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VLS (gaitscan) Case study

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Robertisaacs, Dec 19, 2009.


  1. Members do not see these Ads. Sign Up.
    I recently had a rather interesting VLS from a Gaitscan land in my inbox. Its a bit of an unusual one. I would appreciate any thoughts from any community members who are used to analysing this type of data (where you at Graham?)

    Case history, young lady who recently had 1st ray surgery and double neuroma excisions. I guess I don't really have to tell you were it hurts do I! Hurts there a LOT.

    The second picture is the static scan BTW. Sorry the quality isn't great, I'll try to improve it.

    [​IMG]

    What say you?
     
  2. DTT

    DTT Well-Known Member

    Hi Rob

    My first thoughts are

    Neither 1st ray is doing little if anything, the 234 mets are being overloaded, Early heel lift on both, both medial heel strike.

    It would appear from the 1st and 5th rays which are ? dorsiflexed the 234 would be in a plantar flexed position ? from surgery.

    Both MTJ are overloaded at heel lift

    Generally both feet are showing gross instability especially the right.

    Just my thoughts
    Cheers
    Derek;)
     
  3. David Smith

    David Smith Well-Known Member

    Robert

    Is this like a Christmas quiz??

    Do you have any other VLS data (is that an abbreviation for vertical load scan?) Like total force / time curve.

    Are we looking at pressures of forces on these scans?What was the subjects body weight and what does 100% y axis represent? is it 100% = max applied pressure / or force or does 100% = bodyweight? Are there data of actual time or applied forces instead of relative scales? E.G. Left stance might be 250ms longer than right and peak forces might be much different between left and right feet.

    From what your current data shows I would guess that right is cavus foot, valgus forefoot, equinus ankle short right leg, early heel lift short step, flat foot strike, apropulsive gait. Left is less cavus but claw toes, longer step with a more rolling heel to toe off action - more propulsive than right. I would guess she had surgery on the right foot, is that correct?

    I could make a better guess if you could provide the extra data.:dizzy:

    Where is Gaitscan land is Santa there?:santa:

    All the best for Christmas, Dave
     
  4. Bleedin 'eck Dave, you don't want much do you?!

    I don't got a total force time curve. I got the ticker tape bit if that helps!

    [​IMG]

    I don't think I have any absolute data values. Sorry.

    The foot itself is not particularly cavus although there is a fair bit of equinus. The Gait is antalgic and BOTH feet had surgery. Both had 1st MPJ surgery and double neurectomies. The forefoot looks very convex in the frontal plane....

    Its not a quiz as such :D. Its a patient who's had a lorra surgery, and is still having a lot of grief a year on. I asked for them to have a pressure scan to see if it would tell me a bit more about what the 1st met and windlass is doing to help me with my orthotic consideration.

    And Gaitscan MIGHT be where santa is. A jolly old fellow with a booming laugh and white hair wasn't he? :D;) :santa:

    Cheers
    Robert
     
  5. DTT

    DTT Well-Known Member

    You got more than that !!


    :santa::D

    Yep;)

    And a very happy Christmas to all and a super and PEACEFUL 2010:santa:
    cheers
    Derek;)
     
    Last edited: Dec 21, 2009
  6. :santa:
     
  7. Mart

    Mart Well-Known Member

    Hi Robert

    Is this single step or averaged data?

    It seems to be single step. I feel these values remove a lot of useful info because they are normalised. There is no indication of contact duration so speed cannot be inferred and patient may have very assymetric loading times and loading forces (limping) and this cannot be determined. Judging by left foot contact times there appears to be avoidance for forefoot loading with lesser toes taking disparate pressure. Again I feel there is problem with data is presented because there is no indication of force compared to body weight, is large lesser toe pressure simply a factor of little contact area or is there a lot of force causing this? How soon post op was this. What is the point of doing post op gait study if still in pain from healing?

    cheers

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  8. Mart

    Mart Well-Known Member

    Hi Robert

    Is this single step or averaged data?

    It seems to be single step. I feel these values remove a lot of useful info because they are normalised. There is no indication of contact duration so speed cannot be inferred and patient may have very assymetric loading times and loading forces (limping) and this cannot be determined. Judging by left foot contact times there appears to be avoidance for forefoot loading with lesser toes taking disparate pressure. Again I feel there is problem with data is presented because there is no indication of force compared to body weight, is large lesser toe pressure simply a factor of little contact area or is there a lot of force causing this? How soon post op was this. What is the point of doing post op gait study if still in pain from healing?

    cheers

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  9. Mart

    Mart Well-Known Member


    Hi Derek

    Please explain how you reached this interpretation what you stated make no sense to me.


    thanks

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  10. efuller

    efuller MVP



    There has got to be a very high lateral arch as it never contacts the ground. This will tend to increase pressures under the forefoot and heel. It looks like she saw a surgeon who thought: forefoot pain = neuroma. Since it still hurts, it sounds like it's not neuromas. Looking at the location of high pressures you would think that mets 2-4 would hurt. If you throw an equinous on top of that, it would mean spending more time in the locations of high pressure. From the data presented I would want to put them in a device that contacted the lateral and medial arches to reduce forces on the forefoot, had cushioning under all the mets and perhaps an extension under mets 1 and 5 to increase force there and decrease force in the high pressure areas under mets 2-4 and the device should have a heel lift to decrease the time spent entirely on the forefoot. That is treating the pressure analysis pictures, so other data could change the prescription.

    You did say that we could infer the painful location from the printouts. When I look at the printouts I would guess that there would be pain in mets 2-4. Is this correct?

    Regards,

    Eric

    Cheers
     
  11. DTT

    DTT Well-Known Member


    Hi Martin

    Sorry I actually did the scans for Robert to try and ascertain 1st ray function for his patient.

    The data sheet shows the values taken from the 10 reference points on each foot. The normal value is shown in the white columns. The actual value is shown and highlighted with in the other columns. red = overload,green=within the normal parameters, Blue = there is not enough pressure or the moment has happened to quickly .

    The Impulse column( Time x pressure) is then put into graph format as you can see . The left is the pressure the bottom line is the time in milliseconds. The coloured lines correspond to the miniature at the side where each part of the foot is allocated its own colour

    If I had better IT skills I could probably get the motion analysis off of the scan but I don't know how to do it and cant find anyone that does. sorry:eek: That is of course unless Paul Barratt reads this and can help?? He is the clinical podiatrist for the system??

    I never did a full examination of the patient as it was Rob's patient and my remit from him was just to scan her, which I did 4 times after 15 attempts ( until I was happy with her gait and contact). In the resulting analysis of all the scans whilst there was obviously a slight variance in the actual values, but the overall function was the same on all 4 scans.

    The comments I made were those I made to Rob when I sent him the scans and I,m sure he will be back here to expand on the clinical situation with this very unfortunate patient.

    Eric is exactly right she is in pain with 234 mets which are all overloaded. She is onto the mets too quickly because of the early heel lift, so on them too long = overload.

    I hope that helps
    Cheers
    Derek;)
     
    Last edited: Dec 22, 2009
  12. Mart

    Mart Well-Known Member


    Hi Derek

    Thanks for reply.


    Now I am even more confused.


    My understanding of the table is that apart from the column with impulse the values represent proportion of contact time not pressure ie purely temporal data.
    I assume that adjacent column is normal data (hence color coding). If ths is true there is no indication from table apart from the impulse regarding actual pressure values - correct?

    The graphs represent proportions of total pressure for the anatomic related sites for that step so reflect table with a bit of relative pressure but no force data.

    Based on this, my initial impression was that left foot looked less normal given apparent unloading of lesser mets during late midstance. It seems from your and Eric's interpretation that the right foot is one that hurts.

    I dont understand how you both figure from this data that

    there was early heel lift

    or

    overload of metatarsal heads 2-3-4

    there is granted slightly increased contact time but how does this represent overload given we do not knbow what the load was?

    Also were do you get an early heel rise from?

    cheers

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  13. DTT

    DTT Well-Known Member


    There is more data contained in the motion analysis ie % of time in stance etc but as I said I cant seem to get that off the system to bring it here, again sorry.
    I have used this system for around 8 years and as a diagnostic aid I find it useful, Robert has seen it working hence he requested the scan. In a way I have an unfair advantage as I saw the patient and was given the Hx by Rob hence I dont want to comment too much on the clinical side, Rob can do that himself, but I'm happy to try and explain the system if it helps as far as my knowledge will allow.

    Cheers
    Derek;)
     
  14. Got it in one guess! These are also the sites where the neuroma's were excised. One of them is now over a year post op and still exquisitly painful. Patient has been referred (not by me) for an ultrasound to see if there is a "regrowth or stump neuroma."

    Given the pressure profile I'm not sure I'd want to dive in again even if the scan DID show a stump neuroma.

    That particular statement interested me. How long after a neurectomy would you expect a foot to be significantly painful if it IS a neuroma? And if the pain persists for over 12 months would you consider it more likely that the neuroma was not the initial cause of the problem or that a stump neuroma / regrowth has arisen in its place?

    Thanks Eric. :drinks

    Regards
    Robert
     
  15. This assumes that duration of loading in isolation is key. This is not true. Impulse is probably more key, i.e., force x time. So we could have a 100N that lasts 1 sec 100x 1 = 100 or we could have a 1N force that lasts 5 sec: 1 x 5 = 5. So just because "you spend too long on the met heads during the cycle" it doesn't necessarily follow that "there must be overload on them because the weight is there for too long".
     
  16. DTT

    DTT Well-Known Member

    Hi Simon

    Impulse column is as I said represented in the graph and the impulse column.
    My understanding is, if the bodyweight is on a say a met head for too long then that met head is then in an advancing position with more weight on it than it should have so hence overloaded??

    As Robeer asked me to do the scan to examine 1st ray motion/pressure which shows in all the scans as having very little function which I'm sure Rob will fill in with the clinical symptoms.

    I bow to your greater knowledge of these matters but that is just my understanding.
    Cheers
    Derek;)
     
  17. DTT

    DTT Well-Known Member

    Hi Rob

    Having (Yesterday) spoken to a friend that had a neuroma op many years ago,she quoted being in pain for 8 YEARS after the op and visited a pod every 2 weeks to have the callus removed from the op site for 5 of those 8 years !!

    I assume things have advanced since then but seeing your patient she is in obvious pain so....
    Cheers Buddy
    Derek;)
     
  18. Mart

    Mart Well-Known Member

    Thanks Derek

    You made 4 points in reply to my confusion over your interpretation.


    1 the first 3 columns by my understanding represent intial contact, final contact and contact duration as proportion of total conact period. So what we are seeing from this data is a delay in onset of left foot forefoot and normal onset of right foot forefoot contact and delay in offloading of forefoot both feet.

    2 Simon already explained misinterpretation of this data. the force/time integral may well simply be factor of increased load time and without actual peak pressure or force/time integral values we cannot make an assumption of overload.

    3 Unless I am missunderstanding the data there is no indication of body weight, the pressure data appears normalised to the contact period, nothing to do with body weight. From this point of view it is possible there was offloading of the right foot and in reality below normal loading.

    4 you interpretation doesnt make sence to me. the blue values simply reflect a late forefoot conact and reduced period of conact for those sites, the plantar calcaneal area contact values for both feet are entirely normal in all respects which would not be true if there was early heel raise.

    Can you understand why I am getting confused by your interpretation?

    thanks

    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  19. Hey Mart.

    Do you feel that you CAN interpret anything from this data?

    I'm no expert on this type of system, however regarding your second point

    It would seem to me that one could assume overload from the relative location of impulse / peak pressure. Whatever the 2-4 data is, whether long time and low pressure or short time and high pressure, its substantially higher than under the 1st.

    The impulse for one 1st met is 1.6% of the total forefoot impulse. That, to me, suggests that that joint is not taking a meaningful amount of load. Which means the others must be taking more.

    Mart, leaving alone the limitations of one system over another, I'd appreciate anything you could add based the data we DO have.

    Thanks:drinks:santa:

    Robert
     
  20. Robedrt, I wasn't referring specifically to this data, I was merely stating that just because an area of the foot is loaded longer than another area on cannot assume that the longer loading = overloading.
     
  21. Mart

    Mart Well-Known Member

    I feel there is insufficient data here to make any meaningful generalisation of how these feet behave, as you can tell I take issue with your and Erics interpretation but would be glad to change my mind on that if there is good reason to.

    It would be interesting to look at the other data from these steps to see what might be reasonable assumptions.

    Because by definition the impulse (force/time integral) requires both the force and the time values to evaluate meaning it is impossible to determin the mechanical effect from this data. Simon already demonstrated this. If you provided the actual force/time data for those regions it would then have more meaning. Tissue injury seems correlated to both peak pressures and force/time integrals, however the anatomic impulses are only displayed in your data proportional to other areas, so they may well below normal even though the durations are proportionaly extended.

    I have a bit of holy grail currently to try and flesh out some interpretation "protocols" which might be agreed upon.

    The first stage is to do what you have done here and put up some case studies to look at. If we collectively and candidly interpret the data publicallyand allow some consensus to develop then perhaps with some critical thought this might be acheivable.

    :drinks

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  22. Robert is this from our friend that you asked for our out of the box advice on another thread and I suggested the MBT with ankle braces ?( the rocker bottom road)
     
  23. All things are possible Mike. ;).

    Yeah same one. It's a challenging case! The most recent x rays, taken static wb, apparently show the 1st met to be neither shortened nor dorsiflexed. Given the lesion pattern of pain and callus, the non wb assessment, and the patients report this seemed incongruous which is why I wanted the ground up view. To see what happens in gait.

    Well spotted that man!
     
  24. efuller

    efuller MVP

    So, to plantar palpation is it tender on the met heads or between them or both or you can't tell. Neuromas should be more painful between the met heads. I'd agree about "going back in". There is a pretty obvious problem with the pressure distribution. If you fix that and there is still pain then maybe go and look for the stumps.


    In theory if the pain is in the nerve, when you cut the nerve out the pain should go away immediately. If the symptoms did not change at all after the surgery (not counting time off feet for recovery from surgery) then you certainly can say that it was not a neuroma in the first place.

    Cheers,

    Eric
     
  25. efuller

    efuller MVP

    My interpretations are based on the static stance picture and the maximum pressure plot picture that is at the top right side of one of the printouts. In the static stance picture it looks like there are four heels instead two heels and two forefeet. That is a very unusual printout. In both of those pictures there is hardly any pressure on the toes. Usually in gait you will see pressure on the toes and the first toe can have pressures higher than the metatarsal heads. I already mentioned the lack of lateral midfoot contact on the ground.

    There is a discrepency between the numerical data and the observational data of an early heel off. I based some of my reasoning on the observational report of an early heel off. With 20/20 hindsight I can defend choosing the observation over the step data because there was data from only a single step.


    The problem with analysis of pressure roll overs is that you have to have an idea of whether the gait causes the pain or the pain causes the gait. Sometimes it is one and sometimes its the other. However, the data presented in this case is pretty hard to achieve by avoiding pain. (Try to simultaneously lift your fifth and first met heads off the ground while keeping mets 2-4 on the ground.) If you look at a pressure plot and the high pressures coincide with the location of pain then you can pretty easily make the case that the pain is from the gait.

    Cheers,

    Eric
     
  26. Mart

    Mart Well-Known Member

    Thanks Eric

    I was trying to avoid being too much of a party pooper but you raise an important issue here.

    I am not sure how the data is being portrayed in the middle image which is the one I think you are talking about (2 red blobs at right and 2 yellow blobs at left)

    It is so unusual and conflicting with the other data that I felt there were2 explainations.

    either the diagram was of double limb support relaxed calcaneal stance position which seemed unlikely since it would not have had any % values attatched

    OR

    it represented the entire peak pressure picture thoughtout the steps

    OR

    single frame during midstance after forefoot contact

    BUT

    either way the lower pressure thresholds appear to have been set so high that they missed the low pressure values. For another clue look at the COP trajectory images posted later, there is quite a different picture and again the thresholds are not stated but clearly different. Since there is no information about the thresholds it is impossible to tell for sure but that is what I am thinking.

    If I am right then you should not make the assumption about lateral border or toes.


    What is weird and makes no sence is if you look at the pressure %/time curves for the left foot; the lesser digits have the maximum peak pressures (dark green curve) which conflict with all the other data. Is the software giving an erroneus colour key, is the data from a different step or should I be getting a bit more sleep? I agree about the plantar digital area 1st toe peak pressures normally being elevated higher than metatarsal heads if walking at reasonable velocity.

    cheers

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
    Last edited: Dec 23, 2009
  27. Mart

    Mart Well-Known Member

    Sorry Eric I do not understand what you mean about observational data of early heel off, I did not see anything relating to this.

    I agree about the pain issue and always assume pain avoidance pattern in those with pain during data collection. As as a rule I defer pressure measurement if I can eyeball obvious pain avoidance strategy.

    I think that your point regarding lifting 1st and 5th ray may be mute given my last post comments on thresholds. However if the 1st and 5th rays are overly compliant to dorsiflexion ground reaction force then I think that relative 2/3/4 pressure elevation with inhibititory dorsiflexion of toe extensors during midstance plausible. I'll give it a shot next time I am messing around with my system and see if this is true!

    cheers

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  28. efuller

    efuller MVP


    Robert wrote in post # 4
    The foot itself is not particularly cavus although there is a fair bit of equinus. The Gait is antalgic and BOTH feet had surgery. Both had 1st MPJ surgery and double neurectomies. The forefoot looks very convex in the frontal plane.... ​

    My mistake for inferring that there was an early heel off from the above. The observational data would be a fair bit of equinus. Antalagic and equinous are consistant with the timing of the heel off.

    Mart, Your comments about not having the threshold is a valid one. We cannot be sure of what we are looking at. But, if we assume that the thresholds were set resonably then we can work with was given. I would probably change my opinion if I was told the thresholds were set high.

    Even if the thresholds were set high, it's still really difficult to get a low reading on both 1st and 5th met heads and high readings on mets 2-4 unless there is some really unusual anatomy.

    Regards,

    Eric
     
  29. Bruce Williams

    Bruce Williams Well-Known Member


    Lots going on here Robert. See the delay in the frames of the CoP progression lines above at the heel bil. This means a huge delay in this area adn that is reflected espcecially in the F/T curves in your initial post, on the right > left heel.
    Rediculoously high M3 pressures. Long slow buildup of the FF curves bilateral and little if any sub 1 or 5 met head pressures.
    What does the patients foot look like wbing adn nwbing? does she have a FF equinus and a very stable RF, maybe a neutral heel on wbing or even varus?
    those are my thoughts as you requested.
    Expect a short limb left, but If my assumption is correct on the FF equinus you will need to either manipulate the AJ or add 3-6 mm of HL bilateral, plus more on the short limb to equalize decrease the FF pressures. I'd utilize a digital wedge, similar to a cluffy wedge as well to engage the metatarsals 1 adn 5, only 1-5!, and probably a lateral FF wedge to direct the CoF to and thru the 1st met as the foot moves towards propulsion. also accomodate the 3rd met bilateral.

    good luck and happy xmas!
    Bruce
     
  30. Mart

    Mart Well-Known Member

    Thanks Eric

    if I get time I'll try an simulated antalgic forefoot step tomorrow, see what it looks like and post results.

    cheers


    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  31. Mart

    Mart Well-Known Member

    Hi Bruce

    Please spell this out for me buddy bit by bit if you have time :empathy:

    you said

    "See the delay in the frames of the CoP progression lines above at the heel bil. This means a huge delay in this area adn that is reflected espcecially in the F/T curves in your initial post, on the right > left heel."

    where can you see a delay in the COP progression which is not normal - I cannot see it from this data?


    you said
    " Long slow buildup of the FF curves bilateral ."


    Shouldn't there be a an early rapid build up in forefoot pressures caused by premature unloading of heel if there is early heel lift?

    If you look at the data it is the opposite, I cannot see how anyone sees an early heel lift in any of this data, the time to peak pressure under the heel is actually retarded; look at the peak time to pressure column for both feet :bash:


    you said
    "Expect a short limb left"

    why?

    The only index I can think of (and I would attribute very low evidence weighting to this from a single stance) is from contact duration which was longer on left side.

    Wouldn't that indicate functionally longer left side lower limb (inverted pendulum longer frequency)? Also if you look at the gradient of the right foot heel contact it is relatively much steeper which is consistent with that idea since COM will fall from greater height after longer side stance (assuming knee extended) and 1st rocker will have smaller segment of heel to roll on due to slightly more anterior tibial position at heel contact of shorter limb.

    BTW the T2-5 mask for the left foot is actually positioned anterior to metatarsal heads not on digits which is why the dark green trace is very misleading for the left foot!

    cheers and happy Xmas to all to the foot geeks too

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  32. Mart

    Mart Well-Known Member

    Hi Eric

    I just took a snapshot of myself relaxed calcaneal stance position and then using same data adjusted lowest cutoff threshold to 3 levels to illustrate effect. I think you will agree that there is a striking resemblance to what we were discussing of vanishing metatarsal heads 1 and 5 and my foot anatomy is not that unusual. One clue from Roberts data which supports this similarity is the total conact area which will be a function of threshold values. If you look at the walking data vs the static dat there is approximately 50% decreased SA. I tried to emulate that a bit in my portrail below and there is similar change. The problem with the data Robert posted as I see it, is that unless we make assumptions which may be false it is impossible to make meaningful interpretation.

    pa1.jpg

    pa2.jpg

    pa3.jpg

    cheers

    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  33. Mart

    Mart Well-Known Member

    Hi Bruce

    I think there are pitfalls for misinterpretation of pressure curves. The main problem I see with commenting on Roberts data is uncertainty about what it represents.

    To illustrate this I just had a quick browse through some of my files to find something approximating to Robert's data. Here is exactly the same data represented through 4 different lenses. Would you say that this data shows ridiculously high metatarsal head pressure? If not how does it differ?

    pf4.jpg

    pf5.jpg

    pf6.jpg

    pf7.jpg


    cheers

    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  34. efuller

    efuller MVP

    In the second set of pictures where there is a roll over process and there are dots for the location of center of pressure for each frame, you can see a denser grouping of dots toward the heel of the right foot when compared to the left. If you assume that sampling rate is the same for both steps, then there is a delay of the COP progression on the right compared to the left.


    Mart, I agree with you that there is not an early heel lift in this data. However, there was a clinical report of equinus. This is where the art of melding clinical data and pressure plate data comes in. If this person were pain free and had an equinus then there would be an earlier heel off when compared to when the patient is avoiding forefoot pressure and choosing to delay their heel off. So, we may have a patient who has normal heel off times, but is late for their usual heel off. Yes, you cannot know this for sure, but it is a plausable explanation.


    Mart, I also have trouble with limb length prediction from force plate data. One school of thought is that you see higher forces on the long limb because the CoM has to be accelerated higher to get over the long limb. Another school of thought is that the short limb will have higher forces because it will have fallen farther. Both schools of thought have problems with varying amounts of knee flexion. The peak forces can be reduced, in both cases, by shock absorption of the knee or continued knee flexion that would not lift the center of mass. There are many variables that go into whole foot force time curve. Remember Groucho walking

    :santa:

    Eric
     
  35. efuller

    efuller MVP

    Mart,

    I agree with you that you should question that the data you receive. How often have you had a patient change their story on the location on their foot that hurts the most? It is important to remember the data that led to your conclusions, so that you can change your conclusion when the data changes. However at some point you have to work with what you got. The disclaimer, "based on the available information", is a good one.

    I hate to tell you this Mart, but your feet are also not normal. ;) I didn't do any numbers, but in my experience a large majority of feet, in static stance, have their styloid contact the ground.

    Does SA = surface area?

    I agree that total contact area will decrease as you set the threshold measurement higher. However, there are some feet that have a smaller area of their foot contact the ground because of a high lateral arch. This is something I probalbly learned using a pressure measurement system.

    So, given the available data, I feel my explanation of the data is plausable and meaningful. Now, if Robert admits he manipulated the threshold on his pressure measurement system, then I would have to trust his posts less.

    Cheers,:drinks
    Eric
     
  36. DTT

    DTT Well-Known Member

    Hi Eric

    Can I just make the point, there is NO Facility to manipulate any data on my system ( Roberts data) = What you see is what you get, which is what it says on the manufacturers tin.

    I think you and obviously others understand the data produced and the indications of that data which is what Robert requested and perhaps his request for help on that data to get a resolution of his patients pain should be paramount ??;)

    Merry Christmas to you and all on Pod A :santa:

    Cheers
    Derek;)
     
  37. Mart

    Mart Well-Known Member

    Hi Derek


    I think that these gait systems have the potential to help understanding regarding our patient’s foot behaviour and guide clinical reasoning.

    That said I feel there are so many pitfalls to interpretation that attempts to understand what that might amount to are warranted otherwise the whole process is undermined.

    My comments regarding this thread were intended to test the interest of others a little to see if this is a good forum to explore this.

    At risk of sounding pedantic when you say there is no facility in the software to manipulate the data I feel that is a dodgy statement. What the software does is ONLY to manipulate the data and if the parameters and meaning of the data are unclear then it loses meaning. I am not familiar with the software control which you have but would be surprised if there is no control of basic parameters such as threshold values and cell averaging. Cell averaging and threshold values are used by the software to make the pictures “look nice” and attempt to smooth out measurement artefacts but depending on the algorithm can have quite profound effect on the way the data appears.

    If there is sufficient interest amongst those of us who use this technology clinically to work up some sound interpretation protocols I think that would be very valuable and to my knowledge has not been done before. I don't feel sufficient confidence in my understanding of this subject to do this alone. It is probably not for the faint hearted, requiring quite a bit of work and steep learning curve.

    As a starting point this might include;

    Looking at value of calibration check of measurement system, typically I would do this by comparing the measured body weight against the actual measured standing force. A problem I see with making this work this is understanding the effects of the hidden algorithms that the system manufactures use to compensate for sensor artifacts.

    How we might use concurrent use of synchronised video to check for targeting or “off balance step” and check behaviour of segments above foot for explanations for plantar forces, especially when they vary unpredictably step to step.

    A look at what is regarded as normative pressure and timing data, there is little published on this and I have never seen any attempt to see how the various system manufacturers define their normal ranges. An issue which effects this profoundly is gait velocity and I am not sure how the manufacturers normative data ranges account for this.

    A check list of pitfalls, amongst which I would recommend looking at the issue of how we interpret pressure/ time vs force/time curves.

    Hope you, Eric, Bruce and others might be up for this. I have another thread gathering dust related to this issue which remains neglected because of my time restraints but intend to get back to it in the New Year.

    Time to go and see if Santa’s lurking

    Cheers and have a great holiday

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  38. Mart

    Mart Well-Known Member

    There is a lot that many consider not normal about me other than my feet, case in point; I am logged on to podarena at 11 pm on Xmas Eve.

    anyhoo . . . . . yes SA = surface area

    time to go find some chimneys to jump down


    :santa2:
     

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