator


    Calm down dear. No words were being inserted into you. If you look again you'll find they were questions.
  27. Number of things already discussed like rate of loading, strap position etc, but just to quickly add in as I don't care for podiatric social media much these days:

    Quality of the load cell? Probably Ian's was the best. Also quality of bearing etc- I used Bosch linear bearings which cost a plenty packet, all for the fun of it.
    How do we know when the supination resistance is overcome? Mine was the best, as I used a goniometer clamped to the heel, while Craig and Ian went on "visual observations" of when movement occurred. Still improvement to be made with regard to this.
    Ensuring the "fingers" are applied to the same position and depth across subjects- mine used a targeting system to reduce between test variance in terms of the postion of the force application relative to foot anatomy, couldn't overcome between subject variance though. Craig's is pretty constant in this respect.

    What was I was thinking about when I made this very expensive jig for the fun of it? If I cast one foot in a position of 50% reduction in supination resistance, then another and another and another, all with 50% reduction in their individual supination resistances, I'd end up with feet cast weightbearing in different positions, yet with one kinetic variable adjusted by the same amount across all individuals for a clinical trial of foot orthoses... just a dream. Still better than 99% of the crap being knocked out presently in terms of controlling variables of the foot orthoses in clinical trials. I called it kinetically quantified casting and presented it at a number of conferences- didn't take off, probably because I was the only one with the kit to do it; but couldn't get ethical approval to do it. My country, responsible for some of the greatest scientific break throughs of all time is truly wonderful at stifling scientific endeavour right now.

    As for this current offering? It's rubbish, don't waste your money on a luggage scale than can be procured for virtually nothing on t'interweb - if it was as simple as putting a luggage scale on a strap... duh...

    For those that haven't realised, having been someone passionate about advancing our profession via the internet for the last 20 years, I have now become someone who couldn't care less anymore, having watched the monster that is social media ruin the academic discussion that we once had. When it's all about financial reward, then The dream truly is over. wake up.

    See y'all on the other side, it was fun:
    Last edited: May 22, 2017
  28. Couple of my slides from back then. Please forget to visit the advert at the bottom of this page. FFS. I didn't give my permission to be part of an advertising campaign any more than I gave permission for my writing here to form part of a chapter in a book... never mind. It was fun, that stopped some time ago, now it's just a chore. Just not for me anymore, thanks Craig good luck with that future.

    Attached Files:

    Last edited: May 22, 2017
  29. Dieter Fellner

    Dieter Fellner Well-Known Member

    Thanks Ian, I'm very calm and much too old to care. By the way, you will know, when you pen your response, what you're doing. I'll continue to let authors know when the narrative format assumes an unnecessarily patronizing tone.

    Kevin, in your office - do you provide in-or out-of-network services? I recently made the switch to in-network. Patients every 15 minutes. That puts quite a stress on time. Imaging and interpretation, HPI, PE, discussion with patients, placing orders, writing up notes etc.

    How do you organize the time to provide a 'good' clinical exam.
  30. Dieter Fellner

    Dieter Fellner Well-Known Member

    I am also curious about the function of the extra blue 'dongle' .....

    Attached Files:

  31. It's to attach the strap to a Brannock foot measure.
  32. timharmey

    timharmey Active Member

    Wasps or Exeter ?
  33. FuzzyBear22

    FuzzyBear22 Welcome New Poster

    Dieter, happy new year….a few years have passed since the last entry above.
    Did the extra little plastic part help at all? I’m thinking of ordering a Keystone device and wondering how you’ve got on. I prefer a more science approach to clinic and am keen to have reliability even if just myself. I can’t stand the guess work
  34. Gab Moisan

    Gab Moisan Member

    Hi. My team and I just got this paper accepted in Musculoskeletal Care:
    The Keystone device as a clinical tool for measuring the supination resistance of the foot: A reliability study

    Gabriel Moisan,Sean McBride,Pier-Luc Isabelle,Dominic Chicoine
    First published: 21 December 2021

    We evaluated the intra and interrater reliability of the Keystone device. We found good reliability for both. Considering the cheap retail price, I believe it is worth purchasing for clinical (and research) purposes. However, there is a long learning curve with the device. I would suggest experimenting on a lot of feet before comparing measurements between days (I would say at least 50 to 100 feet).

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