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Validity of F-scan System

Discussion in 'General Issues and Discussion Forum' started by Camel_Toe, Apr 17, 2009.

  1. Camel_Toe

    Camel_Toe Welcome New Poster

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    Have there been many studies that have established the F-scan system as a valid measurement of plantar pressure?
  2. David Smith

    David Smith Well-Known Member


    I'm assuming that by the term validity you mean the reliability of accuracy and precision of the tool and not the logical validity of the method.

    Accuracy of the Iscan Pressure Measurement System
    David R.Wilson*, Mark J. Eichler and Wilson C. Hayes
    *Department of Mechanical Engineering
    Queen’s University
    Kingston, Ontario, CANADA, K7L 3N6
    Orthopaedic Biomechanics Laboratory
    Beth Israel Deaconess Medical Center
    and Harvard Medical School,
    Boston, MA, USA
    June 2000


    The Iscan system can be used to measure continuously changing force and pressure distribution at biomechanical interfaces. The objective of this study was to determine how accurately the Iscan system measures force and force distribution in static loading. Known absolute and relative loads were applied to
    Iscan sensors using custom-built indentors loaded in a servohydraulic test machine. Over the 35 trials, the mean error for the absolute measurement of force was 6.5% and the standard deviation of the error was 4.4%. The mean error in the force distribution measurement over the 25 trials was 0.86 % and the standard deviation of the error was 0.58%. The results suggest that, when calibration, conditioning and testing protocols are developed carefully, the Iscan system measures force and pressure distribution more accurately than Fuji Prescale film.

    Measuring contact area, force, and pressure for bioengineering applications: Using Fuji Film and TekScan systems
    Medical Engineering & Physics, Volume 28, Issue 5, Pages 483-488
    K. Bachus, A. DeMarco, K. Judd, D. Horwitz, D. Brodke


    The goal of this study was to compare the TekScan I-Scan™ Pressure Measurement System with two methods of analysis involving the Fuji Film Prescale Pressure Measuring System in estimating area, force and pressure. Fuji Film and TekScan sensors were alternately placed between a cylindrical peg and a finely ground steel base plate, and compressed with known forces. All Fuji stains were digitally scanned and analyzed. The Erase method of Fuji Film analysis consisted of manually removing portions of the image judged by the user to be outside the perimeter of the stain. The second method of Fuji Film analysis, termed the Threshold method, used the threshold tool to analyze only those pixels that were stained from loading. The TekScan system utilized special matrix-based sensors interfaced with a Windows™ compatible desktop computer that was equipped with specialized data acquisition hardware and analysis software.

    The data from this study did not support the hypothesis that all three methods would have accuracies within ±5% of a known value, when estimating area, force and pressure. Specifically, the TekScan system was found to be more accurate than either of the Fuji Film methods when estimating area and pressure.

    Now! not wanting to be unfair to CT because this type of question appears quite regularly but it took less than 2 minutes of Googling time for me to find many comparative studies two of which are posted above. I wonder why some people expect others to do their work for them, when it is just so easy to do for themselves. Is it laziness? the lack of motivation to satisfy idle curiosity with a few minutes simple work or are there other motives??
    I'm not trying to be harsh, just wondering?.

    Two great free resources Google Scholar - Pub Med Central.

  3. efuller

    efuller MVP

    It depends on the usage. I've stood on an F-scan sensor for 6 minutes and my weight increased by 50%. So, I would not use it for total force over 6 minutes. However, it may be quite accurate for forces over a step, if it is correctly calibrated and the sensors are not damaged as they are placed.

    It depends,

  4. Asher

    Asher Well-Known Member

    I've recently purchased the FScan in-shoe system with TAM and CoM'nalysis. I'm still at the stage of reading and understanding the manual but I pretty much have my head around how it works.

    What I don't have a good understanding of is exactly how I will use it. It can obviously do a lot of stuff but which bits are the clinically useful bits. I would be grateful for any advice on which measures to focus on. I realise from previous threads that different practitioners use FScan differently.

    Many thanks

  5. Boots n all

    Boots n all Well-Known Member

    Hi Rebecca,
    l too am looking at purchasing the systems that Tekscan have, not completely convinced of it as a cost. Factor in both the purchase and the time it takes to implement, then the unknown ongoing cost of insole replacement, regarding how often that will need to happen?

    l think it will be a great tool as we find ourselves dealing with more and more Diabetics, its just a matter of passing those costs onto the client l guess.:empathy:
    As you can see l am clearly in two minds on this part of my new project.

    May l ask how time consuming is it to set up for each client please?

    We are currently building a Gait lab. and casting room 11 X 7 meters, l plan also on purchasing Silicon coach, any thoughts on this system or similar?

  6. Asher

    Asher Well-Known Member

    Hi David,

    Don't know yet as I haven't started using it on patients. I have done two recordings of myself and at that very early stage, it took longer than I expected as its a bit fiddly and you have to be pretty careful of the sensors altogether (cutting / placement ...). But I'm sure I'll get the hang of it.

    I use Siliconcoach. I don't use it anywhere near its full capacity, just look for timing and symmetry of heel-off and high gear/low gear propulsion. I haven't bothered with videosynchronisation with the FScan but its available.

    Hey, are you going to the Goldcoast - might catch up with you there. Pat (Fscan guy from USA) will be going through some particulars with me at his booth.

    Last edited by a moderator: Apr 23, 2009
  7. Boots n all

    Boots n all Well-Known Member

    l would love to Rebecca, but l am saving up my time away from work as l am off to Europe for the IVO in November.
    Pat is coming out to see me on the 7th...yet to be confirmed, to run through the Fscan systems/ equipment with me to show just what it can do for me and my clients.....sooooo many questions for him.

    Thanks for the response.
  8. Asher

    Asher Well-Known Member

    There's no doubt it is impressive. But which bits are important to prescribing / changing a treatment intervention - that is the most important thing to focus on. I'm still making my way through this side of things ...

  9. vcameron

    vcameron Welcome New Poster


    I have used the F-scan in-shoe system and the F-scan HR Walkway for patients with RA. I undertook a validity study, and I found both pieces of equipment to be reliable and repeatable.

    In terms of how the systems can be used in the clinic, well, the possibilities are endless! For me with the RA patients, pressure time integral was probably one of the most important outcomes that I looked at. The pressure time integral is the area under the curve, so that amount of time that the pressure is exerted on any part of the foot. High pressure for a prolonged period of time will invariably cause more damage than high pressure that is transitory.

    I think the f-scan is a very practical tool for clinical practice, as recordings can be made easily and quickly. The thing that took me the most time was calibration, however, I believe that Tekscan are dealing with this issue. The only other thing that I would add is that the sensor insoles are not very robust. I was fortunate to have a separate pair of insoles for each of my patients (for research purposes), but I would guess that perhaps each insole could be used about 20-30 times before results are affected. A pair of insoles is about £19, so this is worth taking into consideration.

  10. Asher

    Asher Well-Known Member

    Hi Vicki, thanks for that.

    Wow, a pair here cost $122!
  11. efuller

    efuller MVP

    That cost is scary. Ten years ago, in the US, they were 25$ a pair. The sensors are based on a pressure sensative ink that can dry out. The published literature from the company says that you can use the sensors aproximately 6 times. The sales rep will tell you that they can last considerably longer with the key being not to fold them when you put them in a shoe. The sales rep also mentioned taping around the edge of the insole to prevent drying of the ink. However, that's not in the company literature.

    Usage: The most useful place I found for them was in neuropathic feet that you were trying to off load.

    One of the main problems with computerized pressure analysis is the question of whether the pain causes the gait, or does the gait cause the pain. Sometimes it's one and sometimes it's the other.


    Eric Fuller
  12. Asher

    Asher Well-Known Member

    I would have thought that its relatively obvious to see which areas need to be off-loaded (callused areas / bony prominences). Besides, at what threshold do you consider requiring of off-loading?

    I am under the impression that this technology is useful to gauge timing and symmetry issues.

  13. efuller

    efuller MVP

    I didn't use it that much. There was one patient I can recall with a trans met amputation that several people had tried to pad. The amputation created a situation that was difficult to figure out. It healed after my first attemp showed a hot spot and then with modification the second try did not show a hot spot.

    There will be no single value of pressure that will work for all people. Without pressure measurement we have always dispensed a device that we think will work without knowing whether pressures will be reduced. It would be an interesting study to do. Is compare ulceration rates with and without pressure measurement. Do the study with experiended orthotic makere versus inexperienced. I think it might be shown to be an excellent teaching tool. However, that might not help you in your clinic.

    There's another study that is yet to be done. Are timing and symmetry issues predictive of pathology or therapeutic response. I know Howard Dannenberg has talked about this a lot, but I don't think that he has written up his recipe.

    I think there might be something valuable there. It would be nice to know what numbers to look for. Sometimes I wonder whether people looking at a computer screen and the roll over process is about the same as someone visually observing gait. Unless you get some numbers, it is still quite subjective.


  14. Google: "gait symmetry" lots published.

    This is interesting:
  15. Asher

    Asher Well-Known Member

    From what I can make of it, there are two measures that are useful with the FScan in-shoe (or other) equipment:

    1.Looking at how the COF progresses for each foot and whether it moves forward symmetrically in regard to timing (COF timing) and direction (COF trajectory).

    2.Force / time graphs for each step or for the ‘average’ of collected steps.

    To do anything with this data collected, you would have to know what is normal / ideal. So, what does the normal / ideal COF trajectory look like and what does the normal ideal force / time curve look like?

    Tekscan say that the ideal COF trajectory is relatively straight from the heel to the 2nd MPJ. Is that the case? The ideal force / time curve is not discussed other than to mention deviations from an undefined normal. Should the second hump be a bit higher than the first, should they be of equal amplitude?? What about the gradient of the up and down slopes? I understand that symmetry would be a good thing to look for but just because each foot's F/T curve is the same doesn't mean they are normal / ideal.

    The ideal pressure profile is also not discussed other than to mention deviations from an undefined normal. Should one look for a ‘decent’ amount of pressure under the first metatarsal head to denote windlass function? Would high pressure under the IPJ of the hallux suggest functional hallux limitus? How can the pressure profile actually be used in a useful way?

    I'm sorry if this is basic stuff but its all new to me.

  16. Asher

    Asher Well-Known Member

    Just to clarify, the COF measures and F/T curves are not the useful measures with Fscan. I should have said with the Timing Analysis Module (TAM) add-on of of Fscan.

    The pressure profiles come with the standard software.

    I have yet to get into the CoM'nalysis add-on.


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